Chemostratigraphic, palynostratigraphic, and sequence stratigraphic analysis of the Woodford Shale, Wyche Farm Quarry, Pontotoc County, Oklahoma

Abstract

Understanding mudrocks and shale reservoirs has become a significant area of interest within industry and academia in recent years. Of particular interest is understanding the pervasive variability present within these units. This variability became apparent when conventional approaches, such as lithostratigraphic analysis and well log correlation, were coupled with recent developments in palynostratigraphy and chemostratigraphy. A single shallow Woodford Shale research core in the western Arkoma Basin from Pontotoc County, Oklahoma, was used to identify three scales of stratigraphic cyclicity. By comparing the relative abundances of continental sourced pollen and spores to marine-derived acritarchs over a stratigraphic interval, it was possible to extrapolate the overall trends in shoreline trajectory. Conventional well log analysis, such as gamma ray logs, provided a balanced understanding of the interplay between localized changes in sedimentation and regional shifts in the stratigraphic base level, in addition to providing a means to tie these analyses to extensive subsurface data sets. Chemostratigraphic correlations resolved subtle, but stratigraphically significant, shifts in localized patterns in sedimentation. Using these approaches, the Lower and Middle Woodford Shale can be divided into four chemostratigraphic parasequences within a transgressive systems tract defined by well log and core analysis. The Upper Woodford can be separated into an additional four chemostratigraphic parasequences within a highstand systems tract. Chemostratigraphic data also revealed the changing bottom water conditions present at the time of deposition, with a period of localized anoxic conditions recorded in the Lower and Upper Woodford in this part of the basin. These localized changes in sedimentation and environmental conditions can be nested into two longer term regional transgressions and regressions.

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.…”

Sedimentary Evolution Characteristics of Fine-Grained Lithofacies under the High-Resolution Isochronous Shelf System: Insights from the Wufeng-Longmaxi Shales in the Sichuan Basin

“…With the successful exploitation of gas in shale units in North America, such as the Barnet, Marcellus, and Woodford shales, and in China, including the Wufeng-Longmaxi shales [1][2][3], marine shale has attracted the attention of international sedimentologists. However, marine shale is a type of fine-grained sediment with small-scale cyclic characteristics and strong heterogeneity, and accurately understanding and predicting the lateral and vertical sedimentary characteristics of organic-rich marine shale changes have become key scientific issues [4][5][6][7][8].…”

A Diagenetic Study of the Wolfcamp Shale, Midland Basin, West Texas

“…XRF proxies were used in conjunction with thin section examination to test interpretations and to assess for trends: titanium (Ti) and zirconium (Zr) to evaluate continental sources; silicon/aluminum ratio (Si/Al) were used to help distinguish biogenic/authigenic quartz from detrital quartz; and calcium (Ca) and strontium (Sr) for carbonates (Pearce and Jarvis, 1992;Banner, 1995;Pearce et al, 1999;Tribovillard et al, 2006;Turner et al, 2015). Diagenetic proxies determined from this study were sulfur (S), iron (Fe), barium (Ba), zinc (Zn), and phosphate (P) associated with authigenic mineral formation.…”