REGIONAL SEDIMENTOLOGY, CONODONT BIOSTRATIGRAPHY AND CORRELATION OF MIDDLE CAMBRIAN LOWER ORDOVICIAN (QUESTIONABLE) STRATA OF THE FINNEGAN AND DEADWOOD FORMATIONS, ALBERTA SUBSURFACE, WESTERN CANADA SEDIMENTARY BASIN

Detailed sedimentological and paleontological analysis of 187 cores fr om the Alberta subsurface allow for a better understanding of depositi onal settings and preserved stratigraphy of Middle Cambrian to possibl y Lower Ordovician strata within the Western Canada Sedimentary Basin. Facies analysis indicates that the Cambrian successions were emplaced and reworked as mixed elastic and carbonate ramps or marine shoals wi thin a broad, shallow, marine intracontinental basin, south of the Pea ce River Arch, and east of the West Alberta Arch, in an area that has been called the Lloydminster Embayment. Locally, pre-existing basement highs pierced the marine embayment, shedding coarse elastic debris, d isrupting the stacking patterns of the sedimentary successions, and re sulting in overstep relationships and condensed sections. Much of the history of Middle Cambrian to Early Ordovician in the Alberta subsurfa ce is one of repeated cycles of erosion and deposition of bath clastic s and carbonates that resulted in a very fragmentary preserved stratig raphy. In the subsurface of Alberta and Saskatchewan the upper part of the Sauk II subsequence consists of the Deadwood Formation. In the Al berta subsurface, the Deadwood Formation is a transgressive, elastic-d ominated, shelf-ramp succession. This is overlain by reworked platform al carbonates, with varying amounts of elastic debris, that have been traditionally termed the ''Finnegan'' Formation. Detailed core logging , facies and geophysical-log analysis of subsurface data during the pr esent study indicates that, where distinctive geophysical log-markers or other marker horizons in core are absent, it is impossible to defin itively differentiate ''Finnegan'' from Deadwood strata. Conodont bios tratigraphy shows the presence of a paraconodont-dominated zone overla in by the Proconodontus, Eoconodontus and Cordylodus zones. The top of the succession is diachronous, ranging in age from latest Cambrian to possibly earliest Ordovician. Distinction of the Finnegan and Deadwoo d formations is very difficult in the Alberta Plains subsurface. It is proposed here that the term ''Finnegan'' be abandoned, and that all u nits previously assigned to the ''Finnegan'' unit now be included as p art of the Deadwood Formation. Similarly, other stratigraphic units ar e difficult to separate in the subsurface without traceable geophysica l or seismic markers. Future work should critically examine the applic ability of existing stratigraphic nomenclature to the Alberta Plains s ubsurface.