High Resolution Seismic Reflection to Characterize Small Scale Mechanisms of Large Scale Natural Dissolution in the Hutchinson Salt Member
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High resolution seismic reflection to characterize small scale mechanisms of large scale natural dissolution in the Hutchinson Salt Member by Brett E. Judy Submitted to the Department of Geology and the Faculty of the Graduate School of the University of Kansas in partial fulfillment of the requirements for the degree of Master of Science Advisory Committee: ______________________________ Richard D. Miller, Chairman ______________________________ Don W. Steeples ______________________________ J. Douglas Walker Date Defended: _____02-13-2015______ The Thesis Committee for Brett E. Judy certifies that this is the approved version of the following thesis: High resolution seismic reflection to characterize small scale mechanisms of large scale natural dissolution in the Hutchinson Salt Member ______________________________ Richard D. Miller, Chairman Date approved: _____02-13-2015________ ii Abstract High resolution seismic reflection imaging of the local scale processes along the eastern natural dissolution front of the Hutchinson Salt Member were correlated with its regional scale progression to define a more complete dissolution model that accounts for all observations along the front. 2-D high resolution seismic reflection imaging suggests dissolution along the eastern margin has resulted in a complex system of dissolution channels that have intruded westward into the salt body. Anomalous thinning of the rock salt and resulting sinkholes imaged between 8-20 km from the dissolution front provide evidence to support protruding dissolution has extended west into the salt body in a very irregular fashion. Subsidence features along the eastern margin appear to increase in width (>700 m) due to episodic re-activation of subsidence after long periods of dormancy. Time varying access to unsaturated water continues to expand these dissolution corridors and is forming expansive solution networks that grossly make up the dissolution front. It is suggested that dissolution is predominantly progressed horizontally through the salt interval driven by both hydrologic and geologic influences. Geometric distortion of reflections from the salt interval indicate recent activity (e.g. Brandy Lake) and dormant paleo dissolution networks that discontinuously span a zone approximately 6 km wide along the eastern margin of the Hutchinson salt. High resolution seismic imaging of subsidence related to Brandy Lake is indicative of the complex dissolution history along the front. This dynamic dissolution zone has resulted in the formation of four seismically identified and interpreted subsidence episodes that directly correspond to recent road subsidence along the western flank of Brandy Lake. This unique growth structure represents the continued westward encroachment of horizontally driven dissolution channels into the salt. iii Acknowledgments: I would like to acknowledge and thank everyone on my thesis committee: Rick Miller who provided me with a great opportunity, imparted his knowledge to me and who helped me through revisions of a very rough first draft; Don Steeples for both revisions and his past research which was often consulted during the processing of my data; Doug Walker for his support and work through the revision process I would also like to thank my co-workers: Shelby Peterie for her direction and guidance throughout my time in Kansas; Julian Ivanov for his knowledge and assistance during processing (and dietary council); Mary Brohammer for her assistance with software licenses and figure creation; all the students who I have worked with at the Kansas Geological Survey for their advice and assistance (and donuts). I would also like to thank my wife Cynthia who has been a support throughout my academic career and for her aid in the creation of figures. iv Table of Contents Introduction ....................................................................................................................................1 Research Focus .............................................................................................................................3 Geologic Background.....................................................................................................................9 Hutchinson Salt Member ............................................................................................................13 Evaporite Dissolution .................................................................................................................14 Hydrology and Dissolution along the Eastern Margin ......................................................15 Sinkhole Formation and Subsidence Mechanics ........................................................................21 Seismic Reflection Characteristics .............................................................................................23 Summary of 2003 Seismic Data Interpretation .........................................................................24 Methods .........................................................................................................................................28 Data Acquisition along U.S. Highway 50 ..................................................................................28 Vibroseis Method .......................................................................................................................29 High-resolution seismic reflection data processing ...................................................................29 Common-Midpoint (CMP) Sort Processing ...............................................................................36 Fold and Resolution ...................................................................................................................42 Post Processing .............................................................................................................................43 Acoustic Impedance Inversion ...................................................................................................43 Horizon Flattening .....................................................................................................................44 Results and Interpretation ..........................................................................................................51 Interpretation of the Eastern Dissolution Margin ......................................................................58 Interpretation of Brandy Lake Sinkholes ...................................................................................61 Interpretation of the Eastern Dissolution Margin Continued .....................................................69 Discussion/Conclusion .................................................................................................................78 References .....................................................................................................................................84 List of Figures Figure 1: Region of study and isopach of the Hutchinson Salt Member ........................................4 Figure 2: Currently accepted dissolution model of the Hutchinson Salt ........................................5 Figure 3: Ortho-photo of dissolution patterns in Reno County, KS ...............................................6 Figure 4: Arial Image of Brandy Lake and LiDAR elevation profile...........................................10 Figure 5: Geology Log from WD#2 .............................................................................................11 Figure 6: Cross-section between Hutchinson, KS and Newton, KS .............................................12 Figure 7: Net Salt Isopach of the Hutchinson Salt ........................................................................16 Figure 8: Outline of the Wellington Aquifer ................................................................................17 Figure 9: Conceptual cartoon of natural dissolution progression .................................................20 Figure 10: Tensional Dome model ...............................................................................................22 Figure 11: Seismically imaged Paleo-Sinkhole along U.S.50 ......................................................26 Figure 12: Fault imaged approximately 15 km west of the front .................................................27 Figure 13: Photo of geophones planted in 1 m arrays .................................................................30 Figure 14: Photo of receiver stations along U.S. 50 .....................................................................30 v Figure 15: Photo of IVI Minivib I.................................................................................................31 Figure 16: Outline of rolling fixed survey design .........................................................................31 Figure 17: Processing Flow ..........................................................................................................33 Figure 18: Shot Gather, Pre-correlation whitening .......................................................................37 Figure 19: Spectrally Balanced Shot Gather .................................................................................38 Figure 20: Shot Gather with First Arrival Mute applied ...............................................................39 Figure 21: Shot Gather with Surgical Mute applied .....................................................................40 Figure 22: Fully Processed CMP Gathers .....................................................................................41