Frontal and Lateral Submarine Lobe Fringes: Comparing Sedimentary Facies, Architecture and Flow Processes

Abstract

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.

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

“…6). This variation is also documented in the Tanqua depocenter (Rozman, 2000;Prélat et al, 2009;Groenenberg et al, 2010) and is interpreted to relate to differences in flow processes in distal frontal versus distal lateral run outs (Spychala et al, 2017b).…”

“…Beds with similar thickness, grain size, and sedimentary structures are grouped into facies. Facies are used to interpret environments of deposition within the context of extensive paleoenvironmental reconstructions already undertaken in the Laingsburg depocenter (e.g., Grecula et al, 2003;Figueiredo et al, 2010Figueiredo et al, , 2013Di Celma et al, 2011;Flint et al, 2011;Van der Merwe et al, 2014;Spychala et al, 2015Spychala et al, , 2017aSpychala et al, , 2017bBrooks et al, 2018b). A physical correlation framework was established by walking out stratigraphic surfaces between sections.…”

“…Maps are extended beyond extremities of the input data by the surfacing algorithm, with unrealistic values removed and observed trends applied. Paleogeographic maps utilize data from previous studies in the Karoo (Grecula et al, 2003;Figueiredo et al, 2010Figueiredo et al, , 2013Di Celma et al, 2011;Flint et al, 2011;Van der Merwe et al, 2014;Spychala et al, 2015Spychala et al, , 2017aSpychala et al, , 2017bBrooks et al, 2018b) and represent gross depositional environments for each study interval. Unit C, D, E, and F paleogeographic maps are modified from Van der Merwe et al (2014) incorporating data from Spychala et al (2015) and Brooks et al (2018b).…”

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system, Pennsylvanian Ross Sandstone Formation, western Ireland

“…These include the deposits of a range of composite and transitional flow types, the origin of which is in many cases related to distal flow transformations whereby turbulence is damped and flows with a component of turbulent grain suspension evolve to those with variable cohesion. These types of beds are often relatively mud‐rich and are commonly encountered in the outer and marginal parts of deep‐water systems (Talling et al ., ; Barker et al ., ; Southern et al ., ; Fonnesu et al ., ; Spychala et al ., ). Event beds of this type described in the literature include slurry flows (Lowe & Guy, ; Lowe et al ., ), cogenetic turbidite–debrite beds (Haughton et al ., ; Talling et al ., ), hybrid event beds (HEBs; Haughton et al ., ), transitional flow deposits (Kane & Pontén, ) and matrix‐rich beds (Terlaky & Arnott, ).…”

“…Work in South Africa by Hodgson () and Spychala et al . () showed that HEBs in the Permian‐aged Tanqua Karoo Basin were common in lobe fringe deposits formed during the onset of fan initiation cycles and during fan growth.…”