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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 799

Last Page: 799

Title: Quantitative Environmental Gradient Model for Interpreting Habitats of Microfossil Assemblages: ABSTRACT

Author(s): Richard A. Park

Article Type: Meeting abstract


A robust Q-mode ordination model has been derived from samples of diverse microfossils from Atlantic, Gulf, and Pacific coastal localities representing many different Cenozoic marine environments. Major environmental-gradient complexes are defined on the basis of their relations to major microfossil ecoclines; gradient complexes include depth of water, distance offshore, and rate of sedimentation/nutrient enrichment. By using principal taxonomic and bionomic groups that differ widely in ecologic requirements and tolerances, it is possible to obtain maximum information in spite of "noise" occasioned by heterogeneous groups. Because the groups are not restricted in time or geographic area, it is also possible to compare assemblages from different eras and provinces. Easily ecognized groups that are used include several types of foraminifers, ostracodes, and ectoprocts, radiolarians, diatoms, sponge spicules, echinoid spines, holothurian sclerites, fish scales, and alcyonarian spicules.

Q-mode-cluster analysis defines discrete microfossil biotopes that can be arrayed in the model, and these can be related to well-known depositional environments such as lagoons, beaches, deltas, carbonate banks, outer continental shelves, and deep-water borderland basins. However, unknown samples are interpreted best in light of the multidimensional model, recognizing the influences of independent gradients; in this way anomalous assemblages usually can be resolved readily. Present microorganism death assemblages are used to validate the model and confirm interpretations based on indicator microfossil groups and independent sedimentological and stratigraphic evidence.

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Copyright 1997 American Association of Petroleum Geologists