Proglacial lacustrine argillite with dropstone (Konnarock Formation, Neoproterozoic, ~750 Ma; roadcut at Rt. 58-Rt. 755 intersection, west of Konnarock, Virginia, USA) 3

            Proglacial lacustrine argillite with dropstone from the Precambrian of Virginia, USA.

The Snowball Earth Glaciations during the Neoproterozoic were the most significant ice ages that Earth ever experienced - two or three of them occurred in succession.  The most extreme models describing Snowball Earth have glacial ice completely covering all continents and all oceans, even at the equator.  Some models, called “Slushball Earth”, have Earth’s equatorial oceanic areas not completely frozen over.  Each Snowball Earth Glaciation was followed by a super-greenhouse climate.  The resulting sedimentary record of these “freeze-fry” events typically consists of glacial tillites and overlying cap carbonates.  These units are preserved at many localities on Earth.

Shown above is argillite with a granite dropstone.  Dropstones are formed when glaciers over bodies of water melt and release their ice-entrained sediment grains.  Larger dropstones that fell into fine-grained sediments (= mud, as in the case here) deform the underlying layers and often have arched, draping sediment layers above.  The granite is derived from the 1.0 to 1.3 billion year old Cranberry Gneiss.

Stratigraphy: Konnarock Formation, Neoproterozoic, ~750 Ma

Locality: roadcut on the eastern side of Rt. 58, on the southern side of the Rt. 58-Rt. 755 intersection, west of the town of Konnarock, southeastern Washington County, southwestern Virginia, USA (= stop 3A of Merschat et al., 2014, Geological Society of America Field Guide 35: 63-101.) (36º 39' 36.00" North latitude, 81º 39' 11.63" West longitude)

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Taken on: October 15, 2016

Tags:

Snowball

Earth

glaciation

ice

age

ages

Konnarock

Formation

Precambrian

Proterozoic

Neoproterozoic

Virginia

argillite

proglacial

lake

lakes

lacustrine

facies

dropstone

granite

dropstones « less

Sets appears in: • Virginia Rocks & Fossils • Dropstones more » • Neoproterozoic Rocks & Fossils • Konnarock Formation (Neoproterozoic, ~750 Ma; Virginia, USA) « less

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