ASSOCIATION OF SEDIMENTS IN FLUVIOGLACIAL DELTAS (EVIDENCE FROM NORTHWESTERNMOST RUSSIA)

Abstract

Rock associations in fluvioglacial deltas reflect climatic cyclicity. Climatic cycles determined the accumulation of sediments in the association of hydrodynamic, debris, and turbidity flows. Hydrodynamic flows formed successively the near-summit part of the delta (pebble and boulder) and its frontal slope in the course of accumulation of the pebble, sand-pebble or sandy and, less common pebble-boulder layers inclined toward the basin. Decrease in energy of flows in the basin resulted in successive reduction of particle grain-size along these layers and toward distal areas of the delta during its formation. The formation of the deltaic frontal slope was followed by the initiation of debris and turbidity flows. They spread along the floor of marine and freshwater basins and deposited successively gravel material, different-size sands, and varved clay. In the study region, sediments of the association under consideration include sand and sand-gravel deposits (up to 40% of total reserves in the Murmansk region) and almost all known brick clay deposits.