The analyses are done. Because you are supposed to do an 'integrated approach' you are working on 'integrating' your data and doing an interpretation that fits in with everything.
After a short or long search for patterns (as a geologist you are at least talented in pattern-spotting), you will find that no easy existing model fits with all data (or worse: every existing model fits with all data) which gives you the chance to chose the model you like best and alter it a bit. You are using an auxilliary hypothesis which explaines why this model, which is adequate in general, is not working properly for the data you are involving.
The best ist to raise a whole set of model assumptions which are not easy to be proven or disproven. Imagine it as a daughter company, to which you can export your credit risks in order to keep the bilance of your adapted existing model clean.
If there are some new data that appear to falsify your model you are employing your daughter company of auxilliary theses to explain why they are not at all problematic.
Given your business concept is good you even manage to invert contradicting data - under the light of your additional theses they actually support your model.
As you can handle it flexibly, you can of course add to or remove from the stock of your daughter company at free will. A good idea is to pay attention to fashions (if 'Milankovich cycles' or 'metamorphic core complexes' or 'climate change' are en vogue you may think about including them).
Successful model constructors manage to give their constructs the appearance of inner coherence (e.g. by means of categories, definitions and a quantitative bluff package) and sell them to others who 'succesfully' convert them to new areas and problems.
And then everything collapses - some new conflicting data pushes your model to the point of absurdity. Usually the new data fit in with a much more parsimonious alternative model. And no one will understand how you could have been so stupid to overlook that possibility in the first place...
Mittwoch, 26. November 2008
Dienstag, 25. November 2008
Fieldwork Photo of the Weak
The Neverending Outcrop: Younger stratigraphic succession near Madygen, SW Kyrgyzstan.
The greyish-brownish Madygen Formation is overlayn uncomformably by varicoloured continental Jurassic strata which in turn are separated by an uncomformity from reddish deposits of the facially diverse Cretaceous including massive conglomeratic banks.
Paleogene: A yellowish marine succession containing mass occurrences of oysters and massive carbonates is followed by younger continental deposits of the Tertiary.
Note the roofs of premises belonging to the village of Madygen.
The greyish-brownish Madygen Formation is overlayn uncomformably by varicoloured continental Jurassic strata which in turn are separated by an uncomformity from reddish deposits of the facially diverse Cretaceous including massive conglomeratic banks.
Paleogene: A yellowish marine succession containing mass occurrences of oysters and massive carbonates is followed by younger continental deposits of the Tertiary.
Note the roofs of premises belonging to the village of Madygen.
Freitag, 21. November 2008
Tectonics & Paleo (III):
The shearing of fossils and how to reverse it
Let's start in 2D: You have a flat fossil and regard only the deformation in the two dimensions of the fossil plane:
Easy, you may say. Fossils specimens like that are good strain indicators and it's not difficult to deduce the amounts of simple shear and flattening/lengthening necessary to transform the undeformed into the deformed specimens or vice versa:
There was a story, my tectonics prof told me from his study time when he was working for a famous German paleontologist: He was doing the retrodeformation of fossils using some kind of algorithm/ computing procedure - but only, until his sponsor found that he could reach the same effect by holding the fossil oblique over a photocopying machine (you can imagine what a disillusionment that was...).
In some cases, however, the problem is not as simple as in the example displayed above. Insect wings from Madygen and other localities often display a considerable amount of deformation but occur isolated and as palaeontological samples they have not been taken oriented (i.e. referenced to a system of external coordinate axes).
What was the original shape?
This question is crucial if you want to define and distinguish taxa (how many unnecessary species have been erected because the similarity of fossil specimens got lost in deformation?) but also searching for intraspecific variation, e.g. branching points that are highly variable in individuals of the same species.
My "bureau-mate" Olivier Bethoux, paleoentomologist, is currently doing his postdoc research working on that problem. I won't say much about his solution which involves morphometrics/ landmark analysis but keep you informed about results when they are published.
Easy, you may say. Fossils specimens like that are good strain indicators and it's not difficult to deduce the amounts of simple shear and flattening/lengthening necessary to transform the undeformed into the deformed specimens or vice versa:
There was a story, my tectonics prof told me from his study time when he was working for a famous German paleontologist: He was doing the retrodeformation of fossils using some kind of algorithm/ computing procedure - but only, until his sponsor found that he could reach the same effect by holding the fossil oblique over a photocopying machine (you can imagine what a disillusionment that was...).
In some cases, however, the problem is not as simple as in the example displayed above. Insect wings from Madygen and other localities often display a considerable amount of deformation but occur isolated and as palaeontological samples they have not been taken oriented (i.e. referenced to a system of external coordinate axes).
What was the original shape?
This question is crucial if you want to define and distinguish taxa (how many unnecessary species have been erected because the similarity of fossil specimens got lost in deformation?) but also searching for intraspecific variation, e.g. branching points that are highly variable in individuals of the same species.
My "bureau-mate" Olivier Bethoux, paleoentomologist, is currently doing his postdoc research working on that problem. I won't say much about his solution which involves morphometrics/ landmark analysis but keep you informed about results when they are published.
Montag, 17. November 2008
Fieldwork Photo of the Week
You can see the rise of our club room one day after the arrival in Madygen. Gas bottles, sample boxes, and limestone boulders are integral parts of the construction.Borrowed this photo of a tent erection from this year's Madygen participant Daniel Rutte, who started an exchange semester in Golden, Colorado, shortly after the field trip and after becoming a Bachelor in Freiberg (but only 'of Science' unless I'm much mistaken).
Samstag, 15. November 2008
Triassic critters: Kazacharthrans
Kazacharthrans - or Katzen, as we call them (jokingly) in German - are an endemic group of small branchiopod crustaceans which were named after the former Soviet Republic of Kazakhstan, where the type locality is situated. All yet known occurrences are restricted to the Middle Triassic to Lower Jurassic of Central Asia (Kazakhstan, Mongolia, Turkmenistan, the northwestern Chinese Province Xinjiang, and Kyrgyzstan: the Madygen Formation).
The closest recent relatives of kazacharthrans and an anatomically quite similar group are the tadpole shrimps (Notostraca), including the 'living fossil' species Triops cancriformis, which has not changed since its earliest occurrence in the Triassic.
Kazacharthran head shield from Madygen; width: 1.2 cm.
The most complete body fossils from Madygen consist of a relatively large cephalothoracic shield (see pic) and a segmented tail with a small and spiny shield at the end (telson). Madygen finds show the head shield often considerably deformed. As the animals were subject to moulting, the abundancy of kazachthran body fossils is raised by the preservation of exuviae.
The riddle of kazachrathran radiation. Kazacharthrans are regarded as a Triassic offspring from the lineage of the otherwise conservative group of notostracans which have persisted since the Carboniferous without larger anatomical changes. As the Kazacharthra develop a relatively high diversity (14 genera, >20 species described) in a narrow spatial and temporal window, the crucial questions is, what their speciality (and fate) was.
Sebastian Voigt (who is in charge of the Madygen project here in Freiberg) is a paleoichnologist and also working on kazacharthran trace fossils and their ethological and ecological implications (see ref below), using the ichnia of recent triopsids for comparison (the reminiscence of a childhood dream to have those lovely trackmakers in your aquarium). Understanding the palaeoenvironment and fossil association of kazachathran body and trace fossils in the Madygen Fm will hopefully help to understand the peculiarity of "Katzen".
Refs:
Chen P., K.G. McKennzie & Zhou, H.(1996): A further research into Late Triassic Kazacharthra from Xinjiang Uigur autonomous region, NW China. - Acta Palaeontologica Sinica 35(3): 272-301.
Preliminary results on Madygen kazacharthrans can be found in the abstract volume of the 2007 fall meeting of the German Palaeontological Society (pdf, 33MB):
Voigt, S.(2007): Kazachartran body and trace fossils from shallow lake deposits of the Madygen Formation (Middle to Upper Triassic, Kyrgyzstan, Central Asia). In: O. Elicki & J.W. Schneider (eds): Fossile Ökosysteme. - Wissenschaftliche Mitteilungen 36, Institut für Geologie, TU Freiberg, p. 160
The closest recent relatives of kazacharthrans and an anatomically quite similar group are the tadpole shrimps (Notostraca), including the 'living fossil' species Triops cancriformis, which has not changed since its earliest occurrence in the Triassic.
Kazacharthran head shield from Madygen; width: 1.2 cm.The most complete body fossils from Madygen consist of a relatively large cephalothoracic shield (see pic) and a segmented tail with a small and spiny shield at the end (telson). Madygen finds show the head shield often considerably deformed. As the animals were subject to moulting, the abundancy of kazachthran body fossils is raised by the preservation of exuviae.
The riddle of kazachrathran radiation. Kazacharthrans are regarded as a Triassic offspring from the lineage of the otherwise conservative group of notostracans which have persisted since the Carboniferous without larger anatomical changes. As the Kazacharthra develop a relatively high diversity (14 genera, >20 species described) in a narrow spatial and temporal window, the crucial questions is, what their speciality (and fate) was.
Sebastian Voigt (who is in charge of the Madygen project here in Freiberg) is a paleoichnologist and also working on kazacharthran trace fossils and their ethological and ecological implications (see ref below), using the ichnia of recent triopsids for comparison (the reminiscence of a childhood dream to have those lovely trackmakers in your aquarium). Understanding the palaeoenvironment and fossil association of kazachathran body and trace fossils in the Madygen Fm will hopefully help to understand the peculiarity of "Katzen".
Refs:
Chen P., K.G. McKennzie & Zhou, H.(1996): A further research into Late Triassic Kazacharthra from Xinjiang Uigur autonomous region, NW China. - Acta Palaeontologica Sinica 35(3): 272-301.
Preliminary results on Madygen kazacharthrans can be found in the abstract volume of the 2007 fall meeting of the German Palaeontological Society (pdf, 33MB):
Voigt, S.(2007): Kazachartran body and trace fossils from shallow lake deposits of the Madygen Formation (Middle to Upper Triassic, Kyrgyzstan, Central Asia). In: O. Elicki & J.W. Schneider (eds): Fossile Ökosysteme. - Wissenschaftliche Mitteilungen 36, Institut für Geologie, TU Freiberg, p. 160
Samstag, 8. November 2008
Fieldwork Photo of the Week
July or August 2007 at "Sharov Quarry": Toilo, who is living in Madygen, is talking to me while I am dripping some fixation solution on a fish or plant fossil.That pile of weathered shale debris we are sitting on is the product of Sharov's group in the 1960s and of our work. The photo is taken from the position of the outcrop wall.
The Sharov locality is the place where all hiherto described Madygen tetrapods, most insects and fishes, and some of the best plant fossils have been found.
Tectonics & Paleontology (II): Sclerochronology
Some five years ago I had one of my first presentation-preparing seminars and the list of available topics included 'sclerochronology', supervised by the tectonophysics prof. Searching the literature I found that the term referred to the study of the accretionary growth of mineralized organismic hard parts - a bit like the tree-ring chronology transferred to animal skeletons ('interesting', so I thought and chose 'sclerochronology' for my seminar talk).
There were many papers on mollusc life strategies and environmental change during the younger Cenozoic, mostly analyzing some long-living clams. Not many studies involved 'sclerochronology' as an actual dating method, often researchers were looking for either ontogenetic signals or climatic signals, often involving distinct taxa, localities, and stratigraphic levels for comparison.
Among the animal groups considered were brachiopods, bivalves, corals, belemnites, fish (otoliths) but also higher vertebrates: Enamel and accretionary growing bone can yield sclerochronological data - the method is also called 'skeletochronology' when applied on vertebrate hard parts.
And the link to tectonics? If you consider the cross section of a shell as representing a time series of fast and slow growth phases and phases of arrested growth, how exactly can you expect a tectonic signal to show up? I asked my tectonophysics prof what story he wanted me to tell and it was this:
A reference book on Quaternary dating methods (Lettis et al. 2000) also includes a chapter on sclerochronology in recent to subrecent corals inhabiting a shallow tropical tectonically active shelf. If the shelf area is part of a block which is elevated over another block by thrust faulting (as under compression along a convergent tectonic plate margin), this tectonic movement - which is not continuous but (mostly) discrete with larger earthquakes releasing most of the stress - can have consequences for the coral growth:
During an earthquake (along a thrust fault) the uppermost part of a colony is lifted over the water level, dies, and stops growing, while deeper-lying sections stay intact and continue their growth. If you count the annual growth bands and locate the points of growth arrestment after an earthqake you can derive the timing of earthquakes and also the amount of vertical displacement for each event. These data are sufficient for deriving the earthquake characteristic of the responsible fault - a classical aim of paleoseismology.
You could argue that all that has nothing to do with deep time processes and you are right: While the paleobiological and paleoclimatological approaches employing sclerochronology are not strictly limited in time, sclerochronological dating is restricted to the youngest few thousand years of the Holocene.
Some refs: Sclerochronology
... & Tectonics:
Buddemeier, R.W. & F.W. Taylor (2000): Sclerochronology. In: Lettis, W.R., J.S. Noller & J.M. Sowers (eds): Quarternary Geochronology: Methods and Applications. - Washington, AGU, pages 25- 40.
... in vertebrates
MacFadden, B.J. (2004)(ed): Incremental Growth in Vertebrate Skeletal Tissues: Paleobiological and Paleoenvironmental Implications. In: Palaeogeography, Palaeoclimatology, Palaeoecology 206(3-4).
... in marine animals
Schöne, B.R. & D. Surge (2005)(eds): Looking back over Skeletal Diaries - High-resolution Environmental Reconstructions from Accretionary Hardparts of Aquatic Organisms. In: Palaeogeography, Palaeoclimatology, Palaeoecology 228(1-2).
There were many papers on mollusc life strategies and environmental change during the younger Cenozoic, mostly analyzing some long-living clams. Not many studies involved 'sclerochronology' as an actual dating method, often researchers were looking for either ontogenetic signals or climatic signals, often involving distinct taxa, localities, and stratigraphic levels for comparison.
Among the animal groups considered were brachiopods, bivalves, corals, belemnites, fish (otoliths) but also higher vertebrates: Enamel and accretionary growing bone can yield sclerochronological data - the method is also called 'skeletochronology' when applied on vertebrate hard parts.
And the link to tectonics? If you consider the cross section of a shell as representing a time series of fast and slow growth phases and phases of arrested growth, how exactly can you expect a tectonic signal to show up? I asked my tectonophysics prof what story he wanted me to tell and it was this:
A reference book on Quaternary dating methods (Lettis et al. 2000) also includes a chapter on sclerochronology in recent to subrecent corals inhabiting a shallow tropical tectonically active shelf. If the shelf area is part of a block which is elevated over another block by thrust faulting (as under compression along a convergent tectonic plate margin), this tectonic movement - which is not continuous but (mostly) discrete with larger earthquakes releasing most of the stress - can have consequences for the coral growth:
During an earthquake (along a thrust fault) the uppermost part of a colony is lifted over the water level, dies, and stops growing, while deeper-lying sections stay intact and continue their growth. If you count the annual growth bands and locate the points of growth arrestment after an earthqake you can derive the timing of earthquakes and also the amount of vertical displacement for each event. These data are sufficient for deriving the earthquake characteristic of the responsible fault - a classical aim of paleoseismology.
You could argue that all that has nothing to do with deep time processes and you are right: While the paleobiological and paleoclimatological approaches employing sclerochronology are not strictly limited in time, sclerochronological dating is restricted to the youngest few thousand years of the Holocene.
Some refs: Sclerochronology
... & Tectonics:
Buddemeier, R.W. & F.W. Taylor (2000): Sclerochronology. In: Lettis, W.R., J.S. Noller & J.M. Sowers (eds): Quarternary Geochronology: Methods and Applications. - Washington, AGU, pages 25- 40.
... in vertebrates
MacFadden, B.J. (2004)(ed): Incremental Growth in Vertebrate Skeletal Tissues: Paleobiological and Paleoenvironmental Implications. In: Palaeogeography, Palaeoclimatology, Palaeoecology 206(3-4).
... in marine animals
Schöne, B.R. & D. Surge (2005)(eds): Looking back over Skeletal Diaries - High-resolution Environmental Reconstructions from Accretionary Hardparts of Aquatic Organisms. In: Palaeogeography, Palaeoclimatology, Palaeoecology 228(1-2).
Sonntag, 2. November 2008
Tectonics and Paleontology (I): Series Intro
In Germany paleontologists often have graduated in geoscience study programs. At some universities, such as my Freibergian alma mater, paleontology is mostly taught as a branch of geology dealing with fossils for the purpose of solving geoscientific problems: Fossils provide information about the age of sedimentary rocks (biostratigraphy) or their maturity (see for example: conodont alteration index) or formation conditions (biofacial analysis) or are relevant for paleogeographic reconstructions (paleobiogeography) or for paleoclimatic inference. As a matter of fact fossils are useful and paleontology is not the end in itself, no art pour l'art...
...and so forth. Perhaps some of you heard a similar story.
There are some advantages, though, when you are coming from the geological side: You know your rocks and minerals alright. You have learned how to draw maps and what geoinformation is and all those analytical methods for rock samples and how to get a picture of an ancient biotope from sedimentological criteria and how to find the most fossiliferous places and strata.
In my M.Sc. studies of geology/paleontology I was supposed to chose 3 out of 13 electives, including petrology, tectonics/geodynamics, geology of mineral deposits, geochemistry, sedimentology, pedology, hydrogeology, geotechnics, paleontology, mathematical geology/ geoinformatics and mineralogy. I did a bit of everything with the exception of hydrogeology and focussed on all that non-applied basic research stuff, including paleontology and tectonics.
And when the project in Kyrgyzstan started somewhat later than expected I did - not only for reasons of timing - my master thesis on fissures and normal faults in the Ethiopian rift (see here). Over the years I found more and more links between tectonics and paleontology including rather subtle ones. Some posts will help me to keep them in mind.
...and so forth. Perhaps some of you heard a similar story.
There are some advantages, though, when you are coming from the geological side: You know your rocks and minerals alright. You have learned how to draw maps and what geoinformation is and all those analytical methods for rock samples and how to get a picture of an ancient biotope from sedimentological criteria and how to find the most fossiliferous places and strata.
In my M.Sc. studies of geology/paleontology I was supposed to chose 3 out of 13 electives, including petrology, tectonics/geodynamics, geology of mineral deposits, geochemistry, sedimentology, pedology, hydrogeology, geotechnics, paleontology, mathematical geology/ geoinformatics and mineralogy. I did a bit of everything with the exception of hydrogeology and focussed on all that non-applied basic research stuff, including paleontology and tectonics.
And when the project in Kyrgyzstan started somewhat later than expected I did - not only for reasons of timing - my master thesis on fissures and normal faults in the Ethiopian rift (see here). Over the years I found more and more links between tectonics and paleontology including rather subtle ones. Some posts will help me to keep them in mind.
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