This makes them important archives for the reconstruction of past sediment budgets, climate and anthropogenic pollution, as well as reservoirs for hydrocarbons and carbon sequestration (Galy et al., 2007 Sømme et al., 2011 Bell et al., 2018a Jobe et al., 2018 Rabouille et al., 2019 Pohl et al., 2020). Lobe deposits, therefore, are not simple radial sheet-dominated systems as commonly envisaged. Thickness variations of lobe elements can be extremely abrupt without erosion, particularly in distal areas where isopach maps reveal a finger-like distal fringe to lobes. Each lobe is built by many lobe elements, which also display compensational stacking patterns over a kilometre scale. Between successive lobes are thin-bedded, very fine-grained sandstones and siltstones that do not change lithofacies over several kilometres and therefore are identified as a different architectural element. The Fan 3 lobe complex comprises six distinct fine-grained sandstone packages, interpreted as lobes, which display compensational stacking patterns on a 5 km scale.
Detailed study (bed-scale) of a single-lobe complex (Fan 3) over a 15 km by 8 km area has helped to define a four-fold hierarchy of depositional elements from bed through to lobe element, lobe and lobe complex. Extensive outcrops in the Tanqua depocentre, south-west Karoo Basin, provide these three-dimensional constraints on lithofacies distributions, stacking patterns, depositional geometries and the stratigraphic evolution of submarine lobe deposits at a scale comparable with modern lobe systems. Sea floor and shallow seismic data sets of terminal submarine fan lobes can provide excellent planform timeslices of distributive deep-water systems but commonly only limited information on cross-sectional architecture.
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