Nitrogen isotope ratios of Cretaceous Atlantic sedimentary sequences, supplement to: Rau, Greg H; Arthur, Michael A; Dean, Walter E (1987): 15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry. Earth and Planetary Science Letters, 82(3-4), 269-279

DOI

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 delta15N 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 delta15N 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 N2-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.

Identifier
DOI https://doi.org/10.1594/PANGAEA.714244
Related Identifier https://doi.org/10.1016/0012-821X(87)90201-9
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.714244
Provenance
Creator Rau, Greg H; Arthur, Michael A; Dean, Walter E
Publisher PANGAEA - Data Publisher for Earth & Environmental Science
Publication Year 1987
Rights Creative Commons Attribution 3.0 Unported
OpenAccess true
Representation
Language English
Resource Type Supplementary Collection of Datasets
Format application/zip
Size 3 datasets
Discipline Earth System Research
Spatial Coverage (-70.028W, -19.188S, 9.386E, 35.495N); North Atlantic/BASIN; South Atlantic/RIDGE
Temporal Coverage Begin 1975-03-03T00:00:00Z
Temporal Coverage End 1983-05-05T00:00:00Z