Theoretical aspects of the formation of fossil assemblages are explored for the purpose of obtaining criteria and methods for the reconstruction of circumstances of preservation of shallow-water marine organisms. Models are developed which represent: (1) a death assemblage preserved under conditions of rapid burial; (2) an assemblage preserved in situ under conditions of gradual accumulation; and (3) an assemblage composed almost entirely of remains transported to the site of burial.

The histories represented by the models influence the following features of fossil assemblages: faunal composition, morphologic composition, density, disassociation of hard parts, fragmentation, surface condition of fossils, chemical and mineralogical composition of fossils, orientation, dispersion, and the texture and structure of the sedimentary aggregate. The expressions of these features indicate that biological criteria are more indicative of the mode of accumulation than physical criteria.

The stretched-line method of sampling provides a means of obtaining objective and repeatable measures of features of the fossil assemblages in place. It is restricted to sediments in which fossils can be recovered readily. A rank-correlation analysis of 11 samples from the Pleistocene Millerton formation of Tomales Bay, California, is given as an example of a means of evaluating the interrelations of variables measured by the line technique.

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