The majority of the Middle Cambrian Wheeler Formation in the Drum Mountains was deposited during a single 3rd order sequence. Superimposed onto this sequence are three indistinct 4th order cycles and twenty distinct 5th order cycles. These higher other cycles were likely deposited within short intervals of geologic time (204 to 405 ky). The lower sequence boundary zone occurs within the Swasey Formation. The Transgressive Surface is the contact between the Swaset and Wheeler Formations. The Maximum Flooding Surface is located near the top of the lower Wheeler Formation, which also approximates the base of the Ptychagnostus atavus range zone. The upper sequence boundary is marked by stromatolites, which occur near the top of the upper member of the Wheeler Formation in the Drum Mountains. Deposition of the Wheeler Formation in the Drum Mountains was controlled by eustacy and tectonics. Local normal faulting associated with Middle Cambrian postrifting thermal subsidence may have caused some of the 5th order cycles. The cycles and surfaces defined in this stratigraphic analysis, and the base of the Ptychagnostus atavus and P. gibbus range-zones, can be used to correlate strata occurring in other localities in the eastern Great Basin. In addition, this study enables the evaluation of the effect of tectonics (faulting) versus global eustacy on the sedimentary regime occurring within the Middle Cambrian House Range Embayment. (95 pages)

The majority of the Middle Cambrian Wheeler Formation in the Drum Mountains was deposited during a single 3rd order sequence. Superimposed onto this sequence are three indistinct 4th order cycles and twenty distinct 5th order cycles. These higher order cycles were likely deposited within short intervals of geologic time (204 to 405 ky). The lower sequence boundary zone occurs within the Swasey Formation. The Transgressive Surface is the contact between the Swasey and Wheeler Formations. The Maximum Flooding Surface is located near the top of the lower Wheeler Formation, which also approximates the base of the Ptychagnostus atavus range zone. The upper sequence boundary is marked by stromatolites, which occur near the top of the upper member of the Wheeler Formation in the Drum Mountains. Deposition of the Wheeler Formation in the Drum Mountains was controlled by eustacy and tectonics. Local normal faulting associated with Middle Cambrian postrifting thermal subsidence may have caused some of the 5th order cycles. The cycles and surfaces defined in this stratigraphic analysis, and the base of the Ptychagnostus atavus and P. gibbus range-zones, can be used to correlate strata occurring in other localities in the eastern Great Basin. In addition, this study enables the evaluation of the effect of tectonics (faulting) versus global eustacy on the sedimentary regime occurring within the Middle Cambrian House Range Embayment.

The Middle Cambrian Wheeler Formation is interpreted as having been deposited in the shallow ramp and deeper basin environments of the House Range embayment (HRE), presumably, during a single third-order sequence. In the Drum Mountains, the Wheeler Formation (295 m thick) is dominated by proximal and distal ramp deposits; at Ma~um Pass, the Wheeler Formation (190m thick) is dominated by basinal shale deposits. The Wheeler Formation contains only one biozone marker; the first appearance of Ptyhagnostus atavus. Lack of other chronostratigraphic markers and distinctive stratal patterns in the basinal facies makes correlation along this ramp-to-basin transect difficult. Therefore, carbon-isotope stratigraphy and total organic carbon analysis were tested for their utility as intra basinal correlation tools. 813Ccarbonate isotope values range from -1.7% to 0.07%o (PDB) at Marjum Pass and -1.1% to 1.4% (PDB) in the Drum Mountains; previously reported 813Ccarbonate values in the Great Basin for this time interval range between -2% to 2% (PDB). Both localities show small-scale isotope variability, however, this variability is thought to be the result of local isotopic effects and was not used for correlation. TOC values obtained from both sections increase upsection, define a distinct peak, then decrease upsection. These peaks are associated with shale facies and occur near the maximum flooding surface in both sections, indicating that the TOC results could be used for correlation between sections. The lithologic cyclicity recognized in the shallow-water deposits at the Drum Mountains locality have also been recognized in the deeper-water deposits at Ma~um Pass. At each locality the meter-scale cycles shallow upward and display similar stacking patterns. Because cyclicity is preserved in both sections and the total stratigraphic thickness and cycle thickness decrease toward the embayment-controlling fault, it is probable that the cyclicity was the result of small-scale eustatic changes in sea level rather than episodic tectonism. This ramp-to-basin correlation also supportS the validity of P. atavus as a global biostratigraphic marker. The first appearance of Ptydnagostus atavus has been found below the interpreted maximum flooding surface and was coeval with transgression in both localities, indicating that its appearance was likely synchronous.

No description available.