The Upper Hamra Member of Said and Issawi (1964) is a clastic/carbonate succession at Qor El Hamra
east of the Bahariya Oasis in the Western Desert, Egypt. Earlier, the authors changed this member into a
new informal name, the Al Humaymat formation (Priabonian) at the Siwa Oasis, which consists generally
of carbonate sediments and overlays the mushroom rock of the Mokattam Formation (Late Lutetian). The
thickness of the Al Humaymat formation is about 22 m recorded at the El Qara section and at the El Arag
section reaches 5 m, where the collected fauna from this formation is represented by larger foraminifera
Nummulites fabianii retiatus, Gaziryina aff. pulchellus, Silvestriella tetraedra and Grzybowskia sp. are
assigned to Late Eocene (Priabonian). The base of the Al Humaymat formation is composed of grey marl
to varicolored small scale tabular cross-bedded limestone, which reflects sheet flood deposits with a
great unconformity surface; the middle part is composed of reefal limestone and sandy limestone. The
upper part of this formation is characterized by earthy white limestone, which is overlain by very hard
brown ferruginous paleosol bands and pockets, which represent distal floodplain deposits.
Here it is interesting to notice that the Early and Late Priabonian decrease in depth of the sea over the
studied area seems to be a reflection of a global decrease in depth of the sea as suggested from eustatic
curves published by Haq et al., l987. |
