Petrophysical properties of volcanic rocks are controlled by lithology and subsequent modificatio... more Petrophysical properties of volcanic rocks are controlled by lithology and subsequent modification by alteration processes. Investigating the linkages, using a range of different techniques, are important to establish how petrophysical properties can inform about the alteration state of volcanic rocks. Here, we compile petrophysical data and correlate these with geochemical and mineralogical analyses acquired from a volcanic sequence on the Naturaliste Plateau, offshore southwest Australia (IODP Site U1513). The sequence consists of alternating basalt lava flows and volcaniclastic deposits, intruded by multiple dolerite dikes. Variable alteration intensities from fresh-slight to strong are quantified using Chemical Index of Alteration. Intervals of slightly altered dikes exhibit low porosity and high values of bulk density, P-wave velocity and thermal conductivity. The increase of alteration intensity corresponds to decreases in bulk density to ∼2 g/cm3, P-wave velocity to ∼2000 m/s, thermal conductivity to ∼1.2 W/(m·K) and an increase in porosity up to 50%. Natural Gamma Ray and magnetic susceptibility vary downhole with rock composition and at lithologic boundaries. The distinct variations exhibit a good correlation with primary lithologic characteristics and secondary mineralogical and textural changes attributed to alteration processes. We provide synthesis models of petrophysical variation with alteration intensity. Although differences in primary lithology and alteration type introduce limitations and uncertainties, there is a reasonable applicability of our results to rapidly characterize the alteration intensity and volcanic stratigraphy in volcanic sequences and to calibrate wireline log-based determinations. This will help others to develop strategies for exploration, drilling, and geophysical research of volcanic rocks.
Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present... more Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present during the deposition of organic-rich sediments. For example, TME concentrations controlled by changes in primary productivity and redox conditions are widely used in paleoenvironmental studies. Recently, these proxies have undergone a resurgence of interest and are commonly used in large-scale (10–1000 km) studies. However, applying these geochemical proxies at basin scale while ignoring variations in sedimentation rates (SR) may lead to misinterpretation of paleoenvironmental conditions. Here, we show how SR can affect the geochemical records and may lead to incorrect interpretations of TME evolution. Accounting for SR, we computed the authigenic fraction accumulation rates of key TMEs in the Upper Montney Formation and Doig Phosphate (Triassic, western Canada), and we correct the concentration of these elements in the Vaca-Muerta Formation (Jurassic–Cretaceous, Argentina). Our SR-cor...
Abstract The Late Jurassic was a period of major global carbon cycle perturbations with episodes ... more Abstract The Late Jurassic was a period of major global carbon cycle perturbations with episodes of anoxia leading to regional accumulation of organic matter in sediments worldwide. The Tubiegatan section (SW Gissar Mountains, Uzbekistan) located in the Northern Tethys, shows atypical organic-rich limestone and marl deposits (up to 6% of total organic carbon) marked by pronounced negative excursions of δ13Ccarb (amplitude of ca. 12‰) and δ13Corg (amplitude of ca. 4‰) recorded during the Middle Oxfordian (Transversarium Zone). A transdisciplinary approach including sedimentology, palynofacies characterization, mineralogy, organic and inorganic geochemistry was carried out to elucidate the origin of these organic-rich deposits. Highest TOC are measured in nodular limestones, and lowest δ13Ccarb values in thinly laminated facies consisting in alternances of infra-millimeter-thick organic and carbonate laminae. In the latter, the presence of organic-carbonate peloids and of possible remnants of exopolymeric substances associated with clay indicate that these structures are probably mineralized laminated benthic microbial mats (i.e., stromatolites). Rock-Eval pyrolysis coupled to palynofacies analyses point to a dominant altered marine organic matter of probable algal/microbial origin, with subordinate continental phytoclasts inputs in the upper part of the organic-rich interval. Trace elements (U/Th, V/Cr and Mo/Al ratios) indicate two anoxic episodes coinciding with the highest TOC, punctuated by dysoxic periods. Such O2-depleted conditions have allowed the preservation and probably the development of anaerobic microbial communities in the microbial mats. In these latter, sulfate reduction probably had a significant contribution to the production of carbonates, which would explain the precipitation of pyrite and the relatively low δ13Ccarb values. The progressive decrease then disappearance of kaolinite from the base of the organic-rich interval, is interpreted as a progressive aridification of the Amu Darya Basin during the Transversarium Zone, culminating with the progradation of a large-scale gypsum sabkha overlying the organic deposits. Overall, the organic-rich deposits could record the onset of the disconnection of the Amu Darya Basin from the open sea to the south, induced by compression and subsequent uplifts in the Afghan and Central Iranian blocks. The elevated evaporation, coupled with the presence of hydrological barriers (such as coral reefs) could have led to the formation of local to regional anoxic conditions in the Amu Darya Basin. Similar microbial organic accumulations are recently known throughout the Tethys (e.g., Arabian Plate, Western Europe) and from other oceans (e.g., Central Atlantic, Pacific) during the Late Jurassic, suggesting common controlling factors. The increase of organic matter storage worldwide coupled with potential methane release could have in turn induced major perturbations of the carbon cycle during the Oxfordian-Kimmeridgian interval. The relatively shallow anoxia model proposed in this study contrasts with the well-known organic carbon-rich pelagic models proposed for the Jurassic anoxia (e.g., Toarcian, Kimmeridgian) and Cretaceous OAEs.
Geological Society, London, Special Publications, 2015
Limestones at the Puech de la Suque Global Boundary Stratotype Section and Point (GSSP) of the Gi... more Limestones at the Puech de la Suque Global Boundary Stratotype Section and Point (GSSP) of the Givetian–Frasnian boundary show a drastic change towards much higher magnetic susceptibility values in the Givetian rocks. Different rock magnetic parameters indicate that ferromagnetic minerals are the main controlling factor. The ferromagnetic fraction is composed of low- (magnetite-type) and high-coercivity (hematite and goethite) phases. Confirmed by the spectral reflectance, high coercivity minerals are fluctuating along the section with a higher abundance in the basal Frasnian. These phases may be of secondary origin and produced during burial stage. The magnetite-type phase contains two different grain-size populations. The identified that Stable Single-domain/Superparamagnetic (SSD/SP) particles are of diagenetic origin and their amount decreases slightly upwards. A second group of magnetite grains correspond to coarse-grained particles identified using the squareness v. coercive f...
Late Devonian time (Famennian, 376--362 Ma BP) is a period of both intense orogenic activity and ... more Late Devonian time (Famennian, 376--362 Ma BP) is a period of both intense orogenic activity and drastic climatic variations with the onset of a major glaciation event upon parts of the Gondwanian Southern America and Africa situated in high southern latitudes. This global cooling event is coeval with a significant fall in the atmospheric CO_2 content as suggested both by
... Averbuch, O., Tribovillard, N., Devleeschouwer, X., Riquier, L., Mistiaen, B. and Van Vliet-L... more ... Averbuch, O., Tribovillard, N., Devleeschouwer, X., Riquier, L., Mistiaen, B. and Van Vliet-Lanoe, B. (2005), Mountain building-enhanced ... of atmospheric CO 2 content (and the associated greenhouse effect) by increased silicate weathering (eg Raymo, 1991; François et al., 1993 ...
In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge co... more In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge commonly substitutes for Si (in small proportions) in silicates. Studying the evolution of the respective proportions of Ge and Si through time allows us to better constrain the ...
Developments in Palaeontology and Stratigraphy, 2005
ABSTRACT The Late Devonian Frasnian-Famennian (F-F) mass extinction event coincides in many place... more ABSTRACT The Late Devonian Frasnian-Famennian (F-F) mass extinction event coincides in many places with the depositionof Corg-rich “Kellwasser” facies. Four F-F boundary sections representative of platform and basin environments from widely separated locations (Morocco, Germany, and France) were analysed for inorganic geochemistry, especially trace elements (redox and productivity proxies), in order to describe paleodepositional environments for the Kellwasser horizons. Ni/Co, V/Cr, U/Th, and V/(V+Ni) ratios, as well as redox trace metal concentrations indicate that oxygen-depleted conditions existed during the times of Kellwasser facies deposition. In platform settings, dysoxic conditions seem to be limited to the Late Frasnian. In basinal settings, oxygen depletion was stronger and persisted into the Early Famennian. Enrichments of Ba, Cu, Ni, that are limited to the Late Frasnian, show that surface productivity was relatively high and organic matter could accumulate, especially in the deeper environments. The stratigraphical distribution of several geochemical markers are linked with two positive excursions of the δ13Ccarb signal that result from enhanced organic matter burial. Reducing conditions likely resulted from high productivity of Late Devonian marine ecosystems. Intense nutrient supply resulted probably from the biogeochemical recycling of nutrients, and/or runoff from emerged lands. Coupled with other factors, such as rapid sea-level fluctuations and climatic changes, oxygen-depleted conditions and eutrophication would have modified Late Devonian environments and could be possible factors in the F-F mass mortality.
The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of wid... more The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of widespread burial of organic matter in marine sediments, underlined by a positive carbon-isotope (δ13C) excursion observed worldwide. Within this episode of O2-depleted conditions, a short interval of cooling, termed as the Plenus Cold Event, has been recorded in many sites and sections in the northern hemisphere (Tethyan domain, Western Interior Seaway, proto-North Atlantic Ocean). But, its record and its impact on the biogeochemical cycles of carbon and nitrogen in the southern part of Central Atlantic Ocean has not been explored yet. Here, we present a detailed geochemical study of the Deep Sea Drilling Project site 367 (Cape Verde) based on a compilation of previous and new data of carbon and nitrogen isotope signals as well as trace element concentrations. The aim of this study is to better constrain the evolution of oxygenation in the water column and the associated changes in nitroge...
The tectonic and paleoceanographic setting of the Great Australian Bight (GAB) and the Mentelle B... more The tectonic and paleoceanographic setting of the Great Australian Bight (GAB) and the Mentelle Basin (MB; adjacent to Naturaliste Plateau) offered an outstanding opportunity to investigate Cretaceous and Cenozoic climate change and ocean dynamics during the last phase of breakup among remnant Gondwana continents. Sediment recovered from sites in both regions during International Ocean Discovery Program Expedition 369 will provide a new perspective on Earth’s temperature variation at sub-polar latitudes (60°–62°S) across the extremes of the mid-Cretaceous hot greenhouse climate and the cooling that followed.
Abstract The Cenomanian-Turonian boundary (~94 Ma) was marked by an episode of widespread organic... more Abstract The Cenomanian-Turonian boundary (~94 Ma) was marked by an episode of widespread organic carbon burial largely associated with low oxygen concentrations in bottom oceanic waters, named Oceanic Anoxic Event 2 (OAE 2). In the Vocontian Basin (SE France), the Pont d'Issole section exposes a 22 m interval called Niveau Thomel, the local sedimentary expression of the OAE 2, characterized by levels of laminated dark shales with marine-derived organic matter enrichments (up to 2.5 wt%). An episodic disruption in total organic carbon (TOC) enrichment is observed in bioturbated limestones within the Niveau Thomel, reflecting bottom-water reoxygenation associated to the Plenus Cold Event. Oscillations in redox conditions during the OAE 2 are evidenced by variations in the degree of pyritisation of the sediments reflecting suboxic to anoxic conditions associated with organic-rich intervals. These variations are additionally highlighted by enrichments in redox-sensitive trace elements (Mo, V, Zn) in sediments containing at least 1.5 wt% TOC, which may reflect a threshold between suboxic and anoxic conditions at Pont d'Issole section. Low Mn and Fe concentrations in >0.3 wt% TOC samples mark a large O2 depletion in pore waters. Phosphorus released from the sediments under deoxygenated conditions could have contributed to sustain the primary productivity in the basin, promoting further O2 consumption. A large negative excursion in the sulfur isotopic composition of pyrite (δ34Spy) with minimum values down to −40‰ suggests that microbial sulfate reduction was non sulfate-limited and was characterized by pyrite precipitation in an open system with regard to the marine sulfate reservoir. This feature is probably linked to a higher sulfate availability within the Vocontian Basin due to important Large Igneous Province outgassing at the onset of the OAE 2.
Petrophysical properties of volcanic rocks are controlled by lithology and subsequent modificatio... more Petrophysical properties of volcanic rocks are controlled by lithology and subsequent modification by alteration processes. Investigating the linkages, using a range of different techniques, are important to establish how petrophysical properties can inform about the alteration state of volcanic rocks. Here, we compile petrophysical data and correlate these with geochemical and mineralogical analyses acquired from a volcanic sequence on the Naturaliste Plateau, offshore southwest Australia (IODP Site U1513). The sequence consists of alternating basalt lava flows and volcaniclastic deposits, intruded by multiple dolerite dikes. Variable alteration intensities from fresh-slight to strong are quantified using Chemical Index of Alteration. Intervals of slightly altered dikes exhibit low porosity and high values of bulk density, P-wave velocity and thermal conductivity. The increase of alteration intensity corresponds to decreases in bulk density to ∼2 g/cm3, P-wave velocity to ∼2000 m/s, thermal conductivity to ∼1.2 W/(m·K) and an increase in porosity up to 50%. Natural Gamma Ray and magnetic susceptibility vary downhole with rock composition and at lithologic boundaries. The distinct variations exhibit a good correlation with primary lithologic characteristics and secondary mineralogical and textural changes attributed to alteration processes. We provide synthesis models of petrophysical variation with alteration intensity. Although differences in primary lithology and alteration type introduce limitations and uncertainties, there is a reasonable applicability of our results to rapidly characterize the alteration intensity and volcanic stratigraphy in volcanic sequences and to calibrate wireline log-based determinations. This will help others to develop strategies for exploration, drilling, and geophysical research of volcanic rocks.
Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present... more Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present during the deposition of organic-rich sediments. For example, TME concentrations controlled by changes in primary productivity and redox conditions are widely used in paleoenvironmental studies. Recently, these proxies have undergone a resurgence of interest and are commonly used in large-scale (10–1000 km) studies. However, applying these geochemical proxies at basin scale while ignoring variations in sedimentation rates (SR) may lead to misinterpretation of paleoenvironmental conditions. Here, we show how SR can affect the geochemical records and may lead to incorrect interpretations of TME evolution. Accounting for SR, we computed the authigenic fraction accumulation rates of key TMEs in the Upper Montney Formation and Doig Phosphate (Triassic, western Canada), and we correct the concentration of these elements in the Vaca-Muerta Formation (Jurassic–Cretaceous, Argentina). Our SR-cor...
Abstract The Late Jurassic was a period of major global carbon cycle perturbations with episodes ... more Abstract The Late Jurassic was a period of major global carbon cycle perturbations with episodes of anoxia leading to regional accumulation of organic matter in sediments worldwide. The Tubiegatan section (SW Gissar Mountains, Uzbekistan) located in the Northern Tethys, shows atypical organic-rich limestone and marl deposits (up to 6% of total organic carbon) marked by pronounced negative excursions of δ13Ccarb (amplitude of ca. 12‰) and δ13Corg (amplitude of ca. 4‰) recorded during the Middle Oxfordian (Transversarium Zone). A transdisciplinary approach including sedimentology, palynofacies characterization, mineralogy, organic and inorganic geochemistry was carried out to elucidate the origin of these organic-rich deposits. Highest TOC are measured in nodular limestones, and lowest δ13Ccarb values in thinly laminated facies consisting in alternances of infra-millimeter-thick organic and carbonate laminae. In the latter, the presence of organic-carbonate peloids and of possible remnants of exopolymeric substances associated with clay indicate that these structures are probably mineralized laminated benthic microbial mats (i.e., stromatolites). Rock-Eval pyrolysis coupled to palynofacies analyses point to a dominant altered marine organic matter of probable algal/microbial origin, with subordinate continental phytoclasts inputs in the upper part of the organic-rich interval. Trace elements (U/Th, V/Cr and Mo/Al ratios) indicate two anoxic episodes coinciding with the highest TOC, punctuated by dysoxic periods. Such O2-depleted conditions have allowed the preservation and probably the development of anaerobic microbial communities in the microbial mats. In these latter, sulfate reduction probably had a significant contribution to the production of carbonates, which would explain the precipitation of pyrite and the relatively low δ13Ccarb values. The progressive decrease then disappearance of kaolinite from the base of the organic-rich interval, is interpreted as a progressive aridification of the Amu Darya Basin during the Transversarium Zone, culminating with the progradation of a large-scale gypsum sabkha overlying the organic deposits. Overall, the organic-rich deposits could record the onset of the disconnection of the Amu Darya Basin from the open sea to the south, induced by compression and subsequent uplifts in the Afghan and Central Iranian blocks. The elevated evaporation, coupled with the presence of hydrological barriers (such as coral reefs) could have led to the formation of local to regional anoxic conditions in the Amu Darya Basin. Similar microbial organic accumulations are recently known throughout the Tethys (e.g., Arabian Plate, Western Europe) and from other oceans (e.g., Central Atlantic, Pacific) during the Late Jurassic, suggesting common controlling factors. The increase of organic matter storage worldwide coupled with potential methane release could have in turn induced major perturbations of the carbon cycle during the Oxfordian-Kimmeridgian interval. The relatively shallow anoxia model proposed in this study contrasts with the well-known organic carbon-rich pelagic models proposed for the Jurassic anoxia (e.g., Toarcian, Kimmeridgian) and Cretaceous OAEs.
Geological Society, London, Special Publications, 2015
Limestones at the Puech de la Suque Global Boundary Stratotype Section and Point (GSSP) of the Gi... more Limestones at the Puech de la Suque Global Boundary Stratotype Section and Point (GSSP) of the Givetian–Frasnian boundary show a drastic change towards much higher magnetic susceptibility values in the Givetian rocks. Different rock magnetic parameters indicate that ferromagnetic minerals are the main controlling factor. The ferromagnetic fraction is composed of low- (magnetite-type) and high-coercivity (hematite and goethite) phases. Confirmed by the spectral reflectance, high coercivity minerals are fluctuating along the section with a higher abundance in the basal Frasnian. These phases may be of secondary origin and produced during burial stage. The magnetite-type phase contains two different grain-size populations. The identified that Stable Single-domain/Superparamagnetic (SSD/SP) particles are of diagenetic origin and their amount decreases slightly upwards. A second group of magnetite grains correspond to coarse-grained particles identified using the squareness v. coercive f...
Late Devonian time (Famennian, 376--362 Ma BP) is a period of both intense orogenic activity and ... more Late Devonian time (Famennian, 376--362 Ma BP) is a period of both intense orogenic activity and drastic climatic variations with the onset of a major glaciation event upon parts of the Gondwanian Southern America and Africa situated in high southern latitudes. This global cooling event is coeval with a significant fall in the atmospheric CO_2 content as suggested both by
... Averbuch, O., Tribovillard, N., Devleeschouwer, X., Riquier, L., Mistiaen, B. and Van Vliet-L... more ... Averbuch, O., Tribovillard, N., Devleeschouwer, X., Riquier, L., Mistiaen, B. and Van Vliet-Lanoe, B. (2005), Mountain building-enhanced ... of atmospheric CO 2 content (and the associated greenhouse effect) by increased silicate weathering (eg Raymo, 1991; François et al., 1993 ...
In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge co... more In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge commonly substitutes for Si (in small proportions) in silicates. Studying the evolution of the respective proportions of Ge and Si through time allows us to better constrain the ...
Developments in Palaeontology and Stratigraphy, 2005
ABSTRACT The Late Devonian Frasnian-Famennian (F-F) mass extinction event coincides in many place... more ABSTRACT The Late Devonian Frasnian-Famennian (F-F) mass extinction event coincides in many places with the depositionof Corg-rich “Kellwasser” facies. Four F-F boundary sections representative of platform and basin environments from widely separated locations (Morocco, Germany, and France) were analysed for inorganic geochemistry, especially trace elements (redox and productivity proxies), in order to describe paleodepositional environments for the Kellwasser horizons. Ni/Co, V/Cr, U/Th, and V/(V+Ni) ratios, as well as redox trace metal concentrations indicate that oxygen-depleted conditions existed during the times of Kellwasser facies deposition. In platform settings, dysoxic conditions seem to be limited to the Late Frasnian. In basinal settings, oxygen depletion was stronger and persisted into the Early Famennian. Enrichments of Ba, Cu, Ni, that are limited to the Late Frasnian, show that surface productivity was relatively high and organic matter could accumulate, especially in the deeper environments. The stratigraphical distribution of several geochemical markers are linked with two positive excursions of the δ13Ccarb signal that result from enhanced organic matter burial. Reducing conditions likely resulted from high productivity of Late Devonian marine ecosystems. Intense nutrient supply resulted probably from the biogeochemical recycling of nutrients, and/or runoff from emerged lands. Coupled with other factors, such as rapid sea-level fluctuations and climatic changes, oxygen-depleted conditions and eutrophication would have modified Late Devonian environments and could be possible factors in the F-F mass mortality.
The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of wid... more The Oceanic Anoxic Event 2, at the Cenomanian-Turonian boundary (∼93.9 Ma), was an episode of widespread burial of organic matter in marine sediments, underlined by a positive carbon-isotope (δ13C) excursion observed worldwide. Within this episode of O2-depleted conditions, a short interval of cooling, termed as the Plenus Cold Event, has been recorded in many sites and sections in the northern hemisphere (Tethyan domain, Western Interior Seaway, proto-North Atlantic Ocean). But, its record and its impact on the biogeochemical cycles of carbon and nitrogen in the southern part of Central Atlantic Ocean has not been explored yet. Here, we present a detailed geochemical study of the Deep Sea Drilling Project site 367 (Cape Verde) based on a compilation of previous and new data of carbon and nitrogen isotope signals as well as trace element concentrations. The aim of this study is to better constrain the evolution of oxygenation in the water column and the associated changes in nitroge...
The tectonic and paleoceanographic setting of the Great Australian Bight (GAB) and the Mentelle B... more The tectonic and paleoceanographic setting of the Great Australian Bight (GAB) and the Mentelle Basin (MB; adjacent to Naturaliste Plateau) offered an outstanding opportunity to investigate Cretaceous and Cenozoic climate change and ocean dynamics during the last phase of breakup among remnant Gondwana continents. Sediment recovered from sites in both regions during International Ocean Discovery Program Expedition 369 will provide a new perspective on Earth’s temperature variation at sub-polar latitudes (60°–62°S) across the extremes of the mid-Cretaceous hot greenhouse climate and the cooling that followed.
Abstract The Cenomanian-Turonian boundary (~94 Ma) was marked by an episode of widespread organic... more Abstract The Cenomanian-Turonian boundary (~94 Ma) was marked by an episode of widespread organic carbon burial largely associated with low oxygen concentrations in bottom oceanic waters, named Oceanic Anoxic Event 2 (OAE 2). In the Vocontian Basin (SE France), the Pont d'Issole section exposes a 22 m interval called Niveau Thomel, the local sedimentary expression of the OAE 2, characterized by levels of laminated dark shales with marine-derived organic matter enrichments (up to 2.5 wt%). An episodic disruption in total organic carbon (TOC) enrichment is observed in bioturbated limestones within the Niveau Thomel, reflecting bottom-water reoxygenation associated to the Plenus Cold Event. Oscillations in redox conditions during the OAE 2 are evidenced by variations in the degree of pyritisation of the sediments reflecting suboxic to anoxic conditions associated with organic-rich intervals. These variations are additionally highlighted by enrichments in redox-sensitive trace elements (Mo, V, Zn) in sediments containing at least 1.5 wt% TOC, which may reflect a threshold between suboxic and anoxic conditions at Pont d'Issole section. Low Mn and Fe concentrations in >0.3 wt% TOC samples mark a large O2 depletion in pore waters. Phosphorus released from the sediments under deoxygenated conditions could have contributed to sustain the primary productivity in the basin, promoting further O2 consumption. A large negative excursion in the sulfur isotopic composition of pyrite (δ34Spy) with minimum values down to −40‰ suggests that microbial sulfate reduction was non sulfate-limited and was characterized by pyrite precipitation in an open system with regard to the marine sulfate reservoir. This feature is probably linked to a higher sulfate availability within the Vocontian Basin due to important Large Igneous Province outgassing at the onset of the OAE 2.
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Papers by Laurent Riquier