45 Hydrogeology (Posters)

Added due to amount of discipline abstracts submitted.

Wednesday, 11 March 2026
9:00 AM - 12:00 PM
RCC, Lower Level Hall

X-ray diffraction studies of cave sediment from a karst system located near Barahona, Puerto Rico: New mineralogical constraints.

Paper number: 45-8
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

Investigations of cave sediments are an important multidisciplinary endeavor for understanding geological, environmental and anthropogenic records in karst systems. Cave sediment is comparatively understudied in a system located near Barahona, Puerto Rico. In addition to its geological significance, this system is recognized to have very likely been a site of native habitation over at least a few thousand years. Detailed studies on the cave sediments can offer important constraints for future archaeological studies in the cave system as well as insight into the broader surrounding environment. Samples (n=14) from the upper 2 cm of sediment on the floor of Gemelos cave in this system have been investigated using inductively coupled plasma–mass spectrometry (ICP-MS) and scanning transmission electron microscopy–energy dispersive spectroscopy (STEM-EDS) to characterize their geochemical variation. Chemical weathering index (CIA) values are variable from 37.5 (low) to 83.2 (high), with the average values being moderate CIA (58.7). The siderophile trace elements have variable concentrations (V: 31 to 126 ppm; Cr: 38 to 177 ppm; Ni: 17 to 74 ppm; Co: 4 ppm to 37 ppm). Bulk basic powder X-ray diffraction on samples indicates that there are three general sediment sample types based on dominant mineralogy: 1) Gypsum + calcite + minor quartz +/- feldspars; 2) calcite + quartz +/- feldspars; 3) Gypsum + quartz + hydroxyapatite. Poorly-crystalline peaks broadly consistent with goethite and Fe-Al oxyhydroxide minerals were observed in all samples. Previous electron microscopy demonstrated high crystallinity of Fe-Al oxyhydroxides, but an abundance of amorphous oxyhydroxides and other phases may exist. Hydroxyapatite-bearing samples are consistent with samples with high bulk P content. Bulk sample mineralogy is consistent with some aspects of previous major element chemistry but seems incongruent with certain elemental concentrations observed; mainly Ca. These basic X-ray diffraction results place new constraints and context on an understudied karst system.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411688

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