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Abstract

Significant discrepancies have existed regarding rate and timing of the uplift of Lutao (Green Island), located at the border of the ongoing collision between the Eurasia continental plate and the Philippine Sea Plate. To document its neotectonic history, two cores were drilled into Holocene coral reefs exposed at the southeastern coast of Lutao. Twelve pristine fossil corals, nine taken from cores and three on the surface, were ²³⁰Th dated. The results show that the coral reefs started to develop at 8,736 ± 56 yr BP (before 1950 CE) with uplift rate varying from 3.6 mm/yr during 8.7–6.0 kyr BP to 1.2 mm/yr in the past six thousand years. Our study strongly suggests that the uplift rate can vary significantly on millennial time scale. Caution should be used when extrapolating uplift rate estimates based on Mid-late Holocene corals to early times for tectonic active locations, such as Lutao.

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... This formation is composed of late Pleistocene-Holocene coral reef and red soil with reef limestone fragments (Chen et al., 1994). The outer rim of the island is covered by Holocene-raised coral reefs with a thickness of <15 m (Inoue et al., 2011;Shen et al., 2018). Our sampling area named Chao-Jih hot spring is located in the southeastern corner of Lutao (Fig. 1b). ...
... In addition, four reef rock samples with different degrees of alteration were collected across the hydrothermal field (Fig. 1b). These reef rocks are algal-coral bundstones and/ or bioclastic calcarudites with light tan to beige in colour (Shen et al., 2018). ...
... The DIC contents are almost constant with the Ca contents, further suggesting the contribution of the coral reef is limited for the high Ca concentrations of the Lutao vent fluids. (2) The Holocene-raised coral reef only covers a thickness of <15 m (Shen et al., 2018), much shallower than the estimated depth of the reaction zone (about 70 m, Chen et al., 2020b). In addition, the temperature of the Lutao reaction zone is only about 175 ± 25 • C. Extensive interaction between the heated hydrothermal fluid and the coral reef is unlikely to occur. ...
Article
The chemical and isotopic characteristics of calcium (Ca) in subduction zones are closely related to the budget of Ca and carbon cycles. Here we investigate the ultra-high Ca concentrations that characterize the hydrothermal fluids discharged from two types of vents, named the Zhudanqu brine vent (ZDQ) and the Huwaichi vapor spring (HWC), in the Lutao hydrothermal system at the north Luzon arc. The Ca concentrations of up to 159 mM and Ca/Cl ratio of up to 0.26 in the ZDQ vent fluids are possibly the highest ever reported for Ca enrichment in global seawater-circulated hydrothermal/geothermal systems. The differences in chemical compositions between the ZDQ and the HWC vent fluids are primary controlled by subcritical phase separation. The brine phase constitutes the ZDQ vent fluids, while the HWC vent fluids represent mixtures of the vapor phase and seawater. Both the vapor and the brine phases exhibit similar δ44/40Ca values (0.72 ± 0.05‰), suggesting no significant Ca isotope fractionation has occurred during phase separation. The hydrothermal endmember before phase separation (the “Lutao endmember”) presents depletions of 213 ± 15 mM of Na, 24.4 ± 0.4 mM of SO4²⁻, and 10.2 mM of K, and enrichment of 130.2 ± 5.5 mM of Ca with respect to the percolated seawater. The total gained Ca is 154.6 ± 5.9 mM with a δ44/40Ca value of 0.67‰ – 0.77‰ (0.72 ± 0.05‰), considering anhydrite precipitation during hydrothermal circulation. The Holocene raised coral reef is unlikely to contribute substantial Ca into the Lutao system. Much of the gained Ca (111.6 ± 7.5 mM) is produced by high-degree albitization of the Lutao host rock, which is promoted by the low water/rock ratio (~ 2), slightly alkaline conditions, and relatively lower temperature of the Lutao system with respect to most mid-ocean ridge hydrothermal systems. Ca derived from this process inherits the Ca isotopes of plagioclase in the Lutao host rocks (δ44/40Ca = 0.82 ± 0.06‰). According to mass and isotopic balances, the recycled marine carbonate is proposed to contribute 43 ± 13.4 mM Ca with a δ44/40Ca value of 0.46−0.63+0.35‰ into the Lutao system. Such isotopically lighter Ca is derived from either pore fluids expulsed from underlying Philippine Sea sediments, or more probably, carbonate-bearing subduction fluids from the subducting South China Sea sediments and slab. The carbonate solubility in the subduction fluids could maintain at 600 mM near the reaction zone. The carbonate-rich fluids were subsequently migrated into the Lutao reaction zone and released an additional 43 ± 13.4 mM Ca via dolomitization. A small amount (~ 9%) addition of carbonate-rich fluids would not significantly change the budgets of Na, Mg, and Cl but could generate substantial Ca enrichment and Ca isotopic variations.
... The fossil scleractinian community in the study of Wang et al. (2006) was also composed of specimens of Acropora, Acanthastrea, Cyphastrea, Dipsastreae, Favites, Goniopora, Goniastrea, Galaxea, Pachyseris, Porites, and Turbinaria, which was the only representative of the dendrophylliids (Wang et al. 2006). More diverse scleractinian communities have been reported from uplifted Holocene terraces in Ludao and Lanyu (Inoue et al. 2011;Ota et al. 2015;Shen et al. 2018). The fossil specimens presented in our study constitutes the first report of Late Miocene scleractinian fossils from Shulin area, northern Taiwan, which hold environmental and ecological information that inform us on the formation of the Taiwanese scleractinian community at a much earlier time than the previous studies in the country on the scleractinian fossils (Hu and Tao 1982;Hu 1987aHu , b, 1988Hu , 1990Wang 1997;Yamaguchi and Ota 2004;Wang et al. 2006;Inoue et al. 2011;Ota et al. 2015;Shen et al. 2018). ...
... More diverse scleractinian communities have been reported from uplifted Holocene terraces in Ludao and Lanyu (Inoue et al. 2011;Ota et al. 2015;Shen et al. 2018). The fossil specimens presented in our study constitutes the first report of Late Miocene scleractinian fossils from Shulin area, northern Taiwan, which hold environmental and ecological information that inform us on the formation of the Taiwanese scleractinian community at a much earlier time than the previous studies in the country on the scleractinian fossils (Hu and Tao 1982;Hu 1987aHu , b, 1988Hu , 1990Wang 1997;Yamaguchi and Ota 2004;Wang et al. 2006;Inoue et al. 2011;Ota et al. 2015;Shen et al. 2018). ...
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The recently exposed outcrops along the Dahan River in Shulin, northern Taiwan revealed diverse and abundant marine fossils including molluscs, shark and ray teeth, sand dollars, and otoliths from a wide range of fish taxa. In addition, numerous small and fragile fossil scleractinians were found and identified here as Dendrophyllia sp., from the mainly azooxanthellate (90%) dendrophylliid family. Lithology of the outcrops are mainly composed of grey sandstones from the Tapu Formation (Late Miocene), overlying on a layer of basaltic tuff. The absolute ageof the boundary between the Tapu Formation and the underlying Nanchuang Formation is 8 Ma, which provides indications on the maximum age possible for the scleractinian fossils found in this study. Back then, the marine ecosystem in which the sampled Dendropyllia specimens grew was probably a turbid shallow coastal environment with muddy to sandy bottom, likely at the vicinity of a river estuary, as suggested by the combined presence of previously reportedfish otoliths. To our knowledge, this is the first record of Dendrophyllia fossils from Taiwan.
... At approximately 50-60 m inland from the reef edge is a 0.5 m step up from the modern intertidal zone onto the Holocene emerged reef surface. Coring by Shen et al. (2018) identified that the emerged reef comprises various carbonate lithofacies, including algal-coral boundstones, bioclastic calcrudites and bioclastic-volcanic arenites. Thickness of the emerged reef is up to 15 m overlying volcanic basement. ...
... Radiocarbon dating by Inoue et al. (2011) of fossil Acropora digitifera sampled at 2.34 m amsl yielded a 14 C age of 6,091-6,385 cal yr BP (2σ range). More recent uranium-series age-dating of fossil corals suggest that the surfaces of emerged Holocene reef terraces in SE Ludao formed approximately 6,759-5,812 years BP, and that uplift rates have been in the order of 1.2 mm/yr over the past 6,000 years (Shen et al., 2018). ...
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This work investigated the characteristics of a boulder field on the exposed south east coast of Ludao Island (Green Island) in southern Taiwan. Although the region regularly experiences seasonal Pacific typhoons, fieldwork on Ludao was prompted following the double-strike of Typhoon Tembin in August 2012, which followed an unusual looping track and was one of the strongest storms to affect the island in recent decades. In Wen Cuen Bay, large limestone and volcanic clasts (10 ³ –10 ⁵ kg) occur both as isolated individuals and also grouped into distinct clusters across the gently-sloping emerged reef platform of Holocene age. Some individuals reach megaclast proportions. Observations revealed limited evidence for the production of new coastal boulders by Typhoon Tembin. However, clustering, stacking and notable imbrication of old large clasts provide evidence for multiple high-energy palaeoevents. Stacking and imbrication are significant depositional features, implying that (partial) lifting by wave transport was responsible. Boulders deposited by Typhoon Tembin suggest that storm produced minimum flow velocities of 3.2–5.1 m/s. This range of minimum flow velocity (MFV) values is lower than the 4.3–13.8 m/s range inferred from the pre-Tembin boulders, which indicates that older storm washovers must have been stronger, judging from their ability to stack and imbricate large clasts. One explanation for high upper values of palaeoevent MFVs is that localized funnelling of water flow through narrow relict channels (inherited spur-and-groove morphology, oriented perpendicular to the modern reef edge) concentrates onshore flow energy into powerful confined jets. Support for this hypothesis is the positioning and train-of-direction of the main imbricated boulder cluster at the landward head of one such feature. Geomorphic controls amplifying wave-driven flow velocities across the emerged Holocene reef mean that a palaeotyphoon origin is sufficient for explaining large clast stacking and imbrication, without the need to invoke a tsunami hypothesis.
... As Hantoro et al. (1994) point out, their uplift estimate for Alor is twice as fast as those calculated for nearby Atauro and Sumba islands, while being slower than rates more recently estimated for Rote (Roosmawati and Harris, 2009) and Timor (Cox, 2009). Furthermore, uplift rates are known to vary over time (Shen et al., 2018), particularly in such a tectonically active region (Pedoja et al., 2014). ...
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We report archaeological findings from a significant new cave site on Alor Island, Indonesia, with an in situ basal date of 40,208–38,454 cal BP. Twenty thousand years older than the earliest Pleistocene site previously known from this island, Makpan retains dense midden deposits of marine shell, fish bone, urchin and crab remains, but few terrestrial species; demonstrating that protein requirements over this time were met almost exclusively from the sea. The dates for initial occupation at Makpan indicate that once Homo sapiens moved into southern Wallacea, settlement of the larger islands in the archipelago occurred rapidly. However, the Makpan sequence also suggests that the use of the cave following initial human arrival was sporadic prior to the terminal Pleistocene about 14,000 years ago, when occupation became intensive, culminating in the formation of a midden. Like the coastal sites on the larger neighbouring island of Timor, the Makpan assemblage shows that maritime technology in the Pleistocene was highly developed in this region. The Makpan assemblage also contains a range of distinctive personal ornaments made on Nautilus shell, which are shared with sites located on Timor and Kisar supporting connectivity between islands from at least the terminal Pleistocene. Makpan’s early inhabitants responded to sea-level change by altering the way they used both the site and local resources. Marine food exploitation shows an initial emphasis on sea-urchins, followed by a subsistence switch to molluscs, barnacles, and fish in the dense middle part of the sequence, with crabs well represented in the later occupation. This new record provides further insights into early modern human movements and patterns of occupation between the islands of eastern Nusa Tenggara from ca. 40 ka.
... The volcanic rocks building the island range from basaltic andesite to dacite but are dominated by andesite (Chen, 1986;Chen and Lin, 1980;Wang and Chung, 1990). Holocene (~8700 a) raised coral reefs cover the outer rims of the island (Inoue et al., 2011;Shen et al., 2018). ...
Article
The Lutao hydrothermal field is an intertidal arc-volcanic system located offshore southeast Taiwan, hosting a Zhudanqu (ZDQ) vent and a Huwaichi (HWC) spring with strongly contrasting fluid chemistry. Low Mg, moderately enriched Cl, and H⁺ with respect to seawater indicate that the ZDQ endmember was derived from the brine phase that was formed during low-degree subcritical phase separation. In contrast, the endmember for the HWC vent fluids is related to the vapor phase. Temperature and pressure of the phase separation were estimated as ~150 °C and ~7 bar, respectively. The water/rock ratio was roughly calculated as about 2. The Lutao hydrothermal system was slightly affected by semi-diurnal tides, by some combination of tidal loading and tidal currents. The time delay between tides and the response of the hydrothermal system was about 3 h. While freshwater was almost absent in the HWC vent fluids at normal conditions, the typhoon “Fung-wong” on Sep 21st, 2014, led to intrusions of freshwater into the vent fluids with a percentage of ~16%. Both the ZDQ and the HWC endmember compositions showed some changes after the typhoon event, suggesting a cooling of the reaction zone. After the typhoon passed by, the hydrothermal system began to recover, evidenced by increasing percentages of the HWC endmember and decreasing freshwater contributions. The flux of the HWC endmember was estimated as 460–560 L h⁻¹ based on these observations. This study, for the first time, reports a shallow-depth tidal-influenced hydrothermal system that was temporarily cooled by a tropical storm.
... Biostratigraphy analysis using the Olympus SZ61 binocular microscope to identify the types of fossil planktonic and benthonic for a mini ferain determining the age of rocks and paleobathimetry [9][10][11][12][13][14][15][16][17][18][19]. Tectonic analysis to calculate the uplift rate based on absolute age data of limestone, paleobathimetry and current position of elevation [20][21][22]. Results and discussion. The measured section results at the research location helped to determine the thickness of one stratigraphy path way and determine the exact position of the sample for biostratigraphy analysis. ...
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The uplift rate of Gorontalo limestone is highly dependent on the completeness of age and depth data. All data needed can be obtained based on complete biostratigraphy analysis. The research material used was a 24 meter thick limestone out crop. The aim of the research was to determine the absolute age of limestone, paleobathimetry and uplift rate of limestone in the research area. The three methods used consisting of the measured section(MS), biostratigraphy analysis and tectonic analysis. Bio datum in the limestone is only one, namely LO Globoquadrina dehiscens. Determination of paleobathimetry using two methods. The uplift rate of limestone is 0.0699-0.0724 mm/year.
... The Taiwan orogeny led to the rapid uplift of nearby Taiwan Island (1.2-3.6 km/m.y.) (Shen et al. 2018), which would have provided a significant volume of sediments to the deep sea (Liu et al. 2016). This uplift occurred contemporaneous with development of the northeastern depocenter. ...
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Based on approximately 11,000 km of seismic reflection data collected across the South China Sea oceanic basin, we describe the sedimentary filling characteristics of the basin since its Oligocene opening, as well as connections between this history and contemporaneous regional tectonic events. The seismic lines are spaced ~50 km apart, and the data are tied to International Ocean Discovery Program (IODP) Expedition 349 drilling data. Basin filling occurred in three phases, with basin-wide mean sedimentation rates increasing through time. During the Oligocene to middle Miocene, sediments accumulated primarily in the northern East and Northwest Sub-basins, with a mean basin-wide sedimentation rate of 8 m/m.y. The presence of these deposits over deep basement floor indicates that seafloor spreading initiated in these northern regions. During the late Miocene, deposition occurred primarily in the Northwest Sub-basin and partly in the southern East Sub-basin, with a mean basin-wide sedimentation rate of 30 m/m.y. Basin filling during this time seems to have been linked to slip reversal of the Red River Fault and collision of the North Palawan Block with the Luzon Arc. During the Pliocene and Pleistocene, sediments accumulated rapidly in the northeastern and southern East Sub-basin and the Southwest Sub-basin. The mean basin-wide sedimentation rate was 70 m/m.y. Basin filling during this phase seems to have been associated with the Taiwan and North Palawan collisions, SCS subduction along the Manila Trench, and Tibetan Plateau uplift. Gravity flow deposits predominate throughout the basin fill.
Article
Emergent coral reef terraces in northwest Luzon Island, Philippines are studied to understand relative sea level (RSL) changes and uplift along the Manila Trench forearc region during the Late Quaternary. Coral reef sequences in Currimao, Badoc, and Badoc Island were mapped and were described based on geomorphological characteristics, elevation patterns, and ages. The lower emergent coral reef terraces, which are dated Holocene, are subdivided into three to possibly four terrace steps (TI–TIV in ascending order) with the highest terrace (TIII–TIV) rising up to ~7–9 m amsl. The well‐preserved staircase morphology and meter‐scale terrace risers possibly imply episodes of abrupt RSL changes that resulted from coseismic uplift during the mid‐Holocene. Around 6.8 kyr BP, ~3 m of rapid uplift (possibly coseismic) is inferred to account for the vertical separation of TI (6.2 kyr BP at 3.5 m amsl) and TII (6.8 kyr BP at 6.6 m amsl) in Currimao site. A subsequent episode of RSL fall occurred at 6 kyr BP, based on dated coral samples, and has emerged the lowest terraces in the study sites. New geomorphic and radiometric data suggest that the mid‐Holocene sea‐level highstand in northwest Luzon occurred at around 7–6 kyr BP. From the elevation and thorium‐230 age of dated terrace surfaces, we estimated Holocene uplift rates from 0.17 ± 0.12 to 0.82 ± 0.15 mm/yr across the three study sites. The estimated uplift rates of northwest Luzon are relatively lower than the uplift rates reported in similar tectonically active regions of the west Pacific such as Papua New Guinea, Taiwan, New Zealand, and Japan. The geomorphological characteristics and age of emergent coral reef terraces reported in this study offer insights on the preservation of long‐term deformation along the northwest Luzon coastal plain that is bordered by a subduction zone and upper‐plate faults.
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Over at least the past millennium, the Mentawai segment of the Sunda megathrust has failed in sequences of closely timed events rather than in single end-to-end ruptures—each the culmination of an earthquake “supercycle.” Here we synthesize the sixteenth- and seventeenth-century coral microatoll records into a chronology of interseismic and coseismic vertical deformation. We identify at least five discrete uplift events in about 1597, 1613, 1631, 1658, and 1703 that likely correspond to large megathrust ruptures. This sequence contrasts with the following supercycle culmination, which involved only two large ruptures in 1797 and 1833. Fault slip modeling suggests that together the five cascading ruptures involved failure of the entire Mentawai segment. Interseismic deformation rates also changed after the onset of the rupture sequence, as they did after the 1797 earthquake. We model this change as an altered distribution of fault coupling, presumably triggered by the ~1597 rupture. We also analyze the far less continuous microatoll record between A.D. 1 and 1500. While we cannot confidently delineate the extent of any megathrust rupture during that period, all evidence suggests that individual major ruptures involve only part of the Mentawai segment, often overlap below the central Mentawai Islands, often trigger coupling changes, and occur in clusters that cumulatively cover the entire Mentawai segment at the culmination of each supercycle. It is clear that each Mentawai rupture sequence evolves uniquely in terms of the order and grouping of asperities that rupture, suggesting heterogeneities in fault frictional properties at the ~100 km scale.
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Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises mainly from the interaction of eustatic (land ice volume and thermal expansion) and isostatic (glacio- and hydro-) factors. We fit RSL histories from near-, intermediate-, and far-field locations with noisy-input Gaussian process models to assess rates of RSL change. Records from near-field regions (e.g., Antarctica, Greenland, Canada, Sweden, and Scotland) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacio-isostatic uplift with rates of RSL fall as great as −69 ± 9 m/ka. Intermediate-field regions (e.g., mid-Atlantic and Pacific coasts of the USA, Netherlands, Southern France, St. Croix) display variable rates of RSL rise from the cumulative effect of eustatic and isostatic factors. Fast rates of RSL rise (up to 10 ± 1 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field RSL records exhibit a mid-Holocene highstand, the timing (between 8 and 4 ka) and magnitude (between <1 and 6 m) of which varies among South America, Africa, Asia, and Oceania regions.
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Fossil coral microatolls from fringing reefs above the great (M_W 8.6) megathrust rupture of 2005 record uplift during the historically reported great earthquake of 1861. Such evidence spans nearly the entire 400-km strike length of the 2005 rupture, which was previously shown to be bounded by two persistent barriers to seismic rupture. Moreover, at sites where we have constrained the 1861 uplift amplitude, it is comparable to uplift in 2005. Thus the 1861 and 2005 ruptures appear to be similar in both extent and magnitude. At one site an uplift around AD 1422 also appears to mimic the amount of uplift in 2005. The high degree of similarity among certain ruptures of this Nias–Simeulue section of the Sunda megathrust contrasts with the substantial disparities amongst ruptures along other sections of the Sumatran portion of the Sunda megathrust. At a site on the northwestern tip of Nias, reefs also rose during an earthquake in AD 1843, known historically for its damaging tsunami along the eastern coast of the island. The coral microatolls also record interseismic vertical deformation, at annual to decadal resolution, spanning decades to more than a century before each earthquake. The corals demonstrate significant changes over time in the rates of interseismic deformation. On southern Simeulue, interseismic subsidence rates were low between 1740 and 1820 but abruptly increased by a factor of 4–10, two to four decades before the 1861 rupture. This may indicate that full coupling or deep locking of the megathrust began only a few decades before the great earthquake. In the Banyak Islands, near the pivot line separating coseismic uplift from subsidence in 2005, ongoing interseismic subsidence switched to steady uplift from 1966 until 1981, suggesting a 15-year-long slow slip event, with slip velocities at more than 120% of the plate convergence rate.
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Two new formalisms are developed for the gravitationally self-consistent solution of sea level equation that governs the redistribution of the glacial melt water on a viscoelastic earth. The first formalism is a purely spectral technique based on an extension of Dahlen's (1976) theory for determining the equilibrium oceanic tide on an elastic planet. The second formalism, called 'pseudospectral', permits gravitationally self-consistent solutions of the sea level equation to much higher degree and order, making it possible to determine very accurately the low degree signal in the ocean water redistribution. As a consequence, the pseudospectral formalism will be especially useful in the gravitationally self-consistent analysis of present-day secular variations in the low-degree zonal harmonics of the earth's geoid.
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Late glacial to post glacial sea-level changes provide direct evidence of the progress of melting of large ice sheets during the last deglaciation but, although the correlation between ice and ocean volumes is incontrovertible, the causal link is commonly obscured. Local effects including tectonics, isostatic and hydroisostatic responses and equatorial ocean-syphoning impose additional signals that hide the true picture.A detailed regional study of the Western Indian Ocean based on the analysis of drill cores carried out through modern reefs, in combination with observations and sampling of reef foreslopes, and investigations of outcrops provides a comprehensive data base. Sites from a range of tectonic settings include the microcontinental margins of Madagascar, the granitic Seychelles, and the isolated volcanic islands of Réunion, Mauritius and the Comoros in which the effects of subsidence can be shown to be small. These cover a range of latitudes, and comparisons with adjacent sites on continental margins allow the construction of sea-level curves that closely reflect the eustatic response and disengage this from the effects of other mechanisms.The Mayotte foreslope in the Comoro Islands provides the first coral reef record of sea-level change during the early deglaciation in the Indian Ocean (110–115 m below present sea level between 18,000 and 17,000 yr BP). Two distinctive reef terraces, at 90 and 60 m water depth are dated at 13,600 yr BP and partly attributed to the Younger Dryas period (12,700–11,600 cal yr BP). Reef drowning at around 13,500 yr BP may correspond to Meltwater Pulse 1A, and although there were surges in the rate of sea-level rise, most notably between 11,950 and 11,350 yr BP, there is little evidence to support a well-defined Meltwater Pulse 1B.Reconstructed Holocene sea-level curves are in good agreement and reflect a rapid sea-level rise of about 6 mm yr−1 between 10,000 and 7500 yr BP, followed by a clear inflection around 7500 yr BP when the rate fell to 1.1 mm yr−1. Modern reefs started to grow 8000–9000 years ago. In the post-glacial period the rate of sea-level rise was 1–1.5 mm yr−1 before stabilization at its present level 3000–2500 years ago.Curves for the 10,000–6000 yr−1 BP interval correspond closely with those predicted by theoretical models but lie below these in the subsequent period. In particular, and with the exception of the margins of the Madagascar microcontinent influenced by hydroisostatic processes, they do not reflect predicted higher sea-level stands during the late Holocene.
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Lanyu and Lutao Islands to the southeast of Taiwan are located in the northern extension of the Luzon Arc. Crustal deformation of these islands provides a key to understand the collision of the Luzon Arc against Taiwan. To clarify the style and the rate of vertical movement during the Holocene, uplifted coral reefs fringing these two islands were investigated. Living corals were also investigated for comparison with fossil corals. It was found that Isopora palifera lives dominantly in the upper slope of the present-day fringing coral reefs in Lanyu Island at an average depth of 101 ± 46 cm (one standard deviation) below mean sea level. Using I. palifera as an accurate indicator of paleo-sea levels, Holocene relative sea-level changes were reconstructed. Lanyu Island has been uplifted continuously at a rate of 2.0 mm yr−1, at least during the late Holocene from 2,269 cal. yr BP to the present. Lutao Island has been uplifted at an average rate of 1.2 mm yr−1, since at least 5,749 cal. yr BP, although it is unclear whether the uplift was continuous. The present observations, combined with the GPS displacement field and deep crustal structure, suggest that the continuous uplift is related to aseismic slip on the Longitudinal Valley Fault.
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The disastrous effects of the 1999 Chi-Chi earthquake in Taiwan demonstrated an urgent need for better knowledge of the island's potential earthquake sources. Toward this end, we have prepared a neotectonic map of Taiwan. The map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40-m resolution digital elevation model, augmented by geodetic and seismologic data. The active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the Eurasian continental margin have created two neotectonic belts in Taiwan. In the southern part of the orogen both belts are in the final stage of consuming oceanic crust. Collision and suturing occur in the middle part of both belts, and postcollisional collapse and extension dominate the island's northern and northeastern flanks. Both belts consist of several distinct neotectonic domains. Seven domains (Kaoping, Chiayi, Taichung, Miaoli, Hsinchu, Ilan, and Taipei) constitute the western belt, and four domains (Lutao-Lanyu, Taitung, Hualien, and Ryukyu) make up the eastern belt. Each domain is defined by a distinct suite of active structures. For example, the Chelungpu fault (source of the 1999 earthquake) and its western neighbor, the Changhua fault, are the principal components of the Taichung Domain, whereas both its neighboring domains, the Chiayi and Miaoli Domains, are dominated by major blind faults. In most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid-7 values.
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Records of relative sea-level change extracted from corals of the Mentawai islands, Sumatra, imply that this 700-kilometer-long section of the Sunda megathrust has generated broadly similar sequences of great earthquakes about every two centuries for at least the past 700 years. The moment magnitude 8.4 earthquake of September 2007 represents the first in a series of large partial failures of the Mentawai section that will probably be completed within the next several decades.
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14C-dated Holocene coastal uplift, conventional and satellite geodetic measurements, and coseismic and aseismic fault slip reveal the pattern of distributed deformation at Taiwan resulting from convergence between the Philippine Sea plate and Eurasia; as in other subduction orogenic settings, the locus of strain release and accumulation is strongly influenced by changes in fault geometry across strike. Uplift evidence from the islands of Lutao and Lanhsu is consistent with progressive oblique collision between the Luzon arc and the Chinese continental margin. In the Coastal Range, geodetic and seismic records show that shortening is taken up serially by discontinuous slip on imbricate faults. The geodetic data point to net extension across the Central Range, but deformed Holocene shorelines in the Hengchun Peninsula at its southern extremity suggest that the extension is a superficial effect partly caused by blind reverse faulting. The fastest shortening rates indicated by geodesy are recorded on the Longitudinal Valley fault and across the Chukou fault within the fold-and-thrust belt. In the former, the strain is dissipated mainly as aseismic reverse and strike-slip displacement. In contrast, the fold-and-thrust belt has witnessed five earthquakes with magnitudes of 6.5 or above in the 20th century, including the 1999.9.21 Chi-Chi earthquake (magnitude approximately 7.6) on a branch of the Chukou fault. The neotectonic and geodetic data for Taiwan as a whole suggest that the fold-and-thrust belt will continue to host the majority of great earthquakes on the island.
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Seismic rupture produced spectacular tectonic deformation above a 400-kilometer strip of the Sunda megathrust, offshore northern Sumatra, in March 2005. Measurements from coral microatolls and Global Positioning System stations reveal trench-parallel belts of uplift up to 3 meters high on the outer-arc islands above the rupture and a 1-meter-deep subsidence trough farther from the trench. Surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward. A saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 Sumatra-Andaman rupture. The southeastern edge abuts a predominantly aseismic section of the megathrust near the equator.
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Study focused on the neotectonic characteristics of Lutao is expected to provide valuable information regarding both the rate and the mechanism of uplift of southeastern Pacific island arc. From an investigation of aerial photographs and geomorphology, the authors have identified seven levels of marine terraces that have developed on Lutao. Radiocarbon ages obtained from the carbonate samples veneered on top of the two lower marine terraces are 1 to 9 ka (Holocene) and 33 to 36 ka, respectively. It is believed that each level of marine terrace corresponds to one transgression-regression cycle, which is the result of interaction between crustal movement and sea level change. By plotting the altitudes of the terraces on a coordinate on which a reliable sea level has already been established, the long-term uplift rate of Lutao can be deduced, i.e., 3.4 mm/yr. -from Authors
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Consideration of eustatic and hydro-isostatic effects on late Quaternary sea levels in the tropical Pacific Ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post-mid-Holocene time. Annular atoll reefs, perched atop carbonate platforms which cap buried volcanic edifices, are underlain by 8-28 m of Holocene limestone disconformably overlying a substratum of last-interglacial or older limestone. Comparable thicknesses (9-23 m) of Holocene sediment are present beneath atoll lagoons that are uniformly <85 m deep. During glacio-eustatic drawdowns in global sea level by 120-125 m, carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs. Modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges. Slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last-interglacial reef edifices by the amounts needed to provide accommodation space for Holocene reef growth during the postglacial eustatic rise in sea level. Modern atoll reef caps began to grow after ∼9 ka when rising Holocene sea level overtopped degraded remnants of interglacial reefs, but remained submerged until carbonate buildups approached sea level in mid-Holocene time (6-4 ka). Classic atoll morphology, with circlets of multiple islets dotting annular reefs, formed in combination with late Holocene hydro-isostatic drawdown in tropical Pacific sea level in response to equatorial ocean siphoning, a facet of global isostatic adjustment (GIA) to deglaciation. Early Holocene eustatic rise in sea level and late Holocene hydro-isostatic decline in sea level combined to produce a regionally variable mid-Holocene highstand in tropical Pacific sea level that stood 1.0-2.6 m above modern sea level. Cemented mid-Holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non-migratory (pinned) islets that were not present along atoll rims until after the local crossover date, when ambient high-tide level first fell below mid-Holocene low-tide level. Existing atoll landforms have a time depth generally <1-2 ka.
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Precisely quantifying the current climate-related sea level change requires accurate knowledge of long-term geological processes known as Glacial Isostatic Adjustments (GIA). Although the major postgla-cial melting phase is likely to have ended 6–4 ka BP (before present), GIA is still significantly affecting the present-day vertical position of the mean sea surface and the sea bottom. Here we present empirical rsl (rel-ative sea level) data based on U/Th dated fossil corals from reef platforms of the Society Islands, French Pol-ynesia, together with the corresponding GIA-modeling. Fossil coral data constrain the timing and amplitude of rsl variations after the Holocene sea level maximum (HSLM). Upon correction for isostatic island subsi-dence, we find that local rsl was at least 1.5 6 0.4 m higher than present at 5.4 ka. Later, minor ampli-tude variations occurred until 2 ka, when the rsl started dropping to its present position with a rate of 0.4 mm/yr. The data match with predicted rsl curves based on global ice-sheet chronologies confirming the role of GIA-induced ocean siphoning effect throughout the mid to late Holocene. A long lasting Late Holocene highstand superimposed with second-order amplitudinal fluctuations as seen from our data sug-gest that the theoretical predicted timing of rsl change can still be refined pending future calibration.
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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.
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We have developed techniques for measuring 234U and 230Th on Faraday cups with precisions of 1–3 epsilon units (1 ε-unit=1 part in 104) using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Using a Thermo-Scientific Neptune with desolvation nebulization, we obtained ionization/transmission efficiencies of 1–2% for both U and Th. We set up protocols to correct for tailing, prepared U and Th gravimetric standards, tested a Th mass fractionation correction procedure based on U isotopes, and identified natural calcite samples likely to be in U–Th isotopic secular equilibrium. The measured atomic ratios, 234U/238U=54.970 (±0.019)×10−6 and 230Th/238U=16.916 (±0.018)×10−6, for these calcite samples were identical within errors (quoted 2σ uncertainties calculated combining all sources of error). Half-life values calculated from these ratios are consistent with previous values, but have much smaller errors: 245,620±260 a for 234U and 75,584±110 a for 230Th (quoted 2σ uncertainties calculated using all sources of error). In calculating a 230Th age, some of the systematic errors included in estimating the full error in the half-lives effectively cancel. Removing these uncertainties (uncertainty in the 238U half-life value, uncertainty in our gravimetric uranium and thorium standards, and uncertainty in the absolute isotopic composition of the uranium standard), yields effective uncertainties for the purposes of 230Th dating of ±70 a for the 234U half-life value and ±30 a for the 230Th half-life value. Under ideal circumstances, with our methods, the 2σ uncertainty in age, including uncertainty in half-life values is ±10 a at 10 ka, ±100 a at 130 ka, ±300 a at 200 ka, ±1 ka at 300 ka, ±2 ka at 400 ka, ±6 ka at 500 ka, and ±12 ka at 600 ka. The isotopic composition of a sample with an age <800 ka can clearly be resolved from the isotopic composition of a sample in secular equilibrium, assuming closed system behavior. Using these techniques, we analyzed a Sanbao Cave (Hubei, China) stalagmite that formed between 510 and 640 ka ago. As the half-life values were determined independent of the Sanbao Cave ages, the observed co-variation between stalagmite δ18O and Northern Hemisphere summer insolation is consistent with accurate ages and half-life values.
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Hanauma Bay on the southeast coast of Oahu is a breached compound explosion crater invaded by the sea. Ten core holes through an active fringing reef within the bay provided 63 samples for which C14 dates have been determined. These ages indicate that (1) the reef started growing about 7,000 yr ago; (2) most of its vertical growth was during the interval from 5,800 to 3,500 radiocarbon years ago, when its average upward growth rate was 1 m/300 yr; and (3) during the past 3,000 yr, it advanced seaward at the rate of 1 m/45 yr. The data indicate that Koko Bench at -5 m was formed at least 5,800 radiocarbon years ago when the sea stood from 5 to 9 m below its present level. This result is contrary to a previously suggested date of origin of 4,100 to 4,400 yr ago. During the past 3,500 yr, sea level on the reef has risen to its present position at a decreasing rate, but at an overall rate for the interval of 1 m/∼2,900 yr. It is unlikely that sea level ever stood appreciably higher than at present during the past 3,500 yr. Volcanic ash at the base of several cores marks the latest eruption of nearby Koko Crater, which the C14 dates place at no later than 5,800 and possibly 7,000 or more radiocarbon years ago. In most cases, the radiocarbon dates follow a sequence that is consistent with stratigraphic position, but age inversions occur that are clearly beyond the statistically defined errors in age. They are probably caused by irregularities in the growth pattern of the reef near channels and large pockets. The profile of ages in this most extensively dated reef indicates that casual and sparse sampling of a reef could lead to dubious results in interpreting reef history and chronology of sea levels.
Article
A spectacular flight of terraces occurs on the northeast seaboard of Huon Peninsula, New Guinea. The terraces are clearly developed for more than 80 km and rise to over 600 m. They are built dominantly of coral reefs but include subordinate deltaic gravel formations. Interpretation of the reef succession depends on analysis of facies changes across a number of sections, and this is developed after prior analysis of reefs, lagoons, deltas, and submarine terraces on the modern coast. A record of sea-level changes relative to the rising land is determined for each section. Radiometric dating of the terrace reefs indicates Pleistocene sea-level maxima at the following times (yr B.P.): 30,000, 40,000 to 50,000, 60,000, 80,000, 105,000, 120,000, 140,000, 185,000, 220,000. Good agreement with dated reefs elsewhere reinforces these age estimates. Tectonic uplift has varied along the terraced area, because heights of terraces diminish from southeast to northwest, parallel to the coast; and yet records of relative sea-level changes are similar between sections. By assuming that upper Pleistocene interglacial sea levels were little different from the present level, tectonic and sea-level changes can in principle be separated. Using least-squares search, a " best estimate" sea-level curve and corresponding tectonic uplift pattern are derived on the basis of 11 sections. The sea-level curve compares well with Emiliani's generalized paleotemperature curve for the upper Quaternary.
Article
This paper is concerned with the tectonic trends that can be deduced from the Holocene raised shorelines between Ch'eng-kung and Hsin-she, along a 65-km long coastal sector in the eastern Coastal Range of Taiwan. Sequences of up to eight superimposed shorelines have been identified in a single section. Twelve new radiocarbon dates (six of which were obtained by accelerator mass spectrometry) of in-situ marine samples (up to 40 m in altitude) have confirmed a Holocene age. However, it is difficult to define clearly the upper marine boundary in the highest Holocene coastal terraces, which have been uplifted to 65–70 m, but have been capped by, and often also interfingered with, alluvial deposits. High uplift rates, ranging from 2.5–3.0 to over 8 mm/yr, have been inferred along the coast, providing evidence of differential uplift. In some cases uplift movements appear to have occurred by steps, probably spasmodically. Recurrence periods of fast uplifts seem to be of the order of at most 1000 yr. This means that a new spasmodic movement may be imminent, because the last displacement (4–6 m) has been dated about 1000 yr BP.
Article
New determinations of the half-lives of 235U and 238U have been made. Improved techniques have allowed the half-life values to be measured with greater accuracy than has been heretofore achieved. Samples were prepared by molecular plating and counted in a intermediate-geometry α-proportional counter with an extremely flat pulse-height plateau. The small amount of residual nonplated uranium was counted in a 2π counter. Energy analysis with a silicon-junction detector was used to measure the presence of "foreign" activities. For 235U, the measured specific activity was (4798.1±3.3) (dis/min)/(mg 235U), corresponding to a half-life of (7.0381±0.0048) × 108 yr. For 238U, the specific activity was measured as (746.19±0.41) (dis/min)/(mg 238U), corresponding to a half-life of (4.4683±0.0024) × 109 yr. Errors quoted are statistical (standard error of the mean), based upon the observed scatter of the data. This scatter exceeds that expected from counting statistics alone. We believe that systematic errors, if present, will no more than double the quoted errors.
Article
A very common but important observation of collided and accreted volcanic arcs is that the forearc regions of these arcs are largely or even entirely missing. The processes and mechanisms responsible for the removal and transport of the forearc materials from the collisional belts are thus important issues in understanding tectonics and crustal growth. The young and ongoing collision between the Luzon volcanic arc and the Eurasian continental margin that forms the island of Taiwan provides a rare opportunity to examine these processes and mechanisms as they occur. From observations of a new detailed 3-D tomography combined with relocated hypocenters of two earthquake sequences occurred in 2003 and 2006, we found that the Luzon forearc lithosphere initially underthrusts westward after the collision began. As the collision proceeds, the forearc basement then subducts eastward beneath the colliding and accreting Luzon arc along a major fault system in eastern Taiwan. Thus the Luzon forearc lithosphere appears to be removed by tectonic erosion and is being transported eastward into the mantle. Our results from the active Taiwan orogen will provide important insights for interpreting rock records from many old arc-continent collisional belts in the world.Highlights► The Luzon forearc lithosphere initially underthrusts westward. ► As the collision proceeds, the forearc basement then subducts eastward beneath the Luzon arc. ► The Luzon forearc lithosphere appears to be removed by tectonic erosion.
Article
DATING of coral reef terraces can provide a record of changes in sea level, which should be pronounced during the transition between glacial and interglacial periods. Cores drilled from coral reefs at Barbados in the equatorial west Atlantic1have revealed the sea-level changes that occurred during the Younger Dry as event at the end of the Last Glacial Maximum (~11,000 yr BP). It has not been known, however, whether Pacific coral reefs can grow at a rate sufficient to keep up with the rise in sea level during such a transition. Here we report results obtained from a 52-m drill core from the post-glacial reef at Huon Peninsula, Papua New Guinea, spanning the interval from 7,000 to 11,000 14C yr BP, which show that coral growth kept pace while the relative sea level rose by 50m. Although the tectonic environment is very different from that at Barbados, the two records compare well when corrections are made for local tectonic uplift, showing that sea-level rise was similar at both locations. The rate of rise was greatest between 9,000 and 10,00014C yr BP, corresponding to the time of the Younger Dryas.
Article
By examining different parts of the sea-level curves of the past 20 000yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the Earth's rheology. Observations from sites away from the former Arctic ice sheets, such as the Australian and South Pacific region, are particularly important for contraining the total meltwater volumes added into the oceans in the past 20 000yr and the rates at which this occurred. Differential sea-levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about (1-2) x 1020 Pa s-1 while differential values from islands of different sizes are suggestive of a somewhat lower value. The lower mantle (taken to be below 670km depth) viscosity is about two orders of magnitude greater than this. The estimated ice and rheological models explain many of the Holocene sea-level observations throughout the Australian and southern Pacific region. -from Authors
Article
Drill cores from Holocene reefs on Tahiti (French Polynesia) reveal a framework composed of massive branching acroporids encrusted by coralline algae associated with sessile vermetid gastropods and arborescent foraminifers. Laminated micritic crusts form coatings over coral branches or, more commonly, over related encrusting organisms throughout the cored reef sections; these crusts appear as a major structural and volumetric component of the reef framework. The microbial nature of these micritic crusts is inferred from their typical organic growth forms and geometry, the occurrence of microbial remains and stable isotope measurements. The reef communities accumulated at depths less than 5 m below mean sea level in a high energy environment throughout vertical growth from 7140 ± 170 yr bp to the present. The nature of the involved benthic communities, stable isotope data and high calcification rates of microbially encrusted corals strongly suggest that local environmental conditions have been optimal for reef development for the last 7000 years. The causes of the predominance of microbial communities over actual encrusters (red algae, foraminifers) remain problematic and could be related to short term fluctuations in ecological parameters. Microbial micritic crusts seemingly played a prominent role in protecting the coralgal colonies from bioeroders and grazers and, possibly, in strengthening the framework, due to rapid lithification. The record of similar microbial crusts in other Quaternary reef tracts suggests that microbial communities may have played a more prominent role in Quaternary reefs than presently recognized.
Article
1] Isotopically dated corals from the central New Hebrides and New Georgia Island Group, Solomon Islands, indicate that both forearcs underwent rapid late Quaternary subsidence that was abruptly replaced by hundreds of meters of uplift at rates up to $8 mm/yr, while total plate convergence was only a few kilometers. Two mechanisms that might account for these rapid reversals in vertical motion include (1) a ''displacement'' mechanism in which the forearc is displaced upward by the volume of an object passing beneath on the subducting plate (as the object moves deeper and vacates the base of the forearc, the forearc subsides to near its original position) and (2) a ''crustal shortening'' mechanism in which the forearc thickens and uplifts because of horizontal shortening when a large object impinges on the forearc and abruptly increases interplate coupling on the shallow end of the main thrust zone. Rapid subsidence follows when the impinging object is broken or otherwise decoupled, shallow interplate coupling becomes weak, and the uplifted forearc extends and subsides. The displacement mechanism surely plays a role on timescales over which plates converge tens of kilometers, but it fails to explain the geographic pattern, short time frame, and abruptness of the change from subsidence to uplift that we observe. The crustal shortening mechanism is preferred because it allows the observed abrupt uplift when an object impinges on a forearc and causes locking of a shallow segment of the interplate thrust zone. Citation: Taylor, F. W., et al. (2005), Rapid forearc uplift and subsidence caused by impinging bathymetric features: Examples from the New Hebrides and Solomon arcs, Tectonics, 24, TC6005, doi:10.1029/2004TC001650.
Article
This paper addresses the question of the magnitude and time dependence of the globally averaged (eustatic) rise of sea level that occurred subsequent to the time of Last Glacial Maximum (LGM) at approximately 21,000 calendar years before present. Through the analysis of relative sea level (RSL) histories predicted by a realistic mass conserving and gravitationally self-consistent theory of postglacial sea level change, it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history. One such location is the Island of Barbados in the Caribbean Sea, a site from which a coral based record exists that extends from mid-Holocene to LGM. Because of the sea level ambiguity that is inherent to coral based records, however, it is important that the global ice-equivalent eustatic sea level curve inferred on the basis of the Barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals. It is shown that, when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the Barbados observations, where the maximum relative sea level (RSL) depression is assumed to be near 120 m, then the theory misfits the record from the Sunda Shelf in the Indonesian Archipelago as well as the record from J. Bonaparte Gulf in northern Australia. Both of these recently published records appear to constrain the LGM low stand of RSL to a value above 120 m. The implications of these results for interpretation of the long coral derived records from the Huon Peninsula of Papua, New Guinea and the island of Tahiti are also discussed. r 2001 Published by Elsevier Science Ltd.
Article
Cores from ten holes, drilled to a maximum depth of 30 m, on Tarawa atoll in the central Pacific have been utilised in a study of the Holocene development of the atoll. Four dominant lithologies, in descending order, are cay rock, unconsolidated sediment, corals and leached limestone. Petrographic and radiometric age analyses indicate that the Holocene reef has developed on a previous (last interglacial) reef; the latter shows the effects of both vadose and phreatic freshwater diagenesis. Hydrological investigations beneath the present islands indicate the presence of freshwater lenses up to 29 m thick; the modern lenses are unrelated to freshwater diagenetic imprints preserved within the limestones. Vertical accretion rates of 5–8 m/1000 years for the Holocene reef section on Tarawa are significantly higher than rates measured for other Pacific atolls. The dated coral sequences suggest a more rapid rate of sea level rise during the early Holocene, and a relatively earlier stabilisation of sea level than has been suggested previously.
Article
 A review of the literature provides 92 estimates of the middle to late Holocene sea-level highstand on Pacific Islands. These data generally support geophysical model calculations that predict a +1 to 3 m relative sea-level highstand on oceanic islands due to the Earth’s rheological response to the melting of the last continental ice sheets and subsequent redistribution of meltwater. Both predictions and observations indicate sea level was higher than present in the equatorial Pacific between 5000 and 1500 y B.P. A non-linear relationship exists between the age and elevation of the highstand peak, suggesting that different rates of isostatic adjustment may occur in the Pacific, with the highest rates of sea-level fall following the highstand near the equator. It is important to resolve detailed sea-level histories from insular sites to test and refine models of climatic, oceanographic, and geophysical processes including hydroisostasy, equatorial ocean siphoning, and lithospheric flexure that are invoked as mechanisms affecting relative sea-level position. We use a select subset of the available database meeting specific criteria to examine model relationships of paleosea-surface topography. This new evaluated database of paleosea-level positions is also validated for testing and constraining geophysical model predictions of past and present sea-level variations.
Article
The east coast of the Coastal Range in Taiwan is well known for its multiple Holocene marine terraces and their very rapid uplift. The study area extends from Hualien to Taitung over ca 150 km of coastline. Here, we present some new data on the age and height of Holocene marine terraces, and we discuss their significance for Holocene coastal tectonics.The Holocene marine terrace sequence is subdivided into a maximum of 10 steps. The highest and oldest terrace, mostly underlain by transgressive deposits, represents the sea-level position of the culmination of Holocene sea-level rise and reaches up to ca 80 m above sea level. Transgressive deposits are radiocarbon dated at several sites, back to ca 13,000 yr BP. The lower terraces are mostly erosional ones, overlain by thin coral beds in situ, less than 1 m thick, and indicate successive lowering of relative sea level during the late Holocene. The uplift rate of the coast is very high, ranging from 5 to 15 m/ka.Three tectonic subregions, A–C, are identified, based on the pattern of marine terrace features and uplift rate. The presence of many steps during Holocene time implies that intermittent uplifts, associated with large earthquakes at intervals of one thousand to several hundred years, have repeatedly occurred in this coastal area, but with different time and amount at each subregion. The uplift of subregion A resulted from an onshore active fault (Milun fault). Causative faults for the uplift of the subregions B and C are not identified. Offshore active faults, striking obliquely to the coastline, appear to be causative faults.
Article
This paper reviews recent studies of Holocene coastal uplift in tectonically active areas near the plate boundaries of the western Pacific Rim. Emergent Holocene terraces exist along the coast of North Island of New Zealand, the Huon Peninsula of Papua New Guinea, the Japanese Islands, and Taiwan. These terraces have several features in common. All comprise series of subdivided terraces. The highest terrace is a constructional terrace, underlain by estuarine or marine deposits, and the lower terraces are erosional, cutting into transgressive deposits or bedrock. The highest terrace records the culmination of Holocene sea-level rise at ca. 6–6.5 ka BP. Lower terraces were coseismically uplifted. Repeated major earthquakes have usually occurred at ka intervals and meter-scale uplift. The maximum uplift rate and number of terraces are surprisingly similar, about 4 m/ka and seven to four major steps in North Island, Huon Peninsula, and Japan. Taiwan, especially along the east coast of the Coastal Range, is different, reaching a maximum uplift rate of 15 m/ka with 10 subdivided steps. They record a very rapid uplift. Comparison between short-term (Holocene) and long-term since the last interglacial maximum (sub-stage 5e) uplift rates demonstrates that a steady uplift rate (Huon Peninsula) or accelerated uplift toward the present (several areas of Japan and North Island) has continued at least since isotope sub-stage 5e. Rapid uplift in eastern Taiwan probably started only in the early Holocene, judging from the absence of any older marine terraces. Most of the causative faults for the coastal uplift may be offshore reverse faults, branched from the main plate boundary fault, but some of them are onshore faults, which deformed progressively with time.
Article
Perturbations to the Earth's gravity field and solid surface associated with glacial isostatic adjustment (GIA) cause the total (observable) sea-level change to depart from the eustatic curve, which is defined as a spatially uniform height shift of the ocean surface to accommodate any mass gained/lost from grounded ice. In this study we apply a state-of-the-art model of GIA-induced sea-level change to quantify the magnitude and spatial form of this departure at the global scale for a range of model parameters with an aim to identify regions that are well suited to obtain accurate and precise estimates of eustatic sea level (and therefore past grounded ice volume). In general, our results indicate that eustatic sea level is not a directly measurable quantity and so must be estimated by subtracting a model-derived estimate of non-eustatic contributions from observations. In this regard, we use our results to isolate regions where this procedure can be applied with optimal accuracy and precision. That is, where (1) the GIA predictions are relatively insensitive to plausible ranges in input parameters and (2) where the non-eustatic contribution is small (i.e., the predicted sea level closely approximates the eustatic value). We present maps that can be employed by the field community to identify areas where sea-level reconstructions would be well suited to arrive at robust estimates of eustatic sea level. Note that sea-level changes associated with tectonic motion and changes in ocean water temperature/salinity, which also lead to departures from eustasy, are not considered in this analysis.
Article
Relative sea levels in oceanic islands that are situated sufficiently far from glaciated regions were studied in relation to the rheological structure of the earth's mantle. The local hydro-isostatic adjustment associated with the mantle flow from the oceanic side to an inland side depends on the size of the island, the effective upper-mantle viscosity and the elastic plate thickness. The relative sea level has a significant dependence on the upper mantle rheology for islands with a radius larger than 10 km, but it is almost independent of the upper mantle rheology for islands with a radius less than 10 km. In other words, the observed sea-level changes in such small islands follow the global isostatic adjustment which depends strongly on the lower mantle viscosity. In fact, the relative sea levels in small oceanic islands impose important constraints on the lower-mantle viscosity. On the other hand, the effective upper-mantle viscosity and the elastic plate thickness are determined by analyzing the relative sea levels for islands greater than 10 km. The observed sea-level curves in Japan and New Zealand are consistent with the effective viscosity of the upper mantle, equal to 2 to 6 × 1021 poises. The effective elastic plate thickness for Japan and New Zealand is estimated to be less than 50 km and greater than 100 km, respectively. The thickness of the lithosphere obtained by sea-level curves in Japan and New Zealand is compatible with the results obtained by seismological studies.
Article
We have re-determined the and half-lives to be 245,250±490 years (2σ) and 75,690±230 years (2σ), respectively. Using high precision thermal ionization mass spectrometric (TIMS) methods, we measured and atomic ratios in 4 different materials that were likely to have behaved as closed systems for 106 years or more: zircons with concordant , , and ages, Iceland Spar, Table Mountain Latite, and aliquots of a solution of Harwell uraninite (HU-1). We calibrated the TIMS multipliers using U-500, U and Th gravimetric standards, and U double spike. Consistent values for all measured materials and consistent values for all materials with the exception of our HU-1 solution support the secular equilibrium status. The new half-lives agree within error with previously determined values; however, errors in our values are generally smaller than those in the earlier determinations. Our half-life is about 3‰ higher than that commonly used in dating laboratories and our half-life is about 4‰ higher. ages calculated with the new half-lives are generally older than those calculated with the previously used half-lives. The difference in age, though, is small throughout the age range because our revised and half-lives are offset from earlier values in the same sense (both to higher values). In the case of dating materials older than 350 ka in laboratories that rely solely on gravimetric standardization procedures, use of our decay constants and their associated errors will considerably reduce the errors in age arising from uncertainty in the decay constants.
Article
The active collision between the Luzon arc and the Asian continent in the Taiwan area is investigated in terms of plate kinematics and geological records. Regarding plate kinematics, the tectonic evolution of the collision can be reconstructed by superimposing the paleopositions of Luzon arc on the pre-collisional Asian continental margin. Regarding geological records, the collisional history can be interpreted from the stratigraphy of the Coastal Range and the Western Foothills and from the diastrophism of the Central Range of Taiwan. By incorporating geological information into plate kinematics, it appears that the Luzon arc could have begun overriding the Asian continental margin in the late Middle Miocene (about 12 Ma). In the Late Miocene, the impingement of the arc deformed part of the continental margin and might have caused metamorphism of part of the Central Range, but no distinct effects were produced in the sedimentary record. In Mio-Pliocene times (about 5 Ma), the arc changed its direction of motion from north-northwesterly to west-northwesterly and began to override the continental margin rapidly. The accretionary wedge grew increasingly to emerge above sea level and feed continental detritus to the Luzon forearc basin and to induce foreland subsidence on the continental margin. In the early Late Pliocene (about 3 Ma), the collision drastically uplifted the mountain ranges in northern Taiwan, which shed voluminous orogenic sediments into the forearc and foreland basins. As the collision propogated toward the west and the south, the forearc and foreland basins were progressively accreted to the collisional orogen which eventually grew up to its present configuration.
Article
Late Holocene sea-level highstands of amplitude are endemic to equatorial ocean basins. These highstands imply an ongoing and moderate, sub-mm/yr, sea-level fall in the far field of the Late Pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment (GIA; Clark et al., 1978). Mitrovica and Peltier (1991) coined the term ‘equatorial ocean syphoning’ to describe the GIA-induced sea-level fall and they provided the first physical explanation for the process. They argued that water migrated away from far-field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions. We provide a complete physical explanation for the origin of equatorial ocean syphoning, and the associated development of sea-level highstands, using numerical solutions of the equation that governs meltwater redistribution on spherical, viscoelastic Earth models. In particular, we separate the total predicted sea-level change into contributions associated with ice and meltwater loading effects, and, by doing so, isolate a second mechanism that contributes significantly to the ocean syphoning process. Ocean loading at continental margins induces a ‘levering’ of continents and a subsidence of offshore regions that has also long been recognized within the GIA literature (Walcott, 1972). We show that the influx of water into the volume created by this subsidence produces a sea-level fall at locations distant from these margins—indeed over the major ocean basins—that is comparable in amplitude to the syphoning mechanism isolated by Mitrovica and Peltier (1991).
Article
The 131 stations of the ‘Taiwan GPS Network’ were surveyed 4–6 times from 1990 to 1995 with dual-frequency geodetic receivers. The standard deviation of an observed baseline length with its linear trend removed is in the range of 6–10 mm for a 3–120 km long baseline. The average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the GPS stations relative to Paisha, Penghu, situated at the Chinese continental margin. To the south of Fengping, in the northern Coastal Range, the velocity vectors of stations in Lanhsu, Lutao, and the Coastal Range trend in the directions of 306°–322° with rates of 56–82 mm/yr. In contrast, there is a dramatic decrease in the rates to the north of Fengping. This may be caused by the motion along the NE-SW-trending thrusts which obliquely cut the northern Coastal Range. A discontinuity of about 30 mm/yr in the rates along with a remarkable change in the directions of station velocity is observed across the Longitudinal Valley, then the moving directions gradually shift to the west for the stations in the Western Foothills. In the Kaohsiung-Pingtung coastal area, the station velocities are even directed toward the southwest. To the north of the Peikang High, the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast. Significant NW-SE extensional deformation is found in the Ilan Plain and northern Taiwan. In general, the pattern of the velocity field for GPS stations in the Taiwan area is quite consistent with the directions of present-day tectonic stress.
Article
Quaternary marine terraces have been investigated along a 1000 km stretch of the coast of Argentinian Patagonia. Fossil mollusc shells, most in living position and collected from raised beaches, were dated using the U-series, ESR and methods. Our analyses show that Holocene sea-level in this region culminated 7000 to 8000 BP at 6–7 m amsl. This beach slightly increases in altitude southward. The last interglacial stage (5e) was identified at 16–17 m amsl whereas the highest and morphologically most distinctive radiometrically dated terrace at 250,000 to 330,000 BP exists at an elevation of 33–35 m amsl. We estimate a constant rate of tectonic uplift of 0.09 m/1000 yr since the middle Pleistocene. Using this estimate of the local rate of tectonic uplift we correct relative sea-level (r.s.l) observations for the Holocene epoch. In turn, the inferred Holocene sea-level histories are compared with those predicted using the ICE-4G (VM2) model of the global process of glacial isostatic adjustment. This model accurately predicts r.s.l history from all sites along the northern part of the east coast of the South American continent (Venezuela, Brazil). However, along the southern part of the coast of Argentinian Patagonia there is evidence of an influence that is not accurately represented in this version of the model of the global process of glacial isostatic adjustment. We suggest that this influence could be connected to the presence of the broad continental shelf that is located offshore of this region, but the influence of significant neotectonic uplift cannot be dismissed.
Article
As many as six levels of emerged Holocene coral terraces occur along 40 km of coastline on the Huon Peninsula, Papua New Guinea, recording uplift history since culmination of the postglacial transgression. The Holocene reef crest, ca. 6000 yr B.P., is tilted down to the northwest, parallel to the coast and concordant with the deformation of the last interglacial coral reef terrace, and descends from 23 to 12 m in the study area. The pattern and rate of deformation have been uniform in the late Quaternary because average uplift rates have remained the same since the last interglaciation. The Holocene terraces described here are erosional features with regressive encrusting corals, developed upon the Holocene transgressive reef. The multiple levels represent episodic, probably coseismic uplift, which has occurred repeatedly in the last ca. 6000 yr. Significant longshore variation in the age of the lowest terrace, from 1700 to 2500 yr B.P., suggests independent coseismic uplift on different sectors of the coast. This is supported by age-height relationships of the higher Holocene terraces. Nonlinear uplift during the Holocene, with recurrence intervals increasing toward the present, is clearly recorded by the regressive terraces in each subregion. Some of the Holocene regressive terraces grade laterally into fluvial terraces capped with debris-flow deposits, probably reflecting seismically triggered mass movement.
Article
A significant body of new information about the development of coral reefs during the last 23 ka has been generated in the last three decades. In the Indo-Pacific province, structures from a variety of geodynamic settings have been investigated using subsurface drilling and submersible diving. This paper is based principally on the re-examination of the core dataset from the literature, with reconversion of many previously published radiocarbon ages into calendar dates.Seven framework and three detrital facies were identified on the basis of the nature and growth shapes of dominant framework builders, and on that of the texture of sediments, respectively. Framework facies in high-hydrodynamic energy settings were dominated by an association of coralline algae and robust-branching corals (Acropora robusta group, A. gr. humilis, A. palifera, Pocillopora damicornis) with locally encrusting coral forms (faviids). In moderate energy environments, these were replaced by domal (Porites), tabular-branching (Acropora gr. hyacinthus) and arborescent (Acropora gr. muricata), whereas sheltered areas included an association of arborescent, foliaceous (Montipora, Pavona) and encrusting coral species. Detrital facies comprise coral rubble, carbonate sand and mud. On compositional and textural bases, four main sand subfacies were recognized: coralgal rudstone to packstone; coral–molluscan grainstone/packstone; molluscan–foraminiferal grainstone/packstone; and green algal (Halimeda) grainstone/packstone. Despite some overlaps in the sand facies association, each subfacies can provide additional support to reconstruction of paleoreef environments.Three types of framework facies association were identified within entire reef-margin sequences: framework of homogeneous composition reflecting stability of environmental conditions through time; superimposition of two distinct frameworks, usually as deeper water corals overlain by shallower, higher energy ones, and recurrent alternations of shallower and deeper coral assemblages. The two last associations resulted probably from lateral displacements of coral communities in response to rapid changes in accommodation space. Such facies transitions also are described from backreef sediment piles: gravel graded into sand and mud successively as a result of upward shallowing. The degree of reef development seems to be linked to coral community structure. Communities consisting principally of branching and domal coral forms favoured substantial accretion and the formation of well-developed reefs, whereas assemblages comprising foliaceous and encrusting colonies produced only incipient reefs. Within reef systems, the proportions of detritus over framework tend to increase as hydrodynamic energy declines. The Indo-Pacific reef systems are classified into four anatomy types on the basis of dominant depositional patterns: balanced aggrading/onlapping, unbalanced aggrading/downlapping, prograding and backstepping types. Vertical accretion rates of frameworks are highly variable and are not directly dictated by coral growth habits. However, the highest rates recorded (up to 20 mm year−1) relate to tabular- and arborescent-acroporid rich sections. Abrupt variations in the aggradation rates of framework are recorded in sequences at the transitional zone between two distinct coral assemblages. In detritus-dominated sequences, accumulation rates range from 0.2 to about 40 mm year−1, with higher values suggesting intense hurricane-controlled deposition. In addition, accretion rates also seem to depend on water-energy conditions. In high-energy environments, aggradation rates did not exceed 12 mm year−1, but reached 25 mm year−1 in more protected areas. By contrast, lateral accretion operated at an average rate of 90 mm year−1 in agitated waters, while it did not exceed the mean rate of 55 mm year−1 in calm waters. Changes in accretion rates appear to be linked to reef growth modes. In the reef zones driven by a “keep-up” mode, mean vertical accretion rates range at around 6 mm year−1. The reef zones developed through a “catch-up” mode at rates of 3–4 mm year−1. There was little variation in accretion rates according to latitude.At the Last Glacial Maximum, from 23 to about 19 ka BP, reefs (Reef Generation RGO) only developed along what were to become the foreslopes of present reefs, forming accumulations a few metres thick at vertical rates of up to 1 mm year−1. The rapid postglacial rise in sea level, from about 19 to 6.5 ka BP, was accompanied by the settlement of three successive reef generations (the so called RGI, RGII and RGIII), within the periods 17.5–14.7, 13.8–11.5 and 10 ka BP to the Present.During the Postglacial transgression, regional to local differences in gross morphology and internal architecture of the reefs have been determined by differing sea-level histories in combination with neotectonics and typographic factors. Locally, reef colonization seems to have been facilitated or prevented chiefly by small-scale topographic features. Development during subsequent deglaciation was probably largely independent of variations in sea surface temperatures. Water turbidity also seems to have been only a minor determinant of reef settlement and growth, but may locally have controlled the composition of coral communities, resulting in the growth of turbidity-tolerant domal and foliaceous forms.Changes in atmospheric CO2 levels remained within the tolerance thresholds for reef calcification. The three main reef growth episodes coincide roughly with rapid increases in atmospheric pCO2. Dust input and variations in sea surface salinities seem to have had a very limited control on reef growth. The LGM was characterized by salinities comparable with those of the present, but by higher dust fluxes. By contrast, nutrient levels, hydrodynamic energy, and to a lesser, extent coral recruitment in relation to substrate availability and ocean circulation, have played major roles in determining reef accretion patterns at both local and regional scales. Two periods of increased upwelling in the western Indian Ocean, at 15.3 and 11.5–10.8 ka BP, coincided with the demise of RGI and RGII. During deglaciation, high-frequency storm events probably led to a scarcity of typical growth framework reefs and favoured the formation of structures composed of reworked and recemented coral framework. Storm control may have been particularly important in the mid-Holocene when water depths over incipient reefs were greater than 5 m. From the LGM to the early Holocene, coral settlement has probably declined due to a lack of suitable nurseries, until the modern patterns of ocean circulation were established and thus favoured larval dispersal from refuges. It is highly desirable to improve analysis of the core database and to increase the number of core-transects, including forereef sites, to enhance our knowledge of Recent reef development.
Article
Coral reefs drilled offshore of Barbados provide the first continuous and detailed record of sea level change during the last deglaciation. The sea level was 121 ± 5 metres below present level during the last glacial maximum. The deglacial sea level rise was not monotonic; rather, it was marked by two intervals of rapid rise. Varying rates of melt-water discharge to the North Atlantic surface ocean dramatically affected North Atlantic deep-water production and oceanic oxygen isotope chemistry. A global oxygen isotope record for ocean water has been calculated from the Barbados sea level curve, allowing separation of the ice volume component common to all oxygen isotope records measured in deep-sea cores.
Article
A technique has been developed to quantify ultratrace 231Pa (50-2000 ag; 1 ag = 10(-18) g) concentrations in seawater using isotope-dilution thermal ionization mass spectrometry (TIMS). The method is a modification of a process developed by Pickett et al. (Pickett, D. A.; Murrell, M. T.; Williams, R. W. Anal. Chem. 1994, 66, 1044-1049) and extends the technique to very low levels of protactinium. The procedural blank is 16 +/- 15 ag (2sigma), and the ionization efficiency (ions generated/atom loaded) approaches 0.5%. Measurement time is <1 h. The amount of 231Pa needed to produce 231Pa data with an uncertainty of +/-4-12% is 100-1000 ag (approximately 3 x 10(5) to 3 x 10(6) atoms). Replicate measurements made on known standards and seawater samples demonstrate that the analytical precision approximates that expected from counting statistics and that, based on detection limits of 38 and 49 ag, protactinium can be detected in a minimum sample size of surface seawater of approximately 2 L for suspended particulate matter and <0.1 L for filtered (<0.4 microm) seawater, respectively. The concentration of 231Pa (tens of attograms per liter) can be determined with an uncertainty of +/-5-10% (2sigma) for suspended particulate matter filtered from 5 to 10 L of seawater. For the dissolved fraction, 0.5-1 L of seawater yields 231Pa measurements with a precision of 1-10%. Sample size requirements are orders of magnitude less than traditional decay-counting techniques and significantly less than previously reported ICP-MS techniques. Our technique can also be applied to other environmental samples, including cave waters, rivers, and igneous rocks.