The Indiana Geological Survey has completed a three-year geologic mapping project in Monroe County, Indiana, with support from USGS STATEMAP. This project anticipated the need for geologic information to guide planning in and around Bloomington, a major population center along the proposed corridor for the Interstate 69 extension from Indianapolis to Evansville. The recently published geologic map of the Bloomington Quadrangle, located in the center of Monroe County, provides detailed mapping where Interstate 69 interchanges are planned and where urban growth is likely. The map will aid planners in assessing geologic hazards, such as karst features, and evaluating resources of dimension stone found in the Salem Limestone (Mississippian) and crushed stone resources of the Blue River Group (Mississippian).

The Bloomington Quadrangle component of the Monroe County project applied Indiana Geological Survey three-dimensional computer mapping techniques to large-scale (1:24,000) geologic mapping. The map was created by modeling rock unit boundary surfaces with computer gridding

and contouring software using a variety of data sources. The rock unit models were tested to ensure that isolated exposures and subsurface occurrences of map units would fall between the appropriate upper and lower contacts. Outcrop and sub crop lines were generated by computing intersections between the contact-surface models and the bedrock-surface model. The resulting intersection lines were used to generate the bedrock-unit polygons shown on the geologic map. Unconsolidated deposits shown on the map were hand-drawn and then digitized, to ensure proper registration with topographic features.

The three-dimensional geologic modeling procedures used to create the Bloomington Quadrangle geologic map are designed to facilitate the production of derivative map products that will complement the geologic map and address specific planning needs. Map users will also be able to link to the project database for more detailed information and updates, as well as having access to geographic information system layers that are compliant with North American Geologic Map Data Model standards.

Abstract I Methods: Modeling Indiana Bedrock IV

Data III

Conclusion VI

Computer-Generated Geologic Map of the Bloomington 7.5-Minute Quadrangle, Indiana Carolyn M. Estell, Todd A. Thompson, Brian D. Keith, and Walter A. Hasenmueller

cmunk@indiana.edu

Indiana Geological SurveyIndiana University611 N. Walnut GroveBloomington, IN 47405http://igs.indiana.edu/

Presentation 58-5

Monroe County Digital Elevation Model (DEM)A 10-meter composite DEM for the county was interpolated for the project area from existing 1:24,000-

scale or larger hypsography with a contour spacing of 10 feet or less (see map to the right). The DEM used for the project was filtered twice with a Gaussian low-pass filter to remove artifacts like string-of-pearls.

Project DataThe Monroe County project database integrates data from new field work and drilling with existing public-domain data from a variety of sources, including petroleum-well records, water-well records, and archived data including information from student thesis work and work maps from previous studies as well as Indiana Department of Transportation highway borings.

Over 1070 records were used in the creation of this geologic map with 267 data points in the Bloomington quadrangle (see map to the left).

Project DatabaseThe database is organized around geologic boundary surfaces,

specifically those found in Indiana (see image on the right). This database format allowed for flexibility generating queries necessary for modeling Indiana geology.

Data for boundary surface was prioritized based on its confidence level. For example, priority was given to new field data when archived data was in the same location. Information on unit thickness or horizon elevation was exported to a spreadsheet for use in generating boundary surface models.

Introduction: Monroe County Project II

LocationMonroe County is located in south-central Indiana with the Bloomington 7.5-Minute quadrangle located near the center of the county (see map to the left). The Bloomington 7.5-Minute quadrangle geologic map is the first 1:24,000-scale map to be published from the three-year, Monroe County STATEMAP Project.

Geologic Setting The project area is on the eastern flank of the Illinois Basin, and rock units dip gently westward (about 30 to 35 ft/mile). Rock units range in age from Early Mississippian to Early Pennsylvanian in age and form bands that trend in a general north-south direction (see map to the right).

SignificanceThe county has significant mineral resources potential. The most notable resource is the Salem Limestone. This unique dimension stone forms the exterior of world-famous architecture, including the Empire State Building and the National Cathedral. Other carbonate rocks found in the county provide abundant crushed and chemical stone resources. The Mt. Carmel Fault and Leesville Anticline are complex, north-south trending structures

located in the eastern part of the county along which natural gas storage fields are located (see map to the right).

Gridding methods Two gridding algorithms were used generating the Geologic Map of the Bloomington 7.5-Minute Quadrangle.

Bedrock SurfaceMonroe County is covered with a thin, nearly continuous, blanket of unconsolidated material, with the exception of two large valley systems. The average depth of unconsolidated material is approximately 10 feet (see picture on right).

The bedrock-surface model used to generate the geologic map of Bloomington 7.5-Minute Quadrangle was generated using the following steps.

1: To create an accurate bedrock-surface model the DEM, or topographic surface, was filtered twice, or smoothed, with a Gaussian low-pass filter.

2: The smoothed topographic surface was lowered eight feet.

A second bedrock-surface model was created using the same filtering process, but the surface was only lowered three feet. Two bedrock-surface models were created because the amount of unconsolidated material on the steeper terrain in the east is thinner than the unconsolidated material found in the central and western portions of the county.

Computer-Generated Geologic MappingBoundary Surfaces Three boundary surfaces were used to create the framework of our geologic model: Borden Group top, Sanders Group top, and the Blue River Group top. These surfaces were chosen based on the amount and quality of data available for each surface throughout Monroe County. Borden Group top data was limited to information west of the Mt. Carmel Fault. This provided the structural control for the Leesville Anticline.

Modeling Steps1: Export data from database to a spreadsheet2: Evaluate and test data to ensure units fall between appropriate contacts 2a-c: Add additional control points, if necessary (see diagram on right)3: Grid data using one aforementioned algorithm with 50 m grid spacing4: Filter grid with Gaussian low-pass filter, if necessary5: Spline grid to 10 m grid spacing

Thickness Models to Generate New Boundary Surface ModelThe West Baden Group, Ste. Genevieve Limestone, St. Louis Limestone, and the Harrodsburg Limestone and Ramp Creek Formation Boundary were generated by following the modeling steps listed below and shown in the figure to the left.

Modeling Steps1: Select boundary surface model with good control2: Generate thickness model of geologic unit directly adjacent to the boundary surface3: Add or subtract the boundary surface model grid and the thickness model grid4: New boundary surface model is generated

Thickness Models to Generate Additional Data for Structural Control To add structural control to the eastern extent of the Borden Group boundary surface model and the western extent of the Sanders Group boundary surface model the following modeling steps were followed. Steps 1 and 2 are the same as the previous modeling steps. Steps 3, 4, and 5 are shown on the left.

Modeling Steps 1: Select boundary surface with good control2: Generate thickness model of appropriate geologic unit 3: Calculate residuals using boundary surface data points against the thickness model4: Add calculated data points to existing data5: Grid data to create new boundary surface

DEM of Monroe County

Illustrated Bedrock Surface Modeling

Typical Exposure as Shown in Database Form

Results: Bloomington 7.5-Minute Quadrangle Geologic Map V

Quarried land (Holocene)–Land disturbed by active or abandoned dimension-stone or crushed-stone quarry activity.

Made and modified land (Holocene)–Land disturbed by numerous episodes of shallow excavation and grading in densely urbanized areas and fill associated with major highways, dams, and other large structures.

Alluvium (Holocene)–Overbank and channel deposits of modern streams on valley bottoms. Mainly silt and clay, locally sandy and stony.

Terrace-colluvium-fan complex (Pleistocene and older)– Undifferentiated deposits of older streams, lakes, colluvium, alluvial fans, and outwash that form terraces that stand a few feet to as much as 70 feet above the level of the present-day valleys.

West Baden Group undivided (Mississippian, Chesterian)–The West Baden Group consists of two limestone and three siliciclastic formations: in descending order, the Elwren Formation, Reelsville Limestone, Sample Formation, Beaver Bend Limestone, and Bethel Formation. The Reelsville is not present in the map area.

Paoli Limestone (Mississippian, Chesterian)–Dominantly buff to medium pinkish gray skeletal packstone to grainstone that is variably oolitic in the upper part.

Ste. Genevieve Limestone (Mississippian, Valmeyeran)–Oolitic, skeletal, micritic, and detrital limestone with minor amounts of shale, dolomite, and chert.

Database Form

Generating Outcrop Polygons Each boundary surface model was subtracted from the appropriate bedrock-surface model. The line where the two surfaces intersect has a zero value (see picture on the left). This line represents the outcrop/subcrop pattern of the boundary surface, specifically the contact surface (see image on the right).

Field Checking Adjustments to our geologic models were made to better match field observations. For example, one key area was the location of the St. Louis Limestone along Indiana State Road 45/46 where it clearly outcrops along the road. Our model was adjusted by adding new data to fit field observations.

Methods: Modeling Indiana Bedrock Continued

Data Distribution Throughout Monroe County

Natural Neighbor–chosen for modeling structural tops of the Borden, Sanders, and Blue River Group surfaces because of the quantity and distribution of data, and amount of computing time.

Radial Basis Function–used for modeling the thickness of Salem, Paoli, and the Ste. Genevieve Limestones. This function is not an exact gridding method so smoothing was minimized to honor the data.

Monroe County Geology and Structure

Blue Area is Monroe County, Indiana

Derivative MapsThe three-dimensional geologic modeling procedures used to create the Bloomington 7.5-Minute Quadrangle Geologic Map are designed to facilitate the production of derivative map products that will complement the geologic map and address specific planning needs. Possible derivative map products include crushed stone resource potential, dimension stone resource potential, unconsolidated thickness, and overburden.

Data AccessMap users will be able to link to the project database for more detailed information and updates, and have access to geographic information system (GIS) layers that are compliant with North American Geologic Map Data Model standards. The GIS layers will be accessible and available for downloading though A GIS Atlas for Indiana (http://129.79.145.7/arcims/statewide_mxd/index.html) hosted by the Indiana Geological Survey (see image on the left). These layers may also be incorporated into the USGS National Geologic Map Database (http://ngmdb.usgs.gov/).

St. Louis Limestone (Mississippian, Valmeyeran)–Thin beds of medium- to dark-gray-brown micritic, pelletal, and skeletal limestone; calcareous shale; and silty dolomite. Nodules and thin discontinuous beds of mottled light-gray and dark-gray chert are locally conspicuous.

Salem Limestone (Mississippian, Valmeyeran)–Crossbedded skeletal limestone that is medium- to coarse-grained, tan, grayish-tan, and light gray, porous, fairly well sorted, which occurs in exceptionally thick beds. Thin dolomite beds occasionally present.

Harrodsburg Limestone and Ramp Creek Formation undivided (Mississippian, Valmeyeran)–The Harrodsburg is dominantly well-cemented bryozoan limestone. Includes dolomite, shale, and very argillaceous limestone and minor amounts of chert. Geodes and silicified material conspicuous near base of the formation. The Ramp Creek, situated below the Harrodsburg, consists of interbedded skeletal limestone, and siltstone. Chert and geodes are common.

Borden Group undivided (Mississippian, Valmeyeran)–The upper Borden consists mostly of siltstone, fine-grained sandstone, and sandy shale with minor amounts of impure crinoidal limestone. Geodes and chert present in upper part.

Contact–Approximately located

Cross Section Line–A-A'

Cross SectionA A'

Correlation Chart

Description of Map Units

Generating Outcrop/Subcrop Polygon

Building Foundation in Bloomington

A GIS Atlas for Indiana Showing Bedrock Geology

Outcrop/Subcrop Polygon