Tag Archives: turbidites

Geopic of the week: The Maumelle Chaotic Zone

Chaotic zone

This is a picture of sandstone and shale of the Maumelle chaotic zone that outcrops along highway 10 west of North Little Rock, Arkansas.  The Maumelle chaotic zone is part of the Jackfork Formation which forms the bedrock around much of the Little Rock area.  The chaotic zone is called that because of the disarray the rock is in there.  In the example above, broken blocks of sandstone are interspersed with disorganized shale beds that have been rolled, squashed and otherwise deformed (rock hammer at center is for scale).  The rocks weren’t deposited this way but were originally organized into horizontal beds on a deep-water ocean slope.  Before they could be hardened into solid rock, the slope failed and the beds were transported down hill in a massive submarine landslide. 

 

Note:  Other interpretations for this zone have been proffered.  The author of this blog prefers the above interpretation.

 

For more views of the Maumelle chaotic zone click here

Geopic of the week: Turbidite deposits in Baumgartner Quarry

The Baumgartner quarry is located a little South of Kirby Arkansas along highway 27 in the Ouachita Mountains.  It exposes approximately 160 m. (590 ft.) of the upper Jackfork Formation which consists of interbedded sandstone and shale deposited  about 300 million years ago when the area that is now the Ouachita Mountains was a deep ocean basin.  Deep oceanic deposits such as these are the kind petroleum geologists explore for oil.  Because these deposits are exposed at the surface in southern Arkansas, geo-scientists from all over come here to study our rocks and gain a greater understanding of the deeply buried rocks they look for oil in in places like the Gulf of Mexico.  This is a view looking west along strike.

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