Sequence Stratigraphy: A Historical Perspective

Abstract

Sequence stratigraphy was originally defined by Sloss as the study of genetically related strata that are bounded by unconformities. A sequence was regarded as a lithostratigraphic unit. The definition has been expanded to [open quotes]bounded by unconformities of their correlative conformities[close quotes] and a sequence was changes to a chronostratigraphic unit. In petroleum exploration within shelf areas of foreland and continental margin basins and cratonic basins, two types of unconformities are particularly important, both related to sea level changes. The first type of unconformity, a subaerially exposed lowstand surface of erosion (LSE, sequence boundary), is caused by relative sea level lowering. The boundary is recognized by incised paleovalleys, paleosols, and missing facies. The second type of unconformity is a transgressive surface of erosion (TSE, sometimes called a ravinement surface), and occurs where shoreface erosion moves over coastal plain deposits during a relative sea level rise. Examples of subtle stratigraphic traps in siliciclastic rocks associated with unconformities are discussed for the Lower Pennsylvanian strata of the mid-continent region. Also reviewed are the problems of applying the new sequence stratigraphic terminology in relation to established terminology.