MODE OF ORIGIN OF DISPERSED CLASTS IN JURASSIC SHALES - SOUTHERN PARTOF THE YANA-KOLYMA FOLD BELT, NORTH-EAST ASIA

In an effort to estimate climatic conditions in high latitudes, we und ertook field studies of Middle to Late Jurassic clast-bearing mudrocks in northeastern Russia. Most of the enclosed clasts, previously attri buted to seasonal ice rafting, consist of rip-up shale clasts associat ed 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 t he 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 th is time, in accord with GCM results suggesting strong seasonality in t he Jurassic high latitudes. The evolution of Jurassic climate is still to be defined, however, as other reports of clasts in Bajocian-Tithon ian mudrocks in the region remain unevaluated.