dropstone
Sign in to savethumb|300px|A dropstone of quartzite in layered [[rhythmite at Itu, Brazil]] Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks or pyroclastic beds. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is evidence that they were not transported by normal water currents, but rather dropped in vertically through the air or water column, such as during a volcanic eruption.
Article
10 sectionsContents
- Background
- Origin of dropstones
- Glaciers
- Volcanoes
- Turbidity currents
- Biological rafts
- Meteorites
- See also
- References
- External links
thumb|300px|A dropstone of quartzite in layered [[rhythmite at Itu, Brazil]] Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks or pyroclastic beds. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is evidence that they were not transported by normal water currents, but rather dropped in vertically through the air or water column, such as during a volcanic eruption.
== Background == When deposited into fine layered mud, such evidence includes an impact depression beneath the dropstone, and indication that the mud has been squeezed up around the edges of the falling rock. Subsequent deposits of mud drape over the dropstone and its crater. Glacial dropstones, involving rocks falling out of icebergs, are one of the most common types of dropstone preserved in the geological record, particularly when deposited in low-energy deep sea or lake environments. Dropstones differ from erratics found in glacial till in that they are deposited in a lake or marine environments. Dropstones may also be deposited by a variety of non-glacial means.