Monday, January 25, 2010

Picture of the Week - Brachipods underfoot

This is a picture of my foot standing on a local outcrop.

The outcrop is located on the north side of Route 209/199 in Kingston just west of the Kingston-Rhinecliff Bridge across the Hudson.  There are four limestone formations present at this location - the Manlius, Coeymans, Kalkberg, and New Scotland Formations.  These fossils are in the New Scotland limestone (named after a town near Albany where this limestone was first studied).

The New Scotland limestone formed from shallow seafloor sediments deposited during the Early Devonian Period of geologic time some 400 million years ago.  Fossils of over 300 marine invertebrates have been recovered from this rock unit.  I'm standing on an ancient seafloor (now tilted about 30 degrees from horizontal).

If you looked at this rock bed close up, you would see that it's composed almost entirely of shell fossils.  These animals belong to a group called brachiopods.  They may superficially look like modern bivalves (clams, oysters, mussels, etc) but belong to an entirely different phyla - kingdom animalia, phylum brachiopoda for these fossils vs. kingdom animalia, phylum mollusca for the modern bivalves we're all famiar with from the seashoor or our dinner plates. Brachiopods are still around, but relatively rare.  Back during the Devonian Period, however, they were incredibly abundant and diverse.

It's easy to transport yourself back to the Devonian Period in your imagination.  Floating in a shallow sea miles from land (called the Helderberg Sea by modern geologists).  On the sunlit seafloor,  garden of brachipods floated in the currents attached to the seafloor with a fleshy stalk.  Shells agape, the filter fed from the plankton-rich waters.  Echinoderms and snails slithered through the sediments while trilobites swam above them.  The seas were warm and subtropical as New York was about 30 degrees south of the equator at the time.  Strange looking fish swam in these seas.  In some areas on Earth, life had started coming out onto land - primitive plants and insects with the earliest amphibians soon to evolve.

That's the neat thing about being a geologist.  For most people, it's just a gray rock on the side of the road that thousands of people drive by each day without giving it a second thought.  When geologists crawl around on that rock, however, we can read a story there and transport ourselves back in time.

1 comment:

  1. I've recently moved to Ellenville, look forward to finding these formations. Thankmyou for the post.LeeC