This is Mary Campbell Cave, a rock shelter with overhanging sandstone in Cuyahoga Gorge, northeastern Ohio. A little above the floor of the rock shelter is the Mississippian-Pennsylvanian unconformity, consisting of sandstones and pebbly sandstones above and mudshales below. Paleotopographic relief is evident at the boundary.

Of the different types of unconformities, this one consists of horizontal sedimentary rocks over horizontal sedimentary rocks, and is thus a disconformity.

This contact is one of the most significant erosion surfaces in the Phanerozoic of North America. It is the boundary between two megasequences, the Kaskaskia Megasequence below and the Absaroka Megasequence above. Megasequences are also called Sloss Sequences, after the geologist Larry Sloss - <a href="https://www.geosociety.org/gsatoday/archive/24/3/pdf/i1052-5173-24-3-24.pdf" rel="nofollow">www.geosociety.org/gsatoday/archive/24/3/pdf/i1052-5173-2...</a>).

At this site, the entire Middle and Upper Mississippian are gone (eroded and/or non-deposited), plus the lower half of the Lower Pennsylvanian.

The gray shale unit below the unconformity is the Meadville Shale, one of many members of the Lower Mississippian Cuyahoga Formation, a mixed-siliciclastics unit. At Cuyahoga Gorge, the Meadville Shale is weathered gray silty shale (mudshale). Downsection and off-trail, the lower Meadville Shale consists of interbedded shales, siltstones, and (apparently) fine- to very fine-grained sandstones. Occasional trace fossils, sole markings (tool marks & grooving), and hummocky cross-stratification are seen in the lower Meadville.

The rocks above the unconformity are part of the Lower Pennsylvanian Sharon Member (a.k.a. Sharon Formation; Sharon Sandstone; Sharon Conglomerate). This unit consists of quartzose sandstones, pebbly sandstones, conglomeratic sandstones, and quartz-pebble conglomerates. The conglomerate is sometimes nicknamed "puddingstone" (a British term) and weathered-out pebbles are often called "lucky stones". The Sharon in Cuyahoga Gorge has angular cross-bedding, tangential cross-bedding, overturned cross-bedding, controted pebble beds, possible dish structures, cahnneling, and Liesegang banding. Honeycomb weathered cliff faces of Sharon are common.

Stratigraphy: Sharon Member (basal Pottsville Group, upper Lower Pennsylvanian) over Meadville Shale (Cuyahoga Formation, Lower Mississippian)