Blackened Limestone Pebbles: Fire at Subaerial Unconformities

Abstract

Introduction

Field Observations & Some Experimental Results

Discussion

Submarine Blackening & Accumulation of Salt-and-Pepper Sands

Conclusions

Acknowledgements

References

Conclusions

Simple experiments and observations have shown that pebbles of limestone (soilstone crust, coral, poorly cemented grainstone, and molluscs) can blacken almost instantaneously during natural forest fires. Temperatures between 400° and 500°C readily cause blackening and can account for the bulk of angular black pebbles observed in Pleistocene and Holocene limestones throughout the Caribbean.

The fact that fire-blackened pebbles occur in young rocks where their processes of formation can be observed suggests that they should be equally abundant in ancient rocks. Once observed and analyzed, the presence of ancient black pebbles could provide valuable clues to the environment of deposition and the nature of underlying unconformities.

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