Modelling tidal current-induced bed shear stress and palaeocirculation in an epicontinental seaway: the Bohemian Cretaceous Basin, Central Europe

Abstract

Lower to Middle Turonian deposits within the Bohemian Cretaceous Basin (Central Europe) consist of coarse-grained deltaic sandstones passing distally into fine-grained offshore sediments. Dune-scale cross-beds superimposed on delta-front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse-grained sand across the entire depth range of the clinoforms (ca 35 m). Bi-directional, alongshore-oriented, trough cross-set axes, silt drapes and reactivation surfaces indicate tidal activity. However, the Bohemian Cretaceous Basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands. The presence of tidally-influenced deposits in a setting where co-oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic. The Imperial College Ocean Model, a fully hydrodynamic, unstructured mesh finite element model, is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain-size distributions, bedform types and palaeocurrent orientations. The model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present-day North European shelf seas that surround the British Isles. The model predicts a microtidal to mesotidal regime for the Bohemian Cretaceous Basin across a range of sensitivity tests with elevated tidal ranges in local embayments. Funnelling associated with straits increases tidal current velocities, generating bed shear stresses that were capable of forming the sedimentary structures observed in the field. The model also predicts instantaneous bi-directional currents with orientations comparable with those measured in the field. Overall, the Imperial College Ocean Model predicts a vigorous tide-driven palaeocirculation within the Bohemian Cretaceous Basin that would indisputably have influenced sediment dispersal and facies distributions. Palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests. Accurate modelling of these parameters, in this instance, requires greater palaeogeographic certainty than can be extracted from the available rock record.

A high-resolution carbon-isotope record of the Turonian stage correlated to a siliciclastic basin fill: Implications for mid-Cretaceous sea-level change

“…As a result, a major clastic wedge formed in the early Middle Turonian, prograding to the SE, obliquely along basin axis ( Fig. 1; Uličný et al, 2009;Mitchell et al, 2010). This pattern persisted, with minor intervening transgressions, until the end of deposition of TUR 3.…”

“…The style of basin filling during the Turonian and early Coniacian was dominated by repeated progradation of coarse-grained deltas and adjoining shorefaces, affected by redistribution of clastics by strong along-shore currents of tidal origin (Uličný, 2001;Mitchell et al, 2010). The resulting basic building blocks of stratigraphy are sheet-like sandstone bodies, lobate in plan view, typically between 10 and 25 m thick, but in some cases reaching up to 100 m in thickness in the case of deep-water Gilbert-type deltas (Uličný et al, 2009).…”

“…In the NW depocentre, the expression of this surface varies between a clear MTS in the western area, with a relatively lower long-term supply, and a rather subdued transgressive surface in the eastern part, where maximum supply was directed during the axial progradation of the TUR 2-3 deltaic system (cf. Uličný et al, 2009;Mitchell et al, 2010). The basin-scale correlations suggest that the highstand deposition of TUR 3 is condensed in the basal glauconitic / phosphatic bed in Bch-1, whereas most of the TUR 3 strata in the basin centre belong to a falling stage to lowstand systems tract (LST).…”

Six commercially viable ways to remove CO2 from the atmosphere and/or reduce CO2 emissions

“…Part of the continental shelf between the Shetland Isles and France, i.e. the Southern Bight of the North Sea, the English Channel and the Irish Sea, is covered with sand waves, and in and around the Channel, an area of well over 100,000 km 2 experiences bed stresses capable of transporting gravel [10,11]. If a volume of 0.35 km 3 coarse olivine is spread over 35,000 km 2 of this area, this would compensate 5% of the world's CO 2 emissions, that is more than the combined emissions of the adjoining countries, the UK, France, Ireland, Belgium and the Netherlands together [9].…”

Upper Cenomanian–Lower Turonian ammonoids from the Saxonian Cretaceous (lower Elbtal Group, Saxony, Germany)

“…In the Early Turonian, the still relatively narrow strait between the Westsudetic Island and the Bohemian Massif (Osterzgebirge) was characterized by cross-bedded, tidally influenced sands (Schmilka Formation; see Voigt 1999, Mitchell et al 2010. These shallow-water deposits grade, with a transitional facies of bioturbated, silty-argillaceous, fine-grained sandstones and silts, into finegrained basinal deposits characterizing the "Pläner-Fazies" of the Dresden area (calcareous siltstones and silty marls of the Brießnitz Formation; Fig.…”