Gondwana

About: Gondwana is a research topic. Over the lifetime, 6078 publications have been published within this topic receiving 263050 citations. The topic is also known as: Gondwanaland.

Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike stratigraphic continuity of the northern Indian margin

Abstract: New mapping in eastern Bhutan, in conjunction with U-Pb detrital zircon and δ 13 C data, defi nes Lesser Himalayan tectonostratigraphy. The Daling-Shumar Group, 2–6 km of quartzite (Shumar Formation) overlain by 3 km of schist (Daling Formation), contains ~1.8–1.9 Ga intrusive orthogneiss bodies and youngest detrital zircon peaks, indicating a Paleoproterozoic deposition age. The Jaishidanda Formation, 0.5– 1.7 km of garnet-biotite schist and quartzite, stratigraphically overlies the Daling Formation beneath the Main Central thrust, and yields youngest detrital zircon peaks ranging from ~0.8–1.0 Ga to ca. 475 Ma, indicating a Neoproterozoic–Ordovician(?) deposition age range. The Baxa Group, 2–3 km of quartzite, phyllite, and dolomite, overlies the DalingShumar Group in the foreland, and yields ca. 0.9 Ga to ca. 520 Ma youngest detrital zircon peaks, indicating a Neoproterozoic– Cambrian(?) deposition age range. Baxa dolo mite overlying quartzite containing ca. 525 Ma detrital zircons yielded δ 13 C values between +3‰ and +6‰, suggesting deposition during an Early Cambrian positive δ 13 C excursion. Above the Baxa Group, the 2–3 km thick Diuri Formation diamictite yielded a ca. 390 Ma youngest detrital zircon peak, suggesting correlation with the late Paleo zoic Gondwana supercontinent glaciation. Finally, the Permian Gondwana succession consists of sandstone, siltstone, shale, and coal. Our deposition age data from Bhutan: (1) reinforce suggestions that Paleoproterozoic (~1.8–1.9 Ga) Lesser Himalayan deposition was continuous along the entire northern Indian margin; (2) show a likely east ward continuation of a Permian over Cambrian unconformity in the Lesser Himalayan section identifi ed in Nepal and northwest India; and (3) indicate temporal overlap between Neoproterozoic–Paleozoic Lesser Himalayan (proximal) and Greater Himalayan–Tethyan Himalayan (distal) deposition.

Reconciling fossils and molecules: Cenozoic divergence of cichlid fishes and the biogeography of Madagascar

Abstract: Aim The biogeographical origins of the extant vertebrates endemic to Madagascar are largely unsolved, but have often been related to vicariance in the context of fragmentation of the supercontinent Gondwana in the Mesozoic. Such hypotheses are especially appealing in the case of cichlid fishes, which show phylogenetic relationships reflecting the temporal successions of the breakup of Gondwana. We used molecular clock data to test this assumption. Location Fragments of the 16S rRNA gene and of the nuclear Tmo-4C4 locus, partly obtained from Genbank from South American, African, Malagasy and Indian cichlids were analysed. Methods Based on monophyletic cichlid radiations in African lakes, we calibrated a molecular clock. The obtained rates were used to estimate the age of divergence of the major cichlid clades. Results The results agreed better with a Cenozoic than with a Mesozoic divergence, and were in accordance with the fossil record. Sequence divergences of the 16S and 12S rRNA genes of most lineages of Malagasy terrestrial and freshwater vertebrates from their non-Malagasy sister groups were below saturation and many were relatively similar to those of cichlids. Main conclusions A Cenozoic dispersal from continental landmasses may explain the origin of most extant Malagasy vertebrate groups better than a Jurassic/Cretaceous vicariance.

Stratigraphy and tectonics of Permo-Triassic basins in the Netherlands and surrounding areas

Abstract: This thesis addresses different aspects of the geological development during the Permian and Triassic (300 to 200 Ma) of the Netherlands and surrounding areas. The study area encompasses the Southern Permian Basin (SPB), a large intracratonic basin stretched out from the United Kingdom in the west to Lithuania in the east. This study revealed that, rather than one basin, the SPB actually comprised three basins, separated by subtle swells. The basins each originated differently with specific subsequent histories High-resolution stratigraphic correlations of the Permo-Triassic interval were carried out to (i) align the various stratigraphic schemes, and (ii) to define a single basin-wide stratigraphic framework for the SPB (Chapter 1). High resolution sequence stratigraphy as a correlation tool is presented in Chapter 2. Two new tectonic pulses in the Late Permian (Zechstein) are presented in Chapter 3. A detailed overview of the stratigraphy and tectonics of the Permian and Triassic in the Netherlands is presented in Chapter 4. The regional synthesis is presented in Chapter 5. It includes a series of new, high-resolution, paleogeographic maps illustrating the current insights in basin evolution. One of the recommendations of this study is a revision and redefinition of some units in the Permian and Triassic lithostratigraphy of the Netherlands (Appendix 1). Following the Variscan Orogeny, at the end of the Carboniferous (300 Ma), the Netherlands was situated in the interior part of the super-continent Pangea, north of the Alpine-style Variscan Mountain chain, which formed as a result of the accretion of the Gondwana to Laurussia plates. These mountains supplied the bulk of the sediments to the Netherlands until Mid Triassic times; further, they formed a barrier for humid air masses from the Tethys. Climatic conditions were arid to semi-arid for most of the Middle Permian to Middle Triassic, becoming slightly more humid during the Late Triassic. Marine incursions in the basin have been recorded in the Late Permian from the north, and from the late Early Triassic onwards from the Tethys. Late Carboniferous to Middle Permian rift/wrench tectonics triggered slab detachment and extrusive volcanism during a prolonged period (Early to Middle Permian). These processes resulted in the collapse of the Variscan Mountains. Initially molasse-type sediments were deposited, followed by eolian sediments and salts. Subsidence was essentially driven by thermal lithosphere contraction. Desert sediments (Rotliegend) were deposited during the Middle Permian, followed by cyclic evaporites of the Zechstein (Late Permian). The Triassic evolution is dominated by a complex interplay of climate, transgressions and short-lived pulses of rift tectonics. Cyclic sedimentation in the EarlyTriassic is attributed to climatic Milankovitch cyclicity. From the Middle Triassic onwards, rifting concentrated in the Central North Sea, Horn and Gluckstadt Grabens. During the pulses, up to 4,500 m of salt and fine-grained clastics accumulated here. Late Triassic compression, related to the closure of the Paleo-Tethys, resulted in the doming of Fennoscandia. Delta systems from the this high built out southward over the SPB during relatively humid periods. A major marine transgression flooded the area during the youngest part of the Triassic.

Timing and Duration of the Calc‐Alkaline Arc of the Pampean Orogeny: Implications for the Late Neoproterozoic to Cambrian Evolution of Western Gondwana

Abstract: The Pampean Orogen in the Eastern Sierras Pampeanas contains two paired magmatic belts, an eastern calc‐alkaline magmatic belt and a western peraluminous granite/high‐grade metasedimentary belt. The relationship between the two belts and their relative timing are constrained through new U‐Pb zircon ages on granodiorites, monzogranites, and associated volcanic rocks from Sierra Norte and the easternmost Sierras de Cordoba. These ages indicate that calc‐alkaline arc magmatism was active over at least a 30‐m.yr. period from 555 to 525 Ma, terminating at the same time that peraluminous magmatism and associated high‐grade metamorphism began in the adjoining metasedimentary belt (525–515 Ma). These temporal relationships and the metamorphic characteristics of the two belts appear to be in conflict with previously proposed models for the Pampean Orogeny as a continental‐collision event, but they are consistent with models that propose eastward‐dipping subduction of oceanic crust initiated at ca. 555 Ma,...