Ontogeny ofHybocrinus punctatus (Miller and Gurley), an ordovician crinoid     

James C. Brower  Julia Veinus 《Mathematical Geosciences》1975,7(2):129-147

Relative growth of the Ordovician crinoid Hybocrinus punctatus (Miller and Gurley)was studied using regression, correlation, and R-mode factor analysis. Systematic growth gradients of both initial intercepts and slopes existed throughout the calyx. Development of a single plate was best correlated with growth of the directly adjacent plates and was less well correlated with that of more distant plates. A total of 86 percent of the R-mode correlation matrix variance is associated with overall size increase of all dimensions and size-correlated shape changes. Most of the remaining variance is linked with divergent growth of small groups of specimens with respect to various shape parameters.  相似文献   

The statistical zap versus the shotgun approach     

James C. Brower  Julia Veinus 《Mathematical Geosciences》1974,6(4):311-332

Multivariate analysis is used in the search for one or more types of structure. The statistical zap applies a single method to determine one preselected type of structure. Several zaps suffice to ascertain several types of structure. The statistical shotgun represents an alternative approach. Here, a series of methods is applied to the data with the intent of ascertaining all possible types of structure that may exist. If strong structure is present, an appropriate zap will probably reveal it, and a variety of techniques will determine the same general structure. If only the main structure is required, the zap is adequate. In this situation, the shotgun will display a basic consistency which is at least reassuring. However, zaps may fail to detect a more subtle secondary structure of geological interest which will be displayed by the shotgun. For weakly structured data, a zap will only determine one type of structure but the shotgun reveals all. Study of the ontogeny of Parastylonurus myops(Clarke), a Lower Silurian eurypterid from New York (USA) shows the virtues of the statistical shotgun.  相似文献   

Climate variability,snow, and physiographic controls on storm hydrographs in small forested basins,western Cascades,Oregon     

Reed M. Perkins  Julia A. Jones 《水文研究》2008,22(25):4949-4964

Large floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (<1 km²) basins with old‐growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30‐year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (<150 mm precipitation), controlling for precipitation, the presence of a snowpack on near‐saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near‐saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain‐on‐snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain‐on‐snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain‐on‐snow floods at the large basin scale. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Improving seasonal matching in the STARS model by adaptation of the resampling technique     

Julia Lutz  Friedrich-Wilhelm Gerstengarbe 《Theoretical and Applied Climatology》2015,120(3-4):751-760

  相似文献   

Geomorphological,stratigraphic and geochronological evidence of fast Pleistocene coastal uplift in the westernmost part of the Corinth Gulf Rift (Greece)     

N. Palyvos  M. Mancini  D. Sorel  F. Lemeille  D. Pantosti  R. Julia  M. Triantaphyllou  P.‐M. De Martini 《Geological Journal》2010,45(1):78-104

Rapid extension and active normal faulting in the western extremity of the Corinth Gulf are accompanied by fast coastal uplift. We investigate Pleistocene uplift west of Aigion, by attempting to date remains of marine terraces and sedimentary sequences by calcareous nannoplankton and U‐series analyses. Net uplift initiated recently, due to abandonment of an older rift‐bounding fault zone and increase in activity on the presently active, coastal fault zone. This change apparently coincides with an abrupt slow down (or, termination) of secondary fault block tilting within the broader hangingwall block of the older zone, indicated by an angular unconformity that dates in the early part of MIS10 (∼390–350 ka BP, preferably, in the earlier part of this period). Net uplift driven by the coastal zone resulted in the formation of MIS9c (330 ka) and younger terraces. The formation of the unconformity and the initiation of net uplift coincide temporally with a ∼300–400 ka unconformity recognized by recent studies in a wide area offshore Aigion i.e. they could be part of an evolutionary event that affected the entire western part of the Corinth Rift or, a large area therein. Uplift rate estimates at four locations are discussed with reference to the morphotectonic context of differential uplift of secondary fault blocks, and the context of possible increase in uplift rate with time. The most reliable and most useful estimate for uplift rate at the longitude of the studied transect is 1.74–1.85 mm/year (time‐averaged estimate for the last ∼240 ka, based on calcareous nannoplankton and sequence‐stratigraphic interpretation). Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

From whom Bells tolls: Reclassifying Bells among CR chondrites and implications for the formation conditions of CR parent bodies     

Yves Marrocchi  Emmanuel Jacquet  Julia Neukampf  Johan Villeneuve  Michael E. Zolensky 《Meteoritics & planetary science》2023,58(2):195-206

The ungrouped carbonaceous chondrite (CC) Bells has long been considered petrographically similar to CM chondrites based on its matrix abundance and degree of aqueous alteration, but also shows significant isotopic affinities to CR chondrites. Its taxonomic status is thus important for clarifying the relationship of the CRHB (formerly “CR”) clan with other CCs. In this study, we measured the oxygen isotopic compositions of olivines in type I chondrules and isolated olivine grains in Bells. Bells olivines mostly have ∆¹⁷O > −4‰, similar to CR chondrites but unlike other CCs that are rich in refractory inclusions, in which chondrules are generally richer in ¹⁶O. Therefore, Bells is a CR chondrite (albeit an anomalous one), most similar to the rare, matrix-rich CRs like Al Rais. These chondrites (i) may not necessarily derive from the same primary parent body as mainstream CRs, (ii) bear witness to significant variations of the matrix/chondrule ratio within the CRHB clan, and (iii) may be a good analog for samples retrieved by the space mission OSIRIS-REx.  相似文献   

Pockmarks on either side of the Strait of Gibraltar: formation from overpressured shallow contourite gas reservoirs and internal wave action during the last glacial sea-level lowstand?     

Ricardo León  Luis Somoza  Teresa Medialdea  Francisco Javier González  Carmen Julia Gimenez-Moreno  Raúl Pérez-López 《Geo-Marine Letters》2014,34(2-3):131-151

Integrating novel and published swath bathymetry (3,980 km²), as well as chirp and high-resolution 2D seismic reflection profiles (2,190 km), this study presents the mapping of 436 pockmarks at water depths varying widely between 370 and 1,020 m on either side of the Strait of Gibraltar. On the Atlantic side in the south-eastern Gulf of Cádiz near the Camarinal Sill, 198 newly discovered pockmarks occur in three well localized and separated fields: on the upper slope (n=14), in the main channel of the Mediterranean outflow water (MOW, n=160), and on the huge contourite levee of the MOW main channel (n=24) near the well-known TASYO field. These pockmarks vary in diameter from 60 to 919 m, and are sub-circular to irregularly elongated or lobate in shape. Their slope angles on average range from 3° to 25°. On the Mediterranean side of the strait on the Ceuta Drift of the western Alborán Basin, where pockmarks were already known to occur, 238 pockmarks were identified and grouped into three interconnected fields, i.e. a northern (n=34), a central (n=61) and a southern field (n=143). In the latter two fields the pockmarks are mainly sub-circular, ranging from 130 to 400 m in diameter with slope angles averaging 1.5° to 15°. In the northern sector, by contrast, they are elongated up to 1,430 m, probably reflecting MOW activity. Based on seismo-stratigraphic interpretation, it is inferred that most pockmarks formed during and shortly after the last glacial sea-level lowstand, as they are related to the final erosional discontinuity sealed by Holocene transgressive deposits. Combining these findings with other existing knowledge, it is proposed that pockmark formation on either side of the Strait of Gibraltar resulted from gas and/or sediment pore-water venting from overpressured shallow gas reservoirs entrapped in coarse-grained contourites of levee deposits and Pleistocene palaeochannel infillings. Venting was either triggered or promoted by hydraulic pumping associated with topographically forced internal waves. This mechanism is analogous to the long-known effect of tidal pumping on the dynamics of unit pockmarks observed along the Norwegian continental margin.  相似文献   

Natural variability of summer rainfall over China in HadCM3   总被引：1，自引：0，他引：1  

Yonghui Lei  Brian Hoskins  Julia Slingo 《Climate Dynamics》2014,42(1-2):417-432

Summer rainfall over China has shown decadal variability in the past half century, which has resulted in major north–south shifts in rainfall with important implications for flooding and water resource management. This study has demonstrated how multi-century climate model simulations can be used to explore interdecadal natural variability in the climate system in order to address important questions around recent changes in Chinese summer rainfall, and whether or not anthropogenic climate change is playing a role. Using a 1,000-year simulation of HadCM3 with constant pre-industrial external forcing, the dominant modes of total and interdecadal natural variability in Chinese summer rainfall have been analysed. It has been shown that these modes are comparable in magnitude and in temporal and spatial characteristics to those observed in the latter part of the twentieth century. However, despite 1,000 years of model simulation it has not been possible to demonstrate that these modes are related to similar variations in the global circulation and surface temperature forcing occurring during the latter half of the twentieth century. This may be in part due to model biases. Consequently, recent changes in the spatial distribution of Chinese summer rainfall cannot be attributed solely to natural variability, nor has it been possible to eliminate the likelihood that anthropogenic climate change has been the driving factor. It is more likely that both play a role.  相似文献   

Hydrologic responses to climate change: considering geographic context and alternative hypotheses     

Julia A. Jones 《水文研究》2011,25(12):1996-2000

  相似文献   

A search for distant radio galaxies from SUMSS and NVSS – III. Radio spectral energy distributions and the z–α correlation     

Ilana J. Klamer  Ron D. Ekers  Julia J. Bryant  Richard W. Hunstead  Elaine M. Sadler  Carlos De Breuck 《Monthly notices of the Royal Astronomical Society》2006,371(2):852-866

  相似文献