Late Quaternary Sequence Stratigraphy: Variations, Lessons, and Potential Problems

John R. Suter

Fluvial valley incision driven by increasing gradient during eustatic fall is a primary tenet of sequence stratigraphy. The base of this fluvial incision is the sequence boundary, considered the most important chronostratigraphic surface in time-rock correlation. While it is axiomatic that shorelines regress and fluvial channels extend across the emergent continental shelf when sea level falls, the nature and timing of this response is not uniform. In the late Quaternary of the northern Gulf of Mexico, a recognizable spectrum of incision types and valley fill facies formed in response to the same glacio-eustatic cycle. Continental-scale rivers (the Mississippi), extrabasinal rivers, and basin-fringe and coastal plain streams produced markedly different geometries and faci s. Incised valleys do not follow simple cross-shelf courses to the shelf margin, but show complex networks of multiple trunk streams and tributaries at a variety of orientations. These formed in response to allogenic factors such as eustasy, growth faulting, and diapirism, and autogenic factors such as avulsion, delta switching, stream capture, and variations in discharge and sediment supply and caliber. The base of fluvial incision, and thus the sequence boundary, is a time-transgressive surface. Its age and extent varies throughout the basin and within given systems, and the time involved in its formation is not small compared to the duration of the sequence. Although this surface still has chronostratigraphic significance and correlation utility, correctly predicting ts geometry and the stratal architecture of the related depositional sequence requires recognition of the roles of both allogenic and autogenic factors.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995