Facies Relationships and Paleoenvironments of a Tide-Dominated Delta--An Estuarine-Barrier Complex in a Mesotidal Setting, Upper Cretaceous, Drumheller, Alberta: ABSTRACT

Abstract

The transition between the Bearpaw and Horseshoe Canyon Formations (100 m thick) near Drumheller represents an upward-coarsening deltaic sequence. A detailed field sedimentologic investigation of these rocks has led to the recognition of several distinct lithofacies. In stratigraphic order, the lithofacies of the subaqueous part of the delta are: (1) an offshore bar cross- and hummocky-stratified sandstone, (2) a prodelta marine shale and siltstone, (3) a distal mouth-bar shale, (4) siltstone and sandstone with Chondrites, and (5) a proximal mouth-bar sandstone and minor shale with Teichichnus, Rhizocorallium, Lockeia, and other burrows. The subaerial part of the delta and the interdeltaic shoreline sediments consist of 15 lithofacies that can be grouped as follows: estua ine distributary channel; barrier; back-barrier; tidal inlets; tidal channels and flats; peat swamp; and middle to upper delta-plain meandering rivers and overbank complexes. Trace fossils associated with these are: Teredolites borings, Ophiomorpha, Teichichnus?, Cylindrichnus, Palaeophycus, Asterosoma, and Anemonechnus?. Vertical lithofacies transitions suggest a few transgressive episodes. This sequence was deposited in a mesotidal, embayed shoreline, where a system of meandering distributary channels formed estuarine, tidally dominated deltas flanked by mesotidal barrier-island complexes. Minor transgressions of the sea interrupted the generation of a simple prograding sequence and resulted in formation of very complex facies relations. End_of_Article - Last_Page 621------------