ABSTRACT

Reports of Precambrian trace fossils are rare and generally doubtful. Unequivocal evidence of biogenic structures has been recorded for the first time from layers in shallow-water sedimentary rocks of a Proterozoic sequence (= 1,300 m.y. ago) in the Godavari Valley of south India.

Five different suites of structures have been noted. Each of these suites is closely related to a particular lithofacies with a well-defined position in the stratigraphic sequence. Vertical burrows and spreiten distributed in delicate sheets are confined to limestone facies. Inclined burrows making interconnected networks are profuse in a shale sequence, locally with low rank metamorphism. Surface trail marks and horizontal to nearly horizontal burrows, exposed on the bedding planes, are confined to the shallow, sub-tidal sandy facies. Vertical boring structures have been recorded from a thick limestone of possible lagoonal origin.

Close relation of sedimentary lithofacies and morphotypes of the biogenic structures and their stratigraphic zonation is clearly demonstrated in Ramgundam (79°26′E, 18°45′N) and Somanpalli (80°15′E, 18°46′N). Observations in other parts of the valley reveal that these trace fossil suites may be used as an excellent aid in paleofacies interpretation and in stratigraphic correlation of the nonfossiliferous, deformed sequence.

Preferred en echelon orientation of the features of positive relief at high angle to ripple crests; highly sinuous, lobated, and irregular pattern on bedding planes; linear grooves with parallel ridges on either side; intersection of sinuous relief features or grooves; and gentle U-shapes of the contacts of the features with bedding surfaces all point to biogenic origins for these structures.

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