Franklinian Research Articles

Early Paleozoic (Cambrian to Early Devonian) Tectonic Framework, Canadian Cordillera

Uppermost Proterozoic to Lower Devonian rocks in the Cordillera of western Canada accumulated within two ancestral continental margin systems--the Canadian Cordilleran and southwestern Franklinian miogeoclines. These miogeoclines are separated by the Ogilvie Arch. Prominent features of the southwestern Franklinian Miogeocline are the Richardson Trough, a failed arm or aulacogen opening northward into the outer Franklinian Miogeocline, and, west and east of it, the Porcupine and Lac des Bois platforms. The Canadian Cordilleran Miogeocline formed in Late Proterozoic as the result of rifting, and although the newly formed margin was Atlantic-type, it continued to have distinct periods of rifting and extension with volcanism, throughout its history. The Canadian Cordilleran Miogeocline is divided by numerous northeast-trending linear features interpreted to reflect the position of ancestral strike-slip or transfer faults. More than six major block segments are recognized. From south to north they are: the Montana Block, bordered north by the Moyie-Dibble Creek fault systems; the Alberta Block, bordered north by the Hay River and Great Slave Lake fault systems, and divided into the Peace and Southern Prairies sub-blocks along the Rimbey Magnetic-Snowbird Tectonic zones; the Macdonald Block bordered north by the Liard Line; the Blackwater Block, bordered north by the Fort Norman Line; and the Mackenzie Block, bordered north by the southwestern Franklinian Miogeocline. Many facies changes occur across these blocks and their bounding ancestral transfer or strike-slip fault zones, and these or associated faults are likely keys to independent tectonic histories, such as that demonstrated by the Peace River Arch. The most prominent and well known northeast-trending lineament is the Liard Line. Apparent on geological maps of Canada, or the Canadian Cordillera, is a northeastward swing of structural trends north of this feature. The Canadian Cordilleran Miogeocline to the north shows extensive preservation of lower Paleozoic (to Lower Devonian) strata northeastward to the Canadian Shield, whereas to the south the same rocks are generally preserved in only the Cordilleran deformed belt. Although Lower Paleozoic rocks in the south have been substantially cut by younger erosional events, facies and thickness patterns, in fringing Lower Paleozoic strata, indicate that the pattern of erosion and nondeposition is as much due to Lower Paleozoic tectonics and paleogeography as it is due to younger exposure or erosion. This profound change, and the connection to the Franklinian, divides the Canadian Cordilleran Miogeocline into three fundamental parts. The Liard Line is interpreted to have been an ancient transfer fault zone across which there was a reversal in the direction of asymmetry within the master separation fault system that formed the ancestral continental margin in Late Proterozoic time. The wide area north of the Liard line has a large outer miogeoclinal basin (Selwyn Basin), discrete rift systems (Misty Creek Embayment, Mackenzie Trough, Root Basin), a peculiar zone of high crustal attenuation and sediment accumulation (Liard Depression). In addition, it is complicated by several different arches or highs (Mackenzie, Redstone, McConnell, Keele, Bulmer Lake, Niddery, etc.). This northern half of the Canadian Cordilleran Miogeocline has the characteristics of a lower plate margin and is here defined as the Northern Cordilleran Lower Plate Zone, comprising the Blackwater and Mackenzie blocks. The Canadian Cordilleran Miogeocline south of the Liard Line is narrowly preserved in the Cordillera and consists of the White River, Robson and Kechika troughs, and their marginal Macdonald and Bow platforms. The eastern miogeocline is dominated by Lower Paleozoic paleotopographic highs (Montania, West Alberta Ridge, Peace River Arch and Macdonald High). This southern zone has the characteristics of an upper plate margin and is here defined as the Southern Cordilleran Upper Plate Zone, comprising the Montana, Alberta and Macdonald blocks. A previous upper-lower plate model of the Canadian Cordilleran Miogeocline is reviewed and its criteria of width, structural complexity and uplift-subsidence are found to be useful as plate-type indicators. However, the use of gneisses to indicate lower crust, transitional gradients base on isopleths, and Cambrian zero edges are found to be equivocal. The Canadian Cordilleran Miogeocline non passive character is compared to that of Mesozoic-Tertiary continental margins, which are also fundamentally non passive, suggesting that models for plate tectonic drifting phases need to be revised.

Geology of Outstanding Arctic Aerial Photographs 3. Margin of Sverdrup Basin, Lyall River, Devon Island

ABSTRACT An outstanding aerial photograph of northern Grinnell Peninsula, Devon Island is reproduced with a geological interpretation. The area was occupied by three successive depositional basins: the Franklinian Miogeosyncline, the Arctic Platform and the Sverdrup Basin. Remnants of all three are preserved. The exposed section is more than 3300 m (11,000 ft) thick, including 12 Ordovician to Cretaceous map units and six unconformity surfaces. Three major deformations produced two intersecting structural trends. The Cornwallis Fold Belt developed first, with deformation ending in Late Devonian time. Its northerly trend was rejuvenated and influenced all younger structures. The Ellesmerian Orogeny occurred between Late Devonian and mid-Pennsylvanian time and included two phases. The first phase included a southward compression that put an east-west overprinting on northern parts of the Cornwallis Fold Belt. It apparently occurred before deposition of the Mississippian Emma Fiord Formation. This is a shaly and coaly transitional unit representing the earliest stages of the Sverdrup Basin. It apparently filled topographic lows in a fresh-water lake, as subsidence followed the first phase of folding. The second phase of the Ellesmerian Orogeny was contemporaneous with marked regional downwarping that developed the Sverdrup Basin. The phase was marked at Lyall River by folding and faulting near the zone of flexure. The topographic relief created provided coarse conglomerate to the contemporaneous Canyon Fiord Formation. A narrow east-trending, furrow-shaped high within the Sverdrup Basin was emergent through Canyon Fiord deposition. South of this high and largely cut off from the main basin was the narrow Lyall River Embayment of the Sverdrup Basin. The early history of the Sverdrup Basin was influenced greatly by pre-existing structure. The flexure that produced the basin caused an abrupt increase in the northward plunge of the Cornwallis Fold Belt. Numerous normal faults exposed in the area probably were active in the Cretaceous-Tertiary Eurekan Orogeny. They were controlled by older structures.