Late Cretaceous-Early Cenozoic Indicators of Continental Extension on the Laptev Sea Shore (North Verkhoyansk)

Andrei Prokopiev

A set of graben-like basins (Kengdey, Sogo, Kunga, Bykov Channel) with Paleogene predominantly clastic succession is known within North Verkhoyansk. Study of composition and depositional environments of clastic rocks showed some variation in their evolution. Accumulation of sediments of the largest Kengdey graben (Early Eocene) occurred in the frequently changing depositional environments such as lacustrine, alluvial-lacustrine, swampy and littoral-marine. In general, the area represented a coastal-continental plain, periodically flooded by sea and surrounded, along the periphery, by mountain uplifts. Deposition of sediments of the Kengdey graben occurred in subtropical warm and humid climate, which was favorable for intense weathering processes. The absence in sediments of monazite, which has been found in all Cenozoic basins to the east, indicates that during Early Eocene to the east of the Kengdey graben there was an upland or mountain range separated it from other sedimentary basins. In the second half of Early Eocene, garnet began to be supplied into the basin, which might be related to the erosion of Carboniferous-Permian rocks. Sedimentation conditions in the Kunga graben (Early-Middle Eocene) were similar to those in the Kengdey graben. In the oldest Sogo graben (Late Paleocene), sedimentation occurred under predominance of lacustrine environments. Warm and humid climate was favorable for intense chemical weathering in provenance areas with weakly dissected topography. Sedimentation in the Bykov Channel graben (Early Eocene) occurred, at its early stages, in lacustrine-alluvial environments. In the upper part of the section, alternation of sediments deposited in lacustrine-swampy and littoral-marine environments likely represents interruptions occurred during subsidence of the graben basement. Rocks of the Kengdey and Bykov Channel grabens are locally folded with dip angles up to 35-45o pointing to a local Cenozoic compression. Between the Kengdey and Kunga grabens there are dolerite dike swarms intruding Permian deposits and radiating outward from the center with volcanic breccia. U-Pb zircon dating of 3 dykes yielded crystallization ages as 86±4 Ma, 86.2±1.3 Ma, and 89±2, which indicates that the dikes are Santonian to Coniacian and likely represent the first stages of a regional-scale extension. The above described grabens are filled in with Paleogene deposits and considered to be formed in Paleogene at an early stage of rifting in the area of continental continuation of the Gakkel spreading ridge (Grachev, 1996). The data we obtained indicate that extension related to the opening of the Eurasia basin within the continent probably started earlier, in the Late Cretaceous, and could be accompanied by volcanic activity and emplacement of dikes. Study by A.Prokopiev, A.Khudoley, V.Ershova and D.Vasiliev was partly supported by TGS-NEOPEC Geophysical Company and RFBR grants 13-05-00700 and 12-05-33018.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013