Exploring a new breadth of cyclic steps on distal submarine fans

Abstract

Research on the depositional record of submarine fans and related turbidite systems has highlighted the importance of channel, lobe and levée-overbank architectural elements as fundamental building blocks. However, many of the characteristics and processes of deposits left by flows traversing those fans remain elusive, because flows seem to be able to go unconfined for long distances. Offshore southern California (USA), the La Jolla Canyon decreases in relief to become an approximately U-shaped channel across the basin floor of the San Diego Trough. The La Jolla Channel gradually loses confinement and transitions to a network of scours, some of which align to form incipient channels, and fields of bedforms. High-resolution seafloor topography, CHIRP seismic-reflection data, sediment cores and hydrodynamic flow analysis are used to explore these features. The focus is on two regions of bedforms: (i) a field of net-depositional, concentric bedforms across the eastern levée-overbank upstream from the terminus of the La Jolla Channel; and (ii) a linear train of more erosional bedforms approximating an incipient channel adjacent to the present mouth of the La Jolla Channel. These bedforms are interpreted to be among a class of upper-flow-regime bedforms called cyclic steps, which were formed by densimetric Froude supercritical turbidity currents that spilled out of the present La Jolla Channel. The highresolution data for the La Jolla Fan provide valuable insights into the characteristics of supercritical bedforms likely common to distal submarine fans, as well as on sedimentary processes likely important for submarine fan growth into sedimentary basins. In particular, the pattern of evolution of the La Jolla Fan suggests that cyclic steps with wavelengths on the order of tens of metres to a few hundreds of metres could be fundamentally important for the evolution of the distal submarine fans with relatively low-relief main channels.

Quantifying the three‐dimensional stratigraphic expression of cyclic steps by integrating seafloor and deep‐water outcrop observations

“…Small-scale sediment waves (<300 m wavelength, <8 m wave height) occur in a wide range of environments including the proximal flanks of volcanic islands, submarine canyon/channels and lobes, and delta channels and slopes (e.g. Casalbore et al, 2021;Fildani et al, 2021;Piper et al, 1985;Piper & Savoye, 1993;Babonneau et al, 2013;Paull et al, 2013;Mazi eres et al, 2014;Gales et al, 2019;Normandeau et al, 2019b;Vanderkerhove et al, 2020;Fig. 1A to C). These features are commonly interpreted as long-wavelength upper-flow-regime bedforms called cyclic steps, which are triggered by cyclic step flow instabilities (Cartigny et al, 2011;Symons et al, 2016;Slootman & Cartigny, 2020).…”

Digital re‐evaluation of down‐dip channel‐fill architecture in deep‐water slope deposits: Multi‐scale perspectives from UAV‐SfM

“…The prevalence of upslope‐migrating bedforms on sea floor slopes from prodelta channels to submarine fan lobes is now widely appreciated based on numerous high‐resolution sea floor surveys from around the world (Babonneau et al, 2013; Carvajal et al, 2017; Fildani et al, 2020; Hughes Clarke, 2016; Normandeau et al, 2019; Paull et al, 2011; Smith et al, 2005; Zhong et al, 2015). Although these bedforms are commonly identified on steep slopes in locations with a distinct change in flow confinement, there is uncertainty regarding their prevalence and preservation in different segments along submarine sediment‐routing systems (Covault et al, 2017).…”

Giant meandering channel evolution, Campos deep-water salt basin, Brazil

“…We measured meander wavelengths by automatically identifying inflection points along the channel centerline (see Sylvester et al [2013] and Sylvester and Pirmez [2017] for details). Figure 8 shows our measurements of channel elements in the Campos Basin plotted with those of other systems from the Bengal Fan (Kolla et al, 2012), the Dalia channel system offshore West Africa (Abreu et al, 2003), the Joshua Channel of the eastern Gulf of Mexico (Posamentier, 2003;Kramer et al, 2016), the Veracruz Fan of the western Gulf of Mexico (Winter, 2018), the Hikurangi Channel offshore New Zealand (McArthur and Tek, 2021), the Puchkirchen and basal Hall Formations of the Molasse Basin, Austria (Hubbard et al, 2009), and the La Jolla Channel offshore southern California, USA (Fildani et al, 2021). We replotted data collected by Pirmez (1994) for the Amazon Channel.…”