Prior to paleoecologic interpretation of fossils and their surrounding matrix, it is necessary to judge the adequacy of the geologic record to depict depositional site ecology. In a study of the ecology of Mugu Lagoon, several aspects of sediment and organism distribution are of interest. The aim of this work is to determine how well the Recent ecology of this area may be preserved in the record. The approach being used follows.

The sediments found within this physiographic setting are being analyzed in detail for grain size, organic matter, and carbonate. The significance of their distribution and character is being determined in relation to distance from the tidal inlet, tide levels, subaqueous and intertidal marsh vegetation, and fauna. Sedimentary structures from different environments of deposition are being described, and the importance of biogenic structures judged.

The flora of the lagoon is zoned by tidal level. Subtidal eelgrass serves as a refuge and feeding ground, and is being tested for an endemic fauna. Eelgrass and the salt marsh serve as an effective baffle system to trap fine-grained sediments; these are being studied for distinct structures and organism remains.

The fauna of the lagoon is being sampled, using ¼-sq. m. quadrats in conjunction with special dredging apparatus. Living organisms and shell remains are sorted, tabulated, and compared. In this manner the relations of the faunal elements can be compared to environmental parameters of the lagoon and to each other.

From preliminary results, the following points of paleoecologic interest can be made:

Post-depositional changes resulting from diagenesis and lithification commonly can be discovered with micro- or macroscopic techniques. Penecontemporaneous changes, caused directly or indirectly by the work of many kinds of organisms, may be quantitatively more important. These latter changes commonly are more difficult to discover and assess.

Although sediments and primary structures are functions of available material and energy, even moderate populations of animals can rework the sediments so that only biogenic structures are preserved, or the sediment can become apparently homogeneous.

Living populations of animals with hard parts are well represented by shell remains from the same quadrat, but absolute numbers of living and dead representatives of the same species are quite variable. Fossil population from this kind of environment should be largely in place, with little post-depositional transportation.

Rapid dissolution of shells can occur in some depositional environments.

Examples illustrating these points are presented.

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