Middle to Late Cambrian Marine Transgression Depositional System of the Peri-Gondwana Terranes: An Example from Al Bashair Formation of the Huqf Region, Oman

The Al Bashair Formation corresponds to the lowermost part of the Andam Group (Haima Supergroup) that crops out in the Huqf region of central Oman. Al Bashair Formation is an important deep hydrocarbon-producing subsurface reservoir in the interior Oman Salt Basin. The current outcrop-based stratigraphic and facies analysis of the Al Bashair Formation in the Huqf region has shed new insights to better understand the spatial and temporal distribution of the depositional facies and construct a reliable depositional model. The results have shown that the Al Bashair Formation can be divided into two informal members. The lower informal member contains ca. 120 m thick interval of thinly interbedded (ca. 5–25 cm) sandstone, siltstone, and red mudstone packages with (ca. 1 m) carbonate layers. The mudstones sometimes exhibit the presence of desiccation mud cracks. The sandstones show different body fossils, such as trilobites, brachiopods, and echinoderms, trace fossils and halite molds. The carbonate layers include stromatolites and oolitic grainstones. The oolitic grainstones show the presence of herringbone cross beddings. The upper member of the Al Bashir Formation contains about 160 m thick interval of coarsening upward cycles of red mudstones, siltstones, and sandstones. The sandstones lack body fossils and show less frequent trace fossils including Cruziana and U-shape (Arenicolites) borrows. The sandstones show the presence of hummocky and swaley cross-stratifications. The described rock intervals of Al Bashair Formation support deposition in tide- and frequently storm-dominated shallow marine ranging from supratidal to subtidal settings.