ALBERT

Description: This study tests and improves on previously published early and middle Miocene 87Sr/86Sr marine correlations, presents Sr isotopic age correlations for this interval using the new timescale of Cande and Kent [1992 doi:10.1029/92JB01202], and evaluates Sr isotopic changes against an inferred glacioeustatic proxy. We generated a latest Oligocene to early late Miocene 87Sr/86Sr isotope record from Ocean Drilling Program (ODP) Hole 747A; this site provides an excellent magnetostratigraphic record during most of this interval for independent age estimates, very good foraminiferal preservation, and excellent core recovery. Comparisons of new 87Sr/86Sr data from Hole 747A with previously published data from Deep Sea Drilling Project (DSDP) Sites 608 [Miller et al., 1991 doi:10.1029/90PA01941] and 588 [Hodell et al., 1991 doi:10.1130/0091-7613(1991)019〈0024:VITSIC〉2.3.CO;2] yield the following results: (1) confirmation and refinement of the early Miocene Sr isotope changes, (2) improved definition of the timing of the changes in slope of 87Sr/86Sr near 15.4 Ma and 22.8 Ma, (3) improved Sr isotopic age resolution for the middle Miocene with resolution as good as +/- 0.7 m.y., and (4) identification of an inflection in the Sr isotope record at 28.0 Ma based on the combined records from DSDP Site 522 [Miller et al., 1988 doi:10.1029/PA003i002p00223] and ODP Hole 747A. We have been unable to determine the cause of middle Miocene offset between Site 588 and Hole 747A data, although we believe it may be attributed to problems in the age assignments for Hole 588A for the interval ~14-11 Ma and Site 747 for the interval 11-8 Ma. Because Hole 747A results provide a better chronology than Site 588 for most of the Miocene and a better middle Miocene Sr isotope record than Site 608, we propose that Hole 747A serves as the best reference section for Miocene 87Sr/86Sr variations from ca. 23 to 11 Ma. Using 87Sr/86Sr data from Sites 522, 608, and 747A, we relate late Eocene to early Miocene inflections in the 87Sr/86Sr isotope record to oxygen isotope increases and decreases inferred to represent glacioeustatic events. The decreases (deglaciations) observed in the ?18O record apparently lead the 87Sr/86Sr inflections by 1 to 1.5 m.y.

Description: Information on possible resource value of sea floor manganese nodule deposits in the eastern north Pacific has been obtained by a study of records and collections of the 1972 Sea Scope Expedition.

Description: Sediments were collected with Eckman and Petersen dredges from the bottom of Trout Lake, northern Wisconsin, at 221 stations. Sampling was done with a spud sampler at 32 stations, and core samples were obtained with a Jenkins and Mortimer and a Twenhofel sampler at 17 stations. The shore and offshore deposits of the shores of Trout Lake and the shores of the islands are described. Megascopic descriptions are given of the samples collected with the Eckman and Petersen dredges. Sediments on bottoms of about 10 meters or deeper are mainly gyttja, or crusts composed of mixtures of organic matter, ferric hydroxide, and some form of manganese oxide. The latter deposits are extensive. Detailed descriptions of some of the samples of sands are given, and generalizations respecting size and distribution are made. Tables showing quartiles, medians, and coefficients of sorting and skewness of the coarse sediments collected from the bottom are given in tables. Mechanical analyses of all fine sediments, mainly gyttja, were not made, as previous experience seems to have demonstrated that results have no sedimentational value. Organic matter of the gyttja was determined and also the percentages of lignin in the organic matter. Core samples are composed almost entirely of fine materials, mainly gyttja, and determinations were made on these samples in the same way as on the samples obtained with the Eckman and Petersen dredges. Studies of the core samples show that the fine sediments usually contain in excess of 90 per cent moisture and there is very little change in the moisture content from top to bottom of cores. A map shows the distribution of the iron and manganese deposits. These deposits were found to contain 10 to 20 per cent of organic matter, 11 to 16 per cent of metallic iron, and 12 to 30 per cent of metallic manganese. No stratification of any kind was found in any of the deep-water sediments of Trout Lake except in the iron and manganese crusts. Absence of stratification is considered to be due to the slow rate of deposition and the mixing of sediments by organisms which dwell in them. The data indicate that the rate of deposition in the deep waters of Trout Lake is of the order of 1 foot in 15,000 years.

Description: During the cruise of the" Mabahiss" from Zanzibar to Colombo at Station 133 (1° 25' 54" S. to 1° 19' 42" S. and 66° 34' 12" E. to 66° 35' 18" E.) several small rock fragments were brought up in the Monegasque net; and, since at this position there is no possibility of the material being transferred by floating Ice, these specimens are of some interest as samples of oceanic rock foundations. All the rocks have a black appearance, but in the majority this skin is of negligible thickness. Exceptionally, however, it may attain to 1/3 in. (St. 133, 8), and then the specimens are rounded. The coating is made of dark opaque manganese material. At Station 166 one or two similar specimens of angular basalt were found in the trawl consisting mainly of manganese nodules.

Description: We correlated Miocene d18O increases at Ocean Drilling Program Site 747 with d18O increases previously identified at North Atlantic Deep Sea Drilling Project Sites 563 and 608. The d18O increases have been directly tied to the Geomagnetic Polarity Time Scale (GPTS) at Site 563 and 608, and thus our correlations at Site 747 provide a second-order correlation to the GPTS. Comparison of the oxygen isotope record at Site 747 with records at Sites 563 and 608 indicates that three as-yet-undescribed global Miocene d18O increases may be recognized and used to define stable isotope zones. The d18O maxima associated with the bases of Zones Mila, Milb, and Mi7 have magnetochronologic age estimates of 21.8, 18.3, and 8.5 Ma, respectively. The correlation of a d18O maximum at 70 mbsf at Site 747 to the base of Miocene isotope Zone Mi3 (13.6 Ma) provides a revised interpretation of four middle Miocene normal polarity intervals observed between 77 and 63 mbsf at Hole 747A. Oxygen isotope stratigraphy indicates that the reversed polarity interval at 70 mbsf, initially interpreted as Chronozone C5AAr, should be C5ABr. Instead of a concatenated Chronozone C5AD-C5AC with distinct Chronozones C5AB, C5AA, and C5A (as in the preliminary interpretation), d18O stratigraphy suggests that these normal polarity intervals are Chronozones C5AD, C5AC, and C5AB, whereas Chronozones C5AA-C5A are concatenated. This interpretation is supported by the d13C correlations. The upper Miocene magnetostratigraphic record at Hole 747A is ambiguous. Two upper Miocene d18O events at Site 747 can be correlated to the oxygen isotope records at Site 563 and 608 using the magnetostratigraphy derived at Hole 747B. Our chronostratigraphic revisions highlight the importance of stable isotope stratigraphy in attaining an integrated stratigraphic framework for the Miocene.