Alexander (Sandy) Grist

Subsidence and sedimentation in offshore basins at rifted continental margins are intimately related to the uplift and exhumation of the sediment source areas. An understanding of the regional and temporal distribution of onshore denudation is critical in the evaluation of models of rifted margin development. Offshore strata are often inaccessible and can only be studied in samples obtained from wells, and the loss of the onshore geological record through erosion requires that estimates of regional denudation of near-surface rocks in these environments be obtained by other means. Through the application of low-temperature thermochronometry we can elucidate the time-temperature histories recorded in the extant strata, and provide quantitative constraints on the development of these coupled margin - source region systems. In this thesis apatite fission track (FT) and (U-Th)/He thermochronology and vitrinite reflectance are used to obtain estimates of cooling and inferred denudation for 3 onshore areas; 1) the Triassic - Early Jurassic Fundy Basin, a failed rift that was subsequently inverted and exhumed as part of the onshore of the southern Canadian Atlantic margin; 2) the Sverdrup Basin, a Late Paleozoic - Mesozoic intracratonic basin and failed rift in the Canadian Arctic Archipelago that developed following the Ellesmerian Orogeny, and was subsequently inverted during the Paleogene Eurekan Orogeny; 3) the Nares Strait - Kane Basin - Smith Sound region of eastern Ellesmere Island and western Greenland, which was exhumed during Late Paleozoic and Mesozoic time as a sediment source region for the Sverdrup Basin, and was also affected by the Eurekan Orogeny. Geologically constrained FT inverse and (U-Th)/He forward thermal models for the southern Canadian Atlantic onshore margin demonstrate that most rift-related exhumation likely occurred during the rift-drift transition in Early Jurassic time. These models also suggest that significant (ca. 25 oC) post-Paleocene cooling has occurred that can be explained by a combination of limited exhumational cooling related to decreased eustatic sea level, and the propagation to depth of decreased paleo-mean annual surface temperatures. FT modelling of the Sverdrup Basin demonstrates that basin inversion was initiated during latest Cretaceous - Early Paleocene time. Cooling is greatest in the hanging walls of thrust faults, and significant thermal history discontinuities occur across faults, suggesting these structures were active during the Eurekan Orogeny, and are therefore likely to be poor traps for hydrocarbons generated during Mesozoic burial heating. Thermal modelling of the Nares Strait - Kane Basin - Smith Sound region are consistent with at least two phases of denudational exhumation that are likely related to Sverdrup Basin subsidence, one during early rifting and widespread clastic sedimentation in Late Paleozoic time, and one during a period of increased subsidence rates and high sediment supply during Triassic time. FT and (U-Th)/He data for the Nares Strait region reflect relative plate movements between Ellesmere Island and Greenland during the Eurekan Orogeny, including mafic volcanism and exhumation cooling following flank uplift, or transpression, and minor thrust exhumation. The data also suggest only minor thermal effects from this tectonism along the strait, indicating that it may have been partitioned into a broad belt across Ellesmere Island.

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Pages: 436
Supervisor: Marcos Zentilli