Deep vs. shallow – two contrasting theories? A tectonically activated Late Cretaceous deltaic system in the axial part of the Mid-Polish Trough: a case study from southeast Poland
Authors: Remin Zbyszek , Cyglicki Michał , Niechwedowicz Mariusz 
Published: March 2022

Abstract. The Polish Basin is a part of a trans-European sedimentary basin comprising
the Central European Basin System and stretching from Denmark through
Germany to southeastern Poland, and even further to the south into Ukraine.
It experienced uplift during the Late Cretaceous, which consequently
resulted in the inversion of its axial part (i.e., the Mid-Polish Trough) and
development into the Mid-Polish Anticlinorium. In many existing
paleotectonic interpretations, southeast Poland – i.e., the subsurface San
Anticlinorium and the present-day Roztocze Hills – was included in the
Mid-Polish Trough during the Late Cretaceous, representing its axial, most
subsiding part. This paleotectonic model was the basis for facies and
bathymetric interpretations that assumed Upper Cretaceous sediments,
deposited close to the axial part of the Mid-Polish Trough (e.g., in the
Roztocze Hills), constituted the deepest facies. In recent years, several
studies have contradicted this notion. A growing body of data suggests that
this area (southeast Poland) was already a landmass by the Coniacian and
Santonian – and certainly in the Campanian and Maastrichtian – rather than
forming the deepest part of the Polish Basin. The shallow marginal marine, cyclic middle Campanian, marly to sandy
deposits, recently discovered in the Roztocze Hills, were interpreted to be
of deltaic origin. This has led to the adoption of new facies and
bathymetric models, which – notably – are in stark opposition to most
previous interpretations. Notably, the new interpretation implies the
presence of a landmass in the place where, in prior frameworks, the deepest
and most subsiding part of the Polish Basin (i.e., Mid-Polish Trough) was
located during the Cretaceous. Here, we document this Late Cretaceous depositional system – the Szozdy
delta developed in the axial part of the Mid-Polish Trough. These middle
Campanian deposits crop out extensively in the Roztocze Hills region, close
to the village of Szozdy, and exhibit coarsening-upward tripartite
cyclothems. Three facies associations have been distinguished: (1) dark grey
calcareous mudstones, (2) a yellow calcareous sandstone, and (3) calcareous
gaize lithofacies. The sequence, as a whole, was accumulated via the
repeated progradation and abandonment of deltaic complexes on the delta
front platform setting, with the primary transport direction originating
from the axis of the inverting Mid-Polish Trough (thus from the subsurface
San Anticlinorium) toward the northeast. This interpretation is supported by
a suite of sedimentological, palynofacies, and heavy mineral data. The development of the Szozdy delta system is framed in the context of the
dynamic tectonic processes operating contemporaneously in southeast Poland:
that is, tectonic inversion (uplift) on one hand, and the generation of new
accommodation space via enhanced subsidence on the other. This discovery
sheds new light on our understanding of Late Cretaceous facies distribution,
bathymetry, and paleogeography and might potentially suggest a different burial
history than assumed so far.