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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Microfacies of Abu Dhabi Lower Cretaceous Section (United Arab Emirates)

Ahmed A. Abdul Ghani1; Abdulla E. Al Mansoori1

(1) EUFR, Abu Dhabi Company for Onshore Oil Operations (ADCO), Abu Dhabi, United Arab Emirates.

The Lower Cretaceous subsurface section of Abu Dhabi (K_10 to K_90) is composed of a carbonate sequence reaching 2,900 ft thick, deposited over a time-span of nearly 30 MM years. 60 lithofacies types have been recognized deposited in different environments, ranging from restricted supertidal to deep basinal sediments. Thamama Group consists of four formations which, in ascending order, are Habshan, Lekhwair, Kharaib and Shuaiba. The Habshan Formation is deposited up-dip on a wide and gentle carbonate ramp developed during the initial Cretaceous flooding of the stable cratonal platform, and embodies the progradation over, and subsequent filling of the old Middle to Late Jurassic cratonal margin depression. Habshan Formation consist mainly of grainy, peloial, sometimes intraclastic, and less commonly, oolitic limestone, with some lime packstone-wackestone; highly dolomitic in the lower parts. During deposition of the Lekhwair Formation, minor tectonic pulses created a series of minor transgression and regression. Cyclic sedimentation took place in the area, the lower part consist mainly of wackestone - mudstone which grade upwards into Skeletal, peloidal packstone-grainstone. Kharaib Formation is composed of four sedimentary cycles. The porous, grain-supported limestones represent regressive phases, whereas the dense limestone units represent restricted platform. Shuaiba Formation is the terminal event in the deposition of Thamama Group, and records the differentiation of the stable craton in early Aptian time into an intrashelf basin surrounded by shallow carbonate shelf facies. Shuaiba basinal facies have been termed the Bab Member, consists mainly of dark grey, dense argillaceous lime mudstone-wackestone and shales. On the shelf margin of this basin, calcareous algae and foraminifera with biohermal rudists accumulated a bioclastic peloidal, grainstone and floatstone-rudstone sediments.