Abstract This book is the final product of the Circum-Arctic Lithosphere Evolution (CALE) project. The project’s ultimate goal is to link the onshore and offshore geology in order to develop a self-consistent set of constraints for the opening of the Amerasia Basin. The circum-Arctic is divided into seven regions, each with its own research team; the teams included geophysicists and geologists working together to integrate geological and geophysical data, from onshore to offshore. This work is summarized in the 18 papers contained in this volume.

Abstract The New Siberian Islands are affected by a number of Mesozoic tectonic events. The oldest event (D1a) is characterized by NW-directed thrusting within the South Anyui Suture Zone combined with north–south-trending sinistral strike-slip in the foreland during the Early Cretaceous. This compressional deformation was followed by dextral transpression along north–south-trending faults, which resulted in NE–SW shortening in the Kotelny Fold Zone (D1b). The dextral deformation can be related to a north–south-trending boundary fault zone west of the New Siberian Islands, which probably represented the Laptev Sea segment of the Amerasia Basin Transform Fault in pre-Aptian–Albian times. The presence of a transform fault west of the islands may be an explanation for the long and narrow sliver of continental lithosphere of the Lomonosov Ridge and the sudden termination of the South Anyui Suture Zone against the present Laptev Sea Rift System. The intrusion of magmatic rocks 114 myr ago was followed by NW–SE-trending sinistral strike-slip faults of unknown origin (D2). In the Late Cretaceous–Paleocene, east–west extension (D3) west of the New Siberian Islands initiated the development of the Laptev Sea Rift System, which continues until today and is largely related to the development of the Eurasian Basin.

Abstract The Laptev Sea in the Siberian Arctic represents a unique tectonic junction of an active spreading ridge, the Gakkel Ridge in the Eurasian oceanic basin, with the Siberian Arctic continental margin. New long-offset seismic profiles acquired in recent years provide a reliable basis for deciphering the structural and seismic stratigraphic characteristics of the Laptev Rift System. The tectonic development of the Laptev Shelf represents a sequence of four phases controlled by relative plate movements: (1) intense brittle normal faulting (an initial rifting or stretching phase) affected the entire shelf in the Late Cretaceous(?)–Paleocene(?); (2) a thinning/exhumation phase resulted in exhumation of the lower continental crust and probably upper mantle in the western part of the rift system – this phase is inferred to have occurred during the Late Paleocene to Early Eocene, preceding and accompanying continental break-up in the Eurasia Basin; (3) a stalled rift phase characterized by either a dramatically reduced rate of extension, or a non-extension/compression regime controlled by major reorganization of the plate movements – the onset of this fourth phase is inferred to coincide with the initiation of seafloor spreading in the southern Eurasia Basin at around 53–50 Ma; and (4) reactivation of the rifting in the mid-Miocene (a second rift phase).

Abstract Transform-margin development around the Arctic Ocean is a predictable geometric outcome of multi-stage spreading of a small, confined ocean under radically changing plate vectors. Recognition of several transform-margin stages in the development of the Arctic Ocean enables predictions to be made regarding tectonic styles and petroleum systems. The De Geer margin, connecting the Eurasia Basin (the younger Arctic Ocean) and the NE Atlantic during the Cenozoic, is the best known example. It is dextral, multi-component, features transtension and transpression, is implicated in microcontinent release, and thus bears close comparison with the Equatorial Shear Zone. In the older Arctic Ocean, the Amerasia Basin, Early Cretaceous counterclockwise rotation around a pole in the Canadian Mackenzie Delta was accommodated by a terminal transform. We argue on geometric grounds that this dislocation may have occurred at the Canada Basin margin rather than along the more distal Lomonosov Ridge, and review evidence that elements of the old transform margin were detached by the Makarov–Podvodnikov opening and accommodated within the Alpha–Mendeleev Ridge. More controversial is the proposal of transform along the Laptev–East Siberian margin. We regard an element of transform motion as the best solution to accommodating Eurasia and Makarov–Podvodnikov Basin opening, and have incorporated it into a three-stage plate kinematic model for Cretaceous–Cenozoic Arctic Ocean opening, involving the Canada Basin rotational opening at 125–80 Ma, the Makarov–Povodnikov Basin opening at 80–60 Ma normal to the previous motion and a Eurasia Basin stage from 55 Ma to present. We suggest that all three opening phases were accompanied by transform motion, with the right-lateral sense being dominant. The limited data along the Laptev–East Siberian margin are consistent with transform-margin geometry and kinematic indicators, and these ideas will be tested as more data become available over less explored parts of the Arctic, such as the Laptev–East Siberia–Chukchi margin.

Abstract Sparse data have hindered efforts to characterize the general geology and petroleum systems in the Siberian Arctic in and east of the Laptev Sea, a region whose potential has often been discounted. Recent acquisition and interpretation of 13,000+ line-km of new long offset, long record reflection data in the North Chukchi, East Siberian, and Laptev Seas has clarified the geometry and inter-relationships of several basins in this enormous 3 × 106 km 2 area devoid of wells. The 16 sec (PSTM) and 40 km (PSDM) data image a number of attractive late Mesozoic and Cenozoic extensional basins superimposed on older Phanerozoic fold belts that lie below acoustic basement. These basins all relate in various ways to the opening of the Arctic Ocean, and many contain 7.5 to 10 km of sedimentary fill and, up to 20 km in the case of the North Chukchi Basin. A variety of stratigraphic fill styles related to their underlying tectonics can be observed. For example, late-stage (postrift) architecture in the North Chukchi Basin shows Tertiary deltaic sequences traversing over 400 km northward overlying Late Cretaceous rift-fill sediments which contain potential source rocks. In contrast, the Laptev Sea exhibits successions related to a passive margin subsidence history, with low-angle sedimentary systems tracts including well-developed ancient shelf margins and lowstand systems, all cut by intra-continental extensional structures on trend with the active Gakkel Ridge spreading center. Slightly older sediment fill occupies rifts under the East Siberian Sea. The observed potential petroleum systems in this region offer source, reservoir and seal lithologies and hydrocarbon migration geometries to access shelf margin, lowstand depositional systems in addition to the potential within the Neogene rifts.

Abstract 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.

There is growing concern about the rapidity and extent of climate change in recent decades in the Arctic. The changes already evident in the Arctic, such as the cyclonic shift in the distribution of Atlantic and Pacific water masses, atmospheric pressure and winds, as well as the thinning and retreat of the sea ice, will be felt first and most dramatically around the circum-Arctic shelves, which comprise nearly 50% of the area of the Arctic Ocean. In this context, the Laptev Sea and its Siberian hinterland are of particular interest because of their distance both from the Atlantic and Pacific Oceans. River discharge into the Laptev Sea constitutes a key source for the Arctic freshwater input, and it generates a shallow brackish layer on top of the halocline. The shallow Laptev Sea shelf is a major area of sea-ice production that links the Siberian shelves of the Arctic Ocean with the Nordic seas. During the Last Glacial Maximum, most of these shelves were above sea level and developed thick permafrost sequences; today they are submarine, after having experienced the postglacial late Pleistocene and Holocene transgression. The history of the submarine permafrost and its modern state of decay are largely unknown.

We investigate the fate of permafrost since the Last Glacial Maximum in the Laptev and East Siberian Seas, a submergent coastal environment. The shelf here is up to 700 km wide and less than 80 m deep, a large area highly sensitive to changes in environmental conditions. Climate and sea-level histories and the terrestrial and coastal geomorphology of the region are combined with direct observations from drilling campaigns to review existing notions on the distribution, thickness, physical state, and history of the development of terrestrial and offshore permafrost since the Last Glacial Maximum. Drilling transects running perpendicular to the coast in the nearshore zone show that the interface between unfrozen and frozen sediments varies in its angle of inclination as a result of a number of factors, primarily coastal retreat rate. A conceptual model of permafrost development prior to submergence suggests that thermokarst and nearshore processes are critical in altering the development of permafrost in the submarine environment.