Connecticut Surficial Stratified Drift

These deposits originate from glacial meltwater, either deposited by streams, through settling in glacial lakes or in glacial marine environments. Stratified drift deposits are commonly located in major river valleys, where glacial meltwater drainage channels have persisted into modern times, and in dry valleys more common in the uplands where the deposits are remnants of ancient glacial drainage. These deposits are primarily comprised of one or more vertically stacked units of gravel, sand, and fine-grained deposits known as fines. For example, a coarse-grained stratified drift deposit can be comprised of solely gravel or gravel on the surface overlying sand below (e.g. vertically stacked). Connecticut Stratified Drift is derived from the Surficial Aquifer Texture compilation extracted from the Surficial Materials Map of Connecticut (Stone et al 1992). Areas of surficial aquifer texture defined as coarse grained deposits either on the surface or in the subsurface are combined to create a single, coarse-grained stratified drift mapping unit. Stratified drift as coarse grained fluvial deposits, are variably sorted, and may or may not have a strongly layered appearance. Areas of surficial aquifer texture defined as fine grained deposits either on the surface or in the subsurface are combined to create a single, fine-grained stratified drift mapping unit. Course-Grained stratified drift deposits include the Coarse and the Fine overlying Coarse surficial texture classes. The Coarse texture class is comprised of the following surficial material deposits: Sand, Gravel, Sand and Gravel, Alluvium overlying Sand, Alluvium overlying Sand and Gravel, Alluvium overlying Sand and Gravel overlying Sand, Gravel overlying Sand, Gravel overlying Sand and Gravel, Gravel overlying Sand and Gravel overlying Sand, Sand and Gravel overlying Sand, Sand and Gravel overlying Sand overlying Sand and Gravel, Sand overlying Gravel, Sand overlying Sand and Gravel, Swamp overlying Sand, Swamp overlying Sand and Gravel, Swamp overlying Sand overlying Sand and Gravel. The Fine overlying Coarse surficial texture class is comprised of the following surficial material deposits: Alluvium overlying Fines overlying Gravel, Alluvium overlying Fines overlying Sand, Alluvium overlying Fines overlying Sand and Gravel, Fines overlying Gravel, Fines overlying Sand, Fines overlying Sand and Gravel, Sand and Gravel overlying Fines overlying Sand and Gravel, Sand overlying Fines overlying Sand and Gravel, Swamp overlying Fines overlying Sand. Fine-Grained stratified drift deposits include the Fines and the Coarse overlying Fines surficial texture classes. The Fines texture class is comprised of the following surficial material deposits: Fines, Alluvium overlying Fines, Salt Marsh overlying Fines, and Swamp overlying Fines. The Coarse overlying Fine surficial texture class is comprised of the following surficial material deposits: Alluvium overlying Sand and Gravel overlying Fines, Alluvium overlying Sand and Gravel overlying Sand overlying Fines, Alluvium overlying Sand overlying Fines, Gravel overlying Fines, Gravel overlying Sand overlying Fines, Salt Marsh overlying Sand overlying Fines, Sand and Gravel overlying Fines, Sand and Gravel overlying Sand overlying Fines, Sand overlying Fines, Swamp overlying Sand overlying Fines. The Surficial Aquifer Texture Map was prepared from the Surficial Materials Map of Connecticut (Stone, J.R., Schafer, J.P., London, E.H. and Thompson, W.B., 1992, U.S. Geological Survey special map, 2 sheets, scale 1:125,000) to describe unconsolidated areas of the subsurface with similar properties relative to ground water flow. Surficial aquifers are unconsolidated geologic deposits capable of yielding a sufficient quantity of groundwater to wells. Surficial aquifer textures were identified from original surficial materials mapping for use in ground water applications. These are qualitative interpretations of material properties relative to ground water flow. Surficial aquifer texture groups were identified to represent aquifer textures with similar hydraulic conductivities. Some interpretations were made beneath postglacial alluvium and swamp deposits. Alluvium without a subsurface interpretation was classified as having similar hydrologic properties as till. Alluvium areas with subsurface interpretations of fines or coarse grained deposits were classified as having the hydrologic characteristics of the underlying deposits. The aquifer textures include areas of till, fine grained, fine overlying coarse grained, coarse grained, coarse overlying fine grained deposits, artificial fill, beach, salt marsh, swamp, and water. Aquifer texture groups include areas of fine grained , fine overlying coarse grained, coarse grained, and coarse overlying fine grained deposits. Surficial materials not included in the surficial aquifer texture groups include till, artificial fill, beach, salt marsh, swamp, and water. All textural terms follow the grain size classification of Stone et al 1992, modified from Wentworth, 1922. The surficial aquifer texture classifications are suitable for use at 1:24,000 scale. Original mapping of the Surficial Materials Map of Connecticut is preserved as polygon attribute values in this data layer, and is herein described. The Surficial Materials Map of Connecticut portrays the glacial and postglacial deposits of Connecticut in terms of their aerial extent and subsurface textural relationships. Glacial Ice-Laid Deposits (thin till, thick till, end moraine deposits) and Postglacial Deposits (alluvium, swamp deposits, marsh deposits, beach deposits, talus, and artificial fill) are differentiated from Glacial Meltwater Deposits. The meltwater deposits are further characterized using four texturally-based map units (g = gravel, sg = sand and gravel, s = sand, and f = fines). In many places a single map unit (e.g. sand) is sufficient to describe the entire meltwater section. Where more complex stratigraphic relationships exist, "stacked" map units are used to characterize the subsurface (e.g. sg/s/f - sand and gravel overlying sand overlying fines). Where postglacial deposits overlie meltwater deposits, this relationship is also described (e.g. alluvium overlying sand). Map unit definitions (Surficial Materials Polygon Code definitions, found in the metadata) provide a short description of the inferred depositional environment for each of the glacial meltwater map units. This map was compiled at 1:24,000 scale, and published at 1:125,000 scale. Connecticut Surficial Materials is a 1:24,000-scale, polygon and line feature-based layer describing the unconsolidated glacial and postglacial deposits of Connecticut in terms of their grain-size distribution (texture) as compiled at 1:24,000 scale for the Surficial Materials Map of Connecticut. Glacial meltwater deposits (stratified deposits) are particularly emphasized because these sediments are the major groundwater aquifers in the State and are also the major source of construction aggregate. These deposits are described in terms of their subsurface distribution of textures as well as their extent. The texture of meltwater deposits through their total vertical thickness in the subsurface is shown to the extent that it is known or can be inferred. In some places only one textural unit (such as SG - Sand and Gravel) describes the whole vertical extent of the meltwater deposits; in other places 'stacked units' (such as SG/S/F - Sand and Gravel overlying Sand overlying Fines) indicate changes of textural units in the subsurface. Polygon features represent individual textural (surficial material) units with attributes that describe textural unit type and size. Examples of polygon features that are postglacial deposits include floodplain alluvium, swamp deposits, salt-marsh and estuarine deposits, talus, coastal beach and dune deposits, and artificial fill. Examples of glacial ice-laid deposits include till, thin till, thick till and end moraine deposits. Examples of glacial melt-water deposits include gravel, sand and gravel, sand, and very fine sand, silt and clay. Additional polygon features are incorporated to define surface water areas for streams, lakes, ponds, bays, and estuaries greater than 5 acres in size. Line features describe the type of boundary between individual textural units such as a geologic contact line between two different textural units or a linear shoreline feature between a textural unit and an adjacent waterbody. Data is compiled at 1:24,000 scale and is not updated. The occurrence of stratified drift deposits has significance for land drainage characteristics. Where the deposits are of reasonable thickness, they influence the transport and accumulation of ground water, waste water, and pollutants. These stratified drift deposits are also of economic value, as they are used widely in a number of societal applications, particularly in construction and roadway maintenance. Depending on local conditions, tratified drift deposits may or may not be good sources for groundwater aquifers. These stratiified drift data alone do not indicate the potential yield of ground water acquifers in Connecticut. Thick areas of course grained deposits are delineated on the Surficial Aquifer Potential Map of Connecticut. The Surficial Aquifer Potential Map of Connecticut may be a useful tool for watershed classification relative to potential ground water availability. Surficial aquifer texture groups were prepared to describe unconsolidated areas of the subsurface with similar properties relative to ground water flow. The Surficial Aquifer Texture classifications are based on the Surficial Materials Map of Connecticut, and are 1:24,000-scale data suitable for geologic and environmental mapping and analysis purposes. Not intended for maps printed at map scales greater or more detailed than 1:24,000 scale (1 inch = 2,000 feet.). Not intended for analysis with other digital data compiled at scales greater than or more detailed than 1:24,000 scale. Development of the Surficial Aquifer Texture Map was supported by the Connecticut Department of Environmental Protection Nonpoint Source Management Program, through Section 319 of the Federal Clean Water Act, administered by the US Environmental Protection Agency. Note, the Surficial Materials layer is complemented by the Quaternary Geology layer, which is based on the 1:24,000-scale compilation sheets for the 1:125,000-scale Quaternary Geologic Map of Connecticut and Long Island Sound Basin (U.S.G.S. Scientific Investigations Map 2784). The Quaternary Geologic Map of Connecticut and Long Island Sound Basin provides information on the distribution of depositional environments of glacial meltwater deposits.