Abstract. Species of the fusiform peridiniacean dinoflagellate cyst genera Svalbardella Manum, 1960, emend. (Eocene–Oligocene) and Palaeocystodinium Alberti, 1961 (Late Cretaceous–Miocene), have been examined from the high to middle latitudes of the Northern Hemisphere: Spitsbergen, Norwegian-Greenland Sea, Labrador Sea, western North Atlantic, and the North Sea basin. The genus Svalbardella is emended to comprise species with smooth or finely ornamented surfaces and for which one or both horns are bluntly rounded. Svalbardella clausii sp. nov. has a narrow range restricted to the lowermost Chattian (close to the NP24–NP25 boundary and within Chron C9n), and it therefore appears a useful stratigraphical marker. This species has a wide distribution across the North Atlantic, having been reported from the North Sea basin, western North Atlantic, and the Labrador Sea. Svalbardella clausii sp. nov. overlaps stratigraphically with the reoccurrence interval of Svalbardella cooksoniae Manum, 1960, and spans the Oi-2b cooling maximum. Its presence may therefore be related to the establishment of cooler surface waters at this time. Svalbardella kareniae sp. nov. has a discordant occurrence: Lower Oligocene and Lower Miocene of the Norwegian Sea at Deep Sea Drilling Project Site 338 and Ocean Drilling Program Site 643, respectively, and mid-Oligocene of the North Sea. Its distribution suggests that Svalbardella kareniae sp. nov. favours more open marine conditions. Palaeocystodinium obesum Fensome et al., 2009, described from offshore eastern Canada where it has a highest occurrence in the Lower Oligocene, is emended to include specimens with a finely ornamented periphragm and traces of tabulation in addition to the archeopyle.
{"title":"New species of the dinoflagellate cyst genus Svalbardella Manum, 1960, emend. from the Paleogene and Neogene of the northern high to middle latitudes","authors":"K. Śliwińska, M. Head","doi":"10.5194/jm-39-139-2020","DOIUrl":"https://doi.org/10.5194/jm-39-139-2020","url":null,"abstract":"Abstract. Species of the fusiform peridiniacean dinoflagellate cyst\u0000genera Svalbardella Manum, 1960, emend. (Eocene–Oligocene) and Palaeocystodinium Alberti, 1961\u0000(Late Cretaceous–Miocene), have been examined from the high to middle\u0000latitudes of the Northern Hemisphere: Spitsbergen, Norwegian-Greenland Sea,\u0000Labrador Sea, western North Atlantic, and the North Sea basin. The genus\u0000Svalbardella is emended to comprise species with smooth or finely ornamented surfaces\u0000and for which one or both horns are bluntly rounded. Svalbardella clausii sp. nov. has a narrow\u0000range restricted to the lowermost Chattian (close to the NP24–NP25 boundary\u0000and within Chron C9n), and it therefore appears a useful stratigraphical\u0000marker. This species has a wide distribution across the North Atlantic,\u0000having been reported from the North Sea basin, western North Atlantic, and\u0000the Labrador Sea. Svalbardella clausii sp. nov. overlaps stratigraphically with the reoccurrence\u0000interval of Svalbardella cooksoniae Manum, 1960, and spans the Oi-2b cooling maximum. Its presence\u0000may therefore be related to the establishment of cooler surface waters at\u0000this time. Svalbardella kareniae sp. nov. has a discordant occurrence: Lower Oligocene and Lower\u0000Miocene of the Norwegian Sea at Deep Sea Drilling Project Site 338 and Ocean\u0000Drilling Program Site 643, respectively, and mid-Oligocene of the North Sea.\u0000Its distribution suggests that Svalbardella kareniae sp. nov. favours more open marine\u0000conditions. Palaeocystodinium obesum Fensome et al., 2009, described from offshore eastern Canada\u0000where it has a highest occurrence in the Lower Oligocene, is emended to\u0000include specimens with a finely ornamented periphragm and traces of\u0000tabulation in addition to the archeopyle.","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47591646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The aim of this paper is to document three well-preserved morphotypes of Middle Jurassic (Bajocian) planktonic foraminifera from the continental margin of northwestern Australia. This location is on the southern shelf of the Middle Jurassic Tethys Ocean, and these occurrences of planktonic or meroplanktonic species are the first to be reported from the Jurassic of the Southern Hemisphere. The morphotypes include a new subspecies of Globuligerina bathoniana (Pazdrowa): Globuligerina bathoniana australiana n. ssp. Two other taxa are also described: Globuligerina altissapertura n. sp. and Mermaidogerina loopae n. gen. n. sp. The microstructure of the wall is shown in scanning electron microscope images. The change from chamber to chamber in the formation of the surface ornament by secondary lamination, and its subsequent burial within the wall, is demonstrated in detail.
摘要本文的目的是记录来自澳大利亚西北部大陆边缘的中侏罗世(巴荷世)浮游有孔虫的三种保存完好的形态类型。这个位置位于中侏罗世特提斯洋的南陆架上，这些浮游生物或浮游生物物种的出现是南半球侏罗纪的第一次报道。形态类型包括一种新亚种:Globuligerina bathoniana australiana n.ssp。另外还描述了两个分类群:Globuligerina altissapertura n. sp和Mermaidogerina loopae n. gen. n. sp。扫描电镜图像显示了壁的微观结构。从墓室到墓室，通过二次层压形成的表面装饰的变化，以及随后在墙壁内的埋藏，都被详细地展示出来。
{"title":"Middle Jurassic (Bajocian) planktonic foraminifera from the northwest Australian margin","authors":"M. Apthorpe","doi":"10.5194/jm-39-93-2020","DOIUrl":"https://doi.org/10.5194/jm-39-93-2020","url":null,"abstract":"Abstract. The aim of this paper is to document three\u0000well-preserved morphotypes of Middle Jurassic (Bajocian) planktonic\u0000foraminifera from the continental margin of northwestern Australia. This\u0000location is on the southern shelf of the Middle Jurassic Tethys Ocean, and\u0000these occurrences of planktonic or meroplanktonic species are the first to\u0000be reported from the Jurassic of the Southern Hemisphere. The morphotypes\u0000include a new subspecies of Globuligerina bathoniana (Pazdrowa): Globuligerina bathoniana australiana n. ssp. Two other taxa are also\u0000described: Globuligerina altissapertura n. sp. and Mermaidogerina loopae n. gen. n. sp. The microstructure of the wall is\u0000shown in scanning electron microscope images. The change from chamber to\u0000chamber in the formation of the surface ornament by secondary lamination,\u0000and its subsequent burial within the wall, is demonstrated in detail.","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43037545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Knowledge of past variations in sea-ice extent is crucial for understanding the relationship between climate change and changes in sea ice. Diatom assemblages could be applied as a proxy for paleo-sea-ice extent; this requires accurate information on the modern species that are indicative of sea ice. Scanning electron microscope observations were performed on modern diatom assemblages in sea ice, sinking particles, and surface sediments in the Sea of Okhotsk. A sea-ice sample was collected in the southwestern Sea of Okhotsk near Hokkaido island in February 2013. Fragilariopsis cylindrus was the dominant diatom species in the sea-ice sample, accounting for 87 % of the total diatom assemblage. Time-series sediment traps were deployed during 1998–2000 at two stations, M4 and M6, off Sakhalin island. Total diatom fluxes ranged from 105 to 108 valves m−2 d−1 with noticeable seasonality. During the sea-ice covering period, the total diatom flux decreased by 1 or 2 orders of magnitude. The highest diatom fluxes were observed in spring and summer. The diatom species composition in sinking particles also showed pronounced seasonal changes. During summer and fall, the Shionodiscus trifultus group and Neodenticula seminae were the major diatom taxa. During the sea-ice covering period, Fragilariopsis cylindrus and Bacterosira bathyomphala resting spores were abundant. Both the sea-ice-related species showed similar flux patterns except for the spring bloom after sea-ice retreat: F. cylindrus fluxes exhibited pronounced spring bloom peaks of 108 valves m−2 d−1; in contrast, the fluxes of Bacterosira bathyomphala resting spores during the spring bloom were 1 order of magnitude lower than those of F. cylindrus. Surface-sediment core XP98-MC4 was obtained near station M6 sediment-trap site off Sakhalin island. The relative abundance of Fragilariopsis cylindrus in the surface-sediment diatom assemblage was only 6.4 %, markedly lower than that in the sediment-trap samples (43.4 %). In the surface sediment, the relative abundances of diatom taxa with heavily silicified valves such as B. bathyomphala resting spores, Shionodiscus variantius, and Thalassionema nitzschioides were greater than their relative abundances in sinking particles.
{"title":"An assessment of diatom assemblages in the Sea of Okhotsk as a proxy for sea-ice cover","authors":"H. Nakamura, Y. Okazaki, S. Konno, T. Nakatsuka","doi":"10.5194/jm-39-77-2020","DOIUrl":"https://doi.org/10.5194/jm-39-77-2020","url":null,"abstract":"Abstract. Knowledge of past variations in sea-ice extent is crucial\u0000for understanding the relationship between climate change and changes in\u0000sea ice. Diatom assemblages could be applied as a proxy for paleo-sea-ice\u0000extent; this requires accurate information on the modern species that are\u0000indicative of sea ice. Scanning electron microscope observations were\u0000performed on modern diatom assemblages in sea ice, sinking particles, and\u0000surface sediments in the Sea of Okhotsk. A sea-ice sample was collected in the\u0000southwestern Sea of Okhotsk near Hokkaido island in February 2013.\u0000Fragilariopsis cylindrus was the dominant diatom species in the sea-ice sample, accounting for 87 % of the total diatom assemblage. Time-series sediment traps were\u0000deployed during 1998–2000 at two stations, M4 and M6, off Sakhalin island.\u0000Total diatom fluxes ranged from 105 to 108 valves m−2 d−1 with noticeable seasonality. During the sea-ice covering period,\u0000the total diatom flux decreased by 1 or 2 orders of magnitude. The highest\u0000diatom fluxes were observed in spring and summer. The diatom species\u0000composition in sinking particles also showed pronounced seasonal changes.\u0000During summer and fall, the Shionodiscus trifultus group and Neodenticula seminae were the major diatom taxa. During the\u0000sea-ice covering period, Fragilariopsis cylindrus and Bacterosira bathyomphala resting spores were abundant. Both the\u0000sea-ice-related species showed similar flux patterns except for the spring\u0000bloom after sea-ice retreat: F. cylindrus fluxes exhibited pronounced spring bloom peaks\u0000of 108 valves m−2 d−1; in contrast, the fluxes of\u0000Bacterosira bathyomphala resting spores during the spring bloom were 1 order of magnitude lower than\u0000those of F. cylindrus. Surface-sediment core XP98-MC4 was obtained near station M6 sediment-trap site off Sakhalin island. The relative abundance of\u0000Fragilariopsis cylindrus in the surface-sediment diatom assemblage was only 6.4 %, markedly lower\u0000than that in the sediment-trap samples (43.4 %). In the surface sediment,\u0000the relative abundances of diatom taxa with heavily silicified valves such\u0000as B. bathyomphala resting spores, Shionodiscus variantius, and Thalassionema nitzschioides were greater than their relative abundances in\u0000sinking particles.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48930636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. X-ray micro-computed tomography (micro-CT) is used to resolve the detailed internal architecture of the siliceous skeletons of two well-preserved middle Cambrian (Miaolingian Series) radiolarians from the Inca Formation of the Georgina Basin, Australia. Digital dissections of specimens of Archeoentactinia incaensis and A. tetractinia reveal for the first time that both are exclusively composed of tetractine spicules. A basal layer consisting of robust spicules together with an interwoven meshwork of smaller spicules is observed in both micro-CT models. Detailed structural analysis with the aid of a digitally inserted artificial sphere shows that the framework spicules are likely to have been added one by one as the radiolarian cell enlarged. The timing of spicule genesis may be an important factor controlling the morphology of different groups of spicular radiolarians. Observation of these fundamental skeletal structures suggests that the type genus of Archeoentactiniidae Archeoentactinia belongs to Echidninidae; thus, Archeoentactiniidae is a junior synonym of Echidninidae.
{"title":"Skeletal architecture of middle Cambrian spicular radiolarians revealed using micro-CT","authors":"Jiani Sheng, S. Kachovich, J. Aitchison","doi":"10.5194/jm-39-61-2020","DOIUrl":"https://doi.org/10.5194/jm-39-61-2020","url":null,"abstract":"Abstract. X-ray micro-computed tomography (micro-CT) is used to\u0000resolve the detailed internal architecture of the siliceous skeletons of two\u0000well-preserved middle Cambrian (Miaolingian Series) radiolarians from the\u0000Inca Formation of the Georgina Basin, Australia. Digital dissections of\u0000specimens of Archeoentactinia incaensis and A. tetractinia\u0000reveal for the first time that both are exclusively\u0000composed of tetractine spicules. A basal layer consisting of robust spicules\u0000together with an interwoven meshwork of smaller spicules is observed in both\u0000micro-CT models. Detailed structural analysis with the aid of a digitally\u0000inserted artificial sphere shows that the framework spicules are likely to\u0000have been added one by one as the radiolarian cell enlarged. The timing of\u0000spicule genesis may be an important factor controlling the morphology of\u0000different groups of spicular radiolarians. Observation of these fundamental\u0000skeletal structures suggests that the type genus of Archeoentactiniidae Archeoentactinia\u0000belongs to Echidninidae; thus, Archeoentactiniidae is a junior synonym of\u0000Echidninidae.","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45701992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. We have analyzed marine palynomorphs (mainly dinocysts and acritarchs) from the Integrated Ocean Drilling Program Site U1307 in the Labrador Sea in order to establish a detailed biostratigraphy for the Late Pliocene to Early Pleistocene. We have defined three magnetostratigraphically calibrated dinocyst and acritarch biozones in the Late Pliocene to Early Pleistocene. Zone LS1 is defined based on the highest occurrence of Barssidinium graminosum and covers the later Pliocene from 3.21 to 2.75 Ma. Zone LS2 is marked by the acme of Pyxidinopsis braboi which occurs between 2.75 and 2.57 Ma, thus encompassing the Plio–Pleistocene transition. Finally, zone LS3 extends from 2.57 to 2.23 Ma in the Early Pleistocene. The palynostratigraphic record of IODP Site U1307 is difficult to correlate to other North Atlantic and Nordic Seas sites mainly because of a different temporal resolution and a lack of well-defined biostratigraphic marker species at the basin scale. The low abundance, discontinuous occurrence and asynchronous events of warm-water Pliocene taxa such as Invertocysta lacrymosa, Impagidinium solidum, Ataxiodinium confusum, Melitasphaeridium choanophorum and Operculodinium? eirikianum suggest cooler conditions in the Labrador Sea than elsewhere in the North Atlantic, reflecting a strong regionalism. Nevertheless, as recorded at other locations in the North Atlantic, the disappearance of many dinocyst and acritarch taxa around 2.75 Ma at Site U1307 reflects a strong ecological response accompanying the intensification of the Northern Hemisphere glaciation.
{"title":"Dinocyst and acritarch biostratigraphy of the Late Pliocene to Early Pleistocene at Integrated Ocean Drilling Program Site U1307 in the Labrador Sea","authors":"A. Aubry, S. De Schepper, A. de Vernal","doi":"10.5194/jm-39-41-2020","DOIUrl":"https://doi.org/10.5194/jm-39-41-2020","url":null,"abstract":"Abstract. We have analyzed marine palynomorphs (mainly dinocysts and\u0000acritarchs) from the Integrated Ocean Drilling Program Site U1307 in the\u0000Labrador Sea in order to establish a detailed biostratigraphy for the Late\u0000Pliocene to Early Pleistocene. We have defined three\u0000magnetostratigraphically calibrated dinocyst and acritarch biozones in the\u0000Late Pliocene to Early Pleistocene. Zone LS1 is defined based on the highest\u0000occurrence of Barssidinium graminosum and covers the later Pliocene from 3.21 to 2.75 Ma. Zone LS2\u0000is marked by the acme of Pyxidinopsis braboi which occurs between 2.75 and 2.57 Ma, thus\u0000encompassing the Plio–Pleistocene transition. Finally, zone LS3 extends from\u00002.57 to 2.23 Ma in the Early Pleistocene. The palynostratigraphic record of IODP Site U1307 is difficult to correlate\u0000to other North Atlantic and Nordic Seas sites mainly because of a different\u0000temporal resolution and a lack of well-defined biostratigraphic marker species\u0000at the basin scale. The low abundance, discontinuous occurrence and asynchronous\u0000events of warm-water Pliocene taxa such as Invertocysta lacrymosa, Impagidinium solidum, Ataxiodinium confusum, Melitasphaeridium choanophorum and Operculodinium? eirikianum suggest cooler conditions in\u0000the Labrador Sea than elsewhere in the North Atlantic, reflecting a strong\u0000regionalism. Nevertheless, as recorded at other locations in the North\u0000Atlantic, the disappearance of many dinocyst and acritarch taxa around 2.75 Ma at Site U1307 reflects a strong ecological response accompanying the\u0000intensification of the Northern Hemisphere glaciation.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44571033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Kendall, F. Gradstein, Christopher Jones, Oliver Thomas Lord, D. Schmidt
Abstract. Changes in morphology during ontogeny can have profound impacts on the physiology and biology of a species. Studies of ontogenetic disparity through time are rare because of the lack of preservation of developmental stages in the fossil record. As they grow by incremental chamber accretion and retain evidence of growth in their shell, planktic foraminifera are an ideal group for the study ontogenetic disparity through the evolution of a higher taxon. Here, we quantify different developmental stages in Jurassic foraminifers and infer the evolutionary implications of the shape of these earliest representatives of the group. Using a Zeiss Xradia micro-CT scanner, the development of Globuligerina bathoniana and Globuligerina oxfordiana from the Bathonian sediments of Gnaszyn, Poland, and Globuligerina balakhmatovae and Globuligerina tojeiraensis from the Kimmeridgian Tojeira Formation of Portugal was reconstructed. Disparity is low through the early evolution of planktic foraminifers. The number of chambers and range in surface area per unit volume are lower than in modern specimens. We interpret this morphology as an indication of opportunistic behaviour. The low morphological plasticity during the juvenile stage suggests that strong constraints on the juveniles, described in the modern ocean, were already acting on Jurassic specimens. The high surface area per unit volume in these developmental stages points towards the need to satisfy a higher metabolic demand than in the adult specimens. We are interpreting the lower chamber numbers as indicative of short life cycles and potentially rapid reproduction, both of which may have allowed these species to exploit the nutrient-rich waters of the Jurassic Tethys Ocean.
{"title":"Ontogenetic disparity in early planktic foraminifers","authors":"S. Kendall, F. Gradstein, Christopher Jones, Oliver Thomas Lord, D. Schmidt","doi":"10.5194/jm-39-27-2020","DOIUrl":"https://doi.org/10.5194/jm-39-27-2020","url":null,"abstract":"Abstract. Changes in morphology during ontogeny can have profound\u0000impacts on the physiology and biology of a species. Studies of ontogenetic\u0000disparity through time are rare because of the lack of preservation of\u0000developmental stages in the fossil record. As they grow by incremental\u0000chamber accretion and retain evidence of growth in their shell, planktic\u0000foraminifera are an ideal group for the study ontogenetic disparity through\u0000the evolution of a higher taxon. Here, we quantify different developmental\u0000stages in Jurassic foraminifers and infer the evolutionary implications of\u0000the shape of these earliest representatives of the group. Using a Zeiss Xradia\u0000micro-CT scanner, the development of Globuligerina bathoniana and Globuligerina oxfordiana from the Bathonian sediments of\u0000Gnaszyn, Poland, and Globuligerina balakhmatovae and Globuligerina tojeiraensis from the Kimmeridgian Tojeira Formation of Portugal\u0000was reconstructed. Disparity is low through the early evolution of planktic\u0000foraminifers. The number of chambers and range in surface area per unit\u0000volume are lower than in modern specimens. We interpret this morphology as an\u0000indication of opportunistic behaviour. The low morphological plasticity\u0000during the juvenile stage suggests that strong constraints on the juveniles,\u0000described in the modern ocean, were already acting on Jurassic specimens.\u0000The high surface area per unit volume in these developmental stages points\u0000towards the need to satisfy a higher metabolic demand than in the adult\u0000specimens. We are interpreting the lower chamber numbers as indicative of\u0000short life cycles and potentially rapid reproduction, both of which may have\u0000allowed these species to exploit the nutrient-rich waters of the Jurassic\u0000Tethys Ocean.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42469866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Edgar, S. Bohaty, H. Coxall, P. Bown, S. Batenburg, C. Lear, P. Pearson
Abstract. The Middle Eocene Climatic Optimum (MECO) at ca. 40 Ma is one of the largest of the transient Eocene global warming events. However, it is relatively poorly known from tropical settings since few sites span the entirety of the MECO event and/or host calcareous microfossils, which are the dominant proxy carrier for palaeoceanographic reconstructions. Ocean Drilling Program (ODP) Pacific Ocean Site 865 in the low-latitude North Pacific (Allison Guyot) has the potential to provide a useful tropical MECO reference, but detailed stratigraphic and chronological constraints needed to evaluate its completeness were previously lacking. We have addressed this deficit by generating new high-resolution biostratigraphic, stable isotope, and X-ray fluorescence (XRF) records spanning the MECO interval (∼38.0–43.0 Ma) in two holes drilled at Site 865. XRF-derived strontium ∕ calcium (Sr∕Ca) and barium ∕ strontium (Ba∕Sr) ratios and Fe count records allow correlation between holes and reveal pronounced rhythmicity, enabling us to develop the first composite section for Holes 865B and 865C and a preliminary cyclostratigraphy for the MECO. Using this new framework, the sedimentary record is interpreted to be continuous across the event, as identified by a pronounced transient benthic foraminiferal δ18O shift of ∼0.8 ‰. Calcareous microfossil biostratigraphic events from widely used zonation schemes are recognized, with generally good agreement between the two holes, highlighting the robustness of the new composite section and allowing us to identify planktic foraminiferal Zones E10–E15 and calcareous nannofossil Zones NP15–18. However, discrepancies in the relative position and ordering of several primary and secondary bioevents with respect to published schemes are noted. Specifically, the stratigraphic highest occurrences of planktic foraminifera, Acarinina bullbrooki, Guembelitrioides nuttalli, and Morozovella aragonensis, and calcareous nannofossils, Chiasmolithus solitus and Sphenolithus furcatolithoides, and the lowest occurrence of Reticulofenestra reticulata all appear higher in the section than would be predicted relative to other bioevents. We also note conspicuous reworking of older microfossils (from planktic foraminiferal Zones E5–E9 and E13) into younger sediments (planktic foraminiferal Zones E14–15) within our study interval consistent with reworking above the MECO interval. Regardless of reworking, the high-quality XRF records enable decimetre-scale correlation between holes and highlight the potential of Site 865 for constraining tropical environmental and biotic changes, not just across the MECO but also throughout the Palaeocene and early-to-middle Eocene interval.
{"title":"New composite bio- and isotope stratigraphies spanning the Middle Eocene Climatic Optimum at tropical ODP Site 865 in the Pacific Ocean","authors":"K. Edgar, S. Bohaty, H. Coxall, P. Bown, S. Batenburg, C. Lear, P. Pearson","doi":"10.31223/osf.io/m64gk","DOIUrl":"https://doi.org/10.31223/osf.io/m64gk","url":null,"abstract":"Abstract. The Middle Eocene Climatic Optimum (MECO) at ca. 40 Ma is one of the largest of\u0000the transient Eocene global warming events. However, it is relatively poorly\u0000known from tropical settings since few sites span the entirety of the MECO\u0000event and/or host calcareous microfossils, which are the dominant proxy\u0000carrier for palaeoceanographic reconstructions. Ocean Drilling Program (ODP)\u0000Pacific Ocean Site 865 in the low-latitude North Pacific (Allison Guyot) has\u0000the potential to provide a useful tropical MECO reference, but detailed\u0000stratigraphic and chronological constraints needed to evaluate its\u0000completeness were previously lacking. We have addressed this deficit by\u0000generating new high-resolution biostratigraphic, stable isotope, and X-ray\u0000fluorescence (XRF) records spanning the MECO interval (∼38.0–43.0 Ma) in two holes drilled at Site 865. XRF-derived\u0000strontium ∕ calcium (Sr∕Ca) and barium ∕ strontium (Ba∕Sr) ratios and Fe count\u0000records allow correlation between holes and reveal pronounced rhythmicity,\u0000enabling us to develop the first composite section for Holes 865B and 865C\u0000and a preliminary cyclostratigraphy for the MECO. Using this new framework,\u0000the sedimentary record is interpreted to be continuous across the event, as\u0000identified by a pronounced transient benthic foraminiferal δ18O\u0000shift of ∼0.8 ‰. Calcareous microfossil\u0000biostratigraphic events from widely used zonation schemes are recognized,\u0000with generally good agreement between the two holes, highlighting the\u0000robustness of the new composite section and allowing us to identify planktic\u0000foraminiferal Zones E10–E15 and calcareous nannofossil Zones NP15–18.\u0000However, discrepancies in the relative position and ordering of several\u0000primary and secondary bioevents with respect to published schemes are noted.\u0000Specifically, the stratigraphic highest occurrences of planktic foraminifera,\u0000Acarinina bullbrooki, Guembelitrioides nuttalli, and Morozovella aragonensis, and calcareous nannofossils, Chiasmolithus solitus and Sphenolithus furcatolithoides, and the lowest occurrence of\u0000Reticulofenestra reticulata all appear higher in the section than would be predicted relative to other\u0000bioevents. We also note conspicuous reworking of older microfossils (from\u0000planktic foraminiferal Zones E5–E9 and E13) into younger sediments\u0000(planktic foraminiferal Zones E14–15) within our study interval consistent\u0000with reworking above the MECO interval. Regardless of reworking, the\u0000high-quality XRF records enable decimetre-scale correlation between holes\u0000and highlight the potential of Site 865 for constraining tropical\u0000environmental and biotic changes, not just across the MECO but also\u0000throughout the Palaeocene and early-to-middle Eocene interval.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42437090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M.A. De Lira Mota, G. Harrington, T. Dunkley Jones
Abstract. New data from a continuously cored succession, the Mossy Grove core, near Jackson, central Mississippi, recovered ∼137 m of marine clays (Yazoo Formation), spanning ∼5 Ma and including the critical Eocene–Oligocene transition (EOT) event. These clay-rich sediments yield well-preserved calcareous microfossil and palynomorph assemblages. Here, we present a new organic-walled dinoflagellate cyst (dinocyst) biostratigraphic framework, including the recognition of 23 dinocyst bioevents. These are integrated with new age constraints based on calcareous nannofossil biostratigraphy and a reassessment of the existing radiometric dates and planktonic foraminiferal biostratigraphy, permitting the establishment of a robust and significantly refined age model for the core. According to this new age model, a major increase in sedimentation rate – from ∼2.1 to ∼4.7 cm kyr−1 – is observed at a core depth of ∼89.1 m (∼34.4 Ma). In the new age model the section is significantly older than previously thought, by up to 1 Ma, with the Eocene-Oligocene boundary (∼33.89 Ma) placed ∼34 m below the level previously identified. With these more accurate age estimates, future isotopic and palaeoecological work on this core can be more precisely integrated with other, globally distributed records of the EOT.
摘要来自密西西比州中部杰克逊附近的Mossy Grove岩心连续岩心演取的新数据，恢复了~ 137 m的海相粘土(Yazoo组)，跨越~ 5 Ma，包括始新世-渐新世过渡(EOT)事件。这些富含粘土的沉积物产生保存完好的钙质微化石和孢粉组合。在此，我们提出了一个新的有机壁甲藻囊(dinocyst)生物地层格架，包括对23个dinocyst生物事件的识别。这些数据与基于钙质纳米化石生物地层学的新年龄限制相结合，并对现有的放射性测年和浮游有孔虫生物地层学进行了评估，从而为岩心建立了一个强大且非常精确的年龄模型。根据这个新时代模型，在岩心深度为~ 89.1 m (~ 34.4 Ma)处，沉积速率从~ 2.1增加到~ 4.7 cm kyr−1。在新时代模型中，这一剖面比先前认为的要老得多，老了1 Ma，始新世-渐新世边界(~ 33.89 Ma)比先前确定的水平低了~ 34 m。有了这些更精确的年龄估计，未来关于该岩心的同位素和古生态工作可以更精确地与其他全球分布的EOT记录相结合。
{"title":"Organic-walled dinoflagellate cyst biostratigraphy of the upper Eocene to lower Oligocene Yazoo Formation, US Gulf Coast","authors":"M.A. De Lira Mota, G. Harrington, T. Dunkley Jones","doi":"10.5194/jm-39-1-2020","DOIUrl":"https://doi.org/10.5194/jm-39-1-2020","url":null,"abstract":"Abstract. New data from a continuously cored succession, the Mossy Grove core, near Jackson, central Mississippi, recovered ∼137 m of\u0000marine clays (Yazoo Formation), spanning ∼5 Ma and including\u0000the critical Eocene–Oligocene transition (EOT) event. These clay-rich\u0000sediments yield well-preserved calcareous microfossil and palynomorph\u0000assemblages. Here, we present a new organic-walled dinoflagellate cyst\u0000(dinocyst) biostratigraphic framework, including the recognition of\u000023 dinocyst bioevents. These are integrated with new age\u0000constraints based on calcareous nannofossil biostratigraphy and a\u0000reassessment of the existing radiometric dates and planktonic foraminiferal\u0000biostratigraphy, permitting the establishment of a robust and significantly\u0000refined age model for the core. According to this new age model, a major\u0000increase in sedimentation rate – from ∼2.1 to\u0000∼4.7 cm kyr−1 – is observed at a core depth of\u0000∼89.1 m (∼34.4 Ma). In the new age model the\u0000section is significantly older than previously thought, by up to 1 Ma, with\u0000the Eocene-Oligocene boundary (∼33.89 Ma) placed\u0000∼34 m below the level previously identified. With these more\u0000accurate age estimates, future isotopic and palaeoecological work on this\u0000core can be more precisely integrated with other, globally distributed\u0000records of the EOT.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2020-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46764835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Jentzen, J. Schönfeld, Agnes K. M. Weiner, M. Weinkauf, D. Nürnberg, M. Kučera
Abstract. The state of a population of planktic foraminifers at a certain time reflects multiple processes in the upper ocean, including environmental conditions to which the population was exposed during its growth, the age of the cohorts, and spatiotemporal patchiness. We carried out depth-stratified (0–60, 60–100 m) replicated sampling off Puerto Rico in autumn 2012, revisiting three stations previously sampled in autumn 1994 and spring 1995, in order to analyze seasonal and interannual variability of planktic foraminifers and the stable isotopic composition of their tests. The merged dataset from all three sampling campaigns allows us to assess short- and long-term changes in foraminiferal population dynamics and the spatial assemblage coherency along the shelf edge. All three sample series cover more than 2 weeks during either spring (1995) or autumn (1994, 2012) and include the time of the full moon when reproduction of some surface-dwelling planktic foraminifers has been postulated to take place. Our analyses indicate that interannual variability affected the faunal composition, and both autumn assemblages were characterized by oligotrophic tropical species, dominated by Trilobatus sacculifer and Globigerinoides ruber (white and pink variety). However, G. ruber (white) had a higher abundance in 1994 (37 %) than in 2012 (3.5 %), which may be partially due to increasing sea surface temperatures since the 1990s. Between 60 and 100 m water depth, a different faunal composition with a specific stable oxygen isotope signature provides evidence for the presence of the Subtropical Underwater at the sampling site. Measurements on T. sacculifer sampled in autumn 2012 revealed that test size, calcification and incidence of sac-like chambers continued to increase after full moon, and thus no relation to the synodic lunar reproduction cycle was recognized. During autumn 2012, outer bands of hurricane Sandy passed the Greater Antilles and likely affected the foraminifers. Lower standing stocks of living planktic foraminifers and lower stable carbon isotope values from individuals collected in the mixed layer likely indicate the response to increased rainfall and turbidity in the wake of the hurricane.
{"title":"Seasonal and interannual variability in population dynamics of planktic foraminifers off Puerto Rico (Caribbean Sea)","authors":"A. Jentzen, J. Schönfeld, Agnes K. M. Weiner, M. Weinkauf, D. Nürnberg, M. Kučera","doi":"10.5194/jm-38-231-2019","DOIUrl":"https://doi.org/10.5194/jm-38-231-2019","url":null,"abstract":"Abstract. The state of a population of planktic foraminifers at a\u0000certain time reflects multiple processes in the upper ocean, including\u0000environmental conditions to which the population was exposed during its\u0000growth, the age of the cohorts, and spatiotemporal patchiness. We carried\u0000out depth-stratified (0–60, 60–100 m) replicated sampling off Puerto\u0000Rico in autumn 2012, revisiting three stations previously sampled in autumn 1994 and spring 1995, in order to analyze seasonal and interannual\u0000variability of planktic foraminifers and the stable isotopic composition of\u0000their tests. The merged dataset from all three sampling campaigns allows us\u0000to assess short- and long-term changes in foraminiferal population dynamics\u0000and the spatial assemblage coherency along the shelf edge. All three\u0000sample series cover more than 2 weeks during either spring (1995) or\u0000autumn (1994, 2012) and include the time of the full moon when reproduction\u0000of some surface-dwelling planktic foraminifers has been postulated to take\u0000place. Our analyses indicate that interannual variability affected the\u0000faunal composition, and both autumn assemblages were characterized by\u0000oligotrophic tropical species, dominated by Trilobatus sacculifer and Globigerinoides ruber (white and pink variety).\u0000However, G. ruber (white) had a higher abundance in 1994 (37 %) than in 2012 (3.5 %), which may be partially due to increasing sea surface temperatures\u0000since the 1990s. Between 60 and 100 m water depth, a different faunal\u0000composition with a specific stable oxygen isotope signature provides\u0000evidence for the presence of the Subtropical Underwater at the sampling\u0000site. Measurements on T. sacculifer sampled in autumn 2012 revealed that test size,\u0000calcification and incidence of sac-like chambers continued to increase after\u0000full moon, and thus no relation to the synodic lunar reproduction cycle was\u0000recognized. During autumn 2012, outer bands of hurricane Sandy passed\u0000the Greater Antilles and likely affected the foraminifers. Lower standing\u0000stocks of living planktic foraminifers and lower stable carbon isotope\u0000values from individuals collected in the mixed layer likely indicate the\u0000response to increased rainfall and turbidity in the wake of the hurricane.\u0000","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2019-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46835095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Deep-sea benthic foraminifera provide important markers of environmental conditions in the deep-ocean basins where their assemblage composition and test chemistry are influenced by ambient physical and chemical conditions in bottom-water masses. However, all foraminiferal studies must be underpinned by robust taxonomic approaches. Although many parts of the world's oceans have been examined, over a range of geological timescales, the Neogene benthic foraminifera from the southern Indian Ocean have only been recorded from a few isolated sites. In this study, we have examined 97 samples from Neogene sediments recovered from three ODP sites in the southern Indian Ocean (Sites 752, Broken Ridge; 1139, Kerguelan Plateau; 1168, west Tasmania). These data cover a range of palaeolatitudes and water depths during the Miocene. More than 200 species of benthic foraminifera were recorded at each site and, despite their geographic and bathymetric separation, the most abundant taxa were similar at all three sites. Many of these species range from late Oligocene to early Pliocene demonstrating relatively little faunal turnover of the most abundant taxa during the key palaeoclimatic shifts of the Miocene. We illustrate and document the occurrence of the 52 most abundant species (i.e. those with >1 % abundance) encountered across the three study sites.
{"title":"Latest Oligocene to earliest Pliocene deep-sea benthic foraminifera from Ocean Drilling Program (ODP) Sites 752, 1168 and 1139, southern Indian Ocean","authors":"Dana Ridha, I. Boomer, K. Edgar","doi":"10.5194/jm-38-189-2019","DOIUrl":"https://doi.org/10.5194/jm-38-189-2019","url":null,"abstract":"Abstract. Deep-sea benthic foraminifera provide important markers of\u0000environmental conditions in the deep-ocean basins where their assemblage\u0000composition and test chemistry are influenced by ambient physical and\u0000chemical conditions in bottom-water masses. However, all foraminiferal\u0000studies must be underpinned by robust taxonomic approaches. Although many\u0000parts of the world's oceans have been examined, over a range of geological\u0000timescales, the Neogene benthic foraminifera from the southern Indian Ocean\u0000have only been recorded from a few isolated sites. In this study, we have\u0000examined 97 samples from Neogene sediments recovered from three ODP sites in\u0000the southern Indian Ocean (Sites 752, Broken Ridge; 1139, Kerguelan Plateau; 1168,\u0000west Tasmania). These data cover a range of palaeolatitudes and water depths\u0000during the Miocene. More than 200 species of benthic foraminifera were\u0000recorded at each site and, despite their geographic and bathymetric\u0000separation, the most abundant taxa were similar at all three sites. Many of\u0000these species range from late Oligocene to early Pliocene\u0000demonstrating relatively little faunal turnover of the most abundant taxa\u0000during the key palaeoclimatic shifts of the Miocene. We illustrate and\u0000document the occurrence of the 52 most abundant species (i.e. those with\u0000 >1 % abundance) encountered across the three study sites.","PeriodicalId":54786,"journal":{"name":"Journal of Micropalaeontology","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2019-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46784254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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