No description available.

This study is based on a regional grid of seismic data acquired by Merlin Geophysical. The main emphasis of this thesis was on the detailed structural mapping of the Danish Central Graben, since this area has the highest density of well and seismic data. The principal objective of the study was to explain why the North Sea Rift changes strike in the Danish Sector, from the N-S trending Dutch Central Graben, to the NW-SE trending U.K/Norwegian Central Graben. The Danish Central Graben opened initially in the Late Carboniferous, as part of a regional dextral transtensile deformation that affected much of Europe. The initial extensional structures developed by reactivation of a pre-existing basement fabric. The NNW trending Coffee Soil Fault bounding the rift, is interpreted as a planar structure transecting the entire crust, and is thought to have developed by extensional reactivation of an east-verging Caledonian thrust. Basement shear zones identified on the rift shoulders on the Ringkobing-Fyn High are interpreted as the along-strike continuation of the Caledonides of Southern Norway, offset to the east by syn-orogenic transform motion along fracture zone elements of the Tornquist Zone. The WNW trending fault zones that dominate the structural grain in the Danish Central Graben are shown to be closely related to WNW trending fracture zones on the Ringkobing-Fyn High, which are regarded as splay shears of the Tornquist Zone. The WNW trending transverse fault zones segment the Danish Central Graben. The segmentation exerted a fundamental influence on the structural and stratigraphic development of the rift, in that individual segments were free to subside at different rates, in different styles, at different times. Two main phases of rifting are recognised, Permo-Triassic, and Middle and Upper Jurassic. These two phases have contrasting patterns of subsidence, and contrasting structural expression, particularly as regards the extent of the involvement of the transverse fault zones. The Permo-Triassic phase is characterised by parallelism of stratal configurations, and horizontal subsidence of the graben floor, whereas the Jurassic phase is characterised by strongly divergent configurations and asymmetric, rotational subsidence directed towards and controlled by the Coffee Soil Fault. Active rifting ceased at the end of the Jurassic, and Lower Cretaceous sediments are found to onlap extant fault scarps in a passive infill of the rift basin. The major bounding structures of the rift change strike abruptly in several incremental steps across the points of intersection with the transverse segment boundaries. The re-orientation of the rift is therefore explained as a consequence of the underlying presence of the earlier transform dominated basement fabric. A model for the formation of the North Sea Rift is proposed, which draws heavily on observations of the fracture patterns in continental rifts such as the Oslo Rift and the Rio Grande Rift, and is a development of the Megashear-Rhombochasm concept of S.W.Carey.

The evolution of the Western Mediterranean takes place between the converging African and Eurasian plates, therefore the motion between them cannot be determined directly. The motion between them is the finite difference between the independent seafloor spreading systems in the Central and North Atlantic Oceans. Primary magnetic anomaly data from the North and Central Atlantic was reexamined. All Late Cretaceous and Cenozoic anomalies (Anomaly 34 - Anomaly 2) were remapped. Fracture zones were remapped using bathymetic maps, topographic profiles from ship tracks, SEASAT altimetry (geoid deflection) data, and SEASAT derived gravity images. Fracture zones were used as the primary control for the determination of rotation parameters. Finite difference solutions were computed between matched anomalies using the newly determined rotation parameters for each ocean with parameters of Pindell et al. (1988) used for Early Cretaceous and Jurassic spreading in the Central Atlantic. The product was a kinematic model describing the motion of Africa with respect to Europe from 175 Ma to the present. The motion of Africa was seen to be much smoother and not marked by the sharp, unusual direction changes that characterized previous work. On a gross scale the motion could be divided into phases that correlated with major geological events, but on a smaller scale it was clear that relative motion between Africa and Eurasia did little more than set very broad boundary conditions within which a variety of geological events occurred. Africa's motion is divisible into several distince phases. From the Jurassic start of seafloor spreading until the Late Cretaceous Quiet Zone (KQZ) the motion between the plates was sinistral strike-slip. During the KQZ, but prior to Anomaly 34 (84 Ma, Campanian) Africa's motion changed to northeasterly directed compression. Shortly after Anomaly 30 (68 Ma), close to the Cretaceous-Tertiary boundary, until after Anomaly 24 (55 Ma, mid-Eocene) there was a period of little relative motion between the two plates. After Anomaly 24 strong relative motion recommenced between Africa and Eurasia. Africa continued on a trajectory between N and NNE until the Middle Miocene (Anomalies 5A - 5D) when motion became directed to the NW. Within the relative motion framework a model for the geological evolution of the Western Mediterranean Sea is evolved. Although the Western Mediterranean is a Neogene phenomena the history of the region prior to this time is also examined, albeit in less detail. Among the major problems for which solutions are suggested is the convergence direction of Iberia with respect to Europe and the reason extension initiated in the Tyrrhenian Sea.

A detailed study of a portion of the Valley and Ridge Province in eastern Tennessee was conducted to decipher its geologic nature and relation to surroundings and the Blountian phase of deformation. This area known as Crums Knob and is located nine miles south of Greenville, TN. Locally, the area owes its anomalous topography to inherited geologic structures. Crums Knob is bound in the north and south by tear faults and the main topographic feature represents a series of SW plunging folds. Deformation in three phases: folding, thrust faulting, and refolding. Stratigraphic relations show facies changes which affect the mechanical behavior of the Tellico Sandstone. When the sandstone is Underlain by the Lower Shale Unit or Lenoir Limestone, minor folds and thrust faulting occur within the Tellico Sandstone. But when it is underlain by the Knox Group, it deforms in the same way as the Knox Group forming broader folds.In a regional context, the following may be concluded: 1) The Blountian phase occurred from Upper Cambrian to the Middle Ordovician times, resulting in uplift of the terrain to the southeast. 2) The Middle Ordovician basin was developed as an isostatic response to the uplift. 3) Isostatic movements took place along fractures that were oriented W-NW and E-NE. As a result eroded limestone clasts were deposited along these fractures preserving the fractures' initial orientation. 4) During the Alleghanian Orogeny (?), there was a reactivation of these fractures moving blocks either: A) upward to form ramps as a response to the back load of advancing thrust sheets, or B) downward as a response to the direct load of the transported sheets. 5) Either of these movements controlled the pattern of tear faults in the Middle Ordovician basin in terms of their distribution density and length. 6) The Blountian Phase is diachronous, and its effects in the southeast were earlier than those in the northern regions.This area has not been mapped in detail and it merits a more intensive study regarding its petrographic and stratigraphic nature. / Department of Geology

The Southern Uplands of Scotland is interpreted as a Lower Palaeozoic accretionary complex which formed on the northern margin of the Iapetus Ocean. Seven conglomerates which contain detritus derived from the north-west, from sources on the Laurentian continental margin, were studied. Granite clasts in five of the conglomerates have distinct petrographic and geochemical characteristics which indicate that separate source areas supplied detritus to the Southern Uplands at different times. The Llandeilo Corsewall Point and Caradoc Glen Afton conglomerates, which occur in Tracts 1 and 2 of the Northern Belt, contain granite clasts that yield similar Rb-Sr whole-rock isochron ages (c. 1,200 Ma, 600-660 Ma and c. 475 Ma) and similar Sm-Nd model ages. This suggests that the clasts in the two conglomerates were derived from related sources. Some of the granite clasts in the early Ashgill Shinnel Formation conglomerate, which occurs in Tract 3 of the Northern Belt, resemble those in the Corsewall Point conglomerate, but most are petrographically and geochemically distinct, and yield younger Sm-Nd model ages. The lower Llandovery Pinstane Hill conglomerate occurs in Tract 4 of the Central Belt, and contains granitic detritus which yields a Rb-Sr whole-rock isochron age of 458 ± 26 Ma and has similar characteristics to the clasts in the Shinnel Formation conglomerate. The granite clasts in the Corsewall Point and Glen Afton conglomerates are of a different age to the granite intrusions of northern Scotland, and are unlikely to have been derived from this region. Conglomerates in the Midland Valley contain granite clasts with different petrographic and isotopic characteristics to those supplied to the Southern Uplands during the Llandeilo and Caradoc. However, north-west Newfoundland has a similar igneous history to that recorded by the Southern Uplands clasts, which could be derived from this region. The clasts supplied to the Shinnel Formation and Pinstane Hill conglomerates during the Ashgill and Llandovery have more in common with the granitic detritus in the Midland Valley. Thus, the Southern Uplands form a distinct Caledonian terrane which was south-east of Newfoundland in the Llandeilo, and was affected by sinistral strike-slip displacements during and after accretion.

A wide variety of tectonic settings are juxtaposed at the southern margins of the Iberian Peninsula. The regional geology comprises an Atlantic passive margin in western Iberia, the convergent eastern part of the Azores-Gibraltar plate boundary zone between Africa and Eurasia, and an orogenic arc (the Betic-Rif mountains) surrounding an extensional basin (the Alboran Sea). The complex tectonic history of the southern Iberian margins is recorded in its sediments and structure, and these were investigated in this study using multichannel seismic reflection techniques in conjunction with other marine geophysical data. Multichannel seismic reflection and well data from the Gulf of Cadiz have shown that the earliest sediments are Triassic evaporites, followed by Jurassic carbonates, which form rotated fault blocks in the Gulf of Cadiz. Backstripping and thermal modelling has indicated that a rifting event took place in the Late Jurassic, which stretched the crust by ~20-50%. Gravity modelling, and mapping of stretching factors, has suggested that two zones of thinning underlie the Gulf of Cadiz, which are related to the original rifting event. Backstripped subsidence curves indicate passive margin thermal subsidence until the Miocene, when westward-directed thrusting and loading from the Betic-Rif mountain belt is reflected in a typical foreland basin tectonic subsidence signature of accelerated subsidence with time. A giant, chaotic body of allochthonous sediment was emplaced into the central Gulf of Cadiz as westward migration of the Gibraltar Arc led to oversteepening of the margin west of the Gibraltar Straits, while the Alboran Sea was simultaneously undergoing active extension. These allochthonous deposits are composed mainly of Triassic evaporites and Palaeogene shales. In the Gulf of Cadiz and Seine Abyssal Plains this body has the appearance of an accretionary wedge, but a 300 km long northern lobe of the body extends into the Horseshoe Abyssal Plain. This lobe is interpreted as being a cumulative mass wasting feature, formed by the gravity-driven downslope transport of large allochthonous masses as debris flows and slides and slumps, encouraged by a regional gradient and a pre-existing trough in the Horseshoe Abyssal Plain. The total volume of sediments involved was of the order of 72 000 km 3 , and the time of emplacement has been estimated as being Tortonian on the basis of seismic correlation with core data at DSDP site 135. This chaotic unit has formed a series of longitudinal diapiric ridges in the northern Gulf of Cadiz, which have been interpreted to act as a transport system for gas generated in the lower slope area to migrate to the upper slope where gas-related features are seen. Gas hydrates are present beneath the lower continental slope, as inferred from a bottom-simulating reflection on seismic reflection profiles.

No description available.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 69-78). Also available on the World Wide Web.

Thesis (M.S.)--Ohio University, August, 2006. / Title from PDF t.p. Includes bibliographical references.