Abdel Aziz Tantawy - Profile on Academia.edu (original) (raw)
Papers by Abdel Aziz Tantawy
Stratigraphy of the Late Cretaceous-Early Tertiary sediments of Sin El-Kaddab-Wadi Abu Ghurra stretch, southwest of the Nile Valley
ABSTRACT Five Late Cretaceous-Early Tertiary successions outcropping along the western scarp whic... more ABSTRACT Five Late Cretaceous-Early Tertiary successions outcropping along the western scarp which faces the Nile Valley between Sin El Kaddab in the south and Wadi Abu Ghurra in the north, Western Desert, have been critically investigated both lithologically and micropaleontologically. This enabled a correlation with comparable K-T successions in Egypt. The succession is subdivided into a number of lithologic and biostratigraphic units, and the foraminifera are used to interprete the stratigraphy and paleoecology of the region. Biostratigraphic interpretation reveals that the Campanian/Maastrichtian boundary cuts through the lower part of Kiseiba Formation which represents the southern nearshore facies of Qusier Formation and the greater part of Dakhla Formation. The Maastrichtian/Danian boundary lies in the north within the upper third part of the Dakhla Formation, whereas in the south it is coincident with the lithologic boundary between Kiseiba and Kurkur formations. A distinct ...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2015
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.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
The Gongzha section of Tibet, China is located at the northern margin of the Indian Plate (SE Tet... more The Gongzha section of Tibet, China is located at the northern margin of the Indian Plate (SE Tethys) and is characterized by hemipelagic grey marls and marly limestones, light grey limestones and silty limestones, but no organic-rich sediments. High-resolution biostratigraphy reveals an expanded Cenomanian-Turonian (CT) boundary interval and the δ 13 C record includes the main features of the classical positive carbon-isotope excursion that characterizes the CT oceanic anoxic event. The biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed, except for a short interval marked by peak abundance of Heterohelix that indicates a significantly dysoxic environment during the δ 13 C "b" peak excursion. The overall decreasing trend in redox-sensitive trace elements (RSTE) during the maximum δ 13 C excursion confirms the absence of significant longer-lasting anoxia in the Gongzha section. Enrichments in RSTE are linked to phases of increased detrital input. Chemical weathering indices suggest that the upper Cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the CT boundary. In the early Turonian lower weathering indices suggest a warm, drier climatic regime with reduced continental runoff. Phosphorus mass-accumulation rates show a significant peak at the onset of the positive δ 13 C excursion, followed by a decrease up to the basal Turonian. This pattern is positively correlated with the long-term decrease in detrital index as also observed in numerous other CT boundary sections (e.g., Eastbourne, Pueblo, and Whadi El Ghaib, Sinaï). Long-term phosphorus accumulation in the Gongzha section is therefore associated with changes in detrital input. The overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of Cenomanian, coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2009
The biotic effects of volcanism have long been the unknown factors in creating biotic stress, and... more The biotic effects of volcanism have long been the unknown factors in creating biotic stress, and the contribution of the Deccan volcanism to the K-T mass extinction remains largely unknown. Detailed studies of the volcanic-rich sediments of Indian Ocean Ninetyeast Ridge Sites 216 and 217 and Wharton Basin Site 212 reveal that the biotic effects of late Maastrichtian volcanism on planktic foraminifera and calcareous nannofossils are locally as severe as those of the K-T mass extinction. The biotic expressions of these high stress environments are characterized by the Lilliput effect, which includes reduced diversity by eliminating most K-strategy species, and reduction in specimen size (dwarfing), frequently to less than half their normal adult size of both r-strategy and surviving K-strategy species. In planktic foraminifera, the most extreme biotic stress results are nearly monospecific assemblages dominated by the disaster opportunist Guembelitria, similar to the aftermath of the K-T mass extinction. The first stage of improving environmental conditions results in dominance of dwarfed low oxygen tolerant Heterohelix species and the presence of a few small r-strategy species (Hedbergella, Globigerinelloides). Calcareous nannofossil assemblages show similar biotic stress signals with the dominance of Micula decussata, the disaster opportunist, and size reduction in the mean length of subordinate r-strategy species particularly in Arkhangelskiella cymbiformis and Watznaueria barnesiae. These impoverished and dwarfed late Maastrichtian assemblages appear to be the direct consequences of mantle plume volcanism and associated environmental changes, including high nutrient influx leading to eutrophic and mesotrophic waters, low oxygen in the water column and decreased watermass stratification.
Climatic and environmental changes documented in the upper Paleocene to lower Eocene of Egypt
Eclogae Geologicae Helvetiae
ABSTRACT
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a an... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in d 13 C org for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 d 13 C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian-Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.
The response of shallow-water sequences to oceanic anoxic event 2 and mid- Cenomanian events 1a a... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-
Cenomanian events 1a and 1b was investigated along the west African margin
of Morocco north of Agadir (Azazoul) and correlated with the deep-water
sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy,
mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach
section results show double peaks in d13Corg for mid-Cenomanian events 1a
and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic
oceanic anoxic event 2 d13C excursion (Rotalipora cushmani extinction, top of
CC10a biozone) and laminated (anoxic) black shale. In the shallow
environment north of Agadir, a fluctuating sea-level associated with dysoxic,
brackish and mesotrophic conditions prevailed during the middle to late
Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and
benthonic foraminiferal assemblages. Anoxic conditions characteristic of
oceanic anoxic event 2 (for example, laminated black shales) did not reach
into shallow-water environments until the maximum transgression of the early
Turonian. Climate conditions decoupled along the western margin of Morocco
between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary,
as also observed in eastern Tethys. North of Agadir alternating humid and dry
seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was
dry and seasonal. This climatic decoupling can be attributed to variations in
the Intertropical Convergence Zone and in the intensity of the north-east trade
winds in tropical areas.
During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an a... more During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (w100 m) depths with largely dysaerobic bottom waters (abundant low O 2 tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred w500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.
Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in ... more Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, d 13 C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian-early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, lowoxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak d 13 C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the d 13 C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the d 13 C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first d 13 C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous d 13 C shift, but delayed effects of OAE2 dependent on water depth.
Earth and Planetary Science Letters, 2007
Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of... more Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact, the event deposit and the K-T boundary event. The K-T boundary, as identified by the negative δ 13 C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K-T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with recolonization of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay-and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K-T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.
Cretaceous Research, 2007
During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an a... more During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (w100 m) depths with largely dysaerobic bottom waters (abundant low O 2 tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred w500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.
From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insights from the Wadi Nukhul Section (Sinai, Egypt)
From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insight... more From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insights from the Wadi Nukhul Section (Sinai, Egypt)
![Research paper thumbnail of Corrigendum to: “High stress late Maastrichtian – early Danian palaeoenvironment in the Neuquén Basin, Argentina” [Cretaceous Research 28 (2007) 939–960]](https://attachments.academia-assets.com/39248069/thumbnails/1.jpg)
](Cretaceous Research, 2009
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a an... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in d 13 C org for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 d 13 C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian-Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.
Cretaceous Research, 2001
Cretaceous Research, 2011
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 δ 13 C 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 δ 13 C 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 δ 13 C 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. Gebhardt et al., 2010). OAE2 is characterized by a ~2-3‰ positive shift in carbon isotopes and up to 6‰ in organic carbon that reflects an increase in productivity and/or carbon burial (Arthur et al.
Calcareous nannofossils of the Paleocene-Eocene transition at Qena Region, Central Nile Valley, Egypt
Micropaleontology, 2006
ABSTRACT The Paleocene-Eocene transition is exposed at Gebel Serai, 50km east of Qena, and at Tar... more ABSTRACT The Paleocene-Eocene transition is exposed at Gebel Serai, 50km east of Qena, and at Taramsa, 10km west of Qena in the central Nile Valley of Egypt. The continuous deposition across the P/E boundary, the negative delta C-13 excursion (CIE), the good preservation and high diversity of the calcareous nannofossil assemblages as well as the occurrence of distinctive floral events confer to these localities a potential role as P/E reference-sections. A major nannofossil turnover occurs around the P/E boundary (NP9a/NP9b subzonal boundary) marked by an abrupt decrease of Fasciculithus spp. at the onset of CIE concomitant with a sharp decrease in the abundance of Toweius spp.. The middle and upper part of the CIE-interval are characterized by successive shifts of oligotrophic, warm-water taxa, including the first acme of Coccolithus pelagicus/subpertusa, followed by a rapid increase in abundance of Rhomboaster spp., a sharp increase of long-armed, asymmetrical discoasters, and a second shift of Coccolithus pelagicus/subpertusa. Immediately above the CIE-interval and continuing up to the top of the section, a gradual increase of Toweius spp. accompanied by a gradual decrease in Coccolithus pelagicus/subpertusa indicates a return to a cooler, mesotrophic to eutrophic environment.
![Research paper thumbnail of Corrigendum to: “High stress late Maastrichtian – early Danian palaeoenvironment in the Neuquén Basin, Argentina” [Cretaceous Research 28 (2007) 939–960]](https://attachments.academia-assets.com/50257874/thumbnails/1.jpg)
](Cretaceous Research, 2009
The Cenomanian-Turonian boundary is marked by an Oceanic Anoxic Event (OAE 2) characterized by fi... more The Cenomanian-Turonian boundary is marked by an Oceanic Anoxic Event (OAE 2) characterized by finely laminated organic carbon rich sediments deposited under oxygen depleted conditions, coinciding with a positive shift in 13C isotope excursion. The main goal of the present research is to get a better understanding of mechanisms which triggered these OAEs, and particularly the paleoenvironmental conditions which characterized the onset of that major anoxic event and their evolution. demonstrated that the onset of the Cenomanian-Turonian OAE was triggered by a short-lived but significant increase in phosphorus burial. Then bottom waters became anoxic and switched from being a P sink to a P source, sustaining the productivity in a positive feedback loop. Increased aridity, removal of atmospheric CO2 by burial as organic carbon in black shales and reduction in nutrient availability may have been factors bringing about the return to more oxic oceans. However, Total Phosphorus (Ptot) and trace metals behaviour is not well known at larger scale, away from main black shales source (Western Tethys and Central Atlantic). It is especially interesting to see if P distribution will show a similar maximum predating the positive carbon excursion. We investigate therefore the section of Gongzha (Tibet, China) located at the north margin of the Indian plate in the Tethys Himalayas zone (SE Tethys). These sediments are deposited in open marine basin and slope settings under hemipelagic environment . Clay analyses show that the sediments have been overprinted by burial diagenesis and tectonic processes, but the biostratigraphy by foraminifera and nannofossils, microfacies and carbon stable isotopes data indicate a quite good preservation and absence of significant hiatus. Carbon isotope analyses exhibit the classical C-T positive shift with a first peak near the end of R. cushmani zone, a second in the lower part of W. archaeocretacea zone, followed by a plateau which ends the excursion. A bloom of Heterohelix and Guembelitria, low oxygen tolerant foraminifera, is observed in the upper part of the 13C shift (W. archaeocretacea zone) indicative of depleted oxygen conditions. Significant peaks in Ptot is observed at the onset of the 13C shift, followed by a depletion at the end of R. cushmani zone, persisting up to the end of W. archaeocretacea zone. In Tibet, P distribution patterns during OAE2 are quite similar to the ones observed in numerous sections in western Tethys and Central Atlantic (England, Italia, Spain and USA, Mort et al., 2007) and appear therefore to be global, coinciding partly with increased detrital inputs. Trace-metals values are under background level compared with sections characterized by strong anoxic conditions and redox sensitive elements such as Va, Ni, Co, U, generally indicative of anoxic conditions, do not show any increase during the maximum of 13C excursion and Heterohelix and Guembelitria shifts. This suggests that dysoxic rather than anoxic conditions prevailed in Tibet area during OAE 2. Increased Mg, Na, Ca contents to the detriment of Al suggest a change to more arid climate conditions from the base of archaeocretacea zone upwards.
Stratigraphy of the Late Cretaceous-Early Tertiary sediments of Sin El-Kaddab-Wadi Abu Ghurra stretch, southwest of the Nile Valley
ABSTRACT Five Late Cretaceous-Early Tertiary successions outcropping along the western scarp whic... more ABSTRACT Five Late Cretaceous-Early Tertiary successions outcropping along the western scarp which faces the Nile Valley between Sin El Kaddab in the south and Wadi Abu Ghurra in the north, Western Desert, have been critically investigated both lithologically and micropaleontologically. This enabled a correlation with comparable K-T successions in Egypt. The succession is subdivided into a number of lithologic and biostratigraphic units, and the foraminifera are used to interprete the stratigraphy and paleoecology of the region. Biostratigraphic interpretation reveals that the Campanian/Maastrichtian boundary cuts through the lower part of Kiseiba Formation which represents the southern nearshore facies of Qusier Formation and the greater part of Dakhla Formation. The Maastrichtian/Danian boundary lies in the north within the upper third part of the Dakhla Formation, whereas in the south it is coincident with the lithologic boundary between Kiseiba and Kurkur formations. A distinct ...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2015
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.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
The Gongzha section of Tibet, China is located at the northern margin of the Indian Plate (SE Tet... more The Gongzha section of Tibet, China is located at the northern margin of the Indian Plate (SE Tethys) and is characterized by hemipelagic grey marls and marly limestones, light grey limestones and silty limestones, but no organic-rich sediments. High-resolution biostratigraphy reveals an expanded Cenomanian-Turonian (CT) boundary interval and the δ 13 C record includes the main features of the classical positive carbon-isotope excursion that characterizes the CT oceanic anoxic event. The biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed, except for a short interval marked by peak abundance of Heterohelix that indicates a significantly dysoxic environment during the δ 13 C "b" peak excursion. The overall decreasing trend in redox-sensitive trace elements (RSTE) during the maximum δ 13 C excursion confirms the absence of significant longer-lasting anoxia in the Gongzha section. Enrichments in RSTE are linked to phases of increased detrital input. Chemical weathering indices suggest that the upper Cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the CT boundary. In the early Turonian lower weathering indices suggest a warm, drier climatic regime with reduced continental runoff. Phosphorus mass-accumulation rates show a significant peak at the onset of the positive δ 13 C excursion, followed by a decrease up to the basal Turonian. This pattern is positively correlated with the long-term decrease in detrital index as also observed in numerous other CT boundary sections (e.g., Eastbourne, Pueblo, and Whadi El Ghaib, Sinaï). Long-term phosphorus accumulation in the Gongzha section is therefore associated with changes in detrital input. The overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of Cenomanian, coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2009
The biotic effects of volcanism have long been the unknown factors in creating biotic stress, and... more The biotic effects of volcanism have long been the unknown factors in creating biotic stress, and the contribution of the Deccan volcanism to the K-T mass extinction remains largely unknown. Detailed studies of the volcanic-rich sediments of Indian Ocean Ninetyeast Ridge Sites 216 and 217 and Wharton Basin Site 212 reveal that the biotic effects of late Maastrichtian volcanism on planktic foraminifera and calcareous nannofossils are locally as severe as those of the K-T mass extinction. The biotic expressions of these high stress environments are characterized by the Lilliput effect, which includes reduced diversity by eliminating most K-strategy species, and reduction in specimen size (dwarfing), frequently to less than half their normal adult size of both r-strategy and surviving K-strategy species. In planktic foraminifera, the most extreme biotic stress results are nearly monospecific assemblages dominated by the disaster opportunist Guembelitria, similar to the aftermath of the K-T mass extinction. The first stage of improving environmental conditions results in dominance of dwarfed low oxygen tolerant Heterohelix species and the presence of a few small r-strategy species (Hedbergella, Globigerinelloides). Calcareous nannofossil assemblages show similar biotic stress signals with the dominance of Micula decussata, the disaster opportunist, and size reduction in the mean length of subordinate r-strategy species particularly in Arkhangelskiella cymbiformis and Watznaueria barnesiae. These impoverished and dwarfed late Maastrichtian assemblages appear to be the direct consequences of mantle plume volcanism and associated environmental changes, including high nutrient influx leading to eutrophic and mesotrophic waters, low oxygen in the water column and decreased watermass stratification.
Climatic and environmental changes documented in the upper Paleocene to lower Eocene of Egypt
Eclogae Geologicae Helvetiae
ABSTRACT
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a an... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in d 13 C org for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 d 13 C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian-Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.
The response of shallow-water sequences to oceanic anoxic event 2 and mid- Cenomanian events 1a a... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-
Cenomanian events 1a and 1b was investigated along the west African margin
of Morocco north of Agadir (Azazoul) and correlated with the deep-water
sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy,
mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach
section results show double peaks in d13Corg for mid-Cenomanian events 1a
and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic
oceanic anoxic event 2 d13C excursion (Rotalipora cushmani extinction, top of
CC10a biozone) and laminated (anoxic) black shale. In the shallow
environment north of Agadir, a fluctuating sea-level associated with dysoxic,
brackish and mesotrophic conditions prevailed during the middle to late
Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and
benthonic foraminiferal assemblages. Anoxic conditions characteristic of
oceanic anoxic event 2 (for example, laminated black shales) did not reach
into shallow-water environments until the maximum transgression of the early
Turonian. Climate conditions decoupled along the western margin of Morocco
between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary,
as also observed in eastern Tethys. North of Agadir alternating humid and dry
seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was
dry and seasonal. This climatic decoupling can be attributed to variations in
the Intertropical Convergence Zone and in the intensity of the north-east trade
winds in tropical areas.
During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an a... more During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (w100 m) depths with largely dysaerobic bottom waters (abundant low O 2 tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred w500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.
Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in ... more Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, d 13 C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian-early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, lowoxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak d 13 C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the d 13 C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the d 13 C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first d 13 C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous d 13 C shift, but delayed effects of OAE2 dependent on water depth.
Earth and Planetary Science Letters, 2007
Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of... more Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact, the event deposit and the K-T boundary event. The K-T boundary, as identified by the negative δ 13 C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K-T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with recolonization of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay-and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K-T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.
Cretaceous Research, 2007
During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an a... more During the late Maastrichtian to early Danian the Neuquén Basin of Argentina was adjacent to an active volcanic arc to the west and an extensive land area to the northeast. Mineralogical and geochemical studies of the Bajada del Jagüel in the Neuquén Basin indicate a generally warm climate with seasonal changes in humidity and an open seaway to the South Atlantic that maintained marine conditions. Biostratigraphic and quantitative foraminiferal and nannofossil analyses indicate that sediment deposition during the late Maastrichtian (zones CF4-CF2, N. frequens) occurred in relatively shallow middle neritic (w100 m) depths with largely dysaerobic bottom waters (abundant low O 2 tolerant benthics) and fluctuating sea level. Calcareous nannofossils indicate a high stress marine environment dominated by Micula decussata. Planktic foraminifera mimic the post-K/T high stress environment with alternating blooms of the disaster opportunists Guembelitria and low oxygen tolerant Heterohelix groups, indicating nutrient-rich surface waters and an oxygen depleted water column. The high stress conditions were probably driven by high nutrient influx due to upwelling and terrestrial and volcanic influx. The K/T boundary is marked by an erosional surface that marks a hiatus at the base of a 15-25 cm thick volcaniclastic sandstone, which contains diverse planktic foraminiferal zone P1c assemblages and nannofossils of zone NP1b immediately above it. This indicates deposition of the sandstone occurred w500 ky after the K/T hiatus. No evidence of the Chicxulub impact or related tsunami deposition was detected.
From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insights from the Wadi Nukhul Section (Sinai, Egypt)
From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insight... more From the Cretaceous-Tertiary Boundary to the Paleocene-Eocene Thermal Maximum (PETM): New Insights from the Wadi Nukhul Section (Sinai, Egypt)
Cretaceous Research, 2009
The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a an... more The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in d 13 C org for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 d 13 C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian-Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.
Cretaceous Research, 2001
Cretaceous Research, 2011
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 δ 13 C 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 δ 13 C 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 δ 13 C 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. Gebhardt et al., 2010). OAE2 is characterized by a ~2-3‰ positive shift in carbon isotopes and up to 6‰ in organic carbon that reflects an increase in productivity and/or carbon burial (Arthur et al.
Calcareous nannofossils of the Paleocene-Eocene transition at Qena Region, Central Nile Valley, Egypt
Micropaleontology, 2006
ABSTRACT The Paleocene-Eocene transition is exposed at Gebel Serai, 50km east of Qena, and at Tar... more ABSTRACT The Paleocene-Eocene transition is exposed at Gebel Serai, 50km east of Qena, and at Taramsa, 10km west of Qena in the central Nile Valley of Egypt. The continuous deposition across the P/E boundary, the negative delta C-13 excursion (CIE), the good preservation and high diversity of the calcareous nannofossil assemblages as well as the occurrence of distinctive floral events confer to these localities a potential role as P/E reference-sections. A major nannofossil turnover occurs around the P/E boundary (NP9a/NP9b subzonal boundary) marked by an abrupt decrease of Fasciculithus spp. at the onset of CIE concomitant with a sharp decrease in the abundance of Toweius spp.. The middle and upper part of the CIE-interval are characterized by successive shifts of oligotrophic, warm-water taxa, including the first acme of Coccolithus pelagicus/subpertusa, followed by a rapid increase in abundance of Rhomboaster spp., a sharp increase of long-armed, asymmetrical discoasters, and a second shift of Coccolithus pelagicus/subpertusa. Immediately above the CIE-interval and continuing up to the top of the section, a gradual increase of Toweius spp. accompanied by a gradual decrease in Coccolithus pelagicus/subpertusa indicates a return to a cooler, mesotrophic to eutrophic environment.
Cretaceous Research, 2009
The Cenomanian-Turonian boundary is marked by an Oceanic Anoxic Event (OAE 2) characterized by fi... more The Cenomanian-Turonian boundary is marked by an Oceanic Anoxic Event (OAE 2) characterized by finely laminated organic carbon rich sediments deposited under oxygen depleted conditions, coinciding with a positive shift in 13C isotope excursion. The main goal of the present research is to get a better understanding of mechanisms which triggered these OAEs, and particularly the paleoenvironmental conditions which characterized the onset of that major anoxic event and their evolution. demonstrated that the onset of the Cenomanian-Turonian OAE was triggered by a short-lived but significant increase in phosphorus burial. Then bottom waters became anoxic and switched from being a P sink to a P source, sustaining the productivity in a positive feedback loop. Increased aridity, removal of atmospheric CO2 by burial as organic carbon in black shales and reduction in nutrient availability may have been factors bringing about the return to more oxic oceans. However, Total Phosphorus (Ptot) and trace metals behaviour is not well known at larger scale, away from main black shales source (Western Tethys and Central Atlantic). It is especially interesting to see if P distribution will show a similar maximum predating the positive carbon excursion. We investigate therefore the section of Gongzha (Tibet, China) located at the north margin of the Indian plate in the Tethys Himalayas zone (SE Tethys). These sediments are deposited in open marine basin and slope settings under hemipelagic environment . Clay analyses show that the sediments have been overprinted by burial diagenesis and tectonic processes, but the biostratigraphy by foraminifera and nannofossils, microfacies and carbon stable isotopes data indicate a quite good preservation and absence of significant hiatus. Carbon isotope analyses exhibit the classical C-T positive shift with a first peak near the end of R. cushmani zone, a second in the lower part of W. archaeocretacea zone, followed by a plateau which ends the excursion. A bloom of Heterohelix and Guembelitria, low oxygen tolerant foraminifera, is observed in the upper part of the 13C shift (W. archaeocretacea zone) indicative of depleted oxygen conditions. Significant peaks in Ptot is observed at the onset of the 13C shift, followed by a depletion at the end of R. cushmani zone, persisting up to the end of W. archaeocretacea zone. In Tibet, P distribution patterns during OAE2 are quite similar to the ones observed in numerous sections in western Tethys and Central Atlantic (England, Italia, Spain and USA, Mort et al., 2007) and appear therefore to be global, coinciding partly with increased detrital inputs. Trace-metals values are under background level compared with sections characterized by strong anoxic conditions and redox sensitive elements such as Va, Ni, Co, U, generally indicative of anoxic conditions, do not show any increase during the maximum of 13C excursion and Heterohelix and Guembelitria shifts. This suggests that dysoxic rather than anoxic conditions prevailed in Tibet area during OAE 2. Increased Mg, Na, Ca contents to the detriment of Al suggest a change to more arid climate conditions from the base of archaeocretacea zone upwards.