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The 2 to 5 km thick, sandstone‐dominated (>90%) Jura Quartzite is an extreme example of a mature Neoproterozoic sandstone, previously interpreted as a tide‐influenced shelf deposit and herein re‐interpreted within a fluvio‐tidal deltaic depositional model. Three issues are addressed: (i) evidence for the re‐interpretation from tidal shelf to tidal delta; (ii) reasons for vertical facies uniformity; and (iii) sand supply mechanisms to form thick tidal‐shelf sandstones. The predominant facies (compound cross‐bedded, coarse‐grained sandstones) represents the lower parts of metres to tens of metres high, transverse fluvio‐tidal bedforms with superimposed smaller bedforms. Ubiquitous erosional surfaces, some with granule–pebble lags, record erosion of the upper parts of those bedforms. There was selective preservation of the higher energy, topographically‐lower, parts of channel‐bar systems. Strongly asymmetrical, bimodal, palaeocurrents are interpreted as due to associated selective preservation of fluvially‐enhanced ebb tidal currents. Finer‐grained facies are scarce, due largely to suspended sediment bypass. They record deposition in lower‐energy environments, including channel mouth bars, between and down depositional‐dip of higher energy fluvio‐ebb tidal bars. The lack of wave‐formed sedimentary structures and low continuity of mudstone and sandstone interbeds, support deposition in a non‐shelf setting. Hence, a sand‐rich, fluvial–tidal, current‐dominated, largely sub‐tidal, delta setting is proposed. This new interpretation avoids the problem of transporting large amounts of coarse sand to a shelf. Facies uniformity and vertical stacking are likely due to sediment oversupply and bypass rather than balanced sediment supply and subsidence rates. However, facies evidence of relative sea level changes is difficult to recognise, which is attributed to: (i) the areally extensive and polygenetic nature of the preserved facies, and (ii) a large stored sediment buffer that dampened response to relative sea‐level and/or sediment supply changes. Consideration of preservation bias towards high‐energy deposits may be more generally relevant, especially to thick Neoproterozoic and Lower Palaeozoic marine sandstones. [ABSTRACT FROM AUTHOR]

Despite extensive outcrop and previous sedimentologic study, the role of tidal processes along sandy, wave- and river-dominated shorelines of the North American Cretaceous Western Interior Seaway remains uncertain, particularly for the extensive mid-Campanian (ca. 75-77.5 Ma) tidal deposits of Utah and Colorado, USA. Herein, paleotidal modeling, paleogeographic reconstructions, and interpretations of depositional process regimes are combined to evaluate the regional-scale (hundreds to thousands of kilometers) basin physiographic controls on tidal range and currents along these regressive shorelines in the "Utah Bight", southwestern Western Interior Seaway. Paleotidal modeling using a global and astronomically forced tidal model, combined with paleobathymetric sensitivity tests, indicates the location of stratigraphic units preserving pronounced tidal influence only when the seaway had a deep center (~400 m) and southern entrance (>100 m). Maximum tidal velocity vectors under these conditions suggest a dominant southeasterly ebb tide within the Utah Bight, consistent with the location and orientation of paleocurrent measurements in regressive, tideinfluenced deltaic units. The modeled deep paleobathymetry increased tidal inflow into the basin and enhanced local-scale (tens to hundreds of kilometers) resonance effects in the Utah Bight, where an amphidromic cell was located. However, the preservation of bidirectional, mudstone-draped cross-stratification in fine- to medium-grained sandstones requires tides in combination with fluvial currents and/or local tidal amplification below the maximum resolution of model meshes (~10 km). These findings suggest that while regional-scale controls govern tidal potential within basins, localized physiography exerts an important control on the preservation of tidal signatures in the geologic record. [ABSTRACT FROM AUTHOR]