Comment on: “Anatomy of a mass extinction: Sedimentological and taphonomic evidence for drought-induced die-offs at the Permo–Triassic boundary in the main Karoo Basin, South Africa” by R.M.H. Smith and J. Botha-Brink, Palaeogeography, Palaeoclimatology, Palaeoecology 396:99-118

Gastaldo, Robert A.; Neveling, Johann

doi:10.1016/j.palaeo.2014.06.027

Cited by 10 publications

(7 citation statements)

References 28 publications

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“…Both thinlybedded greenish-gray and reddish gray siltstone occur, often interbedded on a dm to mm scale. Such features are not indicative of eolian deposits (Gastaldo and Neveling, 2016), and an eolian depositional mechanism is not supported by the results of the current study, either.…”

Section: Eolian Inputcontrasting

confidence: 97%

“…Coloration of Karoo siltstones straddling the vertebrate-defined PTB has been debated as to its utility and significance (Gastaldo and Neveling, 2016;Neveling et al, in press). Geochemical data, along with observations of color and sedimentary structures, reported in the current study enable a thorough examination of previously proposed mechanisms of coloration, and the proposal of a new mechanism that better fits with the observed results.…”

Section: Mechanisms For Colorationmentioning

confidence: 99%

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Petrography, Mineralogy, and Geochemistry of Greenish- And Reddish-Gray Siltstones Straddling the Vertebrate-Defined Permian–triassic Boundary in South Africa

Li¹

2016

Geological Society of America Abstracts With Programs

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The Permian-Triassic Mass Extinction (PTME) is considered the largest in Earth's history, yet the terrestrial response is not well understood. The Karoo Basin, South Africa, hosts abundant exposures of terrestrial deposits that span the Permian-Triassic Boundary (PTB). The terrestrial PTB is defined by a turnover in vertebrate assemblage zones and has been associated with a transition from greenish-gray to reddish-gray siltstone. The current PTME model states that the siltstone color change is a reflection of aridification and eolian deposition, which is believed to represent rapid climate change directly linked with the event. Greenish-and reddish-gray siltstones were collected from below, at, and above the vertebrate-defined PTB at Old Lootsberg Pass, Eastern Cape Province, and Bethulie, Free State Province, to test this hypothesis. Samples are examined petrographically, mineralogically, and geochemically. The presence of primary structures attributed to fluvial processes indicates in-channel, fluvial origin of most samples. Greenish-and reddish-gray siltstones are chemically indistinguishable for most major elements, except for Na, Ti, and Mn. Mössbauer spectroscopy reveals that the reddish-gray color is likely due to the presence of finelydispersed hematite, not a lower Fe 2+ /Fe 3+ ratio. Hematite primarily occurs as coatings on illite and chlorite. Titanite, rutile, and ilmenite are also found in the reddish-gray siltstones. CIA-K values indicate that these rocks represent deposits in environments with a constantly high water table. Combined, the results indicate that the reddish-gray coloration is secondary to greenish-gray color, and is a product of diagenetic hematite formation under saturated-sediment conditions, likely due to interaction with water in the environments.

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Section: Eolian Inputcontrasting

confidence: 97%

Section: Mechanisms For Colorationmentioning

confidence: 99%

Petrography, Mineralogy, and Geochemistry of Greenish- And Reddish-Gray Siltstones Straddling the Vertebrate-Defined Permian–triassic Boundary in South Africa

Li¹

2016

Geological Society of America Abstracts With Programs

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“…Scale in millimeters. Sheldon 2005), such an approach has been, and continues to be, taken in the interpretation of siltstone successions in the Karoo Basin transitioning the Daptocephalus (formerly Dicynodon; Viglietti et al 2016) and Lystrosaurus Assemblage Zones (but see Gastaldo and Neveling 2016).…”

Section: Discussionmentioning

confidence: 99%

Siltstones Across the Daptocephalus ( Dicynodon ) and Lystrosaurus Assemblage Zones, Karoo Basin, South Africa, Show No Evidence For Aridification

Li¹,

Gastaldo²,

Neveling³

et al. 2017

Journal of Sedimentary Research

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Changes in the record of vertebrate-assemblage zones in the Karoo Basin, South Africa, serve as a model for the response of terrestrial ecosystems to the end-Permian biotic crisis. Vertebrate turnover from the Daptocephalus to Lystrosaurus Assemblage Zone is believed to have begun with the appearance of subtle siltstonecolor variance and is coeval with a unique, laminated lithofacies, both of which are interpreted by other workers to represent evidence for an aridification trend. The laminated facies consists of interbedded greenish-gray and dark reddish-gray siltstone, with coloration of the latter reported as a function of an increasing eolian component. The current study combines stratigraphy, petrography, geochemistry, and rock magnetic properties of an interlaminated succession and lateral equivalents at Old Lootsberg Pass in the Eastern Cape Province to determine whether such subtle color variance is a function of aridification and, hence, climate change. Siltstones were evaluated from intervals both below and above a pedogenic nodule-bearing feldspathic wacke that is physically correlated over a. 0.5 km distance. The lower succession consists of interbedded greenish-gray (sensu latu) and reddish-gray (sensu latu) siltstone in which undisturbed and minimally disturbed primary sedimentary, along with few secondary biogenic structures, are interpreted to represent deposition in an abandoned channel-fill complex. Massive greenish-gray and dark reddish-gray siltstone above the channel complex demonstrate that coloration is variable across laterally equivalent strata. Both lithologies were assessed using X-ray fluorescence, X-ray diffraction, Mössbauer spectroscopy, scanning electron microscopy with EDS, and bulk magnetic susceptibility, stepwise acquisition of an isothermal remanent magnetization (IRM), and backfield direct field demagnetization. Our data indicate that there is no statistically significant difference in major-element concentrations between lithologies and that subtle color difference is a function of the presence of fine (, 1 wt. %) hematite in the reddishgray rocks. Hence, the abundance of Fe is not responsible for either color. Rather, hematite is found to be localized as reticulate, surficial coatings on both illite and chlorite flakes, the only two clay species identified in the study. Similarly, there is no clear distinction in the magnetic mineralogy of sample suites; both magnetite and maghemite vary in abundance. These data lead to an interpretation that the presence of hematite is early diagenetic and the landscape in the earliest part of the Lystrosaurus Assemblage Zone was not arid. In contrast, the landscape was wet, that allowed for the continued growth of a Permian-age flora under conditions of high water table that experienced temporal fluxes in the hydrological regime promoting spatial color modification of sediment. modified by climatic and environmental conditions after deposition (DiMichele and Gastaldo 2008; Gastaldo and Demko 2011). In addition, terrestrial successions span...

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“…Facies changes in the Karoo Basin were attributed by Ward et al (2000), Smith & Botha-Brink (2014) and Botha et al (2020) to reflect an increase in sediment load relative to discharge following a catastrophic destruction of plant ecosystems and a change to a warmer, drier, and more seasonal climate at the PTB. There is, however, a dispute over exactly where the EPE and PTB are located within the succession that is not yet fully resolved (Gastaldo et al, 2015(Gastaldo et al, , 2018Gastaldo & Neveling, 2016). Gastaldo et al (2020) noted that the base of the Lystrosaurus Assemblage Zone (equated with the vertebrate-defined EPE in the Karoo Basin) is at least 300 kyr older than the marine EPE, and significantly pre-dates the transition from mudrock-dominated (Palingkloof Member) to sandstone-dominated (Katberg Formation) successions.…”

Section: Facies Changes Across the Permo-triassic Boundarymentioning

confidence: 99%

“…Other studies, however, have concluded little or no apparent change in depositional environment or palaeogeography across the PTB and/or EPE, or non-synchronous changes (e.g. McLoughlin et al, 1997;Yu et al, 2007;Yang et al, 2010;Gastaldo et al, 2015;Gastaldo & Neveling, 2016;Fielding et al, 2019;Wignall et al, 2020). The emerging pattern is one of spatial and temporal heterogeneity in the record of the end-Permian palaeoenvironmental crisis on land.…”

Section: Introductionmentioning

confidence: 99%

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin, eastern Australia

et al. 2020

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Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end-Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high-resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end-Permian Extinction occurs at the top of the uppermost coal bed, and the Permo-Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal-forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat-forming mires, no significant long-term change in depositional style (grain size, sediment-body architecture, or sediment dispersal direction) was noted across the end-Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end-Permian Extinction marks the base of a long-term, progressive trend towards better-drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end-Permian Extinction were re-established. The age of the floral extinction is constrained to 252.54 AE 0.08 to 252.10 AE 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U-Pb ages on zircon grains. Another new age indicates that the return to 30

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Comment on: “Anatomy of a mass extinction: Sedimentological and taphonomic evidence for drought-induced die-offs at the Permo–Triassic boundary in the main Karoo Basin, South Africa” by R.M.H. Smith and J. Botha-Brink, Palaeogeography, Palaeoclimatology, Palaeoecology 396:99-118

Cited by 10 publications

References 28 publications

Petrography, Mineralogy, and Geochemistry of Greenish- And Reddish-Gray Siltstones Straddling the Vertebrate-Defined Permian–triassic Boundary in South Africa

Petrography, Mineralogy, and Geochemistry of Greenish- And Reddish-Gray Siltstones Straddling the Vertebrate-Defined Permian–triassic Boundary in South Africa

Siltstones Across the Daptocephalus ( Dicynodon ) and Lystrosaurus Assemblage Zones, Karoo Basin, South Africa, Show No Evidence For Aridification

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin, eastern Australia

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