Abstract

Lehman Caves is a two-mile-long cave system in the northern portion of Great Basin National Park. Formed ~10-2 Ma within the middle Cambrian Pole Canyon Limestone, Lehman Caves exhibits a ramiform pattern because of its hypogenic speleogenesis and prolific fracture sets. The cave contains numerous rooms and a variety of identified speleothems. This research focuses on cave turnips, a globally rare speleothem that occurs in abundance in Lehman Caves, and focuses on determining their overall morphology, speleogenesis, and relationship to other cave features. Cave turnips were investigated through spatial mapping and morphologic measuring in each room studied. In situ photographs of turnips and their relationship to other features were documented. This work proposes a new size classification system based on four morphologic measurements taken on 1017 in situ turnips. The length, width at base, width at center, and width at tip were summed for each turnip, and this designates its size classification: micro-turnip (<200 >mm), meso-turnip (200-349 mm), or macro-turnip (≥350 mm). In addition, the presence/absence of condensation corrosion and the proximity of the basal attachment to the ceiling, fractures, or cave shields were noted for each turnip. Results show that 46% are micro-turnips, 43% are meso-turnips, and 11% are macro-turnips. Approximately 46% of all turnips are corroded, and micro-turnips dominate this fraction (55%). About 59% of meso-turnips and 71% of macro-turnips are not corroded. The majority of micro-turnips (56%) form along fractures; the majority of meso-(53%) and macro-turnips (59%) form along the ceiling. From this data, we infer that condensation corrosion is more likely to occur in smaller turnips. Because micro-turnips most likely form along fractures, we interpret the fractures have more condensation formation, causing increased corrosion during micro-turnip speleogenesis. 3 This study hypothesizes that cave turnips fall under a new type of speleothem formation known as bubble formations. Two cave turnips on loan from the National Park Service were uranium-thorium age-dated, and the age-dates were interpreted based on turnip speleogenesis. We hypothesize that turnip genesis begins as a soda straw, an abnormal bubble forms on the tip, and calcitic water flows over the bubble, creating the unique hollow turnip shape. Dot density maps were created of the various cave rooms, depicting the 1017 turnips. Room maps display spatial location of turnip size, presence/absence of condensation corrosion, and the type of basal attachment for each turnip located throughout the rooms studied. Documenting cave turnips in Lehman Caves is important, as the cave system preserves these globally rare speleothems. Lehman’s abundant turnips allow for a new size classification based on morphological characteristics, in addition to advancing the preservation, education, and inspiration mission of the National Park Service.

Advisor

Judge, Shelley

Department

Geology

Disciplines

Geology | Speleology

Publication Date

2023

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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© Copyright 2023 Ryan James Johnston