MINNESOTA GEOLOGICAL SURVEY PRISCILLA C. GREW, Director PALEOZOIC LITHOSTRATIGRAPHIC NOMENCLATURE FOR MINNESOTA John H. Mossier Report of Investigations 36 ISSN 0076-9177 UNIVERSITY OF MINNESOTA Saint Paul - 1987 PALEOZOIC LITHOSTRATIGRAPHIC NOMENCLATURE FOR MINNESOTA CONTENTS Abstract. Structural and sedimentological framework • Cambrian System • 2 Mt. Simon Sandstone. 2 Eau Claire Formation • 6 Galesville Sandstone • 8 Ironton Sandstone. 9 Franconia Formation. 9 St. Lawrence Formation. 11 Jordan Standstone. 12 Ordovician System. 13 Prairie du Chien Group. 14 Oneota Dolomite. 14 Shakopee Formation. 15 St. Peter Sandstone. 17 Glenwood Formation. 17 Platteville Formation. 18 Decorah Shale. 19 Galena Group • 22 Cummings ville Formation. 22 Prosser Limestone. 23 Stewartville Formation • 24 Dubuque Formation. 24 Maquoketa Formation. 25 Devonian System • 25 Spillville Formation • 26 Wapsipinicon Formation 26 Cedar Valley Formation • 26 Northwestern Minnesota. 28 Winnipeg Formation • 28 Red River Formation. 29 Acknowledgments • 30 References cited. 30 Appendix--Principal gamma logs used to construct the composite gamma log illustrated on Plate 1. 36 ILLUSTRATIONS Plate 1 • Paleozoic lithostratigraphic nomenclature for Minnesota • .in pocket Figure 1. Paleogeographic maps of southeastern Minnesota • 3 2. Map showing locations of outcrops, type sections, and cores, southeastern t1innesota • 4 3. Upper Cambrian stratigraphic nomenclature 7 iii Figure 4. Lower Ordovician stratigraphic nomenclature • • • • 14 5. Upper Ordovician stratigraphic nomenclature 20 6. Middle Devonian stratigraphic nomenclature. • • . • • 27 7. Map showing locations of cores and cuttings in northwestern Minnesota • • • • • • • • • • • • • • • • • • 29 TABLE Table 1. Representative cores in Upper Cambrian formations •••••• 5 The University of Minnesota is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, religion, color, sex, national orgin, handicap, age, veteran status, or sexual orientation. iv PALEOZOIC LITHOSTRATIGRAPHIC NOMENCLATURE FOR MINNESOTA by John H. Mossler ABSTRACT Significant changes are made in stratigraphic nomenclature for the Paleozoic formations of Minnesota that reflect subsurface data acquired since 1969 and accord with changes in nomenclature in adjoining states. For the Cambrian section, dolostone that intertongues with the lower part of the Eau Claire Formation in the subsurface of south-central and southwestern Minnesota is interpreted to be a tongue of the Bonneterre Formation of northwestern Iowa. The Reno Member of the Franconia Formation, together with the Birkmose Member, is now interpreted to compose most of the formation, whereas the Tomah Member is now interpreted to have very re­ stricted subsurface distribution; an additional dolostone member, here in­ formally named the Davis, is recognized in the subsurface in south-central Minnesota. The uppermost member of the overlying Jordan Sandstone is here renamed the Coon Valley Member. For the Ordovician section, the Galena is now elevated to group status. The Cummingsville Formation, Prosser Limestone, and Stewartville Formation-­ formerly members of the Galena--now correspond in rank with their equiva­ lents in adjoining states. In the Devonian sequence, formerly classified as entirely Cedar Valley Formation in Minnesota, the recently named Spillville Formation is recog­ nized in the base of the sequence, and the Wapsipinicon Formation is now known to extend into Minnesota from Iowa. The name Cedar Valley is retained for the overlying Devonian rock unit. STRUCTURAL AND SEDIMENTOLOGICAL FRAMEWORK The Paleozoic rocks of southeastern Minnesota parts of the sequences, if ever present, have were deposited in the shallow marine Hollandale been stripped away. embayment (Austin, 1969) that lay between the Transcontinental Arch and Wisconsin Dome and Arch Maximum marine inundation of the North (Fig. 1). These rocks record three of the major American continent occurred during deposition of shallow marine incursions that crossed the North the Tippecanoe sequence, and it is the only American continent during Phanerozoic time sequence represented in northwestern Minnesota (Sloss, 1963). The Sauk sequence includes rocks (Plate 1). deposited during the first incursion in Late Cambrian and Early Ordovician time (Plate 1). Marine and continental sedimentary rocks of The second major marine incursion, the Tippe­ Late Cretaceous age overlie Paleozoic rocks along canoe, includes all Middle and Late Ordovician the western margin of the Hollandale embayment in strata; in Iowa (Bunker and others, 1985) it also southeastern Minnesota, and questionable Jurassic contains Silurian rocks. Overlying Devonian for­ rocks as well as Late Cretaceous rocks overlie mations are part of the Kaskaskia sequence. The the Paleozoic rocks in northwestern Minnesota. tops of all sequences are characterized by inter­ These rocks, which are not shown on Plate 1, are regional unconformi ties. These rock sequences generally shale, siltstone, and minor units of are much thinner in Minnesota and represent sandstone and carbonate. They are considered to shorter intervals of time than nearer the margins be part of a later sedimentary sequence, the Zuni of the North American continent. Southeastern (Sloss, 1963), that was deposited during Late Minnesota lies near the center of the craton and Mesozoic time by marine incursion from a seaway was one of the last parts of the continent to be across the western continental interior. Paleo­ flooded during marine transgressions, and signifi­ zoic rocks are buried by as much as 350 feet (107 cant erosion occurred at the end of each sequence. m) of Cretaceous rocks in extreme southwestern In Minnesota only lower parts of the Tippecanoe parts of the Hollandale embayment in Minnesota; and Kaskaskia sequences are present, and upper however, Cretaceous rocks, where they are present over Paleozoic rocks, are generally about 50 to Minnesota are separated from the Hollandale 100 feet (15 to 30 m) thick. embayment by the Transcontinental Arch and the Sioux ridge (Fig. 1), which formed passive high­ Continental glaciation during the Quaternary lands throughout much of Paleozoic time. created thick sequences of outwash and till that covered most earlier geologic features in Minne­ sota. As a result, most Paleozoic exposures in CAMBRIAN SYSTEM southeastern Minnesota are along major stream valleys or in the "driftless" area of extreme Classification of Cambrian rocks in Minnesota southeastern Minnesota where glacial deposits are began to develop during the late 1800s in outcrop thin and discontinuous or absent (see insert map, areas of Minnesota and Wisconsin, and has been Plate 1). In northwestern Minnesota all Paleozoic undergoing modifications until the present. All rocks are covered by a thick layer of Quaternary Cambrian rocks in the Upper Mississippi region drift. are considered to be Late Cambrian in age, although paleontological evidence for assigning a The Hollandale embayment extended southward Late Cambrian age to the lowermost sandstone through east-central and southeastern Minnesota units generally is lacking. Because classifica­ and western Wisconsin, across eastern Iowa into tions of Late Cambrian chronostratigraphic units the Ozark basin of southern Missouri, and into for North America (Plate 1) are based upon the ancestral Illinois basin (Bunker and others, paleontological studies that were carried out 1985) (Fig. 1). The Hollandale embayment fol­ from outcrops along the St. Croix and Upper lowed the trace of predecessor basins formed Mississippi Ri ver valleys of Minnesota and along the Middle Proterozoic Midcontinent rift Wisconsin, local place names are applied to the system. Minor recurrent movements, such as might stage names and series names for Late Cambrian be caused by isostatic adjustment along the strata (Howell and others, 1944; Berg and others, large-scale faults bounding grabens, basins, and 1956). Prior to 1956, as exemplified by Stauffer horsts of the Proterozoic rift system, are respon­ and Thiel's classification (1941) (see Fig. 3, sible for development and configuration of the col. 2), the Cambrian stratigraphic column was early Paleozoic Hollandale embayment, as well as subdivided mainly on the basis of faunal zones for the many smaller structures that later devel­ (trilobi tes), a system of limited usefulness to oped within it, such as the Twin Cities basin everyone but paleontologists. In 1956 a new (Fig. 2), numerous small, gently folded synclines classification was proposed that adhered to the and anticlines, and small faults. Differential then new system of dual nomenclature, in which uplift during Late Proterozoic time is respon­ lithostratigraphic and biostratigraphic units are sible for the irregular distribution of Middle independent (Berg and others, 1956) (see Fig. 3, Proterozoic sedimentary rocks beneath the Paleo­ col. 3). It is this classification that has been zoic rocks. At the northern end of the Hollan­ used with minor modifications up to present (Fig. dale embayment, Cambrian rocks overlap Middle 3, col. 4). Proterozoic lava flows, and along the north­ western and northeastern margins of the embay­ Most lithostratigraphic descriptions of Cam­ ment, Paleozoic rocks directly overlie Archean brian formations in this report, with the excep­ and Early Proterozoic metamorphic and igneous tion of the Jordan Sandstone, are based upon core rocks; gneiss and rocks of the