Supratidal Dolostones: An Overemphasis on Their Significance in Geologic Record?: ABSTRACT

Abstract

Numerous discoveries of recent dolomite forming primarily in the supratidal zone have prompted analogies with ancient dolostones. Although evidence seems to support most of these contentions, it is likely that overgeneralization has resulted; many dolostones lack definitive evidence of supratidal and/or evaporitic conditions. Detailed field and laboratory examinations of three dolomitic units in New York (Little Falls, Upper Cambrian; Herkimer, Middle Silurian; Lockport, Middle Silurian) and one in California (Lost Burro, Middle to Upper Devonian) show that the dolomite, all of replacement type, represents original carbonate sediments of variable environmental deposition. These dolostones are not extremely fine grained, as is modern supratidal dolomite; replacement may have begun penecontemporaneously, but generally continued later into diagenesis. Stromatolites, mudcracks, and intraclasts in the Little Falls and Lockport dolostones strongly suggest intertidal to supratidal occurrences; Lost Burro carbonates accumulated in a nearshore, perhaps slightly hypersaline, subtidal environment; Herkimer carbonates apparently formed in a neritic environment of normal salinity. Several other dolomitic units, cursorily examined, contain evidence (particularly faunal) of not having accumulated in an evaporitic, supratidal setting. In some recent carbonate deposits (e.g., Sugarloaf Key, Florida; Coorang Lagoon, Australia), dolomite formation may not be related directly to high salinities. End_of_Article - Last_Page 561------------