Compilation of results of the STRATAGEM project as ISO-image of the final CD-ROM

The study of the Neogene (Miocene to Holocene) stratigraphic record on the glaciated Atlantic margin of NW Europe has, to date, largely been undertaken on an ad-hoc basis. Whereas a systematic approach to understanding the stratigraphic development of Palaeogene and older strata has been undertaken in areas such as the North Sea, West of Shetland and Norway, the problem of establishing a Neogene framework has been only partly addressed by academia and the oil industry. In most cases where a Neogene stratigraphy has been constructed, this has been largely in response to problem solving and risk assessment in a restricted area. Nevertheless, in the past few years it has become increasingly apparent that there is a common history in the Neogene development of the passive Atlantic margin of NW Europe, between mid-Norway and SW Ireland. The inspection and interpretation of an extensive geophysical and geological database has identified several regionally significant and correlatable unconformities along this continental margin. Thus, a regional approach to the stratigraphical development of the Neogene succession on the glaciated European Atlantic margin is undertaken in this volume.

Planktonic foraminiferal oxygen isotopes of ODP Site 143-865 samples

Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the d18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high d18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust d18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the d18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ion microprobe using 10 ?m pits with an analytical reproducibility of ±0.34 per mil (2 standard deviations). In situ measurements of d18O in these domains yield consistently lower values than those published for conventional multispecimen analyses. Assuming that the original d18O is largely preserved in the basal areas of muricae, this new d18O record indicates Early Paleogene (~49-56 Ma) tropical SSTs in the central Pacific were 4°-8°C higher than inferred from the previously published d18O record and that SSTs reached at least ~33°C during the Paleocene-Eocene thermal maximum. This study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep-sea sediments.

Anelastic strain recovery and elastic properties of ODP Leg 123 oceanic basalt samples

A knowledge of rock stress is fundamental for improving our understanding of oceanic crustal mechanisms and lithospheric dynamic processes. However, direct measurements of stress in the deep oceans, and in particular stress magnitudes, have proved to be technically difficult. Anelastic strain recovery measurements were conducted on 15 basalt core samples from Sites 765 and 766 during Leg 123. Three sets of experiments were performed: anelastic strain recovery monitoring, dynamic elastic property measurements, and thermal azimuthal anisotropy observations. In addition, a range of other tests and observations were recorded to characterize each of the samples. One common feature of the experimental results and observations is that apparently no consistent orientation trend exists, either between the different measurements on each core sample or between the same sets of measurements on the various core samples. However, some evidence of correspondence between velocity anisotropy and anelastic strain recovery exists, but this is not consistent for all the core samples investigated. Thermal azimuthal anisotropy observations, although showing no conclusive correlations with the other results, were of significant interest in that they clearly exhibited anisotropic behavior. The apparent reproducibility of this behavior may point toward the possibility of rocks that retain a "memory" of their stress history, which could be exploited to derive stress orientations from archived core. Anelastic strain recovery is a relatively new technique. Because use of the method has extended to a wider range of rock types, the literature has begun to include examples of rocks that contracted with time. Strong circumstantial evidence exists to suggest that core-sample contractions result from the slow diffusion of pore fluids from a preexisting microcrack structure that permits the rock to deflate at a greater rate than the expansion caused by anelastic strain recovery. Both expansions and contractions of the Leg 123 cores were observed. The basalt cores have clearly been intersected by an abundance of preexisting fractures, some of which pass right through the samples, but many are intercepted or terminate within the rock matrix. Thus, the behavior of the core samples will be influenced not only by the properties of the rock matrix between the fractures, but also by how these macro- and micro-scale fractures mutually interact. The strain-recovery curves recorded during Leg 123 for each of the 15 basalt core samples may reflect the result of two competing time dependent processes: anelastic strain recovery and pore pressure recovery. Were these the only two processes to influence the gauge responses, then one might expect that given the additional information required, established theoretical models might be used to determine consistent stress orientations and reliable stress magnitudes. However, superimposed upon these competing processes is their respective interaction with the preexisting fractures that intersect each core. Evidence from our experiments and observations suggests that these fractures have a dominating influence on the characteristics of the recovery curves and that their effects are complex.

Rare earth elements in standard samples of ocean Fe-Mn nodules and crusts

Contents of rare earth elements (REE) in standard samples of Fe-Mn nodules (SDO-5, 6), Fe-Mn crust (SDO-7), and red clay (SDO-9) have been determined by ICP-MS and instrumental neutron activation analysis. Reproducibility of ICP-MS was 5-6%. These results are discussed and compared with other data. It has been found that distribution of REE in the standard samples of ocean Fe-Mn ores and red clay is highly homogenous.

Absolute abundances of dinoflagellate cysts in surface sediment samples from four sites: Lycopodium marker-grain method

Absolute abundances (concentrations) of dinoflagellate cysts are often determined through the addition of Lycopodium clavatum marker-grains as a spike to a sample before palynological processing. An inter-laboratory calibration exercise was set up in order to test the comparability of results obtained in different laboratories, each using its own preparation method. Each of the 23 laboratories received the same amount of homogenized splits of four Quaternary sediment samples. The samples originate from different localities and consisted of a variety of lithologies. Dinoflagellate cysts were extracted and counted, and relative and absolute abundances were calculated. The relative abundances proved to be fairly reproducible, notwithstanding a need for taxonomic calibration. By contrast, excessive loss of Lycopodium spores during sample preparation resulted in non-reproducibility of absolute abundances. Use of oxidation, KOH, warm acids, acetolysis, mesh sizes larger than 15 µm and long ultrasonication (> 1 min) must be avoided to determine reproducible absolute abundances. The results of this work therefore indicate that the dinoflagellate cyst worker should make a choice between using the proposed standard method which circumvents critical steps, adding Lycopodium tablets at the end of the preparation and using an alternative method.