Benjamin Gill | Virginia Tech (original) (raw)
Papers by Benjamin Gill
Redox-sensitive elements, such as U and Mo, are valuable proxies for oxygen availability in the a... more Redox-sensitive elements, such as U and Mo, are valuable proxies for oxygen availability in the ancient atmosphere and ocean. Scott et al. (2008) inferred three stages from the secular trend of Mo concentrations in organic matter-rich shales: 1) shales older than 2.2 Ga have low but above crustal average Mo concentrations; 2) shales ca. 2.2 Ga show a dramatic increase in Mo concentrations after the rise of atmospheric oxygen; 3) shales straddling the Precambrian-Cambrian boundary show a second rise in Mo concentrations. Both Mo and U are released during oxidative continental weathering but removed via different pathways from the ocean; Mo is predominantly enriched in shales deposited under euxinic conditions, whereas U only requires anoxic conditions to be scavenged from the water column. These elements therefore can provide complementary, but independent, information about the redox state of the ocean and atmosphere. Our compilation of U concentrations from >2.2 Ga organic matte...
The rise of atmospheric oxygen between 2.47 and 2.32 Ga undoubtedly had a significant impact on g... more The rise of atmospheric oxygen between 2.47 and 2.32 Ga undoubtedly had a significant impact on global biogeochemical cycles and particularly, the intensity of oxidative continental weathering. While the timing of atmospheric oxygenation is well-constrained, the redox -state of the deep ocean throughout the Proterozoic is less known. The distribution of redox-sensitive elements, such as uranium and molybdenum, in ancient sedimentary rocks provides insight into the response of the deep ocean to this dramatic geochemical change. Here we present a compilation of U concentrations in marine black shales, from the Archean to the present to track the coupled redox evolution of the atmosphere and oceans, and to decipher changes in the uranium cycle itself. Since riverine delivery represents the only significant source of uranium to the oceans, and scavenging by organic matter-rich sediments beneath suboxic to anoxic waters represents the only significant sink, uranium concentrations in blac...
The Toarcian Ocean Anoxic Event (OAE) was a time of profound perturbations in the carbon cycle an... more The Toarcian Ocean Anoxic Event (OAE) was a time of profound perturbations in the carbon cycle and biosphere. However, many questions surround this interval, including the global-versus-local nature of the event. Unlike Cretaceous OAEs, the Toarcian lacks an available deep ocean record. Consequently, most studies have focused on geochemical data from stratigraphic sections in the north European epicontinental seaway (NEES) where the global relevance of the geological, paleontological and geochemical records has been questioned. At the heart of this debate is the observation that black, organic-rich shales within the NEES show little to no enrichment in some redox-sensitive elements (e.g., Mo) beyond crustal concentrations. Because the nature of the connection between the NEES and the open ocean is under debate, the muted metal enrichments have been interpreted as a drawdown of either the global or local marine reservoirs. Additionally, little work has been done to access the redox c...
Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored trac... more Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored tracers for euxinia in the ancient ocean on local and global scales. With the successes, however, has also come increasing awareness of the complexity. The purpose of this talk is to synthesize the broad range of refining and defining proxy developments and applications over the past several years, as a progress report and roadmap for future applications. Among the key topics are (1) our new and refined models for Mo uptake and burial under euxinic conditions, including a rigorous mechanistic understanding of the apparent coupling between Mo and organic matter sinks; (2) our comprehensive view of how Mo is taken up, fractionated isotopically, and buried [or recycled] beneath oxic bottom waters, particularly as coupled to Mn and Fe cycles; (3) our improved perspective on how and when Mo isotopes can be fractionated under permanent or transient euxinia, leading to a more effective use of the g...
Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored trac... more Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored tracers for euxinia in the ancient ocean on local and global scales. With the successes, however, has also come increasing awareness of the complexity. The purpose of this talk is to synthesize the broad range of refining and defining proxy developments and applications over the past several years, as a progress report and roadmap for future applications. Among the key topics are (1) our new and refined models for Mo uptake and burial under euxinic conditions, including a rigorous mechanistic understanding of the apparent coupling between Mo and organic matter sinks; (2) our comprehensive view of how Mo is taken up, fractionated isotopically, and buried [or recycled] beneath oxic bottom waters, particularly as coupled to Mn and Fe cycles; (3) our improved perspective on how and when Mo isotopes can be fractionated under permanent or transient euxinia, leading to a more effective use of the g...
Nature, Jan 23, 2015
Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate ... more Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate fluctuations, a potential rise in atmospheric oxygen or re-organization of the seafloor redox landscape, and the initial diversification of animals. It is widely assumed that the inferred redox change facilitated the observed trends in biodiversity. Establishing this palaeoenvironmental context, however, requires that changes in marine redox structure be tracked by means of geochemical proxies and translated into estimates of atmospheric oxygen. Iron-based proxies are among the most effective tools for tracking the redox chemistry of ancient oceans. These proxies are inherently local, but have global implications when analysed collectively and statistically. Here we analyse about 4,700 iron-speciation measurements from shales 2,300 to 360 million years old. Our statistical analyses suggest that subsurface water masses in mid-Proterozoic oceans were predominantly anoxic and ferruginous (d...
Geochmica et Cosmochimica Acta
IOP Conference Series: Earth and Environmental Science, 2009
This article was submitted without an abstract, please refer to the full-text PDF file.
The Late Cambrian SPICE event is an inorganic carbon isotope excursion that is documented in carb... more The Late Cambrian SPICE event is an inorganic carbon isotope excursion that is documented in carbonate rocks around the world. At most localities, the excursion begins near 0 per mil and rises to between + 4 and +5 per mil. These localities include China, Siberia, Kazakhstan, Australia, and North America (Great Basin, US midcontinent, and Applachian regions). There is only
Time-varying abundances of trace elements in the oceans have been argued to play a major role in ... more Time-varying abundances of trace elements in the oceans have been argued to play a major role in shaping the path of eukaryotic evolution. The dissolved marine concentrations of many bio-essential trace metals are controlled by the redox-state of the ocean-atmosphere system. For example, chalcophillic elements may become bio-limiting on geological timescales under widespread sulfidic conditions. Zn-binding proteins are fundamental to
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
ABSTRACT Several mass extinction events occurred in the Late Devonian, but the trigger for these ... more ABSTRACT Several mass extinction events occurred in the Late Devonian, but the trigger for these events remains elusive. In this study, geochemical evidence in the Late Devonian Antrim Shale, Michigan Basin, U.S.A., records episodic euxinia contemporaneous with these extinction events. Diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the Kellwasser Crisis. In this study, carbon, sulfur, iron and trace metal geochemistry preserved in the Antrim Formation validates the establishment and expansion of euxinic conditions associated with the Kellwasser Crisis and the Frasnian–Famennian boundary. The strength of the sequential extraction iron mineral data presented here, in concert with trace metal and sulfur isotope proxies, provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions. During the time of the Frasnian–Famennian boundary extensive sulfide oxidation at the chemocline, the result of Fe-limiting conditions within the basin, provides an alternative explanation for the oceanic decline in δ34SSO4 during, and following, the Frasnian–Famennian event. Our geochemical evidence, indicating the presence of anoxia in the Michigan Basin, is consistent with data from other globally distributed locations. Euxinia should be considered a key driver for these global extinction events, and possibly others such as the Hangenberg Event in the Late Devonian.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Me... more A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Member limestone of the upper Ediacaran Dengying Formation, Yangtze Gorges area, South China. It is characterized by horizontal tunnels connected with short vertical burrows and surface trails. The horizontal burrows are elliptical or bilobed in transverse cross-section, preserved in full relief, and filled with carbonate intraclasts, micrites, as well as calcite and silica cements. They occur exclusively in silty, crinkled, and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats; no burrows have been found in intraclastic layers adjacent to the microlaminated layers. The vertical traces are filled with the same material as the burrows, but they typically project through the crinkled microlaminae and are exposed on the bedding surface. The surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs. The burrow infill has δ 18 O carb and δ 13 C carb values distinct from, but intermediate between, microlaminated and intraclastic layers, consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements, intraclasts, and micrites. Bedding plane bioturbation intensity (20-40%)-measured as percentage of bedding plane area covered by L. trevallis traces-is comparable to similar measurements in pre-trilobite Cambrian carbonates. The exclusive occurrence of L. trevallis within microbial mats may have both taphonomic and ecological significance. These mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows, and they may have also facilitated early diagenetic cementation of burrow infill, thus facilitating burrow preservation. The close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources. The trace makers of L. trevallis were better able to utilize the resources around them than many other Ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late Ediacaran oceans at the dawn of the agronomic revolution.
Nature, 2014
A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is requi... more A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is required to explain the role of oxygen-minimum zones (OMZs) in controlling the fixed nitrogen inventory of the global ocean. Apparent imbalances in geochemical nitrogen budgets have spurred numerous studies to measure the contributions of heterotrophic and autotrophic N2-producing metabolisms (denitrification and anaerobic ammonia oxidation, respectively). Recently, 'cryptic' sulphur cycling was proposed as a partial solution to the fundamental biogeochemical problem of closing marine fixed-nitrogen budgets in intensely oxygen-deficient regions. The degree to which the cryptic sulphur cycle can fuel a loss of fixed nitrogen in the modern ocean requires the quantification of sulphur recycling in OMZ settings. Here we provide a new constraint for OMZ sulphate reduction based on isotopic profiles of oxygen ((18)O/(16)O) and sulphur ((33)S/(32)S, (34)S/(32)S) in seawater sulphate through oxygenated open-ocean and OMZ-bearing water columns. When coupled with observations and models of sulphate isotope dynamics and data-constrained model estimates of OMZ water-mass residence time, we find that previous estimates for sulphur-driven remineralization and loss of fixed nitrogen from the oceans are near the upper limit for what is possible given in situ sulphate isotope data.
a b s t r a c t 24-n-Propylcholestane (24-npc), a C 30 sterane compound derived from sterol precu... more a b s t r a c t 24-n-Propylcholestane (24-npc), a C 30 sterane compound derived from sterol precursors which are the major sterol constituents of modern pelagophyte microalgae, occurs in certain Neoproterozoic rocks and oils and throughout the Phanerozoic rock record. This broad distribution leads 24-npc to be widely considered a reliable indicator of open to partially restricted marine depositional conditions for source rocks and oils. Here we report two significant hiatuses in the occurrences of 24-npc in the Lower Paleozoic marine rock record: the first in the Middle-Late Cambrian and the second in the Late Ordovicianearly Silurian transition for a range of lithofacies (carbonates and siliciclastic rocks), organic carbon contents (both organic-lean and organic-rich), and paleoceanographic environments (shelf and deeper water marine settings) and observed offshore of two paleocontinents, Laurentia and Baltica. The Ordovician-Silurian gap is at least 9 million years, and possibly up to 20 million years, in duration. Robust older occurrences of 24-npc steranes in some Neoproterozoic rocks and oils suggest that oceanographic conditions in our intervals of Lower Paleozoic time were unfavorable for the proliferation of pelagophyte algae as phytoplankton. Caution should therefore be applied when interpreting a lacustrine versus marine depositional environmental setting for source rocks and oils in these intervals of Early Paleozoic time using lipid biomarker assemblages.
Redox-sensitive elements, such as U and Mo, are valuable proxies for oxygen availability in the a... more Redox-sensitive elements, such as U and Mo, are valuable proxies for oxygen availability in the ancient atmosphere and ocean. Scott et al. (2008) inferred three stages from the secular trend of Mo concentrations in organic matter-rich shales: 1) shales older than 2.2 Ga have low but above crustal average Mo concentrations; 2) shales ca. 2.2 Ga show a dramatic increase in Mo concentrations after the rise of atmospheric oxygen; 3) shales straddling the Precambrian-Cambrian boundary show a second rise in Mo concentrations. Both Mo and U are released during oxidative continental weathering but removed via different pathways from the ocean; Mo is predominantly enriched in shales deposited under euxinic conditions, whereas U only requires anoxic conditions to be scavenged from the water column. These elements therefore can provide complementary, but independent, information about the redox state of the ocean and atmosphere. Our compilation of U concentrations from >2.2 Ga organic matte...
The rise of atmospheric oxygen between 2.47 and 2.32 Ga undoubtedly had a significant impact on g... more The rise of atmospheric oxygen between 2.47 and 2.32 Ga undoubtedly had a significant impact on global biogeochemical cycles and particularly, the intensity of oxidative continental weathering. While the timing of atmospheric oxygenation is well-constrained, the redox -state of the deep ocean throughout the Proterozoic is less known. The distribution of redox-sensitive elements, such as uranium and molybdenum, in ancient sedimentary rocks provides insight into the response of the deep ocean to this dramatic geochemical change. Here we present a compilation of U concentrations in marine black shales, from the Archean to the present to track the coupled redox evolution of the atmosphere and oceans, and to decipher changes in the uranium cycle itself. Since riverine delivery represents the only significant source of uranium to the oceans, and scavenging by organic matter-rich sediments beneath suboxic to anoxic waters represents the only significant sink, uranium concentrations in blac...
The Toarcian Ocean Anoxic Event (OAE) was a time of profound perturbations in the carbon cycle an... more The Toarcian Ocean Anoxic Event (OAE) was a time of profound perturbations in the carbon cycle and biosphere. However, many questions surround this interval, including the global-versus-local nature of the event. Unlike Cretaceous OAEs, the Toarcian lacks an available deep ocean record. Consequently, most studies have focused on geochemical data from stratigraphic sections in the north European epicontinental seaway (NEES) where the global relevance of the geological, paleontological and geochemical records has been questioned. At the heart of this debate is the observation that black, organic-rich shales within the NEES show little to no enrichment in some redox-sensitive elements (e.g., Mo) beyond crustal concentrations. Because the nature of the connection between the NEES and the open ocean is under debate, the muted metal enrichments have been interpreted as a drawdown of either the global or local marine reservoirs. Additionally, little work has been done to access the redox c...
Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored trac... more Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored tracers for euxinia in the ancient ocean on local and global scales. With the successes, however, has also come increasing awareness of the complexity. The purpose of this talk is to synthesize the broad range of refining and defining proxy developments and applications over the past several years, as a progress report and roadmap for future applications. Among the key topics are (1) our new and refined models for Mo uptake and burial under euxinic conditions, including a rigorous mechanistic understanding of the apparent coupling between Mo and organic matter sinks; (2) our comprehensive view of how Mo is taken up, fractionated isotopically, and buried [or recycled] beneath oxic bottom waters, particularly as coupled to Mn and Fe cycles; (3) our improved perspective on how and when Mo isotopes can be fractionated under permanent or transient euxinia, leading to a more effective use of the g...
Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored trac... more Concentrations and isotope trends of molybdenum in organic-rich shales are among the favored tracers for euxinia in the ancient ocean on local and global scales. With the successes, however, has also come increasing awareness of the complexity. The purpose of this talk is to synthesize the broad range of refining and defining proxy developments and applications over the past several years, as a progress report and roadmap for future applications. Among the key topics are (1) our new and refined models for Mo uptake and burial under euxinic conditions, including a rigorous mechanistic understanding of the apparent coupling between Mo and organic matter sinks; (2) our comprehensive view of how Mo is taken up, fractionated isotopically, and buried [or recycled] beneath oxic bottom waters, particularly as coupled to Mn and Fe cycles; (3) our improved perspective on how and when Mo isotopes can be fractionated under permanent or transient euxinia, leading to a more effective use of the g...
Nature, Jan 23, 2015
Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate ... more Sedimentary rocks deposited across the Proterozoic-Phanerozoic transition record extreme climate fluctuations, a potential rise in atmospheric oxygen or re-organization of the seafloor redox landscape, and the initial diversification of animals. It is widely assumed that the inferred redox change facilitated the observed trends in biodiversity. Establishing this palaeoenvironmental context, however, requires that changes in marine redox structure be tracked by means of geochemical proxies and translated into estimates of atmospheric oxygen. Iron-based proxies are among the most effective tools for tracking the redox chemistry of ancient oceans. These proxies are inherently local, but have global implications when analysed collectively and statistically. Here we analyse about 4,700 iron-speciation measurements from shales 2,300 to 360 million years old. Our statistical analyses suggest that subsurface water masses in mid-Proterozoic oceans were predominantly anoxic and ferruginous (d...
Geochmica et Cosmochimica Acta
IOP Conference Series: Earth and Environmental Science, 2009
This article was submitted without an abstract, please refer to the full-text PDF file.
The Late Cambrian SPICE event is an inorganic carbon isotope excursion that is documented in carb... more The Late Cambrian SPICE event is an inorganic carbon isotope excursion that is documented in carbonate rocks around the world. At most localities, the excursion begins near 0 per mil and rises to between + 4 and +5 per mil. These localities include China, Siberia, Kazakhstan, Australia, and North America (Great Basin, US midcontinent, and Applachian regions). There is only
Time-varying abundances of trace elements in the oceans have been argued to play a major role in ... more Time-varying abundances of trace elements in the oceans have been argued to play a major role in shaping the path of eukaryotic evolution. The dissolved marine concentrations of many bio-essential trace metals are controlled by the redox-state of the ocean-atmosphere system. For example, chalcophillic elements may become bio-limiting on geological timescales under widespread sulfidic conditions. Zn-binding proteins are fundamental to
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
ABSTRACT Several mass extinction events occurred in the Late Devonian, but the trigger for these ... more ABSTRACT Several mass extinction events occurred in the Late Devonian, but the trigger for these events remains elusive. In this study, geochemical evidence in the Late Devonian Antrim Shale, Michigan Basin, U.S.A., records episodic euxinia contemporaneous with these extinction events. Diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the Kellwasser Crisis. In this study, carbon, sulfur, iron and trace metal geochemistry preserved in the Antrim Formation validates the establishment and expansion of euxinic conditions associated with the Kellwasser Crisis and the Frasnian–Famennian boundary. The strength of the sequential extraction iron mineral data presented here, in concert with trace metal and sulfur isotope proxies, provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions. During the time of the Frasnian–Famennian boundary extensive sulfide oxidation at the chemocline, the result of Fe-limiting conditions within the basin, provides an alternative explanation for the oceanic decline in δ34SSO4 during, and following, the Frasnian–Famennian event. Our geochemical evidence, indicating the presence of anoxia in the Michigan Basin, is consistent with data from other globally distributed locations. Euxinia should be considered a key driver for these global extinction events, and possibly others such as the Hangenberg Event in the Late Devonian.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Me... more A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Member limestone of the upper Ediacaran Dengying Formation, Yangtze Gorges area, South China. It is characterized by horizontal tunnels connected with short vertical burrows and surface trails. The horizontal burrows are elliptical or bilobed in transverse cross-section, preserved in full relief, and filled with carbonate intraclasts, micrites, as well as calcite and silica cements. They occur exclusively in silty, crinkled, and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats; no burrows have been found in intraclastic layers adjacent to the microlaminated layers. The vertical traces are filled with the same material as the burrows, but they typically project through the crinkled microlaminae and are exposed on the bedding surface. The surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs. The burrow infill has δ 18 O carb and δ 13 C carb values distinct from, but intermediate between, microlaminated and intraclastic layers, consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements, intraclasts, and micrites. Bedding plane bioturbation intensity (20-40%)-measured as percentage of bedding plane area covered by L. trevallis traces-is comparable to similar measurements in pre-trilobite Cambrian carbonates. The exclusive occurrence of L. trevallis within microbial mats may have both taphonomic and ecological significance. These mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows, and they may have also facilitated early diagenetic cementation of burrow infill, thus facilitating burrow preservation. The close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources. The trace makers of L. trevallis were better able to utilize the resources around them than many other Ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late Ediacaran oceans at the dawn of the agronomic revolution.
Nature, 2014
A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is requi... more A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is required to explain the role of oxygen-minimum zones (OMZs) in controlling the fixed nitrogen inventory of the global ocean. Apparent imbalances in geochemical nitrogen budgets have spurred numerous studies to measure the contributions of heterotrophic and autotrophic N2-producing metabolisms (denitrification and anaerobic ammonia oxidation, respectively). Recently, 'cryptic' sulphur cycling was proposed as a partial solution to the fundamental biogeochemical problem of closing marine fixed-nitrogen budgets in intensely oxygen-deficient regions. The degree to which the cryptic sulphur cycle can fuel a loss of fixed nitrogen in the modern ocean requires the quantification of sulphur recycling in OMZ settings. Here we provide a new constraint for OMZ sulphate reduction based on isotopic profiles of oxygen ((18)O/(16)O) and sulphur ((33)S/(32)S, (34)S/(32)S) in seawater sulphate through oxygenated open-ocean and OMZ-bearing water columns. When coupled with observations and models of sulphate isotope dynamics and data-constrained model estimates of OMZ water-mass residence time, we find that previous estimates for sulphur-driven remineralization and loss of fixed nitrogen from the oceans are near the upper limit for what is possible given in situ sulphate isotope data.
a b s t r a c t 24-n-Propylcholestane (24-npc), a C 30 sterane compound derived from sterol precu... more a b s t r a c t 24-n-Propylcholestane (24-npc), a C 30 sterane compound derived from sterol precursors which are the major sterol constituents of modern pelagophyte microalgae, occurs in certain Neoproterozoic rocks and oils and throughout the Phanerozoic rock record. This broad distribution leads 24-npc to be widely considered a reliable indicator of open to partially restricted marine depositional conditions for source rocks and oils. Here we report two significant hiatuses in the occurrences of 24-npc in the Lower Paleozoic marine rock record: the first in the Middle-Late Cambrian and the second in the Late Ordovicianearly Silurian transition for a range of lithofacies (carbonates and siliciclastic rocks), organic carbon contents (both organic-lean and organic-rich), and paleoceanographic environments (shelf and deeper water marine settings) and observed offshore of two paleocontinents, Laurentia and Baltica. The Ordovician-Silurian gap is at least 9 million years, and possibly up to 20 million years, in duration. Robust older occurrences of 24-npc steranes in some Neoproterozoic rocks and oils suggest that oceanographic conditions in our intervals of Lower Paleozoic time were unfavorable for the proliferation of pelagophyte algae as phytoplankton. Caution should therefore be applied when interpreting a lacustrine versus marine depositional environmental setting for source rocks and oils in these intervals of Early Paleozoic time using lipid biomarker assemblages.