Submarine landslides found in the Senonian deposits in Daghestan
Abstract
In the summer of 1937 the author of this paper had an opportunity of observing horizons of crumpled brecciated rocks (7 to 12 meters in width) in the midst of quiet undisturbed Senonian limestones. The fauna gathered in this horizon shows that we are here in presence of upper layers of the Campanian stage. The character of the horizons of the brecciated rocks indicates that they originated during the period of stratification. Apparently a sliding down of sediments took place here when they were yet in a plastic state, which was accompanied by washing out. There often appear, in the hanging wall of the breccia horizon, fine pebbles or layers of conglomerate (up to 1 meter in width). The fragmental material met with here consists of the same limestones. The cause of the sliding down of sediments the author sees in the change of the slope of the bottom of the basin under the influence of tectonic movements. In these cases different portions of the bottom were uplifted above the sea-level, were washed out and gave coarse fragmental material. Many investigators admit the probability of an increase in tectonic movements by that time. V. V. Belousov (2) adduces arguments in support of the opinion that in regions of development of dome-shaped fields (whereto the north-eastern part of Daghestan also belongs) a slow growth of domes took place. He is of opinion that dome-forming commenced at the beginning of the Upper Cretaceous time, that is considerably in advance of folding. The author of the present paper supposes that such domes were just those upheavals along the slopes of which sediments slided. In the subsequent folding the anticlinal folds arrange themselves conformably to the position of the domes. Slide breccias coincide usually with synclinal zones and are absent in the crests of anticlines. In the vaults of anticlines, we sometimes meet with a seeming disappearance of horizons and with local unconformities.
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References
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