ABSTRACT

Identical thinly interlaminated dolostones and dolomitically mottled bahamites occur in the Marjum Limestone of western Utah and in zones G through L of the Highland Peak Formation in eastern Nevada. Both intervals are in the late Middle Cambrian Bolaspidella Zone.

The dolomite in the dolostone laminae, as well as that occuring as aggregates mottling the bahamites, is composed of evenly grained, loosely interlocked cryptocrystalline rhombs which are believed to have been formed by primary and by early diagenetic precipitation. The dolomite aggregates in the bahamites rim silt size grains composed of cryptocrystalline calcite. Post-diagenetic metasomatic dolomite is always coarser grained than the calcite in the bahamite aggregates, is more unevenly grained and coarser than the earlier dolomite, and does not occur in aggregates. The laminations may be the result of seasonal changes at the site of deposition.

Intraformational breccia-conglomerate layers composed of platy intraclasts of the above rocks in a matrix of fine-grained calcite are strong evidence of a primary and early diagenetic origin for the dolomite. These coarse clastic rocks are restricted to the interlaminated units of the same composition and are the result of subaqueous processes rather than subaerial desiccation and erosion. Synaeresis and intrastratal erosion or solution seems to have caused the development of cracks across the laminations as well as between laminae of different composition. The local stripping of indurated and cracked bottom material was guided by weak bonding between dolostone and bahamite laminations and was probably caused by storm waves or possibly tsunamis acting simultaneously over wide areas. >

The association of the above rock types with oolitic calcarenites and beds of algal limestone suggests that they were deposited on surfaces similar to the Bahama Banks.