Sequence stratigraphy in organic-rich marine mudstone successions using chemostratigraphic datasets

Abstract

Sequence stratigraphy is commonly used to understand basin history and the distribution of conventional reservoir facies. Establishing a sequence stratigraphic framework in organic-rich mudstone successions is challenging because macroscale sedimentological and petrophysical variations can be subtle, while biostratigraphic and seismic data may be unavailable or of limited use. For these reasons, it is becoming increasingly common for chemostratigraphic profiles to be integrated with other datasets to facilitate sequence stratigraphic interpretation. This paper summarizes the whole-rock inorganic geochemical proxies relevant to sequence stratigraphic analysis in fine-grained, organic-rich marine units and reviews studies that have incorporated chemostratigraphic trends for sequence stratigraphy. This synthesis demonstrates that chemostratigraphic datasets are useful in identification of transgressive-regressive cycles, allowing for a preliminary summary of the chemostratigraphic characteristics of the maximum flooding surface, maximum regressive surface, transgressive systems tract, and regressive systems tract to be established based on existing work. A preliminary synthesis of the chemostratigraphic characteristics of the highstand systems tract is also possible for highstand systems tracts recognized using other criteria. However, a chemostratigraphic means of identifying the correlative conformity and basal surface of forced regression in order to subdivide the regressive systems tract into the lowstand systems tract, falling-stage systems tract, and highstand systems has not yet been demonstrated. Further work is also required in order to establish the differences in the chemostratigraphic signature of surfaces and systems tract depending on the depositional setting. Chemostratigraphic proxies are an emergent and promising tool for the identification of cyclicity in organic-rich mudstone intervals, which will become increasingly useful as further research is conducted on the topic.