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The Star Peak Group in and near the Sonoma Range one-degree quadrangle, northwestern Nevada, is redefined to include the mainly calcareous strata that overlie the predominantly volcanic rocks of the Koipato Group and in turn are overlain by the terrigenous clastic rocks of the Auld Lang Syne Group. The Star Peak Group ranges in age from late Spathian (latest Early Triassic) to late Karnian (middle Late Triassic), and it is as much as 1,200 m thick. Although the paleogeography of the group has been affected locally by post-Triassic low-angle faulting, widespread formational units within the Star Peak genetically relate all parts of its outcrop region and obviate the need to separate these rocks into different major structural blocks, as has been done in the past.

In the older parts of the Star Peak Group, complex stratigraphic patterns among a variety of carbonate and terrigenous clastic rocks resulted from localized relative uplift, first early and then late in Middle Triassic time. Widespread diagenetic secondary dolomitization of calcareous rocks in the older part of the section further complicates the primary stratigraphic patterns. Following the earlier of these intra-Star Peak tectonic episodes, regionally uniform calcareous rocks of late Anisian age blanketed most of the outcrop area. These rocks contain a rich pelagic fauna and were evidently deposited below wave base. The more western of these rocks grade upward into dark cherty limestone which was deposited in basinal and slope environments concomitantly with uplift and erosion, during Ladinian time, in the central part of the Star Peak outcrop area. South and southeast of the uplifted area, subsidence and peritidal deposition took place followed by deposition of supratidal algal-laminate dolomite. This dolomite was deposited across the beveled uplift and correlates with platform-margin and basinal limestone farther west. Thereafter, lower Karnian platform limestone thickly blanketed the outcrop area and built regressively westward out over the basinal deposits. Following a widespread mid-Karnian break in deposition, local erosion, and deposition of terrigenous clastic rocks, platform carbonate rocks again blanketed the outcrop area during late Karnian time and extended an unknown distance westward, perhaps as far as the original site of the Sierran–eastern Klamath belt.

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