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Estimating volumetric fossil abundance from cross-sections; a stereological approach

Michael Lyle McKinney
Estimating volumetric fossil abundance from cross-sections; a stereological approach
Palaios (February 1986) 1 (1): 79-84


The number of fossils exposed in a stratigraphic or microscopic cross-section is proportional to the number contained per unit volume within the rock. However, it is also affected by the average size and shape of the fossils. The larger and more spherical a fossil is, the greater are its chances of being exposed (intersected) by a random planar cut. Thus, where fossils are randomly distributed and oriented in a hard matrix, it can be shown that: Na = Nv(kx), where Na is the number per unit area counted in cross-section, Nu is the number per unit volume, k is a shape factor, and x is the mean length. Since we can directly obtain Na, k, and x, it is possible to solve for, and thus estimate, Nu, volumetric abundance: Nu = Na/kx. Properly analyzed, volumetric abundances can yield insight into the paleoecological abundances of fossil species. A case study of six echinoid species co-occurring in the upper Eocene carbonates of Florida illustrates the methodology. Sampling of some 92 square m of cross-section shows volumetric abundances ranging from about 21 individuals/cubic m for the smallest species to as low as 0.036 individuals/cubic m for the largest. Thus, the former appears to be about 580 times more common in the rock. Assuming they had similar chances of burial and preservation (which can be experimentally estimated and corrected for), this also reflects their relative abundance in the late Eocene ecosystem. This greatly contrasts with estimates made from a simple cross-sectional count which indicates that the smallest species is only 81 times as common. Hence no adjustment for the artifacts of size and shape on the probability of exposure results in an erroneous estimation 7 times too low.

ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 1
Serial Issue: 1
Title: Estimating volumetric fossil abundance from cross-sections; a stereological approach
Affiliation: Univ. Tenn., Dep. Geol. Sci., Knoxville, TN, United States
Pages: 79-84
Published: 198602
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 12
Accession Number: 1986-035939
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N24°30'00" - N31°00'00", W87°30'00" - W80°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 1986
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