<p> Previous workers in the Hamilton area have pointed out the occurance of lead and zinc mineralization within the Mid-Silurian carbonate beds. They also mentioned the existance of bitumens in these rock units.</p> <p> Analysis of 30 dolomite samples and separated bitumens by atomic absorption for Cu, Pb, Zn showed that the localization of the metals in the carbonates was controlled by the concentration of the bitumens in the rocks.</p> <p> Analysis of 5 bitumens samples by atomic absorption for Cu, Pb, Zn suggested that the bitumens act merely as a reducing agent and are not preferred sites for base metal accumulation.</p> / Thesis / Bachelor of Science (BSc)

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.

No description available.

This dissertation represents an investigation of the mid-Paleozoic tectono-thermal and kinematic evolution of the crust in eastern coastal Maine as recorded by the plutonic rocks of this region. The first chapter describes the plutonic rocks of the Coastal Maine Magmatic Province. A tectonic model is developed in which late Ordovician-Silurian bimodal magmatism is interpreted to reflect crustal melting as a result of intraplating of mantle melts at high crustal levels during a period of tension. Large scale melting of lower crustal source regions, represented by voluminous intrusion of Devonian granites, reflects a period of transpression during which upwelling mantle melts were confined to the base of the crust. The diversity of granitic plutons reflects changes in the mineral assemblages present during partial melting, and in some instances, modification as a result of mixing/mingling with mantle melts. The second chapter examines the effect of accessory minerals on the initial Pb isotopic signature of anatectic granites. Their initial Pb isotopic composition reflects (a) the age, type, modal distribution, and heterogeneity in the initial U and Th content of the accessory phase(s) present in the source, (b) variation in melt composition and temperature during partial melting, (c) the fraction of the source melted, and (d) the extent to which the melt is homogenized prior to crystallization. It is shown that granitic plutons derived by crustal anatexis of a common source material are not required to have similar initial lead isotopic compositions. The third chapter presents the results of a Pb isotopic investigation of selected plutonic rocks from the Coastal Maine MagmaticProvince. This study was designed to test and refine petrogenetic models presented in Chapter 1. The Pb isotopic signature of the granitic plutons reveals the presence of two lithologically heterogeneous source regions beneath the Avalon Composite Terrane. The upper crustal source region has an mean V-Pb age of -2.0 Ga and the high 207Pb/204Pb-206Pb/204Pb characteristic of Avalonian crust. The lower crustal source region has an average U-Pb age of -1.3 Ga and lower 207Pb/204Pb. This source region may represent either the autochthonous basement to the Avalon platform or the eastern extension of the basement to the Gander Terrane of central Maine. / Ph. D.

No description available.

The three approaches followed herein aim to improve our understanding of the paleobiodiversity andevolution of Silurian radiolarians. The first approach provides an exhaustive taxonomic description ofan entirely new radiolarian fauna recovered from two sections of the Cape Phillips Formation in theCanadian Arctic which accumulated in two different paleoenvironmental settings. The samples are datedby graptolites of the Gorstian Lobograptus progenitor Zone. The obtained radiolarian fauna includes 28species, of which 3 are new, and exhibits some of the best preserved Silurian radiolarians known so far.The stratigraphic range of several species was also extended. Then, in a second approach, a CT-Scan3D reconstruction of a specimen of Gyrosphaera cavea was conducted in order to resolve significantinternal structure taxonomic issues. Higher level radiolarian classification is based on internal structures,and classical methods of observing these features repeatedly failed to uncover them. The 3D imagingrevealed a «double» coiling of the specimen that has proved useful in understanding how it grew.Eventually, the third approach is a completion of published taxonomic works in the Silurian with theaim of providing diversity trends through analyses of these radiolarian occurrences. A biotic crisis canbe observed in the Homerian, exhibiting both high extinction and low origination rates, and may belinked with enhanced marine productivity. / De tre projekten som utvecklas här har som mål att fokusera på trender inom evolutionen ochmångfalden av en grupp planktoniska mikroorganismer från Silur (från -443 till -419 Ma). I ett förstaprojekt beskrivs en helt ny fauna radiolarier som hittats i två lokaliteter på de kanadensiska arktiskaöarna, och som har deponerats i olika miljöförhållanden under Silur. Detta material daterades med hjälpav graptoliter, en grupp utdöda svalgsträngsdjur som är mycket användbara för paleozoiska dateringar,till en ålder överensstämmande med Gorstian (-427 till -425 Ma). Denna kanadensisk-arktiska fauna avradiolarier består av 28 arter (varav 3 är nya) och uppvisar några av de bäst bevarade fossilerna frånSilur överhuvudtaget. Den stratigrafiska bredden, vilket är livstiden, av flera arter har också förlängts.Därefter, i ett andra projekt, skapades en 3D-rekonstruktion av ett exemplar av Gyrosphaera cavea medhjälp av mikrotomografi för att observera och beskriva komplexa interna strukturer. Faktum är attklassificeringen av Radiolaria består till stor del av analysen och beskrivningen av dessa internastrukturer och många klassiska metoder som har använts för att observera dem, såsom med hjälp avsvepelektronmikroskop, har misslyckats konsekvent. 3D-avbildningen visade en komplex dubbelrullandeav strukturen i exemplaret, som har visat sig vara användbart i sökandet för att förstå dennesutveckling. Det tredje projektet är slutförandet av en samling av samtliga publicerade arbeten röranderadiolarier från Silur med syfte att klargöra trender inom diversitet för hela perioden genom analyser avförekomsten av dessa radiolarier. Ett utdöende kan observeras under Homerian (-430 till -427 Ma), somtroligen orsakades av frekventa utdöenden och en låg artbildningshastighet.

Scolecodonts (= jaws of the polychaete worms) have always been a relatively neglected group of microfossils. In the Prague Basin (Czech Republic), only two major studies exclusively focused on scolecodonts have been published. The aim of the present research was to fill in this gap - by a restudy of the historical collections of Žebera and Šnajdr, and its comparison with results gained from newly collected late Silurian samples and scolecodont faunas from other areas. It has turned out that the jawed polychaete fauna in the Prague Basin was much more diversified than previously reported. The last report on late Silurian scolecodonts by Šnajdr (1951) concluded that there are four determined and two species left in open nomenclature present. Restudy of the original collection has shown that there are at least 11 different species from families Mochtyellidae, Polychaetaspidae, Ramphoprionidae, Paulinitidae, Atraktoprionidae, Skalenoprionidae and Hadoprionidae. The new collection from similar stratigraphical level gained at least 25 species, including one newly described ("Mochtyella" pragensis). The taxonomic re-study also focused on the species Kettnerites kosoviensis that is a type species of the genus and was described in the Prague Basin. The new samples come from the limestone which is in contrast to...

Thesis advisor: Christopher J. Hepburn / The Nashoba terrane in eastern Massachusetts comprises Cambrian-Ordovician mafic to felsic metavolcanic rocks and interlayered sediments metamorphosed during the mid-Paleozoic and intruded by a series of dioritic to granitic plutons during the Silurian to earliest Carboniferous. This work comprises two parts discussing the Sm-Nd isotope characteristics and major and trace element geochemistry of the Nashoba terrane: the first discusses the Cambrian-Ordovician metamorphosed units, the second discusses the Silurian-Carboniferous plutons. Part I: The Nashoba terrane in eastern Massachusetts lies between rocks of Ganderian affinity to the northwest and Avalonian affinity to the southeast. Its relationship to either domain was unclear and has been investigated. Major and trace element geochemical data indicate a mix of arc, MORB, and alkaline rift related signatures consistent with an origin of the terrane as a primitive volcanic arc-backarc complex built on thinned continental crust. Newly determined Sm-Nd isotopic data clarifies the original tectonic setting. Amphibolites of the Marlboro and Nashoba Formations have high εNd values (+4 to +7.5) consistent with formation in a primitive volcanic arc with minimal interaction between arc magmas and crust. Intermediate and felsic gneisses have moderate εNd values between +1.2 and –0.75 indicating a mixture of juvenile arc magmas and an evolved (likely basement) source. Depleted mantle model ages of 1.2 to 1.6 Ga indicate a Mesoproterozoic or older age for this source. Metasedimentary rocks have negative εNd values between –6 and –8.3 indicating derivation primarily from an isotopically evolved source (or sources). The model ages of these metasedimentary rocks (1.6 to 1.8 Ga) indicate a source area of Paleoproterozoic or older age. The εNd values and model ages of the intermediate and felsic rocks and metasedimentary rocks indicates that the basement to the Nashoba terrane is Ganderian rather than Avalonian. The Nashoba terrane therefore represents a southward continuation of Ganderian arc-backarc activity as typified by the Penobscot and/or Popelogan-Victoria arc systems and the Tetagouche-Exploits backarc basin in the northern Appalachians. Part II: Between 430 and 350 Ma the Nashoba terrane experienced episodic dioritic and granitic plutonism. Previous workers have suggested a supra-subduction zone setting for this magmatism based on the calc-alkaline nature of the diorites. Previously determined major and trace element geochemical data along with newly determined Sm-Nd isotopic data indicate that a subduction zone was active beneath the Nashoba terrane during the majority of the 430 to ca. 350 Ma magmatism (and likely throughout). Trace element geochemistry indicates a strong arc component in all magmas and suggests that the various Silurian to Carboniferous plutonic rocks of the Nashoba terrane could all have been derived by modification of a slightly enriched NMORB-type source via subduction zone input and crustal contamination. Most of the rocks from this period have intermediate εNd values consistent with contamination of juvenile magmas by an evolved source. The late Proterozoic model ages for most of these rocks suggest the Ganderian basement of the Nashoba terrane as the source of evolved material. One rhyolite from the nearby Newbury Volcanic Complex (of unknown affinity) has a moderately negative εNd value consistent with derivation by partial melting of Cambrian-Ordovician metasedimentary rocks of the Nashoba terrane. This suggests that the Newbury Volcanic Complex formed as the surface expression of mid-Paleozoic Nashoba terrane plutonism. Geochemical and isotopic similarities between the plutonic rocks of the Nashoba terrane and widespread contemporary Ganderian plutonism suggest that the Nashoba terrane remained a part of Ganderia during its transit and accretion to the Laurentian margin. Significantly younger model ages in the youngest granitic rocks indicate that Avalonian crust may have underthrust the Nashoba terrane after 400 Ma and contributed to the generation of these granites. / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Silurian strata of eastern North America have been thoroughly studied for nearly two centuries. Through these investigations a general understanding of unit distribution and correlative relationships were established throughout the region. Many of these interpretations remain valid still to this day, however, with advancements in stratigraphic methodologies in the last few decades (e.g., sequence-, chemo-, and biostratigraphy), numerous discrepancies have come to light with regards to the chronostratigraphic correlation of several stratigraphic intervals throughout the region. A number of these discrepancies within the lower Silurian (Llandovery—lower Wenlock) have been resolved in the last two decades permitting the establishment of refined depositional models and sequence stratigraphic hierarchies for strata deposited during this interval of time for the Appalachian, Illinois, and Michigan basins. Though these studies provided significant improvement to the chronostratigraphy of eastern North America, there remained a large under-evaluated stratigraphic interval spanning the remainder of the Silurian (Wenlock—Pridoli), which is host to expansive evaporite reserves and hydrocarbon resources throughout eastern North America. As such, it is critical that these strata are accurately and precisely correlated throughout the region and that temporal constraint be applied to these resources in order to evaluate their potential and develop predictive models for their future utilization. The investigation herein provides high-resolution chronostratigraphic analyses of several core and outcrop from the eastern, southwestern, and western margins of the Appalachian Basin. These analyses included the integration of δ13Ccarb chemostratigraphy, conodont biostratigraphy, sequence stratigraphy, and subsurface geophysical data. The work herein now permits the establishment of global series and stage boundaries for the upper Silurian throughout the Appalachian and Michigan basins and also addresses regional miscorrelations within strata on both the eastern and western margins of the Appalachian Basin to provide a united sequence stratigraphic hierarchy between the Appalachian, Illinois, and Michigan basins.

Rocks of Paleozoic, Tertiary, and Quaternary age are represented in the northern part of the Malad Range. The Paleozoic rocks are represented by thirteen formations that are characterized lithologically by quartzites, shales, and carbonates. The oldest formation in the mapped area of Paleozoic age is the Brigham Formation, and the youngest formation is the Jefferson Formation of late Devonian age. The rocks of Tertiary age are conglomerates, shales, and limestones and are represented by the Wasatch Formation, the Salt Lake Formation, and boulders. Quaternary rocks include sediments of the Lake Bonneville Group and alluvium. The faults in the mapped area were formed during two periods of movement. The east-west-trending faults, northeast-trending faults, and northwest-trending faults are a consequence of compressional forces during Laramide orogenic activity. The north-south-trending faults were the result of Basin and Range block faulting during middle and late Tertiary times.