THE APPLICATION OF HIGH-RESOLUTION SEQUENCE STRATIGRAPHY TO FLUVIAL SYSTEMS - A CASE-STUDY FROM THE UPPER CARBONIFEROUS BREATHITT-GROUP, EASTERN KENTUCKY, USA

The Pennsylvanian Pikeville, Hyden and Four Corners formations of the Breathitt Group in eastern Kentucky, USA, contain six major facies ass ociations along with a number of subassociations. These facies associa tions are offshore siltstone, rhythmically bedded mouthbar heteroliths , predominantly fine-grained floodplain deposits, minor channel fills, major distributary channels and major, stacked fluvial bodies. The st acked fluvial bodies are incised into a variety of open marine and del ta plain deposits, have widths of several kilometres and exhibit a ran ge of sandy fill types. These fluvial complexes are interpreted as inc ised valley fills. Parasequences and parasequence sets are not identif iable. Nonetheless, it is possible to identify systems tracts on the b asis of sequential position, facies associations and systematic change s in architectural style and sediment body geometries. The studied por tion of the Breathitt Group comprises stacked 4th-order sequences, whi ch occur in lowstand, transgressive and highstand sequence sets relate d to the development of a lower frequency base level cycle. In the low stand sequence set, incision associated with successive 4th-order sequ ence boundaries has commonly removed all the HST and TST of the underl ying sequences, such that succeeding 4th-order incised valley fills ar e amalgamated. Within the transgressive sequence set, incision is at a minimum and incised valley fills tend to stack discretely with the ma ximum amount of fine-grained TST and HST between them. The highstand s equence set is transitional between the lowstand and transgressive seq uence sets in terms of the amount of transgressive and highstand depos its preserved. Incised valley fills tend to stack discretely.