Conclusions

The structure, isopach, and mean normalized gamma ray maps reveal two major trends in the Lower Permian strata of the Hutchinson Area: northwest-southeast and north-south to northeast-southwest. The northwest-southeast trend is reflected in the configuration of the base of the Quaternary Equus Beds and the present-day Arkansas River drainage, and aligns with the Arkansas River Lineament (ARL). The north-south trend may be structurally controlled by the Voshell Anticline (Watney et al., 2003).

Variations in lithology, as inferred from maps of gamma ray intensity, do not always correspond to variations in the isopach maps, but appear to align with the northwest-southeast (and to a lesser degree, north-south) structural trends. Combinations of the gamma ray and isopach maps indicate plausible evidence for focused, oriented evaporite dissolution that corresponds with and parallels major lineaments identified in the area, the ARL and Voshell Anticline. Inferred episodic opening of fracture clusters along lineament boundaries perhaps facilitated temporary access of undersaturated water to beds containing evaporites leading to intermittent evaporite dissolution. Oriented fractures may have also provided weaknesses in the bedrock surface that offered a structural template as courses of stream drainages were defined. Subtle uplift and tilting associated with minor episodic structural movements, especially along the lineaments, may have also helped to define oriented depositional patterns inferred from isopach and gamma ray mapping. Structural reactivation in relationship to the local geology including basement heterogeneity is further described in Watney et al. (2003).

Combined high-resolution isopach and gamma ray mapping coupled with a knowledge of the lithofacies provides an effective means to resolve temporal changes in depositional and diagenetic patterns and trends that appear to be linked to significant structural lineaments. Structural activity along these lineaments is apparently episodic, and coarser stratigraphic mapping may leave this activity undistinguishable. The inferred structural deformation is at large enough scales (100’s of feet to miles) that it is also difficult to detect and characterize with localized studies or examination of limited outcrops. Yet, the potential impact of such structural lineaments on rock properties, particularly anisotropy, cannot be overestimated. High-resolution stratigraphic mapping at sufficient spatial dimensions provides one approach to the detection and characterization of these structural lineaments.

References

Watney, W. L.; Berg, J. A.; and Paul, S. E., 1988, Origin and distribution of the Hutchinson Salt Member (lower Leonardian) in Kansas; in, Morgan, W. A.; and Babcock, J. A. (eds.), Permian rocks of the mid-continent: Society of Economic Paleontologists and Mineralogists, Midcontinent Section, Special Publication, no. 1, p. 113-135.

Watney, W. L.; Nissen, S. E.; Bhattacharya, S.; and Young, D., 2003, Evaluation of the role of evaporite karst in the Hutchinson, Kansas, gas explosions, January 17 and 18, 2001; in Johnson, K. S.; and Neal, J. T. (eds.), Evaporite karst and engineering/environmental problems in the United States: Oklahoma Geological Survey Circular 109, in press.