Structure of the Olenek fold zone – Control from Balanced Cross-section

Sergey Nilov

The Olenek fold zone is located in the northern part of the Siberian Craton separating it from the Laptev Sea sedimentary basin. Lower Cretaceous to Upper Permian rocks clastic rocks are exposed, but older rock units including Vendian and Riphean carbonate and clastic rocks are known from boreholes. The Olenek fold zone contains a set of folds usually interpreted as a shear zone with sinistral sense of shearing, although it has common features with frontal thrust zone of a large thrust and fold belt as well. Structures of the Olenek fold zone overprint those from the Verkhoyansk fold and thrust belt implying that formation of the Olenek fold zone is related to a younger tectonic event. Interpretation of the deep structure as a thin-skinned thrust-controlled structural domain is based on potential fields and seismic data (e.g. Prokopiev et al., 2001). Two structurally different complexes separating by a major thrust are identified. The upper structural complex consists of Cretaceous to Carboniferous rocks and contains gentle folds with steep (~ 80 degree) NE-dipping axial planes. Back thrust is recognized in the central part of the Ust’-Olenek anticline likely marking a triangle zone. The lower structural unit has more complicated structure with a set of duplexes that consists of Silurian to Riphean rocks. The lower structural unit is separated from the undeformed basement by a basal thrust. To produce structural restoration 2D Move software was used. First, we unbuckled folds and restored displacements along thrusts in the upper structural complex back to get horizontal bedding of Cretaceous to Carboniferous rocks. After that, the same procedure was applied to the lower structural unit. In the final restoration, the basal thrust has very irregular shape pointing to wrong identification of the sequence of events and that the lower structural unit with duplex structures was deformed before the upper structural unit. Modification of the structure of the lower unit was also done. Despite of difference in structural style, both structural units show quite small shortening with approximately 2.2% shortening in the upper unit and 13.4% shortening in the lower unit, implying that thick Riphean succession likely occurs to the northeast from the Ust’-Olenek anticline.

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