Intersite discrepancy in the amplitude of marine negative δ13C excursion at the onset of early Aptian oceanic anoxic event 1a; reconciliation through Sr isotopic screening of peculiar diagenetic overprint on the Pacific reference section (Deep Sea Drilling Project Site 463)

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doi: 10.1130/2015.2511(17)
Author(s): Ando, Atsushi
Author Affiliation(s): Primary:
National Museum of Natural History, Department of Paleobiology, Washington, DC, United States
Volume Title: Origin, evolution, and environmental impact of oceanic large igneous provinces
Volume Author(s): Neal, Clive R., editor; Sager, William W.; Sano, Takashi; Erba, Elisabetta
Source: The origin, evolution, and environmental impact of oceanic large igneous provinces, edited by Clive R. Neal, William W. Sager, Takashi Sano and Elisabetta Erba. Special Paper - Geological Society of America, Vol.511, p.329-339. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0072-1077 CODEN: GSAPAZ
Note: In English. 59 refs.; illus., incl. 1 table, strat. col.
Summary: Among various paleoenvironmental proxy records across the lower Aptian Selli Level (Umbria-Marche basin, Italy) and its equivalents (i.e., sedimentary expressions of oceanic anoxic event [OAE] 1a), one very intriguing feature is a prominent negative δ13C excursion at the base of this sedimentary unit, generally by as much as a few per mil in marine carbonates. This early Aptian δ13C event has received special attention as an important clue to the genesis of OAE 1a, but the exact amplitude of this relatively short lived δ13C variation is not precisely constrained, and this fact has been an obstacle in paleoenvironmental modeling. Particularly enigmatic is the large amplitude, by -7 ppm, in pelagic limestones at the central Pacific Deep Sea Drilling Project (DSDP) Site 463; it may be a primary δ13C signal, considering its deposition in a fully open-ocean setting and a conservative burial diagenetic environment. Nevertheless, new Sr isotope data help identify a peculiar diagenetic overprint on the lower Aptian interval of this site. While the majority of examined samples represent slightly shifted, but acceptable, 87Sr/86Sr ratios for marine carbonates of this age, markedly unradiogenic 87Sr/86Sr ratios are recorded within and just below the Selli Level-equivalent interval. In particular, extremely unradiogenic 87Sr/86Sr ratios (0.70623-0.70642) are detected at exactly the same interval as the most negative δ13C values and a smectite-rich lithology. It is therefore proposed that hitherto unknown diagenetic process, or processes, under peculiar interstitial-water geochemistry, resulting from volcanic ash alteration, played a role for the paired δ13C-87Sr/86Sr anomaly at DSDP Site 463. By removing the δ13C data from samples that possess the highly unradiogenic 87Sr/86Sr ratios, the amplitude of early Aptian negative δ13C excursion is reevaluated to be -2.7 ppm or -3.3 ppm, facilitating comparison with published δ13C records from other sections. The refined Site 463 δ13C profile further implies that the early Aptian negative δ13C event is better described as a twin excursion.
Year of Publication: 2015
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Aptian; C-13/C-12; Carbon; Carbonate rocks; Chemostratigraphy; Cretaceous; DSDP Site 463; Deep Sea Drilling Project; Diagenesis; Geochemical anomalies; IPOD; Isotope ratios; Isotopes; Leg 62; Limestone; Lower Aptian; Lower Cretaceous; Mesozoic; Metals; Mid-Pacific Mountains; North Pacific; Northwest Pacific; Oceanic anoxic events; Organic compounds; Overprinting; Pacific Ocean; Pore water; Sedimentary rocks; Sr-87/Sr-86; Stable isotopes; Strontium; Total organic carbon; Volcanism; West Pacific
Coordinates: N212101 N212101 E1744004 E1744004
Record ID: 2015055234
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States

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