Publication Date:
2012-06-01
Description:
A recent study has suggested that early Cambrian trace-fossil–bearing strata in the Wood Canyon Formation (California) provide the oldest evidence for metazoans in continental environments (Kennedy and Droser, 2011). Although the search for superlatives in the history of terrestrial life is an attractive vein of research, suspected fossil evidence must be presented within a robust sedimentological framework. This is complicated in strata deposited prior to the evolution of land plants because the differentiation of clastic continental and shallow marine sediments is problematic (Dott et al., 1986). Lower Paleozoic clastic successions are often typified by sheet-like sandstones regardless of marine or continental influence, and confident paleoenvironmental interpretation of such successions is usually reliant on the occurrence of body fossils or minerals such as glauconite. Some sedimentary structures, such as hummocky cross-stratification, may imply a marine influence, but such signatures are indicative of process rather than environment per se, and must be treated with great caution (Davies et al., 2011a). It is acutely inadvisable to use the absence of such physical features as support for a fluvial origin, as advocated by Kennedy and Droser.
Print ISSN:
0091-7613
Electronic ISSN:
1943-2682
Topics:
Geosciences
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