Category Archives: GeoPic of the Week

Geo-pic of the week: A lively sea in North Arkansas

 

Starfish pit 2Starfish pit 1

Starfish pit 4Starfish pit 6

Starfish pit 5Starfish pit 3     

The above pictures are of sandstone beds from a quarry in North Arkansas developed in a rock formation called the Batesville Sandstone.  Though it formed in a marine setting, the Batesville is typically composed of fairly homogeneous, flat-bedded rock with little evidence of inhabitation.  This spot is an exception.  The pictures clearly indicate the depositional environment was teaming with sea life at the time the sediment was emplaced.  

The abundant trace fossils, which preserve the activity of organisms rather than their physical form, show a variety of behaviors common to marine invertebrate animals that lived in Arkansas more than 330 million years ago.  Remnants of grazing traces of various snail and worm-like critters (A), resting traces (starfish; B), Dwelling burrows (sea-anemone or bivalve?; C), and locomotion trails (D) are indicators of the conditions present in North Arkansas near the end of Mississippian time.   

Geo-pic of the week: Aerial Photography

Aerial Photo-Central Arkansas

Sometimes the best way to see what’s on the ground is to get as far away from it as possible.  Geologists use a variety of tools to do just that.  One of those tools is aerial photography.

The picture above shows the Arkansas River where it leaves the mountainous western uplands and enters the bottomlands of the Mississippi Alluvial Plain, east of Little Rock (upper left).  Driving east across that boundary, it’s easy to get the impression that the Mississippi Alluvial Plain is a broad flat expanse of land with little to no distinguishing features.  That’s far from the case as this photo reveals.  

From high-altitude imagery, subtle relic features created by the Arkansas River can be easily recognized.  Note the swirling landforms that characterize the lowlands on the right side of the picture.  Over time the Arkansas River has meandered through the valley carving new channel courses and abandoning old reaches of channel.  The continually changing river has left a mosaic of oxbow lakes (water-filled abandoned channels) and arc-shaped river deposits known as point bars.