Evaluating the temporal link between the Karoo LIP and climatic–biologic events of the Toarcian Stage with high-precision U–Pb geochronology

Sell, Bryan; Ovtcharova, Maria; Guex, Jean; Bartolini, Annachiara; Jourdan, Fred; Spangenberg, Jorge E.; Vicente, Jean-Claude; Schaltegger, Urs

doi:10.1016/j.epsl.2014.10.008

Cited by 154 publications

(101 citation statements)

References 57 publications

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“…Durations of the ammonite zones in the Toarcian are based on cycle-stratigraphy of zones in France and Portugal, so giving an age of c. 183 Ma for the falciferum Ammonite Zone. This is confirmed by correlation of ash beds in a sedimentary succession with ammonites in Peru, and by matching carbon isotopic excursions between continents (Sell et al 2014). High-precision U-Pb dating of zircons from the Peruvian ash beds places the top of the tenuicostatum Zone at 183.22 ± 0.25 Ma, and the middle of the bifrons Zone at 181.99 ± 0.13 Ma, so confirming an age for the intervening falciferum Zone around 183 Ma.…”

supporting

confidence: 50%

“…The T-OAE spanned the upper part of the underlying semicelatum Ammonite Subzone, and extended through the exaratum Ammonite Subzone, peaking at about one-third of the way through the latter (van de Schootbrugge et al 2005). The entire T-OAE isotopic excursion has been estimated as lasting 0.3-0.5 myr (Boulila et al 2014) or 0.6 ± 0.1 myr (Huang & Hesselbo 2014), with the two major anoxic episodes, termed T-OAE1 and T-OAE2, falling on either side of the 183 Ma age estimate (Ikeda & Hori 2014;Sell et al 2014). The substantial carbon isotopic anomaly has been explained by input of large volumes of isotopically light carbon from the Karoo-Ferrar basaltic province (Suan et al 2010;Burgess et al 2015).…”

Section: A Time Of Environmental Crisismentioning

confidence: 99%

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The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life

Williams

Benton

Ross

2015

JGS

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The Strawberry Bank Lagerstätte provides a rich insight into Early Jurassic marine vertebrate life, revealing exquisite anatomical detail of marine reptiles and large pachycormid fishes thanks to exceptional preservation, and especially the uncrushed, 3D nature of the fossils. The site documents a fauna of Early Jurassic nektonic marine animals (five species of fishes, one species of marine crocodilian, two species of ichthyosaurs, cephalopods and crustaceans), but also over 20 species of insects. Unlike other fossil sites of similar age, the 3D preservation at Strawberry Bank provides unique evidence on palatal and braincase structures in the fishes and reptiles. The age of the site is important, documenting a marine ecosystem during recovery from the end-Triassic mass extinction, but also exactly coincident with the height of the Toarcian Oceanic Anoxic Event, a further time of turmoil in evolution.

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supporting

confidence: 50%

Section: A Time Of Environmental Crisismentioning

confidence: 99%

The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life

Williams

Benton

Ross

2015

JGS

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“…Existing U-Pb dates from the Umkondo LIP are quite close together in age implying the the province was emplaced rapidly (within ca. 3 million years) as is the case for some other well-constrained intraplate large magmatic events such as the Central Atlantic Magmatic Province (Blackburn et al, 2013) and the Karoo-Ferrar Province (Sell et al, 2014;Burgess et al, 2015). Notably, this magmatic history contrasts with the evidence for prolonged magmatic activity in the Keweenawan Midcontinent Rift wherein applications of paleosecular variation analyses need to be cognizant of the evidence for progressive directional change that is associated with rapid plate motion rather than secular variation (Davis & Green, 1997;Swanson-Hysell et al, 2009, 2014a.…”

Section: Paleosecular Variationmentioning

confidence: 80%

“…This assumption, while shown to be true in this study, is complicated by the spatial overlap of the Umkondo Province with other dolerite intrusions with a range in U-Pb isotopic ages. These include the 1.93 Ga Moshaneng dolerites in Botswana (Hanson et al, 2004b), the 1.88-1.87 Ga Mashonaland Igneous Province in Zimbabwe and coeval dolerites intruding the Waterberg Group in South Africa (Hanson et al, 2004bSöderlund et al, 2010), post-1.83 Ga dolerite sills in the Soutpansberg Group (Brandl, 1981(Brandl, , 1985Geng et al, 2014), and the widespread 0.18 Ga Karoo LIP (Sell et al, 2014). It is a testament to the mild post-2.0 Ga metamorphic history of the interior of the Kalahari Craton that dolerites dated at ca.…”

Section: Umkondo Sills In Botswanamentioning

confidence: 99%

A new grand mean palaeomagnetic pole for the 1.11 Ga Umkondo large igneous province with implications for palaeogeography and the geomagnetic field

Swanson‐Hysell¹,

Kilian²,

Hanson

2015

Geophysical Journal International

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corresponds with a normal or reversed geomagnetic field relative to other continents can constrain the relative orientations between cratons with time-equivalent data. This interpretation is particularly important in comparison to Laurentia as it bears on Kalahari's involvement and position in the supercontinent Rodinia. The dominance of south-directed declinations within the Umkondo Province was previously used to suggest that these directions are the same polarity as reversed directions from the early magmatic stage of the Keweenawan Midcontinent Rift of Laurentia. Two Umkondo sills with northerly declinations have U-Pb baddeleyite ages of ca. 1109Ma that are temporally close to dated Midcontinent rift units having reversed directions. Based on this comparison, and paleomagnetic data from younger units in the Kalahari Craton, we favor the option in which the sites with northerly declinations from the Umkondo Province correspond to the reversed polarity directions from the early magmatic stage in the Midcontinent Rift. This interpretation allows for the Namaqua-Natal metamorphic belt of Kalahari to be a conjugate to the Grenville margin of North America and for Kalahari to have become conjoined with Laurentia within the supercontinent Rodinia subsequent to Umkondo LIP magmatic activity. IntroductionPaired paleomagnetic and geochronologic data demonstrate that between ca. 1112 and 1108 Ma there was large-scale magmatism across the Kalahari Craton over an area of ∼2 x 10 6 km 2 ( Fig. 1; Hanson et al., 2004a). Extrusive components of this province are exposed as tholeiitic basalts that occur at the top of the Umkondo Group in Zimbabwe and Mozambique (Swift, 1962;McElhinny, 1966;Moabi et al., 2015) and as rhyolite lavas, pyroclastics and tholeiitic basalts within the Kgwebe Formation of northern Botswana (Modie, 1996;Hanson et al., 2006). However, the majority of exposed remnants of the Umkondo Large Igneous Province (LIP) are shallow-level mafic intrusions de Kock et al., 2014) which are interpreted as feeders to more extensive flood lavas that have largely eroded away (Hanson et al., 2004a).The widespread extent of these intrusions has led to the inference that the lavas covered nearly Swanson-Hysell et al. (2015) (2011) for sources for the geological data. The inset map shows the location of the main map and the broader geological context. The thick translucent gray line on the inset map indicates the interpreted shape of the Kalahari Craton on the interior of the late Mesoproterozoic orogenic belts that is used in the paleogeographic reconstructions (Fig. 4) (Hanson et al., 2004bSöderlund et al., 2010), post-1.83 Ga dolerite sills in the Soutpansberg Group (Brandl, 1981(Brandl, , 1985Geng et al., 2014), and the widespread 0. basement correspond to the Umkondo event is a reasonable one, it is largely untested since there are precise age constraints for only a small fraction of the total exposed intrusions. If high-quality paleomagnetic data can be generated from a given sill, the distinct paleomagnetic poles ...

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“…However, the main factors controlling the production and the preservation of OM in these units remain controversial. The Early Jurassic was an interval of climatic warming and major perturbations of the global carbon cycle triggered by massive volcanic eruptions of the Central Atlantic Magmatic Province (CAMP; Marzoli et al, 1999;Whiteside et al, 2007) and the Karroo-Ferrar large igneous province (LIP; Encarnación et al, 1996;Minor and Mukasa, 1997;Svensen et al, 2007Svensen et al, , 2012Sell et al, 2014). Emission of greenhouse gases during these eruptions resulted in "greenhouse Earth" conditions by the early Toarcian (Pálfy and Smith, 2000;Weissert, 2000;Jenkyns, 2003).…”

Section: Introductionmentioning

confidence: 99%

Redox conditions and depositional environment of the Lower Jurassic Bächental bituminous marls (Tyrol, Austria)

Neumeister¹,

Algeo²,

Bechtel³

et al. 2016

AJES

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A suite of trace elements (TEs) characterized by an affinity to reducing environments, including molybdenum (Mo), uranium (U), vanadium (V), copper (Cu), and nickel (Ni), were used to investigate secular variations in environmental redox conditions during deposition of the Bächental bituminous marls (Bächentaler Bitumenmergel). These marls, which belong to the Sachrang Member of the Lower Jurassic Middle Allgäu Formation in the Northern Calcareous Alps, are subdivided on the basis of Al-normalized TE concentrations and concentration ratios into three units that correspond to major shifts in depositional redox conditions. The lower and upper units (Units 1 and 3, respectively) were deposited under suboxic to transiently anoxic conditions. The removal of TEs to the sediment was connected to siliciclastic input, diagenetic processes, and organic-matter accumulation in the sediment. In contrast, the middle unit (Unit 2) was characterized by intense anoxia as reflected in strong TE enrichments and peak total organic carbon (TOC) contents up to 13 %. Enrichment of TEs was linked mainly to adsorption onto organic matter in Unit 2, reflecting control of TE enrichment by the availability of an organic substrate. Comparison of inorganic and organic (e.g., pristane/phytane ratio, gammacerane index) geochemical proxies for environmental conditions permits detection of periods with elevated surface-water bioproductivity. A flourishing of algal and planktonic organisms contributed to the significant increase of TOC content at the base of Unit 2. This increase corresponds to the time-equivalent early Toarcian oceanic anoxic event characterized by the global occurrence of organic-rich sediments.Eine Auswahl an Spurenelementen (Mo, U, V, Cu, Ni), charakterisiert durch ihre Affinität zu reduzierenden Milieus, wurde verwendet um Variationen der vorherrschenden Redoxbedingungen während der Ablagerung der unterjurassischen Bächentaler Bitumenmergel (Sachrang-Member der Mittleren Allgäu-Formation in den Nördlichen Kalkalpen) zu untersuchen. Die Bitumenmergelabfolge wurde auf Basis dieser Spurenelementdaten in drei Einheiten unterteilt. Anorganisch-geochemische Parameter reflektieren wechselnde Umweltbedingungen während der Ablagerung der Bitumenmergel. Der untere und der obere Bereich (Units 1 und 3) der Bächentaler Bitumenmergel wurden unter suboxischen bis teils anoxischen Bedingungen abgelagert. Die Anreicherung der Spurenelemente im Sediment erfolgte durch siliziklastischen Eintrag, diagenetische Prozesse und Akkumulation von organischem Material. Maximalgehalte an Spurenelementen und von organischem Detritus (bis zu 13 %) bestätigen durchgehend anoxische Bedingungen während der Ablagerung des Mittelteils des Profils (Unit 2). Die Fixierung der Spurenelemente im Sediment erfolgte in diesem Bereich ausschließlich durch Adsorption an organischem Material. Folglich war die Verfügbarkeit von organischem Material der limitierende Faktor für die Spurenelementanreicherung. Der Vergleich der anorganisch-geochemischen und organisc...

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Evaluating the temporal link between the Karoo LIP and climatic–biologic events of the Toarcian Stage with high-precision U–Pb geochronology

Cited by 154 publications

References 57 publications

The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life

The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life

A new grand mean palaeomagnetic pole for the 1.11 Ga Umkondo large igneous province with implications for palaeogeography and the geomagnetic field

Redox conditions and depositional environment of the Lower Jurassic Bächental bituminous marls (Tyrol, Austria)

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