Abstract Analyses of deltaic facies successions highlight recurring ichnological patterns that reflect a variety of physicochemical stresses imposed upon infaunal organisms by the interaction of various delta-front processes. Analysis of numerous ancient deltaic deposits in Canada, the United States, Australia, and offshore Norway persistently show reductions in bioturbation intensity and impoverishment in ichnological diversity, compared to those of nondeltaic shorelines. Some facies locally demonstrate sporadic colonization and recolonization of substrates left denuded by episodic depositional conditions. Deltaic ichnological suites also locally display size reductions of ichnogenera and a paucity of suspension-feeding ethologies. Resulting trace-fossil suites are overwhelmingly dominated by deposit-feeding behaviors, even in sandy facies. Such ichnological characteristics largely reflect increased sedimentation rates and heightened fluvial discharge, which serve to impede infaunal colonization. River-derived stresses are profound: salinity changes, hypopycnal-flow-induced water turbidity, distributary flood discharges with accompanying phytodetrital (comminuted plant debris) pulses, hyperpycnal-flow-induced sediment gravity flows, and fluid-mud deposition all conspire to produce the overall depauperate nature of the ichnological assemblage. Freshet-discharge events during river floods, accompanied by hyperpycnal conditions, may lead to the episodic introduction of reduced-salinity waters immediately above the sediment-water interface in delta-front and prodelta depositional settings. Such conditions may facilitate development of syneresis cracks and promote reductions in infaunal populations. Wave energy generally buffers fluvial effects, by dispersing suspended sediment offshore and encouraging the thorough mixing of waters of contrasting salinity. High mud concentrations near the delta front damp wave energy, however, limiting its effectiveness in remediating the benthic ecosystem, particularly immediately following distributary flood discharges and storm events. In wave-dominated settings, strong alongshore drift also operates to extend river-derived stresses considerable distances downdrift from distributary mouths. Where asymmetric deltas are formed, markedly different ichnological characteristics are expressed on either side of distributary-channel mouths. Updrift settings typically retain classic shoreface assemblages, whereas downdrift environments commonly acquire markedly stressed suites. Storm energy may be effective in dispersing mud and mixing waters, but it also results in erosion and episodic sediment deposition. Concomitant precipitation induces river floods, returning river-derived stresses to the delta front. Tidal energy and its effects on the infaunal communities of deltas are poorly documented. Tidal flux may trap mud plumes against the delta front, elevating water turbidity. Pronounced mud flocculation coupled with increased settling velocity associated with tidal mixing also leads to rapid deposition of thick fluid muds, particularly in low-lying areas, hampering or precluding colonization. Tidal energy also leads to marked changes in energy and salinity near the sediment-water interface at several time scales. Deltaic ichnological suites are characterized by structures of opportunistic trophic generalists, though mainly those of facies-crossing deposit feeders. High water turbidity, particularly near the sea floor, precludes most suspension-feeding behavior, and suppresses the development of the Skolithos ichnofacies, even in many proximal delta-front deposits. Ichnological characteristics record the dynamic interplay and relative importance of these different processes, both temporally and spatially, on delta systems.

Abstract The depositional environments existing at the end of the Cretaceous Period continued into the Paleocene Epoch as the Laramide Orogeny continued to affect the western margin of the basin. Thick sequences of sediments derived from the Cordilleran Orogen were deposited in the Beaufort Sea in the north, while continental Paleocene beds were widely distributed in the south, spreading eastward from the rising Rocky Mountains across the Interior Platform. The thickest Tertiary sediments in the southern part of Western Canada Basin are preserved along the eastern side of the Rocky Mountain Foothills and within the adjacent Alberta Syncline (Fig. 4J.1). These strata originally extended much more widely across the Interior Plains, but occur now only as erosional remnants, the largest being the Cypress Hills of southern Alberta and Saskatchewan (Fig. 4J.2) and their eastern extension along the Saskatchewan-United States border from Wood Mountain to Turtle Mountain in Manitoba. Tertiary sediments of the eastern Canadian Cordillera and Interior Plains are almost wholly continental, contrasting with the thick marine and nonmarine section encountered in the region of Mackenzie Delta and Beaufort Sea. Tertiary sediments are extensively developed in Mackenzie Delta, Arctic Coastal Plain, and on the Arctic Continental Shelf. Limited exposures are found in the Caribou Hills on the eastern side of Mackenzie Delta (Fig. 4J.3), along the western margin of the delta, in the Richardson Mountains, and in a small area near Babbage River on Yukon Coastal Plain. Other occurrences are found in Bonnet Plume Basin, Brackett Basin near Norman Wells, and

Abstract Triassic rocks of the Interior Platform and eastern Cordillera of Canada have long been recognized as an interesting and variable sequence of marine strata occupying an elongate belt that extends from the United States border on the south to 69°N latitude and Beaufort Sea on the north (Fig. 4G.1, 4G.2). Triassic deposits are best developed in Western Canada Basin of British Columbia and Alberta, where they occupy three main physiographic provinces, Rocky Mountains on the west, Rocky Mountain Foothills, and Interior Plains to the east. Triassic rocks also occur in Liard River area of southern Yukon Territory and within northern Yukon Territory and District of Mackenzie in the British, Barn, Richardson, Selwyn, Wernecke, and northwestern Ogilvie Mountains. However, because much more published information on Triassic rocks in Western Canada Basin is available, and because of the greater development and economic importance of the system there, most of this report will be directed toward the region south of latitude 60°N. Triassic rocks of the Rocky Mountains, Foothills, and Interior Plains comprise over 1200 m (Fig. 4G.1) of westward-thickening, siliciclastic and carbonate rocks and lesser amounts of evaporites. Contained marine faunas range in age from Griesbachian to Norian. The Triassic rocks of northern Yukon Territory display similar lithofacies but lack evaporites. The strata form a marine wedge deposited along a topographically low, tectonically stable continental shelf and shoreline, a continuation of Permian conditions at the passive western margin of the North American Craton. They form part of what is referred to as