EXTENDING UPPER CAMBRIAN SEQUENCE STRATIGRAPHY FROM THE TEXAS CRATON ACROSS THE UTAH–NEVADA CARBONATE PLATFORM INTO SLOPE DEPOSITS IN SOUTHERN NEVADA

The House Range and Confusion Range in western Utah expose 9.8 km of lower Cambrian to lower Triassic marine carbonates. Research on the upper Cambrian–Lower Ordovician Notch Peak and House Formations produced detailed conodont and trilobite biozonations, many useful brachiopods, and a detailed sequence stratigraphy. Six decades of work by many specialists made these rocks a Laurentian standard for correlation.

The Wilberns Formation in cratonic Texas comprises shallow marine grainstones with cross-bedding and abundant glauconite. Some sequence boundaries are marked by thin microbial beds or subtle disconformities.

Coeval Utah strata are passive margin platform carbonates with fewer disconformities. Sea-level drops at some sequence boundaries produced shifts from lime mudstone to grainstone (or the reverse at sea-level rises). Sea-level drops at some sequence boundaries produced thin oolite or stromatolite beds, some capped by exposure surfaces.

Lithofacies were influenced by proximity to the House Range Embayment, a half-graben trough bounded on the southeast by a Cambrian growth fault. It extended southwest to southern Nevada and influenced Cambrian lithofacies.

The upper Cambrian in the South Egan Range, Nevada was deposited in this Embayment. Coeval strata in the Delamar Mountains, Sheep Range, Meadow Valley Mountains, and Arrow Canyon Range were deposited far south of the Embayment and were poorly known until our recent study. Lithologies, sequences, and faunas in these five ranges compare closely with Utah strata, and we extend the names Notch Peak Formation and House Limestone and their members into those eastern Nevada ranges.

The Hales Limestone at Tybo, Hot Creek Range, Nevada comprises deep marine strata that may have formed on a slope at the edge of the House Range Embayment rather than on the Continental Slope, as previously thought. Sequence boundaries there formed quite differently from shallow lithofacies. Shelf carbonates developed pore water pressures equal to hydrostatic pressure. Sea-level drops reduced hydrostatic pressure, causing over-pressured shelf-edge carbonates to destabilize, slide downslope, and reform at Tybo as folded slumps, debris-flow breccias, and turbidites that are coeval with sequence boundaries at sea-level drops in shallower Nevada, Utah, and Texas strata.