Unraveling stratigraphic complexities of transgressive surfaces with trace fossil omission suites and juxtaposed softground suites

Abstract

Recognizing stratigraphically important bounding surfaces relies on assessing the facies that juxtapose these surfaces as well as the trace fossil omission suite associated with the surface. The ability to differentiate between purely transgressive surfaces and those that conceal earlier stratigraphic surfaces that allude to a more complex history of development regarding the identification of allogenic surfaces of sequence stratigraphic significance that might have otherwise been overlooked. This study analyzes four examples of transgressive surfaces of erosion from Cretaceous-aged strata, with three of the examples representing a TSE/SB (amalgamated transgressive surface of erosion with a sequence boundary) that mask earlier base level falls. Consideration of variable omission suites along depositional strike and dip highlights the influence of substrate rheology on the nature of omission suites. In this study we demonstrate marked changes in the omission suite along bounding surfaces along proximal to distal trends that arise due to changes in underlying rheology. Finally, detailed core analysis is shown to be an imperative asset to subsurface investigation to address the limitations of using wireline well data alone in identifying stratigraphically important surfaces for more accurate regional mapping and characterization of transgressive surfaces. This study highlights that many stratigraphically important surfaces such as those that correspond to a TSE/SB may go unnoticed if utilizing wireline data alone. Overall, this study provides a comprehensive approach to further understanding and identifying transgressive surfaces in the rock record, especially those that demarcate a more complex history other than simple transgressive ravinement.

Keywords:

• Palimpsest
• softground
• stiffground
• omission suite
• ichnology
• stratigraphy
• transgression
• transgressive surface
• marine flooding surface
• transgressive surface of erosion
• wave ravinement
• Clearwater Formation
• Wabiskaw Member

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This article was funded by Cenovus Energy; BP energy; chinese national offshore oil corporation (cnooc); Woodside.