See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/325576131 Luczaj-(2013)-Geoscience Wisconsin Niagara Escarpment(GS22-a01) Article · September 2013 CITATIONS READS 0 465 1 author: John Luczaj University of Wisconsin - Green Bay 27 PUBLICATIONS 321 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Niagara Escarpment View project Eastern Wisconsin Diagenesis View project All content following this page was uploaded by John Luczaj on 05 June 2018. The user has requested enhancement of the downloaded file. GEOLOGY OF THE NIAGARA ESCARPMENT IN WISCONSIN John A. Luczaj ABSTRACT The Niagara Escarpment is a 650-mile (1,050 km) long discontinuous bedrock ridge that runs from western New York near Niagara Falls, through southern Ontario and the Upper Peninsula of Michigan into eastern Wisconsin. In Wisconsin, the escarpment runs from Rock Island on the tip of Door County all the way south to Ashippun in Dodge County and is the most prominent topographic feature in the eastern part of the state. It includes the mainly west and northwest-facing escarpments that have developed on resistant eastward-dipping Silurian dolostones that overlie the much softer Ordovician Maquoketa Shale. The geologic feature we see today was a culmination of many depositional, tectonic, and erosional processes that have operated over hundreds of millions of years. Together, these events have produced spectacular cliffs and ledges that overlook lowlands to the west beginning at Horicon Marsh in the south all the way north to the bay of Green Bay west of the Door Peninsula. This article is intended as a comprehensive review of the geologic history of this region as it pertains to the Niagara Escarpment. INTRODUCTION known as a cuesta. It ranges in height from small The Niagara Escarpment is the topographic expres- ledges a few feet (meters) high to cliffs over 200 sion of a bedrock unit that extends at least 650 mi ft (60 m) high in parts of Door County. The cuesta (1,046 km) from eastern Wisconsin through the Upper exists because of a complex interplay between ancient Peninsula of Michigan, through Manitoulin Island and marine sedimentary environments, development of the Bruce Peninsula into southern Ontario and into the Michigan structural basin to the east, and sub- the Niagara area of New York. This internationally sequent erosion by rivers and glaciers. The Niagara recognized geologic feature was named for the region Escarpment’s importance to the region’s ecology, around Niagara Falls in New York and Ontario where materials industry, and tourism industry has long been the Niagara River plunges over the Silurian Lockport recognized (Anderson and others, 2002; Kasprzak Dolostone into a gorge cut through the underlying and Walter, 2001; Kluessendorf and Mikulic, 1989; lower Silurian and uppermost Ordovician mudstones Mikulic and others, 2010; this issue). In 1852, and sandstones. T.C. Chamberlin (1877) used the term “ledge” to The Niagara Escarpment is eastern Wisconsin’s describe the Niagara Escarpment throughout eastern most prominent topographic feature. It runs for Wisconsin. Local vernacular names for rocks along approximately 230 mi (370 km) from the tip of Door and near the Niagara Escarpment include “the ledge” County southward to Dodge County (fig. 1), with in areas to the south between Green Bay and Fond sporadic exposures further to the south in Waukesha du Lac, as well as “the bluff” to the north in Door County where the bedrock escarpment is mostly County, reflecting the important relationship between concealed beneath glacial sediments (Kasprzak and local culture and the escarpment in Wisconsin. Others Walter, 2001). It is the best developed in a series of in northeastern Wisconsin have used the term “the parallel escarpments in eastern Wisconsin that are ridge” (for example, Kox, 1985). present along the western margin of the ancestral Despite this recognition, there has not been a com- Michigan basin. The Niagara Escarpment is defined prehensive peer-reviewed scientific review article by the western edge of a discontinuous topographic dedicated to the geology of the Niagara Escarpment ridge of eastward dipping Silurian dolostone, formally in Wisconsin. With a few exceptions, limited 1 Department of Natural and Applied Sciences, University of Wisconsin–Green Bay, 2420 Nicolet Drive, Green Bay, Wisconsin 54311-7001 • [email protected] Wisconsin Geological and Natural History Survey GEOSCIENCE WISCONSIN • Volume 22, Part 1 • published online 2013 Niagara Escarpment in eastern Wisconsin Y A B N E N E A R G G I H C I M E K A L O G A B E N N I W E K A L 0 8 16 24 32 Miles Niagara Escarpment Figure 1. Digital elevation model with hillshade showing the location of the Niagara Escarpment in Wisconsin. Location data Digital elevation model sources: Niagara Escarpment Resource with shaded relief | Wisconsin Network (NERN), outcrops, well construction Geological and Natural History Survey | Projection: NAD 1983 reports, USDA soil maps, and other sources. HARN Wisconsin TM 2 • GEOSCIENCE WISCONSIN attention has been paid to the bedrock of northeast- region (for example, Shrock 1939, 1940; Sherrill, ern Wisconsin in peer-reviewed literature, especially 1978; Kluessendorf and Mikulic, 1989; Harris outside of groundwater and paleontological investiga- and Waldhuetter, 1996; Harris and others, 1998; tions. For example, the North Central Section of the Kluessendorf and Mikulic, 2004; Mikulic and others, Geological Society of America’s Centennial Field 2010). Most of the region is covered by Pleistocene Guide (Volume 3) contains descriptions for eleven glacial sediments, ranging in thickness from less than different locations in Wisconsin, but none for eastern a meter to over 330 ft (100 m) in buried bedrock val- Wisconsin (Biggs, 1987). The Wisconsin Geologic leys. As a result, outcrop exposures and even road cuts and Natural History Survey also maintains a list of are spotty, at best, except in the Door Peninsula region over 100 descriptions of outcrops to illustrate vari- in northeastern Wisconsin or along the escarpment ous geologic formations, features, and characteristics edge in other counties. Most information known about in Wisconsin. However, there is only one outcrop the bedrock in the region has been gathered from description listed for Door, Brown, or Calumet coun- stone quarries, a small number of road cuts, water well ties, where the bulk of the Niagara Escarpment is construction reports, and a few drill cores. located in Wisconsin. This article, along with others Wisconsin’s geologic history is preserved in rocks in this special issue of Geoscience Wisconsin, will and sediments from three distinctly different periods help to close this gap by providing a general review of of time, with long intervals of erosion or nondeposi- existing literature and set the stage for new research tion occurring between each. Rocks from the first of being conducted in the region. these three time intervals are generally referred to as Precambrian rocks. This refers to the part of Earth’s GEOLOGIC SETTING AND past that occurred before the Cambrian Period, which STRATIGRAPHY began 541 million years ago (Ma). Rocks that make Chamberlin (1877) noted that although Wisconsin up the foundation of all continental landmasses are could not properly be described as either mountainous mostly made of these older igneous and metamorphic or sunk to a dead level (below sea level), it was “the rocks and are collectively termed “Precambrian base- golden mean in a gently undulating diversified sur- ment.” The second interval of Earth’s history that is face.” The relatively modest topography he described recorded in Wisconsin includes mainly sedimentary is the product of hundreds of millions of years of rocks of the Early to Middle Paleozoic Era. The mountain building, intense erosion, encroachment youngest of the three intervals was recorded dur- of the oceans, and influx of glacial ice. Today, the ing the later part of the Quaternary Period (2.6 Ma eastern Wisconsin region lies on the western flank of to 11,800 years ago). Figure 2 shows a generalized the ancestral Michigan basin and is bordered by the bedrock geologic map for Wisconsin and Michigan. Wisconsin arch to the west, the Canadian shield to A brief summary of each of these parts of the geo- the north, and the Illinois basin to the south. The rela- logic record is presented below because the history tively thin sequence of 2,300 ft (<700 m) of Paleozoic and character of these rocks has been important in the rocks in northeastern Wisconsin gently dips to the east development and evolution of the Niagara Escarpment into the ancestral Michigan basin, where the thick- in Wisconsin. ness of the sedimentary section increases substantially Precambrian history to over 15,700 ft (4,800 m). It is the eastward dip Although there are ancient Archean age rocks pre- of these sedimentary rocks, especially those of the served in our region, the part of North America we Silurian System, which allowed for later erosion to call Wisconsin was assembled during the Proterozoic produce the Niagara Escarpment. Eon during a mountain building event known as the Research on the rocks in northeastern Wisconsin Penokean Orogeny. The Penokean Orogeny occurred has been long lived, but restricted in scope because of over a 50 million year stretch of time 1,880 to 1,830 the limited number of natural exposures of bedrock. Ma. A collision involving three separate landmasses The most comprehensive publication that covers the that accreted together formed what is now the northern geology of eastern Wisconsin is that of Chamberlin half of Wisconsin (fig. 3). The first of two collisions (1877), but others have also published on the sedi- involved the older, and much larger, Archean Superior mentology and stratigraphy of Silurian rocks in the VOLUME 21 2013 • 3 020 40 80 Lake Superior Miles Kilometers 025 50 100 150 200 pЄ pЄ O S S D Lake Huron pЄ O M Є S S J Lake Michigan M D Pn O M Lake Erie D Pn FigureFigure 2a.