Glassy objects from DSDP Hole 5-32 in the northeastern Pacific Ocean

Small glassy spheres, ellipsoids, teardrops, cylinders and dumbbells occur in large numbers in Tertiary deep sea clays cored in the northeastern Pacific by the Deep Sea Drilling Project. These objects morphologically resemble microtektites, but have the composition of an oceanic tholeiite. On the basis of their composition and stratigraphic relationship it is considered that they are of volcanic origin and most likely have been formed in deep water by submarine volcanic processes.

Tecnología cerámica : estudios experimentales sobre la cerámica del sitio arqueológico San Ignacio (Noroeste de Mendoza)

El propósito de este trabajo es explorar la disponibilidad de materias primas que pudieron ser utilizadas en el proceso de manufactura de la cerámica gris del sitio arqueológico San Ignacio, en el Valle de Potrerillos, ubicado al Norte de la provincia de Mendoza (640 dC). Se pretende, además, reproducir las técnicas de producción y cocción cerámica, a fin de obtener un producto de características análogas a las de la colección estudiada. La metodología utilizada presentó las siguientes etapas: recolección de materiales arcillosos; caracterización de las propiedades físicas en estado crudo; análisis químicos; desarrollo experimental de cocción y ensayos post-cocción de los mismos. Los productos obtenidos muestran una buena estructura y sinterización, aunque no se logró una atmósfera completamente reductora con este tipo de combustible.

Infiltración y erosión

Esta monografía se enmarca en el manejo de los recursos hídricos en grandes redes de riego. En ella se describe el caso del río Mendoza, en la provincia homónima, el que fuera regulado en el año 2002. Este río nace en la Cordillera de los Andes, y presenta un importante arrastre de sólidos en suspensión, los que actualmente son retenidos en gran medida por el embalse Potrerillos. Las “aguas claras" que se erogan del embalse producen problemas erosivos, los que a su vez estarían ocasionando una mayor infiltración en los canales, y con ello un incremento en la recarga de acuíferos en ciertas zonas, así como problemas derivados del ascenso de la freática en otras. Se citan procesos ocurridos en otros distritos de riego frente a la regulación de los ríos, para concluir que el del río Mendoza es un caso susceptible de sufrir ciertos per-juicios, ya señalados en la Manifestación General de Impacto Ambiental del embalse Potrerillos, los que actualmente se están presentando en la red de riego. A partir de los estudios de sedimentología en el río Mendoza, se hace un análisis técnico de los fenómenos asociados al cambio de las características físicas del agua. Luego se describen los procesos erosivos, de acuerdo con la hidráulica clásica. Se define la Eficiencia de conducción (Ec), la infiltración en canales y su importancia en distintos distritos de riego, para luego mencionar los estudios realizados en el área del río Mendoza. Se analiza el desarrollo espacial que ha tenido el oasis, la escasa programación que tuvo su traza y la antigüedad de la misma. La descripción de los suelos permite concluir acerca de la importancia de su estructura y del papel que juegan las porciones finas, aún en minoría, que integran las distintas clases texturales con respecto a la Ec. Se describen los criterios con que se distribuye el agua en Mendoza, analizándose los caudales distribuidos actualmente, para relacionarlos con los niveles freáticos. Se mencionan además distintas acciones encaradas por la provincia para mitigar los efectos de las aguas claras. El análisis de los métodos utilizados para medir la Ec, permite apreciar el estado de la ciencia al respecto. Un análisis de las ventajas y de las desventajas de los distintos métodos, y de los resultados que con ellos se obtienen, permite concluir que el método de entradas y salidas es el que mejor se adapta en Mendoza, incluyendo además aspectos metodológicos de la medición. También se concluye en que la Ec. está insuficientemente evaluada; las fracciones finas de los suelos en muchos casos gravitan más que la textura frente a la Ec; por ello, se considera que el estudio de la Ec en las distintas áreas de manejo es necesario para entender los procesos de revenición y recarga de acuíferos, y que las pérdidas administrativas pueden gravitar más que la Ec. Se recomienda continuar con los trabajos de evaluación de Ec, al ser necesarios para todas las actividades en la cuenca; se desaconseja en este río el ajuste de modelos de predicción de Ec; las características de los suelos obligan a interpretar y aplicar con criterio la bibliografía internacional, pero aún así no se pueden hacer generalizaciones acerca de de la Ec en Mendoza.

Chemistry of igneous rocks from, the Celebes Sea basement

Major and trace elements, mineral chemistry, and Sr-Nd isotope ratios are reported for representative igneous rocks of Ocean Drilling Program Sites 767 and 770. The basaltic basement underlying middle Eocene radiolarianbearing red clays was reached at 786.7 mbsf and about 421 mbsf at Sites 767 and 770, respectively. At Site 770 the basement was drilled for about 106 m. Eight basaltic units were identified on the basis of mineralogical, petrographical, and geochemical data. They mainly consist of pillow lavas and pillow breccias (Units A, B, D, and H), intercalated with massive amygdaloidal lavas (Units Cl and C2) or relatively thin massive flows (Unit E). Two dolerite sills were also recognized (Units F and G). All the rocks studied show the effect of low-temperature seafloor alteration, causing almost total replacement of olivine and glass. Calcite, clays, and Fe-hydroxides are the most abundant secondary phases. Chemical mobilization due to the alteration processes has been evaluated by comparing elements that are widely considered mobile during halmyrolysis (such as low-field strength elements) with those insensitive to seafloor alteration (such as Nb). In general, MgO is removed and P2O5 occasionally enriched during the alteration of pillow lavas. Ti, Cs, Li, Rb, and K, which are the most sensitive indicators of rock/seawater interaction, are generally enriched. The most crystalline samples appear the least affected by chemical changes. Plagioclase and olivine are continuously present as phenocrysts, and clinopyroxene is confined in the groundmass. Textural and mineralogical features as well as crystallization sequences of Site 770 rocks are, in all, analogous to typical mid-ocean-ridge basalts (MORBs). Relatively high content of compatible trace elements, such as Ni and Cr, indicate that these rocks represent nearly primitive or weakly fractionated MORBs. All the studied rocks are geochemically within the spectrum of normal MORB compositional variation. Their Sr/Nd isotopic ratios plot on the mantle array (87Sr/87Sr 0.70324-0.70348 with 143Nd/144Nd 0.51298-0.51291) outside the field of Atlantic and Pacific MORBs. However, Sr and Nd isotopes are typical of both Indian Ocean MORBs and of some back-arc basalts, such as those of Lau Basin. The mantle source of Celebes basement basalts does not show a detectable influence of a subduction-related component. The geochemical and isotopic data so far obtained on the Celebes basement rocks do not allow a clear discrimination between mid-ocean ridge and back-arc settings.

Paleomagnetism at DSDP Sites 86-576 and 86-578

The upper sections of Deep Sea Drilling Project Sites 576 (32°21.4'N, 164°16.5'E) and 578 (33°55.6'N, 151°37.7'E) both have stable detrital remanence that can be correlated with the standard reversal stratigraphy. Site 576 contains all reversals above the base of the Gilbert Epoch (5 m.y.) at about 25 m, whereas Site 578 contains a remarkable section of about 60 reversals extending to Anomaly 5B (15 m.y.) at about 150 m sub-bottom depth. In both cases, the paleomagnetic stratigraphy breaks down when accumulation rates drop below 2 m/m.y. At both sites, authigenic manganiferous clays deposited from 70 to 16 m.y. ago accumulated at about 0.4 m/m.y. Similarly, at both sites, the Pleistocene pulse of eolian debris increased accumulation rates by about 6 m/m.y.**2. From 16 to 2 m.y. ago, however, sediment accumulated at Site 578 about five times as rapidly as at Site 576, apparently because of augmented input to the western site by bottom currents.

Pollen record and lithology of a profile from Dumfriesshire, Scotland

Four samples, G5, G7, G8, and G10, collected by Dr W. W. Bishop from an exposed section in the bank of the River Annan, at Roberthill Farm, Dumfriesshire (S35, 110794) were submitted for pollen analysis (Table I.). The samples, with the exception of the uppermost, were from thin peat layers that lie in the middle of a series of water- laid sands, silts and clays several feet in thickness and now rather strongly arched. The lowermost sample, G5, was taken from an organic layer about | in. thick overlying fine sand and underlying some 2.5 in. of grey, silty fine sand. A narrow layer of sandy peat immediately above the silty, fine sand yielded sample G7, and G8 was collected from a similar peaty layer separated from G7 by more sandy- silty peat. The uppermost sample, G10, was taken from light grey clay 13 in. above sample G8.

(Appendix A) Organic facies at DSDP Hole 93-603B

The Palynology of two sections recovered during Leg 93 drilling by the Deep Sea Drilling Project in the continental rise along the western margin of the North Atlantic is reported. In Hole 603B at Site 603, the dinoflagellate stratigraphy indicates that the interval from Cores 603B-82 to 603B-26 ranges in age from late Berriasian to Santonian. The BlakeBahama Formation ranges from late Berriasian to Aptian. The Hatteras Formation ranges from Aptian to Cenomanian, although the uppermost part may be Turonian. Dinoflagellate evidence from the middle part of the Plantagenet Formation indicates an age from late Coniacian or early Santonian to Santonian within the interval of Cores 603B-28 to 603B-26. Magnetic polarity evidence of the stratigraphy of the Early Cretaceous for the western North Atlantic indicates a reliable correlation with the dinoflagellate zonation. The stratigraphic sequence of palynologically defined organic facies in carbonaceous claystone lithologies in Hole 603B shows that organic stratigraphic units consisting predominantly of fecal-pellet-derived, pelagic organic matter (xenomorphic facies) alternate with units consisting predominantly of terrigenous organic matter (tracheal and exinitic facies), corresponding to that described from other sites in the North Atlantic. A terrigenous organic facies is identified for the first time from the Plantagenet Formation. The claystone organic facies and major lithofacies are closely correlated. The tracheal and exinitic facies occur in carbonaceous terrigenous claystones and claystone turbidites associated with sandstone/siltstone terrigenous turbidites. The xenomorphic facies occurs in claystones within pelagic limestones lacking any turbidites, and in blackish, noncalcareous claystones which correlate in age with the marine-carbon-rich sapropels which are widespread in the North Atlantic Cenomanian. This facies also occurs with an admixture of terrigenous organic particles in the Blake-Bahama Formation, but the mixture is consistent with the submarine fan setting of this interval. The concentration of refractory organic matter (carbonized particles) in the micrinitic and carbonized tracheal facies is considered to be the result, at least in part, of the oxidation of sediment buried below a surface slowly accumulating pelagic clays below the carbonate compensation depth. The progressive increase in number of dinoflagellate species per stage through the Early Cretaceous (except for the late Barremian-Aptian) may have resulted indirectly from the generally progressive rise in global sea level during this time. At Site 605, the dinoflagellate stratigraphy across the Cretaceous/Tertiary boundary is remarkably close to that published from the Maestrichtian and Danian of Denmark. The Maestrichtian/Danian boundary is placed precisely within Section 605-66-1 by dinoflagellate evidence, agreeing with that predicted by other microfossils. The new dinoflagellate-cyst-based genus, Pierceites and its new species P. schizocystis, and the new combination P. ( = Trithyrodinium) pentagonum (May) are proposed. Diacanthum hollisteri Habib, type species of Diacanthum, is emended to accommodat e cysts with the archeopyle formulas P3'', 2P2''-3'', 2P3''-4'', and 3P2''-3''-4''.

Trace element concentrations and Li isotope composition in DSDP and ODP sediments from island arcs

We have studied the sedimentary and basaltic inputs of lithium to subduction zones. Various sediments from DSDP and ODP drill cores in front of the Mariana, South Sandwich, Banda, East Sunda and Lesser Antilles island arcs have been analysed and show highly variable Li contents and d7Li values. The sediment piles in front of the Mariana and South Sandwich arcs largely consist of pelagic sediments (clays and oozes). The pelagic clays have high Li contents (up to 57.3 ppm) and Li isotope compositions ranging from +1.3? to +4.1?. The oozes have lower Li contents (7.3-16 ppm) with d7Li values of the diatom oozes from the South Sandwich lower (+2.8? to +3.2?) than those of the radiolarian oozes from the Mariana arc (+8.1? to +14.5?). Mariana sediment also contains a significant portion of volcanogenic material, which is characterised by a moderate Li content (14 ppm) and a relatively heavy isotope composition (+6.4?). Sediments from the Banda and Lesser Antilles contain considerable amounts of continental detritus, and have high Li contents (up to 74.3 ppm) and low d7Li values (around 0?), caused by weathering of continental bedrock. East Sunda sediments largely consist of calcareous oozes. These carbonate sediments display intermediate to high Li contents (2.4-41.9 ppm) and highly variable d7Li values (-1.6? to +12.8?). Basaltic oceanic crust samples from worldwide DSDP and ODP drill cores are characterised by enrichment of Li compared to fresh MORB (6.6-33.1 vs. 3.6-7.5 ppm, respectively), and show a large range in Li isotope compositions (+1.7? to +11.8?). The elemental and isotopic enrichment of Li in altered basalts is due to the uptake of isotopically heavy seawater Li during weathering. However, old oceanic crust samples from Sites 417/418 exhibit lighter Li isotope compositions compared to young basaltic crust samples from Sites 332B and 504B. This lighter Li isotope signature in old crust is unexpected and further research is needed to explore this issue.

Geochemistry of sediments and kerogenes of ODP Hole

The organic matter contained within a series of Albian to Cenomanian, dark gray to black marls was characterized using pyrolysis techniques and analysis (elemental and carbon isotopes) of isolated kerogens. It was concluded that this material had a marine affinity. Variations in geochemical characteristics reflect differences in the extent of preservation, rather than changes in organic provenance. These changes appear to reflect differences in water depth and the position of the depositional site relative to the oxygen-minimum zone. Sediments displaying the most elevated levels of organiccarbon and hydrogen enrichment probably reflect sedimentation within the oxygen-minimum zone. Waters within the oxygen-minimum zone were probably dysaerobic, rather than anoxic. The presence of at least trace quantities of oxygen at the depositional site explains the poor degree of organic preservation and the material's largely gas-prone characteristics.