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91.
Javier García-Veigas Luis Gibert Dioni I. Cendón David Artiaga Hugo Corbí Jesús M. Soria Tim K. Lowenstein Enrique Sanz 《Basin Research》2020,32(5):916-948
The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO4 isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out. 相似文献
92.
Houda El Kerni Hasnaa Chennaoui Aoudjehane David Baratoux Mohammed Aoudjehane Andr Charrire Hassan Ibouh Pierre Rochette Yoann Quesnel Minoru Uehara Thomas Kenkmann Gerwin Wulf Michael Poelchau Van Binh Nguyen Maria Aboulahris Samira Makhoukhi Georges Aumaître Didier Bourls Karim Keddadouche 《Meteoritics & planetary science》2019,54(10):2483-2509
Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km2) and 1:15,000 (2.25 km2) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1‐2 and br2) could be produced by erosion–sedimentation–consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31°59′13.73?N, 5°30′55.14?W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4–4.2 km in diameter. Cosmogenic nuclide data (36Cl) constrain the local erosion rates between 220 ± 22 m Ma?1 and 430 ± 43 m Ma?1. These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3–1.9 Ma. This age is older than the Agoudal iron meteorite age (105 ± 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data. 相似文献
93.
Sidney Van Den Bergh 《Astronomische Nachrichten》1979,300(5):225-228
It is shown that there is no significant dependence of the frequency with which barred spirals occur on environment. Therefore, the difference between normal and barred spirals must be largely due to initial conditions. The excess of early type galaxie (in particular ellipticals and SO's) among the statistically selected binary samples is probably caused by a contamination by cluster members and will therefore result in a systematic overestimate of the masses of binary galaxies. The large fraction of multiple first-ranked galaxies found in rich clusters of BAUTZ -MORGAN type I is surprising in view of tidal effects and dynamical friction, which should lead to the destruction of such massive binary systems on a time scale much shorter than the age of the Universe. 相似文献
94.
G. De Backer M. Vantorre C. Beels J. De Pré S. Victor J. De Rouck C. Blommaert W. Van Paepegem 《Applied Ocean Research》2009,31(3):143-156
The results of an elaborate experimental investigation on bottom slamming of axisymmetric objects are presented. Drop tests have been performed on a hemisphere and two conical shapes with different deadrise angles. The test setup is designed so as to prevent small rotations of the test objects which cause scatter in the measurement data. The pressure distribution and evolution as well as the body motion parameters are measured during impact. By means of a high speed camera the water uprise is visualized and the wetting factor is determined for the cones. The results are compared with a three-dimensional asymptotic theory for axisymmetric rigid bodies with constant entry velocity. The ratio between the registered peak pressures and the asymptotic theory are in accordance with comparable experiments in the literature. The asymptotic theory, however, is found to be quite conservative, since the measured peak pressure levels appear to be approximately 50% to 75% of the theoretical levels. 相似文献
95.
96.
Els Verfaillie Steven Degraer Kristien Schelfaut Wouter Willems Vera Van Lancker 《Estuarine, Coastal and Shelf Science》2009
Mapping ecologically relevant zones in the marine environment has become increasingly important. Biological data are however often scarce and alternatives are being sought in optimal classifications of abiotic variables. The concept of ‘marine landscapes’ is based on a hierarchical classification of geological, hydrographic and other physical data. This approach is however subject to many assumptions and subjective decisions. 相似文献
97.
Stphane Pochat Sbastien Castelltort Gaël Choblet Jean Van Den Driessche 《Marine and Petroleum Geology》2009,26(8):1350-1364
Growth strata are used to determine the kinematics of synsedimentary structures such as faults. Classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments. This has lead many previous works to identify a cyclic activity for growth faults. Here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the Niger delta. We show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip. Suspended-load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers. Bedload processes result in a preferential thickening of sand layers in the hanging wall. These high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved. Our study emphasizes the important conclusion that stable fault growth, and related displacement rates, can appear to be punctuated when viewed at the scale of sedimentary cycles. It follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles. 相似文献
98.
Reef development varies considerably around the high, raised‐limestone islands of the Commonwealth of the Northern Mariana Islands (CNMI). Here we examine the modern assemblages at 30 sites for coral composition, colony density, colony size, and fidelity. We defined four reef types and hypothesize the presence of environmentally driven ecological stasis, whereby the environment continuously selects for coral species membership, defines colony sizes, and over time creates the noted reef types. Our results show that constructional spur‐and‐groove reefs supported significantly larger coral‐colony sizes and higher coral species richness compared with high‐relief interstitial framework, low‐relief incipient, and non‐constructional coral assemblages. Non‐constructional reefs supported much smaller coral colony sizes, despite similar population densities, and were consistently found in association with high wave exposure. The distinct coral assemblages found on interstitial framework and low‐relief incipient reefs were not affiliated with any wave exposure regime, but were located adjacent to large watersheds and on islands with unique geological history. These assemblages were nested within the spur‐and‐groove species pool. Overall, modern coral cover was well predicted by bathymetric slope and watershed size, while species richness was additively influenced by two proxies of pollution, suggesting the latter is better suited for establishing management targets. In contrast with previous studies that suggested modern assemblages were biologically controlled in the CNMI, we show reef assemblages and reef development are highly influenced by long‐term environmental forcing. 相似文献
99.
T. Van Engeland K. Soetaert A. Knuijt R.W.P.M. Laane J.J. Middelburg 《Estuarine, Coastal and Shelf Science》2010
Dissolved organic nitrogen (DON) dynamics in the North Sea was explored by means of long-term time series of nitrogen parameters from the Dutch national monitoring program. Generally, the data quality was good with little missing data points. Different imputation methods were used to verify the robustness of the patterns against these missing data. No long-term trends in DON concentrations were found over the sampling period (1995–2005). Inter-annual variability in the different time series showed both common and station-specific behavior. The stations could be divided into two regions, based on absolute concentrations and the dominant times scales of variability. Average DON concentrations were 11 μmol l−1 in the coastal region and 5 μmol l−1 in the open sea. Organic fractions of total dissolved nitrogen (TDN) averaged 38 and 71% in the coastal zone and open sea, respectively, but increased over time due to decreasing dissolved inorganic nitrogen (DIN) concentrations. In both regions intra-annual variability dominated over inter-annual variability, but DON variation in the open sea was markedly shifted towards shorter time scales relative to coastal stations. In the coastal zone a consistent seasonal DON cycle existed with high values in spring–summer and low values in autumn–winter. In the open sea seasonality was weak. A marked shift in the seasonality was found at the Dogger Bank, with DON accumulation towards summer and low values in winter prior to 1999, and accumulation in spring and decline throughout summer after 1999. This study clearly shows that DON is a dynamic actor in the North Sea and should be monitored systematically to enable us to understand fully the functioning of this ecosystem. 相似文献
100.
With the UK Marine Bill promoting the creation of a network of marine protected areas and similar commitments in other countries there is a need for tools to assist in their design and management. Although physical science often drives designation, the implementation of marine protected areas also encompasses political and socio-economic issues. This paper focuses on one tool in the armoury of decision-makers: choice experiments. It illustrates its application to the quantification of aspects of socio-economic value not readily incorporated into the evaluation of the costs and benefits of marine protected areas utilising cold-water deep coral reefs off the Republic of Ireland. 相似文献