Geology of Beaufort-Mackenzie Basin and Eastern Part of Northern Interior Plains: Regional Arctic Geology of Canada
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Abstract:
The eastern part of the northern Interior Plains is underlain by rocks of Cenozoic, Mesozoic, and Paleozoic age. The region is bounded on the east by the Coppermine arch, composed of lower Paleozoic and Precambrian rocks. The plains region is a northwest-dipping homocline, interrupted in its western part by the Kugaluk arch, a north-trending pre-Cretaceous uplift. Mesozoic rocks of the Interior Plains consist of Cretaceous sandstones, mudstones, and shales with a composite thickness of about 3,000 ft (900 m) along Anderson and Horton Rivers. The Lower Cretaceous units are correlated with similar rocks on Banks Island. On the mainland, these strata are disconformably overlain by varicolored clastic units of Late Cretaceous and early Tertiary age. Westward, in the region of the Mackenzie delta, the Tertiary Reindeer Formation consists of a northward-thickening sequence of poorly consolidated to unconsolidated cherty gravels, crossbedded sands, and coal and ash beds. Its maximum outcrop thickness is about 4,000 ft (1,250 m). In the nearby B.A.-Shell-I.O.E. Reindeer D-27 well, the Reindeer Formation is 3,970 ft (1,210 m) thick and underlies 790 ft (250 m) of Quaternary and recent sediments. Microfaunal studies show that the Reindeer Formation overlies 2,200 ft (670 m) of Late Cretaceous clastic rocks which, in part, may be equivalent to the Moose Channel Formation, which crops out on the west side of the delta adjacent to the Richardson Mountains. These Upper Cretaceous rocks in the Reindeer well lie unconformably on 5,690 ft (1, 50 m) of Lower Cretaceous sandstones and mudstones which can be correlated with similar units in the eastern Richardson Mountains. Offshore seismic profiles obtained during the 1969 Arcticquest survey indicate the presence of a thick sequence of sedimentary rocks, the lower part of which has been deformed into broad domal structures. These lower rocks are unconformably overlain by nearly flat-lying younger rocks. This unconformity may be the same as that separating the Lower and Upper Cretaceous rocks in the Reindeer well. Analyses of the profiles indicate that these younger rocks may have been intruded by diapiric structures.Keywords:
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In eastern and central Alberta, topography on the Pre-Cretaceous surface reflects the presence of a northwest-trending drainage system which intermittently carved into older Paleozoic rocks from Late Mississippian until earliest Cretaceous time. Lower Cretaceous sedimentary rocks mapped across the area fill and cover the valley and ridge system. To the west, successively younger units subcrop at the Pre-Cretaceous surface. As a result, unconformity bounded Jurassic quartz sandstones are present beneath Cretaceous sandstones and, in the absence of paleontologic control (usual situation), can only be distinguished with difficulty. The tendency has been to include these sands in the Lower Cretaceous Basal Quartz, masking the unconformity surface. Subsequent interpretation f Lower Cretaceous sedimentation patterns is seriously affected. Mineralogically pure, fine-grained quartz sandstones of the Rock Creek Member (Middle Jurassic) in west-central Alberta are distinct from quartz sandstones of Early Cretaceous age, which have greater grain-size variation and significantly higher percentages of unweathered chert grains. The resulting Jurassic subcrop pattern reveals cuestas of resistant Rock Creek sandstone, similar to those composed of Mississippian carbonates farther east. Erosional lows on the surface of the Rock Creek Member are commonly filled by estuarine and nearshore sediments of the Ellerslie Member, reflecting invasion of the Early Cretaceous sea into the sea. End_of_Article - Last_Page 599------------
Sedimentation
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The Maranhao intracratonic basin of northern Brazil lies in the states of Maranhao and Piaui, southeast of the mouth of the Amazon River, and is about 600,000 sq. km. in area. Adjacent on the north, are the very much smaller Sao Luis and Barreirinhas coastal basins. The great sedimentary cycles in the Maranhao basin's history deposited a little more than 3,000 meters of sediments, 2,500 meters of which are Paleozoic and the remainder, Mesozoic. Two major erosional unconformities separate the three cycles, the first between Mississippian and Pennsylvanian time, the other during the Jurassic. The lower cycle transgresses folded Cambro-Ordovician and pre-Cambrian rocks and consists of Upper Silurian (?), Lower, Middle, and Upper Devonian marine gray sandstones and dark shales, with continental sediments in the basal part. Marine, deltaic, and finally continental gray Mississippian sandstones form the top of the sequence. A humid and temperate climate prevailed during this deposition. Resting in slight angular unconformity on this sequence is a second cycle deposited during a warm and semi-arid climate, consisting of Pennsylvanian eolian sandstones, anhydrites, red dolomites, thin marine limestones, and continental redbeds; followed by Permian chert beds, anhydrites, dolomites, eolian sandstones, and redbeds; ending with Triassic fluvial and eolian sandstones. Jurassic basalt overlies the Triassic. Diabase of the same age intrudes all rocks of Triassic or older age. A third and final cycle of Cretaceous strata onlaps Paleozoic, Triassic, and Jurassic beds along the north flank of the basin. The Lower Cretaceous sequence begins with lacustrine black shales carrying thin anhydrites and marine limestones, passing to marine sandstones and gray shales, and finally to reddish, continental clastics. Early Cretaceous subsidence in the northern Maranhao basin downwarped the Jurassic unconformity surface, giving the basin an over-all tilt toward the north. The axis of greatest sediment accumulation during the Silurian-Devonian-Mississippian cycle lies along the eastern and southeastern margins of the basin, which is also the area of greatest Jurassic basic igneous intrusive activity. A strong northwestward shift of the focus of subsidence occurred during the Permian and Triassic. The greatest thickness of these younger rocks coincides with the area of basalt extrusion and relatively mild intrusive activity. Fissures to the surface permitting Jurassic extrusion apparently occurred only in areas which had strong subsidence during Late Triassic, whereas the areas of greatest intrusion were those with thick sediments, but no appreciable Triassic subsidence. Only mild pre-Jurassic deformation occurred in most of the Maranhao basin. Jurassic diabase intrusives have created very numerous, large domes that have altered the smaller pre-Jurassic structure and seriously hampered exploration methods. Surface geological, seismic, and gravity methods can not differentiate domes caused by diabase sills and prospective pre-diabase folds. The magnetometer may be able to distinguish the two types. Only in the southwest corner of the Maranhao basin, where moderate compressional folding occurred, are the pre-diabase structures not likely to be masked by diabase domes. The Sao Luis coastal basin has a maximum sedimentary thickness of about 4,500 meters, 2,500 meters of which are Lower-Middle Cretaceous deltaic and continental clastics. The Cretaceous lies unconformably on about 2,000 meters of Devonian-Mississippian (?) dark marine shale. The basin is an ovate graben with bounding normal faults which may have 2,000 meters of displacement. Some of the faulting was contemporaneous with deposition. Although exploration methods function well in this diabase-free basin, source rocks in the Cretaceous and reservoir rocks in the Paleozoic are lacking. In the Barreirinhas basin, maximum sedimentary thickness may exceed 10,000 meters, 8,000 meters of which are probably Lower, Middle, and Upper Cretaceous. More than 3,000 meters of Lower-Middle Cretaceous dark marine shales of the southeastern part of the basin change facies toward the northwestern part to mostly continental and deltaic sandstones. This unit lies deformed and tilted beneath more than 3,500 meters of horizontal Albian marine limestone. Then Turonian marine limestone, shale, End_Page 1475------------------------------ and sandstone overlie the Albian limestones, possibly unconformably. Unconformably overlying Turonian rocks are marine limestone, shale, and sandstone of Late Campanian age. No diabase sills have been found. The Barreirinhas basin is an elongate graben bounded on at least three sides by faults with throws exceeding 3,000, perhaps 4,000 meters. Subsidence occurred along these faults contemporaneously with deposition. The best oil shows in the area of this study were from Lower Cretaceous sandstones and Albian limestones of this basin. Strong facies changes, penecontemporaneous deformation, and thick, interfingering source and reservoir rocks make the Lower Cretaceous Itapecuru-Tutoia Formation the most attractive in the most prospective basin of the three studied.
Red beds
Devonian
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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.
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The northern Alaska potential petroleum province comprises the Mesozoic Colville geosyncline in the foothills of the Brooks Range and the ancient Arctic platform on the present coast, a total onshore area of about 70,000 sq mi (181,300 sq km). Depths to pre-Mississippian rocks range from less than 3,000 ft (914 m) on the platform to more than 20,000 ft (6,096 m) in the southern part of the geosyncline. The Arctic platform was uplifted in Devonian time, when it was one of the sources of the thick wedge of Upper Devonian clastic beds deposited on the site of the present Brooks Range. The platform persisted into the Mesozoic as a relatively stable source area which was onlapped by Mississippian and Pennsylvanian carbonate beds and Permian to lowest Cretaceous clastic beds from the ancient Arctic Alaska basin on the south. The platform facies probably contains the most favorable Mississippian to Jurassic reservoir rocks; these include an average total of about 500 ft (152 m) of sandstone and 1,000 ft (305 m) of limestone and dolomite at depths less than 15,000 ft (4,572 m) within an onshore area of about 20,000 sq mi (51,800 sq km). This Mississippian to Jurassic platform facies grades outhward into basinal source rocks that have an average thickness of about 6,000 ft (1,830 m). The platform basement itself locally may include pre-Mississippian dolomite reservoir rocks. Cretaceous rocks in the Colville geosyncline, derived from a late Mesozoic orogenic belt in the Brooks Range, are mostly nonprospective graywacke and shale in a narrow disturbed belt along the front of the range. Molasse deposits of marine subgraywacke and shale that grade upward and southward into nonmarine rocks fill the rest of the geosyncline. They comprise about 9,000 ft (2,740 m) of shale and sandstone deposited during an Early Cretaceous regressive cycle and as much as 6,000 ft (1,830 m) deposited in a Late Cretaceous regression after an erosional interval. Lower Cretaceous sandstone beds have an average aggregate thickness of 750 ft (229 m) in an area of 46,000 sq mi (119,140 sq km). The best known Lower Cretaceous reservoirs are in the area of predominantly marine sandstone; owever, migration of generally northwest-trending shorelines across the entire area during Early Cretaceous time enhances the overall petroleum potential. Sandstone beds in the Upper Cretaceous have an aggregate thickness of about 750 ft (229 m) in an area of 20,000 sq mi (51,800 sq km) in the eastern part of the geosyncline, and are locally very porous and permeable. Black marine shale at the base of the Upper Cretaceous regressive strata is a probable source for oil and gas, both in the overlying sandstone and in the unconformably underlying Lower Cretaceous sandstone. Poorly known nonmarine Tertiary rocks that cover about 7,500 sq mi (19,425 sq km) in the northeast part of the geosyncline are more than 2,000 ft (610 m) thick and resemble the nonmarine Upper Cretaceous rocks. Both the Tertiary and the Upper Cretaceous probably thicken offshore above unconformities.
Geosyncline
Devonian
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Abstract The Devonian System, represented predominantly by shallow-water marine carbonate, is widespread in Montana, Wyoming, eastern Idaho, North Dakota, South Dakota, and northwestern Nebraska. It comprises cratonic rocks in the east and miogeosynclinal rocks in the west. The cratonic rocks thicken generally northward from their southern limit in Wyoming across a broad shelf that occupies most of Wyoming and Montana. In northern Montana, they are as much as 1,250 feet thick. Cratonic rocks also thicken eastward from areas of Early Mississippian erosional thinning in central and eastern Montana to as much as 2,000 feet in the intracratonic Williston basin centered in northwestern North Dakota. The miogeosynclinal rocks, which moved eastward on low-angle thrust faults, abut against cratonic rocks along a north-trending disturbed belt in western Wyoming, western Montana and eastern Idaho. The miogeosynclinal rocks thicken abruptly westward from 1,000 feet near this belt to about 3,000 feet near the east edge of the Idaho batholith. Farther west they have been buried beneath younger rocks, altered by the batholith, or eroded. Five subdivisions of the Devonian System are treated separately: 1. Upper Lower Devonian (Coblenzian) marginal and nearshore marine carbonate rocks and related continental and estuarine discontinuous sinkhole and channel-fill deposits. 2. Upper Middle Devonian (Givetian) carbonate rocks that contain a 525-foot-thick evaporitic sequence in the Williston basin. 3. Lower Upper Devonian (Frasnian, toI) cyclically deposited carbonate rocks that include thick beds of dolarenite and dolomitized calcarenite on the west. 4. Upper Upper Devonian (Famennian, toII-IV) evaporitic rocks overlain by fossilferous open-marine shale and limestone. 5. Undivided uppermost Devonian (Famennian, to V-VI) and lowermost Mississippian (Tournaisian, cuI-lower cuIIα) carbonaceous and clastic rocks deposited in six shallow basins interspersed among areas uplifted during the penecontemporaneous Antler orogeny.
Devonian
Batholith
Late Devonian extinction
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Cretaceous marine and continental sedimentary rocks, of Albian and possibly Cenomanian ages, crop out in the south half of the Mitchell quadrangle in central Oregon. More than 70 sq mi of Cretaceous rocks is exposed along a northeast-trending, doubly plunging anticline. The sequence, 9,023 ft thick as described along three principal reference sections, lies with angular unconformity on Permian metasedimentary rocks, and is overlain unconformably by Tertiary lava flows and volcanic sedimentary rocks. In part, the rocks have been faulted complexly and there are numerous fault-controlled and randomly oriented intrusions of Tertiary age. These rocks are divided into two intertonguing formations. One, a widespread and thick sequence of marine mudstone with subordinate siltstone and sandstone, is defined herein as the Intertonguing intricately with the marine rocks are conglomerate and sandstone; these, predominantly of fluvial and deltaic origin, are defined herein as the Creek The total sequence consists of the Basal of the Hudspeth Formation, a thin sandstone and conglomerate unit lying unconformably on the Permian basement rock; a thick mudstone and siltstone unit referred to as the Main Mudstone member of the Hudspeth Formation; and 11 numbered conglomerate and sandstone members of the Gable Creek Formation intertonguing with a like number of mudstone and siltstone members of the Hudspeth Formation. Seven tongues of the Gable Creek Formation wedge out southward into the marine facies of the Hudspeth Formation; the four other tongues thin southward. Three Hudspeth Formation marine tongues wedge out northward into the Gable Creek Formation; the six other tongues thin northward. Shapes of tongues, textural and thickness variations, primary sedimentary structures, and current-flow directions indicate that during middle Cretaceous time there was a rising landmass on the north. Very large volumes of coarse sediment were delivered by a major river to a shallow-marine embayment, and extensive alluvial piedmont and delta plains projected into the sea. Swinging distributaries, episodic uplift of the source area, and intermittent subsidence of the basin caused the shoreline to fluctuate and produce a complex intertonguing of fluvial-deltaic sediments with marine sediments.
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Late Precambrian and early Paleozoic sedimentary, volcanic, and plutonic rocks of the Avalon Peninsula, Newfoundland, represent the most easterly flank of the Appalachian folded belt. The oldest rocks, which form the Harbour Main Group, are predominantly subaerial basaltic to rhyolitic volcanic rocks and intercalated tuff and sedimentary beds. These volcanics, which are cut by Holyrood granitic rocks 574 ± 11 m.y. old, are overlain unconformably by about 7,000 ft of siltstone, slate, and graywacke of the Conception and equivalent Connecting Point Groups. In the west, Bull Arm volcanic rocks low in the Musgravetown Group overlie Connecting Point rocks. North-trending horsts were formed south and east of Conception Bay and also in the northwest part of the Avalon Pen nsula in later Precambrian time, and contributed detritus to the intervening shallow basin and probably to the eastern flank of the Avalon Peninsula. In the easternmost part of the Avalon Peninsula, the Cabot Group is about 15,000 ft thick and is believed to be lithostratigraphically equivalent to the arkosic Hodgewater Group, which was deposited in shallow water in the central basin. The latter group changes facies westward across the regional NNE structural trend, and forms the more clastic beds of the Musgravetown Group; these clastic sediments were deposited on Bull Arm volcanic rocks in a dominantly deltaic environment. The arkosic rocks in and west of the Central Avalon basin are overlain with discordance by thin beds of white quartzite of the Random Formation, which is overlain by Lower Cambrian shale and limestone containing fossils of Atlantic affinity. On the eastern horst, however, Lower Cambrian beds lacking white quartzite lie with angular unconformity on rocks of the Harbour Main and Conception Groups, and lie nonconformably on the Holyrood Granite.
Siltstone
Detritus
Basement
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The Parras basin, in southern Coahuila and western Nuevo Leon, Mexico, contains 4,500-6,000 meters of Upper Cretaceous and lower Tertiary terrigenous sedimentary rocks. Approximately 1,500-2,100 meters of Lower Cretaceous carbonate rocks and 2,000-3,000 meters of Triassic and (or) Jurassic evaporites, carbonates, and terrigenous rocks flank parts of the basin and underlie large areas within the basin. The Triassic and (or) Jurassic sedimentary rocks exhibit complex facies relations. Lower Cretaceous carbonate rocks are remarkably uniform in large areas of northeastern Mexico. Most of the Upper Cretaceous and lower Tertiary sediments were deposited in a boot-shaped, shallow, subsiding basin between the present-day Sierra Madre Oriental and Coahuila platform. The Upper Cretaceous-lower Tertiary Difunta Group displays intertonguing relations between two distinct lithic types: red, non-marine to brackish-water sandstone and shale alternate with gray to black, brackish-water to marine, calcareous sandstone and shale. Regionally the red strata pinch out or change facies toward the north and east in the basin where marine deposition was continuous from Late Cretaceous to early Tertiary time. Some redbeds change facies down depositional dip into gray marine strata. Red strata also have been discovered in the Upper Cretaceous Parras Shale, which normally is gray to black, calcareous shale, 1,200-1,500 meters thick. During Paleocene or Eocene time, the sediments of the Parras basin were deformed contemporaneously with the adjacent Sierra Madre Oriental structural belt. Deformational intensity in the Upper Jurassic and Lower Cretaceous carbonate rocks of the nearby Sierra Madre appears to be related to the distribution and thickness of the Minas Viejas (Triassic and [or] Jurassic) evaporites. The type and degree of deformation within the Parras basin are not uniform as indicated by three factors. (1) Overturned folds and imbricate thrusts, which probably do not extend below the Parras Shale, characterize the constricted western part of the basin; (2) broad, elongate, open folds in the southeastern part extend downward to folds in Lower Cretaceous strata; and (3) broad, open, domal folds in the n rtheast are related to Lower Cretaceous uplifts on the surface and at depth.
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Abstract In the region north of 64° latitude between the Mackenzie River and the Canadian Shield, a wedge of Paleozoic sediments decreases in thickness from a maximum of 10,000 feet at Point Separation in the northwest to zero along the edge of the Shield. These sediments were deposited on a shelf area subject to epeirogenic movements with minor warping. Unconformities are present in the Middle Cambrian, Middle Ordovician, Middle Silurian, Lower Devonian, top of the Middle Devonian and at the top of the Upper Devonian. Sands, shales and evaporitic sediments of the Early and Middle Cambrian were followed by thick marine platform carbonates deposited intermittently from late Middle Cambrian to early Middle Devonian time. A clastic marine succession deposited during late Middle and Late Devonian was interrupted in some areas by the Kee Scarp platform and reef at the end of the Middle Devonian. No beds with ages between Late Devonian and Early Cretaceous are known in the area. Eastern bevelling of the lower Paleozoic sediments occurred in this lacuna. For most of the Cretaceous period, a north-south seaway existed and marine shales with basal sandstones were deposited. During the Laramide Orogeny, the area became land and the Franklin Mountains were formed. Erosion removed much of the Cretaceous rock and subsequent deposition was limited to continental Tertiary beds in a small basin. There are 102,250 cu. miles and 12,000 cu. miles respectively of Paleozoic and Cretaceous strata. Of this bulk 49,000 cu. miles of marine shales and carbonates are potential source beds, 37,800 cu. miles of shallow water, marine dolomites are of more dubious value as source beds and 12,400 cu. miles of dolomite, limestone and lesser sandstone are potential reservoir beds. Hydrocarbon shows at the surface and in wells occur in the Cretaceous and Middle and Upper Devonian beds. Norman Wells, with 500 MM bbls. of STO in place in a Kee Scarp reef, is the only oil field. The area is relatively unexplored. Seventy-six exploratory wells have been drilled but most of these are close to the Mackenzie River. Because of climatic and geographical factors this is a region in which only very large fields are likely to be economic under present conditions. Hydrocarbon potential exists in the area, the northeast-trending trough in the Northern Anderson Plains where thick Paleozoic sediments are preserved is the most promising. Cretaceous beds preserved in the downwarp southwest of Great Bear Lake have possibilities for production from the basal sand.
Devonian
Geosyncline
Red beds
Late Devonian extinction
Marine transgression
Isopach map
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Abstract The Arctic Archipelago has a land area of about 525,000 square miles of which some 300,000 are Phanerozoic rocks. Seven major structural elements are recognized: they are described from southeast to northwest. (1) A probably Tertiary volcanic province, covering a small part of southeastern Baffin Island. (2) The Precambrian Shield that is exposed over large areas of southeastern and eastern parts of the Archipelago. Extensions of Shield form two and possibly three cratonic arches within the Arctic Lowlands. (3) The Arctic Lowlands which are characterized by essentially undisturbed and relatively thin coverings of Cambrian, Ordovician, Silurian and Devonian strata. Cretaceous to early Tertiary rocks are exposed in the Lowlands of Banks Island. The Arctic Lowlands are situated between exposures of the Shield and the Franklinian Geosyncline. They extend from Banks Island to central east Ellesmere Island. Most exposures throughout this vast area represent a dolomite formation that bears the Arctic Ordovician fauna and ranges into the Silurian. (4) The Franklinian Geosyncline that represents a region of profound subsidence from Cambrian to Devonian. Miogeosyndinal facies characterize that part of the geosyncline adjacent to the Arctic Lowlands and extend through Melville, Bathhurst, Cornwallis, northwest Devon, and southern and eastern Ellesmere Island. Within the miogeosynline, Cambrian, Ordovician and Silurian rocks attain a maximum thickness of about 20,000 feet and are essentially carbonates and shales with minor evaporites and sandstones. Ordovician and Silurian carbonates occupy the inner side (nearest the Shield) of the miogeosyncline, and shales the outer. Middle to early late Devonian rocks are locally 17,000 feet thick and represented mainly by quartzose clastics and lesser carbonates. The part of the Franklinian Geosyncline exposed in northern Axel Heiberg and Ellesmere Island is eugeosynclinal in character. The geology of this region is poorly known. Nevertheless, low rank metamorphic equivalents of sandstone, greywacke, siltstone, shale, chert and carbonate rocks are known to be represented. Locally these rocks attain a maximum thickness of about 40,000 feet. Volcanic rocks are also present. In northwest Ellesmere, volcanic rocks are about 30,000 feet thick and lie stratigraphically above Silurian graptolites. The rocks of the eugeosyncline have yielded only a few poorly preserved fossils of Ordovician and Silurian age. Gneissic rocks exposed on the north coast of Ellesmere are approximately 545 million years old on the basis of radiometric age determinations. Their structural relation to the Ordovician and Silurian in this region is unknown. Stocks of granite, norite, and peridotite intrude the gneissic rocks. Early Palaeozoic movements (late Silurian or early Devonian) produced northtrending folds on Cornwallis and eastern Bathurst Islands and probably also Grinnell Peninsula. Movements along the Boothia Cratonic Arch also took place at this time and produced northerly structures and contemporary fanglomerates on Somerest and Prince of Wales Islands. Mid-Palaeozoic movements affected the remainder of the miogeosyncline and produced east-west trending folds on Melville and Bathurst Islands, the Grinnell Peninsula; and northeasterly trending folds that extend from southwest, and through central Ellesmere Island. The strike of the severely deformed eugeosynclinal rocks is northeasterly in northern Ellesmere; northerly in northern Axel Heiberg. Throughout the Geosyncline the deformed rocks are overlain unconformably by Middle Pennsylvanian rocks. Deformation therefore, took place between early Late Devonian and Middle Pennsylvanian. The Minto Arch of Victoria Island probably underwent uplift at about the same time. Rocks of late Devonian, late Mississippian and Early Pennsylvanian age are unknown in the Archipelago. (5) The Sverdrup Basin is centered in southwestern Axel Heiberg Island and extends from northern Prince Patrick Island to northern Ellesmere Island. It is filled with Middle Pennsylvanian to early Tertiary sediments that are separated from Rocks of the Franklinian Geosyncline by a profound unconformity. The long axis of the Sverdrup Basin appears roughly to coincide with, and parallels, the transition zone between the lower Palaeozoic miogeosyncline and eugeosyncline. The Permo-Pennsylvanian includes carbonate, shale, sandstone and evaporites; the Mesozoic comprises alternating marine shale and non-marine sandstone. The region of the axis of the Sverdrup Basin is characterized by a conformable sequence that reaches a maximum thickness of the order of 50,000 feet. Along the margins of the Basin the sequence is much thinner, and incomplete, mainly from unconformities and overstep. Early Tertiary rocks are entirely non-marine with coal seams. They were followed by Tertiary earth movements that produced mainly northerly trending thrust faults and folds, and also diapiric intrusions of upper Palaeozoic evaporites. In northwestern Melville Island and southwestern regions of Ellesmere Island an angular unconformity (Late Palaeozoic earth movement) separates Middle Pennsylvanian and Early Permian rocks, but this deformation does not appear to have affected the main body of the Sverdrup Basin. (6) The Prince Patrick Uplift includes southern Prince Patrick Island and a small part of the northern extremity of Banks Island. The Uplift appears to involve an inlier of Devonian rocks that are cut by north trending normal faults, and there is evidence that the Uplift experienced repeated movements within the Mesozoic. It is suggested that the structures exposing late Precambrian rocks at Nelson Head on the south coast of Banks Island are related to the Prince Patrick Uplift, and that both regions represent culminations along a largely buried Precambrian structural high analagous to the Boothia and Minto Arches. (7) The Arctic Coastal Plain, a narrow strip of late Tertiary and early Pleistocene non-marine clastic sediments that borders on the Arctic Ocean and extends from Banks of Meighen Island. These sediments (Beaufort formation) rest unconformably upon all older formations and dip gently to the northwest. Relatively recent faulting has probably taken place. This is indicated by the presence of probable faults displacing the Beaufort formation and by many straight and arcuate coast lines that strongly suggest fault-line scarps.
Geosyncline
Devonian
Archipelago
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