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CHEMOSTRATIGRAPHY OF CENOMANIAN–TURONIAN CARBONATES OF THE SARVAK FORMATION, SOUTHERN IRAN
Author(s) -
Hajikazemi E.,
AlAasm I.S.,
Coniglio M.
Publication year - 2012
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/j.1747-5457.2012.00525.x
Subject(s) - subaerial , geology , cenomanian , diagenesis , chemostratigraphy , unconformity , paleontology , geochemistry , carbonate , cretaceous , radiogenic nuclide , paleosol , isotopes of carbon , sedimentary rock , total organic carbon , chemistry , mantle (geology) , loess , organic chemistry , environmental chemistry
Stable‐isotope and trace‐element analyses from five surface and subsurface sections of the mid‐Cretaceous Sarvak Formation in southern and offshore Iran confirm the presence of the regional‐scale Turonian unconformity and of a more local Cenomanian–Turonian unconformity. The geochemical results indicate the presence of previously unrecognized and/or undifferentiated subaerial exposure surfaces. Sarvak Formation carbonates at or near palaeo‐exposure surfaces show varying degrees of diagenetic modification, and more extensive alteration is associated with longer periods of exposure. The subaerial exposure and associated diagenetic processes greatly influenced reservoir quality and amplified karstification and evolution of porosity in the Upper Sarvak Formation. The palaeo‐exposure surfaces are identified by their negative δ 13 C values (as low as – 6.4%) and negative δ 18 O values (as low as –9.4%), together with low Sr concentrations and relatively high 87 Sr/ 86 Sr ratios. These geochemical characteristics are interpreted to be the result of the interaction of the Sarvak Formation carbonates with meteoric waters charged with atmospheric CO 2 . The meteoric waters also caused karstification and soil formation which in some places extends a few metres below the exposure surfaces. Depleted carbon values were not recorded in areas where palaeosols are not well developed or where the uppermost layers of the Sarvak Formation have been removed by erosion.