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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)

   null (Ed.)

   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 at 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. 

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2. Tectonic inversion of an intracontinental rift basin: An example from the opening and closure of the Paleo-Tethys Ocean, northern Tibetan Plateau

   https://doi.org/10.1130/B37605.1  

   Li, Jie; Wu, Chen; Li, Xiaogang; Zuza, Andrew V; Haproff, Peter J; Zhao, Yonghui; Zhao, Wentao; Yue, Yahui; Ding, Lin (May 2024, Geological Society of America Bulletin)

   Suture zones located across the Tibetan region clearly demarcate the rift-and-drift and continental accretion history of the region. However, the intraplate responses to these marginal plate-tectonic events are rarely quantified. Our understanding of the Paleo-Tethyan orogenic system, which involved ocean opening and closing events to grow the central Asian continent, depends on the tectonic architecture and histories of major late Paleozoic−early Mesozoic orogenic belts. These opening and collision events were associated with coupled intracontinental deformation, which has been difficult to resolve due to subsequent overprinting deformation. The late Paleozoic−early Mesozoic Zongwulong Shan−Qinghai Nanshan belt in northern Tibet separates the Qilian and North Qaidam regions and is composed of Carboniferous−Triassic sedimentary materials and mantle-derived magmatic rocks. The tectonic setting and evolutional history of this belt provide important insight into the paleogeographic and tectonic relationships of the Paleo-Tethyan orogenic system located ∼200 km to the south. In this study, we integrated new and previous geological observations, detailed structural mapping, and zircon U-Pb geochronology data from the Zongwulong Shan−Qinghai Nanshan to document a complete tectonic inversion cycle from intraplate rifting to intracontinental shortening associated with the opening and closing of the Paleo-Tethyan Ocean. Carboniferous−Permian strata in the Zongwulong Shan were deposited in an intracontinental rift basin and sourced from both the north and the south. At the end of the Early−Middle Triassic, foreland molasse strata were deposited in the southern part of the Zongwulong Shan during tectonic inversion in the western part of the tectonic belt following the onset of regional contraction deformation. The Zongwulong Shan−Qinghai Nanshan system has experienced polyphase deformation since the late Paleozoic, including: (1) early Carboniferous intracontinental extension and (2) Early−Middle Triassic tectonic inversion involving reactivation of older normal faults as thrusts and folding of pre- and synrift strata. We interpret that the Zongwulong Shan−Qinghai Nanshan initiated as a Carboniferous−Early Triassic intracontinental rift basin related to the opening of the Paleo-Tethyan Ocean to the south, and it was then inverted during the Early−Middle Triassic closing of the Paleo-Tethyan Ocean. This work emphasizes that pre-Cenozoic intraplate structures related to the opening and closing of ocean basins in the Tethyan realm may be underappreciated across Tibet. 

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3. Expedition 359 Scientific Prospectus: Sea Level, Currents, and Monsoon Evolution in the Indian Ocean

   https://doi.org/10.14379/iodp.sp.359.2014  

   Betzler, C.; Eberli, G.P.; Giosan, L.; Alvarez Zarikian, C.A. (November 2014, Scientific prospectus)

   null (Ed.)

   International Ocean Discovery Program (IODP) Expedition 359 is designed to address sea level, currents, and monsoon evolution in the Indian Ocean. Seven proposed drill sites are located in the Maldives and one site is located in the Kerala-Konkan Basin on the western Indian continental margin. The Maldives carbonate edifice bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. It has great potential to serve as a key area for better understanding the effects of this global evolution in the Indo-Pacific realm. Based mainly on seismic stratigraphic data, a model for the evolution of this carbonate bank has been developed, showing how changing sea level and ocean current patterns shaped the bank geometries. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system is thought to be directly linked to the evolving Indian monsoon. Fluctuations in relative sea level control the stacking pattern of depositional sequences during the lower to middle Miocene. This phase was followed by a two-fold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and the deposition of giant sediment drifts. The shapes of drowned banks attest to the occurrence of these strong currents. The drift sediments, characterized by off-lapping geometries, formed large-scale prograding complexes, filling the Maldives Inner Sea basin. Because the strong current swept most of the sediment around the atolls away, relict banks did not prograde, and steady subsidence was balanced by aggradation of the atolls, which are still active today. One important outcome of Expedition 359 is ground-truthing the hypothesis that the dramatic, pronounced change in the style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. Answering this question will directly improve our knowledge on processes shaping carbonate platforms and their stratigraphic records. Our findings would be clearly applicable to other Tertiary carbonate platforms in the Indo-Pacific region and to numerous others throughout the geological record. In addition, the targeted successions will allow calibration of the Neogene oceanic δ13C record with data from a carbonate platform to platform-margin series. This is becoming important, as such records are the only type that exist in deep time. Drilling will provide the cores required for reconstructing changing current systems through time that are directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. These data will be valuable for a comparison with proposed Site KK-03B in the Kerala-Konkan Basin (see Geological setting of the Kerala-Konkan Basin, below) and other monsoon-dedicated IODP expeditions. The proposed site in the Kerala-Konkan Basin provides the opportunity to recover colocated oceanic and terrestrial records for monsoon and premonsoon Cenozoic climate in the eastern Arabian Sea and India, respectively. The site is located on a bathymetric high immediately north of the Chagos-Laccadive Ridge and is therefore not affected by strong tectonic, glacial, and nonmonsoon climatic processes that affect fan sites fed by Himalayan rivers. The cores are expected to consist of a continuous sequence of foraminifer-rich pelagic sediments with subordinate cyclical siliciclastic inputs of fluvial origin from the Indian Peninsula for the Neogene and a continuous paleoclimate record at orbital timescales into the Eocene and possibly the Paleocene. 

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4. A c. 1900 Ma Tethyan-type ophiolite in the Penokean Orogen, Pembine, Wisconsin (USA): Insights from the volcanic stratigraphy

   https://doi.org/10.1016/j.precamres.2023.107223  

   Guice, George L.; Viete, Daniel R.; Holder, Robert M.; Roy, Supratik (December 2023, Precambrian Research)

   Orogenic ophiolites are a hallmark of Phanerozoic plate tectonics, containing igneous lithologies that provide constraints on fundamental tectono-magmatic processes. The c. 1900Ma Pembine Ophiolite (Wisconsin, USA) is associated with the Penokean Orogen and represents a rare example of a proposed Paleoproterozoic ophiolite. The Penokean Orogen shares broad characteristics with Phanerozoic (<541 Ma) orogens, but the origin of the Pembine Ophiolite remains unclear, with the mafic volcanic rocks interpreted as representing either an intra-oceanic arc or continental back arc setting. To test these hypotheses, we present the results of petrography, bulk-rock geochemistry and mineral chemistry for a suite of 34 Pembine rocks, as well as U-Pb zircon geochronology for two samples. Based on trace elements established as immobile in the studied rocks, we demonstrate that mafic volcanism progressed (up-stratigraphic-section) from mid-ocean ridge-like to boninitic. The chemical evolution is identical to that observed in < 250 Ma ophiolites in the Himalayan–Alpine Orogen, which record forearc spreading during the nascent stages of subduction in the Tethys Ocean. We interpret the Pembine Ophiolite as forearc lithosphere formed during subduction initiation and obducted to the margin of the Superior Craton during the Penokean Orogeny. The processes responsible for forming (and preserving) this example of a Paleoproterozoic ophiolite may not have been dissimilar to those operating on the Phanerozoic Earth. 

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5. Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

   https://doi.org/10.1130/GES02127.1  

   Trop, Jeffrey M.; Benowitz, Jeffrey A.; Koepp, Donald Q.; Sunderlin, David; Brueseke, Matthew E.; Layer, Paul W.; Fitzgerald, Paul G. (November 2019, Geosphere)

   The Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone. These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska. 

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