Assembly, configuration, and break-up history of Rodinia: A synthesis

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Global continental and ocean basin reconstructions since 200 Ma

New investigations of the Southwest Indian and Arctic ridges reveal an ultraslow-spreading class of ocean ridge that is characterized by intermittent volcanism and a lack of transform faults. We find that the mantle beneath such ridges is emplaced continuously to the seafloor over large regions. The differences between ultraslow- and slow-spreading ridges are as great as those between slow- and fast-spreading ridges. The ultraslow-spreading ridges usually form at full spreading rates less than about 12 mm yr-1, though their characteristics are commonly found at rates up to approximately 20 mm yr-1. The ultraslow-spreading ridges consist of linked magmatic and amagmatic accretionary ridge segments. The amagmatic segments are a previously unrecognized class of accretionary plate boundary structure and can assume any orientation, with angles relative to the spreading direction ranging from orthogonal to acute. These amagmatic segments sometimes coexist with magmatic ridge segments for millions of years to form stable plate boundaries, or may displace or be displaced by transforms and magmatic ridge segments as spreading rate, mantle thermal structure and ridge geometry change.

An ultraslow-spreading class of ocean ridge

Patterns in the spatial distribution of organisms provide important information about mechanisms that regulate the diversity of life and the complexity of ecosystems. Although microorganisms may comprise much of the Earth's biodiversity and have critical roles in biogeochemistry and ecosystem functioning, little is known about their spatial diversification. Here we present quantitative estimates of microbial community turnover at local and regional scales using the largest spatially explicit microbial diversity data set available (> 10(6) sample pairs). Turnover rates were small across large geographical distances, of similar magnitude when measured within distinct habitats, and did not increase going from one vegetation type to another. The taxa-area relationship of these terrestrial microbial eukaryotes was relatively flat (slope z = 0.074) and consistent with those reported in aquatic habitats. This suggests that despite high local diversity, microorganisms may have only moderate regional diversity. We show how turnover patterns can be used to project taxa-area relationships up to whole continents. Taxa dissimilarities across continents and between them would strengthen these projections. Such data do not yet exist, but would be feasible to collect.

Spatial scaling of microbial eukaryote diversity

Rifting, lithosphere breakup and volcanism: Comparison of magma-poor and volcanic rifted margins

Most models of melt generation beneath mid-ocean ridges predict significant reduction of melt production at ultraslow spreading rates (full spreading rates &<20 mm x yr(-1)) and consequently they predict thinned oceanic crust. The 1,800-km-long Arctic Gakkel mid-ocean ridge is an ideal location to test such models, as it is by far the slowest portion of the global mid-ocean-ridge spreading system, with a full spreading rate ranging from 6 to 13 mm x yr(-1) (refs 4, 5). Furthermore, in contrast to some other ridge systems, the spreading direction on the Gakkel ridge is not oblique and the rift valley is not offset by major transform faults. Here we present seismic evidence for the presence of exceptionally thin crust along the Gakkel ridge rift valley with crustal thicknesses varying between 1.9 and 3.3 km (compared to the more usual value of 7 km found on medium- to fast-spreading mid-ocean ridges). Almost 8,300 km of closely spaced aeromagnetic profiles across the rift valley show the presence of discrete volcanic centres along the ridge, which we interpret as evidence for strongly focused, three-dimensional magma supply. The traces of these eruptive centres can be followed to crustal ages of approximately 25 Myr off-axis, implying that these magma production and transport systems have been stable over this timescale.

Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge

The Eastern Barents, Kara, Laptev, East Siberian seas and the western Chukchi Sea occupy a large part of the Eurasian Arctic epicontinental shelf in the Russian Arctic. Recent studies have shown that this huge region consists of over 40 sedimentary basins of variable age and genesis which are thought to bear significant undiscovered hydrocarbon resources. Important tectonic events controlling the structure and petroleum geology of the basins are the Caledonian collision and orogeny followed by Late Devonian to Early Carboniferous rifting, Late Palaeozoic Baltica–Siberia collision and Uralian orogeny, Triassic and Early Jurassic rifting, Late Jurassic to Early Cretaceous Canada Basin opening accompanied by closure of the South Anyui Ocean, the Late Mesozoic Verkhoyansk–Brookian orogeny and Cenozoic opening of the Eurasia Oceanic Basin. The majority of the sedimentary basins were formed and developed in a rift and post-rift setting and later modified through a series of structural inversions. Using available regional seismic lines correlated with borehole data, onshore geology in areas with no exploration drilling, and recent Arctic-wide magnetic, bathymetry and gravity grids, we provide more confident characterization of the regional structural elements of the Russian Arctic shelf, and constrain the timing of basin formation, structural styles, lithostratigraphy and possible hydrocarbon systems and petroleum play elements in frontier areas.

Tectonic history and petroleum geology of the Russian Arctic Shelves: an overview

Arctic lithosphere — A review

The paper summarizes the results of geological and geophysical studies of the Siberian Arctic Shelf (Laptev, East Siberian and Chukchi seas), which is one of the largest continental shelves on Earth. This region consists of as many as 22 significant sedimentary basins of variable age and genesis which are expected to bear significant undiscovered volumes of hydrocarbons. Two major groups of the basins are identified based on the age of the underlying crustal basement: (1) post-Hauterivian/Barremian basins resting on the Late Mesozoic folded basement; and (2) older (Late Palaeozoic to Early Mesozoic?) basins preserved outboard of the Late Mesozoic deformational front in the northern part of the East Siberian and Chukchi seas. At least two significant tectonic events caused the overall tectonic pattern of the shelf as well as formation and structural styles of its individual crustal domains and the sedimentary basins: (1) Late Mesozoic convergence and subsequent collision of the Arctic Alaska–Chukchi Microplate with the Verkhoyansk–Kolyma/Omolon margin of the North Asia Continent around 130–125 Ma (the Verkhoyansk–Brookian compressional event); and (2) a series of Cretaceous and Cenozoic extensional events related to the origin of the Arctic oceanic basins. Based on 2D regional multichannel seismic reflection data constrained by onshore geology, plate tectonic models and inter-regional correlations, as well as on gravity and magnetic grids, the structural styles, lithostratigraphy and possible hydrocarbon systems of the offshore sedimentary basins are considered.

https://mem.lyellcollection.org/content/memoirs/35/1/819.full.pdf

Chapter 25 Tectonic setting, structure and petroleum geology of the Siberian Arctic offshore sedimentary basins

The vast Eurasian Arctic epicontinental shelf and adjoining mainland has a very complex structure and tectonic history as a result of a series of continent–continent collisions, accretion of terranes and crustal extension phases during Neoproterozoic and Phanerozoic times. Significant parts of major Eurasian fold belts extend far north into the Arctic below thick infill of post-orogenic sedimentary basins, where their architecture remains highly disputed. Large Eurasian Arctic sedimentary basins formed as a result of orogenic collapse, back-arc extension, or intracontinental extension associated with the breakup of the Laurussia, Laurasia, Pangea and Eurasia supercontinents. There are over 40 sedimentary basins of variable age and genesis which are thought to bear significant undiscovered hydrocarbon resources in the region. This article reviews the current state-of-knowledge of Eurasian Arctic tectonics and highlights questions that remain to be addressed. The overall focus is on the Russian sector of the Arctic being less known to a broad geoscience community.

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Sergey S. Drachev

Papers

Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge

Tectonic history and petroleum geology of the Russian Arctic Shelves: an overview

Arctic lithosphere — A review

Chapter 25 Tectonic setting, structure and petroleum geology of the Siberian Arctic offshore sedimentary basins

Fold belts and sedimentary basins of the Eurasian Arctic