EXTENSIONAL STRAIN PARTITIONING IN THE NORTHERN ARKOMA BASIN, ARKANSAS

While broad variations in foreland basin architecture are controlled by lithospheric flexure parameters, sub-basin scale variations are likely controlled by other factors (e.g., regional fault patterns and local rock mechanical heterogeneity). Here, we resolve the detailed structural architecture of the northern Arkoma foreland basin using high resolution 3D geologic modeling. 3D mesh surfaces of the Boone Formation, Wapanucka Limestone, and several horizons within the Atoka Formation were constructed. These surfaces were built from ca. 20,000 well tops and surface geologic map contacts using the MOVE software. The mesh surfaces are offset by a complex 3D fault network, allowing detailed analysis of along-strike and down-dip variations in fault displacement.

The 3D model reveals a regular and repeated fault segmentation pattern wherein E-W striking, left-stepping en échelon normal faults are segmented by NE striking, dextral oblique-normal fault zones and lineaments. Maximum vertical separation along the E-W normal faults is generally focused between the NE-trending zones, suggesting that the latter are strain transfer structures that dissipated and delocalized the extensional strain during normal fault evolution. Maximum vertical separation and fault localization also correlate to areas with high-amplitude positive magnetic anomalies interpreted as intrusive Mesoproterozoic rocks. This suggests that the basement intrusives concentrated stress, leading to localized faulting within the sedimentary cover, possibly due to a mechanically favorable fabric or high rock strength and rigidity. Statistical analysis of the 3D model suggests that the majority of net normal-sense vertical separation is accommodated by fault strands with medium to large separation (400-1200 m) Lastly, the 3D modeling constrains the main phase of growth faulting to be middle to upper Atokan.