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- Title
Distal alluvial deposits in a foreland basin setting--the Lower Freshwater Molasse (Lower Miocene), Switzerland: sedimentology, architecture and palaeosols.
- Authors
Platt, Nigel H.; Keller, Beat
- Abstract
The Lower Freshwater Molasse (Untere Süsswasser Molasse) crops out over a wide area of the Swiss Molasse Basin. Coarse grained alluvial fan conglomerates dominate in proximal basin areas along the Alpine front. These conglomerates pass northwards into sandstones and mudstones of an extensive north-eastward draining meandering river system which ran parallel to the basin axis. Sedimentological study of outcrops, quarry exposures and boreholes in the basal Miocene ('Aquitanian') has permitted detailed facies analysis of this distal alluvial sequence. The distal Aquitanian is made up of distinct 'architectural elements' characterized by their geometries and sedimentary structures. Each may be assigned to a particular depositional selling: meander belt, levees, crevasse channels and splays, overbank fines and palaeosols, and lacustrine. Meander belt sandstones were deposited in mixed load channels with a dominant bedload component, Sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2-15 m thick and 1501500 m wide. Interbedded rippled, laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30-100g m across. Small scale crevasse channel sandstones 2-4 m thick and 5-10 m across pass laterally into metre scale, medium to fine grained crevasse sandstone sheets. Rare laminated lacustrine siltstones occur only in the north-east part of the basin. Floodplain mudstones and marls make up the remainder of the succession. These display a variety of pedogenic features recording cyclical palaeosol development. Palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis, reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage. Analysis of the organization and distribution of the various sediment bodies...
- Subjects
SWITZERLAND; SUGARCANE products; MIOCENE stratigraphic geology; SEDIMENTOLOGY
- Publication
Sedimentology, 1992, Vol 39, Issue 4, p545
- ISSN
0037-0746
- Publication type
Article
- DOI
10.1111/j.1365-3091.1992.tb02136.x