relationship of deep troughs in the eastern lake superior...

Acknowledgments

We wish to thank Bill Blewett for his discussion regarding theglacial history and bedrock topography of the eastern UpperPeninsula of Michigan. We also wish to thank the MichiganDepartment of Natural Resources for providing us with digitalelevation data.

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AuTrain-Whitefish Channel

Kingston Outwash Plain

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Figure 14. Perspective view across U.P. and Lakes Superior and Michigan. View to the west.

Figure 3. Map showing structural features of the Lake Superior basin largelyinterpreted from geophysical data (Mariano and Hinze, 1994). Note the location of the Keweenaw fault compared to occurrence and trend of troughs visible in the bathymetric images. There appears to be structural control of their morphology and location.

Figure 6. A system of near-orthogonal joints has been measured in the coastal exposures of the Jacobsville Sandstone on the Upper Peninsula of Michigan (Hamblin, 1958 p. 130). The system is approximately parallel to the two trends of the trenches.


Figure 7. Principle morainic systems in the Great Lakes region. From Farrand (1988).

Relationship of Deep Troughs in the Eastern Lake Superior Basin and Large-scale Glaciofluvial Landforms

in the Central Upper Peninsula of Michigan1 2 3 3REGIS, Robert S. , PATTERSON, Carrie Jennings , WATTRUS, Nigel , and RAUSCH, Deborah , (1) Northern Michigan Univ, 3119

Seaborg Science, Marquette, MI 49855-5342, [email protected], (2) Minnesota Geol Survey, 2642 University Ave. W, St. Paul, MN 55144-1057, (3) Large Lakes Observatory, University of Minnesota, Duluth, 10 University Drive, 215 RLB, Duluth, MN 55812-2496

Figure 5. Bedrock topography of the Upper Peninsula combined with Lakes Superior/Michigan bathymetry and Lower Peninsula DEM.

Introduction

Researchers have been aware of the unusually deep bedrock troughs in the eastern basin of Lake Superior for more than 40 years (Laidly, 1961). The troughs, which can reach several kilometers in width, have been interpreted in a variety of ways. Speculative theories of their origin include formation by:

· a south-trending stream system formed during the Tertiary or an interglacial period that was modified by glaciation and offset by normal faulting (Farrand and Zumberge, 1966; Farrand, 1969); · erosion of pre-existing fractures by glacial ice; (Laidly, 1961); · erosion by glacial meltwater confined within tunnel valleys (Wright, 1971).

The south-trending system of troughs includes the deepest spot (406 m below lake level) in the lake. Some of the troughs are incised more than 200 m into the generally flat bedrock of the lake bottom in this area, which averages 175 to 200 m below water level (Laidly, 1961). The Blue Heron Trough was the subject of a recent geophysical investigation conducted by Wattrus and Rausch. It was clear from this preliminary investigation that there is very little sediment on the bedrock in the upland areas. The troughs themselves are partly filled with Holocene lake sediment and debris slumping from the trough sides. Beneath this fill, the detailed geophysics revealed:

· A linear ridge of seismically-chaotic sediment oriented parallel to the long-axis of the trench (Rausch, unpublished data); · Wedge-shaped accumulations of sediment that crossed the trenches in several places (Rausch, unpublished data).

More ship-board geophysics is planned for next summer by Wattrus, Patterson and Regis.

Statement of Hypothesis

We believe that the trenches were formed by south-flowing subglacial streams. Our work supports the hypothesis of Wright (1971).

We base this conclusion on:the distribution, character and gradient of the trenches (figure 2);the landforms revealed during detailed geophysics of the Blue Heron trench;the spatial relationship of the trenches with large ice-contact, glaciofluvial

landforms on the Upper Peninsula of Michigan,

During the course of this investigation, we realized that the trenches extend beyond the Lake Superior basin and into the Lake Michigan basin. The implications of this discovery will be discussed in the second half of the poster.

· · ·

Glacial geology

On shore in the Upper Peninsula (UP) of Michigan, the trenches are spatially correlative with large outwash fans of the Munising moraine(figures 7 and 8). The trenches in the lake bottom rise steeply to the south until they reach the heads of outwash on the UP. The largest of these fansis the Kingston Outwash Plain (figures 8 and 9; Blewett and Rieck, 1987; Blewett, 2002).

The Kingston Lake Kettle Chain (figures 10 and 11) has been tentatively interpreted as a partly filled bedrock valley that is obscured by the Kingston Outwash plain (Blewett and Rieck, 1987). Its position correlatesto one of the offshore bedrock trenches and it appears to be a continuationof the same bedrock valley.

A 60-m deep, south trending bedrock valley that terminates near Miners Castle, east of Munising (Blewett, 2002) is also clearly associated with an offshore trench (figure 12).

The Au Train channel (figure 13) is continuous with an offshore trench tothe north in Lake Superior and leaves the UP on the southern shore at LittleBay de Noc. From there it continues south as a trench on the floor of Lake Michigan,then on the floor of Green Bay and from there crosses the Door Peninsula. It terminates in a large subaqueous fan on the western floor ofLake Michigan (Hughes, 1963 and 1993). We believe the Au Train Channel originated subglacially with the other trenches. It was later used as anoutlet for Glacial Lake Minong (Farrand, 1969). Difficulty in correlatingthe channel to a lake level may be resolved by interpreting its unusual depth as subglacial, rather than subaerial, in origin (Coleman et al, 1994).

Glacial lakes that occupied the Lake Michigan basin (Coleman, 1994, Hansel etal 1985) include:

· Glacial Lake Chicago, named by Leverett, 1897 · Glenwood II, 12,900 - 12,700ybp, corresponds to the Port Huron advance · Two Creeks low phase, 12,000 - 11,800ybp, correponds to Twocreekan time · Calumet phase, 11,800 - 11,200ybp, corresponds to Two Rivers advance

In summary, the trenches, rather than terminating off shore as had previously been stated, (Farrand, 1969):

· continue onto the UP; · feed large fans at the Munising ice margin; · extend beneath the outwash fans on the UP which partially obscure them; cross the UP into the Lake Michigan basin and beyond.

Implications of the unexpected continuation of the trenches into the Lake Michigan basin

As our project evolved we realized that the trenches continued into LakeMichigan, the Lower Peninsula of Michigan, and Wisconsin. We are currently investigating the nature and extent of similar features that have been reported in Lake Huron and Lake Erie.

The Paleozoic rocks of the Michigan Basin are similar to those of the Superior basin. They are generally undeformed, nearly flat-lying, clastic and carbonate formations. They become progressively younger to the south.

Although similar bedrock extends into southern Lake Michigan, the trenches do not, unless they are obscured by thick lake sediment in the southern half of the basin.

The trenches appear to terminate at the Manistee limit. This is the limit of red, fine-grained till in eastern Wisconsin (the Kewaunee Formation), and till of the Port Huron or Manistee phases in Western Michigan(Wedron Formation).

There are also large fans, both subaqueous and subaerial, at the termini of these trenches in these areas.

Figure 13. Perspective views of the central Upper Peninsula and trenches in the Lake Superior basin. Top view is toward thenortheast. Bottom view is toward the west. Colors represent elevations above sea level (green-red = land).

Summary of the dynamic history of the ice in this region

Ice from the Michigan Basin retreated into the Superior basin and readvanced multiple times, each of lesser extent than the former, reworking red, clayey lake sediment from a proglacial lake (Black, 1969; Farrand, 1969; Wright, 1971; Monaghan, 1990). The extent of the trough-forming ice advances into Wisconsin are marked by the limits of the red clayey till of the Kewaunee Formation (Alden, 1906 and 1918; Mickelson and Evenson, 1975; Mickelson et al., 1984) and either the Port Huron or theManistee Moraine in Michigan (Monaghan, 1990).

Previously unrecognized ice positions include: · A slight retreat represented by a subparallel, ice-marginal channel slightly to the north of Grand Valley in northwest Michigan. · A retreat to the northern Door Peninsula and extreme northwest Michigan as indicated by an ice-marginal channel that crosscuts the trenches.Previously recognized positions are: · the Newberry Moraine on the south shore of the UP, initially recognized by Leverett (1929). · the Munising Moraine, along the north shore of the UP. Its position was also originally recognized by Leverett (1929).

Image Processing Methodology and Data

ERDAS Imagine was used to process all raster data. ArcView was used to add vector data. USGS Digital Elevation Model (DEM) 30m data was acquired from the Michigan DNR. Bathymetric data was derived from NOAA. Bedrock topography data was extracted from Michigan DNR water well files. Alldata was rectified to common coordinates (UTM). Datasets were “clipped” using vector outlines and mosaiced together to produce a continuous dataset of elevations. Processing included level-slicing, topographic relief generation (illumination from315 degrees, 10x VE), and 3-D perspective views.

Figure 1. Three separate images of the Blue Heron Trough. A) Contouredimage of the trough constructed from data extracted from the NOAA database. Blue =deepest areas, red = shallowest. Soundings indicated by red dots. B) Contoured image constructed from 1999 multibeam data. Grid interval is 10 m. C) Shaded relief image constructed from the 1999 multibeam data. Light source located 50 degrees above horizon at an azimuth of 180 degrees. (UTM Zone 16, axes units in meters North/East).

Bedrock Geology

The Lake Superior basin is structurally controlled by rifting that occurred 1.1 billion years ago (figure 3). Mesoproterozoic rocks of the Keweenawan Supergroup related to 1) rifting, 2) subsidence, and 3) sedimentation within the rift, include a stack of sandstone that reaches a kilometer in thickness. The troughs we are studying are incised into the JacobsvilleSandstone, a feldspathic and quartzose sandstone. The appearance of the troughs is distinctly different on either side of the Keweenaw Fault. The formation of the Jacobsville Sandstone was syndepositional with the movement on the Keweenaw fault, an arcuate reverse fault that developed from closure of the rift basin. Faulting offset and isoclinally folded the lower beds of the sandstone but the upper beds are continuous. However, the sandstone is much thicker north of the fault (Manson and Halls, 1994; Mariano and Hinze, 1994).

Basal Cambrian sandstones and resistant overlying Ordovician limestone of the Michigan Basin are found in most of the eastern Upper Peninsula. The slightly south-dipping limestones form a cuesta that trends roughlyeast-west (figures 4 and 5). A system of near-orthogonal joints (figure 6) hasbeen measured in the coastal exposures of the Jacobsville Sandstone (Hamblin, 1958 p. 130). The system is approximately parallel to the twotrends of the trenches.

In summary it is clear that:

· the structure and bedrock geology of the Lake Superior basin are factors controlling the expression of the troughs. · However, there is no process related to bedrock deposition or deformation that can explain the origin the troughs.

Figure 2. Profile along the Blue Heron Trench, across the Upper Peninsula,into Lake Michigan. Line of profile in lower figure.

References:

Alden, W.C., 1906. Description of the Milwaukee Quadrangle, Wisconin: U.S. Geological Survey Geological Atlas, Folio 140, 12 p.Alden, W.C., 1918. The Quaternary geology of southeaster Wisconsin: U.S. Geological Survey Professional Paper 106, 356 p.

thBlack, R.R., 1969. Valderan Glaciation in Western Upper Michigan. Proceedings, 12 Conference on Great Lakes Research, International Association of Great Lakes Research, p. 116 123.Bergquist, S.C. 1936. The Pleistocene history of the Tahquamenon and Manistique drainage region of the northern peninsula of Michigan. Michigan Geological Survey Publication 40, Geological Series 34, part 1 pp.7-148.Blewett, W.L., 2002, Late Wisconsin History of Eastern Upper Michigan: A Review, Field Guide for the 48th Midwest Friends of the Pleistocene, p1-21.Blewett, W.L., and Rieck, R.L., 1987, Reinterpretation of a Portion of the Newberry Moraine in Northern Michigan, Bulletin Geological Society of America, v. 98, p. 169-175.Coleman, S.M., Clark, J.A., Clayton, L, Hansel, A.K., And Larsen, C.E., 1994, Deglaciation, Lake Levels, and Meltwater Discharge in the Lake Michigan Basin, Quaternary Science Reviews, v. 13, p. 879-890Cutler, P.M., D.M. Mickelson, P.M. Colgan, D.R. MacAyeal and B.R. Parizek, 2001. Influence of the Great Lakes on the dynamics of the southern Laurentide ice sheet: Numerical experiments. Geology, 29 (11), 969 1064. Divins, D.L., T.L. Holcombe and D.F. Reid, 1996. Contributions to the lake floor

th geomorphology of the Great Lakes, Geological Society of America, 28 Annual Meeting, Abstracts with Programs Geological Society of America 28 (7), p. 267. Farrand, W.R., and J.H. Zumberge, 1966. Geomorphology of the Floor of Lake Superior. Abstracts with Program, Geological Society of America, 1966. Geological Society of America Special Paper 101, p. 66. Farrand, W.R., 1988, Glacial Lakes Around Michigan, MDNR Bulletin 4, 16 p.

thFarrand, W.R., 1969. The Quaternary History of Lake Superior. Proceedings, 12 Conference on Great Lakes Research, International Association of Great Lakes Research, p. 181 197.Halls, H.C., and G.F. West, 1971, A Seismic Refraction Survey in Lake Superior. Canadian Journal of Earth Sciences, 8, p. 610 630. Hamblin, W.K., 1958. Cambrian Sandstones of Northern Michigan. Michigan Dept. of Conservation, Geological Survey Division, Publication 51.Hansel, A.K., D.M. Mickelson, A.F. Scneider, C.E. Larsen, 1985, Late Wisconsinan and Holocene History of the Lake Michigan Basin, in P.F. Karrow and P.E. Calkin, eds, Quaternary Evolution of the Great Lakes, GSA Special Paper 30, p. 39-53.Hughes, J.D., 1963. Physiography of a six quadrangle area in the Keweenaw Peninsula north of Portage Lake: PhD dissertation, Northwestern University, Evanston, Illinois, 228 p.Hughes, J.D., 1993. When Green Bay Was a Valley: The Au Train-Whitefish-Green Bay Spillway. In Schneider, A.F., editor, Pleistocene Geomorphology and Stratigraphy of the

th Door Peninsula, Wisconsin, guidebook, Midwest Friends of the Pleistocene, 40 Annual Meeting. Kalliokoski, J., 1982. Proterozoic Sedimentary Rocks: Jacobsville Sandstone. Chapter 7E, Geology and Tectonics of the Lake Superior Basin, Geological Society of America Memoir 156, 147 156.Laidly, W.T., 1961. Submarine valleys in Lake Superior. Geographical Review, 51 (2), p. 277-283.Leverett, F., 1929. Moraines and shorelines of the Lake Superior basin. U.S. Geological Survey Professional Paper 154-A, 72 pp.Manson, M.L., and Halls, H.C., 1993. Post-Keweenawan compressional faults in the eastern Lake Superior region and their tectonic significance. Canadian Journal of Earth Sciences, 31 (4), 640 651.Mariano, J., and W.J. Hinze, 1993. Structural interpretation of the Midcontinent Rift in eastern Lake Superior from seismic reflection and potential-field studies. Canadian Journal of Earth Sciences, 31 (4) 619 628.Mickelson, D.M., and E.B. Evenson, 1975. Pre-Two-Creekan age of the type Valders till, Wisconsin. Geology, v. 3, p. 587 590.Mickelson D.M., L. Clayton, R.W. Baker, W.N. Mode and A.F Schneider, 1984. Pleistocene stratigraphic units of Wisconsin: Wisconsin Geological and Natural history Survey Miscellaneous Paper 84-1, 97 p. Monaghan, G.W., 1990. Systematic variation in the clay-mineral composition of till sheets; Evidence for the Erie Interstade in the Lake Michigan basin. Geological Society of America, Special Paper 251, 43 50.Morey, G.B., P.K. Sims, W.F. Cannon, M.G. Mudrey Jr., and D.L. Southwick, 1982. Geologic Map of the Lake Superior Region Minnesota, Wisconsin, and Northern Michigan. Minnesota Geological Survey Map S-13, 1:1,000,000.Wright, H.E., 1971. Retreat of the Laurentide Ice Sheet From 14,000 to 9,000 years ago. Quaternary Research, 1, 316 330.

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Upper Peninsulaof Michigan

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Figure 8. General glacial landforms of the central U.P. of Michigan

Figure 9. Profiles across fans of the Kingston Outwash Plain.Figure 10. Perspective drawing of Kingston Outwash Plain and kettle chain

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Me

ters

AM

SL

VE=6x Meters

Modern Lake Superior shoreline

Modern Lake Michigan Shoreline


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VE= 10x.

Figure 11. Topographic map of the Kingston Kettle chain.

Figure 12. Topographic map of the Miners River (bedrock) valley.

Figure 4. Cambro-Ordovician Cuesta in the Upper Peninsula of Michigan

Figure 9

Figure 10

(From Blewett and Rieck, 1987)

We are currently investigating:

· The extent of this type of drainage system in the sedimentary rock substrates of the Great Lakes; · The evolution and dynamics of our proposed subglacial drainage system.

Our preliminary conclusion is that these trenches represent thenormal drainage that develops near the margins of an ice lobe when is rests on erodible rock. Although the trenches aredramatic and the drainage events appear to be large in volume and periodic, we do not believe that they are either rare orcatastrophic. It is the way lobes work.

relationship of deep troughs in the eastern lake superior...

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