A late Albian-early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a ... more A late Albian-early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a d13C increase associated with oceanic anoxic event 1d (OAE 1d), is described from Ocean Drilling Program sites 1050 and 1052 in the subtropical Atlantic. Foraminifera are well preserved at these sites. Paleotemperatures estimated from benthic d18O values average ~14°C for middle bathyal Site 1050 and ~17°C for upper bathyal Site 1052, whereas surface temperatures are estimated to have ranged from 26°C to 31°C at both sites. Among planktonic foraminifera, there is a steady balance of speciation and extinction with no discrete time of major faunal turnover. OAE 1d is recognized on the basis of a 1.2 per mill d13C increase (~100.0-99.6 Ma), which is similar in age and magnitude to d13C excursions documented in the North Atlantic and western Tethys. Organic-rich "black shales" are present throughout the studied interval at both sites. However, deposition of individual black shale beds was not synchronous between sites, and most of the black shale was deposited before the OAE 1d d13C increase. A similar pattern is observed at the other sites where OAE 1d has been recognized indicating that the site(s) of excess organic carbon burial that could have caused the d13C increase has (have) yet to be found. Our findings add weight to the view that OAEs should be chemostratigraphically (d13C) rather than lithostratigraphically defined.
Austral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/P... more Austral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/Pg) boundary at Ocean Drilling Program Hole 690C (Maud Rise, Weddell Sea) and International Ocean Drilling Program Hole U1514C (southeast Indian Ocean) show a much different record of post-extinction recovery than anywhere outside the circum-Antarctic region. Species of Woodringina and Parvularugoglobigerina, genera with well-documented evolutionary successions within the early Danian P0 and Pα biozones at tropical/subtropical and mid-latitude localities, are absent from southern high latitude sequences. This study proposes new criteria for biostratigraphic correlation of the lowermost Danian Antarctic Paleocene AP0 and AP1 Zones using stratophenetic observations from Scanning Electron Microscope images of lower Danian planktonic foraminifera at deep-sea sites in the southern South Atlantic and southern Indian Ocean. The small but distinctive species Turborotalita nikolasi (Koutsoukos) is a highly reliable index species for the lowermost Danian as it consistently occurs immediately above the K/Pg boundary at multiple southern high latitude sites, which is consistent with its distribution at middle and low latitudes. Also useful for cross-latitude correlation is Parasubbotina neanika n. sp., which first appears within the lowermost Danian worldwide. The geographic distribution of the New Zealand species Antarcticella pauciloculata (Jenkins) and Zeauvigerina waiparaensis (Jenkins), as well as Eoglobigerina maudrisensis n. sp. from just above the K/Pg in the southern South Atlantic and southern Indian Ocean, helps define the extent of the Austral Biogeographic Province and provides evidence for marine communication via marine seaways across Antarctica. While An. pauciloculata was previously considered a benthic species, new stable isotope evidence demonstrates that it lived a planktonic mode of life. It is possible this species evolved from a benthic ancestor and that the benthic to planktonic transition occurred through an intermediate tychopelagic lifestyle at a time when calcareous plankton were less abundant as a result of the terminal Cretaceous mass extinction.
Oxygen isotope analyses of well-preserved foraminifera from Blake Nose (30°N paleolatitude, North... more Oxygen isotope analyses of well-preserved foraminifera from Blake Nose (30°N paleolatitude, North Atlantic) and globally distributed deep-sea sites provide a long-term paleotemperature record for the late Albian-Maastrichtian interval that is difficult to reconcile with the existence of significant Cretaceous ice sheets. Given reasonable assumptions about the isotopic composition of Cretaceous seawater, our results suggest that middle bathyal water temperatures at Blake Nose increased from ~12°C in the late Albian through middle Cenomanian to a maximum of 20°C during the latest Cenomanian and earliest Turonian. Bottom waters were again ~12°C during the middle Campanian and cooled to a minimum of 9°C during the Maastrichtian. Correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from Blake Nose. Comparison of global bottom-water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late Albian through late Cenomanian to a hot greenhouse phase during the latest Cenomanian through early Campanian, then to cool greenhouse conditions during the mid-Campanian through Maastrichtian.
A late Albian-early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a ... more A late Albian-early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a d13C increase associated with oceanic anoxic event 1d (OAE 1d), is described from Ocean Drilling Program sites 1050 and 1052 in the subtropical Atlantic. Foraminifera are well preserved at these sites. Paleotemperatures estimated from benthic d18O values average ~14°C for middle bathyal Site 1050 and ~17°C for upper bathyal Site 1052, whereas surface temperatures are estimated to have ranged from 26°C to 31°C at both sites. Among planktonic foraminifera, there is a steady balance of speciation and extinction with no discrete time of major faunal turnover. OAE 1d is recognized on the basis of a 1.2 per mill d13C increase (~100.0-99.6 Ma), which is similar in age and magnitude to d13C excursions documented in the North Atlantic and western Tethys. Organic-rich "black shales" are present throughout the studied interval at both sites. However, deposition of individual black shale beds was not synchronous between sites, and most of the black shale was deposited before the OAE 1d d13C increase. A similar pattern is observed at the other sites where OAE 1d has been recognized indicating that the site(s) of excess organic carbon burial that could have caused the d13C increase has (have) yet to be found. Our findings add weight to the view that OAEs should be chemostratigraphically (d13C) rather than lithostratigraphically defined.
Austral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/P... more Austral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/Pg) boundary at Ocean Drilling Program Hole 690C (Maud Rise, Weddell Sea) and International Ocean Drilling Program Hole U1514C (southeast Indian Ocean) show a much different record of post-extinction recovery than anywhere outside the circum-Antarctic region. Species of Woodringina and Parvularugoglobigerina, genera with well-documented evolutionary successions within the early Danian P0 and Pα biozones at tropical/subtropical and mid-latitude localities, are absent from southern high latitude sequences. This study proposes new criteria for biostratigraphic correlation of the lowermost Danian Antarctic Paleocene AP0 and AP1 Zones using stratophenetic observations from Scanning Electron Microscope images of lower Danian planktonic foraminifera at deep-sea sites in the southern South Atlantic and southern Indian Ocean. The small but distinctive species Turborotalita nikolasi (Koutsoukos) is a highly reliable index species for the lowermost Danian as it consistently occurs immediately above the K/Pg boundary at multiple southern high latitude sites, which is consistent with its distribution at middle and low latitudes. Also useful for cross-latitude correlation is Parasubbotina neanika n. sp., which first appears within the lowermost Danian worldwide. The geographic distribution of the New Zealand species Antarcticella pauciloculata (Jenkins) and Zeauvigerina waiparaensis (Jenkins), as well as Eoglobigerina maudrisensis n. sp. from just above the K/Pg in the southern South Atlantic and southern Indian Ocean, helps define the extent of the Austral Biogeographic Province and provides evidence for marine communication via marine seaways across Antarctica. While An. pauciloculata was previously considered a benthic species, new stable isotope evidence demonstrates that it lived a planktonic mode of life. It is possible this species evolved from a benthic ancestor and that the benthic to planktonic transition occurred through an intermediate tychopelagic lifestyle at a time when calcareous plankton were less abundant as a result of the terminal Cretaceous mass extinction.
Oxygen isotope analyses of well-preserved foraminifera from Blake Nose (30°N paleolatitude, North... more Oxygen isotope analyses of well-preserved foraminifera from Blake Nose (30°N paleolatitude, North Atlantic) and globally distributed deep-sea sites provide a long-term paleotemperature record for the late Albian-Maastrichtian interval that is difficult to reconcile with the existence of significant Cretaceous ice sheets. Given reasonable assumptions about the isotopic composition of Cretaceous seawater, our results suggest that middle bathyal water temperatures at Blake Nose increased from ~12°C in the late Albian through middle Cenomanian to a maximum of 20°C during the latest Cenomanian and earliest Turonian. Bottom waters were again ~12°C during the middle Campanian and cooled to a minimum of 9°C during the Maastrichtian. Correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from Blake Nose. Comparison of global bottom-water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late Albian through late Cenomanian to a hot greenhouse phase during the latest Cenomanian through early Campanian, then to cool greenhouse conditions during the mid-Campanian through Maastrichtian.
Upper Cretaceous sediments recovered during the Tanzania Drilling Project in 2007 to 2009 reveal ... more Upper Cretaceous sediments recovered during the Tanzania Drilling Project in 2007 to 2009 reveal long intervals with exceptionally well preserved planktic and benthic foraminifera, allowing for single species carbon and oxygen isotope and geochemical analyses. We present results of an ongoing study in which we focus on the paleoceanographic and paleoclimatic history at low latitudes during the Turonian period of global warmth. The studied material contains abundant and well diversified foraminifera faunas indicating an outer shelf to upper slope position. Consistently present calcareous species are used for carbon and oxygen isotope measurements. To enhance our understanding of the stable isotope data we study intra-species offsets and their relation to carbonate geochemistry of the shells, by applying a combination of light-microscope and SEM imaging with microprobe and cathodoluminescence-based geochemical analyses. For example, various aragonitic-shelled species of the genus Epistomina show a striking offset in carbon isotopes while displaying similar values in oxygen isotopes, as compared to other benthic species. Cross plots of carbon and oxygen isotopes show distinct clustering of data points for individual species, pointing to species-specific fractionation during the foraminifer’s life time. Cross plots of the elemental shell compositions also show species-specific clusters of data points, possibly indicating primary and/or early-diagenetic mineralogical differences that potentially affect the isotopic shell chemistry apart from or along with the vital effects. The influence of diagenetic alteration is studied by comparing isotope data and geochemical composition of the shells from samples with different degrees of preservation. Our study aims at providing important information for selecting species that are suitable for studies of stable isotopes and temperature reconstructions in the Cretaceous. Furthermore, we compare single species measurements of pristine shells with isotope data from bulk sediments to assess the reliability of bulk sediment data, as they are increasingly used for chemostratigraphic correlation and reconstruction of relative temperature trends in the Cretaceous.
Paleoclimatic greenhouse conditions of the mid-Cretaceous are still far from being understood as ... more Paleoclimatic greenhouse conditions of the mid-Cretaceous are still far from being understood as evidenced by the controversy on glaciations during the Turonian – one of the warmest periods of the Mesozoic. Absolute paleotemperature estimates and reconstructions of stability or fluctuation of climate and sea-level critically depend on high-resolution records of well-preserved fossil material. We present a data compilation of grain-size, foraminiferal assemblages and single-species stable isotopes from Turonian clayey siltstones with exceptionally well-preserved microfossils that were drilled in Tanzania and represent a low-latitudinal record. The data indicate stable environmental conditions during the Early and most of the Middle Turonian, arguing against a glaciation during that period. In the uppermost H. helvetica Zone and lower M. schneegansi Zone (Middle/Late Turonian), two phases of simultaneous shifts in benthic foraminifera associations, an increase in grain-size and sifts in foraminiferal d13C appear to reflect a stepwise shallowing in relative sea-level, which is supported by a dramatic increase in planktic biserial foraminifera during the second phase. A change in foraminiferal preservation at this level precludes interpretation of d18O data, but absence of simultaneous d18O shifts in benthic and planktic foraminifera during the first phase does not support the glaciation hypothesis as a cause for the regression.
The sediments of the southern coastal Tanzania contain exceptionally well preserved microfossils ... more The sediments of the southern coastal Tanzania contain exceptionally well preserved microfossils and have been targeted in recent years by the “Tanzania Drilling Project” (TDP), an informal collaboration of researchers studying Cretaceous-Neogene paleoclimate. Drilling in 2007 was near Lindi, where previous TDP works had cored ~35 m of upper Campanian-lower Maastrichtian claystones and mapped upper Campanian to lower Oligocene sediments based on scarce surface exposures. During 2007, a total of 380 m of core was recovered. Three holes collectively spanned the uppermost Albian to upper Cenomanian (Planomalina buxtorfi sub-Zone to Rotalipora cushmani Zone) and include organic carbon isotopic evidence suggesting recovery of at least the base of OAE2; two holes recovered a thick sequence of the lower to middle Turonian (Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones) with the Coniacian marker Dicarinella concavata in the highest samples; and one hole recovered the lower to upper Campanian (Globotruncanita elevata to Radotruncana calcarata Zones). Stratigraphic gaps exist in the lower Cenomanian, upper Turonian and Santonian, and the Cenomanian-Turonian boundary is not demonstrably conformable. Lithologies include thin intervals of light, coarse sandstones and sandy siltstones with occasional woody debris separating thicker intervals of dark claystone containing rare bivalves and ammonites and thin interbeds of silt to fine sandstone. Organic-rich, finely laminated claystones were also recovered at parts of the Turonian sequence. Beyond the refinements to knowledge of the local stratigraphy and subsurface geology, these results coupled with ongoing geochemical and biostratigraphic studies are being used to examine Late Cretaceous greenhouse climates. Of particular interest is the temperature history in the region, whether sedimentological and geochemical data together support Late Cretaceous glacial episodes, and how the tropical-subtropical East African shelf environment behaved during OAE2 and other Late Cretaceous events.
Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 659
Upper Cretaceous sediments recovered during the Tanzania Drilling Project from 2007 to 2009 inclu... more Upper Cretaceous sediments recovered during the Tanzania Drilling Project from 2007 to 2009 include long intervals with exceptionally well preserved planktic and benthic foraminifera providing an excellent sample base for generating stable carbon and oxygen isotopic records as well as other geochemical data. Our study examines inter-species variation in stable isotopic values and their relation to the shell carbonate geochemistry and preservation by applying a combination of light-microscope and SEM imaging with microprobe and cathodoluminescence-based geochemical analyses. Our goal is to evaluate which species are best suited for studies of stable isotopes and temperature reconstructions in the Cretaceous. We present results from a Turonian sequence with relatively stable environmental conditions as inferred from minimal variation in intra-specific d13C and d18O values across the section. The studied material contains abundant and diverse benthic foraminifer assemblages that indicate an outer shelf to upper slope paleodepth. We performed single species d13C and d18O measurements for 18 calcareous benthic and 10 planktic species. Cross plots of d13C and d18O show distinct offsets between clusters of data points for individual species, reflecting a combination of differences in habitat and disequilibrium fractionation due to metabolic effects or an infaunal mode of life. Offsets in d18O between two groups of trochospiral planktic foraminifera apparently reflect water depth-related differences in temperature during their lifetime. An expected offset is observed between benthic species with aragonitic versus calcitic tests, but systematic offsets among aragonitic species indicate that micro-habitat or vital effects also influence measured values. The lowest d13C values among the calcitic benthic foraminifera were observed for species of the genus Lenticulina. Because we did not observe differences in their preservation relative to other benthic species, the isotope results suggest a strong influence of metabolic effects on isotopic fractionation for Lenticulina species. Among the calcitic benthic species studied the two species Berthelina berthelini and Lingulogavelinella convexa appear to have close-to-equilibrium values and are preferred for paleoenvironmental reconstructions.
Calcispheres constitute the second-most abundant calcareous microfossils of many Late Cretaceous ... more Calcispheres constitute the second-most abundant calcareous microfossils of many Late Cretaceous rocks and show significant spatial and temporal blooms, the most important of which is the Late Cenomanian - Early Turonian global calcisphere bioevent associated with OAE2. Because of their common appearance calcispheres could give substantial paleo-ecological information if their taxonomic affinities would be better known. However, a lack of morphological features limits our understanding of what these microfossils actually are. The most common calcispheres belong to the genus Pithonella. They are 20 to 180 micrometers in diameter and have been interpreted as calcareous cysts of dinoflagellates. However, the dinoflagellate cyst nature of Pithonelloideae has been controversial due to their lack of dinoflagellate-specific features. Unusually well-preserved Pithonelloideae are abundant in the Turonian from Tanzania. The pristine specimens reveal a number of shell-morphological features that have never been described before. Our study aims at revising the taxonomy of this complex microfossil group based on these new morphological findings. We combine light-optical imaging, SEM-imaging, cross-section study and microprobe analysis on single specimens. Most crucial to the determination of their taxonomic affinity with dinoflagellates is our discovery of an operculum-like structure that can be associated with the apical 3’ plate known from the peridinialean tabulation pattern of dinoflagellates. Furthermore, comparison between Pithonella sphaerica and the known calcareous dinoflagellate cyst Pirumella krasheninnikovii reveals striking biomineralogical similarities in wall-crystal architecture and chemistry. Such similarity hints at a common biomineralisation principle in both species. Stable oxygen isotope values of Pithonella plot with the values of planktic foraminifera suggesting a habitat of Pithonella near the water surface.
Uncertainties in reconstructing palaeotemperatures and CO2-levels in the Cretaceous mainly arise ... more Uncertainties in reconstructing palaeotemperatures and CO2-levels in the Cretaceous mainly arise from various degrees of diagenetic overprinting of most Cretaceous sediments. In the Tanzania Drilling Project exceptionally well preserved foraminiferal shells have been retrieved from Cenomanian and Turonian sediments with low carbonate and high clay content. This allows for a comparison of the primary shell material of individual species concerning their mineralogy, chemistry and stable isotopes. It further offers the unique opportunity to compare pristine shells that are glassy with slightly re-crystallized shells that are still well preserved and hollow, but appear more “frosty” or less translucent. The influence of these first processes of diagenetic alteration on the shell geochemistry and isotope signatures is studied by applying a combination of light microscope imaging, scanning electron microscope analyses, cathodoluminescence and microprobe observations. To exclude variation due to environmental factors or vital effects we compare specimens from the same sample and within the same species. Cathodoluminescence studies confirmed the presence of aragonitic shells for a number of species, testifying to the excellent preservation of the material. Their isotopic composition shows a considerable offset as compared to other benthic species. There is also a large difference in oxygen isotopes between benthic and planktic foraminifera. Slightly re-crystallized shells of benthic foraminifera show isotope values that fall within the range of variability of the species. However, the presence of cement can lead to a decrease in δ18O and becomes evident from bright orange linings under the cathodoluminescence microscope and from a rough shell surface under the SEM. Microprobe analysis reveals that manganese and iron increase in the cemented areas while strontium decreases. A similar trend is observed by comparing the shell chemistry of glassy and less translucent specimens of the same species, indicating some alteration of the primary shell material during re-crystallization.
Uploads
Papers by Kenneth MacLeod