Architecture and controls of thick, intensely bioturbated, storm-influenced shallow-marine successions: an example from the Jurassic Neuquén Basin (Argentina)

Abstract

Thick (>100 m-thick), highly bioturbated storm-influenced shallow-marine deposits are not frequent in the stratigraphic record, but they tend to be unusually common in aggradational to retrogradational successions. Individual storm-event beds have typically low preservation in these successions, yet depositional settings are characterized on the basis of storms processes. We present a sedimentological study of a thick, bioturbated exhumed succession deposited during the early post-rift stage of the Neuquén Basin (Argentina) and compare its stratigraphic record with examples developed worldwide, in order to discuss controlling factors on the total destruction of storm-event beds during several million years. The Bardas Blancas Formation (170-220 m thick) is dominated by muddy sandstones and sandy mudstones, but it also includes subordinate proportions of clean sandstones and pure mudstones, collectively representing different environments of a storm-influenced shoreface-offshore system. The offshore transition and proximal offshore strata invariably comprises intensely bioturbated deposits, with only a few preserved HCS-sandstone beds. The unit shows a long-term aggradational pattern involving ca. 7-10 Myr and is associated with low riverine influence.By combining the observations and interpretations of the Bardas Blancas Formation with other subsurface and exhumed intensely bioturbated, shallow-marine successions we dispute the general assumption that they can be associated to low frequency or low magnitude of storms. Alternatively, we propose that the long-lived efficiency of benthic fauna on destroying most if not all the storm-event beds that reached the offshore-transition sector, results from the combination of two or three factors: deposition in relatively confined marine depocentres, persistent low riverine influence, and long-term aggradational stacking pattern. As these conditions can be recreated in a variety of basin styles, such as rift, early post-rift, and foreland settings, the recognition of thick, bioturbated successions as the ones discussed here can be used to infer more realistic constrains for depositional models and better predict facies distribution in these storm-influenced systems.

On depositional processes governing along‐strike facies variations of fine‐grained deposits: Unlocking the Little Ice Age subaqueous clinothems on the Adriatic shelf

“…Interpretation. Diagnostic structures, such as hummocky cross-stratification and upwardfining truncated laminae suggest deposition under combined-flow erosion and traction transport followed by suspended load to suspension settling from waning currents, as documented elsewhere for storm-dominated deposits (Nummedal & Swift, 1987;Arnott & Southard, 1990;Lazar et al, 2015b;Grundv ag et al, 2021;Schwarz et al, 2021). The relative increase in Ni content suggests a sediment supply mainly from the Po River (Amorosi et al, 2022).…”

“…By the time this current reaches the central/southern sector, it splits into multiple branches that flow off the shelf reaching variable depths downslope (e.g. Sellschopp & Alvarez, 2003;Rice et al, 2013;Chiggiato et al, 2016;Foglini et al, 2016;Marini et al, 2016;Rovere et al, 2019).…”

“…13). The NAdDW in the KS02-357 area generally flows around 90 m or deeper (Sellschopp & Alvarez, 2003;Rice et al, 2013;Marini et al, 2016), thus offshore of the sediment core location.…”

Sedimentología de la Formación La Anita, Cretácico Superior de la Cuenca Austral, provincia de Santa Cruz, Argentina

“…La AF2 se dispone conformando Interpretación: La presencia de facies arenosas con HCS y laminación horizontal reflejan depositación tractiva a partir de flujos combinados formados durante eventos de tormenta (Myrow y Southard, 1996;Dumas y Arnott, 2006), mientras que, por otro lado, las areniscas masivas son el resultado del retrabajo por organismos de estas capas de tormenta durante condiciones de buen tiempo (Bann et al, 2008;Buatois y Mángano, 2011). Los cuerpos amalgamados de capas generadas por tormenta podrían indicar una alta periodicidad de flujos de relajación generados después de los eventos de tormenta, los cuales erosionan las formas de lecho que se generan durante condiciones de buen tiempo (Dott y Bourgeos, 1982;Isla et al, 2018;Schwarz et al, 2020). La presencia de clastos de cuarzo tamaño grava y los abundantes restos vegetales que se han registrado en estos depósitos sugieren la presencia de una cercana desembocadura de un río y la influencia de procesos fluviales durante la acumulación de estos depósitos (Bhattacharya, 2006;Bann et al, 2008;Moyano Paz et al, 2018).…”

“…Interpretación: La marcada alternancia entre capas de areniscas masivas con alto IB y areniscas estratificadas con abundantes estructuras de tipo HCS que caracteriza a los depósitos de la AF2, indica el patrón de "lam-scram" que caracteriza la depositación bajo la alternancia de olas de buen tiempo y eventos de tormenta (Fig. 5.2a; Howard y Frey, 1984; MacEachern y Pemberton y MacEachern, 1997;Bann et al, 2004Bann et al, , 2008MacEachern y Bann, 2008;Buatois y Mángano, 2011, Buatois et al, 2012Moyano Paz et al, 2020;Schwarz et al, 2020). Las capas generadas por los depósitos de tormenta presentan los valores más bajos de IB y las estructuras biogénicas presentes se encuentran adaptadas para la colonización de sustratos bajo condiciones de alta energía y elevadas tasas de sedimentación.…”