3 research outputs found
Early Badenian transgression on the outer flank of Western Carpathian Foredeep, Hluchov area, Czech Republic
This
multidisciplinary
study, based on borehole cores from the Hluchov
area in Czech Republic,
docu-
ments
an early
Badenian
marine transgression on the outer flank of the Western Carpathian
Foredeep
. The
shallow-marine deposits represent coastal transgression over a terrestrial topography of weathered pre-Cenozoic
bedrock. The lower facies association (FA1) consists of
siliciclastic
sediment derived from local substrate erosion.
Facies indicate a wave-dominated environment with unstable bottom, variable rate of sediment supply and an
incremental rise of relative sea level. The upper facies association (FA2) consists of carbonates indicating a major
landward shift of shoreline, decline in
siliciclastic
input and further sea-level rise. The succession represents a
transgressive
to
highstand
systems tract.
The maximum flooding surface,
ca
. 1 m above the FA1/FA2 boundary, is signified by an anomalous decrease
in K and Th, an increased Th/K ratio and highest U concentration. The heavy-mineral assemblages in FA1 confirm
local sediment provenance, whereas those in FA2 indicate broader sediment derivation, including volcanic
component from contemporaneous
rhyolitic to
rhyodacitic
eruptions. The deposits contain a wide range of marine
fauna, with the foraminifers and molluscs indicating an early Badenian age. Molluscs, bryozoans and echinoderms
indicate a normal-salinity environment with a decreasing hydraulic energy. Foraminifers
indicate salinity
fluctua-
tions
in the lowest part of the succession. The isotopic composition of mollusc shells shows marked inter-species
differences and a general negative shift in the
d
13
C and
d
18
O values, indicating diagenetic
alteration. The impact
of diagenetic
processes appears to have been controlled by sedimentary facies. The highly negative
d
13
C and
d
18
O
values correspond to sediment layers with the highest Th/K ratios and hence low clay content. Sediment
permea-
bility
was thus probably crucial in controlling the differential circulation and impact of diagenetic
fluids
Sedimentological and palaeocological records of the evolution of the south west ern part of the Carpathian Foredeep (Czech Republic) during the early Badenian
The depositional environment of the southern part of the Carpathian Foredeep in the Czech Republic was studied in two boreholes using sedimentological and palaeontological methods. Eight lithofacies were recognised within cores of the early Badenian deposits, comprising two facies associations, namely deposits of a coarse-grained Gilbert delta and offshore deposits. As sem blages of foraminifers document the early Badenian (Middle Miocene age). Two types of assemblages were recognised: (1) primary taphocoenoses reflecting the original environment of sedimentation, i. e. a relatively deep sublittoral (circalittoral) environment with low to normal ox ygen bottom conditions and deep-water euryoxibiont foraminifers, numerous planktonic foraminifers, agglutinated foraminifers and mixed assemblages of deep- and shallow-water foraminifers, (2) secondary taphocoenoses of shallower sublittoral (infralittoral) condition redeposited into the basin by gravity currents. These assemblages contain shallow-water foraminifers coupled with an abundant and diverse bryozoan fauna