Archive for January, 2014

Wooster’s Fossils of the Week: Trace fossils making ghostly shells (Upper Cretaceous of Mississippi)

January 26th, 2014

Entobia gastropod Prairie Bluff Chalk FormationThe unusual fossil above was collected by Megan Innis (’11) and myself in Mississippi during a May 2010 paleontological expedition with Caroline Sogot and Paul Taylor of The Natural History Museum, London. That splendid trip has contributed already to one high profile publication (Sogot et al., 2013) and no doubt more will come from the excellent collections we made. All the fossils in this post came from the Prairie Bluff Chalk Formation (Maastrichtian) exposed at the intersection between Highway 25 and Reed Road in Starkville, Mississippi (locality C/W-395).

The specimen is a marine gastropod (fancy name for a snail), which is hard to believe considering no shell is preserved. The shape of the original aragonitic shell has been taken by a series of interlocking blobs, each with a sediment-filled tube extending outwards. These are casts of chambers made by a boring clionaid sponge. The resulting trace fossil is known as Entobia, a form we have seen several times in this blog. The sequence of events: (1) The sponges excavated cavities connected by tunnels into the aragonite shell of the gastropod, maintaining connections to the seawater for filter-feeding; (2) the cavities and tubes filled with fine-grained calcareous sediment after the death of the sponges; (3) the aragonite gastropod shell dissolved away, probably at the same time the sediment filling the cavities was cemented; (4) the fossil was exhumed as a series of natural casts of the sponge cavities — the trace fossil Entobia.
Entobia bivalve 1 exterior Prairie Bluff Chalk FormationThere were many other such fossil ghosts at this locality, such as the apparent bivalve shell fragment above.
Entobia cast close Prairie Bluff Chalk FormationIn this closer view (taken with my new extension tubes on the camera) we see some of the interlocking sponge chamber casts. On the surfaces of some you can just make out a reticulate pattern that represents tiny scoop-like excavations by the sponges. In the upwards-extending tubes there are a few green grains of the marine mineral glauconite.

As a paleontologist it is always sobering to see a fossil preserved in such an odd way. Were it not for these circumstances of boring, filling and cementation, the shells would have completely disappeared from the fossil record. Every fossil we have, really, is a victory of improbable preservation.

References:

Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.

Schönberg, C.H. and Shields, G. 2008. Micro-computed tomography for studies on Entobia: transparent substrate versus modern technology, p. 147-164. In: Current Developments in Bioerosion. Springer; Berlin, Heidelberg.

Sogot, C.E., Harper, E.M. and Taylor, P.D. 2013. Biogeographical and ecological patterns in bryozoans across the Cretaceous-Paleogene boundary: Implications for the phytoplankton collapse hypothesis. Geology 41: 631-634.

Sohl, N.F. 1960. Archeogastropoda, Mesogastropoda, and stratigraphy of the Ripley, Owl Creek, and Prairie Bluff Formations, p. A1-A151. In: Late Cretaceous gastropods in Tennessee and Mississippi: U.S. Geological Survey Professional Paper 331-A.

Taylor, P.D. and Wilson, M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.

Wilson, M.A. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.

Experiential Learning on Ice (with some water)

January 19th, 2014

Tom Lowell, Aaron Diefendorf and four students from the University of Cincinnati met up with the Wooster Geologists to core Browns Lake. We thank Marvin Sandy, who manages the bog for the Nature Conservancy for guidance and permission to do this work.
coresite

Coring Browns Lake from an ice platform on a winters day in Northeast Ohio. Four cores were taken – the longest of which was 17 meters. The mud in the cores is a record of 15,000 years of environmental change since the last Ice Age.
Browns Lake Bog is own by the Ohio Department of Natural Resources and managed by the Nature Conservancy.

Browns Lake Bog is owned by the Ohio Department of Natural Resources and managed by the Nature Conservancy.

pitcher

Pitcher plants are among the special biology of the bog. Note the ice forming within the pitcher.

auger

First a hole is augured to determine water depth in the basin. It is about 5 feet deep with 4-6 inches of ice.

A look at the drilling rig - anchored in the ice, tied down with ice screws.

A look at the drilling rig – anchored in the ice, tied down with ice screws and straps.

 

pipe

A look down the long axis of the drill pipe – note the corer sticking out of the ice stored in the lake to prevent it from freezing. The water is the warmest place on the site.

Tom explains the theory and Doug and Nick move into the practice phase.

Tom, the core boss,  explains the theory and Doug and Nick move into the practice phase.

humor

Tom and Michael share a coring joke – it help to have a sense of humor standing on ice for 6 hours at 15 degrees F with a breeze.

meter

Another meter of core is brought up – ready to be described, wrapped and archived. About half of the 40 meters of core went to Cincinnati for further analyses.

Lunch on the boardwalk

Lunch on the boardwalk

oscar_andy

Oscar and Andy take a break from the core archiving. Note the water that moves up through the hole in the ice. The weight of the rig and crew cause elastic and some plastic deformation to occur – after the rig is removed the ice slowly pops back into shape.

The last of the gear moves to the parking lot.

The last of the gear moves to the parking lot.

Thanks to Jesse Wiles for the photography.

The geese point the way back to Wooster. Thanks to Jesse Wiles for the photography.

 

 

 

 

 

 

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part III — those crinoids had company)

January 19th, 2014

Crinoid with platyceratid (cross-section) 585The last installment of our analysis of a Lower Carboniferous fossiliferous siderite concretion given to the department by Sam Root. In part I we looked at the crinoid stems and calices on the outside and discuss the formation of siderite concretions and the preservation of this particular assemblage. In part II we had our first look at polished sections of the concretion, taking special note of the crinoid stem morphology and its replacement by the mineral marcasite. For part III you were promised a molluscan surprise.

In the top view you can see that we have a section that fortuitously cut right through the center of a crinoid head. The stem is visible at the bottom, with the calyx and attached arms above. Crowning the calyx is a thin semi-circle of shell nestled open-side-down across the crinoid oral surface. This we can tell from the shell morphology is a parasitic platyceratid gastropod caught in place on its crinoid host. Nice.
Platyceratid Lower Carboniferous 585 annotatedThree years ago we received a fossil donation from the Calhoun family of local Lower Carboniferous fossils, including this beauty pictured above. It is a crinoid calyx (you can tell by the polygonal plates) with a cap-shaped platyceratid gastropod (Palaeocapulus acutirostre) preserved in place on top of it between the arms (now missing). I drew a line across the image to indicate the likely plane of section through a similar pair in our siderite concretion. In section the platyceratid would be recorded as a thin shelly top on the calyx.

Platyceratids have long been known as Paleozoic associates of crinoids. For many years we thought of them as simply coprophagous, meaning they were consuming crinoid feces as they exited the anus. (Awkward conversation, I know.) Careful work by Tom Baumiller (1990) showed that this arrangement (which would not have directly harmed the crinoid because it was, after all, done with the food) was likely not the case. He found trace fossil evidence that the platyceratids were likely accessing crinoid stomach contents directly through some sort of proboscis, and that these parasitized crinoids were stunted in their growth and thus directly harmed (but not killed — no good parasite wants to lose its meal ticket). Our new specimen was thus likely a miserable little crinoid, even if it didn’t have a brain to sort out its feelings.
Stem Calyx 121413As one last view of our crinoids in the concretion, look at the detail in the crinoid stem just below the calyx. The lumen is visible in the center of the stem, as well as the alternating ornaments on the columnals.

This has been a fun specimen to examine. Thanks, Sam!

References:

Baumiller, T.K. 1990. Non-predatory drilling of Mississippian crinoids by platyceratid gastropods. Palaeontology 33: 743-748.

Donovan, S.K., and Webster, G.D. 2013. Platyceratid gastropod infestations of Neoplatycrinus Wanner (Crinoidea) from the Permian of West Timor: speculations on thecal modifications. Proceedings of the Geologists’ Association 124: 988–993.

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part II — the inside story)

January 12th, 2014

 

1 Cross-section macro 2 121413Last week’s specimen was a Lower Carboniferous fossiliferous siderite concretion from an unknown location, but likely from the Wooster area. It was donated to the department by Emeritus Geology Professor Sam Root. The concretion has beautiful crinoids preserved in it, including several stems of at least two types and three calices (crowns or heads).

I took a chance and cut the concretion with a rock saw if there were interesting features on the inside. There were indeed! In the image above you see at the bottom a cross section through a broken crinoid stem showing the articulated columnals. Above it are sections of crinoid arms (the white and grey spots) each trailing a pair of delicate pinnules (the feeding parts of the arms that carried tube feet). The arms are coming from an intact calyx that is not in the plane of the section.
2 Micro 1 121413In this closer view of the above stem we see the complex anatomy of the crinoid stem. We also see the amazing mineralogy of these specimens in a way we could not from the outside. The light brown matrix is, as we’ve said, the concretion made primarily of siderite (an iron carbonate) and clay. The crinoid columnals, which were originally made of calcite (calcium carbonate), have a silvery metallic material replacing them. This is the iron sulfide mineral marcasite. The white mineral on the inside of the stem on the left is quartz (silicon dioxide). It filled in open spaces inside the stem. To confuse things (nothing is ever easy in this business!) on the right end of the stem marcasite has filled in the cavities instead of quartz.
3 Macro close 121413This view of another stem in cross-section shows a fourth mineral in the system: calcium carbonate. It can be seen as the glassy material in the middle of the structure. It is not the original calcite that made up the columnals. It is instead a later mineral that, like the quartz and marcasite in the previous image, filled in open spaces within the stem. The marcasite, quartz and calcite are thus secondary minerals introduced to the fossil long after its burial. We call these chemical and physical changes to the original mineralogy diagenesis.
4 Fearnhead 2008 Fig 2Since this cross-section view of the crinoid stems is surprisingly complicated, here is a diagram from Fearnhead (2008, figure 2). The top is a crinoid columnal looking at its articulating surface. At the bottom is a cross-section. In our crinoids you can easily make out the lumen as a hollow space running through the center of the stems (filled with marcasite, calcite or quartz). The zygum is that portion of the columnal replaced by marcasite.

Lat week I mentioned that there was a molluscan surprise revealed upon cutting open this concretion. I’ll save that for part III of this series. Same channel next week!

References:

Fearnhead, F.E. 2008. Towards a systematic standard approach to describing fossil crinoids, illustrated by the redescription of a Scottish Silurian Pisocrinus de Koninck. Scripta Geologica 136: 39-61.

Last official meeting of Wooster Team Israel

January 10th, 2014

Team Israel 2013 011014WOOSTER, OHIO — Above you see Wooster Team Israel 2013 veterans Lizzie Reinthal, Steph Bosch and Oscar Mmari (whom I seem to have caught with his mouth full). Since I’m starting a research leave this semester, we took a last chance to have an evening meeting with pizza, lemon dessert, popcorn and a movie in the warm Wilson living room. It is wintry Ohio outside, but we all have memories of the beautiful Negev:

GoodbyeMakhteshGadol070713a

And what was the movie? You really don’t need to ask, do you?

Lawrence poster

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part I)

January 5th, 2014

Cobble Top 121413Last year Wooster emeritus geology professor Sam Root generously donated the above pictured siderite concretion to our paleontology collections. He had received it from a friend who didn’t know where it came from originally so we have no location. The fossils in it, though, show it is Lower Carboniferous in age and could well be from local outcrops of the Cuyahoga Formation. Sam knew this is a cool specimen so he wanted to see what we could make of it.

In the top view we can see crinoid stems running transversely across the surface. Remarkably, two crinoid calices (the arm-bearing crown of the crinoid at the top of the stem) are visible. The larger one is in the lower left. You can see the top of the stem to the farthest left, and then the calyx and attached arms to the right. The second calyx is in the upper right with the arms extending down and towards us. Finding one crinoid calyx with the delicate arms still attached is impressive; finding two in the same slab is a real treat.
Siderite Concretion Carboniferous 585Above is the other side of the concretion. Again a crinoid stem can be seen transverse across the surface. This stem is different from those on the other side, though. It does not have external sculpture, and it is separated into distinct pluricolumnals as if someone sawed through it at regular intervals.
Cobble closer 121413A closer view of the above shows yet another crinoid calyx, this one almost entirely buried in the rock with the arms extending to the surface. The arms have smaller sub-arms (pinnules) still attached. Amazing.

The concretion is made of the mineral siderite (an iron carbonate) that precipitated in fine-grained sediments around the fossils after they were buried. This usually takes place under subsurface anoxic and slightly acidic conditions. The crinoids with all their small and easily-disarticulated parts were buried quickly on the ancient seafloor, probably by a storm-induced pulse of silts and clays. The decay of their soft parts produced hydrogen sulfide gas ad carbon dioxide, triggering the geochemistry that caused the precipitation of siderite around them. The hard concretion that resulted was likely in a matrix of soft shale. The strength of the siderite kept the fossils from being crushed by the weight of sediment above. At some point many millions of years later, the shale eroded away and the concretion was freed to be picked up by some lucky person.

The crinoid stem that is divided into regular increments is interesting on its own. These segments with multiple columnals (the poker chip-like individual elements) are called pluricolumnals. They likely broke at pre-set weaknesses in the connective tissue of the living crinoid, something we see in their living descendants. This may have allowed them to break off their stems (autotomize) when in danger so that the calyx and remaining stem could float away for re-establishment elsewhere.

This concretion is so interesting that I (forgive me, Sam) could not resist cutting it open to see what is inside. The inner view is even more fascinating and will be revealed next week in part II of this story. As a teaser, it involves four minerals and a surprising mollusk!

References:

Baumiller, T.K. and Ausich, W.I. 1992. The broken-stick model as a null hypothesis for crinoid stalk taphonomy and as a guide to the distribution of connective tissue in fossils. Paleobiology 18: 288-298.

Gautier, D.L. 1982. Siderite concretions; indicators of early diagenesis in the Gammon Shale (Cretaceous). Journal of Sedimentary Research 52: 859-871.