The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

Environmental analysis of paleoceanographic systems based on molybdenum–uranium covariation

[1] Sedimentary molybdenum, [Mo]s, has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic-rich marine facies deposited under oxygen-depleted conditions A detailed analysis of [Mo]s–total organic carbon (TOC) covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that (1) [Mo]s, while useful in distinguishing oxic from anoxic facies, is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and (2) patterns of [Mo]s-TOC covariation can provide information about paleohydrographic conditions, especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal These inferences are based on data from four anoxic silled basins (the Black Sea, Framvaren Fjord, Cariaco Basin, and Saanich Inlet) and one upwelling zone (the Namibian Shelf), representing a spectrum of aqueous chemical conditions related to water mass restriction In the silled-basin environments, increasing restriction is correlated with a systematic decrease in [Mo]s/TOC ratios, from ∼45 ± 5 for Saanich Inlet to ∼45 ± 1 for the Black Sea This variation reflects control of [Mo]s by [Mo]aq, which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal (the “basin reservoir effect”) The temporal dynamics of this process are revealed by high-resolution chemostratigraphic data from Framvaren Fjord and Cariaco Basin sediment cores, which exhibit long-term trends toward lower [Mo]s/TOC ratios following development of water column stratification and deepwater anoxia Mo burial fluxes peak in weakly sulfidic environments such as Saanich Inlet (owing to a combination of greater [Mo]aq availability and enhanced Mo transport to the sediment-water interface via Fe-Mn redox cycling) and are lower in strongly sulfidic environments such as the Black Sea and Framvaren Fjord These observations demonstrate that, at timescales associated with deepwater renewal in anoxic silled basins, decreased sedimentary Mo concentrations and burial fluxes are associated with lower benthic redox potentials (ie, more sulfidic conditions) These conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction (eg, silled basins) and are not valid for low-oxygen facies in open marine settings such as continent-margin upwelling systems

/pdf/mo-total-organic-carbon-covariation-in-modern-anoxic-marine-2do2lpkttq.pdf

Mo–total organic carbon covariation in modern anoxic marine environments: Implications for analysis of paleoredox and paleohydrographic conditions

Organic-carbon-rich strata or "black shales," including dark gray to black, laminated, carbonaceous mudrocks characterized by impoverished benthonic faunas, or devoid of metazoan life, have long intrigued geol­ ogists, both because of their widespread distribution at certain times in the past and their early recognition as potential hydrocarbon source rocks. One of the major obsessions of many early workers, to the mid1900s, was the application of uniformitarian principles to depositional models for black shales. Thus, although it was recognized that some black shale units were unusually widespread, many early workers sought less extensive, modern analogues for environments of formation of dark-colored, rela-

MARINE BLACK SHALES: Depositional Mechanisms and Environments of Ancient Deposits

A critical look at iron paleoredox proxies: New insights from modern euxinic marine basins

THE Black Sea, the world's largest anoxic marine basin, is frequently used as a modern analogue for the formation of organic-rich sediments and carbonaceous rocks1–3, on the widely held assumption that anoxic conditions promote the preferential preservation of organic matter in sediments. Data for testing this hypothesis have so far been equivocal4–7, but here we use radiocarbon ages obtained using accelerator mass spectrometry for the organic fraction of recent Black Sea sediments to estimate the organic carbon accumulation rates. These range from 0.69 to 2.09 g C m−2 yr−1 and are significantly lower than earlier estimates based on varve counting6. Depending on the value taken for the rate of primary production in the Black Sea4,8, between 0.7 and 2.1% of the organic carbon is preserved in the bottom sediments. When compared with carbon accumulation rates in equivalent oxygenated environments9, these results indicate that the modern Black Sea is not a site of anomalously high organic carbon accumulation. This suggests that anoxic conditions in the water column may not be a prerequisite for the preservation of organic matter in marine sediments, and that models of the origin of carbonaceous facies in the geological record may therefore need to be modified.

Low organic carbon accumulation rates in black sea sediments

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Low organic carbon accumulation rates in black sea sediments