dropstone


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dropstone

(ˈdrɒpˌstəʊn)
n
1. (Geological Science) obsolete an old name for stalactites
2. geology an isolated rock fragment deposited in sedimentary rock through the water column
References in periodicals archive ?
I encountered a beautifully preserved Ordovician Rugosa coral dropstone in a core that couldn't be more than 3 million years old, thin beds of bright blue and purple clays, and black minerals that faded as I tried to describe them.
"We put the major dropstone event at 2.5 million years, but we think we have evidence for a much earlier time for the beginning of major glaciation." Rock analyses, he says, suggest a "tentative" date of 3.5 million years ago and an "extremely tentative" date of 8 million years ago for glacial onset.
Boulders of baksteenkalk, on the other hand, are dropstones which fell from melting ice floes associated with the river system known as the 'Baltischer Urstrom' or the Eridanos (Rhebergen et al.
The latter are composed of fragments of basalts identified to belong to James Ross Island Volcanic Group (JRIVG) and plutonic rocks (mainly granites), all of them were probably transported by icebergs (dropstones).
The cobbles present within the thickest part of the peat (area of Section A) may be dropstones derived from ice-rafting (C.R.
Some conglomeratic and shale levels with out-sized clasts are interpreted as dropstones. There are some sandstone levels displaying undulated cross-bedding.
When he presented a paper in 1963 on a "Great Infra-Cambrian Glaciation" he was shot down by critics who interpreted his glacial dropstones as products of marine mudslides.
They lack graded beds and coarse silt and sand strata that often characterize glacial lake sediments (varves) and have a low percentage of dropstones. The implication is that active glaciers were not directly calving into these bodies of water, but dammed the basin outlets at lower elevations.
Subsequent studies, including the discovery of a plethora of "dropstones" in equatorial sediments, verified Harland's thesis.
(1996), and Martin (1999), these clasts are interpreted as ice-rafted dropstones. Only few core sections on the islands (Lassi) and from Suur-Katla Bay (Kiipli et al.
Scientists have found similar dropstones in Cretaceous deposits from the Northern Hemisphere, and the rocks also are found in sediments from other warm periods.