My major field of interest is paleontology. One of my interests is the relationship between ontogeny and phylogeny in organisms and in interpreting the function of various morphologic features of fossils, many of which have no modern counterparts for comparative analysis. Morphometric computer techniques, such as cluster analysis and factor analysis, are especially useful in these studies.
I am also investigating the application of these and other computer techniques to other types of geologic problems.Another of my interests are conodonts, the microscopic, tooth-like skeletal remains of extinct organisms of unknown affinity. Conodonts are of great stratigraphic utility in Paleozoic rocks, and understanding the environmental factors involved in controlling conodont distribution patterns in these rocks increases their stratigraphic usefulness.
I am currently investigating the distribution of conodont biofacies in Pennsylvanian age rocks of the mid-continent region of the United States.
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James R. Besancon
My principal research is into ordering of cations in minerals during cooling of igneous rocks. Because the rate of ordering of iron and magnesium into separate crystal sites is very rapid, it may be possible to work out thermal histories of volcanic eruptions, and evaluate models for transport of magmas in volcanoes. Determination of degree of ordering is done very simply, with a Mossbauer spectrometer. Samples are heated for varying lengths of time in a controlled atmosphere furnace, quenched, and degree of order measured. Changes in reflectance spectra with cation order are being investigated with Dr. Roger Burns (MIT) and Dr. Stephen Pratt (Brown University).
Cation ordering may also be detected by changes in optic axial angle, using the spindle stage and polarizing microscope. Development of an adequate theoretical model for this is being attempted, and automation of spindle stage measurements allows rapid and precise measurement of optical parameters.
The Massabesic gneiss, a preCambrian formation near Raymond, NH, is intruded by a number of identifiable granitic rocks. In an attempt to pin down the age of various parts of the gneiss, the age of these intrusions is being measured by Rb-Sr isotope variations. In addition, textural and chemical data are being collected on a porphyritic magnetite granite which is conspicuous in this area.
Student Projects:
Recent student research under my direction has been on the work mentioned above, and in addition:
1. Field geology of the volcanic rocks in South Natick (with Meg Thompson).
2. Petrology of the Cape Neddick layered gabbro.
3. Cooling history of ophiolites in Newfoundland and Baltimore, MD, by cation ordering studies.
4. Age of the Westwood Granite (with Meg Thompson and Dr. Samuel Bowring (MIT).
5. Ultramafic Xenoliths of the Dish Hill Volcano.
Margaret D. Thompson
Since 1980, I have been carrying on detailed field mapping of the Late Proterozoic Roxbury Conglomerate, Brighton Volcanic Complex, Mattapan Volcanic Complex and associated granites comprising the bedrock formations of south and west Boston. Having delineated the regional stratigraphy and structure of these units, I am now trying to relate them to the larger tectonic picture. Map-scale fault patterns thus furnish evidence for Lat Proterozoic normal faulting, while multiple microstructures in the conglomerate appear to record Late Paleozoic deformation. It remains to date most of these rocks and structures quantitatively.
Student Projects:
Students have shared in most of this work both as summer field assistants and through their own research projects. Past 350 and 370 topics include:
1. Stratigraphy and Structure of the Stonybrook Reservation (Boston, Mass). 2. Clast Lithotype analysis of the Roxbury Conglomerate in the Newton Quadrangle.
3. Stratigraphy of the "Brighton" Volcanics in the Kennard Conservation Area (Newton, Mass).
4. Mattapan ash-flow tuffs in the Needham Town Forest, Needham, Mass.
5. Stratigraphy of the Mattapan Volcanics in the Sherborn Area.
Present and future projects include:
1. Geochronology of Westwood Granite and Mattapan Volcanics, Westwood, MA.
2. Argon dating of mica fabric in Roxbury Conglomerate.
3. Stratigraphy and cleavage development in Cambridge Argillite.