Wooster’s Fossils of the Week: Bivalve escape trace fossils (Devonian and Cretaceous)

January 29th, 2012

It is time again to dip into the wonderful world of trace fossils. These are tracks, trails, burrows and other evidence of organism behavior. The specimen above is an example. It is Lockeia James, 1879, from the Dakota Formation (Upper Cretaceous). These are traces attributed to infaunal (living within the sediment) bivalves trying to escape deeper burial by storm-deposited sediment. If you look closely, you can see thin horizontal lines made by the clams as they pushed upwards. These structures belong to a behavioral category called Fugichnia (from the Latin fug for “flee”). They are excellent evidence for … you guessed it … ancient storms.
The specimens above are also Lockeia, but from much older rocks (the Chagrin Shale, Upper Devonian of northeastern Ohio). Both slabs show the fossil traces preserved in reverse as sediment that filled the holes rather than the holes themselves. These are the bottoms of the sedimentary beds. We call this preservation, in our most excellent paleontological terminology, convex hyporelief. (Convex for sticking out; hyporelief for being on the underside of the bed.)

The traces we know as Lockeia are sometimes incorrectly referred to as Pelecypodichnus, but Lockeia has ichnotaxonomic priority (it was the earliest name). Maples and West (1989) sort that out for us.
Uriah Pierson James (1811-1889) named Lockeia. He was one of the great amateur Cincinnatian fossil collectors and chroniclers. In 1845, he guided the premier geologist of the time, Charles Lyell, through the Cincinnati hills examining the spectacular Ordovician fossils there. He was the father of Joseph Francis James (1857-1897), one of the early systematic ichnologists.

References:

James, U.P. 1879. The Paleontologist, No. 3. Privately published, Cincinnati, Ohio. p. 17-24.

Maples, C.G. and Ronald R. West, R.R. 1989. Lockeia, not Pelecypodichnus. Journal of Paleontology 63: 694-696.

Radley, J.D., Barker, M.J. and Munt, M.C. 1998. Bivalve trace fossils (Lockeia) from the Barnes High Sandstone (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England. Cretaceous Research 19: 505-509.

Wooster’s Fossils of the Week: Sponge and clam borings that revealed an ancient climate event (Upper Pleistocene of The Bahamas)

September 11th, 2011

This week’s fossils celebrate the publication today of a paper in Nature Geoscience that has been 20 years in the making. The title is: “Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral”, and the senior author is the geochronological wizard Bill Thompson (Woods Hole Oceanographic Institution). The junior authors are my Smith College geologist friends Al Curran and Brian White and me.

The paper’s thesis is best told with an explanation of this 2006 image:
This photograph was taken on the island of Great Inagua along the coast. The flat dark surface in the foreground is the top of a fossil coral reef (“Reef I”) formed during the Last Interglacial (LIG) about 123,000 years ago. It was eroded down to this flat surface when sea-level dropped, exposing the reef to waves and eventually terrestrial weathering. The student sitting on this surface is Emily Ann Griffin (’07), one of three I.S. students who helped with parts of this project. (The others were Allison Cornett (’00) and Ann Steward (’07).) Behind Emily Ann is a coral accumulation of a reef (“Reef II”) that grew on the eroded surface after sea-level rose again about 119,000 years ago. These two reefs show, then, that sea-level dropped for about 4000 years, eroding the first reef, and then rose again to its previous level, allowing the second reef to grow. (You can see an unlabeled version of the photograph here.) The photograph at the top of this post is a small version of the same surface.

The significance of this set of reefs is that the erosion surface separating them can be seen throughout the world as evidence of a rapid global sea-level event during the Last Interglacial. Because the LIG had warm climatic conditions similar to what we will likely experience in the near future, it is crucial to know how something as important as sea-level may respond. The only way sea-level can fluctuate like this is if glacial ice volume changes, meaning there must have been an interval of global cooling (producing greater glacial ice volume) that lowered sea-level about 123,000 years ago, and then global warming (melting the ice) that raised it again within 4000 years. As we write in the paper, “This is of great scientific and societal interest because the LIG has often been cited as an analogue for future sea-level change. Estimates of LIG sea-level change, which took place in a world warmer than that of today, are crucial for estimates of future rates of rise under IPCC warming scenarios.” With our evidence we can show a magnitude and timing of an ancient sea-level fluctuation due to climate change.

Much of the paper concerns the dating techniques and issues (which is why Bill Thompson, the essential geochronologist, is the primary author). It is the dating of the corals that makes the story globally useful and significant. Here, though, I want to tell how the surface was discovered in the first place. It is a paleontological tale.

In the summer of 1991 I worked with Al Curran and Brian White on San Salvador Island in The Bahamas. They were concentrating on watery tasks that involved scuba diving, boats and the like, while I stayed on dry land (my preferred environment by far). I explored a famous fossil coral exposure called the Cockburntown Reef (Upper Pleistocene, Eemian) that Brian and Al had carefully mapped out over the past decade. The Bahamian government had recently authorized a new harbor on that part of the coastline and a large section of the fossil reef was dynamited away. The Cockburntown Reef now had a very fresh exposure in the new excavation quite different from the blackened part of the old reef we were used to. Immediately visible was a horizontal surface running through the reef marked by large clam borings called Gastrochaenolites (see below) and small borings (Entobia) made by clionaid sponges (see the image at the top of this post).
Inside the borings were long narrow bivalve shells belonging to the species Coralliophaga coralliophaga (which means “coral eater”; see below) and remnants of an ancient terrestrial soil (a paleosol). This surface was clearly a wave-cut platform later buried under a tropical soil.


My colleagues and I could trace this surface into the old, undynamited part of the Cockburntown Reef, then to other Eemian reefs on San Salvador, and then to other Bahamian islands like Great Inagua in the far south. Eventually this proved to be a global erosion surface described or at least mentioned in many papers, but its significance as an indicator of rapid eustatic sea-level fall and rise was heretofore unrecognized. Finally getting uranium-thorium radioactive dates on the corals above and below the erosion surface placed this surface in a time framework and ultimately as part of the history of global climate change.

This project began 20 years ago with the discovery of small holes left in an eroded surface by humble sponges and clams. Another example of the practical value of paleontology.

References:

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral. Nature Geoscience (DOI: 10.1038/NGEO1253).

White, B.H., Curran, H.A. and Wilson, M.A. 1998. Bahamian coral reefs yield evidence of a brief sea-level lowstand during the last interglacial. Carbonates and Evaporites 13: 10-22.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

Wooster’s Fossils of the Week: barnacle borings (Middle Jurassic of Israel)

August 7th, 2011

Tiny little trace fossils this week in a Jurassic crinoid stem from the Matmor Formation of the Negev Desert. They are borings produced by barnacles, which are sedentary crustaceans more typically found in conical shells of their own making. These barnacles are still around today, so we know quite a bit about their biology. (More on how in a minute.) These acrothoracican barnacles drill into shells head-down and then kick their legs up through the opening to filter seawater for food. They’ve been doing it since the Devonian Period (Seilacher, 1969; Lambers and Boekschoten, 1986).

This particular trace fossil is Rogerella elliptica Codez & Saint-Seine, 1958. It is part of a diverse set of borings in the Matmor Formation (Callovian) of Hamakhtesh Hagadol, Israel, recently described in Wilson et al. (2010).

We know so much about boring barnacles because Charles Darwin himself took an almost obsessive interest in them early in his scientific career. While on his famous voyage in the HMS Beagle, Darwin noticed small holes in a conch shell, and he dug out from one of them a curious little animal shown in the diagram below.


Cryptophialus Darwin, 1854

He called it “Mr. Arthrobalanus” in his zoological notes. He figured out early that it was a barnacle, but he was astonished at how different it was from others of its kind. He later gave it a scientific name (Cryptophialus Darwin, 1854) and took on the problem of barnacle systematics and ecology. Eight years and four volumes later his young son would ask one of his friends, “Where does your father do his barnacles?” The diversity of barnacles played a large role in Darwin’s intellectual development and, consequently, his revolutionary ideas about evolution (Deutsch, 2009).

Burrowing barnacle diagram from an 1876 issue of Popular Science Monthly.

References:

Codez, J. and Saint-Seine, R. de. 1958. Révision des cirripedes acrothoracique fossiles. Bull. Soc. géol. France 7: 699-719.

Darwin, C.R. 1854. Living Cirripedia, The Balanidae, (or sessile cirripedes); the Verrucidae. Vol. 2. London: The Ray Society.

Deutsch, J.S. 2009. Darwin and the cirripedes: Insights and dreadful blunders. Integrative Zoology 4: 316–322.

Lambers, P. and Boekschoten, G.J. 1986. On fossil and recent borings produced by acrothoracic cirripeds. Geologie en Mijnbouw 65: 257–268.

Seilacher, A. 1969. Paleoecology of boring barnacles. American Zoologist 9: 705–719.

Wilson, M.A., Feldman, H.R. and Krivicich, E.B. 2010. Bioerosion in an equatorial Middle Jurassic coral-sponge reef community (Callovian, Matmor Formation, southern Israel). Palaeogeography, Palaeoclimatology, Palaeoecology 289: 93-101.

Wooster’s Fossil of the Week: Ancient shrimp burrows (Middle Jurassic of Israel)

July 10th, 2011

This week we have a trace fossil, the burrow Thalassinoides. It is represented by one of my favorite images, reproduced above, showing a very large Thalassinoides suevicus in the Zohar Formation (Middle Jurassic, Callovian) of Makhtesh Qatan in the Negev of southern Israel. Holding the scale is Wooster geologist and Independent Study student Allison Mione (’05) during our 2004 Israel expedition. These burrows were originally described as giant desiccation cracks, but I.S. student Kevin Wolfe (’05), Israeli geologist Yoav Avni and I reinterpreted them as burrows in a rocky shore complex (see Wilson et al., 2005).

Thalassinoides is a complex trace fossil that is today made primarily by thalassinidean crustaceans (a type of shrimp; see below). We know a lot about how the burrows are made today by shrimp, and our knowledge is growing about how the ancient systems were excavated, at least in the Mesozoic and later. We have fossil shrimp preserved in Thalassinoides from the Jurassic (Sellwood, 1971) and the Cretaceous (Carvalho et al., 2007).

Pestarella tyrrhena, a modern thalassinidean shrimp. Image from Wikipedia.

Reconstruction of Mecochirus rapax in a Cretaceous Thalassinoides. A) In its burrowing life mode; B) Predominantly horizontal Thalassinoides suevicus burrow systems showing two successive event levels, with Mecochirus in life position. From Carvalho et al. (2007, fig. 3).

The burrow systems in the Zohar Formation of Israel were critical in working out the depositional environment of these carbonate sediments. We could see that first the water was comparatively deep (below wavebase) with worm burrows (Planolites). Then relative sea level dropped and the Thalassinoides burrows cut through the Planolites fabric, showing that the sediment was become stiffer. Finally bivalve borings (Gastrochaenolites) in the same rock indicated that the sediment had cemented into a shallow water hardground. This hardground showed tidal channels cut into its top surface (Wilson et al., 2005).

This work was done with virtually no “body fossils”, meaning evidence of the actual bodies of the organisms living in and on the sediment. Trace fossils, evidence of organism activity, were the only indications of this significant environmental change. This is why the study of trace fossils (ichnology) should be a part of the education of every paleontologist and sedimentologist.

References:

Carvalho, C.N., Viegas, P.A. and Cachao, M. 2007. Thalassinoides and its producer: Populations of Mecochirus buried within their burrow systems, Boca Do Chapim Formation (Lower Cretaceous), Portugal. Palaios 22: 104-109.

Sellwood, B.W. 1971. A Thalassinoides burrow containing the crustacean Glyphaea undressieri (Meyer) from the Bathonian of Oxfordshire. Palaeontology 14: 589-591.

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178.

Bioerosion on oysters across the Cretaceous-Paleogene Boundary in Alabama and Mississippi (USA) (Senior Independent Study Thesis by Megan Innis)

April 8th, 2011

This is my research team at a road-cut locality in Mississippi. (Photo courtesy of George Phillips.)

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Megan Innis, a senior geology major from Whitmore Lake, Michigan. Here is a link to Megan’s final PowerPoint presentation as a movie file (which can be paused at any point). You can see earlier blog posts from Megan’s field work by clicking the Alabama and Mississippi tags to the right.

During the summer of 2010, I traveled to Alabama and Mississippi with my research team including Dr. Mark Wilson, Dr. Paul Taylor, and Caroline Sogot.  Our trip was about ten days and included fieldwork and research. The purpose of our research was to collect fossils from below and above the Cretaceous-Paleogene (K/Pg) boundary to try and understand the Cretaceous mass extinction from a microfaunal level.

I chose to focus my thesis on oysters and the sclerobionts associated with these calcareous hard substrates.  Although my study was focused on oysters, I also collected a wide variety of other specimens including nautiloids, ammonites, belemnites, corals, sharks teeth, and bryozoans.

The oyster species present in each system.

When I got back to school in August, I identified all of my oyster species (three total) and began to identify and collect data for the sclerobionts. The oysters from the Cretaceous included Exogyra costata and Pycnodonte convexa and the oysters from the Paleogene included Exogyra costata, Pycnodonte convexa, and Pycnodonte pulaskiensis.

Sample specimens that I collected in Alabama and Mississippi. The oysters in yellow boxes and circles are the oyster species that were used in my study.

I identified nine sclerobionts including Entobia borings; Gastrochaenolites borings; Oichnus borings; Talpina borings; serpulids; encrusting oysters; encrusting foraminiferans; Stomatopora bryozoans; and “Berenicia” bryozoans.  My research showed:

1) Bioerosion of oyster hard substrates was common in the Late Cretaceous and Paleogene and sclerobionts were abundant before and after the extinction.

2) Entobia sponge borings appear to increase in abundance across the K/Pg boundary and become more common in the Paleogene.

3) Gastrochaenolites borings, made by bivalves, and serpulids were more prevalent in the Late Cretaceous, suggesting boring bivalves and serpulids were significantly reduced after the extinction.

4) Encrusting oysters and foraminiferans were more common in the Late Cretaceous, but also relatively abundant on Pycnodonte pulaskiensis in the Paleogene.

5) Encrusting bryozoans were more common in the Late Cretaceous and absent in the Paleogene, suggesting bryozoans were severely affected by the extinction.

6) Talpina borings were only found on Pycnodonte pulaskiensis in the Paleogene, but no significant data was collected elsewhere.

To my knowledge, this is the first study of bioerosion on oysters across the K/Pg boundary.

Wooster’s Fossil of the Week: A brittle star trace fossil from the Jurassic of Utah

February 13th, 2011

This week we have a trace fossil that looks almost exactly like the animal that made it. A trace fossil is evidence of organism activity recorded in the rock record. The photograph above shows one of my favorite specimens: Asteriacites lumbricalis von Schlotheim 1820 from the Middle Jurassic (Bathonian) Carmel Formation in southwestern Utah. I collected it while doing fieldwork with Wooster student Steve Smail too long ago for either of us to mention.

This fossil was made when a brittle star (ophiuroid) burrowed into carbonate sediment to either hide from predators or to look for a bit of food. Brittle stars are echinoderms that appeared in the Ordovician and are still very much alive today (see below). This Jurassic trace was formed when a brittle star essentially vibrated its way down into the loose sediment in a manner many of their descendants do today. The result is what appears to be an impression of the body (an external mold) but is actually formed by action of the animal.

Green Brittle Star (Ophiarachna incrassata) courtesy of Neil at en.wikipedia.

The trace fossil Asteriacites is far more common in the rock record than the brittle stars and seastars that made it. These traces thus often indicate the occurrence of organisms in critical intervals where they would otherwise be unknown. For example, Asteriacites lumbricalis is found in Lower Triassic rocks showing that brittle stars were part of the recovery fauna after the Permo-Triassic Mass Extinction (see, for a Wooster example, Wilson & Rigby, 2000).

Wooster’s Fossil of the Week: A chewed-up leaf (Upper Cretaceous of Kansas)

February 6th, 2011


This week’s fossil is a departure from our usual set of marine invertebrate animals. Above is a leaf of Viburnum lesquereuxii from the Dakota Formation of Ellsworth County, Kansas. The rocks enclosing it are from the Upper Cretaceous Cenomanian Stage, roughly 93-99 million years old. The leaf is preserved as a carbonized film in excellent detail.

What is cool about this particular leaf is that it has damage from insects that fed on the softer tissues between the veins. These feeding trace fossils are distinguished by smooth edges around the circular holes where the plant grew to seal off the torn cells. The leaf-eating insects may have been beetles or some kind of caterpillars. Viburnum is a common and diverse group of plants today, and they still experience significant insect herbivory, as shown below.

Beetles chewing holes in a modern Viburnum (http://www.maine.gov/agriculture/pesticides/gotpests/bugs/vib-leaf-beetle.htm).

Viburnum is a flowering plant, an angiosperm. This group appeared in the earliest Cretaceous (about 140 million years ago) and started a rapid rise to dominance just about the time this fossil leaf and its insect pests were alive. This little ecological vignette gives us an insight into the early days of our modern flora.

Thoroughly bored at GSA: A Wooster Geologist Faculty Talk

October 31st, 2010

DENVER, COLORADO — How I very much enjoy those few minutes AFTER giving a presentation, especially a Geological Society of America talk. That sense of renewed life, the rush of completing a task which was months in preparation, and the step back into the inviting shadows of the lecture room. I’ll just repeat my first and last slides below, and then link to the abstract. You will, I hope, see the joke in my blog post title!

« Prev