RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES5004, doi:10.2205/2005ES000180, 2005
[43] Evidence for Late Pleistocene reorganizations of a continental drainage network linked to the Sea of Okhotsk is also relevant to this discussion. The Amur, Amgun, Togur, and Uda River basins exhibit traces of vast paleo-lakes and repetitive river-flow diversions, while the morphology of adjacent mountain ranges and uplands is made conspicuous by a number of canyon-like breaches. In particular, there is geomorphic evidence for past deflections of the Middle Amur River to the south and southwest, toward the Japan and Yellow Seas via the Ussury- and Sungary-River valleys. Also, several abandoned valleys attest to a few episodes when the Lower Amur River, on reaching certain positions, was deflected southeastward to Tartar Strait. It is also clear that lower reaches of the Uda River were impounded and their discharge was rerouted to the Lower Amur by a lake-and-channel system extending parallel to the sea's shoreline, while the upper reaches of the same Uda River were, and still are, deflected to the south, across the mountain ridges of Tukuringra and Dzhagdy [Nikolskaya, 1969].
[44] These reorganizations of network of drainage, like many other phenomena of this kind, were believed to have been controlled by neotectonics; i.e., ascribed to the effects of recent crustal displacements. There was a tendency to associate formation of paleolakes and river diversions with river damming by rising fault-blocks, and breaching of mountain ranges with tectonic faulting and antecedent river incisions [Lebedev, 1995].
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Figure 6 |
[46] Having moved from the present shoreline for 300-350 km landward, the western margin of the Okhotsk ice sheet would ensure formation of the ice-dammed lakes and overflow channels, and would force all the river deflections and re-routings into Tartar Strait, the Sea of Japan and the Yellow Sea. All these discharge reorganizations were due to advances and retreats of the ice sheet's margin. The lake and river geography would experience step-by-step changes during retreat of the ice margin. One of the steps, shown in Figure 6a, would favor a complete turnover of several rivers, such as the Amgun', Ussuri and Sungari. Another step, depicted in Figure 6, forced the marginal meltwater runoff, when a few waterways would provide shortcuts from the Lower Uda River to the Lower Amur River, from where the water would turn southeastward, crossing the northern Sikhote Alin' Range into Tartar Strait. As for the meltwater lake of the Upper Uda River, its outlets crossed the adjacent Tukuringra and Dzhagdy Ranges by a series of overflow channels and joined the Zeya River flow during both the steps. Thus, as we already emphasized, the concept of an Okhotsk ice sheet and its damming effects can naturally account for the drainage reorganizations displayed in Figure 6.
Citation: 2005), "Back-arc" marine ice sheet in the Sea of Okhotsk, Russ. J. Earth Sci., 7, ES5004, doi:10.2205/2005ES000180.
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