Chemical characterization of clastic cave sediments and insights into particle transport and storage in karst aquifers

Abstract

Chemical characterization of clastic cave sediments and insights into particle transport and storage in karst aquifers Jill L. Riddell Cave sediments can be divided into two groups: precipitates and clastics. Precipitates are speleothems, or lithologic or mineral features that are chemically precipitated in the cave environment. Clastic cave sediments are frequently described by depositional facies, sorting, and particle size (Bosch and White, 2004). Robust analytical chemical analyses of these sediments to quantify their physical and chemical components is rarely performed although some chemical characterization of mineralogy and paleomagnetism has become prevalent in recent years (Chess et al., 2010; Sasowsky et al., 2007). The organic carbon content of cave sediments can be representative of organic carbon concentrations in the larger karst system and concentrations of organic carbon in cave sediments can be used to estimate the potential retardation of organic contaminants through the entire karst system. The ability of karst sediments to be a sorbent for metals and organic contaminants, and store and transport contaminants is positively correlated with the amount of organic carbon in the sediment; yet these concentrations are rarely reported in karst sediments. This dissertation seeks to fill the gap in the mineralogy and chemical components of cave sediments; quantify the organic carbon content of cave sediments relative to depositional facies; and measure the adsorption of an organic microsphere onto a cave sediment to explore sediment-contaminant interactions. A case study from Dropping Lick Cave in Monroe County, WV, is presented where a variety of analytical techniques were used to determine the active fraction ( < 2mm) mineralogy and chemical components of the sediment The sediments were silt and sand-sized particles consisting of quartz, some clay or silicate minerals, dolomite, and amorphous materials. The particle size and total carbon was within the same range reported for the < 2mm fraction in other clastic cave sediments in this region, in the central United States, and in Puerto Rico. The preliminary mineralogy of the sediments is congruent with the mineralogy of surrounding siliciclastic rocks indicating that the source of the sediment is erosional products from nearby Peters Mountain and its slopes. Particle size, TOC, and total nitrogen were measured in sediments representing different facies in Butler Cave, Virginia, USA. TOC concentrations ranged from 0.08 – 0.87 weight percent and C:N molar ratio ranged from 3 – 15, indicating a possible terrestrial source of organic carbon in these sediments. TOC concentrations