Geochemistry of Organic Carbon in South Atlantic Sediments from Deep Sea Drilling Project Leg 75

Meyers, Philip A; Brassell, Simon C.; Hue, A.Y.

doi:10.2973/dsdp.proc.75.129.1984

Cited by 16 publications

(9 citation statements)

References 15 publications

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“…Considering the good agreement between the CHN (URI) and the RE and LECO determinations, we suspect that the CHN (UM) OC determinations are in error. Earlier comparison of shipboard OC determinations on Leg 75 samples with those done by CHN analyzer at the University of Michigan showed generally good agreement (relative standard deviation ±8.87°7o, Meyers et al, 1984). These comparisons, however, used shipboard bomb CaCO 3 values and hence avoided possible errors from carbonate C measurement by differences that are evident in the present comparison of procedures.…”

Section: Organic Carbonmentioning

confidence: 70%

A Geochemical Note: Comparison of Techniques for Obtaining CaCO3, Organic Carbon and Total Nitrogen in Limestones and Shales

Arthur

1987

Initial Reports of the Deep Sea Drilling Project

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Contents of organic carbon and carbonate carbon were determined on the same set of Cretaceous samples from DSDP Hole 603B in three different laboratories in order to assess the degree of comparability of organic carbon and carbonate values obtained by different labs using the same or different methods. We report the results of analyses for organic carbon using two different CHN analyzers, LECO, and Rock-Eval II and for carbonate carbon by CHN (total C minus C after acidification), the carbonate bomb technique, and CaCO 3 calculated on the basis of total calcium obtained from X-ray fluorescence and induction-coupled plasma techniques. In addition, total nitrogen was obtained by two different labs using a CHN analyzer, but different bases for calculation were used.The various techniques for organic carbon analysis yielded comparable results, with the exception of those obtained by one of the CHN analyses of acid-treated samples. The calculation of organic carbon values and comparison on a whole-rock basis is very sensitive to errors in determination of carbonate contents, and this factor explains most, but not all, of the disparities between the data sets. The carbonate bomb technique gives CaCO 3 values that correspond well with those calculated from total calcium concentrations (XRF and ICP analyses), whereas the CaCO 3 calculated from CHN total carbon minus acid-soluble carbon consistently overestimated CaCO 3 . Total nitrogen and C/N results from the two different CHN analyses are not comparable and are subject to more error than the factor related to error in estimation of CaCO 3 .

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Section: Organic Carbonmentioning

confidence: 70%

A Geochemical Note: Comparison of Techniques for Obtaining CaCO3, Organic Carbon and Total Nitrogen in Limestones and Shales

Arthur

1987

Initial Reports of the Deep Sea Drilling Project

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“…Once deposited the decomposition begins, but rapidly strips oxygen from pore waters and from the few centimetres above the bottom, so preservation of organic material is ensured (e.g. Meyers et al 1984). The sedimentary features that the authors observed can be explained by erosion of autochthonous layers, or of the upper parts of turbidites, by later turbidity currents charged with shallow water debris.…”

Section: Discussionmentioning

confidence: 87%

Mid-Cretaceous of the Gibraltar Arch Area

Thurow

Kuhnt

1986

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Summary Mid-Cretaceous depositional environments of the Gibraltar Arch and adjacent areas exhibit at the Cenomanian-Turonian boundary a special type of organic carbon-rich siliceous sedimentation which is intercalated in all the different environments—from the shelf down to the deep—of this area. This will be called the Cenomanian-Turonian Boundary Event (CTBE). Summarizing the most important features of the CTBE it can be pointed out: (1) the initiation of the CTBE is nearly coeval; (2) very high TOCs, especially at the base of Turonian; (3) kerogen is exclusively of type (I-) II in the undiluted strata; (4) independent of given palaeogeographic setting (e.g. E. and W. margin of the Atlantic ocean); (5) bituminous sedimentation is also very pronounced in environments with high detrital input and strong dilution (e.g. deep sea fans). Here too, most strata comprise kerogen of type II; (6) as far as we know, there is a striking co-occurrence of these sediments with strong enrichment in biogenic silica from diagenetically altered radiolaria, but there is no link between good preservation of radiolaria and bituminous sediments (e.g. Scaglia-facies); (7) rich radiolarian faunas are common in the carbon-rich and carbon-free sediments of shallow marine and deep sea environments; (8) the important change in the evolution of planktonic organisms (foraminifera/radiolaria) which marks the Cenomanian-Turonian boundary coincides with the peak of anoxic conditions and biogenic silica-rich sedimentation. All these features of the CTBE observed in the Gibraltar Arch area are comparable with coeval DSDP-facies in the North Atlantic and allow on-shore-off-shore tracing of the CTBE.

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“…[3]); and (3) other organic geochemical and petrographic criteria (e.g. [22,23]). In contrast, the organic matter at Site 603 is mainly of terrigenous origin on the basis of optical [24] and other organic geochemical parameters [25].…”

Section: Source Effectsmentioning

confidence: 99%

15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry

Rau

Arthur

Dean

1987

Earth and Planetary Science Letters

169

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At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower 815N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have 815N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C-and N-isotopic compositions similar to organic matter of modern terrestrial origin.The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphoric zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by Nz-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.

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Geochemistry of Organic Carbon in South Atlantic Sediments from Deep Sea Drilling Project Leg 75

Cited by 16 publications

References 15 publications

A Geochemical Note: Comparison of Techniques for Obtaining CaCO3, Organic Carbon and Total Nitrogen in Limestones and Shales

A Geochemical Note: Comparison of Techniques for Obtaining CaCO3, Organic Carbon and Total Nitrogen in Limestones and Shales

Mid-Cretaceous of the Gibraltar Arch Area

15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry

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