Deep vs shallow – two contrasting theories? A tectonically activated Late Cretaceous deltaic system in the axial part of the Danish-Polish Trough; a case study from SE Poland
Authors: Remin Zbyszek , Cyglicki Michał , Niechwedowicz Mariusz 
Published: June 2021

Abstract. The Danish-Polish Trough – a large Trans-European sedimentary basin stretching from Denmark, through Germany, to south-eastern Poland and even further to the south into Ukraine, had undergone an uplift during the Late Cretaceous, which in consequence resulted in its inversion and development into the Mid-Polish Anticlinorium. In many existing paleotectonic interpretations, SE Poland, i.e. the subsurface San Anticlinorium and the recent-day Roztocze Hills area was included during the Late Cretaceous into the Danish-Polish Trough, representing its axial and most subsiding part. Such a paleotectonic model was the basis for facies and bathymetric interpretations, assuming that upper Cretaceous sediments deposited close to the axial part of the Danish-Polish Trough (e.g. Roztocze) were represented by the deepest facies. Several studies performed in recent years contradict this concept. The growing amount of data indicates that already from the Coniacian-Santonian times, this area was a land-mass rather than the deepest part of the basin – the same is true for the Campanian and Maastrichtian times. Additionally, recent discoveries of cyclic middle Campanian deposits of shallow deltaic origin, along with a decreasing contribution of terrigenous material towards the NE, have led to the adoption of new facies and bathymetric models, being all in opposite to most of the previous interpretations. The new interpretation implies the presence of a land-mass area in the place where formerly the deepest and most subsiding part of the Danish-Polish Trough was located. Here we document in detail the Late Cretaceous deltaic system, i.e. the Szozdy delta developed in the axial part of the Danish-Polish Trough. The middle Campanian deposits which crop out extensively in the middle Roztocze Hills region, close to the village of the Szozdy, exhibits coarsening-upward tripartite cyclothems. The sequence was deposited in a shallow-water, delta front platform setting. Three facies associations have been distinguished: (1) dark grey calcareous mudstone, deposited in prodelta environment, (2) yellow calcareous sandstone unit, interpreted as prograding delta front lobe deposits of fluvially-dominated though wave/tidally influenced setting, and (3) calcareous gaize unit deposited in areas cut-off from the material supply. The sequence as a whole was accumulated by repeated progradation and abandonment of deltaic complexes. This interpretation is supported by the new sedimentological, palynofacies, and heavy mineral data. The latter is also discussed in the context of their possible source rock provenance, which might suggest a different burial history than thought so far. The development of the Szozdy delta system is placed next to dynamic tectonic processes operating at that time in SE Poland, i.e. the inversion on the one hand, and the generation of new accommodation space for the deltaic deposits by enhanced subsidence. This discovery shed new light on our understanding of facies distribution, bathymetry, paleogeography, and paleotectonic evolution of the south-easternmost part of the inverting Danish-Polish Trough into the Mid-Polish Anticlinorium during the Late Cretaceous times.