early oligocene
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An integrative taxonomic revision of slug-eating snakes (Squamata: Pareidae: Pareineae) reveals unprecedented diversity in Indochina
Slug-eating snakes of the subfamily Pareinae are an insufficiently studied group of snakes specialized in feeding on terrestrial mollusks. Currently Pareinae encompass three genera with 34 species distributed across the Oriental biogeographic region. Despite the recent significant progress in understanding of Pareinae diversity, the subfamily remains taxonomically challenging. Here we present an updated phylogeny of the subfamily with a comprehensive taxon sampling including 30 currently recognized Pareinae species and several previously unknown candidate species and lineages. Phylogenetic analyses of mtDNA and nuDNA data supported the monophyly of the three genera Asthenodipsas, Aplopeltura, and Pareas. Within both Asthenodipsas and Pareas our analyses recovered deep differentiation with each genus being represented by two morphologically diagnosable clades, which we treat as subgenera. We further apply an integrative taxonomic approach, including analyses of molecular and morphological data, along with examination of available type materials, to address the longstanding taxonomic questions of the subgenus Pareas, and reveal the high level of hidden diversity of these snakes in Indochina. We restrict the distribution of P. carinatus to southern Southeast Asia, and recognize two subspecies within it, including one new subspecies proposed for the populations from Thailand and Myanmar. We further revalidate P. berdmorei, synonymize P. menglaensis with P. berdmorei, and recognize three subspecies within this taxon, including the new subspecies erected for the populations from Laos and Vietnam. Furthermore, we describe two new species of Pareas from Vietnam: one belonging to the P. carinatus group from southern Vietnam, and a new member of the P. nuchalis group from the central Vietnam. We provide new data on P. temporalis, and report on a significant range extension for P. nuchalis. Our phylogeny, along with molecular clock and ancestral area analyses, reveal a complex diversification pattern of Pareinae involving a high degree of sympatry of widespread and endemic species. Our analyses support the “upstream” colonization hypothesis and, thus, the Pareinae appears to have originated in Sundaland during the middle Eocene and then colonized mainland Asia in early Oligocene. Sundaland and Eastern Indochina appear to have played the key roles as the centers of Pareinae diversification. Our results reveal that both vicariance and dispersal are responsible for current distribution patterns of Pareinae, with tectonic movements, orogeny and paleoclimatic shifts being the probable drivers of diversification. Our study brings the total number of Pareidae species to 41 and further highlights the importance of comprehensive taxonomic revisions not only for the better understanding of biodiversity and its evolution, but also for the elaboration of adequate conservation actions.
A new species Lepidozona luzanovkensis sp. nov. from Paleocene deposits of Ukraine is described. This find is much earlier than the known finds from the late Eocene or Early Oligocene, which increases the age of the genus Lepidozona Pilsbry, 1892 by several million years.
Ding et al. (Science 2020) proposed that the extant lineages of the alpine flora of the Tibet Himalaya Hengduan region emerged by the early Oligocene. We argue that these results are based on misclassifying high montane taxa as alpine and that their data support alpine habitats only at about 7.5 mio years before present.
Rare earth elements and yttrium (REY) are widely recognized as strategic materials for advanced technological applications. Deep-sea sediments from the eastern South Pacific and central North Pacific were first reported as potential resources containing significant amounts of REY that are comparable to, or greater than, those of land-based deposits. Despite nearly a decade of research, quantitative abundances and spatial distributions of these deposits remain insufficient. Age controls are generally absent due to the lack of biostratigraphic constraints. Thus, the factors controlling the formation of REY-rich sediments are still controversial. In this study, the REY contents of surface sediments (<2 m depth) in 14 piston cores from the Middle and Western Pacific were investigated. The results show that deep-sea sediments with high REY contents (>1000 μg/g) were mainly concentrated around seamounts (e.g., the Marshall Islands). The REY contents of surface sediments generally decreased with distance from the seamounts. Biostratigraphic and fish teeth debris (apatite) Sr isotopic stratigraphy of one piston cores (P10) from the Middle Pacific indicate that deep-sea sediments with high REY contents were aged from early Oligocene to early Miocene. Since the opening of the Drake Passage during the early Oligocene, the northward-flowing Antarctic Bottom Water (AABW) would have led to an upwelling of nutrients around seamounts with topographic barriers, and at the same time, AABW would delay the rate of sediment burial to try for enough time for REY entering and enriching in the apatite (fish teeth debris). Understanding the spatial distribution of fertile regions for REY-rich sediments provides guidance for searching for other REY resources in the Pacific and in other oceans.
<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>
<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>
<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>
<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>
<p>The Antarctic and Southern Ocean is an area that was greatly affected by climatic changes during the Middle Eocene to Early Oligocene (E/O). This study aims to document climate-induced changes of the marine palynomorphs (mostly dinoflagellate cysts) by developing a Circum-Antarctic biozonation, and establishing the distribution and effects of cooling on the palynomorph assemblages and the palaeoenvironment. Samples were obtained from four sites by the Ocean Drilling Program (ODP) and Deep Sea Drilling Project (DSDP) and the palynological content was analyzed. These sites were selected as they may record effects of circulation changes and cooling trends, reflecting climate changes. ODP site 696B, was inner neritic and located in the South Orkney microcontinent, Weddell Sea. The other three sites were pelagic with ODP 699A located on the Northeast Georgia Rise, Falklands, ODP 748B located in the Western part of the Raggart Basin, Kerguelen Plateau and DSDP 277 located in Cathedral Depression on the Southern Campbell Plateau. From this analysis a comprehensive record of the local climatic transitions was ascertained, utilising assemblages of fossil organic-walled dinoflagellate cysts (dinocysts), acritarchs, prasinophyte algae, microforaminiferal linings, scoledonts and terrestrial material. The establishment of a standard nannofossil biostratigraphy provided a temporal framework of the marine palynomorphs in each site. Key dinocyst datums recognised as first or last occurrences that correlated reliably between sites, were compared with the nannofossil zones of each site. The purpose was to provide a Middle Eocene/Early Oligocene dinocyst biostratigraphy that temporally constrains the assemblages. Six primary datums and two secondary datums resulted, which lead to the recognition of four biozones and established a new biozonation in the Southern Ocean. The zones identified various dinocyst events, giving an indication of their probable palaeoenvironments. The Circum-Antarctic distribution pattern of palynomorph assemblages was documented in each site as a total abundance of grains per gram. The ranges and composition of palynomorph assemblages of each site were displayed as a percentage of total abundance. To document any cooling effects the dinocysts were separated into Gonyaulacoid or Peridinioid assemblages to best illustrate their preferred palaeoenvironment. Key findings showed that the pelagic and inner neritic sites differed greatly. Site 696B was the most climatically stable site and dominated by Peridinioid dinocysts which are predominantly heterotrophic. They are most common in an inner neritic palaeoenvironment, but are also present in nutrient upwellings and eutrophic surface waters with lower sea surface temperatures. Terrestrial material dominates all marine palynomorphs in this site which was shallow and warm with few changes up to the E/O boundary ~33.7 Ma, but became more variable in the Early Oligocene. In comparison, the pelagic sites (699, 748B, 277) were unstable, with missing or condensed sediments and no palynomorphs present at differing times. They were mostly dominated by Gonyaulacoid dinocysts, which are autotrophs and generally located in outer neritic to open ocean palaeoenvironments. The non dinocysts of Prasinophyte algae and Leiosphaeridia palynomorphs appeared in higher abundances in the pelagic sites than in the inner neritic sites. Specific dinocyst markers identified temperature changes within the pelagic sites, subsequently highlighting the climatic changes that occurred during the Middle Eocene/Early Oligocene. From ~46 Ma the pelagic sites recorded conditions that were oceanic and cooler. Between ~44 - ~41.5 Ma, a warming in site 748B indicated enhanced stratification and elevated nutrient availability. This was not the case in site 696B and may be due to warm temperatures already present. From ~41.4 Ma the pelagic sites showed that the palaeoenvironment continued to cool, indicated by the presence of Leiosphaeridia and Prasinophyte algae. The palaeoenvironment was oceanic with upwelling and offshore sea surface productivity, illustrated by the Gonyaulacoid and Peridinioid dinocysts present. During the Late Eocene from ~37 Ma a transitional and changeable palaeoenvironment was shown by the high numbers of Operculodinium spp present in sites 696B and 277. From ~33.7 Ma (E/O boundary) in the pelagic sites, most Peridinioid dinocysts had disappeared and very few Gonyaulacoid dinocysts were present. In contrast the inner neritic site (696B) Peridinioid dinocysts were still dominant, and a more gradual disappearance of all the marine palynomorphs was evident.</p>
<p>The Antarctic and Southern Ocean is an area that was greatly affected by climatic changes during the Middle Eocene to Early Oligocene (E/O). This study aims to document climate-induced changes of the marine palynomorphs (mostly dinoflagellate cysts) by developing a Circum-Antarctic biozonation, and establishing the distribution and effects of cooling on the palynomorph assemblages and the palaeoenvironment. Samples were obtained from four sites by the Ocean Drilling Program (ODP) and Deep Sea Drilling Project (DSDP) and the palynological content was analyzed. These sites were selected as they may record effects of circulation changes and cooling trends, reflecting climate changes. ODP site 696B, was inner neritic and located in the South Orkney microcontinent, Weddell Sea. The other three sites were pelagic with ODP 699A located on the Northeast Georgia Rise, Falklands, ODP 748B located in the Western part of the Raggart Basin, Kerguelen Plateau and DSDP 277 located in Cathedral Depression on the Southern Campbell Plateau. From this analysis a comprehensive record of the local climatic transitions was ascertained, utilising assemblages of fossil organic-walled dinoflagellate cysts (dinocysts), acritarchs, prasinophyte algae, microforaminiferal linings, scoledonts and terrestrial material. The establishment of a standard nannofossil biostratigraphy provided a temporal framework of the marine palynomorphs in each site. Key dinocyst datums recognised as first or last occurrences that correlated reliably between sites, were compared with the nannofossil zones of each site. The purpose was to provide a Middle Eocene/Early Oligocene dinocyst biostratigraphy that temporally constrains the assemblages. Six primary datums and two secondary datums resulted, which lead to the recognition of four biozones and established a new biozonation in the Southern Ocean. The zones identified various dinocyst events, giving an indication of their probable palaeoenvironments. The Circum-Antarctic distribution pattern of palynomorph assemblages was documented in each site as a total abundance of grains per gram. The ranges and composition of palynomorph assemblages of each site were displayed as a percentage of total abundance. To document any cooling effects the dinocysts were separated into Gonyaulacoid or Peridinioid assemblages to best illustrate their preferred palaeoenvironment. Key findings showed that the pelagic and inner neritic sites differed greatly. Site 696B was the most climatically stable site and dominated by Peridinioid dinocysts which are predominantly heterotrophic. They are most common in an inner neritic palaeoenvironment, but are also present in nutrient upwellings and eutrophic surface waters with lower sea surface temperatures. Terrestrial material dominates all marine palynomorphs in this site which was shallow and warm with few changes up to the E/O boundary ~33.7 Ma, but became more variable in the Early Oligocene. In comparison, the pelagic sites (699, 748B, 277) were unstable, with missing or condensed sediments and no palynomorphs present at differing times. They were mostly dominated by Gonyaulacoid dinocysts, which are autotrophs and generally located in outer neritic to open ocean palaeoenvironments. The non dinocysts of Prasinophyte algae and Leiosphaeridia palynomorphs appeared in higher abundances in the pelagic sites than in the inner neritic sites. Specific dinocyst markers identified temperature changes within the pelagic sites, subsequently highlighting the climatic changes that occurred during the Middle Eocene/Early Oligocene. From ~46 Ma the pelagic sites recorded conditions that were oceanic and cooler. Between ~44 - ~41.5 Ma, a warming in site 748B indicated enhanced stratification and elevated nutrient availability. This was not the case in site 696B and may be due to warm temperatures already present. From ~41.4 Ma the pelagic sites showed that the palaeoenvironment continued to cool, indicated by the presence of Leiosphaeridia and Prasinophyte algae. The palaeoenvironment was oceanic with upwelling and offshore sea surface productivity, illustrated by the Gonyaulacoid and Peridinioid dinocysts present. During the Late Eocene from ~37 Ma a transitional and changeable palaeoenvironment was shown by the high numbers of Operculodinium spp present in sites 696B and 277. From ~33.7 Ma (E/O boundary) in the pelagic sites, most Peridinioid dinocysts had disappeared and very few Gonyaulacoid dinocysts were present. In contrast the inner neritic site (696B) Peridinioid dinocysts were still dominant, and a more gradual disappearance of all the marine palynomorphs was evident.</p>
