E.Gusev & M.Ryazanova. 

Major features of Cenozoic geodynamics of the Laptev Sea continental margin

 


In general Laptev Sea continental margin were submerged during Late Cenozoic, but the eastern part of transitional zone has experienced several phases of tectonic stability and even weak uplift. Regional subsidence of the shelf area during Late Cretaceous – Cenozoic time was practically compensated by sedimentation: the result of this process is extremely flat relief of the Laptev Sea shelf. Distribution of sedimentary cover thickness shows several regularities: to the west from 128 E sediment thickness sharply increased, but to the east from this longitude sediments are concentrated within narrow grabens while total thicknesses decreased. Opposite regularities are common for both Cenozoic and Quaternary deposits distribution. Within Laptev Sea shelf hinge zone is spatially located on the prolongation of the axis of mid-ocean Gakkel Ridge.

Seismic lines, crossing the eastern part of the Laptev Sea continental margin, shows that the shelf break in the eastern part of the sea since Paleocene progressively propagated towards open ocean due to progradation of depositional wedge to the deep sea floor. Strong terrigenous input to the continental margin is the reason of smooth relief of the shelf and continental slope. Several phases of weak uplift of the eastern part of the Laptev Sea continental margin probably led to steep relief of continental slope dissected by very deep submarine canyons. The last phase of such uplift had occurred during Holocene as the outer periphery of the shelf adjacent to the shelf break is characterised by sharply reduced thicknesses of recent deposits. Shelf break there is splited to series of prominent bends corresponding to ancient shorelines. The age of the upper bend is evaluated as the most young (Sartan according Siberian scheme and Late Weichselian according European scheme). Canyons of continental slope dissect modern shelf break and occur up to this shoreline. The absence of prolongations of these canyons, valleys and channels constrains the evidence of their submarine erosion. In the central and western parts of the Laptev Sea margin submarine canyons occur only beneath shelf break and sometimes these canyons are limited by prominent bends below shelf break.

In the East Siberian Sea spacious delta is revealed on the prolongation of the ancient Sartan (?) shoreline. It is characterised by broad valley limited by prominent blade form of relief. Change of river mouths configuration from estuaries in the Western Laptev Sea to the deltas in the Eastern Laptev Sea was marked by American scientists (Holmes & Creager, 1974). This regularity also contrains the evidence of the weak tectonic uplift in the eastern part of continental margin.



Reference to this abstract:

Gusev E., Ryazanova M.  Major features of Cenozoic geodynamics of the Laptev Sea Continental Margin. Quaternary Environment of the Eurasian North (QUEEN), Fifth QUEEN Workshop, Lund, Sweden, 7-10 April, 2000, p. 49.



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