Rock Canyon near Provo, Utah County: A Geologic Field Laboratory

In Nevada and Utah, sedimentation in the Cordilleran miogeosyncline began before the appearance of Cambrian fossils and continued without orogenic interruption through the Triassic. During the Jurassic, deformation and regional metamorphism occurred in the western part of the miogeosyncline, and the area of sediment accumulation shifted onto the Colorado Plateau. A major source of clastic material appeared along the eastern margin of the Cordilleran miogeosyncline in Early Cretaceous time; this source supplied the sediments that filled the Cretaceous to Paleocene Rocky Mountain geosyncline. Clasts in the Cretaceous conglomerates show an inverted stratigraphy, reflecting successive exposure of older and older rocks in an evolving orogenic belt along the eastern side of the Cordilleran miogeosyncline. This source area was the Sevier orogenic belt, which had a history of deformation through most of the Cretaceous (Sevier orogeny). Decollement thrusts with displacements of tens of miles are the characteristic structures of the belt, but several large folds are also known. The largest thrusts are overlain unconformably by uppermost Cretaceous conglomerates. Thrusting in the Sevier orogenic belt had virtually ceased by the time the Laramide orogeny began east of the Sevier belt in latest Cretaceous time. Laramide mountains were the result of uplift of great blocks of crystalline basement along nearly vertical, reverse, and steep thrust faults. The Uinta arch, which intersects the Sevier orogenic belt almost at a right angle, is the only one of these basement uplifts closely involved with the deformation of the Cordilleran miogeosyncline. North-south-trending regional normal faulting of post-Oligocene age has broken up the orogenic belt so that it is not immediately recognizable on geologic maps. Arch ranges, intrusive domes, and gravity slides are additional complications of the Tertiary geology, but widespread Tertiary deposits, particularly Oligocene ignimbrites, make a paleogeologic reconstruction possible; thus, the Sevier orogenic belt can be viewed as it existed before the normal faulting.

Paleoseismic investigation at Rock Canyon, Provo segment, Wasatch Fault Zone, Utah County, Utah

Seismic mapping of shallow bedrock shelves in the hanging wall of the Wasatch fault

The mapped area, which includes the eastern part of the Richmond and the western part of the Naomi peak quadrangles, Utah-Idaho, is located in the central part of northern Utah and southeastern Idaho. It is located along the eastern side of Cache Valley and western side of the Bear River Range. Cache Valley is in the Basin and Range province and the Bear River Range is in the Middle Rocky Mountain province. The mapped area is about 8.6 miles long, in the north-south direction, and 7.8 miles long, in the east-west direction. The Mutual Formation of Precambrian age is the oldest stratigraphic unit exposed in the mapped area. It consists of purple and brown quartzite. The Brigham Formation of Early Cambrian age and the Langston Formation of Middle Cambrian age overlie the Mutual in stratigraphic succession. The Salt Lake Formation of Tertiary age unconformably overlies older rocks; it is also faulted against the Mutual Formation. A major landslide of Precambrian, Cambrian, and Ordovician formations is present in the southern part of the mapped area. It is unconformably overlapped by the Salt Lake Formation. The Lake Bonneville Group of late Pleistocene age is present in Cache Valley and overlaps older rocks along the western side of the Bear River Range. The Precambrian and Cambrian stratigraphic units, except for those of the landslide, dip eastward and form the western flank of the Logan Peak syncline. A small disharmonic asymmetrical anticline, in the Langston and Ute Formations of Cambrian age, indicates eastward movement. Two beddingplane faults locally eliminate the basal Naomi Peak Limestone Member of the Langston Formation. A major normal fault, which is nearly vertical, extends along the base of the Bear River Range. Another normal fault, which is probably nearly vertical, parallels the western edge of the foothills. The folding and bedding-plane thrust faulting involve eastward movement and occurred during the Sevier orogeny. This orogeny began during late Jurassic time and extended into the early part of the Tertiary Period. Basin and Range normal faulting began early in the Tertiary Period. The normal faults produced great relief between Cache Valley and the Bear River Range. The landslide surface is thought to have formed as a west-dipping thrust fault. Reversed movement on this fault, due to removal of support on the valley side, produced the major landslide. (58 pages)

In central Utah, the major pre-Mississippian unconformity is fairly well understood at most of the localities where it is recognized. However, the unconformity is more enigmatic in Rock Canyon of the central Wasatch Range. At this locality, dolomitization of most pre-Mississippian rocks obscures stratigraphic identification of Devonian and older units. The absence of any identifiable angular relationship further complicates resolution. Because of this, both identification of the stratigraphic level of the unconformity and, consequently, its magnitude remain controversial. Large-size dolomite samples taken in Rock Canyon at closely spaced intervals for the 3.6-m directly below definite Upper Devonian rocks yield microfossils, including conodonts, in the uppermost 1.6-m of that interval that indicate no unconformity exists between the Cambrian Maxfield Limestone and the Upper Devonian-Lower Mississippian Fitchville Dolomite at the horizon previously identified as unconformable. Rather, an unknown thickness of dolomitized Upper Devonian Pinyon Peak Formation and probable older rock (possibly Bluebell Dolomite and Victoria Formation) occurs between the top of definite Maxfield and base of the Fitchville. The identification of the unconformity horizon remains unknown. Our preliminary work outlines a promising procedure for future understanding of the magnitude and stratigraphic level of the unconformity.

In central Utah, the major pre-Mississippian unconformity is fairly well understood at most of the localities where it is recognized. However, the unconformity is more enigmatic in Rock Canyon of the central Wasatch Range. At this locality, dolomitization of most pre-Mississippian rocks obscures stratigraphic identification of Devonian and older units. The absence of any identifiable angular relationship further complicates resolution. Because of this, both identification of the stratigraphic level of the unconformity and, consequently, its magnitude remain controversial. Large-size dolomite samples taken in Rock Canyon at closely spaced intervals for the 3.6-m directly below definite Upper Devonian rocks yield microfossils, including conodonts, in the uppermost 1.6-m of that interval that indicate no unconformity exists between the Cambrian Maxfield Limestone and the Upper Devonian-Lower Mississippian Fitchville Dolomite at the horizon previously identified as unconformable. Rather, an unknown thickness of dolomitized Upper Devonian Pinyon Peak Formation and probable older rock (possibly Bluebell Dolomite and Victoria Formation) occurs between the top of definite Maxfield and base of the Fitchville. The identification of the unconformity horizon remains unknown. Our preliminary work outlines a promising procedure for future understanding of the magnitude and stratigraphic level of the unconformity.

Lithologically distinct coeval strata of Lower Cretaceous age occur in four northeasttrending belts in the Goodnews Bay and Bethel quadrangles, southwestern Alaska. The belts are, from southeast to northwest, the Buchia Ridge belt, Ungalikthluk belt, Mount Gratia belt, and Eek Mountains belt. The belts are largely bounded by thrust faults. Rocks in the Mount Gratia and Eek Mountains belts are stongly deformed and infolded with older rocks, whereas the Ungalikthluk and Buchia Ridge belts are mildly deformed and (except for intrusive rocks of Tertiary age) include only rocks of Early Cretaceous age. The Buchia Ridge belt is composed mainly of graywacke and related rocks defined as the graywacke of Buchia Ridge. This formation is exposed in a wedge-shaped area of about 350 km2 in the Goodnews Bay A-2, A-3, B-2, and B-3 quadrangles. The beds of this unit are deformed into a southeast-dipping homocline in a thrust sheet that is underlain and overlain by highly deformed older volcanic and sedimentary strata of Jurassic and Early Cretaceous(?) age. The graywacke of Buchia Ridge is estimated to be about 5,000 m thick. The lower part of the formation is thick-bedded graywacke, siltstone, and conglomerate; the upper part shale, shaly siltstone, and thin-bedded graywacke and calcarenite. The lower part contains abundant Buchia of Valanginian age; the upper part sparse Inoceramus and Belemnitesof Hauterivian age. If the section is not repeated by faults or folds, it is the thickest, least deformed section of Lower Cretaceous sedimentary rocks known in southwestern Alaska. The Ungalikthluk belt consists of isolated synclinal outcrop areas of limestone, greenish limy grit, and conglomerate overlain by noncalcareous graywacke and grit. Although the total outcrop area is no more that 4 km2 , these erosional remnants form a distinct belt northwest of the Buchia Ridge belt. Locally, Buchia crassicolis is found in the limestone, indicating that the Ungalikthluk sequence is coeval with the graywacke of Buchia Ridge. The Mount Gratia belt, up to 25 km wide and extending more than 120 km northeast from the central part of the Goodnews Bay B-5 quadrangle, is bounded on the southeast and northwest sides by southeast-dipping reverse faults. Rocks within the belt are strongly folded and cut by many faults. 1 2 CONTRIBUTIONS TO STRATIGRAPHY Stratigraphy in the Mount Gratia belt is not definitely known because of structural complexity, but in general consists of an upper section of thickbedded graywacke, shale, and other sedimentary rocks and a lower section of multicolored tuff and other volcanic rocks. Locally, there are small areas of Permian and Triassic rocks that are probably faulted in. The occurrence of Buchia crassicolis and radiolarians identified as forms of Early Cretaceous (Valanginian) age within the Mount Oratia belt again indicates contemporaneity with rocks in the other belts. The Eek Mountains belt, 2-25 km in width, extends northeastward about 75 km from the Goodnews Bay C-6 quadrangle. The belt encompasses a large anticline consisting of older rocks flanked by Cretaceous rocks. The rocks in the belt are strongly folded and commonly overturned northwestward. The Lower Cretaceous (Valanginian) section in the Eek Mountains belt consists of graywacke, shale, argillite, and conglomerate at least 1,000 m thick. The tuff and other volcanogenic rocks of the Mount-Oratia belt have not been identified within the Eek Mountains sequence. Buchia crassicolis has been found in thin calcareous beds and in pebbly sandstone at several places within the Eek Mountains belt, thus substantiating an age coeval with rocks in the other three belts.

The region is in the southwestern portion of the San Gabriel Mountains, north of Los Angeles, California. Stratigraphically it is composed of a section of Neogene rocks with some up-faulted older rock. The normal sequence as represented here is: Upper Modelo, unconformity; Pico, conformity; Saugus, angular unconformity; Quaternary terraces. The basement rock, composed largely of para-gneiss, schist and intrusive granite, has been faulted up from below. Its age is pre-Miocene, possibly pre-Jurassic. The structure of the region is characterized by faults of the dip-slip vertical or steeply normal type. Geologically the history of the region is: invasion of the sea during Miocene time, deposition of the Modelo formation, broad uplift and subsequent denudation; faulting at the opening of the Pliocene, a second incursion of the sea, deposition of the Pico formation; orogenesis north of the region here described followed by withdrawal of the sea in Upper-Pliocene time, deposition of the Saugus formation (Piedmont Deposit); active faulting and orogenesis at the close of the Pliocene; continuous erosion with short resting stages during the Quaternary.

The upper Tick Canyon area, approximately seven square miles in extent, lies between Agua Dulce Canyon and Mint Canyon in the easternmost pelt of the Ventura Basin in southern California. This area was mapped in detail on a scale of 1000 feet to one inch and the stratigrephic and structural relationships of the exposed rocks were established. The oldest rocks in the area are of highly metamorphosed metasedimentary and metavolcanic types, which are intruded by igneous bodies of presumed pre-Cretaceous age. This crystalline complex is in fault contact with the rocks of the Vasquez series, the oldest unit in a thick section of Tertiary sedimentary and volcanic rocks. The Vasquez series is perhaps Oligocene in age and was deposited under nonmarine conditions in an elongate trough of fault-block origin. The rocks are mainly fine-to coarse- grained elastic sediments. Interlayered with them are basaltic and andesitic flows and shallow intrusive masses, that form with the sediments a total section of about 4500 feet. This section thickens rapidly east of the area mapped. Overlying the Vasquez strata with a distinct angular unconformity is a series of conglomerates and siltstones of the late Lower Miocene Tick Canyon formation. This unit is approximately 900 feet thick, but thins rapidly to the west within the area under consideration. The Upper Miocene Mint Canyon formation, which also consists of nonmarine elastic sedimentary rocks overlies the Tick Canyon formation throughout the area. These two formations probably are separated by an unconformity, along which there may be local angular discordance of a few degrees. Almost flat-lying, Pleistocene stream deposits occur throughout the area at an elevation of several hundred feet above the present, newly alluviated valley bottoms. Some strike-slip faulting with northeasterly trend took place after Mint Canyon time, perhaps during the Pliocene epoch. This may be related to the San Andreas fault, which lies ten miles to the northeast. All folds and faults that involve the sedimentary beds probably can be related to adjustments taking place in the underlying crystalline rocks. The forces causing these adjustments probably were active throughout much of Tertiary and Quaternary time, and activities do not appear to have ceased as yet.

Recent stratigraphic studies in three widely separated localities in southeastern Idaho and western Utah have revealed a startling continuity of both individual rock units and of rock sequences over a distance of some 300 mi parallel to the strike of a late Precambrian and Cambrian depositional trough. Between 15,000 and 25,000 ft of beds were deposited in the axis of the trough, whereas only 1000 to 3300 ft of correlative rocks were laid down on the shelf to the east. In several areas a diamictite is present near the base of the sequence; this is underlain locally and overlain generally by argillites containing lenticular limestones and dolomites; these in turn are succeeded by quartzitic rocks containing a thick grayish-red to maroon unit—the Mutual Formation. In each area the sequence includes, at the top, quartzites typical of the basal Cambrian. Deposition in the basin was essentially continuous from late Precambrian into Cambrian time but was interrupted by uplift and erosion on the shelf. The hinge line of the ancient seaway is inferred to have coincided roughly with the present “Wasatch line,” but erosion prior to deposition of the Tintic Quartzite has removed most of the data needed to establish this with certainty. Rocks in each of the three areas described here in detail are regarded as allochthonous and appear to have been thrust eastward during the Sevier orogeny. A precise reconstruction of the sedimentary basin must therefore await not only additional stratigraphic studies in such areas as the Promontory Range of Utah and the Bannock and Malad Ranges of southern Idaho, but also final resolution of the structural events.

The objective of this study is to test models for the origin of widespread secondary magnetizations in the Mississippian Deseret Limestone. The Delle Phosphatic Member of the Deseret Limestone is a source rock for hydrocarbons, and modeling studies indicate that it entered the oil window in the Early Cretaceous during the Sevier orogeny. Paleomagnetic and rock magnetic results from the Deseret Limestone and the stratigraphically equivalent Chainman Shale in central and western Utah indicate that the units contain two ancient magnetizations residing in magnetite. Burial temperatures are too low for the magnetizations to be thermoviscous in origin, and they are interpreted to be chemical remanent magnetizations (CRMs). Fold tests from western Utah indicate the presence of a prefolding Triassic to Jurassic CRM. Geochemical (87Sr/86Sr, δ13C, and δ18O) and petrographic analyses suggest that externally derived fluids did not alter these rocks. This CRM was acquired at the beginning of the oil window and is interpreted to be the result of burial diagenesis of organic matter. A second younger CRM in western central Utah is apparently postfolding and is probably Late Cretaceous to early Tertiary in age. On the basis of the thermal modeling, the timing overlaps with the oil window. These results are consistent with a connection between organic matter maturation and remagnetization. Modeling of the smectite‐to‐illite transformation in the Deseret Limestone suggests a mean age prior to acquisition of both CRMs, although the range for illitization overlaps with the Triassic to Jurassic CRM. The results of this study support the hypothesis that pervasive CRMs can be related to burial diagenetic processes. In addition, paleomagnetism can be used to determine the timing of such processes, which can benefit hydrocarbon exploration efforts.

Geologic map of the Thistle quadrangle, Utah County, Utah - Insight into the structural-stratigraphic development of the Southern Provo salient of the Sevier fold-thrust belt

Field relations suggest that thrust faulting began in western Wyoming and eastern Utah with movement on the Absaroka thrust, possibly during the Late Cretaceous. It seems likely that the Darby thrust became active shortly thereafter. Intraplate deformation of the Absaroka package occurred during or after the Eocene, resulting in belts of folds and faults along the Commissary, Tunp, and Crawford trends. This Absaroka intraplate deformation resulted from compression produced by movement on the Ogden thrust to the west. The Ogden thrust is exposed along the Wasatch fault between Ogden and Salt Lake City, Utah and extends as far east as the Devil's Slide area, west of Croyden Utah. This thrust has not previously been recognized. The Precambrian crystalline rocks of the Wasatch Mountains are carried on the Ogden thrust along with Paleozoic and Mesozoic sedimentary rocks that crop out east of the range. The Willard thrust moved after the Ogden and initiated still farther to the west. The Willard includes Proterozoic and lower Paleozoic rocks not recognized on any of the more easterly thrust sheets. The unique occurrence of oil and gas within the Absaroka package is related to many factors including its initial geometry and the remigration of fluidsmore » associated with the post-Eocene modification of this geometry. The source of pre-Maestrichtian sediments to the Cretaceous Interior Seaway becomes problematic as a result of this analysis, as does the assumption that the seaway was a foredeep related to flexural loading by the thrust belt.« less

Stratigraphic and time-stratigraphic cross sections of Phanerozoic rocks, western Uinta Mountains through the San Pitch Mountains-Wasatch Plateau to western San Rafael Swell, Utah (Summit, Wasatch, Utah, Juab, Sanpete, and Emery Counties)

Miocene and Pliocene sedimentary and volcanogenic rocks drilled in Holes 467, 468, and 469 of Leg 63 resemble rocks of the same age that have been sampled from other parts of the southern California borderland. The purpose of this report is to compare in general terms the composition, thickness, and age of the preQuaternary rocks drilled at these sites with rocks from two test wells, seafloor outcrops, and island areas. From these comparisons, inferences are made concerning the developmental history of the borderland. Emphasis is placed on the composition and origin of coarse clastic and volcaniclastic Miocene rocks. Because the stratigraphic sequences on the mainland shelf, in nearshore basins, and on parts of the northern Channel Islands are unlike the sections in the DSDP holes, they are omitted from most of the comparisons. From the DSDP cores, 275 samples, chiefly coarsegrained Miocene rocks, were selected and examined. Thin sections of 78 of these selected samples were studied. All available seafloor samples of volcanic and volcaniclastic rocks from the borderland north of 32 °N (exclusive of the mainland shelf and nearshore banks) were re-examined for this report (Fig. 1). Igneous rocks are classified according to petrographic determination of mineral content and not on geochemical analysis. Chronostratigraphic assignments follow the usage of Bukry (this volume). The upper Tertiary sections drilled in two deep stratigraphic test wells, one west of Point Conception (OCS-CAL 78-164 No. 1), the other at the southeast end of Cortes Bank (OCS-CAL 75-70 No. 1), are dissimilar in many respects to those in the DSDP holes. Though information on recently drilled deep exploratory wells on the southern part of Santa Rosa-Cortes Ridge and near Santa Barbara Island is proprietary, the location of these holes suggest that they spudded in middle Miocene or older rocks and penetrated stratigraphic sequences that are, for the most part, older than those in the DSDP holes. Stratigraphic sections of Miocene and Pliocene rocks on some of the islands are reviewed, as they provide possible analogues for subsea sequences that ordinarily are represented only by widely spaced, short cores.