Petrography and Diagenesis of Jurassic Oncolytic Limestone in the Amran Group, Yemen Arab Republic PDF

Keywords

limestones, geology, Yemen Arab Republic

Abstract

The oncolytic and oolitic limestones within the Jurassic Amran Group of Yemen Arab Republic (Y.A.R) display characteristics depositional and diagenetic structures. The oncoids have four types of laminations; (1) micritic, (2) grumose, (3) organodetrital-bearing and (4) clastic bearing laminations. Most of these laminae are concentric and continuous suggesting continued movements or agitated conditions during deposition. Some laminae are discontinuous and show local growth reflecting short periods of mild agitation or quiet conditions. The porosity of the studied facies is the result of early and late diagenetic history. It includes primary pore spaces represented by fenestral vugs and secondary pore spaces resulting from the dissolution of carbonate grains as well as cement. Cementation and compaction are the main factors reducing the porosity of these sediments. Compaction due to burial is represented by concavo-convex and sutured contacts and microstyloites.