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Steven M Bohaty - One of the best experts on this subject based on the ideXlab platform.
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the early to middle Eocene transition an integrated calcareous nannofossil and stable isotope record from the northwest atlantic ocean integrated ocean drilling program site u1410
Paleoceanography and Paleoclimatology (2019) (In press)., 2019Co-Authors: C Cappelli, Steven M Bohaty, Claudia Agnini, Paul R Bown, Thomas Westerhold, M De Riu, V Lobba, Yuhji YamamotoAbstract:The early to middle Eocene is marked by prominent changes in calcareous nannofossil assemblages coinciding both with long‐term climate changes and modification of the North Atlantic deep‐ocean circulation. In order to assess the impact of Eocene climate change on surface‐water environmental conditions of the Northwest Atlantic, we developed calcareous nannoplankton assemblage data and bulk stable isotope records (δ18O and δ13C) across an early to middle Eocene interval (~52–43 Ma) at IODP Site U1410 (Southeast Newfoundland Ridge, ~41°N). At this site, early Eocene sediments are pelagic nannofossil chalk, whereas middle Eocene deposits occur as clay‐rich drift sediments reflecting the progressive influence of northern‐sourced deep currents. Between the end of Early Eocene Climatic Optimum and the Ypresian/Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm‐water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. The most prominent period of accelerated assemblage change occurred during a ~2 Myr phase of relatively high bulk δ18O values possibly related to the post‐EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the middle Eocene interval, early Lutetian (~47.4 to 47 Ma) stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a potential restoration of warmer conditions. Importantly, our data indicate that the ~2 Myr‐interval immediately following the EECO was crucial in establishing the modern calcareous nannofossil assemblage structure and also reveal that the establishment of Reticulofenestra‐dominated assemblage occurred prior to the onset of persistent deep‐current system in the Northwest Atlantic.
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synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Elizabeth L KipAbstract: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.
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Synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Francien PeterseAbstract:Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO_2 concentrations are crucial for developing better projections of future climate change. Deep-ocean^ 1 , 2 and high-latitude^ 3 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 data^ 4 – 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 forcing^ 7 , 8 , rather than changes in ocean circulation^ 9 , 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 CO_2 reconstructions^ 8 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 estimates^ 11 . A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.
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Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific
Climate of the Past Discussions, 2015Co-Authors: K. M. Pascher, Giovanni Cortese, C. J. Hollis, Steven M Bohaty, R. M. MckayAbstract:Abstract. The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene–Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40–33 Ma) to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM) event – a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma) there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are absent. These data indicate that, once the Tasman Gateway was fully open in the early Oligocene, a frontal system similar to the present day was established, with nutrient-depleted subantarctic waters bathing the area around DSDP Site 277, resulting in a more oligotrophic siliceous plankton assemblage.
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significant southern ocean warming event in the late middle Eocene
Geology, 2003Co-Authors: Steven M Bohaty, James C ZachosAbstract:A prominent middle Eocene warming event is identified in Southern Ocean deep-sea cores, indicating that long-term cooling through the middle and late Eocene was not monotonic. At sites on Maud Rise and the Kerguelen Plateau, a distinct negative shift in δ 1 8 O values (∼1.0‰) is observed ca. 41.5 Ma. This excursion is interpreted as primarily a temperature signal, with a transient warming of 4 °C over 600 k.y. affecting both surface and middle-bathyal deep waters in the Indian-Atlantic region of the Southern Ocean. This isotopic event is designated as the middle Eocene climatic optimum, and is interpreted to represent a significant climatic reversal in the midst of middle to late Eocene deep-sea cooling. The lack of a significant negative carbon isotope excursion, as observed during the PalEocene-Eocene thermal maximum, and the gradual rate of high-latitude warming suggest that this event was not triggered by methane hydrate dissociation. Rather, a transient rise in pCO 2 levels is suspected, possibly as a result of metamorphic decarbonation in the Himalayan orogen or increased ridge/arc volcanism during the late middle Eocene.
Matthew Huber - One of the best experts on this subject based on the ideXlab platform.
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synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Elizabeth L KipAbstract: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.
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Synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Francien PeterseAbstract:Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO_2 concentrations are crucial for developing better projections of future climate change. Deep-ocean^ 1 , 2 and high-latitude^ 3 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 data^ 4 – 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 forcing^ 7 , 8 , rather than changes in ocean circulation^ 9 , 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 CO_2 reconstructions^ 8 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 estimates^ 11 . A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.
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Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate
Climate of The Past Discussions, 2018Co-Authors: Michiel Baatsen, M. A. Kliphuis, Anna Von Der Heydt, Peter K Bijl, Appy Sluijs, Matthew Huber, Henk A DijkstraAbstract:While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To understand Antarctic glaciation at the Eocene-Oligocene Transition (~ 34 Ma) as well as middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Here, we present a set of high resolution coupled climate simulations using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with new detailed 38 Ma geographical boundary conditions with a different radiative forcing. With 4 × pre-industrial concentrations of CO 2 (i.e. 1120 ppm) and CH 4 (~ 2700 ppb), the equilibrium sea surface temperatures correspond well to available late middle Eocene (42–38 Ma) proxies. Being generally cooler, the simulated climate with 2 × pre-industrial values is a good analog for that of the late Eocene (38–34 Ma). Deep water formation occurs in the South Pacific Ocean, while the North Atlantic is strongly stratified and virtually stagnant. A shallow and weak circumpolar current is present in the Southern Ocean with only minor effects on southward oceanic heat transport within wind-driven gyres. Terrestrial temperature proxies, although limited in coverage, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. Climate sensitivity is similar (~ 0.7 °C/Wm 2 ) to that of the present-day climate (~ 0.8 °C/Wm 2 ; 3 °C per CO 2 doubling), with significant polar amplification despite very limited sea ice and snow cover. High latitudes are mainly kept warm by albedo and cloud feedbacks in combination with global changes in geography and the absence of polar ice sheets. The integrated effect of geography, vegetation and ice accounts for a 6–7 °C offset between pre-industrial and 38 Ma Eocene boundary conditions. These 38 Ma simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates. The general circulation and radiative budget allow for mild high-latitude regions and little to no snow and ice cover, without making equatorial regions extremely warm.
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early paleogene temperature history of the southwest pacific ocean reconciling proxies and models
Earth and Planetary Science Letters, 2012Co-Authors: Christopher J Hollis, John Creech, Kyle W R Taylor, Luke Handley, Benjamin R Hines, Erica M. Crouch, Hugh E G Morgans, Matthew Huber, Richard D. Pancost, Jennifer S CramptonAbstract:We present a new multiproxy (TEX86, δ18O and Mg/Ca), marine temperature history for Canterbury Basin, eastern New Zealand, that extends from middle PalEocene to middle Eocene, including the PalEocene–Eocene thermal maximum (PETM) and early Eocene climatic optimum (EECO). In light of concerns that proxy-based sea surface temperature (SST) estimates are untenably warm for the southwest Pacific during the Eocene, we review the assumptions that underlie the proxies and develop a preliminary paleo-calibration for TEX86 that is based on four multiproxy Eocene records that represent an SST range of 15–34 °C. For the southwest Pacific Paleogene, we show that TEX86L exhibits the best fit with the Eocene paleo-calibration. SSTs derived from related proxies (TEX86H, 1/TEX86) exhibit a systematic warm bias that increases as TEX86 values decrease (a warm bias of 4–7 °C where TEX86<0.7). The TEX86L proxy indicates that southwest Pacific SST increased by ∼10 °C from middle PalEocene to early Eocene, with SST maxima of 26–28 °C (tropical) during the PETM and EECO and an SST minimum of 13–16 °C (cool–warm temperate) at the middle/late PalEocene transition (58.7 Ma). The base of the EECO is poorly defined in these records but the top is well-defined in Canterbury Basin by a 2–5 °C decrease in SST and bottom water temperature (BWT) in the latest early Eocene (49.3 Ma); BWT falls from a maximum of 18–20 °C in the EECO to 12–14 °C in the middle Eocene. Overall, cooler temperatures are recorded in the mid-Waipara section, which may reflect a deeper (∼500 m water depth) and less neritic depositional setting compared with Hampden and ODP 1172 (∼200 m water depth). The high SSTs and BWTs inferred for the PETM and EECO can be reconciled with Eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto-East Australian Current is taken into account.
Philip D Gingerich - One of the best experts on this subject based on the ideXlab platform.
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Primates in the Eocene
Palaeobiodiversity and Palaeoenvironments, 2012Co-Authors: Philip D GingerichAbstract:The mammalian order Primates made its first appearance in the fossil record during the PalEocene–Eocene thermal maximum (PETM), the global greenhouse warming event that marks the beginning of the Eocene. Two primate superfamilies, Tarsioidea and Adapoidea, dominate early and middle Eocene primate faunas. Warm climates enabled primates to thrive, and warming events within the Eocene facilitated cosmopolitan dispersal. Declining diversity at the end of the Eocene reflects environmental cooling. Fossils of earliest Tarsioidea and Adapoidea are similar dentally, often confused, and appear closely related as stem or crown Haplorhini. The superfamily Tarsioidea is represented by a single genus, Tarsius , living today, while Adapoidea appear to be ancestral to living Anthropoidea. Little is known of the Eocene history of strepsirrhine Lemuroidea and Lorisoidea. Temporal scaling of molecular clock ages suggests that Strepsirrhini appeared before Haplorhini in the PalEocene or possibly with Haplorhini at the beginning of the Eocene. Substantial skeletons of Eocene primates like those of adapoid Darwinius and Europolemur from Messel in Germany and Notharctus and Smilodectes from western North America constrain phylogenetic interpretation of primate relationships much more than dental remains ever can. A specialised grasping foot distinguishes early primates from other mammals. Traits associated in a functional complex include replacement of claws by nails on all digits; movement of the pedal fulcrum from the metatarsals to the tarsals; elongation of digit IV relative to digit III, with reduction of digit II and sometimes III; and then secondary development of a grooming claw or claws on digits II and sometimes III. The specialised grasping foot of early primates was later moderated in the emergence of anthropoid primates.
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new early Eocene tapiromorph perissodactyls from the ghazij formation of pakistan with implications for mammalian biochronology in asia
Acta Palaeontologica Polonica, 2012Co-Authors: Pieter Missiaen, Philip D GingerichAbstract:Early Eocene mammals from Indo-Pakistan have only recently come under study. Here we describe the first tapiromorph perissodactyls from the subcontinent. Gandheralophus minor gen. et sp. nov. and G. robustus sp. nov. are two species of Isectolophidae differing in size and in reduction of the anterior dentition. Gandheralophus is probably derived from a primitive isectolophid such as Orientolophus hengdongensis from the earliest Eocene of China, and may be part of a South Asian lineage that also contains Karagalax from the middle Eocene of Pakistan. Two specimens are referred to a new, unnamed species of Lophialetidae. Finally, a highly diagnostic M3 and a molar fragment are described as the new eomoropid chalicothere Litolophus ghazijensis sp. nov. The perissodactyls described here, in contrast to most other mammalian groups published from the early Eocene of Indo-Pakistan, are most closely related to forms known from East and Central Asia, where Eocene tapiromorphs are diverse and biochronologically impo...
Meral Kaya - One of the best experts on this subject based on the ideXlab platform.
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stratigraphy and tectono sedimentary evolution of the upper cretaceous tertiary sequence in the southern part of the malatya basin east anatolia turkey
Journal of Asian Earth Sciences, 2007Co-Authors: Mehmet Onal, Meral KayaAbstract:Abstract The Malatya Basin is situated on the southern Taurus-Anatolian Platform. The southern part of the basin contains a sedimentary sequence which can be divided into four main units, each separated by an unconformity. From base to top, these are: (1) Permo-Carboniferous; (2) Upper Cretaceous–Lower PalEocene, (3) Middle-Upper Eocene and (4) Upper Miocene. The Upper Cretaceous–Tertiary sedimentary sequence resting on basement rocks is up to 700 m thick. The Permo-Carboniferous basement consist of dolomites and recrystallized limestones. The Upper Cretaceous–Lower PalEocene transgressive–regressive sequence shows a transition from terrestrial environments, via lagoonal to shallow-marine limestones to deep marine turbiditic sediments, followed upwards by shallow marine cherty limestones. The marine sediments contain planktic and benthic foraminifers indicating an upper Campanian, Maastrichtian and Danian age. The Middle-Upper Eocene is a transgressive–regressive sequence represented by terrestrial and lagoonal clastics, shallow-marine limestones and deep marine turbidites. The planktic and benthic foraminifers in the marine sediments indicate a Middle-Upper Eocene age. The upper Miocene sequence consists of a reddish-brown conglomerate–sandstone–mudstone alternation of alluvial and fluvial facies. During Late Cretaceous–Early PalEocene times, the Gunduzbey Group was deposited in the southern part of a fore-arc basin, simultaneously with volcanics belonging to the Yuksekova Group. During Middle-Late Eocene times, the Yesilyurt Group was deposited in the northern part of the Maden Basin and the Helete volcanic arc. The Middle-Upper Eocene Malatya Basin was formed due to block faulting at the beginning of the Middle Eocene time. During the Late PalEocene–Early Eocene, and at the end of the Eocene, the study areas became continental due to the southward advance of nappe structures. The rock sequences in the southern part of the Malatya Basin may be divided into four tectonic units, from base to top: the lower allochthon, the upper allochthon, the parautochthon and autochthonous rock units.
Claudia Agnini - One of the best experts on this subject based on the ideXlab platform.
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the early to middle Eocene transition an integrated calcareous nannofossil and stable isotope record from the northwest atlantic ocean integrated ocean drilling program site u1410
Paleoceanography and Paleoclimatology (2019) (In press)., 2019Co-Authors: C Cappelli, Steven M Bohaty, Claudia Agnini, Paul R Bown, Thomas Westerhold, M De Riu, V Lobba, Yuhji YamamotoAbstract:The early to middle Eocene is marked by prominent changes in calcareous nannofossil assemblages coinciding both with long‐term climate changes and modification of the North Atlantic deep‐ocean circulation. In order to assess the impact of Eocene climate change on surface‐water environmental conditions of the Northwest Atlantic, we developed calcareous nannoplankton assemblage data and bulk stable isotope records (δ18O and δ13C) across an early to middle Eocene interval (~52–43 Ma) at IODP Site U1410 (Southeast Newfoundland Ridge, ~41°N). At this site, early Eocene sediments are pelagic nannofossil chalk, whereas middle Eocene deposits occur as clay‐rich drift sediments reflecting the progressive influence of northern‐sourced deep currents. Between the end of Early Eocene Climatic Optimum and the Ypresian/Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm‐water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. The most prominent period of accelerated assemblage change occurred during a ~2 Myr phase of relatively high bulk δ18O values possibly related to the post‐EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the middle Eocene interval, early Lutetian (~47.4 to 47 Ma) stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a potential restoration of warmer conditions. Importantly, our data indicate that the ~2 Myr‐interval immediately following the EECO was crucial in establishing the modern calcareous nannofossil assemblage structure and also reveal that the establishment of Reticulofenestra‐dominated assemblage occurred prior to the onset of persistent deep‐current system in the Northwest Atlantic.
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synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Elizabeth L KipAbstract: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.
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Synchronous tropical and polar temperature evolution in the Eocene
Nature, 2018Co-Authors: Margot J Cramwinckel, Steven M Bohaty, Peter K Bijl, Matthew Huber, Ilja J Kocken, Claudia Agnini, Joost Frieling, Aaron Goldner, Frederik J Hilgen, Francien PeterseAbstract:Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO_2 concentrations are crucial for developing better projections of future climate change. Deep-ocean^ 1 , 2 and high-latitude^ 3 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 data^ 4 – 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 forcing^ 7 , 8 , rather than changes in ocean circulation^ 9 , 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 CO_2 reconstructions^ 8 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 estimates^ 11 . A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.
