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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 53 (1969)

Issue: 3. (March)

First Page: 721

Last Page: 722

Title: Recognition of Shallow Previous HitMarineNext Hit Environments: ABSTRACT

Author(s): Philip H. Heckel

Article Type: Meeting abstract


Shallow-Previous HitmarineNext Hit environments encompass a great variety of conditions from shoreline to a depth of about 600 ft. In sedimentary rocks, these environments are inferred most readily from diverse assemblages of fossils whose modern relatives are Previous HitmarineNext Hit. Some sparse and restricted biotas may represent fully Previous HitmarineNext Hit environments in which certain factors were unfavorable to many types of organisms. Many unfossiliferous black shales represent a foul environment that supported no benthonic life and are inferred to be Previous HitmarineNext Hit mainly by stratigraphic relations. Previous HitMarineNext Hit environments that lack significant sedimentation would be represented in the record only by a submarine paraconformity.

Recognition of Previous HitmarineNext Hit subenvironments is possible through direct lithic analogy with distinctive modern sediments of known depositional environments, such as oolite, sea-margin carbonate laminites, and certain organism-controlled features such as reefs. In less distinctive Previous HitmarineNext Hit facies, subenvironments are difficult to discriminate because visible differences may have resulted from a complex interplay of many variable factors that did not coincide to produce unique subdivisions. Ecologic consideration of fossil assemblages may distinguish clear-water from turbid-water, or soft-substrate from hard-substrate environments. Petrographic considerations also allow environmental inference. The presence of calcilutite indicates a quiet-water environment

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that might be either shallow and protected from water agitation by a physical barrier, or deep and protected by water depth itself. The presence of calcarenite composed of whole shells exhibiting little fragmentation or abrasion might indicate only local organic proliferation or lack of dilution by fine sediment. In contrast, calcarenite composed of fragmented, abraded, well-sorted, skeletal grains indicates water turbulence and winnowing of fines, processes which are more probable in shallow water.

Environmental syntheses based on stratigraphic, petrographic, and paleontologic criteria can bring into focus certain aspects of ancient Previous HitmarineNext Hit environments that are difficult to determine from the record. On a local scale, detailed facies mapping in undeformed rocks may allow detection of original topography that controlled facies changes. On a larger scale, systematic lithic variation along the outcrop of an entire stage of rocks may provide a regional picture of the lateral succession of ancient Previous HitmarineNext Hit environments across an epicontinental basin. Perhaps one of the best modern laboratories to study analogs of ancient Previous HitmarineTop epicontinental deposition is the Sahul-Arafura shelf and Gulf of Carpentaria between orogenic New Guinea and cratonic Australia.

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