Sedimentology of Quaternary perched springline and paludal tufas: criteria for recognition, with examples from Guadalajara Province, Spain   总被引：2，自引：0，他引：2  

Martyn Pedley  Juan Antonio González Martín†  Salvador Ordóñez Delgado‡  MªÁngeles García Del Cura§ 《Sedimentology》2003,50(1):23-44

Outcrop‐scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model. At the field scale, four end‐member models encompass the tufa continuum: (1) perched springline; (2) paludal; (3) fluvial; and (4) lacustrine tufas. Individual bed types can occur with variable dominance within several of these models, but one or more beds are characteristically dominant only within a single tufa model, so it can be differentiated from relatively isolated outcrop fragments. Two models (perched springline tufas and paludal tufas) are known in outline only in the literature despite being present within the Quaternary deposits of most karstic regions. Perched springline tufas generally form lobate, fan‐shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences. Mature deposits show a subhorizontal top and a steep face on the downflow side. The steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle. Tufa deposits lying downslope of the mounds are usually detrital in nature, especially if some dismantling of the mound has occurred. The relatively thin subhorizontal lobe‐top deposits commonly contain organic‐rich deposits. Paludal tufas develop predominantly in waterlogged valley bottom situations, where line‐sourced waters emerge from valley side and bottom aquifers. Lime mud precipitation predominates in these sites. Mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences. Tufa spring‐mounds may form where lesser volumes of water are involved. Individual tussocks (phytoherm cushions) of grasses and rushes are the most diagnostic feature of the model, but sapropels and peats may be intercalated. Diagenesis in both models is rapid. Lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation. The resulting highly porous and permeable fabrics remain fresh in Holocene tufas, but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits. Dissolution in many perched springline tufas is small scale. Many large cavities are primary, but with later coatings of speleothems. Early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction.  相似文献   

Excursion to Swanage,Lulworth Cove,and Bournemouth: Whitsuntide,May 14th to 18th, 1910     

F. Hovenden  H.W. Monckton  W. Theophilus Ord  A. Smith Woodward  W.P.D. Stebbing 《Proceedings of the Geologists' Association. Geologists' Association》1910,21(10):510-IN3

  相似文献   

Distribution and abundance of the Pacific sardine (Sardinops sagax) in the Gulf of California and their relation with the environment   总被引：1，自引：0，他引：1  

Manuel O. Nevrez-Martínez  Daniel Lluch-Belda  Miguel A. Cisneros-Mata  J. Pablo Santos-Molina  Ma. De los Angeles Martínez-Zavala  Salvador E. Lluch-Cota 《Progress in Oceanography》2001,49(1-4)

In 1989–90 the small pelagic fishery of the Gulf of California began to show a very marked decline in the catch of its main component, the Pacific sardine (Sardinops sagax). The catch plummeted from 292,000 t in 1988–89 to 7000 t in 1991–92 and 1992–93. This caused a serious economic crisis in the local fishery fleet and industry, and resulted in the loss of 3000 jobs. In 1993–94 the fishery showed signs of recovery as the abundance of the Pacific sardine began to recover. The catch improved to 128,000 t in 1993–94 and further to 215,000 t in 1996–97. In trying to understand this great variability, we proposed the hypothesis that the distribution and the abundance of the Pacific sardine of the Gulf of California is determined by the wind patterns (upwelling) and the sea surface temperature. The results of analyzing data from 25 cruises showed the period of low relative abundance between 1990 and 1993 and one of high abundance between 1993 and 1996. The range of the sardine's distribution expanded as its abundance increased and contracted when abundances were low. The relationship between the abundances of the sardine and environmental variables proved to nonlinear and bell-shaped. The adjusted pattern explained 78.8% of the variability of the sardine abundance. The highest abundance are produced by moderate upwelling (13–18 m³s⁻¹ per 10 m of coastline) and sea surface temperatures of between 19°C and 25°C.  相似文献   

Storm Dispersal of Volcanogenic Sands from Buenos Aires, Where Heavy-Metal Concentrations Are Heavy-Mineral Segregations     

Federico I. Isla  Salvador Aliotta 《Marine Georesources & Geotechnology》1999,17(4):357-370

The southeastern beaches and inner shelf of the Buenos Aires coastline are dominated by storms coming from the south and southeast. Erosion is dominant at the coastal cliffs and abrasion platforms, while deposition is extended below the 9-m contour depth. In relation to sand abundance on the inner shelf, there is a northward transition between shelly sand sheets, a fine-sand ribbon field, and sand ridges with oblique megaripples. Side-scan records indicate the selective sorting processes that lead to grain size diminishing to the north, and heavy-mineral enrichment, either at the beach or on the shelf. These storm-induced effects should be considered when evaluating placers on the inner shelf or monitoring the heavy-metal content in sediments. Two-way analyses of variance (ANOVA) tests were used to establish the grain-size effects on heavy-metal analysis.  相似文献   

Morphodynamics and seismostratigraphy of a deep hole at tidal channel confluence     

Silvia Susana Ginsberg  Salvador Aliotta  Guillermo O. Lizasoain   《Geomorphology》2009,104(3-4):253-261

  相似文献   

Polarimetric profiles of 27 millisecond pulsars     

S. M. Ord  W. van Straten  A. W. Hotan  M. Bailes 《Monthly notices of the Royal Astronomical Society》2004,352(3):804-814

  相似文献   

Analysis of housing price by means of STAR models with neighbourhood effects: a Bayesian approach     

Asuncion Beamonte  Pilar Gargallo  Manuel Salvador 《Journal of Geographical Systems》2010,12(2):227-240

In this paper, we extend the Bayesian methodology introduced by Beamonte et al. (Stat Modelling 8:285–311, 2008) for the estimation and comparison of spatio-temporal autoregressive models (STAR) with neighbourhood effects, providing a more general treatment that uses larger and denser nets for the number of spatial and temporal influential neighbours and continuous distributions for their smoothing weights. This new treatment also reduces the computational time and the RAM necessities of the estimation algorithm in Beamonte et al. (Stat Modelling 8:285–311, 2008). The procedure is illustrated by an application to the Zaragoza (Spain) real estate market, improving the goodness of fit and the outsampling behaviour of the model thanks to a more flexible estimation of the neighbourhood parameters.  相似文献   

Evidence of site amplification from ground motion of the last two large crustal earthquakes in central-western Argentina     

Alvarado  Patricia  Christiansen  Rodolfo  Gregori  Salvador Daniel  Saez  Mauro 《Natural Hazards》2020,102(3):1011-1031

Natural Hazards - The present study has investigated site amplification effects from the analysis of peak ground accelerations (PGA) and spectral accelerations (SA) of the last two major crustal...  相似文献   

An interface-condition substitution strategy for theoretical study of dissolution-timescale reactive infiltration instability in fluid-saturated porous rocks     

Chongbin Zhao  Bruce E. Hobbs  Alison Ord 《国际地质力学数值与分析法杂志》2019,43(8):1576-1593

A theoretical study of reactive infiltration instability is conducted on the dissolution timescale. In the present theoretical study, the transient behavior of a dissolution-timescale reactive infiltration system needs to be considered, so that the upstream region of the chemical dissolution front should be finite. In addition, the chemical dissolution front of finite thickness should be considered on the dissolution timescale. Owing to these different considerations, it is very difficult, even in some special cases, to derive the first-order perturbation solutions of the reactive infiltration system on the dissolution timescale. To overcome this difficulty, an interface-condition substitution strategy is proposed in this paper. The basic idea behind the proposed strategy is that although the first-order perturbation equations in the downstream region cannot be directly solved in a purely mathematical manner, they should hold at the planar reference front, which is the interface between the upstream region and the downstream region. This can lead to two new equations at the interface. The main advantage of using the proposed interface-condition substitution strategy is that through using the original interface conditions as a bridge, the perturbation solutions for the dimensionless acid concentration, dimensionless Darcy velocity, and their derivatives involved in the two new equations at the interface can be evaluated just by using the obtained analytical solutions in the upstream region. The proposed strategy has been successfully used to derive the dimensionless growth rate, which is the key issue associated with the theoretical study of dissolution-timescale reactive infiltration instability in fluid-saturated porous rocks.  相似文献   

Faulting and fluid flow in porous rocks and sediments: implications for mineralisation and other processes     

A. C. Barnicoat  H. A. Sheldon  A. Ord 《Mineralium Deposita》2009,44(6):705-718

Faults in sedimentary rocks can act as fluid pathways or barriers to flow and display a range of deformation styles. These features can be explained by behaviours observed in deformation experiments on sedimentary rocks that reveal a transition from dilatant brittle faulting and permeability enhancement to cataclasis and permeability reduction, with increasing porosity, grain size and confining pressure. This transition implies that faults in sedimentary rocks are unlikely to act as fluid pathways shallower than ~3 km, unless the sediments have undergone early cementation, or have been exposed following burial and uplift. This has important implications for many geological processes, including fluid circulation in geothermal systems, formation of sediment-hosted mineral deposits and earthquakes in subduction zones. Stratiform Zn–Pb deposits that have been interpreted as syngenetic, seafloor deposits could instead be interpreted as early epigenetic deposits representing the depth at which faults change from fluid pathways to barriers.  相似文献