| Abstract |
- Upper Cambrian through Middle Devonian carbonate andclastic sequences of the northern part of the Fish Creek Rangerepresent shallow-shelf sedimentation in the Cordilleranmiogeosyncline. The lower and middle Paleozoic section exposedin the northern Fish Creek Range fits well within regional facies patterns and paleogeographic reconstructions.The Upper Cambrian Dunderberg Shale was deposited in amuddy outer shelf embayment which extended eastward into theEureka area. The embayment was eliminated as seas regressed inlate Dresbachian time and marine carbonate sedimentation (represented by the Catlin Member o-f the Wind-fall Formation) wasestablished. The argillaceous Bullwhacker Member of theWindfall was deposited in deeper shelf waters as the seatransgressed briefly during Trempeleauian time.Shallow-shelf carbonates of the Lower Ordovician GoodwinLimestone are succeeded by Ninemile Formation strata representing deposition in a muddy embayment
- Upper Cambrian through Middle Devonian carbonate andclastic sequences of the northern part of the Fish Creek Rangerepresent shallow-shelf sedimentation in the Cordilleranmiogeosyncline. The lower and middle Paleozoic section exposedin the northern Fish Creek Range fits well within regional facies patterns and paleogeographic reconstructions.The Upper Cambrian Dunderberg Shale was deposited in amuddy outer shelf embayment which extended eastward into theEureka area. The embayment was eliminated as seas regressed inlate Dresbachian time and marine carbonate sedimentation (represented by the Catlin Member o-f the Wind-fall Formation) wasestablished. The argillaceous Bullwhacker Member of theWindfall was deposited in deeper shelf waters as the seatransgressed briefly during Trempeleauian time.Shallow-shelf carbonates of the Lower Ordovician GoodwinLimestone are succeeded by Ninemile Formation strata representing deposition in a muddy embayment, similar to the LateCambrian embayment in the Eureka area. Regression followed, anda shallow-water Girvanella-rich carbonate bank prograded westward during Whiterockian (early Middle Ordovician) time,represented by the lower part of the Antelope Valley Limestone.Mudstone and wackestone of the upper part of the Antelope ValleyLimestone was deposited in quieter, deeper, or more protectedenvironments shoreward of the bank margin.Basal sands of the Eureka Quartzite prograded westwardacross the carbonate shelf during the Middle Ordovician.Carbonate sedimentation persisted in some areas in siltyembayments, and is represented by the Copenhagen Formation.Transgression began during Eureka deposition, and shelf-lagooncarbonates of the Hanson Creek Formation were deposited astransgression continued during Late Ordovician and earliestSilurian time .The lower part of the Silurian-Lower Devonian Lone MountainDolomite in the Fish Creek Range is transitional to outerplatform carbonate-bank deposits at the type section to thenorthwest, and to restricted, inner-platform deposits of thepartly correlative Laketown Dolomite to the east. Rhythmicallyalternating, shallow subtidal and restricted peritidal depositsform the upper part of the Lone Mountain in the study area, andreflect progradation of peritidal environments as the earliestDevonian sea regressed.Younger Devonian rocks in the Fish Creek Range lie within anorth-trending transitional belt in which shallow, eastern lithofacies(predominantly dolomite) and deeper-water, limestonelithofacies intertongue. Peritidal deposits of the Beacon PeakDolomite prograded westward during the mid-Early Devonian. Subtidal, fossiliferous limestone of the Bartine Member of theMcColley Canyon Formation was deposited as transgression beganduring Emsian time (qronberoi to inversus conodont Zones). Limemudstone, wackestone, and packstone of the Coils Creek Member ofthe McColley Canyon Formation was deposited in quieter, slightlydeeper, shelf waters during late Emsian time (inversus Zone).Regression followed during latest Emsian time (serotinusZone). Dolomite and crinoidal dolomite of the Sadler RanchFormation (latest Emsian to Eifelian) was deposited in shallowwaters of the outer shelf. The overlying Coarse CrystallineMember of the Oxyoke Canyon Sandstone is a regressive sequence ofquartzose dolomite and dolomite-cemented sandstone deposited onthe inner platform, where beach and intertidal environments wereseparated by a low-relief coastline.Thick-bedded, peritidal dolomite of the lower part of theSentinel Mountain-Bay State interval represents progradation ofperitidal facies across the shallow platform during early MiddleDevonian time. The upper part of the Sentinel Mountain-Bay Stateinterval was deposited in more circulated, shallow-marinecarbonate-bank environments.The lower part of the Devils Gate Limestone in the study areareflects deposition in shallow, agitated shelf waters and quieter,deeper, shelf lagoons and embayments. Inundation of the carbonateplatform followed and is reflected by a shift to deeper waterfacies during Frasnian (early Late Devonian) time.The Fish Creek Range was affected by Sevier hinterland deformation during the Late Mesozoic; N to N15E-trending folds reflect overall east-west compression. Upper Cretaceous granitic rockswere emplaced at depth beneath the southwest side of the studyarea, where conodont alteration indices from Paleozoic collectionsindicate paleotemperatures of 500-600 C. Two-mica granitic dikes,exposed at McCulloughs Butte, intrude Ordovician rocks.Thermal effects may have promoted initial gravity slidingof the Silurian-Devonian section off of the Ordovician sectionat the Hanson Creek level (Upper Ordovician-Lower Silurian).Low-angle normal faulting within this stratigraphic level ispervasive in the northern part of the Fish Creek Range. It isinterpreted that faulting at the Hanson Creek level wasinitiated at about the same time that the Upper Cretaceousintrusion was emplaced. Movement along the faults may havecontinued or been renewed during Oligocene extension.Low-angle normal faulting at the Silurian and LowerDevonian levels post-dates faulting at the Upper Ordovicianlevel. It is interpreted that these faults developed duringOligocene uplift and extension.Volcanism and shallow intrusive activity affected thenorthern Fish Creek Range during earliest Oligocene time, and isrepresented by the Ratto Springs Rhyodacite. High-angle normalfaults typical of basin-and-range extension are common throughout the area and represent the most recent phase of deformation.
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| Additional Information |
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Previous issue date: 1989-02-17
- For master (tiff) digital images of maps contained in this document contact scholarsarchive@oregonstate.edu
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