Unravelling the depositional environments wthin the Lower Andam Group (Al Bashair Formations, Late Cambrian) of north-central Oman

Abstract

The Al Bashair Formation is interpreted in this study to have been deposited in marginal marine settings (supratidal to subtidal).  Support for this interpretation comes from the range of lithologies and sedimentary structures present, the types of body and trace fossils, and the presence of gypsum pseudomorphs and halite moulds.  Carbonate rocks are absent from the upper half of the Al Bashair Formation and the interval becomes much muddier than the lower half.  These features allow the division of the Al Bashair Formation stratigraphically into two parts, the Lower Unit and the Upper Unit. Previously it has been thought that the mudstone intervals in the Al Bashair succession were deposited in a deeper water setting than the carbonate and sandstone strata. However, detailed study of the succession at outcrop shows that these mudstone intervals are always associated with terrestrial sedimentary structures, particularly those produced by pedogenesis, indicating they were subaerially exposed for sufficient time for soils to form soon after their deposition.  This indicates that the succession of the Upper Unit of the Al Bashair Formation generally was deposited in an overall more landward setting than the underlying unit, and the “Intra-Al Bashair Boundary” cannot be interpreted as a maximum flooding surface. Furthermore, the study confirms the sedimentological similarity of the Al Bashair Formation across the northern salt basins of Oman, and similarity to the exposed succession in the QMH area.  The detailed examination of the subsurface and outcrop succession of the Al Bashair Formation suggests a low gradient for the shelf during Al Bashair time in the north-central part of Oman.EThOS - Electronic Theses Online ServiceGBUnited Kingdo