Chapter

Expedition 371 summary

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... International Ocean Discovery Program (IODP) Expedition (Exp.) 371 aimed to better constrain the timing and dynamics of northern Zealandia paleogeography during the Cenozoic (Sutherland et al., 2018(Sutherland et al., , 2019b. A total of 2,506 m sediments and volcanic rocks were recovered from cores drilled at six sites ( Figure 1) with the scientific drillship JOIDES Resolution (JR). ...
Article
Full-text available
The absolute position during the Cenozoic of northern Zealandia, a continent that lies more than 90% submerged in the southwest Pacific Ocean, is inferred from global plate motion models, because local paleomagnetic constraints are virtually absent. We present new paleolatitude constraints using paleomagnetic data from International Ocean Discovery Program Site U1507 on northern Zealandia and Site U1511 drilled in the adjacent Tasman Sea Basin. After correcting for inclination shallowing, five paleolatitude estimates provide a trajectory of northern Zealandia past position from the middle Eocene to the early Miocene, spanning geomagnetic polarity chrons C21n to C5Er (∼48–18 Ma). The paleolatitude estimates support previous works on global absolute plate motion where northern Zealandia migrated 6° northward between the early Oligocene and early Miocene, but with lower absolute paleolatitudes, particularly in the Bartonian and Priabonian (C18n–C13r). True polar wander (solid Earth rotation with respect to the spin axis), which only can be resolved using paleomagnetic data, may explain the discrepancy. This new paleomagnetic information anchors past latitudes of Zealandia to Earth's spin axis, with implications not only for global geodynamics, but also for addressing paleoceanographic and paleoclimate problems, which generally require precise paleolatitude placement of proxy data.
... Paleomagnetic Directions and Anisotropy of Magnetic Susceptibility Dallanave et al. (2020) recently published paleomagnetic data from carbonate rocks exposed in the Koumac region of northern New Caledonia. New Caledonia is the emergent part of the northernmost Norfolk Ridge, which is in turn part of a large continental mass that is submerged for more than 90%, referred to as Zealandia (Mortimer et al., 2017;Sutherland et al., 2019). The sampled section (Sommet-Khian, 260 stratigraphic meters) consists of a massive basal pelagic micrite (0-83 m) overlain upsection by terrigenous-rich calciturbidites (83-260 m). ...
Article
Full-text available
Paleogeographic reconstructions largely rely on paleomagnetic data, mostly in the form of paleomagnetic poles. Compilations of poles are used to determine so called apparent polar wander paths (APWPs), which capture the motion through time of a particular location with respect to an absolute reference frame such as the Earth's spin axis. Paleomagnetic datasets from sedimentary rocks are particularly relevant, because of their spatial distribution and temporal continuity. Several criteria have been proposed through the years to assess the reliability of paleomagnetic datasets. Among these, the latitudinal-dependent elongation of a given paleomagnetic directions distribution, predicted by a widely accepted paleosecular variations model, has been applied so far only to investigate inclination flattening commonly observed in sedimentary rocks. We show in this work that this concept can be generalized to detect "contamination" of paleomagnetic data derived from tectonic strain, which is not always detected by field observation only. After generating different sets of simulated geomagnetic directions at different latitudes, we monitored the variations in the shape of the distributions after applying deformation tensors that replicate the effect of increasing tectonic strain. We show that, in most cases, the "deformation" of the dataset can be detected by elongation vs. inclination ratios not conforming to the values predicted by the paleosecular variations model. Recently acquired paleomagnetic directions and anisotropy of magnetic susceptibility (AMS; a parameter very sensitive to tectonic strain) data from New Caledonia verifies the results of these simulations and highlights the importance of measuring AMS when using sedimentary paleomagnetic data for paleogeographic reconstruction. We suggest to include always AMS measurement and analysis of the distribution shape to assess sedimentary paleomagnetic data used for paleogeographic reconstructions.
... This overall record includes several stratigraphic gaps, notably one spanning the early to middle Eocene (56-45 Ma) and one spanning the middle Miocene to Pliocene (13-2 Ma). Unusually high sedimentation rates in the early Paleocene, early Oligocene, and middle Miocene could indicate sequence thickening by tectonic activity (see the Expedition 371 summary chapter [Sutherland et al., 2019b]). ...
Article
Full-text available
The Kuroshio Current (KC) and Kuroshio Current Extension (KCE) form a western boundary current as part of the North Pacific Subtropical Gyre. This current plays an important role in regulating weather and climate dynamics in the Northern Hemisphere in part by controlling the delivery of moisture to the lower atmosphere. Previous studies indicate the KCE responded dynamically across glacial and interglacial periods throughout the Pliocene‐Pleistocene. However, the response of the KCE during Pleistocene super‐interglacials has not been examined in detail. We present a ∼2.2 Ma record of X‐ray fluorescence elemental data from Ocean Drilling Program Hole 1207A and employ hierarchical clustering techniques to demonstrate paleoenvironmental changes around the KCE. Time‐frequency analysis identifies significant heterodyne frequencies, which suggests there were nonlinear interactions between high‐latitude and low‐latitude climate regulating expansion and contraction of the North Pacific Subtropical Gyre prior to the onset of the Mid‐Pleistocene Climate Transition (MPT). We observe two periods of elevated ln Ca/Ti, which may represent sustained warmth with northward migrations of the KCE in the northwestern Pacific. These intervals correspond to Marine Isotope Stages 29‐25, 15, and 11‐9 and occur around recent climatic transitions, the MPT and Mid‐Brunhes Event. Northward expansion of the subtropical gyre during these exceptionally warm interglacials would have delivered more heat and moisture to the high latitudes of the northwest Pacific. Furthermore, enhanced evaporation from the warm KCE vented to the lower atmosphere may have preconditioned the Northern Hemisphere for ice volume growth during two of the most recent periods of climate transition.
Preprint
Full-text available
The evolution of the Cenozoic Icehouse over the past 30 million years (Myr) from a unipolar to a bipolar world is broadly known; however, the exact development of orbital-scale climate variability is less well understood. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of the Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30 Myr), which constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this site. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30–13 Ma); 2) increased eccentricity-modulated precession pacing appears after the mid Miocene Climate Transition (mMCT) (~14–8 Ma); 3) strong obliquity pacing appears in the late Miocene (~7.7–3.3 Ma) following the increasing influence of high-latitude processes. The lowest CaCO3 content (92–94 %) occur between 18.5–14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climate Optimum (~17–14.5 Ma) by 1.5 Myr. The emergence of precession-pacing of CaCO3 deposition at Site 1264 after ~14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or an influx of cooler, less corrosive deep-waters. The highest %CaCO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8–3.3 Ma at Site 1264, which is broadly, but not exactly, contemporaneous with the LMBB in the equatorial Pacific Ocean. The global expression of the LMBB may reflect an increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.
Article
Full-text available
The evolution of the Cenozoic cryosphere from unipolar to bipolar over the past 30 million years (Myr) is broadly known. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere, and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca / Fe) data collected at Ocean Drilling Program Site 1264 (Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (∼ 316 m; 30 Myr). This constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this location. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and the carbon cycle: (1) strong ∼ 110 kyr eccentricity pacing prevails during Oligocene–Miocene global warmth (∼ 30–13 Ma), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (∼ 14–8 Ma), and (3) pervasive obliquity pacing appears in the late Miocene (∼ 7.7–3.3 Ma) following greater importance of high-latitude processes, such as increased glacial activity and high-latitude cooling. The lowest CaCO3 content (92 %–94 %) occurs between 18.5 and 14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climatic Optimum (∼ 17–14.5 Ma) by 1.5 Myr. The emergence of precession pacing of CaCO3 deposition at Site 1264 after ∼ 14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 between 14 and 13 Ma is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or recurrent influxes of cooler, less corrosive deep waters. The highest carbonate content (%CaCO3) and MARs indicate that the late Miocene–early Pliocene Biogenic Bloom (LMBB) occurs between ∼ 7.8 and 3.3 Ma at Site 1264; broadly contemporaneous with the LMBB in the equatorial Pacific Ocean. At Site 1264, the onset of the LMBB roughly coincides with appearance of strong obliquity pacing of %CaCO3, reflecting increased high-latitude forcing. The global expression of the LMBB may reflect increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes, due to enhanced glacial activity and increased meridional temperature gradients. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.
Article
Full-text available
The dip angles of slabs are among the clearest characteristics of subduction zones, but the factors that control them remain obscure. Here slab dip angles and subduction parameters, including subduction duration, the nature of the overriding plate, slab age and convergence rate, are determined for 153 transects along subduction zones for the present‐day. We present a comprehensive tabulation of subduction duration based on isotopic ages of arc initiation and stratigraphic, structural, plate tectonic and seismic indicators of subduction initiation. We present two ages for subduction zones, a long‐term age and a reinitiation age. Using cross correlation and multivariate regression, we find that: (1) subduction duration is the primary parameter controlling slab dips with slabs tending to have shallower dips at subduction zones that have been in existence longer; (2) the long‐term age of subduction duration better explains variation of shallow dip than reinitiation age; (3) overriding plate nature could influence shallow dip angle, where slabs below continents tend to have shallower dips; (4) slab age contributes to slab dip, with younger slabs having steeper shallow dips; and (5) the relations between slab dip and subduction parameters are depth‐dependent, where the ability of subduction duration and overriding plate nature to explain observed variation decreases with depth. The analysis emphasizes the importance of subduction history and the long‐term regional state of a subduction zone in determining slab dip and are consistent with mechanical models of subduction.
Article
Full-text available
Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2 concentrations are crucial for developing better projections of future climate change. Deep-ocean1,2 and high-latitude3 palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data4-6 to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing7,8, rather than changes in ocean circulation9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2 reconstructions8 yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates11.
Article
Full-text available
Studying the dynamics of past global warming events during the late Paleocene to middle Eocene informs our understanding of Earth's carbon cycle behavior under elevated atmospheric pCO2 conditions. Due to sparse data coverage, the spatial character of numerous hyperthermal events during this period is still poorly constrained. Here we present a high-resolution, benthic foraminiferal stable isotope record for northwest Pacific ODP Site 1209 (Leg 198) spanning 44 to 56 Ma with 5 kyr resolution. An existing Paleocene section was extended into the middle Eocene creating an unprecedented 22 Myr single-site record. Several identified carbon isotope excursions correspond in timing and magnitude to hyperthermal layers previously described elsewhere. Maxima in scanning X-ray fluorescence Fe intensities and pronounced minima in the wt% coarse fraction characterize carbonate dissolution for all of the hyperthermal events. The new astronomically calibrated stable oxygen isotope record assists in defining the onset, duration, and demise of the Early Eocene Climate Optimum (EECO, 49.14 to 53.26 Ma) and the onset of global cooling after the EECO (49.14 Ma). The cooling trend was interrupted by two warming episodes at 47.2 and 46.7 Ma. A major positive shift in the benthic foraminiferal carbon isotope record occurring from 51.2 to 51.0 Ma is now confirmed to be global. Benthic foraminiferal δ¹³C records from Atlantic and Pacific Oceans converge from 52.0 to 47.5 Ma pointing to a closer connection of deepwater convection initiating well in advance of the final connection ~40 Ma ago or an increase in bottom water formation around Antarctica.
Article
Full-text available
We conducted an integrated magneto-biostratigraphic study of a 37 m-thick composite section exposed at two sites near Nouméa (New Caledonia). The section contains a transition from pelagic micrite to terrigenous-rich calciturbidites. This transition, observed regionally in coeval records of New Caledonia, marks a shift from pelagic sedimentation on a stable continental submarine plateau to turbidite deposition indicating development of a slope in a convergent tectonic regime. The studied section spans magnetic polarity Chrons C22r to C20r, calcareous nannofossil zones CNE5 to CNE10, and radiolarian zones RP9 to RP11 (49.5 to c. 44 Ma), and the micrite–turbidite transition occurred around 45.3 Ma (early middle Eocene). This transition could be the onshore correlative of a regional switch from tectonic extension to compression, which has been inferred from analysis of new seismic profiles acquired for the Tasman–northern Zealandia area, and that has been interpreted as precursor of the Tonga–Kermadec subduction initiation.
Article
Full-text available
The Poya Terrane of New Caledonia is a composite lithotectonic unit made of i) Campanian-Paleocene E-MORB and BABB-type basalts and abyssal argillite (Poya Terrane Basalts); and ii) Coniacian-Santonian sandstone, turbidite and abyssal argillite (Kone Facies) intruded by Early Eocene E-MORB sills. Remapping reveals that the Kone Facies is more extensive than previously thought . Field data, petrography and U-Pb geochronology of detrital zircons show that Kone Facies sediments have the same provenance as coeval autochthonous sediments (Formation a Charbon), albeit with more abundant contemporaneous zircons. They accumulated on the eastern continental slope of the Norfolk Ridge, and eventually mixed with abyssal argillite. Temporally, sill emplacement is related to subduction inception at ca. 56 Ma, thus suggesting a possible genetic link. We postulate that either: i) E-MORB intrusion was related to oblique extension and thinning of the down going plate; or alternatively, ii) the “enriched” (off axis?) partial melt zone of the ancient ridge swept the lower plate continentward, generating E-MORB dikes in the upper marginal basin crust, and sills in passive margin sediments before it became extinct. Thereafter, sliced marginal basin upper crust, passive margin sediments and associated dolerite sills were obliquely accreted to the fore-arc region, and in the NE part of the terrane, subducted and recrystallized into the blueschist facies. The Poya Terrane was eventually thrust onto the Norfolk Ridge when the latter reached the subduction zone and debris from the thrust sheet fed mid- to Late Eocene syntectonic basins. At the same time, mafic portions of the Poya Terrane were subducted at depth where they recrystallized into the eclogite facies, mixed with serpentinite to form the Pouebo mélange, and finally were exhumed in the fore-arc region. Finally, Late Oligocene faulting and hydrothermal events overprinted the NE part of the terrane in probable connection with post-obduction granitoid emplacement.
Article
Full-text available
The early Eocene "equable climate problem", i.e. warm extratropical annual mean and above-freezing winter temperatures evidenced by proxy records, has remained as one of the great unsolved problems in paleoclimate. Recent progress in modeling and in paleoclimate proxy development provides an opportunity to revisit this problem to ascertain if the current generation of models can reproduce the past climate features without extensive modification. Here we have compiled early Eocene terrestrial temperature data and compared with climate model results using a consistent and rigorous methodology. We test the hypothesis that equable climates can be explained simply as a response to increased greenhouse gas forcing within the framework of the atmospheric component of the Community Climate System Model (version 3), a climate model in common use for predicting future climate change. We find that, with suitably large radiative forcing, the model and data are in general agreement for annual mean and cold month mean temperatures, and that the pattern of high latitude amplification recorded by proxies can be largely, but not perfectly, reproduced.
Article
Full-text available
The early Eocene represents a time of major changes in the global carbon cycle and fluctuations in global temperatures on both short- and long-time scales. These perturbations of the ocean-atmosphere system have been linked to orbital forcing and changes in net organic carbon burial, but accurate age models are required to disentangle the various forcing mechanisms and assess causal relationships. Discrepancies between the employed astrochronological and radioisotopic dating techniques prevent the construction of a robust time frame between ~ 49 and ~ 54 Ma. Here we present an astronomically tuned age model for this critical time period based on a new high-resolution benthic δ13 C record of ODP Site 1263, SE Atlantic. First, we assess three possible tuning options to the stable long-eccentricity cycle (405-kyr), starting from Eocene Thermal Maximum 2 (ETM2, ~ 54 Ma). Next we compare our record to the existing bulk carbonate δ13 C record from the equatorial Atlantic (Demerara Rise, ODP Site 1258) to evaluate our three initial age models and compare them with alternative age models previously established for this site. Finally, we refine our preferred age model by expanding our tuning to the 100-kyr eccentricity cycle of the La2010d solution. This solution appears to accurately reflect the long- and short-term eccentricity-related patterns in our benthic δ13 C record of ODP Site 1263 back to at least 52 Ma and possibly to 54 Ma. Our time scale not only aims to provide a new detailed age model for this period, but it may also serve to enhance our understanding of the response of the climate system to orbital forcing during this super greenhouse period as well as trends in its background state.
Chapter
Full-text available
We review the tectonic evolution of the southwest Pacific east of Australia from ca 120 Ma until the present. A key factor that developed early in this interval and played a major role in the subsequent geodynamic history of this region was the calving off from eastern Australia of several elongate mlcrocontinental ribbons, including the Lord Howe Rise and Norfolk - New Caledonia Ridge. These microcontinental ribbons were isolated from Australia and from each other during a protracted extension episode from ca 120 to 52 Ma, with oceanic crust accretion occurring from 85 to 52 Ma and producing the Tasman Sea and the South Loyalty Basin. Generation of these microcontinental ribbons and intervening basins was assisted by emplacement of a major mantle plume at 100 Ma beneath the southern part of the Lord Howe Rise, which in turn contributed to rapid and efficient eastward trench rollback. A major change in Pacific plate motion at ca 55 Ma initiated east-directed subduction along the recently extinct spreading centre in the South Loyalty Basin, generating boninitic lithosphere along probably more than 1000 km of plate boundary in this region, and growth of the Loyalty-D'Entrecasteaux arc. Continued subduction of South Loyalty Basin crust led to the arrival at about 38 Ma of the 70-60 million years old western volcanic passive margin of the Norfolk Ridge at the trench, and west-directed emplacement of the New Caledonia ophiolite. Lowermost allochthons of this ophiolite are Maastrichtian and Paleocene rift tholeiites derived from the underthrusting passive margin. Higher allochthonous sheets include a poorly exposed boninitic lava slice, which itself was overridden by the massive ultramaflc sheets that cover large parts of New Caledonia and are derived from the colliding forearc of the Loyalty-D'Entrecasteaux arc. Post-collisional extensional tectonism exhumed the underthrust passive margin, parts of which have blueschist and eclogite facies metamorphic assemblages. Following locking of this subduction zone at 38-34 Ma, subduction jumped eastward, to form a new west-dipping subduction zone above which formed the Vitiaz arc, that contained elements which today are located in the Tongan, Fijian, Vanuatu and Solomons arcs. Several episodes of arc splitting fragmented the Vitiaz arc and produced first the South Fiji Basin (31 -25 Ma) and later (10 Ma to present) the North Fiji Basin. Collision of the Ontong Java Plateau, a large igneous province, with the Solomons section of the Vitiaz arc resulted in a reversal of subduction polarity, and growth of the Vanuatu arc on clockwise-rotating, older Vitiaz arc and South Fiji Basin crust. Continued rollback of the trench fronting the Tongan arc since 6 Ma has split this arc and produced the Lau Basin-Havre Trough. This southwest Pacific style of crustal growth above a rolling-back slab is applied to the 600-220 Ma tectonic development of the Tasman Fold Belt System in southeastern Australia, and explains key aspects of the geological evolution of eastern Australia. In particular, collision between a plume-triggered 600 Ma volcanic passive margin and a 510-515 Ma boninitic forearc of an infra-oceanic arc had the same relative orientation and geological effects as that which produced New Caledonia. A new subduction system formed probably at least several hundred kilometres east of the collision zone and produced the Macquarie Arc, In which the oldest lavas were erupted ca 480 Ma. Continued slab rollback induced regional extension and the growth of narrow linear troughs in the Macquarie Arc, which persisted until terminal deformation of this fold belt in the late-Middle to Late Devonian. A similar pattern of tectonic development generated the New England Fold Belt between the Late Devonian and Late Triassic. Parts of the New England Fold Belt have been broken from Australia and moved oceanward to locations in New Zealand, and on the Lord Howe Rise and Norfolk - New Caledonia Rise, during the post-120 Ma breakup. Given that the Tasman Fold Belt System grew between 600 and 220 Ma by crustal accretion like the southwest Pacific since 120 Ma facing the open Pacific Ocean, we question whether the eastern (Australia-Antarctica) part of the Neoproterozoic Rodinian supercontinent was Joined to Laurentia.
Article
Full-text available
The Mead Stream section (South Island, New Zealand) consists of a 650-m-thick series of continuous, well-exposed strata deposited on a South Pacific continental slope from the Late Cretaceous to the middle Eocene. We examined the uppermost Paleocene–middle Eocene part of the section, which consists of ~360 m of limestone and marl, for detailed magnetic polarity stratigraphy and calcare- ous nannofossil and foraminifera biostra- tigraphy. Magneto-biostratigraphic data indicate that the section straddles magnetic polarity chrons from C24r to C18n, calcar- eous nannofossil zones from NP9a to NP17 (CNP11–CNE15, following a recently revised Paleogene zonation), and from the Waipawan to the Bortonian New Zealand stages (i.e., from the base of the Ypresian to the Barto- nian international stages). The Mead Stream section thus encompasses 17 m.y. (56–39 Ma) of southwest Pacific Ocean history. The ages of calcareous nannofossil biohorizons are consistent with low- to midlatitude data from the literature, indicating that during the early–middle Eocene, the low- to midlatitude calcareous nannofossil domain extended at least to ~50°S–55°S in the South Pacific. Correlation of the magnetic polarity stratig- raphy from the Mead Stream section with the geomagnetic polarity time scale allows us to derive sediment accumulation rates (SAR), which range between 8 and 44 m/m.y. Comparing the SAR with paleotemperature proxy records, we found that two intervals of increased SAR occurred during the early Eocene climatic optimum (52–50 Ma) and during the transient warming event peak- ing with the middle Eocene climatic opti- mum (40.5 Ma). This correlation indicates that, at Mead Stream, the climate evolution of the early–middle Eocene is recorded in a sedimentation pattern whereby, on a million- year time scale, warmer climate promoted continental weathering, transportation, and accumulation of terrigenous sediments.
Article
Full-text available
The Cretaceous to early Paleogene (ca. 140–50 Ma) was characterized by a greenhouse baseline climate, driven by elevated concentrations of atmospheric CO2. Hypotheses for the elevated CO2 concentrations invoke an increase in volcanic CO2 production due to higher oceanic crust production rates, higher frequency of large igneous provinces, or increases in pelagic carbonate deposition, the last leading to enhanced carbonate subduction into the mantle source regions of arc volcanoes. However, these are not the only volcanic sources of CO2 during this time interval. We show here that ocean-continent subduction zones, manifested as a global chain of continental arc volcanoes, were as much as 200% longer in the Cretaceous and early Paleogene than in the late Paleogene to present, when a cooler climate prevailed. In particular, many of these continental arcs, unlike island arcs, intersected ancient continental platform carbonates stored on the continental upper plate. We show that the greater length of Cretaceous–Paleogene continental arcs, specifi cally carbonate-intersecting arcs, could have increased global production of CO2 by at least 3.7–5.5 times that of the present day. This magmatically driven crustal decarbonation flux of CO2 through continental arcs exceeds that delivered by Cretaceous oceanic crust production, and was suffi cient to drive Cretaceous–Paleogene greenhouse conditions. Thus, carbonate-intersecting continental arc volcanoes likely played an important role in driving greenhouse conditions in the Cretaceous–Paleogene. If so, the waning of North American and Eurasian continental arcs in the Late Cretaceous to early Paleogene, followed by a fundamental shift in western Pacific subduction zones ca. 52 Ma to an island arc–dominated regime, would have been manifested as a decline in global volcanic CO2 production, prompting a return to an icehouse baseline in the Neogene. Our analysis leads us to speculate that long-term (>50 m.y.) greenhouse-icehouse oscillations may be linked to fl uctuations between continental-and island arc–dominated states. These tectonic fluctuations may result from large-scale changes in the nature of subduction zones, changes we speculate may be tied to the assembly and dispersal of continents. Specifically, dispersal of continents may drive the leading edge of continents to override subduction zones, resulting in continental arc volcanism, whereas assembly of continents or closing of large ocean basins may be manifested as large-scale slab rollback, resulting in the development of intraoceanic volcanic arcs. We suggest that greenhouse-icehouse oscillations are a natural consequence of plate tectonics operating in the presence of continental masses, serving as a large capacitor of carbonates that can be episodically purged during global fl are-ups in continental arcs. Importantly, if the global crustal carbonate reservoir has grown with time, as might be expected because platform carbonates on continents do not generally subduct, the greenhouse-driving potential of continental arcs would have been small during the Archean, but would have increased in the Neoproterozoic and Phanerozoic after a significant reservoir of crustal carbonates had formed in response to the evolution of life and the growth of continents.
Article
Full-text available
[1] To understand the climate dynamics of hypothesized past greenhouse intervals, it is essential to constrain tropical sea-surface temperatures (SST), yet existing proxy records give conflicting results. Here we present the first Mg/Ca-based study of pre-Quaternary SST and investigate early Paleogene (late Paleocene through late middle Eocene; 58.6–39.8 Ma) tropical temperatures, using planktonic foraminifera belonging to the genus Morozovella from Ocean Drilling Program Site 865 on Allison Guyot (western central equatorial Pacific Ocean). Calcification temperatures similar to or warmer than modern tropical SST are calculated using a range of assumptions regarding diagenesis, temperature calibration, and seawater Mg/Ca. Long-term warming is observed into the early Eocene (54.8–49.0 Ma), with peak SST between 51 and 48 Ma and rapid cooling of 4°C beginning at 48 Ma. These findings are inconsistent with the δ18O-based SST previously estimated for this site.
Article
Full-text available
Significance Reconstructions of ancient high-latitude climates can help to constrain the amplification of global warming in polar environments. Climate models cannot reproduce the elevated high-latitude temperature estimates in the Eocene epoch, possibly indicating problems in simulating polar climate change. Widely divergent near-Antarctic Eocene sea surface temperature (SST) estimates, however, question the evidence for extreme warmth. Our analysis of multiple temperature proxies near the Antarctic Peninsula improves intersite comparisons and indicates a substantial zonal SST gradient between the southwest Pacific and South Atlantic. Simulations of Eocene ocean temperatures imply that the formation of deep water in the southwest Pacific partly accounts for this SST gradient, suggesting that climate models underestimate Eocene SSTs in regions where the thermohaline circulation leads to relatively high temperatures.
Article
Full-text available
The late Paleocene to early Eocene was marked by major changes in Earth surface temperature and carbon cycling. This included at least two, and probably more, geologically brief (<200-k.yr.) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and the Eocene thermal maximum-2 (ETM-2). The long-term rise in warmth and short-term “hyperthermal” events have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and intense global climate change. However, the causes, environmental impact, and relationships remain uncertain because detailed and coupled proxy records do not extend across the entire interval of interest; we are still recognizing the exact character of the hyperthermals and developing models to explain their occurrence. Here we present lithologic and carbon isotope records for a 200-m-thick sequence of latest Paleocene–earliest Eocene upper slope limestone exposed along Mead Stream, New Zealand. New carbon isotope and lithologic analyses combined with previous work on this expanded section shows that the PETM and ETM-2, the suspected H-2, I-1, I-2, and K/X hyperthermals, and several other horizons are marked by pronounced negative carbon isotope excursions and clay-rich horizons. Generally, the late Paleocene–early Eocene lithologic and δ13C records at Mead Stream are similar to records recovered from deep-sea sites, with an important exception: lows in δ13C and carbonate content consistently span intervals of relatively high sedimentation (terrigenous dilution) rather than intervals of relatively low sedimentation (carbonate dissolution). These findings indicate that, over ∼6 m.yr., there was a series of short-term climate perturbations, each characterized by massive input of carbon and greater continental weathering. The suspected link involves global warming, elevated greenhouse-gas concentrations, and enhanced seasonal precipitation.
Article
Full-text available
The southwestern Pacific Ocean region hosts submerged continental margins, ridges, sedimentary basins, and volcanic arcs located around Papua New Guinea, New Zealand, Australia, and Fiji. The geological history of this vast region has remained controversial, and to improve understanding of the processes that controlled its geodynamical evolution, it is essential to place each piece of available data in a regional spatiotemporal framework. To this end, a new map, entitled “Structural Provinces of the Southwest Pacific,” was released by the Geological Survey of New Caledonia in May 2011. The publication consists of two parts: (1) a 40-page booklet of geological notes, which documents the nature and age of each structure and contains an associated list of references; and (2) a 3- x 4-foot poster of a structural map revealing the nature of the basement, location, and type of the main structural features (see simplified version in Figure 1) and the age of formation using the international standards for geological color codes established by the Commission for the Geological Map of the World (CGMW) (see http://ccgm.free.fr/index.html).
Article
Full-text available
The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" - the Eocene Modelling Intercomparison Project, and syntheses of early Eocene terrestrial and SST temperature data, we present a self-consistent inter-model and model-data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO2, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO2 level which would give optimal early Eocene model-data agreement, based on those models which have carried out simulations with more than one CO2 level, is in the range 2000 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO2 during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates, which could be used as a metric for weighting future climate predictions.
Article
Full-text available
Dee Stream in the Clarence River valley of New Zealand bisects a well‐exposed section of marine sedimentary rocks deposited in the early Paleogene at high southern latitudes. One hundred metres of strata lying within this section and comprising cm‐dm well‐bedded, siliceous limestone with marly partings was mapped, logged, and sampled to establish a detailed foraminiferal and carbon isotope stratigraphy and to examine environmental changes across the Paleocene‐Eocene thermal maximum (PETM). Although low abundance and poor preservation of planktic and benthic foraminifera characterises much of the Paleocene, foraminifera and carbon isotopes clearly show that the section spans the upper Paleocene to lower Eocene planktic foraminiferal zones from Zone P4 to Subzone P6b, and the Subbotina triloculinoides to Pseudohastigerina wilcoxensis Zones. The δ C record correlates closely to other δ C curves generated from other key early Paleogene carbonate sequences. The Dee Stream logged section contains a1m thick PETM interval at 26.5 m at the base of Zone P5, or the Morozovella velascoensis Subzone. Here, benthic foraminifera undergo significant extinction, Morozovella aequa makes its first appearance, and the δ C of carbonate decreases by 2‰. The benthic foraminifer Bulimina tuxpamensis dominates benthic assemblages immediately following the onset of the PETM interval, suggesting dysoxic bottom waters during this event. In conjunction with other recently examined sections from the Marlborough region, the thick and apparently continuous Paleogene record at Dee Stream provides an important site for understanding environmental change on high‐latitude continental margins during the Paleogene, including the PETM.
Article
The New Caledonia Trough (NCT) is a 2000-3000 m deep bathymetric feature that extends 2500 km from Taranaki, New Zealand, to the western margin of New Caledonia (Northern Zealandia, SW Pacific). The underlying sedimentary basin originates from Cretaceous extension, but underwent a significant Eocene tectonic event that shaped its present physiography. We present an analysis of the basin based on multibeam data, seismic profiles and rock samples collected on the TAN1312 and TAN1409 Expeditions onboard R/V Tangaroa, combined with legacy data. We focus on the southern part of the basin, where new data reveal a link between compressive deformation of Paleocene strata and their potential reworking into the basin. On the western basin side, Upper Cretaceous to Paleocene strata were deformed by local reverse faults and folds that created a sub-circular bathymetric ridge and seabed exposure. This folded unit (seismic Unit 2) is sharply overlain by a restricted interval imaged as chaotic high-amplitude reflections that are interpreted as syntectonic mass-transport deposits due to slope oversteepening (seismic Unit 1b). This unit is stratigraphically below the main basin onlap surface and seismic mapping revealed that it rapidly thins away from the mouth of a present day submarine canyon imaged on the western slope of the basin, and that is diverted by exposures of Unit 2 deformed strata. Deformed and syntectonic intervals are in turn overlain by a flat-lying unit (seismic Unit 1a) we interpret as reflecting a passive basin fill. Our new data provide insight into an extensive deep-water basin that is remote from terrigenous sediment sources, and new constraints on its Cenozoic tectonic history. Stratigraphic ages are constrained by seismic ties to Taranaki basin petroleum wells and biostratigraphic dating of dredged samples. This specific site has particular significance for understanding tectonic events in the southwest Pacific. Indeed, our observations show that deformation is younger than the Paleocene and is envisaged to be a local expression of a widespread Cenozoic compressive event (called "TECTA", Tectonic Event of the Cenozoic in the Tasman Area), which affected the region after the Mesozoic rifting. On a regional perspective, this study provides new insights on the evolution of the submerged Zealandia continent and associated geodynamic processes such as Gondwana break-up and initiation of the Tonga-Kermadec subduction.
Article
We report the U-Pb age, and trace element and hafnium isotope composition of zircons recovered from clastic metasedimentary rocks that span a range of metamorphic grades (prehnite-pumpellyite to eclogite facies) across the high-pressure metamorphic belt of Northern New Caledonia. We use these data to evaluate the sedimentary source and environment of formation of these rocks, as well as their respective metamorphic evolution.
Article
A 4.9 Mkm2 region of the southwest Pacific Ocean is made up of continental crust. The region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent- Zealandia. Zealandia was formerly part of Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup.
Article
Eocene onset of subduction in the western Pacific was accompanied by a global reorganization of tectonic plates and a change in Pacific plate motion relative to hotspots during the period 52–43 Ma. We present seismic-reflection and rock sample data from the Tasman Sea that demonstrate that there was a period of widespread Eocene continental and oceanic compressional plate failure after 53–48 Ma that lasted until at least 37–34 Ma. We call this the Tectonic Event of the Cenozoic in the Tasman Area (TECTA). Its compressional nature is different from coeval tensile stresses and back-arc opening after 50 Ma in the Izu-Bonin-Mariana region. Our observations imply that spatial and temporal patterns of stress evolution during western Pacific Eocene subduction initiation were more varied than previously recognized. The evolving Eocene geometry of plates and boundaries played an important role in determining regional differences in stress state.
Article
Sandstone, mudstone and limestone samples dredged in the Reinga and Aotea basins, NW New Zealand during voyage TAN1312 provide age and lithological constraints on the Cretaceous–Neogene succession. A total of 46 micropaleontology and 7 macropaleontology samples were examined along with 84 thin-sectioned petrographical samples. Some were examined by X-ray diffraction and porosity-permeability analyses. Late Cretaceous sandstones are dominated by feldspathic and lithofeldspathic compositions, with mixed granitic plutoniclastic and volcaniclastic provenance; a comparison with Pakawau Group of Taranaki Basin is appropriate. Late Cretaceous–Paleogene mudstones are widespread and display close petrographical and age similarities to the Whangai Formation facies of other parts of New Zealand and fine-grained carbonate facies of the Weber and Amuri formations of eastern North and South Islands, respectively. Cretaceous limestone and Paleogene sandstone were not recovered. Carbonates and mudstones dominate the Neogene succession of Reinga and Aotea basins; rare Neogene sandstones have feldspatholithic compositions and resemble Waitemata Group sandstones of the northern North Island. In terms of petroleum prospectivity, Cretaceous sandstones represent a potential reservoir facies but are lithic with low permeability.
Article
Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity and temperature will evolve in our warming world but past warming events may provide insight. Here we employ paleo reconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 million years ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3 - 5.6 to 3.7 - 6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates this result indicates climate sensitivity increase with global warming.
Article
Clinoenstatite-bearing boninites (CE-boninite) from the serpentinite sole of the Cenozoic ophiolite of New Caledonia near Nepoui have been dated by the 40Ar/39Ar method, yielding two plateau ages of 47.4 ± 0.9 Ma and 50.4 ± 1.3 Ma. Coarser grained, geochemically similar boninite-series felsic dikes consistently yielded U-Pb zircon ages of ca. 54 Ma. Nepoui CE-boninites display whole rock geochemical features similar to that of Cape Vogel boninites (Papua-New Guinea). They similarly have been generated by low degree hydrous melting of depleted peridotite. High contents in LILE and LREE, and some elemental ratios suggest source enrichment by subduction-derived fluids and melts. However, unlike the Cape Vogel boninite, moderately depleted MORB-like isotopic signatures (EpsNd50 = 7.9) rule out the role of OIB-like, or E-MORB component that might account for the relatively high LREE and LILE contents measured in the rocks. Nd isotopic ratios and positive anomalies in Zr and Hf are closely similar to that of the slightly older felsic dikes (55-50 Ma) that crosscut the peridotite from the ophiolite in New Caledonia. Most of these magmas have been generated by slab melting during the early stages of intra-oceanic subduction. The Early Eocene subduction started at or near the “oceanic” ridge and involved young and hot lithosphere; therefore, slab-derived melts may have reacted locally with hot depleted peridotites. Finally, water influx into the mantle wedge during the subduction of slightly older (cooler and hydrated) lithosphere initiated a low degree partial melting event in the mantle wedge and generated the CE-boninite magma. Geochemical modeling of hydrous melting of a depleted mantle re-enriched by slab melts suggest that the additional slab melt component was derived from the partial melting of a BABB-like barroisite-bearing eclogite, similar to some elements of the Eocene HP-LT Pouebo terrane. This potential magma source is similar to the BABB-like HT amphibolites of the metamorphic sole of the ophiolite, which have the same origin. Geochemical modeling also suggests that CE-boninite magma may have been in equilibrium with the enstatite-bearing gabbro cumulates that crop out in several places of the Massif du Sud. However, modeling fails in establishing that harzburgite of the same massif simply corresponds to the melting residue of this process. It appears that ultra-depleted supra-subduction peridotites of the Massif du Sud are probably not directly related to the overlying gabbro cumulates.
Chapter
One of the youngest and best-preserved exposures of blueschist-and eclogite-facies rocks on Earth occurs in an elongate NW-SE-trending range in northeastern New Caledonia. This high-pressure (HP) terrane evolved within the Australia-Pacific plate boundary zone and records a middle Tertiary history of subduction burial, metamorphism, and exhumation.40Ar and fission track thermochronology was undertaken in the New Caledonian HP terrane to further constrain the timing and rates of cooling and exhumation, as well as to evaluate tectonic models. Oceanic and sedimentary protoliths were subducted at rates of 6-16 mm/yr and metamorphosed under HP conditions at ca. 44 Ma. Subsequently, rapid cooling occurred from 40 to 34 Ma as the HP terrane was exhumed at rates of ∼5 mm/yr. The HP terrane was exhumed largely as a coherent block to relatively shallow crustal levels, primarily via ductile shearing associated with crustal extension. Since the early Oligocene (<34 Ma), exhumation rates decreased to <0.3 mm/yr as brittle normal faulting and erosional processes continued to exhume blueschists and eclogites from relatively shallow (i.e., cool) crustal depths. Exhumation of the HP terrane temporally coincides with obduction of ultra-mafic rocks in southern New Caledonia, and seafloor spreading in the North Loyalty Basin. We propose a model whereby HP metamorphism at ca. 44 Ma was followed by rapid exhumation from 40 to 34 Ma, translation, and Oligocene (<34 Ma) juxtaposition of the HP terrane against the other basement terranes of New Caledonia.
Article
Although plate tectonics is well established, how a new subduction zone initiates remains controversial. Based on plate reconstruction and recent ocean drilling within the Izu-Bonin-Mariana, we advance a new geodynamic model of subduction initiation (SI). We argue that the close juxtaposition of the nascent plate boundary with relic oceanic arcs is a key factor localizing initiation of this new subduction zone. The combination of thermal and compositional density contrasts between the overriding relic arc and the adjacent old Pacific oceanic plate promoted spontaneous SI. We suggest that thermal rejuvenation of the overriding plate just before 50 Ma causes a reduction in overriding plate strength and an increase in the age contrast (hence buoyancy) between the two plates, leading to SI. The computational models map out a framework in which rejuvenated relic arcs are a favorable tectonic environment for promoting subduction initiation, while transform faults and passive margins are not.
Article
The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence of dense lithosphere along faults adjacent to buoyant lithosphere, would result in extension and magmatism. The rock record of subduction initiation is typically obscured by younger deposits, so evaluating these possibilities has proved elusive. Here we analyse the geochemical characteristics of igneous basement rocks and overlying sediments, sampled from the Amami Sankaku Basin in the northwest Philippine Sea. The uppermost basement rocks are areally widespread and supplied via dykes. They are similar in composition and age—as constrained by the biostratigraphy of the overlying sediments—to the 52–48-million-year-old basalts in the adjacent Izu–Bonin–Mariana fore-arc. The geochemical characteristics of the basement lavas indicate that a component of subducted lithosphere was involved in their genesis, and the lavas were derived from mantle source rocks that were more melt-depleted than those tapped at mid-ocean ridges. We propose that the basement lavas formed during the inception of Izu–Bonin–Mariana subduction in a mode consistent with the spontaneous initiation of subduction.
Article
We present the first comprehensive seismic-stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500 to 3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (1) Cretaceous rifting during eastern Gondwana breakup; and (2) initiation and Cenozoic evolution of Tonga-Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic-reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic-stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200-300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra-continental basin with no known correlative. The overlying unit FW2b records syn-rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into deltas in the northern part of the basin, as suggested by truncation surfaces on basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post-rift sedimentation and passive subsidence as the Tasman Sea opened and Fairway Basin drifted away from Australia. Subsidence led to flooding of basement highs and burial of wave-cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga-Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues has supplied carbonate detrital sediments into the basin, most likely during sea level lowstands. Fairway Basin contains a nearly-continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.This article is protected by copyright. All rights reserved.
Article
New Caledonia lies at the northern tip of the Norfolk ridge, a continental fragment separated from the east Gondwana margin during the Late Cretaceous. Stratigraphic data for constraining the convergence that led to ophiolitic nappes being obducted over Grande Terre during the Eocene are both few and inaccurate. To try and fill this gap and determine the onset of the convergence, we investigated the lithology, sedimentology, biostratigraphy and geodynamic context of the Late Cretaceous - Palaeogene sedimentary cover-rock succession of northern New Caledonia. We were able to establish new stratigraphic correlations between the sedimentary units, which display large southwest-verging overfolds detached along a basal argillite series, and reinterpret their interrelationships. The sediments from the Cretaceous-Paleocene interval were deposited in a post-rift pelagic environment and are mainly biogenic with minimal terrigenous input. From the base up, they comprise black organic-rich sulphide-bearing argillite, black chert (silicified equivalent of the argillite), micritic with chert, and micrite rich in planktonic foraminifera. These passive-margin deposits are found regionally on the Norfolk Ridge down to New Zealand, and on the Lord Howe Rise, and were controlled primarily by regional or global environmental factors. The overlying Eocene deposits mark a change to an active-margin regime with distal calciturbidite and proximal breccia representing the earliest Paleogene flysch-type deposits in New Caledonia. The change from an extensional to a compressive regime marks the beginning of the pre-obduction convergence and can be assigned fairly accurately in the Koumac-Gomen area to the end of the Early Eocene (Late Ypresian, Biozone E7) at c 50 Ma. From this period on, the post-Late Cretaceous cover in northern New Caledonia was caught up and recycled in a southwest-verging accretionary complex ahead of which flysch was deposited in a flexural foreland basin. The system prograded southwards until the Late Eocene collisional stage, when the continental Norfolk ridge entered the convergence zone and blocked it. At this point the autochthonous and parautochthonous sedimentary cover and overlying flysch of northern New Caledonia was thrust over the younger flysch to the south to form a newly defined allochthonous unit, the 'Montagnes Blanches' nappe, that is systematically intercalated between the flysch and the obducted ophiolite units throughout Grande Terre.
Article
This paper presents 34 geochemical analyses, 24 Ar-Ar ages and two U-Pb ages of igneous rocks from the back-arc basins and submarine ridges in the Coral Sea-New Caledonia region. The D'Entrecasteaux Ridge is a composite structural feature. Primitive arc tholeiites of Eocene age (34-56 Ma) are present along a 200 km length of the ridge and arguably were part of the initial line of subduction inception between Fiji and the Marianas; substantial Eocene arc edifices are only evident at the eastern end where Bougainville Guyot andesite breccias are dated at 40 ± 2 Ma. The South Rennell Trough is confidently identified as a 28-29 Ma (Early Oligocene) fossil spreading ridge and hence the flanking Santa Cruz and D'Entrecasteaux basins belong in the group of SW Pacific Eocene-Early Miocene backarc basins that include the Solomon Sea, North Loyalty and South Fiji basins. The rate and duration of spreading in the North Loyalty Basin is revised to 43 mm/year between 28 and 44 Ma, longer and faster than previously recognized. The direction of its opening was to the southeast, that is parallel to the continent-ocean boundary and perpendicular to the direction of coeval New Caledonia ophiolite emplacement. Medium and high-K alkaline lavas of 23-25 Ma (Late Oligocene) age on the northern Norfolk Ridge are an additional magmatic response to Pacific trench rollback.
Article
The Adio Limestone at the base of the Palaeogene flysch in the central part of New Caledonia has long been attributed to the Late Eocene. New data now enable us to assign it a Palaeocene age based on a characterisation of its benthic foraminiferal microfauna and also on the presence of an overlying sequence of typical calciturbidite dated as Early Eocene by its planktonic microfauna. This new age assignation indicates a major Palaeocene reorganisation of this northern part of the Norfolk Ridge, which can be associated with the beginning of the convergence phase and the onset of the northeast-dipping subduction in the oceanic South Loyalty Basin. The Adio area in this scenario would represent the initial expression of a foreland bulge uplifted in response to the onset of subduction to the northeast.
Article
Our understanding of the dynamics of plate motions is based almost entirely upon modeling of present-day plate motions. A fuller understanding, however, can be derived from consideration of the history of plate motions. Here we investigate the kinematics of the last 120 Myr of plate motions and the dynamics of Cenozoic motions, paying special attention to changes in the character of plate motions and plate-driving forces. We analyze the partitioning of the observed surface velocity field into toroidal (transform/spin) and poloidal (spreading/subduction) motions. The present-day field is not equipartitioned in poloidal and toroidal components; toroidal motions account for only one third of the total. The toroidal/poloidal ratio has changed substantially in the last 120 Myr with poloidal motion decreasing significantly after 43 Ma while toroidal motion remains essentially constant; this result is not explained by changes in plate geometry alone. We develop a self-consistent model of plate motions by (1) constructing a straightforward model of mantle density heterogeneity based largely upon subduction history and then (2) calculating the induced plate motions for each stage of the Cenozoic. The “slab” heterogeneity model compares rather well with seismic heterogeneity models, especially away from the thermochemical boundary layers near the surface and core-mantle boundary. The slab model predicts the observed geoid extremely well, although comparison between predicted and observed dynamic topography is ambiguous. The midmantle heterogeneities that explain much of the observed seismic heterogeneity and geoid are derived largely from late Mesozoic and early Cenozoic subduction, when subduction rates were much higher than they are at present. The plate motion model itself successfully predicts Cenozoic plate motions (global correlations of 0.7–0.9) for mantle viscosity structures that are consistent with a variety of geophysical studies. We conclude that the main plate-driving forces come from subducted slabs (>90%), with forces due to lithospheric effects (e.g., oceanic plate thickening) providing a very minor component (<10%). For whole mantle convection, most of the slab buoyancy forces are derived from lower mantle slabs. Unfortunately, we cannot reproduce the toroidal/poloidal partitioning ratios observed for the Cenozoic, nor do our models explain apparently sudden plate motion changes that define stage boundaries. The most conspicuous failure is our inability to reproduce the westward jerk of the Pacific plate at 43 Ma implied by the great bend in the Hawaiian-Emperor seamount chain. Our model permits an interesting test of the hypothesis that the collision of India with Asia may have caused the Hawaiian-Emperor bend. However, we find that this collision has no effect on the motion of the Pacific plate, implying that important plate boundary effects are missing in our models. Future progress in understanding global plate motions requires (1) more complete plate reconstruction information, including, especially, uncertainty estimates for past plate boundaries, (2) better treatment of plate boundary fault mechanics in plate motion models, (3) application of numerical convection models, constrained by global plate motion histories, to replace ad hoc mantle heterogeneity models, (4) better calibration of these heterogeneity models with seismic heterogeneity constraints, and (5) more comprehensive comparison of global plate/mantle dynamics models with geologic data, especially indicators of intraplate stress and strain, and constraints on dynamic topography derived from the stratigraphic record of sea level change.
Article
Radiochronological dating of detrital zircon extracted from the Boghen terrane metasediments allows a Jurassic age to be assigned. This terrane was formerly considered as the "pre-Permian basement" of New Caledonia. Its sedimentological features, its Late Jurassic high-pressure metamorphism (ca 150 Ma) and its association with the arc-related volcano-sedimentary complex of the Central Chain Terrane indicate that the Boghen terrane was an accretionary complex formed during the Jurassic period along the East-Gondwana active margin. The age spectrum of detrital zircons is consistent with a derivation from the Permian-Mesozoic Southeast-Gondwana arc system and the Antarctic continent. To cite this article: D. Cluzel, S. Meffre, C. R. Geoscience 334 (2002) 867-874.
Article
The opening or closing of major oceanic gateways or seaways through plate tectonics can significantly change surface and/or deep ocean circulation. This clearly has led to fundamental changes in the Earth's environmental system, global climate, and marine and terrestrial biogeography. Ocean circulation changes resulting from gateway development can significantly affect global heat transfer, and thus climate. However, these climatic effects should be considered within an Earth System context involving a variety of integrated environmental feedbacks. The opening of the Tasmanian Gateway during the Eocene-Oligocene transition (˜33.5 Ma), and later Seaway expansion, led to critical changes in Southern Hemisphere Ocean circulation resulting from the development of the Antarctic Circumpolar Current (ACC). Gateway opening initiated thermal isolation of Antarctica leading to the crossing of a major global climatic threshold and to significant Antarctic ice expansion. Much of this climate change resulted, not from circulation changes alone, but through environmental feedback mechanisms associated with ice expansion and cooling. These included increased albedo, ice sheet elevation, atmospheric changes, increased Southern Ocean productivity, and intensification of thermohaline circulation leading to expansion of deep cold waters. Cooling of the deep ocean and the continents also likely led to decreased atmospheric greenhouse gases CO2 and CH4 that, in turn, contributed to pronounced cooling in the earliest Oligocene. Antarctic circumpolar circulation continued to strengthen during the Oligocene through early Neogene in response to further Seaway expansion, increasing thermal isolation of Antarctica and related development of the Antarctic System. Results of ODP Leg 189 have confirmed that the initial main opening of the Tasmanian Gateway at the Eocene/Oligocene boundary (˜33.5 Ma) coincided with major ice growth and cooling on Antarctica, as reflected by oceanic isotopic and biotic trends. This continues to implicate gateway opening as fundamental in triggering the shift in the Earth System at the beginning of the Oligocene. Changes in the paleobiogeography of planktonic microfossil assemblages in the SW Pacific, and in shallower marine groups of the New Zealand Platform, are critical for reconstructing paleoceanographic changes resulting from Tasmanian Gateway evolution. The distribution of late Eocene planktonic microfossil assemblages in the SW Pacific, and of shallower marine taxa on the New Zealand Platform, are consistent with the influence of a broad, warm subtropical gyre from the north that extended to high southern latitudes. Also, at high latitudes in the SW Pacific, a cool, narrow northward-flowing countercurrent from the Antarctic dominated assemblages on the eastern Tasmanian margin prior to gateway opening. The planktonic microfossil sequences record fundamental shifts in ocean circulation associated with gateway opening during the Eocene/Oligocene transition. Changes in the distribution of South Pacific calcareous microfossil assemblages and radiolarians, and stable isotopic gradients, appear consistent with the hypothesis that surface-ocean heat transfer towards Antarctica was disrupted by the developing Antarctic Circumpolar Current at the beginning of the Oligocene, and that its development contributed to Antarctic cryosphere expansion.
Article
Stratigraphic data from petroleum wells and seismic reflection analysis reveal two distinct episodes of subsidence in the southern New Caledonia Trough and deep-water Taranaki Basin. Tectonic subsidence of ~2.5 km was related to Cretaceous rift faulting and post-rift thermal subsidence, and ~1.5 km of anomalous passive tectonic subsidence occurred during Cenozoic time. Pure-shear stretching by factors of up to 2 is estimated for the first phase of subsidence from the exponential decay of post-rift subsidence. The second subsidence event occured ~40 Ma after rifting ceased, and was not associated with faulting in the upper crust. Eocene subsidence patterns indicate northward tilting of the basin, followed by rapid regional subsidence during the Oligocene and Early Miocene. The resulting basin is 300–500 km wide and over 2000 km long, includes part of Taranaki Basin, and is not easily explained by any classic model of lithosphere deformation or cooling. The spatial scale of the basin, paucity of Cenozoic crustal faulting, and magnitudes of subsidence suggest a regional process that acted from below, probably originating within the upper mantle. This process was likely associated with inception of nearby Australia-Pacific plate convergence, which ultimately formed the Tonga-Kermadec subduction zone. Our study demonstrates that shallow-water environments persisted for longer and their associated sedimentary sequences are hence thicker than would be predicted by any rift basin model that produces such large values of subsidence and an equivalent water depth. We suggest that convective processes within the upper mantle can influence the sedimentary facies distribution and thermal architecture of deep-water basins, and that not all deep-water basins are simply the evolved products of the same processes that produce shallow-water sedimentary basins. This may be particularly true during the inception of subduction zones, and we suggest the term ‘prearc’ basin to describe this tectonic setting.
Article
Cenozoic sediments of the equatorial Pacific show large spatial and temporal changes resulting from the tectonic and paleoceanographic evolution of the region. The tectonic evolution involves rotation of the Pacific plate across the equator, a gradual subsidence with increasing age of the flanks of the ancestral East Pacific rise, and changes in height, shape, and position of the rise. The principal paleoceanographic changes include variations in biological productivity at the sea surface, and temporal changes in the characteristics of the bottom water and its circulation pattern which are related to the history of Antarctic glaciation. Between 45 and 38 rri.y.B.P., extensive carbonate dissolution resulted in low carbonate accumulation rates, extensive erosion, and the formation of only a narrow equatorial carbonate zone. Around 38 m.y.B.P., carbonate input increased and carbonate dissolution decreased abruptly, the equatorial calcareous zone widened, and accumulation rates greatly increased. This was caused by a change in bottom water characteristics resulting from the first significant development of sea ice around Antarctica. About 33 m.y. ago, carbonate dissolution at depth began to increase again, but initially this increase was compensated either by a large increase in the carbonate supply or by a depression of the lysocline. As a result, a very broad equatorial carbonate zone with maximal accumulation rates persisted until about 26 m.y. ago. The steepening of the dissolution gradient may have resulted from a decreasing influx of Antarctic bottom water, while the change in supply may have been related to the final closure of the Tethys seaway. Around 15 m.y.B.P., major growth of the Antarctic ice took place, leading to a further increase in the dissolution rate. At that time, development of the configuration of sources and mechanisms characteristic of the present circulation of intermediate and deep water may have begun. As a result, erosion increased and the equatorial zone of carbonate deposition narrowed. It is also possible that the fertility of the equatorial region increased somewhat. Finally, around 3-4 m.y.B.P., the onset of the Arctic glaciation marked the beginning of a period of large and rapid changes in depositional conditions which cannot be resolved with Deep Sea Drilling Project data.
Article
Over the next few centuries, with unabated emissions of anthropogenic carbon dioxide (CO2), a total of 5000 Pg C may enter the atmosphere, causing CO2 concentrations to rise to approximately 2000 ppmv, global temperature to warm by more than 8(°)C and surface ocean pH to decline by approximately 0.7 units. A carbon release of this magnitude is unprecedented during the past 56 million years-and the outcome accordingly difficult to predict. In this regard, the geological record may provide foresight to how the Earth system will respond in the future. Here, we discuss the long-term legacy of massive carbon release into the Earth's surface reservoirs, comparing the Anthropocene with a past analogue, the Palaeocene-Eocene Thermal Maximum (PETM, approx. 56 Ma). We examine the natural processes and time scales of CO2 neutralization that determine the atmospheric lifetime of CO2 in response to carbon release. We compare the duration of carbon release during the Anthropocene versus PETM and the ensuing effects on ocean acidification and marine calcifying organisms. We also discuss the conundrum that the observed duration of the PETM appears to be much longer than predicted by models that use first-order assumptions. Finally, we comment on past and future mass extinctions and recovery times of biotic diversity.
Article
The Mariana fore-arc southeast of Guam consists of ophiolitic lithologies related to subduction initiation and early-arc development. Ages of zircons extracted from gabbroic rocks within this sequence are 51.5±0.7 Ma, synchronous with similar rocks from the Bonin fore-arc 1700 km to the north. Basalts collected from the Izu fore-arc are similar to those of the Bonin and Mariana fore-arcs extending the distance of this ophiolitic geology to the entire 3000 km length of the IBM fore-arc. The Tonga fore-arc has similar lithologies and ages, suggesting that subduction began nearly simultaneously along much of the western margin of the Pacific plate. We postulate that closing of the Tethyan suture provided the trigger for subduction initiation in the Western Pacific. The volume of basalt erupted near western Pacific trenches associated with subduction initiation and early-arc development in the early Eocene could rival the volumes of large igneous provinces. The eruption of these basalts corresponds with the height of the Early Eocene Climatic Optimum (EECO), when global atmospheric temperatures were likely at or near their Cenozoic maximum. Therefore, CO2 vented during this volcanism as well as that associated with the North Atlantic Igneous Province, the Siletzia terrane, and slab rollback and detachment beneath central and east Asia were likely responsible for the EECO.
Article
The southwest Pacific between Australia, New Zealand and New Caledonia is a block of continental crust, Zealandia, that moved away from Australia and Antarctica after a long period of subduction beneath eastern Gondwana. We use > 100,000 line-km of seismic-reflection profiles to identify intra-continental basins related to the Gondwana active margin, overlain with erosional unconformity by retrogradational strata. We interpret this regional-scale first-order unconformity, the Eastern Gondwana Composite Surface, and seismic-stratigraphic megasequence pattern to represent the transition from subduction to continental breakup and separation of eastern Gondwana. Rocks that make up the lower seismic-stratigraphic megasequence (Zealandia-3, Permian to Early Cretaceous) have been drilled near New Zealand and can be correlated with Murihiku Supergroup rocks. Farther north on the Lord Howe Rise, we correlate this megasequence with Triassic to Jurassic rocks of the Clarence-Moreton Basin of eastern Australia. We reinterpret the Fairway-Aotea Basin to be underlain by a wedge of Zealandia-3 deposits thrust in a retro-arc-like foreland basin that was active immediately prior to breakup. The lower rift and retrogradational megasequence (Zealandia-2, Late Cretaceous to Eocene) we correlate with the Pakawau and Kapuni Groups of Taranaki Basin, New Zealand, and the “Formation à charbon” and “phtanites” of New Caledonia. The boundary with the shallowest megasequence (Zealandia-1, Late Eocene to present) is the “Eocene-Oligocene Unconformity”, which is primarily overlain by pelagic carbonate rocks. This regional unconformity likely represents the onset of the modern Tonga-Kermadec subduction system.
Article
South Maria Ridge (34°S) is a 1500 km submarine ridge and bank system, less than 500 m deep, slowly accumulating photic and sub‐photic, clean skeletal carbonate gravels and sands having over 80%, and generally over 95%, CaCO3, mainly calcite. Contributing factors include the negligible supply of terrigenous sediment, the availability of stable rocky substrates for colonisation by epibenthos, and the prominent upwelling of nutrient‐rich waters, stimulating organic growth. Sediments comprise fragmental remains of diverse bryozoan colonies (10–74%), with lesser amounts of mainly infaunal bivalves (2–20%), gastropods (2–10%), ahermatypic corals (0–18%), calcareous red algae (1–16%), and benthic foraminifers (3–15%), and small contributions from serpulids, barnacles, echinoids, brachiopods, sponges, and pteropods. Major species are identified. The distribution of skeletal types is controlled initially by substrate, bathymetry, and energy level, and subsequently by topographically influenced tidal flow dispersal. However, the present sediment distribution pattern has been complicated by eustatic sea level changes. Modern zones of carbonate production are centred mainly on the shallower portions of the ridge, in the vicinity of Three Kings and Middlesex Banks. Below 150–200 m depth the skeletal sediments become increasingly relict. A rough bathymetric zonation of faunal types remains, but their depths are on average 100–150 m below their modern counterparts, supporting emplacement during the low sea level of the Last (Otiran) Glaciation. The skeletal deposits are temperate‐latitude limestones in the making, with properties significantly different from their better known tropical counterparts but closely analogous to many Cenozoic limestones in New Zealand.
Article
Latest Oligocene and Early Miocene volcanic rocks occur on the Northland Peninsula, New Zealand, and record the inception of Cenozoic subduction-related volcanism in the North Island that eventually evolved to its present manifestation in the Taupo Volcanic Zone. This NW-striking Northland Arc is continuous with the Reinga Ridge and comprises two parallel belts of volcanic centres ca. 60 km apart. A plethora of tectonic models have been proposed for its origins. We acquired new trace element and Sr–Nd isotope data to better constrain such models. All Northland Arc rocks carry an arc-type trace element signature, however distinct differences exist between rocks of the eastern and western belt. Eastern belt rocks are typically andesites and dacites and have relatively evolved isotope ratios indicating assimilated crustal material, and commonly contain hornblende. Additionally some eastern belt rocks with highly evolved isotope compositions show fractionated REE compositions consistent with residual garnet, and some contain garnetiferous inclusions in addition to schistose crustal fragments. In contrast, western belt rocks are mostly basalts or basaltic andesites with relatively primitive Sr–Nd isotope compositions, do not contain hornblende and show no rare earth element evidence for cryptic amphibole fractionation. Eastern and western belt rocks contain comparable slab-derived fractions of fluid-mobile trace elements and invariably possess an arc signature. Therefore the difference between the belts may be best explained as due to variation in crustal thickness across the Northland Peninsula, where western belt centres erupted onto a thinner crustal section than eastern belt rocks.
Article
Bending of the lithosphere at subduction zones generates stresses that contribute to the force balance on plates. We determine the net horizontal force on subducting plates by imposing a simple kinematic description of strain in the equations that govern the mechanical equilibrium of a thin viscous sheet. The magnitude of the force depends on the velocity, thickness, and curvature of the subducting plate. Using representative values for old oceanic lithosphere, we obtain an effective horizontal force that is nearly 40% of the buoyancy force due to slabs in the upper mantle.
Article
We used a three-plate, best-fit algorithm to calculate four sets of Euler rotations for India (Capricorn) - Africa (Somali), India (Capricorn)-Antarctic, and Africa (Somali)-Antarctic motion for twelve time intervals between Chrons 20 and 29 in the early Cenozoic. Each set of rotations had a different combination of data constraints. The first set of rotations used a basic set of magnetic anomaly picks on the Central Indian Ridge (CIR), Southeast Indian Ridge (SEIR) and Southwest Indian Ridge (SWIR), but did not incorporate data from the Carlsberg ridge and did not use fracture zones on the SWIR. The second set added fracture zone constraints from the region west of the Bain FZ on the SWIR and also included corrections for Nubia-Somalia and Lwandle-Somalia motion on the western and central SWIR, respectively. The third set of rotations used the basic constraints from the first rotation set and added data from the Carlsberg ridge. The fourth set of rotations combined both the additional SWIR constraints of the second data set and the Carlsberg ridge constraints of the third data set. Data on the Indian plate side of the Carlsberg ridge (Arabian Basin) were rotated to the Capricorn plate before being included in the constraints. We found that the rotations constrained by the Carlsberg ridge data set diverged from the other two sets of rotations prior to anomaly 22o. We concluded that, relative to the rest of the CIR, there is a progressively larger separation of anomalies on the Carlsberg ridge, starting at anomaly 22o and increasing to over 100 km for anomaly 26. These observations support two alternative interpretations. First, they are consistent with a distinct Seychelles microplate in the early Cenozoic. The sense of the misfit on the Carlsberg ridge is consistent with roughly 100 to 150 km of convergence across a boundary between the Seychelles microplate and Somali plate between Chrons 26 and 22 running from the Amirante Trench and extending north to the Carlsberg ridge axis. Alternatively, the misfit is consistent with convergent motion of the same magnitude between the Indian and a proto-Capricorn plate east of the CIR between Chrons 26 and 22. Our work also sharpens the dating of the two major Eocene events that Patriat and Achache (1984) recognized in the Indian Ocean: a large but gradual slowdown on the CIR and SEIR starting shortly after Chron 23o (51.9 Ma) and continuing until Chron 21y (45.3 Ma), a period of 6.6 Ma, followed two or three million years later by an abrupt change in spreading azimuth on the CIR and SEIR which occurred around Chron 20o (42.8) Ma and which was completed by Chron 20y (41.5 Ma). No change in spreading rate accompanied the change in spreading direction.