The thick-bedded tail of turbidite thickness distribution as a proxy for flow confinement: Examples from tertiary basins of central and northern Apennines (Italy)

Abstract

8The assessment and meaning of turbidite thickness statistics represent open research questions 9 for both applied and pure sedimentology. Yet thickness data collected in the field are often 10 incomplete and/or biased toward or against certain thickness classes due to bed geometry, erosion 11 and/or operational filed constraints, which largely undermine tackling such questions. However, in 12 situations where turbidity currents are ponded by basin topography so to deposit basin-wide 13 tabular beds and erosion is negligible, some of the variables of the 'bed thickness equation' can be 14 relaxed, making easier to investigate what the primary controls on turbidite thickness statistics are. 15This study reviews the bed thickness statistics of the non-channelized parts of the infill of four 16 tertiary basins of Central-Northern Apennines (Italy), where bed geometry and sedimentary 17 character have been previously assessed. Though very different in terms of size and, arguably, 18 character of feeder system and source area, these basins share a common evolution to their 19 turbidite fill with upward transition from an early ponded to a late unconfined setting of deposition. 20Based on comparison of thickness subsets from diverse locations and stratigraphic heights within 21 the basin fills of the case studies, this paper seeks to answering the following questions: i) how 22 data collection choices and field operational constraints (e.g. location, outcrop quality, use of 23 thickness from single vs. multiple correlative sections, length of the stratigraphic section from which 24 thicknesses were retrieved) can affect statistics of an empirical distribution of turbidite thicknesses? 25 ii) how depositional controls of confined vs. unconfined basins can modify the initial thicknesses 26 distribution of turbidites?; iii) is there in turbidite thickness statistics a 'flow confinement' signature 27 2 which can be used to distinguish between confined and unconfined depositional settings? Results 28 suggests that: i) best practices of data collection are crucial to a meaningful interpretation of 29 turbidite thickness data, especially in presence of stratigraphic and spatial trends of bed thickness; 30 ii) a systematic bias against cm-thick Tcd Bouma sequence turbidites deposited by small volume 31 low density flows exists, which can significantly modify the low-end tail of an empirical frequency 32 distribution of bed thickness; iii) thickness statistics of beds starting with a basal Ta/Tb Bouma 33 division bear a coherent relationship to the transition from ponded to unconfined depositional 34 settings, consisting in a reduction of variance and mean and, consequently, modification of the 35 initial thickness-frequency scaling relationship. This research highlights the role of flow stripping, 36 sediment by-pass and bed geometry in altering the initial thickness distribution of ponded turbidites 37 suggesting how, on the contrary, fully ponded mini-basins represents the ideal setting for further 38 research link...

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

“…Marini et al ., ). Examples include: the Ordovician Cloridorme Formation of Quebec, Canada (Pickering & Hiscott, ); the Permian Laingsburg Formation of Karoo Basin, South Africa (Grecula et al ., ); the Late Cretaceous Vallcarga Formation of south‐central Pyrenees, Spain (Van Hoorn, ); the Eocene Hecho Group of south‐central Pyrenees, Spain (Mutti & Johns, ; Shanmugam & Moiola, ; Remacha et al ., ); the Eocene Kusuri Formation in Sinop Basin, north‐central Turkey (Janbu et al ., ); the Eocene–Oligocene Grès d'Annot Formation of the Alpine foreland, south‐eastern France (Kneller & McCaffrey, ; McCaffrey & Kneller, ; Salles et al ., ; Tinterri et al ., ); the Miocene turbidites of the Tabernas–Sorbas Basin, south‐eastern Spain (Haughton, , ; Hodgson & Haughton, ); and several turbidite units of the Central and Northern Apennines, among which include the Miocene Marnoso‐Arenacea (Tinterri et al ., ), Laga and Castagnola (Milli et al ., ; Marini et al ., ) formations. The controversial issues include interpretation of turbidite sedimentation over the sea‐floor palaeotopography of slump folds in mass‐transport complexes (Pickering & Corregidor, ; Moscardelli & Wood, ; Kneller et al ., ).…”

“…Evidence of flow reversals in turbidites has generally attributed to the reflection of 'contained' (fully ponded) flows, with the relatively thick mud cap of turbidites ( Fig. 18E) invoked as key supporting evidence (Pickering & Hiscott, 1985;Haughton, 1994Haughton, , 2000Kneller & McCaffrey, 1999;McCaffrey & Kneller, 2001;Grecula et al, 2003;Salles et al, 2014;Patacci et al, 2015;Marini et al, 2016;Tinterri et al, 2016). However, this concept may require some caution, because flow reversals can occur without containment, while thick mud caps may reflect either en masse deposition from a trailing flow of fluidal mud or hemipelagic fallout between consecutive turbidity currents Baas et al, 2009Baas et al, , 2016Leszczy nski et al, 2015).…”

“…The main controversy surrounded the interpretation of sedimentary features such as the varying local palaeocurrent directions, mud-cap thicknesses and the spatial architecture and thickness trend of turbidite beds (e.g. Marini et al, 2016). Examples include: the Ordovician Cloridorme Formation of Quebec, Canada (Pickering & Hiscott, 1985); the Permian Laingsburg Formation of Karoo Basin, South Africa (Grecula et al, 2003); the Late Cretaceous Vallcarga Formation of south-central Pyrenees, Spain (Van Hoorn, 1970); the Eocene Hecho Group of south-central Pyrenees, Spain (Mutti & Johns, 1978;Shanmugam & Moiola, 1988;Remacha et al, 2005); the Eocene Kusuri Formation in Sinop Basin, north-central Turkey (Janbu et al, 2007); the Eocene-Oligocene Gr es d'Annot Formation of the Alpine foreland, south-eastern France (Kneller & McCaffrey, 1999;McCaffrey & Kneller, 2001;Salles et al, 2014;Tinterri et al, 2016); the Miocene turbidites of the Tabernas-Sorbas Basin, south-eastern Spain (Haughton, 1994(Haughton, , 2000Hodgson & Haughton, 2004); and several turbidite units of the Central and Northern Apennines, among which include the Miocene Marnoso-Arenacea (Tinterri et al, 2016), Laga and Castagnola (Milli et al, 2013;Marini et al, 2016) formations.…”

“…Turbidity currents are the principal mechanism for the delivery of coarse sediment to deep-water environments (D _ zuły nski et al, 1959;Normark et al, 1993;Piper & Mutti, 1992;). The impact of tectonic sea-floor topography on turbidity current hydraulics and sediment dispersal has long been debated on the basis of outcrop and seismic data, laboratory experiments, sporadic instrumental measurements in modern environments and forward numerical modelling (Mutti & Johns, 1978;Mutti, 1979;Pickering & Hiscott, 1985;Shanmugam & Moiola, 1988;Kneller et al, 1991;Hodgson et al, 1992;Pickering et al, 1992;Alexander & Morris, 1994;Haughton, 1994;Kneller, 1995;Morris & Alexander, 2003;Lamb et al, 2004Lamb et al, , 2006Nasr-Azadani & Meiburg, 2014;Oluboyo et al, 2014;Marini et al, 2016;Wang et al, 2016;Doughty-Jones et al, 2017). Progress in understanding the response of a turbidity current to specific topographic features was hindered on the one hand by the difficulty of studying such flows in natural deep-water settings and, on the other hand, by the scale limitation of laboratory flume-tank experiments.…”

Quantification of the bed‐scale architecture of submarine depositional environments

“…Both sandstone bed thickness and mudstone-interval thickness decrease from confined to unconfined to semiconfined lobe deposits ( Figure 6). This relationship is expected for confined to unconfined and confined to semiconfined as the flow within a confined system is unable to laterally expand, creating a thicker bed for a given flow volume Marini et al, 2015Marini et al, , 2016Prélat et al, 2010). However, the lower bed thickness results for proximal semiconfined compared to proximal-unconfined lobe deposits are counterintuitive and may represent the higher degree of erosion and/or bypass for proximal portions of semiconfined lobe deposits, creating a lower characteristic bed thickness ( Figure 6; Jobe, Sylvester, Howes, et al, 2017;Prather et al, 1998).…”