Abstract The period since the 1960s witnessed significant progress in our ability to decipher the clastic rock record from a wide range of sedimentary environments, and spanning many spatio-temporal scales, from millimetric to that of the sedimentary basin, and involving processes acting on timescales of seconds to millions of years. This review assesses advances in four areas of fluvial sedimentology: the nature of alluvial dunes, the role of fine-grained suspended sediment, the linking of facies models and channel planform, and the reconstruction of drainage networks within ancient sedimentary successions. The synthesis reveals that we require new thinking and research to: (1) address the range of stratification produced by dunes and their palaeohydraulic implications; (2) evolve new bedform phase diagrams capable of incorporating the reality that many fluids transport fine-grained sediment, both in flow and within the bed, which may significantly modify the bedform morphology and phase space when compared with existing bedform stability diagrams; (3) develop new alluvial facies models in which planform channel pattern is not the fundamental discriminant; and (4) re-establish consideration of process mechanics as the heart of developing ideas and debates concerning fluvial deposit preservation and alluvial architecture.

Abstract: This study investigates the Neogene strata of the AND-2A core recovered by the ANDRILL–Southern McMurdo Sound Project in the Victoria Land Basin, Antarctica, as an analog for assessing controls on reservoir quality in glacimarine deposits. The succession comprises a series of depositional sequences formed in marine environments within a failed rift under the influence of repeated advances and retreats of glacial ice, with attendant changes in sea level and sediment supply. Stratal cycles (sequences) typically follow a vertical succession from a basal diamictite deposited in ice-proximal settings fining upward into shoreface sandstone, muddy sandstone, and mudrock. The fining-upward sequence then coarsens upward into coastal and nearshore muddy sandstones and sandstones. Changes in paleoclimate mode through the Neogene caused variations in sequence development, including changes in sequence thickness, variety and range of facies, changes in the completeness of sequences, and changes in the proportion and character of diamictites. Results show that reservoir quality in glacimarine sandstone is dramatically affected by the presence of diagenetic carbonate precipitated during burial from connate cryogenic brine. Strong correlations exist between carbonate cement abundance, paleoclimate, and sequence stratigraphic systems tract. Sandstones that formed during the coldest (polar and subpolar) climate regimes have relatively low porosities (<15%) due to occlusion of pore space by carbonate cement. Decreased production and deposition of mud-sized material during the coldest climate conditions produced sequences characterized by higher overall permeability that were prone to infiltration by brine upon burial, leading to cementation. By contrast, the sandstones formed during relatively temperate climate regimes preserve higher porosities (25–45%) and lack significant cementation. Sequence stratigraphic relationships indicate that these porous sandstones are best developed in highstand delta systems that formed during ice minima. Individual sandstone bodies, which extend laterally over several kilometers, are enclosed by muddy lithologies. Porosity in these sandstones was retained as a result of discharge of dilute meltwater during deposition and subsequent isolation of sands between impermeable barriers. Trends identified in this study may prove useful in predicting and locating target reservoirs in other glaciogenic and glacimarine settings worldwide.

Abstract: Criteria for recognizing a high-paleolatitude context for sedimentary successions are not widely established. Herein, we provide a facies analysis of the Permian succession of the high-paleolatitude Denison Trough in the southwestern Bowen Basin of Queensland, eastern Australia, and we use this analysis to highlight criteria that may be used to diagnose a high-paleolatitude context in this and other successions. A unified facies scheme for several formations, combining sedimentological and ichnological criteria, recognizes both deltaic and nondeltaic facies within the succession. Whereas a full array of deltaic facies is evident, ranging from distal prodelta to coastal plain, a more limited array of nondeltaic facies is recognized, ranging from shelfal to lower shoreface. The dominance of deltaic facies in the succession suggests that coastlines were overwhelmingly deltaic in aspect. The absence of middle and upper (nondeltaic) shoreface deposits suggests that shallow-water settings were constantly under physico–chemical stresses associated with deltaic efflux, and/or that such deposits were excised by transgressive ravinement following deposition. Deltas were mostly arcuate in planform, consistent with strong wave influence, although some show a more irregular or lobate plan morphology, suggesting significant fluvial influence. Four intervals within the Permian succession (coded P1 to P4) preserve evidence of formation under the direct or indirect (glaciomarine) influence of glacial ice. Palpable evidence of the high-paleolatitude context of the succession is preserved only in these intervals, most commonly in the form of dropstones, glendonite pseudomorphs after ikaite, gravel-grade clasts with modified shapes, and diamictites. In addition to vertical changes into and out of glacial intervals, paleolatitudinal changes in glacially influenced facies are evident across the 25- to 30-degree meridional transect from the Bowen Basin south to the Tasmanian Basin. Outside of glacial intervals P1 to P4, there are few sedimentological or ichnological indicators of high-paleolatitude deposition. Facies characteristics of deposition under glacial influence are therefore crucial to diagnosing the high-paleolatitudinal context of this and other successions.