This paper presents the results of a petrographic and scanning electron microscope study of carbonate sediments and cements found within basalts cored at Ocean Drilling Program Site 1001. The basaltic sequence is pervasively cut by fractures that show vugs filled by carbonate cements. This study focuses on the nature of micritic sediment and cements and documents the occurrence of two types of micrites. The first (m1) has been observed at only one location (interval 165-1001A-54R-5, 13-18 cm). It consists of recrystallized pelagic carbonate, which was infiltered from the seafloor and deposited within the newly formed cavities within the basalt. The second micrite (m2) is more widespread and is present as an asymmetrical, mostly geopetal lining of fractures and cavities. Optical microscopy reveals laminae characterized by undulated upper surfaces that contain micritic lumps forming pseudopeloids. Typically, these structures are considered to result from the dismantling of microbial filamentous mats.
The data generated in this study present evidence for a new mechanism for the origin of micrite that is commonly found within basalt sequences. Results from previous studies indicate this cement is formed in situ, but the new data indicate precipitation is controlled by processes related to microbial activity. At this stage of study, additional data are needed to determine whether this precipitation process takes place in marine or marine-modified pore waters.
1Leckie, R.M., Sigurdsson, H., Acton, G.D., and Draper, G. (Eds.), 2000. Proc. ODP, Sci. Results, 165 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/165_SR/165TOC.HTM>. [Cited YYYY-MM-DD]
2Earth Sciences Department, University of Southern California, Los Angeles, CA 90089-0740, U.S.A. mmutti@earth.usc.edu
Date of
initial receipt: 23 June 1998
Date of acceptance: 19 January 1999
Ms 165SR-015