Explanatory notes to the digital geological map of the Rax ... - KATER

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KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ 13 Fig. 3
KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ 1.4 Tyrolic Nappe System (Göller Nappe) TRIASSIC ROCKS (51) – (44) In the southernmost parts of the Göller Nappe only a few occurences of Wetterstein dolomite (51) are preserved due to tectonic dissection. In this area they are mainly of lagoonal origin. According to the Early Carnian regression the marin to brackish Lunz Sandstone (50) has filled up the basins between the Wetterstein platforms. In areas outside the project area they locally contain coal seams. A subsequent following transgression has lead to partly hypersalinar conditions, causing the deposition of limestones and dolomites with local evaporites (gypsum) - the Opponitz Formation (49) . Far behind the Dachstein reef barrier a large lagoonal environment extended all over the NCA with the intertidal Hauptdolomit (48) in distal parts, “Plattenkalk” (47) as a transitional facies and thick bedded Dachstein limestone (46) in the subtidal lagoon. In the Uppermost Triassic ("Rhaetian") once again increasing terrigenious influx has reduced the carbonate platforms. The Hauptdolomit area and parts of the Dachstein lagoon became covered by the marly Kössen Formation (45) borderd by Rhaetian reefs. A local recurrence of carbonatic sedimentation has lead to the deposition of an “Upper” Dachstein limestone (44). JURASSIC ROCKS (43) – (34) At the beginning of Jurassic the Austroalpine shelf drowned completely, basinal conditions prevailed until the Early Cretaceous with the only exception of local Plassen carbonate platforms (Late Jurassic - Earliest Cretaceous) in southern parts of the NCA, especially in the realm of Juvavic nappes. Parts of the Hettangian are often missing at the base of the Jurassic limestones. The reason - subaereal exposure or submarine non-deposition - is still in discussion. Neptunian sills and dykes filled with red or grey Liassic limestones are known, cutting down several meters into the Norian shallow water carbonates. Irregular drowning and synsedimentary faulting has caused a complex seafloor topography with reddish/grey crinoidal limestones (Hierlatz Limestone, 43) and red ammonoid limestones (Adnet Limestone, 42) mainly above subsided former shallow carbonate platforms. Grey marly/cherty limestones of Allgäu Formation (40) have been deposited in the deeper troughs between. Very thin condensed sequences of these and other Jurassic red limestones are summarized as Jurassic condensed limestones in general (41). Jurassic red limestones are bioclastic wackestones, mainly made of nannoplankton (Schizosphaerella, coccoliths) and very finegrained biodetritic material. After globigerinids had evolved in the Middle Jurassic, they also became a major component of these sediments along with the tiny shells ("filaments") of the probably planctonic juvenile forms of the bivalve Bositra. The macrofauna mainly consists of crinoids and in some places brachiopods and ammonites. Ferromanganese hardgrounds and nodules are frequent. Less condensed sequences are composed of grey limestones with chert (39), with limestone breccias (38) and red limestones with chert nodules or intercalated layers of thin bedded red radiolarite (37). 14
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Explanatory notes to the digital geological map of the Rax ... - KATER

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