Middle Jurassic–Early Cretaceous foraminiferal biozonation of the Amran Group, eastern Sana’a Basin, Yemen

Two sections of strata assigned to the Amran Group at Jabal Salab and Jabal Yam in the eastern Sana’a governorate were sampled and correlated. These sections are part of a carbonate platform that extends from the city of Marib in the east to Naqil Ibn Ghailan, 20 km east of the city of Sana’a to the west. Palaeontological analysis of samples recovered has resulted in identification of 123 foraminiferal species, which are used to subdivide the sequence of the Amran Group into five biostratigraphic zones, aged between Bathonian (Middle Jurassic) and Berriasian (Early Cretaceous). The proposed biozones are those of Riyadhella rotundata, Kurnubia jurassica, Ammomarginulina sinaica, Alveosepta jaccardi and Pseudocyclammina sulaiyana/Furitilla caspianseis. These biozones were constructed and correlated with the equivalent zones reported from several localities

Middle Jurassic–Early Cretaceous foraminiferal biozonation of the Amran Group, eastern Sana’a Basin, Yemen

Two sections of strata assigned to the Amran Group at Jabal Salab and Jabal Yam in the eastern Sana’a governorate were sampled and correlated. These sections are part of a carbonate platform that extends from the city of Marib in the east to Naqil Ibn Ghailan, 20 km east of the city of Sana’a to the west. Palaeontological analysis of samples recovered has resulted in identification of 123 foraminiferal species, which are used to subdivide the sequence of the Amran Group into five biostratigraphic zones, aged between Bathonian (Middle Jurassic) and Berriasian (Early Cretaceous). The proposed biozones are those of Riyadhella rotundata, Kurnubia jurassica, Ammomarginulina sinaica, Alveosepta jaccardi and Pseudocyclammina sulaiyana/Furitilla caspianseis. These biozones were constructed and correlated with the equivalent zones reported from several localities

The Jurassic succession of Ras Sharwayn, South-eastern Yemen

Four Jurassic stratigraphic units have been recognised at Ras Sharwayn, about 300 km east of Al-Mukalla along coast of the Gulf of Aden. The Kohlan Formation (60 m) unconformably overlies the crystalline basement. Its lower and middle part consist of fluviatile sandstone and conglomerate. The upper part is made up of transitional coarse- and fine-grained sandstones and siltstones. The sequence ends with shallow marine fine-grained sandstones. The Shuqra Formation (71 m) can be divided into two members. The lower Calcareous-marly Member (45 m) consists of grey bioclastic limestone and subordinate nodular marl (inner to mid ramp). Its age is Late Oxfordian. The upper Carbonate Member (26 m) changes from basal reddish marly limestones (mid ramp) to thick beds of red-brown, coarsely crystalline limestones and dolomites (inner ramp). The topmost beds contain fossils of colonial organisms, essentially stromatoporoids. Its age is Late Oxfordian, and possibly earliest Kimmeridgian. The Madbi Formation (>30 m) consists of yellowish marl alternating with marly limestone and bioclastic limestone (coquinas) corresponding to storm layers (mid to outer ramp). With regard to its age, a specimen of Orthosphinctes sp., collected a few metres from the base, possibly refers to the Early Kimmeridgian. The Madbi Formation ends with an unconformity surface. The informal elastic unit (56 m) (including the Naifa Formation) consists, from bottom upwards, of: red-brown dolomite; grey detrital limestone with quartz grains; massive, white conglomerate with well rounded limestone clasts, quartz and bioclasts (e.g. colonial organisms). The last lithotypes are gravity flow deposits, accumulated at the base of a scarp possibly tectonic in origin, approximately at the Jurassic-Cretaceous boundary. This detailed lithological, sedimentological and biostratigraphical study has provided revised litostratigraphical subdivision and nomenclature and improved the stratigraphic control