ABSTRACT In this paper, we present a case study to demonstrate the potential of photogrammetry in cyclostratigraphic applications. To this end, we considered an ~300-m-thick section exposing the Lower Jurassic Calcare Massiccio Formation in the Marche Apennines of central Italy. The Calcare Massiccio comprises a thick succession of peritidal shallow-water carbonates displaying a prominent sedimentary cyclicity, where supratidal and subtidal facies alternate. The section investigated in this study is exposed on the wall of an active quarry and is almost completely inaccessible because it is vertical and because of safety and liability regulations. This setting prevents the application of standard sampling and facies analysis techniques on the whole series. An accurate three-dimensional model of the quarry wall was therefore produced by processing ~360 digital images through photogrammetry and generating a high-resolution (centimeter-scale) point cloud of the outcrop with red-green-blue (RGB) values associated with each point. An ~150-m-long log representing color variations on a continuous portion of the exposed succession was then extracted from the point cloud by converting the original RGB values to grayscale values. The main facies were directly investigated in an ~10-m-long accessible section that was logged and sampled, and it was established that supratidal facies with planar stromatolites and teepee structures are darker in color, while subtidal facies, made of bioturbated mudstones to floatstones with gastropods and oncoids, display lighter color. This provided ground-truth data with which to interpret the grayscale variations in terms of facies alternations. Time-series analysis was then carried out on the grayscale series, and this revealed prominent cyclicities. Because the biochronostratigraphic framework of the Calcare Massiccio is poor, the potential orbital origin of these frequencies was tested with the average spectral misfit technique. Preliminary results suggest that the observed spectral features are compatible with Milankovitch periods and that astronomical forcing might have been a major driver in the deposition of the Calcare Massiccio Formation. Furthermore, they testify to the great potential of photogrammetry in cyclostratigraphic applications, especially when large-scale, inaccessible outcrops have to be investigated.

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.