MESOSCOPIC STRUCTURAL AND CYBER-MAPPING ANALYSIS OF THE RELATIONSHIP BETWEEN THE COLLINGS RANCH CONGLOMERATE AND THE VIOLA GROUP, SOUTHERN OK

We present results from mesoscopic structural analysis and cyber-mapping studies (creation and analysis of three-dimensional photo-realistic digital replica of outcrops) aimed at understanding the relationship between the Collings Ranch Conglomerate and the Viola Group in the Arbuckle Mountains in Southern Oklahoma. The Pennsylvanian Collings Ranch polymict conglomerate is widely recognized as being deposited in a pull-apart basin that resulted from left-lateral strike-slip movement along a releasing bend in the Washita Valley Fault. This basin is bounded on the south by the Washita Valley Fault and on the north by the Collings Ranch Fault. The Collings Ranch Conglomerate is located in the northern limb of the N-verging asymmetrical Arbuckle Anticline where it forms long wavelength sag synclinal structures locally overlying the variably dipping limestone beds of the Ordovician Viola Group. Hence, the relationship between the Collings Ranch Conglomerate and the Viola Group has been considered as an angular unconformity outcropping on the northern margin of the pull-apart basin. Our mesoscopic structural analysis and cyber-mapping studies (where it focused on outcrops exposed along Highway I-35 on the northern limb of the Arbuckle Anticline) generally agree with the pull-apart model but adds new observations that helps in understanding the relationship between the Collings Ranch Conglomerate and the Viola Group in a better detail. (1) The variable dips of the carbonate beds of the Viola Group (which have been previously interpreted as indicating a synclinal structure) are in fact the manifestation of tilting of bedding planes due to shearing along individual fault planes of the Collings Ranch Fault. (2) The relationship between the Collings Ranch Conglomerate and the Viola Group can be considered as an angular unconformity from a geometrical point of view. However, loading stress associated with the deposition of the conglomerate resulted in the development of layer-parallel growth faults on the underlying steeply-dipping limestone beds of the Viola Group. This indicates that the Collings Ranch Conglomerate was affected by syn-depositional deformation in the form of normal faults. This might have been synchronous with the left-lateral strike-slip movement and the formation of the pull-apart basin.