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41.
Linking sedimentation rates and large‐scale architecture for facies prediction in nonmarine basins (Paleogene,Almazán Basin,Spain)
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Luis Valero Pedro Huerta Miguel Garcés Ildefonso Armenteros Elisabet Beamud Miriam Gómez‐Paccard 《Basin Research》2017,29(Z1):213-232
This article focuses on the relationships between the large‐scale stratigraphic architecture of the Almazán basin infill and the sedimentation rates (SR) calculated for precise time intervals. Our aim was to improve the understanding of the timing and causes of the architectural changes, their significance in terms of accommodation space and sediment supply and their relationship with climate and tectonics. The study area includes the Gómara fluvial fan, the main sediment transfer system of the Almazán basin during Paleogene times. Its large‐scale architecture shifted through time between a stacking pattern of low density ribbon‐like and high density sheet‐like channel fills. Laterally to the fluvial system, mudstone and evaporitic mudstone units represented evaporitic mudflats which passed laterally into palustrine/lacustrine limestone units interpreted as lakes and ponds. Stacked calcretes occurred in distal alluvial and distal floodplain settings. A magnetostratigraphy encompassing 2600 m guided by available fossil mammal biochronology has provided a temporal framework that spans the complete Paleogene infill of the basin, from Late Lutetian to Late Oligocene, filling a gap in the Cenozoic chronostratigraphy of Spanish basins. This permits to constrain the kinematics of the structures both in the basin and in its margins, and to provide the timing for the depositional sequences. These data, combined with a magnetostratigraphic map, where magnetic reversals were traced through the Gómara monocline, allow a detailed analysis of the SR variability across the fluvial system and its adjacent depositional environments. The results show that high sedimentation rates (around 30–40 cm kyr?1) are related to fluvial environments with low density ribbon‐shaped channels, while low SR (around or below 10 cm kyr?1) are related to high density sheet‐like channels. Laterally, mud dominated environments with high SR (15–20 cm kyr?1) grade into palustrine/lacustrine carbonated environments with low SR (around 9 cm ky?1). The lowest SR (about 3 cm kyr?1) are related to the development of stacked calcrete profiles in distal floodplain and in the connection of distal alluvial and palustrine/lacustrine units. 相似文献
42.
Richard D. Brodeur Matthew T. Wilson Lorenzo Ciannelli Miriam Doyle Jeffrey M. Napp 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26)
The distribution, size, length-specific weight, growth, and feeding of age-0 walleye pollock (Theragra chalcogramma) were examined along with their prey distribution patterns in two contrasting transects over a 4-year period (1994–1997) in relation to biophysical properties of frontal regions around the Pribilof Islands, Bering Sea. There were significant interannual differences in catch of age-0 pollock, but transect and habitat differences (inshore vs. front vs. offshore) were not significant for either catch or size of pollock. There were significant variations in length-specific weight and growth of pollock, but the trends were inconsistent. Copepods dominated the zooplankton biomass in all habitats and years; there were no consistent differences in the densities of the dominant zooplankton taxa among the habitats. There were, however, strong habitat and transect differences in juvenile pollock diet, particularly for the larger and presumably rarer prey taxa (euphausiids, chaetognaths, fish). We did not find any evidence that occupying a particular habitat was beneficial to young pollock, although other factors (e.g. bioenergetic advantage and predation refuge) that we did not examine here could have been more variable and critical to pollock survival. In a physically dynamic system such as the Pribilof Islands, age-0 pollock may need to continuously search for optimal conditions of high prey availability and low predation pressure. 相似文献
43.
Abstract. A mixed population of unicellular and colonial cyanobacteria was transferred into culture from a hypersaline helio-thermal pond in the vicinity of the Dead Sea. The entire complex of strains, incubated in Dead Sea water of varying salinity and temperature, showed a pronounced shift of the maximal growth from a salinity of 72 g l-1 at 30 o C up to 142 g 1-1 at 50 o C. Over the above range of salinities and temperatures, these cyanobacteria were capable of about four divisions per day, providing that any increase in salinity was coupled with the suitable increase in temperature. The above peculiar adaptation can explain the prominent success of this group of microorganisms in the extreme and unstable ecological conditions of hypersaline habitats. Amounts of slime accumulating in the cultures were proportional to the incubation temperature. 相似文献
44.
45.
James P. Cowen Miriam A. Bertram Edward T. Baker Richard A. Feely Gary J. Massoth Melanie Summit 《Deep Sea Research Part II: Topical Studies in Oceanography》1998,45(12):2713-2737
Event plumes form as episodic discharges of large volumes of hydrothermal solutions in response to magmatic diking/eruptive events. In consequence, event plumes represent the sudden injection of exploitable reduced chemical substrates, as well as inhibitory constituents, and likely induce successional changes in the microbial community structure and activity within event plume waters. In response to a major seismic event detected beginning 28 February 1996 at the northern Gorda Ridge, a series of three rapid response and follow-up cruises (GREAT 1, 2 and 3) were mounted over a period of three months. This report focuses on time-series measurements of manganese geomicrobial parameters in the two event plumes found in association with this seismic event.Scanning transmission electron microscopy, elemental microanalysis, and radioisotope (54Mn) uptake experiments were employed on samples collected from vertical and tow-yo casts from the three cruises. Numbers of bacteria and ratios of metal precipitating capsuled bacteria to total bacteria were greatest in the youngest (days old) plume, EP96A, found during GREAT 1; however, when normalized to the hydrothermal temperature anomaly, the greatest values were found in a second event plume, EP96B, discovered during GREAT 2 (up to 1 month old). Early capsule bacteria and particulate Mn distributions may have been influenced by entrainment of resuspended sediment, while those of the oldest (2–3 months) plume sample may have been subjected to preferential aggregation and particle settling. 相似文献
46.
Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta
Horst Uwe Keller Sonia Fornasier Stubbe F. Hviid Jörg Knollenberg Miriam Rengel Gabriele Cremonese Detlef Koschny Ekkehard Kührt Holger Sierks Cesare Barbieri Hans Rickman Michael F. A'Hearn Maria-Antonella Barucci Vania da Deppo Björn J.R. Davidsson Stefano Debei Fritz Gliem José J. Lopez Moreno Giampiero Naletto Angel Sanz Andrés 《Icarus》2007,187(1):87-103
The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain. 相似文献
47.
Silvia E. Ibarra-Obando Miriam Poumian-Tapia Hem Nalini Morzaria-Luna 《Estuaries and Coasts》2010,33(3):753-768
Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition
and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion.
Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal
marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals,
short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average
species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid
estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries. 相似文献
48.
Hydrogen sulfide in hydrothermal vent fluid at the 21°N site is enriched in 34S relative to Mid-Ocean Ridge basalts, probably by addition of H2S reduced from seawater sulfate by FeO-bearing basalt. Metalliferous sulfides are depleted in 34S relative to the fluid from which they apparently precipitated, the degree of depletion reflecting the microenvironment in which each mineral crystallised and/or kinetic effects. Isotopic compositions of coexisting sulfides in a basal mound are consistent with equilibration at around 445°C, though heating to such a high temperature seems unlikely. Similar sulfides in a black smoker and in a dead chimney are out of isotopic equilibrium at any temperature, apparently reflecting a complex series of replacement mineralisations and post-depositional oxidation, respectively. 相似文献
49.
Diagenetic effects on the distribution of uranium in live and Holocene corals from the Gulf of Aqaba
Boaz Lazar Rivka Enmar Miriam Bar-Matthews Mordechai Stein 《Geochimica et cosmochimica acta》2004,68(22):4583-4593
We investigated the effects of diagenetic alteration (dissolution, secondary aragonite precipitation and pore filling) on the distribution of U in live and Holocene coral skeletons. For this, we drilled into large Porites lutea coral-heads growing in the Nature Reserve Reef (NRR), northern Gulf of Aqaba, a site close to the Marine Biology Laboratory, Elat, Israel, and sampled the core material and porewater from the drill-hole. In addition, we sampled Holocene corals and beachrock aragonite cements from a pit opened in a reef buried under the laboratory grounds. We measured the concentration and isotopic composition of U in the coral skeletal aragonite, aragonite cements, coral porewater and open NRR and Gulf of Aqaba waters.Uranium concentration in secondary aragonite filling the skeletal pores is significantly higher than in primary biogenic aragonite (17.3 ± 0.6 compared to 11.9 ± 0.3 nmol · g−1, respectively). This concentration difference reflects the closed system incorporation of uranyl tri-carbonate into biogenic aragonite with a U/Ca bulk distribution coefficient (KD) of unity, versus the open system incorporation into secondary aragonite with KD of 2.4. The implication of this result is that continuous precipitation of secondary aragonite over ∼1000 yr of reef submergence would reduce the coral porosity by 5% and can produce an apparent lowering of the calculated U/Ca - SST by ∼1°C and apparent age rejuvenation effect of 7%, with no measurable effect on the calculated initial U isotopic composition.All modern and some Holocene corals (with and without aragonite cement) from Elat yielded uniform δ234U = 144 ± 5, similar to the Gulf of Aqaba and modern ocean values. Elevated δ234U values of ∼180 were measured only in mid-Holocene corals (∼5000 yr) from the buried reef. The values can reflect the interaction of the coral skeleton with 234U-enriched ground-seawater that washes the adjacent granitic basement rocks.We conclude that pore filling by secondary aragonite during reef submergence can produce small but measurable effects on the U/Ca thermometry and the U-Th ages. This emphasizes the critical importance of using pristine corals where the original mineralogy and porosity are preserved in paleooceanographic tracing and dating. 相似文献
50.
The walls of many deep-sea foraminiferal tests containabiogenic and biogenic, precipitated and agglutinated,components. Both environmental and genetic factorscan contribute to the great diversity in test form andcomposition in benthic foraminifera. Yet, smallspecimen size and the remoteness of the deep-seaenvironment have limited our ability to describe therelative influence of these biological and chemicalfactors. The use of fossilized foraminiferal tests aspaleo-indicators requires that we understand thecontrols on test composition. Test wall morphologyand composition were examined inforaminifera that colonized experimental substratesdeployed on a seamount in the central North Pacific. Three types of agglutinated forms were identified. Atriserial (Eggerella-like) and two-chambered(Hyperammina-like) form contained a Ca-rich(CaCO3) precipitate and the chamber walls of anencrusting two-chambered form was Ba-rich(BaSO4). We discuss the composition of thesebiologically precipitated minerals in the context ofthe environmental conditions during the life of theseforaminifera. 相似文献