Geological arguments against a Late Cretaceous(?) age for the freshwater limestone bodies in the Köves Valley, (Vértes Hills, Hungary)

Abstract

In a recent paper SIKLÓSY et al. (2006) — following PEREGI &
KORPÁS (2002) and SIKLÓSY (2003) — described calcite bodies in
the Vértes Hills, Hungary. The geochemical character of these
bodies is supposed to be similar to those related to the Late
Cretaceous(?) lamprophyre magmatism, known in the Transdanubian Range (HORVÁTH et al. 1985a, SZABÓ et al. 1993, GYALOG
& HORVÁTH, 2004). The geochemical tracers would enable a Late
Cretaceous(?) age to be confirmed for both the calcite dykes, and
some of the travertine cones. In our short paper we list geological
observations and arguments which support the Cretaceous – early
Palaeogene age of the red calcite dykes, but which contradict
giving the same age to the circular freshwater limestone.
The red, brownish red calcite dykes are exposed on a subhorizontal denudation surface; the latter was formed in the course
of several episodes of subtropical denudation during the Late
Cretaceous to Middle Eocene (Figures 1, 2). Clasts of these dykes
can be found in the basal conglomerate or limestone layers of
Middle Eocene (Bartonain) age (KERCSMÁR 1995, 2004). These
dykes are similar to those described in other parts of the
Transdanubian Range, and they can be presumed to be related to
Late Cretaceous lamphrophyre magmatism (SZABÓ et al. 1993,
DEMÉNY et al. 1997, GYALOG & HORVÁTH 2004). It is to be noted
that in all except one case, the formation of the dykes cannot be
better estimated than as having occured in the Albian to Middle
Eocene period.
On the other hand, the freshwater limestone bodies occur on
the slopes of the Quaternary (Pliocene?) Köves Valley (Figure 3).
If these bodies had formed in the Late Cretaceous the valleys would
have existed already at that time. However, the Köves Valley
terminates in the Kápolnapuszta depression, which started to form
only in the Late Miocene (FODOR et al. 2004). The age of the valley
(and thus the travertine cone inside) could hardly be older than Late
Miocene.
We also question the possibility that the travertine cone would
have been precipitated in subsurface caves; no formation
mechanism of the caves (e.g. hydrothermal/descending cold
water), no driving force for water circulation, and no other
examples of appropriately sized caves have been discussed or
demonstrated.
Finally, we comment on the conclusions drawn from the
appearance of accessory minerals, such as monacite, xenotime,
zircon and rutile in the travertine cones; these minerals are also
cited as proofs of the connection with Cretaceous magmatic rocks.
These minerals are often angular in shape (SIKLÓSY et al. 2006,
Table IV/2, 4) and can hardly be low-temperature hydrothermal in
origin. It is probable (but not discussed in detail) that minerals were
derived from denudation processes (e.g. wind or slope wash) and
incorporated into the precipitating calcite on the surface, at the
moment of water discharge.