Examining fault growth using syntectonic terrestrial strata at high-resolution time, Ebro Basin, NE Spain James Carrigan [1], Josep Parés [2], and David Anastasio [1] [1] EES Department, Lehigh University, Bethlehem, PA [2] CNIEH, Burgos, Spain E Significance / Justification Syntectonic sedimentation records the kinematics occurring during deformation through some encoding process. Foreland basins are important in the petroleum system but terrestrial deposits typically lack easily dated features such as biostratigraphy or other chronologic controls Anhysteretic remanent magnetization (ARM) measurements can be used as an objective proxy for climatic forcing when using accurate orbital models ARM measurements can provide 10 4 – 10 5 yr resolution in active settings to allow for detailed analyses View looking east at growth strata highlighted in yellow. The Geologic map of site locality. Inset map shows the unconformity is indicated with the red dashed line. site location in the Pyrenees. Site Location Samples were collected in fluvial/alluvial syntectonic terrestrial growth strata in conglomerates, sandstones, and siltstones. Paleomagnetic cores were collected using typical techniques while rock magnetic samples were crushed and sieved before further analysis. Absolute Ages Virtual Geomagnetic Poles were also calculated to construct a magnetic reversal stratigraphy. Samples were thermally demagnetized, in 15 steps, until stable directions, inferred as ChRM, were identified. ◦ Sites collected at ~15m interval with ≥5 specimens per site to allow for robust statistics A total of 1.5km of section was collected Cyclostratigraphic Ages ARM measurements are produced by applying a time decaying field and biasing field to the sample. This isolates a particular range of magnetic minerals, in this case detrital magnetite. ◦ Samples were collected at 75 cm intervals in order to have 4-5 sites per 20kyr based on preliminary sediment accumulation rates Additional magnetic characterization was conducted, which showed that magnetite was a small fraction of the total sample. ◦ IRM and AMS data were collected to better understand the character of the rocks sampled Methods Magneto-reversal stratigraphy for this locality. VGP’s were calculated by Josep Parés. Chron boundaries have been correlated to C15r-C12r giving Eocene / Oligocene ages. ? Plot of magnetization to stratigraphic distance derived from ARM measurements. ARM was conducted with 100mT peak field and 97 nT biasing field to isolate detrital magnetite. Broad, low frequency signal (approximately 1Ma period) is apparent in the data, which can be refined as shown in the conclusions. Magnetic characterization of some samples. The percentages given are the amount of magnetization due to a specific mineral. Folding rates determined from magneto stratigraphy and measured dip values. Fastest rates are on the order of 30° / Ma Results We aim to run further analyses to determine if the dominant cyclicity changes with changes in lithology. We expect that the conglomerates in the section would not record high frequency variations. We will examine the difference between ARM and AMS measurements to see which method provides a more consistent time frame. Earlier work has focused more heavily on AMS time series analysis, which may or may not be applicable to our study. This data set will complement our existing data. Finally, we will construct a forward model that adequately explains the data in order to see the growth of the underlying fault. This forward model will be constrained by our high frequency time in order to produce faulting and folding kinematics on tens of thousands of year timescales. Ongoing Work We can recover a significant signal from the ARM measurements that suggests multi level forcing at ~1.3Myr 400kyr, 12kyr, and 10kyr (at 25cm/kyr) above the 95% confidence interval ARM can give resolution orders of magnitude higher than magnetic reversal stratigraphy during long, hundreds of thousands to millions of years, chrons The use of unoriented samples allows for simple collection procedures and means many types of lithologies or sediments can be sampled. Conclusions 2.5m3.0m 330m 100m Long Eccentricity Precessional to sub-precessional Generalized Strat Column Bedding Magnetic Stratigraphy Pregrowth Growth Time averaged rate Chron averaged rates Literature Cited Aziz, H.A., Hilgen, F., Krijgsman W., Sanz E., and Calvo, J.P. (2000) Astronomical forcing of sedimentary cycles in the middle to late Miocene continental Calatayud Basin (NE Spain). Earth and Plant. Sci. Lett., 177, Ford, M., Williams, E.A., Artoni, A., Vergés, J., and Hardy S. (1997) Progressive evolution of a fault-related fold pair growth strata geometries, Sant Llorenç de Morunys, SE Pyrenees. Journal of Structural Geology, 19, Gunderson, K.L., Anastasio, D.J., Pazzaglia, F.J., and Picotti, V. (2013) Fault slip rate variability on yr timescales for the Salsomaggorie blind thrust fault, Northern Apennines, Italy. Tectonophys., 608, Latta, D.K., Anastasio, D.J., Hinnov, L.A., Elrick, M., Kodama, K.P., (2006) Magnetic record of Milankovitch rhythms in lithologically noncyclic marine carbonates. Geology, 34, Ogg, J.C. (2012) Geomagnetic polarity time scale In Gradstein, F.M., Ogg, J.G., Schmitz, M.D., and Ogg, G.M (Eds.) The Geologic Time Scale 2012 (p ). Waltam, MA: Elsevier. Acknowledgements Marisa Repasch, now at the University of New Mexico, provided field assistance and conducted preliminary data analysis Ken Kodama of Lehigh University provided guidance and stimulated discussion on magnetic topics Funding for this project was provided by AAPG L. Austin Weeks Memorial Grant Earth and Environmental Sciences Department Graduate Student Grant, Lehigh University Work Presented here is part of an ongoing M.S. Thesis of James Carrigan at Lehigh University. For more information or to contact the author please feel free to reach me at