Olistostrome
A disrupted, heterogeneous sedimentary mass-transport deposit, commonly with blocks in a finer matrix.
Language and route: Italian geological coinage olistostroma. The scientific term was introduced in Italian geological usage, built from Greek elements expressing sliding and a bed or layer. The English form olistostrome reflects that Italian technical term.
Literal gloss: Slide-layer / accumulation of slipped material
The name and its history
G. Flores · 1955, Fourth World Petroleum Congress (Rome)
- What does the word literally mean?
- The English geological word reflects Italian olistostroma, a coinage using Greek olisthánō ‘slip, slide’ and strôma ‘layer, bedding’. The immediate scientific route is Italian, not a direct borrowing of a classical Greek word.
- What did the original author mean?
- Flores's Italian formation olistostroma (1955) denoted chaotic block-bearing masses among normally stratified Tertiary deposits in Sicily; his related olistolith designated individual displaced blocks.
- Why was the name needed?
- Conventional lithostratigraphic descriptions struggled to distinguish large sedimentary mass-transport units from tectonically sheared chaotic complexes in Sicilian geology.
- What evidence supported the original concept?
- The 1955 World Petroleum Congress report is the identified original venue. Pini and colleagues' dedicated historiographical review traces use from Flores's Sicilian units through later international geological debate.
- How has geology changed the concept?
- The term moved from a regional, sedimentary interpretation to a wider mass-transport category; some structurally overprinted examples may be better described as tectonic mélanges, so field criteria and depositional evidence matter.
Further historical context
G. Flores introduced olistostrome and related olistolith in work presented at the Fourth World Petroleum Congress in Rome in 1955. The problem arose in mapping central Sicilian successions in which chaotic bodies containing large blocks occurred between otherwise more orderly layers.
The original concept described mechanically transported, heterogeneous material behaving as a semi-fluid mass. Later use widened across the Apennines and other orogenic belts, and its interpretation became entangled with debates over gravity-driven submarine transport versus tectonic mixing in mélanges. A disrupted rock assemblage is not automatically an olistostrome without sedimentological evidence.
Editorial qualification
1955 Flores attribution supported by dedicated modern historiography; the primary congress paper itself not transcribed in this edition.
Related names
Sources
- Treccani: olistostròma — Greek elements and geological meaning
- Festa et al.: origin and significance of olistostromes — Definition, origin, historic proposal
- Scottish Geology Trust: glossary — Geological definition
- Broquet (1970), history of olistostromes and olistoliths — Historian account of Flores 1955 congress introduction
- Pini et al. (2010), Olistostromes and olistoliths: a historical review — Historical specialist review of the 1955 Flores coinages and later mélange controversy