Article

Coral variation in two deep drill cores: Significance for the Pleistocene development of the Great Barrier Reef

June 2003
Sedimentary Geology 159(1):61-80

Authors:

The University of Sydney

Variations in lithology and coral assemblages in drill cores from outer- and inner-shelf reefs are used to characterize the Pleistocene development of the Great Barrier Reef. Based on petrographic, isotopic and seismic characteristics, the outer-shelf core from Ribbon Reef 5 is divided into three sections: (1) a main reef section from 0 to 96 m is composed of six reef units, (2) a rhodolith section from 96 to 158 m is interbedded with two thin reef units and (3) a basal section from 158 to 210 m is composed of non-reefal skeletal grainstones and packstones. Two distinct coral assemblages identified in this core represent a shallow, high-energy community and lower-energy community. These two assemblages are repeated throughout the main reef section, with some units recording transitions between assemblages, and others composed of only a single assemblage. These coral assemblage data also correlate with transitions recorded by coralline algae. Using similar criteria, the inner-shelf core from Boulder Reef is divided into two sections: (1) an upper carbonate-dominated section from 0 to 34 m is comprised of four reef units and (2) an underlying mud section from 34 to 86 m is composed of siliciclastics and two thin, coral-bearing units. The four reef units in the upper section are dominated by a single coral assemblage representing a community typical of low energy, turbid environments. Taken together, these data indicate that: (1) reef growth on the inner shelf initiated later than on the outer shelf, (2) true reef ‘turn-on’ in outer shelf areas, as represented by the main reef section in Ribbon Reef 5, was preceded by a transitional period of intermittent reef development and (3) the repeated occurrence of similar coral assemblages in both drill cores indicates that the Great Barrier Reef has been able to re-establish itself, repeatedly producing reefs of similar composition over the last 500 ky, despite major environmental fluctuations in sea level and perhaps temperature.

Environmental controls on the resilience of Scott Reefs since the Miocene (North West Shelf, Australia): Insights from 3D seismic data

Article

May 2023
MAR PETROL GEOL

North and South Scott Reefs are isolated carbonate platforms separated by an inter-reef channel on the NWS, Australia. They evolved from a barrier reef in the Miocene, and into isolated carbonate build-ups (ICB’s) during the Pliocene, and finally to the isolated carbonate platforms that continued to present day. However, the timings of coral reef turn on and off are not well constrained with respect to global climatic changes in this region. The North West Shelf (NWS) of Australia recorded marked climatic and oceanographic changes through the Cenozoic. For example: (1) the Mid Miocene Climatic Optimum (MMCO), leading to the onset of ICB’s and carbonate platform development; (2) the Mid Pleistocene Transition (MPT) (ca. 0.8–0.6 Ma) and the associated change in regional climate from wet to dry; and (3) glacial-interglacial variability through the Pleistocene until present day. Availability of high resolution and extensive 3D seismic data provides a unique opportunity to investigate the evolution of these reefs using seismic stratigraphy and seismic geomorphology. Four main phases of carbonate factory evolution (Phase I-IV) were identified from the Miocene to present. A chrono-stratigraphic framework is constructed, detailing relative sea-level (RSL) changes and the impact of global (e.g., climate, eustasy) and regional (e.g., tectonics, oceanography) forcing parameters on their development. Seismic stratigraphy reveals that despite rapid accommodation rate changes, the oceanographic setting, antecedent topography and rapid vertical reef accretion played a key role in the persistence of Scott Reefs. It is likely that the Indonesian throughflow (ITF) current has been a critical component in controlling the local climate. The Leeuwin current, tides, swells and wind regimes similarly exert a major influence on the NWS climate, whilst the inter-reef channel likely bypassed terrigenous sediment influx away from the reefs, avoiding periods of inundation during wet climates.

Environmental Controls on the Resilience of Scott Reefs Since the Miocene (North West Shelf, Australia): Insights from 3D Seismic Data

Article

Jan 2022

Microstructural characteristics of the stony coral genus Acropora useful to coral reef paleoecology and modern conservation

Article

Full-text available

Mar 2021

Identification of fossil corals is often limited due to poor preservation of external skeleton morphology, especially in the genus Acropora which is widespread across the Indo‐Pacific. Based on skeleton characteristics from thin section, we here develop a link between the internal skeleton structure and external morphology. Ten characteristics were summarized to distinguish Acropora and five related genera, including the type and differentiation of corallites, the skeleton nature of corallites (septa, columellae, dissepiments, wall), and calcification centers within septa. Acropora is distinctive for its dimorphic corallites: axial and radial. Isopora is similar to Acropora but possess more than a single axial corallites. Montipora and Astreopora (family Acroporidae) have monomorphic corallites and a synapticular ring wall, with clustered calcification center in the former and medial lines in the latter. Pocillopora and Porties are classified by distinctive dissepiments, columellae and septa. These microstructural skeleton characteristics were effective in the genus identification of fossil corals from drilled cores in the South China Sea. Eighteen detailed characteristics (ten of axial corallites, four of radial corallites, and four of coenosteum) were used in the Acropora species classification. The axial corallites size and structure (including corallite diameter, synapticular rings, and septa), the septa of radial corallites, and the arrangement of coenosteum were critical indicators for species identification. This identification guide can help paleoenvironmental and paleoecological analyses and modern coral reef conservation and restoration.

Australia’s Great Barrier Reef

Chapter

Jan 2019

DEGLACIAL ORIGIN OF BARRIER REEFS ALONG LOW LATITUDE MIXED-SILICICLASTIC AND CARBONATE CONTINENTAL SHELF EGDES

Conference Paper

Jan 2018

Spatio-temporal patterns in the postglacial flooding of the Great Barrier Reef shelf, Australia

Article

Dec 2018
CONT SHELF RES

The shelf of the Great Barrier Reef (GBR) was progressively marine flooded from the last glaciation maximum (LGM) (ca 20 ka BP) until the last sea-level highstand (ca 6 ka BP), affecting the depositional evolution of the GBR margin and associated deposits. However, the physiographic variables related to this process have not been fully characterized, especially in relation to the sedimentary processes at the shelf margin. For this study, we used a bathymetric model of the entire shelf and a shelf margin sub-set, divided into 33 latitudinal zones. Postglacial marine flooding was simulated and flooded area (km2), flooding magnitude (km2 per sea-level increment), flooding rate (km2. ky−1) and coastline length (km) were estimated for each zone, from 130 m to 0 m below present sea level, representing the period from 20 ka to 6 ka BP. Our results show that the postglacial marine flooding did not occur uniformly and that some sub-regions (e.g. the southern-central GBR) had early and rapid flooding. Coastal complexity increased in the mid-postglacial, reaching maximum values at around 9 ka BP. This reflects a coastal landscape evolving from a linear, laterally connected coast to a complex coast dominated by estuaries and lagoons, partly returning to its initial linearity during highstand. Flooding trends and geological evidence make two depositional relationships apparent. Firstly, the timing and magnitude of the off-shelf sediment flux appears linked to the presence and orientation of a shelf-edge rim, and to the extension and morphology of the evolving drainage network. Secondly, the periods of shelf-edge reef development and demise seem to respond to the remobilisation, trapping or redirection of fine sediments. We propose a sedimentation model for the shelf margin and the slope driven by the interplay of sea-level rise and shelf physiography, and we highlight two fundamental processes: (1) the cross-shelf sediment transport related to coastline retreat under rising sea levels, and (2) the effectiveness of transient embayments in redirecting or trapping sediments. The quantifications provided in this study have implications in the estimation of Pleistocene carbonate budgets and the atmospheric carbon cycle, as well as for past human migrations.

Chapter 15 – Australia’s Great Barrier Reef. In: Sheppard C (ed) World Seas: An Environmental Evaluation. Volume II: The Indian Ocean to the Pacific. Elsevier, pp. 333-362.

Chapter

Sep 2018

Coral community changes in the Great Barrier Reef in response to major environmental changes over glacial-interglacial timescales

Article

Feb 2017
PALAEOGEOGR PALAEOCL

The Ribbon Reef 5 borehole offers a unique record of reef growth spanning the entire history of the northern Great Barrier Reef (GBR). Previous studies have reported the main stratigraphical, lithological and chronological patterns, as well as basic descriptions of the coralgal assemblages, but no detailed coral community analysis was undertaken. We present a quantitative analysis of the nature and distribution of Pleistocene coral communities and apply several statistical tools to define recurrent coral associations and compare the eight reef-building cycles recognized throughout the evolution of the GBR. The start of significant reef building occurs at 137 m based on a major change in coral community structure and the inception of the reef cycles (Cy1–8). This revision, along with available stratigraphical and chronological data, suggests that barrier reef initiation may have occurred prior to MIS 11, earlier than previous reports. The coral assemblages at 137 m reflect the transition from lower mesophotic (60–100 m) to upper mesophotic (30–60 m) settings, while the eight reef cycles above are characterized by three recurrent shallow-water reef-coral associations: Porites-Montipora-faviids (Po-Mo-Fa), pocilloporids (Poc), and Acropora-Isopora (Acro-Iso). Typically, these cycles begin with the Po-Mo-Fa association and end with the Acro-Iso association, reflecting shallowing and a catch-up growth mode. However, the first two cycles are characterized by a transitional phase dominated by the Poc association. The dominance of pocilloporids during the early stages of the GBR's history and the long-term shift to an Acropora-Isopora-dominated community may reflect an increase in competitive pressure of acroporids over pocilloporids. Our findings are consistent with the view that reef coral community structure is predictable over 100-kyr time scale. However, variations within reef cycles highlight the importance of environmental changes operating at millennial time scales. Further studies are needed to better refine the reef chronology and clarify the influence of environmental variables (i.e. sea surface temperature, turbidity) on reef coral community structure.

The evolution of the Great Barrier Reef during the Last Interglacial Period

Article

Dec 2016
GLOBAL PLANET CHANGE

Quaternary coral, coralline algal and vermetid assemblages as sea-level indicators: a review

Article

Dec 2022

Corals, coralline algae and vermetid gastropods are indirect (marine limiting) relative sea-level (RSL) indicators. The precision in sea-level reconstruction based on fossils of those organisms depends on the probable palaeodepth in which they grew. Constraining such palaeodepth depends, in turn, on the available information about the habitats of their living counterparts. Diverse genera, species and species assemblages of corals, coralline algae and vermetid gastropods have historically been proposed as reliable indicators of narrow, shallow depth ranges. However, the increased information on depth distribution of marine benthos in the last two decades has challenged some early assumptions about depth ranges of taxa considered diagnostic of precise palaeodepths. Here, the authors test the reliability of coral, coralline algal and vermetid assemblages that have been extensively used in RSL reconstructions in the light of data from Ocean Biogeographical Information System (OBIS) and other recently published data. In the Indo-Pacific province, these data support the use of the robust-branching and the shallow, high-energy encrusting coral assemblages with a 0 to 10 m uncertainty. In both cases many component species have unimodal distributions and both median and average water depths are shallower than 10 m. The reliability of these coral assemblages as indicative of shallow water depths is strengthened when corals are encrusted by thick plants of the coralline alga Porolithon gr. onkodes. According to OBIS data, coralline algae of this species group in the Indo-Pacific are restricted to very shallow waters (95% probability of occurrence shallower than 0.2 m and in 99.6% of records shallower than 6 m). However, such a narrow depth range and the overall scarce data on coralline algal species in the OBIS database are questionable due to difficulties of coralline algal species identification with the naked eye. A comprehensive survey of the modern distribution of coralline algae at One Tree Reef (southern Great Barrier Reef) indicates that P. gr. onkodes has a log-normal distribution with median depth of less than 5 m and 95% of occurrence probability of thick crusts (> 0.2 mm) shallower than 8.8 m. Data on modern distribution of vermetids are scarce. In the OBIS database, vermetid species are reported from relatively wide depth ranges. However, relatively high densities (> 10 individuals per m2) on coral and coralline algal surfaces only occur from above mean low tide to some 6 m depth. In the Western Atlantic-Caribbean province Acropora palmata is the most precise RSL marker and no additional components of fossil assemblages improve its palaeodepth information. The confident use of coralgal and vermetid assemblages as RSL indicators relies on the identification of fossil corals and coralline algae at the species or species-group level. The scarcity of available data highlights the need for further studies on distribution of coralline algal species and vermetid in modern coral reefs from a variety of oceans and reef settings.

Fraser Island (K'gari) and initiation of the Great Barrier Reef linked by Middle Pleistocene sea-level change

Article

Full-text available

Nov 2022
NAT GEOSCI

The eastern Australia coastline is characterized by impressive coastal landforms and an extensive northward-moving longshore drift system that have been influenced by a stable, long-term tectonic history over the Quaternary period. However, the timing and drivers of the formation of two conspicuous landscape features—Fraser Island (K’gari) and the Great Barrier Reef—remain poorly understood. Here we use optically stimulated luminescence and palaeomagnetic dating to constrain the formation of the extensive dunes that make up Fraser Island, the world’s largest sand island, and adjacent Cooloola Sand Mass in southeastern Queensland. We find that both formed between 1.2 Ma and 0.7 Ma, during a global climate reconfiguration across the Middle Pleistocene transition. They formed as a direct result of increased amplitude of sea-level fluctuations associated with increasing global ice volume that redistributed previously stored sediment across the continental shelf. The development of Fraser Island dramatically reduced sediment supply to the continental shelf north of the island. This facilitated widespread coral reef formation in the southern and central Great Barrier Reef and was a necessary precondition for its development. This major reorganization of the coastal sedimentary system is probably not unique to eastern Australia and should be investigated in other passive-margin coastlines.

Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Article

Dec 2018
GLOBAL PLANET CHANGE

Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG–01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora, Acropora gr. humilis, Dipsastraea gr. pallida, Porites, and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora, including A. gr. humilis, and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales.

Depositional environments beneath the shelf-edge slopes of the Great Barrier Reef, inferred from foraminiferal assemblages: IODP Expedition 325

Article

Nov 2018
PALAEOGEOGR PALAEOCL

To understand sea-level changes since the Last Glacial Maximum (LGM) and their effects on coral reef systems, the shelf-edge slopes of the Great Barrier Reef (GBR) were cored during the Integrated Ocean Drilling Program (IODP) Expedition 325. Recovered unconsolidated sediments beneath the submerged shelf edge reefs contain abundant foraminiferal tests, which record changes in depositional environments and paleo-water depths. A total of 177 sediment samples were collected from 17 holes along three transects located within two geographical areas (Noggins Pass and Hydrographers Passage), and were analyzed to determine stratigraphic changes in foraminiferal assemblages (2–0.5 mm size fraction). Results show that four foraminiferal assemblages (A, B, C and D) are delineated by multivariate analyses (Q-mode cluster analysis and non-metric multidimensional scaling: NMDS), and these assemblages correspond to a back-reef to reef margin zone (0–10 m deep; Assemblage A), an upper photic zone (10–30 m deep) associated with hard substrates (Assemblage B), an intermediate to lower photic zone (30–90 m deep) characterized by soft substrates (Assemblage C), and a lower photic zone (90–130 m deep) only found in modern shelf slopes (Assemblage D). Gradual shifts in these four foraminiferal assemblages superimposed on a two-dimensional NMDS ordination mainly reflect water-depth gradients and the relative dominance of two substrate types (hard and soft substrates). Pre-LGM (older than Marine Isotope Stage 3: ≥MIS3) sediments along transects at Hydrographers Passage were deposited at intermediate to lower photic zones. In contrast, relatively shallow-water sequences found in ≥MIS3 deposits at Noggins Pass likely owe their origin to either turbidite and/or land slide processes. The lack of Assemblage D in ≥MIS3 deposits from all transects could be related to lowering temperature and/or increasing terrestrial influences (i.e. more light attenuation). Shallowing upward sequences found in LGM (MIS 2) deposits at Hydrographers Passage are likely related to stepwise sea-level falls to the full extent of the LGM. These foraminifer-based paleoenvironmental interpretations suggest that the GBR shelf edge slopes have changed their depositional environments continuously in response to sea-level fluctuations during the last glacial cycle.

Reef Carbonate Productivity During Quaternary Sea-Level Oscillations

Article

Full-text available

Mar 2018
GEOCHEM GEOPHY GEOSY

Global variations in reef productivity during the Quaternary depend on external parameters that may alter the global chemical balance in the oceans and atmosphere. We designed a numerical model that simulates reef growth, erosion and sedimentation on coastlines undergoing sea‐level oscillations, and uplift or subsidence. We further develop a probabilistic evaluation that accounts for variable vertical ground motion, erosion, and foundation morphologies. Absolute sea‐level change appears primordial, as productivity must have increased by an order of magnitude since the onset of the glacial cycles, ca 2.6 Ma. But most important is relative sea‐level change, i.e. eustasy modulated by uplift or subsidence, that rejuvenates the accommodation space and exposes pristine domains of the shore to active reefs at each cycle. Integrated over the long‐term, vertical land motion sets the pace of reef growth: productivity in tectonically unstable domains is thus expected to be up to ten times higher than stable regions, if any. We quantify the global length of reef coasts and the probability density functions for slopes and uplift rates. Productivity waxes during transgressions to reach 2‐8 GtCaCo3/yr and wanes during highstands, which may contribute to increase atmospheric pCO2 by several tens of ppm during deglaciations. Over the last 1.5 Ma, reefs precipitated ∼0.8 10 6GtCaCO3 (∼500 103 km3), the equivalent of a 1 meter thick layer spread over the entire surface of the Earth. This production modulates the calcium budget, for it represents some 30% of the modern Ca flux in the ocean.

pyBadlands: A framework to simulate sediment transport, landscape dynamics and basin stratigraphic evolution through space and time

Article

Full-text available

Apr 2018
PLOS ONE

Understanding Earth surface responses in terms of sediment dynamics to climatic variability and tectonics forcing is hindered by limited ability of current models to simulate long-term evolution of sediment transfer and associated morphological changes. This paper presents pyBadlands, an open-source python-based framework which computes over geological time (1) sediment transport from landmasses to coasts, (2) reworking of marine sediments by longshore currents and (3) development of coral reef systems. pyBadlands is cross-platform, distributed under the GPLv3 license and available on GitHub (http://github.com/badlands-model). Here, we describe the underlying physical assumptions behind the simulated processes and the main options already available in the numerical framework. Along with the source code, a list of hands-on examples is provided that illustrates the model capabilities. In addition, pre and post-processing classes have been built and are accessible as a companion toolbox which comprises a series of workflows to efficiently build, quantify and explore simulation input and output files. While the framework has been primarily designed for research, its simplicity of use and portability makes it a great tool for teaching purposes. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195557

A unified framework for modelling sediment fate from source to sink and its interactions with reef systems over geological times

Article

Full-text available

Mar 2018

Understanding the effects of climatic variability on sediment dynamics is hindered by limited ability of current models to simulate long-term evolution of sediment transfer from source to sink and associated morphological changes. We present a new approach based on a reduced-complexity model which computes over geological time: sediment transport from landmasses to coasts, reworking of marine sediments by longshore currents, and development of coral reef systems. Our framework links together the main sedimentary processes driving mixed siliciclastic-carbonate system dynamics. It offers a methodology for objective and quantitative sediment fate estimations over regional and millennial time-scales. A simulation of the Holocene evolution of the Great Barrier Reef shows: (1) how high sediment loads from catchments erosion prevented coral growth during the early transgression phase and favoured sediment gravity-flows in the deepest parts of the northern region basin floor (prior to 8 ka before present (BP)); (2) how the fine balance between climate, sea-level, and margin physiography enabled coral reefs to thrive under limited shelf sedimentation rates after ~6 ka BP; and, (3) how since 3 ka BP, with the decrease of accommodation space, reduced of vertical growth led to the lateral extension of reefs consistent with available observational data.

Postglacial fringing-reef to barrier-reef conversion on Tahiti links Darwin's reef types.

Article

Jan 2014

Montaggioni 2005

Data

Full-text available

Jul 2016

Expedition 389 Preliminary Report: Hawaiian Drowned Reefs

Book

Full-text available

May 2024

The implications of structural control on the miocene carbonate reservoirs of Bakr-Al Hamd oil fields, Gulf of Suez

Article

Full-text available

Mar 2024

The present work aims to provide a tectonostratigraphic model of the Miocene carbonate reservoirs accumulated in Bakr-Al-Hamd ridge to help unlock an estimated statistical yet-to-find over 10 MMbbl of oil. The structural ridge is located in the western central Gulf of Suez and the hydrocarbon exploration within this NE-dipping structural high began in 1951. The model integrated several interpreted 3-D seismic volumes and their attributes, a complete set of well-log data, borehole images, and the resultant extensional structures from the natural and physical models. The structural model proposed the following: (1) a major gulf-parallel curved and faulted detachment between the two differentially strained sections of Miocene and Pre-Miocene sediments which were distinguished by seismic attributes and confirmed by borehole images, (2) the synthetic Gulf-parallel faults which represent footwall collapsing structural style of extensional faults, delineated Al Hamd Miocene Nullipore carbonate reservoir, (3) south-westward dislocation of the western gulf-parallel boundary fault of Al Hamd Nullipore facies and its allocation at the present-day shoreline, (4) three classification of the Miocene carbonate reef were interpreted; fringe reef in Bakr ridge, barrier reef in Al-Hamd, and patch reef in the intra-field. The achievements of the present study prompted exploration activity and two discoveries were announced in 2021 and 2022 in the vicinity of Bakr and Al-Hamd intra-fields. The recent discoveries penetrated more than 200 m of Miocene carbonate reef and dolomitic reservoirs accumulated on the detachment surface. The present study workflow could be used in similar petroliferous rift basins to maximize hydrocarbon resources, enhance production performance, and revive brownfields.

Influence of reef isostasy, dynamic topography, and glacial isostatic adjustment on sea-level records in Northeastern Australia

Article

Full-text available

Sep 2023

Understanding sea level during the peak of the Last Interglacial (125,000 yrs ago) is important for assessing future ice-sheet dynamics in response to climate change. The coasts and continental shelves of northeastern Australia (Queensland) preserve an extensive Last Interglacial record in the facies of coastal strandplains onland and fossil reefs offshore. However, there is a discrepancy, amounting to tens of meters, in the elevation of sea-level indicators between offshore and onshore sites. Here, we assess the influence of geophysical processes that may have changed the elevation of these sea-level indicators. We modeled sea-level change due to dynamic topography, glacial isostatic adjustment, and isostatic adjustment due to coral reef loading. We find that these processes caused relative sea-level changes on the order of, respectively, 10 m, 5 m, and 0.3 m. Of these geophysical processes, the dynamic topography predictions most closely match the tilting observed between onshore and offshore sea-level markers.

Expedition 389 Scientific Prospectus: Hawaiian Drowned Reefs

Book

Full-text available

Aug 2023

Drilling 1100-km-long seafloor ridges reveals how palaeoshorelines control carbonate shelf morphologies (North West Shelf, Australia)

Article

Full-text available

Jul 2023
QUATERNARY SCI REV

The Rowley Shelf, the southern half of the tropical, carbonate-dominated, North West Shelf of Australia, is covered with linear ridges that can be tracked parallel to the coast over 1100 km between the modern coast and the 140 m isobath. Here, we investigate the origin and nature of these ridges based on the integration of extensive borehole data, high-resolution geophysical data, age dating and compaction analysis. Our investigation reveals that each ridge consists of now-submerged relict coastal deposits that were formed over the last 200,000 years through wave, tidal, fluvial and aeolian processes. These features were dominantly preserved through early diagenesis and illustrate the longest continuous submerged palaeoshorelines reported to date. The distribution of relict coastal features, and therefore early diagenesis, controls the morphology of the continental shelf. First, relict coastal features tend to be stacked on top of each other, resulting in the formation of composite diachronous coastal deposits that form distinctive steps on the seabed, up to 10s m high. Second, relict coastal features form a hard substrate that controls the location of coral reefs along the shelf. Reefs, including a 20-m-thick MIS 3 drowned coral reef described here for the first time, as well as modern reefs of the Muiron Islands, Montebello Islands and Dampier Archipelago, are all developed on top of relict coastal features. The distribution, size and mineralogy of relict coastal features highlight climatic changes along the Rowley Shelf. High relative sea levels (RSL) are associated with low carbonate production and up to 50% of terrigenous grains, while low RSL deposits exhibit increased carbonate production and reduced terrigenous grain content. This asymmetry is interpreted to reflect the onset of the monsoon associated with increased fluvial runoffs during interglacial periods. Lastly, our work shows that compaction analyses are critical for palaeoenvironment and RSL reconstructions. Indeed, the accumulation of 50 m of sediment on a RSL indicator can result in an offset of the measurement by 12.7 m.

Tidal dynamics drive ooid formation in the Capricorn Channel since the Last Glacial Maximum

Article

Full-text available

Nov 2022
MAR GEOL

Relative sea-level changes can dramatically alter coastal geomorphology and coastlines, which, in turn, can fundamentally alter tidal regimes. The Great Barrier Reef (GBR) has undergone around 120 m of relative sea level (RSL) rise since the Last Glacial Maximum, ∼20,000 years ago (ka). Ooid grains (sand sized carbonate sediment) that formed in shallow water (>5 m depth) and under prolonged hydrodynamics forcing are now found at depth ranging between 100 and 120 m under the present day GBR Gulf of Capricorn. The apparent inconsistency between preferential conditions for their formation and the actual environment where they are found at present-day could be used to infer past regional hydrodynamic conditions. Here, we focus on the regional changes in the GBR tidal dynamics over the last 16.8 ka to show that sea-level rise on the GBR has caused significant changes on tidal patterns and dynamics. To do so, we used the first multi-scale palaeo-tidal finite element coastal tidal model of the GBR over five time slices (present day, ∼10 ka, ∼12 ka, ∼15 ka and 16.8 ka), representing the position of RSL at 0 m, 20 m, 45 m, 75 m and 96 m below present. We show that favourable conditions for ooid formation only existed for a short period of time between 16.8 and 11 ka. At that time, the Gulf of Capricorn was a wide shallow shelf with strong currents constantly agitating grains, providing rapid burial, exposure and re-burial cycles. We show that these conditions only existed for a short period of time and hence explain the presence of ooid grain formation in the GBR at that time. We propose ooids formed within the Capricorn Channel at a time of lower RSL than expected and then underwent sub-tidal transportation to their final deposition place via tidal currents, explaining the inconsistency with their age and the depth at which they were found.

The influence of reef isostasy, dynamic topography, and glacial isostatic adjustment on the Last Interglacial sea-level record of Northeastern Australia.

Preprint

Full-text available

Aug 2022

Understanding sea level during the warmest peak of the Last Interglacial (125,000 yrs ago; Marine Isotope Stage 5e) is important for assessing future ice-sheet dynamics in response to climate change, and relies on the measurement and interpretation of paleo sea-level indicators, corrected for post-depositional vertical land motions. The coasts and continental shelves of northeastern Australia (Queensland) preserve an extensive Last Interglacial record in the facies of coastal strandplains onland and fossil reefs offshore. However, there is a discrepancy (amounting to tens of meters) in the elevation of sea-level indicators between offshore and onshore sites. Here, we assess the influence of geophysical processes that may have changed the elevation of these sea-level indicators since the Last Interglacial. We modeled sea-level change due to: i) dynamic topography; ii) glacial isostatic adjustment, and iii) isostatic adjustment due to coral reef loading, which we term "reef isostasy". These processes caused relative sea-level changes on the order of, respectively, 10 m, 5 m, and 0.3 m since the Last Interglacial. Of these geophysical processes, the dynamic topography predictions most closely match the tilting observed between onshore and offshore sea-level markers. However, we found that these combined geophysical processes cannot explain the full amplitude of the observed discrepancy between onshore and offshore sea-level indicators.

The microfacies distribution pattern of Cozumel Island in southeastern Mexico: An atoll-like model led by quaternary glacioeustatic sea-level changes

Article

Jul 2022
J S AM EARTH SCI

Isolated carbonate banks in stable tectonic settings are ideal for understanding the architecture of sedimentary systems and their response to flooding events. Within these environments, sea-level changes play a primary role in depositing sedimentary units during high sea levels and unconformities during sea-level drops. Microfacies analysis and geologic interpretation, combined with a High Resolution Digital Elevation Model from LiDAR data were used to reevaluate the sediment distribution pattern of Cozumel Island, proposing a new depositional model. The chronostratigraphic framework was established by correlating the exposure surfaces (caliches) of Cozumel with others in adjacent regions. The study of several sections around the island led to the identification of two lithostratigraphic units. Unit 1 comprises two coral reef facies associations (FAs 0 and 1), separated by the Caliche-0 layer. The upper limit of Unit 1 is represented by the Caliche 1 layer and the karst features developed during Marine Isotopic Stage (MIS) 6. Unit 2 was deposited over the ancient karst topography as the lower limit, with Caliche 2 as the upper limit. Unit 2 comprises three facies associations (FAs-2A, B, C), consistent with the protected, open lagoon and the facies of the platform margin, establishing atoll-like depositional conditions. Unit 2 developed during the last interglacial MIS 5e, whereas the Caliche 2 layer started to develop in a post-MIS 5e event during the sea-level drop. This exposed the previous depositional environments to meteoric diagenesis with the formation of the caliche layer. The Caliche 2 layer stabilized the landscape until the present day. Unit 2 correlates to certain morphostratigraphic and geomorphological structures (Terraces I, II, III) on the island. The emplacement of sand islands (FAs-2A), preexisting topography, relative sea-level variations, and sediment supply lead to the pattern and configuration of the depositional model. In addition, the evolution of Cozumel Island during the MIS 5e is similar to other Holocene atoll-like islands in the Caribbean region.

Cryptic diversity and spatial genetic variation in the coral Acropora tenuis and its endosymbionts across the Great Barrier Reef

Article

Full-text available

Jul 2022
EVOL APPL

Genomic studies are uncovering extensive cryptic diversity within reef‐building corals, suggesting that evolutionarily and ecologically relevant diversity is highly underestimated in the very organisms that structure coral reefs. Furthermore, endosymbiotic algae within coral host species can confer adaptive responses to environmental stress and may represent additional axes of coral genetic variation that are not constrained by taxonomic divergence of the cnidarian host. Here, we examine genetic variation in a common and widespread, reef‐building coral, Acropora tenuis, and its associated endosymbiotic algae along the entire expanse of the Great Barrier Reef (GBR). We use SNPs derived from genome‐wide sequencing to characterise the cnidarian coral host and organelles from zooxanthellate endosymbionts (genus Cladocopium). We discover three distinct and sympatric genetic clusters of coral hosts, whose distributions appear associated with latitude and inshore‐offshore reef position. Demographic modelling suggests that the divergence history of the three distinct host taxa ranges from 0.5 – 1.5 million years ago, preceding the GBR’s formation, and has been characterised by low to moderate ongoing inter‐taxon gene flow, consistent with occasional hybridisation and introgression typifying coral evolution. Despite this differentiation in the cnidarian host, A. tenuis taxa share a common symbiont pool, dominated by the genus Cladocopium (Clade C). Cladocopium plastid diversity is not strongly associated with host identity but varies with reef location relative to shore: inshore colonies contain lower symbiont diversity on average but have greater differences between colonies as compared to symbiont communities from offshore colonies. Spatial genetic patterns of symbiont communities could reflect local selective pressures maintaining coral holobiont differentiation across an inshore‐offshore environmental gradient. The strong influence of environment (but not host identity) on symbiont community composition supports the notion that symbiont community composition responds to habitat, and may assist in the adaptation of corals to future environmental change.

Submarine landslide morphometrics and slope failure dynamics along a mixed carbonate-siliciclastic margin, north-eastern Australia

Article

Feb 2022
GEOMORPHOLOGY

Comparatively little work has been carried out on the morphology and distribution of submarine landslides on mixed carbonate-siliciclastic margins. The morphometric analysis of 84 open slope submarine landslides on the Great Barrier Reef (GBR) margin of north-eastern Australia provides useful insights into slope failure dynamics and frequency distribution of landslides on mixed margins. Our analysis has revealed that the slope area affected by failures (12.6% of the margin) is similar to siliciclastic-dominated passive margins, although the total volume of remobilized sediment (73 km³) is comparatively small. Landslide scars lie at shallower depths to the south of the margin (mean of 576 m vs 1517 m to the north) and there is good correlation between the depth at origin and depth at termination for the GBR landslides. The cumulative frequency distribution of volume, area and total length of the GBR landslides does not fit to common distributions (e.g., power law, logarithmic or exponential) for the entire dataset. Still, the cumulative frequency distribution of landslide dimensions can be statistically explained either by a power law similar to other passive margins, or by a lognormal distribution similar to some siliciclastic margins. Morphometric characteristics, such as the volume of sediment released per unit width and the probability function of volume distribution suggest that slope failures mainly involved relatively unconsolidated sediments. We find that the disintegration by debris flows was the dominant process along the entire GBR margin and that their spreading efficiency and mobility was relatively low. Margin stratigraphy, fluid overpressure at the base of the slope, and detachment surfaces at the boundary between different lithologies that separate sedimentary cycles may have preconditioned the slope to fail. This compilation provides a robust morphometric framework that allows comparison with existing and future slope failure databases, and lays the foundation for performing numerical simulations to assess the landslide-generated tsunamigenic hazards along the GBR margin.

Coralline algal assemblages record Miocene sea-level changes in the South China Sea

Article

Sep 2021
PALAEOGEOGR PALAEOCL

We have previously shown that the coralline algal assemblages (CAAs) of the South China Sea may indicate post-Pliocene paleo-water depth changes; however, the pre-Pliocene coralline algal compositions and related sea-level significance remain to be elucidated. In the present study, we explore the Miocene coralline algal compositions and their role in recording the sea level, and show the distribution, classification, type, abundance, and diversity of Miocene coralline algae from 213 petrologic thin sections using a coral-reef carbonate sequence from the northern South China Sea. The diversity and abundance of coralline algae in the early and late Miocene are higher than those in the middle Miocene. Eleven genera were identified and grouped into seven CAAs, showing a water depth range from <5 m to >25 m. At 18.67–17.98 Ma, the coral reef was in a stagnation/drowning stage, with rising sea levels exceeding the development of the coral reef. At 17.98–16.78 Ma, the coral reef was in a rapid development during a rapid rise in sea level. Additionally, at 16.78–14.79 Ma, low coralline algal abundance was observed, and the corals were sporadically distributed at a relatively stable sedimentation rate, suggesting a decline in coral reef development. At 14.79–10 Ma, the coral reef development was remarkably slow or stagnant. Furthermore, at 10–5.3 Ma, the coral reefs developed slowly, indicating a gradual rise in the sea level. The sea-level changes indicated by coral reef development are consistent with the long-term global sea-level changes, indicating that the composition and assemblage of Miocene coralline algae can be used to accurately relay the sea-level history.

Large-scale margin collapses along a partly drowned, isolated carbonate platform (Lansdowne Bank, SW Pacific Ocean)

Article

Apr 2021
MAR GEOL

The Lansdowne Bank is a partly drowned, isolated carbonate platform of around 4000 km² located 300 km west of New Caledonia, in the SW Pacific Ocean, in water depths of 20 to 100 m. New multibeam bathymetric data, high resolution seismic reflection profiles and sediment gravity cores have been acquired on the bank top and adjacent slopes. This dataset reveals an almost continuous 4 km wide outer reef rim located in ca. 50 m water depth, surrounding a gently deepening inner platform, reaching up to 100 m water depth. The bank is bordered by very steep slopes showing numerous erosional morphologies such as canyons, channels and gullies. Along with these bypass features, spectacular bank margin collapses and slope failures are evidenced by up to 20 km-wide bank edge and intraslope failure scars, respectively, resulting in a typical “scalloped” geometry of the bank margin. These failure scars can lead to a complete collapse of the outer reef rim and impact subsequent reef development. Bank margin collapses are evidenced by hectometer to kilometer-scale blocks and debris shed on the slope, likely emplaced by rock fall/avalanching processes originating from the brittle failure of early cemented bank edge and upper slope sediments. In turn, failures triggered on the un-cemented mud-prone middle to lower slopes likely generate more cohesive, submarine debris flows that could be at the origin of erosive morphologies within the debris fields. Estimated individual failure volumes can reach up to 3 km³. Quaternary sea-level lowstands, that would have led to platform exposure, fracturing and karstification, and the development of an erosional sea cliff, as well as subsequent rising sea-level are believed to play a significant role in mass wasting event emplacement, yet “bottom up” submarine processes such as the upslope propagation of bypass morphologies by retrogressive headward erosion cannot be ruled out. In terms of geomorphic and stratigraphic constraints, the documented bank margin collapses affect a terrace located in 70 m water depth around the bank, which, depending on its age and origin, could provide a minimum age for collapse events. Finally, considering the shallow water depth of failure headscarps, the volumes of material involved in the slides as well as their vicinity to the nearby main island of New Caledonia, numerical simulations of the tsunamigenic potential of submarine slides have been performed. They showed that these slides would have been able to produce a meter-scale wave that would reach the northern coast of the island in less than an hour.

Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration

Article

Full-text available

May 2020

Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world’s largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change. The causes of the Upper Pleistocene megafauna extinction in Australia and New Guinea are debated, but fossil data are lacking for much of this region. Here, Hocknull and colleagues report a new, diverse megafauna assemblage from north-eastern Australia that persisted until ~40,000 years ago.

The Influence of Carbonate Platforms on the Geomorphological Development of a Mixed Carbonate‐Siliciclastic Margin (Great Barrier Reef, Australia)

Article

Full-text available

Apr 2020
GEOCHEM GEOPHY GEOSY

Sedimentation regimes on the Great Barrier Reef margin often do not conform to more conventional sequence stratigraphic models, presenting difficulties when attempting to identify key processes that control the margin's geomorphological evolution. By obstructing and modifying down‐shelf and down‐slope flows, carbonate platforms are thought to play a central role in altering the distribution and morphological presentation of common margin features. Using numerical simulations, we test the role of the carbonate platforms in reproducing several features (i.e., paleochannels, shelf‐confined fluvial sediment mounds, shelf‐edge deltas, canyons, and surface gravity flows) that have been described from observational data (seismic sections, multibeam bathymetry, sediment cores, and backscatter imagery). When carbonate platforms are present in model simulations, several notable geomorphological features appear, especially during lowstand. Upon exposure of the shelf, platforms reduce stream power, promoting mounding of fluvial sediments around platforms. On the outer shelf, rivers and streams are re‐routed and coalesce between platforms, depositing shelf‐edge deltas and incising paleochannels through knickpoint retreat. Additionally, steep platform topography triggers incision of slope canyons through turbidity currents, and platforms act as conduits for the localized delivery of land and shelf‐derived sediments to the continental slope and basin. When platforms are absent from the topographic surface, the model is unable to reproduce many of these features. Instead, a more typical “reciprocal‐type” sedimentation regime arises. Our results demonstrate the essential role of carbonate platform topography in modulating key bedload processes. Therefore, they exert direct control on the development of various geomorphological features within the shelf, slope, and basin environments.

The Variable Influences of Sea Level, Sedimentation and Exposure on Holocene Reef Development over a Cross-Shelf Transect, Central Great Barrier Reef

Article

Full-text available

Oct 2018
Diversity

Coral reefs globally are impacted by natural and anthropogenic stressors that are compounded by climate change. Understanding past reef responses to natural stressors (cyclones, sea-level change, freshwater inputs, and sedimentation) can provide important insights to further understand recent (within the past century) trends in coral cover and diversity. Here we use a compilation of recently published data to investigate the Holocene development of five fringing reefs that are located on a cross-shelf transect on the central Great Barrier Reef, and that are exposed to varying degrees of natural and anthropogenic sedimentation, storm exposure, and Holocene sea-level change. Forty-two reef cores collected using a combination of manual percussion coring and hydraulic drilling techniques, were analysed and dated using uranium-thorium methods. The chronostratigraphic records of reef development established using 105 recently published radiometric ages and seven new uranium-thorium ages from the reef cores and fossil microatolls preserved across the reef flats were compared to investigate cross-shelf variations in reef development. This is the first study to conduct an internal investigation of reef framework across an inshore–offshore gradient to examine the varying levels of influence of sedimentation, sea level and cyclones. Our observations from the central Great Barrier Reef show that reefs furthest offshore from the mainland coast were typically initiated earliest after the post-glacial marine transgression. Reef flat size, morphology, and growth style varied according to constraints placed on reef development by the composition, depth, shape, and relief of the underlying substrate. We establish that terrigenous sedimentation had a marked effect on the development of inshore reefs closest to the mainland (within 10 km of the mainland coast). Periods of relatively high terrigenous sedimentation correspond with enhanced reef accretion rates, and also resulted in a superior record of palaeo-ecological coral composition (i.e., better preservation) at inshore sites. In contrast, mid-Holocene cyclones played a seemingly more important role in the development of reefs >10 km from the mainland; although cyclones clearly affect reefs closer inshore, their geomorphology is affected by a range of controlling factors. Insights provided by these five Holocene reef chronostratigraphies provide useful baseline understanding of reef condition and growth along a cross-shelf transect where the reefs are exposed to variable stressors.

Response of the Great Barrier Reef to sea-level and environmental changes over the past 30,000 years

Article

Full-text available

Jun 2018
NAT GEOSCI

Previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea-level change since the Last Glacial Maximum, however, how reefs responded to these changes remains uncertain. Here we document the evolution of the Great Barrier Reef (GBR), the world's largest reef system, to major, abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological, biological and geochronological records from fossil reef cores. We show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation (∼20.5-20.7 thousand years ago (ka)), then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period (∼20-10 ka). Growth was interrupted by five reef-death events caused by subaerial exposure or sea-level rise outpacing reef growth. Around 10 ka, the reef drowned as the sea level continued to rise, flooding more of the shelf and causing a higher sediment flux. The GBR's capacity for rapid lateral migration at rates of 0.2-1.5 m yr⁻¹ (and the ability to recruit locally) suggest that, as an ecosystem, the GBR has been more resilient to past sea-level and temperature fluctuations than previously thought, but it has been highly sensitive to increased sediment input over centennial-millennial timescales. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

Coralline red algae from late Palaeocene–earliest Eocene carbonates of Meghalaya, N–E India: palaeocommunity and trophic-level implications

Article

Full-text available

Dec 2018

Coralline red algae are important skeletal components of the Sylhet Limestone platform deposits outcropping in Meghalaya, N–E India. These are highly abundant in the presently studied Late Palaeocene–earliest Eocene carbonate succession pertinent to the Lakadong Limestone. The coralline algae are mainly represented by melobesioid and sporolithacean taxa characterised by encrusting, warty, lumpy, fruticose, and unconsolidated growth forms. Larger benthic foraminifera are also abundant in the examined biotic assemblages. Herein, the aspects of palaeocommunity analysis and trophic-level reconstruction have been approached as well. Special emphasis has been given to the dominant fossil coralline algae by means of discussion on their systematic descriptions and contribution to the community structure as one of the primary producers. Palaeocommunity analysis through the evaluation of the fossil assemblages makes it possible to interpret trophic-group differentiation in primary producers and various consumer groups. A schematic food web organization supported by the recorded biogenic components has also been deciphered.

Benthic communities under anthropogenic pressure show resilience across the Quaternary

Article

Full-text available

Sep 2017

The Southeast Pacific is characterized by rich upwelling systems that have sustained and been impacted by human groups for at least 12 ka. Recent fishing and aquaculture practices have put a strain on productive coastal ecosystems from Tongoy Bay, in north-central Chile. We use a temporal baseline to determine whether potential changes to community structure and composition over time are due to anthropogenic factors, natural climatic variations or both. We compiled a database (n = 33 194) with mollusc species abundances from the Mid-Pleistocene, Late Pleistocene, Holocene, dead shell assemblages and live-sampled communities. Species richness was not significantly different, neither were diversity and evenness indices nor rank abundance distributions. There is, however, an increase in relative abundance for the cultured scallop Argopecten, while the previously dominant clamMulinia is locally very rare. Results suggest that impacts from both natural and anthropogenic stressors need to be better understood if benthic resources are to be preserved. These findings provide the first Pleistocene temporal baseline for the south Pacific that shows that this highly productive system has had the ability to recover from past alterations, suggesting that if monitoring and management practices continue to be implemented, moderately exploited communities from today have hopes for recovery.

Towards a new paleotemperature proxy from reef coral occurrences

Article

Full-text available

Dec 2017

Global mean temperature is thought to have exceeded that of today during the last interglacial episode (LIG, ~ 125,000 yrs b.p.) but robust paleoclimate data are still rare in low latitudes. Occurrence data of tropical reef corals may provide new proxies of low latitude sea-surface temperatures. Using modern reef coral distributions we developed a geographically explicit model of sea surface temperatures. Applying this model to coral occurrence data of the LIG provides a latitudinal U-shaped pattern of temperature anomalies with cooler than modern temperatures around the equator and warmer subtropical climes. Our results agree with previously published estimates of LIG temperatures and suggest a poleward broadening of the habitable zone for reef corals during the LIG.

High resolution hyperspectral imaging of diagenesis and clays in fossil coral reef material: A nondestructive tool for improving environmental and climate reconstructions

Article

Aug 2017
GEOCHEM GEOPHY GEOSY

Hyperspectral imagery (1000-2500 nm) was used to quantitatively map carbonate and clay minerals in fossil reef cores that are relevant to accurately reconstructing past environmental and climatic conditions. Techniques were developed using hyperspectral imagery of fossil reef corals and cores acquired from three different geological settings, and were validated against independent measures of calcite to aragonite ratios. Aragonite, calcite and dolomite were distinguished using a combination of the wavelength position and asymmetry of the primary carbonate absorption between 2300 and 2350 nm. Areas of core containing small amounts of calcite (> 2-5%) were distinguished from aragonite in imagery of two cores, enabling quantitative maps of these minerals to be constructed. Dolomite was found to be the dominant mineral in another core. Trace amounts of the aluminum-rich clay mineral kaolinite were detected, quantified and mapped in one core using its diagnostic absorption feature near 2200 nm. The amounts of clay detected from hyperspectral imagery were below the limits of detection by standard X-ray diffraction techniques but its presence was confirmed by Fourier Transform Infrared Spectroscopy. Hyperspectral imagery acquired at high spatial resolution simplifies vetting procedures for secondary carbonate minerals in coral reef cores, significantly reduces sampling time and costs, and is a powerful non-destructive tool to identify well-preserved coral aragonite in cores for uses in paleoclimate, paleoenvironment and paleoecosystem reconstruction.

Gloria Knolls Slide: A prominent submarine landslide complex on the Great Barrier Reef margin of north-eastern Australia

Article

Dec 2016
MAR GEOL

We investigate the Gloria Knolls Slide (GKS) complex on the Great Barrier Reef margin of north-eastern Australia, the largest extant mixed carbonate-siliciclastic province in the world. Based on the most complete bathymetric and sub-bottom profile datasets available for the region, we describe the main surface and subsurface geomorphologic characteristics of this landslide complex. The GKS forms a 20 km along-slope and 8 km across-slope indentation in the margin, extending from 250 to 1350 m depth, and involves a volume of 32 km³ of sediment remobilized during three events. Three main seafloor terrains can be distinguished based on seafloor morphology: a source area, a proximal depositional area and a distal depositional area. The source area includes a main headwall scarp with a maximum height of 830 m and a secondary scarp at 670 m depth. The proximal depositional area is flat and smooth, and lacks debris exposed on the seafloor. The distal depositional area has a hummocky surface showing a distinctive cluster of eight knolls and over 70 small debris blocks. A dredge sample from the top of the largest knoll at a depth of 1170 m reveals the presence of a cold-water coral community. In the sub-bottom profiles, the mass-transport deposits in the GKS are identified below the background sediment drape as partially confined, wedge-shaped bodies of mostly weak amplitude, transparent reflectors in the proximal depositional area; and more discontinuous and chaotic in the distal depositional area. The failed sediment slabs of the GKS were evacuated, transported and disintegrated downslope in three events following a sequential failure process spreading successively from the lower slope to the upper slope. The first event initiated at the lower slope at the depth of the secondary scarp, moved downslope and disintegrated over the basin floor leaving coherent blocks. The subsequent second and third events were responsible for the formation upslope of the main scarp in the GKS. The timing of emplacement of the first GKS event, constrained by radiometric age of fossil biota from the surface of the largest slide block, was at least before 302 ± 19 ka. The presence of alternating mixed carbonate and siliciclastic lithologies that build the slope might have played an important role as a preconditioning factor in this region. Preliminary estimations suggest that unusually large seismic events were the most likely triggering mechanism for the GKS. This work contributes to the understanding of large mass-movement deposits in mixed carbonate-siliciclastic margins and provides a useful morphologic characterization and evolutionary model for assessing its tsunamigenic potential with further numerical simulations. In addition, the discovery of a cold-water coral community on top of the largest knoll has implications for identifying similar landslide-origin cold-water coral communities on the GBR margin.

IODP Expedition 325: Great Barrier Reefs Reveals Past Sea-Level, Climate and Environmental Changes Since the Last Ice Age

Article

Sep 2011

The timing and courses of deglaciations are key components in understanding the global climate system. Cyclic changes in global climate have occurred, with growth and decay of high latitude ice sheets, for the last two million years. It is believed that these fluctuations are mainly controlled by periodic changes to incoming solar radiation due to the changes in Earth’s orbit around the sun. However, not all climate variations can be explained by this process, and there is the growing awareness of the important role of internal climate feedback mechanisms. Understanding the nature of these feedbacks with regard to the timing of abrupt global sea-level and climate changes is of prime importance. The tropical ocean is one of the major components of the feedback system, and hence reconstructions of temporal variations in sea-surface conditions will greatly improve our understanding of the climate system. The Integrated Ocean Drilling Program (IODP) Expedition 325 drilled 34 holes across 17 sites in the Great Barrier Reef, Australia to recover fossil coral reef deposits. The main aim of the expedition was to understand the environmental changes that occurred during the last ice age and subsequent deglaciation, and more specifically (1) establish the course of sea-level change, (2) reconstruct the oceanographic conditions, and (3) determine the response of the reef to these changes. We recovered coral reef deposits from water depths down to 126 m that ranged in age from 9,000 years to older than 30,000 years ago. Given that the interval of the dated materials covers several paleoclimatologically important events, including the Last Glacial Maximum, we expect that ongoing scientific analyses will fulfill the objectives of the expedition. doi:10.2204/iodp.sd.12.04.2011

ReefCoreSeg: A clustering-based framework for multi-source data fusion for segmentation of reef cores

Article

Full-text available

Jan 2023

Coral reefs are among the most biologically diverse and economically valuable ecosystems on Earth, but they are threatened by climate change. Understanding how reefs developed over geological timescales can provide important information about past environmental changes and their impacts on reef systems. Significant effort and capital have been invested in drilling and analyzing reef cores. Recognizing coral and sediment patterns visually from fossil reefs is a laborious task that demands domain expertise. Unsupervised machine learning methods, such as clustering that have been used for image segmentation in remote sensing can be repurposed for reef core segmentation. In this paper, we present a numerical framework that utilizes clustering and classification methods to fuse multiple sources and formats of data for the segmentation and annotation of reef cores. The framework produces an annotated image of a reef core with six lithologies identified; Massive corals, encrusted corals, coralline algae, microbialite, sand, and silt. We utilize reef cores recovered from Expedition 325 of the International Ocean Discovery Program (IODP) to the Great Barrier Reef. We use image and physical properties data to segment reef cores. The results show that Gaussian Mixture Models can accurately segment the image with a clear visual distinction between two major classes: Massive corals and stromatolitic microbialites. Furthermore, the random forest classifier performed best in creating annotations for the segmented image with an accuracy of 96%.

Coral records of relative sea-level changes

Chapter

Jan 2023

Geochemical significance of Acropora death assemblages in the northern South China Sea: Implications for environmental reconstruction using branching corals

Article

Aug 2022
PALAEOGEOGR PALAEOCL

The geochemistry preserved in coral skeletons provides access to pre-instrumental records of environmental changes. While a variety of proxies have been established for coral paleoclimatology, their applications to the use of Acropora to generate longer-term reconstructions have been studied less. Here, we examine the geochemical proxies (i.e., Sr/Ca, Li/Mg, δ¹⁸O, δ¹³C, δ¹¹B, and B/Ca) of dead Acropora assemblages collected from a fringing reef off Hainan Island in the northern South China Sea. These samples have been precisely dated using UTh isotopes and record reef development episodes since the mid-Holocene, allowing us to assess their potential as paleoclimate archives. The sea surface temperature (SST) trend reconstructed by Sr/Ca and Li/Mg exhibits better consistency with each other, and they have recorded the SST shifts around 5–4 ka BP and the subdued variability during the Medieval Climate Anomaly (MCA), whereas the δ¹⁸O-SST record exhibits less clear variations over the past 7000 years. However, the universal Li/Mg-SST calibration tends to underestimate the SST reconstruction from tropical corals, highlighting the importance of using a site- and species-specific calibration of the Li/Mg-SST. Boron systematics are used to reconstruct the carbonate chemistry of coral calcifying fluid (CF), which reveals significant differences between the ancient and modern corals. The pH of the coral CF (pHcf) is significantly lower in the modern Acropora compared to the ancient corals, with a mean difference of ~0.08 pH, corroborating the pronounced influence of ocean acidification on the coral CF chemistry. The dissolved inorganic carbon of the coral CF (DICcf) is also lower for modern Acropora, and this decreasing trend seems to have persisted over the past 7000 years. In addition, the skeletal δ¹³C is closely related to the CF carbonate chemistry, highlighting the intrinsic relationship between the coral internal carbon pool used for calcification and the up-regulation of the pHcf.

Coral community of Holocene coral reef in the southern South China Sea and its significance for reef growth

Article

Jul 2022
PALAEOGEOGR PALAEOCL

Ancient coral reefs are rich archives of historical process and vital baselines for future development. Coring gives a window into the growth of ancient coral reefs and the fossil coral community's response to paleoenvironment. Well NK-1 drilled from Meiji Reef is the longest scientific core with the highest recovery in the South China Sea. This study focused on the upper section of the Well NK-1 accumulated during the Holocene. From 8200 yr BP, Holocene reef initiated on the substrates of Pleistocene limestone and stopped accreting vertically at 4800 yr BP. It consisted of an initiation and fast reef growth (5.6 mm yr⁻¹) from 8200 yr BP to 7300 yr BP, a shift to slow reef growth (2.0 mm yr⁻¹) between 7300 yr BP and 5400 yr BP, a return to a rapid reef growth (8.8 mm yr⁻¹) from 5400 yr BP to 4800 yr BP, and finally a cessation of upward accretion and a reinforced lateral progradation since 4800 yr BP. A total of 11 coral genera and 16 Acropora species were identified from the Holocene segment of the core. The diversity of coral communities had an impact on reef growth. Coral communities with less genera and absolute predominance of branching Acropora were corresponded with a rapid vertical accumulation of reef framework with higher accretion rate. Acropora corals with rapid growth and dispersion by fragmentation were principal reef-builders during the Holocene, with A.valida being the most prevalent coral species. The highest Acropora species richness occurred at the geological era of 5400–5300 yr BP when reef accumulated with the fastest upward accretion rate of 23.1 mm yr⁻¹. This intricate and detailed pattern presented a new and novel model for the development of Holocene reef, indicating that the coral community and key reef builders were crucial to reef growth. These findings are extremely helpful for understanding the current ecological state of modern coral reefs as well as their potential response to global climate change.

Constraining rapid sea level change through radiometric dating of corals growing over a range in paleowater depths

Article

Apr 2022

Corals do not all grow near the sea surface. Different species favour different ranges in depth and can survive at different depths from 0 to 5 m to over 0–100 m. Fossil corals, as markers of sea level, are the preferred choice in radiometric dating. Timing and magnitude of sea-level variations are determined from the location and age of a set of in-situ coral samples, and mark the lower bound in sea level. In addition, they have to be assigned an uncertainty to define the upper bound in sea level. This is referred to as the paleowater depth (PWD) and creates a major ambiguity in estimating the appropriate span of habitable depth in sea level. This uncertainty also has an impact on constraining the timing and magnitude of rapid changes in sea level. However, there are approaches that may minimize PWD uncertainties. These include assessing sea level data for groups of coral, during relatively stable sea levels, rather than individually. If samples were recovered in multiple drill-cores, along a sea-bed transect, tighter PWD constraints may apply for samples, in each core, depending on the magnitude of the slope of the sea bed. This method is particularly useful in cases of rapid sea level change over shallow continental shelves when the shift in the shoreline, with sea level change, is large. In these circumstances, the presence of a shallow-water reef established up or down-slope is indicative of a rapid change in sea level.

‘A Close and Friendly Alliance’: Biology, Geology and the Great Barrier Reef Expedition of 1928–1929

Chapter

Sep 2021

Study of the Tectonic/Erosion/Eustatism coupling on the morphogenesis of the Cape Laundi coral reef terrace sequence (Sumba Island, Indonesia)

Thesis

Full-text available

Mar 2021

Denovan Chauveau

During the Quaternary, the significant and frequent variations in sea level, associated with tectonic uplift, locally caused the emergence of coral reefs, forming coral reef terrace sequences. They are widespread throughout the world and form an important part of coastal geological formations. From global to local scales, coral reef terrace sequences are essential records of sea level, paleoclimate, and tectonics in the Quaternary. This thesis aims to improve the understanding of the morphogenesis of coral reef terrace sequences by studying the different processes of generation (tectonic movements, eustatic variations, reef bioconstructions) and degradation (marine erosion, continental denudation) of these sequences. For this purpose, a precise geomorphological analysis of the emerged coral reef terraces sequence at Cape Laundi (Sumba Island, Indonesia) was carried out through field surveys and the use of DEM, differential GPS data and satellite images. Dating (230Th/U) and modeling were carried out to constrain the sequence generation processes. To quantify degradation, continental denudation rates (chemical and alluvial) are calculated from the 36Cl cosmonuclides concentrations measured in the limestones forming the terraces. The main results of this thesis have, among others, highlighted 1) the different stages of coral reef terrace morphogenesis, especially those associated with the last interglacial stage (MIS 5), 2) the reoccupation phenomena (constructive and erosive) affecting the lowest terraces of the Cape Laundi sequence, 3) the ratio between continental and marine denudation rates, and 4) the formation and migration processes of eustatic-triggered knickpoints (incision waves) generated along coastal streams draining the sequence. By this way, this thesis disentangles the tectonic, erosive, and eustatic components, as well as their coupling, responsible for the formation of the emerged coral reef terraces sequence at Cape Laundi.

DEFESA -TESE DE DOUTORADO KARINA MASSEI A BIOGEOGRAFIA MARINHA E O SABER LOCAL DO RECIFE DO SEIXAS (JOÃO PESSOA/PB) PARA APLICAÇÃO DE PRÁTICAS AMBIENTAIS ABRIL 2019 JOÃO PESSOA, PARAÍBA UNIVERSIDADE FEDERAL DA PARAÍBA PROGRAMA REGIONAL DE PÓS-GRADUAÇÃO EM DESENVOLVIMENTO E MEIO AMBIENTE

Thesis

Apr 2019

Karina Massei

Este estudo apresentou dados novos e relevantes sobre a geomorfologia, geofísica e biota do ambiente recifal do Seixas/PB, sendo um dos pioneiros nesse ambiente recifal com esse nível de detalhamento. Os estudos geológicos, geofísicos e geoquímicos evidenciaram a existência de compartimentos (praia, plataforma interna e recife), áreas (abrigada, platô recifal e batida) e feições geomorfológicas (canal, planície recifal, crista, frente recifal, pós-recife), indicando que os processos deposicionais do fundo marinho sofreram influência oceanográfica. Não foi possível encontrar a rocha-base de sustentação para a edificação do recife através de três perfurações com profundidade máxima de 250 cm, os resultados das lâminas petrográficas, do difratograma de raios-X analisados e do material coletado nos mergulhos realizados na parede externa do recife demonstraram que o recife do Seixas é uma formação biogênica carbonática coral-algal recente - associada com a evolução da linha de costa, com a elevada sedimentação costeira e agindo em conjunto com a elevação do nível do mar (Período Quaternário Holocênico) -, apoiada no terraço marinho de abrasão sob a planície costeira moldada pela Bacia Sedimentar Paraíba, mais precisamente na Sub-bacia Alhandra e dista aproximadamente 30 km do talude continental nordestino. Atualmente, o recife possui 1,18 km2 de área consolidada com altura máxima de 6 m. A partir de uma base consolidada arenítica ocorreu o assentamento e povoamento de organismos bentônicos, passando por processos de sucessões continuamente. Perfazendo uma área amostral de 225 m², com esforço amostral de 120 h de pesquisas visuais subaquáticas (uso de transectos e fotoquadrados) foi possível mapear as comunidades macroalgais, coralíneas e íctica e verificar que as variáveis ambientais profundidade e granulometria exercem influência na estruturação das comunidades. Em uma cobertura dominada por macroalgas (68,99%), corais, hidrocorais e zoantídeos (7,62%), estruturas calcárias - rodolitos (9,73%), sedimento não-consolidado (11,89%) e sedimento consolidado (1,77%), foram identificados 1435 peixes recifais, representados pelas famílias Haemulidae (696 indivíduos), Labridae-Scarinae (272 indivíduos), Pomacentridae (248 indivíduos), Acanthuridae (108 indivíduos) e em menor número de indivíduos, as famílias Epinephelidae, Mullidae, Sciaenidae, Holocentridae e Gobiidae. Como análise geral, a relação entre as áreas Abrigada e Platô e entre as áreas Batida e Platô, aponta a área Platô como um ambiente de ecótono. A nível de endemismo, quatro famílias coralíneas da ordem Escleractinia e oito espécies da ictiofauna são endêmicas da Província Biogeográfica Atlântico Sul, corroborando com a caracterização geral desta província (baixa diversidade com alto grau de endemismo, sobrevivendo em águas turvas). Através de oficinas e mapas conceituais construídos pelos usuários locais, constatou-se que o grupo dos pescadores é o que mais conhece o ambiente, seja pela necessidade da navegação (formação rochosa) e da pesca (locais de maior oferta, maior número de indivíduos, sendo o hidrocoral “coral-de-fogo” o mais conhecido devido à fauna associada). A junção do conhecimento científico correlacionado com o contexto biogeográfico e saber local adquirido resultaram na aplicação de três práticas ambientais (desvendando as criaturas marinhas, trilha ecológica e rota subaquática) envolvendo a comunidade local conforme premissas da ciência cidadã. O contexto biogeográfico marinho atribuído às práticas para o microcosmo recifal do Seixas foi fundamentado pelos processos históricos e ecológicos de como surgiu este ambiente geológico e de onde vieram as comunidades biológicas, demonstrando as conectividades numa visão local até global dos dias atuais. Palavras-chave: ambiente recifal, geologia sedimentar, comunidade recifal, saber local, práticas ambientais.

A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef

Article

Mar 2020
SEDIMENT GEOL

The fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change. The spatial and temporal pattern of the initiation of the Holocene Great Barrier Reef presents a case study of reef response to rapid sea-level rise. Past studies have been limited by the lack of well-dated and closely spaced reef core transects and have not closely examined the composition of the reef-building communities through time. This study presents 80 new high precision UTh and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of One Tree Reef, southern Great Barrier Reef, to document three distinct stages of Holocene reef development in unprecedented detail. Temporal constraints on changing paleoecological assemblages of coral, coralline algae and associated biota revealed three distinct phases of reef development, consisting of: 1)a fast, shallow and clear-water reef initiation from 8.2 until 8 ka; 2)a shift to slower, deeper and more turbid-water reef growth from 8 to 7 ka; and 3)a return to shallow and rapid branching coral growth in clear-water conditions as the reef “catches up” to sea-level. A minimum lag prior to reef initiation of 700 years was identified, which differs in length depending on reef environment and Pleistocene substrate height. In this new model, reef growth initiated on the topographically lower leeward margin and patch reef, prior to the start of windward margin development, contrary to the traditional reef growth model. While there was a shift to conditions less favorable for reef growth at 8 ka, this did not prevent the slow accretion of more sediment-tolerant coral communities. The majority of the reef reached sea level by ~6 ka. This new conceptual model of Holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea-level rise following inundation.

The Changing Face of Reef Building

Chapter

Jul 2016

Declining calcification and accelerating sea-level rise have brought us ever closer to the point where coral reefs may not be able to keep pace. Even if this is insufficient to change reef-community structure or totally overtop low reef islands in the twenty-first century, the impacts on reefs and the organisms that depend on them will still be profound. Patterns of sea-level rise have varied spatially in the past due to both local tectonics and regional crustal responses to deglaciation. The result has been regionally disparate sea-level histories that complicate our understanding of the links between past sea level and reef development.

Reef growth, and sea level change: The environmental signature

Article

Full-text available

Jan 1985

The 7,000 yr sea-level curve in French Polynesia: geodynamic implications for mid-plate volcanic islands.

Conference Paper

Full-text available

Jan 1988

Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge

Article

Full-text available

Jan 1996

LETTERS TO NATURE example, ~50-40 mmyr1 is roughly equivalent to discharge rates of 16,000 km3 yr~' for MWP-1 A). A third meltwater pulse, smaller than the two other, was identified at ~7,600cal. yr bp in a compilation of Caribbean corals together with the Barbados curve . ...

Limited Membership in Pleistocene Reef Coral Assemblages from the Huon Peninsula, Papua New Guinea: Constancy During Global Change

Article

Full-text available

Mar 1996

J. M. Pandolfi

One of the most intriguing questions in community ecology remains unanswered: Are ecological communities open assemblages with each species reacting individually to environmental change, or are they integrated units consisting of multispecies assemblages acting in concert? I address this question for marine organisms by examining the taxonomic composition and diversity of Indo-Pacific reef coral communities that have undergone repeated global change between 125 and 30 Ka (thousand years before present). Investigation of community constancy through time relies on two critical questions: (1) Are there significant differences in taxonomic composition among communities from different times? and if not, (2) Are the observed patterns in temporal similarity significantly different from expected patterns resulting from a random sampling of the available within-habitat species pool? Constancy in taxonomic composition and species richness of Pleistocene reef coral assemblages is maintained through a 95-k.y. interval in the raised reef terraces of the Huon Peninsula, Papua New Guinea. Fossil reef coral assemblages show limited membership in species composition despite repeated exposure to marked fluctuations in sea level (up to 120 m) and sea-surface temperatures (up to 6°). During the 95-k.y. interval, the reefs experienced nine cycles of perturbation and subsequent reassembly with similar species composition. Spatial differences in reef coral species composition were greater among the three study sites than among reefs of different ages. Thus local environmental parameters associated with riverine and terrestrial sources had a greater influence on reef coral composition than global climate and sea level changes. The ecological dynamics of reef communities from Papua New Guinea are in marked contrast to those of Quaternary terrestrial and level bottom marine communities which appear to show unlimited community membership on both larger and smaller time scales. Differences in community assembly among ecosystems mean either that coral reefs are fundamentally different or that different ecological patterns and processes are occurring at different temporal scales.

Reef growth and sea level: an environmental signature.

Conference Paper

Full-text available

Jan 1985

Continuous record of reef growth over the past 14 k.y. on the mid-Pacific island of Tahiti

Article

Full-text available

Jun 1997
GEOLOGY

Two boreholes were drilled through coralgal sequences in the barrier-reef edge of the mid-Pacific island of Tahiti, and their bases were radiometrically dated at 10.23 (±0.05) and 13.77 (±0.05) ka (thousand calendar years). The sequences are composed mainly of the reef-edge Acropora gr. danai-robusta and Hydrolithon onkodes assemblage, occasionally replaced by reef-slope tabular Acropora-Neogoniolithon or domal Porites-Lithophyllum assemblages. The response of reef growth to sea-level rise has varied according to the framework type, and vertical accretion rates have ranged from 9.3 to 20.6 mm · yr-1. From a general trend of long-term, continuous, sea-level rise tracked by growth, the reef-edge coralgal assemblages have experienced two distinct changes controlled by the antecedent paleotopography and internal reef processes. During the past 13.8 k.y. at Tahiti, there is no evidence of any reef-drowning event primarily caused by global glacio-eustatic perturbations as has been recorded in the Caribbean.

Sea Surface Temperatures in the Western Equatorial Pacific During Marine Isotope Stage 11

Article

Full-text available

Jan 2003

Mg/Ca data from ODP Hole 806B on the Ontong Java Plateau, western equato-rial Pacific, indicate that marine isotope stage (MIS) 11 was the warmest inter-glacial episode of the last 450 ky. Sea surface temperatures (SSTs) for MIS 11, as calculated from Mg/Ca, reached just above 30°C. MIS 11 is also character-ized by the longest sustained period (~20 ky) of SST ≥ 29°C. The maximum in MIS 11 SST is flanked by strong minima in SST (25 to 26°C) in glacial MIS 10 and 12. The changes in SST, as indicated by Mg/Ca, lead the changes in δ 18 O at the climate transitions by as much as 7-9 ky, suggesting that temperature changed before ice volume and/or local hydrology. Warm tropical Pacific SST during MIS 11 is supported by uplifted reefs of coeval age containing warm-water fauna on the Chilean coast. A super-interglacial in the tropical Pacific during MIS 11 would undoubtedly have influenced global climate through direct heat exchange and influence on atmospheric H 2 O and CO 2 .

Patterns in the distribution of coral communities across the central Great Barrier Reef

Article

Full-text available

Oct 1982

Terry Done

Despite the pre-eminence of the Great Barrier Reef, there has been little systematic description of its biotic communities, and in particular, of the corals themselves. Only recently have the problems of coral taxonomy been sufficiently resolved to allow a beginning to be made in rectifying this deficiency. The present study describes seventeen assemblages of corals which occupy the major habitat types found in and near the central Great Barrier Reef. The habitats studied range from the wave swept reef flats of Coral Sea atolls to the slopes of small reefs occupying sheltered, muddy conditions near the coast. These, and the array of reefs between, have characteristic suites of coral communities which provide the basis for a classification of reefs into non-Acropora reefs and various Acropora reefs. It is speculated that the faunistic differences are maintained because reefs are primarily self-seeded and because the majority of larvae from external sources are of species which are already present. The greatest diversity of both species and community types was found on reefs near the middle of the continental shelf, while the oceanic atolls and nearshore silt-affected reefs are almost equally depauperate.

Holocene sea-level changes and reef development in South-Western Indian Ocean

Article

Full-text available

Jan 1997

The sedimentological and chronological study of Holocene reef sequences recovered in drill cores through modern reefs of Mauritius, Réunion Island and Mayotte allows the reconstruction of sea level changes and reef growth patterns during the Holocene. The branching-coral facies systematically predominates over coral head facies throughout the Holocene reef sequences, and Acropora is the main frame builder among the branching forms. The reconstructed sea level curves, based both on identification of coral assemblages and on radiometric U/Th ages, are characterized by a rapid rise between 10 and 7.5 ky BP, followed by a clear inflection between 7.5 and 7 ky BP. The stabilization of sea level at its present level occurred between 2000 and 3000 years ago, probably without a higher sea level stand. Rates of vertical reef accretion range between 0.9 and 7 mm. y-1. In Mauritius, and also probably in Réunion Island, the reef first tracked, then caught-up to sea level to reach an equilibrium position (“catch-up” growth), while the barrier reef margin off Mayotte has been able to keep pace with rising sea level (“keep-up” growth).

Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge. Nature 382, 241-244

Article

Full-text available

Jul 1996

The timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets and their effects on the Earth's surface. Moreover, the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans, which probably disturbed the ocean's thermohaline circulation and, hence, global climate. Sea-level increase bear witness to the melting of continental ice sheets, but only two such records - from Barbados and New Guinea corals - have been accurately dated. But these corals overlie active subduction zones, where tectonic movements are large and often discontinuous (especially in New Guinea), so the apparent sea-level records may be contamined by a complex tectonic component. Here we date fossil corals from Tahiti, which is far from plate boundaries (and thus is likely to be tectonically relatively stable) and remote from the locations of large former ice sheets. The resulting record indicates a large sea-level jump shortly before 13,800 calendar years BP, which correponds to meltwater pulse 1 A in the Barbados coral records. The timing of this event is more accurately constrained in the Tahiti record, revealing that the meltwater pulse coincides with a short and intense climate cooling event that followed the initiation of the Bolling-Allerod warm period, but preceded the Younger Dryas cold event by about 1 000 years. (Résumé d'auteur)

Sea-Surface Temperature from Coral Skeletal Strontium/Calcium Ratios

Article

Full-text available

Aug 1992

Seasonal records of tropical sea-surface temperature (SST) over the past 105 years can be recovered from high-precision measurements of coral strontium/calcium ratios with the use of thermal ionization mass spectrometry. The temperature dependence of these ratios was calibrated with corals collected at SST recording stations and by 18O/16O thermometry. The results suggest that mean monthly SST may be determined with an apparent accuracy of better than 0.5°C. Measurements on a fossil coral indicate that 10,200 years ago mean annual SSTs near Vanuatu in the southwestern Pacific Ocean were about 5°C colder than today and that seasonal variations in SST were larger. These data suggest that tropical climate zones were compressed toward the equator during deglaciation.

The evolution of the carbonate platforms of northeast Australia

Article

Jan 1989

The carbonate platforms of northeast Australia, the Great Barrier Reef province and the Eastern, Queensland, and Marion Plateaus, contain a record of the complex interactions between the factors that controlled carbonate deposition over the past 60 m.y. Analysis of the extensive geological and geophysical data shows that both long-term (plate motion and subsidence) and short-term (rifting, eustasy, climate, oceanography, and collision) factors influenced platform evolution. General conclusions applicable to other carbonate platforms may be deduced from analysis of the factors that controlled deposition on the northeast Australian platforms. -from Authors

Scleractinia of Eastern Australia. Part III. families Agariciidae, Siderastreidae, Fungiidae, Oculinidae, Merulinidae, Mussidae, Pectinidae, Caryophyllidae, Dendrophylliidae

Article

Jan 1980

Evolution of Modern Caribbean Fringing Reef, Galeta Point, Panama

Article

Jan 1976
AAPG BULL

P. W. Glynn I. G. Macintyre

Sedimentation on Low Isles Reef and its relation to coral growth

Article

Quaternary and Tertiary Subtropical Carbonate Platform Development on the Continental Margin of Southern Queensland, Australia

Chapter

May 2009

The continental margin of eastern Australia extends from the tropics to temperate latitudes (10°–44°S), and is one of the largest areas of modern carbonate sedimentation in the world. A joint survey carried out by the Japan National Oil Corporation and the Australian Geological Survey Organisation on the continental shelf off Fraser Island, southern Queensland, has delineated a distinct subtropical biotic assemblage, composed principally of coralline algae, forming a narrow zone between the tropical and temperate assemblages on the shelf. This assemblage is present both as surface sediments and build-ups. The coralline algae form thick crusts and rhodoliths, and are associated with low species diversity hermatypic corals and large benthic foraminifers, as well as bryozoans, Halimeda and molluscs. In addition, seismic reflection profiling and dredging of the outer shelf and upper continental slope has revealed that up to three carbonate platforms are present. Two platforms are considered to be Early to late Middle Miocene in age, whereas the overlying platform, beneath and seawards of the present Gardner Banks, is considered to be Quaternary. Dredged samples consist of a variety of carbonate rocks, in particular, coral–algal wackestone–packstone–boundstones and rhodolith float-stone to rudstones. Dolomitic limestones and well-lithified limestones occur on the shelf edge and continental slope. These have diagenetic features suggesting both marine and meteoric environments.

Sedimentary facies and sedimentation of tropical to subtropical carbonates east off Australia and its relation to the East Australian Current

Article

Jan 1994

Environmental Control of Magnetic Properties of Upper Slope Sediments near the Great Barrier Reef: Results from Leg 133, Site 820

Article

Nov 1993

Paleomagnetic analysis of sediment samples from Ocean Drilling Program (ODP) Leg 133, Site 820, 10 km from the outer edge of the Great Barrier Reef, is undertaken to investigate the mineral magnetic response to environmental (sea level) changes. The magnetic susceptibility (K) record is central for describing and understanding the magnetic properties of the sediments, and their relationship to glacio-eustatic fluctuations in sea level. Three prominent magnetic susceptibility peaks, at about 7, 32 and 64 mbsf, are superimposed on a background of smaller susceptibility oscillations. Fluctuations in susceptibility and remanence in the "background' zone are controlled predominantly by variations in the concentration, rather than the composition of ferrimagnetics, with carbonate dilution playing an important role (type-A properties). The sharp susceptibility maxima occur at the start of the marine transgressions following low stands in sea level (high δ 18O, glacial maxima); and are characterized by a stable single-domain remanence, with a significant contribution from ulta-fine, superparamagnetic grains (type-C properties). During the later marine transgression, the susceptibility gradually returns to low values and the remanence is carried by stable single-domain magnetite (type-B properties). The A, B, and C types of sediment have distinctive ARM/K ratios. Throughout most of the sequence a strong inverse correlation exists between magnetic susceptibility and both CaCO 3 and δ 18O variations. The main magnetic characteristics of the sediments are thought to reflect sea-level-controlled variations in the sediment source regions and related run-off conditions. Some preliminary evidence is seen that biogenic magnetite may play a significant role in the magnetization of these sediments. -from Authors

Relationships between reef growth and sea level in the Great Barrier Reef

Article

Jan 1985

The Origin of the Great Barrier Reef-The Impact of Leg 133 Drilling

Article

May 2009

Drilling of the shallow fore-reef slope during Leg 133 of the Ocean Drilling Program has allowed the definition of an event history critical for understanding the initiation and evolution of the Great Barrier Reef. Within or immediately before the time period of isotope stages 8 and 9, a fundamental change in climate, driven by a switch from 19 000-yr obliquity to 100 000-yr precessional orbital cycles, led to raised sea surface temperatures and the initiation of the Great Barrier Reef. It is therefore only 300 000 yr old and an ecosystem response to environmental change. Subsequent development occurred as a series of high sea-level slices effected by four or five sea-level oscillations and growing progressively retrogressively to the west. The subreef section, although unknown, is postulated to be analogous to a mid to outer shelf coralline dominated environment comparable with that growing on the shelf to the south of the Great Barrier Reef today. The vertical and lateral (latitudinal) facies variations obey Walther's Law of Succession as a consequence of a sedimentary response to subsidence, latitude and climate change.

The 7000 yr sea level curve in French Polynesia geodynamic implication for mid-plate volcanic islands

Article

Jan 1988

Recent corals of the Marshall Islands

Article

Jan 1954

J.W. Wells

Scleractinia of Eastern Australia. Part IV. Family Poritidae

Article

Jan 1982

Scleractinia of Eastern Australia. Part II. Families Faviidae, Trachyphylliidae

Article

Jan 1977

Succession and diversity in the Pleistocene coral reefs of the Kenya coast

Article

Jan 1980

Alistair Crame

Great Barrier Reef bores, 1926 and 1937. Descriptions, analyses and interpretations

Article

Facies models in exploration-the carbonate platforms of north-east Australia

Article

Jan 1988

The carbonate platforms of north-east Australia encapsulate a record of tectonic, eustatic, climatic and oceanographic dynamism that has controlled their formation. Collectively, the Great Barrier Reef and the Queensland and Marion Plateaus, together with the rift basins that separate them, define a new model for carbonate platform evolution with important exploration consequences. Cretaceous rifting, Paleocene breakup, Cainozoic northward drift with concomitant climatic changes, Neogene subsidence pulses, and sea-level perturbations have combined to produce tropical carbonate platforms overlying temperate, mixed carbonate/siliciclastic facies. The Great Barrier Reef tropical shelf platform thins to the south; reefs first developed in the north in the Early to Middle Miocene along the west- to east-trending distal margin of a foreland basin. The reefs of the Queensland and Marion Plateaus developed in the Middle Miocene and are the precursors of the carbonate platforms of the central and southern Great Barrier Reef. The Miocene Marion Plateau barrier and platform reefs backstepped to become the Plio-Pleistocene Great Barrier Reef. Three energy- and climate-related carbonate facies associations define new prospecting scenarios: the tropical, high energy reef model; the tropical, low energy, Halimeda bioherm model; and the subtropical, low energy, deep water, red algal/ foram/bryozoan bioherm model. These facies occur within four distinct structural/sedimentological associations: the progradative platform margin, the backstepped platform margin, the foreland basin, and the fault block association. The models can be readily applied to the Gulf of Papua/Torres Shelf and the Canning Basin and may produce exciting new insights into carbonate plays in these areas.

Coral Terraces on the Huon Peninsula, North Eastern Papua New Guinea. Living Hermatypic Coral Assemblages at Huon Peninsula, Papua New Guinea.

Article

Jan 1995

Recent coral reefs are well-developed along the coast of Huon Peninsula. Most of them are of the fringing type, although reefs with narrow lagoons are found at Sialum and Gitua. We studied the hermatypic coral assemblages with SCUBA at the reef of Sialum and the fringing reef of Hubegong about 30 km southeast of Sialum.Sialum reef has a typical lagoon and reef crest with a narrow channel across the crest. The lagoon is about 3 km in length, and about 200 m in width. Its bottom is flat and shallower than 12 m. The crest is partly emerged up to a few meters at the central part of the barrier, while the other parts are almost at mean sea level. A reef slope has a groove and spur structure, and inclines steeply with several terraces to a depth of 20m.No lagoon and reef crest are developed on the Hubegong coast. We made topographic profiles on the reef slope from 0 to 21 m in depth. The slope inclines at an angle of about 25°. Small terraces were recognized at depths of 3 m and 15 m. Groove and spur morphology is not formed in this area. Hermatypic corals are very abundant in the shallower part (0-5 m), but rare in the deeper. Coarse-grained detritus and boulders derived from the coral patches cover the deeper slope. Hermatypic corals disappear at depths deeper than 30 m.Forty-three coral genera (including sub-genera) and 80 species were identified at Sialum and Hubegong. These numbers are not as large as might be expected for typical Indo-Pacific reef assemblages. This is due not only to the poorness of the actual assemblage but also to shortness of time available. Species identified in this region are similar to those of typical IndoPacific assemblages.Coral coverage is very high in the coral thicket but almost 0% on the bottom of the lagoon and on the reef crest. It exceeds 30% in the shallower forereef and decreases to 0% in the deeper part.We define 4 assemblages on the basis of the transect survey and other data, as follows.Lagoon Assemblage : The assemblage is distributed inside of the lagoon from 0 to 10 m in depth. It is characterized by the presence of A. formosa, A. pulchra, M. digitata, and P. cylindrica.Shallow Reef Slope Assemblage : It is distributed on the shallow part of the reef slope from 0 to 3 m in depth, and is defined by such species as A. hyacinthus, A. monticulosa, and A. humilis.Middle Reef Slope Assemblage : The habitat of this assemblage ranges from 3 to 5m in depth on the reef slope. A. palifera is the diagnostic species.Deep Reef Slope Assemblage : This assemblage inhabits the deeper reef slope from a depth of 5 to 30 m. As L. scabra, the representative of the assemblage is rare, massive Faviidae corals are more conveniently used for the assemblage definition.

Coralline algae as indicators of sea-level

Article

Jan 1986

W.H. Adey

Calcified crustose coralline algae occur from the arctic to the tropics in the ocean’s photic zone. However, in warmer seas, particularly supersaturated waters, growth is more rapid and secondary lithification more extensive leading to a greater frequency of bioherm and biostrome development. The generic and species composition of tropical and colder seas differ considerably and a depth zonation of genera and species is characteristic of all waters. Depth characterization of fossil material can be carried out on the basis of community structure. However, precision of determination is likely to be within the ±5–10 m range. In tropical and temperate waters, and particularly in supersaturated seas, coralline bioherms (algal ridges and trottoir) develop in close association with sea level and can be precision (±10 cm) indicators of that level. Wave action control of grazing, and temperature and salinity/pH enhancement of growth and secondary mineralization are factors determining the extent of bioherm development. 14C dating along with consideration of the above factors and coralline community structure can lead to great confidence in the use of crustose corallines for sea-level determination. Basic techniques and information needed for preparation and identification of crustose corallines is provided.

New constraints on the origin of the Australian Great Barrier Reef: Results from an international project of deep coring

Article

Jun 2001
GEOLOGY

Two new boreholes provide the first direct evidence of the age of the Australian Great Barrier Reef. An inner shelf sequence (total depth, 86 m; basal age = 210 ± 40 ka) comprises a dominantly siliciclastic unit (thickness ∼52-86 m), overlain by four carbonate units (total thickness 0-34 m). A shelf-edge and slope sequence (total depth 210 m) reveals three major sections: (1) a lower section of resedimented flows deposited on a lower slope, (2) a mid-section including intervals of corals, rhodoliths, and calcarenites with low-angle graded laminae, and (3) an upper section of four shelf-margin coral-reef units separated by karst surfaces bearing paleosols. Sr isotope and magnetostratigraphic data indicate that the central Great Barrier Reef is relatively young (post Brühnes-Matuyama boundary time), and our best estimate for the onset of reef growth on the outer barrier system is ca. 600 ± 280 ka. This date suggests that reef initiation may have been related to the onset of full eccentricity-dominated glacio-eustatic sea-level oscillation as inferred from large-amplitude "saw-tooth" 100 k.y. δ18O cycles (after marine isotope stage 17), rather than to some regional environmental parameter. A major question raised by our study is whether reef margins globally display a similar growth history. The possibility of a global reef initiation event has important implications for basin to shelf partitioning of CaCO3, atmospheric carbon dioxide levels, and global temperature change during Quaternary time.

Growth fabrics and growth rates of Holocene reefs in the Great Barrier Reef ( Australia).

Article

Jan 1983

Presents results from 61 holes drilled into 24 reefs throughout the Great Barrier Reef Province between 15 o30'S and 25 o50'S. Eleven holes penetrated to the Pleistocene and nearly 250 radiocarbon dates have been recorded. Analysis of drill-hole core has delineated five major biosedimentologic facies - coralline algal facies, coral-head framework facies, branching-coral framework facies, detrital carbonate facies, and detrital siliciclastic facies. Latitudinal uniformity in framework facies contrasts markedly with major regional variations in detrital facies, the reefs of the mid-shelf of the central region being dominated by clastic carbonates. Depositional and framework growth rates are outlined for each of these facies and their stratigraphic implications are discussed. -after Authors

Evolution of modern Caribbean fringing reef, Galeta Point, Panama. Am Assoc Pet Geol Bull

Article

Jul 1976

Thirteen closely spaced core holes were drilled across a modern fringing reef at Galeta Point, Panama, along two transect lines which, when combined, extend from inshore mangroves to the outer reef slope. Cores indicate that the reef is at least 14 m thick and directly overlies the calcareous argillaceous silt-stone of the middle Miocene Gatun Formation. Cores contain six distinct sedimentologic units: reef Acropora palmata, fore-reef coral heads, fore-reef talus, fore-reef pavement, reef-flat rubble, and back-reef sediments facies. Eighteen radiocarbon dates of coral samples from cores permitted detailed reconstruction of the stages of development of Galeta reef. Refs.

The evolution of the carbonate platforms of northeast Australia

Chapter

Jan 1989

Reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the Indo-Pacific province

Article

Dec 1999

The coralgal framework within the outer reef margin of many Indo-Pacific reefs exhibits three main shallow-water communities, the environmental significance of which can be inferred by comparison with their modern counterparts. A community dominated by tabular Acropora gr. hyacinthus/cytherea with branching Pocillopora damicornis, P. eydouxi, Montipora digitata: occasional domal faviids and mm-thick crusts of the coralline algae Lithophyllum and Mesophyllum (mainly), typical of the 6 - 15 m paleodepth range; a community including robust-branching Acropora gr. danai/robusta, A. humilis, A. digitifera and subordinate Favia stelligera, Echinopora gemmacea, associated to vermetid gastropods and thick coralline crusts of Hydrolithon cf. onkodes and Neogoniolithon cf. fosliei flourishing in depths less than 6 m; in medium-to-high water-energy settings, a community composed of domal Porites cf. lutea and P. cf. lobata with occasional Acropora gr. danai/robusta and cm-thick crusts of coralline algae in sheltered habitats in depths less than 10 m. These biological assemblages allow us to determine relationships between reef growth and paleobathymetry and, consequently, to reconstruct regional relative sea-level curves. High water-energy reefal assemblages provide stronger evidence for reconstructing sea-level curves than low-energy buildups, because they have generally been controlled by a keep-up growth mode. Subsiding reef sites seem to be more reliable indicators of sea-level Variations because they usually present expanded reef sequences.

Modern Coral Reefs of Western Atlantic: New Geological Perspective

Article

Nov 1988
AAPG BULL

Ian G. Macintyre

Contrary to popular belief of the late 1960s, western Atlantic Holocene reefs have a long history and are not feeble novice nearshore veneers that barely survived postglacial temperatures. Rather, the growth of these reefs kept pace with the rising seas of the Holocene transgression and their development was, for the most part, controlled by offshore wave-energy conditions and the relationship between changing sea levels and local shelf topography. Thus, the outer shelves of the eastern Caribbean in areas of high energy have relict reefs consisting predominantly of Acropora palmata, a robust shallow-water coral. The flooding of adjacent shelves during the postglacial transgression introduced stress conditions that terminated the growth of these reefs. When, about 7000 yr ago, shelf-water conditions improved, scattered deeper water coral communities reestablished themselves on these stranded shelf-edge reefs, and fringing and bank-barrier reefs began to flourish in shallow coastal areas. At the same time, the fragile and rapidly growing Acropora cervicornis and other corals flourished at greater depths on the more protected shelves of the western Caribbean and the Gulf of Mexico. As a result, late Holocene buildups more than 30 m thick developed in those areas. 7 figures.

The Nature and Significance of Microatolls

Article

Nov 1978

Microatolls, those coral colonies with dead, flat tops and living perimeters, result from a restriction of upward growth by the air/water interface. The principal growth direction is horizontal and is recorded in the internal structure, though fluctuations in water depth can influence the surface morphology producing a terraced effect. The morphology of the basal surface of the colony is controlled by the sand/water interface such that the thickness of the coral records the depth of water in which it lived. In open water at the margin of reefs in the Northern Province of the Great Barrier Reef, tall-sided uneven-topped microatolls live, whereas, on the reef flats in rampart-bounded moats and ponds, thin flat-topped and terraced microatolls are abundant. Because water in moats can be ponded to levels as high as high water neaps (1.6 m above datum at Cairns) and still have daily water replenishment, microatolls on reef flats can grow to levels 1.1 m higher than open-water microatolls (which grow up to a maximum elevation of low water springs, i.e. 0.5 m above datum). This imposes a major constraint on the use of microatolls in establishing sea level history. The two factors controlling pond height during one sea stand (relative to the reef) are tidal range (which governs the height of high water neaps) and wave energy (which governs the height of ramparts which enclose moats). Dating and levelling fossil microatolls exposed on the reefs show that 4000 years (a) B.P., high water neaps was at least 0.7 m higher than it is at present.

Pleistocene Perspectives on Coral Reef Community Structure

Article

Dec 1992

Jeremy B C Jackson

Composition and zonation of coral reef communities are unstable on the scale of human lifetimes, but stable on average over thousands to hundreds of thousands of years. Traditional small-scale ecological studies can miss community patterns which are obscured by the noise of short-term change. Tests for stability require monitoring of populations over many generations—millenia for long-lived corals and forest trees. The only recourse is the fossil record.

Distribution of marine organisms and its geological significance in the modern reef complex of the Ryukyu Islands

Article

Nov 1995
SEDIMENT GEOL

Extensive investigations of biota in the reef complex around the Ryukyu Islands have revealed ecologic specificity of many benthic organisms and have shown that characteristic assemblages are found in each of the topographic zones and sub-areas. The moat is divisible into a nearshore seagrass bed and an offshore sand bottom. Both inner reef flat and outer reef flat are characterized by abundant occurrences of hermatypic corals and nonarticulated coralline algae. However, the former is dominated by branching and foliaceous forms of corals and various, large, fleshy, erect forms of algae, whereas the latter is dominated by encrusting and tabular forms of corals, lacking these algae. Corals and coralline algae are not present on the reef crest, which is covered by rubble and gravel, where algal turf and Sargassum are spreading. Encrusting and tabular forms of corals flourish on the shallower part of the reef slope, with high coverage, while, with increasing depth, the coverage decreases and the dominating coral forms change, with hemispherical and encrusting forms on the middle part of reef slope, and foliaceous and encrusting forms on the deeper part of reef slope. Nonarticulated coralline algae are distributed throughout the reef slope. The composition of coral and coralline algal assemblages changes dramatically with increasing depth. Foraminiferal-algal nodules, rhodoliths, are the most abundant constituent on the island shelf, commonly with Cycloclypeus carpenteri. There are likely to be two types of shelves in tropical to subtropical regions: nutrient-rich Halimeda-dominant and nutrient-poor rhodolith-dominant. Sediments abundant in bryozoan skeletons occur occasionally on the shelf.

Scleratinia of Eastern Australia. Part V. Family Acroporidae

Book

Jan 1984

Terrigenous sedimentation and coral reef growth: A conceptual framework

Article

Mar 1999
MAR GEOL

The role of terrigenous (and non-framework carbonate) sedimentation has not been prominent in models of coral reef growth and evolution. We derive and discuss a semi-quantitative model which relates coral reef growth to sedimentation. The model is independent of coral biology and is based upon the relative net rates of framework and non-framework sediment accumulation and/or removal. The model might enable some forecasting of long-term responses to changes in sedimentation regime and other environmental factors. The occurrence of turbid-zone reefs is successfully explained in regions of very high turbidity but with little or no net sediment accumulation. Potential future use of the model may include aiding prediction of the effects of other geological and oceanographic factors on the growth or demise of coralline communities.

Lithification of carbonate sediments in the Heron Island Reef, Great Barrier Reef

Article

Jan 1962

W.G.H. Maxwell

In this reef area lithification has resulted in the formation of beach rock at the surface and reef rock in the subsurface. The process of lithification which leads to the formation of beach rock is an unusual and interesting one, but does not play a major rôle in the consolidation of reef sediments. Beach rock results largely from the protective action of encrusting algae and to a less degree from carbonate precipitation from sea water. Because of the general lack of “fines” in reef flat and beach sands, matrix recrystallisation plays no part in beach rock formation. By contrast, the reef rock from the subsurface generally contains a higher percentage of fines and, below 100 feet, this material has been largely recrystallised to form a strong binding medium. The process of recrystallisation is apparently selective, those sediments with high matrix, high coral/algal ratio and low MgCO3 content showing the highest degree of recrystallisation. Depth of burial shows no direct relationship to this process. Thus, of the two lithifying processes operative in the reef province, the less spectacular one of compaction and recrystallisation is the more important. Beach rock formation is significant in its influence on the present distribution of carbonate sands, but it makes little or no contribution to the total rock mass underlying the present reef.

Reef algae

Article

Jan 1986

Coral successions in Upper Tortonian reefs in SE Spain

Article

Oct 2007
Lethaia

Martin, Jose M., Braga, Juan C. & Rivas, Pascual 1989 07 15: Coral successions in Upper Tortonian reefs in SE Spain. Lethaia, Vol. 22, pp. 271–286. oslo. ISSN 0024–1164, During the Upper Tortonian (Upper Miocene), the Almanzora river corridor, a small Neogene basin in SE Spain, harboured coral reefs growing in three different environments: in fan deltas, beyond the influence of coarse terrigenous sedimentation; in the abandoned lobes of a delta complex; and on coastal margins. All of these reefs are composed of several successive beds, each of which may be made up mainly of Porites embedded in silt or of an initial Porites level followed by a silt-free Tarbellastraea level on top. Porites may be associated with corallines. This structure is interpreted as being the result of an ecological succession repeated over and over again. A pioneer association consisting mainly of Porites. by colonizing the substrate and continuing to grow through relatively adverse silt-deposition conditions, prepares the ground for Tarbellastraea to take over. A return to the previous conditions halts the growth of the Tarbellastraea colonies and the Porites association once more establishes itself in the silt, or else the renewed rate of deposition is sufficiently heavy to suffocate the whole bioconstruction.*Ecological succession. coral reefs, Tortonian, southeast Spain.

Response of reef coral communities to sea-level rise: A Holocene model from Mauritius (Western Indian Ocean)

Article

Dec 1997
SEDIMENTOLOGY

The fringing reef at Pointe-au-Sable (Mauritius, Indian Ocean) was used to examine the effects of Holocene sea-level rise on coral growth. This reef is about 1000 m wide and comprises a forereef slope (30 m maximum depth), a narrow reef crest and a very shallow backreef (1·5 m maximum depth). Four major coral communities were recognized, which developed within relatively narrow depth ranges: a Pachyseris/Oulophyllia community (deeper than 20 m), an Acropora‘tabulate’Faviid community (20–6 m); a robust branching Acropora community (less than 6 m) and a Pavona community (less than 10m). Three high-recovery cores show the Holocene reef sequence is a maximum of 19·3 m thick and comprises four coral biofacies which are similar to counterparts identified in modern communities: robust branching, tabular-branching, robust branching-domal and foliaceous coral facies. A minimum sea-level curve for the past 7500 years was constructed. Using distribution patterns of coral biofacies and radiocarbon dates from corals, reconstruction of reef growth history indicates that both offshore and onshore reef zones were developing coevally, aggrading at rates of 4·3 mm year−1 from 6900 years B.P. The reef caught up with sea-level only after sea-level stabilized. Changes in coral community and reef growth rates were driven principally by increasing water agitation due to the decrease in accommodation space. Based on the composition of the successive coral assemblages, the reef appears to have grown through successive equilibrium stages.

Model of fringing reef development in response to progressive sea level fall over the last 7000 years – (Kikai-jima, Ryukyu Islands, Japan)

Article

Sep 1998

Kikai-jima in the central Ryukyu Islands of Japan is fringed by exposed terraces of Holocene reefs, which formed as a result of periodic local tectonic uplift associated with subduction/collision. The terraces form four topographically distinct features (TI-IV) around the island and represent reefs that grew to sea level at 9000–6065 y BP, 6065–3390 y BP, 3790–2630 y BP, and 2870 to 1550 y BP. The modern reef terrace has been growing since approximately 1550 y BP. The reef terraces were uplifted sequentially around 6050 y BP (4 m), 3390–3790 y BP (2.5 m), 2630–2870 y BP (1 m) and 1550 y BP (2.5 m). Five sites were studied to define reef development in response to periodic relative sea level fall and different stillstand recovery periods. Thirty coral genera and 70 species were recorded from four distinct shallow reef flat to upper reef slope and one deeper reef slope coral assemblage. Significant lateral variations in total coral abundance, genera number, diversity, and the coverage density of Acropora spp. and Faviids occur both within and between the terraces. Stratigraphically, drill core and outcrop data recorded shallowing upward sequences characterised by tabulate Acropora spp. overlying massive Porites sp. and Faviids. The biological variations may represent growth strategies responding to initial colonisation, episodic perturbation (relative sea level fall) and differing recovery times during stillstands, and indicate a reef ecosystem stable and strong enough to recover after substantial perturbations. However, this study suggests that relatively small geological changes have had substantial biological effects, and modelling indicates that such changes would have been more profound had a third factor, such as substrate angle, varied more dramatically. In such a case, the drowning growth strategy exhibited in the drill core transect may have been more prevalent, and reefs would be struggling to grow around Kikai-jima today.

Internal structure and Holocene evolution of One Tree Reef, southern Great Barrier Reef

Article

Jun 1982

Analysis of core from six drill holes and ten vibrocores from One Tree Reef has delineated five major biosedimentological facies: algal pavement, coral head facies, branching coral facies, reef flat rubble facies and sand facies. Holocene growth began around 8,000 years B.P. with a high energy coral head facies on windward margins and a lower energy branching coral facies on patch reefs and on leeward margins. Vertical accumulation rates for these two principal facies are not greatly different; the coral head facies grew at 1.8–7.3 m/1,000 years and the branching coral facies at 0.6–8.3 m/1,000 years. Growth was initially much slower than the rate of sea level rise, a situation which changed only after sea level stabilized around 6,200 years B.P. A facies evolution model with rigidly imposed time constraints divides growth into three phases, i.e. vertical growth to sea level, transitional adjustment of biofacies at sea level, and leeward progradative phases.

Reconciliation of late quaternary sea levels derived from Coral Terraces at Huon Peninsula with Deep Sea Oxygen isotope records

Article

Jun 1996
EARTH PLANET SC LETT

A major discrepancy between the Late Quaternary sea level changes derived from raised coral reef terraces at the Huon Peninsula in Papua New Guinea and from oxygen isotopes in deep sea cores is resolved. The two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka (ka = 1000 yr before present), but between 70 and 30 ka the isotopic sea levels are 20–40 m lower than the Huon Peninsula sea levels derived in earlier studies. New, high precision U-series age measurements and revised stratigraphic data for Huon Peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic δ18O data. Using the sea level and deep sea isotopic data, oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from Greenland ice cores. The record of ice volume changes through the last glacial cycle now appears to be reasonably complete.

Community Structures of Recent and Pleistocene Hermatypic Corals in the Ryukyu Islands, Japan

Article

Jan 1986

Toru Nakamori

Ecological features such as diversity and coverage of the Recent hermatypic corals in Ishigaki-jima and Sesoko-jima in the Ryukyu Islands are measured by a transect method. Communities, growth form and zonation of the corals are discussed on the basis of the measurements. Fifty-one coral genera and 144 species are recorded in this study and 11 hermatypic coral communities are recognized on the basis of the ratio of species. Six topographic areas are discriminated in the coral reefs in these two islands. Each community is distributed in the specific topographic area, but the same community does not necessarily appear in the same topographic area of different reefs. On the other hand, the distributions of the dominant growth forms of corals within a reef are fairly constant not only in the Ryukyu Islands but also in the Indo-Pacific Region. Relationships between the diversity and coverage of the hermatypic corals apparently show the ecological succession and support the intermediate disturbance hypothesis (Connell, 1978). The growth forms of Porites australiensis indicate eco-morphological variations. They are spherical, hemispherical and laminar at depths of 0, 10 and 30 m respectively. The growth rate of the corallum of P. australiensis decreases exponentially with depth. The increasing rate of corallum surface area is constant, having no relation to water depth. A model for corallum eco-morphology of P. australiensis is proposed in relation to light intensity. Stratigraphy of the Ryukyu Group is investigated in Hateruma-jima, Miyako-jima, Okinawa, Okierabu-jima and Kikai-jima. The strata in these islands are correlated with one another on the basis of radiometric ages and nannoplankton biostratigraphy. Ecological studies of fossil hermatypic corals are carried out on five formations of almost the same age; the Takanasaki Formation (Hateruma-jima), Miyako-jima Limestone (Miyako-jima), Naha Formation (Okinawa), Okierabu-jima Formation (Okierabu-jima) and Takigawa Formation (Kikai-jima). The rate of fossil corals to the total rock volume is determined for each taxonomic and morphological group. Fifty-two genera and 70 species are identified. Five fossil communities (Communities A-E) are recognized on the basis of measurments, which can be correlated to the Recent ones. The number of genera decreases and equitability increases with increasing latitude. The rate of fossil corals to the total rock volume also decreases with latitude. Depositional environments of six facies of the Ryukyu Group (coral limestone, rhodolith limestone, detrital limestone, Cycloclypeus-Operculina limestone, calcareous sandstone and conglomerate) are inferred by utilizing paleontological and sedimentological information. Paleogeography of the five islands are reconstructed based on the distributions of the coral communities and the depositional environment of the facies. hermatypic coral reef Ryukyu Islands community coverage diversity zonation Ryukyu Group stratigraphy paleogeography

Tropical Temperature Variations Since 20,000 Years Ago: Modulating Interhemispheric Climate Change

Article

Mar 1994

Tropical sea surface temperatures (SSTs), as thermodynamically recorded in Barbados corals, were 5°C colder than present values 19,000 years ago. Variable tropical SSTs may explain the interhemispheric synchroneity of global climate change as recorded in ice cores, snowline reconstructions, and vegetation records. Radiative changes due to cloud type and cloud cover are plausible mechanisms for maintaining cooler tropical SSTs in the past.

Foraminifera from H.B.R. Wreck Island No. 1 Well, and Heron Island Bore, Queensland. Their taxonomy and stratigraphic significance. 1—Lituolacea and Miliolacea

Jan 1968
69

Lloyd

Lloyd, A.R., 1968. Foraminifera from H.B.R. Wreck Island No. 1 Well, and Heron Island Bore, Queensland. Their taxonomy and stratigraphic significance. 1—Lituolacea and Miliolacea. BMR J. Aust. Geol. Geophys. 92, 69–114

Coral variation in two deep drill cores: Significance for the Pleistocene development of the Great Barrier Reef

Abstract

No full-text available

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