Cyclicity in Non-Marine Foreland-Basin Sedimentary Fill: The Messinian Conglomerate-Bearing Succession of the Venetian Alps (Italy)
- M. Marzo and
- C. Puigdefábregas
Published Online: 14 APR 2009
Copyright © 1993 The International Association of Sedimentologists
How to Cite
Massari, F., Mellere, D. and Doglioni, C. (1993) Cyclicity in Non-Marine Foreland-Basin Sedimentary Fill: The Messinian Conglomerate-Bearing Succession of the Venetian Alps (Italy), in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch32
- Published Online: 14 APR 2009
- Published Print: 16 SEP 1993
Print ISBN: 9780632035458
Online ISBN: 9781444303995
- sedimentary fill of the Venetian foreland basin;
- alluvial fan conglomerate deposits, ranging from debris;
- channel sequences, dominated by thick sets;
- Cyclicity in non-marine foreland-basin sedimentary fill;
- Varve-like finely laminated alternations of muddy siltstone and mudstone
Messinian-age continental deposits in the sedimentary fill of the Venetian foreland basin show a cyclical organization. Three facies associations have been recognized: (i) alluvial fan conglomerate deposits, ranging from debris flows to shallow braided gravels and sands; (ii) channel sequences, dominated by thick sets or cosets of planar cross-bedded conglomerate, interpreted as the record of a master system of sinuous and relatively deep rivers, laterally confined by muddy banks and characterized by perennial flow and prolonged floodstages; (iii) fine-grained clastics deposited in a lacustrine basin that formed near the thrust front.
Two ranks of cyclicity have been recognized. Small-scale cycles 12–25 m thick are laterally persistent; each of them comprises a sharp-based lower member of alluvial-fan/fluvial conglomerate/sandstone and an upper fine-grained lacustrine member. These cycles have periods of less than 30 ka and are thought to record the alternating contraction and expansion of the lake system, as a response to fifth-order climatic fluctuations.
Large-scale cyclicity is expressed by unconformity-bounded megasequences hundreds of metres thick, with coarsening-upward and then fining-upward (progradational–retrogradational) trends; the younger of them are bounded by angular unconformities grading along-strike into paraconformities. The evolution of a thrust-cored anticline influenced the geometry of the unconformities: pure compression, generating a growth fold with horizontal axis, produced along-dip angular unconformities. Local transpressive motion resulted in both along-dip and along-strike angular unconformities. Eustatic modulation of large-scale cyclicity may be ruled out, due to the existence of a regional base level for continental sedimentation during the Messinian. The megasequences may record either the pulsatory growth of the thrust-cored anticline, or the interaction of relatively continuous deformation with some external factor, such as climatically modulated fourth-order cyclical changes in the regional base level.