Abstract

The Macumber Formation is the most distinctive and widespread carbonate of the Windsor Group (Mississippian). The formation is divisible typically into two distinct lithosomes. Lithosome A, the lower unit, is a slabby, thickly laminated, cross-stratified, pelletted, oncolitic, sparsely fossiliferous limestone. Lithosome B, the upper unit, is a fissile, thinly laminated, vuggy, dolomitic, unfossiliferous, mud-cracked, brecciated, algal stromatolite. Discontinuous, thick, boulder-sized calcirudite near the top of the lithosome has been called the Pembroke Formation. The carbonate of the Macumber and Pembroke Formations is overlain by red, gypsiferous, terrigenous lutite, marl, or locally, coarse, thick, red fanglomerate. Both Lithosome A and B are almost identical to strand-line carbonates of the Persian Gulf, Bahaman Islands, Florida Bay, and Australia. Lithosome A was deposited in the shallow subtidal to intertidal zone; Lithosome B in the high intertidal to low subtidal zone. The Macumber Formation and overlying lithosomes of the basal Windsor Group record sudden marine transgression followed by slow regression. Underlying red terrigenous detritus is overlain by subtidal then intertidal carbonate. Overlying high intertidal and low supratidal carbonates were fragmented by desiccation and scour, the clasts heaped into channel-fill breccia in all dimensions. This breccia, in part the Pembroke Formation, is a natural consequence of the Macumber environment. Penecontemporaneous dolomite, gypsum, and/or red terrigenous detritus record passage of the hypersaline, high-supratidal environment over the depositional site. The lateral progression of bio- and lithosomes is interpreted from both vertical and longitudinal profiles. The seaward succession of lithotopes is from red, terrigenous, usually fine-grained alluvial fans to supratidal, dolomitizing salt flats with saline lakes and lagoons, through strandline carbonates with channels and algal mats to shallow, restricted lagoons, and finally toward more turbulent, more normal marine conditions. Rock units of the basal Windsor Group record environment, but not time except along depositional strike.

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