Paleontology

 

Microanalytical Paleontology

In the summer of 1997, at the Gordon Research Conference on the Origin of Life, Harvard Univ. paleontologist Andy Knoll and I got into a conversation about how standard analytical techniques of mineralogy might be applied to the study of fossils. That conversation led to a series of collaborations with Knoll students. My first efforts were simply to map fossil carbon in plant fossils, such as ancient wood and a variety of species from the famed Rhynie Chert of Scotland (Boyce et al., 2001; 2003; 2007). Kevin Boyce worked at the Geophysical Lab with Marilyn Fogel on isotopes and with George Cody on x-ray microscopy as well.

 

I’ve subsequently worked with Prof. Nora Noffke (Old Dominion University) on a variety of Archean samples with evidence of ancient microbial mats (Noffke et al. 2003; 2006a; 2006b; 2007).

Boyce, C.K., R.M.Hazen and A.H.Knoll (2001) Nondestructive, in situ, cellular-scale mapping of elemental abundances including organic carbon in permineralized fossils. Proceedings of the National Academy of Sciences (US), 98: 5970-5974.

Noffke, N., N. Nhleko and R. M. Hazen (2003) Earth’s earliest microbial mats in a siliciclastic marine environment (2.9 Ga Mozaan Group, South Africa). Geology 31, 673-677.

Hazen, R.M., A. Steele, G. D. Cody, M. L. Fogel and W. T. Huntress, Jr. (2003) Biosignatures and abiosignatures. Astrobiology 2, 512-513.

Boyce, C.K., G.D.Cody, M.L.Fogel, R.M.Hazen, C. M. O’D. Alexander and A. H. Knoll (2003) Chemical evidence for cell wall lignifications and the evolution of tracheids in early Devonian plants. International Journal of Plant Science 164, 691-702.

Noffke, N., N. Beukes, J. Gutzmer and R. M. Hazen (2006a) Spatial and temporal distribution of microbially induced sedimentary structures: a case study from siliciclastic storm deposits of the 2.9 Ga Witwatersrand Supergroup, South Africa, Precambrian Research 146, 35-44.

Noffke, N., K. A. Eriksson, R. M. Hazen and E. L. Simpson (2006b) A new window into Early Archean life: microbial mats in Earth's oldest siliciclastic tidal deposits (3.2 Ga Moodies Group, South Africa). Geology 34, 253-256.

Noffke, N., N. Beukes, R. M. Hazen and D. Swift (2007) Exceptionally preserved microbial mats of Meso-Archean age: the Sinqueni Formation, Pongolo Supergroup, South Africa. Geobiology, in press.

Boyce, C. K., C. L. Hotton, M. L. Fogel, G. D. Cody, R. M. Hazen and A. H. Knoll (2007) Devonian landscape heterogeneity recorded by a giant fungus. Geology 35, 399-402.

I. Research with Prof. Kevin Boyce (Univ. Chicago):

1. Early wood fossils that show cellular structures: These were our first tests of electron microprobe analysis of carbon in ancient fossils.In these maps red indicates the highest concentration of carbon.

 

This map shows portions of several annual growth rings, each several cells thick.

 

 

2. Work on the Rhynie chert: described in the abstract from Boyce et al. (2003): “Anatomically preserved land plant fossils from the Lower Devonian Rhynie Chert contain conducting tissues with cells that range from dark colored, elongated cells without secondary wall thickenings to tracheids similar to those of extant tracheophytes. A suite of tissue-specific microanalytical techniques was used to assess lignification in fossils of Aglaophyton, Rhynia, and Asteroxylon. Isotope ratio mass spectrometry provides millimeter-scale resolution of carbon isotopic abundances, whereas soft X-ray carbon (1s) spectromicroscopy provides micron-scale resolution of the preservation of organic molecular functionality. The isotopic and organic chemistry of Rhynie Chert plants suggests that the earliest vascular thickenings were probably unlignified and that cell wall lignification may have first appeared in the outer cortex. Only later, it seems, was lignin deposited in conducting cells to produce the true tracheids seen today in vascular plants.”

Carbon element maps of trachiids from the Devonian Rhynie Chert of Scotland reveal cellular details.

3. Work on Prototaxites: From the abstract by Boyce et al. (2007): “The enigmatic Devonian fossil Prototaxites Dawson 1859 consists of tree-like trunks up to a meter in diameter and eight meters long built of interwoven tubes 5 to 50 microns in diameter. Carbon isotopic abundances of Prototaxites specimens from five localities differ from those of contemporaneous vascular plants, exhibiting a range of δ¹³C values, within and between localities, of up to 13‰. Pyrolysis-gas chromatography/mass spectrometry (GCMS) highlights compositional differences between Prototaxites and co-occurring plant fossils and supports interpretation of isotopic distinctions as biological rather than diagenetic in origin. Such a large isotopic range is difficult to reconcile with autotrophic metabolism, suggesting instead that, consistent with anatomy-based interpretation as a fungus, Prototaxites was a heterotroph that lived on isotopically heterogeneous substrates. Light isotopic values found in Prototaxites approximate those of vascular plants from the same localities; in contrast, heavy extremes appear to reflect consumption of primary producers with carbon-concentrating mechanisms, such as cryptobiotic soil crusts or, possibly, bryophytes. Prototaxites biogeochemistry, thus, suggests that a biologically heterogeneous mosaic of primary producers characterized land surfaces well into the vascular plant era.”

 

Optical image, A., and electron probe map of carbon abundance, B, of Prototaxites anatomy in cross section. Red indicates high and blue/black low abundance of carbon in the electron probe map, qualitatively demonstrating confinement of organic matter to tube walls. These microscopic filaments, shown here in cross section, point to the fungal nature of the organism. Scale bar is 20 microns.

Carbon isotopic values for Prototaxites and associated fossils. Upper Devonian fossils from Kettle Point, Ontario. Lower Devonian fossils from south shore of Gaspé peninsula, Quebec (diamonds), north shore of Gaspé peninsula, Quebec (squares), Baxter State Park, Maine (Xs), Pin Sec Point, New Brunswick (triangles). Kevin Boyce realized that the range of values from a single locality suggest that Protaxites is a saprophyte, and thus a giant fungus!

II. Research with Prof. Nora Noffke (Old Dominion University) on ancient microbial mats: Noffke has pioneered the study of Archean microbially induced sedimentary structures (MISS), such as wrinkle textrures, roll-up features, filamentous mat-like structures, and distinctive binding and trapping of sedimentary grains.

 

Microbially-induced sedimentary structures (MISS): ancient microbial mats from the 3.2 billion-year-old Pongola Group, South Africa. We have found original carbon-rich filaments associated with some of these structures.

Microbial mat features from the Brixton Formation, South Africa.

Microbial mat features from the Moodies Group, South Africa.

 

III.Research on Doushanto, China, phosphatic microfossils with Prof. Shuihai Xiao (Virginia Tech). Summer intern David Olesh from Harvard University also did research on these specimens.

Phosphatic embryo, 4-cell stage.

 

IV. Eozoons????: OK, so here’s an enigma. Does anybody have any information on so-called “eozoons” from the Precambrian Belt Formation? Here’s a description of a recent find of enigmatic carbonate rocks from the Langel Ranch, Manhattan, Montana. On August 13, 2007, I had the opportunity to examine briefly a carbonate outcrop near the banks of the Gallatin River, located just below the home of Tom and DeeAnn Langel on their ranch in Manhattan, Montana. The outcrop represents approximately 8 meters in vertical section, and perhaps 10 meters in lateral extent. Outcrop and hand specimens feature two interleaved lithologies – a blue-grey limestone and a buff chert – that form a variety of unusual patterns, as illustrated below. By the way, my hunch is that these rocks represent some kind of physical separation of immiscible fluids – one aqueous and carbonated, the other siliceous and oil-rich. But if anyone knows, please let me know!

MicroRaman spectroscopic analysis reveals that the grey portions are primarily calcium carbonate, whereas the buff regions are a predominantly silica (chert?) with a significant component of organic carbon. Pyrolysis GCMS indicates that the organic carbon is primarily in the form of alkanes and alkenes, with little aromatic content, suggesting a very mature (and ancient) organic-rich zone, perhaps like an oil shale.

Electron microprobe analysis (a 2 x 2 mm area) underscores the sharp compositional contrast between these carbonate- and silica/organic-rich layers. Could these have been deposited as immiscible phases? What physical or chemical process could have resulted in this variety of patterns in such a small outcrop?

These electron microprobe images show a 0.6 x 0.6 mm area, with chert on the bottom and limestone on the top. The contact is not as sharp as it appears in hand specimen.

This 0.2 x 0.2 mm area features an 80-micron carbon-rich globule, which we take to be a kerogen-like concentration. These objects, which are general >20 microns, occur in both lithologies, though more abundantly in the chert (see next image).

 

 

Calvert County Fossil Collecting

Since 1993 Margee and I have actively collected fossils along the Miocene cliffs of the western shore of the Chesapeake Bay. Most specimens, including molluscs and vertebrate remains, have been found in the float. We donate most of these specimens to middle school science teachers for use in classrooms. However, we have also found a few important mammal specimens, including whale, dolphin, and seal material. These specimens are donated to the Calvert marine Museum.

 

The lower jaw of a small dolphin, collected in Zone 11 at the base of the cliff approximately 1 mile south of Dare's Beach. Collected November 23, 2007.