Previous Next Tübinger Geowissenschaftliche Arbeiten, Series A, Vol. 52, pp. 146 - 147.
Abstracts of the 4th Workshop on Alpine Geological Studies, Tübingen 21-24 Sept. 1999

P127

Sequence stratigraphy of Late Triassic Distal Periplatform Limestones from the Northern Calcareous Alps an example from the Kälberstein Quarry (Berchtesgaden Hallstatt Zone)

Hans-Jürgen Gawlick* 1, Florian Böhm 2


 1 

Institut für Geowissenschaften: Prospektion und Angewandte Sedimentologie, Montanuniversität Leoben, Austria

 2 

GEOMAR, Forschungszentrum für Marine Geowissenschaften, Kiel, Germany

 * 

Correspondence:  Peter Tunner Straße 5, A-8700 Leoben, Austria (Hans-Juergen.Gawlick@unileoben.ac.at)

 

The Carnian-Norian section of deeper-water Hallstatt limestones, exposed at the Kälberstein quarry (Berchtesgaden), is described and given a sequence stratigraphic interpretation. The biostratigraphic results demonstrate that the section comprises a complete succession from the latest Carnian (Tuvalian 3/I) to the late Norian (Sevatian 2). As expected from the periplatform setting of the Hallstatt Zone, calculated sedimentation rates are partly conform with prograding sequences observed on the contemporary Dachstein platform. However, discrepancies exist, mainly for the middle Norian, which are not well explained by local factors. This points to an incomplete knowledge of the platform sequences. The sequence stratigraphic framework based on platform data should be complemented with data from the periplatform Hallstatt Zone. Available published data for the Late Triassic converge on the presence of three major transgressional events during the Late Carnian to Early Rhaetian interval:

1. A major transgression took place in the Tuvalian 3 (top of Opponitz Fm., in Krystyn and Lein 1996). The following highstand phase probably started in the latest Tuvalian and was possibly interrupted by a short transgression during the higher Lacian 1. The late Tuvalian/early Lacian transgressive beds form the base of the progradational Hauptdolomit, Dolomia Principale and Dachsteinkalk deposited during the subsequent highstand of the Lacian.

2. The next major transgression happened during the later Alaunian. This trangressive beds form the base of the Sevatian platform progradation connected to a highstand phase.

3. The third major transgression took place during the early Rhaetian 1 with pelagic limestones encroaching the formerly prograding Dachstein platform.

The Kälberstein succession agrees well with the Tuvalian-Lacian platform sequences (Fig. 1): We find intermediate sedimentation rates during the latest Tuvalian corresponding to a progradational platform interval. The transgression of the higher Lacian 1 is not clearly visible with the biostratigraphic resolution of our section. However, there is a period of likely strong condensation during the Lacian 1/1 which could be interpreted as a lowstand interval preceeding the transgression. The platform progradation of the Lacian 1-2 is well reflected in high sedimentation rates. The rate quickly drops in the late Lacian and remains at a very low level until the Alaunian 3. This points to either lowstand/emergence or transgressive conditions on the platform, while according to Krystyn and Lein (1996) highstand conditions were maintained until the middle Alaunian.

The short sedimentation pulse in the Kälberstein section during the Alaunian 3/2, indicating highstand shedding, is in contradiction to the platform record, where a transgressive phase is assumed at this time. In the context of the reported widespread increase of tectonic activities around the Alaunian/Sevatian boundary, we cannot exclude local tectonics as a cause of this discrepancy. However, increased sedimentation rates of the late Alaunian are a widespread phenomenon in the Hallstatt Zone. Moreover, reliable indications of tectonic activities in the Hallstatt Zone are only known from the early Sevatian. We assume that a short progradational phase exists in the Alaunian 3/2 of the Dachstein platform, which has so far been overlooked.

Finally, the Sevatian progradation is only weakly reflected in our data with rates comparable to the late Tuvalian transgressive phase. The most likely explanation is that the bulk of the exported sediments was stored in basins close to the platform margins (Zlambach facies), which formed in connection with the early Sevatian tectonic activities.

We conclude that the sedimentation rates of the Kälberstein section are strongly influenced by platform export during the Tuvalian-Lacian and possibly the Alaunian. Discrepancies with the platform record in the late Lacian and Alaunian emphasize the fragmentary nature of the Alpine sequence stratigraphic framework for the Norian and underscore the need of further investigations both in platform areas and in the periplatform record of the Hallstatt Zone.

  

Krystyn, Leopold , 1985,  Bericht 1984 über geologische Aufnahmen in den Kalkalpen auf Blatt 94 Hallein.. Jb. Geol. B.-A., 128(2):263-264.

Krystyn, Leopold ,   Lein, Richard , 1996,  Triassische Becken- und Plattformsedimente der östlichen Kalkalpen.. Exkursionsführer Sediment 96, Berichte der Geol. B.-A., 1996/33:1-23.

Schlaf, J. ,   Krystyn, Leopold ,   Lein, Richard , 1997,  Sequenzstratigraphie obertriadischer Karbonatplattformen aus den Julischen Alpen.. Schriften d. Alfred Wegener Stiftung, Terra Nostra, 97/2:210-211.

Fig. 1 - Chronostratigraphy, facies and sedimentation rate estimates for the Kälberstein quarry section.

Figure 1  

Chronostratigraphy, facies and sedimentation rate estimates for the Kälberstein quarry section, compared to the sequence stratigraphic framework for the adjacent platforms. Sequences of the Kälberstein section are interpretations based on sedimentation rates. Two tectonic events are expressed in the Kälberstein section, indicated by neptunian dykes filled by sediments of the higher Lacian 1 and the higher Alaunian 1. HST,TST,LST: highstand-, transgressive-, lowstand systems tract, respectively, TECTONIC: tectonic event. Platform sequences mainly based on Krystyn and Lein (1996), Krystyn (1985) and Schlaf et al. (1997). Dashed lines in sedimentation rate plot are error range estimates, allowing for 0.2 Ma uncertainty for the subzone durations and 1 m uncertainty for the interval thickness.