Mode of origin of dispersed clasts in Jurassic shales, southern part of the Yana-Kolyma fold belt, North East Asia

In an effort to estimate climatic conditions in high latitudes, we undertook field studies of Middle to Late Jurassic clast-bearing mudrocks in northeastern Russia. Most of the enclosed clasts, previously attributed to seasonal ice rafting, consist of rip-up shale clasts associated with turbidites and blocks and slabs of intrabasinal sediments. The emplacement processes for these materials are here considered to have been gravity driven mass movements. Evidence of ice rafting, not of the best quality but including penetration structures in adjacent shale, is restricted to one locality in mudrocks of the Kolyma River area, which are tentatively assigned to the middle to late Bathonian. Marked seasonality with freezing winters therefore may have characterized this time, in accord with GCM results suggesting strong seasonality in the Jurassic high latitudes. The evolution of Jurassic climate is still to be defined, however, as other reports of clasts in Bajocian-Tithonian mudrocks in the region remain unevaluated.