Warunki klimatyczne środowiska sedymentacji martwicy karniowickiej

Małgorzata Ćwiżewicz, Joachim Szulc



Rotliegendes deposits in the Sudetes occur in two NW-SE trending synclinorial depressions - Intrasudetic and North-Sudetic basins. The basins are separated from the adjacent areas by faults which were already active when the basins were filled. The basins started in to existence as large accumulation areas in the early Carboniferous (NSS) and Stephanian (NPS). During the Stephanian and early Permian the Sudetes were characterized by basin-and-range style of geodynarnic activity, sedimentation, and topography. The most important factors which influenced the basin infills and facies patterns were the rate and style of basin floor subsidence and of sediment supply.
The Permo-Carboniferous sedimentary sequence of the Sudetes reveal a long lasting climatic control, and continual change of warm climate from wet to arid, which resulted in a gradual change from peat-forming to red bed sedimentation. Climatic conditions for plant vegetation got systematically worse. Lacustrine sediments appear to be especially good paleoclimatological indicators. An amount and degree of preservation of organic matter within lacustrine horizons gradually decrease up the Stephanian-Saxonian succession. The Upper Saxonian fanglomerates display features typical of arid alluvial fans including caliche horizons more common and better developed up the sequence.
During the Stephanian and Autunian three major events of rapid subsidence caused rejuvenation of the Sudetic landscape, which led to intense accumulation of 179 coarse grained alluvial material along the basin margins. During these alluvial phases the north-western parts of both basins were levelled and occupied by vast alluvial braidplains while their south-eastern parts were topographically more diversified due to the existence of several smaller subbasins. The subsidence events• alternated with periods of "normal rate", permanent subsidence. Then the landscape was levelled successively and the basins were filled with fluvial sediments. During these fluvial phases the axial zones of the basins were dominated by river systems with the prevailing longitudinal transport direction. The continual filling of the basins under a relatively slow subsidence resulted in worse drainage conditions and, eventually, resulted in the formation of lakes. During the Autunian three distinct lacustrine phases left thick sequences of lake sediments. Such a scheme of repeated basin evolution stages from alluvial to lacustrine environment is reflected by three asymmetric, fining upward cyclothems. These large scale features of the basin filling successions are allocyclic, i.e. they were initiated and controlled by extra-basinal factors.
The lacustrine sediments in both basins contain symmetric, transgressive-regressive sequences. These reflect an autocyclic mechanism of lake evolution, which seems to be characteristic of some intermontane basins. The main factor controlling lake shore progradation, lake transgression, as well as water retention in the basin is the basin slope inclination. If the slope inclination is higher than the critical angle, then the shore progradation and lake regression take place. On the other hand, if the slope inclination sufficiently decreases, mainly due to basin filling, then the retented water floods the basin.

Pełny tekst: