Tertiary Tectonics Research Articles

Paleomagnetic results for Eocene volcanic rocks from northeastern Washington and the tertiary tectonics of the Pacific Northwest

The direction of remanent magnetization for 102 sites in Eocene volcanic and volcaniclastic rocks of the O'Brien Creek Formation, Sanpoil Volcanics, and Klondike Mountain Formation suggests approximately 25° of clockwise rotation of a 100 by 200 km area in northeastern Washington. The volcanic rocks consist chiefly of rhyodacite and quartz latite flows, with intercalated ash flow tuff and volcaniclastic layers. These rocks have been sampled at 102 sites distributed among five volcanotectonic depressions: the Toroda Creek, Republic, Keller, and First Thought grabens and the Spokane‐Enterprise lineament. The volcanic rocks probably range in age from 55 m.y. to about 48 m.y., and the 50‐ to 48‐m.y.‐old volcanic rocks within this suite appear to be rotated as much as the older rocks. Previous investigators have shown that 40‐m.y.‐old and younger plutonic rocks of northwestern Washington are not rotated; hence we infer that the north‐central Washington rocks were rotated to their present declination between 48 and 40 m.y. B.P. (during the middle and/or late Eocene). During early Eocene time this region was extended in a westward direction through crustal necking, gneiss‐doming, diking, and graben formation. Internal deformation of the region related to this crustal extension was extreme, but most bedrock units that were formed concurrent with the crustal extension were probably in place prior to the rotation; hence we infer that the rotation was chiefly accommodated by movement on faults peripheral to the sampled area. Faults active during Paleogene time appear to define boundaries of a triangular crustal block (the Sanpoil block), encompassing much of northeastern Washington, northern Idaho, northwestern Montana, and adjacent parts of British Columbia. The faults include the Laramide thrusts of the Rocky Mountain thrust belt, the strike‐slip faults of the Lewis and Clark line, and strike‐slip faults of the Straight Creek‐Fraser zone. We suggest that during early Eocene time the Sanpoil block was extended westward through crustal necking and dilation and then during the middle Eocene was rotated clockwise and thrust over the craton in a final stage of Laramide thrusting. The “motor” driving these deformations presumably was interaction of North America with oceanic lithosphere off its western margin; such interaction probably involved right‐oblique underthrusting and dextral shear.

Perspectives on World-Class Carbonate Petroleum Reservoirs: ABSTRACT

A synthesis of geologic attributes and reservoir properties is provided for 41 carbonate petroleum fields. From throughout the world, 55 scientists developed detailed case studies of carbonate reservoirs ranging in age from Ordovician to Miocene and in size from 1.7 × 103 to 32.0 × 109 bbl initial oil in place (IOIP). The objective was to focus on the detailed depositional and diagenetic history of a significant number of carbonate reservoirs, and secondarily to characterize their petrophysical evolution and reservoir volumetrics. An attempt was made to develop a complete anatomy of each field, which includes among many other attributes: regional paleosetting, tectonics, entrapping facies, source rocks, reservoir dimensions, and fluid data. Using a chronological arrangement, broad trends through time become evident. A progression of reservoir types occurs through the Phanerozoic, from peritidal and subaerially exposed facies in Paleozoic examples, through a long-term sequence of shallow-shelf sands and reefs, to relatively deep-marine facies in the Cretaceous and Tertiary. These last range from periplatform debris flows to deep-shelf pelagic chalks and deep-basinal mixed lithofacies that have been diagenetically altered, mainly to dolomite. No trends are seen, however, in the occurrence of pinnacle or other reefs through the Phanerozoic. Many of the largest fields occur in Tertiary mobile belts and other regions affected by Tertiary tectonics, principally in carbonates of Cretaceous to Miocene age. Furthermore, at least nine of the largest fields owe their reservoir productivity largely to fracturing, and at least ten smaller fields involve some fracturing. In contrast, the great number and diversity of reservoirs of shallow-epeiric, platform, peritidal, and sabkha origins are also evident, with reserves between 70 and 700 × 106 bbl IOIP. Shallow reef-mound, atoll, or pinnacle reef fields of large magnitude, all in carbonates of phototropic, warm-water, marine origin, are common over structures, particularly those related to subjacent salt diapirs. Non-salt-supported shallow shelves and reefs have smaller fields of less than 200 × 106 bbl IOIP. Future requirements include much more knowledge about (1) the extent, diversity, and recognition of deep-marine carbonates; (2) the frequency, size, orientation, and contribution to reservoir productivity of fractures; and (3) a large information base, generated by postmortem studies of the vast number of reservoirs which are destined to become candidates for supplemental recovery methods. End_of_Article - Last_Page 148------------

Seismic Stratigraphy and Cenozoic Evolution of West Sumatra Forearc Basin

Late Tertiary (Neogene) sediments deposited in the Sunda forearc reveal the stratigraphic and structural evolution of this active plate margin. A dense grid of multichannel seismic reflection data and information from 17 exploratory wells were used to establish a detailed seismic-stratigraphic framework of the forearc region from 0° to 6°N. Several important tectonic cycles are recognized: Paleogene orogeny, Neogene subsidence, and late Tertiary tectonism. Superimposed on these regional tectonic events are three major transgressive-regressive cycles of sedimentation related to changes in sea level and provenance. Paleogene and older metasedimentary and metamorphic rocks comprise basement beneath the landward (inner) margin of the forearc basin. Both basement rocks and lower Tertiary sedimentary rocks were deformed and eroded approximately 25 to 30 Ma. The continental shelf was exposed to subaerial erosion, and basin deposits were restricted offshore, coincident with a worldwide lowstand of sea level in the Oligocene. The Paleogene orogeny probably occurred prior to the erosional event that cut the prominent angular unconformity on the shelf. The Neogene history of forearc basin development is characterized by subsidence and nearly continuous sedimentation. A basal transgression began in latest Oligocene time and culminated in the middle Miocene. Alternating sequences of limestone and shale comprise two second-order cycles of sedimentation that are superimposed on an overall transgressive event. A major regressive sequence followed in the Pliocene, owing to an influx of siliciclastic clay, silt, and sand derived from Sumatra. Sedimentation rates were high, and large volumes of terrigenous material were deposited in deltaic systems on the shelf. The shelf-slope break prograded basinward nearly 10 km (6 mi) through lateral accretion and aggradation during a relative highstand or stillstand of sea level.

Fluvial sedimentation on a quivering craton: Influence of slight crustal movements on fluvial processes, upper Jurassic Morrison formation, western Colorado plateau

One of the most important challenges facing the fluvial sedimentologist is identification of processes outside the stream channel that influence deposition of fluvial sediments. Detailed studies in the lower sequence of the Salt Wash Member (Morrison Formation, Upper Jurassic) demonstrate that crustal deformation at the site of deposition may considerably influence braided-stream processes. Late Jurassic crustal movements in the western part of the Colorado Plateau are interpreted largely from thickness variations and facies distribution, but other features such as vertical repetition of facies, coincidence with at least parts of present-day folds, and the geographic distribution of bedding parameters measured in the fluvial deposits, are also used as corroborating evidence of syndepositional tectonism. These features indicate that several of the large uplifts and basins in the region as well as some of the smaller folds within them were actively moving during deposition of the lower sequence. Tectonic activity altered the stream gradients, which in turn governed sinuosity, flow regime, energy levels, and sediment distribution. Cross-bedding studies indicate that reduced gradients within downwarped areas led to slight increases in sinuosity of the braided-stream channels and of the small sub-channels within them. The lowered gradients apparently resulted in a decrease in the depth of the channels and allowed the streams to flood more readily, producing abundant upper-flow regime horizontal laminations in the channel deposits. In addition, greater quantities of sediment containing higher proportions of sand were deposited in downwarped areas than in positive localities. The inability of the streams to transport bed load through downwarped areas indicates loss of stream energy. However, an increase in the quantity of upper-flow regime horizontal laminations in the same downwarped areas suggests that an increase in flow regime is not necessarily accompanied by an increase in energy levels, at least in regions of slight tectonic activity where the local configuration of the stream channels may change appreciably. Strata presently dip less than 2° throughout most of the region, and this relatively small amount of deformation reflects the combined effects of Late Jurassic, Cretaceous and Tertiary tectonism. This demonstrates that the amount of structural deformation at the site of deposition may appear to be insignificant, yet it can cause appreciable changes in the nature of braided-stream deposits.

California and Saudi Arabia--Geologic Contrasts: ABSTRACT

Assessing hydrocarbon futures in unexplored basins involves geology by analogy. These assessments are needed to help quantify the amount of oil and gas postulated. It is important for the geology and geologic history of known producing basins to be defined in some systematic way, so that their favorable or unfavorable attributes may be recognized, and subsequently looked for in untested basins. The California and Arabian analogs are important. Through 1978, approximately 265 fields were discovered in California, containing 22 billion bbl of oil, 53% being in the 10 largest fields, ranging in size from 0.6 to 2.4 billion bbl. These fields occur in several different sedimentary basins. Through 1978, about 50 fields were found in Saudi Arabia containing 206 billion bbl of oil, 78% in the 10 largest fields, ranging in size from 7 to 83 billion bbl. All these fields occur in one part of a single very large basin. The contrasts in field size distribution and in the total amount of oil present are explained by the dramatically different geology and geologic histories. California's surface geology is characterized by rare Precambrian, isolated Paleozoic, and widespread Mesozoic accreted terranes and intrusions, and by highly uplifted and depressed Tertiary sedimentary prisms bounded by widespread high-angle thrusting and strike-slip and normal faulting. Numerous families of medium to small anticlines and fault traps, commonly involving moderately dipping to overturned beds, have resulted from Tertiary tectonism, which segmented California dramatically. The sediments associated with the oil and gas are largely local fine to coarse-grained clastics, shed from nearby highlands, but with one important regional chert-limestone-dolomite sequence. Saudi Arabia is characterized by a broad Precambrian shield area, flanked on the east by very long, gently dipping cuestas of Paleozoic and Mesozoic sediments, with an upper thin veneer of nearly flat Tertiary strata. Most structures involving the Mesozoic and Cenozoic are large, but gentle and unfaulted, representing a passive reaction of the sediments to underlying mild basement distortion and/or movement of Cambrian salt, all occurring while the Arabian plate continued to subside and tip to the northeast. The sediments associated with the oil are largely widespread carbonates of uniform thickness, with one interbedded sandstone wedge, and some shale. The contrasts between California and Saudi Arabia oil fields and geology result from contrasting plate-tectonic settings and history. End_of_Article - Last_Page 1199------------

Tectonic Evolution of the Apennines: ABSTRACT

Italy's backbone is a fold-thrust belt of Cretaceous to Holocene tectonic age. It involves Paleozoic basement, thick Mesozoic carbonates, exotic terranes of western Mediterranean origin, and eastward migrating foredeeps. Foothills structures contain commercial mixtures of immature and mature gas. These structures and the giant Malossa field nearby encourage exploration. Plate motions, a quantitative tool in Apennine exploration, result from 2 components. Crustal coherence across the eastern Mediterranean invokes the motions between Europe and Africa, and Tertiary tectonics of the western Mediterranean add a local component. The Apennines are a collision belt with a polarity flip in the north and persistence in the south. Fossil arc material is scarcely recognized, but plate-size clastic sources include European foreland highs and Tethyan terranes in the north, and the Betic-Sardinian belt in the south. Recent volcanism occurs in 3 settings: arc, bent and fragmented foreland, and basin-range type extension. Refraction-seismic data suggest thrust repetitions of the Moho at odds with surface structure in polarity and location. In detail, these data are contestable, but their regional significance must be honored. It confirms estimates of stretching at Tethyan passive margins, flexing of visco-elastic foreland, 3-dimensional overlap of Europe, Alps, and Apennines, and, perhaps, crustal shear zones mapped at the surface. Style elements common to fold-thrust belts include ramps with decollements, duplexes, and blind thrusts. Interleaving thrust arcs suggest crustal control of ramps. Polyphase recumbent folds in several settings record the attaining of critical taper. Normal faulting is abundant and similar to the Idaho-Utah thrust belt. End_of_Article - Last_Page 798------------

Listric normal faulting and the reconstruction of the synmetamorphic structural pile of the Cyclades

Summary There are late, post-metamorphic faults on the Aegean island of Syros that are demonstrably listric normal. Breccias associated with these faults are identical to those of late low-angle faults elsewhere on the island. It is therefore proposed that these low-angle faults are the toes of listric normal faults. This provides a basis for delineating a structural succession prior to faulting in which apparently ‘allochthonous’ rocks were originally at a higher level in the pile. This is consistent with the observed structural succession on Syros. The highest structural units are greenschists with similar kinematic axes to those of the blueschists below, but with a contrasting deformation style. These greenschists may have been derived from the ‘roof’ of the convergence zone in which the blueschist metamorphism took place. Similar fault patterns can be inferred for many of the neighbouring islands, which are horst blocks. Many show peripheral ‘upper units’ of weakly- or non-metamorphic rocks. The ‘upper units’ are inferred to have been originally at a high level in a pile built up during early Tertiary tectonism and are not remnants of a far-travelled nappe emplaced in the Miocene.

Tectonic Implications of Tertiary Intrusion and Shearing within the Bitterroot Dome, Northeastern Idaho Batholith

The Bitterroot dome contains plutons of the northeastern Idaho batholith and their regionally metamorphosed country rocks. Several mesozonal to katazonal intrusions in the core of the dome have zircon U-Pb ages (lower intercept on concordia) which range from . Epizonal plutons in the northern Idaho batholith region have Eocene K-Ar ages. An extensive mylonite zone developed on the eastern margin of the dome during the latter stages of uplift. Zircon (lower intercept) ages from three sheared plutons in this zone are , and The fact that significant shallow to deep-seated intrusion and mylonitization occurred during Eocene time requires a careful evaluation of Early Tertiary tectonism in the northern Idaho batholith region. Cretaceous events appear to include multiple deformation, metamorphism, and intrusion of mesozonal to katazonal plutons into the evolving root zone of the northern Rocky Mountain overthrust belt. Early Tertiary events appear to include intrusion of mesozonal to epizonal plutons into the Late Cretaceous igneous-metamorphic complex and diapiric uprise of the Bitterroot dome accompanied by mylonitization on its eastern flank that was superimposed on the already existing thrust system.

The Phanerozoic development of the Kangerdlugssuaq area, East Greenland

This paper presents an up-to-date description of the state of knowledge on the post-Precambrian geology of the Kangerdlugssuaq area, which is a key area for theearly stages of continental break-up in the North Atlantic. The area is analogous to present-day Iceland but differs from Iceland in that continental crust is present and the erosional level is deeper. The area was affected by the Caledonian orogeny as revealed by the Batbjerg intrusion, which contains screens of Palaeozoic limestones and unique potassic rocks which relate it to the Assynt Province of Scotland. Basin formation in the early Cretaceous heralded a period of sedimentation and volcanism which formed deposits several kilometres in thickness. The basalts are believed to have been extruded just prior to anomaly 24 (i.e. 55 - 53 m.y. ago) which reaches the coast just north of this area. The basalts are overwhelmingly tholeiites of "plume" type and include picrites. They may be derived from two different mantle sources. Layered gabbroic intrusions which are penecontemporaneous with the basalts are widespread in the area and a number of ultramafic plugs also occur. Syenites, both under- and oversaturated, are the most voluminous rock types of the area at the present erosional level and are somewhat later. The syenites show abundant signs of contamination with the country rocks. The Gardiner complex is the eroded core of a nephelinitic volcano and contains melilite rocks and carbonatites. Related nephelinitic lavas are found in inland areas. In the area many dike swarms are recognized which vary from tholeiitic to strongly alkaline suites emplaced between ca. 55 and 35 m.y. ago and which give good evidenceof the magmatic and chronological development of the area. Tertiary tectonism includes three main elements: the well known coastal flexure, amajor dome centred on Kangerdlugssuaq and regional plateau uplift.

Tertiary Kenai Group, Cook Inlet, Alaska, Tectonic and Depositional Model Applied to Barranca Formation (Upper Triassic), Central Sonora, Mexico: ABSTRACT

The Barranca Formation contains important deposits of coal and, where metamorphism was more intense, some of North America's most valuable graphite reserves. Information derived from petroleum exploration supports a Tertiary model for the Cook Inlet basin that applies to the Barranca. Since a fore-arc basin has existed near Cook Inlet through the present time, the modern Cook Inlet could also be an analog of the Barranca basin. The Kenai Group in the Cook Inlet area consists of fluvial-deltaic, swamp, and estuarine sediments about 4,600 m thick that represent three sedimentation phases: (1) the Oligocene to Miocene West Foreland, Hemlock, and lower Tyonek formations contain conglomerate, graywacke, siltstone, tuff, basalt flows, and coal; (2) siltstone, shale, carbonate, and coal of the Miocene upper Tyonek and lower Beluga formations indicate lower energy deposition; and (3) the Pliocene upper Beluga and Sterling Formations are mostly coarse clastic rock. The three members of the Barranca Formation, which is over 1,500 m thick, indicate gross changes from high to low to high-energy deposition. The upper and lower members contain sandstone, conglomerate, minor shale, and coal, and enclose a middle member that consists of coal, nonmarine to shallow marine shale and siltstone, and some conglomerate and impure sandstone. The rocks within each member, and mainly within the middle one, indicate that shallow marine incursions interrupted fluvial and swamp sedimentation. Paleogeographic and tectonic similarities between the two areas suggest that detailed aspects of Cook Inlet sedimentary environments apply to the Barranca Formation. End_of_Article - Last_Page 542------------

Comments on Early Tertiary tectonism and lateritization

Comments on Early Tertiary tectonism and lateritization

Continental Margin Off Western Africa: Senegal to Portugal

About 22,000 km of continuous seismic-reflection, magnetic, and gravity profiles, 118 radiosonobuoy recordings, 98,000 km of geophysical profiles from previous investigations, 15 deep-sea-drilling logs, and many dredge samples served to reconstruct the history of the continental margin and adjacent deep-ocean floor between Senegal and Portugal. Initial structures of the margin south of Morocco formed by divergence when Africa and North America separated 180 m.y. ago. The margin off western Portugal had a similar origin when the Iberian Peninsula and North America separated about 80 m.y. ago. Between these two divergent segments the area of the Strait of Gibraltar formed by a combination of translation from 180 to 72 m.y. ago and plate convergence from 63 m.y. ago to the p esent, with convergence becoming more intense during the past 10 m.y. Oldest sedimentary rocks atop basement include an evaporite of Late Triassic to Early Jurassic age. When the apron deposited by upbuilding and outbuilding became thick enough, mobility of the evaporites deformed the overlying sediments especially north of the Canary Islands. Except off Morocco and the Strait of Gibraltar and possibly off southern Senegal the sedimentary blanket is dominantly calcareous, reflecting the general lack of fluvial influx. Included is a middle-Late Jurassic algal reef that constitutes the lower continental slope off Morocco. During Aptian-Cenomanian time the deep ocean off much of northwestern Africa had only sluggish bottom circulation, recorded by organic-rich sediments. A major hiatus in deep-ocean sedimentary rocks and in three prominent sedimentary ridges (off Madeira, near Agadir canyon, and north of Conception bank) probably was caused by temporarily intensified circulation. Tertiary tectonics modified the divergent margin south of Morocco by folding of shelf strata off the western High Atlas, emplacement of the Canary Island Ridge, folding of slope strata off Spanish Sahara, and uplift of the Cape Verde plateau. These orogenies also may have uplifted oceanic basement beneath the upper rise and formed the volcanic seamounts along this ridge. Maximum modification by Tertiary diastrophism occurred on the margin of translation-convergence near the Strait of Gibraltar. There, the convergence phase caused uplift of Gorringe bank. Plate convergence also deformed sediments atop oceanic basement, aided by the mobility of Triassic-Jurassic evaporites. More recently, probably because of uplift of the Iberian Peninsula during the Pliocene, well-stratified Miocene and younger deposits atop the deformed lower unit slid oceanward away from the peninsula, with the megaslide coming to rest against the Moroccan continental slope. Associated folding also involved the lower deformed sequence.

Tertiary Stratigraphy and Tectonism in Svalbard and Continental Drift

An arm of the North Atlantic seaway reached Svalbard during the Paleocene, either in advance of, or in response to, early drift of Greenland away from the Eurasian continental block. Initial Tertiary sediments in Svalbard were marine, littoral, and paludal clastics and coals formed during an oscillating northeastward transgression of the sea. Second and third depositional cycles followed consisting of marine clay units that grade upward into fine or, locally, coarse regressive sandstone. Through the early stages of the third depositional cycle (mid? Eocene) movements were epeirogenic, and transgressions were toward a land area in northeastern Svalbard. Although Greenland had been drifting away from Norway along the Spitsbergen fracture zone (dextral transform fault), ther is no evidence of contemporaneous tectonic interaction between the Greenland and Barents blocks. The third depositional cycle was brought to a close by an influx of clastic material from the west in response to rapid uplift either within or along the western margin of the basin. Continued uplift in the west provided a flood of detritus that eventually filled the basin with plant-bearing alluvial, fluviatile, and paludal sediments. Uplift culminated in upthrusting, folding, and local overthrusting of the central or western part of the Tertiary basin; only the northeastern part of the basin is preserved now in the strongly asymmetrical Spitsbergen trough. Tectonism was the result of Greenland pressing against the Barents block while moving parallel with it (transpression), and the resulting structures show dextral shear as well as compressional features. Subsequent parting of the G eenland and Barents blocks resulted in tensional stress with dextral shear (transtension) and the formation of large grabens filled with locally derived, coarse-clastic sediments within the uplifted western margin of the trough. Separation is thought to have been completed by latest Oligocene or possibly early Miocene time.

Geology and Petrology of the Cambria Felsite, a New Oligocene Formation, West-Central California Coast Ranges

Geologic mapping in the Cambria and Black Mountain areas, western San Luis Obispo County, California, has led to recognition of the two stratigraphically and petrologically distinct extrusive felsic igneous units: (1) the Obispo Formation; and (2) a new unit, named here the Cambria Felsite. The Obispo Formation was deposited above the Rincon Shale and below the Monterey Formation during middle Miocene time. The Cambria Felsite rests with angular unconformity on Franciscan rocks of Jurassic and (or) Cretaceous age, and occurs as clasts in the nonmarine Lospe Formation of Oligocene age. Textural and mineralogic intergradations exist between the Cambria Felsite and the nearby upper Oligocene hypabyssal volcanic necks, plugs, lava domes, and dikes of the Morro Rock–Islay Hill complex; this suggests that the Cambria Felsite represents an effusive equivalent of the Morro Rock–Islay Hill. Cambria tuffs are enriched in alkalis plus silica and are depleted in ferromagnesian constituents relative to samples of the Morro Rock type. Chemical contrasts in the two units probably arose either because of a winnowing of airborne crystals from the glassy shards or because of magma fractionation in the conduits followed by pyroclastic eruption of the upper portions of the melt columns. No obvious correlation exists between the two-stage silicic volcanism, separated by a 10-m.y quiescent interval, and middle Tertiary plate tectonics. However, generation of these igneous rocks was probably a thermal response of the western margin of the continental crust-capped Americas plate to underflow of the Farallon plate, resulting in Morro Rock and Cambria units, followed by a complex encounter with the East Pacific Rise, resulting in the Obispo Formation.

Tertiary plate tectonics and high-pressure metamorphism in New Caledonia

The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs.

Tertiary Tectonics of the White Pine-Grant Range Region, East-Central Nevada, and Some Regional Implications: Discussion

Tertiary Tectonics of the White Pine-Grant Range Region, East-Central Nevada, and Some Regional Implications: Discussion

Tertiary Tectonics of the White Pine-Grant Range Region, East-Central Nevada, and some Regional Implications: Reply

Research Article| January 01, 1970 Tertiary Tectonics of the White Pine-Grant Range Region, East-Central Nevada, and some Regional Implications: Reply E. M MOORES; E. M MOORES Department of Geology, University of California, Davis, California 95616 Search for other works by this author on: GSW Google Scholar R. B SCOTT; R. B SCOTT Department of Geology, Florida State University, Tallahassee, Florida 32306 Search for other works by this author on: GSW Google Scholar W. W LUMSDEN W. W LUMSDEN Department of Geology, Long Beach State College, Long Beach, California 90801 Search for other works by this author on: GSW Google Scholar Author and Article Information E. M MOORES Department of Geology, University of California, Davis, California 95616 R. B SCOTT Department of Geology, Florida State University, Tallahassee, Florida 32306 W. W LUMSDEN Department of Geology, Long Beach State College, Long Beach, California 90801 Publisher: Geological Society of America Received: 08 Jul 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1970, 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 (1970) 81 (1): 323–330. https://doi.org/10.1130/0016-7606(1970)81[323:TTOTWP]2.0.CO;2 Article history Received: 08 Jul 1969 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 E. M MOORES, R. B SCOTT, W. W LUMSDEN; Tertiary Tectonics of the White Pine-Grant Range Region, East-Central Nevada, and some Regional Implications: Reply. GSA Bulletin 1970;; 81 (1): 323–330. doi: https://doi.org/10.1130/0016-7606(1970)81[323:TTOTWP]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 No Abstract available 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.

Tertiary Tectonics of the White Pine–Grant Range Region, East-Central Nevada, and Some Regional Implications

The White Pine-Grant Range area is a 400 sq mile region located in east-central Nevada, east of the Antler erogenic front, and west of the Sevier-Laramide thrust belt. About 20,000 feet of Paleozoic rock are overlain by 3000 to 5000 feet of Eocene-Oligocene sedimentary and volcanic rocks, and 0 to 10,000 feet of Mio-Pliocene sedimentary rocks. The near concordance of Paleozoic and early Tertiary strata indicates that the major deformation of the area is post-Oligocene in age. Mesozoic tectonic movements were limited to the formation of gentle folds and high-angle faults of limited displacement. The structure of the area is dominated by north-trending folds, some overturned, which involve both Tertiary volcanic and Paleozoic rocks. These folds are cut by a series of low-angle faults emplacing younger rocks over older; six faults are present in the White Pine Range and two in the northern Grant Range. A series of complex discrete slide masses 1 to 3 miles long characterizes the southwestern Horse Range; a relatively unfaulted overturned Paleozoic section characterizes the southeastern Horse Range. Displacement along these faults increases from the center toward the ends of the ranges; the faults are not continuous throughout the length of the range, and probably do not represent features of a regional d ecollement. Relations suggest that deformation or movement on these faults was probably nearly surficial, partly a product of uplift of the ranges and partly the result of basement extension. Much observable movement took place during deposition of Mio-Pliocene sediments, accompanied by emplacement of gravity slide masses and monolithic breccia of Paleozoic and volcanic rock in the Mio-Pliocene sedimentary basin. Differences in intensity of folding and degree of low-angle faulting in the White Pine, Horse Range, and northern Grant Ranges suggest that these areas were deformed separately. The north-trending folds may be the result of gravity effects on the flanks of major uplifted blocks, but probably reflect a period of postvolcanic crustal shortening in this region.

Evolution tectonique des regions du Bas-Verdon

Abstract Fault folds, secondary fault complex, Tertiary tectonism, Triassic-Pliocene tectonic phases, France

Geologic History of Site of Uinta Basin, Utah: ABSTRACT

The Uinta basin in northeastern Utah includes an area of 9,300 square miles. The differential vertical movements which created the basin and its rim began in Paleocene or Eocene time, during the deposition of the Wasatch Formation. The synclinal axis of the basin trends easterly and is slightly convex northward. The basin is asymmetric with a broad gently-dipping south flank and a north flank which is up to 10 miles wide with beds near vertical and locally overthrust. The configuration of the Uinta basin is controlled in part by pre-existing structures and geologic trends, but much of the present rim is the result of Tertiary tectonics. The dominant tectonic factor in the development of the basin is the rise of the Uinta Mountains block and the simultaneous subsidence of the synclinal axis of the basin. This major flexure in the crust probably conforms to the edge of the late Precambrian trough in which the rocks of the Uinta Mountains block were deposited. This belt of Precambrian rocks was essentially dormant until Eocene when it began to rise from depths of about 16,000 feet below sea level to elevations of 7,000 to 13,000 feet above sea level. During lower Paleozoic the Uinta basin area was on a stable crust just east of the Cordilleran geosyncline. In the Pennsylvanian Period the Uncompahgre uplift formed a mountain range part of which now underlies the southeastern part of the present basin. This major tectonic feature had a northwest trend, and several small folds or faults with similar trends developed in the eastern part of the basin. These structures were gradually masked by Mesozoic sediments. Slight Tertiary upwarping and differential compaction allow some of these structures to be reflected as folds plunging into the eastern part of the Uinta basin. In Cretaceous time the Rocky Mountain geosyncline occupied the region and received clastic sediments from the Cordilleran geanticline in western Utah. In Late Cretaceous time easterly directed compressive forces resulted in folding and over thrusting at the western edge of the Uinta basin area and possibly also caused slight arching of the eastern edge. During Tertiary time western North America was elevated above sea level. Concurrent with this epeirogeny the mountain ranges and basins of the Rocky Mountain Region were developed by differential uplift. To the west of the Rockies the Basin and Range province was also elevated, and tilted fault-block mountains and valleys were created. This difference between the Rockies and the Basin and Range province reflects the difference in the Paleozoic between the stable block and the geosyncline. The Uinta basin was outlined in Tertiary time by the central part not being elevated as high as its rim. The northern sector of the rim was the most active in pushing upward. The eastern and southern sectors of the rim were formed by the stable elements supported by the Douglas Creek arch and part of the Uncompahgre block. The southwestern sector of the rim was formed by the San Rafael swell, a Tertiary anticline formed by subsidence of adjacent areas and probably localized by an upper Paleozoic positive trend. The western sector of the rim of the Uinta basin was created by the interplay of tilting of fault blocks above the eastern margin of the Paleozoic geosyncline and north-trending faults that developed over Mesozoic troughs which, in turn, were superimposed on the margin of the geosyncline. The structure of the Uinta basin is the result of regional uplift of a heterogeneous area of the crust which incorporated both the sturdy and the weak, or weakened, products of prior deformations. The absence of intrusive igneous rocks is striking. End_of_Article - Last_Page 1880------------