Stratigraphy and Depositional Environments of the Lower Mississippian Joana Limestone in Southern White Pine and Northern Lincoln Counties, Nevada

The Lower Mississippian Joana Limestone in the southern Schell Creek and Egan ranges of east-central Nevada is composed of three depositional facies: the unbedded wackestone with grainstonelpackstone facies or Facies 1; the bedded wackestone with mudstone facies or Facies 2; and the restricted wackestone, mudstonelshale facies, or Facies 3. Facies 1 is characterized by Waulsortian-type carbonate buildups with massive unbedded wackestone cores, grainstone flanking beds and grainstonelpackstone capping units. Facies 2 is characterized by an upward progression of sedimentary bedding types from thinly laminated to large scale trough cross-bedding that indicates a shoaling upward of this facies. Facies 3 is characterized by sparse wackestones, - mudstones, and shale which show a decrease in both faunal types and diversity and an increase in fine elastics. The restricted wackestone, mudstonelshale facies grades upward into the Mississippian Chainman Shale. The age of the Joana Limestone is confirmed as late K'inderhookian to early Osagean based primarily on conodonts and foraminifera. In the middle beds of the Joana ~imestoie, the previously unreported upper Siphonodella crenulata conodont zone occurs which helps correlate the Joana Limestone with regional transgressivelregressive sea level events. Color alteration indices of these conodonts are 1.5 to 2, and occur in the oil generation window. Additionally, oil staining was observed in numerous samples located primarily in the lower half of the formation, represented by Facies 3, the unbedded waekestone with grainstonelpackstone facies.