Basin Platform Transitions in Upper Jurassic Carbonates of the Amran Group, Yemen

Christian Weiss
Institute of Palaeontology, Germany
[email protected]

The Amran Group consists of an 800–1,200-m-thick carbonate sequence. Outcrops in the Yemen mountains consist of shallow-water facies types with shallowing upward cycles. In the study area, the Marib Province, those facies types inter-finger with basinal facies types of the Marib-Sabwah Basin. Facies analyses made on thin sections of several profiles, X-ray diffraction (XRD) analyses of the insoluble residue and geochemical datasets were used to reconstruct the transition between the deeper-water basin facies and the shallow-water facies types of a carbonate platform. A sedimentary ramp setting can be reconstructed by the lateral distribution of the different facies types. They show a low slope with ooid sandbars and lagoonal facies types, which change to fossil wacke and packstones of a deeper-water setting. The basin facies is represented by mudstones. The stratigraphy is based on foraminifers, and supported by clay mineral and chemostratigraphic analysis. One focus of the study is the position of reefs on the carbonate ramp. They appear as different types depending on water depth, and can be divided based on the composition of reef-building organisms.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain