Late Miocene cyclicity and intercore correlations for ODP Sites 127-794 and 127-797

During Leg 127, the formation microscanner (FMS) logging tool was used as part of an Ocean Drilling Program (ODP) logging program for only the second time in the history of the program. Resistivity images, also known as FMS logs, were obtained at Sites 794 and 797 that covered nearly the complete Yamato Basin sedimentary sequence to a depth below 500 mbsf. The FMS images from these two sites at the northeastern and southwestern corners of the Yamato Basin thus were amenable to comparison. A strong visual correlation was noticed between the FMS logs taken in Holes 794B and 797C in an upper Miocene interval (350-384 mbsf), although the two sites are approximately 360 km apart. In this interval, the FMS logs showed a series of more resistive thin beds (10-200 cm) alternating with relatively lower resistivity layers: a pattern that was manifested by alternating dark (low resistivity) and light (high resistivity) banding in the FMS images. We attribute this layering to interbedding of chert and porcellanite layers, a common lithologic sequence throughout Japan (Tada and Iijima, 1983, doi:10.1306/212F82E7-2B24-11D7-8648000102C1865D). Spatial frequency analysis of this interval of dominant dark-light banding showed spatial cycles of period of 1.1 to 1.3 and 0.6 m. This pronounced layering and the correlation between the two sites terminate at 384 mbsf, coincident with the opal-CT to quartz transition at Site 794. We think the correlation in the FMS logs might well extend earlier in the middle Miocene, but the opal-CT to quartz transition obscures this layering below 384 mbsf. Although 34 m is only a small part of the core recovered at these two sites, it is significant because it represents an area of extremely poor core recovery and an interval for which a near-depositional hiatus was postulated for Site 797, but not for Site 794.

Table 2 Analytical data of the samples by the "Dipole CHIM" at the Yingezhuang gold deposit

CHIM method involves extracting metal ions of electromobile forms in either anodes or cathodes, facilitated by a man-made electric field. This paper presents two newly developed CHIM alternatives that are electrified by a low voltage dipole. The firstly improved technique enables cationic ions to be extracted in a single cathode, whereas the secondly improved technique allows both anionic and cationic species to be extracted simultaneously in an anode and in a cathode. Compared with the traditional CHIM methods, the innovative techniques developed in this paper are characterized by simple instrumentation, low cost and easy operation in field, and in particular enables simultaneous extraction of anionic and cationic species of elements, from which more information can be derived with higher extraction efficiency. Field tests at several well-known mine areas in China confirm the effectiveness and efficiency of the new techniques in exploring for deeply buried ore bodies.