Thick Conglomerate Research Articles

Cretaceous Basin-to-Shelf Transition in Northern Alaska: Deposition of the Fortress Mountain Formation: ABSTRACT

The Fortress Mountain Formation (Albian) is a sequence of shale, sandstone, and conglomerate exposed as isolated synclinal outcrops in the southern foothills province of the Brooks Range. The formation overlies a variety of severely deformed older rocks, particularly the Okpikruak Formation of Neocomian age. The unit records a significant change in the depositional architecture of the North Slope Cretaceous and is closely tied to the evolution of the Brooks Range orogenic belt. Detailed stratigraphic and sedimentologic studies of the Fortress Mountain Formation within the type region and at easternmost exposures have demonstrated a systematic change in lithology and bedding style. The lower 40% of the Fortress Mountain is transitional with the Torok Formation and is composed of thick (up to 2,000-m) intervals of gray to black shale with thin, rhythmically interbedded, fine-grained sandstone beds. This succession is interrupted periodically by allochthonous blocks of conglomerate and conglomeratic sandstone. The sequences record a transition from basin plain to slope sedimentation. The middle 30-40% of the formation is composed of thick conglomerate and conglomeratic sandstone lenses that thin toward the north and are arranged in multiple upward-coarsening se uences and megasequences. End_Page 660------------------------------ Regional dispersal patterns indicate these beds accumulated within the midfan environment of a northward-prograding submarine fan complex. The upper 20-30% of the Fortress Mountain rests above a conspicuous angular discordance and is composed of upward-fining channel sequences of conglomerate, sandstone, and shale. This phase of deposition records progradation of fan-delta and fluvial environments. The regional depositional architecture of the Fortress Mountain records the buildup and sedimentologic evolution of the Cretaceous shelf, which ultimately allowed progradation of overlying deltaic and interdeltaic complexes of the Nanushuk Group and related strata. End_of_Article - Last_Page 661------------

Evidence for Early-Middle Triassic faulting and possible rifting from the Helez Deep Borehole in the coastal plain of Israel

Summary A 600 m thick conglomerate, the Erez conglomerate, was penetrated in the Helez Deep borehole, drilled in the Coastal Plain of Israel. This conglomerate is underlain by a 40 m thick sandy shale of probable Early Triassic age, and is overlain by 190 m of Late Triassic peritidal dolomites. This sedimentary sequence is underlain by metamorphic Precambrian basement. The Erez conglomerate is polymictic, consisting of various types of carbonate fragments, of ages varying from Upper Permian to Anisian. The fragments are angular to subrounded, poorly sorted, ranging in diameter from fractions of a millimetre to several decimetres. The matrix consists of black argillaceous micrite, yielding palynomorphs of Scythian-Anisian age. It is suggested that the Erez Conglomerate is analogous to the thick, well-developed accumulation of polymictic conglomerates along the margins of the Miocene Suez and Plio-Pleistocene Dead Sea rifts, and thus indicating a major faulting phase and possibly an initial stage of rifting during Early-Middle Triassic times. Although an Upper Palaeozoic updoming prior to rifting may be considered, it is not a necessary postulate to explain the borehole data.

Cardium Formation at Seebe, Alberta--Storm-Transported Sandstones and Conglomerates: ABSTRACT

End_Page 644------------------------------The Upper Cretaceous (Turonian) Cardium Formation is one of the most productive oil-bearing formations in Alberta. As a result of detailed mapping of two outcrops near Seebe, Alberta, we have defined five coarsening-upward sequences within this formation. The sequences begin with bioturbated mudstones and coarsen into sandstones, commonly with conglomeratic veneers on top. In sequence 2, a 20-cm thick conglomerate has been molded into symmetrical gravel waves. The sandstones are dominated by hummocky cross-stratification, occurring in the upper parts of sequences 1, 2, 3, and 5. The implication is that these sequences terminate in water deeper than fair-weather wave base (10 to 15 m). The trace-fossil assemblage, dominated by abundant Zoophycos and long horizontal Rhizocorallium, suggests similar depths. Foraminifera recovered from sequences 3 and 4 comprise a highly diverse assemblage of agglutinated species, also supporting deposition below fair-weather wave base. In view of the physical and biologic evidence for deposition in a few tens of meters of water, and the total absence of medium-scale cross-bedding, we suggest that the entire Cardium Formation at Seebe was deposited below fair-weather wave base. The sandstones were emplaced by storm-generated density currents, the same storm both generating the flow and imprinting hummocky cross-stratification on the deposit. Finally, we suggest that the conglomerates were also moved rapidly seaward by density currents, there being no evidence for the traditional beach or transgressive lag interpretation of these rocks. End_of_Article - Last_Page 645------------

Conodonts from the March and Oxford Formations in the Brockville Area, Ontario

Conodont faunas from the March and Oxford Formations of the Brockville area, southeastern Ontario, are described. The specimens are assigned to fifteen species comprising eight genera.The Nepean sandstone, at the bottom of the Paleozoic section, has a thick conglomerate at its base; the overlying sandstones are burrowed and probably of marine origin.Basal March sandstones are blue–gray in color and have been extremely bioturbated. The higher standstones are orthoquartzites with minor burrowing. Both are probably offshore deposits.The Oxford Formation comprises sandy limestones and dolomites as the dominant lithologies. It was probably deposited on a tidal or intertidal flat.The conodont faunas indicate that the March Formation is probably late Tremadocian in age, and that the Oxford Formation is Arenig in age. The Nepean sandstone yielded no conodonts.The March and Oxford conodont faunas are correlated with those from the Columbia Icefields section, Alberta; the House limestone, western Utah; the El Paso Formation of Arizona; the Oneota and Shakopee Formations of the Upper Mississipi valley; and the St. George Formation, Newfoundland.Genera of European affinity are absent and a closer tie with contemporaneous continental North American faunas is suggested.The oldest occurrence of the genus Strachanognathus in this region is noted.

Cenozoic Deposits, Upper Magdalena Valley, Colombia

As much as 12,000 m of nonmarine Cenozoic deposit is preserved in the Upper Magdalena Valley between the Central and Eastern Cordilleras in southwestern Colombia. Near the end of the Cretaceous Period early Andean deformation uplifted the Central Cordillera. Concomitantly the sea began to retreat from the East Andean geosyncline whose axis lay along the site of the Eastern Cordillera. After withdrawal of the sea the latest Cretaceous and Paleocene Guaduas Formation, having an average thickness of 1,000 m, accumulated on a poorly drained lowland stretching eastward to the Llanos. It consists of drab, mottled, and reddish-brown mudstone, and dark-gray sandstone with abundant dark grains of Cretaceous chert and mudstone. Carbonaceous deposits are more common than in any other Cenozoic formation. During the Cenozoic Era a succession of disturbances generated four major alternations of coarse- and fine-grained deposits. The Central Cordilleran provenance persisted, but detritus also was derived increasingly from local sources within the basin and on the site of the Eastern Cordillera, and the Cretaceous sedimentary mantle progressively was stripped from basement blocks. Eocene and early Oligocene Lower and Middle Gualanday deposits, as much as 2,500 m thick, and the Oligocene(?) and early Miocene(?) Upper Gualanday and La Cira formations, as much as 2,000 m thick, constitute two depositional cycles of thick chert-pebble conglomerate overlain by drab, mottled, and reddish-brown mudstone. The third cycle comprises the late Miocene Honda Formation, as much as 3,000 m thick, and composed largely of arkosic and volcanic detritus in local alternations of conglomeratic channel sandstone overlain by floodplain mudstone. A volcanic-rich redbed facies in the upper part of the formation reflects waning accumulation on well-drained alluvial plains. The fourth cycle is the Pliocene(?) Mesa Formation, about 1,000-1,500 m thick, which consists of a lower and upper olygenetic conglomerate and a middle unit of volcanic debris derived from great cones on the Central Cordillera. The upper conglomerate shed largely from the Garzon massif at the southern end of the Eastern Cordillera records the last important aggradation of the region. During and after deposition of the Mesa Formation, the major Andean orogeny, accompanied by continued volcanism on the west, deformed the region and differentially uplifted the entire Eastern Cordillera. With onset of regional uplift, deep erosion produced the present relief.

Cretaceous beds at Coal Creek, Rangitata Valley

Abstract The Tertiary sequence in Coal Creek reported by Mason (1948) was recently re-examined and a thick greywacke conglomerate, not recorded by Mason, was found to form the apparent base of the sequence (Fig. 2a). The conglomerate is over 300 ft thick, consists predominantly of well rounded but poorly sorted, pale-green leached greywacke pebbles commonly ½ to 1 in. across, and contains several thin beds of fine sandstone and dark-grey carbonaceous siltstone up to 1 ft thick that yielded microfloras of late Cretaceous age (samples, S91/523, L2877; S91/524, L2878). Mr D. J. McIntyre, N.Z. Geological Survey (pers. comm.), places the age as probably Mata Series and definitely not older than Raukumara Series or younger than Mata Series.

Tertiary Rocks of Spitbergen

Tertiary Rocks of Spitbergen

Part I. Stratigraphy

The two outstanding achievements of Lapworth's work were the demonstrations, first, that previous stratigraphical arrangements included tectonicaUy duplicated and even triplicated parts of a general succession which, contrary to general belief, could be correlated with those of structurally less complicated areas; and secondly, that this assorted succession, estimated by him to be almost 3000 ft. thick, was equivalent to about 100 ft. of graptolitic shales exposed in the Central Belt of the Southern Uplands. These relationships are well summarized by Peach & Home (1899, pp. 82-3), who accepted Lapworth's succession with no more than minor revisions of formational thicknesses and the transference of the Balclatchie Mudstones, Grits and Conglomerates from the top of the Barr Series to the base of the Ardmillan Series. In effect, all the difficulties experienced by earlier geologists were shown to be due to an inadequate appreciation of the importance of fossil faunas and facies changes, not only in determining successions but also in resolving the structure of the region. Yet, paradoxically, Lapworth paid scant attention to either faunal or lithological changes when preparing his interpretation of the Caradoc sequences, mainly because he believed the Benan Conglomerate to be a reliable datum horizon (1882, pp. 551,659). By using the formation in this capacity he showed that three belts of limestones, exposed around Benan Hill, were not impersistent lenses within a thick conglomerate but simply one limestone member underlying the Benan Conglomerate and brought to the surface by folding. With regard to this particular section he was

UPPER DEVONIAN UNCONFORMITY IN CENTRAL UTAH

Research Article| February 01, 1959 UPPER DEVONIAN UNCONFORMITY IN CENTRAL UTAH J KEITH RIGBY J KEITH RIGBY DEPARTMENT OF GEOLOGY, BRIGHAM YOUNG UNIVERSITY, PROVO, UTAH Search for other works by this author on: GSW Google Scholar GSA Bulletin (1959) 70 (2): 207–218. https://doi.org/10.1130/0016-7606(1959)70[207:UDUICU]2.0.CO;2 Article history received: 07 Apr 1958 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J KEITH RIGBY; UPPER DEVONIAN UNCONFORMITY IN CENTRAL UTAH. GSA Bulletin 1959;; 70 (2): 207–218. doi: https://doi.org/10.1130/0016-7606(1959)70[207:UDUICU]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 Rocks equivalent to the upper Devonian Pinyon Peak limestone and Victoria quartzite occur unconformably above older rock units in central and east-central Utah. This unconformity is perhaps most profound in the Stansbury Range where Pinyon Peak limestone overlies rocks as old as the upper part of the Tintic quartzite and as young as Simonson dolomite. A thick conglomerate occurs below the Pinyon Peak formation at the northern end of the range, and the conglomerate rests upon rocks as young as the Lake-town dolomite. To the south the conglomerate is thin and rests upon lower Simonson dolomite.Pinyon Peak limestone overlies Victoria quartzite which is disconformable upon Simonson dolomite. A similar but much thicker arenaceous unit is exposed on Stansbury Island north of the core of the uplift.The unconformity is present in the Oquirrh and southern Wasatch Mountains where Mississippian rocks rest unconformably upon Upper and Middle Cambrian units and generally rest lower in the section from southwest to northeast. Ophir shale, exposed below the Mississippian and lenticular Devonian rocks in the Central Wasatch southeast of Salt Lake City, represents an area of deep erosion. Northeast of Salt Lake City, the unconformity is at the base of the Upper Devonian clastic unit within the Three Forks or Jefferson formations. Younger rocks appear beneath the unconformity toward the north; a nearly complete and normal section occurs in the vicinity of Logan in the northeastern corner of the state.The thick conglomerate of the Stansbury Range and the more widespread Upper Devonian sandstone, siltstone, shale, and silty carbonate units were probably derived from erosion of the uplifted area. Erosion, not nondeposition, probably accounts for much of the stratigraphic gap immediately below uppermost Devonian and lowermost Mississippian –rocks in the central part of Utah. 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.

Early pre-Cambrian varved slate in northwestern Ontario

INTRODUCTION In 1928, 1929, and 1932 the writer made a study of the Abram series— a “Timiskaming-type” series of early pre-Cambrian age—which has a widespread distribution in northwestern Ontario.[1][1] The most characteristic feature of this series is a thick conglomerate of terrestrial origin. Associated with these coarse clastics are graywackes, siltstones, argillites, iron-bearing formation, and tuffs. It is the purpose of this paper to describe in greater detail the banded argillites, which were restudied in 1934,[2][2] to discuss further their probable origin, and to place on record some pre-Cambrian varve-thickness measurements. BANDED SLATES AND ASSOCIATED STRATA The slates with the most perfect banding are exposed on the islands and mainland of East Bay of Minnitaki Lake, district of Kenora, in northwestern Ontario (Fig. 1). The stratigraphy of this area has been imperfectly known, owing to the complex nature of the structure in which the slates and associated strata are . . . [1]: #fn-3 [2]: #fn-4