The application of high-resolution sequence stratigraphy to fluvial systems: a case study from the Upper Carboniferous Breathitt Group, eastern Kentucky, USA

摘要

The Pennsylvanian Pikeville, Hyden and Four Corners formations of the Breathitt Group in eastern Kentucky, USA, contain six major facies associations along with a. number of subassociations. These facies associations are offshore siltstone, rhythmically bedded mouthbar heteroliths, predominantly fine-grained fioodplain deposits, minor channel fills, major distributary channels and major, stacked fluvial bodies. The stacked fluvial bodies are incised into a variety of open marine and delta plain deposits, have widths of several kilometres and exhibit a range of sandy fill types, These fluvial complexes are interpreted as incised valley fills. Parasequences and parasequence sets are not identifiable. Nonetheless, it is possible to identify systems tracts on the basis of sequential position, facies ssociations and systematic changes in architectural style and sediment body geometries. The studied portion of the Breathitt Group comprises stacked 4th-orcler sequences, which occur in lowstand, transgressive and highstand sequence sets related to the development of a lower frequency base level cycle. In the lowstand sequence set, incision associated with successive 4th-order sequence boundaries has commonly removed all the HST and TST of the underlying sequences, such that succeeding 4th-order incised valley fills are amalgamated. Within the transgressive sequence set, incision is at a minimum and incised valley fills tend to stack discretely with the maximum amount of fine-grained TST and HST between them. The highstand sequence set is transitional between the lowstand and transgressive sequence sets in terms of the amount of transgressive and highstand deposits preserved. Incised valley fills tend to stackdiscretely.