Abstract Drilling and geophysical data demonstrate that the Mississippi Valley graben, the Rough Creek graben, and the Rome trough are fault-bounded graben structures filled with as much as 27,000 feet of Cambrian sediments. Data including stratigraphic tops from 1,764 wells, 106 seismic profiles, aeromagnetic and gravity surveys, and mapped surface geology at a 1:24,000 scale have been used to study seven stratigraphic packages resolvable in both wells and seismic profiles across parts of Kentucky, Ohio, Indiana, Illinois, Missouri, and Tennessee. Detailed analyses of the thickness patterns of these stratigraphic packages have been used to interpret the locations and timing of movements along major faults systems in the study area. Active rifting of the Precambrian crystalline bedrock began by the Early Cambrian, and resulted in thick, sand-rich deposits of the Reelfoot Arkose in the Mississippi Valley graben and Rough Creek graben, and the Rome Formation in the Rome trough. Subsidence continued in these grabens during the Middle to Late Cambrian, leading to an alternating succession of shales and carbonates being deposited (Eau Claire Formation of the Illinois basin and Conasauga Group of the Appalachian basin) on top of the coarse clastic Reelfoot Arkose and Rome Formation. Although the tectonic extension that formed these features ended by the Late Cambrian, fault zone reactivation during the Taconic, Acadian, and Alleghenian Orogenies altered fault block orientations and produced areas of basin inversion, creating the possibility of numerous deep structural traps for hydrocarbons sourced by the Cambrian shales of the Eau Claire Formation and Conasauga Group.

Abstract The Reelfoot rift is one segment of a late Proterozoic(?) to early Paleozoic intracontinental rift complex in the south-central United States. The rift complex is situated beneath Mesozoic to Cenozoic strata of the Mississippi embayment of southeastern Missouri, northeastern Arkansas, and western Tennessee and Kentucky. The rift portion of the stratigraphic section consists primarily of synrift Cambrian and Ordovician strata, capped by a postrift sag succession of Late Ordovician to Cenozoic age. Potential synrift source rocks have been identified in the Cambrian Elvins Shale. Thermal maturity of Paleozoic strata within the rift ranges from the oil window to the dry gas window. Petroleum generation in Elvins source rocks likely occurred during the middle to late Paleozoic. Upper Cretaceous sedimentary rocks unconformably overlie various Paleozoic units and define the likely upper boundary of the petroleum system. No production has been established in the Reelfoot rift. However, at least nine of 22 exploratory wells have reported petroleum shows, mainly gas shows with some asphalt or solid hydrocarbon residue. Regional seismic profiling shows the presence of two large inversion structures (Blytheville arch and Pascola arch). The Blytheville arch is marked by a core of structurally thickened Elvins Shale, whereas the Pascola arch reflects the structural uplift of a portion of the entire rift basin. Structural uplift and faulting within the Reelfoot rift since the late Paleozoic appear to have disrupted older conventional hydrocarbon traps and likely spilled any potential conventional petroleum accumulations. The remaining potential resources within the Reelfoot rift are likely shale gas accumulations within the Elvins Shale; however, reservoir continuity and porosity as well as pervasive faulting appear to be significant future challenges for explorers and drillers.

ABSTRACT New data and review of classic sections from the Middle and Upper Ordovician North American Midcontinent in the Upper Mississippi Valley provide a refined picture of the age, stable isotope geochemistry, faunal composition, and—ultimately—origin of this epeiric ramp succession. Sequence stratigraphic analysis reveals a series of unconformity-bounded, genetically related facies packages. Shallowing and deepening trends are sometimes difficult to resolve due to a paucity of hydrodynamic indicators, yet unconformity surfaces are well marked by hardgrounds and confirmed by negative C-isotope spikes. Recent conodont biostratigraphy, new U-Pb radioisotopic ages for K-bentonites, and correlation of C-isotope profiles to global trends suggest that the succession spans the Darriwilian to Hirnantian epochs. Focus on Platteville to lower Galena Group strata (Sandbian to early Katian) provides a temporally high-resolution look at the onset and evolution of a long-term (>2 m.y.) positive carbon-isotope excursion, short-term perturbations in that record, and relationship to the preservation and diversity of the enclosed fauna and strata. Major changes in authigenic mineral suites and organic carbon content throughout the Upper Ordovician Upper Mississippi Valley suggest at least three major redox cycles. The combined evidence for globally recognized, positive carbon-isotope excursions coincident with these redox cycles, as well as high-frequency, sea-level fluctuations and successive faunal turnover events, suggests far-field responses to multiple global oceanic anoxic events.

ABSTRACT Red Wing, Minnesota, is located in the upper Mississippi River valley near the northern margin of the Driftless Area, a portion of southeast Minnesota and western Wisconsin that was not glaciated in the late Quaternary characterized by river valleys deeply dissected through a sequence of Paleozoic sediments. River terraces are prominent in the field trip area. These terraces developed in two steps. Glacial outwash filled the valleys in the late Quaternary, followed by at least two pulses of incision associated with meltwater drainage from large glacial lakes to the north, including glacial Lake Agassiz. Following the last pulse of meltwater incision, tributary streams built sediment fans in the valley floor which the post-glacial Mississippi River was not able to erode. As a result, large lakes—including Lake Pepin—developed in the valley bottom. Lake Pepin has subsequently shrunk by delta progradation from the north. Evidence of Native American habitation in the area extends to Paleoindian time (ca. 11 ka B.P. calendar), but there is limited evidence of large, horticultural populations until A.D. 700. This timing coincides with the advance of the Lake Pepin delta front from St. Paul south to the Red Wing area. Large village sites were strategically placed on terraces above the Mississippi. Recent application of LiDAR (light detection and ranging) and resistivity surveys have aided ongoing archaeological investigations in the Red Wing area. Burial mound groups are visible in airborne LiDAR elevation data, and resistivity surveys have revealed evidence of an extensive village at the Silvernale site.

ABSTRACT The Minneapolis Chain of Lakes is a focal point of natural beauty in the heart of the city. Given the recreational and aesthetic imperative, these urban waterbodies have for decades been heavily managed for water quality and lake level. In the early stages of development of Minneapolis’ civic infrastructure, the area’s lakes and streams, as well as the Mississippi River, were given special consideration for preservation. This did not, however, mean that the lakes were preserved in their “natural” state, for they were connected by channels, dredged and filled to turn wetlands into open water and dry land, and even reshaped to better conform to the prevailing fashion of design. These manipulations had dramatic effects on the Chain’s smallest lake, Brownie, which became meromictic after a rapid drop in lake level caused by ditching across the divide to Cedar Lake. The lakes and surrounding area were important sources of subsistence for Dakota and Ojibwe people through the middle of the nineteenth century, and some of the earliest substantive interactions between missionaries and Native Americans in Minnesota played out around the Chain of Lakes and nearby Mississippi River valley. The relative orientation of the lakes (and of other groups of lakes in the Twin Cities), and some lakes’ unusual depths relative to surface areas, result from their formation by melting of ice blocks buried in valley train fill during final retreat of the Laurentide ice sheet. Below tens to hundreds of feet of glacial material, mapping of bedrock surfaces indicates the presence of paleo–Mississippi River channels dating from at least two previous interglacials. The integration of multiple subdisciplines of geology and of various basic sciences within paleolimnology and limnogeology, as well as the relevance to students of historical and environmental information, makes lake sediment studies well suited to hands-on, place-based educational approaches as stand-alone courses or laboratories for a number of different core curriculum and nonmajor classes.