Sedimentary Architecture of Storm-Influenced Tidal Flat Deposits of the Upper Mulichinco Formation, Neuquén Basin, Argentina

Abstract

This study reports on the Lower Cretaceous upper Mulichinco Formation in the Neuquén Basin, west-central Argentina. The studied succession comprises shallow marine strata, deposited in a mixed wave and tidal flat environment where ebb-tidal currents dominated. We describe mixed storm-and tide-influenced deposits within progradationally stacked high-frequency sequences and discuss process interaction, sediment dispersal, and preservation potential. These storm and tidal deposits mix spatially on bed, bedset, and sequence scales, suggesting multi-scale process interactions. The study investigates a 12-km-long continuous outcrop, oriented subparallel to the paleocoastline. The succession comprises subtidal flat and meandering tidal channel complexes, with interbedding and interfingering of storm and tidal deposits. The tidal deposits are widespread and comprise moderately sorted sandstones with bimodal paleocurrent directions, single and double mud drapes, reactivation surfaces, and inclined heterolithic stratification. Varying bimodal paleocurrent directions suggest that the paleocoastline was irregular, consisting of both protrusions and bays. Storm deposits are mainly found erosively interbedded with subtidal flat sandstones, and exhibit decimeter-thick, well-sorted hummocky and swaley cross-stratified sandstones. These storm deposits show systematic lateral variations in abundance, from dominant to absent, which are linked to subtle variations in water depth along the irregular paleocoastline. As the tidal deposits are widespread across the study area, and with no significant facies change, the varying dispersal of storm-influenced deposits is considered a product of wave refraction, with converging and diverging wave energy at interpreted positions of coastal protrusions and embayments, respectively. Consequently, the irregular paleocoastline morphology caused spatial variability in wave impact and controlled preservation of interbedded storm and tidal deposits at the coastal protrusions while facilitating complete tidal remobilization of sediments in the embayments. With no evidence for fluvial influence, ebb-tidal currents are considered as the main drivers for sediment dispersal onto the subtidal flat, through the meandering tidal channels.

Tidal dynamics in palaeo-seas in response to changes in bathymetry, tidal forcing, and bed shear stress

“…6a, 6b; 7) than on the more open EMSS, indicating that the funnelling of the basin had a stronger impact on the simulated flow speed and the bed shear stress values than on the tidal amplitude. The corollary of these flow speed and bed shear stress spatial variations would be reflected in the rock record, characterised by different sediment grain sizes (Yalin & Karahan, 1979;van Rijn, 1993;Ward et al, 2015; and different sedimentary architecture (Hori et al, 2002;Costas et al, 2011, Sleveland et al, 2020 despite the similar tidal amplitudes.…”

Hutchison Medallist 1. Wave-Dominated to Tide-Dominated Coastal Systems: A Unifying Model for Tidal Shorefaces and Refinement of the Coastal- Environments Classification Scheme

“…Third, due to the fact that wave size above shallowly submerged tidal flats is mainly a function of water depth, wave energy at any point on the tidal flat will change rapidly over each tidal cycle (namely tidal modulation of wave energy). Such depositional processes are attributed with forming two unique sedimentary deposits: wave bundles (Yang et al 2008a) and tidally modulated storm deposits (Vaucher et al 2017;Yang and Chang 2018;Sleveland et al 2020) as a result of the interaction of waves and reversing tidal currents over a single tidal cycle. Tidally modulated storm deposits (Vaucher et al 2017) and wave bundles also form in TMS.…”

“…Tidal shorefaces interpreted from the rock record (Table 1) have been identified either by recognizing the interbedding of clear tidal and wave/storm signatures in the deposits (Basilici et al 2012;Wei et al 2016;Bádenas et al 2018;Kalifi et al 2020;Sleveland et al 2020) and/or by documenting tidal modulation of wave processes (Smosna and Bruner 2016;Vaucher et al 2017Vaucher et al , 2018aVaucher et al , 2020MacNaughton et al 2019;Angus et al 2020). Tidal signatures used in these studies include tidal bundles, herringbone structures, lenticular, wavy, and flaser bedding, and mud drapes (Fig.…”

“…A) Two parasequences that both show a shallowing-upward profile from offshore to subtidal-flat environments. The subtidal flat (STf) showcases a gradual transition from storm (sandstone) to tidal (muddy sandstone) deposits preserved in the storm-influenced (medium-energy) subtidal flat of the Upper Mulichinco Formation (Barranca Los Loros, Early Cretaceous, Argentina; modified after Sleveland et al 2020). B) Regressive sequence that defines the Fezouata Shale and Zini Formation (Early Ordovician), which is overlain by the transgressive Tachilla Formation (Middle Ordovician), Morocco.…”

“…We compare and contrast two closely related tidal-shoreface variants, open-coast tidal flats (OCTF) and tidally modulated shorefaces (TMS), both of which have been proposed for mixed wave-tide coastlines. Over the past 10 years, deposits interpreted as either OCTF or TMS have been described from the sedimentary record and this literature is summarized and compared to the original models (Table 1; Basilici et al 2012;Smosna and Bruner 2016;Wei et al 2016;Vaucher et al 2017Vaucher et al , 2020Bádenas et al 2018;MacNaughton et al 2019;Angus et al 2020;Kalifi et al 2020;Sleveland et al 2020). We then propose a unified model for tidal shorefaces taking into account the multiple variants described so far.…”