published_or_final_version / Earth Sciences / Master / Master of Philosophy

This thesis utilizes several geophysical methods to study the Siljan Ring impact structure, focusing on the western part of the structure. This thesis, and the three papers upon which it is based, reports on attempts to delineate the Paleozoic rocks at depth within the annular ring graben and characterize their structure. In addition, the nature of the basement, which underlies these sedimentary rocks is investigated. Papers I and III focus on analysis of the down-hole logging and borehole core data. As well as the acquisition, processing and interpretation of 2D high-resolution reflection seismic data from the Mora area. The borehole log responses were compared with the core lithology from the Mora 001 borehole and information from two other cores (Mora VM 2 and Mora MV 3) in order to interpret the logs. The logs reveal significant changes in the lithology between boreholes, indicating a very high level of structural complexity, which is attributed to impact tectonics. In addition, the log data revealed a high sonic velocity contrast between the Silurian and Ordovician successions and a higher apparent temperature gradient than in the northern part of the structure. The interpretation of the high-resolution 2D seismic data suggest that the Mora area has been significantly affected by the impact. Several potential faults were identified in the area and interpreted to be post depositional and related to the impact. In paper II, a 2D seismic profile from the Orsa area (12 km) located in the northwestern part of the Siljan Ring was re-processed. To compliment this seismic line, first break traveltime tomography results, vintage seismic OPAB profiles, new and pre-existing gravity data, aeromagnetic data and the bedrock geological map were used to present a geological model along the Orsa profile. Reprocessing of the seismic data resulted in improved stacked and migrated sections and better imaging of the top of the crystalline basement than the original processing. Integrated interpretation of the seismic profiles suggests that the area has been significantly affected by faulting and that the depth to the basement varies greatly along the different profiles.

54 Summary In this experimental study, selected Devonian limestones of the Prague Basin (i.e. samples from the historic quarry of Branické skály) were examined to find their suitability for production of hydraulic limes or for natural cement. Four representative samples of the dvorecko-prokopské limestone were sampled in the form of blocks weighing approximately 10 kg each, from the layer of the quarry wall that had been chosen based on literature research. A detailed mineralogical-petrographic examination of samples was the first step, in an attempt to obtain their mineralogical composition, microstructure and texture. Samples were analysed by polarizing microscopy and cathodoluminescence of thin sections, and X-ray diffraction of insoluble residues determined by treatment with both the hydrochloric acid and the acetic acid solution. Mineralogical composition of the insoluble residuals was illite, kaolinite, quartz and Na-plagioclase (albite). Two samples contained among above mentioned mineral phases also chlorite. The utility of studied limestones for the production of hydraulic binders (hydraulic limes and natural cement) was derived from both the calculations based on obtained chemical analyses (included standard cement and lime indexes and modules) and the firing experiments. The firing experiments...

MSc., Faculty of Science, University of the Witwatersrand, 2011 / Granitoid intrusions are numerous in southwestern Rajasthan and are useful because they can provide geochronological constraints on tectonic activity and geodynamic conditions operating as the time of intrusion, as well as information about deeper crustal sources. The particularly voluminous Neoproterozoic felsic magmatism in the Sirohi region of Rajasthan is of particular interest as it may have implications for supercontinental (Rodinia and Gondwana) geometry. The Mt. Abu granitoid pluton is located between two major felsic suites, the older (~870-800 Ma) Erinpura granite and the younger (~751-771 Ma) Malani Igneous Suite (MIS). The Erinpura granite is syn- to lateorogenic and formed during the Delhi orogeny, while the MIS is classified as alkaline, anorogenic and either rift- or plume-related. This tectonic setting is contentious, as recent authors have proposed formation within an Andean-type arc setting. The Mt. Abu granitoid pluton has been mapped as partly Erinpura (deformed textural variant) and partly younger MIS (undeformed massive pink granite). As the tectonic settings of the two terranes are not compatible, confusion arises as to the classification of the Mt. Abu granitoid pluton. Poorly-constrained Rb-Sr age dating place the age of formation anywhere between 735 ± 15 and 800 ± 50 Ma. The older age is taken as evidence that the Mt. Abu intrusion was either a late phase of the Erinpura granite. However, U-Pb zircon geochronology clearly indicates that the Mt. Abu felsic pluton is not related to- or contiguous with- the Erinpura granite suite. The major results from this study indicate that the all textural variants within the Mt. Abu pluton were formed coevally at ~765 Ma. Samples of massive pink granite, mafic-foliated granite and augen gneiss from the pluton were dated using U-Pb zircon ID-TIMS at 766.0 ± 4.3 Ma, 763.2 ± 2.7 Ma and 767.7 ± 2.3 Ma, respectively. The simple Mt. Abu pluton is considered as an enriched intermediate I- to A-type intrusion. They are not anorogenic A-types, as, although these felsic rocks have high overall alkali and incompatible element enrichment, no phase in the Mt. Abu pluton contains alkali rich amphibole or pyroxene, nor do REE diagrams for the most enriched samples show the gull-wing shape typical of highly evolved alkaline phases. The alkali-enriched magma may be explained by partial melting of a crustal source such as the high-K metaigneous (andesite) one suggested by Roberts & Clemens (1993), not derivation from a mantle-derived mafic magma. The fairly restricted composition of Mt. Abu granitoids suggests that partial melting and a degree of assimilation/mixing may have been the major factors affecting the evolution of this granitoid pluton; fractional crystallization was not the major control on evolution of these granitoids. Revdar Rd. granitoids that are similar in outcrop appearance and petrography to Mt. Abu granitoids also conform to Mt. Abu granitoids geochemically and are classified as part of the Mt. Abu felsic pluton. Mt. Abu samples from this study have a maximum age range of 760.5-770 Ma, placing the Mt. Abu pluton within the time limits of the Malani Igneous Suite (MIS) as well as ~750 Ma granitoids from the Seychelles. Ages of the Sindreth-Punagarh Groups are also similar. These mafic-ultramafic volcanics are thought to be remnants of an ophiolitic mélange within a back-arc basin setting at ~750-770 Ma. The three Indian terranes are spatially and temporally contiguous. The same contiguity in space and time has been demonstrated by robust paleomagnetic data for the Seychelles and MIS. These similarities imply formation within a common geological event, the proposed Andean-type arc (Ashwal et al., 2002) on the western outboard of Rodinia. The implications are that peninsular India did not become a coherent entity until after this Neoproterozoic magmatism; Rodinia was not a static supercontinent that was completely amalgamated by 750 Ma, as subduction was occurring here simultaneous with rifting elsewhere. Pageiv The Mt. Abu pluton has undergone deformation, with much of the pluton having foliated or augen gneiss textures. The timing of some of the deformation, particularly the augen gneiss and shear zone deformation, is thought to have occurred during intrusion. The Mt. Abu and Erinpura granitoids have experienced a common regional metamorphic event, as hornblende (Mt. Abu) and biotite (Erinpura) give 40Ar/39Ar ages of 508.7 ± 4.4 Ma and 515.7 ± 4.5 Ma, respectively. This event may have reactivated older deformatory trends as well. The temperature of resetting of argon in hornblende coincides with temperatures experienced during upper-greenschist to lower-amphibolite facies metamorphism. These late Pan-African ages are the first such ages reported for the Sirohi region and southern part of the Aravalli mountain range. They offer evidence for the extension of Pan-African amalgamation tectonics (evidence from southern India) into NW India. The age of formation of the Erinpura augen gneiss magma is 880.5 ± 2.1 Ma, thus placing the Erinpura granitoids within the age limits of the Delhi orogeny (~900-800 Ma; Bhushan, 1995). Most deformation observed here would have been caused by compression during intrusion. The Erinpura granitoids are S-type granitoids due to their predominantly peraluminous nature, restricted SiO2-content, normative corundum and the presence of Al-rich muscovite and sillimanite in the mode. Weathered argillaceous metasedimentary material may also have been incorporated in this magma, while the presence of inherited cores suggests relatively lower temperatures of formation for these granitoids as compared to the Mt. Abu granitoids. The age of inheritance (1971 ± 23 Ma) in the Erinpura augen gneiss is taken as the age of the source component, which coincides with Aravalli SG formation. The Sumerpur granitoids differ from the Erinpura granitoids in terms of macroscopic and microscopic texture (undeformed, rarely megaporphyritic) but conform geochemically to the Erinpura granitoid characteristics and may thus be related to the Erinpura granitoid suite.The Revdar Rd. granitoids that are similar in macroscopic appearance to Erinpura granitoids also conform geochemically, and may similarly belong to the Erinpura granite suite. A Revdar Rd. mylonite gneiss with the Erinpura granitoids’ geochemical signature was dated at ~841 Ma, which does not conform to the age of the type-locality Erinpura augen gneiss dated here, but later intrusion within the same event cannot be ruled out because of the uncertainty in the age data (~21 Ma). The presence of garnet in one Revdar Rd. (Erinpura-type) sample implies generation of these granitoids at depth and/or entrainment from the source, similar to the S-type Erinpura granitoids. The Ranakpur granitoids differ significantly from both the Erinpura and Mt. Abu intrusives due to their low SiO2-content and steep REE profiles (garnet present in the source magma); they are thought to have been generated under higher pressures from a more primitive source. The deeper pressure of generation is confirmed by the absence of a negative Eu-anomaly. The Ranakpur quartz syenite dated at 848.1 ± 7.1 Ma is younger by ~30 m.y. than the Erinpura augen gneiss. It is within the same time range as numerous other granitoids from this region as well as the Revdar Rd. granitoid dated in this study. The prevalence of 830- 840 Ma ages may indicate that a major tectonic event occurred at this time. The Ranakpur quartz syenite may have been generated near a subduction or collision zone, where thickened crust allows for magma generation at depth. The deeply developed Nb-anomaly in the spider diagram also implies a larger subduction component to the magma. The Swarupganj Rd. monzogranite is interpreted to have formed by high degrees of partial melting from a depleted crustal source and is dissimilar to other granitoids from this study. More sampling, geochemical and geochronological work needs to be done in order to characterize this intrusion. Pagev The Kishengarh nepheline syenite gneiss is situated in the North Delhi Fold Belt and is the oldest sample dated within this study. The deformation in this sample is due to arc- or continental- collision during a Grenvillian-type orogeny related to the amalgamation of the Rodinia supercontinent (and peninsular India), dated by the highly reset zircons at ~990 Ma. This is considered a DARC (deformed alkaline rock and carbonatite) and represents a suture zone (Leelanandam et al., 2006). The primary age of formation of this DARC is older than 1365 ± 99 Ma, which is the age of xenocrystic titanites from the sample. The granitoid rocks from this study area (Sirohi region) range widely in outcrop appearance, petrography and geochemistry. Granitoids from the Sirohi region dated in this study show a range of meaningful ages that represent geological events occurring at ~880 Ma, ~844 Ma, ~817 Ma, ~789 Ma, ~765 Ma and ~511 Ma. Granitoid magmatism (age of formation) in this region is predominantly Neoproterozoic, and the number of events associated with each granitoid intrusion as well as diverse tectonic settings implies a complexity in the South Delhi Fold Belt that is not matched by the conventional and simplified view of a progression from collision and orogeny during Grenvillian times (Rodinia formation), through late orogenic events, to anorogenic, within-plate (rift-related) alkaline magmatism during Rodinia dispersal. Instead, it is envisaged that convergence and subduction during the formation of Rodinia occurred at ~1 Ga (Kishengarh nepheline syenite deformation), with a transition to continental-continental collision at ~880-840 Ma (Erinpura and Ranakpur granitoids). This was then followed by far-field Mt. Abu and MIS magmatism, related to a renewed period of subduction at ~770 Ma. The last deformatory event to affect this region was that associated with the formation of Gondwana in the late Pan-African (~510 Ma).

Soil seed banks are a reservoir of viable seeds present in the soil in plant communities. They have been studied and characterized in various ways in different habitats. However, these studies are limited to modern seed banks. This study extends seed bank studies to the Paleozoic Era. It was hypothesized that size distribution and seed density in Paleozoic seed banks exhibit similar patterns as in modern seed banks. Seed sizes and seed density of fossil seed from Wise Virginia were estimated. Modern seed bank information was obtained from published data. Data were analyzed using one-way ANOVA and Kruskal-Wallis test. The Paleozoic size distribution was predominated by larger seeds and the estimated seed density of 19 200 seeds m-3 falls within the range of modern seed banks but at a higher end of modern seed bank densities. During the Paleozoic they were sufficient to insure regeneration of these economically important forests.

La plate-forme Saharienne paléozoïque, comprenant les bassins péri-Hoggar (Murzuq, Illizi, Mouydir, Ahnet, Reggane et Tim Mersoï) sont définies comme des bassins intracratoniques. Ils ont été dominés par des mouvements verticaux lents et à grande longueur d'onde, conduisant à une subsidence globale à faible vitesse (i.e. ca. 10 m/Ma à 50 m/Ma) et à l'accumulation d'une couverture sédimentaire étendue de type plate-forme (environnements de dépôts peu profonds), rythmée par des périodes pulsatiles d’augmentation et de diminution du taux de subsidence probablement déclenchées par des événements géodynamiques régionaux. Les mouvements verticaux de la plate-forme ont créé plusieurs arches également appelés dômes, paléo-topographies (e.g. les arches de la Tihemboka, d’Amguid El Biod, d’Arak-Foum Belrem et de l’Azzel Matti) et des bassins (en forme de synclinal) de différentes longueurs d'onde allant de plusieurs centaines à plus de milliers kilomètres. La persistance d’un ensemble assez uniforme de mouvements verticaux semble contrôler l’architecture des bassins, ce qui semble indiquer un contrôle à grande échelle (i.e. lithosphérique). Ce dernier contrôle spatialement et temporellement la dynamique sédimentaire de dépôt et d'érosion. Plusieurs périodes d'érosion majeures ont considérablement tronqué les sédiments préexistants sur de vastes zones, produisant des discordances régionales, restreintes et amalgamées sur les arches, qui séparent la couverture sédimentaire de la plateforme. À travers une approche intégrée multidisciplinaire originale allant d’une analyse géologique de bassin, associant le substrat et l’architecture de bassin à une modélisation thermomécanique numérique de la lithosphère, cette étude a permis de décrypter les facteurs de forçage des bassins intracratoniques de la plate-forme saharienne (bassins péri-Hoggar).L'architecture en Arches-Bassins est mise en évidence par l'identification de structures tectono-sédimentaires (onlap divergents, troncatures…). Cette architecture se caractérise par des variations d'épaisseur et des partitionnements de faciès, organisés par des failles normales planes sub-verticales formant des systèmes d'horst-graben souvent associés à des plis forcés dans la couverture. Connectés et nucléés aux grandes zones de méga-cisaillement, les systèmes d'horst-graben sont inversés (inversion positive) ou réactivés (plis forcés) au cours d'événements géodynamiques successifs (par exemple : extension cambro-ordovicienne, rebond glaciaire ordo-silurien, extension/ compression Siluro-Dévonien «Calédonienne», extension/compression du dévonien tardif et compression «hercynienne»).Formée sous une lithosphère précambrienne de type accrétionnaire héritées de plusieurs paléo-orogénèses (e.g. Eburnéenne, Panafricaine), une zonation des substrats sous l’architecture en Arches-Basins est observée : Les terranes Archéen à Paléoprotérozoïque se situent sous les hauts structuraux et les terranes méso-néo-protérozoïques sous les dépressions.Sur la base de ces observations géologiques et de l’hypothèse de densités différentielles conservées (impliquant un potentiel isostatique) entre les différents terranes accrétées héritées (i.e. les terranes archéennes et protérozoïques) dans la lithosphère, un modèle numérique thermo-mécanique 2D est proposé. Les facteurs de forçage du premier et du second ordre, respectivement caractérisés par de faible taux de subsidence et par leurs déviations cycliques pendant de longues durées (250 Ma), sont bien contraint par le modèle réconciliant aussi l’architecture tectono-stratigraphique singulière en Arches-Basins. Les différentes simulations ont montré l’importance des anomalies thermiques, de la tectonique (faible taux de déformation) et de l’apport externes en sédiments sur la dynamique de ces bassins intracratoniques. Le flux sédimentaire contrôle la vitesse et la durée de remplissage du bassin jusqu'à l'équilibre isostatique (…). / The Paleozoic Saharan platform including the peri-Hoggar Basins (i.e. Murzuq, Illizi, Mouydir, Ahnet, Reggane and Tim Mersoï basins) are defined as intracraonic basins. Their histories have been dominated by slow long-wavelength vertical motions leading to overall low subsidence rate (i.e ca. 10 m/Ma to 50 m/Ma) and accumulation of an extensive cover of platformal sediments (i.e. shallow deposits environments), rhythmed by pulsatile periods of increasing and decreasing rate probably triggered by regional geodynamic events. The vertical motions of the platform produced several arches also called domes, swells, highs, ridges (e.g. the Tihemboka, Amguid El Biod, Arak-Foum Belrem and Azzel Matti Arches) and basins (syncline-shaped) with different wavelengths going from several hundred to more than a thousand kilometres. The persistence of a rather uniform pattern of vertical motions seems to control the architecture of the basins indicating a large-scale control (i.e. lithospheric). This latter controls spatially and temporally the deposition and the erosion dynamics. Several major erosion events significantly truncated the pre-existing sediments over wide areas, producing regional unconformities, especially restricted and amalgamated on arches, which separate the platformal cover into divisions. Through an original multidisciplinary integrated approach going from a geological basin analysis, coupling the substrate and the basin architecture to a numerical thermo-mechanical modelling of the lithosphere, this study has led to decipher the forcing factors of the intracratonic basins of the Saharan platform.The Arches-Basins architecture is highlighted through the identification of tectono-sedimentary structures (growth strata, truncatures…). This architecture is featured by thickness variation and facies portioning, organized by sub-vertical planar normal faults (sometimes blind faults) forming horst-graben systems associated with forced folding in the cover. Connected and nucleated to major mega-shear zones, horst-graben systems are inverted (positive inversion) or reactivated (forced folds) during successive geodynamic events (e.g. Cambro-Ordovician extension, Ordo-Silurian glacial rebound, Siluro-Devonian “Caledonian” extension/compression, late Devonian extension/compression and “Hercynian” compression).Formed under a Precambrian lithosphere of accretionary type, inherited during several paleo-orogenies (e.g. Eburnean, Pan-African), a substrates zonation of the Arches-Basins framework is described, where the Archean to Paleoproterozoic terranes are forming the structural highs and the Meso-Neoproterozoic terranes the structural lows.Based on these geological observations and the hypothesis of conserved differential densities (implying an isostatic potential) between the inherited different accreted terranes in the lithosphere (i.e. archean and proterozoic terranes), a 2D thermo-mechanical numerical model is proposed. The first and second order forcing factors, respectively recorded in the subsidence rate pattern by the low long-lived and by their cyclic deviations, are well constrained reconciling the singular Arches-Basins tectono-stratigraphic architecture. The different simulations have shown the importance of thermal anomaly, tectonics (weak strain rate) and external sediment supply on the dynamic of these intracratonic basins. Where, sediment flux controls the speed and the duration of basin infill until achievement of the isostatic equilibrium. The thermal anomaly and the tectonics compel the tectono-stratigraphic complexification such as the arches framework (intra-arches, boundary secondary arches…) and the stratigraphy architecture (wedges, diachronic unconformities) (…).

Le domaine valaisan dessine la suture majeure qui marque la limite entre les zones internes et externes des Alpes occidentales et dont l'interprétation géodynamique était controversée. Cette suture est constituée d'une série de flysch (le flysch valaisan) et d'un complexe magmatique et sédimentaire (le complexe du Versoyen). Suivant les auteurs, les roches magmatiques d'affinité tholéïtique pourraient représenter: 1) une klippe d'origine piémontaise (suture d'hyper-collision), 2) une écaille ophiolitique située au front d'un prisme d'accrétion (suture océanique), 3) un complexe magmatique lié à un amincissement crustal (inversion structurale). Le but de ce travail était de trouver des arguments qui permettaient de résoudre cette controverse. Ainsi les résultats de ce travail montrent que : - Dans la région du col du Petit-Saint-Bernard (frontière franco-italienne), certaines tholéïtes sont recoupées par des filons leucocrates qui correspondent à des liquides différenciés, cogénétiques du magmatisme. Les datations UlPb sur les zircons contenus dans l'un de ces filons indiquent un âge Carbonifère supérieur- Permien inférieur pour le magmatisme du Versoyen. - Ce magmatisme présente des caractères géochimiques et isotopiques, intermédiaires entre ceux des N-MORB et des T-MORB, dans les régions du col du Petit-Saint-Bernard et de Visp (Suisse). Ces tholéïtes dériveraient de la fusion partielle d'un manteau appauvri (de type N-MORB), avec probablement la participation d'une source enrichie (de type OIB), ce qui est en accord avec une mise en place dans un domaine en cours d'océanisation. - Le complexe du Versoyen est affecté par un métamorphisme polyphasé éclogitique, puis schiste bleu et enfin schiste vert. La paragénèse éclogitique correspond à des conditions de Haute-Pression et Basse-Température (P > 13Kb, 425 < T < 475°C) qui traduisent un enfouissement à grande profondeur, lié à une subduction. Les datations Ar/Ar réalisées sur les phengites donnent des âges de refroidissement proches de 33 Ma et permettent d'établir le chemin P-T-t de ce complexe au cours de l'exhumation des éclogites. - Le complexe du Versoyen est affecté par une déformation syn-schiste vert qui correspond à un jeu normal vers le SE. La comparaison entre les données de terrain et les données sismiques ECORS suggère que les failles normales se prolongent en profondeur et s'applatissent vers 10-15 km. Cette déformation postérieure à 38 Ma explique en partie l'exhumation des éclogites. Ce jeu normal est contemporain de chevauchements dans la zone externe et pourrait accommoder un réamincissement crustal au cours de la collision alpine. Ces données montrent que l'individualisation du substratum du domaine valaisan est liée au cycle hercynien et que ses relations complexes avec le flysch sus-jacent sont liées à une inversion structurale anté-flysch, alors que son évolution tectono-métamorphique est controlée par une extension succèdant aux phases compressives.

This Thesis presents the results of a study of the "High Zagros", the most internal part of the Zagros-Fold-Thrust-Belt (ZFTB). On map view, the High Zagros is exposed in two separated domains (Western and Eastern High Zagros respectively) and partly hidden as an under-plated region beneath the Sanandaj-Sirjan Domain. The High Zagros is the only place in the ZFTB where the Paleozoic rocks are widely exposed.A primary objective was to reevaluate the structural style and kinematic evolution of the High Zagros. It is shown that the most significant geological elements within this area are large scale faulted detachment folds, associated with a complex system of thrust faults segmented by strike-slip faults. This work suggests that the existence of active Ordovician and/or Silurian décollements led to the development of duplex structures which are confined in the core of the anticlines. A two-step kinematic scenario, similar to the one already proposed elsewhere in the belt, is proposed for the High Zagros. Firstly, a thin-skinned phase led to establish detachment folding over the basal Hormuz salt. Then, a thick-skinned phase resulted in the basement thrusting and allowed the exhumation of Lower Paleozoic succession.After this presentation of the tectonic context of the High Zagros, the thesis focuses on the tectonic significance of the pre-Permian unconformity, which was known through a major hiatus between Cambro-Ordovicien to Early Permian and between Devonian to Permian rocks in the western and eastern High Zagros respectively. It is shown that (1) the High Zagros presents below the unconformity a large "Arch-and-Basin" geometry; and that (2) only extensional features such as normal faults and rotated blocks, without evidence of contractional deformation, can be observed below the unconformity. Thermal uplift of possible Late Devonian is proposed as a probable mechanism explaining both the uplift and the diffuse extensional deformation. This proposal strongly modifies the "classical" interpretation of the pre-Permian hiatus as a far effect of the Variscan Orogeny.Thermal modeling based on maturity data from potential source rocks cropping out in the High Zagros has been performed. The most probable modeled scenario suggests an important heat flow during the Devonian and the erosion of ~3900m of the sedimentary pile prior to the deposition of Permian sequence. This outcome reinforces our interpretation of a thermal uplift scenario responsible for pre-Permian vertical movements. On the other hand, a set of new (U-Th)/He ages obtained from the Lower Paleozoic, Devonian and early Permian clastic rocks show a partial reset of zircon grains. These two results are fairly consistent with the published data describing a major thermo-tectonic event during Late Devonian-Early Carboniferous in the Levant Arch (Israel, Jordan) and suggest a common mechanism at the scale of the Arabian Plate.

Regional fracture patterns were determined from 2,419 fracture measurements collected from 11 quarries in a portion of East-Central Indiana. When the entire study area was considered, three orthogonal fracture systems were evident. The master system appeared at every station andhad fracture sets striking from N17W to N6W and N85E to N68E. The secondary systems were more inconsistent in respect to their appearance from quarry to quarry and had fracture sets striking approximately N45W and N48E, and N75W and N20E, respectively. The fractures were vertical or nearly so and were interpreted as being extensional in nature.The regional fracture patterns became apparent after data from several quarry walls, including fractures of varying persistence and intensity, were considered in combined plots for each data collection site.Suggested major mechanisms of fracturing include: 1) warping of the Cincinnati Arch, 2) the propagation of pre-existing joints in the basement rock upward into younger material, 3) the release of older residual stresses by the production of positive structural relief with associated erosional unloading, and 4) recent compressive stresses caused by the same mechanism that drives sea-floor spreading.Ball State UniversityMuncie, IN 47306

This is an analysis of fractures occurring within the Paloezoic sedimentary rocks in a portion of southeastern Indiana. Fifteen hundred seventy-two fractures were used in analysis of distribution, orientation, pervasiveness, persistence, and intensity. The data collected is representative of eight counties and seventeen different collection sites.All fracture data were given an associated numerical value identifying each variable used for analysis and recorded into computer data files. A computer program was used for statistical analysis and construction of equal area nets which graphically displayed the distribution of variables. The compilation of the fracture data allowed for close interpretative analyses of variables and correlation of the orientation and distribution of the fractures within the study area.This study revealed that two orthogonal fracture systems exist in southeastern Indiana. The fracture set containing the largest percentage of those measured is oriented N11W with its compliment oriented N73W. The orientation of the second largest fracture set is N8E with its compliment oriented N82°W.The effects of the tectonic history as well as contemporary stress on the area are discussed relative to their effects on the overall distribution of fracture sets.Evidence is presented to substantiate a reactivation of the Cincinnati Arch as indicated in the Devonian-Mississippian lithologic units from data collected in the southeastern portion of the study area. Fracture data correlating to these units displays a rotation of the major fracture set maxima 90w. This data is supported by radiometric dates from the Belfast member of the Brassfield Limestone in which Laskouski, et.al., correlated a reactivation of the arch.Also within this study are lithologic descriptions of all the Paleozoic formations used for data collection. These descriptions were developed over a three year period from extensive field observation.A map of the study area is presented displaying the distribution and orientation of the fractures recorded at each data collection site. / Department of Geology