Facies and Core-Based Sequence Stratigraphic Framework of Early Cretaceous Shu’Aiba Buildup, Shaybah Field, Saudi Arabia
The objective of this study was to construct a detailed facies-based sequence stratigraphic framework using cores, logs and isotope data for reservoir characterization and development. This study will also help refine our understanding of global climate and sea-level history in the Early Cretaceous.
The Shu’aiba buildup, Shaybah field formed on a ramp bordering an intra-shelf basin and consists of a composite sequence with eight high-frequency sequences in the Early/Late Aptian. Sequences 1 and part of 2 form the TST of the composite sequence, and consist of open-platform Palorbitolina-Lithocodium wackestone and maximum flooding planktonic mudstone. The remaining high frequency sequences formed a platform with a rim of rudist rudstone backed by rudist floatstone back-bank and lagoonal fine skeletal peloidal packstone; slope facies are fine skeletal fragment packstone. The rim initially developed on the windward side, but then later circled the buildup. Aggradational sequences 3 to 5 and slight progradational of sequences 6 and 7 make up the early HST. Sequence 7 marks the deterioration of the Offneria rudist barrier and deposition of widespread lagoonal deposits. The prograding Upper Aptian sequence 8 forms the late HST for the composite sequence and consists of dense argillaceous mudstone in the base that shallow up to a reefal facies of stromatoporoid/rudist rudstone.
Shu'aiba platform deposition was terminated by long-term sea-level fall, followed by karsting. The presence of possible 400-k.y. sequences and 100-k.y. parasequences suggest relatively high-amplitude sea level changes which are not compatible with greenhouse climate pattern. They suggest long- and short-term eccentricity drivers, small ice caps, and an early Cretaceous climate that may have been cooler than generally believed. This is pertinent to the debate concerning whether the Aptian was a time of green-house climate typified by small precessionally-driven sea-level fluctuations, or whether there were small ice sheets at the poles that generated moderate-amplitude, fourth order fluctuations driven by eccentricity.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009