A composite section for Site 1122, constructed using data from Holes 1122A, 1122B, and 1122C, yielded overlapping records for the upper ~83 meters composite depth (mcd). At least one gap in continuity exists in this composite record at ~73 mcd. Three high-resolution data sets proved useful for correlation at this site: magnetic susceptibility (MS) and gamma-ray attenuation porosity evaluator (GRAPE), both measured on whole cores on the MST, and spectral reflectance at 550 nm (the center wavelength of the range measured), measured on split cores. The wavelength of variation in natural gamma-ray intensity (NGR) is too broad to be useful for hole-to-hole correlation at this site. Magnetic susceptibility proved the most reliable measurement for correlation, whereas GRAPE and reflectance records primarily provided confirmation of ties. Exceptions are (1) ties from Cores 181-1122C-3H to 181-1122A-2H and from 181-1122C-4H and 181-1122A-3H, both based on GRAPE density records, and (2) the correlation between Cores 181-1122B-1H and 181-1122C-1H, based on reflectance variability. The final composite section is illustrated in Figure F26.
Hole-to-hole correlation at the top of the sedimentary sequence, including determination of the mudline, presented a particular challenge at Site 1122. Core 181-1122C-1H is undoubtedly a mudline core, whereas Core 181-1122B-1H virtually filled the core liner. A thick sand recovered in Core 181-1122C-1H is represented by high MS and GRAPE density values. This sand was apparently washed out or disturbed in Hole 1122B, an inference based on anomalously low GRAPE density values near the equivalent depth of the sand layer in Core 181-1122B-1H. Excluding this sand layer, magnetic susceptibility and GRAPE density data do not vary enough to allow correlation. However, if one assumes that the top of Core 181-1122B-1H corresponds to the mudline recovered at the top of Core 181-1122C-1H, reflectance records agree well between Cores 181-1122B-1H and 181-1122C-1H. Based on reflectance data, we placed the top of Core 181-1122B-1H at the mudline. An alternative relationship, though less probable, is that the data from Core 181-1122C-1H represent an interval of strata recovered at some ill-defined level above the top of Core 181-1122B-1H. To calculate depths for this alternative relationship, 2.41 m has to be added to all mcd depths in Tables T10 and T11 (both also in ASCII format) except those depths for Core 181-1122C-1H. The relationship advocated here, with the mudline in both Cores 181-1122B-1H and 181-1122C-1H, places the Kawakawa Tephra at ~12.6 mcd in the splice in Core 181-1122A-H1 (Fig. F26).
Two coring irregularities occurred at Site 1122. First, Core 181-1122A-1H was shot when the end of the APC piston had already penetrated the topmost sediment by ~8 m, rather than close to the mudline. This large depth offset of Core 181-1122A-1H is based on convincing correlations via MS, GRAPE, and color reflectance. Additionally, the Kawakawa Tephra (Fig. F26) is found in both Holes 1122A and 1122C at levels agreeing with the composite section correlation (Fig. F26). Second, the top of Core 181-1122C-3H represents an interval that overlaps with the base of Core 181-1122C-2H, including a repeat recovery of the Kawakawa Tephra. The recoring of this interval may be related to advancing the drill string based on core recovery following retrieval of Core 181-1122C-2H.
Two correlations in the composite depth section are based on only small overlaps (1) between Cores 181-1122C-3H and 181-1122A-2H, and (2) between Cores 181-1122C-4H and 181-1122A-3H (Fig. F26). These correlations, based on GRAPE density records, are the least certain overlaps in the composite section. A definite gap exists between Cores 181-1122A-8H and 181-1122C-9H. In this case, we assigned the top of Core 181-1122A-8H a composite depth equal to the base of Core 181-1122C-9H.
Downhole core offsets relative to mbsf depths do not follow a model of 10% stretch between the mbsf and mcd depth scales in the composite section. Instead the offset is ~6-8 m for the extent of Hole 1122A and 2-6 m in Hole 1122C below Core 181-1122C-3H (Fig. F27), with offsets following a slight negative slope below ~20 mbsf. Table T10 contains the offsets between the mbsf and mcd scales resulting from composite section construction.
The spliced record, based primarily on MS and GRAPE data (Fig. F28), extends to 83 mcd. Wherever possible, splice tie points (Table T11) were picked at well-defined maxima or minima where the overlap in data from Holes 1122B and 1122C are correlated. Typically, parameter values differed by less than 10% at tie levels. In all cases, ties were selected so that the spliced record was as free from noise (high-frequency variability) as possible.