Karoo lava-fed deltas and a petrified forest from the Lower Jurassic of southern Gondwana

Bordy, Emese M.; Haupt, Tanya M.; Head, Howard V.

doi:10.1016/j.palaeo.2021.110484

Cited by 7 publications

(26 citation statements)

References 85 publications

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“…In addition, trace fossils (termite nests, vertebrate tracks) and plant remains, especially petrified wood, have also been documented (e.g. Ellenberger, 1970; Bamford, 2004; Bordy, 2008; Bordy et al ., 2009, 2021; Bordy & Head, 2018; Abrahams et al ., 2021; Mukaddam et al ., 2021). The diverse fossil record of the Clarens Formation is the ultimate evidence for wetter conditions and thriving localized ecosystems within this overall desert setting.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…It has a conformable, transitional lower contact with the Elliot Formation and a conformable upper contact with the continental flood basalts of the Drakensberg Group (e.g. Bordy & Head, 2018;Bordy et al, 2020aBordy et al, , 2021; Fig. 1).…”

Section: Geological Backgroundmentioning

confidence: 99%

“…1) have been linked to Early Jurassic playas in south-west Gondwana (e.g. Beukes, 1969Beukes, , 1970Eriksson, 1981Eriksson, , 1986Bordy & Catuneanu, 2002;Bordy & Head, 2018). The regional occurrence of these lacustrine deposits in the lower and upper parts of the Clarens Formation has led to its informal division into three zones, where the middle zone reflects the most arid conditions in the overall succession (Beukes, 1969(Beukes, , 1970Bordy & Head, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Beukes, 1969Beukes, , 1970Eriksson, 1981Eriksson, , 1986Bordy & Catuneanu, 2002;Bordy & Head, 2018). The regional occurrence of these lacustrine deposits in the lower and upper parts of the Clarens Formation has led to its informal division into three zones, where the middle zone reflects the most arid conditions in the overall succession (Beukes, 1969(Beukes, , 1970Bordy & Head, 2018). These three zones are thought to represent wet-to-dry climatic shifts during the Clarens depositional episode from the Sinemurian to the Pliensbachian (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Lake dynamics in an Early Jurassic desert: Evidence from the Clarens Formation in southern Africa

Head

Bordy

2022

Sedimentology

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Interdune deposits are sensitive to climatic fluctuations and ancient interdune lacustrine systems can reveal the drivers of erg dynamics through time and space. This southern African study details the dynamics of interdune deposition in a vast ancient desert system that was active over Pangaea in the Middle Mesozoic and formed part of one of the largest known sand seas in Earth's history. Focusing on the Sinemurian to Pliensbachian Clarens Formation in the main Karoo Basin (south-west Gondwana), three facies associations were identified that formed in meso-scale and macro-scale lakes amongst aeolian dunes and sand sheets of the Clarens erg system. The northern facies association is restricted to interdune hollows within an actively climbing dune system. High-sediment availability and high-wind speeds limited the space available for these meso-scale lakes to expand. Here, migrating dunes outpaced the water table rise promoting the formation of discontinuous lenses of lake deposits, as is typical in erg centres. The southern facies associations developed both in spatially isolated meso-scale lakes, where flooding was controlled by groundwater inundation (water table rise), as well as in macro-scale lakes, where flooding was related to groundwater inundation and floods (surface runoff) that induced terminal splays. Relative to the north, the southern facies associations, with their more significant thickness and lateral extent, show that, here, the basin was characterized by a higher rate of relative subsidence. Moreover, the southern lake systems were established along the erg's margin, where the interdunes expanded during pluvial phases. Ultimately, the facies associations in the Clarens Formation show that the widespread arid conditions in the Early Jurassic of south-west Gondwana were subjected to prolonged and repeated pluvial phases in an otherwise harsh environment. Given the prominence of Jurassic aeolianites across Pangea, this study provides a southern African perspective on global palaeoerg dynamics and Early Jurassic climatic shifts.

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Section: Geological Backgroundmentioning

confidence: 99%

Section: Geological Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Lake dynamics in an Early Jurassic desert: Evidence from the Clarens Formation in southern Africa

Head

Bordy

2022

Sedimentology

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“…Beukes, 1970;Bordy et al 2020bBordy et al , 2021. Currently, the link between the wet period in the terminal Karoo times (Bordy et al 2021) and the global Pliensbachian-Toarcian atmospheric perturbations due to the gas emissions in the Karoo-Ferrar LIP (e.g. Moulin et al 2017) remains unstudied.…”

Section: Geological Settingmentioning

confidence: 99%

Life and land engulfed in the late Early Jurassic Karoo lavas of southern Gondwana

et al. 2022

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The rock record from the late Early Jurassic in southern Africa encompasses the history of voluminous continental flood basalt outpourings associated with the magmatic events in the Karoo–Ferrar Large Igneous Province (LIP) in southern and eastern Gondwana. This multiphase magmatism produced one of Earth’s largest continental flood basalt successions volumetrically and is assumed to have been a main driving mechanism in late Early Jurassic global environmental perturbations, including mass extinctions and changes in climate. In southern Africa, these Lower Jurassic flood basalts are interbedded with fossiliferous sedimentary rocks, which in turn host the last signs of ‘Karoo life’ in the form of fossil plants, invertebrates and vertebrates, including the trackways of hopping mammals and the ultimate Karoo dinosaurs. The sedimentology and palaeontology of the interbeds archived depositional and biotic processes in running water as well as in and around shallow, up to ∼10 m deep freshwater lakes and ponds in the late Early Jurassic. This study explains how a complex freshwater palaeo-habitat prevailed – albeit temporarily – in this extremely stressful environment, which was unlike any modern volcanic system. The evidence collectively points to seasonally wet, warm temperate climatic conditions during the early phases of Karoo volcanism. Moreover, the evidence in the rocks also suggests that the dynamic volcanic conditions resulted in shifting habitats that likely facilitated the migration of the ultimate Karoo biota towards the north and west, away from the main Karoo land of fire, just before Gondwana started to disassemble. This refinement of the environmental dynamics in southern Gondwana presented herein lays the groundwork for future high-resolution volcanological, geochronological and chemostratigraphical studies aimed at the nuanced understanding of the global environmental effect of the Karoo–Ferrar LIP.

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Loess or lake sediments: Resolving the origin of massive beds in the Lower Jurassic of southern Africa

Head

Bordy

2023

Geological Journal

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Throughout Earth's history, dust deposits have been considered sensitive markers of fluctuations in global atmospheric circulation patterns. However, the identification of ancient dust deposits remains problematic, as their massive (structureless) nature impedes an unequivocal classification. In southern Africa, the Lower Jurassic Clarens Formation is dominated by intriguing structureless sandy siltstones that have been interpreted as loess even though classical diagnostic outcrop‐scale loess features are not observed. In this study, we utilized grain characteristics such as size, shape, sorting and fabric to assess the origin of these ubiquitous massive beds, as compared to strata with a known origin in the unit. Based on these grain characteristics, the massive beds can be grouped into six different facies types (Facies 1–6). Facies 1 has very similar grain features to the large‐scale cross‐bedded strata and thus it is interpreted as migrating dune deposits, only apparently massive. The dominant grain size with a large proportion of very fine‐grained sand and the random grain fabric suggests that Facies 2 resulted from sandy dust fall (short‐term suspension), whereas Facies 3 is interpreted as aeolian dust, having features consistent with modern and ancient loess due to its dominant silt grain size and random grain fabric. Features in Facies 4 are undiagnostic and could reflect a range of aeolian processes, although a dominant silt grain size may suggest an overwhelming loess component. Facies 5 and 6 show primary aeolian signatures with the preferred grain orientation being evidence of reworking in an aqueous setting (e.g., lake, stream). These six facies types represent a spectrum of depositional processes that occurred in response to erg migration and climatic changes along this Early Jurassic erg margin. Their facies diversity is evidence for: (1) dry and windy conditions in SW Gondwana during the Sinemurian to Pliensbachian, and (2) reworking of the aeolian sediments in various fluvial and lacustrine settings during the development of one of the largest known sand seas in Earth's history.

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Karoo lava-fed deltas and a petrified forest from the Lower Jurassic of southern Gondwana

Cited by 7 publications

References 85 publications

Lake dynamics in an Early Jurassic desert: Evidence from the Clarens Formation in southern Africa

Lake dynamics in an Early Jurassic desert: Evidence from the Clarens Formation in southern Africa

Life and land engulfed in the late Early Jurassic Karoo lavas of southern Gondwana

Loess or lake sediments: Resolving the origin of massive beds in the Lower Jurassic of southern Africa

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