Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 57. (Budapest 1965)
Csalogovits, I. J.: Geological and petrological conditions of the Szanda - Bercel area
On account of the preclusive circumstances mentioned, the coarse gravel deposited on the Burdigalian gravel can be classified only as belonging to the lower Miocene, and must be a Helvetian sediment that was formed during the pre-orogenic movements connected with the tectonism that preceded the volcanic phase. But it is the Burdigalian gravel that can be regarded as the widespread base of andésite, as the coarse gravel layer is not a widely distributed formation. The Helvetian schlier mentioned by NOSZKY, Sr., does not occur in this area. Errors may arise in interpreting the stratigraphie situation of andésite (concerning its basic rock) if andésite adjoins the Chattian schlier faciès along the fault, or along the contact line. Stratum springs, frequent in the area, do not emerge from under the andésite covers at the boundary of the andésite sediment as could be excepted from impermeable clayey schlier, but at the boundary of the Chattian erosion surface and the Burdigalian gravel layer that forms the base of andésite. The coal layer of Becske is a strint deposit: the hydrogeological conditions make working difficult, both at the foot and roof. No safe estimates can be made, thus working has been discontinued. The layer is described by BENEDEK as follows (Fig. 3). 3. The Tortonian Stage The formations of the Tortonian stage are represented by the rocks of pyroxeneandesite volcanism. Because the immediate roof is missing (litothamnic limestone) the age of the volcanic series in this area cannot be established. Geological and petrological description of the formation will be given later. 4. Pleistocene — Holocene The Pleistocene formations are represented by loess that covers considerable part of the area. In the valleys it is occasionally of the redeposited-clay character. No loam beds occur in the outcrops. The formations are homogenous, limy, and contain snails occasionally (Pupilla sp., Pupa sp.) when occurring in the original form of deposition. The effects of glaciation are indicated by solifluctive, baggy forms that can be noted on the surface of Burdigalian gravel (gravel pits at Becske, Söprős). The Holocene sediments are formed by the clayey sediments of the beds of brooks. The tectonic conditions The geological structure of the area indicates a high degree of tectonism of several phases. The first tectonic phase in indicated by the erosion discordance noted between the Chattian and Burdigalian formations. This tectonic phase is similar to the subsequent ones; it is of expansive character. The somewhat displaced position of the Chattian series is accompanied by faulting displacements — resulting from slackening — and by erosion later on. On the basis of a rhythmicity that does not extend over the levels regionally, and the local formation of coal appearing in the Burdigalian layers, a base of irregular movement can be assumed. The coarse gravel layer deposited on the upper part of the gravel layer indicates a pre-orogenic tectonism that preceded Lower Tortonian volcanism. This may have been a tectonic phase that was temporally connected with the Helvetian, lower rhyolite tuff level. Also the syntectonic movements of volcanism are characterized by crack structures of NW — SE trend which are a result of expansive movement, and in which the uplift of magma took place. The formation of tension structures, related with the
