SINKHOLE MORPHOLOGY AND DISTRIBUTION AS INDICATORS OF HYDROGEOLOGIC CONTROLS ON KARSTIFICATION: QUINTANA ROO, MEXICO

Geologic structures and properties control the orientation and extent of karstification, which in turn influences groundwater flow paths and hydraulic gradients. In areas where surface geology is not well exposed or easily accessible, inferences about local- to regional-scale hydrogeologic controls can be gained through spatial pattern analysis of karst features with interpretation informed by field observations. We present a morphometric approach to characterize karstification at a sub-basin scale (100 km²) in north eastern Quintana Roo, Mexico using a data set of 2,005 depressions identified from a LiDAR-derived Digital Elevation Model (DEM). Depression area approximated a power-law frequency distribution (f=16379a^-0.61) and was similar across mapped geologic units. Depression shape was measured by indexes of circularity and elongation, and results were consistent with regional-scale data. Two groups of depressions were distinguishable by elongation indexes of ≤0.6 and >0.6, which potentially reflect their mode of genesis by enlargement along groundwater flow paths and subsequent collapse of cave passages. Three dominant long-axis orientations were identified at 45^o, 285^o, and 340-350^o, which suggest influence from the intersection of regional fault zones. An Average Nearest Neighbor ratio of 0.5 for all depression centroids indicated significant clustering. The 1^st through 9^th Distance to Nearest Neighbor measurements closely approximated a log-normal distribution and were similar across geologic units as well as across elongation groups, consistent with similar controls and formation processes occurring throughout the study area. Direction to Nearest Neighbor azimuths grouped into two dominant trends at 45^o and 315^o, which are roughly parallel and perpendicular to the coastline, respectively, and are similar to the distribution of linear cave passage in the study area. Depressions commonly exhibited alignment with one another at 315^o, which is consistent with the orientations of mapped cave passage perpendicular to the coastline. These linear trends are interpreted to represent flow paths along coastal deposits of greater permeability and along higher hydraulic gradient.