Archive for May 21st, 2010

Another beautiful fossil hard substrate

May 21st, 2010

Megan Innis studying the Ripley Formation rockground near Greenville, Alabama.

GREENVILLE, ALABAMA — I have a soft spot for hard places.  (Always wanted to say that!)  Much of my career has been spent studying marine hard substrates and the communities that have evolved on and in them.  These include rocks, hardgrounds and shells on seafloors which have been encrusted and bored by diverse organisms for hundreds of millions of years.  In all the many marine environments where these substrates occur, we know the organisms faced one common problem: how to occupy and defend space in an essentially two-dimensional world.  This provides a thread to follow through the long evolution of sclerobionts (hard-substrate dwellers, to use one of my favorite words.)

At the top of the Maastrichtian (Upper Cretaceous) Ripley Formation is a rockground which was bored and encrusted on the seafloor in the classic way.  It was ably described in a paper by Jon Bryan, and we were pleased to see that the surface is still exposed and accessible today.  There were some tasty encrusting bryozoans on some of the cobbles here!

Spondylid bivalve encrusting the Ripley Formation rockground.

Geological fieldwork in the Deep South

May 21st, 2010

An Alabama Creek where, oddly enough, we found superb Paleocene nautiloids in the McBryde Member of the Clayton Formation (N 31.91739°, W 086.68906°).

GREENVILLE, ALABAMA — This is the first time I’ve done fieldwork in the southern USA.  The outcrops are of course very different from my favorite desert locations and oddly similar to those I visited in western Russia last summer.  I’m learning once again not to pass by the muddy creek or grass-covered hillside assuming that no useful rocks or fossils will be present.  Southern geologists Jon Bryan and Peter Harries have been excellent guides here because they know what treasures lurk under the vegetation and on the river banks.

A grassy hillside with beautiful Cretaceous oysters just underneath. We collected the lot by feeling for the fossils with our feet! (N 32.02580°, W 086.76788°)

An intimate visit to the Cretaceous-Tertiary boundary

May 21st, 2010

Cretaceous-Tertiary boundary at Mussel Creek, Lowndes County, Alabama (N 31.97176°, W 086.70414°). Megan's hand marks the level with the Cretaceous below and the Tertiary above.

A closer view of the same boundary. My finger is thrilled to be in such a place.

GREENVILLE, ALABAMA — It is one of the most famous geological horizons.  It marks the end of the Mesozoic Era and the beginning of the Cenozoic.  The “K/T boundary” is dated at 65.5 million years ago (±0.3 my) and is found around the world.  It is the primary datum for our work on this expedition, and we were led right to it by our friend Jon Bryan.  We want to just pause a moment and enjoy the historical and stratigraphic significance of these sediments.  (And yes, I know I should be calling this the more modern “Cretaceous-Paleogene Boundary” as Megan insists, but I grew up with “K/T” since my Berkeley graduate school days and it is hard to give up!)

More later from our hot and muggy day in southern Alabama!