Stratigraphy and paleogeography of a conglomeratic shoreline: the Notikewin Member of the Spirit River Formation in the Wapiti area of west-central Alberta

In the subsurface of the Wapiti area in west-central Alberta, the Notikewin Member of the Upper Cretaceous Spirit River Formation represents a conglomerate-rich shoreline unit that was deposited in the Western Canada Foreland Basin. The Notikewin Member can be divided into four allomembers (T1, R1, R2 and R3), separated by widespread bounding discontinuities. T1 is the lowermost unit and represents deposition in a transgressive, wave-dominated estuary. Conglomerate bodies in this unit are relatively limited in lateral extent and trend perpendicular to regional shoreline trends. R1 records the development of an extensive regressive strandplain unit. During deposition of R2, a barrier spit was formed as sediments were introduced into the shoreline as a result of channel avulsion. This barrier had little progradational extent, instead growing longshore, creating a large estuarine/lagoonal complex. R3 represents a basinward shift of the shoreline resulting in the accumulation of continental deposits. Division of the Notikewin Member into these units indicates that contrary to previous interpretations, barrier deposits formed in Notikewin time did not prograde a great distance as a barrier island/lagoon complex. Implications for gas field development and exploration include a greater understanding of the limited extent of transgressive deposits, and a greater predictability of shoreline geometries that results from division of the Notikewin Member into allostratigraphic framework.