--> Abstract: Composite Barremian to Turonian Carbon Isotope Curve of Oman, by Volker C. Vahrenkamp; #90077 (2008)

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Composite Barremian to Turonian Carbon Isotope Curve of Oman

Volker C. Vahrenkamp
ADCO (formerly PDO)
[email protected]

Carbon-isotope stratigraphy is a valuable tool to constrain time lines and hence the architecture of Early to mid-Cretaceous shallow-water platform carbonates. Using subsurface cores and published outcrop data, a composite curve has been compiled for the Barremian to Turonian time interval of Oman. The curve contained some 738 data points from the Kharaib (48), Shu’aiba (143), Nahr Umr (76) and Natih formations (471). Overall the curve has an excellent match with published reference curves from pelagic sections of the Tethys and hence provides a much-improved time resolution compared to biostratigraphy available for these shallow-water carbonate sequences. The base of the Hawar Member of the Kharaib Formation is characterized by a pronounced negative carbon isotope spike, which correlates with a negative isotope excursion during the earliest Aptian. The Oceanic Anoxic Event 1b is recognized in the lower part of the Nahr Umr Formation, which places the boundary between the Shu’aiba and the Nahr Umr formations in the latest Aptian. A positive carbon-isotope excursion in the lowermost Natih Formation (F and G reservoir units) correlates with an Albian/Cenomanian boundary event. A most likely interpretation of the carbon-isotope curve of the Natih Formation stretches its duration from the Late Albian to the Early Turonian. In addition, several intra-formational time lines can be assigned. A carbon isotope peak during the Natih C&D units corresponds to a Mid-Cenomanian event. A distinct negative excursion during the Natih B is either of local origin related to organic matter deposition or it corresponds with a weak negative trend on the global curve during the Middle Cenomanian. A final positive shift during the Natih A places the top of this unit near the Cenomanian/Turonian boundary. Aspects worth further investigation are shifts in parts of the carbon-isotope curve towards heavier and lighter values compared to pelagic sequences and further time anchor points from Sr-isotope dating.


AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain