Scotland is one of the most valuable regions available for geologic study, as it has been a breeding ground for the discovery and development of many fundamental concepts from the earliest studies in the field through today. Scotland has traditionally been viewed, in a broad sense, as the amalgamation of two components: the eroded remnants of the Caledonide Orogen north of the Highland Boundary Fault (HBF), and the post-Caledonian Old Red Sandstone (ORS) to the south. Studies based in the Scottish Caledonides and the ORS have provided a host of concepts that we now deem fundamental, but much of that has been the byproduct of effort to understand how they were juxtaposed along the HBF. The metamorphosed strata of the Grampian Terrane (GT) lie against pillow basalts and minor sediments associated with the Highland Border Complex (HBC), and undeformed fluvial deposits of the ORS near the Highland Border. The incompatibility of lithologies, but also palaeontologic and radiometric ages, on either side of the fault was seemingly inexplicable, and coined the term “the Highland Border Paradox”. The Highland Border Paradox was used to describe the conflicting idea of continuity between the GT and HBC, despite incompatible lithologies and ages within the section. Several tectonic models have been suggested as a solution to the core of the issue, but a widely accepted solution has so far been elusive. The 40Ar/39Ar method is well-poised to investigate when the Scottish Caledonides were active, and when the ORS was deposited; each valuable in their own dimension but combined represent the best opportunity to understand the Highland Border Paradox to date. Two models exist: one which considers the Midland Valley Terrane (MVT; predominately ORS) to be relatively autochthonous relative to the northern terranes, and another that suggests the MVT is mostly allochthonous, or exotic. This dissertation is designed as a multi-pronged approach to offer an overarching understanding of the relationship between the Scottish Caledonides and the ORS, but with the intention that each chapter is a standalone contribution. We first investigate the relationship between the Grampian Terrane and the Old Red Sandstone by studying the contact that bounds them, which is along the Highland Boundary Fault. The base of the ORS is only reported to be exposed at five localities along the northern margin of the Midland Valley, but the basal unconformity is only found at Stonehaven. Outcrop exposure is not ideal in Scotland, such that the exposure of the contact between the GT and MVT is only exposed at those few localities, and physically tracing contacts between those localities is not possible. Chapter 1 is focused on exposure of the contact from the locality near Stonehaven, where we were surprised to find that no unconformity exists, and that the base of the ORS is a fault. A new age 40Ar/39Ar age of 438 Ma from biotite separated from a dike that crosscuts the Cowie Formation is over 20 Myr older than previous estimates, pushing the base of the ORS well into the Silurian. Fossils of Pneumodesmus Newmani found there, the earliest documented terrestrial and air-breathing fauna in the geologic record, must also be as old as 438 Ma. This pushes back both the timing of when air-breathing animals emerged from land, but also reinstates Stonehaven as the ideal locality to study the earliest life on land. This chapter was designed to be a manuscript for submission to Geology, or a similar journal, as it is a famous locality pertinent to a host of Caledonian studies, is commonly used for teaching, and has broad interest to the scientific community with respect to Pneumodesmus Newmani. Chapter 2 is focused on studying the physical contact between the GT and MVT at its other reported localities: Edzell (North Esk River), Callander, and Balmaha. Detailed field mapping and observations were made for each, also supplemented petrographic details from thin sections as needed. One of the most surprising findings is that, combined with observations from Stonehaven, the base of the ORS is either faulted or not exposed; there is effectively no evidence for a basal ORS unconformity. This releases the constraints that the ORS was deposited strictly after the Caledonian Orogeny, and that the ORS was deposited above the GT/HBC stack as we see it today. In addition, at each of these localities, we identify considerable evidence of faulting in the area between the GT and MVT; most affected is the intervening HBC. This is hard to reconcile with previous interpretations proposed for those localities by proponents of the autochthonous model, as it is based largely on proposed continuity at those localities. It is also difficult to reconcile with the suggestion, in that view, that the HBF only modestly displaces geology, and not responsible for the juxtaposition of the GT and MVT. Evidence at each locality for undeformed units directly juxtaposed with highly deformed rocks implies a significant amount of vertical displacement that has not previously been appreciated, in any previous account. A significant amount of vertical displacement is a characteristic of major strike-slip faults, yet previous strike-slip models for the HBF have invoked movements in a purely lateral sense. Chapter 3 aims to constraint when the GT, Northern Highland Terrane (NHT), and Hebridean Terrane (HT) were exhumed during the Caledonian Orogeny, with a particular focus on the southern region of the GT near the HBF. We employed single-step 40Ar/39Ar analysis of muscovite separated from bedrock exposed throughout the terranes north of the HBF, complementing a similar work by Dewey and Pankhurst (1970). Throughout all the terranes, these ages range from 500-420 Ma, with a concentration of ages ca. 470 Ma. Combined with previous data sets, the NHT appears to have had a younger exhumation, but if our dataset is considered alone that distinction is unclear. The second portion of Chapter 3 presents the results of step-heating 40Ar/39Ar analysis of muscovite separated from metamorphosed GT strata, sampled in transects spanning across the metamorphic zones of the GT. The purpose of the transects is to evaluate when the portion of the GT immediately against the MVT was active. The step-heating analyses range between 471-461 Ma at Stonehaven, 468-453 Ma at North Esk, and 459-447 Ma at Balmaha (combined with Callander). These ages indicate that the Caledonian Orogeny was active at least from ca. 471-447 Ma, whereas the Caledonian Orogeny was previously proposed to be unusually short (10 Myr). As these ages likely capture the latest stage of orogenesis, the actual duration is likely considerably longer, and this is also suggested by the wider range of single-step ages. It is also now difficult to envision a scenario in which the GT was a passive margin through Ordovician times, which is a widely accepted notion. Chapter 4 is designed to investigate the time at which the Midland Valley ORS was deposited, and where its sediments originated from. We obtained three ages from volcanic units interleaved throughout the ORS, including a result of 438 Ma near the base (from Stonehaven), a result of 431 Ma from the Lintrathen Porphyry near mid-section, and a result of 400 Ma at the top of the ORS near Oban. We sampled over ten volcanic units interleaved within the ORS, but most ultimately were unsuitable for age analysis. Despite only obtaining three ages, it is now clear that at least the onset of ORS sedimentation is significantly older than previous estimates, now as far back as 438 Ma, whereas it was previously considered to be mostly Devonian. Considering that the age from Lintrathen at midsection is only 6 Myr younger, and still Silurian, it is possible that a majority of the Midland Valley LORS is Silurian, and deposited within a much more narrow timeframe than previously suggested. The result of 399 Ma from Oban confirms the previous suspicion that the ORS near Oban is unrelated to the ORS in the Midland Valley. Detrital analyses from the Midland Valley ORS indicate a source that ranges in age from mainly 480-420 Ma, which effectively overlaps the Scottish source ages obtained in Chapter 3. This is at odds with a previous hypothesis that suggested the ORS was sourced from large river systems from Scandinavia (including the Western Gneiss Region), analogous to the Himalayan drainages today. In combination, the depositional ages (437 and 431 Ma) and range of detrital ages (480-420 Ma), suggest that the ORS was locally related to the Scottish Caledonides, rather than an exotic origin. So, while it is now clear that displacement along the HBF is more substantial than previously conceived, that displacement was not significant enough to isolate the ORS from a Scottish source.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Microfiche copy available in Archives and Science. / Bibliography: leaves 32-33. / by Jean M. Baranowski. / M.S.

The primary objective of this study of four cores from the Lower Mississippian Price Formation was to determine the dominant controls on diagenesis and porosity as the Price sandstones are potential reservoirs for coalbed methane. Facies analyses of the cores, in combination with outcrop data from previous studies, lead to the conclusions that these rocks represent distal bar and prodelta, wave-reworked distributary mouth bar, and upper delta plain deposits. Petrographically, the sandstones typically are fine-grained lithic arenites that were derived from a low-grade metamorphic provenance with lesser sedimentary and minor plutonic influences. Diagenetically, most sandstones are dominated by siliceous cements and replacements, although some samples from the marine zones are dominated by carbonate cements. No original porosity is preserved and secondary porosity of any type is rare, but where present is usually the result of dissolution of carbonate phases. The age of the rocks and the maximum temperature of diagenesis (found to be >150°C throughout these sections) were strongly influential in diagenesis. The composition of the sediments was also very important in compaction, cementation, replacement, and dissolution. The variation in detrital mineralogy is limited, and this, in combination with temperature and age, results in diagenesis that is relatively homogeneous throughout these sections of the Price Formation. Finally, as porosity in the sandstones is extremely low, it seems highly unlikely that the Price Formation sandstones in this area could be economic producers of methane. / M.S.

High arsenic concentrations (>100 ppb) have been measured in wells completed in the Ordovician St. Peter sandstone aquifer of eastern Wisconsin. The primary source of arsenic is As-bearing sulfide minerals within the aquifer. There is concern that periodic disinfection of wells by chlorination may facilitate arsenic release to groundwater by increasing the rate of sulfide mineral oxidation. Current guidance from the Wisconsin Department of Natural Resources recommends a "low-dose" treatment of 20% of the chlorine strength and 10% of the of the contact time of chlorine treatments used in non-arsenic impacted wells for well disinfection and biofilm removal. In order to provide information pertaining to WDNR's recommendations, St. Peter sulfide minerals were reacted with a range of chlorine "shock-treatments" similar to those occurring in wells. This study focuses on abiotic processes that mobilize arsenic from the solid phase during controlled exposure to chlorinated solutions. Thin sections were made from aquifer material collected at Leonard's Michael quarry, located in Winnebago County, Wisconsin. Bulk arsenic content of this material was measured as 674 ppm. Quantitative EPMA analysis shows As zoning in pyrite grains with concentrations up to 1 wt. % As. After mineral characterization, the thin sections were exposed to solutions of 60 mg/L "free chlorine," 1200 mg/L "free chlorine," and nanopure water (control) at pH 7.0 and pH 8.5 for 24 hours. Thin sections were then analyzed to measure changes in the pyrite surfaces. For solution experiments, aquifer material was crushed to between 250 μm and 355 μm mesh sizes (S.A. ~ 50 cm2/g – 60 cm2/g, Foust et al. 1980) and reacted under the same conditions as the thin sections in a batch reactor. Solution samples were collected periodically during the 24 hour exposure and analyzed for arsenic, iron, and sulfate ion. Pyrite oxidation is shown to dramatically increase with increasing chlorine concentrations as shown by measurements of released sulfate ion, used here as the reaction progress variable. EPMA maps also reveal complete oxidation of pyrite cements to Fe-oxyhydroxides at 1200 mg/L "free chlorine" and pH 7.0. This behavior does not occur at lower concentrations or higher pH. Arsenic release to solution does not appear to be directly correlated to increasing chlorine concentrations, but is governed by Fe-oxyhydroxide nucleation, which inhibits the release of dissolved arsenic at higher concentrations of chlorine. / Master of Science

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