ABSTRACT

Recent studies describe an antipathetic relation between animals which graze or disturb the bottom sediment and the growth of algal mats. Evidence from tidal to shallow subtidal deposits in the Middle Cambrian of Nevada and Utah suggests that under normal salinity conditions trilobites were abundant and algal stromatolites absent. Along the margins of hypersaline pools within the carbonate bank stromatolites flourished. Salinity conditions there were unfavorable for trilobites and other bottom-dwelling invertebrates.

The development of higher than normal salinities across the North American shelf was an important contributing factor in the reported low diversity of animal life in Cambrian through Early Ordovician times.

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