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Sequence Stratigraphy in Mudstone Intervals Using Chemostratigraphic Datasets: An Example From the Devonian Canol Formation

Abstract

Sequence stratigraphy is valuable for subsurface mapping of hydrocarbon reservoirs. However, in mudstone successions, establishing a sequence stratigraphic framework is difficult because sedimentological and petrophysical variations can be subtle, while biostratigraphic and seismic data are typically of limited use. Consequently, chemostratigraphic datasets are being employed to facilitate sequence stratigraphic interpretation of mudstone intervals. The elemental proxies most commonly used include elements that serve as indicators of detrital sediment supply (e.g. Al, Fe, K, Ti, and Zr), proxies that reflect the proportion of biogenic to detrital silica (e.g. Si/Al, Si/Zr, Si-Al cross plots), and paleoredox proxies that can be used to infer degree of basin isolation and water column stratification (e.g. Mo, Ni, Th/U, V). However, the use of elemental proxies is limited by the possibility and degree of differential element migration during diagenesis and surface weathering. Furthermore, unless tied to sedimentological observations, chemostratigraphic data are best suited to the interpretation of trends, which can restrict sequence stratigraphic interpretations to longer term transgressive-regressive cycles. This project reviews previous studies that have used elemental proxies to make sequence stratigraphic inferences and presents chemostratigraphic data from the Devonian Canol Formation, a resource-rich mudstone present in the Northwest Territories, Canada, as an example. A portable x-ray fluorescence analyzer was used to record the elemental composition of outcrop and core samples from the Canol Formation. Preliminary results show that by using the elemental proxies described above, it is possible to interpret transgressive-regressive cycles and important sequence stratigraphic surfaces in the Canol Formation. To date, coarse sequence stratigraphic frameworks have been established using chemostratigraphic profiles. However, we aim to refine and scrutinize chemostratigraphic signatures of sequence stratigraphic surfaces and systems tracts. In addition, ongoing work includes comparing results from the Canol Formation to those of other studies that assess the effect of weathering on elemental composition and considering the implications to sequence stratigraphy. Ultimately, this research aims to demonstrate how outcrop and subsurface chemostratigraphic data can be used to make high-resolution sequence stratigraphic interpretations in mudstone successions.