High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertia... more High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertiary boundary interval in Section 119-738C-20R-5 from the southern Kerguelen Plateau is summarized and interpreted. The change of the calcareous nannoflora and of the planktonic foraminifers is spread over a laminated interval of about 15 cm thickness. The base of this laminated interval lies in uppermost Maestrichtian chalks, 2 cm below a distinct 2-mm-thick "gray clay" layer, which shows the highest iridium enrichment (18 ppb) measured in this section. No shocked quartz or microspherules, characteristic of an impact, were found. No change in the clay mineralogy, which could be expected for a large volcanic or impact event, could be identified. Elevated metal and iridium concentrations (> 1.6 ppb) occur already in the bioturbated uppermost Maestrichtian chalks several centimeters below the "gray clay" and decrease above the iridium peak gradually over a laminated 12...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This monograph has been compiled by members of the Paleogene Planktonic Foraminifera Working Grou... more This monograph has been compiled by members of the Paleogene Planktonic Foraminifera Working Group (hereafter referred to as the Working Group) of the International Subcommission on Paleogene Stratigraphy, International Union of Geological Sciences. It is the second such work in a projected series of three, the first being the Atlas of Paleocene Planktonic Foraminifera published by Smithsonian Institution Press (Olsson and others, 1999). Here we extend that effort to encompass the full flowering of the adaptive radiation of planktonic foraminifera in the Eocene. The atlas has its origins in 1987, when the Working Group was formed. At that time it was clear that a major revision of the Paleogene planktonic foraminifera was necessary in order to synthesize a highly dispersed body of literature and to develop new taxonomic concepts, based, as far as possible, on scanning electron microscopy (SEM). At the first formal meeting a decision was made to focus on the production of an initial ...
Anew relational taxonomic database for planktonic foraminifera (“pforams@mikrotax”) has been cons... more Anew relational taxonomic database for planktonic foraminifera (“pforams@mikrotax”) has been constructed and is now freely available online at http://www.mikrotax.org. It represents a major advance from its predecessor, the CHRONOS online taxonomic database, which has served the research community since 2005. The benefits of the new database to the research and industrial biostratigraphic communities are many, as it will serve as an immediately accessible taxonomic guide and reference for specialists and non-specialists alike by providing access to a wealth of information and images from original authors and from experts who have inserted recent authoritative updates to planktonic foraminiferal taxonomy, phylogeny and biostratigraphy. The database will be continually updated and used as a guide for training current and future generations of students and professionals who will be able to self-educate on planktonic foraminiferal taxonomy and biostratigraphy. Further investigation of s...
... 6979. 4. T. Birkelund, JM Hancock, MB Hart, PF Rawson, J. Remane, F. Robaszynski, F. Schmid ... more ... 6979. 4. T. Birkelund, JM Hancock, MB Hart, PF Rawson, J. Remane, F. Robaszynski, F. Schmid and F. Surlyk, Cretaceous stage boundaries. ... 9. AR Loeblich, Jr and H. Tappan, Cretaceous planktonic foraminifera: Part 1 Cenomanian. Micropaleontology 7 (1961), pp. ...
Marine mudstone sediments recovered from multiple boreholes drilled in southeast Tanzania yield s... more Marine mudstone sediments recovered from multiple boreholes drilled in southeast Tanzania yield some of the best preserved Turonian microfossils in the world, and these specimens provide a valuable new perspective on planktonic foraminiferal and calcareous nannofossil evolution, taxonomy, biostratigraphy, and biodiversity. High sedimentation rates and the consistent presence of well-preserved microfossil assemblages throughout the sequence increase the resolution of biostratigraphic data generated allowing for improved correlation within and outside the depositional basin. The late early-middle Turonian Tanzanian record reveals prolonged species stasis with essentially no changes in relative abundance, no extinctions, and no evolutionary appearances for both calcareous plankton groups until the late middle Turonian. This interval is followed in the late Turonian by two species turnovers. The older of these occurs at the top of the mid-Turonian Helvetoglobotruncana helvetica Zone, where last occurrences of three planktonic foraminiferal species are followed, within several meters, by first occurrences of five foraminiferal species and an increase in the abundance of dwarfed planktonic forms. Changes in the calcareous nannofossil assemblages at this level are modest and include the extinction of one calcareous nannofossil species and an abrupt but temporary spike in the abundance of another species. There are no obvious changes in lithology, bulk sediment geochemistry, or stable isotope values across this first turnover event. The second, larger species turnover occurs at a hiatus within the late Turonian Marginotruncana sinuosa-Huberella huberi Zone and is marked by extinction of three calcareous nannofossil species followed by first appearances of four calcareous nannofossil species. Corresponding with the nannofossil first occurrences is a dramatic increase in the relative abundance of several species of biserial planktonic foraminifera, an increase in average grain size, and a shift in preservation
Geological Society, London, Special Publications, 2001
Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a su... more Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of`critical' events in the Earth's history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous± Palaeogene (K±P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and d 13 C trends from Albian to late Eocene time. Evolution of d 18 O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian±early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian±Cenomanian boundary to Coniacian time and then show a tendency to fall o toward the cool climates of the mid-Maastrichtian. The Albian± Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian± Turonian boundary, and suggest middle bathyal waters with temperatures up to 20 8C in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were ®nally breached to sucient depth to permit ventilation by deep waters¯owing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian±Danian and late Palaeocene±early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroo®ng previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K±P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.
Oxygen isotope data for Upper Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau... more Oxygen isotope data for Upper Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau, 60^oS paleolatitude) exhibit an ˜ 2 ppm excursion to values as low as -4.66 ppm (PDB) coincident with the warmest tropical temperature estimates yet obtained for the open ocean. The lowest planktonic foraminifer δ18O values suggest that the upper ocean was as warm as 30-32^oC. This is an extraordinary temperature for 60^oS latitude but is consistent with temperatures estimated from apparently coeval mollusk δ18O from nearby James Ross Island (65^oS paleolatitude). Glassy textural preservation, a well-defined depth distribution in Site 511 planktonics, low sediment burial temperature (˜ 32^oC), and lack of evidence of highly depleted pore waters argue against diagenesis (even solid-state diffusion) as the cause of the very depleted planktonic values. The lack of change in benthic foraminifer d18O suggests brackish water capping as the mechanism for the low planktonic δ18O values. However, mixing ratio calculations show that the amount of freshwater required to produce a 2 ppm shift in ambient water would drive a 7 psu decrease in salinity. The abundance and diversity of planktonic foraminifera and nannofossils, high planktonic:benthic ratios and the appearance of keeled foraminifera argue against lower-than-normal marine salinities. Isotope calculations and climate models indicate that we cannot call upon more depleted freshwater δ18O to explain this record. Without more late Turonian data, especially from outside the South Atlantic basin, we can currently only speculate on possible causes of this paradoxical record from the core of the Cretaceous greenhouse.
In 2007 and 2009, the Tanzania Drilling Project (TDP) recovered a total of five coreholes from th... more In 2007 and 2009, the Tanzania Drilling Project (TDP) recovered a total of five coreholes from the south-eastern coastal region, around the village of Lindi, that contain the isotope excursion (based on bulk δ13Corg) associated with Oceanic Anoxic Event 2 (OAE2) at the Cenomanian/Turonian boundary. These holes provide expanded successions of a shallowly-buried, predominantly claystone facies that have preserved the calcite component exceptionally well. Calcareous nannoplankton (primary-producers at the base of the oceanic food-chain) preservation in the TDP holes is exceptional, with continuous representation of small and delicate nannofossil taxa, thus affording us the opportunity to shed more light onto the evolutionary record and environmental conditions across this interval of carbon-cycle perturbation that included warming, sea-level rise and extinction. This borehole material allows us to overcome the difficulties faced by previous attempts to document changes in the nannofossil assemblages through OAE2 that were hampered by insufficient temporal resolution, and the poor preservation of fossils due to widespread occurrences of chalk and non-calcareous black shales. Here, we will present new calcareous nannoplankton data from TDP Sites 21, 24, 24B, 26 and 36. Our data show a significant shift in assemblage composition and diversity, accompanied by extinction events, coincident with the first peak of the isotope excursion. These may suggest an onset/increase in oligotrophic marine conditions in that interval.
High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertia... more High-resolution stratigraphic evidence of an apparently complete carbonate-rich Cretaceous/Tertiary boundary interval in Section 119-738C-20R-5 from the southern Kerguelen Plateau is summarized and interpreted. The change of the calcareous nannoflora and of the planktonic foraminifers is spread over a laminated interval of about 15 cm thickness. The base of this laminated interval lies in uppermost Maestrichtian chalks, 2 cm below a distinct 2-mm-thick "gray clay" layer, which shows the highest iridium enrichment (18 ppb) measured in this section. No shocked quartz or microspherules, characteristic of an impact, were found. No change in the clay mineralogy, which could be expected for a large volcanic or impact event, could be identified. Elevated metal and iridium concentrations (> 1.6 ppb) occur already in the bioturbated uppermost Maestrichtian chalks several centimeters below the "gray clay" and decrease above the iridium peak gradually over a laminated 12...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This monograph has been compiled by members of the Paleogene Planktonic Foraminifera Working Grou... more This monograph has been compiled by members of the Paleogene Planktonic Foraminifera Working Group (hereafter referred to as the Working Group) of the International Subcommission on Paleogene Stratigraphy, International Union of Geological Sciences. It is the second such work in a projected series of three, the first being the Atlas of Paleocene Planktonic Foraminifera published by Smithsonian Institution Press (Olsson and others, 1999). Here we extend that effort to encompass the full flowering of the adaptive radiation of planktonic foraminifera in the Eocene. The atlas has its origins in 1987, when the Working Group was formed. At that time it was clear that a major revision of the Paleogene planktonic foraminifera was necessary in order to synthesize a highly dispersed body of literature and to develop new taxonomic concepts, based, as far as possible, on scanning electron microscopy (SEM). At the first formal meeting a decision was made to focus on the production of an initial ...
Anew relational taxonomic database for planktonic foraminifera (“pforams@mikrotax”) has been cons... more Anew relational taxonomic database for planktonic foraminifera (“pforams@mikrotax”) has been constructed and is now freely available online at http://www.mikrotax.org. It represents a major advance from its predecessor, the CHRONOS online taxonomic database, which has served the research community since 2005. The benefits of the new database to the research and industrial biostratigraphic communities are many, as it will serve as an immediately accessible taxonomic guide and reference for specialists and non-specialists alike by providing access to a wealth of information and images from original authors and from experts who have inserted recent authoritative updates to planktonic foraminiferal taxonomy, phylogeny and biostratigraphy. The database will be continually updated and used as a guide for training current and future generations of students and professionals who will be able to self-educate on planktonic foraminiferal taxonomy and biostratigraphy. Further investigation of s...
... 6979. 4. T. Birkelund, JM Hancock, MB Hart, PF Rawson, J. Remane, F. Robaszynski, F. Schmid ... more ... 6979. 4. T. Birkelund, JM Hancock, MB Hart, PF Rawson, J. Remane, F. Robaszynski, F. Schmid and F. Surlyk, Cretaceous stage boundaries. ... 9. AR Loeblich, Jr and H. Tappan, Cretaceous planktonic foraminifera: Part 1 Cenomanian. Micropaleontology 7 (1961), pp. ...
Marine mudstone sediments recovered from multiple boreholes drilled in southeast Tanzania yield s... more Marine mudstone sediments recovered from multiple boreholes drilled in southeast Tanzania yield some of the best preserved Turonian microfossils in the world, and these specimens provide a valuable new perspective on planktonic foraminiferal and calcareous nannofossil evolution, taxonomy, biostratigraphy, and biodiversity. High sedimentation rates and the consistent presence of well-preserved microfossil assemblages throughout the sequence increase the resolution of biostratigraphic data generated allowing for improved correlation within and outside the depositional basin. The late early-middle Turonian Tanzanian record reveals prolonged species stasis with essentially no changes in relative abundance, no extinctions, and no evolutionary appearances for both calcareous plankton groups until the late middle Turonian. This interval is followed in the late Turonian by two species turnovers. The older of these occurs at the top of the mid-Turonian Helvetoglobotruncana helvetica Zone, where last occurrences of three planktonic foraminiferal species are followed, within several meters, by first occurrences of five foraminiferal species and an increase in the abundance of dwarfed planktonic forms. Changes in the calcareous nannofossil assemblages at this level are modest and include the extinction of one calcareous nannofossil species and an abrupt but temporary spike in the abundance of another species. There are no obvious changes in lithology, bulk sediment geochemistry, or stable isotope values across this first turnover event. The second, larger species turnover occurs at a hiatus within the late Turonian Marginotruncana sinuosa-Huberella huberi Zone and is marked by extinction of three calcareous nannofossil species followed by first appearances of four calcareous nannofossil species. Corresponding with the nannofossil first occurrences is a dramatic increase in the relative abundance of several species of biserial planktonic foraminifera, an increase in average grain size, and a shift in preservation
Geological Society, London, Special Publications, 2001
Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a su... more Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of`critical' events in the Earth's history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous± Palaeogene (K±P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and d 13 C trends from Albian to late Eocene time. Evolution of d 18 O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian±early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian±Cenomanian boundary to Coniacian time and then show a tendency to fall o toward the cool climates of the mid-Maastrichtian. The Albian± Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian± Turonian boundary, and suggest middle bathyal waters with temperatures up to 20 8C in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were ®nally breached to sucient depth to permit ventilation by deep waters¯owing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian±Danian and late Palaeocene±early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroo®ng previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K±P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.
Oxygen isotope data for Upper Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau... more Oxygen isotope data for Upper Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau, 60^oS paleolatitude) exhibit an ˜ 2 ppm excursion to values as low as -4.66 ppm (PDB) coincident with the warmest tropical temperature estimates yet obtained for the open ocean. The lowest planktonic foraminifer δ18O values suggest that the upper ocean was as warm as 30-32^oC. This is an extraordinary temperature for 60^oS latitude but is consistent with temperatures estimated from apparently coeval mollusk δ18O from nearby James Ross Island (65^oS paleolatitude). Glassy textural preservation, a well-defined depth distribution in Site 511 planktonics, low sediment burial temperature (˜ 32^oC), and lack of evidence of highly depleted pore waters argue against diagenesis (even solid-state diffusion) as the cause of the very depleted planktonic values. The lack of change in benthic foraminifer d18O suggests brackish water capping as the mechanism for the low planktonic δ18O values. However, mixing ratio calculations show that the amount of freshwater required to produce a 2 ppm shift in ambient water would drive a 7 psu decrease in salinity. The abundance and diversity of planktonic foraminifera and nannofossils, high planktonic:benthic ratios and the appearance of keeled foraminifera argue against lower-than-normal marine salinities. Isotope calculations and climate models indicate that we cannot call upon more depleted freshwater δ18O to explain this record. Without more late Turonian data, especially from outside the South Atlantic basin, we can currently only speculate on possible causes of this paradoxical record from the core of the Cretaceous greenhouse.
In 2007 and 2009, the Tanzania Drilling Project (TDP) recovered a total of five coreholes from th... more In 2007 and 2009, the Tanzania Drilling Project (TDP) recovered a total of five coreholes from the south-eastern coastal region, around the village of Lindi, that contain the isotope excursion (based on bulk δ13Corg) associated with Oceanic Anoxic Event 2 (OAE2) at the Cenomanian/Turonian boundary. These holes provide expanded successions of a shallowly-buried, predominantly claystone facies that have preserved the calcite component exceptionally well. Calcareous nannoplankton (primary-producers at the base of the oceanic food-chain) preservation in the TDP holes is exceptional, with continuous representation of small and delicate nannofossil taxa, thus affording us the opportunity to shed more light onto the evolutionary record and environmental conditions across this interval of carbon-cycle perturbation that included warming, sea-level rise and extinction. This borehole material allows us to overcome the difficulties faced by previous attempts to document changes in the nannofossil assemblages through OAE2 that were hampered by insufficient temporal resolution, and the poor preservation of fossils due to widespread occurrences of chalk and non-calcareous black shales. Here, we will present new calcareous nannoplankton data from TDP Sites 21, 24, 24B, 26 and 36. Our data show a significant shift in assemblage composition and diversity, accompanied by extinction events, coincident with the first peak of the isotope excursion. These may suggest an onset/increase in oligotrophic marine conditions in that interval.
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