Porifera-microbialites of the Lower Liassic (Northern Calcareous ...

42
4.11. Rettenbachalm/Jaglingbach (RJ)
Geological Setting:
� East of Bad Ischl, Liassic limestones are exposed along the Jaglingbach (north of the
Rettenbachalm, ÖK50 / Blatt 96 Bad Ischl, R 07 7885, H 52 8425). The section crops out at the river
bed that is accessible by a small forest track that starts at the parking lot west of Rettenbachalm
(Fig. 22).
� Here the river bed is formed by folded red Liassic limestones (knobby Adnet facies type with
ferromanganese crusts) that smoothly dip to SE (Pl. 5 C-E). About 200 m to the north where two
river branches come together (with several swirl pools), the red limestones are preserved in
cracks and on top of grey Triassic Dachsteinkalk limestones. Following the river in NE direction,
the eastern bank shows cherty limestones of the Allgäu Formation (Scheibelberg limestones).
� As given by Böhm (1992) and shown by Schäffer (1982) the Jurassic sequence seems to be an
autochthonous part of the Höllengebirge nappe, where a basin had formed on top of the drowned
Triassic carbonate platform in Lower Sinemurian time.
Facies Analyses:
Fig. 22. Location map of the
Triassic-Jurassic boundary section at
the river bed of Jaglingbach.
� “Knobby Adnet facies along the river bed” (samples RJ 1-6, Pl. 5E-G) and “Liassic red
limestones at river junction” (sample RJ 8): Red limestones that formed as breccias with rounded
clasts of spiculites. Sponge spicules in the clasts are present in high abundances. All are isolated
ones that do not show any arrangement of former skeletal structures. Most of them are thick-
rayed monaxons, tetraxons and dichotriaens that belong to non-rigid demosponges. To a lesser