X-radiographic prints were made from slab samples to investigate sedimentary structures collected from drift deposits drilled along the Blake-Bahama Outer Ridge and Sohm Abyssal Plain during Ocean Drilling Program Leg 172.
All samples are composed of fine-grained silt- and clay-sized sediments, except the foraminiferal sand. The sediments are mixtures of components such as carbonate (nannofossils and foraminifers) and siliciclastic sediments. Samples can be divided into two groups: (1) samples containing distinct sedimentary structures derived from such episodic currents as turbidity currents or benthic storms (Group I) and (2) samples containing sedimentary structures associated with changes in color or magnetic susceptibility but not associated with the distinct structures in visual inspections compared to Group I (Group II). Group II is considered to represent more common sedimentary processes in this region because the frequency of occurrence of these structures is much higher than that of Group I.
X-radiographic prints revealed more detailed sedimentary structures compared to visual inspections for Group I sediments. For Group II sediments, it was revealed that changes in color or magnetic susceptibility are sometimes associated with line structures even though they are not observed in visual inspections. Detailed descriptions of these sedimentary structures are given in this paper. Although further investigation is needed to discover the intensity of the currents that formed these structures, the features observed here aid our understanding of sedimentation in the deep-sea environment.
1 Yokokawa, M., 2001. Sedimentary structures of contourites and turbidites observed by X-radiographic prints: samples from Blake-Bahama Outer Ridge and Sohm Abyssal Plain. In Keigwin, L.D., Rio, D., Acton, G.D., and Arnold, E. (Eds.), Proc. ODP, Sci. Results, 172 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/172_SR/chap_07/chap_07.htm>. [Cited YYYY-MM-DD]
2 Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. miwa@user.center.osaka-u.ac.jp
Initial
receipt: 15 November 1999
Accepted: 28 July 2001
Web publication: 28 February 2001
Ms 172SR-204