Search

The Thluicho Lake Group is a middle-Paleoproterozoic succession of greenschist-facies continental elastic rocks that was deposited on variably mylonitized crystalline basement rocks in the southwestern Rae Province of the Canadian Shield, near the end of 2.02-1.92-Ga Thelon-Taltson orogenesis. Two informal formations are proposed for this fining- upward succession. The Powder Lake formation comprises predominantly coarse-grained rocks including conglomerate (Gulo Lake member), pebbly sandstone (Camel Lake member), and sandstone (Wellington Lake member), whereas the overlying Camsell Portage formation consists of sandstone to siltstone (Falls member), rhythmic sandstone and argillite (Waterloo Lake member), and argillite (Slate Island member). The two informal formations represent two principal facies associations: a lower conglomerate-sandstone facies association representing an alluvial fan to distal braided plain that underwent episodic flash flooding events and an upper sandstone siltstone-mudstone facies association representing a lacustrine environment. The Thluicho Lake basins are interpreted to have been symmetrical and elongate, and are broadly parallel to older, west- to northwest-trending basement structures. Transverse alluvial fans and braided rivers and/or fan deltas developed on elevated basin margins and drained into a large perennial lake. Similarities in lithology, age, and provenance suggest that the Thluicho Lake Group may correlate with the more extensive Nonacho Group to the north. Both groups represent remnants of a strike-slip and intermontane basin system that formed in the hinterland of the Taltson orogen at ca. 1.92 Ga. [ABSTRACT FROM AUTHOR]

Recent studies generally have inferred that the onset of convergence in the Delamerian Orogeny in southeastern Australia commenced at the end of the Early Cambrian (∼514 Ma) after the deposition of Kanmantoo Group sediments. Correlative sequences in Antarctica provide evidence that convergent deformation (Ross Orogeny) commenced between 580 and 540 Ma, leading to the interpretation that the locus of deformation migrated or jumped northward along the paleo-Pacific margin of Gondwana. However, the absence of upper Neoproterozoic sequences in the southern Adelaide Rift Complex requires either significant pre-Kanmantoo erosion (for which there is no evidence) or a depositional hiatus due to uplift. New Rb-Sr data from solution cleavage in Brachina Formation sedimentary rocks at Hallett Cove, South Australia, date deformation at 554 ±10 Ma, while 40Ar/39Ar data on white mica in the center of the cleavage yield a relatively flat plateau-like segment with an age of 533 ±15 Ma. Additional evidence for a pre- 514-Ma onset of deformation is provided by a 525 ± 7-Ma 40Ar/39Ar age for biotite that developed in a mylonite within a Mesoproterozoic granitic gneiss in the Myponga basement inlier to the south of Hallett Cove. Thus, the data imply that convergence commenced more or less synchronously with contraction during the Ross Orogeny in Antarctica. Deposition of the Cambrian Kanmantoo Group therefore occurred in a synorogenic setting analogous to deposition of the upper Byrd Group in Antarctica. [ABSTRACT FROM AUTHOR]

Temperature-dependent clay mineral assemblages and vitrinite reflectance data have been used to investigate levels of diagenesis from the Apenninic-Maghrebian fold-and-thrust belt in eastern Sicily at the footwall of the Peloritani-Calabride Arc. Data are from units sampled along a regional transect between the Nebrodi Mountains to the north and Mount Judica to the south. These units developed in very different tectonic settings from those of oceanic to passive continental margin domains deformed during the Cenozoic mountain building and related active margin deposits. The integration of organic and inorganic thermal indicators allowed us to distinguish among different tectonic settings, with thermal maturity generally decreasing from hinterland to foreland as a result of progressively less severe thermal evolution and/or tectonic loading during the mountain building. Specifically, the highest vitrinite reflectance (VRo%) values (ca. 0.60%-0.75%) and percentages of illite layers in illite-smectite (I-S; 60%-80%) are found in trench-involved and accreted passive margin units. Lower VRo% values (0.20%-0.47%) and percentages of illite layers in IS (30%-60%) are found in thrust-top and foredeep basin deposits and far-traveled Sicilide units that have escaped involvement in trench evolution. Furthermore, either sedimentary or long-lived tectonic burial (at least more than 5 m.yr.) seem to have affected levels of diagenesis of the studied successions. The correlation between organic and inorganic thermal indicators is satisfactory for most of the samples derived from hemipelagic and siliciclastic deposits, whereas it is poor for some proximal siliciclastics. A tentative calculation of paleotemperatures is also proposed for the studied tectonostratigraphic units. [ABSTRACT FROM AUTHOR]

The Sverdrup Basin of the Canadian Arctic Islands contains a sedimentary record, with only short breaks, from Early Carboniferous to Late Cretaceous time and can be used to document the nature of sediments delivered from northern Canada and Greenland. Sm-Nd isotopic analysis of 72 sedimentary rock samples from the Sverdrup Basin, coupled with trace element characterization, shows that for most of Carboniferous to Late Cretaceous time, the sediment supply in the northern part of North America was dominated by a single broad provenance; 56 of the 72 samples lie squarely within the Nd isotopic evolution of a clastic sedimentary cover delivered to the region following 450--350 Ma Caledonian and Franklinian mountain building in Greenland and the Canadian Arctic Islands. Cratonic Shield sources in Greenland and Canada are hardly evident in the record, and significant contributions to the sediment budget from any source other than the post-mid-Paleozoic orogenic cover occurred only during four relatively short periods. First, during Carboniferous time, pre--Late Ordovician rocks of the Franklinian orogen contributed to alluvial clastic rocks in small rift basins in northern Ellesmere Island. Second, during Early Cretaceous time, Shield basement contributed to more widespread deltaic deposits in central and southern Ellesmere Island. Third, minor volcanic contributions to much of the basin occurred during Late Triassic-- materials from Caledonian and Franklinian mountains dominated the provenance of the continental and continent-margin sedimentary system for at least 370 m.yr., a period of time extending far beyond the existence of the mountains themselves. This dominance was achieved by recycling of widespread Middle and Upper Devonian strata into Mesozoic units in the Canadian Arctic and Cordillera. We assess the extent to which the results call for cover of the Greenland-Canad. [ABSTRACT FROM AUTHOR]