Number, altitude and geomorphic position of .four topographic levels in Appalachians (Kittatinny, Schooley, Harrisburg and Parker-Strait) appeared to be completely identical to four topographic level described in the Urals. The two intermediate surfaces in the Appalachians (i. e. Schooley and Harrisburg) however considered to be Tertiary in age, whereas the corresponding surfaces at the Urals believed to be Mesozoic. The author argues for the age of the Harrisburg sirface to be Late Jurassic-Early Cretaceous, which is the same as that of the analogous Uralian surface. It suggests the other surfaces at the Appalachians could be synchronous to the Uralian ones.
A concept of synriftogenic origin of planation surfaces is introduced. In the authors opinion the topography downwearing to the base level proceeds under conditions (and within the zones) of active destructive (riftogenic) endo- and exogenous geomorphogenesis, rather than under conditions of relative tectonic stability. The riitogenesis and connected endogenous-exogenous downwearing of the Earth's surface the authors consider to be the main processes which transform orogenic formations into platformian plateplains and plate-seas.
Геоморфология и народное хозяйство
Morphostructural framework of the region consists of arcuate and sub-rectilinear morpholineaments which indicate fault and fracture zones active during the neotectonic stage. They control boundaries of neotectonic block morphostructures differing in altitude, as well as outlines of ring structures. When morphostructures had been compared with data on deep structure of the area, it appeared that local elevations within the under-salt sedimentary cover (which are known or presumed to contain oil and gas) are located either within neotectonic subsidence areas near fault zones or within slightly elevated nlorphoblocks; they are mostly situated near points where arcuate morpholineaments (delineating large ring structures) cross regional sub-rectilinear lineaments. Such a morphostructural position should be considered as a geomorphological criterion of not yet identified buried structural forms promising for the oil and gas searches.
The analysis of recent dynamics of sea coast and marine placers location as well as heavy minerals distribution within the productive sand layer when compared with the lagoon coast evolution during the Holocene showed the marine placers formation during the Holocene to be inherited from earlier stages. They are connected with processes of bars and barrier-beaches formation and deep differentiation of debris under condition of relatively closed systems of ingression coasts during the early Holocene. Now they do not receive any noticeable supply any more. Normal component of the load movement remain the leading factor in the placers formation.
Методика научных исследований
The author works out a morphological system (which is a presentation of the Earth's surface composition and structure as a totality of point, linear and areal elements and their spatial relations) to apply to the topography mapping and description. Morphological map is considered as a -formalised cartographic model which is strictly homomorphic to the real Earth surface. An universal legend of the morphological map is introduced (as well as a unified form of a topography description) based on a universal scale and object character of the morphological system. A notion of the Earth surface anisotropy and local structural coordinate grid anisotropy are introduced, a technique of the coordinate grid construction is suggested. The importance of the grid is emphasized with view to relief description, morphometric constructions and estimation of the similarity of the Earth surface areas with each other and with experimental models. A form is developed of landform presentation as symbolic formal models-sets of spatially correlated elements recorded in a certain order. Their combinations are classified according to their composition, number of members and vertical and lateral associations. Some ways of the morphological system application to the topography dynamics interpretation are outlined.
Научные сообщения
A geomorphological scheme of the Walvis Ridge has been compiled on the basis of data obtained by soviet and foreign specialists. The scheme and geological and geophysical data available show the ridge to be a complicate block-volcanic formation, its structure changing along the axis direction. Three morphological provinces are distinguished which differ in the floor topography and internal structure: eastern-most important-block province, central province of plateau massives and western province of volcanic mountains. Provinces as well as individual blocks are delimited with faults. Morphological and geophysical data suggest the Walvis Ridge to be ancient structure which is now in the process of downwearing and subsidence.
Morphostructural analysis of the Azerbaijan Great Caucasus brought the authors to the following conclusions: 1) existing morphostructures of the area resulted from tangential and vertical movements under conditions of the general compression of the region, 2) over thrust-block framework of the Great Caucasus was preconditioned by ancient and recent f aults and thrusts system, block movements along longitudinal faults being most important, 3) the transversal morphostructural segments of the East Caucasus are separated from the SE Caucasus by West Caspian morphostructural knots system and differ in morphotectonic history and structure, 4) Miocene orogenic movements formed series of thrust sheets, at fer the sheets had been formed they were involved into posterior tectonic movements, which resulted in fold-block-thrust morphostructures.
The paper introduces a technique of flow pattern calculation for the case of many channeled stream based on calculation of discharge distribution between the branches, the «frag1nents» method being applied to individual branches, The calculation was made for the case of the channel-forming discharge. The analysis of flow pattern of the middle reaches of the Lena River constructed on the basis of the suggested technique allowed to investigate the secondary branching of the main channel and to find the cause of new islands formation. Main flow circulation schemes in a wide channel are given which accounts for secondary branching of main channels.
Structure and morphology of the West Australian Basin floor and its surroundings are described. Four main levels of the floor are delimited using the notion of topographic zonality, detailed analysis of their morphology allowed to verify the basin's boundaries. Structural-geomorphological elements of the basin's frame are subdivided into two groups those formed simultaneously with formation and evolution of the continental margin and those formed when the zone in front of the basin underwent breaking and subsiding.
Five segments of valleys without streams (wind gaps) are discovered within the area under consideration. Alluvium under the valleys floor was dated palynologically and four stages of the drainage system development were reconstructed during the Late Pleistocene-Holocene. The drainage network changes are established to tend as a whole to a formation of a new large stream and water divide of NW direction. The cause of the changes is upwarping of the structure buried under volcanic rocks of the Okhotsk-Chukchi volcanogenic belt.
The forested linear hollows at the Priobskoye Plateau are unique morphological formations, not to be found elsewhere on the Earth. Their formation was controlled by many factors in turns. Their evolution passed tectonic, erosional, eolian and fluvial stages. Their linearity and parallellism resulted from their formation along the Late Pleistocene fault-lines of NE strike; the faults are possibly associated with taphrogeny.
A possibility is discussed of searches of buried elevations in the lower structural stage using structural-geomorphological methods, a rational complex of investigations being developed. The study suggested includes a detailed analysis of the landforms morphology and present-day relief-forming processes by means of aerial and space photos interpretation as well as analysis of neotectonic movements by stages.
Buried valleys of the paleo-Volga and paleo-Kama tributaries of Pliocene age differ from the main paleo-valley in greater slope, elevated floor and smaller width. In the paleoSviaga valley during the Early Akchagylian the flow was a kind of lake-river, with pronounced dynamical axis and lateral zones of stagnant water, Present large water reservoirs resemble these paleo-valleys to a certain extent.
Хроника
Геоморфологические аспекты VI Всесоюзной Школы морской геологии (15-22 апреля 1984 г., г. Геленджик)
ISSN 2949-1797 (Online)
