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Alexander Rohrmann

Alexander Rohrmann
Karl-Liebknecht-Strasse 24,
Haus 27,
14476 Potsdam
Germany
(+49)-331 977 5700
rohrmann @ geo.uni-potsdam.de

 

Research Interests

Structural geology
Geochronology
Surface processes
Terrestrial sedimentology
Tectonic Geomorphology

My interest focuses on the complex feedbacks between tectonic, surface and climate processes. I take a field-based approach that entails geological mapping, structural and basin analysis, geochemistry combined with thermochronology, and cosmogenic nuclide dating to solve different aspects of spatiotemporal patterns of surface processes and their tectonic and/or climatic forcing mechanisms.

Aims of my research efforts to date include:
(1) quantifying the dynamic relationships between tectonics and climate with respect to the development of orographic barriers, (2) deciphering process rates at a variety of time scales to better understand the discrepancies between long-term (i.e., geological) and short-term process rates of deformation and erosion, (3) studying active and inactive thrust belts to better understand changes of tectonic style, timing of deformation, uplift and erosion foreland systems, (4) understanding the role of crustal anisotropies in localizing compressional reactivation, and hence causing disparate patterns of uplift in broken foreland settings, (5) the late Cenozoic tectonic evolution of Asia and South America.

Most recently, I have been investigating wind erosion in central Asia and its tectonic and climatic implications, the formation and style of intermontane basin development in NW Argentinia, and the influence of aridity on the plateau development in Tibet. In my future professional career I hope to investigate more deeply terrestrial archives that hold valuable information of past tectonic activity, and its forcing of climatic conditions.

Current PhD Projects

Spatiotemporal distribution of the δ D rainfall signal in intermontane basins in NW-Argentina, derived from recent to Miocene organic material in sediments

The Andes represent a major orographic barrier to atmospheric circulation and moisture transport in South America. Moist air masses derived from the Atlantic Ocean and Amazon Basin are progressively lifted and cooled during ascent, which produces intense rainfall along the ranges along the eastern Andean Plateau margin. The continuous rainout of moisture along the eastern plateau margin promotes aridification of the interior parts of the plateau. The sharp contrast between humid conditions in the eastern lowlands and arid conditions in the plateau interior is also found in the δ D signal of rainfall across the eastern margin.

We will quantitatively explore the complex feedback between range uplift, localization of rainfall along the mountain front and the successive formation of rain- shadows on the back side of the range through the use of lipid biomarkers as a proxy of rainfall amounts. Our use of lipid biomarkers as a proxy of rainfall amounts is a cutting edge technique, which still needs to be tested and improved. Ultimately, the use of this technique will give us the unique opportunity to derive paleo-rainfall amounts worldwide through geological history.

We will collect a transect sampling the modern vegetation and streams in a traverse from the Andean foreland basin to the eastern margin of the Puna Plateau to determine the recent δ D signal of precipitation. These results will be compared to a stratigraphic section in the Miocene Palo Pintado Fm from the intermontane Calchaqui Valley in the transition between the northernmost Sierras Pampeanas and the Puna. Here, we systematically sampled organic- rich sediment for alkene biomarkers. The comparison of the data from the modern transect, which provides the spatial distribution of the δ D signal of rainfall, and the data from the stratigrapic section, which furnishes a spatially fixed temporal change of δ D, enables us to track the successive eastward migration of orographic barriers towards the foreland. The barrier controls the distribution and iamount of rainfall, which may have changed significantly over time. The data set will ultimately help to quantitatively document the creation of a rainshadow, which reflects the successive development of orographic barriers, intermontane basins, and the compartmentalization of the Andean foreland.

The Miocene Palo Pintado Fm documents the only wet interval in the Cenozoic history in the southern Central Andes. However, the exact paleo-environmental conditions and atmospheric boundary parameters, which led to this unique wet phase, are not well understood. In addition, we would like to characterize the atmospheric boundary conditions, through the use of numerical modeling by using the derived δ D rainfall amount data set. The results will give valuable insight into the atmospheric state during this time interval.

Advisors: Manfred R. Strecker, Dirk Sachse

Education

Since 2009
Ph.D student at the, Department of Geoscience, University of Potsdam, Germany
PhD advisors: Manfred Strecker (University of Potsdam), Paul Kapp (University of Arizona)

2009
MSc in Geoscience, Department of Geosceince, University of Arizona, U.S.A.
MSc advisors: Paul Kapp, Peter Reiners, Jon Pelletier

2007-2009
MSc student in Geology, Department of Geoscience, University of Arizona, U.S.A

2007
Pre-Diploma in Geoscience, Department of Geoscience, University of Potsdam, Germany

2004-2007
Diploma student in Geology, Department of Geoscience, University of Potsdam, Germany

Career aspirations

My main professional aim is an academic career with a position that ideally combines teaching and research. I gained teaching experience as a teaching assistant in a course taught by Prof. Andy Cohen at the University of Arizona. I was entrusted with teaching the laboratory section of this course and was fascinated by the different aspects of this work that nurtured my interest in an academic career.

Professional Experience

2009
Visiting graduate-student researcher at the University of Arizona, using the (U-TH)/He dating facility of Prof. Peter Reiners and the cosmogenic nuclide dating lab of Prof. Jay Quade

2009
Teaching assistant, “Advanced structural mapping in the Pyrenees (Spain)”, Department of Geoscience, University of Potsdam, Germany

2008
Teaching assistant, “Introduction to Stratigraphy and Sedimentology”, Department of Geoscience, University of Arizona, U.S.A

2008-2009
Research assistant, Department of Geoscience, University of Arizona, U.S.A

2006
Student assistant, “Desire”, GFZ Potsdam, Germany

2005-2007
Student assistant,”Denudation and erosion in the Sutlej- Valley, NW India” and “Inversion of moment tensors in anisotropic media with applications on cluster earthquakes in Vogtland/NW Bohemia”, Department of Geoscience, University of Potsdam, Germany

Honors/scholarships/grants

2008
Recipient of the first “Farouk El-Baz Student Research Award” of the Geological Society of America, for outstanding research in arid environments and to encourage and promote desert research.

2008
GPSC Travel Grant to participate in the AGU fall meeting, San Francisco, U.S.A

Publications

Submitted:

Rohrmann, A., Gyunn, J., Kapp, P., Reiners, P., Carrapa, B., (submitted to Nature): Minimal erosion on the Tibetan Plateau and implication for Plateau development

To be submitted:

Rohrmann, A., Kapp, P., Heermance, R., McCalister, A., (to be submitted) Wind-enhanced tectonics, quantifying severe wind erosion in the Qaidam basin, China

Heermance, R., Kapp, P., Rohrmann, A., McCalister, A., (to be submitted): Paleoyardangs: Evidence for extreme wind erosion in the stratigraphic record

Kapp, P., Pelletier, J., Rohrmann, A., Heermance, R., Russel, J., (to be submitted): Speculations about the history of wind erosion in the Qaidam Basin and its implications for tectonics, paleoclimate, and the source of the Loess Plateau

Conference Contributions & abstracts

Geodaze, Tucson, U.S.A
Rohrmann, A.; Kapp, P.; Pelletier, J.; Russel, J.; (2008): Wind-enhanced tectonics in the Qaidam Basin and implications for the source of the Loess Plateau

2008 Joint Meeting of The Geological Society of America, Houston, U.S.A
Kapp, P.; Rohrmann, A.; Pelletier, J. (2008): Wind-enhanced tectonics in the Qaidam Basin and implications for the source of the Loess Plateau

American Geophysical Union, Fall Meeting 2008, San Francisco, U.S.A
Rohrmann, A.; Kapp, P; Reiners, P. (2008): Minimal erosion in central Tibet since the Eocene and implications for plateau development, abstract #T32A-08;

5th International Symposium on Tibetan Plateau, Beijing, China
Kapp, P.; Rohrmann, A.; Volkmer, J. (2009): The tectonic history and formation of the Tibetan Plateau

American Geophysical Union, Fall Meeting 2009, San Francisco, U.S.A
Heermance, R.; Kapp, P.; Rohrmann, A.; McCallister, A. (2009): Extreme winds during the Quaternary deduced from yardang preservation within lacustrine sediments in the Qaidam Basin, China, abstract #PP21B-1341

Workshops, shortcourses, training

Shortcourse “Dating Quaternary Sediments”, University of Bern, Switzerland, 2006
Shortcourse “Rheology of Rocks”, Geologische Vereinigung, GFZ Potsdam, Germany, 2007
Shortcourse “Balanced Cross-sections”, Geologische Vereinigung, Freie University Berlin, Germany, 2007
Shortcourse “Geology and Geophysics applied in industry”, University of Arizona, U.S.A, 2008

Affiliations

Geological Society of America (GSA)
American Geophysical Union (AGU)
Deutsche Geologische Vereinigung (GV)

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