BH250-244
Title
Subject
Description
Minor Mineals: quartz, sanidine, zircon
The Lava Creek Tuff is a geologically significant pyroclastic deposit formed during one of the largest volcanic eruptions in North America. It is part of the Yellowstone volcanic system and represents the most recent of three major caldera-forming eruptions associated with the Yellowstone Caldera.
The Lava Creek Tuff, particularly the Lava Creek B (LCB) member, forms a vast ash-flow sheet covering more than 7,500 km² (2,900 mi²) across Wyoming, Montana, and Idaho. This deposit was generated during a catastrophic supereruption about 631,000 years ago, which expelled approximately 1,000 km³ (240 cu mi) of volcanic material and led to the formation of the Yellowstone Caldera.
During this supereruption, an immense volume of ash was ejected high into the atmosphere, blanketing much of the western United States. This widespread ashfall is preserved across numerous states, including California. A well-known distal occurrence is the Lava Creek Ash near Shoshone, on the eastern margin of Death Valley, where it occurs as a fine-grained tephra layer derived from the eruption. Deposited around 631,000 years ago, this ash layer serves as a key stratigraphic marker and is widely used in paleoenvironmental and geochronologic reconstructions across the western and central United States
Compositionally, the Lava Creek B, Ash is a high-silica rhyolitic glass with phenocrysts of sanidine, quartz, and minor biotite. During my time in graduate school, I studied over 350 volcanic ash layers from the Turkana Basin in East Africa, spanning the Pliocene–Pleistocene. These ashes, chemically and stratigraphically distinct, formed the basis for a robust regional tephrochronological framework in East Africa. Among the samples I analyzed from the Turkana Basin members, was a specimen of Tulu Bor Alpha (3. 4 Ma old), and remarkably, its chemistry closely resembled that of the Lava Creek B ash.
Though separated by continents, formed in different tectonic settings, and of different ages, these two ashes are both widespread, compositionally similar, and reflect the convergent nature of silicic magma evolution in large-scale volcanic systems.
Pristine, unaltered volcanic glass shards are valuable tools for fingerprinting the geochemical signature of erupting volcanoes. They also provide a means for establishing precise temporal correlations within individual basins and across multiple sedimentary basins.
Glass shard morphology varies widely, including forms such as flat, frothy, stretched, and bubble wall junction types. The Lava Creek B ash layer is characterized predominantly by flat glass shards.
These glass shards are particularly well-suited for teaching relief and refractive index using the Becke line method with various immersion oils in mineralogy and optical mineralogy courses, due to their clarity and consistent optical properties.
Coverage
Nearby Geographic Feature: Death Valley
GPS Coordinates: 35.969856, -116.275897