Gary L. Kinsland

SURFACE EXPRESSION OF THE CHICXULUB CRATER

Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the crater. Late Tertiary sedimentation was mostly restricted to the region within the buried crater, and a semicircular moat existed until at least Pliocene time. The topographic expression of the crater is a series of features concentric with the crater. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the crater floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes. These interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km.

Visualization and interpretation of geologic data in 3D virtual reality

We have developed an argument and evidence from our experiences for the utility of 3D virtual reality (3DVR) systems in the interpretation of 3D geologic data. Interpretation of 3D data by geoscientists is performed in “the mind.” Visualization of 3D data in 3DVR environments is an efficient method of getting the data into the mind. Descriptions of visualization and interpretation of several different geologic data sets in 3DVR environments illustrate the advantages of 3DVR. Despite the advantages of visualization in 3DVR, several reasons exist for the present limited use of 3DVR by geoscientists. With the relatively recent availability and affordability of smaller hardware and software systems, we believe 3DVR should become commonplace on the desktops of geoscience interpreters.

Composable Volumetric Lenses for Surface Exploration

We demonstrate composable volumetric lenses as interpretational tools for geological visualization. The lenses provide a constrained focus region that provides alternative views of datasets to the user while maintaining the context of surrounding features. Our rendering method is based on run-time composition of GPU shader programs that implement per-fragment clipping to lens boundaries and surface shader evaluation. It supports composition of lenses and the user can influence the resulting visualization by interactively changing the order in which the individual lens effects are applied. Multiple shader effects have been created and used for interpretation of high-resolution elevation datasets (like LTDAR and SRTM) in our lab.

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico.

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

A High-Resolution Seismic Survey to Image the Top of Salt at Avery Island, Louisiana

Abstract A shallow high-resolution 2D seismic reflection survey was acquired to image the top of the salt dome at Avery Island, Louisiana. The goals were to identify the salt-sediment interface and to gain a better understanding of its location within the subsurface. Previous seismic studies were unable to properly image the top of salt. The survey was conducted using a 48-channel seismograph with an Elastic Wave Generator as the source. Source and receiver intervals were set at 10 ft (3m) in order to properly illuminate salt surface features at maximum expected depth (~530 ft). Because local well information was unavailable during processing and analysis, the survey results are not calibrated to a known geologic section or to any direct velocity measurements. Analysis of the seismic stack shows five well-defined reflectors near the north end of the profile. Measured stacking velocities associated with deep events were observed to be greater than 2,000 m/s. This indicates possible pore space salt cementation in sediments above the salt body. To the south, the top of salt is interpreted to approach the surface with one area displaying evidence of a possible collapse feature. The five reflectors expand northward from the edge of the top of salt, and show evidence of minor faulting. This is consistent with draping and post-sedimentation movement. Further studies to better identify the collapse feature and to calibrate seismic to stratigraphy by well coring is warranted.