Archive for November 15th, 2009

A very bored Permian brachiopod

November 15th, 2009

boredbrach111409

COLLEGE STATION, TEXAS–I never get tired of that too-obvious joke. I found the above productid brachiopod on the last outcrop of our little Texas expedition. It has been drilled by barnacles, which leave a distinctive slit-shaped hole with a tiny little comma shape at one end. It may not look special here photographed on my backpack in the sunlight, but it is. Hard substrate communities in the Permian are still poorly known. This specimen tells us that a future trip may reveal many more such specimens.

Paleontologists (and anyone else) should be able to tell me whether these borings were produced during the life of the brachiopod or after its death. Your determination can be posted in the comments below!

Two West Texas outcrops: which looks more inviting?

November 15th, 2009

texasoutcrop111409albanyoutcrop111409COLLEGE STATION, TEXAS–The upper one is the base of the Valera Formation on US Highway 84 (N31.88196°, W99.47115°) and the lower one is the lower Bead Mountain Formation on Route 6 near Albany; both are Permian and both have delicious microconchid fossils along with much else.  You can imagine which is the more pleasant to work on.

I have been very impressed with the Permian geology of this part of Texas.  The fossils and sedimentary rocks are very accessible and sufficiently mysterious to generate at least two paleontology and sedimentology projects, including future Independent Study work by Wooster students.  Sure there are fire ants, rattlesnakes, and very fast country road driving, but it wouldn’t be Texas without them!  (And the barbecue … all beef, dry-rubbed barbecue …)

The puzzle of gypsum

November 15th, 2009

Our Permian sections on this Texas trip have had thick beds of gypsum only a meter or three beneath our fossiliferous limestones and shales.

An outcrop of sedimentary gypsum below the Valera Formation (Permian).

An outcrop of sedimentary gypsum below the Valera Formation (Permian).

Gypsum (calcium sulfate) is an evaporite mineral, indicating when the Permian shallow sea in this case was much saltier than normal (hypersaline).  Our fossils show a restricted nature (lower diversity than normal, and generally smaller shells), but they were still living in at least close to normal salinities.  This is especially the case with our numerous echinoids.  We even have evidence of some evaporites within our fossiliferous limestones.  It is a curious juxtaposition of depositional environments.

A new family of fossil clams from the Triassic of Israel

November 15th, 2009

The latest issue of the journal Palaeontology has an article describing a new family of large clams from the Triassic of southern Israel. The authors include Allison Mione (’05), who pursued this project as part of her geology Independent Study.

A specimen of the new clam family Ramonalinidae from the Triassic of southern Israel in Makhtesh Ramon.

A specimen of the new clam family Ramonalinidae from the Triassic of southern Israel in Makhtesh Ramon.

The Ramonalinids: a new family of mound-building bivalves of the Early Middle Triassic
by Thomas E. Yancey, Mark A. Wilson and Allison C.S. Mione

Abstract: Ramonalina n. gen. is a large thick-shelled bivalve abundant in mounds preserved in the Gevanim Formation (late Anisian, Middle Triassic) of southern Israel. This bivalve was an edgewise-recliner with a flattened anteroventral (functionally basal) surface and partially fused valves. It is the basis of a new family, the Ramonalinidae, which is descended from the myalinids through adaptation to edgewise positioning. Ligamental attachment was inadequate to hold valves together on large adults, resulting in valve displacement followed by shell secretion in the apical area that fused valves together and caused irregular growth on abapical areas. The ramonalinids formed large, nearly monospecific mounds on firm mud substrates in shallow marine waters. These are the largest Middle Triassic bivalve mounds known.

(For a well-written account of this story, please see the February 27, 2010, article by John Mangels in the Cleveland Plain Dealer.)