Genetyczna klasyfikacja osadów morenowych

Jan Rzechowski

Abstract


GENETIC CLASSIFICATION OF MORAINIC DEPOSITS

Summary

The Commission on the Origin and Lithology of Quaternary Deposits, INQUA, took the initiative to unify both the nomenclature and the systematics of morainic deposits. The classification of morainic deposits presented in this paper is one of possible answers to this initiative. The term - moraine - was left by the present author to determine the form produced by a glacier, whereas the material melted out of the glacier ice is consequently called by him - morainic deposit. This latter was formed at the cost of the glacier. The present classification of morainic deposits is based on genetical criteria. On the one hand, the palaeogeographical conditions of deglaciation, the dynamics of sedimentary processes and the way of formation of morainic deposits are considered for various taxonomical grades, on the other one, each taxonomical unit is determined by a specific complex of lithological features (Tables 1 and 2). The following are taxonomical units distinguished by the present author: I order - genetical type, II order - group of facies, III order - facies, IV order - subfacies, V order - family, VI order - lithotype (stratigraphic or regional). The morainic deposits, according to the conception or A. P. Pavlov, are a genetical type. They may be subdivided into the following two groups of facies: II A – subaeral (continental) facies, and II B - subaqueous (underwater) facies - in relation to the site of deglaciation (on land and underwater). Group II A includes both ablation till facies (III 1) and basal till facies (III 2), whereas group II B comprises, depending upon the kind of water basin in which the melting out of rock matrial in a glacier takes place, the following facies: thalassotopic facies (III 3), limnotopic facies (III 4) and fluviotopic facies (III 5). In the subaqueous morainic deposits transition formations are frequently found to pass into type aqueous deposits (marine, lacustrine or fluvial). The dynamics of glaciations and deglaciation processes is reflected in the form of the appearance of morainic deposits. This fact was a basis to distinguish the following subfacies (IV): active ice subfacies, stagnant ice subfacies, and dead ice subfacies (on land); as well as drift ice subfacies and ice tongue subfacies (among subaqueous facies). The frequency of the individual subfacies is changing and depends, first of all, upon the physic-dynamical nature of a glacier and the kind of the subglacial relief. Thus, the ablation facies (III 1) may be divided into the stagnant ice subfacies (IV 1) end the dead ice subfacies (IV 2). The basal till facies comprises, in addition to the subfacies mentioned above (IV 4 and IV 5), the active (piled) ice subfacies (IV 3), too. The morainic deposits of this subfacies were formed during the inland ice advance onto the terrain hindrances such as thresholds, edges, elevations, a.o. In this case, the active ice was piled up, and after its melting, morainic deposits were laid down, characterized by a considerable thickness determined by the height of the hindrance. Small, distinctly wedged out patches and lenticles of the morainic deposits, are a remainder of the dead ice blocks. The morainic material melted out of various blocks and fragments of the glacier ice floating in a water basin was previously graded fractionally and then sedimented. In the deposits of sensu strict aqueous sedimentation it makes lenticles and intercalations. These are morainic deposits of drift ice subfacies (IV 6 and IV 8). Morainic deposits of ice tongues may have been formed when the glacier front was on the bottom of a water basin. This took place in shallow water (littoral) basins. The families of morainic deposits were distinguished on the basis of lithological criteria. Here are two families distinguished: boulder clays (V 1, V 3, V 5, V 6, V 8, V 11, V 14 and V 16) and boulder sands and gravels (V 2, V 4, V 7, V 9, V 12 and V 15). Within the drift ice subfacies a family of graded boulder clays (V 10 and V 13) occurs. The family of boulder sands and gravels was not distinguished in the drift ice subfacies, mainly due to some difficulties in separating these deposits from the sands of water sedimentation sensu stricto. Each family, e.g. that of boulder clays, includes a series of stratigraphical or regional lithotypes (VI). The subdivision into lithotypes depends upon the vertical and horizontal lithologic variations in morainic deposits of a given family. The amount of lithotypes is not constant and, first of all, depends on the exactness of geological reconnaissance made in the region considered. At present, for example, we can determine the lithotypes of boulder clays for various Pleistocene stratigraphical units that correspond to both glacial epochs and stages. A complex of the features determining a lithotype is not uniform either in the individual regions or stratigraphical horizons. A differentiation in properties of the lithotypes is for the most part of quantitative character, and only sporadically of qualitative one. Each feature of the morainic deposits appears in a definite relation to the remaining features of these deposits. Such mutual relations are a result of the genesis of the morainic deposits, thought to be an algebraic sum of all the weathering, denudation and sedimentary processes that take place under the definite historic-palaeogeographical, facial and physic-dynamical conditions. It should be added here that the genetic classification presented in this paper concerns unaltered morainic deposits only.


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