Harilaos Tsikos - Profile on Academia.edu (original) (raw)
Papers by Harilaos Tsikos
Paleoceanography, 2005
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
Proc. 1st Meeting C. …, Jan 1, 2005
The largest deposit of excellently preserved Mio-Pliocene vertebrate faunas in SouthAfrica is loc... more The largest deposit of excellently preserved Mio-Pliocene vertebrate faunas in SouthAfrica is located at the well known Langebaanweg (LBW) site along South Africa’s west coast in the southwestern Cape. This research deals with a core (BH2) drilled at Langebaanweg ‘E’ Quarry, which captures Miocene fluvial deposits that unconformably underlie the Mio-Pliocene deposits. The aim of the study is to constrain fluctuations in climate and ecosystems in the region during the Miocene, using a combination of sedimentology, palynology, and biogeochemistry. The latter is a novel application and includes bulk C and N isotope measurements as well as branched GDGT (glycerol dialkyl glycerol tetraether) membrane lipid compositions of the organic fraction of the core. The mean annual temperature (MAT) at time of deposition and ambient pH values were calculated using the Methylation index of Branched Tetraethers (MBT) and Cyclization ratio of Branched Tetraethers (CBT) proxies. The core samples analy...
Paleoceanography, 2005
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
Organic material from the Noordhoek area on the western margin of the Cape Peninsula, South Afric... more Organic material from the Noordhoek area on the western margin of the Cape Peninsula, South Africa, was obtained from a ~ 50 m-long drill-core dominated by fluvio-lacustrine siliciclastic sediments. The aim of this study is to constrain fluctuations in climate and the decline of tropical vegetation elements along the southwestern coast and the Cape Peninsula of South Africa, during the Late Cenozoic phase, when the Benguela upwelling system was established. The approach was to combine palynological, biogeochemical (tetraether lipids) and stable isotope (C, N) studies of the organic-bearing record from the Noordhoek area on the western margin of the Cape Peninsula. Bulk C and N isotope data of sediment organic matter, point to a predominantly C 3 higher plant source vegetation. Mean annual air temperature (MAT) from the analyses of tetraether lipids (MBT′–CBT index) was compared with palynomorphs from partly unpublished data of a previously drilled core adjacent to the study site. The palynomorphs are of subtropical affinities, and suggest that an open riparian forest would have existed in the early to middle Miocene of the southwestern coast of South Africa. Together these data sources allow vegetation and climate reconstructions of subtropical conditions during the early to middle Miocene, which comprised fluctuating open riparian forest and swamp vegetation. Temperatures rose in the middle Miocene and were higher than those of the present day.
Journal of the Geological Society, 2005
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4‰ for TOC and phytane and c. 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak ä 13 C values for all components are followed by intervals of high, near-constant ä 13 C in the form of an isotopic plateau. Recognition of an unambiguous return to background ä 13 C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil Quadrum gartneri at or near the Cenomanian-Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the ä 13 C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.
Geological Magazine, 2004
We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for the Vigl... more We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for the Vigla Shale Member of the Ionian Zone in NW Greece, in order to characterize organic carbon-rich strata that potentially record the impact of Cretaceous Oceanic Anoxic Events (OAEs). In a section exposed near Gotzikas (NW Epirus), we sampled a number of decimetre-thick, organic carbon-rich units enclosed within marly, locally silicified, Vigla Limestone (Berriasian-Turonian). All these units are characterized by largely comparable bulk geochemical characteristics, indicating a common marine origin and low thermal maturity. However, the stratigraphically highest of these black shales is further distinguished by its much higher total organic-carbon (TOC) content (28.9 wt %) and Hydrogen Index (HI) (529), and much enriched δ 13 C org value (−22.1 ‰). Planktonic foraminiferal and calcareous nannofossil biostratigraphy indicate a lower to middle Albian age for the strata immediately above, and a lower Aptian age for the strata below, the uppermost black shale. In terms of molecular organic geochemistry, the latter black shale is also relatively enriched in specific isoprenoidal compounds (especially monocyclic isoprenoids), whose isotopic values are as high as −15 ‰, indicating a substantial archaeal contribution to the organic matter. The striking similarities between the molecular signatures of the uppermost Vigla black shale and coeval organic-rich strata from SE France and the North Atlantic (ODP Site 1049C) indicate that this level constitutes a record of the Paquier Event (OAE 1b).
Journal of the Geological Society, 2005
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4‰ for TOC and phytane and c. 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak ä 13 C values for all components are followed by intervals of high, near-constant ä 13 C in the form of an isotopic plateau. Recognition of an unambiguous return to background ä 13 C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil Quadrum gartneri at or near the Cenomanian-Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the ä 13 C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.
Paleoceanography, 2007
1] Organic carbon-rich shales from localities in England, Italy, and Morocco, which formed during... more 1] Organic carbon-rich shales from localities in England, Italy, and Morocco, which formed during the Cenomanian-Turonian oceanic anoxic event (OAE), have been examined for their total organic carbon (TOC) values together with their carbon, nitrogen, and iron isotope ratios. Carbon isotope stratigraphy (d 13 C org and d 13 C carb ) allows accurate recognition of the strata that record the oceanic anoxic event, in some cases allowing characterization of isotopic species before, during, and after the OAE. Within the black shales formed during the OAE, relatively heavy nitrogen isotope ratios, which correlate positively with TOC, suggest nitrate reduction (leading ultimately to denitrification and/or anaerobic ammonium oxidation). Black shales deposited before the onset of the OAE in Italy have unusually low bulk d 57 Fe values, unlike those found in the black shale (Livello Bonarelli) deposited during the oceanic anoxic event itself: These latter conform to the Phanerozoic norm for organic-rich sediments. Pyrite formation in the pre-OAE black shales has apparently taken place via dissimilatory iron reduction (DIR), within the sediment, a suboxic process that causes an approximately À2% fractionation between a lithogenic Fe(III)oxide source and Fe(II) aq . In contrast, bacterial sulfate reduction (BSR), at least partly in the water column, characterized the OAE itself and was accompanied by only minor iron isotope fractionation. This change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from 10to10 to 10to7 mm. The gradual, albeit irregular increase in Fe isotope values during the OAE, as recorded in the Italian section, is taken to demonstrate limited isotopic evolution of the dissolved iron pool, consequent upon ongoing water column precipitation of pyrite under euxinic conditions. Given that evidence exists for both nitrate and sulfate reduction during the OAE, it is evident that redox conditions in the water column were highly variable, in both time and space. Citation: Jenkyns, H. C., A. Matthews, H. Tsikos, and Y. Erel (2007), Nitrate reduction, sulfate reduction, and sedimentary iron isotope evolution during the Cenomanian-Turonian oceanic anoxic event, Paleoceanography, 22, PA3208,
Carbon-isotope stratigraphy of the Cenomanian-Turonian Oceanic Anoxic Event: correlation and implications based on three key-localities
Journal of The Geological Society, 2004
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4
International Journal of Earth Sciences, 2006
Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphi... more Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes) and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate-black shale succession of the Ionian Zone (western Greece), provide the first evidence for the Cenomanian-Turonian oceanic anoxic event (OAE2, 'Bonarelli' event) in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich (44.5 wt% TOC), carbonate-free black shale, near the Cenomanian-Turonian boundary within the Vigla limestone formation (Berriasian-Turonian). Compared to the 'Bonarelli' black-shale interval from the type locality of OAE2 in Marche-Umbria, Italy, this black shale exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched d 13 C values for both bulk organic matter (-22.2&) and specific organic compounds are up to 5& higher than those of underlying organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian-Turonian black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N 2 -fixing cyanobacteria in Cretaceous oceans during the Cenomanian-Turonian and early Aptian oceanic anoxic events.
No evidence for large-scale thermogenic methane release by the Karoo-Ferrar large igneous province
2007 GSA Denver Annual Meeting (2831 October 2007). Paper No. 111-31, Presentation Time: 1:30 PM... more 2007 GSA Denver Annual Meeting (2831 October 2007). Paper No. 111-31, Presentation Time: 1:30 PM-5:30 PM. NO EVIDENCE FOR LARGE-SCALE THERMOGENIC METHANE RELEASE BY THE KAROO-FERRAR LARGE IGNEOUS PROVINCE. ...
Mechanisms of black shale deposition at the NW African shelf during the Cenomanian/Turonian oceanic anoxic event: implications for climate coupling and global organic carbon burial
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
The Mineralogy and Geochemistry of the Voëlwater Banded Iron-formation, Northern Cape Province
A review of fluid-rock interaction processes in the Kalahari manganese field, South Africa, using host-rock stable isotope geochemistry
Low δ57Fe values record the onset of Palaeoproterozoic bacterial manganese reduction
Hydrothermal aegirine from the Palaeoproterozoic Hotazel iron-formation, Kalahari Manganese Field, South Africa, and its possible implications
Paleoceanography, 2005
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
Proc. 1st Meeting C. …, Jan 1, 2005
The largest deposit of excellently preserved Mio-Pliocene vertebrate faunas in SouthAfrica is loc... more The largest deposit of excellently preserved Mio-Pliocene vertebrate faunas in SouthAfrica is located at the well known Langebaanweg (LBW) site along South Africa’s west coast in the southwestern Cape. This research deals with a core (BH2) drilled at Langebaanweg ‘E’ Quarry, which captures Miocene fluvial deposits that unconformably underlie the Mio-Pliocene deposits. The aim of the study is to constrain fluctuations in climate and ecosystems in the region during the Miocene, using a combination of sedimentology, palynology, and biogeochemistry. The latter is a novel application and includes bulk C and N isotope measurements as well as branched GDGT (glycerol dialkyl glycerol tetraether) membrane lipid compositions of the organic fraction of the core. The mean annual temperature (MAT) at time of deposition and ambient pH values were calculated using the Methylation index of Branched Tetraethers (MBT) and Cyclization ratio of Branched Tetraethers (CBT) proxies. The core samples analy...
Paleoceanography, 2005
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
Organic material from the Noordhoek area on the western margin of the Cape Peninsula, South Afric... more Organic material from the Noordhoek area on the western margin of the Cape Peninsula, South Africa, was obtained from a ~ 50 m-long drill-core dominated by fluvio-lacustrine siliciclastic sediments. The aim of this study is to constrain fluctuations in climate and the decline of tropical vegetation elements along the southwestern coast and the Cape Peninsula of South Africa, during the Late Cenozoic phase, when the Benguela upwelling system was established. The approach was to combine palynological, biogeochemical (tetraether lipids) and stable isotope (C, N) studies of the organic-bearing record from the Noordhoek area on the western margin of the Cape Peninsula. Bulk C and N isotope data of sediment organic matter, point to a predominantly C 3 higher plant source vegetation. Mean annual air temperature (MAT) from the analyses of tetraether lipids (MBT′–CBT index) was compared with palynomorphs from partly unpublished data of a previously drilled core adjacent to the study site. The palynomorphs are of subtropical affinities, and suggest that an open riparian forest would have existed in the early to middle Miocene of the southwestern coast of South Africa. Together these data sources allow vegetation and climate reconstructions of subtropical conditions during the early to middle Miocene, which comprised fluctuating open riparian forest and swamp vegetation. Temperatures rose in the middle Miocene and were higher than those of the present day.
Journal of the Geological Society, 2005
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4‰ for TOC and phytane and c. 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak ä 13 C values for all components are followed by intervals of high, near-constant ä 13 C in the form of an isotopic plateau. Recognition of an unambiguous return to background ä 13 C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil Quadrum gartneri at or near the Cenomanian-Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the ä 13 C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.
Geological Magazine, 2004
We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for the Vigl... more We present new stable (C, O) isotopic, biostratigraphic and organic geochemical data for the Vigla Shale Member of the Ionian Zone in NW Greece, in order to characterize organic carbon-rich strata that potentially record the impact of Cretaceous Oceanic Anoxic Events (OAEs). In a section exposed near Gotzikas (NW Epirus), we sampled a number of decimetre-thick, organic carbon-rich units enclosed within marly, locally silicified, Vigla Limestone (Berriasian-Turonian). All these units are characterized by largely comparable bulk geochemical characteristics, indicating a common marine origin and low thermal maturity. However, the stratigraphically highest of these black shales is further distinguished by its much higher total organic-carbon (TOC) content (28.9 wt %) and Hydrogen Index (HI) (529), and much enriched δ 13 C org value (−22.1 ‰). Planktonic foraminiferal and calcareous nannofossil biostratigraphy indicate a lower to middle Albian age for the strata immediately above, and a lower Aptian age for the strata below, the uppermost black shale. In terms of molecular organic geochemistry, the latter black shale is also relatively enriched in specific isoprenoidal compounds (especially monocyclic isoprenoids), whose isotopic values are as high as −15 ‰, indicating a substantial archaeal contribution to the organic matter. The striking similarities between the molecular signatures of the uppermost Vigla black shale and coeval organic-rich strata from SE France and the North Atlantic (ODP Site 1049C) indicate that this level constitutes a record of the Paquier Event (OAE 1b).
Journal of the Geological Society, 2005
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4‰ for TOC and phytane and c. 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak ä 13 C values for all components are followed by intervals of high, near-constant ä 13 C in the form of an isotopic plateau. Recognition of an unambiguous return to background ä 13 C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil Quadrum gartneri at or near the Cenomanian-Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the ä 13 C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.
Paleoceanography, 2007
1] Organic carbon-rich shales from localities in England, Italy, and Morocco, which formed during... more 1] Organic carbon-rich shales from localities in England, Italy, and Morocco, which formed during the Cenomanian-Turonian oceanic anoxic event (OAE), have been examined for their total organic carbon (TOC) values together with their carbon, nitrogen, and iron isotope ratios. Carbon isotope stratigraphy (d 13 C org and d 13 C carb ) allows accurate recognition of the strata that record the oceanic anoxic event, in some cases allowing characterization of isotopic species before, during, and after the OAE. Within the black shales formed during the OAE, relatively heavy nitrogen isotope ratios, which correlate positively with TOC, suggest nitrate reduction (leading ultimately to denitrification and/or anaerobic ammonium oxidation). Black shales deposited before the onset of the OAE in Italy have unusually low bulk d 57 Fe values, unlike those found in the black shale (Livello Bonarelli) deposited during the oceanic anoxic event itself: These latter conform to the Phanerozoic norm for organic-rich sediments. Pyrite formation in the pre-OAE black shales has apparently taken place via dissimilatory iron reduction (DIR), within the sediment, a suboxic process that causes an approximately À2% fractionation between a lithogenic Fe(III)oxide source and Fe(II) aq . In contrast, bacterial sulfate reduction (BSR), at least partly in the water column, characterized the OAE itself and was accompanied by only minor iron isotope fractionation. This change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from 10to10 to 10to7 mm. The gradual, albeit irregular increase in Fe isotope values during the OAE, as recorded in the Italian section, is taken to demonstrate limited isotopic evolution of the dissolved iron pool, consequent upon ongoing water column precipitation of pyrite under euxinic conditions. Given that evidence exists for both nitrate and sulfate reduction during the OAE, it is evident that redox conditions in the water column were highly variable, in both time and space. Citation: Jenkyns, H. C., A. Matthews, H. Tsikos, and Y. Erel (2007), Nitrate reduction, sulfate reduction, and sedimentary iron isotope evolution during the Cenomanian-Turonian oceanic anoxic event, Paleoceanography, 22, PA3208,
Carbon-isotope stratigraphy of the Cenomanian-Turonian Oceanic Anoxic Event: correlation and implications based on three key-localities
Journal of The Geological Society, 2004
We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) an... more We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian-Turonian boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4
International Journal of Earth Sciences, 2006
Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphi... more Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes) and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate-black shale succession of the Ionian Zone (western Greece), provide the first evidence for the Cenomanian-Turonian oceanic anoxic event (OAE2, 'Bonarelli' event) in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich (44.5 wt% TOC), carbonate-free black shale, near the Cenomanian-Turonian boundary within the Vigla limestone formation (Berriasian-Turonian). Compared to the 'Bonarelli' black-shale interval from the type locality of OAE2 in Marche-Umbria, Italy, this black shale exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched d 13 C values for both bulk organic matter (-22.2&) and specific organic compounds are up to 5& higher than those of underlying organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian-Turonian black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N 2 -fixing cyanobacteria in Cretaceous oceans during the Cenomanian-Turonian and early Aptian oceanic anoxic events.
No evidence for large-scale thermogenic methane release by the Karoo-Ferrar large igneous province
2007 GSA Denver Annual Meeting (2831 October 2007). Paper No. 111-31, Presentation Time: 1:30 PM... more 2007 GSA Denver Annual Meeting (2831 October 2007). Paper No. 111-31, Presentation Time: 1:30 PM-5:30 PM. NO EVIDENCE FOR LARGE-SCALE THERMOGENIC METHANE RELEASE BY THE KAROO-FERRAR LARGE IGNEOUS PROVINCE. ...
Mechanisms of black shale deposition at the NW African shelf during the Cenomanian/Turonian oceanic anoxic event: implications for climate coupling and global organic carbon burial
1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T... more 1] High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid-Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from 2g/m2AˊyrpriortotheOAE2to2 g/m 2 Á yr prior to the OAE2 to 2g/m2AˊyrpriortotheOAE2to12 g/m 2 Á yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that 22% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only 20.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2. Citation: Kolonic, S., et al. (2005), Black shale deposition on the northwest African Shelf during the Cenomanian/Turonian oceanic anoxic event: Climate coupling and global organic carbon burial, Paleoceanography, 20, PA1006,
The Mineralogy and Geochemistry of the Voëlwater Banded Iron-formation, Northern Cape Province
A review of fluid-rock interaction processes in the Kalahari manganese field, South Africa, using host-rock stable isotope geochemistry
Low δ57Fe values record the onset of Palaeoproterozoic bacterial manganese reduction
Hydrothermal aegirine from the Palaeoproterozoic Hotazel iron-formation, Kalahari Manganese Field, South Africa, and its possible implications