SEDIMENTOLOGICAL CHANGES ACROSS THE ORDOVICIAN-SILURIAN BOUNDARY IN HADELAND AND THEIR IMPLICATIONS FOR REGIONAL PATTERNS OF DEPOSITION IN THE OSLO REGION

Basin faulting and global eustatic sea-level fluctuations during the l atest Ordovician and early Silurian generated new and complex sediment ation patterns in the Oslo Region. In eastern Hadeland a fall in sea l evel, possibly in the earliest Hirnantian, resulted in the incision of channels which were later filled by carbonate debris flows and finall y became emergent during the period of maximum withdrawal, The drownin g of these deposits as sea level rose was followed by the deposition o f storm-dominated shelf-derived carbonate and siliciclastic sediments. During this period transport was from the north and east. A subsequen t gradual shallowing culminated in local emergence. The early Silurian was marked by new shelf-flooding and by the delivery of siliciclastic sediments, again from the east. In contrast with earlier models, an e astern pattern of derivation is thought to have been a general feature of the basin during the late Ordovician and early Silurian.