ABSTRACT

Although much has been written about estuaries and estuarine sediments, very few facies models have been proposed to date and considerable ambiguity remains in coastal classification schemes. Current stratigraphic concepts fail to elucidate not only the differences between certain deltaic, estuarine, and lagoon-fill sequences, but also the pronounced similarities between many riverine and salt-marsh estuarine sequences. These distinctive latero-vertical successions, recent and ancient, warrant increased scrutiny and conceptual refinement.

Preliminary stratigraphic models and definitions presented here--based largely upon modern Georgia estuaries--should provide a broad framework for further evaluation and clarification of the above facies relationships. From that standpoint, an estuarine sequence consists of complex, intertidal to subtidal, mostly channel-form facies dominated to some extent by tidal effects, typically displaying abrupt variations in sediment texture and composition, and in physical and biogenic sedimentary structures. Subtle to pronounced salinity gradients may be discernible; nevertheless, the features most diagnostic of the overall sequence are 1) tidally influenced channel-form deposits, and 2) characteristic bioturbate textures and trace fossils.