Abstract: Detailed Surface Structure Yields Clues to Deep Structure

Philip L. Martin

The unique three-dimensional perspective afforded by the stereoscopic viewing of aerial photos permits the accurate outcrop tracing of many exposed Appalachian bedrock units. When carefully drawn on 7.5 minute topographic maps, the intersections of these outcrop traces yield a dense network of elevation control points. Contouring these data produces a detailed surface structure map which neither overemphasizes micro-geology nor glosses over structural detail which could have more significance than first meets the eye. Often structural features are revealed which never have been mapped before, simply because the geomorphic expression of certain units can be followed in stereo on aerial photos, while the accurate and continuous field mapping of the same units, by convention l methods, is obstructed by the naturally-concealing products of humid climates, such as soil and vegetation.

Such maps, when overlain on well- or seismic-controlled subsurface maps, exhibit some dramatic, if not always direct, overprinting of deep features. These analogs reinforce the concept of the upward, modified, transfer of discrete pre-Alleghenian structural features, probably through sporadic reactivation along already-weakened zones. It also is highly probable that this process produced some depositional surface topography which strongly influenced depositional patterns and facies, especially in Lower Devonian time.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas