SEQUENCE STRATIGRAPHY OF MIDDLE DEVONIAN (LATEST EIFELIAN-EARLY GIVETIAN) DEPOSITS IN NORTHERN OHIO AND NEW YORK: IMPLICATIONS FOR EUSTASY AND FAUNAL TRACKING

Middle Devonian (latest Eifelian-early Givetian) sediments of northern Ohio, deposited on the eastern and western flanks of the Findlay Arch in the Appalachian and Michigan basins, show similar patterns of third- and fourth-order depositional sequence architecture; these can be correlated into the Skaneateles-lower Ludlowville formations of New York based on pattern and conodont/goniatite evidence. The upper portion of the Delaware Limestone (latest Eifelian - Givetian?) in the Sandusky region east of the Findlay Arch (EFA) displays a shallowing upward trend of sea level regression and is sharply (disconformably?) overlain by coral rich-beds. In the Toledo region along the western flank of the Findlay Arch (WFA), coeval coral-rich beds, the lower, “blue limestone” ( units 1-7) of the Silica Shale, rest unconformably on the Eifelian Dundee Limestone. The coral beds are interpreted as deposits of an initial transgression (TST), equivalent to the Stafford Limestone (basal Skaneateles Fm.) in New York. This coral-bearing limestone is everywhere overlain by a high-stand succession of grey to black mudrocks (Levanna Sh. [NY], Plum Brook Sh. [EFA], Silica Sh. [WFA]). Moreover, both the Plum Brook and Silica shale are sub-divisible into three small-scale argillaceous limestone-to-shale cycles that appear to correlate with the Delphi Station, Pompey and Butternut members of the Skaneateles Fm. in central NY. In all areas an uppermost, dark, leiorhynchid brachiopod-rich shale is sharply and unconformably overlain by a second coral-rich limestone (Centerfield [NY], lower Prout Ls. [EFA], lower Ten Mile Creek Fm. [WFA]) representing the transgressive base of the next third order sequence. These high-resolution correlations in two basins suggest allocyclic control and imply the need for revision of Middle Devonian sea-level curves. Further, the appearance of taxa typical of the upper Hamilton of New York in the lower Hamilton strata of the Findlay Arch region proves the earlier appearance of these forms in shallower water facies and supports a model of faunal tracking.