The expression and interpretation of marine flooding surfaces and erosional surfaces in core; examples from the Upper Cretaceous Dunvegan Formation, Alberta foreland basin, Canada

This paper presents examples of marine flooding surfaces and erosional surfaces in core and well logs from the Upper Cretaceous Dunvegan Formation, Alberta, Canada. Two categories of surface are defined. The first category comprises those surfaces associated with relative sea-level rise and includes the transgressive surface of erosion and several types of flooding surfaces, including minor, major and maximum marine flooding surfaces. The second category of surfaces comprises those associated with relative sea-level fall and includes the sequence boundary and its correlative surfaces. The sequence boundary is most readily recognized as an erosional surface at the base of incised valleys but correlative surfaces can include subaerial exposure surfaces in interfluve areas, marine erosional surfaces at the base of incised sharp-based shorefaces and correlative conformities in the seaward realm. A transgressive surface of erosion may be coincident with or may enhance the unconformity associated with the sequence boundary in a landward position and may pass seaward into a flooding surface. The Dunvegan Formation is characterized by seven major marine flooding surfaces, each with a sharp contact between shallow-water sediments and overlying deeper water mudstones. These easily recognized surfaces could be correlated over hundreds of kilometres and were chosen as the bounding discontinuities for seven defined allomembers. Less extensive, minor marine flooding surfaces were used to recognize shingled offlapping units within each allomember. Sequence boundaries were also identified and used to separate highstand and lowstand systems tracts within several of the allomembers. Where the transgressive surface of erosion can be recognized, it is used to distinguish lowstand from transgressive systems tracts. The identification of systems tracts allows interpretation of the Dunvegan allomembers in terms of fourth-order, relative sea-level changes.