Sea‐level reconstructions from the Peri‐Vocontian Zone (South‐east France) point to Valanginian glacio‐eustasy     

BENJAMIN GRÉSELLE  BERNARD PITTET 《Sedimentology》2010,57(7):1640-1684

The Valanginian is a period of global environmental change as illustrated by sedimentary, palaeontological, geochemical and climatic perturbations. A production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions. During the same time interval, a major positive excursion in δ¹³C, the Weissert Event, suggests perturbations of the carbon cycle from the latest Early Valanginian to the Early Hauterivian. In order to better understand the link between these changes, sea‐level fluctuations have been reconstructed in detail from the Middle Berriasian to the earliest Hauterivian. Sections from the Peri‐Vocontian Zone (South‐east France) have been investigated because of the good quality of outcrops on the carbonate platforms, their margins and in the Vocontian Basin. Sections ranging from the most proximal zone (Swiss Jura) to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy, and correlated at high resolutions. Using the identified small, medium and large‐scale sequences as well as depositional geometries, sea‐level fluctuations were reconstructed. Two main trends are evidenced during the studied interval: (i) the peak amplitude (magnitude) of the sea‐level fluctuations increased gradually from the Middle Berriasian to the Early Valanginian, and reached a maximum (more than 50 m) from the middle Early Valanginian to the Valanginian/Hauterivian boundary; and (ii) sea‐level variations were quite symmetrical during the Late Berriasian, slightly asymmetrical during the Early Valanginian and strongly asymmetrical (fast sea‐level rise, slow fall) from the latest Early Valanginian to the earliest Hauterivian. Moreover, three orders of sea‐level fluctuations were recognized in the sedimentary rocks of the Peri‐Vocontian Zone. Platform‐basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea‐level variations, mainly by the two eccentricity cycles of 100 and 400 kyr. The increase in the amplitude of the sea‐level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the Early Valanginian. Fast transgressions followed by slower regressions would correspond to waxing and waning of high‐latitudinal ice during most of the Valanginian, especially from the latest Early Valanginian to the latest Late Valanginian. Glacio‐eustatic sea‐level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the Valanginian.  相似文献   

Sequential and climatic framework of the growth and demise of a carbonate platform: implications for the peritidal cycles (Late Jurassic,North‐eastern France)     

CÉDRIC CARPENTIER  BERNARD LATHUILIÈRE  SERGE FERRY 《Sedimentology》2010,57(4):985-1020

The Middle Oxfordian of the eastern Paris Basin constitutes a remarkable example of the growth and demise of a carbonate platform. Fischer plots, sedimentary and diagenetic features allow the identification of four depositional cycles (S5 to S8) in the Transversarium Zone; they are inserted in a lower frequency cycle of increased/decreased accommodation space (SoIII). The long‐term period of accommodation creation occurred during the older S5 and S6 cycles, the maximum accommodation zone being located in the lower part of the S6 cycle. This high accommodation period was tectonically controlled and was coeval with local distensive activity of a Hercynian fault. A major minimum accommodation zone exists during the S8 cycle. At that time, the platform was isolated and presented both a windward and a leeward margin. The growth of the platform was favoured by a warm and arid climate, oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea‐level. These palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material. The death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea‐level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate. In the eastern Paris Basin, during the Middle Oxfordian, the parasequences are ordered and present ‘greenhouse’ characteristics. In contrast, at the beginning of the S8 cycle, the randomness in the thickness of contiguous parasequences increased. Decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch‐down parasequences.  相似文献   

Symplectic Mapping for Trojan-Type Motion in the Elliptic Restricted Three-Body Problem     

Zsolt Sándor  Bálint Érdi 《Celestial Mechanics and Dynamical Astronomy》2003,86(4):301-319

A symplectic mapping for Trojan-type motion has been developed in the secularly changing elliptic restricted three-body problem. The mapping describes well the characteristics of Trojan-type dynamics at small eccentricities. By using this mapping the boundary of the stability region has been studied for different values of the initial eccentricities of hypothetical Jupiter's Trojans. It has been found that in the secularly changing elliptic case the chaotic diffusion at the border of the stability region is stronger than simply in the elliptic case. An explanation of this observation might be the destruction of the chain of islands of the 13:1 secondary resonance between the short and long period component of the Trojan-like motion, caused possibly by the indirect perturbations of Saturn.  相似文献   

Auroras Observed in Portugal in Late 18th Century Obtained from Printed and Manuscript Meteorological Observations     

JosÉ M. Vaquero  Ricardo M. Trigo 《Solar physics》2005,231(1-2):157-166

We present a new catalogue of observations of the aurora borealis at Lisbon, i.e., at low-latitudes, in the late 18th century by Jacob Præ torius and Henrique Schulze, two German artillery officers. Dates of 18 auroras compiled by Præ torius and Schulze are compared with those published in other catalogues for that period. The number of annual auroras observed by the two Germans is then compared with two indices of solar activity showing a very good level of consistency between all time series. Finally, we have assessed the number of auroras observed taking into consideration the phase of the lunar cycle and the geomagnetic latitude of Lisbon.  相似文献   

C/1995 O1 (Hale-Bopp): Gas Production Curves And Their Interpretation     

BOCKELÉE-MORVAN  D.  RICKMAN  H. 《Earth, Moon, and Planets》1997,79(1-3):55-77

The discovery of C/1995 O1 (Hale-Bopp) at 7 AU from the Sun provided the first opportunity to follow the activity of a bright comet over a large range of heliocentric distances r_h. Production rates of a number of parent molecules and daughter species have been monitored both pre- and postperihelion. CO was found to be the major driver of the activity far from the Sun, surpassed by water within 3 AU whose production rate reached 10³¹ s⁻¹ at perihelion. Gas production curves obtained for various species show several behaviours with r_h. Gas production curves contain important information concerning the physical state of cometary ices, the structure of the nucleus and all the processes taking place inside the nucleus leading to outgassing. They are relevant to the study of several other phenomena such as the sublimation from icy grains, dust mantling or seasonal effects. For some species, such as H₂CO or HNC, they permit to constrain their origin in the coma. We discuss models of subsurface gas production in distant comets and predictions of how such a source may vary as the comet moves along its orbit, approaching perihelion and receding again. Features in the observed gas production curves of comet Hale-Bopp are generally interpretable in terms of either subsurface production (typical example: CO at large r_h) or free sublimation (typical example: H₂O). Possible implications for the vertical stratification of the cometary ices are reviewed, and preference is found for a model with crystallization of amorphous ice close to the nuclear surface. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Geomorphology and Geoarchaeology: cross-contribution     

Éric Fouache  Kosmas Pavlopoulos  Patricia Fanning 《Geodinamica Acta》2013,26(5-6):207-208

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Newly identified “Tunnunik” impact structure,Prince Albert Peninsula,northwestern Victoria Island,Arctic Canada     

Keith DEWING  Brian R. PRATT  Thomas HADLARI  Tom BRENT  Jean BÉDARD  Robert H. RAINBIRD 《Meteoritics & planetary science》2013,48(2):211-223

Regional geological mapping of the glaciated surface of northwestern Victoria Island in the western Canadian Arctic revealed an anomalous structure in otherwise flat‐lying Neoproterozoic and lower Paleozoic carbonate rocks, located south of Richard Collinson Inlet. The feature is roughly circular in plan view, approximately 25 km in diameter, and characterized by quaquaversal dips of approximately 45°, decreasing laterally. The core of the feature also exhibits local vertical dips, low‐angle reverse faults, and drag folds. Although brecciation was not observed, shatter cones are pervasive in all lithologies in the central area, including 723 Ma old dikes that penetrate Neoproterozoic limestones. Their abundance decreases distally, and none was observed in surrounding, horizontally bedded strata. This circular structure is interpreted as a deeply eroded meteorite impact crater of the complex type, and the dipping strata as the remnants of the central uplift. The variation in orientation and shape of shatter cones point to variably oriented stresses with the passage of the shock wave, possibly related to the presence of pore water in the target strata as well as rock type and lithological heterogeneities, especially bed thickness. Timing of impact is poorly constrained. The youngest rocks affected are Late Ordovician (approximately 450 Ma) and the impact structure is mantled by undisturbed postglacial sediments. Regional, hydrothermal dolomitization of the Ordovician limestones, possibly in the Late Devonian (approximately 360 Ma), took place before the impact, and widespread WSW–ENE‐trending normal faults of probable Early Cretaceous age (approximately 130 Ma) apparently cross‐cut the impact structure.  相似文献   

THE STORM OF NOVEMBER 1826 IN THE CANARY ISLANDS: POSSIBLY A TROPICAL CYCLONE?     

JOSÉ BETHENCOURT‐GONZÁLEZ  PEDRO DORTA‐ANTEQUERA 《Geografiska Annaler: Series A, Physical Geography》2010,92(3):329-337

This work analyses a storm that occurred in the Canary Islands early in November 1826. Through a study based on historical climate data, some of the adverse effects of the storm are described and some of the possible causes are discussed. The main goal of this work is to establish an approximate reconstruction of this historical event which will allow us to compare it to a recent meteorological event that had a great impact on the archipelago: “Tropical Storm Delta”, in November 2005. Studying and reviewing the origin of the 1826 storm verifies the hypothesis that extremely violent perturbations have not only occurred in the Canaries on other occasions, but that these past events were also more intense and had more serious consequences than Delta. Therefore, the idea that other tropical perturbations have occurred in the region of the Canary Islands before Delta is presented.  相似文献   

Mid-Cretaceous hydrothermal vents and authigenic carbonates in a transform margin, Basque-Cantabrian Basin (western Pyrenees): a multidisciplinary study     

LUIS M. AGIRREZABALA 《Sedimentology》2009,56(4):969-996

A comprehensive study of authigenic carbonates and associated fauna in Late Albian organic‐rich, deep‐water deposits (the Black Flysch Group) reveals that carbonate precipitation was a by‐product of the anaerobic oxidation of hydrocarbon‐rich hydrothermal fluids. The authigenic carbonates are exposed along the Kardala and Alkolea sea cliffs in the western Pyrenees. The two vent carbonates occur 1 km apart adjacent to the synsedimentary, right‐reverse Mutriku fault, but in contrasting structural domains: the Kardala carbonates occur on a structural ridge (hangingwall) and the Alkolea carbonates are positioned at the base of an erosional scarp (folded downward footwall). The similarity in pattern of the carbonate phases and complex paragenetic events for both vent precipitates implies that hydrothermal fluid generation processes and pore‐water evolution during early and late diagenesis were similar. Nevertheless, a comparison of the geochemistry, fossil fauna and morphology of carbonate structures of both precipitates suggests that the vented hydrocarbon type, flow intensity and temperature of hydrothermal fluids were different. At the Kardala vent, intense focused flow of hot (up to 109 °C), oil‐rich fluids were generated, allowing the development of a relatively abundant chemosynthesis‐based fauna. In contrast, at the Alkolea vent, diffuse flows of warm, thermogenic methane‐rich fluids were expelled to the sea floor and no chemosynthetic fauna developed. These differences are related to the contrasting structural setting of each locality. Similar δ¹³C_org values for both pyrobitumen‐fills and host unit organic matter suggest that the hydrocarbon source was the Black Flysch Group. Contact alteration of these organic‐rich sediments by syndepositional hydrothermal fluids generated hydrothermal petroleum (oil and gas hydrocarbons) which probably migrated updip to the sea floor by contemporary compression tectonics.  相似文献   

Braided rivers within an arid alluvial plain (example from the Lower Triassic,western German Basin): recognition criteria and expression of stratigraphic cycles     

S. BOURQUIN  F. GUILLOCHEAU  S. PÉRON 《Sedimentology》2009,56(7):2235-2264

Based on a detailed sedimentological analysis of Lower Triassic continental deposits in the western Germanic sag Basin (i.e. the eastern part of the present‐day Paris Basin: the ‘Conglomérat basal’, ‘Grès vosgien’ and ‘Conglomérat principal’ Formations), three main depositional environments were identified: (i) braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits; (ii) marginal erg (i.e. braided rivers, aeolian dunes and aeolian sand‐sheets); and (iii) playa lake (an ephemeral lake environment with fluvial and aeolian sediments). Most of the time, aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity, such as wind‐worn pebbles (ventifacts), sand‐drift surfaces and aeolian sand‐sheets. In such arid continental environments, stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension. Elementary stratigraphic cycles, i.e. the genetic units, have been identified for the three main continental environments: the fluvial type, fluvial–aeolian type and fluvial/playa lake type. At the time scale of tens to hundreds of thousands of years, these high‐frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland. Lower Triassic deposits from the Germanic Basin are preserved mostly in endoreic basins. The central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the Hercynian (Variscan)–Appalachian Mountains. Consequently, a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition, whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments.  相似文献