--> Sequence Stratigraphy of the Late Jurassic Arab Formation, Saudi Arabia

AAPG Middle East Region Geoscience Technology Workshop:
3rd Edition Carbonate Reservoirs of the Middle East

Datapages, Inc.Print this page

Sequence Stratigraphy of the Late Jurassic Arab Formation, Saudi Arabia

Abstract

The upper three carbonate-evaporite sequences of the Late Jurassic Arab Formation demonstrate depositional variations related to facies belt distribution within each sequence. The depositional lithofacies reflect punctuated and increased restriction of inner ramp settings. The inner ramp settings encompasses several facies associations including the peritidal facies association, the lagoon facies association, the shoal facies association, and the subtidal facies association. Eight depositional lithofacies are identified within these facies associations and were used to construct high-resolution sequence stratigraphic framework for the Kimmeridgian carbonates. The peritidal facies association is represented by bottom growth anhydrite of the salina, displacive skhaba anhydrite of the supratidal, and the cryptalgal laminites of the intertidal setting. The lagoon facies association is composed of microbial-lump, coated-grain grainstone and thrombolitic packstone. The microbial development is controlled by water circulation and depth, in which thrombolites are likely to grow in relatively deeper waters compared to the microbial-lump grainstone. The shoal facies association consists of peloidal packstone and grainstone and ooid grainstone. Towards the shoreline, the peloidal lithofacies fringes thrombolites and/or microbial lithofacies which may stimulate microbial filaments within it. The ooid grainstone of the shoal shows cross bedding which may be reworked up dip and re-deposited along the shoreline around the sabkha and peritdal areas. The subtidal facies association represents the most distal depositional settings observed and is composed of gastropod- and intraclast-floatstone. The vertical and lateral facies succession is used to infer three composite sequences within an overall progressively shallowing upward trend. The first (oldest) composite sequence is composed of three 4th-order sequences, in which the first and third sequences are capped by anhydrite, whereas the second sequence is capped by oolitic grainstone. The maximum flooding surface for this interval falls within the second 4th-order sequence marked by the thickest deposit of the most distal facies, the gastropod floatstone. In comparison, one 4th-order sequence represents the second evaporite-capped composite sequence, with its maximum flooding interval dominated by oolitic grainstone. Finally, the youngest sequence is composed of two 4th-order sequences, in which the lower sequence is capped by thrombolitic and stromatolitic facies and the upper sequence ends with anhydrite. The maximum flooding interval of this composite sequence is marked by oolitic grainstone within the lower 4th-order sequence. The stratigraphic architecture of the three composite sequences shows upward and basinward facies migration indicating progradation to the north, corroborated by the southward reduction in the overall thickness of the sequences.