332-8 Magnetic Susceptibility and Orbital Cycles of Cleveland Shale Member Intervals, Ohio Shale, Upper Devonian, from Ohio Drill Cores

Abstract:

Magnetic susceptibility (MS) was measured through the Upper Devonian Cleveland Shale Member of the Ohio Shale at high resolution in three drill cores: OGS 2811 (Ross County: RC), OGS 2736 (Delaware County: DW), and OGS 6426 (Cuyahoga County: CH). Multitaper spectral analysis (MTM) and TimeOpt sedimentation rate optimization were applied to identify Milankovitch-band periodicities in depth-domain MS. Biostratigraphic control places the lowermost Cleveland Shale in the aculeatus Zone based on the occurrence of Bispathodus aculeatus antiposicornis in the uppermost Huron Shale along with other taxa representative of this zone in the basal Cleveland. Long-ranging species of Bispathodus, Branmehla, Palmatolepis, and Polygnathus were recovered through the entire Cleveland interval, none of which are diagnostic of higher zones. All three cores preserve sedimentation rates of approximately 1.07-1.25 cm/kyr and record orbital cycles consistent with precession (~16.85-22 kyr) and obliquity (~37-41 kyr). The obliquity cycle is expressed at every ~1.5 m, while the precession occurs at every ~0.68 m. The two longer cores (RC and DW) additionally resolve short-eccentricity cycles of ~95-126 kyr. Spectral comparison of the complete CH record against the uppermost 8 m of the RC and DW cores reveals identical Milankovitch cycles at the same depth-domain frequencies, which indicates that only the upper portion of the Cleveland Shale is preserved and that the base of the Cleveland Shale is diachronous.

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