The Silurian and Lower Devonian geology of Ringerike, southern Norway.

The Ringerike area of southern Norway has been re-mapped and the general geology, sedimentology, fossil fauna and flora, and structure of the Silurian and Lower Devonian has been studied and compared with other areas. Special attention has been paid to the abundant primary sedimentary structures and these have been used to interpret the conditions of deposition and the palaeogeography. During the Llandovery, shallow-water conditions gave way to a slightly deeper environment where sediments resembling calcareous flysch were deposited by atypical turbidity currents on an undulating shelf trending a little north of east. Shallowing to a level above wave base resulted in the accumulation of shell banks in the middle Llandovery, followed by lower energy sedimentation of red mudstones, unusual in that they are fully marine: their possible origin is discussed. The highest Llandovery consists of shallow-water nodular limestones: bentonites are common at this horizon. The Wenlock commences with deepening and renewal of turbidity current activity, first with the production of calcareous siltstones, later with increase in bioclastic limestones. Development of small patch reefs follows, and the Wenlock ends with well-bedded limestones. The Ludlow continues shallow. Fully marine carbonate deposition with a rich brachiopod-coral fauna alternates with a peculiar platy carbonate facies with, limited fauna, mainly ostracodal lout with algae and eurypterids: this is prohahly lagoonal. A number of red mud-cracked horizons indicate periodic emergence. Some bentonites are present. There is a rapid hut conformable change from marine Ludlovian to typical red-bed development (the Ringerike Sandstone), hut the crustacean and fish faunas show that these beds should still he considered Ludlovian in age. The higher unfossiliferous red-heds may well extend up into the Lower Devonian. The primary structures, especially crossstratification, show that clastics from the rising Caledonides in the north were heing spread out over a wide alluvial plain.