BH250-238
Title
BH250-238
Subject
Diamictite
Description
Major Minerals: quartz, calcite, oxides, microcline
The outcrop of this diamictite in the eastern Death Valley region exposes rocks of the Kingston Peak Formation, one of the most important Neoproterozoic stratigraphic units in western North America. The Kingston Peak Formation records major environmental and tectonic changes during the Cryogenian Period, approximately 720–635 million years ago. These rocks are especially significant because they preserve evidence related to the global Snowball Earth glaciations, when continental ice may have extended into low latitudes and profoundly altered Earth’s climate system.
At this locality where sample BH250-238 is collected, the surrounding exposure also preserves a possible transitional interval between the underlying Beck Spring Dolomite and the basal Kingston Peak Formation (KP1) (see photo BH250-238 Transitions). The lighter-colored, more resistant beds lower on the slope are consistent with carbonate-rich strata of the Beck Spring Dolomite, whereas the darker, platy, slope-forming beds above resemble the finer siliciclastic rocks (BH250-238c) typical of lower Kingston Peak strata. This upward lithologic change reflects a broader transition from shallow-marine carbonate platform deposition into deeper-water siliciclastic sedimentation, basin instability, and glacial influence associated with Cryogenian rifting (Mike Smith, Class of 1999, personal communication).
The diamictite sampled nearby, represented by BH250-239, is also characteristic of the Kingston Peak Formation. Diamictite is a coarse, poorly sorted sedimentary rock composed of a muddy to sandy matrix containing scattered pebbles, cobbles, and larger clasts of varied lithologies. Clasts range from angular to subrounded, indicating mixed transport histories and variable source distances (see photos). In outcrop, these rocks commonly resemble breccia or conglomerate depending on clast abundance and matrix content. Their unsorted texture suggests deposition by high-energy processes such as debris flows, sediment gravity flows, glacial meltwater transport, or direct ice rafting into marine basins.
Stratigraphically, the Kingston Peak Formation overlies the Beck Spring Dolomite, a carbonate deposit, and is overlain by the Noonday Dolomite (BH250-242b, figure-BH250-238), a famous post-glacial cap carbonate deposited after Cryogenian deglaciation. This succession records one of the most dramatic environmental transitions in Earth history: carbonate platform seas of the Beck Spring were replaced by tectonically active basins receiving glacially influenced siliciclastic sediments of the Kingston Peak, followed by rapid marine flooding and renewed carbonate deposition of the Noonday Dolomite (BH250-242b).
Comparable Cryogenian diamictites are also preserved in the Tambien Group of Tigray Ethiopia, where they record the lead-up to and onset of Sturtian glaciation along the northern margin of the Arabian-Nubian Shield. Integrated stratigraphy, chemostratigraphy, and geochronology from these Ethiopian successions have provided some of the most important age constraints on Snowball Earth events. U-Pb zircon ages and carbon-isotope data indicate that environmental instability and major carbon-cycle perturbations preceded the Sturtian glaciation, with critical dates clustering around 719 million years ago, just prior to global ice advance. Key studies by Yuem Park, Nicholas L. Swanson-Hysell, Scott A. MacLennan, Adam C. Maloof, Bereket Haileab and collaborators (2015, 2018, 2019) demonstrated globally synchronous carbon-isotope change and helped constrain the timing of the Sturtian Snowball Earth.
The outcrop of this diamictite in the eastern Death Valley region exposes rocks of the Kingston Peak Formation, one of the most important Neoproterozoic stratigraphic units in western North America. The Kingston Peak Formation records major environmental and tectonic changes during the Cryogenian Period, approximately 720–635 million years ago. These rocks are especially significant because they preserve evidence related to the global Snowball Earth glaciations, when continental ice may have extended into low latitudes and profoundly altered Earth’s climate system.
At this locality where sample BH250-238 is collected, the surrounding exposure also preserves a possible transitional interval between the underlying Beck Spring Dolomite and the basal Kingston Peak Formation (KP1) (see photo BH250-238 Transitions). The lighter-colored, more resistant beds lower on the slope are consistent with carbonate-rich strata of the Beck Spring Dolomite, whereas the darker, platy, slope-forming beds above resemble the finer siliciclastic rocks (BH250-238c) typical of lower Kingston Peak strata. This upward lithologic change reflects a broader transition from shallow-marine carbonate platform deposition into deeper-water siliciclastic sedimentation, basin instability, and glacial influence associated with Cryogenian rifting (Mike Smith, Class of 1999, personal communication).
The diamictite sampled nearby, represented by BH250-239, is also characteristic of the Kingston Peak Formation. Diamictite is a coarse, poorly sorted sedimentary rock composed of a muddy to sandy matrix containing scattered pebbles, cobbles, and larger clasts of varied lithologies. Clasts range from angular to subrounded, indicating mixed transport histories and variable source distances (see photos). In outcrop, these rocks commonly resemble breccia or conglomerate depending on clast abundance and matrix content. Their unsorted texture suggests deposition by high-energy processes such as debris flows, sediment gravity flows, glacial meltwater transport, or direct ice rafting into marine basins.
Stratigraphically, the Kingston Peak Formation overlies the Beck Spring Dolomite, a carbonate deposit, and is overlain by the Noonday Dolomite (BH250-242b, figure-BH250-238), a famous post-glacial cap carbonate deposited after Cryogenian deglaciation. This succession records one of the most dramatic environmental transitions in Earth history: carbonate platform seas of the Beck Spring were replaced by tectonically active basins receiving glacially influenced siliciclastic sediments of the Kingston Peak, followed by rapid marine flooding and renewed carbonate deposition of the Noonday Dolomite (BH250-242b).
Comparable Cryogenian diamictites are also preserved in the Tambien Group of Tigray Ethiopia, where they record the lead-up to and onset of Sturtian glaciation along the northern margin of the Arabian-Nubian Shield. Integrated stratigraphy, chemostratigraphy, and geochronology from these Ethiopian successions have provided some of the most important age constraints on Snowball Earth events. U-Pb zircon ages and carbon-isotope data indicate that environmental instability and major carbon-cycle perturbations preceded the Sturtian glaciation, with critical dates clustering around 719 million years ago, just prior to global ice advance. Key studies by Yuem Park, Nicholas L. Swanson-Hysell, Scott A. MacLennan, Adam C. Maloof, Bereket Haileab and collaborators (2015, 2018, 2019) demonstrated globally synchronous carbon-isotope change and helped constrain the timing of the Sturtian Snowball Earth.
Coverage
Location: Death Valley, California, USA
Nearby Geographic Feature: Death Valley
GPS Coordinates: 35.681897, -116.405733
Nearby Geographic Feature: Death Valley
GPS Coordinates: 35.681897, -116.405733
Date
2023
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 238. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-238,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/311.