Level‐bottom brachiopod communities in the Middle Devonian of New York

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Abstract
Depositional environments of the Onondaga Limestone from central to southeastern New York are found to be normal, subtidal marine, due to the absence of characteristic supratidal or intertidal sedimentary features and the presence of a typical, diverse, marine level-bottom community framework. Post-mortem transport was not extensive, as evidence by low articulation ratios, lack of abraded values and complete ontogenetic gradations within species, which preculudes large scale winnowing. Sedimentation rates appear to have been greatest in eastern New York where the Onondaga Limestone reaches a thickness almost 3 times that of the strata in central New York. Shaly beds in the central area represent periods of cessation of carbonate deposition rather than an influx of clastic material. Deposition terminated with the onset of deeper water characterized by a westerly advance of terrigenous sedimentation (the Marcellus Shale of the Hamilton Group). Nine brachiopod communities can be recognized in the Onondaga Limestone. There is a strong correlation between sediment-substrate and community type, reflecting the sedimentologic control of brachiopod community distribution. Sandy facies, cherty limestones and coral biostromes and bioherms are associated with inner-neritic deposition in Edgecliff time; argillaceous lime muds and lime sands are characteristic of mid-neritic deposition in Nedrow to Moorehouse time; highly argillaceous lime muds are associated with outer-neritic deposition in Seneca time.