REVISIONS AND CLARIFICATION OF BASAL CAMBRIAN SANDSTONE STRATIGRAPHY IN KENTUCKY

Cambrian sandstones of different thicknesses commonly overlie the Precambrian surface in Kentucky. For many years, these sandstones were termed “basal sandstones” (informal or formal usage) and equated with either the Mount Simon Sandstone of the Illinois Basin or the Potsdam Sandstone of the Appalachian Basin. The sandstones themselves do not contain biostratigraphically significant fossils. Age is mostly based on correlations to surrounding areas constrained by fossils in overlying strata. But in Kentucky’s deep grabens, basal sandstones are offset by hundreds to thousands of feet from sandstones readily correlated to the Mount Simon or Potsdam in surrounding states. Significantly, the thicknesses of strata between the tops of the basal sandstones to the base of the younger Knox Group in the grabens are much thicker than out of the grabens. Using the term basal sandstone for sandstones of different ages in different parts of the state is confusing and can lead to misinterpretations.

Herein, the Kentucky Geological Survey defines the sandstones above the Precambrian surface in different parts of Kentucky and provides relative ages and correlations to sandstones in surrounding states. The basal Cambrian sandstone in western Kentucky, north of the Rough Creek Graben and west of the Grenville Front is the Middle Cambrian ‘Mount Simon Sandstone’ (similar usage to bordering Indiana and Illinois). In western Kentucky, within the Rough Creek Graben and Reelfoot Rift (Mississippi Valley Graben) and west of the Grenville Front is the ‘Reelfoot Arkose’ (similar usage to bordering SE Missouri), inferred to be Lower Cambrian in age, similar to sandstones above the Precambrian in the Rome Trough of eastern Kentucky. The basal sandstone in eastern Kentucky, north of the Rome Trough and east of the Grenville Front is the Middle Cambrian ‘Basal Sandstone’ (similar usage to bordering Ohio and transitional between the Mount Simon and Potsdam Sandstones in other states), and in eastern Kentucky, within and south of the Rome Trough is the Lower Cambrian ‘Chilhowee Group’ (similar usage to bordering Tennessee and Virginia). Establishing these new distinctions has the potential to improve the accuracy of future tectonic and depositional models of the Early to Middle Cambrian, as well as studies of carbon storage potential.