Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Geochemical properties and organic characteristics are essential to understanding the general depositional dynamics of a cave. Most work on clastic cave sediments focuses on physical properties of sediments. Little work has been done on bulk organic matter and geochemical properties.
This project reports physical and geochemical characterization of cave sediments from two caves in the northern karst region of Puerto Rico: El Tallonal Cave and Cueva Clara. Core and grab samples were collected and analyzed for particle size, total organic carbon, total nitrogen, organic matter characteristics using fluorescence spectroscopy, and major and minor elements using X-ray fluorescence (XRF). The sediments were poorly to extremely poorly sorted despite being seemingly homogeneous. Sand- and silt-sized grains composed most of the sediments from both locations. Within El Tallonal Cave, differences in organic chemical properties between saturated and unsaturated sediments were observed. The maximum value of total organic carbon, total nitrogen, and organic C/N ratios were higher, and the range was greater in saturated sediments. A three-component parallel factor analysis (PARAFAC) model was created using collected excitation-emission matrices on organic matter extracted from the sediments. All three modeled components were humic acid-like. Proportions of the modeled components differ between saturated and unsaturated sediments. Elemental concentrations collected using XRF on El Tallonal Cave sediments revealed that Al and Si are negatively correlated, suggesting that clay minerals and quartz occur together resulting in Si dominating in those sediments. Trace elements (Cr, Mn, Co, Ni, As, Rb, and Nb) correlated positively with Ti, implying these elements are sourced from the same parent material. Correlations between Fe, Al, and Mn with P, Co, and As suggest that sorption or co-precipitation with Fe, Al, and Mn oxides is a possible retention mechanism within El Tallonal Cave sediments. No relationship between grain size and geochemical properties was observed. Preliminary comparison with soil and bedrock from the Luqillo Mountains located within the central highlands of Puerto Ricop show similar concentrations of Ti and Zr within El Tallonal Cave sediments suggesting these elements are conservative during transport.
Results of this thesis show that sediment deposition and chemistry in individual caves are complex natural systems. Heterogeneity among cores within single caves was observed. Future studies are needed to better understand the differences observed in saturated and unsaturated sediments, as well as to further explore the mechanisms controlling the geochemical trends observed in cave sediments.
Downey, Autum R., "Physical and chemical properties of clastic sediments from two caves in the northern karst region of Puerto Rico" (2020). Graduate Theses, Dissertations, and Problem Reports. 7716.