The Tumlin Sandstone (Holy Cross Mts, Central Poland): Lower Triassic deposits of aeolian dunes and interdune areas

Abstract

Recognition of the Lower Triassic sedimentary environment of the Tumlin Sandstone (Holy Cross Mts, Central. Poland) has been based mainly on sedimentary features observed in large quarry exposures. The Tumlin Sandstone, c 100 m thick, is characterized ,by a very large-scale hi~-angle cross-stratification which is thought to have been formed on lee-slopes of aeolian dunes, mainly as a result of a grainfall process. The cross-strata usually pass downdip into sub horizontal, laminated deposits accumulated over the interdune area. These deposits contain in places subordinary intercalations formed by ephemeral waters, both flowing (lenses of structureless sandstones) and stagnant (mudstone layers). The cross-stratified sandstones with the underlying subhorizontal deposits form, as a rule, thick layers separated by extensive erosional bounding surfaces that are subhorizontal, and sligthly concave upward over a considerable distance. Their windward parts usually display a wide scoop-like forms resultant from a wind erosion; the details of its formation remain however unclear. The sedimentary environment of the Tumlin Sandstone is to be regarded as a field of transversal dunes migrating northward due to prevailing unidirectional winds. This field occupied part of a midcontinental basin situated at the axis ,of the maximum subsidence of the Danish-Polish Trough.