Laterally accreted deposits in low efficiency turbidites associated with a structurally-induced topography (Oligocene Molare Group, Tertiary Piedmont Basin, NW Italy)

Abstract

The origin of laterally accreted deposits in ancient deep marine successions is often controversial. Indeed, not always do these features imply the occurrence of meanders or high-sinuosity turbidite channels, but they can be generated by other causes, such as sediment-gravity-flow dynamics controlled by the morphology of tectonically confined mini-basins. This work discusses laterally accreted deposits composed of sharp-based, normally graded beds in a very small tectonically controlled mini-basin. These beds, characterized by a well-defined asymmetrical cross-current facies tract, form well-developed lateral-accretion surfaces dipping in directions ranging between W and SW, and perpendicular to the paleocurrents directed towards the N. For this reason, these deposits have always been interpreted as point bars related to meandering channels. A new detailed stratigraphic framework and facies analysis have led to an alternative interpretation, namely that these deposits record lateral deflections of small volume, longitudinally segregated turbidite dense flows against a structurally controlled morphological high. This interpretation is also supported by a comparison to other tectonically controlled turbidite systems that are characterized by higher degrees of efficiency but show similar laterally accreted deposits and cross-current facies tracts.

Sedimentary characteristics and depositional model of hyperpycnites in the gentle slope of a lacustrine rift basin: A case study from the third member of the Eocene Shahejie Formation, Bonan Sag, Bohai Bay Basin, Eastern China

“…Bed types were defined based on the vertical stacking patterns of lithofacies, which bounded the base and top by an eroded surface or intervening mudstone (Southern et al, 2017; Tinterri & Civa, 2021; Yang et al, 2020). Bedsets are distinguished based on the distributions of bed types, thickness variation of beds and vertical arrangements of beds (Southern et al, 2017; Tinterri & Civa, 2021; Yang et al, 2020). The materials used for facies analyses were based on more than 500 m of the full core.…”

“…The concepts of a bed, deposited by one event, and of bedsets characterizing the hyperpycnites in Es3z come from Campbell (1967). Bed types were defined based on the vertical stacking patterns of lithofacies, which bounded the base and top by an eroded surface or intervening mudstone (Southern et al, 2017; Tinterri & Civa, 2021; Yang et al, 2020). Bedsets are distinguished based on the distributions of bed types, thickness variation of beds and vertical arrangements of beds (Southern et al, 2017; Tinterri & Civa, 2021; Yang et al, 2020).…”

“…The materials used for facies analyses were based on more than 500 m of the full core. Terminology related to the facies analyses in this study follows the principles of Yang et al (2019Yang et al ( , 2020, Southern et al (2017) and Tinterri and Civa (2021).…”

Evolution of a turbidite system in a narrow basin setting: the Ropianka Fm (Campanian–Paleocene) in the Skole Nappe of the Polish Carpathians

“…However, in comparison with well-established examples of asymmetrical confined basins (cf. Tinterri and Tagliaferri, 2015;Tinterri et al, 2016Tinterri et al, , 2017Cunha et al, 2017;Tinterri and Civa, 2021), this local asymmetrical facies distribution is less pronounced, perhaps owing to the mixed sandmud character of the Skole Basin, higher efficiency of the flows, and the connection with the eastern part of the basin. The asymmetrical topography may have been inherited after the rifting stage of the proto-Silesian Basin (cf.…”