Till and bedrock of the Clinton-Concord-Grafton-Medfield 12 quad area in East Central Massachusetts - till_bedrock
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The till_bedrock data layer is part of a comprehensive study to produce a statewide digital map of the surficial geology at a 1:24,000-scale. This compilation of surficial geologic materials defines the areas of exposed bedrock, and the boundaries between glacial till, glacial stratified deposits, and overlying postglacial deposits. The till_bedrock layer shows areas of thin till, thick till, bedrock outcrops, and areas of abundant outcrop and shallow bedrock for a 12-quadrangle area in east-central Massachusetts. Thin till and bedrock outcrops polygons are mutually exclusive, thick till polygons overlie areas of thin till, and abundant outcrop/shallow bedrock polygons overlie areas of thin till and bedrock outcrops. This data layer should be used in conjunction with the overlying stratified_deposits and postglacial data layers.Keywords:
Bedrock
Outcrop
Quadrangle
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Western Lake Ontario sediments record a till–mud–till sequence over bedrock and a thick layer of partly distorted glaciolacustrine clay unconformably overlying this. Another unconformity separates this clay from younger fine (lacustrine?) deposits, which are also distorted. Modern foreset and bottomset beds of the Niagara River overlap the lacustrine and glaciolacustrine deposits.In eastern Lake Ontario, thick glaciolacustrine clays overlie bedrock and the infilling ice-marginal deposits. These glaciolacustrine clays are severely distorted, and in the deepest parts of the area patches of overlying lacustrine (?) clay are preserved. A distorted terracelike deposit is preserved at higher elevation in the St. Lawrence trough. Bedrock, lag gravels, and sandy deposits characterize shallow-water areas.We suggest that after the fall of lake levels in the Lake Ontario basin, during the post-Iroquois lake phases, glaciolacustrine clays were subject to distortion by ice action at the time of the Greatlakean stadial. This deformation was more severe at the east end of the basin. At its lowest level, the surface of early Lake Ontario following the post-Iroquois phases was below the present lakebed in much of western Lake Ontario. Ice-wedge casts formed in sediments at both ends of the basin, soon after the initiation of early Lake Ontario, and are correlated with the Algonquin (St. Narcisse) glacial phase. Whereas there are significant accumulations of modern mud in the western basin of Lake Ontario, in the Kingston basin there is little except in the St. Lawrence trough.
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Glacial lake
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Southeastern Cape Breton Island is host to several fonner industrial minerals and base metals mines discovered by traditional prospecting methods but present exploration is hampered by a complex glacial history. Late Wisconsinan ice advances resulted in the deposition of five distinct tills. The basal grey till (LLI) is a compact, fine-grained till found in local depressions. The regional red till contains 10-30% clasts, 20-30% clay, and was deposited by an eastward ice advance (LL2). Northward (LL-3) and southward (LL4) ice flows were responsible for two hybrid tills that fonned in part through inheritance and overprinting. The local stony till was fonned by a southeasterly ice flow event (LL-5) and contains 35-75% angular local clasts and less than 10% clay. The southern half of the study area is dominated by 50 m high bedrock cored till ridges. Inter ridge areas are overlain by organic deposits and glaciofluvial sediments which can provide anomalous geochemical values. Till samples were collected at a 3-5 km spacing and the <0.063 mm fraction was analyzed. Till geochemical patterns are complex as a result of lithological repetition, complex glacial history, and numerous mineralization types. Considered together stratigraphic, geochemical, and till pebble data indicate that all 5 stratigraphic units have surface expression in the study area necessitating a multi-tiered interpretation of the geochemical datasets. The re-evaluated data suggest that the regional red till which is located primarily in the Loch Lomond basin is
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Research Article| November 01, 1983 Till stratigraphy in the St. Lawrence Valley near Malone, New York: Revised glacial history and stratigraphic nomenclature PETER CLARK; PETER CLARK 1Institute of Arctic and Alpine Research and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309 Search for other works by this author on: GSW Google Scholar P. F. KARROW P. F. KARROW 2Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L3G1 Search for other works by this author on: GSW Google Scholar Author and Article Information PETER CLARK 1Institute of Arctic and Alpine Research and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309 P. F. KARROW 2Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L3G1 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1983) 94 (11): 1308–1318. https://doi.org/10.1130/0016-7606(1983)94<1308:TSITSL>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation PETER CLARK, P. F. KARROW; Till stratigraphy in the St. Lawrence Valley near Malone, New York: Revised glacial history and stratigraphic nomenclature. GSA Bulletin 1983;; 94 (11): 1308–1318. doi: https://doi.org/10.1130/0016-7606(1983)94<1308:TSITSL>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 Compositional parameters are defined for till samples collected from 48 sites in the type areas of the Malone and Fort Covington tills in the St. Lawrence Valley, New York. Till compositional variations are related directly to the influence of the underlying bedrock and are interpreted as facies changes that occur within one extensive till unit. The Fort Covington-Malone drift boundary as previously mapped is disputed. The single till sheet ranges from a gray, silty sand, carbonate-rich facies where underlain by dolostone bedrock in the north to a red, sandy, carbonate-depleted facies where underlain by sandstone and Precambrian metamorphic bedrock to the south. In contrast to previous studies, till fabrics failed to distinguish units and were not useful for correlation.Surface till in the area is correlated with the upper till exposed in St. Lawrence Seaway excavations. The name Fort Covington Till is retained but extended to include surface till in the Adirondack Highlands. The lower till exposed in the Seaway does not outcrop in the area, and the name Malone Till should no longer be used.The surface till may represent glaciation at least throughout the late Wisconsinan. Extension of ice into the Adirondack Highlands is suggested by continuity of the till sheet and by ice flow indicators throughout the Lowlands. Major physiographic elements influenced ice movement in that ice was channeled southward through the Champlain Basin, southwesterly parallel to the St. Lawrence River into the Ontario Basin, and southward into the Adirondacks in a lesser flow strength. 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.
Geological survey
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Quaternary geological investigations were initiated in the Patterson Island area, Reindeer Lake (part of 64E-10 and -15), as part of the multidisciplinary, multi-year Peter Lake Domain Project. The Quaternary component of the project involves surficial mapping at 1:50 000 scale, recording ice-flow indicators, and regional till sampling surveys. Multiple ice-flow directions were documented. The dominant ice-flow direction was to the south-southwest (205° to 210°); becoming more southwesterly (215° to 220°) towards the southern boundary of the map area. Two older regional ice flows were recorded: a more southerly (~190°) direction and a west-southwesterly (228° to 240°) one. Rare, faint striae sets trending 154°/332o (two sets) and 295°/115o (one set) were also recorded. Drift cover in the Patterson Lake area is variable. In the northern two thirds, the terrain is dominated by bedrock (approximately 40 to 50 percent) mantled with a thin (less than 2 m), discontinuous drift cover. Thus, the present day landscape is controlled by the bedrock topography with little geomorphic expression of the glacial deposits. Southward, the drift thickens and is more extensive, with bedrock exposure less than 10 percent. Here, the landscape is more subdued and reflects both glacial geomorphic features and bedrock topography. The dominant surficial sediments in the Patterson Island area are till and organic deposits. Sand and gravel deposits are associated with esker systems, minor meltwater drainage channels, stagnant ice hummocky moraines, and glaciolacustrine littoral deposits. Minor glaciolacustrine silts and sands are not sufficiently extensive to differentiate at this map scale. Till occurs primarily as ground moraine veneer (less than 2 m thick) and plain (greater than 2 m thick), hummocky moraine and stagnant ice moraine. Ridged moraine and streamlined forms such as drumlins and crag and tails are less common. Till composition varies with the type of deposit, thickness and source rocks from which it is derived. At least three facies were identified: a silty-sand to sandy till, sandy till and a gravely sand diamicton. Sporadic lacustrine deposits and raised strandlines, such as sand and cobble beaches, terraces and wave-cut notches indicate that Glacial Reindeer Lake and glacial Lake Agassiz extended further north and west than originally thought. Much of the area below ~350 m asl is characterised by exposed outcrop, boulder lags and winnowed till. A large part of the northern half of the area is not very suitable for drift prospecting, as bedrock, ice marginal and wave-reworked deposits dominate the terrain. Drift prospecting techniques are more applicable in the south where the drift cover is more extensive. Interpretation of pending till compositional data will help determine the effectiveness of till sampling in this region.
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Southeastern Cape Breton is host to several former industrial minerals and base metals mines. These deposits were discovered by traditional prospecting methods; however, subsequent exploration has been hampered by thick glacial overburden, limited outcrop and a complex glacial history. Given these conditions, a detailed understanding of the glacial history of the study area is required in order to properly interpret till geochemistry. Three distinct tills were identified in the study area. The lowermost gray till is fine-grained, compact and contains few clasts. It is sparsely distributed and is usually found in local depressions. The middle red silty till contains some exotic clasts but with local representation; the upper brown sandy till is widely distributed over the study area and contains abundant angular local clasts. Pebble lithologies within the upper two tills suggest that these tills represent, respectively: i) a regional glacial advance and ii) a latter local glacial advance. Large scalloped ridges up to 50 m high dominate the landscape in the southern portion of the study area. The ridges are composed primarily of the upper sandy till and are usually bedrock cored; inter-ridge areas are overlain by post-glacial organic deposits and occasionally late-glacial outwash sand and gravel. Till samples were collected at reconnaissance scale (3-5 km spacing) to determine regional background levels ofbase and precious metals and to identify anomalous areas that may indicate local mineralization. Preliminary data indicate that elevated Pb and Sr concentrations occur in local till samples near known deposits, the distance of dispersal is less than 4 km. Cu and Ba values, closely associated in some deposits, exhibit an easterly regional expression. This may indicate either remobilization ofregional tills or additional occurrences of Cu-Ba mineralization. Background Cu values are also prevalent in the southern half of the project area, possibly reflecting dispersal of sulphide occurrences from the Stirling Group. Ni values are widespread in the southern half and likely represent the westerly regional dispersion of the St. Peter's gabbro.
Outwash plain
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Colluvium
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Surficial mapping (1:50,000 scale) and sampling of Bhorizon soil, basal till and 100 pebbles at each of 406 sites on a 2 km grid is ongoing in NTS 21 0/7 & 8. Till is analyzed for Au + 33 elements, and selected base metals. A till fabric, 264 pebble counts and 486 striae, groove and roche moutonnee measurements indicate an erosive eastward ice movement followed by northeastward and southeastward flowing ice. Lastly, ice flowed in various directions off the Highlands. This is consistent with other areas mapped to the north and south. Periglacial features, suggest that the highest elevations may have been exposed as nunataks during early stages of deglaciation. Granite-boulder erratics from the Mount Elizabeth Intrusive Complex in the center of the area were transported up to 30 km down-ice in an eastnortheast direction. No Canadian Shield erratics have been found. A Late Wisconsinan homogeneous basal till ( <2 m) throughout the area and erratic pebbles in till on the highest elevations suggest that all of the area was glaciated. Ti11 is locally derived. Till thickness increases to the east, as elevations decrease and topography becomes gently rolling. Ablation till and ablation lag over basal till are found in valleys and topographic depressions. Major rivers and brooks contain glaciofluvial (outwash and ice-contact), and postglacial alluvial deposits. Pre-glacial weathered granite (grus); colluvium and bedrock, dominate in steep valleys and on mountains and ridges.
Outwash plain
Deglaciation
Bedrock
Colluvium
Tectonic uplift
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Lithology
Meltwater
Outwash plain
Drumlin
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Synopsis Central Glasgow is an area dominated by the influence of glacial deposition. The landscape is a drumlinized till lowland and in areas close to the River Clyde, up to 26 m O.D., raised beaches were mapped at three distinct levels with patches of fluvioglacial deposits, peat and lacustrine-like sediments within interdrumlin hollows. Till partially covers the fluviatile sediments that infill the Clyde buried bedrock channel. Rockhead and drift thickness maps were constructed revealing the above deposits and their stratigraphic inter-relationships. The buried channel seems to have been cut subglacially and the infilling deposits deposited subglacially. Probably both events occurred prior to and/or during the last major ice advance into the area. The drumlinized till dates from this advance; the raised beaches from Lateglacial times.
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Abstract High-resolution seismic reflection (HRSR) data acquired over the Pesotum Bedrock Valley in central Illinois, USA, helped construct the seismic stratigraphy of a valley fill and the overlying sediments. Integrating these data with drilling and borehole geophysics allowed us to develop a seismo-stratigraphic classification for sediments on undulating and folded bedrock. Seven seismo-stratigraphic units that overlie the bedrock surface were characterized. Seismic units A and B include glacial sediments of multiple Pleistocene glaciations above the Pesotum Bedrock Valley, which completely mask the feature. Seismic units C–F, the valley fill, primarily include tills and glacial lake sediment deposited during the earliest Pleistocene glaciations and preglacial alluvium and colluvium that is draped over in situ weathered bedrock. The preservation of conformable-lying glacial and preglacial deposits and paucity of sand and gravel in the buried valley strongly indicate that little or no incision by glacial meltwaters has occurred. These observations contrast markedly with interpretations from buried valleys elsewhere in North America and northern Europe where valley fills contain significant deposits of sand and gravel in tunnel valleys. The HRSR data assisted the characterization and analysis of heterogeneous sedimentary sequences over a buried valley where existing subsurface information was limited. The extent of Pleistocene-age glacial lakes is inferred from the lateral continuity of silt and clay units.
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Colluvium
Silt
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