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Abstracts: Middle Cambrian Thrombolite Bioherms in the Jangle Limestone Member of the Carrara Formation, Southern Nopah and Resting Springs Ranges, Southeastern California


Thrombolite bioherms are common in the uppermost Jangle Limestone Member of the Carrara Formation at Emigrant Pass in the Southern Nopah Range and in the Resting Springs Range in southeastern California. Three distinct types of these enigmatic microbial structures; domal, ellipsoidal, and stromatolitic, have been recognized. The thrombolites occur within a grainstone and internally have the digitate growth patterns which cause the distinctive external clotted fabric. The thrombolites are restricted to the upper bed of the limestone and differ stratigraphically and sedimentologically in the two areas.

At Emigrant Pass, all three types of thrombolites are present. Large, domal thrombolites have maximum diameters and relief of 2 m and 1 m respectively. Ellipsoidal thrombolites are closely spaced bioherms occurring as parallel ridges on bedding plane outcrops. Stromatolitic thrombolites, averaging 28 cm in height and 27 cm in diameter, are characterized by a dark laminated interval capping a clotted core. The individual structures occur in the uppermost bed of intraclast-bearing grainstone in the Jangle Limestone.

In the Resting Springs Range the bioherms are less abundant, occurring as widely spaced groups along the trend of the outcrop. Domal forms with maximum relief of 1.5 m are separated

by a tabular unit also containing distinctive thrombolite texture. More elongate forms with more subdued relief occur locally. These thrombolites occur approximately a meter below the top of the limestone unit and the infill between the bioherms is an ooid-bearing grainstone which continues to the top of the limestone member.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California