Abstract The Triassic-Jurassic Otuk Formation is a potentially important source rock in allochthonous structural positions in the northern foothills of the Brooks Range in the North Slope of Alaska. This study focuses on three localities of the Upper Triassic (Norian) limestone member, which form a present-day, 110-km-long, east-west transect in the central Brooks Range. All three sections are within the structurally lowest Endicott Mountain allochthon and are interpreted to have been deposited along a marine outer shelf with a ramp geometry. The uppermost limestone member of the Otuk was chosen for this study in order to better understand lateral and vertical variability within carbonate source rocks, to aid prediction of organic richness, and ultimately, to evaluate the potential for these units to act as continuous (or unconventional) reservoirs. At each locality, 1 to 4 m sections of the limestone member were measured and sampled in detail to capture fine-scale features. Hand sample and thin section descriptions reveal four major microfacies in the study area, and one diagenetically recrystallized microfacies. Microfacies 1 and 2 are interpreted to represent redeposition of material by downslope transport, whereas microfacies 3 and 4 have high total organic carbon (TOC) values and are classified as primary depositional organofacies. Microfacies 3 is interpreted to have been deposited under primarily high productivity conditions, with high concentrations of radiolarian tests. Microfacies 4 was deposited under the lowest relative-oxygen conditions, but abundant thin bivalve shells indicate that the sediment-water interface was probably not anoxic. The Otuk Formation is interpreted to have been deposited outboard of a southwest-facing ramp margin, with the location of the three limestone outcrops likely in relatively close proximity during deposition. All three sections have evidence of transported material, implying that the Triassic Alaskan Basin was not a low-energy, deep-water setting, but rather a dynamic system with intermittent, yet significant, downslope flow. Upwelling played an important role in the small-scale vertical variability in microfacies. The zone of upwelling and resultant oxygen-minimum zone may have migrated across the ramp during fourth- or fifth-order sea-level changes.

Abstract The Chenier Plain of southwestern coastal Louisiana is a Holocene strand plain composed of wooded beach ridges (cheniers) and intervening mudflat grassy wetlands. The mudflats form as prograding tidal flats along the open, but low-energy Gulf of Mexico coast; cheniers form from winnowing of sand and shells from the mudflats by waves during transgression. Mudflats are deposited when a Mississippi River delta lobe is nearby to the east, and cheniers are formed when distributaries switch to a more distant location farther east. All of the cheniers have formed within approximately the past 3000 yr or less and are progressively younger toward the present coastline. Spits are attached to the cheniers at estuaries; they grow westward in response to the dominant longshore currents. Currently, mudflats are prograding in Vermillion Parish to the east, while cheniers form in eastern Cameron Parish along with some regressive beach ridge development in western Cameron Parish. This coast is microtidal with low wave energy. A high rate of subsidence as well as sea-level rise characterizes the Chenier Plain, which is subject to increased wave energy and mud transport every year during many cold-front passages and periodic storm surges associated with tropical cyclones of much lower frequency. Major storm surges can inundate the entire Chenier Plain, wreaking havoc on human settlements.