Khuff Sequence 5 (KS5), Oman Mountains: Lateral Facies and Sequence Variability – a Record of Differential Subsidence?

Abstract

This study focuses on the sequence stratigraphy and 3-D modelling of the Khuff Sequence 5 (KS5) in the Oman Mountains (Al Jabal al-Akhdar), Sultanate of Oman. The Lower Khuff sequences (KS5 and KS6) are at this stage poorly understood, since most of the reservoir units are located in the Upper and Middle Khuff sequences (KS1 to KS4). Previous studies (Koehrer et al., 2010, 2011) revealed layer-cake geometries of grainstone bodies in the Middle and Upper Khuff sequences (KS1 to KS4) on outcrop to exploration scales. The key question of this study was if the layer-cake geometries continue to be present or are different in the KS5. Database and Workflow Five outcrop sections in the Oman Mountains form the basis for this project. The sections were logged sedimentologically on a 1:100 scale. In total 1,080 m of KS5 strata was investigated. Data on lithology, sedimentary structures and textures, facies types, components and rock colour were noted. For the determination of facies types an established Khuff facies atlas (Koehrer et al., 2010) was applied. A total of 227 thin sections were analysed for detailed interpretation of depositional environments. Furthermore the natural gammaradiation of the outcrop strata was measured with a spacing of every half a metre. The concept of dynamic stratigraphy (Aigner, 1985; Kerans and Tinker, 1997; Aigner et al., 1998) was applied as workflow for this project. Based on the 1-D analysis of sequences and their stacking patterns, 2-dimensional correlations were constructed, that built the framework for the final 3-dimensional models. Sedimentological Analysis