Plain Strata Research Articles

Shallow Faulting and Folding in the Epicentral Area of the 1886 Charleston, South Carolina, Earthquake

ABSTRACT The moment magnitude (Mw) ∼7 earthquake that struck Charleston, South Carolina, on 31 August 1886 is the largest historical earthquake in the United States east of the Appalachian Mountains. The fault(s) that ruptured during this earthquake has never been conclusively identified, and conflicting fault models have been proposed. Here we interpret reprocessed seismic reflection profiles, reprocessed legacy aeromagnetic data, and newly collected ground penetrating radar (GPR) profiles to delineate faults deforming the Cretaceous and younger Atlantic Coastal Plain (ACP) strata in the epicentral area of the 1886 earthquake. The data show evidence for faults folding or vertically displacing ACP strata, including apparent displacements of near-surface strata (upper ∼20 m). Aeromagnetic data show several northeast (NE)-trending lineaments, two of which correlate with faults and folds with vertical displacements as great as 55 m on the seismic reflection and radar profiles. ACP strata show only minor thickness changes across these structures, indicating that much of the displacement postdates the shallowest well-imaged ACP strata of Eocene age. Faults imaged on the seismic reflection profiles appear on GPR profiles to displace the erosional surface at the top of the upper Eocene to Oligocene Cooper Group, including where railroad tracks were bent during the 1886 earthquake. Some faults coincide with changes in river trends, bifurcations of river channels, and unusual river meanders that could be related to recent fault motion. In contrast to our interpreted NE fault trends, earthquake locations and some focal mechanisms in the modern seismic zone have been interpreted as defining a nearly north-striking, west-dipping zone of aftershocks from the 1886 earthquake. The relationship between the modern seismicity and the faults we image is therefore enigmatic. However, multiple faults in the area clearly have been active since the Eocene and deform strata in the upper 20 m, providing potential targets for field-based geologic investigations.

Characterizing Ground-Motion Amplification by Extensive Flat-Lying Sediments: The Seismic Response of the Eastern U.S. Atlantic Coastal Plain Strata

ABSTRACTWe examine the effects that Atlantic Coastal Plain (ACP) strata have on ground motions in the eastern and southeastern United States. The ACP strata consist of widespread, nearly flat-lying sediments, the upper portions of which are unconsolidated or semiconsolidated. The ACP sediments are deposited primarily on crystalline basement rocks, creating large velocity and density contrasts with the underlying rocks. At 211 sites on ACP strata to thicknesses of 4000 m, we compute spectral ratios relative to the average of four bedrock sites west or northwest of the strata. Sites consist of stations of Earthscope’s USArray Transportable Array (TA), and temporary deployments in the Southeast Suture of the Atlantic Margin Experiment (SESAME), Eastern North American Margin (ENAM) experiment, and the DCShake deployment in Washington, D.C. For the TA and SESAME stations, we use signals from 13 teleseisms and three regional earthquakes as input, combining the north and east components of motion after taking the Fourier transforms. We also include similarly processed site responses from the ENAM and DCShake arrays that were computed in earlier studies. Results show prominent, fundamental resonance peaks at frequencies determined by reverberations in the entire sediment column, and that often define the largest amplifications for each frequency. As frequencies increase, these resonance peaks migrate to thinner ACP strata and increase in amplitude. The peaks are well defined at frequencies below about 1 Hz, but become narrower and less defined regionally at higher frequencies. We develop simple equations to characterize amplification versus ACP thickness, which we approximate by cosine and Gaussian curves with amplifications of 1 on bedrock and rising to the resonance peak, and then decreasing to an average amplification at thicknesses greater than twice the resonance peak. Comparisons with other site corrections for the central and eastern United States based on sediment thickness show similarities on thin ACP strata but divergence on thicker sediments. The results also demonstrate the effectiveness of using teleseismic arrivals to characterize the site responses of sedimentary sequences.

Analysis of floodplain sedimentation, avulsion style and channelized fluvial sandbody distribution in an upper coastal plain reservoir: Middle Jurassic Ness Formation, Brent Field, UK North Sea

Abstract Numerical models and recent outcrop case studies of alluvial-to-coastal-plain strata suggest that autogenic avulsion can control the stacking density and architecture of channelized fluvial sandbodies. The application of these models to subsurface well data was tested by the analysis of upper coastal plain deposits of the late Bajocian Ness Formation in the Brent Field reservoir, UK North Sea. These coastal plain deposits accumulated during the progradation and retrogradation of the wave-dominated ‘Brent Delta’. Sedimentological facies analysis and palaeosol characterization in cores were used to interpret the styles of palaeochannel avulsion. These results were then compared with the dimensions and distributions of channelized fluvial sandbodies that had been quantified by spatial statistical tools (lacunarity, Besag's L function) applied to interpretative correlation panels between closely spaced wells. The results indicate that the distributions of channelized sandbodies may plausibly have been generated by avulsions and that they influence sandbody connectivity and pressure depletion patterns. Intervals of upper coastal plain strata with relatively wide sandbodies that display some clustering in their stratigraphic architecture are associated with a high proportion of avulsions by incision and annexation in core samples. Such intervals display relatively good vertical pressure communication and relatively slow, uniform pressure depletion.

Controls on large‐scale patterns of fluvial sandbody distribution in alluvial to coastal plain strata: Upper Cretaceous Blackhawk Formation, Wasatch Plateau, Central Utah, USA

AbstractCurrent models of alluvial to coastal plain stratigraphy are concept‐driven and focus on relative sea‐level as an allogenic control. These models are tested herein using data from a large (ca 100 km long and 300 m thick), continuous outcrop belt (Upper Cretaceous Blackhawk Formation, central Utah, USA). Many channelized fluvial sandbodies in the Blackhawk Formation have a multilateral and multistorey internal character, and they generally increase in size and abundance (from ca 10% to ca 30% of the strata) from base to top of the formation. These regional, low‐resolution trends exhibit much local variation, but are interpreted to reflect progressively decreasing tectonic subsidence in the upper Blackhawk Formation and overlying Castlegate Sandstone. The trend may also incorporate progressively more frequent channel avulsion during deposition of the lower Blackhawk Formation. Laterally extensive coal zones formed on the coastal plain during shallow‐marine transgressions, and define the high‐resolution stratigraphic framework of the lower Blackhawk Formation. Large (up to 25 m thick and 1 to 6 km wide), multistorey, multilateral, fluvial channel‐complex sandbodies that overlie composite erosion surfaces occur at distinct stratigraphic levels, and are interpreted as fluvial incised valley fills. Low amplitude (<30 m) relative sea‐level variations are interpreted as the dominant control on stratigraphic architecture in the lower Blackhawk Formation, which was deposited up to 50 km inland from the coeval shoreline. In contrast, the high‐resolution stratigraphy of the upper Blackhawk Formation is poorly defined, and channelized fluvial sandbodies are poorly organized. Vertical and laterally offset stacking of a small proportion (<10%) of sandbodies produced ‘clusters’ that are not confined by ‘master’ erosion surfaces. Avulsion is interpreted to dominate the stratigraphic architecture of the upper Blackhawk Formation. This data‐driven analysis indicates that alluvial to coastal plain stratigraphic architecture reflects a combination of various allogenic controls and autogenic behaviours. The relative sea‐level control emphasized in sequence stratigraphic models is only rarely dominant.

Detection of Late Cretaceous and Cenozoic sequence boundaries on the Atlantic coastal plain using core log integration of magnetic susceptibility and natural gamma ray measurements at Ancora, New Jersey

Magnetic susceptibility (MS) and natural gamma ray (NGR) were measured on middle Miocene to Cenomanian coastal plain strata from a continuously cored (356 m total depth; 86% recovery) borehole at Ancora, New Jersey (Ocean Drilling Program Leg 174AX). These measurements were integrated with lithologic descriptions and a downhole NGR log. A simple linear model explains most of the variation of the downhole NGR and the core MS as a consequence of the previously described lithologic variation. Spectral NGR at selected levels shows that NGR activity is mostly due to 40K associated with glauconite and mud, sediment components that also tend to give high MS values. Abrupt deviations from the average values of NGR activity and MS determined by the linear model can be interpreted as due to singular lithologies. For example, an anomalous level with high NGR but not a parallel increase in MS was found at the Navesink/Mount Laurel formation contact and can be attributed to high uranium concentration in phosphorite. Most (27 of 33) of the sequence boundaries independently identified at the Ancora site have sufficient lithological contrasts to be expressed in the NGR and/or MS logs.

Hydrology of part of the Oramiriukwa River basin, southeast of Owerri, Imo State, Nigeria

The Oramiriukwa River is within the sandy coastal plain strata of the Benin formation (Miocene–Recent). The base flow is very high ranging from 79.13–98.56%, which is caused by the excellent hydraulic interconnection between the river and the adjacent unconfined aquifer. Recharge rates are high, estimated to range from 1.8×1012–2.5×1012 m3/year. Coastal sands are medium-to-coarse grained, moderately-to-poorly sorted, angular to subangular, with lenses of clay and clayey fine-grained sands. The coastal sands and clay lenses form aquifer and aquitard systems, which are unconfined to semi-confined. Groundwater recharge potential is high. Runoff from precipitation is low. Groundwater and surface water are fairly acidic; pH ranges from 5.5–6.1 (groundwater) and 5.8–6.5 (surface water), and hardness is generally low. Chemical analysis and percentage sodium show that groundwater and surface water are somewhat potable after some pH modification of the surface water. The waters are good for agricultural use, especially for irrigation and poultry water supply. However, pollution from landfill leachate is serious.

Marine and nonmarine systems tracts in fourth-order sequences in the Early-Middle Cenomanian, Dunvegan Alloformation, northeastern British Columbia, Canada

Abstract The Early to Middle Cenomanian Dunvegan Alloformation is a 3rd-order clastic sequence that was deposited on the western margin of the Alberta foreland basin. The alloformation, comprising ten allomembers (A-J) has been mapped over 33 000 km 2 using 1500 well logs and 40 outcrops. Regional flooding surfaces are used to define allomembers because they are more reliably identified in well logs than are Exxon-type unconformities (although in many instances unconformities and flooding surfaces are coplanar). The Dunvegan records episodic deltaic progradation from NW to SE along the axis of the foreland basin. This paper focuses on an 800 km 2 study area in NE British Columbia where both shallow marine and coastal plain strata are exposed in the valleys of the Peace and Beatton rivers. Marine strata comprise sandier-upward successions that grade from platy mudstone through cm-scale interbeds of wave rippled fine sandstone to dm-scale beds of HCS, commonly including large gutter casts. Successions may be capped by SCS and cross-bedded, fine-grained sandstone, sometimes with a rooted top. The succession of facies suggests a strongly wave-influenced deltaic shoreline. Gutter casts are consistently orientated shore-normal and appear to have been formed by oscillatory wave scour during storms. Sandstone distribution varies between successive progradational packages (‘shingles’) in allomember J, suggesting that delta switching was an important control on depositional cyclicity. Coastal plain deposits include small-scale (few metres) coarsening-upward successions of carbonaceous mudstone, siltstone and fine sandstone interpreted as lake and bay-fill deposits. Decimetre scale sharp-based sandstones may represent crevasse splays whereas lenticular, rippled and crossbedded sandstones were probably deposited in distributary channels. Rooted palaeosols are abundant. Both coastal plain and marine strata are locally replaced by erosive-based bodies of cross-bedded sandstone up to 25 m thick and 0.5–3 km wide, interpreted as incised valley fills underlain by type 1 sequence boundaries. Additional evidence of relative sea-level fall is provided by regressive surfaces of marine erosion beneath sharp-based shoreface sandstones. If attached to highstand deposits, these sandstones are assigned to the falling stage systems tract, whereas detached sandstones are assigned to the lowstand systems tract. During the early part of the transgressive systems tract, sedimentation was confined to incised valleys but later, interfluves were buried by sediments that locally contain dense Thalassinoides burrow systems, Teredolites and well-developed mud drapes, suggestive of brackish, tidally-influenced conditions. Overlying coastal plain strata lack evidence of marine influence and are attributed to the highstand systems tract.

High-Resolution Correlation of Coastal Plain Strata for Definition of Reservoir Attributes: ABSTRACT

High-Resolution Correlation of Coastal Plain Strata for Definition of Reservoir Attributes: ABSTRACT

Palaeovalleys and protozoan assemblages in a Late Carboniferous cyclothem, Sydney Basin, Nova Scotia

ABSTRACTThe early Stephanian Bonar Cyclothem of the Sydney Basin, Nova Scotia, contains an erosional surface cut through coastal plain strata with economic coals and distributary channel bodies. The erosion surface is interpreted as a palaeovalley 20 m deep and at least 7 km wide that marks a sequence boundary formed during relative fall in sea level. The palaeovalley is filled with stacked alluvial channel bodies which become more isolated as the valley fill passes upward into red, alluvial plain deposits, probably laid down in an anastomosed river system. In an adjacent, interfluve area, calcretes and red, vertic palaeosols cap coastal strata. Assemblage analysis of agglutinated foraminifera and thecamoebians indicates that the palaeovalley was filled with freshwater sediments before an initial marine transgression flooded the alluvial surface and adjacent interfluve.Valley incision probably reflects glacioeustatic sea level fall. However, the alluvial nature of the valley deposits suggests that valley filling reflects an abundant sediment supply during lowstand and/or transgressive stages and was not a direct consequence of sea level rise. During the subsequent transgression phase, aggradation was rapid as sediment supply apparently kept pace with rising sea level. Features of both channel and extra‐channel facies suggest that seasonality intensified during the transition from coastal plain to palaeovalley and alluvial plain deposition.

Lithospheric flexure as a control on stratal geometry and fades distribution in Upper Cretaceous rocks of the Alberta foreland basin

AbstractFacies distributions, stratal geometry and regional erosional bevelling surfaces in Upper Cretaceous (Cenomanian‐Santonian) strata of the Alberta foreland basin are interpreted in terms of high‐frequency (probably eustatic) relative changes in sea level, superimposed on longer‐term basin‐floor warping, related to episodic tectonic loading. Thick marine shales correspond to periods of rapid subsidence whereas thin but extensive strandplain sandstones record rapid progradation during slow subsidence. Westward‐thickening wedges of coastal plain strata were deposited during initial downwarping of a near‐horizontal strandplain, prior to marine transgression. Surfaces of erosional bevelling beneath which between 40 and >160m of strata have been removed extend at least 300 km from the present deformation front and are interpreted to reflect forebulge uplift in the east. Uplift appears to have lagged about 0.25‐0.5 Myr behind the onset of accelerated loading. Thin marine sandstones which grade westward into mudstone are interpreted as material winnowed from the crest of the rising forebulge. Subsidence and/or westward migration of the forebulge allowed the sea to flood westward across the eastern flank of the eroded forebulge. The transgressive shoreface cut asymmetric notches which were later blanketed by marine shales which lap out from east to west. The two unconformities which embody the largest erosional vacuity are veneered locally with oolitic ironstone which accumulated in a shallow, sediment‐starved setting on the crest of the forebulge. The consistent pattern of erosional bevelling and lap‐out of transgressive shales might be interpreted as evidence that the forebulge migrated towards the thrust load over a period of <1 Myr.

Jurassic Faults of the Southwest Alabama and Offshore Areas

Four fault groups affecting Jurassic strata occur in the southwest and offshore Alabama areas. They include the regional basement rift trend, the regional peripheral fault trend, the Mobile graben fault system, and the Lower Mobile Bay fault system. The regional basement system rift and regional peripheral fault trends are distinct and rim the inner margin of the eastern Gulf Coastal Plain. The regional basement rift trend is genetically related to the breakup of Pangea and the opening of the Gulf of Mexico in the Late Triassic-Early Jurassic. This fault trend is thought to have formed contemporaneously with deposition of Late Triassic-Early Jurassic Eagle Mills Formation and to displace pre-Mesozoic rocks. The regional peripheral fault trend consists of a group of en echelon extensional faults that are parallel or subparallel to regional strike of Gulf Coastal Plain strata and correspond to the approximate updip limit of thick Louann Salt. Nondiapiric salt features are associated with the trend and maximum structural development is exhibited in the Haynesville-Smackover section. No hydrocarbon accumulations have been documented in the pre-Jurassic strata of southwest and offshore Alabama. Productive hydrocarbon reservoirs occur in Jurassic strata along the trends of the fault groups, suggesting a significant relationship betweenmore » structural development in the Jurassic and hydrocarbon accumulation. Hydrocarbon traps are generally structural or contain a major structural component and include salt anticlines, faulted salt anticlines, and extensional fault traps. All of the major hydrocarbon accumulations are associated with movement of the Louann Salt along the regional peripheral fault trend, the Mobile graben fault system, or the Lower Mobile Bay fault system.« less

The Helena Banks strike-slip (?) fault zone in the Charleston, South Carolina, earthquake area: Results from a marine, high-resolution, multichannel, seismic-reflection survey

In 1981 the U.S. Geological Survey conducted a high-resolution, 12-channel seismic-reflection survey offshore of Charleston, South Carolina, to study young faults that may be earthquake sources. We collected data along 24 profiles, totaling about 600 km, with shotpoints at 10-m intervals. The Helena Banks fault zone (HBFZ) was crossed by 13 high-resolution profiles which, combined with 5 conventional 64-channel profiles acquired in 1979 across the fault zone, provide greater definition of this structure than any similar feature along the Atlantic seaboard or continental margin. The HBFZ trends N66°E and is about 110 km long (the same trend as the underlying Kiawah Triassic(?) basin); it comprises several segments 10–40 km long that trend between N68°E and N77°E, with a mean of N72°E. The left-stepping echelon pattern of the segments (connected by normal faults observed on two profiles) in the HBFZ suggests slip could possibly be left lateral despite high-angle reverse separation (mean fault dip 70° ± 5°) of Coastal Plain strata seen on the individual reflection profiles. Aeromagnetic data constrain the maximum ratio of horizontal to vertical slip from about 10:1 to 100:1. Our interpretation is consistent with the present-day, northeast-trending, maximum horizontal compressional stress field; however, the reflection data cannot independently prove that the main sense of motion on the HBFZ is strike slip. Examination of vertical separations on six segments across the HBF indicates a linear increase with depth of 51 ± 12 m/km which is similar to 36 m/km and 48 m/km reported previously as measured on multichannel seismic-reflection profiles crossing the Gants and Cooke faults, respectively, on land in the meizoseismal area of the 1886 earthquake. We interpret these results to indicate that, as a first approximation, the stress field did not vary significantly in direction or magnitude from Late Cretaceous time to Pleistocene time (and likely to the present) in the Charleston region. The trend of the HBFZ as mapped by the reflection profiles follows the narrow Kiawah Triassic(?) basin, which was delineated by the second vertical derivative of total magnetic intensity. Several reflection profiles indicate that the HBFZ is a compressional reactivation of an extensional Triassic(?) fault zone bounding the basin.

Coal Occurrence in Progradational Deltaic Sequence, Raleigh County, West Virginia: ABSTRACT

Surface outcrops and data from 75 core holes were used to study the Pennsylvanian Kanawha Formation in a 100 mi2 area of western Raleigh County, West Virginia. The interval consists of approximately 1,400 ft of prograding alluvial-deltaic deposits and includes 22 coal seams. The interval developed across drowned orthoquartzite coastal sandstones (Nutall) that mark the approximate top of the New River Formation. Its lower portion (Douglas to Eagle coals) is a generally coarsening-upward, prodelta/distal-deltaic succession of units dominated by dark shale and containing brackish-marine intercalations that extend across most of the area. Coals are widespread but commonly thin (about 1 ft), and the rate of lateral change is low. The top of this lower section is capped by outer deltaic sandstones (Eagle coals). The upper portion of the Kanawha Formation is dominated by outer deltaic strata (to Hernshaw coal) grading upward to inner (Stockton coal) deltaic sandstones. Brackish-marine intercalations associated with autocyclic shifting of detrital lobes are restricted in areal extent. The outer deltaic coal beds are thick (up to about 6 ft) and laterally uniform; succeeding inner deltaic coals are thinner (less than 3-4 ft) and are variable laterally. Deltaic deposits grade upward into lower alluvial plain strata of the Allegheny Formation near the ridge crests. Associated coals locally may be thick (up to 6 ft), but abrupt changes in thickness and shale partings are typical. End_of_Article - Last_Page 1439------------

Sources of Pleistocene and Holocene Sand for Northeast Gulf of Mexico Shelf and Mississippi Fan: ABSTRACT

Grain shape, surface texture, and mineralogic analyses were conducted on the Pleistocene and Holocene sands of the northeast Gulf of Mexico shelf and the Mississippi fan to determine their sources. Two distinct petrologic provinces of sand are present in this area: the Mississippi province, characterized by spherical quartz grains derived from older strata in the drainage basin of the Mississippi River, and the eastern Gulf province, characterized by a mixture of spherical and elongate quartz grains. The former is derived from Cretaceous and Tertiary coastal plain strata; the latter is derived from sedimentary and crystalline rocks of the southern Appalachian Mountains. Sand distribution patterns of these two provinces on the northeast shelf are distinct; Mississippi province sands are found in the western part of the shelf near the Mississippi delta, while Eastern Gulf province sands are found throughout the remaining parts of the shelf. However, sands of the Mississippi fan are a mixture of Mississippi and Eastern Gulf province sand. Glacial sand is uncommon in both the Holocene and Pleistocene deposits of the Mississippi province. End_of_Article - Last_Page 1427------------

Provenance and Areal Distribution of Late Pleistocene and Holocene Quartz Sand on the Southern New England Continental Shelf

ABSTRACT Sand from the southern New England shelf is a mixture of three sand types, each characterized by quartz grains with distinctive morphologies. The first sand type consists of well-rounded and equant grains derived from Tertiary and Cretaceous coastal plain strata which have been smoothed and rounded by chemical and mechanical processes; sands of this type are found in significant quantifies in both the relict fluvial sediment of the middle and outer shelf and in the Recent sediment of Rhode Island Sound, but not in the glacial sediment of the inner and middle shelf. The second sand type consists of highly angular and elongate grains which were transported to the area by glaciers and subsequently reworked in subaqueous environments; this sand type is found in abundance in the relict gla ial moraine and outwash plain sediment of the inner shelf and in the palimpsest sediment of the middle shelf to the west of the relict glacial deposits, but is not generally found in appreciable quantities in the relict fluvial sediment of the middle and outer shelf except in the westernmost part of the study area. A third sand type, heretofore unrecognized in these strata, consists of grains derived from sedimentary rocks exposed in late Paleozoic and Mesozoic basins of southern New England. This sand type is found in appreciable quantities in both relict and Recent fluvial sediment on the entire shelf and in the relict glacial sediment of the inner shelf, indicating that the glacial sediment also was derived from the southern New England area. The patterns of distribution of these thre sand types reflect the paleogeography of the shelf during the late Pleistocene; the resolution of well-defined paleogeographic features by a morphological study of surficial sediment indicates that throughout most of the study area, modern sediment transport processes acting on the shelf have not yet destroyed the provenance record imprinted upon the shelf during the late Pleistocene.

Tectonic Setting and Depositional Environments of Hanna Formation, South-Central Wyoming: ABSTRACT

The Paleocene Hanna Formation was deposited during tectonic events that led ultimately to the development of the Hanna and Carbon structural basins of south-central Wyoming. Early Paleocene uplift prior to deposition of the Hanna Formation resulted in a regional unconformity as observed in the Carbon basin, on the east side of the Hanna basin, and in the area south of these two basins. Subsequent movement of the thrust-fault system on the north side of the present Hanna basin resulted in southward filling of this asymmetrical foreland basin by clastic wedges, which make up facies associations. The Hanna Formation deposited in the Carbon basin has the same facies associations that occur in the southern part of the Hanna basin. Facies associations in the Hanna Formation of the Hanna basin suggest deposition in alluvial-fan and alluvial-plain environments. The alluvial-fan facies can be subdivided into proximal, medial, and distal subfacies. The proximal and upper-medial subfacies, which have been eroded away on the north side of the Hanna basin, probably consisted of medium to coarse gravels and muds deposited by debris flow and sheet floods. The lower-medial subfacies consists of tongues of conglomerate interbedded with mudstones and was probably deposited by sheet floods. This subfacies grades laterally southward into the distal conglomeratic sandstones and gray mudstones that were deposited by braided streams and sheet floods. In the Hanna basin, these distal-fan subfacies grade southward into an alluvial plain facies. In the area of the Carbon basin, all the fan facies are isolated in the Medicine Bow Mountains and associated mountain front, and only the alluvial-plain facies occur in the basin. The alluvial-plain facies in the Hanna Formation can be divided into two subfacies on the basis of thickness and the occurrence of coal and carbonaceous shale. One subfacies consists of overbank and backwater-deposited gray shale and claystone and splay sandstone and siltstone interbedded with backswamp deposits of thin carbonaceous shales and thin coals. These deposits lie laterally from sandstone-filled channel systems. In the Hanna basin this subfacies is thickest near the base of the Hanna Formation. The other subfacies is similar in lithology but contains more backswamp deposits of carbonaceous shale and coal beds. Stacked channel sandstones are also more common in this subfacies. This subfacies is thickest in the central part of the Hanna basin, and makes up most of the alluvial plain strata in the Carbon basin. Analysis of the alluvial-plain sequences in Hanna basin is hampered by poor outcrops and a lack of subsurface correlation. Complete analysis of the coal-bearing subfacies has been possible in the Carbon basin where a stratigraphic framework has been established. From this stratigraphic framework, a sequential strata model has been constructed. Analysis of several coal-bed-bounded sequences in the Carbon basin confirms the sandstone domination of the sequences as shown by the sequential strata model. Also, mapped southeasterly trends of the sandstone bodies indicate the fluvial channel systems of the Hanna basin were continuous into the Carbon basin. End_of_Article - Last_Page 1340------------

Provenance of Quaternary Sediments on the Labrador Continental Shelf and Slope

ABSTRACT Textural and petrographic analysis of Quaternary sediments from twenty-one piston cores obtained at six locations on the Labrador continental shelf and slope has shown the following: (a) sand-silt-clay and silty sand are the most common sediments, (b) texture of sediment in cores obtained at closely spaced intervals varies with water depth, and (c) mineralogic composition of core sediments is broadly related to the Precambrian crystalline rocks of Labrador. The results show that these are relict sediments. They were glacially derived from Labrador or the equivalent Precambrian rocks exposed on the inner shelf during intervals of Pleistocene lower sea level, and transported eastward. Mesozoic/Tertiary coastal plain strata underlying the outer shelf were a lesser sediment source. Submarine reworking of the deposits has occurred.