International Geologiical Congress - Oslo 2008

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AAA-01 Paleogeographic evolution of the Arctic region during the Phanerozoic - Part 2

 

Basin configuration and distribution of Triassic delta lobes in the northern barents sea

 

Tore Hy, NPD (Norway)
Bjoern Anders Lundschien, NPD (Norway)
 

 

During the Triassic, a remarkable system of large clinoform beds extended from Gardarbanken High almost to Kvitøya and continued westwards between Edgeøya and Nordaustlandet. At Kvitøya the Triassic sediments are eroded by the Paleogene uplift, but there are no seismic indications that Kvitøya is the northern limit of the clinoforms. The clinoforms belong to a large delta system with separate lobes prograding from the southeast and moving northwest and west in the Barents Sea. The seismic data show that the delta terminates north of Kvitøya, possibly as far as the Lomonosov ridge.

Flattening of the seismic horizons combined with data from shallow boreholes allows a reconstruction of each lobe and shows the relationship between the deltaic sediments and the black shale developing further offshore. The seismic data and the shallow boreholes demonstrate a classical deltaic development where each lobe has a relatively thin delta plain, a thicker delta front system and thin condensed black shale deposited in an offshore marine environment in front of the delta. The age of the clinoformes and delta lobes within the studied area are progressive younger the further north and west the delta moves, ranging from Olenekian/Anisian/Ladinian age at the Gardarbanken High up to Carnian age east of Kong Karls land.
The basin configuration in Triassic in the northern Barents Sea can be described by a relatively simple model. The basin was rapidly drowned during the Triassic transgression. This created accommodation space for black shale and later progressive deltaic sediment infill. The thickness of the clinoforms from offshore to top delta indicate that the water depth never exceeded 300-400 m. North of the Olga basin the delta lobes subsided very slowly, and larger transgressions are not an important part of the geological record before the main transgression in the late Triassic. Local and smaller transgressions on top of each lobe may occur. The stacking of the lobes has therefore a more lateral pattern than vertical.

Paleocurrent measurements (2007) from outcrops in Upper Triassic deltaic sediments at Hopen, Edgeøya, Barentsøya and even in Aggardbukta show a dominance of paleocurrent directions from south and southeast with one exception at Blanknuten on Edgeøya. The facies interpretation of the measured bed at Blanknuten is uncertain but the paleocurrent measurement was done very near a meander system east of the measured beds and is probably a part of the meander system. The cliffs on southwestern Hopen also have clinoforms dipping towards northwest.

These observations suggest a vast Triassic delta was supplied by sediments transported from the southeast (Siberia or Kola peninsula). The delta reaches Hopen, Kvitøya, Edgeøya, Barentsøya and Aggardbukta during the Late Triassic. More field work is necessary to obtain statistically significant data on paleocurrent directions in order to confirm this hypothesis.

 

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