PETROGENESIS AND DIAGENESIS OF PALEOZOIC WAJID SANDSTIONE, SA’DA AREA, NW. YEMEN
Basim al-Qayim and Jaber Al-Sanabani
Department of Earth and Environmental Sciences.
Collage of Sciences. Sana'a Univesity
Frequent and isolated exposures of the Wajid Sandstone Formation are cropping out around Sa'da basin of NW Yemen., have been closely examined to investigate their petrographic characters, origin and diagenetic evolution.
Petrographically. Most of these sandstone are mature orthoquartzite. They generally consist of suborounded to subangular quartz (>90%) with subordinate feldspars, clays and heavy minerals. Cement is relatively common and is variable nature.
QFL plotting of the detrital grains compositional percentage of these sandstone samples shows that these sediment belong to a "continental block" provenance of complex association of uplifted shield, and deposited in an interior basin.
These sandstone were variably influenced by a series of diagenetic alteration which render the rocks their variable color, hardness and mineralogical characters. The most effective processes includes: compaction, cracking, segmentation (siliceous overgrowth, calcareous and ferruginous cements), kaolinization and leaching. The diagenetic sequence of these processes is discussed in terms of paragenetic relations and changes in diagenetic environments.