Precambrian Sedimentary Basins Research Articles

U-Pb geochronology of monazite in Precambrian tuffs reveals depositional and metamorphic histories

Uranium-lead geochronology of zircon in felsic tuffs plays a key role in the development of chronostratigraphic frameworks for sedimentary successions. This is particularly true for Precambrian basins, where biostratigraphy is of limited use for age determination or stratigraphic correlation. Although zircon is widely used to date tuffs, it can yield null results due to the presence of xenocrystic populations or isotopic resetting. Other potential U-Pb chronometers, such as monazite, which also crystallize from felsic magmas, are largely unreported from felsic tuff layers. Consequently, there has been a lack of studies to evaluate the potential of monazite for U-Pb isotope geochronology of tuffs. We present results of in situ U-Pb ion microprobe dating of monazite that co-exists with zircon in felsic tuffs from two Precambrian basins: the Earaheedy Basin (Frere Formation) in Western Australia and the Bushveld Basin (Lephala Formation) in southern Africa. We show that 207Pb/206Pb ages from monazite in felsic tuffs from the Frere Formation (1891 ± 9 Ma) and the Lephala Formation (2307 ± 9 Ma) are identical to zircon ages from the respective tuffs. Also, monazite in the Bushveld tuff preserves additional information, including a chronological fingerprint of the volcanic source (2.4–2.5 Ga xenocrysts) and the timing of low-grade metamorphism (2.16 Ga overgrowths). The ca. 2.16 Ga low-grade metamorphism identified in the Bushveld Basin is reminiscent of that widely recorded in the Pilbara Craton, Western Australian, lending support to arguments for a connection between the Kaapvaal and Pilbara cratons. Igneous and low-grade metamorphic monazites are readily distinguished based on texture and chemistry. Our study demonstrates that monazite can be used to accurately date felsic tuffs, offering a powerful tool for constraining depositional and metamorphic histories of Precambrian sedimentary basins.

The characteristics of Precambrian sedimentary basin and the distribution of deep source rock: A case study of Tarim Basin in Neoproterozoic and source rocks in Early Cambrian, Western China

Abstract Based on outcrops of the whole basin, drilling and seismic data, this paper makes a systematic analysis of Neoproterozoic basin stratigraphic distribution and tectonic evolution characteristics in Tarim. Under the control of the aggregation and breakup of Rodinia supercontinent, the extensional sedimentary basin formed with North-South differences in the Neoproterozoic, separated by the middle ancient land. There is a sedimentary basin in the north, east-west banded, with two thickness centers, Aksu region in northwest and Manjiaer-Kuruketage region in northeast and maximum thickness about 2 500−3 500 m. There are two sedimentary basins in the south, north-east banded, with two thickness centers, Yecheng and Hetian with maximum thickness about 1 500−2 000 m. The evolution of the basin can be divided into two stages, rift in Nanhuan (Cryogenian) and depression in Sinian (Ediacaran), the latter stage deposits larger range but with thinner thickness of strata. Its main rock types contain volcanic rock, clastic rock, moraine rock and carbonate rock. The distribution of source rock during Early Cambrian period is mainly controlled by the development characteristics of the Neoproterozoic sedimentary basin.

Chapter 1 Precambrian basins of India: stratigraphic and tectonic context

The Indian shield represents a vast repository of the Precambrian geological record. The Precambrian sedimentary basins were developed on four major Archaean nuclei (Dharwar, Bastar, Singhbhum and Aravalli–Bundelkhand; Fig. 1.1) and are comparable to those of Australia, South Africa, Canada and Brazil in scale and importance for global studies of Precambrian crustal evolution. Some of the Indian basinal successions, as elsewhere, contain valuable economic resources. Notwithstanding their global relevance, many aspects of the Indian Precambrian basins and even entire basins are not well known to international readers. Although specialist papers, a book (Naqvi & Rogers 1987) and special publications (e.g. Mazumder & Saha 2012) have been written by several authors on specific aspects of the Precambrian geology of India, a comprehensive account of the time–space distribution of the Precambrian supracrustal successions is lacking; in particular, the interrelation between tectonics and sedimentation, and the similarities and dissimilarities of their evolutionary histories with other comparable successions in other parts of the world are yet to be addressed in any detail. The purpose of the present memoir is to fill in this knowledge gap. In addition, the memoir will assess the potential mineral resources of Indian Proterozoic basins and integrate piecemeal information to provide a comprehensive picture of Indian cratonic evolution during the Precambrian. Fig. 1.1. Sketch map showing four Archaean nuclei in India. Note Proterozoic sedimentary basins (dark grey patches) and the large Deccan basaltic province. SGT, Southern Granulite Terrain; NFB, Nallamalai fold belt; CITZ, Central Indian Tectonic Zone; PG, Pranhita Godavari Valley; Ab, Abujhmar Basin; Am, Ampani Basin; Bh, Bhima Basin; Ch, Chattisgarh Basin; Idv, Indravati Basin; Kal, Kaladgi Basin; Suk, Sukma Basin; Ban, Bangalore; Cd, Cuddapah; Hyd, Hyderabad; K, Kurnool; Kh, Khariar; Nel, Nellore; Ong, Ongole; Vij, Vijaywada (after Saha & Mazumder 2012). The content of the memoir has been divided …

Chapter 3 The Archaean and Proterozoic history of Peninsular India: tectonic framework for Precambrian sedimentary basins in India

Abstract The Precambrian geological history of Peninsular India covers nearly 3.0 Ga. The Peninsula is an assembly of five different cratonic nuclei known as the Aravalli–Bundelkhand, Eastern Dharwar, Western Dharwar, Bastar and Singhbhum cratons along with the Southern Granulite Province. Final amalgamation of these elements occurred either by the end of the Archaean (2.5 Ga) or by the end of the Palaeoproterozoic ( c. 1.6 Ga). Each of these nuclei contains one or more sedimentary basins (or metasedimentary basins) of Proterozoic age. This chapter provides an overview of each of the cratons and a brief description of the Precambrian sedimentary basins in India that form the focus of the remainder of this book. In our view, it appears that basin formation and subsequent closure can be grossly constrained to three separate intervals that also broadly correspond to the assembly and disaggregation of the supercontinents Columbia, Rodinia and Gondwana. The oldest Purana-I basins developed during the 2.5–1.6 Ga interval, Purana-II basins formed during the 1.6–1.0 Ga interval and the Purana-III basins formed during the Neoproterozoic–Cambrian interval.

Precambrian sedimentary basins of India: an appraisal of their petroleum potential

Abstract The Indian Proterozoic Super Basins were part of the Northern Rim of Gondwanaland prior to its break-up along six major radial fractures. The Proterozoic rocks of these basins are extensively exposed in the northern as well as the southern parts of the Indian Peninsula. Based on recently conducted geochemical and seismic surveys within these basins, followed by well drilling in the Son Valley, Ganga Valley, and the Bikaner–Nagaur basin, it is concluded that hydrocarbons have been generated within these basins and conditions conducive to hydrocarbon accumulation exist within them. The discovery of gas within Son Valley has indicated the existence of an active Mesoproterozoic petroleum system that is likely to have continued up to Infracambrian times. Based on the correlation of Indian Proterozoic Super Basins with their analogous Chinese and Australian basins, it appears that elements of a similar petroleum system exist within these basins, together with the possibility of an active Ordovician–Silurian petroleum system within the northernmost Ganga Valley Vindhyans, where sedimentation continued up to the lower Devonian. Modelling and empirical data show that the Chambal Valley, as well as the probably trap-concealed Vindhyans, underwent intense wrenching during Neoproterozoic times, accompanied by good entrapment conditions. Even the peninsular SW Cuddapah Superbasin also appears worth exploring as an element of the Meso–Neoproterozoic petroleum system.

Manganese deposits: Communication 1. Genetic models of manganese ore formation

Major regularities in the formation of manganese rocks and ores have been established on the basis of available published and original data. The proposed genetic classification of main manganese deposits (with model examples) is as follows: sedimentary-diagenetic (Nikopol, Bol’she-Tokmak; Ukraine), (volcanogenic) hydrothermal-sedimentary (deposits of the Atasui area, Kazakhstan; Magnitogorsk Trough, South Urals), epigenetic (catagenetic) (deposits of the Kalahari manganese ore field, South Africa; Usinsk deposit, Kuznetsk Alatau), and supergene (residual, infiltrational, cavern filling, and pisolitic deposits in India, Brazil, South Africa, and Australia). The results suggest the following conclusions: (1) all primary manganese rocks and ores at the known deposits are hydrothermal- and diagenetic-sedimentary formations of marine environments; (2) manganese concentrations achieve the size of deposits at postsedimentary stages of the initial manganiferous sediment and manganese rock transformation (diagenesis, catagenesis, and retrograde diagenesis); (3) indispensable participation of the isotopically light carbon dioxide related to the destruction of organic matter (OM) is a characteristic feature of manganese carbonate formation during diagenesis; and (4) the role of organic carbon in manganese ore formation becomes notable since early stages of Mn accumulation in the Precambrian sedimentary basins (terminal Archean-initial Early Proterozoic).

Facies Associations of Riphean Sedimentary Sequences

Large-scale facies associations typical of intra- and pericratonic Riphean sections of the Volga–Ural region, western slope of the Urals, Timan–Pechora region, Kola Peninsula, outer and inner parts of the Siberian, North American, and Indian platforms are considered. The reconstruction of their lateral and vertical relationships makes it possible to reconstruct principal trends in the evolution of late Precambrian sedimentary basins. Recommended special studies aimed at the restoration of spatial architecture of associations retained in fragments of Riphean sedimentary basins could yield a substantially new information on the basin filling. Such approach has important implications for estimation of the potential of late Precambrian sedimentary basins with respect to the exploration for mineral resources including hydrocarbons.

The tectonic evolution of the Precambrian metamorphic rocks of the Adola Belt (Southern Ethiopia)

The Adola area of Southern Ethiopia comprises two main tectono-stratigraphic units which have undergone polyphase deformation and regional metamorphism. The first one consists of an heterogeneous sequence of high grade and complexly deformed gneisses which are intruded by syn- and post-tectonic granitoids; the second unit comprises an extemsive N-S trending volcano-sedimentary sequence and ultrabasic rocks of greenschist to amphibolite facies metamorphic grade and relatively simple deformation state. The contact between the two units is usually extensively tectonized. Recent structural analysis of the Adola Belt shows that: (1) the tectonic evolution started with extensional faulting and development of basin into which volcano-sedimentary sequence and associated ultrabasic suites were deposited, (2) the first stage compressional event led to the inversion of the Precambrian sedimentary basin and development of thrust tectonics and associated folding phase with sub-horizontal axes and (3) the late-stage in the tectonic evolution is dominated by N-S trending sub-vertical ductile strike-slip shear zones and related sub-vertical folds. The thrust and strike-slip shear belts are up to 500 m wide and occur both within the units defined above and along their boundaries reactivating previous N-S trending discontinuities. These reactivation events locally segment the sequence into five fault-bound tectonic domains each with different deformation style. The shear zones are characterized by the extensive development of mylonitic fault rocks which carry strong superimposed stretching lineations indicating their respective tectonic transport directions. Sense of displacement in all types of shear zones is indicated by shear criteria. The field character of the belt suggests that it is underlain by sialic basement and that it developed from an ensialic basin and not from Wilson cycle plate tectonic processes.

Botryococcus—A planktonic green alga, the source of petroleum through the ages: Transmission electron microscopical studies of oil shales and petroleum source rocks

The hydrocarbon secreting alga Botryococcus has been identified in organic remains of sediments ranging from Precambrian to Recent, and is believed to have been a major source material for petroleum generation throughout the geological time. In some petroleum source rocks of Lower Palaeozoic and Precambrian age, identification of the alga is only possible by electron microscopy. Transmission electron microscopy (TEM) has been used in the present study to identify microstructures of the algal remains in a range of oil shales and petroleum source rocks. It has been established that Botryococcus is the predominant alga in the Kukersite oil shale of Estonia. Similarly, the alga has been shown to be a major contributor to petroleum source rocks in Cambrian and Precambrian sedimentary basins in Australia. TEM has been applied to observations of Botryococcus in torbanites and to products from simulated maturation experiments on torbanite. A comparison with algal remains from Cambrian and Precambrian sediments ranging from undermature to overmature, enabled the distinction of organic matter in various stages of oil generation. Maturation/thermal effects on alginite have been established by reflectance and fluorescence, and compared with experimental results.

Reconstruction of the Precambrian sedimentary basin in the granulite belt of Sri Lanka

Of the two major Precambrian lithological divisions of Sri Lanka, viz. the Highland Group and the Vijayan Complex, the former shows evidence of a highly metamorphosed assemblage of marine-deposited volcanic, volcanoclastic and sedimentary rocks. Using the available major- and trace-element data for the rocks of the Highland Group, an attempt has been made to elucidate the primary features of the depositional environment of the Highland Group in the granulite belt of Sri Lanka. The garnet gneisses belonging to the Khondalite suite have an overall sedimentary parentage, the original clastic sediments being derived from a continental crust. The garnet gneisses of the Highland Group are comparable to early Proterozoic—Archaean shales, a significant depletion in total Fe and a slight Mn enrichment being evident. The charnockites and allied rocks which form an integral part of the Highland Group correspond to an igneous differentiation sequence of basaltic composition. The presence of graphite closely associated with sulphides in the western part of the basin indicates an anoxic—sulphidic type of environment whereas in the eastern part, the conditions were more oxidizing with abundant dolomitic marbles, quartzites and banded Fe formations. In its entirety, the Highland Group of Sri Lanka can be interpreted as a Precambrian sedimentary basin having shelf—slope characteristics and located at a plate junction predating a continent—continent type of collision.

Evolution and subsidence of early Precambrian sedimentary basins

Many of the models for modern sedimentary basins postulate two-stage subsidence; a rapid initial subsidence due to thinning or loading of the crust, followed by a more protracted thermal stage as the lithosphere, which is thinned during the initial stage, relaxes to equilibrium thickness. The geology of a number of Archaean greenstone belts and early Proterozoic cratonic basins in South Africa may be explained by such a model. Rapidly erupted shallow marine or subaerial volcanic rocks predominate in the lower parts of sedimentary-volcanic sequences. These are thought to relate to initial subsidence as (1) accommodation of relatively thick volcanic sequences requires substantial and rapid subsidence, and (2) marginal uplift following these early volcanic intervals is consistent with viscous relaxation following the initial elastic response of the lithosphere to localized loading. Sedimentary sequences overlying initial volcanic dominated intervals may have been deposited during the ensuing phase of more widespread subsidence related to thermal relaxation of the thinned lithosphere. If so, sediment-filled subsidence of ca. 5.5 km in greenstone terrains at 3.5 and 2.6 Ga and of 7-10 km in cratonic shelf basins between 2.7 and 2.1 Ga require increases of lithosphere thickness between ca . 60 and 90 km. These minimum estimates of early Precambrian lithosphere thickness, although crude, are similar to estimates of present lithosphere thickness. In some early Precambrian basins, the cause of subsidence may have been crustal extension with development of faulted grabens that evolved into continental margins, but in cratonic shelf basins faulting did not occur during or after the initial subsidence, and some less obvious causal mechanism must be sought.

The origin of graphite of Sri Lanka

A model for the origin of graphite occurrences of Sri Lanka is discussed in the light of recent views on the geologic history of Sri Lanka. The three modes of graphite occurrences in Sri Lanka are: (i) as disseminated flakes in the country rocks, (ii) as lenses, pods and vugs, and (iii) as veins occupying fractures in rocks. The source of carbon of all three types is shown to be organic matter from microorganisms now known to have lived in Precambrian sedimentary basins. The Highland Series of Sri Lanka in which graphite is found in abundance is considered to be a Precambrian sedimentary basin filled by sandstones, limestones and shales. The continuous filling of the basin followed by deformation resulted in intense folding accompanied by metamorphism. During this process, the hitherto disseminated carbonaceous matter was mobilized in a semi-fluid state with the aid of magmatic fluids known to have pervaded the sediments during the intense folding. The vein graphite deposits were formed in the axial regions of the anticline while the graphite not pressed into pre-existing faults and fractures remained in the disseminated form.

Sedimentary basin development in the Archaean

The time history and magnitude of the subsidence in a sedimentary basin depends on the extent to which the lithosphere is thinned by stretching and on its original thickness. Hence the history and stratigraphic thickness of early Precambrian sedimentary basins, preserved as greenstone belts, should provide estimates of lithospheric thickness during the first half of the earth's history. Only the thickness of shallow-water sediments deposited without faulting is of relevance, and the best available estimates are compatible with all lithospheric thicknesses which have been suggested. The same is true of the estimates of the duration of the subsidence. Nonetheless radiometric dating can probably now provide estimates of the duration of the subsidence which are sufficiently accurate to constrain the models of the earth's thermal history if carried out for this purpose.

Geophysical Exploration for Precambrian-Related Uranium Deposits: ABSTRACT

Genetic models for uranium mineralization found at Proterozoic unconformities between fluvial sandstones and crystalline lithologies include three general geologic features: (1) structural relief at the unconformity; (2) permeable zones controlled by lithology and faulting; and (3) graphitic and sulfide-bearing zones commonly associated with mantled gneiss domes. Though radiometric surveys have been successfully used where the fluvial rocks are thin or eroded away, non-radiometric geophysical methods are commonly used in the interior parts of the sedimentary basins to detect one or more of the above geologic features to define favorable areas for uranium. In the Athasbasca basin of Canada, airborne and ground electromagnetic (EM) methods as currently used are thought to h ve a depth of exploration of 200 m. Application of these non-radiometric geophysical methods to Precambrian sedimentary basins in the United States is not likely to produce as great a depth of exploration because the fluvial cover rocks are not as geophysically transparent as the Athabasca sandstone. We suggest that two approaches be used to improve the End_Page 786------------------------------ depth of exploration and resolution of non-radiometric geophysical methods. The first approach is to use EM methods that have not been commonly used such as the controlled-source or natural-field audiomagnetotelluric method which can have a depth of exploration of several kilometers. The second approach is to use advanced geophysical interpretation methods to define responses from the alteration halos around the uranium mineralization. Advanced Induced Polarization surveys may detect such halos as evidenced by applications in Tertiary sedimentary basins. End_of_Article - Last_Page 787------------

A subdivision of the western English River subprovince

In the western pan of the Superior province, gneisses and plutonic rocks of the English River subprovince form a 100 km wide, east trending unit bound on both north and south by metavolcanic-granitic subprovinces. Recent investigations have resulted in a major twofold subdivision of the western portion of the English River subprovince. The northern part of the subprovince, termed the Ear Falls – Manigotagan gneiss belt, is characterized by a preponderance of sedimentary gneiss that records the development of a major Early Precambrian sedimentary basin. The southern part, termed the Winnipeg River batholithic belt, is a dominantly plutonic terrain with subordinate felsic gneissic rocks and minor metavolcanic and metasedimentary rocks. This latter belt records the almost complete obliteration of a greenstone terrain of unknown age and extent by felsic plutonism. Regional seismic, gravity, and magnetic data reflect the differing physical characteristics of the two bells. The Ear Falls-Manigotagan gneiss belt has a thicker granitic crust, thinner lower crust, thinner total crust, higher Bouguer gravity values, and lower intensity and shorter wavelength magnetic anomalies than the Winnipeg River batholithic bell.

The Cambrian Frontier: ABSTRACT

Precambrian fossils are no longer to be considered oddities of questionable scientific or practical value. New discoveries, new techniques, and the impact of radiometric dating on Precambrian stratigraphy make it possible to set out for the first time the sequence of fossils through Early, Middle, and Late Precambrian time. They fall into four major classes: microfossils (appearing first), stromatolites (including index fossils of economic importance), megafossils (rich faunas in Late Precambrian, with at least 25 taxa representing 6 phyla of soft-bodied organisms at one locality in Australia), and trace fossils (possibly the earliest remains of animals). These occurrences can be related to the history of the biosphere and to modern studies of biochemical evolution. Place in proper relation to the geotectonic framework of sedimentation they support the view that the search for oil should be extended beyond the Cambrian frontier into at least Late Precambrian sedimentary basins. Considerations of the definition of the base of the Cambrian and of events at that time also support this view. End_of_Article - Last_Page 341------------