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Modern bryozoan colony growth forms have been successfully correlated with environmental factors such as local temperature, water depth, and sedimentation rates. Recent studies of living bryozoan communities on the South Australia continental shelf have provided a wealth of comparative data that can be used to study the bryozoan-rich Cenozoic limestones abundant in exposures of beach rocks along the southeastern coast of Australia.
One such unit is the Cellepora Beds, a Miocene group of the Torquay Basin, at Jan Juc, 95km southwest of Melbourne. |
Exposed bryozoan limestone at Jan Juc beach |  Bird Rock - Jan Juc, Australia The Cellepora Beds occupy the upper third of the cliff face here. The unit consists of about 20m of calcareous silts and clays interbedded with large branching colonies of Celleporaria gambierensis, after which the member is named. The interbeds are strongly cemented biosparite containing large branching colonies as well as many smaller specimens.
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Multilaminar and lattice growth forms are |
Seven colony growth forms were identified among the many fossil chelistome bryozoans at Jan Juc: unilaminar, multilaminar, frondose, robust and delicate branching, lattice, and jointed. The relative abundance of each type was recorded, scaled, and compared to recent data that associated bryozoan growth form to environment. The abundance data of several growth forms, when scaled together, indicated that Jan Juc was a level bottom, low inner-shelf region (30 - 50m depth) covered by a bryozoan "meadow" or open thickets, such as those seen in the Bahamas today. This disagreed with an earlier study which proposed a greater depth, but was based on the abundance of only one type of growth form. |
