Description: 59 box and gravity cores from the MANOP cruise with RV KNORR in 1979 were described and alaysed.

Description: The post-middle Miocene evolution of sedimentary patterns in the eastern equatorial Pacific Ocean has been deduced from a compilation and synthesis of CaCO3, opal, and nannofossil assemblage data from 11 sites drilled during Leg 138. Improvements in stratigraphic correlation and time scale development enabled the construction of lithostratigraphic and chronostratigraphic frameworks of exceptional quality. These frameworks, and the high sedimentation rates (often exceeding 4 cm/k.y.) provided a detailed and synoptic paleoceanographic view of a large and highly productive region. The three highlights that emerge are: (1) a middle late Miocene "carbonate crash" (Lyle et al., this volume); (2) a late Miocene-early Pliocene "biogenic bloom"; and (3) an early Pliocene "opal shift". During the carbonate crash, an interval of dissolution extending from -11.2 to 7.5 Ma, CaCO3 accumulation rates declined to near zero over much of the eastern equatorial Pacific, whereas opal accumulation rates remained substantially unchanged. The crash nadir, near 9.5 Ma, was marked by a brief shoaling of the regional carbonate compensation depth by more than 1400 m. The carbonate crash has been correlated over the entire tropical Pacific Ocean, and has been attributed to tectonically-induced changes in abyssal flow through the Panamanian seaway. The biogenic bloom extended from 6.7 to 4.5 Ma, and was characterized by an overall increase in biogenic accumulation and by a steepening of the latitudinal accumulation gradient toward the equator. The bloom has been observed over a large portion of the global ocean and has been linked to increased productivity. The final highlight, is a distinct and permanent shift in the locus of maximum opal mass accumulation rate at 4.4 Ma. This shift was temporally, and perhaps causally, linked to the final closure of the Panamanian seaway. Before 4.4 Ma, opal accumulation was greatest in the eastern equatorial Pacific Basin (near 0°N, 107°W). Since then, the highest opal fluxes in the equatorial Pacific have occurred in the Galapagos region (near 3°S, 92°W).

Description: In the eastern and central Pacific Ocean the most profound change in Neogene calcium carbonate deposition occurred at the late/middle Miocene boundary (about 10 Ma), when carbonate mass accumulation rates (MARs) abruptly dropped. East of the East Pacific Rise (EPR), carbonate deposition essentially ceased. The carbonate compensation depth (CCD) in the Guatemala Basin, for example, rose by 800 m in less than 0.5 Ma. Even the rise crests suffered carbonate losses - Site 846, at the time less than 300 meters deeper than the EPR axis, experienced intervals between 10 and 9 Ma where no carbonate at all was buried. By about 8 Ma carbonate deposition resumed and was concentrated along an equatorial band, suggestive of high surface water carbonate production. East of the EPR, however, CCDs remained shallow since 10 Ma. This event which we have termed the late Miocene carbonate crash marks a fundamental paleoceanographic change that occurred in the eastern Pacific Ocean. Here, we document the changing pattern of carbonate deposition from 13 Ma to 5 Ma by using maps of carbonate MAR reconstructed from ODP Leg 138 and DSDP data. Comparisons to modern oceanographic conditions demonstrate that the late Miocene carbonate crash could not have been caused by an abrupt increase in productivity at 10 Ma or by loss of Corg from continental shelves. Instead it was probably caused by a relatively small reduction in deep-water exchange between the Atlantic and Pacific Oceans through the Panama Gateway prior to the emergence of the isthmus. A small restriction of deep-water exchange through this gateway is sufficient to radically change carbonate MARs in the eastern Pacific.

Description: Geochemical logging is a routine part of the Ocean Drilling Program, yet the reliability of ODP geochemical logs has rarely been evaluated quantitatively. On ODP Leg 117, geochemical logs were obtained at Sites 723, 728, and 731. We report here an evaluation of ODP geochemical log quality based on high-resolution sampling and X-ray fluorescence measurement of 398 core samples from the three sites. At these sites we lacked the complete suite of high-quality logs needed for accurate log-based estimation of elemental percentages; only calcium and silicon logs had magnitudes similar to those from XRF. However, relative variations of log-based elemental abundances could be determined. Our comparisons of the XRF analyses with the character of variations in geochemical logs indicates that the reliability of ODP geochemical logs varies substantially, within short intervals and particularly between sites. In general, the geochemical logs are capable of detecting changes in formation geochemistry that are larger than the following thresholds: 2% for Ca, 2%-6% for Si, 0.5%-1% for K, 0.1% for Ti, 0.5% for Fe, and 0.4% for Al. All sulfur variations observed in the XRF data, as well as many of the iron variations, were below the resolving power of the geochemical logging tools. These precisions are generally similar to those determined at the Conoco test well by Chapman et al. (1987), in spite of the very different ODP logging conditions.

Description: Geochemical well logs were obtained in sediment at Sites 805 and 806 of Ocean Drilling Program Leg 130. Corrections have been applied to the logs to account for variations in bore-hole size, drilling-fluid composition, and drill-pipe attenuation. Oxide and calcium carbonate weight percentages were calculated from the logs and are compared with available carbonate measurements from core. Log-derived CaCO3 values from Hole 805C, though lower than shipboard CaCO3 core measurements, show a similar variation in character. In Hole 806B, log and shipboard CaCO3 sample values have a similar mean and variance. The CaCO3 high-resolution sample values from Hole 806B, however, have a similar mean but a lower variance than the CaCO3 logs. It is probable that discrepancies result from gamma-ray spectrometry tool malfunctions experienced throughout the logging operations of this leg as well as from chlorine-induced interference in the calcium yield. Because the amplitude of CaCO3 variations was extremely low (standard deviation of 1.38 on high-resolution samples), the tool, which has a sensitivity of roughly 2% for Ca, probably would not have been able to detect these variations, even if the tool had been working properly.

Description: Recent modeling studies call on increased ocean heat transport to explain high-latitude warming observed for intervals throughout the middle Pliocene. Possible vehicles for ocean heat transport are the poleward arms of the subtropical gyres. Sites from the California margin (Ocean Drilling Program Leg 167) provide monitors of wind field within the eastern arm of the gyre which may be an indication of basin-wide subtropical gyral strength. At most sites (water depths from 1106 to 4212 m) CaCO3 mass accumulation rate (MAR) was highest in the middle Pliocene (3.5-2.0 Ma). This high CaCO3 MAR 'event' is attributed primarily to higher CaCO3 production due to higher offshore upwelling associated with the zone of the greatest wind stress curl. Thus, in the middle Pliocene, there was enhanced wind stress curl along the California margin, and possibly enhanced North Pacific sub-tropical gyral circulation and meridional ocean heat advection.