Evolution, architecture and hierarchy of distributary deep‐water deposits: a high‐resolution outcrop investigation from the Permian Karoo Basin, South Africa

Abstract

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. 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. 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. 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. 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. Each lobe is built by many lobe elements, which also display compensational stacking patterns over a kilometre scale. 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. Lobe deposits, therefore, are not simple radial sheet-dominated systems as commonly envisaged.

Tectonics and sedimentation of the central sector of the Santo Onofre rift, north Minas Gerais, Brazil

“…Medium-to coarse-grained sandstone turbidites that comprise some thick-bedded, amalgamated and tabular geometry suggest a lobe deposit (Mutti 1992, Haughton et al 2003, 2009). The thickening-upward cycles may indicate an increase in the strength/volume of turbidity currents over time, and suggest that these sequences were deposited in sloped and slope-rise submarine fans (Prélat et al 2009). FA2's rocks are poorly strained, with pressure solution-dominated cleavage transversal to well-preserved bedding.…”

“…The facies sedimentary pattern and the entire stratigraphic architecture of Santo Onofre Group suggest a sudden rise in sea level, which was probably related to rapid tectonic subsidence (Jonhson et al 2001, Prélat et al 2009), explaining the shift in facies in Sítio Novo Group and the change to predominantly clastic sedimentation (shallow water to deep water). Danderfer (2000) interpreted the development of the accommodation space of the Santo Onofre paleo-basin under dextral transtractive tectonics based on structural evidence and the stratigraphic characteristics, with the east-dipping Muquém fault corresponding to the master fault in northern Espinhaço.…”

“…The narrow and restricted occurrence of carbonaceous mudstone facies that are interbedded with fine-grained turbidites from Canatiba Formation suggests the depocenter was located near and along the entire extension of the Santo Onofre fault, occurring probably directly on Sítio Novo Group (this contact is seen only in northern Espinhaço, Danderfer 2000). Therefore, the western portion of the half-graben, where the area of largest subsidence is expected to be located (Prélat et al 2009, Link 2003, Noda & Toshimitsu 2009, Poyatos-Moré et al 2016, suggests a greater ratio of accommodation for sedimentation during stagnant, poorly oxygenated deep water during the sea-level highstand phase. These conditions favored high biological activity, serving as a source of carbonaceous material (Canfield et al 2007, Sato et al 2015.…”

Autogenic influence on the morphology of submarine fans: an approach from 3D physical modelling of turbidity currents

“…They had variable sizes and lobe quantities (from 2 to 4 units), showing thicknesses between 1 and 3 mm. These lobes were considered the smallest hierarchical element in the lobe complexes, according to the Prélat et al (2009) classification.…”

Distal turbidite fan/lobe succession of the Late Oligocene Zuberec Fm. – architecture and hierarchy (Central Western Carpathians, Orava–Podhale basin)

“…[6][7][8][9][10][11]. A key outcrop-derived characteristic of submarine fan deposits is the presence of systematic vertical patterns in bed thickness and grain size distribution.…”