aidan long summer internship project report 2015 (college of science nuig) jm
TRANSCRIPT
Fig. 1: Conodont feeding array.
AIDAN LONG INTERNSHIP PROJECT
SUMMER 2015 Trophic positioning and palaeobiology of the Conodont animal from stable isotope analysis
NUIG College of Science
Supervised by Dr. John Murray, Earth and Ocean Sciences
1
Understandingconodonts&using isotopesforpalaeobiology
Conodonts, a group of extinct jawless marine vertebrates, were prolific in the world’s oceans c.500‐200 million years ago [Ma]. These animals possessed microscopic (typically < 1 mm) phosphatic dental elements in the head region (Fig. 1), which superficially resemble teeth. The extensive preservation of these microfossils in sedimentary rocks worldwide has made them an extremely important tool for dating and correlating the geological record (Barham, 2015). Despite this, relatively little is known about the life habits and palaeoecology of these creatures. They remain quite enigmatic, due in no small part to the fact that their soft‐part anatomy rarely fossilises – at present less than ten complete conodont animal specimens are known from the fossil record.
Three main morphological groups of conodont elements have been identified: P‐, S‐ and M‐elements. Each had a different function in a conodont’s ‘mouth’, and for the basis of our study, only the largest and most morphologically distinct forms, the platform (P) elements, were extracted from the disaggregated shale samples. These were originally positioned caudally of the main feeding array within the ‘mouth cavity’, and their relatively large size, makes them a primary target for isotope analysis (Barham, 2015).
Chemically, conodont elements comprise mainly of calcium carbonate fluorapatite which has the chemical formula [Ca5Na0.14(PO4)3.01(CO3)0.16F0.73(H2O)0.85] with a matrix of collagen and other organic material. The mineral phase has been used for stable isotope analysis in the past. For example, oxygen isotopes (locked in either the carbonate or phosphate phase) can infer the isotopic composition of ancient marine water bodies and ancient sea‐surface temperatures, through several different techniques (e.g. Joachimski et al., 2006; Vennemann et al., 2002).
Compared to the analysis of stable oxygen isotopes in conodont apatite, investigation of other stable isotopes, such as carbon and nitrogen, have not been completed. Carbon and nitrogen stable isotopes have been investigated in more recent fossils and extant animal groups. These have shown that animal tissues are typically more enriched in both heavy isotopes of nitrogen (15N) and carbon (13C) than their food source, defining the functional role of organisms in their food chain (Eggers & Jones, 2000; DeNiro & Epstein, 1981; DeNiro & Epstein, 1978), the distribution ranges of species (Bearhop et al., 1999) and allowing species delineation as well (McCarthy & Waldron, 2000).
ProjectAims
The aim of this project was to test whether stable carbon and, in particular, stable nitrogen isotopic values could be measured from conodont elements. This would involve disaggregating shales of Carboniferous age (using non‐chemically altering means) to identify the conodont‐rich maximum marine flooding surface [mfs] of each shale member, constructing a shale report for each horizon analysed in the process.
Following this, conodont elements were sorted generically into triplicate samples and isotopic analysis would be completed at the Department of Geology in Trinity College Dublin, using a highly sensitive and novel method of mass spectrometry (pioneered by Rooney et al., 2015).
If reliable stable nitrogen values could be acquired from these conodont platform elements, this would be a scientific first (geochemically, palaeontologically, but also chemostratigraphically). Future (possibly postgraduate level) studies could then be carried out on conodont microfossils from other parts of the geological record to compare their values and give a more complete impression of the role the group played in ancient food chains. These values could also be compared to Ichthyolith (microscopic fish teeth and scales) material recovered from the same rock sample during processing.
2
MaterialsandMethods
The conodonts investigated for this project were recovered from shale horizons from two regions in the USA:
• Iowa (Midcontinent basin) and • Illinois (Illinois basin).
The shale samples had actually collected ten years prior (Fig. 2), resulting in approximately twenty eight gallon bags of various coloured shale horizons. 17 of these were collected in Illinois, to the south of Spring Valley (Fig. 2a). The remaining 11 were collected in Iowa, near the Appanoose county dump (Fig. 2b). The bags of samples from each area were then subcategorised into separate horizons discerned based on colour and position in local stratigraphy.
Fig. 2: Carboniferous shale sampling in the United States in 2006. (a) Illinois sampled section, (b) the Iowa section. Person in black jacket is project supervisor John Murray, person in light greyish jacket is Professor Philip Heckel (Iowa State University and, then, Chairman of the International Commission for Carboniferous Stratigraphy).
The shales from both of the sections sampled formed between the middle to late Pennsylvanian of the Carboniferous (~ 300Ma) and lithostratigraphically they are classified thus:
Location: Member Formation: Cyclothem: Age: Shale horizons processed in lab: Reference:
Iowa Nuyaka Creek Shale
Marmaton Fm. Lost Branch Uppermost
Desmoinesian • ApCoDp‐3‐Upr
Dark Grey Shale. Swade (1985)
Illinois Hushpuckney Shale Patoka Fm. Macoupin
Lower Missourian
• SVS‐1‐M‐Upr Dark • SVS‐1‐M‐m
(Darkest at top) • SVS‐1‐M‐Lr Dark
Rosenau et al., (2014).
These particular shales were sampled due to previous published accounts of extremely high abundances of conodont elements and ichthyolith material. Additionally these shales experienced very low levels of post burial heating and diagenetic alteration. The conodonts they contain accordingly display low colour alteration indices of approximately 1 to 1.5, proving their chemical structure has not been altered physically by high temperatures throughout the extent of their burial (Epstein et al., 1977).
3
Shaledisaggregation
Approximately 1 kg of shale was separated from each sample bag and spread over a labelled oven tray, using a spoon and a paper funnel. This was then placed in an industrial oven at 65°‐70° Celsius (C). The tray and shale material were regularly reweighed over the next 24‐48 hours until the sample was completely dry and had stopped losing excess weight (due to water content). For safety reasons, the oven was never left on overnight, and oven gloves were worn at all times. At this point, the dry shale was added to a labelled Pyrex beaker using a paper funnel and hot water was then added to disaggregate the shale. The beaker was covered in foil for insulation and left overnight (Fig. 3a). Experimentally, cold water was added instead to half of the first horizon sampled to compare the reaction differences (see results below).
Fig. 3: Processing Carboniferous shale samples in the palaeontology lab. (a) Hot water added to oven‐dried shale; (b) Three sieves stacked on top of each other in the sieving sink. Note the multi‐head hose; (c) Graded filter paper cones containing sieved sediments on tray in oven; (d) Microfossil picking station in the lab.
The following morning, the disaggregated shale sample was ready for wet sieving. For hygiene and safety, thick plastic gloves and an apron were worn during this part of the process. Four wet sieves were used:
1 mm Top of stack
500 μm
250 μm
125 μm Base of stack
Preliminary attempts included a 63 μm sieve below the 125 μm sieve, but it was later decided to discard this sieve as it was inefficient and problematic due to excessive flooding of the stack. It was also reasoned that the 63 μm to 125 μm fraction would not contain conodonts large enough to pick and confidently identify.
The shale/mud sample was then carefully washed through the sieve stack (Fig. 3b) using a multi‐head hose. The various size fractions recovered were then collected into labelled filter papers, which were placed in the oven to dry at a low temperature (65°‐70° C) for up to 48 hours until completely dry (Fig. 3c). The coarsest grade of residue (>1 mm) was returned to an oven tray for further drying, disaggregation and re‐sieving.
4
Each dried filter paper cone (containing graded sediment residue) was then brought to a collection station in the lab, which was covered by A3 paper. Using a thick brush, the dry residue was swept onto the paper below, ensuring no residue remained on the filter paper. The A3 paper ensured that any spilled residue would not be lost. This residue was then funnelled into a labelled glass container and capped. Glass containers were preferentially used as the residue tends to stick to plastic ones due to static charge. The residue was now ready for the next step of processing; picking. This entire process was repeated once for each of the three Illinois horizons, and twice for the single Iowa horizon. Each horizon had three grades of residue for picking; (125 μm ‐ 250 μm), (250 μm – 500 μm) and (500 μm – 1 mm).
P ickingresidues
The main materials necessary for the picking through a sample residue were a binocular microscope, a petri dish with a gridded base (1 mm squares) and a very fine paint brush (Fig. 3d). Additional containers were also required to store any microfossils recovered. A thin layer of sediment (one grain thick) was spread across the gridded petri dish, and systematically scanned under the microscope. Conodont elements were retrieved and transferred to a cavity slide using the tip of the fine paintbrush. The picking process was very time consuming (took approximately 6 weeks) and required considerable concentration and patience.
5
Results
Shaledisaggregation: Hotvs. Cold
Early in the project, the first horizon selected for sample processing (SVS‐1‐M‐Lr Dark) was divided into two. One half was treated with cold water before sieving and the other half with hot water. The hot water reacted more thoroughly with the shale, disaggregating it more than the cold water batch. This was visually apparent and it was also confirmed when the hot water batch was considerably easier to sieve. It is proposed that using hot water to disaggregate the dried shale samples should be standard protocol for these particular Carboniferous samples.
Shalereport
Below is a description of the residues prepared and examined for each of the four horizons sampled.
SVS‐1‐M‐Lr Dark was the first horizon processed, of which 2 kg was used (~ ¼ Gallon bag). The grains were angular and dark grey and interspersed with organic‐rich detrital fragments. After several days of picking it was decided to process a new horizon as this horizon lacked sufficient microfossil content. This particular horizon is not considered the maximum flooding surface of the Hushpuckney Shale Member.
SVS‐1‐M‐Upr Dark was processed subsequently, using up 900 g of sediment (~ ⅙ Gallon bag). These residues were darker in colour and richer in conodonts in comparison to SVS‐1‐M‐Lr Dark. However, these elements were commonly encrusted with clay/mud, making them less desirable for isotopic analysis due to the surficial contamination and also as they are more difficult to taxonomically determine. There was also a lack of ichthyolith material in this residue, precluding any possibility for comparative analysis with the conodont material. This horizon is also not considered the maximum flooding surface of the Hushpuckney Shale Member.
SVS‐1‐M‐m(Darkest at top) was processed next, disaggregating 1.5 kg (~ ⅕ Gallon bag) of this shale. From the three Illinois horizons analysed, this was by far the richest in terms of platform conodont element yields, as well as having high counts of ichthyolith material. Most microfossils picked were pristine with little clay encrustation. Fragmented (modern) rootlets and lignified material were also present. The dark colour of the grains also suggested that this layer is largely composed of organic material, which is indicative of high fossil content. The condition of the microfossils, and their abundance both suggest that SVS‐1‐M‐m(Darkest at top) is the maximum flooding surface of the Hushpuckney Shale Member, and future projects should focus on processing and picking it solely for the very high yields of large clean microfossils.
ApCoDp‐3‐Upr Dark Grey Shale About 2 kg of this horizon was processed in two batches (~ ¼ Gallon bag) and it had been noted by a previous study to have an exceptionally high yield of conodonts. The residue had a high clay content, making the sieving difficult, but the conodonts present were satisfactory in terms of preservation. The variety of genera present also made this horizon quite favourable. Several other microfossils were also picked such as stick bryozoans and brachiopod valves/spines. The rich microfaunal remnants in this horizon show that this is most likely the maximum flooding surface of the Nuyaka Creek Shale Member.
P icking&Sort ingresults
Over 1000 conodont elements were picked in total (Fig. 4a‐b). Initially two bulk containers of conodonts (of several morphological types) and other microfossils, including ichthyolith material, were filled. One container was from picking the SVS‐1‐M‐m (Darkest at top) horizon and the other was from picking the
6
ApCoDp‐3‐Upr Dark Grey Shale horizon. These both represent the richest microfossil bearing horizons processed during the project.
These two broad sample groupings were then further subdivided (generically) into appropriate samples for future analysis in the mass spectrometer. These subgroupings were: Idiognathodus species, Gondolella species, broken P1 blades, Prioniodids (P), Prioniodids (M/S) and miscellaneous elements (Fig. 4c‐e). Prior to isotopic analysis, these sample cohorts may be further subdivided according to degree of surface contamination (to see if there is a measurable difference between ‘clean’ and ‘dirty’ conodont elements), size (to see if there are any ontogenetic differences in isotopic composition within the same genus).
Fig. 4: Carboniferous conodont and ichthyolith material recovered for future isotopic analysis. (a) Picked, but unsorted microfossils from SVS‐1‐M‐m(Darkest at top). Each conodont element is about 750 μm long; (b) P1 elements from ApCoDp‐3 Upr DGS sorted into taxonomic groups in a cavity slide. Fine paint brush for scale; (c) Sorted Idiognathodids from ApCoDp‐3 Upr DGS, scale as per Fig. 4a; (d) Sorted Gondolella P1 elements from ApCoDp‐3 Upr DGS (ditto scale); (e) Detail of microfossils recovered from SVS‐1‐M‐m(D @ t). Two on left hand side ichthyoliths (microscopic fish teetch), top right is an Idiognathodid and bottom right is a Prioniodid. Grid squares = 1mm2.
7
Discussion/Conclusion
This research project was successful in that conodont microfossils were methodically extracted from Carboniferous shale samples, using very careful methods which minimized the potential for alteration or offset of any potential original stable nitrogen values which they may preserve. Using only water and low temperature (65°‐70°) heating, the conodont elements will hopefully be relatively chemically unaltered from the time they were originally buried in seafloor muds some 300 million years ago.
The identification of the of the maximum marine flooding surfaces of both shale members was a valuable and useful exercise, as it will allow future studies to focus on processing those particular horizons to maximise microfossil yields.
Large numbers of conodont elements, from at least three different genera, were recovered and sub‐sorted, in preparation for further stable isotopic analysis. The final stage of the project will be completed in October 2015 when the various conodont microfossil samples are processed using the nanno‐EA Mass Spec facility in the Department of Geology in Trinity College Dublin. I will travel to TCD with my project supervisor to oversee this phase of the research work.
Regarding the stable nitrogen analysis, several questions must be asked considering the reliability of the organic nitrogen trapped in conodont microfossils, and whether this method of mass spectrometry really reads the nitrogen solely from the elements themselves. Does any surficial sediment contamination on the elements affect these results? Analysis of triplicates of ‘dirty’ and ‘clean’ samples, and comparing the results obtained, will help to test this. It must also be considered that over the past 300 million years of burial, the chemical signature of the organic matter within these microfossils may have been diagenetically altered. Temperature and pressure have long been known to alter the appearance of conodont microfossils, resulting in the creation of a conodont alteration index (Epstein et al., 1977). The elements picked for this project had a CAI index of approximately 1‐1.5. This is relatively low and suggests that they have never been subjected to high temperatures (over 100°), which is promising.
Another consideration is whether the conodont microfossils have been host to post‐mortem microbial activity. As no previous work has been published in this area, it is clearly an area for further research.
Reliable and precise isotope analysis of conodont microfossils has only really become established in the last 15 years. To date, only stable oxygen and carbon values have been analysed and published. The present project’s attempts to record reliable stable (organic) nitrogen and carbon values from conodont elements thus represents, potentially, a significant step forward in our understanding of this enigmatic and extinct fossil grouping. Much work remains to be completed, including further refining the analytical protocol, and comparing the results obtained with coeval fish (ichthyolith) microfossils also present in the shales. Once this work is completed, there is considerable potential to further expand the research project, which I would like to try to pursue at postgraduate level:
Research question: Research strategy:
Did the conodont group evolve palaeoecologically through geological time?
Conodonts existed on Earth from the late Cambrian through to the Late Triassic (some 300 million years of time), and during this time they were an important component of the marine realm, including the zooplankton. Analysis of conodont elements of different ages would allow an assessment of the trophic positioning and palaeoecology of the group during its evolution.
Do conodont isotopic signatures vary due to heating and diagenetic alteration?
Conodonts belonging to the same species/genera, but of differing CAI would be systematically analysed to assess the effects of alteration.
How to conodont isotopic signatures compare with coeval fossil biota?
Various coeval fossil groups, such as ichthyoliths, scolecodonts and palynomorphs have the potential to preserve original organic carbon and nitrogen signatures. Analysis of these would allow comparison with the conodont dataset.
8
Overall, during my internship I gained an invaluable understanding of the inner workings of a scientific lab environment. Hopefully, if stable nitrogen isotopic data can be successfully recovered from the picked and sorted conodont microfossils, and if the data is repeatable, a new realm of palaeobiology will be opened; the oldest fossils to be analysed for nitrogen since dinosaurs – 200+ million years older!
References
Barham, M. 2015. Comprehending Conodonts. Geology today, 31, 74‐80. Bearhop, S., Thompson, D.R., Waldron, S., Russell, I.C., Alexander, G. and Furness, R.W. 1999. Stable isotopes indicate the extent of freshwater feeding cormorants Phalacrocorax carbo shot at inland fisheries in England. Journal of Applied Ecology, 36, 75‐84. DeNiro, M.J. and Epstein, S. 1978. Influence of diet on the distribution of carbon isotopes in animals, Geochimica et Cosmochimica Acta, 42, 495‐506. DeNiro, M.J. and Epstein, S. 1981. Influence of diet on the distribution of nitrogen isotopes in animals, Geochimica et Cosmochimica Acta, 45, 341‐351. Eggers, T. and Hefin Jones, T. 2000. You are what you eat…or are you? TREE, 15, 265‐266. Epstein, A.G., Epstein, J.B. and Harris, L.D. 1977. Conodont colour alteration: an index to organic metamorphism. U.S. Geological Survey Professional Paper, 995, 1‐27. Joachimski, M.M., von Bitter, P.H. and Buggisch, W. 2006. Constraints on Pennsylvanian glacioeustatic sea‐level changes using oxygen isotopes of conodont apatite. Geology, 34, 277‐280. McCarthy, I.D. and Waldron, S. 2000. Identifying migratory Salmo trutta using carbon and nitrogen stable isotope ratios. Rapid Communications in Mass Spectrometry, 14, 1325‐1331. Rooney, A., Goodhue, R. and Clayton, G. 2015. Stable nitrogen analysis of the Upper Devonian palynomorph, Tasminites. Palaeogeography, Palaeoclimatology, Palaeoecology, 429, 13‐21. Rosenau, N.A., Tabor, N.J. and Herrmann, A.D. 2014. Assessing the palaeoenvironmental significance of middle‐late Pennsylvanian conodont apatite δ18O values in the Illinois Basin. PALAIOS, 29, 250‐265. Swade, J.W. 1985. Conodont distribution, palaeoecology, and preliminary biostratigraphy of the upper Cherokee and Marmaton groups (upper Desmoinesian, middle Pennsylvanian) from two cores in south central Iowa. Iowa Geological Survey, 14, 1‐71. Vennemann, T.W., Fricke, H.C., Blake, R.E., O'Neil, J.R. and Colman, A. 2002. Oxygen isotope analysis of phosphates: a comparison of techniques for analysis of Ag3PO4. Chemical Geology, 185(3), 321‐336.