Bartetzko, A. et al. (2002): Interpretation of well-logging data to study lateral variations in young oceanic crust; DSDP/ODP holes 504B and 896A, Costa Rica Rift

ODP 148
ODP 111 504
ODP 137 504
ODP 140 504
ODP 148 504
ODP 148 896

Bartetzko, A.
Aachen University of Technology, Aachen, Federal Republic of Germany

Pechnig, R.

Wohlenberg, J.

Interpretation of well-logging data to study lateral variations in young oceanic crust; DSDP/ODP holes 504B and 896A, Costa Rica Rift
In: Lovell, Mike (editor), Parkinson, Neil (editor), Geological applications of well logs
American Association of Petroleum Geologists, Tulsa, OK, United States
Deep Sea Drilling Project/Ocean Drilling Program Holes 504B and 896A were drilled into the upper oceanic crust of the Costa Rica Rift, only 1 km apart. Thus they provide an excellent opportunity to study lateral variation in the volcanic-rock section of the oceanic crust. Recovery of cores from these holes was poor. Therefore, comparison of one hole with the other is based on continuous information from geophysical well-logging data. Continuous lithologic profiles were created by calibration of logging data to cores, followed by statistical analysis. Four rock types can be distinguished as electrofacies from sets of log responses: massive units of basalt, thin flow-basalts, pillow basalts, and fractured or brecciated basalts. Massive units, thin flow-basalts, and pillow basalts are in both holes. These terms describe morphologies of lava flows. The morphologies can be distinguished by using physical information from logs; the evidence results from characteristic differences in fractured and altered rock. Fractured or brecciated basalts were classified only in Hole 896A; they are restricted to the depth between 350 m and 380 m below seafloor (mbsf). They are related genetically to a fault zone. Comparison of records of the two holes shows that average P-wave velocities and total gamma radiation are similar. In all log responses from Hole 504B, scattering is larger. This is especially true of electrical resistivities and P-wave velocities. Differences among physical properties measured in the two holes can be related to variation in thicknesses of lava flows and variation in fracturing and alteration. Massive units of basalt are much thicker in Hole 504B than in Hole 896A, which explains the higher electrical resistivity and P-wave velocity recorded in this hole. Fractures are more numerous and altered rock more abundant in Hole 896A.
Coverage:Geographic coordinates:
West:-83.4357East: -83.4323

Igneous and metamorphic petrology; Applied geophysics; alteration; basalts; body waves; boreholes; Central America; cores; Costa Rica; Costa Rica Rift; crust; Deep Sea Drilling Project; drilling; DSDP Site 504; East Pacific; elastic waves; electrical methods; facies; faults; gamma-ray spectra; geophysical methods; geophysical surveys; igneous rocks; lava flows; Leg 148; Nazca Plate; Ocean Drilling Program; oceanic crust; ODP Site 896; P-waves; Pacific Ocean; physical properties; plate tectonics; radioactivity methods; resistivity; rift zones; seismic methods; seismic waves; spectra; statistical analysis; stratigraphic units; surveys; volcanic rocks; well-logging;