General characteristics of quartz arenite types and their role in the recognition of sequence stratigraphic boundaries in ancient coastal and near shore sediments. A case study from Egypt and Saudi Arabia

Abstract

Quartz arenites are useful in the recognition of depositional sequences and cycle boundaries in ancient coastal and near shore facies. In this study two types of quartz arenite are recognized: 1) depositional quartz arenite (calcareous, dolomitic, ferruginous and kaolinitic quartz arenites), and 2) diagenetic quartz arenite (orthoquartzite, siliceous quartz arenite, compact quartz arenite, and dedolomitic quartz arenite). Depositional quartz arenite often occurs on the tops (upper boundaries) of the depositional sequences that are bounded by sequence boundaries (with or without evidence of subaerial exposure) or correlative conformity surfaces that mark the change from forced regression to lowstand normal regression. Therefore, depositional quartz arenite can define the upper boundaries of third and fourth-order depositional sequences, cycle bases and tops (boundaries) within lowstand, transgressive and highstand systems tracts. Diagenetic quartz arenite (orthoquartzite, siliceous quartz arenite and dedolomitic quartz arenite) usually occurs at the tops (upper boundaries) of depositional sequences that have subaerial sequence boundary and have been subjected to prolonged subaerial weathering and hence is closely associated with subaerial unconformity sequence boundary surfaces and consequently indicates a sharp drop in sea level. Thus, diagenetic quartz arenite types can be used to recognize the tops (upper boundaries) of first and second-order depositional sequences. Compact quartz arenite that is considered the fourth type of diagenetic quartz arenite consists entirely of packed quartz grains, but lacking cement, occurs at the base of each fining-upward cycle (lower boundaries) in lowstand systems tracts and may define the bases of some different-order depositional sequences.