Stratigraphy and Microfacies of Type Magwa Formation of Kuwait, Arabia; Part 2: Mishrif Limestone Member

Abstract

The upper part of the type Magwa is correlated with the type Mishrif Limestone of southern Iraq, whereas its basal part is equated with the type Rumaila. Therefore both the Mishrif and underlying Rumaila are included as two members within the Magwa Formation, inasmuch as these two rock units, although representing different limestone facies, grade into each other, interdigitate, or change laterally into one dominant facies. A thin-section study of the Mishrif Limestone Member of the type Magwa Formation has led to the recognition of two distinctive microfacies associations: a lower alveolinid, dicyclinid, algal clayey or marly limestone with intercalating shaly bands and some recrystallization, pyritization, or dolomitization; and an upper skeletal, micritic, chalky limestone (coralline, algal, bryozoan, rudistid) with a few benthonic foraminifers and very few planktonics. The latter assemblage leads us to postulate an agitated, littoral-to-supralittoral marine environment for the deposition of the Mishrif Limestone Member, followed by regression to near emergence. The rich collections of fossils prove the late Cenomanian age of the basal Mishrif and leave a possibility that the upper Mishrif can be earl Turonian. The data substantiate the existence of the Wasia/Aruma unconformity, separating the Magwa from the overlying Gudair Limestone.