Lemhi Range Research Articles

Small valley glaciers and the effectiveness of the glacial buzzsaw in the northern Basin and Range, USA

The glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens. Studies to date have largely focussed on regions where large glaciers (tens of kilometres long) have been active. In light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines, we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions. Four ranges in the northern Basin and Range, Idaho, Montana, and Wyoming, USA, were chosen for this analysis. Estimates of maximum Pleistocene slip rates along normal faults bounding the Beaverhead–Bitterroot Mountains (~ 0.14 mm y − 1 ), Lemhi Range (~ 0.3 mm y − 1 ) and Lost River Range (~ 0.3 mm y − 1 ) are an order of magnitude lower than those on the Teton Fault (~ 2 mm y − 1 ). We compare the distribution of glacial erosion (estimated from cirque floor elevations and last glacial maximum (LGM) equilibrium line altitude (ELA) reconstructions) and fault slip rate with three metrics of topography in each range: the along-strike maximum elevation swath profile, hypsometry, and slope-elevation profiles. In the slowly uplifting Beaverhead–Bitterroot Mountains, and Lemhi and Lost River Ranges, trends in maximum elevation parallel ELAs, independent of variations in fault slip rate. Maximum elevations are offset ~ 500 m from LGM ELAs in the Lost River Range, Lemhi Range, and northern Beaverhead–Bitterroot Mountains, and by ~ 350 m in the southern Beaverhead–Bitterroot Mountains, where glacial extents were less. The offset between maximum topography and mean Quaternary ELAs, inferred from cirque floor elevations, is ~ 350 m in the Lost River and Lemhi Ranges, and 200–250 m in the Beaverhead–Bitterroot Mountains. Additionally, slope-elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ELA in the Lemhi Range and Beaverhead–Bitterroot Mountains, suggesting that small glaciers efficiently limit topography. The situation in the Lost River Range is less clear as a glacial signature is not apparent in either slope-elevation profiles or the hypsometry. In the rapidly uplifting Teton Range, the distribution of ELAs appears superficially to correspond to maximum topography, hypsometry, and slope-elevations profiles, with regression lines on maximum elevations offset by ~ 700 and ~ 350 m from the LGM and mean Quaternary ELA respectively. However, Grand Teton and Mt. Moran represent high-elevation “Teflon Peaks” that appear impervious to glacial erosion, formed in the hard crystalline bedrock at the core of the range. Glacier size and drainage density, rock uplift rate, and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography. In the northern Basin and Range, it is only under exceptional circumstances in the Teton Range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw, emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis.

The effect of topography, latitude, and lithology on rock glacier distribution in the Lemhi Range, central Idaho, USA

Statistical analysis of rock glaciers in the Lemhi Range demonstrates that their development and preservation is controlled primarily by annual insolation and lithology. We inspected 171 alpine valleys in the Lemhi Range using optical remote sensing techniques, digital topographic analysis, and field examination. In those valleys, we identified 48 rock glaciers and examined them for lichen cover, evidence of ice presence, specific evidence of movement, and distinctive morphological features. In addition to recording the presence or absence of a rock glacier in each alpine valley, existing rock glaciers were classified according to their morphology. Factors such as topographic shading, lithology, relief, aspect, and elevation determine the development and preservation of rock glaciers. Analysis of these factors in the Lemhi Range shows that elevation > 2600 m, a north-facing aspect (300–60°), and < 2300 h of direct sunlight per year are necessary conditions for the existence of rock glaciers in any form. The majority of alpine valleys in the Lemhi Range meet these requirements. Thus, other parameters, including topographic shading and lithology, must determine occurrence of rock glaciers in the Lemhi Range. Multivariate statistical analysis of controlling parameters demonstrates that annual insolation and latitude influence rock glacier occurrence most strongly. Whereas duration of insolation is a logical controlling factor, latitude is more enigmatic. Additional statistical analysis indicates that the latitude factor is likely a reflection of lithologic changes with latitude along the range. Lithology may affect rock glacier distribution through its effects on hydrology or air ventilation. Moreover, statistical analysis shows that rock glacier occurrence correlates with protalus lobe occurrence, suggesting that protalus lobes play a role in the genesis of rock glaciers in the Lemhi Range. Separate analysis of the classification systems shows that each morphologic class, inferred to correlate with rock glacier activity, is statistically significant and distinguishable from other classes. In addition to the effect of insolation, statistical analysis of the classification system also shows that latitude influences distribution of existing rock glacier classes independent of lithology.

Abstract: Paleogeography of the Late Devonian Jefferson Formation and antecedent Channel Sandstones"in the Lemhi Range, East-Central Idaho"

Abstract: Paleogeography of the Late Devonian Jefferson Formation and antecedent Channel Sandstones"in the Lemhi Range, East-Central Idaho"

Seismicity of the eastern Snake River Plain region, Idaho, prior to the Borah Peak, Idaho, earthquake: October 1972-October 1983

Abstract In December 1971, the Idaho National Engineering Laboratory deployed a network of short-period high-gain vertical seismographs to monitor earthquake activity within a designated study area (43.0° to 44.5°N, 111.5° to 114.0°W) centered on the eastern Snake River Plain. In the 11 yr prior to the 28 October 1983 Borah Peak, Idaho, earthquake, there were 102 events located within the study area with a duration magnitude ( M ) range of 0.7 ≦ M ≦ 3.2. Three microearthquakes ( M ∼ 1) were detected on the eastern Snake River Plain. Seventy-five microearthquakes were located northwest of the eastern Snake River Plain, primarily in the Birch Creek Valley-Beaverhead Mountains region. During the 11-yr period that the Idaho National Engineering Laboratory seismograph stations have been active, there were only two events located inside the study area within 35 km of the epicenter of the Borah Peak, Idaho, earthquake. In the 2.6 yr prior to the Borah Peak, Idaho, earthquake, there were no foreshocks with magnitudes ≧ 1 observed within a 20 km radius of the epicenter. Future large earthquakes in the Lost River Range, Lemhi Range, and segments of the Beaverhead Mountains may also occur without significant foreshock activity.

Quaternary faulting near Arco and Howe, Idaho

Abstract Well-defined high-angle faults were exposed in 1969 by trenching across scarps in alluvial fans along mountain ranges north of Arco and Howe, Idaho. Faulting along both the Arco and Howe scarps disrupts well-developed calcic soils that are considered to be about 30,000 yr old. On the other hand, both scarps are interrupted by gaps occupied by unfaulted alluvial fans that probably are younger than 15,000 yr old. The Arco scarp coincides with a zone of closely spaced faults in alluvial fans along the western foot of the Lost River Range. From Arco, the scarp extends northward about 16 km (10 miles), where it merges into an unstudied scarp in bedrock. At a trench across the scarp 10 km (6 miles) north of Arco, multiple movements in the fault zone have resulted in aggregate vertical displacement of at least 12 m (40 ft). Measured offsets of stratigraphic units exposed in the trench indicate at least two episodes of vertical movement on individual faults. One episode of movement caused a minimum offset of 4.6 to 6.1 m (15 to 20 ft), and another offset was more than 3 m (10 ft). The Howe scarp coincides with a zone of closely spaced faults in alluvial fans along the western foot of the Lemhi Range. A southern part of the scarp trends northwest along the southern part of the range a distance of 15 km (9 miles), and a northern part trends north at least another 6 km (4 miles). These parts of the scarp are separated by a bedrock ridge 3 km (2 miles) wide in which the scarp is indistinct. At a trench aross the scarp about 11 km (7 miles) north of Howe, multiple movements in the fault zone have resulted in aggregate vertical displacement of at least 15 m (50 ft). Measured offsets of stratigraphic units exposed in the trench indicate five or more episodes of vertical movement on individual faults, ranging from 0.3 m (1 ft) to more than 3 m (10 ft).

Calcareous algae and associated microfossils from Mid-Carboniferous rocks in east-central Idaho

Mid-Carboniferous (upper Chesterian–lower Atokan) rocks exposed north of the Snake River Plain in east-central Idaho are assigned to the Arco Hills, Bluebird Mountain and lower Snaky Canyon formations (ascending order). In the southern Lemhi Range, calcareous algae and associated microproblematica from these rocks include representatives of at least 13 genera and genus-level taxa within the Dasycladaceae, Aoujgaliaceae, Ungdarellaceae, and incertae familiae. Local appearances of Masloviporidium delicata and Donezella lutugini are early Morrowan or younger as determined independently by studies of associated foraminifers and conodonts. Beresella polyramosa and Komia abundans are locally restricted to Atokan rocks. These findings are consistent with compiled data on worldwide stratigraphic distributions of these taxa, and suggest that certain Upper Paleozoic calcareous algae may be of limited value in biostratigraphic correlation.

Quaternary tectonic setting of the 1983 Borah Peak earthquake, central Idaho

The 1983 Borah Peak earthquake was accompanied by extensive surface faulting along a part of the Lost River fault that has abundant evidence of latest Quaternary (last 15,000 yr) offset. This fault and two similar range-front normal faults along the Lemhi Range and Beaverhead Mountains lie in an area of basinand-range structure in central Idaho that is part of a roughly V-shaped belt of latest Quaternary surface faulting that extends from the Wasatch fault, through the Yellowstone area, to the Lost River fault. The position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late Cenozoic silicic volcanism along the YellowstoneSnake River Plain axis. The central segments of the Lost River, Lemhi, and Beaverhead faults have been active more recently, and probably more active throughout Quaternary time, than the southern and northern segments. The main 1983 surface faulting occurred in an area of high structural relief along a central segment of the Lost River fault that has ruptured in latest Quaternary time, which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting. Other perspective of fault behavior suggest additional possible sites, and all segments of the range-front faults are regarded as capable of surface faulting.

Upper Paleozoic Paleogeography of Idaho: ABSTRACT

In south-central Idaho, Mississippian rocks were deposited in flysch-trough and carbonate-bank environments. Lower Mississippian detritus shed from the Antler highland accumulated to a thickness of more than 3,000 m in an adjacent elongate flysch-trough and End_Page 785------------------------------ spread eastward to the inner craton margin. In southeastern Idaho, less detritus was available from the Antler highland in Early Mississippian time, and a starved basin developed between the foreland basin on the west and the inner craton margin on the east. Carbonate-bank deposition followed on both sides of the Snake River plain in Late Mississippian time, as the northern flysch basin ceased subsidence. By Middle Pennsylvanian time, the flysch deposits rose to form a highland from which coarse detritus was shed west, east, and south to interfinger with the fine-grained craton-derived, in part subarkosic, sands of the Wood River and Sublett basins, which gradually deepened through Late Pennsylvanian into Early Permian (pre-Phosphoria) time. Carbonate-bank deposition continued into Early Permian time east of the Copper Basin highland. The Lower and Upper(?) Permian Phosphoria Formation is recognized throughout southeastern Idaho and in south-central Idaho as far west as the Lemhi Range. West of the Lemhi Range, mollusk-rich fine-grained Phosphoria-equivalent rocks are known from one locality in the White Knob Mountains and from two localities in the Pioneer Mountains. Fine-grained, banded and graded siltites of Phosphoria age, which resemble continental-rise contourites, are present in the Boulder Mountains. Phosphoria-equivalent andesitic and dacitic volcanic rocks in western Idaho record a contemporaneous volcanic arc west of the continent. End_of_Article - Last_Page 786------------

Petrology of the Kinnikinic Quartzite (Middle Ordovician), East-Central Idaho

ABSTRACT The Kinnikinic Quartzite (Middle Ordovician) forms distinctive white cliffs in much of east-central Idaho. It is a fine- to medium-grained, silica-cemented, supermature quartz arenite. Structureless beds and thin to medium parallel bedding with parallel laminae predominate. Locally abundant, however, are omikron-type cross-laminae, probably subaqueous dunes, formed by predominantly southwestward-flowing paleocurrents. Small-scale ripples and shallow scours are rare. Rare Skolithos tubes. concentrated at local horizons, dominate the sparse trace-fossil assemblage. Anomalously high amounts of undulatory quartz indicate widespread in situ tectonic straining of quartz grains following deposition. Deposition on a shallow, open-marine shelf, swept by moderate to high-energy currents, is indicated by physical and biological sedimentary structures, grain-size trends, lithologic uniformity through considerable lateral extent, and overall paleogeographic setting. In the type area, near Clayton, Idaho, interbeds of shale in generally very fine-grained quartz arenite indicate lower energy conditions westward. This area probably marks the transition from the outer shelf to the continental slope. Differential subsidence during deposition resulted in large lateral differences in thickness of this shallow-water unit. From a maximum preserved thickness of more than 1,500 feet at Mahogany Hills, at Hawley Mountain, and in the central Lemhi Range, the Kinnikinic thins southward to 326 feet near Arco, Idaho, and westward to 266 feet near Ketchum, Idaho. In the northeast, depositional onlap and subsequent pro-Devonian erosion also contributed to this variability in thickness.

Palaeoaplysina (Hydrozoan?) Carbonate Buildups from Upper Paleozoic of Idaho

The plate-shaped calcareous hydrozoan? Palaeoaplysina Krotov is the main fossil in Late Pennsylvanian and Early Permian carbonate buildups in the Lemhi Range and Arco Hills of east-central Idaho. Palaeoaplysina has an internal subparallel canal system imbedded in cellular tissue, and mamelon-like surface protuberances. Other fossils in the buildups include the calcareous phylloid alga Eugonophyllum, other unidentified phylloid algae, crustose bryozoans, and less common gastropods, crinoids, and brachiopods. Buildup sediment accumulated primarily by the baffling and entrapment of loose carbonate pellets, lime mud, and skeletal fragments in protected pockets and hollows between Palaeoaplysina and algal plates. There is a continuum between tabular and lenticular buildup geometries. Broad tabular buildups are typically 2 to 10 m thick and as much as 15 km wide. The basal surfaces of the tabular buildups conform to previous sea-floor topography, whereas upper surfaces are relatively flat and planar, suggesting that the buildups were limited in upward growth because they formed in the uppermost subtidal zone. The abundance of porcelaneous tubular foraminifers (resembling apterrinellids and Hedraites), which encrusted some unpreserved organisms, suggests that some buildups were carpeted by unfossilized vegetation such as noncalcareous algae. Strongly lenticular buildups are typically 2 to 16 m thick and a few tens to hundreds of meters wide. Most were large enough to modify depositional conditions nearby, resulting in fore-mound and back-mound beds. All of the lenticular buildups, and some of the tabular ones, stood topographically above the adjacent sea floor while they formed. Some buildups are stacked one above another. Others are in offlapping sequences which also include lenticular beds of crinoidal-bryozoan lime wackestone and grainstone.

Reverse Gravitative Movement on Earlier Overthrusts, Lemhi Range, Idaho

Research Article| March 01, 1972 Reverse Gravitative Movement on Earlier Overthrusts, Lemhi Range, Idaho EDWARD C BEUTNER EDWARD C BEUTNER Department of Geology, Franklin and Marshall College, Lancaster, Pennsylvania 17604 Search for other works by this author on: GSW Google Scholar Author and Article Information EDWARD C BEUTNER Department of Geology, Franklin and Marshall College, Lancaster, Pennsylvania 17604 Publisher: Geological Society of America Received: 01 Sep 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (3): 839–846. https://doi.org/10.1130/0016-7606(1972)83[839:RGMOEO]2.0.CO;2 Article history Received: 01 Sep 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation EDWARD C BEUTNER; Reverse Gravitative Movement on Earlier Overthrusts, Lemhi Range, Idaho. GSA Bulletin 1972;; 83 (3): 839–846. doi: https://doi.org/10.1130/0016-7606(1972)83[839:RGMOEO]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two large gravity slide blocks moved up to 5 mi southwestward off the Lemhi Range during the latest stages of basin-range uplift. Both detachment faults coincide in part with folded thrust faults along which 1 to 3 mi of eastward displacement occurred during the Mesozoic Sevier orogeny. The detachment faults, which dip 9° to 12° southwest, are not offset by the normal fault zone at the range margin. Sliding was localized by the interception of west-dipping folded thrust surfaces by the range front normal fault zone. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Facies Across Paleozoic Miogeosynclinal Margin of Central Idaho

Middle Paleozoic rocks change facies from east to west across central Idaho reflecting sedimentation in different environments of the Cordilleran geosynclinal complex and its eastern margin. A thin cratonic assemblage of Upper Devonian Jefferson Dolomite, punctuated by local diastems, unconformably oversteps Ordovician Kinnikinic Quartzite and Precambrian Belt strata in southwestern Montana and in the Beaverhead Range along the Idaho-Montana border. West of the southern Lemhi Range the importance of the Devonian regional unconformity diminishes and variable amounts of Upper Ordovician Fish Haven and Silurian dolomites are preserved below Jefferson Dolomite. The basal quartzite-carbonate succession of Kinnikinic Quartzite and Fish Haven, Laketown, and Jefferson do omites thickens markedly in the Lost River Range toward the west. This miogeosynclinal succession is replaced farther west in the Wood River region by Lower Ordovician to Silurian graptolitic shale, chert, and quartzite, the Phi Kappa-Trail Creek sequence of eugeosynclinal affinity. About 3,500 feet of interbedded shaly limestone, dolomite, shale, and quartzite of the Middle-Upper Ordovician Saturday Mountain Formation and the Silurian Laketown Dolomite are present in the Bayhorse region and appear to be transitional in facies between the time-equivalent quartzite-dolomite sequence on the east and the graptolitic shale-chert-quartzite sequence on the south. Since newly measured sections imply approximately north-south facies boundaries and thickness trends, the graptolitic shale-chert-quartzite sequence in the Wood River region lies due north and on depositional trend with transitional facies in the Bayhorse region. This eastward invasion of the graptolitic shale-chert-quartzite sequence into the miogeosynclinal carbonate belt is attributed to thrusting as has been demonstrated for corresponding facies contrasts in Nevada. Contrary to classical concepts of geosynclinal sedimentation, most of the middle Paleozoic detrital rocks on the west side of the miogeosynclinal carbonate belt and intertongued with the carbonates are of quartz sand and mature detrital fines apparently derived from eastern cratonic sources rather than from unknown orogenically active borderlands or volcanic island arcs on the west. In contrast, late Paleozoic orogenic movements in the eugeosynclinal belt caused uplifts from which a thick wedge of coarse detritus forming the Milligen and Wood River Formations spread eastward to intertongue and grade into finer clastics and carbonates of the Brazer Limestone near the craton margin. Late Paleozoic orogenic activity in central Idaho represents a northern continuation of the Antler orogeny of Nevada. The Antler orogeny thus had extremely widespread and profound effects on tectono-stratigraphic patterns of the Cordilleran geosyncline: for the first time in the Paleozoic history of Idaho and Nevada it replaced the craton as a principal source for detrital sediment; in Idaho, the orogeny brought to a close the eugeosynclinal episode of essentially depositional continuity extending from at least early Ordovician to late Devonian. End_Page 569------------------------------

GEOLOGY OF THE BORAH PEAK QUADRANGLE, IDAHO

GEOLOGY OF THE BORAH PEAK QUADRANGLE, IDAHO