MIDDLE MIOCENE BRYOZOA FROM SIWA OASIS, WESTERN DESERT, EGYPT
Forty bryozoan species relating to the orders Cyclostomata and Cheilostomata have been
identified from the Middle Miocene Marmarica Formation in Siwa Oasis. They represent the
most abundant bryozoan species in the studied sections. The whole bryozoan assemblage
includes more than fifty species, all of them are recorded from this locality for the first time
(except four species).
According to their zoarial (=colonial) growth forms, the studied bryofauna are belonging
to the following: erect flexible, erect rigid and encrusting groups: cellariiform, adeoniform,
eschariform, reteporiform, vinculariiform, membraniporiform and celleporiform.
Holoporella polythele and Tretocycloecia dichotoma form a disconnected bryozoan
buildups. Such organic "reefal or at least biohermal" bryozoan record represents environmental
conditions similar to those found in the same stratigraphic horizon in Matruh to the north.
The studied bryozoan assemblage reflects the following paleobiogeographic conditions:
1. Mediterranean affinity of the studied fauna. 2. Monotonous areal conditions allover the
northern Western Desert during the formation of the Marmarica Limestone in the Middle
Miocene. 3. Free and continuos connection with North Africa, from Libya to Morocco. 4.
Limited connection with the north Eastern Desert, Gulf of Suez, Sinai and the Red Sea.
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