Journal of Earth Science & Climatic Change
Open Access

Abstract

The Queih basin hosts a ~2500 m thick Neoproterozoic volcano-sedimentary successions thatunconformably lie over the oldest Precambrian basement. These successions were deposited in alluvial fan, fluviatile, lacustrine, and aeolian depositional environments.Diagenetic minerals from these volcaniclastic successions including pyroclastic (tuffs) and epiclastic sediments were studied by XRD, SEM, and AEM. The studied volcaniclastic sediments have undergone intense and a complex diagenetichistory due to burial and uplift.Diagenetic modifications were dependent mainly on the clastic composition of volcaniclastics, burial depth, and thrust tectonics. The principal diagenetic minerals/cements in the Queih sediments are calcite, quartz overgrowth, iron oxides, mica, and authigenic clays (predominantly kaolinite, illite,and chlorite with minor illite?smectite mixed layers and smectite).The paragenetic sequence is identified with relative diagenetic timings. Early diagenesis is characterized by the mechanical compactionand neo-formation of smectite and kaolinite. Burial diagenesis consists of additional compaction, quartz overgrowth,and precipitation of poikilotopic calcite cement. In addition, burial diagenesis is distinct by the transformation of kaolinite and smectite into dickite and illite. Late diagenesis is related to exhumation and exposure of volcaniclastic sediments one and contact with meteoric water. Clay minerals and their diagenetic assemblages have been distinguished between primary volcaniclastics produced directly by pyroclastic eruptions and epiclasticvolcaniclastics derived from erosion of pre-existing volcanic rocks. Phyllosilicates of the epiclastic rocks display wider compositional variations owing to wide variations in the mineralogical and chemical composition of the parent material. Most of the phyllosilicates (kaolinite, illite, chlorite, mica, and smectite) are inherited minerals derived from the erosion of the volcanic basement complex, which had undergone hydrothermal alteration. Smectites of the epiclastic rocks are beidellite-montmorillonite derived from the volcanic materials altered in the sedimentary environment. Conversely, phyllosilicate minerals of the pyroclastic rocks are dominated by kaolinite, illite, and mica, which were formed by pedogenetic processes with hydrothermal influence. This paper contributes to the differentiation between pyroclastic and epiclasticvolcaniclastic rocks of different depositional settings in a volcanic complex by their clay mineral characterization

Biography

Ezz El DIN Abdel Hakim Kalaf has completed his PhD in 1994 from Cairo University. He is an Associate professor in Cairo University in the Faculty of Science Geology Department. He has published more than 20 papers in reputed journals and is a member of many scientific organizations.