Original paper
Kondensationserscheinungen in der marokkanischen und alpinen Mittelkreide (Apt, Alb).
[Stratigraphic Condensation in the Moroccan and Alpine mid-Cretaceous (Aptian, Albian.]
Bergner, H.D.; Gebhard, G.; Wiedmann, J.
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 165 Heft 1 (1982), p. 102 - 124
23 references
published: Dec 17, 1982
DOI: 10.1127/njgpa/165/1982/102
ArtNo. ESP155016501008, Price: 29.00 €
Abstract
From the western High Atlas (Morocco), the Subalpine Chains (SE-France) and the Helvetic Alps (S-Germany, Austria) mid-Cretaceous (Aptian, Albian) stratigraphic condensations are described and compared. In the Aptian of the western High Atlas two different condensation events can be recognized. The lower one is rich in glauconite and phosphorite and of upper Lower Aptian age. This condensation event is diachronous: ammonite faunas become generally younger from the West to the East. However, the upper one, a marly limestone of Upper Aptian age is isochronous. The lower condensation horizon was formed in a high-energy environment during a transgression episode whereas in the upper horizon low-energy conditions predominated. In contrast, the Aptian and Albian glauconitic-phosphoritic condensed sequences of SE France are of limited lateral extent and vary in their stratigraphic range. They were deposited under high-energy conditions and are preserved as infillings of small syntectonic depressions. In the Helvetic Alps condensation horizons may have smaller (local) as well as larger (regional) lateral distributions. During phases of high sediment input and tectonic movements (“Austrian tectonics”) condensed sequences of only local occurrence were generated (Upper Aptian and Middle Albian) whereas those of larger distribution were formed during phases with lower rate of deposition and tectonic stability (Lower and Upper Albian). The formation of glauconitic-phosphoritic condensation horizons during mid-Cretaceous times can be related to the evolution of subsidence at passive continental margins: the facies characteristics of the condensed sequences are controlled by specific paleogeographical conditions. Condensation follows more or less immediately after a phase of carbonate platform development and, in turn, is in most cases overlain by pelagic series. Condensation is thought to be related to major transgressions and always represents (true) shelf deposits formed between the littoral zone and inner shelf. Wave, current and possibly storm activities have played a major role in sediment starvation. The presence of cold water currents is assumed to exist.
Keywords
Aptian • Albian • condensation • platform • shelf • paleocurrent • undation • wind • submarine relief • regression • phosphorite • glauconite • passive margins • alpine orogeny • section • correlation Alpes maritimes (Nizza region) • Moroccan Atlas; German Alps (Allgäu) • Austrian Northern Alps (Vorarlberg)