Giant cross-beds in the Neoproterozoic Port Askaig Formation, Scotland: implications for snowball Earth

Neoproterozoic environmental change recorded in the Port Askaig Formation, Scotland: Climatic vs tectonic controls

“…Individual sandstone units record a number of different processes including deposition under upper flow regime plane bed conditions or from suspension (horizontally laminated facies), and deposition under other unidirectional currents of varying velocities (rippled and cross-bedded facies). Thick successions of giant cross-beds in sandstone are interpreted to record the migration of large tidal bedforms in a marine setting based on their sedimentary characteristics, internal structure and facies associations (see Arnaud, 2004 for a detailed analysis). Disruption of sedimentary structures within deformed sandstone is indicative of liquefaction and loading.…”

“…Crossbedded sandstone units have planar and trough-shaped foresets with simple and compound internal structure. Foresets dip either randomly or in a preferred southerly direction (Spencer, 1971;Eyles, 1988;Arnaud, 2004).…”

History and evolution of the North-Betic Strait (Prebetic Zone, Betic Cordillera): A narrow, early Tortonian, tidal-dominated, Atlantic–Mediterranean marine passage

“…Some authors (Ashley, 1990) would simply call them very large dunes or, more precisely, very large tidal dunes (Berné, 1991). Tidal dunes up to 20 m high (or slightly higher) have been reported from some present-day, tidal-dominated environments (Harvey, 1966;Twichell, 1983), while dunes of tidal origin up to 40 m in height have been described in the geological record (Kamp et al, 1988;Collier and Thompson, 1991;Smith, 1992;Arnaud, 2004). For the formation of tidal dunes, current velocities of up to 1.5 m/s have been reported from some present-day examples (Harris, 1989;Berné, 1991, ZhenXia et al, 1998.…”

Depositional architecture and peculiar sedimentary features of late Cretaceous Utrillas Formation at Tamajón (Guadalajara, Spain)

“…With the exception of deep sea environments, they have been described in tidal environments, where considering their sizes (length and height), the original bedforms have been termed sand-waves, giant dunes or very large tidal dunes (Ashley, 1990;Smith, 1992); with heights up to 40 m high (e.g., Arnaud, 2004;Martín et al, 2009).…”

“…In most estuarine and deltaic settings they commonly have a fining upward trend from bioturbated muddy sands to sandy ripples, and to stacked simple dunes (Olariu et al, 2012); their lower bounding surfaces are planar (at outcrop scale) and mainly horizontal or dipping at a low angles (Arnaud, 2004). In these environments they are not solitary, single sets of cross-beds; they, however, are usually part of composite, compound dunes with reverse crossbedding directions and abundant reactivation surfaces (Arnaud, 2004;Martín et al, 2009;Olariu et al, 2012). The large-scale sets of cross-bedded conglomerates and sandstones also resemble the coarse-grained Gilbert-type deltas or tidal deltas (e.g.…”