English: This unusual outcrop is in the Ordovician-aged Antelope Valley Limestone of Nevada. The gray rocks are limestone, a biogenic sedimentary rock composed of calcite (CaCO3, calcium carbonate). The rocks have moderately thin, regular laminations that have a zebra stripe-like appearance (zebra limestone). The gray laminations are lime mudstones to fossiliferous wackestones. The lighter laminations are sparry crystalline calcite. Laminations show some soft-sediment deformation. Infilled cavities are present as well (click on the photo once or twice to zoom in and look around - the cavities are gray areas lacking laminations).

This bizarre limestone rock has been discussed at length in the literature. It has been interpreted as stromatolitic bedding. A more recent interpretation attributes the light-colored sparry bands to crystal-filled dilational fissures formed as submarine gas clathrate hydrates converted from ice to gas. Those gases may have also been the propping agents for the cavities (see Krause, 2001). In this scenario, the soft-sediment deformation would form as the generated gases caused differential heaving of overlying sediments.

Stratigraphy: lower Antelope Valley Limestone, Pogonip Group, lower Whiterockian Series, lower Middle Ordovician (sensu traditio)

Locality: Meiklejohn Peak, ~9 air-kilometers east-southeast of the town of Beatty, southern Nye County, southern Nevada, USA (vicinity of 36° 52' 50.22" North latitude, 116° 39’ 55.29" West longitude)

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References:

Ross et al. (1975) - Lithology and origin of Middle Ordovician calcareous mudmound at Meiklejohn Peak, southern Nevada. United States Geological Survey Professional Paper 871. 48 pp.

Krause (2001) - Genesis and geometry of the Meiklejohn Peak lime mud-mound, Bare Mountain Quadrangle, Nevada, USA: Ordovician limestone with submarine frost heave structures - a possible response to gas clathrate hydrate evolution. Sedimentary Geology 145: 189-213.