A depositional model for deep‐lacustrine, partially confined, turbidite fans: Early Cretaceous, North Falkland Basin

Abstract

This paper presents a model of facies distribution within a set of early Cretaceous, deep‐lacustrine, partially confined turbidite fans (Sea Lion Fan, Sea Lion North Fan and Otter Fan) in the North Falkland Basin, South Atlantic. As a whole, ancient deep‐lacustrine turbidite systems are under‐represented in the literature when compared with those documented in marine basins. Lacustrine turbidite systems can form extensive, good quality hydrocarbon reservoirs, making the understanding of such systems crucial to exploration within lacustrine basins. An integrated analysis of seismic cross‐sections, seismic amplitude extraction maps and 455 m of core has enabled the identification of a series of turbidite fans. The deposits of these fans have been separated into lobe axis, lobe fringe and lobe distal fringe settings. Seismic architectures, observed in the seismic amplitude extraction maps, are interpreted to represent geologically associated heterogeneities, including: feeder systems, terminal mouth lobes, flow deflection, sinuous lobe axis deposits, flow constriction and stranded lobe fringe areas. When found in combination, these architectures suggest ‘partial confinement’ of a system, something that appears to be a key feature in the lacustrine turbidite setting of the North Falkland Basin. Partial confinement of a system occurs when depositionally generated topography controls the flow‐pathway and deposition of subsequent turbidite fan deposits. The term ‘partial confinement’ provides an expression for categorising a system whose depositional boundaries are unconfined by the margins of the basin, yet exhibit evidence of internal confinement, primarily controlled by depositional topography. Understanding the controls that dictate partial confinement; and the resultant distribution of sand‐prone facies within deep‐lacustrine turbidite fans, is important, particularly considering their recent rise as hydrocarbon reservoirs in rift and failed‐rift settings.

High‐resolution X‐ray fluorescence profiling of hybrid event beds: Implications for sediment gravity flow behaviour and deposit structure

“…This two‐part H3 structure is not something specific to the Ross Formation but has been noted elsewhere (e.g. Kane & Pontén, ; Popović, ; Kane et al ., ; Wearmouth, ; Angus et al ., ; Dodd et al ., ; Kvale et al., ). Concentrations of mud clasts at the boundary between H3a and H3b suggest possible buoyancy‐driven segregation (Postma et al ., ; Fig.…”

“…Variable mud content distribution has important implications for inferring original flow processes, bed‐level heterogeneity and rock properties such as permeability (Amy et al ., ; Marchand et al ., ; Portén et al ., ; Southern et al ., ; Dodd et al ., ). Thus the type, volume, distribution and habit of mud at bed level are important issues in assessing what is effective porosity and how the ‘net clean’ sandstone components of a deep‐water succession might be connected vertically and laterally.…”

Clastic injectites, internal structures and flow regime during injection: The Sea Lion Injectite System, North Falkland Basin

“…The lobes form a series of compensationally‐offset stacked, tabular deposits (Fig. B and C), that exhibit a complex suite of seismic amplitude architectures in plan view (as described in Dodd et al ., ). Internally, the lobes comprise a series of high density turbidites, low density turbidites and hybrid event beds, interbedded within an otherwise hemi‐limnic mudstone succession (Dodd et al ., ).…”

“…In some examples, angular mud‐clasts contain internal injections of sand with cuspate margins, which terminate abruptly at the edges of the clasts (Figs A, 8C, 8D, 8E and B). The mud‐clasts are lithologically identical to the surrounding host rocks, which are composed of hemi‐limnic mudstones (as defined in Dodd et al ., ).…”

From the Eastern Paratethys to the Pontocaspian basins

“…Submarine and sublacustrine channel-fan systems are well studied (Pimpirev and Sarmiento, 1993;Clark and Pickering, 1996;Soreghan et al, 1999;Allen and Densmore, 2000;Gawthorpe and Leeder, 2000;Hickson and Lowe, 2002;Mack and Stout, 2005;Covault, 2011;Di Celma et al, 2011;Morris et al, 2014;Dodd et al, 2019). The marine and lake systems generally have similar architectural elements but differ in size and controlling processes.…”