Sequence Stratigraphy and Facies Associations of Falher Units C and D, Lower Cretaceous, Alberta Basin, Canada: ABSTRACT

Abstract

The Lower Cretaceous Falher Member (Spirit River Formation) in the Deep Basin of Alberta is composed of 5 units (A-E) comprising the reservoir of the giant Elmworth gas field. Using high resolution sequence stratigraphy, 333 well logs and 65 cores were integrated to understand the evolution of Falher C and D in the study area. Five major faces associations were defined in each unit. The basal surface of Falher D overlies nonmarine deposits (Falher E) and is defined by a marine flooding surface (transgressive surface of erosion) partially modified by a subsequent regressive surface of erosion. Southward, all the facies become more continental and the marine flooding surface passes into a lagoon-on-nonmarine contact. Falher D contains a series of shingled marine sandstone lenses separated by erosional surfaces interpreted as seaward-dipping ravinement surfaces indicating different phases of marine transgression-regression. The Falher C basal surface is a marine flooding surface partially modified by a regressive surface of erosion. The top of Falher C is defined by a marine flooding surface representing an increase in water depth and erosional truncation during shoreface retreat. Falher C is characterized in the south by floodplain deposits and progradational shoreface sediments deposited during high- stand. A relativemore » sea level fail produced a sequence boundary and a seaward shift of the shoreface facies northward. A sea level rise caused the shoreface migration southward (landward), forming a new transgressive surface. Progradational shoreface deposits took place during highstand and the uppermost part of Falher C was filled by aggradational floodplain deposits.« less