Disconformities, i.e., minor surfaces of non-deposition and/or erosion, are considered to be ubiquitous in stratigraphic successions, but their temporal distribution and durations are diffcult to determine. Here, we analyzed the stratigraphic distribution and temporal signifcance of disconformities in eight drillcores of the Upper Devonian Ohio Shale, Appalachian Basin, North America, using ultra-high-resolution-gamma ray logs. These logs record numerous abrupt shifts in background gamma values and/or changes in the amplitude or wavelength of small-scale cycles that likely represent disconformities. Each study core contains from 12 to 34 iden-tifable disconformities, which are relatively more abundant in the Lower Huron, Chagrin, and Cleveland members and less abundant in the Middle Huron and Upper Huron members of the Ohio Shale. However, individual disconformities are generally uncor-relatable at a regional scale, suggesting that such minor hiatuses in sedimentation were areally limited in extent. Time-series analysis demonstrates that the pervasive small-scale cyclicity in these shale successions represents forcing at an orbital precessional scale, on the basis of which we determined the amount of time represented by sediment in each strati-graphic unit of each study section. Compared to their expected durations, the actual depo-sitional time based on cycle analysis implies that the individual study units are variably~10% to~68% complete at a characteristic time scale of~18 k.y.(i.e., the rotational axis precession period). Analysis of hiatal fractal dimensionality(D)shows that the individual study units have D values between 0(complete)and 0.8(highly incomplete);their median D value of~0.25 refects the relatively greater average completeness of this deep-water shale succession compared to typical shallow-marine facies(D =~0.5). Although eustasy controlled frst-order patterns of sedimentary fll in the Appalachian Basin, the apparent non-correlation of most disconformities at a regional scale argues against a dominant eustatic control on their development. Instead, the documented pattern of numerous disconformities of limited lateral extent implies greater infuence by hydrographic(e.g., local current-driven sediment accumulation/erosion)and/or tectonic factors(e.g., local variation in hinterland uplift and sediment delivery). This study demonstrates a novel method of identifying and analyzing the time content of stratigraphic hiatuses, providing general insight into the duration, spatial distribution, and signif-cance of gaps in the stratigraphic record.

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