GEOMORPHIC CAVE ANALYSIS AND ALTERATION OF IGNEOUS FEATURES WITHIN: LAKE SHASTA CAVERNS

Lake Shasta Caverns are a series of 250-millioin-year-old hydrologically connected limestone caves found in Shasta County, California. The caverns lie within the McCloud Limestone Formation (Permian) which is part of a series of accreted island arc terranes collectively known as the Klamath Mountains. Within the limestone caves are two large igneous dikes. This is an uncommon characteristic compared to the numerous caves that are scattered about Shasta County, which are fluvial and epigenic in nature (DeSpain, 2020) with no igneous features. While a few studies have analyzed Lake Shasta Caverns for paleontological and archaeological significance and speleothem isotopic data for paleoclimate analysis, no published work has documented the morphology of the caverns or analyzed igneous cave intrusions relative to the surrounding environment. To address these shortcomings, the objectives of this study are to 1] document the morphology of Lake Shasta Caverns and 2] to analyze and compare alteration/weathering characteristics of dikes within the caves to dikes outside of the caves.To address objective 1, a detailed cave morphological analysis will be conducted through cave surveying and documentation. The documented data will be compared to the work of others such as Bakalowicz et al., 1987; Ford and Williams, 1989; Dubljanskij, 1990; Palmer, 1991, 2007; Dublyanksy, 2000; Klimchouk, 2007; Audra et al., 2009b.To address objective 2, rock samples from both igneous intrusions within the cave were collected and three samples were taken from three igneous intrusions outside of the caves in July, 2021. The samples have undergone chemical and mineral analysis through petrographic, XRD (whole rock and clay fractionated size), and XRF (trace elements and oxides) to compare chemical and mineralogical composition and alteration of the rocks from within the caves to the intrusions outside of the caves.