HR: 16:00h
AN: OS24A-01 INVITED     [Abstracts]
TI: Geological Consequences of Unequal Loading of Sedimentary Units, at Passive, Transform, and Convergent Margins
AU: * Moore, C
EM: cmoore@es.ucsc.edu
AF: Earth Sciences, UC Santa Cruz, Santa Cruz, CA 95064 United States
AU: Dugan, B
EM: dugan@rice.edu
AF: Earth Science, Rice University, Houston, TX 77251 United States
AU: Flemings, P
EM: flemings@geosc.psu.edu
AF: Geosciences, Penn State Univ., University Park, PA 16802 United States
AU: Iturrino, G
EM: iturrino@ldeo.columbia.edu
AF: LDEO, Columbia University, Palisades, NY 10964 United States
AU: Sawyer, D
EM: dsawyer@geosc.psu.edu
AF: LDEO, Columbia University, Palisades, NY 10964 United States
AU: Behrmann, J
EM: jan.behrmann@geologie.uni-freiburg.de
AF: Geologisches Institut, Albert-Ludwigs-Universitat Freiburg, Freiburg, 79085 Germany
AU: John, C
EM: cjohn@es.ucsc.edu
AF: Earth Sciences, UC Santa Cruz, Santa Cruz, CA 95064 United States
AB: An investigation of the effects of unequal loading of permeable sedimentary units and potential lateral flow was a primary objective of IODP Exp. 308 in the Gulf of Mexico. In addition to occurrence at passive margins, the geological consequences of unequal loading of aquifers is prominent at transform and at convergent margins. The development of a pull-apart basin along the San Andreas Transform Fault system resulted in a large difference in sedimentary loading in the upper Miocene Santa Margarita Sandstone near Santa Cruz CA. The overlying diatomaceous mudstone shows a variation in thickness from about 3 km at the basin center to several hundred meters at the basin margin. At the basin margin the underlying sandstone injects the overlying mudstone as dikes and sills and also flowed onto the Miocene seafloor as a sand volcano. In the Late Cretaceous-Paleocene Great Valley Forearc Basin Sequence, similar sandstone dikes and sills occur at the basin margin where the overlying sedimentary cover is minimized. However the lateral variation in thickness of the overlying mudstone sequence (1100m to ~ 800 m) is less dramatic than in the San Andreas Fault system example. The abundance of sills in both the Great Valley and San Andreas Fault system examples unequivocally indicate that the fluid pressures reached lithostatic values. In both examples, hydrocarbons reduced the density of fluids and assisted in reaching fluid pressures equal to the overburden. In the Ursa Basin Exp. 308 measured fluid pressures of ~ 0.6 of effective vertical stress in the muds overlying the unequally loaded permeable sandy "Blue Unit". Drilling and preliminary investigation of the seismic and borehole imaging data indicate no evidence of dikes or sills emanating from the Blue Unit. Therefore, the fluid pressure conditions in the Blue Unit and the overlying muds apparently define a lower limit for the formation of clastic intrusions.
DE: 3036 Ocean drilling
DE: 8104 Continental margins: convergent
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8106 Continental margins: transform
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005