The use of chemostratigraphy to refine ambiguous sequence stratigraphic correlations in marine mudrocks. An example from the Woodford Shale, Oklahoma, USA

Abstract

Application of sequence stratigraphy to fine-grained lithologies has previously been hindered by the difficulty of identifying distinct facies shifts within mudrocks. Three cores from Lincoln, Pottawatomie and Pontotoc Counties in Oklahoma and two outcrops at the Hunton Anticline Quarry in Murray County, OK record both proximal and distal regions of the Arkoma Basin. Handheld X-ray fluorescence data and gamma-ray profiles together with lithological descriptions can be used to develop sequence-stratigraphic interpretations. Stratigraphic successions that are challenging to correlate based on gamma-ray (GR) profiles alone can be correlated accurately by utilizing surfaces that are recognized within chemostratigraphic profiles. Within the Arkoma Basin, Oklahoma, the chemostratigraphic profile of the Woodford Shale is interpreted within a sequence-stratigraphic framework using the following general criteria. The Lowstand Systems Tract (LST) is defined by increasing concentrations of Ti, Zr, Al and K as well as high levels of Mo and V. The Transgressive Systems Tract (TST) is defined by declining concentrations of Ti and Zr, although Al and K may remain elevated; Mo and V also show general declines. The Highstand Systems Tract (HST) is defined by increasing concentrations of Ti, Zr, Al and K, but is distinguished from the LST by low levels of Mo and V. Supplementary material: Chemofacies profiles are available at http://doi.org/10.6084/m9.figshare.c.2849599 .

Using high‐resolution XRF analyses as a sequence stratigraphic tool in a mudstone‐dominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany)

“…As one of the first, Macquaker et al (1998) have clearly demonstrated that this approach is also applicable in distal basinal settings, and not limited to marginal, coarser grained systems as they utilized large-scale fining-upward and coarsening-upward successions within the Kimmeridge Clay Formation to define transgressive and regressive systems tracts (RSTs). In recent years, geochemical proxies indicative of coarser clastic input (e.g., Si/Al, Zr/Al and Zr/Rb) have been increasingly used to delineate sequences and their component systems tract in fine-grained successions (Ver Straeten et al, 2011;Turner et al, 2015Turner et al, , 2016, and a similar approach has been applied in the current study to develop a sequence stratigraphic framework for the Lower Cretaceous mudstone-dominated succession in the eastern LSB. In this regard, an important first step was to evaluate whether geochemical variation determined by XRF-CS measurement can be used to characterize the studied cores in terms of variations in grain size.…”

“…Delineation of stratigraphic sequences and their component systems tracts in such fine-grained sedimentary rocks, however, is challenging, and it is certainly not as straightforward as in coarse-grained sedimentary systems (Ver Straeten et al, 2011). An approach that has recently been used to establish sequence stratigraphic frameworks in mudstone-dominated basinal settings without clear ties to coastal records, is to determine systematic stratigraphic variations in the inorganic and organic geochemistry of sedimentary rocks (Ver Straeten et al, 2011;Turner et al, 2015Turner et al, , 2016. An approach that has recently been used to establish sequence stratigraphic frameworks in mudstone-dominated basinal settings without clear ties to coastal records, is to determine systematic stratigraphic variations in the inorganic and organic geochemistry of sedimentary rocks (Ver Straeten et al, 2011;Turner et al, 2015Turner et al, , 2016.…”

“…The apparent macroscopic-scale homogeneity that dominates most mudstone-dominated sedimentary successions makes a reliable determination of transgressive-regressive facies cycles based on visual inspection alone quite challenging and time consuming. An approach that has recently been used to establish sequence stratigraphic frameworks in mudstone-dominated basinal settings without clear ties to coastal records, is to determine systematic stratigraphic variations in the inorganic and organic geochemistry of sedimentary rocks (Ver Straeten et al, 2011;Turner et al, 2015Turner et al, , 2016. These variations are subsequently used to characterize and define stratigraphic sequences.…”

Introduction to the future of sequence stratigraphy: evolution or revolution?

“…Turner et al (2016) apply sequence stratigraphy to fine-grained strata in Oklahoma, using surfaces and facies shifts recognized through use of chemostratigraphy. They link particular chemostratigraphic signatures to accommodation control to define systems tracts and subdivide the fine-grained strata on this basis.…”

“…These various papers perhaps give some indication of how this could go; if the view of Neal et al (2016) is correct, evolution of the method has already made significant progress in providing a useful and predictive tool. Challenges arising in how to apply the method to new types of data (Turner et al 2016), or how to adapt it for particular forcing mechanisms (Ridente 2016) do not preclude an evolutionary approach. Hampson (2016) arguably also supports this view, because inclusion of multiple interpretations and source-to-sink concepts (Martinsen et al 2010) does not necessarily represent a revolutionary change in ideas about how depositional systems work or how they should be interpreted.…”