geologic atlas of sibley county, minnesota
TRANSCRIPT
Prepared and Published with the Support of
THE SIBLEY COUNTY BOARD OF COMMISSIONERS ANDTHE MINNESOTA ENvIRONMENT AND NATURAL RESOURCES TRUST FUND
AS RECOMMENDED BY THE LEgISLATIvE-CITIzEN COMMISSION ON MINNESOTA RESOURCES
Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification.
coNtoUr INtErval 15 MEtErS
GIS compilation by r.S. livelyEdited by lori robinson
MINNESOTA gEOLOgICAL SURvEYHarvey Thorleifson, Director
Digital base modified from 1990 census tIGEr/line Files of U.S. Bureau of the census (source scale 1:100,000); county border files modified from Minnesota Department of transportation files; digital base annotation by Minnesota Geological Survey.
Universal transverse Mercator Projection, grid zone 151983 North american Datum
1 0 1 2 3 4 5 MILES
8 KILOMETERS
SCALE 1:100 000
1 0 1 2 3 4 5 6 7
locatIoN DIaGraM
COUNTY ATLAS SERIESATLAS C-24, PART A
Sibley County Plate 6—Bedrock Topography
and Depth to Bedrock
GEOLOGIC ATLAS OF SIBLEY COUNTY, MINNESOTA
BEDROCK TOPOgRAPHY
By
John H. Mossler and Julia R. Steenberg
2012
DEPTH TO BEDROCK
By
John H. Mossler and Julia R. Steenberg
2012
R. 31 W. R. 30 W. R. 29 W. R. 28 W. R. 27 W. R. 26 W.
R. 25 W.
T. 112 N.
T. 113 N.
T. 114 N.
R. 31 W.
R. 30 W. R. 29 W.
R. 28 W. R. 27 W. R. 26 W.
R. 25 W.
T. 112 N.
T. 113 N.
T. 114 N.
SEVERANCE
CORNISH
ALFSBORG SIBLEY
KELSO
HENDERSON
MOLTKEBISMARCK
TRANSITDRYDEN
ARLINGTON
JESSENLAND
GRAFTON NEW AUBURN
GREEN ISLE
WASHINGTON
FAXON
LAKE
16
31 36
1
11
1
1
1
666
66
6
31 31 31 3136
36 36
1
1
1 1
1
1 1
1
1
36 3636
36 36
6
6
6
66
6
66
6
31 31 31
3131
31
6
3636
2419
3131 31
36
3635
313131 363636
Swan Lake Sand
Lake
RoundGroveLake
Titlow Lake
SchillingLake
Lake
High
Island
Schauer Lake
LakeSeverance
Washington
Lake
LakesErin
LakeKerry
Silver Lake
ClearLake
Lake
Lake
Altnow
Mud
LakeIndian
Ward Lake
LakeCurran
Rush
River
Branch
Middle
South
Branch
Rush
River
RushRive
rMiddle
Buffalo Creek
Creek
Creek
Creek
Creek
Mile
Eight
Rush
River
Branch
Rush
River
Branch
Rush
River
Branch
South
North
Rush
River
Island
Buffalo
Creek
Beve
ns
Island
High
High
Gibbon Winthrop
Gaylord
Arlington
GreenIsle
NewAuburn
Henderson
)93
)19
)19
)22
)22
)5
)25
)5
)25
)25
)22
)19
)15
)15
94° W.94°15' W.
94°30' W.
94°15' W.94°30' W.
44°30' N.
44°30' N.
44°37' 30" N.
44°37' 30" N.
94° W.RENVILLE COUNTY
CAR
VER
CO
UN
TY
SCOTT COUNTY
CARVER COUNTYMCLEOD COUNTY
MC
LEO
D C
OU
NTY
NICOLLET COUNTY LE SUEUR C
OUNTYREN
VILL
E C
OU
NTY
169
Rive
r
Minnes
ota
NICOLLET COUNTY
LE SUEUR COUNTY
SCOTTCOUNTY
300
300
285
300
300
300
285
255
240
225
330
300
300
300315
300
300
300
300
315
315 300315
315
300
300
315
315
315
300
300
300
300
300
315
315
315
300
315
300
315
300
315
300
300
315
300
315
300
300
270
315
300
315
315
315
315
315
315
315
315
315
300
300
315
300
300
315
315315
300
315
240
315
315
300
315
315
300
315
300
300
300
315
300
300
315
300
315
315
300
315
300
315
315 315
315
315
300
315
300
315
315315
315
315315
315
300
255270285
255
255
285
285
285
270
225
300
300
315
R. 31 W. R. 30 W. R. 29 W. R. 28 W. R. 27 W. R. 26 W.
R. 25 W.
T. 112 N.
T. 113 N.
T. 114 N.
R. 31 W.
R. 30 W. R. 29 W.
R. 28 W. R. 27 W. R. 26 W.
R. 25 W.
T. 112 N.
T. 113 N.
T. 114 N.
SEVERANCE
CORNISH
ALFSBORG SIBLEY
KELSO
HENDERSON
MOLTKEBISMARCK
TRANSITDRYDEN
ARLINGTON
JESSENLAND
GRAFTON NEW AUBURN
GREEN ISLE
WASHINGTON
FAXON
LAKE
16
31 36
1
11
1
1
1
666
66
6
31 31 31 3136
36 36
1
1
1 1
1
1 1
1
1
36 3636
36 36
6
6
6
66
6
66
6
31 31 31
3131
31
6
3636
2419
3131 31
36
3635
313131 363636
Swan Lake Sand
Lake
RoundGroveLake
Titlow Lake
SchillingLake
Lake
High
Island
Schauer Lake
LakeSeverance
Washington
Lake
LakesErin
LakeKerry
Silver Lake
ClearLake
Lake
Lake
Altnow
Mud
LakeIndian
Ward Lake
LakeCurran
Rush
River
Branch
Middle
South
Branch
Rush
River
Rush
River
Middle
Buffalo Creek
Creek
Creek
Creek
Creek
Mile
Eight
Rush
River
Branch
Rush
River
Branch
Rush
River
Branch
South
North
Rush
River
Island
Buffalo
Creek
Beve
ns
Island
High
High
Gibbon Winthrop
Gaylord
Arlington
GreenIsle
NewAuburn
Henderson
)93
)19
)19
)22
)22
)5
)25
)5
)25
)25
)22
)19
)15
)15
94° W.94°15' W.
94°30' W.
94°15' W.94°30' W.
44°30' N.
44°30' N.
44°37' 30" N.
44°37' 30" N.
94° W.RENVILLE COUNTY
CAR
VER
CO
UN
TY
SCOTT COUNTY
CARVER COUNTYMCLEOD COUNTY
MC
LEO
D C
OU
NTY
NICOLLET COUNTY LE SUEUR C
OUNTYREN
VILL
E C
OU
NTY
169
Rive
r
Minnes
ota
NICOLLET COUNTY
LE SUEUR COUNTY
SCOTTCOUNTY
300
300
285
300
300
300
285
255
240
225
330
300
300
300315
300
300
300
300
315
315 300315
315
300
300
315
315
315
300
300
300
300
300
315
315
315
300
315
300
315
300315
300
300
315
300
315
300
300
270
315
300
315
315
315
315
315
315
315
315
315
300
300
315300
300
315
315315
300
315
240
315
315
300
315
315
300
315
300
300
300
315
300
300
315
300
315
315
300
315
300
315
315 315
315
315300
315
300
315
315315
315
315315
315
300
255270285
255
255
285
285
285
270
225
300
300
315
901-950
601-650
651-700
701-750
751-800
801-850
851-900
551-600
501-550
451-500
401-450
INTRODUCTION
The configuration of the bedrock surface in Sibley County is represented by the colors assigned to 50-foot (15-meter) elevation intervals (example: 751 to 800 feet above sea level) on the Bedrock Topography map. The position of the contour intervals was determined from records of water-well construction, scientific borings, and seismic soundings. The seismic data were collected specifically for this project by the Minnesota Department of Natural Resources (Todd Petersen) and the Minnesota Geological Survey (V.W. Chandler) and were focused in the central part of the map area. The somewhat irregular distribution of data can be seen on the Data-Base Map (Plate 1) and should be considered when assessing the reliability of the map at any particular location. Records of drill holes that intersect bedrock are most abundant in the eastern part of the county near populated areas that rely on ground water from bedrock aquifers. There are fewer wells that reach bedrock in rural areas of the county because many of the domestic wells in those areas get sufficient water from sand and gravel beds in the glacial sediment.
The bedrock surface in Sibley County varies from more than 900 feet (274 meters) above sea level in the western part to less than 450 feet (137 meters) above sea level in the extreme northeast part of the county. The most prominent feature of the bedrock topography is an extensive, deeply buried valley network in the central part of the county that deepens to the east. Based on recent mapping, prominent buried bedrock valleys to the north in McLeod County and south in Nicollet County join the valley network in Sibley County and drain east into northwestern Le Sueur County, western Scott County, and continue east into Dakota County, entering the ancestral Mississippi River drainage system south of the Twin Cities metropolitan area (Mossler, 2009; Mossler and Chandler, 2009; Jirsa and others, 2010; Mossler and Steenberg, 2012).
Other highlights of the bedrock topography include the flat uplands developed across the hard, resistant bedrock of the Oneota Dolomite and the St. Lawrence Formation in the western part of Sibley County. The uplands are incised by narrow valleys of softer, less resistant rock formations including the Lone Rock Formation, Wonewoc Sandstone, and Eau Claire Formation. These formations also tend to form more shallowly dipping slopes on the bedrock topography surface in the central part of the county.
REFERENCES
Jirsa, M.A., Boerboom, T.J., Chandler, V.W., Mossler, J.H., Runkel, A.C., and Setterholm, D.R., 2010, Preliminary bedrock geologic map of Minnesota: Minnesota Geological Survey Open-File Report 10-2, scale 1:1,000,000.
Mossler, J.H., 2009, Bedrock topography, pl. 5 of Bauer, E.J., project manager, Geologic atlas of Carver County, Minnesota: Minnesota Geological Survey County Atlas C-21, 5 pls., scale 1:100,000.
Mossler, J.H., and Chandler, V.W., 2009, Bedrock topography, pl. 6 of Lusardi, B.A., project manager, Geologic atlas of Mcleod County, Minnesota: Minnesota Geological Survey County Atlas C-20, 6 pls., scale 1:100,000.
Mossler, J.H., and Steenberg, J.R., 2012, Bedrock topography, pl. 6 of Setterholm, D.R., project manager, Geologic atlas of Nicollet County, Minnesota: Minnesota Geological Survey County Atlas C-25, 6 pls., scale 1:100,000.
INTRODUCTION
The thickness of the glacial sediment is equal to the depth from the land surface to the bedrock surface. To calculate this thickness, a grid of bedrock-surface elevations was subtracted from a corresponding grid of land-surface elevations (30-meter cell size). The surface elevation grid was resampled from the National Elevation 10-meter data set of the U.S. Geological Survey, and the bedrock elevation grid was interpolated from interpretation of water well data (see the Introduction to the Bedrock Topography map). The residual grid was then classified at a 50-foot (15-meter) interval to produce the color-coded Depth to Bedrock map. The angular lines on this map are the result of the mathematical process used to create this model. Because the surface of a lake is regarded as the land surface elevation, the thickness of glacial sediment within lake boundaries includes the depth of the lake water. To calculate the true thickness of sediment beneath the lake it is necessary to subtract the water depth at that location. In places the thickness of the glacial sediment varies greatly over short distances, and mapping at this scale (1:100,000) may not properly resolve such prominent variations. For that reason it is best to consult site-specific data, such as water well records and seismic soundings, wherever they are available.
The thickest sediments in Sibley County occur over deep, pre-glacial valleys in the bedrock surface. In the central part of the county more than 500 feet (152 meters) of sediment overlie a network of deep bedrock valleys. In contrast, bedrock is at or within 50 feet (15 meters) of the land surface in the easternmost part of the county within the Minnesota River valley. Most of the details in the Depth to Bedrock map are related to landforms because the model of the bedrock surface is based on much less data than the land surface topography model.
Depth in feet from the land surface to the bedrock surface
1–50
51–100
101–150
151–200
201–250
251–300
301–350
351–400
401–450
451–500
501-550
Elevation of the bedrock surface in feet above mean sea level
GIS compilation by r.S. livelyEdited by lori robinson
©2012 by the regents of the University of Minnesota
the University of Minnesota is an equal opportunity educator and employer
Digital base modified from 1990 census tIGEr/line Files of U.S. Bureau of the census (source scale 1:100,000); county border files modified from Minnesota Department of transportation files; digital base annotation by Minnesota Geological Survey.
Universal transverse Mercator Projection, grid zone 151983 North american Datum
1 0 1 2 3 4 5 MILES
8 KILOMETERS
SCALE 1:100 000
1 0 1 2 3 4 5 6 7
coNtoUr INtErval 15 MEtErS