Cretaceous-Tertiary ichthyoliths of brown clay intervals

The pattern of ichthyolith distribution established in sequences with stratigraphies based on calcareous or siliceous microfossils is used to provide age correlations for three deep-sea pelagic clay intervals that lack the better known microfossils. At Site 637, approximately 25 m of brown clay in Cores 103-637A-21R through 103-637A-23R underlies upper Miocene sediments and is of Paleocene to early Eocene age. At Site 639, 1.7 m of brown clay in Core 103-639C-2R is Eocene to Oligocene. At Site 640, 3.5 m of clay in Cores 103-640A-1R and 103-640A-2R contains a Cretaceous to Paleocene sequence, with the Cretaceous/Tertiary boundary between 84 and 103 cm in Section 103-640A-2R-1.

Density and biomass of two copepod size fractions and various species obtained during Almirante Irizar cruises to the Drake Passage and Scotia Sea (2000-2003)

The relative importance of small forms of copepods has been historically underestimated by the traditional use of 200-300-µm mesh nets. This work quantified the distribution and abundance of copepods, considering two size fractions (<300 µm and >300 µm), in superficial waters (9 m deep) of the Drake Passage and contributed to the knowledge of their interannual fluctuations among three summers. Four types of nauplii and eleven species of copepods at copepodite and adult stages were identified, with abundance values of up to 13 ind/L and 28,300 µg C/m**3. The <300-µm fraction, composed of Oithona similis, small cyclopoids and nauplii, dominated the copepod communities in the 3 years; it accounted for more than 77% of the total number and for between 40 and 63% of the total biomass. Changes in density and biomass values among the three cruises differed according to copepod size fraction and water mass; the >300-µm fraction showed no changes among the 3 years, both in Antarctic (density and biomass) and in Subantarctic waters (density), whereas the <300-µm fraction showed higher (density and biomass) values in 2001 both in Subantarctic and in Antarctic waters. Sea surface temperature and its anomaly accounted for the largest proportion of variability in copepod density and biomass, particularly for the <300-µm fraction.

Grain-size and bulk and clay mineralogy of ODP Leg 204 sediments

We present grain size, granulometric statistical parameters, and calcium carbonate content of sediment samples from the summit and east and west flanks of southern Hydrate Ridge (Sites 1244-1250). These data are compared with magnetic susceptibility measurements from the same intervals. Bulk and clay mineralogy from Sites 1244 (east flank), 1247 (west flank), and 1250 (summit) are also presented. The integration of these data allows us to characterize the main sedimentary facies and composition of the Quaternary age sediments from southern Hydrate Ridge.

Clay minerals at DSDP Sites 71-511 and 71-513

The distribution of clay minerals, determined by X-ray diffraction, is given for Jurassic to Holocene sediments recovered at DSDP Sites 511 and 513 in the Southwest Atlantic. These data, plus the lithologic and paleoenvironmental information gathered by the shipboard scientists, are used to subdivide the sedimentary sequence into genetic lithologic facies labeled series, seven for Site 511 and two for Site 513. Sediments of these series reflect the main historical and paleoenvironmental events which other means of study have determined to affect this region; particularly important was the opening of the South Atlantic during the Early Cretaceous.

Heavy and light minerals in turbidites from DSDP Hole 19-183, the Aleutian abyssal plain

The Aleutian abyssal plain is a fossil abyssal plain of Paleogene age in the western Gulf of Alaska. The plain is a large, southward-thinning turbidite apron now cut off from sediment sources by the Aleutian Trench. Turbidite sedimentation ceased about 30 m.y. ago, and the apron is now buried under a thick blanket of pelagic deposits. Turbidites of the plain were recovered at site 183 of the Deep Sea Drilling Project on the northern edge of the apron. The heavy-mineral fraction of sand-sized samples is mostly amphibole and epidote with minor pyroxene, garnet, and sphene. The light-mineral fraction is mostly quartzose debris and feldspars. Subordinate lithic fragments consist of roughly equal amounts of metamorphic, plutonic, sedimentary, and volcanic grains. The sand compositions are arkoses in many sandstone classifications, although if fine silt is included with clay as matrix, the sand deposits are feldspathic or lithofeldspathic graywacke. The sands are apparently first-cycle products of deep dissection into a plutonic terrane, and they contrast sharply with arc-derived volcanic sandstones of similar age common on the adjacent North American continental margin. The turbidite sands are stratigraphically remarkably constant in composition, which indicates derivation from virtually the same terrane through a time span approaching 20 m.y. Comparison of Aleutian plain data with the compositions of coeval sedimentary rocks from the northeast Pacific margin shows that the Kodiak shelf area includes possible proximal equivalents of the more distal turbidites. Derivation from the volcaniclastic Mesozoic flysch of the Shumagin-Kodiak shelf is unlikely; more probably the sediments were derived from primary plutonic sources. The turbidites also resemble deposits in the Chugach Mountains and the younger turbidites of the Alaskan abyssal plain and could conceivably have been derived from the coast ranges of southeastern Alaska or western British Columbia. The Aleutian plain sediment most likely was not derived from as far south as the Oregon-Washington continental margin, where coeval sedimentary deposits are dominantly volcaniclastic.