Heat transfer in the subsurface can vary with depth due to variations in the thermal conductivity of the geologic medium as well as variations in groundwater flow velocity. However, traditional thermal response tests (TRTs) do not allow for evaluation of the depth variability of heat transfer. We investigate the potential for using discrete-depth heat dissipation tests in open, water-filled boreholes to evaluate variations in heat exchange rate with depth. Heat dissipation tests were initiated at target depths in a test well using an electrical resistance heater. Heat dissipation was monitored by measuring borehole water temperature through time using a fiber-optic distributed temperature sensing system. Temperature data were used to compare the thermal response at different depths in the borehole. To account for both the thermal conductivity of the geologic medium and the groundwater flow velocity, we used a numerical groundwater flow model (MODFLOW) and solute transport model (MT3DMS) to simulate heat dissipation tests. Simulation results indicate the measured response to a heat dissipation test in an open borehole is strongly dependent on the measurement location within the borehole; thus, data are ambiguous when the measurement location is uncontrolled. However, modeling results also indicate that the thermal response of a heat dissipation test as measured at the center of the borehole is sensitive to variations in thermal conductivity and groundwater flow velocity, suggesting that heat dissipation tests are a potentially useful method for characterizing depth variability in thermal properties if a centralized temperature measurement method is used to monitor the tests.

Abstract The Baraboo Quartzite contains numerous well-preserved sedimentary structures that enable interpretation of environments of deposition. Included are various types of cross-stratification, reactivation surfaces, and tidal bedding. The bulk of the Baraboo was deposited under tidal influence. The remainder represents deposition in a braided stream system. The origin of the tremendous volume of quartz sand remains somewhat unknown.

Abstract Flood-control reservoirs designed and built by federal agencies have been extremely effective in reducing the ravages of floods nationwide. Yet some structures are being removed for a variety of reasons, while others are aging rapidly and require either rehabilitation or decommissioning. The focus of the paper is to summarize collaborative research activities to assess sedimentation issues within aging flood-control reservoirs and to provide guidance on such tools and technologies. Ten flood-control reservoirs located in Oklahoma, Mississippi, and Wisconsin have been examined using vibracoring, stratigraphic, geochronologic, geophysical, chemical, and geochemical techniques and analyses. These techniques and analyses facilitated: (1) the demarcation of the pre-reservoir sediment horizon within the deposited reservoir sediment, (2) definition of the textural and stratigraphic characteristics of the sediment over time and space, (3) the accurate determination of the remaining reservoir storage capacity, (4) the quantification of sediment quality with respect to agrichemicals and environmentally important trace elements over both time and space, and (5) the determination of geochemical conditions within the deposited sediment and the potential mobility of associated elements. The techniques employed and discussed here have proven to be successful in the assessment of sediment deposited within aging flood-control reservoirs, and it is envisioned that these same approaches could be adopted by federal agencies as part of their national reservoir management programs.

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.