TAKING THE OUTCROP HOME: IMAGING OF DEEPWATER CHANNEL ARCHITECTURAL ELEMENTS OF THE JACKFORK FORMATION, ARKANSAS, USING GROUND PENETRATING RADAR AND AERIAL PHOTOGRAMMETRY TO GENERATE AND ANALYLZE DIGITAL VERSIONS OF CLASSIC OUTCROPS (AND THEIR SUBCROPS)

Rock outcrops provide both windows into the past and valuable analogues to the present. In particular, central Arkansas outcrops of the Jackfork Formation (Fm) have long been a key location for the study and understanding of fine—grained, sand-rich, deepwater deposits with learnings impacting both fundamental stratigraphic understanding and offshore resource exploration. A critical aspect of Arkansas Jackfork exposures is that deepwater systems are difficult to model at small (sub-to-ten-meter) scales in the modern due to the low resolution of conventional seismic, limited contrast between sandy channel deposits and silty slope muds, and limited, if any, well control. This work takes increasingly utilized recent technologies of ground penetrating radar (GPR) and photogrammetry to explores the 3D nature and interplay of deepwater stratigraphic elements. The study area consists of outcrops and near-outcrop subcrops of the Jackfork Fm, a middle Pennsylvanian deepwater slope and basin-floor depositional system along the margins of an oblique foreland basin in front of the encroaching Ouachita accretionary prism.

Three primary data sets are collected to help bring outcrops back into the office. GPR data for the top 3-5 meters (m) is collected using a 200 megahertz (MHz) antenna at several sites where adjacent outcrops have been interpreted to contain multiple channel architectural elements including crevasse splays, sheet turbidites, and debris material. GPR data is interpreted for to identify and analyze variances in sedimentary architecture geometries across sites from different relative positions in the depositional system. Where possible, GPR data are collected in grids to enable some three-dimension (3D) interpretation of geometric features.

Also at the outcrop, aerial imagery is collected using unmanned aerial vehicles (drones) and converted using photogrammetry software into 3D outcrop models further enabling geometric analysis of deepwater stratigraphic architectures.

Finally, complementary outcrop rock data is collected from literature review and new outcrop analysis. Basic rock property data for the outcrop can correlated to both GPR and aerial photo data to enable extrapolation of rock properties to inaccessible outcrop and subcrop areas to provide more robust outcrop characterization.

While there is no replacement for direct outcrop observation, emerging technologies do allow researchers to glean ever more insight from the outcrops we have for those times when we cannot be on the outcrop. Application here of GPR and photogrammetry to well-studied Jackfork Fm outcrops provides further understanding of the nature of high net-to-gross deepwater channel deposits.