Showing papers in "Precambrian Research in 1986"

TL;DR: The radiometric results on the Anakapalle rocks are the first evidence in South India for sapphirine formation during the late Proterozoic; other South Indian localities appear to be Archaean in age.

TL;DR: This article studied alteration zones found between sedimentary rocks of the (lowest Proterozoic) Dominion and (Archean) Pongola groups and underlying granitic rocks (Transvaal, South Africa).

TL;DR: The first genuine discovery of the late Precambrian Ediacara-type metazoan remains in China was made by Ding et al. as mentioned in this paper, who described a distinct genus, Paracharnia gen. nov, based on the characteristic polyp leaves, individually freestanding on distinct leaf-stalks along the lateral sides of the median stem.

TL;DR: In this article, it was shown that the early continents formed over mantle sinks and grew rapidly between 2.7 and 3.0 Ga ago, resulting in rapid tonalite production and thus in rapid continental growth.

TL;DR: The Nama assemblage is dominated by leiosphaerid acritarchs and fragments of the ribbon-like macrofossil Vendotaenia, and small unicells and non-septate filaments interpreted as the sheaths of oscillatorian cyanobacteria occur with variable frequency throughout the subgroups, while Chuaria circularis, Bavlinella faveolata and a Comasphaeridium-like form (known from a single specimen) are found as rarer components of the biota as discussed by the authors.

TL;DR: This article used microrelief features commonly preserved in fossil permafrost horizons to provide valuable information on palaeoclimate, including indications of mean annual air temperature, seasonal temperature range, relative precipitation, and evidence for long-term (∼ 104 years) oscillations of climate.

TL;DR: In this paper, the deformation history of the SW-Swedish gneiss belt has been investigated and the principle deformation of central Sweden is suggested to be D4; the ‘Mylonite zone’ of western Sweden appears to have been initiated before D3.

TL;DR: The Subcommission on Precambrian Stratigraphy has been actively working toward an acceptable subdivision of time for more than a decade, and several recommendations, developed sequentially at formal meetings held at intervals of 2−4 years and announced in geologic journals with calls for comment and criticism, are proposed: 1) the recommendation to establish two major time units of Eon rank, Proterozoic and Archaean (Archean), separated by a time boundary at 2500 Ma, is reaffirmed; 2.

TL;DR: Wang et al. as discussed by the authors investigated the late Precambrian Liulaobei Formation, Huainan Group and the Jiuliqiao Formation, Feishui Group in the HuAINAN district, northern Anhui Province, China are further investigated through this progress report.

TL;DR: The lower Proterozoic of the Olary Block is divided into five rock suites defining a conformable stratigraphic sequence correlated with the Willyama Supergroup of the Broken Hill Block.

TL;DR: In this paper, the ages of the three analysed granites suggest that the Napier Complex is the product of at least two temporally discrete episodes of continental crust formation, possibly related to emplacement of magma into the lower crust.

TL;DR: The Waterval Onder Clay Paleosol as mentioned in this paper was found to have formed on Hekpoort Basalt and showed compositional variation and berthierine-rich laminae interpreted as relict bedding.

TL;DR: Petrologic-geochemical studies of the Kola superdeep and other deep borehole sections drilled in the Precambrian basement of the East-European Platform are discussed in this article.

TL;DR: In this paper, carbon and oxygen isotope analyses performed on sedimentary carbonates, organic carbon (kerogen), and structurally bound CO2−3 groups of carbonate fluorapatite (francolite) from four widely separated Indian phosphorite provinces have shown that each of the deposits is characterized by specific (basically facies-dependent) distribution patterns of δ 13Ccarb, δ 14Ocarb and δ 15Capat.

TL;DR: The Kaap Valley tonalite pluton is one of the largest and oldest mafic-trondhjemite gneiss plutons in the immediate environs of the Barberton greenstone belt.

TL;DR: In this paper, a large number of samples of volcanic rocks from boreholes in the Klerksdorp area, Western Transvaal, indicate that the chemical compositions of the lavas are largely unmodified by secondary processes and can be used for classification, stratigraphic studies and petrogenetic interpretation.

TL;DR: In the Yilgarn Block, Western Australia as discussed by the authors, sediment-filled grabens are associated with calc-alkaline granitoid emplacement, which was probably contemporaneous with felsic volcanic activity.

TL;DR: In this article, the authors interpreted profiles of elemental concentrations for four Precambrian paleosols, two developed on basalt and two on granodiorite, and found that the basaltic paleoostosols appear to be the erosional remnants of originally thick soil-saprolite regoliths.

TL;DR: The Precambrian supracrustal rocks of Finland were produced during four main evolutionary stages: (1) late Archaean (Pre-Svecokarelidic) greenstone-schist evolution on an unknown basement; (2) at least four cycles of early Proterozoic (Karelian) continental-epi/pericontinental sedimentation and volcanism on or next to the cratonized late archaean basement; and (3) early Svecofennian eugeosynclinal evolution west of, or in

TL;DR: The Boksputs and Upington sequences of the Areachap Group, present along the eastern margin of the Namaqua mobile belt in southern Africa, contain amphibolites with chemical properties which suggest that they are the metamorphic products of arc related precursors as discussed by the authors.

TL;DR: In this paper, a critical review on the previously supposed Cyclomedusa and other medusoids from the upper Precambrian in southern Liaoning, China demonstrates that they are cyclomedusa -like pseudofossils made by upwards escaping gas bubbles and water currents.

TL;DR: The Bani Ghayy group as discussed by the authors is a series of volcanosedimentary successions associated with an older active continental margin and was deposited in three separate, elongate, fault-bounded grabens, each containing coarse fanglomerate and fan delta deposits along the margin and proximal greywackes toward the centre.

TL;DR: In this article, three types of zircons from an albite diabase sill within the Kiruna Greenstone Group have been investigated to determine their age and order of crystallization, and the results are consistent with the proposed chronostratigraphy of the Jatulian formations in Finland (e.g., Simonen; Merilainen).

TL;DR: The early Proterozoic supracrustal rocks of the Salida area of central Colorado consist of strongly bimodal sequences of volcanogenic rocks as mentioned in this paper, which are distinctly tholeiitic, display a strong iron-enrichment trend, and typically contain less than 50% SiO 2.

TL;DR: The Nsuze Group in southeast South Africa represents an important volcano-sedimentary succession that is markedly different compositionally and lithologically from older and contemporaneous sequences elsewhere in southern Africa as discussed by the authors.

TL;DR: In this paper, the Loch Eil division of the Proterozoic Moine Succession was identified as a shallow marine environment, and three sedimentary facies were identified: siltstone, interbedded siltstones and sandstone.

TL;DR: The Narracoota Volcanics, part of the early Proterozoic Glengarry Group on the northern margin of the Yilgarn Block, were deformed and metamorphosed between 1.7 and 1.8 Ga ago and then covered by sediments of the Padbury Group.

TL;DR: The Koperberg Suite as discussed by the authors is a swarm of anorthositic/dioritic intrusives, collectively termed the koperberg suite, scattered over an area of about 3000 km2 in the northwestern Cape Province (Namaqualand), South Africa.

TL;DR: Within early Archaean to early Proterozoic pelites and volcanics of the Kaapvaal Craton, rocks with above 20% Al2O3 are widely distributed as mentioned in this paper.

TL;DR: A complex caliche profile and numerous widespread zones of carbonate cement occur in a thick sequence of fluvial siliciclastic sandstones and conglomerates that were deposited in the Lake Superior basin during and after continental basaltic volcanism as discussed by the authors.