Alluvial architecture and palaeoenvironments in a proximal foreland basin setting: Upper cretaceous (Cenomanian) Dunvegan formation, British Columbia.

摘要

The Cenomanian Dunvegan alloformation represents a major deltaic complex that prograded at least 400km from NW to SE, parallel to the Cordillera, over about 2 m.y. The study area, near Chetwynd B.C., contains proximal coastal plain deposits of type 1b anabranching fluvial systems correlatable to subsurface log cross-sections that establish an allostratigraphic framework of ten allomembers.; Hydromorphic soils and organic rich lacustrine mud dominate 36 measured sections. Crevasse splays and levees dominate the coarse grained facies. Channel w:t is typically 30.; The alluvial architecture of allomembers G through A reveals changes in the tectonically controlled accommodation rate. A high accommodation rate is represented by lacustrine dominated intervals and a low accommodation rate is represented by palaeosol and crevasse splay dominated intervals. No interfluves or incised valley fills are recognized, suggesting that Sequence Stratigraphic concepts are not applicable to all parts of a progradational clastic deltaic complex.