Internal waves vs. surface storm waves: a review on the origin of hummocky cross‐stratification

Abstract

Terra Nova, 24, 273–282, 2012 Abstract Hummocky cross‐stratification (HCS) is considered a diagnostic structure of surface storm activity at the shoreface–offshore transition. However, the origin of HCS is still debated. Laboratory experiments have not yet reproduced it and direct observations on the continental shelves do not exist. Most hydrodynamic interpretations invoke pure oscillatory flows, unidirectional‐dominated combined flows and oscillatory‐dominated flows, but they all share the assumption of HCS to reflect the combined action of surface storm waves and related currents. Within this context of uncertainties, internal waves (gravity waves propagating along the pycnocline) provide an alternative mechanism to explain the origin of HCS. Internal waves breaking on the shelf create episodic high‐turbulence events and induce upslope‐ and downslope currents as well as oscillatory flows at the depth where the pycnocline intersects the sea floor. In this scenario, both the oscillatory‐ and the unidirectional components needed for HCS to form are not necessarily linked to surface storm waves, but can occur at various depth as far and near there is a pycnocline where internal waves can form.

Lacustrine tempestite and its geological significance in the Cenozoic study of the Qaidam Basin

“…Strong storm flows are always eroding the bottom and laying erosion surfaces on the scoured base (Morsilli and Pomar, 2012) undulating and truncating the underlying stratum (Fig. 3c).…”

Sediment resuspension and nepheloid layers induced by long internal solitary waves shoaling orthogonally on uniform slopes

“…But an alternative view that can explain the presence of erosion surfaces, as well as the occurrence of hummocky cross-stratification beds in the sandy intervals, is the impact of internal waves breaking on the seafloor and their induced up-and downslope currents, as well as their oscillatory flow (e.g. Morsilli and Pomar, 2012;. Shoaling internal solitary waves of the type examined in this study may well contribute to shaping such sedimentary structures.…”

Coupled ‘storm‐flood’ depositional model: Application to the Miocene–Modern Baram Delta Province, north‐west Borneo

“…Synthetic HCS/SCS has also been generated from bed geometries formed under oscillatory‐dominated combined flow (Dumas et al ., ; Dumas & Arnott, ). However, other mechanisms have been proposed to form HCS/SCS in a spectrum of shallow to deep‐marine environments, including: (i) wave‐enhanced sediment gravity flows (Myrow et al ., ; Lamb et al ., ; Basilici et al ., ), which are variably linked to hyperpycnal flows (Ogston et al ., ; Puig et al ., ; Traykovski et al ., ); (ii) short‐lived instability events in high‐energy flows (Quin, ); and (iii) internal gravity waves propagating along the pycnocline (Morsilli & Pomar, ).…”