The karst region of the Western Mecsek Mts. is a hilly area with a maximum elevation
of ~600 m a.s.l. The karst has developed on Triassic limestones, with part of the
drainage basins on lower Triassic sandstones and conglomerates. Our main objective
was to constrain the karst development in time, to identify karstification periods
with respect to climate, and to obtain data on landscape evolution. Cave geometries
were surveyed, and speleothems and allochthonous siliciclastic sediments were extensively
sampled for U-series, cosmogenic radionuclide (CRN) burial and optically stimulated
luminescence (OSL) age determination.Cave passage orientations are dominantly controlled
by tectonic fractures and bedding. Most cavities formed in the vadose zone, only a
few passages show features possibly referring to the phreatic zone. No obvious geomorphic
levels could be identified within the caves. Cave sediments include reworked loess
(dominant), coarse gravels and sands from Triassic red sandstones, red clay, reworked
speleothems (dripstones, carbonate tuff from cave streams), and fragments of the host
rocks. Though several passages used to be filled with fluvially transported sediments,
at present none of the spring caves issues clastic deposits, thus the deep karst system
apparently acts as sediment sink.The CRN burial age of the oldest cave sediments is
~2.5 Ma, in a sinkhole cave now in a valley-side position. The burial ages of sediments
in caves with entrances at or close to present-day valley floors are Middle Pleistocene
to recent.According to the U-series ages, speleothems precipitated at least from the
Middle Pleistocene to the Holocene, with most data concentrating in the last glacial
maximum and in the Holocene, but several ages exceeding the limits of the measurement
method. They formed under all climatic conditions, from glacials to interglacials.
They underwent repeated phases of precipitation and dissolution. Widespread submerged
stalagmites refer to oscillations of the karst water table; measured ages of ~3 ka
and 40-50 ka indicate formation during milder climates, with still lower-than-present
water tables. Based on OSL ages, loess was washed into the caves under both cold and
mild climates in the Late Pleistocene and Holocene. The ages obtained by the different
age determination methods do not allow to distinguish periods with different types
of karst activities, they suggest that both speleothem genesis and sediment transport
happened under all climate types and simultaneously.The burial age of the clastic
infill of the oldest dated cave, which now can practically lacks a drainage area,
be used to infer local incision rate. 2 Ma ago it still received sediment (coarse
sand and sandstone) from non-karstic rocks. Supposing a valley-floor position for
that time at the recent cave entrance gives a valley incision rate of ~15 mm/ky. Pre-
and post-burial surface denudation rates calculated using the CRN data vary between
~12-35 mm/ky.Sandstone cobbles in a cave now lacking non-karstic rocks in the catchment
area indicate drastic drainage changes, the capture of the upper catchment by the
neighbouring watercourse.Research was supported by PURAM, Mecsekérc Ltd. and NKFIH
project FK 124807.
