Deformation of Continental Lithosphere on the Laptev Sea Shelf
Status of project: January 2, 2006
Location of the study area
Source: BGR
The eastern Arctic Ocean is unique among the world's oceans due to its wide continental shelves, and especially to its plate tectonic setting. Today, the total opening rate at the boundary between the North American and Eurasia plates varies between 1.3 cm/a and 0.7 cm/a over a distance of 300 km from seafloor spreading along the Gakkel Ridge in the Eurasia Basin to extension of continental lithosphere on the shallow Laptev Shelf.
In 1997 the Federal Institute for Geosciences and Natural Resources (BGR), Hannover, in cooperation with Sevmorneftegeofizika (SMNG), Murmansk, carried out their third geophysical research expedition on the shelves of the Laptev and East Siberian Seas to better understand the variations within the lithosphere during the rifting process and the tectonic and structural evolution of the crust undergoing extension.
Laptev Sea
Source: BGR
Most MCS data from the Laptev Sea area of the BGR 1997 expedition and additional lines from the BGR 1994 expedition were the data base for the revised structural map shown below.
Major structural elements of the Laptev Sea
Source: BGR
The extension, which affected the Laptev Shelf since the Late Cretaceous resulted in a complex horst and graben system. The main structural elements include the Ust' Lena Rift, the Laptev Horst, the Anisin Basin and the New Siberian Basin.
The most prominent rift basin is the Ust' Lena Rift which is at latitude 75° N at least 300 km wide. The Cenozoic sedimentary cover exceeds 3 km everywhere, increasing up to 13 km in the grabens. The crust beneath the most peneplained basement is subdivided into a seismically transparent upper crustal portion and a up to 6 km thick, highly reflective lower crustal unit. The latter thins when approaching the Ust' Lena Rift.
Prominent seismic characteristics are:
- Absence of a clear Moho-reflection.
- Presence of a lower crustal unit in levels between 12 and 18 km characterized by high reflectivity.
- The down thrown basement underwent penetrative brittle deformation resulting in a series of rotated basement blocks. The early rift phase unconformity LS1 forms the base of the Cenozoic sedimentary infill with thicknesses in the range between 3 and 13 km.
- The westerly dipping M/V Lazarev-Fault penetrating most of the crust bounds the Ust' Lena Rift from the Laptev Horst.
Profile BGR97-01
Source: BGR
The Laptev Horst is a mostly peneplained, north-south-trending and 100-150 km wide uplift. Locally deep reaching faults subdivide the Laptev Horst into several tilted blocks and some halfgrabens with smaller extent and sedimentary infill than the main rift grabens described above. These narrow halfgrabens divide the Laptev Horst into three parts: the North, the South and the East Laptev Horst.
In the northern part of the shelf the complex NS trending Anisin Basin has a basinal infill of up to 10 km thickness. A second axis with a smaller sedimentary cover strikes in NW direction. A prominent fault (IB Kapitan Dranitsin Fault), westerly dipping and listric, forms the boundary between the Anisin Basin and the Kotel'nyi Horst. In the northwestern part of the New Siberian Basin the graben infill is up to 9 km thick.
Profile BGR97-16
Source: BGR
Three major regional unconformities, labeled LS1 (green), LS2 (orange) and LS3 (blue) were identified in the seismic data and mapped.
Unconformity LS1, the most prominent and extensive horizon, was well defined on all the profiles. The low-frequency pattern and the absence of regular reflectivity directly underneath the horizon led to the interpretation as the acoustic basement. The horizon is a distinct erosional unconformity, forming a peneplained surface of several structural highs in the Laptev Sea.
LS2 is recognizable as a distinct unconformity in the basinal infill of the major rift basins of the Laptev Sea. It is absent on the highest standing horsts. The seismic unit between LS1 and LS2 is formed by a moderate to low reflective sequence directly above LS1 which in turn is overlain by a high reflective unit. Unconformity LS2 forms the top of the high reflective seismic unit. The thickness of the unit increases from some 100 m at the edges of the structural highs to about 10 km in the main rift basins.
Unconformity LS3 is a distinct depositional unconformity in both the western and eastern Laptev Sea. It forms the upper surface of a pronounced sequence characterized by sub-parallel reflectors. The thickness of the unit between LS2 and LS3 is less variable and shows values in the range of 1 to 4 km. According to the seismic data unconformity LS3 marks a drastic change in the depositional regime. On the few lines from the outermost shelf and continental slope unconformity LS3 forms the base of a series of prograding and aggrading sequences.
An assumed, about 300 to 400 m (0.4 - 0.6 s twt) and locally even more thick permafrost zone often masks an additional unconformity of inferred Pleistocene age, which is locally present in BGR's seismic records.
| Year | Source | Receiver | Survey [km] | |||
|---|---|---|---|---|---|---|
| volume [l] | guns [no] | streamer length [m] | no. of channels | rec. length [s] | ||
| 1993 | 27.8 | 20 | 2,400 | 48 | 12 | 3,189 |
| 1994 | 49.2 | 32 | 2,925 | 118 | 12 | 3,965 |
| 1997 | 69.8 | 32 | 3,000 | 240 | 12 | 4,623 |
Literature:
Franke, D., Krueger, F. & Klinge, K.D. (2000). Tectonics of the Laptev Sea – Moma 'Rift' region: Investigation with seismologic broadbanddata, Journal of Seismology, 4, 99-116.
Franke, D., Hinz, K., Block, M., Drachev, S.S., Neben, S., Kos'ko, M.K., Reichert, C. & Roeser, H.A. (2000). Tectonics of the Laptev Sea region in north-eastern Siberia. In: N.W. Roland & F. Tessensohn (eds.) ICAM III: III. International Conference on Arctic Margins. Published by the Alfred-Wegener-Institute for Polar and Marine Research and the German Society of Polar Research Bremerhaven, 68 (1998), ISSN 0032-2490, 51-58.
Franke, D., Hinz, K. & Oncken, O. (2001). The Laptev Sea Rift. Marine and Petroleum Geology, 18(10), 1083-1127.
Franke, D., Reichert, Chr. & Hinz, K. (2004). Geology of the East Siberian Sea, Russian Arctic from seismic images: Structures, evolution and implications for the evolution of the Arctic Ocean Basin, Journal of Geophysical Research, Vol. 109, No. B7, B07106, 10.1029/2003JB002687.
Franke, D., Reichert, Chr. & Hinz, K. (2004). Structure and Evolution of Sedimentary Basins on the Shelves of the Laptev Sea and East Siberian Sea, Siberian Arctic. AAPG European Region Conference with GSA, Prague, October 10-13, 2004. Extended Abstracts.
Franke, D. & Hinz, K. (2005). The structural style of sedimentary basins on the shelves of the Laptev Sea and the western East Siberian Sea, Siberian Arctic, Journal of Petroleum Geology, 28(3), 269-286.
Cramer, B. & Franke D. (2005). Indications for an active petroleum system in the Laptev Sea, northeast Siberia, Journal of Petroleum Geology, 28(4), 369-384.