GEOPHYSICAL MODELING STUDIES. CHAPTER I: OCEANIC RIDGE VOLUMES AND SEA LEVEL CHANGE. CHAPTER II: SUBSIDENCE ANALYSES OF ANCIENT MIOGEOCLINE, CANADIAN ROCKY MOUNTAINS. CHAPTER III: PART I: GEOPHYSICAL MODELING OF THE THERMAL HISTORY OF FORELAND BASINS. PART II: THERMAL MODELING OF FORELAND BASINS (OCEAN FLOOR AGES, FLEXURAL RIGIDITY, CORDILLERAN MIOGEOCLINE).

摘要

Eustatic sea level changes are predicted based on changes in calculated ocean basin volumes. The effect of ridge volume change over the last 80 m.y. has been to cause a long-term sea level fall. That fall was primarily a result of decreasing spreading rates from the Late Cretaceous to the Recent. Uncertainties introduced into the calculations result in a large range of sea level curves with a spread of 320 m for the sea level height calculated for 80 m.y.;A geophysical model is developed which considers the thermal effects of rapid subsidence in foreland basin settings. The model is applied to a well in the Alberta basin. The absolute magnitude of the subsidence if found to be the most important factor in dictating the thermal history of the foreland basin and response of the lithosphere to that history. Episodes of rapid subsidence in foreland basins cause significant negative thermal anomalies to form within the sediments and lithosphere. The anomalies affect the timing and degree of maturation of hydrocarbons. The anomalies also have a significant effect on the rigidity of the lithosphere, causing it to relax with time. A buoyancy force results from the heating of the lithosphere as the anomalies decay, forming a significant portion of the force which must be overcome in causing subsidence of the foreland basin. This buoyancy force also results in uplift subsequent to loading. The Alberta basin is found to be locally compensated at present.;The geophysical techniques developed recently for studying the tectonic subsidence history of modern continental margins have been modified and applied to the Cambrian through Ordovician strata in the southern Canadian Rocky Mountains. The form of the tectonic subsidence is found to be that of a thermally cooling plate, consistent with a passive margin setting. The timing of initiation of thermal cooling could not have been earlier than 600 m.y. or later than 550 m.y. This is about 200 m.y. later than had been predicted using more traditional methods. The uncertainty in the calculation of tectonic subsidence is on the order of 500 to 700 m.