Depositional Evolution of Confined Turbidite Basins

Abstract

Confined turbidite basins are a common feature of many structurally complex continental slopes, but their depositional history has never been characterized using outcrop data. A synthesis of outcrop data from Tertiary Alpine basins with subsurface data from the Gulf of Mexico indicates that the progressive infill of confined turbidite basins can be characterized by four phases: (1) Flow ponding, where incoming flows are totally trapped, depositing thick, sheet-like sand-mud couplets. (2) Flow stripping, where the finer, more dilute portion of the flow is able to escape over the confining topography to be deposited elsewhere, causing increased sand/mud ratio within the basin. (3) Flow bypass, either by flows traversing over the filled basin or by switching of feeder channels away from the basin; the former resulting in incision, the latter in abandonment. (4) Blanketing, of the basin and surrounding topography due to base-level rise; this usually takes the form of meandering channel-levee complexes with low sand/mud ratios. Confined basin sequences may be stacked during the episodic growth of the confining topography to a basin, and may appear similar to sea-level-induced depositional sequences.

Fill to spill stratigraphic evolution of a confined turbidite mini-basin succession, and its likely well bore expression: The Castagnola Fm, NW Italy

“…These relationships suggest an increasingly important impact of flow stripping on finer grained sediments, which is in agreement with the ongoing infilling of the basin. In addition, thickness statistics of sandstone beds indicate a decrease in the number of very thick beds, which is consistent with the data modelled by Sinclair and Cowie (2003) Although there is no direct evidence either of younger turbidites downstream of the study area or development of a later phase of incision cutting into the ponded basin fill ('Flow bypass by incision' of Sinclair and Tomasso, 2002), outcrop constraints do not permit these possibilities to be ruled out. However, deposition of hemipelagites and thin bedded fine grained turbidites of the Mt.…”

“…Ponded turbidite systems are common in a range of different geodynamic contexts (e.g. salt-withdrawal mini-basins of continental slopes in passive margins, structurally confined basins of rifted margins and foreland basin systems; Smith 2004) and are well documented from both the subsurface (McGee et al 1994;Holman and Robertson 1994;Winker 1996;Prather et al 1998;Lamers and Carmichael, 1999;Argent et al, 2000;Winker and Booth 2000), near seabed analogues (Beauboeuf and Friedman, 2000;Deptuck et al, 2012;Hay, 2012;Prather et al, 2012a, b) and outcrop (Pickering and Hiscott, 1985;Haughton, 1994;Pickering & Hilton 1998;Sinclair 2000;Tomasso 2001;Sinclair and Tomasso 2002;Amy et al, 2007;Felletti and Bersezio 2010). Flow stripping occurs when the most dilute upper part of a turbidity current suspension cloud is able to escape the basin spilling over the confining topography (Sinclair and Tomasso 2002).…”

“…flow thickness, internal stratification in sediment concentration and grain size, velocity, duration and total discharge) and the height of the enclosing topography (Muck and Underwood 1990;Alexander and Morris 1994;Kneller and McCaffrey 1999). These controlling factors may be time-variant due to changes in sedimentary input and modifications of seafloor bathymetry, including basin infill (Prather et al 1998;Winker and Booth 2000;Sinclair and Tomasso 2002;Felletti and Bersezio 2010;Sylvester et al 2015).…”

“…'R' sands of McGee et al 1994). The stratigraphic evolution of an ideal ponded depositional sequence described by Prather et al (1998) from the Auger Basin was later on revisited and integrated with description of component facies by Sinclair and Tomasso (2002) using the Eocene-Oligocene Annot and Taveyannaz sandstones of the western Alpine foreland basin as depositional analogues. These authors reported evidence of stratigraphic transition from a lower sheet-like succession with thick bedded sandstone-mud cap couplets, interpreted elsewhere as ponded turbidites (Van Andel and Komar 1969;Pickering and Hiscott 1985;Haughton 1994Haughton , 2000, to an increasingly sand-rich upper section with amalgamated to channelized sandstones which is topped by a condensed unit of fine grained turbidites.…”

“…These authors reported evidence of stratigraphic transition from a lower sheet-like succession with thick bedded sandstone-mud cap couplets, interpreted elsewhere as ponded turbidites (Van Andel and Komar 1969;Pickering and Hiscott 1985;Haughton 1994Haughton , 2000, to an increasingly sand-rich upper section with amalgamated to channelized sandstones which is topped by a condensed unit of fine grained turbidites. The depositional model for 'fill and spill' basins of Sinclair and Tomasso (2002) is four-fold and features i) an initial flow ponding phase during which turbidity currents are fully contained by the confining topography of an upper basin; ii) a flow stripping phase which records the partial surmounting of the confining topography by the uppermost, finer grained fraction of turbidity current depositing its load downstream of it in a lower basin; iii) a flow by-pass phase occurring as the upper basin is filled in and the barrier separating it from the lower basin is healed so to induce either by-pass or abandonment of the upper basin and, locally, incision through older deposits; iv) a late-stage blanketing phase during which infilling of the lower basin results in reduction of gradients across the whole systems and backfilling where bypass had previously occurred in association with incision. The first two of these stages are amenable to statistical analysis of the distribution of bed thicknesses (Malinverno 1997;Sylvester 2007;Bersezio et al, 2005;Felletti and Bersezio 2010).…”