A bryozoan paradise in northern Japan

August 5th, 2010

Pleistocene bryozoan-encrusted cobble from Hokkaido, Japan. (All photos courtesy of Paul Taylor.)

KIEL, GERMANY–One of the most interesting presentations at this meeting of the International Bryozoology Association, at least to a paleontologist, was by my friend Paul Taylor (Natural History Museum, London). He described a fauna of bryozoans which inhabited cobbles in a cold-water submarine channel in northern Japan during the Pleistocene (roughly 0.50 to 1.25 million years ago). The cobble-bearing unit was exposed by tectonic action as dry land and forms a deposit colloquially known as “Kokemushi Paradise”.  Kokemushi is the delightful Japanese term for bryozoan.

One of the cobble-encrusting bryozoans under a scanning electron microscope. Note how many of the exquisite little spines are preserved in place.

There are 120 species of bryozoans on these igneous cobbles, which is an extraordinary diversity. Every cobble is encrusted, some with up to 25 species. There are also barnacles, corals, foraminiferans and serpulid worms. For a specialist in hard-substrate faunas (“sclerobionts“), this is a paradise indeed.

The vertical tubes are termed "peristomes" and they extend from the bryozoan apertures. Such delicate structures are rarely preserved in fossils.

When a limited hard surface like that of a cobble is occupied by diverse and abundant sessile organisms, there is inevitably a competition for living space. This competition is recorded in the fossil record by the overlapping of skeletons as one species overgrew another. The Kokemushi Paradise bryozoans show many examples of such space competition. It is not always a simple system of one species always overgrowing another. Sometimes two species will mutually overgrow each other.

A competitive system of overgrowth between two bryozoans.

The Kokemushi Paradise site is, alas, lost to development, but there are hundreds of cobbles preserved in the Natural History Museum in London. Maybe someday a Wooster Independent Study student will get the chance to examine them in paleoecological detail!

A Windy Desert Day for the Wooster Geologists

March 8th, 2010

ZZYZX, CALIFORNIA–The skies were brilliantly clear early this morning when we left the Desert Studies Center for points west. The price for the passage of the front was a stiff wind that kept up all day and even now is whistling in the darkness past our windows. I don’t mind at all.  It reminded me of delightful spring days in the desert when as kids we flew kites so high we could barely see them.

Our first stop was a visit to the extensive sedimentary layers laid down by the Pleistocene Lake Manix in what is now the lower Mojave River Valley.  We drove several miles on Harvard Road and walked across long stretches of desert pavement with ventifacts and occasional wind-polished agates.

Bottom sediments from the pluvial Lake Manix near Harvard Road. For scale, you may notice Megan Innis and Stephanie Jarvis in the central wash.

We then traveled farther west through Barstow to Owl Canyon and Rainbow Basin a few miles northwest of the city. There we met Buzz and Phyllis Sawyer, childhood friends of mine from Barstow and superb natural historians of the desert. We all enjoyed the diverse facies of the Barstow Formation (Middle to Upper Miocene) as well as the plants and animals in this protected area.

Professor Shelley Judge explains the complicated structure of Owl Canyon to her faculty colleagues using traditional geological hand language.

Wind-blown Wooster Geology field trip participants in Rainbow Basin with the famous Barstow Syncline in the background. This photograph was kindly taken by Buzz Sawyer.

Our last stop was Afton Canyon where we completed the Lake Manix story by looking at the outlet through which it catastrophically drained into Soda and Silver Lakes to the east. The sun had set by the time we gathered back at the vans, ending another productive and thought-provoking field day.

Wooster geologists crossing the mighty Mojave River in Afton Canyon. We don't think this is quite the same river Jedidiah Smith encountered.

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