Identification of a Quaternary rock avalanche deposit (Central Apennines, Italy): Significance for recognition of fossil catastrophic mass-wasting

Diethard Sanders, Teresa Dendorfer, R. Lawrence Edwards, Gina E. Moseley, Hugo Ortner, Simon Steidle

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Whereas deposits of extremely-rapid, ‘catastrophic’ mass wastings >105 m3 in volume (for example, the Marocche di Dro rock avalanche in the Southern Alps and the Flims rockslide in the Western Alps) are easily recognized by their sheer mass and blocky surface, the identification of fossil catastrophic mass wastings partly removed by erosion must be based on deposit characteristics. Herein, a ‘fossil’ (pre-last glacial) rock avalanche, previously interpreted as either a till or debris flow, is described. The deposit, informally called ‘Rubble Breccia’, is located in the intramontane Campo Imperatore halfgraben that is bounded by a master fault with up to ca 900 m topographic throw. Based on documentation from field to thin section, and by comparative analysis with post-glacial rock avalanches, tills and debris flows, the Rubble Breccia is reinterpreted as a rock avalanche. The Rubble Breccia consists of an extremely-poorly sorted, disordered mixture of angular clasts from sand to block size. Many clasts show fitted subclast boundaries in crackle, jigsaw and mosaic fabrics, as diagnostic of catastrophic mass wasting deposits. Intercalated layers of angular to well-rounded clasts of coarse sand to fine pebble size, and deformed into open to recumbent folds, may represent shear belts folded during terminal avalanche propagation. The clast spectrum of the Rubble Breccia – mainly shallow-water bioclastic limestones, Saccocoma wackestones and other deep-water limestones and dolostones – is derived from the front range along the northern margin of the basin. Calcite cement found within the Rubble Breccia was dated with the U/Th disequilibrium method to 124.25 ± 2.76 ka bp, providing an ante-quam age constraint to the rock avalanche event. Because catastrophic mass wasting is a common erosional process, fossil deposits thereof should be more widespread than have been identified to date, although this may be a consequence of misidentification. The criteria outlined here provide a template to identify fossil catastrophic mass wasting deposits of any age.

Original languageEnglish (US)
Pages (from-to)2099-2130
Number of pages32
JournalSedimentology
Volume69
Issue number5
DOIs
StatePublished - Aug 2022

Bibliographical note

Funding Information:
The U/Th dating was supported by funding from the Austrian Science Fund (project number Y 1162 – N37) to GEM. The comments of four anonymous reviewers helped to shape presentation of data.

Publisher Copyright:
© 2022 The Authors. Sedimentology published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists.

Keywords

  • Apennines
  • Campo Imperatore
  • U/Th
  • intramontane basin
  • rock avalanche

PubMed: MeSH publication types

  • Journal Article

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