Print this pageMONTGOMERY, PAUL1, ROBERT H. GOLDSTEIN1, EVAN K. FRANSEEN2, and MARK W. HOUNSLOW3
1Dept.
of Geology, University of Kansas, Lawrence
2Kansas
Geological Survey, Lawrence, KS
3School of Environmental
Sciences, University of East Anglia, Norwich, UK
Abstract: Improving Magnetostratigraphy as a Chronostratigraphic Tool in Shallow Water Carbonate Deposits
Magnetostratigraphy has been used successfully to date and correlate finegrained carbonate strata where accumulation has been continuous and biostratigraphic and/or radiometric age control is available. Magnetostratigraphy is increasingly being applied to shallow-water platforms to develop chronostratigraphies where biostratigraphic and absolute age data are sparse. However, paleomagnetic studies in shallow water carbonates are often hampered by low natural remanent magnetization, acquisition of viscous and chemical remanent magnetization, and discontinuous sedimentation.
Our studies of Upper Miocene shallow-water carbonate platforms, SE Spain, illustrate that to get reliable data paleomagnetic studies must use large volume sampling, detailed sampling at unconformities, multiple and replicate measurements, paleomagnetic data reliability classification schemes, demagnetization trend data, and detailed magneto-mineralogical studies to identify the origin-timing of the remanent magnetization. To create a chronostratigraphy primarily based upon magnetostratigraphy we find that magnetic data must be integrated with radiometric dating and biostratigraphy, and that diagenetic data and sequence stratigraphy must be used to correlate reversals to the Geomagnetic Polarity Time Scale (GPTS). The sequence stratigraphic and diagenetic identification of the most important unconformities is used to identify the position of missing chrons.
When used alone, each dating technique is useful, but when integrated as a means of constraining magnetostratigraphy, highresolution chronostratigraphic correlation can be achieved. Provided suitable independent age control is available our methods should be widely applicable to the study of shallow-water carbonates of differing ages.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas