Phanerozoic environments of black shale deposition and the Wilson Cycle

Trabucho‐Alexandre, João; Hay, William W.; Boer, Poppe L. de

doi:10.5194/se-3-29-2012

Cited by 66 publications

(21 citation statements)

References 126 publications

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“…It seems most likely that the high conductivity we observe is due to the occurrence of low-grade metamorphosed graphitic sediments in Palaeozoic suture zones. Early Ordovician time was characterized by an abundance of black shales (Dewey 1988), and during the Ordovician-Silurian times, abundant black shale deposition oc-curred on the drowned carbonate shelf margins of the narrow, closing Iapetus Ocean at tropical latitudes (Leggett 1978;Klemme & Ulmishek 1991;Trabucho-Alexandre et al 2012). These shales represent a major component of flysch within accretionary sedimentary wedges at subduction zones.…”

Section: Discussion a N D I N T E R P R E Tat I O Nmentioning

confidence: 99%

Implications for the lithospheric geometry of the Iapetus suture beneath Ireland based on electrical resistivity models from deep-probing magnetotellurics

Rao¹,

Jones²,

Moorkamp³

et al. 2014

Geophysical Journal International

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S U M M A R YBroad-band and long period magnetotelluric (MT) data were acquired at 39 stations along five NNW-SSE profiles crossing the Iapetus Suture Zone (ISZ) in Ireland. Regional strike analyses indicate that the vast majority of the MT data is consistent with an assumption of a 2-D geoelectric strike direction. Strike is N52 • E for the three easternmost profiles and N75 • E for the two westernmost profiles; these directions correlate well with the observed predominant geological strike of the study region. 2-D inversions of the galvanic distortion-corrected TE and TM mode data from each profile are shown and discussed. As mapped geological variations between the neighbouring profiles suggest a heterogeneous subsurface, it is important to verify the robustness of the presence and geometries of prominent conductivity anomalies by employing 3-D forward and inverse modelling. A high conductivity layer (resistivity of 1-10 m), found at middle to lower crustal depths and presumed to be indicative of metamorphosed graphitic sediments rich in sulphides deposited during the convergence of the Laurentian and Avalonian continents, essentially constitutes the electrical signature of the ISZ. Shallow conductors observed are probably due to black shales that were widely deposited within the sedimentary accretionary wedge during Ordovician time. We interpret the moderately low resistivity at shallow depths from west to east across Ireland as indicative of an increase in maturity of the black shales in the easterly direction. From our conductivity models the southern extent of the ISZ is inferred to lie between the Navan Silvermines Fault and the Navan Tipperary Line, and shows clear resistivity contrast along all the profiles at the southern MT stations. The change in resistivity deduced from the 2-D models is spatially related to the composition of Lower Palaeozoic Ordovician, Silurian, Devonian and Carboniferous rocks. At upper mantle depths of about 60 km, a high conductivity block below the central MT stations is found to lie within the accretionary wedge of the Iapetus suture, and the location of the conductive anomaly corroborates reasonably well with the inferred spreading head of the putative Iceland plume-related magmatic intrusion. The low resistivity upper crust beneath the ISZ is indeed rich in Ordovician rocks with black shale content in the eastern as well as the central part; the western part is largely underlain by a highly resistive block of volcanic and metamorphosed rocks forming crystalline basement.

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Section: Discussion a N D I N T E R P R E Tat I O Nmentioning

confidence: 99%

Implications for the lithospheric geometry of the Iapetus suture beneath Ireland based on electrical resistivity models from deep-probing magnetotellurics

Rao¹,

Jones²,

Moorkamp³

et al. 2014

Geophysical Journal International

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“…This nutrient-rich water mass was similar to that found in other deepwater environments throughout the North Atlantic region. The post-EFT Upper Cretaceous in all three wells is only intermittently enriched in organic carbon, perhaps reflecting the changes in global circulation following the establishment of a deepwater connection between the North Atlantic and South Atlantic (e.g., Leckie et al, 2002;Trabucho-Alexandre, Hay, & de Boer, 2012;Topper et al, 2011;van Andel et al, 1977;Wagreich, 2009). Figure 9.…”

Section: 1002/2017pa003180mentioning

confidence: 99%

The Northern Gulf of Mexico During OAE2 and the Relationship Between Water Depth and Black Shale Development

et al. 2017

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Despite their name, Oceanic Anoxic Events (OAEs) are not periods of uniform anoxia and black shale deposition in ancient oceans. Shelf environments account for the majority of productivity and organic carbon burial in the modern ocean, and this was likely true in the Cretaceous as well. However, it is unlikely that the mechanisms for such an increase were uniform across all shelf environments. Some, like the northwest margin of Africa, were characterized by strong upwelling, but what might drive enhanced productivity on shelves not geographically suited for upwelling? To address this, we use micropaleontology, carbon isotopes, and sedimentology to present the first record of Oceanic Anoxic Event 2 (OAE2) from the northern Gulf of Mexico shelf. Here OAE2 occurred during the deposition of the well‐oxygenated, inner neritic/lower estuarine Lower Tuscaloosa Sandstone. The overlying organic‐rich oxygen‐poor Marine Tuscaloosa Shale is entirely Turonian in age. We trace organic matter enrichment from the Spinks Core into the deepwater Gulf of Mexico, where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the Cenomanian‐Turonian boundary interval. Redox change and organic matter preservation across the Gulf of Mexico shelf were driven by sea level rise prior to the early Turonian highstand, which caused the advection of nutrient‐rich, oxygen‐poor waters onto the shelf. This results in organic matter mass accumulation rates 1–2 orders of magnitude lower than upwelling sites like the NW African margin, but it likely occurred over a much larger geographic area, suggesting that sea level rise was an important component of the overall increase in carbon burial during OAE2.

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“…The connections linking them include organic carbon fluxes (Meyer and Kump, 2008), sea level changes (Landing, 2011), nutrient cycling (Algeo and Scheckler, 1998;Saltzman, 2005;Slomp and Van Cappellen, 2007;Tsandev et al, 2008), and paleogeographic factors (Trabucho-Alexandre et al, 2012). Anoxia greatly enhances the preservation of organic matter by reducing microbiological decay (Canfield, 1994;Tyson, 2005).…”

Section: Implications For Organic Accumulation In O-s Black Shales Onmentioning

confidence: 99%

Global and regional controls on marine redox changes across the Ordovician-Silurian boundary in South China

Liu

Algeo

et al. 2016

Palaeogeography, Palaeoclimatology, Palaeoecology

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The Ordovician-Silurian (O-S) transition coincided with significant environmental and biological changes. In South China, the Yangtze Platform experienced both global and regional events at this time, including sea-level fluctuations, tectonic movements, volcanic eruptions, mass extinction, and widespread anoxia. The O-S transitional strata of the Yangtze Platform comprise organic-rich black shales that are an important oil source rock. To explore the evolution of watermass chemistry and its relationship to organic matter accumulation, we conducted an integrated Fe-S-C geochemical study (i.e., Fe-speciation, δ 13 C org , δ 34 S py , pyrite-S and TOC) of the O-S boundary sections at Datianba (Chongqing Municipality) and Shuanghe (Sichuan Province). These sections were located in the restricted inner Yangtze Sea, in contrast to the previously studied Wangjiawan section, which was deposited in a more open setting of the outer Yangtze Sea. In contrast to the well-oxygenated conditions at Wangjiawan, the Datianba and Shuanghe sections record persistently anoxic, and episodically euxinic, conditions during the Hirnantian, which can be explained by the unique paleogeography and restricted hydrography of the inner Yangtze Sea. We propose that the regional Kwangsian Orogeny, which was driven by collision of the Yangtze and Cathaysia blocks, played a key role in basin development, watermass chemistry changes, and accumulation of Wufeng Formation black shales within the Yangtze Sea. The more widespread black shales of the Lower Silurian Lungmachi Formation were linked to the post-Hirnantian global marine transgression.

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Phanerozoic environments of black shale deposition and the Wilson Cycle

Cited by 66 publications

References 126 publications

Implications for the lithospheric geometry of the Iapetus suture beneath Ireland based on electrical resistivity models from deep-probing magnetotellurics

Implications for the lithospheric geometry of the Iapetus suture beneath Ireland based on electrical resistivity models from deep-probing magnetotellurics

The Northern Gulf of Mexico During OAE2 and the Relationship Between Water Depth and Black Shale Development

Global and regional controls on marine redox changes across the Ordovician-Silurian boundary in South China

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