Planform sinuosity of Proterozoic rivers
22
Citation
208
Reference
10
Related Paper
Citation Trend
Abstract:
Lacking evidence for fluvial lateral-accretion elements in early Palaeozoic systems has been ascribed to an absence of binding by rooted vegetation on subaerial landscapes. Transposing this thesis to earlier geological times, it has been proposed that, likewise, Precambrian landscapes could not have sustained highly sinuous fluvial networks. This paradigm has been hardly ever tested for the Proterozoic, a shortcoming addressed here through review of selected outcrop data and remote sensing of modern sinuous channel-flow configurations. Five sedimentary rock units deposited on Laurentia between 1.6 to 0.7 Ga record diverse palaeogeographic and tectonic settings and yield evidence of lateral accretion and planform sinuosity in fluvial channels over a full range of developmental stages. In the absence of vegetation, multiple processes interacted at craton to channel-reach scales, setting conditions favourable for self-sustained lateral accretion and thus sinuosity. Discharge modulation in perennial channels is interpreted to have had an overriding role, owing to craton-scale catchments capable of sustaining year-round flows or favourable climate settings. Steady sediment supply and local channel-bank strengthening limited braiding, allowing for narrow hydraulic profiles with flow configurations favourable to lateral accretion. Less than 15% of current literature on Proterozoic fluvial rocks reports reliable directional data on palaeoflows and stratal accretion, a bias that undermines literature compilations aimed at gauging the relevance or insignificance of pre-vegetation lateral accretion. Fluvial deposits aggraded on unvegetated landmasses prior to the late Ordovician can only be assessed when comprehensive information on palaeoflow and bar accretion becomes available. The authors thus underline that a lack of evidence for early Palaeozoic lateral-accretion sets should not be used to support the inference that meandering fluvial planforms were a rare occurrence in earlier geological times.Keywords:
Sinuosity
Cite
Citations (0)
An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.
Cite
Citations (0)
A small assemblage of primitive microscopic fossils is here reported for the first time from the lower part of the Belcher Group in Hudson Bay. The microbiota includes chains and clumps of bacteria, and filamentous and spheroidal structures of probable algal or fungal affinities. In addition, a variety of isolated and clustered spheroids and other structures of probable biologic origin is present. The structures are more than 1600 m.y. old, and occur in a black chert associated with thick dolomite beds considered to be of Aphebian (Early Proterozoic) age. Morphologically comparable Precambrian microfossils occur in the Gunflint Formation (Early Proterozoic, Ontario) and the Bitter Springs Formation (Late Proterozoic, central Australia).
Acritarch
Cite
Citations (38)
Summary A new stratigraphic scale of the USSR Precambrian officially adopted by the All-Union Precambrian Meeting in Ufa (1977) and approved by the National Stratigraphic Committee (1978) is discussed. Archean and Proterozoic have been distinguished in the Precambrian, the boundary between being 2600 Ma. Proterozoic is subdivided into the Lower- and Upper-Proterozoic with the boundary between them 1650 Ma. Riphean and Vendian are distinguished in the Upper Proterozoic. More detailed subdivisions of the Upper Proterozoic are Burzyanian, Yurmatian, Karatavian, Kudashian and Vendian. Lithological and palaeontological characteristics of these subdivisions and their radiometric age are given.
Riphean
Radiometric dating
Cite
Citations (18)
Cite
Citations (0)
Abstract. Precambrian glaciations appear to be confined to two periods, one in the early Proterozoic between 2.5 and 2 Gyears BP (Before Present) and the other in the late Proterozoic between 1 and 0.57 Gyear BP. Possible reasons for these broad features of the Precambrian climate have been investigated using a simple model for the mean surface temperature of the Earth that partially compensates for the evolution of the Sun by variations in the atmospheric CO2 content caused by outgassing, the formation of continents and the weathering of the Earth's land surface. It is shown that the model can explain the main changes in the Precambrian climate if the early Proterozoic glaciations were caused by a major episode of continental land building commencing about 3 Gyears BP while the late Proterozoic glaciations resulted from biologicallyenhanced weathering of the land surface due to the proliferation of life forms in the transition from the Proterozoic to the Phanerozoic that began about 1 Gyear BP.
Early Earth
Cite
Citations (17)
Cite
Citations (10)
The anastomosing fluvial system was considered as the same term of the braided fluvial system. Smith and others have recognized the difference between them. They described the anastomosing fluvial system as low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate vegetated islands, and established a depositional model of anastomosing fluvial system based on their great
Sinuosity
Cite
Citations (1)