13Submarine lobe fringe deposits form heterolithic successions that may include a high proportion of 14 hybrid beds. The identification of lobe fringe successions aids interpretation of paleogeographic 15 setting and the degree of basin confinement. Here, for the first time, the sedimentological and 16 architectural differences between frontal and lateral lobe fringe deposits are investigated. Extensive 17 outcrop and core data from Fan 4, Skoorsteenberg Formation, Karoo Basin, South Africa, allow the 18 rates and style of facies changes from axis to fringe settings of lobes and lobe complexes in both 19 down-dip (frontal) and across-strike (lateral) directions to be tightly constrained over a 800 km 2 20 study area. Fan 4 comprises three sand-prone divisions that form compensationally stacked lobe 21 complexes, separated by thick packages of thin-bedded siltstone and sandstone intercalated with 22 2 (muddy) siltstone, interpreted as the fringes of lobe complexes. Lobe-fringe facies associations 23 comprise: i) thick-bedded structureless or planar laminated sandstones that pinch and swell, and are 24 associated with underlying debrites; ii) argillaceous and mudclast-rich hybrid beds; and iii) current 25 ripple-laminated sandstones and siltstones. Typically, frontal fringes contain high proportions of 26 hybrid beds and transition from thick-bedded sandstones over length-scales of 1 to 2 km. In 27 contrast, lateral fringe deposits tend to comprise current ripple-laminated sandstones that transition 28 to thick-bedded sandstones in the lobe axis over several kilometers.

Submarine lobe fringe deposits form heterolithic successions that may include a high proportion of hybrid beds. The identification of lobe fringe successions aids interpretation of paleogeographic setting and the degree of basin confinement. Here, for the first time, the sedimentological and architectural differences between frontal and lateral lobe fringe deposits are investigated. Extensive outcrop and core data from Fan 4, Skoorsteenberg Formation, Karoo Basin, South Africa, allow the rates and style of facies changes from axis to fringe settings of lobes and lobe complexes in both down-dip (frontal) and across-strike (lateral) directions to be tightly constrained over an 800 km2 study area. Fan 4 comprises three sand-prone divisions that form compensationally stacked lobe complexes, separated by thick packages of thin-bedded siltstone and sandstone intercalated with (muddy) siltstone, interpreted as the fringes of lobe complexes. Lobe-23 fringe facies associations comprise: i) thick-bedded structureless or planar-laminated sandstones that pinch and swell, and are associated with underlying debrites; ii) argillaceous and mudclast-rich hybrid beds; and iii) current ripple-laminated sandstones and siltstones. Typically, frontal fringes contain high proportions o hybrid beds and transition from thick-bedded sandstones over length scales of 1 to 2 km. In contrast, lateral fringe deposits tend to comprise current ripple-laminated sandstones that transition to thick-bedded sandstones in the lobe axis over several kilometers. Variability of primary flow processes are interpreted to control the documented differences in facies association. Preferential deposition of hybrid beds in frontal fringe positions is related to the dominantly downstream momentum of the high-density core of the flow. In contrast, the ripple-laminated thin beds in lateral fringe positions are interpreted to be deposited by more dilute low-density (parts of the) flows. The development of recognition criteria to distinguish between frontal and lateral lobe fringe successions is critical to improving paleogeographic reconstructions of submarine fans at outcrop and in the subsurface, and will help to reduce uncertainty during hydrocarbon field appraisal and development.

Sedimentary facies in the distal parts of deep-marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Fm., a downstream transition from thickly-bedded turbidite sandstones to argillaceous, internally layered hybrid beds is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen- and thicken-upwards reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterisation of bed types, including grain size, grain fabric and mineralogical analyses, a process-model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield-strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several km) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine-grained systems without invoking external controls or large-scale flow partitioning, and also explains the abrupt pinch-out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems.

13Sedimentary facies in the distal parts of deep+marine lobes can diverge significantly from those 14 predicted by classical turbidite models, and sedimentological processes in these environments are 15 poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the 16Skoorsteenberg Fm., a downstream transition from thickly+bedded turbidite sandstones to 17 argillaceous, internally layered hybrid beds is observed. The hybrid beds have a characteristic 18 stratigraphic and spatial distribution, being associated with bed successions which generally coarsen+ 19 and thicken+upwards reflecting deposition on the fringes of lobes in a dominantly progradational 20 system. Using a detailed characterisation of bed types, including grain size, grain fabric and 21 mineralogical analyses, a process+model for flow evolution is developed. This is explored using a 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 and spatially isolated higher+quality reservoir sandstones (Zarra, 2007; Kane and Pontén, 2012). 67In this contribution, the spatial and stratigraphic distribution of the various sedimentary facies The dataset comprises 20 sedimentological logs collected in the field and correlated by walking out 84 individual beds (Fig. 1). These logs were collected at 1:20 scale with more detailed logs of 85 individual beds and packages of beds collected at 1:2 scale (Figs. 2+5). Aerial photographs supported 86 field correlation in areas that were difficult to access or were covered (Fig. 2). Data collected 87 include lithology, bed thickness, and palaeocurrent measurements from ripples, flutes and other sole 88 marks. In addition, the equivalent stratigraphic intervals within cores from 7 research boreholes were 89 logged at 1:20 scale (Fig. 3). During the Permian, the Karoo Basin is interpreted as either a retro+arc foreland basin developed 109 inboard of a fold and thrust belt