Younger Sedimentary Rocks Research Articles

Realms of Permian Tectonism and Sedimentation in Western Utah and Eastern Nevada

Realms of sedimentation of Permian rocks include basins, troughs, platforms, and shelves within or adjacent to the Cordilleran miogeosyncline. Peripheral tectonic uplands (Antler and Sonoma orogenic belts on the west, Utah-Wyoming and other shelves on the east), as well as intrageosynclinal positive areas (Northeast Nevada high, Western Utah high, Southern Nevada high, Emery uplift, and others), varied in degrees of tectonism and thus provided different types of detritus and material removed in solution to accumulate in the several depocenters. Oquirrh, Wood River, Bird Spring, Ely, Hamilton-Elko, Ferguson, Pequop-Diamond Creek, Montello-Sublett, Ruby, and Park City basins are the more negative parts of the geosyncline, whereas several shelves and the Riepe Spring, Callvi le, Pakoon, and Kaibab platforms identify the less negative repositories. Starved basins of relatively short geologic duration were present locally. The study area, embracing western Utah, eastern Nevada, and a part of southern Idaho, is about 300 mi (483 km) wide in an east-west direction and about 525 mi (845 km) long north-south. The Permian includes slightly more than 17,000 ft (5,182 m) of sedimentary rocks in northwestern Utah, but thins to featheredges toward the orogenic belts on the west and the craton on the east. Most basinal accumulations exceed 5,000 ft (1,524 m), and many aggregate 6,000-10,000 ft (1,829-3,048 m). Rocks include a vast spectrum of limestone, dolostone, orthoquartzite, siltstone, sandstone, mudstone, gypstone, redbeds, and minor shale. They are of Wolfcampian, Leonardian, and Guadalupian ages. Fusulinids and some corals are abundant and are excellent guide fossils in Wolfcampian and Leonardian rocks, w ereas mollusks (including some ammonoids), brachiopods, sponges, and conodonts have stratigraphic value in younger sedimentary rocks. Conodonts in particular are of index and correlation value in Guadalupian rocks. During Wolfcampian time a thick sequence of orthoquartzite and shelly limestone accumulated in the Oquirrh, Wood River, and Hamilton-Elko basins, whereas bituminous carbonate rocks formed in the Ferguson basin. Clean carbonate sediments and various arenites typified the shelves and platforms. The Leonardian was a time of diversification into deeply subsiding troughs, basins, and areally extensive shelves and platforms; orthoquartzite, limestone, dolostone, some evaporites, redbeds, and related sediments formed. During Guadalupian time basinal carbonate rocks accumulated locally. Very cherty mudstone and carbonate sediment formed in other depocenters, whereas patch reefs, redbeds, sandstone, and evaporites were deposited in other depositional realms. Ochoan rocks, as identified elsewhe e by certain ammonoids and advanced fusulinaceans, are not recognized in the eastern Great Basin, but it cannot be stated with assurance that they are absent. Lower Triassic nonmarine (and marine) rocks disconformably overlie Permian rocks in several places within the study area. Oil is produced in limited quantity from Permian rocks within the study area in Utah, and hydrocarbon shows in wells have been very common. This vast area, however, has not been tested adequately. It is a structurally complex area, and exploration for oil and gas will be hazardous and costly.

Some Age Relations and Structural Features of the Precambrian Volcanic Terrane, St. Francois Mountains, Southeastern Missouri

Precambrian rocks of the St. Francois Mountains consist mostly of silicic ash-flow tuff and intrusive granite. These rocks were formed during two igneous episodes occurring 1415 m.y. ago and 1320 m.y. ago, as determined by whole-rock Rb-Sr measurements. A major volcanic subsidence structure, the Taum Sauk Caldera, displaces rocks of the older group but is intruded along ring fractures by a granite of the younger group. These rocks may be the exposed part of a much more extensive Precambrian volcanic terrane, which is now buried under younger sedimentary rocks.

The effects of Late Triassic and Quaternary tectonic movements on the geomorphological evolution of Brunei and adjacent parts of Sarawak

Quaternary folding, faulting and tilting movements combined with probable compaction of thick, geologically young sedimentary rocks have fundamentally controlled the geomorphological evolution of Brunei and adjacent parts of Sarawak. Areas underlain by anticlinal structures have been up-arched, raised beaches of probable late Mid-Pleistocene age have been faulted and tilted, and drainage has been affected by recent downwarping. DISCUSSION : Reference was made to the present aseismic condition of the area. J. Sutton pointed out that it was difficult to explain this when one considered the abandant evidence for Quaternary warping and uplift. P. H. Stauffer asked about the age of the latest drop in sea level, which gave rise to Recent beach ridges. The speaker replied that there was no direct evidence, but radiocarbon dates indicated that sea level about 5,000 years ago was several feet higher than at present. J. Sutton asked whether the rate of movement along faults in late Tertiary times could be measured. The speaker replied that the movements could not be accurately dated in the Pliocene, but one terrace had tektites and was formed about 700,000 years ago.

Regional Precambrian Tectonics and Stratigraphy of Rocky Mountains with Emphasis on Wyoming Province: ABSTRACT

The most ancient rocks of Precambrian age in the Rocky Mountains are in the Wyoming province. These rocks are in Wyoming and adjacent parts of Montana and South Dakota, and may include rocks older than 3 b.y. The older rocks of this province probably are granitized metasedimentary rocks that have been deformed severely and show no evidence of a regional structural pattern. Younger metasedimentary rocks, including iron formations, are in northeast-trending synclinoriums, but even these units are older than 2.5 b.y. Most areas studied in the Wyoming province have had an extraordinarily complex structural history and many areas show evidence of more than one episode of deformation; several areas have northwest fold systems and shear zones that disrupt earlier structure. The Wyoming province may be bordered on all sides by younger rocks or rocks affected by deformation after 2.5 b.y. Miogeosynclinal rocks of possible middle Precambrian age are along the southeastern border of the province. These rocks may be facies of metasedimentary rocks in Colorado that have been metamorphosed in an event of ~1.7 b.y. Evidence for middle Precambrian metamorphic events also has been found in South Dakota, Nebraska, and Montana. These events cannot be related to regional tectonic trends. For example, Colorado structural trends are east-northeast and northeast, whereas in the Dakotas and Nebraska trends are north-northwest. Precambrian rocks that are younger than middle Precambrian are primarily west and southwest of the Wyoming province. These include Beltian metasedimentary rocks in Idaho and Montana, and probable Beltian and younger sedimentary rocks in Utah and Nevada. In some areas Beltian metasedimentary rocks have been deformed several times; north-northwest to northwest structural patterns appear in many areas. Some Beltian metasedimentary rocks are probably older than ~1.2 b.y. Although fragmentary evidence based on partial mapping of the 10% outcrop area of Precambrian rocks in the Rocky Mountains does not allow establishment of firm regional tectonic patterns or make satisfactory correlations of ages and tectonics, evidence to date suggests a remarkably complete sequence of Precambrian rocks may be present from rocks older than 3 b.y. to rocks of late Precambrian age. End_of_Article - Last_Page 1902------------

Precambrian Rocks and their Relationship to Laramide Structure along the East Flank of the Bighorn Mountains near Buffalo, Wyoming

Research Article| March 01, 1961 Precambrian Rocks and their Relationship to Laramide Structure along the East Flank of the Bighorn Mountains near Buffalo, Wyoming RICHARD A HOPPIN RICHARD A HOPPIN Dept. Geology, State University of Iowa, Iowa City, Iowa Search for other works by this author on: GSW Google Scholar Author and Article Information RICHARD A HOPPIN Dept. Geology, State University of Iowa, Iowa City, Iowa Publisher: Geological Society of America Received: 16 Jun 1959 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 Copyright © 1961, 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 (1961) 72 (3): 351–367. https://doi.org/10.1130/0016-7606(1961)72[351:PRATRT]2.0.CO;2 Article history Received: 16 Jun 1959 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 RICHARD A HOPPIN; Precambrian Rocks and their Relationship to Laramide Structure along the East Flank of the Bighorn Mountains near Buffalo, Wyoming. GSA Bulletin 1961;; 72 (3): 351–367. doi: https://doi.org/10.1130/0016-7606(1961)72[351:PRATRT]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 Precambrian crystalline rocks and younger sedimentary rocks were involved in Laramide deformation in the western part of the United States. Near Buffalo, Wyoming, two high-angle dextral faults striking N. 10° E. cut both the upturned sedimentary rocks and the crystalline basement. As this trend does not correspond to directions of transcurrent faulting expected with east–northeast-west–southwest compression (indicated by the north–northwest-trending Clear Creek thrust and upturned sedimentary rocks), the writer studied Precambrian rocks to see if basement structure controlled the strike of the N. 10° E. faults.The Precambrian complex consists of quartz-biotite-plagioclase gneiss and migmatite with minor hornblende gneiss and amphibolite. These rocks are greatly deformed and partly granitized. Mafic dikes and small ultramafic bodies cut the complex. Early foliation and layering are obscured by later shear fracturing. Three prominent directions of high-angle fractures are N. 10° E., N. 45° E., and N. 75°–80° W.In the sedimentary rocks, N. 45° E. and N. 75° E.–N. 75° W. fracture sets are well developed; the N. 10° E. set is poorly developed.The pronounced development of the N. 10° E. fractures and shear zones in the Precambrian rocks and absence of these structure trends in the sedimentary rocks suggest that these fractures and shears were formed during a Precambrian deformation and provided zones of weakness which controlled Laramide tear faulting. Three diabase dikes in the Precambrian rocks between the faults also follow this direction.The other two trends cutting both the gneisses and the sedimentary rocks are probably Laramide in age, although an east-west dike and a northeast-trending dike in the south end of the area suggest that movement was reactivated along older Precambrian fractures. 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.

GEOLOGY OF THE MAYAGÜEZ AREA, PUERTO RICO

The Mayaguez area forms the southwestern corner of Puerto Rico, west of 67° W. and south of 18° 15′ N. One-third of the 640 square kms is covered by thick alluvium. Unconformities separate a basal complex, two sequences of highly folded igneous and sedimentary rocks, and a younger sequence of gently dipping sedimentary rock. The basal Bermeja complex contains serpentinite, silicified porphyritic volcanic rock with some sedimentary rock, and minor spilite, amphibolitized spilite, and amphibolite. It is exposed chiefly in some anticlinal cores in southwestern Puerto Rico. Limestone, mudstone, andesite, and basalt form the older folded sequence. The Rio Loco formation, bronzite andesite porphyry in part with pillow structures, was extruded perhaps in the Cenomanian. The Mayaguez group includes most of the rocks in southwestern Puerto Rico: the Yauco mudstone, Parguera limestone, Brujo limestone, Melones limestone, Maricao basalt, Sabana Grande andesite, and El Rayo volcanic rocks. The maximum possible age range is Turonian to Maestrichtian. The group ranges in thickness from about 800 m in the south to 3800 m in the north, and it varies in lithology from limestone in the south to mudstone and volcanic rock in the north, indicating a volcanic center to the north during that time. The second folded sequence contains andesitic volcanic rock, bedded tuff, and massive limestone. The San German formation (Maestrichtian) includes andesite, the Cabo Rojo agglomerate member, and the Cotui limestone member. The Jicara formation, massive limestone and bedded tuff, is Paleocene; there is one exposure of an unnamed ? Eocene marl. Post-Eocene limestone and conglomerate are also exposed in the area. The structure of the basement complex is obscured by its massiveness and by the cover of younger rocks. Two major deformations have affected the rocks of southwestern Puerto Rico since Cenomanian to Santonian time. In the Maestrichtian, the first of these formed folds with a N. 60° W. trend, asymmetric or overturned to the south. Near the south coast the folding of thin Mayaguez group rocks was probably influenced by trends in the Bermeja complex which caused deviations in the regional trends and also some overturning to the north. The San German formation, deposited unconformably on the eroded surface of the folded Mayaguez group, contains large allochthonous blocks of older and contemporaneous rocks. These blocks, up to 2 km by 1 km in exposure, were deposited by slumping or sliding due to gravity within and at the base and top of the San German formation near Lajas and San German. Most rocks in the blocks are extremely contorted and contain deformed Foraminifera. The San German and Jicara formations and perhaps the ?Eocene marls were deformed into gentle open folds trending east in the area covered by this report. Oligocene, Miocene, and younger sedimentary rocks have been tilted and uplifted. Large east-west left-lateral transcurrent faults cross the area, offsetting and offset by two sets of transverse faults (N. 45° E., N. 20° W.): most faults are probably Maestrichtian to Oligocene, although minor faulting has continued to the present. Dikes and sills of quartz diorite porphyry and mica-quartz dacite porphyry intrude the ?Maestrichtian San German formation and older units. A diorite plug cuts the Bermeja complex, and a granodiorite plug intrudes the Mayaguez group.

Geology of Mackinac Straits in Relation to Mackinac Bridge

The construction of Mackinac Straits bridge has provided new data on the Paleozoic and Pleistocene history of the Mackinac region. The bedrock includes carbonates, chert, shale, and gypsum of late Silurian and middle Devonian age. Leaching of salt in the Pointe Aux Chenes (Upper Silurian) formation permitted the collapse of overlying rocks and produced the Mackinac breccia, but brecciation was not so intense or of such great magnitude as suggested in earlier studies. The breccia has been reconsolidated by loading under younger sedimentary rocks, recemented by secondary calcite, and perhaps additionally compacted by loading under glacial ice. The breccia has a bearing capacity considerably in excess of the load imposed by the bridge. Glacial deposits above bedrock are till and lacustrine clays of the Valders glacial substage, although older glacial deposits occur on the northern sides of the submerged Mackinac River gorge and a tributary channel. A buried sea stack encountered in probing indicates a level ...

Aeromagnetic Study of Copper River Basin, Alaska: ABSTRACT

An aeromagnetic survey was made of approximately 6,000 square miles of the Copper River Basin, Alaska, in 1954 and 1955. North-south flight lines spaced one mile apart were flown from Latitude 61°45^prime to 63°00^prime. The eastern and western borders of the surveyed areas are at Longitudes 145°00^prime and 147°22^prime. The magnetic patterns closely parallel the generally east-west arcuate geologic grain and seem to be correlative with lithology and with geologic structure. Outcropping areas of volcanic rocks are reflected by the configuration of the magnetic contours. A large area of low-amplitude magnetic anomalies extends from the Chugach Mountains north to about Latitude 62°30^prime. This area may possibly outline a structural basin of Tertiary age superimposed upon a depositional and structural trough of Jurassic and Cretaceous age. Anomaly-producing rock masses in this area are estimated to be a mile or more beneath the surface and are interpreted to be most deeply buried beneath the southern part of the Copper River Basin. The magnetic data suggest that lower Jurassic volcanic rocks exposed in the Talkeetna and Chugach mountains underlie the marine and non-marine sedimentary rocks of the southwestern part of the surveyed area. The change in the magnetic pattern at the northern front of the Chugach Mountains is caused by a contact between these volcanic rocks and the younger sedimentary rocks on the north. The magnetic data suggest that the Wrangell lavas of Tertiary and Quaternary age are present at shallow depths beneath the basin in the vicinity of Mount Drum. End_of_Article - Last_Page 219------------

The igneous rocks of the Kelso District

Inroduction. In early Carboniferous times an extensive area of volcanic activity stretched from the Solway Firth north-eastwards to the neighbourhood of Greenlaw and Duns. The igneous rocks to be described in the following pages are the eroded relics of the northern end of this volcanic belt. Because of post-Carboniferous folding, lava flows at the present day from a U-shaped outcrop separating older and younger sedimentary rocks at the south-west end of a synclinal trough. As the town of Kelso is situated within the syncline, these lavas have long been known as the ‶Kelso traps.″ Previous Geological Work. The igneous rocks of the Kelso district attracted a certain amount of attention in the early days of Scottish geology, but have on the whole been much neglected until recent years. One of the earliest accounts is that of David Milne, later known as David Milne-Home (1837).1 Milne’s paper was accompanied by a small-scale coloured geological map on which the limits of the Silurian, Upper Old Red Sandstone, and Carboniferous sediments are shown with some degree of accuracy. Most of the well-exposed igneous rocks are also indicated. James Nicol made a further contribution to our knowledge of the Kelso traps (1847). His coloured map shows in a general way the south-west end of the Kelso syncline, with a U-shaped outcrop of lavas enclosing Carboniferous sediments. Sir Archibald Geikie, in one of his early contributions to Scottish geology (1863, pp. 37, 47), described a few small outcrops of lava and tuff that occur in