scholarly journals Paleobiogeography of Eocene Radiolarians in the Southwest Pacific

2021 ◽  
Author(s):  
◽  
Kristina Michaela Pascher
Keyword(s):  
High Latitude ◽  
Middle Eocene ◽  
Late Eocene ◽  
Early Eocene ◽  
Low Latitude ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Climatic Optimum ◽  
Total Fauna ◽  
Radiolarian Assemblages

<p>This thesis investigates the effect of climatic and oceanographic changes on the distribution of fossil radiolarian assemblages from the early Eocene to early Oligocene (~56–30 Ma) in the Southwest Pacific. Radiolarian assemblages have been analysed from a series of archived cores collected by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP). The selected cores form a latitudinal transect designed to investigate the ecological change associated with the transition from the warm ‘greenhouse’ climate of the Eocene into the cooler Oligocene, when continental-scale glaciation is believed to have intiated in Antarctica. High-latitude sites were sampled on the Campbell Plateau (DSDP Site 277), Tasman Rise (DSDP sites 280 and 281) and the Tasman Sea (DSDP Site 283 and ODP Site 1172), while mid-latitude sites were sampled both to the west of New Zealand (DSDP sites 207, 206, 592) and east of New Zealand (ODP Site 1123). New foraminifer oxygen (δ¹⁸O) and carbon (δ¹³C) stable isotope data from DSDP sites 277, 207 and 592 are presented and provide additional age control and insights in the climatic and oceanographic changes in the Southwest Pacific during the early Eocene to early Oligocene.  This thesis contributes a comprehensive taxonomic review of Eocene radiolarian taxa with the intention of standardising nomenclature and to resolve synonymies. 213 out of 259 counting groups have been reviewed and assigned to species or subspecies level and 7 new species are yet to be described. All sites have been correlated to the Southern Hemisphere radiolarian zonation, from the upper Paleocene to upper Oligocene (RP6SH to RP17SH). Alternative datums for the base of RP10SH (LO of Artobotrys auriculaleporis) and the base of RP12SH (LO of Lophocyrtis longiventer) are proposed.  The early Eocene climatic optimum (EECO, ~53–49 Ma) can be identified by a negative excursion in foraminiferal δ¹⁸O values at Site 207. The radiolarian assemblages at sites 207 (paleolatitude ~46°S) and 277 (paleolatitude ~55°S) during the EECO are dominated by taxa with low-latitude affinities (Amphicraspedum spp. represents up to 89% of total fauna), but many typical low-latitude genera (e.g. Thyrsocyrtis, Podocyrtis, Phormocyrtis) are absent. Following the EECO, low-latitude taxa decrease at Site 207 and disappear at Site 277. Radiolarians are abundant and very diverse at mid-latitude sites 207 and 206 (paleolatitude ~42°S) during the middle Eocene, and low-latitude taxa are common (up to ~15% of the total fauna at Site 207 and ~10% at Site 206). The middle Eocene climatic optimum (MECO, ~40 Ma), although truncated by poor drilling recovery at Site 277, is identified by a negative shift in foraminiferal δ18O values at this site and is associated by a small increase in radiolarian taxa with low-latitude affinities (up to ~5% of total fauna).  Early in the late Eocene (~37 Ma), a positive shift in δ¹⁸O values at Site 277 is correlated with the Priabonian oxygen isotope maximum (PrOM). Within this cooling event, radiolarian abundance, diversity and preservation, as well as diatom abundance, increase abruptly at Site 277. A negative δ¹⁸O excursion above the PrOM is correlated to a late Eocene warming event (~36 Ma) and is referred to as the late Eocene climatic optimum (LECO). The LECO is identified using stable isotopes at sites 277 and 592. Radiolarian abundance and diversity decline within this event at Site 277 although taxa with low-latitude affinities increase (up to ~10% of total fauna). At Site 592, radiolarian-bearing sediments are only present during this event with up to ~6% low-latitude taxa. Apart from the LECO, late Eocene radiolarian assemblages at Site 277 are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and Oligocene (~38–27 Ma) at DSDP sites 280, 281, 283, and ODP sites 1172 and 1123 and are associated with very high diatom abundance.  Radiolarian assemblages are used for reconstructing the evolution of oceanic fronts. The composition of the assemblages suggests that the oscillation between warm subtropical and cool subtropical conditions can be explained by the varying influence of the warm proto-East Australian Current and cold proto-Ross Gyre. In contrast to temperature reconstructions based on geochemical proxies (TEX₈₆, UK’₃₇ and Mg/Ca), which indicate tropical temperatures throughout most of the Eocene, radiolarians indicate warm subtropical conditions during the EECO. Warm surface water masses may have been transported by the proto-East Australian Current to ~55°S during the EECO. During the middle to late Eocene, cool subtropical conditions prevailed in the Southwest Pacific. Localised occurrences of abundant diatoms indicate upwelling areas close to the Tasman Rise in the middle Eocene. The proliferation of radiolarian assemblages and expansion of high-latitude taxa onto the Campbell Plateau in the latest Eocene is explained by a northward expansion of proto-Ross Gyre. In the early Oligocene (~32 Ma), there is an overall decrease in radiolarian abundance and diversity on the Campbell Plateau (Site 277) and diatoms disappear. Major hiatuses in the region indicate intensified bottom-water currents associated with the establishment of the Antarctic Circumpolar Current. A frontal system similar to present day developed in the early Oligocene, with nutrient-depleted subantarctic waters bathing the southern Campbell Plateau, resulting in a more restricted radiolarian assemblage at Site 277.</p>

scholarly journals Paleobiogeography of Eocene Radiolarians in the Southwest Pacific

2021 ◽  
Author(s):  
◽  
Kristina Michaela Pascher
Keyword(s):  
High Latitude ◽  
Middle Eocene ◽  
Late Eocene ◽  
Early Eocene ◽  
Low Latitude ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Climatic Optimum ◽  
Total Fauna ◽  
Radiolarian Assemblages

<p>This thesis investigates the effect of climatic and oceanographic changes on the distribution of fossil radiolarian assemblages from the early Eocene to early Oligocene (~56–30 Ma) in the Southwest Pacific. Radiolarian assemblages have been analysed from a series of archived cores collected by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP). The selected cores form a latitudinal transect designed to investigate the ecological change associated with the transition from the warm ‘greenhouse’ climate of the Eocene into the cooler Oligocene, when continental-scale glaciation is believed to have intiated in Antarctica. High-latitude sites were sampled on the Campbell Plateau (DSDP Site 277), Tasman Rise (DSDP sites 280 and 281) and the Tasman Sea (DSDP Site 283 and ODP Site 1172), while mid-latitude sites were sampled both to the west of New Zealand (DSDP sites 207, 206, 592) and east of New Zealand (ODP Site 1123). New foraminifer oxygen (δ¹⁸O) and carbon (δ¹³C) stable isotope data from DSDP sites 277, 207 and 592 are presented and provide additional age control and insights in the climatic and oceanographic changes in the Southwest Pacific during the early Eocene to early Oligocene.  This thesis contributes a comprehensive taxonomic review of Eocene radiolarian taxa with the intention of standardising nomenclature and to resolve synonymies. 213 out of 259 counting groups have been reviewed and assigned to species or subspecies level and 7 new species are yet to be described. All sites have been correlated to the Southern Hemisphere radiolarian zonation, from the upper Paleocene to upper Oligocene (RP6SH to RP17SH). Alternative datums for the base of RP10SH (LO of Artobotrys auriculaleporis) and the base of RP12SH (LO of Lophocyrtis longiventer) are proposed.  The early Eocene climatic optimum (EECO, ~53–49 Ma) can be identified by a negative excursion in foraminiferal δ¹⁸O values at Site 207. The radiolarian assemblages at sites 207 (paleolatitude ~46°S) and 277 (paleolatitude ~55°S) during the EECO are dominated by taxa with low-latitude affinities (Amphicraspedum spp. represents up to 89% of total fauna), but many typical low-latitude genera (e.g. Thyrsocyrtis, Podocyrtis, Phormocyrtis) are absent. Following the EECO, low-latitude taxa decrease at Site 207 and disappear at Site 277. Radiolarians are abundant and very diverse at mid-latitude sites 207 and 206 (paleolatitude ~42°S) during the middle Eocene, and low-latitude taxa are common (up to ~15% of the total fauna at Site 207 and ~10% at Site 206). The middle Eocene climatic optimum (MECO, ~40 Ma), although truncated by poor drilling recovery at Site 277, is identified by a negative shift in foraminiferal δ18O values at this site and is associated by a small increase in radiolarian taxa with low-latitude affinities (up to ~5% of total fauna).  Early in the late Eocene (~37 Ma), a positive shift in δ¹⁸O values at Site 277 is correlated with the Priabonian oxygen isotope maximum (PrOM). Within this cooling event, radiolarian abundance, diversity and preservation, as well as diatom abundance, increase abruptly at Site 277. A negative δ¹⁸O excursion above the PrOM is correlated to a late Eocene warming event (~36 Ma) and is referred to as the late Eocene climatic optimum (LECO). The LECO is identified using stable isotopes at sites 277 and 592. Radiolarian abundance and diversity decline within this event at Site 277 although taxa with low-latitude affinities increase (up to ~10% of total fauna). At Site 592, radiolarian-bearing sediments are only present during this event with up to ~6% low-latitude taxa. Apart from the LECO, late Eocene radiolarian assemblages at Site 277 are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and Oligocene (~38–27 Ma) at DSDP sites 280, 281, 283, and ODP sites 1172 and 1123 and are associated with very high diatom abundance.  Radiolarian assemblages are used for reconstructing the evolution of oceanic fronts. The composition of the assemblages suggests that the oscillation between warm subtropical and cool subtropical conditions can be explained by the varying influence of the warm proto-East Australian Current and cold proto-Ross Gyre. In contrast to temperature reconstructions based on geochemical proxies (TEX₈₆, UK’₃₇ and Mg/Ca), which indicate tropical temperatures throughout most of the Eocene, radiolarians indicate warm subtropical conditions during the EECO. Warm surface water masses may have been transported by the proto-East Australian Current to ~55°S during the EECO. During the middle to late Eocene, cool subtropical conditions prevailed in the Southwest Pacific. Localised occurrences of abundant diatoms indicate upwelling areas close to the Tasman Rise in the middle Eocene. The proliferation of radiolarian assemblages and expansion of high-latitude taxa onto the Campbell Plateau in the latest Eocene is explained by a northward expansion of proto-Ross Gyre. In the early Oligocene (~32 Ma), there is an overall decrease in radiolarian abundance and diversity on the Campbell Plateau (Site 277) and diatoms disappear. Major hiatuses in the region indicate intensified bottom-water currents associated with the establishment of the Antarctic Circumpolar Current. A frontal system similar to present day developed in the early Oligocene, with nutrient-depleted subantarctic waters bathing the southern Campbell Plateau, resulting in a more restricted radiolarian assemblage at Site 277.</p>

scholarly journals Paleobiogeography of Eocene Radiolarians in the Southwest Pacific

2021 ◽  
Author(s):  
◽  
Kristina Michaela Pascher
Keyword(s):  
High Latitude ◽  
Middle Eocene ◽  
Late Eocene ◽  
Early Eocene ◽  
Low Latitude ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Climatic Optimum ◽  
Total Fauna ◽  
Radiolarian Assemblages

<p>This thesis investigates the effect of climatic and oceanographic changes on the distribution of fossil radiolarian assemblages from the early Eocene to early Oligocene (~56–30 Ma) in the Southwest Pacific. Radiolarian assemblages have been analysed from a series of archived cores collected by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP). The selected cores form a latitudinal transect designed to investigate the ecological change associated with the transition from the warm ‘greenhouse’ climate of the Eocene into the cooler Oligocene, when continental-scale glaciation is believed to have intiated in Antarctica. High-latitude sites were sampled on the Campbell Plateau (DSDP Site 277), Tasman Rise (DSDP sites 280 and 281) and the Tasman Sea (DSDP Site 283 and ODP Site 1172), while mid-latitude sites were sampled both to the west of New Zealand (DSDP sites 207, 206, 592) and east of New Zealand (ODP Site 1123). New foraminifer oxygen (δ¹⁸O) and carbon (δ¹³C) stable isotope data from DSDP sites 277, 207 and 592 are presented and provide additional age control and insights in the climatic and oceanographic changes in the Southwest Pacific during the early Eocene to early Oligocene.  This thesis contributes a comprehensive taxonomic review of Eocene radiolarian taxa with the intention of standardising nomenclature and to resolve synonymies. 213 out of 259 counting groups have been reviewed and assigned to species or subspecies level and 7 new species are yet to be described. All sites have been correlated to the Southern Hemisphere radiolarian zonation, from the upper Paleocene to upper Oligocene (RP6SH to RP17SH). Alternative datums for the base of RP10SH (LO of Artobotrys auriculaleporis) and the base of RP12SH (LO of Lophocyrtis longiventer) are proposed.  The early Eocene climatic optimum (EECO, ~53–49 Ma) can be identified by a negative excursion in foraminiferal δ¹⁸O values at Site 207. The radiolarian assemblages at sites 207 (paleolatitude ~46°S) and 277 (paleolatitude ~55°S) during the EECO are dominated by taxa with low-latitude affinities (Amphicraspedum spp. represents up to 89% of total fauna), but many typical low-latitude genera (e.g. Thyrsocyrtis, Podocyrtis, Phormocyrtis) are absent. Following the EECO, low-latitude taxa decrease at Site 207 and disappear at Site 277. Radiolarians are abundant and very diverse at mid-latitude sites 207 and 206 (paleolatitude ~42°S) during the middle Eocene, and low-latitude taxa are common (up to ~15% of the total fauna at Site 207 and ~10% at Site 206). The middle Eocene climatic optimum (MECO, ~40 Ma), although truncated by poor drilling recovery at Site 277, is identified by a negative shift in foraminiferal δ18O values at this site and is associated by a small increase in radiolarian taxa with low-latitude affinities (up to ~5% of total fauna).  Early in the late Eocene (~37 Ma), a positive shift in δ¹⁸O values at Site 277 is correlated with the Priabonian oxygen isotope maximum (PrOM). Within this cooling event, radiolarian abundance, diversity and preservation, as well as diatom abundance, increase abruptly at Site 277. A negative δ¹⁸O excursion above the PrOM is correlated to a late Eocene warming event (~36 Ma) and is referred to as the late Eocene climatic optimum (LECO). The LECO is identified using stable isotopes at sites 277 and 592. Radiolarian abundance and diversity decline within this event at Site 277 although taxa with low-latitude affinities increase (up to ~10% of total fauna). At Site 592, radiolarian-bearing sediments are only present during this event with up to ~6% low-latitude taxa. Apart from the LECO, late Eocene radiolarian assemblages at Site 277 are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and Oligocene (~38–27 Ma) at DSDP sites 280, 281, 283, and ODP sites 1172 and 1123 and are associated with very high diatom abundance.  Radiolarian assemblages are used for reconstructing the evolution of oceanic fronts. The composition of the assemblages suggests that the oscillation between warm subtropical and cool subtropical conditions can be explained by the varying influence of the warm proto-East Australian Current and cold proto-Ross Gyre. In contrast to temperature reconstructions based on geochemical proxies (TEX₈₆, UK’₃₇ and Mg/Ca), which indicate tropical temperatures throughout most of the Eocene, radiolarians indicate warm subtropical conditions during the EECO. Warm surface water masses may have been transported by the proto-East Australian Current to ~55°S during the EECO. During the middle to late Eocene, cool subtropical conditions prevailed in the Southwest Pacific. Localised occurrences of abundant diatoms indicate upwelling areas close to the Tasman Rise in the middle Eocene. The proliferation of radiolarian assemblages and expansion of high-latitude taxa onto the Campbell Plateau in the latest Eocene is explained by a northward expansion of proto-Ross Gyre. In the early Oligocene (~32 Ma), there is an overall decrease in radiolarian abundance and diversity on the Campbell Plateau (Site 277) and diatoms disappear. Major hiatuses in the region indicate intensified bottom-water currents associated with the establishment of the Antarctic Circumpolar Current. A frontal system similar to present day developed in the early Oligocene, with nutrient-depleted subantarctic waters bathing the southern Campbell Plateau, resulting in a more restricted radiolarian assemblage at Site 277.</p>

scholarly journals Paleobiogeography of Eocene Radiolarians in the Southwest Pacific

2021 ◽  
Author(s):  
◽  
Kristina Michaela Pascher
Keyword(s):  
High Latitude ◽  
Middle Eocene ◽  
Late Eocene ◽  
Early Eocene ◽  
Low Latitude ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Climatic Optimum ◽  
Total Fauna ◽  
Radiolarian Assemblages

<p>This thesis investigates the effect of climatic and oceanographic changes on the distribution of fossil radiolarian assemblages from the early Eocene to early Oligocene (~56–30 Ma) in the Southwest Pacific. Radiolarian assemblages have been analysed from a series of archived cores collected by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP). The selected cores form a latitudinal transect designed to investigate the ecological change associated with the transition from the warm ‘greenhouse’ climate of the Eocene into the cooler Oligocene, when continental-scale glaciation is believed to have intiated in Antarctica. High-latitude sites were sampled on the Campbell Plateau (DSDP Site 277), Tasman Rise (DSDP sites 280 and 281) and the Tasman Sea (DSDP Site 283 and ODP Site 1172), while mid-latitude sites were sampled both to the west of New Zealand (DSDP sites 207, 206, 592) and east of New Zealand (ODP Site 1123). New foraminifer oxygen (δ¹⁸O) and carbon (δ¹³C) stable isotope data from DSDP sites 277, 207 and 592 are presented and provide additional age control and insights in the climatic and oceanographic changes in the Southwest Pacific during the early Eocene to early Oligocene.  This thesis contributes a comprehensive taxonomic review of Eocene radiolarian taxa with the intention of standardising nomenclature and to resolve synonymies. 213 out of 259 counting groups have been reviewed and assigned to species or subspecies level and 7 new species are yet to be described. All sites have been correlated to the Southern Hemisphere radiolarian zonation, from the upper Paleocene to upper Oligocene (RP6SH to RP17SH). Alternative datums for the base of RP10SH (LO of Artobotrys auriculaleporis) and the base of RP12SH (LO of Lophocyrtis longiventer) are proposed.  The early Eocene climatic optimum (EECO, ~53–49 Ma) can be identified by a negative excursion in foraminiferal δ¹⁸O values at Site 207. The radiolarian assemblages at sites 207 (paleolatitude ~46°S) and 277 (paleolatitude ~55°S) during the EECO are dominated by taxa with low-latitude affinities (Amphicraspedum spp. represents up to 89% of total fauna), but many typical low-latitude genera (e.g. Thyrsocyrtis, Podocyrtis, Phormocyrtis) are absent. Following the EECO, low-latitude taxa decrease at Site 207 and disappear at Site 277. Radiolarians are abundant and very diverse at mid-latitude sites 207 and 206 (paleolatitude ~42°S) during the middle Eocene, and low-latitude taxa are common (up to ~15% of the total fauna at Site 207 and ~10% at Site 206). The middle Eocene climatic optimum (MECO, ~40 Ma), although truncated by poor drilling recovery at Site 277, is identified by a negative shift in foraminiferal δ18O values at this site and is associated by a small increase in radiolarian taxa with low-latitude affinities (up to ~5% of total fauna).  Early in the late Eocene (~37 Ma), a positive shift in δ¹⁸O values at Site 277 is correlated with the Priabonian oxygen isotope maximum (PrOM). Within this cooling event, radiolarian abundance, diversity and preservation, as well as diatom abundance, increase abruptly at Site 277. A negative δ¹⁸O excursion above the PrOM is correlated to a late Eocene warming event (~36 Ma) and is referred to as the late Eocene climatic optimum (LECO). The LECO is identified using stable isotopes at sites 277 and 592. Radiolarian abundance and diversity decline within this event at Site 277 although taxa with low-latitude affinities increase (up to ~10% of total fauna). At Site 592, radiolarian-bearing sediments are only present during this event with up to ~6% low-latitude taxa. Apart from the LECO, late Eocene radiolarian assemblages at Site 277 are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and Oligocene (~38–27 Ma) at DSDP sites 280, 281, 283, and ODP sites 1172 and 1123 and are associated with very high diatom abundance.  Radiolarian assemblages are used for reconstructing the evolution of oceanic fronts. The composition of the assemblages suggests that the oscillation between warm subtropical and cool subtropical conditions can be explained by the varying influence of the warm proto-East Australian Current and cold proto-Ross Gyre. In contrast to temperature reconstructions based on geochemical proxies (TEX₈₆, UK’₃₇ and Mg/Ca), which indicate tropical temperatures throughout most of the Eocene, radiolarians indicate warm subtropical conditions during the EECO. Warm surface water masses may have been transported by the proto-East Australian Current to ~55°S during the EECO. During the middle to late Eocene, cool subtropical conditions prevailed in the Southwest Pacific. Localised occurrences of abundant diatoms indicate upwelling areas close to the Tasman Rise in the middle Eocene. The proliferation of radiolarian assemblages and expansion of high-latitude taxa onto the Campbell Plateau in the latest Eocene is explained by a northward expansion of proto-Ross Gyre. In the early Oligocene (~32 Ma), there is an overall decrease in radiolarian abundance and diversity on the Campbell Plateau (Site 277) and diatoms disappear. Major hiatuses in the region indicate intensified bottom-water currents associated with the establishment of the Antarctic Circumpolar Current. A frontal system similar to present day developed in the early Oligocene, with nutrient-depleted subantarctic waters bathing the southern Campbell Plateau, resulting in a more restricted radiolarian assemblage at Site 277.</p>

scholarly journals Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

2015 ◽  
Vol 11 (4) ◽  
pp. 2977-3018 ◽  
Author(s):  
K. M. Pascher ◽  
C. J. Hollis ◽  
S. M. Bohaty ◽  
G. Cortese ◽  
R. M. McKay
Keyword(s):  
Oxygen Isotope ◽  
High Latitude ◽  
Large Scale ◽  
Middle Eocene ◽  
Late Eocene ◽  
Climate History ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Radiolarian Assemblages

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.

scholarly journals Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the southwest Pacific

2015 ◽  
Vol 11 (12) ◽  
pp. 1599-1620 ◽  
Author(s):  
K. M. Pascher ◽  
C. J. Hollis ◽  
S. M. Bohaty ◽  
G. Cortese ◽  
R. M. McKay ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
High Latitude ◽  
Late Eocene ◽  
Low Latitude ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Abundance And Diversity ◽  
Latest Eocene ◽  
Radiolarian Assemblages ◽  
Drilling Project

Abstract. The long-term cooling trend from middle to late Eocene was punctuated by several large-scale climate perturbations that culminated in a shift to "icehouse" climates at the Eocene–Oligocene transition. We present radiolarian micro-fossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) sites 277, 280, 281, and 283 and Ocean Drilling Project (ODP) Site 1172 to identify significant oceanographic changes in the southwest Pacific through this climate transition (~ 40–30 Ma). We find that the Middle Eocene Climatic Optimum at ~ 40 Ma, which is truncated but identified by a negative shift in foraminiferal δ18O values at Site 277, is associated with a small increase in radiolarian taxa with low-latitude affinities (5 % of total fauna). In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift at Site 277 is correlated with the Priabonian Oxygen Isotope Maximum (PrOM). Radiolarian abundance, diversity, and preservation increase within this cooling event at Site 277 at the same time as diatom abundance. A negative δ18O excursion above the PrOM is correlated with a late Eocene warming event (~ 36.4 Ma). Radiolarian abundance and diversity decline within this event and taxa with low-latitude affinities reappear. Apart from this short-lived warming event, the PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and early Oligocene (~ 38–30 Ma) at DSDP sites 280, 281, 283 and 1172 and are associated with very high diatom abundance. We therefore infer a northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau in the latest Eocene. In the early Oligocene there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are scarce. These data indicate that, once the Antarctic Circumpolar Current was established in the early Oligocene (~ 30 Ma), a frontal system similar to present day developed, with nutrient-depleted Subantarctic waters bathing the area around DSDP Site 277, resulting in a more restricted siliceous plankton assemblage.

An Austral radiolarian biozonation for the Paleogene

Stratigraphy ◽  
2020 ◽  
pp. 213-278
Author(s):  
Christopher J. Hollis ◽  
Kristina M. Pascher ◽  
Annika Sanfilippo ◽  
Akiko Nishimura ◽  
Shin-ichi Kamikuri ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
High Latitude ◽  
Middle Eocene ◽  
Primary Study ◽  
Low Latitude ◽  
Sw Pacific ◽  
Index Species ◽  
Study Sites ◽  
Radiolarian Assemblages

ABSTRACT: We have integrated southern mid- and high-latitude (Austral) radiolarian biozonations with the well-established low-latitude (Tropical) biozonation using new biostratigraphic and magnetostratigraphic constraints on radiolarian bioevents in the Southwest (SW) Pacific, Southeast (SE) Indian and Northwest (NW) Atlantic Oceans. Our primary study sites include Mead Stream, New Zealand, and DSDP Sites 277 and 207 (SW Pacific; 45-54 degrees South at 50 Ma), ODP Site 752 and IODP Site U1514 (SE Indian; 50 degrees South at 50 Ma), and IODP Site U1403 (NW Atlantic; 30 degrees North at 50 Ma). The Austral and Tropical zonal schemes have been calibrated to GPTS2020. We introduce new zonal codes to rectify current confusion surrounding use of "RP" zones. Austral zones are codified as "RPA" zones and Tropical zones are codified as "RPT". Our study finds that radiolarian datums are generally isochronous within the mid-latitude SW Pacific and SE Indian Oceans from Paleocene to middle Eocene and are also isochronous in the high-latitude Southern Ocean (>60 degrees South paleolatitude) over the late middle Eocene to Oligocene interval of overlap. Older radiolarian assemblages are not known from the Southern Ocean. Early to middle Paleocene radiolarian assemblages in the SE Indian Ocean (zones RPA2-RPA5) differ from coeval SW Pacific assemblages by lacking significant numbers of Cretaceous survivors. The reasons for this difference are uncertain. Although the late Paleocene to Eocene radiolarian assemblages in the SW Pacific and SE Indian Ocean lack many low-latitude index species, the timing of Indian Ocean bioevents agrees better with low-latitude biozonations than the SW Pacific, suggesting a stronger connection with low-latitude watermasses. Assemblages from NW Atlantic IODP Site U1403 include numerous low-latitude index species and can be correlated with zones RPT6-RPT13. Many of the species transitions in biostratigraphically important Eocene lineages, however, occur later than in lower latitudes.

scholarly journals On the osteology and phylogenetic affinities of Morsoravis sedilis (Aves) from the early Eocene Fur Formation of Denmark

2011 ◽  
Vol 59 ◽  
pp. 23-35
Author(s):  
Gerald Mayr
Keyword(s):  
Phylogenetic Analysis ◽  
Middle Eocene ◽  
Original Description ◽  
Sister Group ◽  
Late Eocene ◽  
Sister Group Relationship ◽  
Early Eocene ◽  
Early Oligocene ◽  
Small Bird ◽  
Phylogenetic Affinities

Morsoravis sedilis is a small bird from the early Eocene Fur Formation of Denmark, which in the original description was considered to be most closely related to Charadriiformes. Because Morsoravis has subsequently been likened to Pumiliornis tesselatus, an equally enigmatic bird from the middle Eocene of Messel in Germany, I perform here the first phylogenetic analysis including the two taxa. This analysis supports a sister group relationship between Morsoravis and Pumiliornis, and the clade including the two taxa is recovered as the sister taxon of the late Eocene/early Oligocene Eocuculus.I report a possible, albeit lost, second specimen of Morsoravis, and identify derived characters in support of a sister group relationship between Morsoravis and Pumiliornis. The analysis did not resolve the higher-level affinities of the clade including Morsoravis, Pumiliornis, and Eocuculus, and did not confirm charadriiform affinities of Morsoravis. More data on the osteology of the fossils, as well as an improved understanding of the interrelationships of extant birds, are needed for a well-established phylogenetic assignment of these fossil taxa.

Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

1998 ◽  
Vol 11 (6) ◽  
pp. 711 ◽  
Author(s):  
Robert S. Hill ◽  
Leonie J. Scriven
Keyword(s):  
Leaf Morphology ◽  
Middle Eocene ◽  
Late Eocene ◽  
South Eastern ◽  
Early Oligocene ◽  
Extant Species ◽  
Eastern Australia ◽  
South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

Pre-Priabonian Palaeogene formations in southwestern Bulgaria and northern Greece: stratigraphy and tectonic implications

1998 ◽  
Vol 135 (1) ◽  
pp. 101-119 ◽  
Author(s):  
IVAN S. ZAGORCHEV
Keyword(s):  
Late Cretaceous ◽  
Middle Eocene ◽  
Regional Metamorphism ◽  
Late Eocene ◽  
Thin Layers ◽  
The South ◽  
Northern Greece ◽  
The North ◽  
Early Oligocene ◽  
Metamorphic Core

The Paril Formation (South Pirin and Slavyanka Mountains, southwestern Bulgaria) and the Prodromos Formation (Orvilos and Menikion Mountains, northern Greece) consist of breccia and olistostrome built up predominantly of marble fragments from the Precambrian Dobrostan Marble Formation (Bulgaria) and its equivalent Bos-Dag Marble Formation (Greece). The breccia and olistostrome are interbedded with thin layers of calcarenites (with occasional marble pebbles), siltstones, sandstones and limestones. The Paril and Prodromos formations unconformably cover the Precambrian marbles, and are themselves covered unconformably by Miocene and Pliocene sediments (Nevrokop Formation). The rocks of the Paril Formation are intruded by the Palaeogene (Late Eocene–Early Oligocene) Teshovo granitoid pluton, and are deformed and preserved in the two limbs of a Palaeogene anticline cored by the Teshovo pluton (Teshovo anticline). The Palaeocene–Middle Eocene age of the formations is based on these contact relations, and on occasional finds of Tertiary pollen, as well as on correlations with similar formations of the Laki (Kroumovgrad) Group throughout the Rhodope region.The presence of Palaeogene sediments within the pre-Palaeogene Pirin–Pangaion structural zone invalidates the concept of a ‘Rhodope metamorphic core complex’ that supposedly has undergone Palaeogene amphibolite-facies regional metamorphism, and afterwards has been exhumed by rapid crustal extension in Late Oligocene–Miocene times along a regional detachment surface. Other Palaeogene formations of pre-Priabonian (Middle Eocene and/or Bartonian) or earliest Priabonian age occur at the base of the Palaeogene sections in the Mesta graben complex (Dobrinishka Formation) and the Padesh basin (Souhostrel and Komatinitsa formations). The deposition of coarse continental sediments grading into marine formations (Laki or Kroumovgrad Group) in the Rhodope region at the beginning of the Palaeogene Period marks the first intense fragmentation of the mid- to late Cretaceous orogen, in particular, of the thickened body of the Morava-Rhodope structural zone situated to the south of the Srednogorie zone. The Srednogorie zone itself was folded and uplifted in Late Cretaceous time, thus dividing Palaeocene–Middle Eocene flysch of the Louda Kamchiya trough to the north, from the newly formed East Rhodope–West Thrace depression to the south.

The earliest bathymodiolin mussels: an evaluation of Eocene and Oligocene taxa from deep-sea methane seep deposits in western Washington State, USA

2013 ◽  
Vol 87 (4) ◽  
pp. 589-602 ◽  
Author(s):  
Steffen Kiel ◽  
Kazutaka Amano
Keyword(s):  
Deep Water ◽  
Deep Sea ◽  
Hydrothermal Vents ◽  
Middle Eocene ◽  
Late Eocene ◽  
Washington State ◽  
Methane Seep ◽  
Fossil Species ◽  
Early Oligocene ◽  
Western Washington

Bathymodiolin mussels are a group of bivalves associated with deep-sea hydrothermal vents and other reducing deep-sea habitats, and they have a particularly rich early Cenozoic fossil record in western Washington State, U.S.A. Here we recognize six species from middle Eocene to latest Oligocene deep-water methane seep deposits in western Washington. Two of them are new: Vulcanidas? goederti from the middle Eocene Humptulips Formation and Bathymodiolus (sensu lato) satsopensis from the late Oligocene part of the Lincoln Creek Formation. Very similar to the latter but more elongate are specimens from the early Oligocene Jansen Creek Member of the Makah Formation and are identified as B. (s.l.) aff. satsopensis. Bathymodiolus (s.l.) inouei Amano and Jenkins, 2011 is reported from the Lincoln Creek Formation. Idas? olympicus Kiel and Goedert, 2007 was previously known from late Eocene to Oligocene whale and wood falls in western Washington and is here reported from Oligocene seep deposits of the Makah and Pysht Formations. Vulcanidas? goederti occurs at a seep deposit from a paleodepth possibly as great as 2000 m, suggesting that its living relative, Vulcanidas insolatus Cosel and Marshall, 2010, which lives at depths of only 150–500 m, is derived from a deep-water ancestor. The bathymodiolins in western Washington indicate that the group originated at least in the middle Eocene and underwent a first diversification in the late Eocene to Oligocene. Early ontogenetic shells of all fossil species investigated so far, including the middle Eocene Vulcanidas? goederti, reflect planktotrophic larval development indicating that this developmental mode is an ancestral trait of bathymodiolins.

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