BH250-238c

BH250-238c

Shale

The laminated siltstones (BH250-238b) and shales (BH250-238c) of the lower Kingston Peak Formation in Death Valley are commonly found directly above the underlying Beck Spring Dolomite, marking an important stratigraphic and environmental transition in the late Precambrian basin. The contact typically records a change from shallow-water carbonate platform deposition of the Beck Spring Dolomite into deeper-water siliciclastic sedimentation represented by laminated mudstones, siltstones, and eventually diamictite-bearing (BH250-238 and BH250-239) intervals of the Kingston Peak.

These finely laminated siltstones and shales represent quieter intervals of sedimentation that contrast strongly with the coarser diamictites interbedded higher in the section. Their thin bedding suggests settling of suspended clay and silt in low-energy offshore basins. When viewed together with the diamictites, they record repeated environmental shifts: calm background sedimentation interrupted by energetic pulses of glacial debris flows, iceberg rafting, or slope failure. Thus, the transition upward from the Beck Spring Dolomite into lower Kingston Peak mudrocks and diamictites captures the progressive breakdown of a stable carbonate shelf and the onset of tectonically active, climatically unstable Cryogenian conditions that ultimately became associated with Snowball Earth glaciation.

Location: Death Valley, California, USA

Bereket Haileab

From the rock collection of Bereket Haileab. Sample 238c. Housed at Carleton College in Minnesota.

Hand sample