Simsima Fm
Type Locality and Naming
The Simsima Fm represents the re-establishment of marine sedimentation over Oman after the disturbance caused by the nappe emplacement along Oman’s northeast margin associated with the closure of the Neo-Tethys Ocean. Column: Oman Subsurface, Qatar, United Arab Emirates. Type section is Dukhan-65, Qatar, thickness drilled 148 m. Reference section in Oman is well Suneinah-1 in North Oman. Additional reference section is Hawmyat-1 in South Oman. Uppermost formation in the Aruma Gr.
Synonym:
Lithology and Thickness
A variable carbonate unit, containing a variety of shallow-marine limestone facies and subordinate dolomites; commonly very fossiliferous. Yellowish-tan to yellowish-brown dolomitic and calcareous shale, argillaceous dolomite and olive shale with minor interbedded limestone and dolomite. Blue-gray to cream, massive dolomite and limestone. Cream-colored, soft, chalky, fine-grained limestone, with minor interbedded olive to olive-green calcaerous shale in the lower part. Cream-colored, massive, nodular, chalky, fine-grained limestone with abundant small fragmental organic remains.
Relationships and Distribution
Lower contact
Upper contact
It is overlain unconformably by the Umm er Radhuma Fm (Shammar Shale Mbr), with a hiatus of latest Maastrichtian to Early Paleocene duration.
Regional extent
Oman Subsurface, Qatar, United Arab Emirates. On Oman: " The sediments are everywhere of shallow-water facies in Interior Oman, although deep facies occurs further to the northwest and into the eastern United Arab Emirates. In the reference section in the Suneinah-1 well, the Simsima lies on sediments, with much detritus from the nappes, which can be referred to the surface Juweiza Formation (Glennie et al., 1974). In the Al Hajar Mountains, the Simsima can lie directly on the nappes, although a basal clastic unit, the Qahlah Formation (Glennie et al., 1974), may be present. In South Oman, the Simsima occurs only very patchily, although dating imprecision is a constraint. It may not have been deposited over large parts of South Oman, but it is present in the west and is continuous into the Rub’ Al-Khali basin. On the east side of the Al Huqf, small outcrops of Maastrichtian pelagic carbonates suggest open, deeper-marine influence in the down- faulted Arabian Sea margins. It was only confirmed to be present in well Dhahaban South-1 (South Oman). It is assumed to be present in adjacent wells by log correlation (Hawmyat-1)."
GeoJSON
Fossils
Shallow-water carbonate that is commonly very fossiliferous. " Biozone F68, containing three subzones, is characterized by the presence of Siderolites calcitrapoides (Figure 5.4). Omphalocyclus macroporus typifies Sub-biozone F687 in the shallow-water facies. Deeper-water assemblages containing planktic foraminifera of the genera Globotruncana are seen in Sub-biozone F685, which also yields Archaecyclus midorientalis and Lebidorbitoides schenki. Globotruncana arca and Pseudotextularia elegans characterize the lowermost Sub-biozone, F683. This trend with deeper water microfauna in the older sub-biozones is at odds with Sharland et al. (2001) placing their MFS K180 in the upper Simsima Formation."
Age
Depositional setting
The Simsima Fm represents the re-establishment of marine sedimentation over Oman after the disturbance caused by the nappe emplacement along Oman’s northeast margin associated with the closure of the Neo-Tethys Ocean. The sediments indicate an overall shallow-marine and generally high-energy environment, but open-marine foraminifera are occasionally found in this Formation.
Additional Information