Cazadores recolectores del pedemonte mendocino en el 3000 AP (Puesto Lima, Quebrada de Papagayos, Mendoza, Argentina)

Las investigaciones arqueológicas de Mendoza prestaron poca atención al piedemonte oriental de la precordillera en comparación con las realizadas en valles y sectores de precordillera. Sin embargo, el estudio de este sector resulta clave para entender los patrones de asentamiento-subsistencia de las sociedades cazadoras-recolectoras de la región. Por otro lado, si bien se han postulado modelos para explicar las modalidades de articulación entre tierras altas y bajas durante la prehistoria, no se han definido las variaciones en sentido diacrónico. En este trabajo se apunta a describir las características del registro arqueológico del ambiente del piedemonte oriental de la precordillera de Mendoza, y en particular, de un sitio localizado en la Quebrada de Papagayos, para, análisis de la tecnología lítica mediante, proponer hipótesis referidas a los modos de organización tecnológica y del asentamiento hace aproximadamente 3.000 años AP.

Carbonate content in lower Cretaceous sediments of ODP Hole 123-765C

Sediments recovered during Ocean Drilling Program (ODP) Leg 123 from the Argo Abyssal Plain (AAP) consist largely of turbidites derived from the adjacent Australian continental margin. The oldest abundant turbidites are Valanginian-Aptian in age and have a mixed (smarl) composition; they contain subequal amounts of calcareous and siliceous biogenic components, as well as clay and lesser quartz. Most are thin-bedded, fine sand- to mud-sized, and best described by Stow and Piper's model (1984) for fine-grained biogenic turbidites. Thicker (to 3 m), coarser-grained (medium-to-coarse sand-sized) turbidites fit Bouma's model (1962) for sandy turbidites; these generally are base-cut-out (BCDE, BDE) sequences, with B-division parallel lamination as the dominant structure. Parallel laminae most commonly concentrate quartz and/or calcispheres vs. lithic clasts or clay, but distinctive millimeter- to centimeter-thick, radiolarian-rich laminae occur in both fine- and coarse-grained Valanginian-Hauterivian turbidites. AAP turbidites were derived from relatively deep parts of the continental margin (outer shelf, slope, or rise) that lay below the photic zone, but above the calcite compensation depth (CCD). Biogenic components are largely pelagic (calcispheres, foraminifers, radiolarians, nannofossils); lesser benthic foraminifers are characteristic of deep-water (abyssal to bathyal) environments. Abundant nonbiogenic components are mostly clay and clay clasts; smectite is the dominant clay species, and indicates a volcanogenic provenance, most likely the Triassic-Jurassic volcanic suite exposed along the northern Exmouth Plateau. Lower Cretaceous smarl turbidites were generated during eustatic lowstands and may have reached the abyssal plain via Swan Canyon, a submarine canyon thought to have formed during the Late Jurassic. In contrast to younger AAP turbidites, however, Lower Cretaceous turbidites are relatively fine-grained and do not contain notably older reworked fossils. Early in its history, the northwest Australian margin provided mainly contemporaneous slope sediment to the AAP; marginal basins adjacent to the continent trapped most terrigenous detritus, and pronounced canyon incisement did not occur until Late Cretaceous and, especially, Cenozoic time.

A late Quaternary planktonic foraminifer faunal record of rapid climatic changes of sediment core GIK17938-2

A high-resolution planktonic foraminifer record from a core recovered from the South China Sea (SCS) (Sonne 17938-2: 19°47.2'N, 117° 32.3E; 2840 m; Delta t c. 250-1000 years) shows rapid millennial-scale changes in the western Pacific marginal sea climate during the last 30,000 years. The SCS is the largest western Pacific marginal sea off the southeast Asian continent, the area today dominated by seasonal monsoon changes. Quantitative analyses of planktonic foraminifer faunal abundance data frorn the core indicate large downcore variations in the relative abundances of the dominant taxa since about 30,000 years ago in the isotope stage 3. Further analyses indicate that the abundance of G. inflata, a good indicator species for cold SST (~13°-19°C) and deep MLD (~100-125 m) waters shows abrupt shifts. During stages 2 and 3, the abundance record of G. infiata tends to be punctuated by quasi-periodie short intervals (~2000-3000 yrs) where its abundance reaches 15% or greater, superimposed on generally low (5-10%) background values. This pattern suggests an instability of surface ocean conditions of the SCS during the past 30,000 years. The abrupt abundance changes of G. infiata correlate well with similar climatic changes observed from a GISP2 ice core 8180, and North Atlantic core DSDP 609 N. pachyderma (s.) and lithic grain abundances during 'Heinrich evcnts'. These results suggest that the millennial-scale variability of climate is not peculiar to the Atlantic region. Apparently, the rapid SCS climatic changes during Heinrich events are driven by effective mechanisms, of particularly the effects of shifts in the latitudinal position of the Siberia High Pressure System.

Petrology and geochemistry of the Izu-Bonin Forearc tephras

Numerous marine tephra layers cored at Sites 792 and 793 in the Izu-Bonin forearc region offer additional information about the timing and spatial characteristics of arc volcanism and the evolution of island arcs. Explosive volcanism along the Izu-Bonin Arc, with maxima just before rifting of the arc at ~40 and 5-0 Ma, produced black and white tephras of variable grain sizes and chemical compositions. Most of the tephras belong chemically to low-K and low-alkali tholeiitic rock series with a few tephra of the high-K and alkalic rock series. Most of the tephras (low-K series) were derived from the Izu-Bonin Arc, although a few were produced far to the west of the Izu-Bonin Arc (e.g., from the Ryukyu Arc). Black tephras may have come from nearby sources, such as Aogashima, Sumisu, and Torishima islands. The high-K series of tephras, within the sediments younger than 3 Ma, may reflect thickening of the island-arc crust.

Pebbles and carbonate nodules Legs 56-57 Holes

At all DSDP Leg 56 drilling sites, exotic pebbles occur commonly, throughout the cores. Chips of carbonate nodules occur only at Site 434 on the lower inner trench wall. Both exotic pebbles and carbonate nodule chips sometimes tend to be concentrated at particular levels of cores. Exotic pebbles are generally well rounded and consist of various rock types, such as dacite, andesite, basalt, tuff, gabbro, granodiorite, metaquartzite, biotite hornfels, lithic wacke, mudstone, etc., of which dacite occurs commonly at all the sites. Almost all pebbles at Site 436 and most at Sites 434 and 435 may have been rafted by ice. Some at the latter sites may have been derived by down-slope slumping. Carbonate nodules consist of microcrystalline dolomite, manganoan calcite, and siderite; CaCO3 content ranges from 22 to 65 per cent. They are also generally characterized by a high content of P2O5. The nodules are commonly rich in diatom remains, some of which indicate that the nodules are autochthonous. Some nodules contain abundant glass shards, with a modal refractive index of 1.499, almost identical to shards in the surrounding mud and ooze. These facts suggest that the carbonate nodules may have been formed diagenetically, in situ. This may throw light on problems of the formation of carbonate nodules in ancient "geosynclinal" sediments. It is also very important to point out that these carbonate nodules were formed within sediment deposited well below the CCD.

Sedimentology and planktonioc foraminifera of core SU90-08

The observation by Heinrich (1988) that, during the last glacial period, much of the input of ice-rafted detritus to the North Atlantic sediments may have occurred as a succession of catastrophic events, rekindled interest on the history of the northern ice sheets over the last glacial period. In this paper, we present a rapid method to study the distribution of these events (both in space and time) using whole core low-field magnetic susceptibility. We report on approximately 20 cores covering the last 150 to 250 kyr. Well-defined patterns of ice-rafted detritus appear during periods of large continental ice-sheet extent, although these are not always associated within their maxima. Most of the events may be traced across the North Atlantic Ocean. For the six most recent Heinrich layers (HL), two distinct patterns exist: HL1, HL2, HL4, HL5 are distributed along the northern boundary of the Glacial Polar Front, over most of the North Atlantic between ~40° and 50°N; HL3 is more restricted to the central and eastern part of the northern Atlantic. The Nd-Sr isotopic composition of the material constituting different Heinrich events indicates the different provenance of the two patterns: HL3 has a typical Scandinavia-Arctic-Icelandic 'young crust' signature, and the others have a large component of northern Quebec and northern West Greenland 'old crust' material. These isotopic results, obtained on core SU-9008 from the North American basin, are in agreement with the study by Jantschik and Huon (1992), who used K-Ar dating of silt- and clay-size fractions of an eastern basin core (ME-68-89). These data confirm the large spatial scale of these events, and the enormous amount of ice-rafted detritus they represent.

Petrology and geochemistry of volcanic rocks from ODP Sites 134-827, 134-829 and 134-830

Igneous rocks recovered from Ocean Drilling Program (ODP) Leg 134 Sites 827, 829, and 830 at the toe of the forearc slope of New Hebrides Island Arc were investigated, using petrography, mineral chemistry, major and trace element, and Sr, Nd, and Pb isotopic analyses. Basaltic and andesitic clasts, together with detrital crystals of plagioclase, pyroxenes, and amphiboles embedded in sed-lithic conglomerate or volcanic siltstone and sandstone of Pleistocene age, were recovered from Sites 827 and 830. Petrological features of these lava clasts suggest a provenance from the Western Belt of New Hebrides Island Arc; igneous constituents were incorporated into breccias and sandstones, which were in turn reworked into a second generation breccia. Drilling at Site 829 recovered a variety of igneous rocks including basalts and probably comagmatic dolerites and gabbros, plus rare ultramafic rocks. Geochemical features, including Pb isotopic ratios, of the mafic rocks are intermediate between midocean ridge basalts and island arc tholeiites, and these rocks are interpreted to be backarc basin basalts. No correlates of these mafic rocks are known from Espiritu Santo and Malakula islands, nor do they occur in the Pleistocene volcanic breccias at Sites 827 and 830. However, basalts with very similar trace element and isotopic compositions have been recovered from the northern flank of North d'Entrecasteaux Ridge at Site 828. It is proposed that igneous rocks drilled at Site 829 represent material from the North d'Entrecasteaux Ridge accreted onto the over-riding Pacific Plate during collision. An original depleted mantle harzburgitic composition is inferred for a serpentinite clast recovered at 407 meters below seafloor (mbsf) in Hole 829A. Its provenance is a matter of speculation. It could have been brought up along a deep thrust fault affecting the Pacific Plate at the colliding margin, or analogous to the Site 829 basaltic lavas, it may represent material accreted from the North d'Entrecasteaux Ridge.

Chemical composition of ferromanganese manifestations from the Sea of Okhotsk

New data on microstructures and mineral and chemical compositions of ferromanganese crusts sampled from the western slope of the Kuril Island Arc in the Sea of Okhotsk during cruises of R/V Vulkanolog are discussed. The study of the crusts using analytical electron microscopy methods revealed that their manganese phase is represented by vernadite, Fe-vernadite, todorokite, asbolane, and asbolane-buserite, while iron phase consists of hematite, hydrohematite, ferroxyhite, and magnetite. Lithic mineral assemblage includes apatite, quartz, epidote, and montmorillonite. According to chemical analysis most of the crusts contain significant part of volcanogenic and hydrothermal material. It is evident from elevated values of Mn/Fe and (Mn+Fe)/Ti ratios, low concentrations of some trace elements, and positive Eu anomaly.

Petrology and geochemistry of Quaternary tephras of the Izu-Bonin Arc

Quaternary marine tephras in the Izu-Bonin Arc offer significant information about explosive volcanic activities of the arc. Visual core descriptions, petrographic examinations, and chemical and grain-size analyses were conducted on tephras of backarc, arc, and forearc origin. Tephras are black and white and occur in simple and multiple modes with mixed and nonmixed ashes of black and white glass shards. The grain size distributions of the tephras are classified into three categories: coarse, white pumiceous, and fine white and black well-sorted types. The frequency of occurrence of the white and black tephras differs within the tectonic settings of the arc. Chemically, the Quaternary tephras in this region belong to low-alkali tholeiitic series with lower K2O and TiO2 than normal ordinary arc volcanic materials. Several tephras from different sites along the forearc correlate with each other and with tephras in the Shikoku Basin site and with Aogashima volcanics. These volcanic ashes resemble those in other backarc rifting areas, such as in the Fiji, Okinawa (Ryukyu), and Mariana regions.

Age and petrographic characterization of volcanic ash from ODP Leg 198 and Leg 126 sites

In this study of volcanic ash retrieved from Shatsky Rise during Ocean Drilling Program Leg 198, the texture and composition of the volcanic components (glass and crystals) were used to fingerprint ash layers for detailed correlation. Correlations among ash layers in holes drilled at the same site as well as between sites, including sites on different parts (highs) of the rise, were tested. Although high-to-high correlations failed, intrahigh correlations were more successful. Our data suggest a significantly different source for some pyroclastic debris, especially at Site 1208, possibly associated with pumice rafts carried northward from the Izu-Bonin arc by the Kuroshio Current. Other ashes are consistent with rhyolitic to dacitic air fall ash from Asian arc volcanoes. We were not able to texturally distinguish between air fall ash and pumice-raft fallout but suspect that the latter is associated with higher percentages of vesiculated ash components, as we demonstrate occur in more proximal Izu-Bonin pyroclastic deposits.

Messinian and pre-Messinian sediments of ODP Holes 107-652A and 107-654A

Sedimentology, mineralogy, and petrology of the pre-Pliocene sediments drilled at ODP Sites 652 and 654 in the Tyrrhenian Sea (Leg 107) have been studied with emphasis on the lower Messinian to pre-Messinian intervals. Messinian at Site 652 is essentially turbiditic and basinal in character; it was deposited during the syn-rift phase in a strongly subsiding half-graben and is correlatable with emerged coeval sequences; in part with the Laga Formation of the foredeep of Apennines, and in part with the filling of grabens dissecting that chain in the Tyrrhenian portion of Tuscany. The sequence found in Site 654 indicates an upper Tortonian to Messinian transgression accompanying crustal stretching in the western Tyrrhenian Sea and is perfectly correlatable with the so-called "Sahelian cycle" and with "postorogenic" cycles recognized in peninsular Italy and in Sicily.

Petrographic data for samples from DSDP Holes 63-471 and 65-485

Detrital modes of middle Miocene sandstone recovered at Deep Sea Drilling Project Site 471 on the Magdalena Fan support the hypothesis that the fan has been displaced northward from a source hundreds of kilometers to the south near the present mouth of the Gulf of California. The modes are dissimilar to those of modern sand derived from onshore outcrops of Miocene volcanic and volcaniclastic rocks, Neogene sedimentary rocks, and Mesozoic subduction complex. They most closely match sand associated with the mouth of Gulf of California. The overall stratigraphy, sand composition, and diagenesis at Site 471 are consistent with deposition of the Magdalena Fan on young oceanic crust near a spreading ridge at a triple junction.

Composition of Carnian to Norian sandstones from the Wombat Plateau (Table 1)

The Carnian to Norian sediments, as much as 600 m in total thickness, recovered from ODP Sites 759 and 760 on the Wombat Plateau, are generally represented by fluvial-dominated deltaic successions. In general, the Carnian to Norian sandstones are quartzose. The average ratio of monocrystalline quartz grains, total feldspar grains, and total lithic fragments (i.e., Qm:F:Lt ratio) is 71:22:7. This indicates that they were derived mainly from the transitional continental and cratonic interior provenance terranes, such as the Pilbara Precambrian block to the south of the Wombat Plateau. The upper Carnian sediments, however, are characterized by more feldspathic sandstone petrofacies. They typically contain some volcanic rock fragments with trachytic texture and indicate the onset of the incipient rift-related tectonic movement, such as uplift and subsequent abrupt basin subsidence, together with volcanism in the Gondwana continental block. Mixed siliciclastic and carbonate cycles are typically intercalated in the prodelta to delta front deposits that developed mainly in a lagoon-like, restricted marine environment. The restricted marine environment developed during transgressions as the outflow of shallow water was restricted by depositional barriers. Around the barriers and/or delta lobes, carbonate shoals/banks were probably developed and the allochemical components of the neritic limestones may have been transported into the restricted marine environment by overwash processes and/or storm waves. Siliciclastic detritus, on the other hand, was mainly derived accompanied by delta progradation dominated by fluvial processes in the restricted marine environment. Therefore, we interpret the mixed siliciclastic and carbonate cycles in the deltaic successions to be a result of transgression-regression cycles in a deltaic system during the Late Triassic.