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1. Australia Cretaceous Climate and Tectonics

   https://doi.org/10.14379/iodp.proc.369.2019  

   Hobbs, R.W. ; Huber, B.T. ; Bogus, K.A. ( May 2019 , Proceedings of the International Ocean Discovery Program)

   The tectonic and paleoceanographic setting of the Great Australian Bight (GAB) and the Mentelle Basin (adjacent to Naturaliste Plateau) offered an opportunity to investigate Cretaceous and Cenozoic climate change and ocean dynamics during the last phase of breakup among remnant Gondwana continents. Sediment recovered from sites in both regions during International Ocean Discovery Program Expedition 369 will provide a new perspective on Earth’s temperature variation at subpolar latitudes (60°–62°S) across the extremes of the mid-Cretaceous hot greenhouse climate and the cooling that followed. Basalts and prebreakup sediments were also recovered and will provide constraints regarding the type and age of the Mentelle Basin basement and processes operating during the break up of Gondwana. The primary goals of the expedition were to 1. Investigate the timing and causes for the rise and collapse of the Cretaceous hot greenhouse climate and how this climate mode affected the climate–ocean system and oceanic biota; 2. Determine the relative roles of productivity, ocean temperature, and ocean circulation at high southern latitudes during Cretaceous oceanic anoxic events (OAEs); 3. Investigate potential source regions for deep-water and intermediate-water masses in the southeast Indian Ocean and how these changed during Gondwana breakup; 4. Characterize how oceanographic conditions atmore »the Mentelle Basin changed during the Cenozoic opening of the Tasman Gateway and restriction of the Indonesian Gateway; and 5. Resolve questions on the volcanic and sedimentary origins of the Australo-Antarctic Gulf and Mentelle Basin and provide stratigraphic control on the age and nature of the prebreakup successions. Hole U1512A in the GAB recovered a 691 m thick sequence of black claystone ranging from the lower Turonian to the lower Campanian. Age control is primarily based on calcareous nannofossils, but the presence of other microfossil groups provided consistent low-resolution control. Despite the lithologic uniformity, long- and short-term variations in natural gamma radiation and magnetic susceptibility show cyclic alternations that suggest an orbital control of sediment deposition, which will be useful for developing an astrochronology for the sequence. Sites U1513, U1514, U1515, and U1516 were drilled in water depths between 850 and 3900 m in the Mentelle Basin and penetrated 774, 517, 517, and 542 meters below seafloor, respectively. Under a thin layer of Pleistocene to upper Miocene sediment, Site U1513 cored a succession of Cretaceous units from the Campanian to the Valanginian, as well as a succession of basalts. Site U1514 sampled an expanded Pleistocene to Eocene sequence and terminated in the upper Albian. The Cenomanian to Turonian interval at Site U1514 is represented by deformed sedimentary rocks that probably represent a detachment zone. Site U1515 is located on the west Australian margin at 850 m water depth and was the most challenging site to core because much of the upper 350 m was either chert or poorly consolidated sand. However, the prebreakup Jurassic(?) sediments interpreted from the seismic profiles were successfully recovered. Site U1516 cored an expanded Pleistocene, Neogene, and Paleogene section and recovered a complete Cenomanian/Turonian boundary interval containing five layers with high organic carbon content. Study of the well-preserved calcareous microfossil assemblages from different paleodepths will enable generation of paleotemperature and biotic records that span the rise and collapse of the Cretaceous hot greenhouse (including OAEs 1d and 2), providing insight to resultant changes in deep-water and surface water circulation that can be used to test predictions from earth system models. Measurements of paleotemperature proxies and other data will reveal the timing, magnitude, and duration of peak hothouse conditions and any cold snaps that could have allowed growth of a polar ice sheet. The sites contain a record of the mid-Eocene to early Oligocene opening of the Tasman Gateway and the Miocene to Pliocene restriction of the Indonesian Gateway; both passages have important effects on global oceanography and climate. Advancing understanding of the paleoceanographic changes in a regional context will provide a global test on models of Cenomanian to Turonian oceanographic and climatic evolution related both to extreme Turonian warmth and the evolution of OAE 2. The Early Cretaceous volcanic rocks and underlying Jurassic(?) sediments cored in different parts of the Mentelle Basin provide information on the timing of different stages of the Gondwana breakup. The recovered cores provide sufficient new age constraints to underpin a reevaluation of the basin-wide seismic stratigraphy and tectonic models for the region.« less
2. Expedition 369 Scientific Prospectus: Australia Cretaceous Climate and Tectonics

   https://doi.org/10.14379/iodp.sp.369.2016  

   Hobbs, R. ; Huber, B. ; Bogus, K.A. ( September 2016 , Scientific prospectus)

   The unique tectonic and paleoceanographic setting of the Naturaliste Plateau (NP) and Mentelle Basin (MB) offers an outstanding opportunity to investigate a range of scientific issues of global importance with particular relevance to climate change. Previous spot-core drilling at Deep Sea Drilling Project Site 258 in the western MB demonstrates the presence of an expanded upper Albian–lower Campanian chalk, marl, and claystone sequence that is nearly complete stratigraphically and yields calcareous microfossils that are mostly well preserved. This sediment package and the underlying Albian volcanic claystone unit extend across most of the MB and are targeted at the primary sites, located between 850 and 3900 m water depth. Coring the Cretaceous MB sequence at different paleodepths will allow recovery of material suitable for generating paleotemperature and biotic records that span the rise and collapse of the Cretaceous hothouse (including oceanic anoxic Events [OAEs] 1d and 2), providing insight to resultant changes in deep-water and surface water circulation that can be used to test predictions from earth system models. The high-paleolatitude (60°–62°S) location of the sites is especially important because of the enhanced sensitivity to changes in vertical gradients and surface water temperatures. Paleotemperature proxies and other data will reveal themore »timing, magnitude, and duration of peak hothouse temperatures and whether there were any cold snaps that would have allowed growth of a polar ice sheet. The sites are also well-positioned to monitor the mid-Eocene–early Oligocene opening of the Tasman Gateway and the Miocene–Pliocene restriction of the Indonesian Gateway; both passages have important effects on global oceanography and climate. Comparison of the Cenomanian–Turonian OAE 2 interval that will be cored on the Great Australian Bight will establish whether significant changes in ocean circulation were coincident with OAE 2, and over what depth ranges, and whether OAE 2 in the high-latitude Southern Hemisphere was coincident with major changes in sea-surface temperature. Understanding the paleoceanographic changes in a regional context will provide a global test on models of Cenomanian–Turonian oceanographic and climatic evolution related both to extreme Turonian warmth and the evolution of OAE 2. Drilling of Early Cretaceous volcanic rocks and underlying Jurassic(?) sediments in different parts of the MB will provide information on the timing of different stages of the Gondwana breakup and the nature of the various phases of volcanism, which will lead to an improved understanding of the evolution of the NP and MB.« less
3. Data report: Cenozoic and Upper Cretaceous bulk carbonate stable carbon and oxygen isotopes from IODP Expedition 369 Sites U1513, U1514, and U1516 in the southeast Indian Ocean

   https://doi.org/10.14379/iodp.proc.369.206.2022  

   Edgar, K.M. ; MacLeod, K.G. ; Hasegawa, T. ; Hanson, E.M. ; Boomer, I. ; Kirby, N. ( May 2022 , Proceedings of the International Ocean Discovery Program)

   International Ocean Discovery Program (IODP) Expedition 369 recovered pelagic sediments spanning the Albian to Pleistocene at Sites U1513, U1514, and U1516. The cores provide an opportunity to determine paleoclimatic and paleoceanographic dynamics from a hitherto poorly sampled mid-high-latitude location across an ~110 My interval, beginning during the Cretaceous supergreenhouse when eastern Gondwana was still largely assembled and ending during the modern icehouse climate after the final breakup of Gondwana. Here we present ~650 bulk carbonate carbon and oxygen stable isotope data points and plot them alongside shipboard data sets to present a first broad documentation of chemostratigraphic data that reveal the stratigraphic position of key climatic transitions and events at Sites U1513, U1514, and U1516. These records show a pronounced long-term δ13C decrease and δ18O increase from the Albian/Cenomanian through the Pleistocene. Superimposed on this long-term trend are transient δ13C and δ18O events correlated with Oceanic Anoxic Event 2, peak Cretaceous warmth during the Turonian, Santonian to Maastrichtian cooling, the Cretaceous/Paleogene boundary, the Paleocene/Eocene Thermal Maximum, the Early Eocene Climatic Optimum, the Middle Eocene Climatic Optimum, and the Eocene–Oligocene transition. Recognizing these isotopic events confirms and refines shipboard interpretations and, more importantly, demonstrates the suitability of Sites U1513, U1514, andmore »U1516 for future high-resolution paleoceanographic works aimed at illuminating the links between tectonic and oceanographic dynamics and global versus local environmental changes.« less
4. Tasman Frontier Subduction Initiation and Paleogene Climate

   https://doi.org/10.14379/iodp.proc.371.2019  

   Sutherland, R. ; Dickens, G.R. ; Blum, P. ( February 2019 , Proceedings of the International Ocean Discovery Program)

   International Ocean Discovery Program (IODP) Expedition 371 drilled six sites (U1506–U1511) in the Tasman Sea, southwest Pacific, between 27 July and 26 September 2017. The primary goal was to understand Tonga-Kermadec subduction initiation through recovery of Paleogene sediment records. Secondary goals were to understand regional oceanography and climate through intervals of the Cenozoic, especially the Eocene. We recovered 2506 m of cored sediment and volcanic rock in 36.4 days of on-site drilling over a total expedition length of 58 days. The ages of strata at the base of each site were middle Eocene to Late Cretaceous. The cored intervals at five sites (U1506–U1510) sampled mostly nannofossil and foraminiferal ooze or chalk that contained volcanic or volcaniclastic intervals with variable clay content. Paleocene and Cretaceous sections at Site U1509 also contain calcareous clay and claystone. At Site U1511, a sequence of abyssal clay and diatomite was recovered with only minor amounts of carbonate. Wireline logs were collected at Sites U1507 and U1508. Our results provide the first firm basis for correlating lithostratigraphic units across a substantial part of northern Zealandia, including ties to onshore geology in New Caledonia and New Zealand. All six sites provide new stratigraphic and paleogeographic information thatmore »can be put into context through regional seismic stratigraphic interpretation and hence provide constraints on geodynamic models of subduction zone initiation. Evidence from Site U1507 suggests the northern New Caledonia Trough formed during an early stage of Paleogene tectonic change (before 44 Ma). Paleowater depth estimates from Site U1509 indicate that the Cretaceous Fairway-Aotea-Taranaki Basin dramatically deepened (~2000 m) at a similar time. Northern Lord Howe Rise at Site U1506 rose to sea level at ~50 Ma and subsided back to bathyal depths (600–1000 m) by 45 Ma. In contrast, southern Lord Howe Rise, at least near Site U1510, experienced its peak of transient uplift at ~40–30 Ma. A pulse of convergent plate failure took place across the southern part of the region (Sites U1508–U1511) between 45 and 35 Ma. Uplift of Lord Howe Rise was associated with intraplate volcanism, whereas volcanic activity on Norfolk Ridge near Site U1507 started at ~38 Ma and may relate to subduction. Shipboard observations made using cores and logs represent a substantial gain in fundamental knowledge about northern Zealandia. Prior to Expedition 371, only Deep Sea Drilling Project Sites 206, 207, and 208 had penetrated beneath upper Eocene strata in the region. Our samples and results provide valuable new constraints on geodynamic models of subduction initiation because they reveal the timing of plate deformation, the magnitude and timing of vertical motions, and the timing and type of volcanism. Secondary drilling objectives focused on paleoclimate topics were not fully completed, but significant new records were obtained that should contain information on Cenozoic oceanography and climate in the southwest Pacific.« less
5. Amundsen Sea West Antarctic Ice Sheet History

   https://doi.org/10.14379/iodp.proc.379.2021  

   Gohl, K. ; Wellner, J.S. ; Klaus, A. ( February 2021 , Proceedings of the International Ocean Discovery Program)

   The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet (WAIS) because of the great water depth at the grounding line, a subglacial bed seafloor deepening toward the interior of the continent, and the absence of substantial ice shelves. Glaciers in this configuration are thought to be susceptible to rapid or runaway retreat. Ice flowing into the Amundsen Sea Embayment is undergoing the most rapid changes of any sector of the Antarctic ice sheets outside the Antarctic Peninsula, including substantial grounding-line retreat over recent decades, as observed from satellite data. Recent models suggest that a threshold leading to the collapse of WAIS in this sector may have been already crossed and that much of the ice sheet could be lost even under relatively moderate greenhouse gas emission scenarios. Drill cores from the Amundsen Sea provide tests of several key questions about controls on ice sheet stability. The cores offer a direct offshore record of glacial history in a sector that is exclusively influenced by ice draining the WAIS, which allows clear comparisons between the WAIS history and low-latitude climate records. Today, relatively warm (modified) Circumpolar Deep Water (CDW) is impingingmore »onto the Amundsen Sea shelf and causing melting under ice shelves and at the grounding line of the WAIS in most places. Reconstructions of past CDW intrusions can assess the ties between warm water upwelling and large-scale changes in past grounding-line positions. Carrying out these reconstructions offshore from the drainage basin that currently has the most substantial negative mass balance of ice anywhere in Antarctica is thus of prime interest to future predictions. The scientific objectives for this expedition are built on hypotheses about WAIS dynamics and related paleoenvironmental and paleoclimatic conditions. The main objectives are: 1. To test the hypothesis that WAIS collapses occurred during the Neogene and Quaternary and, if so, when and under which environmental conditions; 2. To obtain ice-proximal records of ice sheet dynamics in the Amundsen Sea that correlate with global records of ice-volume changes and proxy records for atmospheric and ocean temperatures; 3. To study the stability of a marine-based WAIS margin and how warm deepwater incursions control its position on the shelf; 4. To find evidence for the earliest major grounded WAIS advances onto the middle and outer shelf; 5. To test the hypothesis that the first major WAIS growth was related to the uplift of the Marie Byrd Land dome. International Ocean Discovery Program (IODP) Expedition 379 completed two very successful drill sites on the continental rise of the Amundsen Sea. Site U1532 is located on a large sediment drift, now called the Resolution Drift, and it penetrated to 794 m with 90% recovery. We collected almost-continuous cores from recent age through the Pleistocene and Pliocene and into the upper Miocene. At Site U1533, we drilled 383 m (70% recovery) into the more condensed sequence at the lower flank of the same sediment drift. The cores of both sites contain unique records that will enable study of the cyclicity of ice sheet advance and retreat processes as well as ocean-bottom water circulation and water mass changes. In particular, Site U1532 revealed a sequence of Pliocene sediments with an excellent paleomagnetic record for high-resolution climate change studies of the previously sparsely sampled Pacific sector of the West Antarctic margin. Despite the drilling success at these sites, the overall expedition experienced three unexpected difficulties that affected many of the scientific objectives: 1. The extensive sea ice on the continental shelf prevented us from drilling any of the proposed shelf sites. 2. The drill sites on the continental rise were in the path of numerous icebergs of various sizes that frequently forced us to pause drilling or leave the hole entirely as they approached the ship. The overall downtime caused by approaching icebergs was 50% of our time spent on site. 3. A medical evacuation cut the expedition short by 1 week. Recovery of core on the continental rise at Sites U1532 and U1533 cannot be used to indicate the extent of grounded ice on the shelf or, thus, of its retreat directly. However, the sediments contained in these cores offer a range of clues about past WAIS extent and retreat. At Sites U1532 and U1533, coarse-grained sediments interpreted to be ice-rafted debris (IRD) were identified throughout all recovered time periods. A dominant feature of the cores is recorded by lithofacies cyclicity, which is interpreted to represent relatively warmer periods variably characterized by sediments with higher microfossil abundance, greater bioturbation, and higher IRD concentrations alternating with colder periods characterized by dominantly gray laminated terrigenous muds. Initial comparison of these cycles to published late Quaternary records from the region suggests that the units interpreted to be records of warmer time intervals in the core tie to global interglacial periods and the units interpreted to be deposits of colder periods tie to global glacial periods. Cores from the two drill sites recovered sediments of dominantly terrigenous origin intercalated or mixed with pelagic or hemipelagic deposits. In particular, Site U1533, which is located near a deep-sea channel originating from the continental slope, contains graded silts, sands, and gravels transported downslope from the shelf to the rise. The channel is likely the pathway of these sediments transported by turbidity currents and other gravitational downslope processes. The association of lithologic facies at both sites predominantly reflects the interplay of downslope and contouritic sediment supply with occasional input of more pelagic sediment. Despite the lack of cores from the shelf, our records from the continental rise reveal the timing of glacial advances across the shelf and thus the existence of a continent-wide ice sheet in West Antarctica during longer time periods since at least the late Miocene. Cores from both sites contain abundant coarse-grained sediments and clasts of plutonic origin transported either by downslope processes or by ice rafting. If detailed provenance studies confirm our preliminary assessment that the origin of these samples is from the plutonic bedrock of Marie Byrd Land, their thermochronological record will potentially reveal timing and rates of denudation and erosion linked to crustal uplift. The chronostratigraphy of both sites enables the generation of a seismic sequence stratigraphy for the entire Amundsen Sea continental rise, spanning the area offshore from the Amundsen Sea Embayment westward along the Marie Byrd Land margin to the easternmost Ross Sea through a connecting network of seismic lines.« less