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A New Look at Northern Maverick Basin Basement Tectonics

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A New Look at Northern Maverick Basin Basement Tectonics A New Look at Northern Maverick Basin The current Eagle Ford play in South Texas has brought exploration interest in the Maverick Basin to the forefront. Structural patterns in the northern area are complex. The Devils River Uplift, in Val Verde County immediately to the northwest, is recognized as a basement-thrust uplift of Late Paleozoic age. A northern sub-basin, related to the greater Maverick Basin, is centered in western Kinney County. Northeast-trending basement high blocks separate it at depth from the broader and deeper sub-basins to the southeast in Maverick County. The Maverick Basin is described in literature as a Jurassic rift valley. Northeast-directed Laramide compression from Mexico produced folded or thrusted anticlines along the southwest flank of the Northern Maverick Basin. To the southeast, the Chittim Anticline in Maverick and Dimmit counties, as well as northeast-trending shear faults across the basins, are also attributed to Laramide compression (ref. Scott, 2004). The magnetic basement structure (Figure1), integrated with a 1981 vibrator seismic line reprocessed in 2011, encouraged a new and different look at basement tectonics and structures of the Northern Maverick Basin. This integrated seismic/magnetic interpretation introduces the concept of a non-rift origin for the Northern Maverick Basin. A major magnetic maximum along the Kinney-Val Verde County line southwest of the Sycamore Creek Monocline is interpreted as a large basement uplift. The uplift could serve not only as a buttress to stop northeasterly-directed thrusts, but could also impose southwesterly- directed thrust splays. In that situation, rather than being a simple rift valley, the Northern ●●● Integrated Geophysics Corporation Maverick Basin would exist as a deep because it is trapped between opposing thrust blocks. Note: this concept is illustrated (Figure 2) by clay cake models (ref. OGCI, 1985). The possibility that thrust sheets of lower Mesozoic or even Ellenburger beds along the northeast flank of the basin could be at favorable drill depths would add to the area’s exploration potential. Published seismic data in the northern sub-basin is limited to one 1981 vibrator line (#1, ref. SAGS/AAPG/SEPM, 1994) which runs northwestward up the Jurassic basin floor as far as the southern end of the Devils River Uplift. A published interpretation, based on the original seismic processing, shows a faulted but relatively flat basement under the basin floor. IGC’s estimated time-depth conversion places the interpreted seismic basement as deep as 45,000-50,000 ft subsea. High-angle north-verging thrust faults provide basement relief at the southeastern and northern portions of line #1. Deep detached thrusts overlie flat areas of seismic basement. IGC’s new basement structure interpretation is based on quantitative depth estimates derived along profiles of PACES public source aeromagnetic data. Along seismic line #1, specific magnetic depth estimates are posted on the seismic image (Figure 3) and are in close agreement with high-energy bands which have been depth-converted from the reprocessed seismic data provided by Pedernales Energy/Texas Hondo Petroleum. IGC’s fault interpretation shown on Figure 3 is based on seismic high-energy bands and magnetic depths. Without honoring the seismic events, a smooth magnetic basement surface could be drawn from depth estimate to depth estimate along the profile, with the deepest part of the trough at 45,000 ft subsea. Without ties to magnetic depths the correlation of, and interpretation of, seismic high- energy bands would be tentative due to their discontinuities and vertical offsets. Interpretation along-line was further strengthened and refined by use of offline magnetic anomalies and depth estimates. Integration of the seismic and magnetic interpretations thus allows development of a complex structural style which fits all the data. IGC Potential Talk: Maverick Basin Page 2 of 3 July 2011 Take Aways Rather than being a simple rift valley, the Northern Maverick Basin begins to look like a deep trapped between opposing thrust blocks. The thrust sheets could bring the lower Mesozoic or Ellenburger beds along the northeast flank of the basin to favorable drill depths. The area’s exploration potential would change. The resulting integrated interpretation of the Northern Maverick Basin offers a new and different look at basement structure and structural style for South Texas. This revision to the Northern Maverick Basin structural environment was based only on public- source data, limited published seismic coverage and sparse well data. The possibilities of delineating new prospective structure-based targets with closely-spaced state of the data are breath-taking. Those interested in additional description of these input magnetic and seismic databases should contact IGC. Author: Michael Alexander The URL for this paper is http://www.igcworld.com/PDF/Maverick_Basin.pdf IGC Potential Talk: Maverick Basin Page 3 of 3 July 2011 .
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