X-Ray Mineralogy Study of Tertiary Deposits, Leg 81, Sites 552–555

Abstract

This X-ray mineralogy study of Tertiary samples recovered from Rockall sites permitted the definition of four mineralogical units and the tracing of the paleoenvironmental evolution in this region. INTRODUCTION The following mineralogical units were defined on the basis of our study: Unit I (upper Paleocene) is characterized by the occurrence of quartz and feldspars as well as by that of clay minerals, namely smectite, illite, kaolinite, and chlorite. Deposits are of a quite marked detrital nature. Unit II (lower Eocene) consists of sediments represented by plagioclase feldspars and zeolites; the major clay mineral components are smectites. These deposits suggest a sedimentation influenced by a basic volcanic environment. The presence of layers rich in kaolinite (Site 555) probably indicates terrigenous inputs developed under leaching warm climates. Unit III (middle Eocene to middle Miocene) is marked by a high carbonate content and dominantly smectite clay minerals: zeolites persist. Sedimentation is of pelagic type attesting to the impact of basic volcanism and/or that of fine-grained terrigenous inputs developed under warm climates with contrasting seasons. Unit IV (from middle/upper Miocene) is also characterized by high carbonate contents. Clay minerals are highly variable (smectite, illite, kaolinite, chlorite). This change in mineralogical composition suggests climatic cooling linked to a change in the hydrological exchanges between the Norwegian Sea and North Atlantic. METHODS Analyses X-ray diffraction was used on a total of 167 Paleocene and Miocene samples. The diffractometer used was a Philips 1310 and operating conditions were as follows: nickle-filtered copper Kα radiation at 40 kv, 20 mA. Total Sediments Dried and pulverized samples of total sediments were analyzed according to the powder diffractogram method. Semiquantitative values of quartz, calcite, and feldspars (K and plagioclase) were estimated from peak heights by comparison with mixed synthetic reference samples. Zeolites were estimated by relative frequencies as abundant, present, or trace on the basis of height of characteristic reflections.

Paleoenvironmental Significance of Cenozoic Clay Deposits from the Norwegian Sea: ODP Leg 104

“…This interpretation agrees with that of Nilsen and Kerr (1978), who maintain that lateritic Paleocene soils existed in the Lofoten Basin. Identical assemblages have also been observed in lower Eocene Rockall sediments (DSDP Leg 81, Site 555, Latouche and Maillet, 1984) and Faeroe Iceland Ridge (Parra et al, 1986).…”

“…These analyses may provide information about the source of detrital minerals, the type of climate prevailing at the time of the formation, and determine the oceanic currents responsible for their transport and settling. This type of investigation has already been applied to a large number of Atlantic DSDP sites (Melieres 1977;Chamley and Robert 1979;Maillet 1979, 1984;Froget 1981;Robert 1982;and Chennaux et al, 1984). Results presented here are compared with those obtained from neighboring drilled sites (DSDP Legs 38, 48B, and 81).…”

“…At that time, the Iceland-Faeroe Ridge sill subsided (Berggren and Hollister 1974;Roberts and Montadert 1979;Berggren and Schnitker 1983) allowing water mass exchange between the Atlantic and the Norwegian Sea. Correlatively, the flow of Norwegian Sea water masses to the south is reflected in the early appearance of illites and chlorites Maillet, 1979, 1984) in sediments of the Rockall region (DSDP Legs 48B and 81).…”

X-Ray Mineralogy of the Clay Fraction from Cenozoic Strata, Leg 94: Comparison with Previous North Atlantic Data

“…The primary objective of this study was to confirm or question hypotheses previously put forward in mineralogical studies of North Atlantic sediments from DSDP Legs 47B, 48, 80, 81, and 82 (Chamley et al, 1979;Chennaux et al, 1985;Maillet, 1979, 1984, andin press). The main conclusions drawn from these studies were as follows:…”

“…Previous DSDP sites in this region are few. Comparison with distant sites, such as those of Legs 48, 80, 81, and 82 (Chennaux et al, 1985;Maillet, 1979, 1984, and in press), show clay-mineralogical similarities. Oceanic input from the north probably accounts for the arrival of these minerals (e.g., illites and chlorites), as in the Rockall region.…”