Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa

Abstract

The integrated results of a facies analysis and provenance study of the Late Triassic to Early Jurassic Elliot Formation (Karoo Supergroup) provide some new insights into the development of the main Karoo foreland system of South Africa. Based on changes in the fluvial style, palaeocurrent pattern, provenance, isopach trends and fossil content, a regional lithostratigraphic subdivision of the Elliot Formation is proposed. In addition, the boundary between the Lower and Upper Elliot formations appears to be a second order sequence boundary. This unconformity was probably generated by the last stage of orogenic loading of the Cape Fold Belt, which interrupted the overall, first order orogenic unloading of the system, suggesting that tectonically controlled flexural subsidence existed in the main Karoo Basin until at least the end of Triassic. The magnitude of this pre-Upper Elliot tectonic event is signified by the presence of outsized quartzite pebbles and boulders, believed to have originated in the Cape Fold Belt. A number of tectonic structures, e.g. pene-contemporaneous normal faults and large-scale convolute bedding, coupled to sandstones with basement uplift/craton interior provenance, and easterly palaeocurrent direction for the Upper Elliot Formation suggest that the first stages of inversion from a compressional to extensional tectonic regime began only in the Early Jurassic.

Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorphMassospondylus

“…Our work at the Rooidraai locality has yielded multiple in situ clutches of eggs as well as fragmentary eggshell and bones, all from a 2-m-thick interval of muddy siltstone 25 m from the top of the Lower Jurassic Upper Elliot Formation ("Stormberg Group," Karoo Supergroup) (11). We refer these finds to the same taxon as the partial clutch containing in ovo embryos of Massospondylus collected in 1976 because the eggs are closely similar in size and structure, and the exposed embryonic bones are indistinguishable from the previously described remains (1,12).…”

“…Much of the finegrained silt in the Upper Elliot and Clarens formations has been interpreted as loess (11), which presumably spread across the region as the climate became warmer and drier, in advance of the large dune fields that covered much of southern Africa and characterize the Clarens Formation. Sedimentological evidence also points to a transition from a large, sinuous meandering channel belt to a sequence of relatively homogeneous muddy siltstones, with evidence of ponds and repeated wetting and drying events in the immediate vicinity of the nesting site.…”

South Africa's coalfields — A 2014 perspective

“…The basement to the Karoo Supergroup fill in both the MKB and in the northern basins is heterogeneous Bordy et al, 2004a;Rutherford, 2009) and this heterogeneity plays a significant control on the nature of the fill, particularly during the early phases of the deposition of the Karoo Supergroup. The main crustal scale blocks for the MKB are shown below in Figure 3.…”

“…An understanding of the basement lithologies is important for interpreting the nature of pre-conditioning prior to the onset of Dwyka glaciation, which provides an important control on the sedimentary fill of the lower parts of the Karoo Supergroup. Catuneanu et al, 1998) showing the position of the Kaapvaal Craton boundaries as proposed by Skinner et al (1992); modified from Bordy et al (2004a).…”

A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism

“…Aardonyx appears to be the closest known sister group to the clade of obligatory quadrupedal sauropodomorphs to retain facultative, if not habitual, bipedalism. (Bordy et al 2004).…”