Tempestite facies variability and storm‐depositional processes across a wide ramp: Towards a polygenetic model for hummocky cross‐stratification

• Published in: Sedimentology
• Main Authors: Jelby, Mads E., Grundvåg, Sten‐Andreas, Helland‐Hansen, William, Olaussen, Snorre, Stemmerik, Lars
• Other Authors: Plink‐Björklund, Piret, Norges Forskningsråd
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Rurikfjellet; Svalbard; Spitsbergen
• Online Access: http://dx.doi.org/10.1111/sed.12671; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fsed.12671; https://onlinelibrary.wiley.com/doi/pdf/10.1111/sed.12671; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/sed.12671

Abstract The hydrodynamic mechanisms responsible for the genesis and facies variability of shallow‐marine sandstone storm deposits (tempestites) have been intensely debated, with particular focus on hummocky cross‐stratification. Despite being ubiquitously utilized as diagnostic elements of high‐energy storm events, the full formative process spectrum of tempestites and hummocky cross‐stratification is still to be determined. In this study, detailed sedimentological investigations of more than 950 discrete tempestites within the Lower Cretaceous Rurikfjellet Formation on Spitsbergen, Svalbard, shed new light on the formation and environmental significance of hummocky cross‐stratification, and provide a reference for evaluation of tempestite facies models. Three generic types of tempestites are recognized, representing deposition from: (i) relatively steady and (ii) highly unsteady storm‐wave‐generated oscillatory flows or oscillatory‐dominated combined‐flows; and (iii) various storm‐wave‐modified hyperpycnal flows (including waxing–waning flows) generated directly from plunging rivers. A low‐gradient ramp physiography enhanced both distally progressive deceleration of the hyperpycnal flows and the spatial extent and relative magnitude of wave‐added turbulence. Sandstone beds display a wide range of simple and complex configurations of hummocky cross‐stratification. Features include ripple cross‐lamination and ‘compound’ stratification, soft‐sediment deformation structures, local shifts to quasi‐planar lamination, double draping, metre‐scale channelized bed architectures, gravel‐rich intervals, inverse‐to‐normal grading, and vertical alternation of sedimentary structures. A polygenetic model is presented to account for the various configurations of hummocky cross‐stratification that may commonly be produced during storms by wave oscillations, hyperpycnal flows and downwelling flows. Inherent storm‐wave unsteadiness probably facilitates the generation of a wide range of hummocky cross‐stratification configurations ...