Generalized lithology and lithogeochemical character of near-surface bedrock in the New England region

Online link https://geo-nsdi.er.usgs.gov/metadata/open-file/03-225/metadata.faq.html
Description This geographic information system (GIS) data layer shows the dominant lithology and geochemical, termed lithogeochemical, character of near-surface bedrock in the New England region covering the states of Connecticut, Maine, Massachusetts, New Hampshire,
Originators Robinson, Gilpin R., Jr. and Kapo, K. E.
Publication U.S. Geological Survey Open-File Report 03-225

Related topics

States or counties

Overview of attributes

The thirty-seven lithogeochemical units are defined for the New
England study region using an alpha-numeric identification: a
lithology code ("Litho_code", numeric) with a modifier code
("Lith_mod", alphabetic).
Example: Litho_code= "33" and Lith_mod= "cs"
Lithogeochemical unit is expressed as "33cs"
There are 20 lithology codes (including a code for water) that
represent rock type, metamorphic grade, and geologic setting.
Each bedrock unit is assigned one of 20 lithology codes based on
the description of the bedrock unit from the state bedrock
geologic maps.  Nine lithological modifier codes are used to
identify minor amounts of carbonate or sulfide minerals, and
subdivide granitic units into subgroups based on their chemical
and mineral characteristics.
The 37 lithogeochemical units are generalized into major rock
group categories (Rock_GpA and Rock_GpB).  Each category under
these headings shares similarities in overall geochemistry and
lithology. Rock Group A ("Rock_gpA") has 8 categories (including
one for freshwater).
Bedrock lithology information was obtained from
separate state source maps, and this results in some
discrepancies in rock group categories between polygons that meet
at state boundaries.  For example, a bedrock polygon that is
split into two polygons by a state border may be be categorized
as "Metamorphic Rocks Undivided" in one state and "Carbonate
Rocks" in the other state, based upon the different
characterization methods used by the originators of each of the
state geologic maps.  However, these discrepancies are relatively
few and do not interfere with the overall lithologic patterns of
the New England study area.
The eight major groups for Rock Group A are further divided into
Rock Group B. Rock Group B ("Rock_GpB") has 19 categories
(including one for freshwater). Each category has an ID code
("R_GpB_ID") that is used as a cross reference to other tabled
information.
Individual bedrock unit codes are designated by state from the
original state geologic maps used to create the digital
coverage (see references for source maps). Names and descriptions
for each bedrock code were gathered from source maps and are
provided in the associated file Bedrock.dbf. The "Bedrock_1"
attribute describes the alphanumeric code given to bedrock units
in the original state map sources (for example, "Trnh" or "Dw3A").
Some units have been combined (example "O-cr+O-cra") during the
digitizing process. "Bedrock_2" may further designate a polygon
as "water" if appropriate, but for  polygons not water bodies
"Bedrock_2" is the same as "Bedrock_1".
The bedrock units shown on the individual state maps for the New
England study region were classified according to a
lithogeochemical scheme modified from Robinson and others (1999).
Specifically, the modification included additional classification
into broad rock groups and the subdivision of granitic bedrock
units into subgroups based on age and magma chemistry, and the
addition of modifying attributes to indicate relative age.
However, this modification to the classification system is
evident in the lithogeochemical units.

A detailed listing and descriptions of the 37 lithogeochemical units is provided in http://pubs.usgs.gov/of/2003/of03-225/unit-description.html Relationships among rock groups and between rock groups and lithogeochemical units are shown in http://pubs.usgs.gov/of/2003/of03-225/rock-groups.html More detailed descriptions of each bedrock unit (grouped by the state in which they occur) are provided in http://pubs.usgs.gov/of/2003/of03-225/bedrock.dbf

ne_lith.dbf

Polygonal map units define bedrock areas with similar lithologic and geochemical properties.

Label Definition
State This item identifies the state locations of polygons. Because the lithogeochemical characterization was derived from information on the state geological map, the state is associated with each polygon to help identify of source of the geologic information.
Hydro_Bsn The coverage is divided by drainage basins based on the USGS National Water Quality Assessment (NAWQA) study areas CONN and NECB. NAWQA program information can be accessed at http://water.usgs.gov/nawqa/studyu.html For purposes of focusing on the area of New England in this coverage, two new drainage areas have been added to the coverage: Northern Maine (N_MAINE) and St. Lawrence/Hudson River (STL_HUD) drainage areas. The N_MAINE drainage area covers the area in Maine not included in the NECB study area. The STL_HUD drainage area combines the small portion of the NAWQA Hudson River basin included in this coverage, and the area of northern Vermont not included in a NAWQA study area.
G_Province The bedrock units shown on the individual state maps for the New England study area have been grouped into 10 geologic provinces. The map units in each province group share common features of lithology, age of formation, geologic setting, and tectonic history. The province groups generally occur as northeast-trending belts that follow the structural fabric of the Appalachian foldbelt and faults in New England. The tectonic map features contained with the state-level bedrock geologic maps and the grouping of bedrock map units by geologic belts in the legends of the state-level bedrock geologic maps were used to define province attributes.
G_Prov_id A one- or two-letter abbreviation for the geologic provinces.
Rock_GpA A broad categorization of lithogeochemical units. Each category under these headings shares similarities in overall geochemistry and lithology.
Rock_GpB Further subdivides the broad categories of lithgeochemical units defined by Rock_GpA.
R_GpB_id Numerical code for Rock_GpB values.
Litho_code Lithogeochemical classification code, developed for this data set. Field is defined as double (width 16, 3 digits to right of the decimal) but all values are integer.
Lith_mod Lithogeochemical classification code, developed for this data set that further subdivides the lithogeochemial groups based on the presence of carbonate and(or) sulfide mineral or on the relative age of the bedrock unit.
Bedrock_1 Bedrock Unit label appearing on the state geologic map used as the source for the lithogeochemical categorization.
Bedrock_2 Bedrock unit codes characterized by state and including value for water bodies. Except for surface waters, this field is the same as Bedrock_1.
X_COORD X coordinate of polygon label point in Albers projection
Y_COORD Y coordinate of polygon label point in Albers projection