ABSTRACT The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of c... more ABSTRACT The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of carbonate and organic matter across the globe, suggesting massive release of 13C-depleted carbon dioxide into the ocean and atmosphere over a very short time interval (probably b20ky). We report a geochemical and mineralogical study of 106 samples spanning the most expanded PETM at the Dababiya Global Stratotype Standard section and Point (GSSP) near Luxor, Egypt. The field and laboratory observations reveal that the deposition occurred in a submarine channel extended laterally about 200 m with the deepest part (~0.88 m) at the designated GSSP, although all bio-zones are present. Stable isotope records of both carbonate and organic carbon show decreases starting 0.6 m below the Paleocene-Eocene boundary (PEB) and culminating at the erosion surface. A persistent shift in δ15Norg values to near zero reflects a gradual increase in bacterial activity. High Ti, K and Zr and low Si contents at the PEB coincide with increased kaolinite contents, which suggests intense chemical weathering under more humid conditions at the PETM onset. Two negative Ce-anomalies indicate intervals of anoxic conditions during the lower and middle PETM (base and top of zone E1). The first anoxic event is represented by a negative Ce-anomaly, high V/C rand V/V+Ni ratios, negative Mn* and an abundance of idiomorphic pyrite crystals that indicate anoxic to euxinic conditions. The anoxic event (middle PETM) is marked by high U, Mo, V, Fe and abundant small sized (2–5 μm) pyrite framboids, increased Cu, Ni, and Cd at the samelevel suggesting anoxic conditions linked to high surface water productivity. Above this interval, oxic conditions returned as indicated by the precipitation of phosphorus and barium. These data reveal an expanded PETM interval marked by intense weathering as a crucial parameter during the recovery phase.
Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated ... more Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ13C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ13C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ13C peak and end at or near the Cenomanian–Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco.► Two sequences of NE Egypt have been investigated to evaluate the response to OAE2. ► Age control based on nannoplankton, foraminifera and ammonite. ► Faunal assemblage is characterized by dysoxic, brackish and mesotrophic conditions. ► The OAE2 δ13C excursion appears comparable to that of open marine environments. ► Anoxic conditions do not appear until the early Turonian sea level transgression.
The discovery of a new Cretaceous/Paleogene (K/Pg) bathyal marine sequence on Gorgonilla Island, ... more The discovery of a new Cretaceous/Paleogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well-preserved glass spherules (microtektites and microkrystites) up to 1.1 mm in diameter. About 70-90 % of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size-grading, delicate spherule textures, welded melt components, and absence of bioturbation or traction transport indicate that the Gorgonilla spherule layer represents an almost unaltered primary suspension settling deposit. Keywords: K/Pg boundary, Chicxulub, spherules, eastern Pacific, Colombia
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excurs... more Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion, the delta13C values remain at approximately 2.0 ppm dipping only slightly in the early Turonian (H. helvetica zone). During the initial phases of the delta13C excursion, 5 planktic species consecutively become extinct (Rotalipora deekei, R. greenhornensis, R. cushmani, P. inornata, G. bentonensis). These are subsequently replaced in the latter stages of the excursions by 5 new species with high depth tolerances, resulting in no net diversity loss. The extinction is therefore likely to have been as a direct result from the increased water mass stratification. A temporary decrease in bottom water productivity is also suggested by oxygenated bottom waters (presence of Cibidicoides) and a minimum of low O_2 tolerant species (hetrohelicids). Elevated HI/OH...
ABSTRACT The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of c... more ABSTRACT The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of carbonate and organic matter across the globe, suggesting massive release of 13C-depleted carbon dioxide into the ocean and atmosphere over a very short time interval (probably b20ky). We report a geochemical and mineralogical study of 106 samples spanning the most expanded PETM at the Dababiya Global Stratotype Standard section and Point (GSSP) near Luxor, Egypt. The field and laboratory observations reveal that the deposition occurred in a submarine channel extended laterally about 200 m with the deepest part (~0.88 m) at the designated GSSP, although all bio-zones are present. Stable isotope records of both carbonate and organic carbon show decreases starting 0.6 m below the Paleocene-Eocene boundary (PEB) and culminating at the erosion surface. A persistent shift in δ15Norg values to near zero reflects a gradual increase in bacterial activity. High Ti, K and Zr and low Si contents at the PEB coincide with increased kaolinite contents, which suggests intense chemical weathering under more humid conditions at the PETM onset. Two negative Ce-anomalies indicate intervals of anoxic conditions during the lower and middle PETM (base and top of zone E1). The first anoxic event is represented by a negative Ce-anomaly, high V/C rand V/V+Ni ratios, negative Mn* and an abundance of idiomorphic pyrite crystals that indicate anoxic to euxinic conditions. The anoxic event (middle PETM) is marked by high U, Mo, V, Fe and abundant small sized (2–5 μm) pyrite framboids, increased Cu, Ni, and Cd at the samelevel suggesting anoxic conditions linked to high surface water productivity. Above this interval, oxic conditions returned as indicated by the precipitation of phosphorus and barium. These data reveal an expanded PETM interval marked by intense weathering as a crucial parameter during the recovery phase.
Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated ... more Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ13C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ13C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ13C peak and end at or near the Cenomanian–Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco.► Two sequences of NE Egypt have been investigated to evaluate the response to OAE2. ► Age control based on nannoplankton, foraminifera and ammonite. ► Faunal assemblage is characterized by dysoxic, brackish and mesotrophic conditions. ► The OAE2 δ13C excursion appears comparable to that of open marine environments. ► Anoxic conditions do not appear until the early Turonian sea level transgression.
The discovery of a new Cretaceous/Paleogene (K/Pg) bathyal marine sequence on Gorgonilla Island, ... more The discovery of a new Cretaceous/Paleogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well-preserved glass spherules (microtektites and microkrystites) up to 1.1 mm in diameter. About 70-90 % of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size-grading, delicate spherule textures, welded melt components, and absence of bioturbation or traction transport indicate that the Gorgonilla spherule layer represents an almost unaltered primary suspension settling deposit. Keywords: K/Pg boundary, Chicxulub, spherules, eastern Pacific, Colombia
Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excurs... more Surface dwelling planktic foraminifera, H. planispira, register a +2.0 to 2.5 ppm delta13C excursion straddling the Harland Shale and Bridge Creek Limestone member (latest Cenomanian) at the Pueblo Stratotype, Colorado. Post-excursion, the delta13C values remain at approximately 2.0 ppm dipping only slightly in the early Turonian (H. helvetica zone). During the initial phases of the delta13C excursion, 5 planktic species consecutively become extinct (Rotalipora deekei, R. greenhornensis, R. cushmani, P. inornata, G. bentonensis). These are subsequently replaced in the latter stages of the excursions by 5 new species with high depth tolerances, resulting in no net diversity loss. The extinction is therefore likely to have been as a direct result from the increased water mass stratification. A temporary decrease in bottom water productivity is also suggested by oxygenated bottom waters (presence of Cibidicoides) and a minimum of low O_2 tolerant species (hetrohelicids). Elevated HI/OH...
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Papers by Gerta Keller
Keywords: K/Pg boundary, Chicxulub, spherules, eastern Pacific, Colombia
Keywords: K/Pg boundary, Chicxulub, spherules, eastern Pacific, Colombia