ARENITE PETROGRAPHY IN SEQUENCE STRATIGRAPHY

Stratigraphic boundary surfaces and internal anatomy of unconformity-bounded units may be deciphered by using properly conceived petrography that identifies compositional, spatial, and temporal characteristics of sand grains. Discussion of two case studies of synorogenic deep marine successions indicates the potential of this method. When intrabasinal source areas are present, relative sea-level changes can exert direct influence on the intrabasinal/extrabasinal grain budget. In this case genetically significant, unconformity-bounded units are not only characterized by their internal facies architecture, but also by internal organization in ''petrosomes'' (as it is for biozones in biostratigraphy). When intrabasinal source areas are narrow or absent, relative sea-level changes only control the timing of the record in deep-sea sands of tectonic modifications in hinterland sources. In this case, unconformity-bounded sequences may be fingerprinted with distinctive detrital compositions. These results emphasize the potential for use of sand petrography in sequence stratigraphy with particular reference to (1) basinal successions, where superposed sequences are conformable, (2) field mapping of structurally complex or poorly exposed areas where sequence-stratigraphic relationships are hidden, and (3) stratigraphic analysis of subsurface bodies.