Geologic Map of the Grand View-Bruneau Area, Owyhee County, Idaho (original) (raw)
Related papers
Journal of volcanology and geothermal research, 2007
Sinker Butte is the erosional remnant of a very large basaltic tuff cone of middle Pleistocene age located at the southern edge of the western Snake River Plain. Phreatomagmatic tephras are exposed in complete sections up to 100 m thick in the walls of the Snake River Canyon, creating an unusual opportunity to study the deposits produced by this volcano through its entire sequence of explosive eruptions. The main objectives of the study were to determine the overall evolution of the Sinker Butte volcano while focusing particularly on the tephras produced by its phreatomagmatic eruptions. Toward this end, twenty-three detailed stratigraphic sections ranging from 20 to 100 m thick were examined and measured in canyon walls exposing tephras deposited around 180°of the circumference of the volcano.
AAPG Bulletin, 1994
High-resolution seismic reflection profiles and well data from the western Snake River plain basin are used to identify a buried lacustrine delta system within Neogene Idaho Group sediments near Caldwell, Idaho. The delta system is detected, 305 m (1000 ft) deep, near the center of the basin by progradational clinoform reflections having dips of 2-5°, a slope typical of prodelta surfaces of modern lacustrine delta systems. The prodelta slope relief, corrected for compaction, indicates the delta system prograded northwestward into a lake basin 255 m (837 ft) deep. Resistivity logs in the prodelta mud and clay facies are characterized by gradual upward increase in resistivity and grain size over a thickness of about 100 m (300 ft). Lithology of the prodelta is mostly calcareous claystone, with several layers of fine sand, some of which fine upward, indicating a density-flow mechanism of transport and deposition. Delta-plain and front sediments are mostly very finegrained, well-sorted sand separated by thin mud layers. These sediments produce several to five cycles of horizontal, high-amplitude reflections with a toplap relationship to prodelta clinoforms. The sands have an abrupt lower contact with prodelta muds and have high resistivity on logs. In this study, permeable lacustrine sands within a predominantly mud and clay section are located by using high-resolution seismic reflection data. Identification of a delta system in the Idaho Group provides insight into the history of Pliocene "Lake Idaho." The present depth of the delta/prodelta facies contact of 305 m (1000 ft) is 445 to 575 m (1460-1900 ft) below the lake deposits on the margins. Estimated subsidence from compaction is 220 m (656 ft), and the remaining 225 to 325 m (740-1066 ft) is attributed to tectonic downwarping and faulting. The original lake area had been reduced to one third of the original 13,000 km 2 (5000 mi 2) by the time the delta front prograded to the Caldwell area. The original lake area may have been sufficient to evaporate most of the inflow, and the lake may have only occasionally spilled into other basins. Diminished area for evaporation later in the history of the lake, combined with reduced evaporation accompanying onset of the ice ages, may have caused the lake to rise and overtop a basin sill about 2 Ma, and subsequently deepen Hells Canyon.
Geological Society of America eBooks, 2023
The Windermere Supergroup in southern British Columbia and its correlatives (such as the Pocatello Formation and lower Brigham Group in southeastern Idaho) along the western North American Cordilleran margin are an archetype of Neoproterozoic to early Paleozoic tectonic, sedimentary, and climatic processes. The central Idaho portion of the margin remains relatively understudied when compared to regions to the south in southeastern Idaho or to the north in northeastern Washington. This is in part a legacy of early workers, who identified the absence of Neoproterozoic and Cambrian strata in east-central Idaho across the Lemhi arch. However, Neoproterozoic and Cambrian rocks are indeed present west of the Lemhi arch within the central Idaho section of the Cordillera. Here, we summarize recent advances in our understanding of these strata within central Idaho and correlate the Pocatello Formation and Brigham Group rocks from northern Utah/southeastern Idaho through central Idaho to northeastern Washington. We also provide new constraints that link Cambrian strata from central Idaho across the Lemhi arch to southwestern Montana. Collectively, this emerging tectono-stratigraphic framework suggests extensive, some likely diachronous, stratigraphic boundaries and magmatic events relating to (1) widespread rifting ca. 720-680 Ma; (2) early and late Cryogenian (Sturtian and Marinoan) glacial sedimentation; (3) base-level drawdown and formation of incised valleys, previously correlated to the Marinoan glacial interval, but which now appear to be younger (ca. 600 Ma) and perhaps related to tectonic activity; (4) onset of the Sauk I transgression 560-530(?) Ma; (5) the ca. 515 Ma Sauk II lowstand, perhaps
Timing and development of the Heise volcanic field, Snake River Plain, Idaho, western USA
Geological Society of America Bulletin, 2005
The Snake River Plain (SRP) developed over the last 16 Ma as a bimodal volcanic province in response to the southwest movement of the North American plate over a fi xed melting anomaly. Volcanism along the SRP is dominated by eruptions of explosive high-silica rhyolites and represents some of the largest eruptions known. Basaltic eruptions represent the fi nal stages of volcanism, forming a thin cap above voluminous rhyolitic deposits. Volcanism progressed, generally from west to east, along the plain episodically in successive volcanic fi elds comprised of nested caldera complexes with major caldera-forming eruptions within a particular fi eld separated by ca. 0.5-1 Ma, similar to, and in continuation with, the present-day Yellowstone Plateau volcanic fi eld. Passage of the North American plate over the melting anomaly at a particular point in time and space was accompanied by uplift, regional tectonism, massive explosive eruptions, and caldera subsidence, and followed by basaltic volcanism and general subsidence. The Heise volcanic fi eld in the eastern SRP, Idaho, represents an adjacent and slightly older fi eld immediately to the southwest of the Yellowstone Plateau volcanic fi eld. Five large-volume (>0.5 km 3) rhyolitic ignimbrites constitute a time-stratigraphic framework of late Miocene to early Pliocene volcanism for the study region. Field relations and high-precision 40 Ar/ 39 Ar age determinations establish that four of these regional ignimbrites were erupted from the Heise volcanic fi eld and form the framework of the Heise Group. These are the Blacktail Creek Tuff (6.62 ± 0.03 Ma), Walcott Tuff (6.27 ± 0.04 Ma), Conant Creek Tuff (5.51 ± 0.13 Ma), and Kilgore Tuff (4.45 ± 0.05 Ma; all errors reported at ± 2σ). The fi fth widespread ignimbrite in the region is the Arbon Valley Tuff Member of the Starlight Formation (10.21 ± 0.03 Ma), which erupted from a caldera source outside of the Heise volcanic fi eld. These results establish the Conant Creek Tuff as a distinct and widespread ignimbrite in the Heise volcanic fi eld, eliminating former confusion resulting from previous discordant K/Ar and fi ssion-track dates. New 40 Ar/ 39 Ar determinations, when combined with geochemical, lithologic, geophysical, and fi eld data, defi ne the volcanic and tectonic history of the Heise volcanic fi eld and surrounding areas. Volcanic units erupted from the Heise volcanic fi eld also provide temporal control for tectonic events associated with late Cenozoic extension in the Snake Range and with uplift of the Teton Range, Wyoming. In the Snake Range, movement of large (≥0.10 km 3) slide blocks of Mississippian limestone exposed 50 km to the east of the Heise fi eld occurred between 6.3 and 5.5 Ma and may have been catastrophically triggered by the caldera eruption of the 5.51 ± 0.13-Ma Conant Creek Tuff. This slide block movement of ~300 vertical meters indicates that the Snake Range had signifi cant relief by at least 5.5 Ma. In Jackson Hole, the distribution of outfl ow facies of the 4.45 ± 0.05-Ma Kilgore Tuff related to eruption from the Kilgore caldera in the Heise volcanic fi eld on the eastern SRP indicates that the northern Teton Range was not a signifi cant topographic feature at this time.