ABSTRACT U.S. Geological Survey (USGS) Monograph 53 by Frank Leverett and Frank Taylor identified more than 20 deltas of late Pleistocene age in the Lower Peninsula of Michigan. To that list, we add many additional deltas discovered during the course of our research. These “relict” deltas are important proxies for paleoenvironmental conditions, particularly wave energies, as well as prevailing wind and longshore drift directions. If dated, they can help to constrain the chronologies of ice retreat and proglacial lake stages. In plan view, relict delta morphologies usually protrude from a paleolake shoreline and are often elongate or cuspate shaped. Most of the deltas identified by Leverett and Taylor have this morphology and are located at the junction of a major present-day river and a relict paleolake shoreline. In this chapter, we map and discuss these deltas, first identified by Leverett and Taylor, while also identifying and describing the other, newly found deltas. All of these deltas formed during the marine isotope stage 2 ice retreat, roughly 28–13 ka. To identify and characterize them, we utilized a variety of data within a geographic information system, mainly a statewide USGS 7.5′ digital raster graphic, a 10 m digital elevation model (DEM), county-level Natural Resources Conservation Service soil data, and schematic lithologic depth profiles interpreted from descriptive water well and oil/gas logs. DEMs were particularly useful, because they can be “flooded” to various elevations of paleolakes. Maps of soil wetness and textural characteristics were also useful in detecting and delineating deltas. In sum, we mapped 61 deltas; 27 had been known from previous works, whereas 34 are newly reported in this study. Most are composed of sandy, well-drained sediments and have smooth, graded longitudinal profiles. Of these, most are perched above a relatively low-relief, poorly drained lake plain. However, unlike several deltas recognized by Leverett and Taylor, we found that many of the newly reported deltas are (1) adjacent to one or more formerly unknown shorelines, (2) not associated with a modern river, (3) complex, and/or (4) broad, coalesced features, deposited by more than one river, with fan-like morphologies. The methods that we used to identify and delineate these deltas can be applied to other regions. Mapping like the kind reported here will aid in a better understanding of the paleocoastal and terrestrial conditions during the late Pleistocene.

Abstract The Michigan basin is a large, relatively deep structure of Paleozoic age centered in the lower peninsula of the state of Michigan. The province includes Michigan's entire lower peninsula, parts of northern Indiana, most of eastern Wisconsin, the eastern part of Michigan’s upper peninsula, western portions of Ontario, and northwestern Ohio. It is defined geologically by a series of subtle structural highs: the post-Silurian Findlay arch forms the southeastern boundary, the Early Ordovician Kankakee arch forms the southwestern boundary, and the Wisconsin Highland and the Wisconsin arch form the western boundary. To the north and northeast is the Canadian Shield, and to the east is the Algonquin arch, a major Precambrian feature in Ontario (Fig. 1). For a more complete discussion of the physiography and age of the Michigan basin, see Fisher and others (1988). In the past, the greatest amount of drilling in the Michigan Basin took place in the sectors in Indiana, Ohio, and Ontario. However, with modern production from the Ohio and Indiana sectors currently in decline, most drilling activity is confined to Michigan’s lower peninsula. For this reason most of the statistical and geological data in this report, unless otherwise stated, will concern the lower peninsula.

A substantial section of Precambrian rock is exposed over an area of approximately 19,400 km 2 (7,500 mi 2 ) in the western part of the Northern Peninsula of Michigan. This province is a portion of the exposed southern terminus of the Canadian Precambrian Shield and contains a large variety of igneous, sedimentary, and metamorphic rocks. Significant amounts of iron and copper from Precambrian rocks of Michigan have provided important contributions to the growth of the state and national economy for nearly 150 years. Archean rocks consist of volcanics, sediments, and younger felsic and mafic intrusives, some of batholitic dimensions. Volcanic and associated sedimentary rocks occur as greenstone belts included in the Ramsay Formation, Gogebic County; Dickinson Group, Dickinson and Iron Counties; and Marquette Greenstone Belt, Marquette County. Volcanic rocks consist of mafic to felsic lava flows and pyroclastics and sediments derived from volcanic rocks. Volcanic flows include amygdaloidal and ellipsoidal varieties. Pyroclastics consist of agglomerate, conglomerate, breccia, and tuff. Sediments are described as graywacke, argillite, siltstone, conglomerate, quartzite, iron formation, and chert. Granite and granitic gneiss, principally tonalite and granodiorite, intrude the periphery and interiors of the greenstone belts. Mafic intrusives, including peridotite, are subordinate. Shearing is prominent in some areas, and metamorphic grade ranges from lower-greenschist to upper-amphibolite facies. Minor amounts of gold and silver have been produced from the Marquette Greenstone Belt. Early Proterozoic strata are subdivided into four groups, in ascending order: the Chocolay, Menominee, Baraga, and Paint River Groups. Copper mineralization occurs in the Kona Dolomite of the Chocolay Group. The Menominee Group contains three major iron formations of equivalent age, the Negaunee Iron Formation of the Marquette Iron Range; the Vulcan Iron Formation of the Menominee Iron and Felch Mountain Districts and the Ironwood Iron Formation of the Gogebic Iron Range. In the Baraga Group, the Goodrich Quartzite contains concentrations of monazite, and the Michigamme Formation has vast amounts of graphitic carbon. The Paint River Group includes the highly productive Riverton Iron Formation. Iron was discovered in 1844 on the Marquette Iron Range, and an early pig-iron industry flourished. The east-west–trending Marquette syncline, containing the Negaunee Iron Formation, is more than 65 km (40 mi) long. The Negaunee has a maximum thickness of 1,060 m (3,500 ft), and iron-formation resources have been estimated at 205 billion long tons. There are four iron formations on this range, three of which have been productive. However, 97 percent of the 588 million tons mined came from the Negaunee. The east-west–trending Menominee Iron-bearing District, in southern Dickinson County, consists of a north and south range segmented by longitudinal faulting. The Vulcan Iron Formation is exposed over a strike length of 28 km (16 mi) and has a maximum thickness of 180 m (600 ft). Production amounted to nearly 82 million long tons. In the Felch Mountain District of central Dickinson County, only eroded remnants of the Vulcan Iron Formation remain. Production of 36 million tons was principally from the Groveland low-grade iron mine. The Gogebic Iron Range, in Gogebic County, is an essentially east-west–trending, northward-dipping sequence of sediments containing the Ironwood Iron Formation. In Michigan, the Ironwood has a strike length of about 40 km (25 mi) and a maximum thickness of about 490 m (1,600 ft). Iron ore production totals 255 million long tons. The Negaunee, Vulcan, and Ironwood iron formations are considered to be stratigraphically equivalent. The Iron River–Crystal Falls District in Iron County is primarily composed of the Paint River Group containing the Riverton Iron Formation. The Paint River Group is outlined in a triangular-shaped basin approximately 260 km 2 (100 mi 2 ) in area. The Riverton has a maximum thickness of 240 m (800 ft) and has been intensely and complexly folded. A high phosphorous and manganese content characterizes the Riverton and its naturally derived iron ores. Production amounted to 207 million long tons. Middle Proterozoic rocks in Michigan consist of a very thick sequence of volcanics and sediments. For the most part, strata dip uninterrupted toward Lake Superior at varying degrees. Native copper was the exclusive mineral produced from the Portage Lake Volcanics in Michigan’s Keweenaw Peninsula. Stratabound native copper mineralization forms ore bodies in amygdaloidal and brecciated tops of lava flows, and in interflow conglomerates. Minor amounts were produced from transverse fissures. Production of refined copper through 1976 amounted to 4,769,465 metric tons (5,257,438 short tons). Sulfide copper (chalcocite) with some native metal is mined from the Nonesuch Formation several thousand feet about the Portage Lake Volcanics in the Porcupine Mountain area. Copper mineralization is confined to siltstone and shale of the basal portion of the Nonesuch. Small amounts of disseminated native copper are produced from the uppermost sandstone of the underlying Copper Harbor Conglomerate. Through 1987, 1,364,800 metric tons (1,504,433 short tons) of refined copper has been produced.

Keweenawan sedimentary rocks of the Lake Superior region consist of four major sequences: pre-volcanic sedimentary rocks, interflow sedimentary rocks, and post-volcanic sedimentary rocks consisting of the Oronto Group and equivalents and the overlying Bayfield Group and equivalents. The oldest pre-volcanic rocks of concern here are those of the Sibley Group (1350–1300 m.y. old), which includes quartzose sandstone, mudstone, and dolomite. Whereas the quartzose sandstone may be fluvial, the finer clastic units and the dolomite appear to be lacustrine (or marine?). Other quartz sandstone units, the Puckwunge Formation, the “Nopeming Formation,” the basal sandstones of the Osier Group, and the Bessemer Quartzite, are probably younger—about 1200–1100 m.y. old. The Bessemer and the lower Sibley are normally polarized, whereas the other units are reversely polarized and on that basis are probably younger. Most of these sandstones probably originated on braided alluvial plains, but the Bessemer, which has a bimodal-bipolar paleocurrent pattern, apparently originated in a standing body of water that was either influenced by tides or had opposing longshore current systems. Immature interflow sedimentary rocks, mostly fluvial sandstones, were derived in large part from the 1200–1100 m.y. old Keweenawan volcanic sequence of which they are a part. They are interbedded with volcanic rocks in several sub-basins along the rift zone. The post-volcanic sedimentary rocks, the Oronto and Bayfield Groups and their equivalents, constitute a thick red bed sequence of conglomerate, sandstone, and siltstone deposited in a large, elongate basin created by tectonic activity along the rift zone. The Oronto Group (Copper Harbor Conglomerate, Nonesuch Shale, and Freda Sandstone in ascending order) is present in northern Wisconsin, western Upper Michigan, and on Isle Royale. The Copper Harbor Conglomerate (to 2100 m thick) is dominantly a fining upward alluvial fan-fluvial clastic wedge. The gray cupriferous, pyritiferous, and carbonaceous Nonesuch Shale is an argillaceous siltstone unit (75–225 m thick) which accumulated under reducing conditions, probably in a lacustrine (and deltaic) environment. The Freda Sandstone (3600 m thick) is a fluvial (and lacustrine?) unit. The Oronto Group was largely derived from Keweenawan volcanic rocks on the basin flanks. In Wisconsin, the more steeply dipping Oronto Group is overlain (unconformably?) by the more mature subhorizontal Bayfield Group, which includes, in ascending order, the feldspathic Orienta Sandstone, the quartzose Devils Island Sandstone, and the feldspathic Chequamegon Sandstone. Geophysical evidence suggests that the group may be as much as 2100 m thick. The Devils Island Sandstone (100 m thick) is apparently the result of the lacustrine reworking of Orienta Sandstone fluvial detritus during a significant pause in, or cessation of, tectonic activity. The source rocks for the Bayfield Group were dominantly pre-volcanic granitic basement rocks, although reworking of Oronto Group detritus also may have been important. In eastern Minnesota, three formations are present—the feldspathic-lithic Solor Church Formation (to 1000 m thick), the feldspathic Fond du Lac Formation (120–600 m thick), and the quartzose Hinckley Sandstone (to 300 m thick). The Solor Church, found only in the subsurface, was deposited southwest of Lake Superior along the rift zone. The Solor Church Formation can be correlated with the Oronto Group, the Fond du Lac with the Orienta Sandstone, and the Hinckley Sandstone with the Devils Island Sandstone. The Solor Church and the Fond du Lac were deposited in a meandering stream-floodplain environment, whereas the Hinckley appears to have been formed by the reworking of Fond du Lac detritus in the same lacustrine environment in which the Devils Island Sandstone was formed. In Michigan, the feldspathic to quartzose Jacobsville Sandstone is a northward-thickening, fault-bordered wedge of regionally variable fluvial sedimentary rocks. The maximum drilled thickness is 868 m, and the geophysically inferred thickness is 3000 m. Most of the conglomerate clasts were derived from deeply weathered source areas to the south and southeast. The Jacobsville also is found at the east end of Lake Superior and beneath Lake Superior. Correlation with the Bayfield Group is likely but uncertain. Paleocurrent data indicate basinward transport of sediment from both the northern and southern flanks of the basin throughout Keweenawan time. The Proterozoic Sibley Group is the oldest of the pre-volcanic sedimentary units in the Lake Superior region, having been dated at about 1340 m.y. ago. The Sibley consists of more than 400 m of strata that may have been deposited in a failed rift basin; part of the unit may be marine, but the sandstones of the Pass Lake Formation at the base of the group may have at least a partial fluvial origin. The Bessemer Quartzite, “Nopeming Formation,” Puckwunge Formation, and the lower sandstones of the Osier Group are lithostratigraphic equivalents, all having been deposited before Keweenawan volcanism began in their respective outcrop areas. Although paleomagnetic data indicate that the Bessemer is older than the other three units, none can be correlated with certainty. The Bessemer Quartzite may be as old as, but is probably somewhat younger than, the Sibley Group. The dispersion of cross-bedding patterns in the Nopeming and the Puckwunge is suggestive of deposition in a fluvial environment, probably on a braided alluvial plain with streams flowing southward into a shallow basin. Paleocurrent data are sparse for the lower sandstones of the Osier Group, but location and stratigraphic position suggest an environment similar to that of the Puckwunge. The Bessemer Quartzite, however, has a contrasting bimodal-bipolar paleocurrent pattern, indicative of a tidally influenced marine or estuarine environment, or a lacustrine environment with opposing current systems. All of the units under consideration here contain some detritus derived from older Proterozoic sedimentary rock units of the Lake Superior region, but the bulk of the quartz-rich sediment may have been derived from the Archean granite-greenstone terranes north and south of the basin. The stable tectonic framework that produced the quartz-rich sediment was ended by the formation of a shallow basin that heralded the onset of volcanism. The coarse, immature, polymictic, red-bed clastic rocks interbedded within the Keweenawan lava flows provide insight about the relationship between these accumulations and the surrounding borderland during rifting. The interflow sedimentary rocks were derived from three major sources: subjacent lava flows, uplifted Keweenawan volcanic and intrusive rocks located some distance from the exposed interflows, and pre-Keweenawan rocks exposed along the periphery of the Keweenawan lavas. The composition of the interflow sedimentary rocks can be used to determine their source. Previous studies of the interflow sedimentary rocks indicate that the rocks were deposited by streams that flowed predominantly on surfaces mantled by Keweenawan lava flows. Paleocurrent data indicate that the streams flowed generally toward the present Lake Superior Basin from surrounding highlands. The site of these highlands, in some instances, coincides with the location of numerous Keweenawan intrusions that may have served as feeder fissures for the lavas. The Keweenawan-age Oronto Group of northern Michigan and Wisconsin includes the Copper Harbor Conglomerate, Nonesuch (Shale) Formation, and Freda Sandstone. These formations are part of a volcanic-clastic sequence created in response to the formation of the Midcontinent Rift System. Although intercalated volcanics are found in the lower one-third of the Oronto Group, a sedimentary depositional regime was dominant. Along the Keweenaw Peninsula, paleocurrent indicators for all three formations show that the predominant depositional directions were northerly. On Isle Royale, the opposite side of the rift, sedimentary structures in the Copper Harbor Conglomerate indicate that flow was to the south and east. Lithologically, the Copper Harbor Conglomerate is a red-brown, basinward-thickening wedge of volcanogenic clastics and subordinate volcanics that fines distally and upsection. Maximum thickness for this formation is about 1830 m. The dominant sandstone type is lithic graywacke. Conglomerate facies are primarily clast-supported and comprised of volcanic clasts with a ratio of mafic to silicic + intermediate clasts of about 2:1. The heavy-mineral suite for the Copper Harbor Conglomerate (as well as the other Oronto Group formations) mainly consists of ilmenite and similar opaque minerals and epidote. Depositionally, the Copper Harbor Conglomerate represents a prograding alluvial fan complex. Interfingering with the Copper Harbor Conglomerate is the Nonesuch (Shale) Formation, an unoxidized sequence of gray-black siltstone, shale, and sandstone with a maximum thickness of 215 m. Besides having been deposited in a reducing environment, the Nonesuch differs from the enclosing redbed sequences by its increased textural maturity and its sulfide and hydrocarbon content. The heavy-mineral suite of the Nonesuch also differs from that of the redbeds only by relative enrichment of chlorite. The Nonesuch is perceived as a rift-flanking lacustrine environment, probably initiated through disruption of existing drainages by alluvial, volcanic, or tectonic processes. As with the underlying Copper Harbor Conglomerate, the contact with the overlying Freda Sandstone is gradational in character. The Freda Sandstone is a ferruginous, lithic sequence of cyclic sandstone and mudstone exceeding 3660 m in maximum thickness. Although similar in appearance to some sandstones of the Copper Harbor Conglomerate, the Freda, overall, is of greater compositional maturity, and conglomerate facies are uncommon. The Freda is dominantly fluvial in origin and appears to have “overridden” the Nonesuch environments. Although complex in detail, the overall depositional model for the Oronto Group is one of simple transgressive-regressive relationships between alluvial fan/lacustrine/fluvial environments. Important aspects of such a model are that (1) all the Oronto Group formations are genetically related with no major unconformities between them; and (2) the intervening Nonesuch Formation is, at least in part, equivalent in age to the upper Copper Harbor and the lower Freda. Keweenawan sedimentary rocks associated with the Midcontinent Rift System form a thick, dominantly red-bed sequence of fluvial-lacustrine origin in eastern Minnesota and northwestern Wisconsin. The strata can be divided into two major sequences on the basis of mineral composition and tectonic setting. The older sequence includes the Oronto Group in northwestern Wisconsin and the Solor Church Formation in southeastern Minnesota. Although these lithostratigraphic units are not entirely correlative, they were derived largely from within the rift system. Both contain variable amounts of quartz, feldspar (plagioclase > K-feldspar), rock fragments (basalt > granite), and other labile constituents. The younger sequence includes the Bayfield Group in Wisconsin, and the Fond du Lac Formation and Hinckley Sandstone in Minnesota. These correlative lithostratigraphic units, derived largely from outside the rift system, contain abundant quartz, feldspar (K-feldspar > plagioclase), and rock fragments (granite > basalt). The Oronto Group and Solor Church Formations were deposited in part contemporaneously with basalt in several grabenlike basins along the axis of the expanding rift system. Subsequently, relative uplift of the axial zone formed a series of half-grabenlike basins along the flanks of the rift system, in which the Bayfield Group and its equivalents in Minnesota were deposited. The transition from Oronto-like to Bayfield-like rocks marks a transition from dominantly extensional to dominantly vertical tectonic processes. This relationship between tectonism and sedimentation may be useful in unraveling the stratigraphic history of the sedimentary rocks in those parts of the Midcontinent Rift System buried by Paleozoic and younger strata. In the Lake Superior syncline the Jacobsville Sandstone is a thick (+900m) fluvial sequence of feldspathic and quartzose sandstones, conglomerates, siltstones, and shales, completely devoid of lava flows or cross-cutting dikes. On the north and south sides of Lake Superior, most of the sandstone occurs as inward-dipping, fault-bounded wedges, separated by regional faults from the Oronto and Bayfield Groups of similar red sandstones, situated on the inner side of the syncline. Sandstones that have been correlated with the Jacobsville at the east end of Lake Superior are probably upper Keweenawan. Similar sandstones in the subsurface in the Michigan Basin are probably Keweenawan, but their precise correlation with the Jacobsville remains uncertain. A lower age limit for the sandstone is established from large basalt clasts derived probably from the Portage Lake Volcanics, and from the occurrence of the sandstone as dikes in the volcanics. The upper age is based on its position below the late Cambrian Munising Sandstone. The sandstone can be inferred to be Precambrian, and probably upper Keweenawan on the proximity, and structural and lithologic similarities (and hence a similar tectonic environment) of the sandstone to the other red sandstones in the Lake Superior syncline. The most precise data is from paleomagnetics, which shows that the Jacobsville on Keweenaw Bay and the Oronto Groups have a similar upper Keweenawan pole position (estimated at 1,100 m.y.), and that the Jacobsville may be slightly younger than the Freda Sandstone. The Jacobsville Sandstone varies from subarkose to quartz sub-lithic arenite, and there are some beds of arkose and of quartzite. Quartz is derived from both metamorphic and volcanic source areas, and none shows overgrowths. Microcline is fresh everywhere whereas plagioclase is fresh to highly altered. Other clasts in sandstones are of mafic and of felsic volcanic rocks, quartz-staurolite schist, garnet, epidote, biotite, muscovite, chlorite, and shale. Conglomerates with abundant clasts of quartz and iron-formation are known from the base of the section, 30 km east of Lake Gogebic from where they increase in thickness and abundance in the section to some 40 km west of the lake. Jacobsville sedimentation was preceded by a long period of volcanic and tectonic quiescence and cratonic stability so that bedrock surfaces became blanketed by paleosols and a surface of chemically resistant debris was dominated by quartz and iron-formation. Erosion was initiated by late Keweenawan warping, perhaps accompanied by basement faulting during which the relative movement along the Midcontinent Rift System was down. Vigorous marginal fluvial systems developed on the south side from uplands dominated by ridges of iron-formation. The resistant debris was removed first, and became deposited in alluvial fans along the deeper basins. Streams flowed across the marginal basins with possibly some local influence on stream direction and sedimentation by faults along the outer margins of active basins. The major movement on the marginal reverse faults was in post-Jacobsville time. Still younger faults affect Paleozoic outliers. Subsequent to burial, the sandstone underwent low-grade alteration so that now the matrix mineralogy changes from microline-plagioclase-kaolinite-montmorillonite near the surface to microline-montmorillonite-illite(chlorite) at depth. If in Michigan the fluvial transport direction was paralleled by a similar groundwater flow direction northerly from ridges of iron-formation, the period of weathering preceding and coinciding with Jacobsville sedimentation may have been the time during which the soft iron ores in the iron ranges were produced by the oxidation and leaching by such groundwaters to depths in excess of 1,200 m.

Abstract The Michigan structural basin is symmetrically centered in the Southern Peninsula of Michigan and extends outward into surrounding states and the Province of Ontario. Outcrops of Precambrian rocks bound the basin to the north; on the east the Algonquin axis in Ontario is the basin border, and to the south and west, the limiting features are the Findlay and Kankakee arches of northern Ohio and Indiana and the Wisconsin arch in central Wisconsin. Paleozoic rocks crop out, or underlie the glacial drift, in circular bands with the youngest rocks occurring near the center of the Southern Peninsula where the floor of the Paleozoic rocks in the basin reaches its maximum depth of about 14,000 feet. Oil production in the Michigan basin had its beginning at Petrolia in Ontario in 1858, but production in volume began with the discovery of the Muskegon field on the west side of the basin and the Mount Pleasant field near the center of the basin in 1928. Approximately 270 oil fields and more than 100 gas fields have been discovered in the basin. The Michigan basin contains about 108,000 cubic miles of sedimentary rocks of which about 80 per cent is Cambrian, Ordovician, and Silurian in age, and most of the remainder Devonian in age. Lithologically, carbonate rocks constitute 47 per cent of the sedimentary rocks of the basin, 12 per cent being evaporites, and the remaining 41 per cent sandstones and shales. More than 95 per cent of the oil has come from carbonate rocks of Middle Devonian age, and most of the gas is from sandstones of Mississippian age. The oil yield to date amounts to 3,700 barrels per cubic mile of sedimentary rock. The producing formations, from oldest to youngest, are the Black River and Trenton limestones of Middle Ordovician age, the upper part of the dolomite of the Niagara Series of Middle Silurian age, and dolomite in the lower part of the Salina formation of Late Silurian age, various limestones and dolomites of Middle and Late Devonian age including the Detroit River group, the Dundee and Rogers City limestones, and Norfolk formation of Canada, the Traverse group, and sandstones of Mississippian age. Accumulation of oil is largely anticlinal, with northwest-southeast trends predominating in the central basin area. Most of the folding took place during late Paleozoic time. The greater part of the oil has been produced from porous zones below unconformities. This is due mainly to the development of secondary porosity at the top of the limestones, but some accumulations beneath unconformities are in porous zones due to secondary dolomitization.