A fault-controlled trough through a carbonate platform: The Middle Cambrian House Range embayment

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During the Cambrian, part of western North America was a rapidly subsiding, passive continental margin. A belt of carbonate deposition dominated the central shelf during Middle Cambrian time. The belt was bounded by fine-grained terrigenous sediments that accumulated in deeper water to the west and in a coastal setting to the east. Rapid and possibly repeated movement along a northeast-southwest–oriented fault produced a conspicuous eastward re-entrant into the carbonate belt, the House Range embayment, in Nevada and Utah during the middle Middle Cambrian. The embayment was an asymmetrical trough that deepened and widened as it extended ∼400 km westward across the shelf toward the edge of the continent. The trough axis lay near its abrupt southern margin which was a normal fault separating an area of continuous shallow-water accumulation to the south from deep-water deposition. The northern flank of the embayment was initially a drowned platform that formed a southward-sloping ramp. Facies within the embayment represent deposition in an anoxic basin, on a deep ramp that was locally steepened, and on a shallow, low-energy ramp. The facies rapidly prograded basinward across the northern flank, and through vertical accretion, a broad carbonate platform was re-established there. In contrast to the northern flank, a continuous sequence of deep-water lithofacies accumulated throughout the late Middle Cambrian in the trough axis of the embayment. This region seemingly subsided more rapidly than did that of the northern flank, and it may have functioned as a sediment bypass zone. Although a source of periplatformal carbonates was nearby, sedimentation rates in the trough were thus inadequate to re-establish a shallow-water depositional setting.