The “Productivity Versus Preservation” Controversy: Cause, Flaws, and Resolution

Tyson, Richard V.

doi:10.2110/pec.05.82.0017

Cited by 105 publications

(72 citation statements)

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“…Instead, a high settling flux of organic matter (i.e., high export productivity in the surface water) [ Pedersen et al ., ] seems to be needed. The basic question whether the different proxies reflect mainly primary productivity or bottom water oxygen concentration or a combination of both (i.e., oxygen exposure time) [ Sinninghe Damsté et al ., ] has been a matter of debate since several decades [ Tyson , ]. It is difficult to separate these two mechanisms because they are intrinsically correlated.…”

Section: Discussionmentioning

confidence: 99%

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

et al. 2014

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The Dansgaard-Oeschger oscillations and Heinrich events described in North Atlantic sediments and Greenland ice are expressed in the climate of the tropics, for example, as documented in Arabian Sea sediments. Given the strength of this teleconnection, we seek to reconstruct its range of environmental impacts. We present geochemical and sedimentological data from core SO130-289KL from the Indus submarine slope spanning the last~80 kyr. Elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the Indus River. In contrast, stadials are characterized by an increased contribution of aeolian dust from the Arabian Peninsula. Decadal-scale shifts at climate transitions, such as onsets of interstadials, were coeval with changes in productivity-related proxies. Heinrich events stand out as especially dry and dusty events, indicating a dramatically weakened Indian summer monsoon, potentially increased winter monsoon circulation, and increased aridity on the Arabian Peninsula. This finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events. Our results strengthen the evidence that circum-North Atlantic temperature variations translate to hydrological shifts in the tropics, with major impacts on regional environmental conditions such as rainfall, river discharge, aeolian dust transport, and ocean margin anoxia.

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Section: Discussionmentioning

confidence: 99%

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

et al. 2014

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“…Three main mechanisms controlling organic enrichment were proposed, including input, preservation and dilution of organic matter (Pedersen and Calvert, ; Schwartzkopf, ; Carroll and Bohacs, ; Bohacs et al ., ; Wei et al ., ; Westermann et al ., ). The input of organic matter is controlled mainly by primary productivity, whereas preservation is closely related to redox conditions (Canfield, ; Katz, ; Tyson, ; Mort et al ., ; Bonis et al ., ). Within the studied section, several lines of evidence indicate that the organic‐rich sediments were deposited under slightly oxic depositional environments, which are unfavourable for organic matter preservation.…”

Section: Discussionmentioning

confidence: 99%

Elemental geochemistry of the early Jurassic black shales in the Qiangtang Basin, eastern Tethys: constraints for palaeoenvironment conditions

Wang

Chen

et al. 2015

Geological Journal

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The early Jurassic black shales are the most important source rocks in the Qiangtang Basin, Tibet. These black shales may provide a useful example for understanding the sedimentary conditions during the early Jurassic in the eastern Tethys. Thirty-two black-shale samples were collected from the Qiangtang Basin to reconstruct the depositional environments during the early Jurassic in the eastern Tethys. The palaeoclimate index Σ(Fe + Mn + Cr + Ni + V + Co)/Σ(Ca + Mg + Sr + Ba + K + Na) varies between 0.58 and 1.14, together with low Sr/Ba (0.20-0.60) and Sr/Cu (1.68-7.88) ratios, indicating a warm humid to semi-humid climatic condition during black-shale deposition. The early Jurassic black shales exhibit slight Ce anomalies (0.89-0.94) and Mn enrichment (EF = 1.2), suggesting a slightly oxic depositional environment. The conditions of the sedimentary water system during black-shale deposition were apparently brackish as evidenced by middle B/Ga (3.96-5.73) and Th/U (3.96-6.51) ratios.

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“…In addition, slow accumulation of inorganic materials would otherwise dilute the organic matter (Creaney and Passey 1993). At low sedimentation rates, increased sedimentation serves to isolate organic matter from an oxidizing water body and enhance organic-carbon content; at higher rates, increased sedimentation rates simply dilute the organic matter (Tyson 2001(Tyson , 2005. Previous studies ascertained the dominated control of only one of these three main factors (e.g., Demaison and Moore 1980;Tyson 1987;Wignall 1994).…”

Section: Introductionmentioning

confidence: 99%

Impact of paleoenvironment, organic paleoproductivity, and clastic dilution on the formation of organic-rich shales: a case study about the Ordovician-Silurian black shales, southeastern Chongqing, South China

Tang

Zhang

et al. 2015

Arab J Geosci

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Three triggering factors, including preservation, organic paleoproductivity, and clastic dilution, for the formation of black shale successions during the Ordovician-Silurian transition have been debated for many years. Preserving conditions are controlled by redox conditions and microbial activities which have close relationship with salinity. Five outcrop sites of the Wufeng-Longmaxi black shales located in the southeastern area of Chongqing are analyzed for their elemental geochemistry, total organic carbon, and clay minerals. Clay minerals and boron are used to reconstruct the paleosalinity (S p ) of the bottom water during this period. Depending on the clay minerals' specific combining pattern, the calculation of S p is modified. The results show that the S p concentration ranges from 1.73 to 16.12‰, with an average value of 9.68‰. This shows an increasing trend from the Late Ordovician to the Early Silurian, indicating oligohaline-mesohaline water. Desalinization of the global ocean in the Late Ordovician was caused by melting of continental glaciers. The S p concentration shows negative correlation with total organic carbon (TOC) content, since the microbial decomposition rates are improved by high salinity. V/(V+Ni) and V/Cr ratios are used to reconstruct the paleoredox conditions of the bottom seawater during the Ordovician-Silurian transition, and the results suggest that the oxygen levels in seawater increased from the Late Ordovician to the Early Silurian and increased landward as a whole. Correlation between redox conditions with the TOC content reveals that anoxic conditions are favorable to the accumulation of organic matter. Ba and (Ba/Al) terr are used to calculate the biogenic Ba, in order to reconstruct organic paleoproductivity. The biogenic Ba shows no apparent relationship with the TOC content, which implies that organic paleoproductivity does not solely control the accumulation of organic matter. Si/Al and Ti/Al ratios are considered as indicators of clastic input. Our data imply that clastic input is quite low in the distal basin around the Ordovician-Silurian boundary, which is consistent with the maximum content of TOC. In the proximal basin, high clastic input dilutes enrichment of organic matter. We may conclude that complex, nonlinear interactions among the three factors most likely lead to the accumulation of organic matter. High preservation, low dilution, and low organic production lead to the formation of organic-rich shale, whereas low preservation, high dilution, and high organic production lead to organic-poor shale. Key PointsPaleoenvironment and organic paleoproductivity of the Yangtze Platform during the Late Ordovician and the Early Silurian are reconstructed.A combination of multiple factors significantly affects the formation of organic-rich shales.

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The “Productivity Versus Preservation” Controversy: Cause, Flaws, and Resolution

Cited by 105 publications

References 0 publications

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

Elemental geochemistry of the early Jurassic black shales in the Qiangtang Basin, eastern Tethys: constraints for palaeoenvironment conditions

Impact of paleoenvironment, organic paleoproductivity, and clastic dilution on the formation of organic-rich shales: a case study about the Ordovician-Silurian black shales, southeastern Chongqing, South China

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