Reading tidal processes where their signature is cryptic: The Maastrichtian meandering channel deposits of the Tremp Formation (Southern Pyrenees, Spain)

Abstract

Tidal currents can propagate tens of kilometres landward from the shoreline, forming dense networks of meandering channels, which drain vegetated areas and range in width from tens to hundreds of metres. Sedimentary products of these inland tidal channels are poorly documented in the stratigraphic record, as most studies on tidal processes occurring in inland areas are focused on fluvio-tidal interaction. The present study contributes to filling this gap, investigating Late Maastrichtian meandering-channel deposits of the Tremp-Graus Basin (Southern Pyrenees, Spain). These deposits accumulated in a growth syncline, which allowed the development of a 20 to 30 km wide, 80 to 100 km long, tidal embayment. Sporadic occurrence of poorly-developed rhythmites and bidirectional currents confirms the occurrence of tidal processes, whereas their local dominance is inferred from several pieces of evidence, including: (i) disproportion between depth of the larger channels and related catchment area; (ii) landward-accretion of pointbar bodies; (iii) landward fining of point-bar bodies, and (iv) reconstruction of palaeo-flow patterns at the meander bend scale. This work shows that three-dimensional architectural modelling and reconstruction of bar planform transformation styles can provide a critical contribution to the understanding of tidal control on sedimentation in inland areas.

Hydrodynamic controls on sedimentary facies of tidal point bars: A case study in the Georgia coastal plain, USA

“…In addition to the tidal forcings, interactions between fluvial and marine processes that occur in the meandering channels of the FMT add more complexity to the estuarine system, and to the sedimentary facies formation and distribution in their related point bars and other bar forms (e.g. Dalrymple & Choi, 2007; Dashtgard et al ., 2012; Kästner et al ., 2017; Ghinassi et al ., 2020; Gugliotta et al ., 2020). Moreover, the architecture of tidal point bars can be further modified in regions subjected to seasonal intense precipitation and windstorms (e.g.…”

“…Given these complexities, tidal point bars often do not conform entirely to traditional theoretical models of fluvial point bars, as observed in modern and ancient point bars located in the FMT (Modern: Sexton & Hayes, 1996; Johnson & Dashtgard, 2014; Bomer et al ., 2019; Fietz et al ., 2021. Ancient: Corbeanu et al ., 2004; Van den Berg et al ., 2007; Olariu et al ., 2015; Shiers et al ., 2019; Cosma et al ., 2020; Ghinassi et al ., 2020) and in modern tidal channels with no significant freshwater input (Land & Hoyt, 1966; Barwis, 1977; Choi & Jo, 2015; Brivio et al ., 2016; Ghinassi et al ., 2017, 2019; Boaga et al ., 2018; Cosma et al ., 2019, 2020, 2021; Choi et al ., 2021).…”

“…(2020, 2021). There are other studies that classify these partially attached bar deposits as ‘elongated tidal bars’ (Dalrymple & Choi, 2007), ‘in‐channel bars’ (Carling et al ., 2015), ‘sidebars’ with barb channels (Leuven et al ., 2016) or even ‘barb deposits’ (Ghinassi et al ., 2020). The bars in this study are classified as tidal point bars because they have been formed by the same basic processes as fluvial point bars (reduction in flow velocity towards the channel inner bank and lateral accretion), but their morphology and stratigraphy are further modified by tidal processes.…”

“…However, although the constant change in current speed and regular flow reversals caused by tides favour the development of IHS deposits, these features can be formed in a variety of other environments. Thus, its use as diagnostic feature of a tidal environment is only appropriate when other tide‐related structures (for example, flaser and lenticular bedding, reactivation surfaces, herringbone cross‐stratification, rhythmic alternations in strata thicknesses and pebble‐size mud clasts) are frequently found together (Dalrymple et al ., 1992; Boyd et al ., 2006; Van den Berg et al ., 2007; Fielding, 2015; Ghinassi et al ., 2020).…”

“…Campanian Neslen Formation, USA: Olariu et al ., 2015; Shiers et al ., 2019. Tremp–Graus–Ager Basin, Spain: Upper Cretaceous: Ghinassi et al ., 2020; Lower Eocene: Martinius, 2012; Cosma et al ., 2020. Late Miocene Solimões Formation, Brazil: Hovikoski et al ., 2008.…”