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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 47 (1963)

Issue: 2. (February)

First Page: 352

Last Page: 353

Title: Role of Bryozoa in Cenozoic Paleoecology: ABSTRACT

Author(s): Alan H. Cheetham

Article Type: Meeting abstract


Distribution and abundance of fossil organisms still furnish the major basis for ecological interpretation of sedimentary rocks because organisms respond to, and therefore record, the whole complex of their surroundings, animate and inanimate. The task of the paleoecologist, resolution of this response into meaningful components, depends on knowledge of the requirements and tolerances of the organisms involved.

Bryozoa are a numerically important element of faunas enclosed in Cenozoic limestones, marls, and calcareous clays. They comprise more than 500 marine, mostly stenohaline genera that collectively are widely distributed in all of the main faunal provinces. Individually these genera tend to be stenothermal and therefore reliable paleoclimatological guides to the position and shifts of the provinces during Cenozoic time.

As part of the sedentary epifauna, bryozoans are especially sensitive to movement of water and consistency of substrate, physical determinants which are themselves consonant with water depth. This sensitivity provided the basis for investigation of two paleobathymetric problems in the Gulf Cenozoic.

1. The depth of accumulation of Quaternary mudlumps at the mouth of South Pass of the Mississippi River was determined by a taxonomic method. The mudlump faunules include 34 species whose present depth ranges are known from published accounts. Analysis of these ranges and comparison with individual Recent faunules yielded a depth of accumulation of 20-50 fathoms, 40 fathoms being the single most probable value.

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2. The paleogeography of the eastern Gulf Coast during Jacksonian (Late Eocene) times was reconstructed by a combination taxonomic-morphologic method. For Tertiary faunules some of the precision lost by using taxonomic data alone, by the change from specific to generic level, is restored by adding morphologic data. This treatment of Jacksonian faunules is an elaboration of one introduced by L. W. Stach in 1936 and consists of determining relative frequencies of zoarial growth forms. Coupled with taxonomic data, these frequencies suggest water depths of 20-50 fathoms in Alabama and western Florida and 5-20 fathoms in peninsular Florida.

The morphologic approach seems especially versatile and capable of extension, but for proper evaluation the adaptive significance of many features, e.g., avicularia and vibracula, must be ascertained.

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Copyright 1997 American Association of Petroleum Geologists