Microfacies and stable carbon isotope stratigraphy of the Cretaceous Natih Formation, Wadi Mu'aydin, Oman

  • Yunlong Zhao

Student thesis: Master's Thesis

Abstract

The late Albian-early Turonian Natih Formation and its time-equivalents are one of the most prolific hydrocarbon reservoirs in the Middle East, yet the stable carbon isotope stratigraphy for the Cenomanian of the Arabian Peninsula is still poorly constrained. Based on the detailed microfacies and stable isotope analysis of numerous rock samples for the Natih Formation outcropping in Wadi Mu'aydin, Oman, this study develops the first stratigraphically-constrained, high-resolution δ13C curve for the shallow-water carbonates of the Natih Formation. Following detailed sedimentary logging and microfacies analysis, eight lithofacies associations are identified, representing a range of carbonate sedimentary environments from shallow, open-marine shelf to inner platform setting. The carbonate succession of the Natih Formation in Wadi Mu'aydin is carbonate-dominated, lacking intra-shelf basinal facies. Following screening for diagenetic effects, the majority of the δ 13C (V-PDB) values of bulk carbonates from the Natih Formation range between 0.109% and 0.441%, falling in the range of Mid-Cretaceous pelagic carbonates (i.e. 1%-0.5%). Systematic variations can be correlated with isotope curves reported from the subsurface Natih Formation of Oman, shallow-water carbonates of the Sarvak Formation outcropping in southwest Iran and pelagic chalk successions of the United Kingdom. Two Oceanic Anoxic Events are identified in the δ 13C curve for the Natih Formation, the Albian/Cenomanian Boundary Event and Mid-Cenomanian Event I. The detailed correspondence between the well-dated pelagic carbonates and the poorly dated shallow-water carbonates suggests that global marine carbon isotope signatures are recorded both in deep-sea and shallow-water carbonate sediments in the same manner and at a similar time resolution. The high-resolution δ13C curve refines the poorly dated chronostratigraphy of the Natih Formation by the recognition of the global carbon isotope events. The carbon isotope stratigraphy confirms a significant palaeo-exposure surface in the investigated shallow-water carbonate sequences by a negative excursion of δ13C values (e.g. the top of the Natih E Member), which suggests a use of carbon isotope trends as a proxy for paleo-exposures. In combination with other data, carbon isotope profiles can be used for basin-to-platform and regional correlations in shallow-water carbonates.
Date of AwardMay 2012
Original languageAmerican English
SupervisorStephen Lokier (Supervisor)

Keywords

  • Earth sciences; Carbon isotopes stratigraphy; Cretaceous Natih Formation Wadi Mu'aydin
  • Oman.

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