Mountains of the Sikhote Alin and East Manchurian mountainous regions occupy
Seventy-five percent of Primorye. The rest of the territory is essentially
flatland, including the Razdolnoye-Khanka Plain and some intermontane depressions.
Structurally, the Razdolnoye-Khanka plain represents an intemontane depression
that separates the said mountain regions, the intermontane depressions
being concentrated along the boundaries of zones and subzones of
mountain regions. Several morphogenetic types of relief form the Sikhote
Alin mountain region.
The Sikhote Alin chain with peaks of parates the Japan and Okhotsk Sea basins.
|The time of Sikhote Alin’s active formation and build up of relief heights is associated with the introduction of magmas a volcanic eruptions in Late Cretaceous and Early Paleogene. That is when the system of magmatogenic domal structures formed.|
In Cenozoic, the relief’s heights
continued to grow and the territory to rise to form against this background
in relatively narrow transversal linear zones as the Verkhneussuri, Zerkalnin,
Maximov, Verkhnebikin and other Cenozoic depressions.
The Zeva-Dagdy, Adinsk, Edinkin, Samarga and smaller volcanic volcanic plateaus of Pliocene and Pliocene-Quarternary time cross the ridge in sublatitudinal directions to pass from its western zone to its eastern zone.
A system of medium-low altitude (up to 1,500 m high) and low-altitude (up to 1,000 m high) massifs and their groups, which formed in introduction of Upper Cretaceous granitoids and in local volcanic eruptions, extends parallel and to the west of Sikhote Alin. The Cenozoic stage of geomorphogenesis showed in destruction of the marginal sections of the massifs, to which narrow valleys of rivers flowing to the northwest, southwest and west are assigned.
The Sikhote Alin chain and mountain massifs are divided by intramontane settling of the relief, drained by such average and big rivers as the Bikin (upper reaches), Kolumbe, Bolshaya Ussurka (middle and upper reaches) and others. Here, magmatic activity was weak to cause appreciable increase in relief altitudes. In sites, where magmatic activity was more intensive, sections of river valleys are of antecedent nature.
The low Vostochnyi Sinii, Kholodnyi and several smaller ranges extend alongside low and medium mountain massifs, being separated from them by intramontane depressions of undoubtedly Cenozoic age. These are primarily the Srednebikinskaya, Marevskaya and several smaller depressions. Again, these also include the already known small blankets of Pliocene basalts. The forming of Vostochny Sinii range is associated with volcanic activity of Late Cretaceous-Early Paleocene with subsequent block deformations in Cenozoic. The Kholodnyi range formed in introduction of minor single Upper Cretaceous intrusions and intensive block movements in Cenozoic. Extending along the western boundary of the range zone described above is a system of intramontane Cenozoic depressions, the largest of which are Arsenievskaya, Khvischanskaya, Malinovskaya and Orekhovskaya.
Sinii range is the westernmost element of the Sikhote Alin Mountain region. This low, occasionally low altitude (300-500 m) structure formed for a long time, but especially in Neocene-Quarternary time under compression and ejection of this narrow (5-15 km) block, restricted by ejection, showing in the relief as benches and abrupt folding of the geomorpholgical surface. Low-altitude sites in the range were subjected to ascending movements of lesser intensity and are to some extent relicts of Pre-Upper Cretaceous relief.
Uplands and plateau-like surfaces are characteristic of the basins of Alchan and Bikin (lower reaches) Rivers. They alternate with narrow faults, relicts of relief development in Cretaceous. Isolated small extrusive, volcanic and volcanoplutonic domes, whose altitudes grow as one moves northward, hover over flat and plateau-like surfaces.
The Strelnikovsky low-mountain range extends along the northwestern boundary of Primorye. With regard to conditions in which it formed, it is reminiscent of Sinii, Vostochnyi Sinii and Kholodnyi ranges.
The Nizhnebikin and Alchan intramontane depressions formed in Cenozoic. Today, they are involved in a weak elevation, their surfaces breaking up intensely. Relicts of basalt plateaus evidence this.
The southern section of Sikhote Alin Mountain region is represented by the low Przhevalsk and Livadia ranges and by the southern tip of the Sikhote Alin and Makarov ranges. The same zone incorporates the Shkotovo basalt plateau of Pliocene age. The ranges are separated relief depressions, occupied by river valleys of high order of magnitude. Pliocene-Quarternary low-altitude swell-like elevations are situated on boundaries with Cenozoic depressions.
So, the mountain country of Sikhote Alin consists of a series of anticline-block faulting ranges divided by intramontane depressions, mostly of Cenozoic age. Transversal zoning is associated with Cenozoic disjunctive structures, but their laying site was predetermined by earlier events. A combination of diagonal and orthogonal disjunctive zones created Sikhote Alin’s vesicular structure. Fault zones form the section boundaries, and their massive central zones have maximal altitudes. These very elements determine the overall stability of the mountain region, and that of its elements and blocks.
The East Manchurian mountain region passes into Primorye only with its eastern ridges. These are the low-altitude Pogranichnyi and Chernye Gory block ranges and the Borisov basalt plateau. The ranges are of Late Neocene-Quarternary age, this being evidenced a whole series of events, and the most important of which are relicts of the Cenozoic depression bonnet that occupies the highest relief sections. The Borisov plateau represents a dome (radius 40-50 km) with flattened central one (up to 5), sloping (10-20) intermediate zone and flat (fewer than 5) marginal zone. The mountain chains articulate with adjacent depressions along benches and abrupt slope folding, and an intermontane plain smoothly changes the plateau.
The Razdolnoye-Khanka intermontane depression is a plain that extends from the lower reaches of Tumangan River to the estuary of Bolshaya Ussurka River. The Nizhnebikin depression is located over its extension. The flatland section of the intermontane depression occupies the lower geomorphological stage. These are baths of Amur Bay, Lake Khanka and Posiet Bay with its inlets, bogged spaces in their coastal sections. Here, younger ones bury Paleocene, Neocene, Lower- and Middle-Quarternary deposits.
The surface of the intermediate geomorphologic stage is ridgy and occasionally complicated by individual mounds or groups of mounds. These are usually uplifts, residual rocks that separate Cenozoic depressions, grabens and graben synclines formed by loose and weakly cemented Paleocene and Neocene sedimentary and sedimentary-volcanogenic rocks with brown coal beds of workable thickness.
The relief of the upper geomorphologic stage of the intermontane depression is composed of mounds and rare ridges, small hills and little mountains. Relicts of Cenozoic depressions are represented by graben-synclines, moulds and flat declivities with thin hood, chiefly composed of Neocene rocks. The Khorol low-hill ridge separates the Khanka group of depressions from the Razdolnoye depression. There is also a low-mountain bridge between the Slavianka and Khasan group of depressions.
Ruins of Cenozoic volcano-tectonic structures, most of them under sea level, still show along the western coast of Amur Bay and Possiet Bay. Centers of volcanic activity are known to exist along the entire intermontane depression, which formed in the regional Ussuri plutonic fault. It is active today, too, this being evidenced by earthquake centers. The Baranov volcano, prepared by Razdolnaya River, is an example.
In Quarternary, the lower geomorphologic stage submerged and is apparently submerging today. The upper geomorphologic stage is rising and is quite active in places. The intermediate stage plays the role of a hinge, its movements being low amplitude and randomly directed. Along the coastline of Peter the Great Bay and the Sea of Japan in the east of Primorye, a narrow strip of low-altitude and hilly relief stretches, its formation being closely associated with the Japan Sea depression. Tectonically, this zone is now more active than the Sikhote Alin Mountain region.
Primorye’s relief is perpetually changing. In some places quite actively, in others less actively. Here, we have briefly characterized only its macro- and certain mesoforms, whose destruction by exogenous processes (from above) depends on numerous factors, including the climate, which did not play a special part in the formation of the forms described above. Groupings of relief microforms and their types and forms, formation rates and life are essentially varied, but nonetheless closely related with macro- and mesoforms.
The Sikhote Alin, East Manchurian and Razdolnaya-Khanka macroforms form the basic relief background. Mesoforms (zones and geomorphologic stages) are its structural framework called cells. Microforms are the pattern with which nature has “decorated” mesoforms. Macroforms may be observed from space, mesoforms from bird’s eyeview or in panorama forms. Some microforms may even be covered with your palm. Relief microforms may be handmade and, if done sensibly, would serve mankind; and if not, would take “revenge”.
S. TASCHI, Candidate of Science (Geology and
Mineralogy), Leading Research Fellow, Laboratory of Geomorphology,
Pacific Institute of Geography, Far East Branch, Russian Academy of Science.