Regressive Events Research Articles

Diagenetic alterations related to marine transgression and regression in fluvial and shallow marine sandstones of the Triassic Buntsandstein and Keuper sequence, the Paris Basin, France

The distribution of diagenetic alterations in Triassic fluvio-deltaic, quartzarenitic to sublitharenitic, lowstand systems tract (LST) sandstones of the Grès á Voltzia Formation, anastomosing fluvial, quartzarenitic transgressive systems tract (TST) sandstones of the Grès á Roseaux Formation, and shallow marine, quartzarenitic to sublitharenitic, TST sandstones of the Grès Coquiller Formation, the Paris Basin (France), can be linked to transgression and regression events, and thus to the sequence stratigraphic context. Near-surface eogenetic alterations, which display a fairly systematic link to the depositional facies and sequence stratigraphic framework, include: (i) cementation by meteoric water calcite ( δ 18O=−8.9‰ and δ 13C=−9.1‰) in the fluvio-deltaic, LST sandstones, (ii) cementation by mixed marine–meteoric calcite ( δ 18O=−5.3‰ to −2.6‰ and δ 13C=−3.9‰ to −1.3‰) and dolomite ( δ 18O=−4.6‰ to −2.6‰ and δ 13C=−2.9‰ to −2.3‰) in the foreshore, TST sandstones and below parasequence boundaries (PB), and transgressive surface (TS), and in the shoreface, TST sandstones below maximum flooding surfaces (MFS), being facilitated by the presence of carbonate bioclasts, (iii) dissolution of detrital silicates and precipitation of K-feldspar overgrowths and kaolinite, particularly in the fluvio-deltaic, LST sandstones owing to effective meteoric water circulation, and (vi) formation of autochthonous glauconite, which is increases in abundance towards the top of the fluvio-deltaic, LST sandstones, and along TS, and in the shoreface, TST sandstones, by alteration of micas owing to the flux of seawaters into the sandstones during transgression, whereas parautochthonous glauconite is restricted to the TS sandstones owing to marine reworking. Mesogenetic alterations, which include cementation by quartz overgrowths and illite, display fairly systematic link to fluvio-deltaic, LST sandstones. This study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution.

Chronology and geochemistry of the volcanic rocks in Woruo Mountain region, northern Qiangtang depression: Implications to the Late Triassic volcanic-sedimentary events

A suite of sedimentary-volcaniclastic rocks intercalated with the volcanic rocks unconformably overlies the Triassic Xiaochaka Formation in the Woruo Mountain region, Qiangtang Basin, northern Tibet. The vitric tuff from the base of these strata gives a SHRIMP zircon U-Pb age of 216 ± 4.5 Ma, which represents the age of the Late Triassic volcanic-sedimentary events in the Woruo Mountain region, and is consistent with that of the formation of the volcanic rocks from the Nadi Kangri Formation in the Nadigangri-Shishui River zone. There is a striking similarity in geochemical signatures of the volcanic rocks from the Woruo Mountain region and its adjacent Nadigangri-Shishui River zone, indicating that all the volcanic rocks from the Qiangtang region might have the same magmatic source and similar tectonic setting during the Late Triassic. The proper recognition of the Late Triassic large-scale volcanic eruption and volcanic-sedimentary events has important implications for the interpretation of the Late Triassic biotic extinction, climatic changes and regressive events in the eastern Tethyan domain, as well as the understanding of the initiation and nature, and sedimentary features of the Qiangtang Basin during the Late Triassic-Jurassic.

Diversity and biogeography patterns of Late Jurassic neoselachians (Chondrichthyes: Elasmobranchii)

Abstract The regional diversity and biogeographic patterns of Late Jurassic neoselachians at genus level in Europe were analysed based on samples and an extensive literature survey of about 40 localities ranging from the Oxfordian to Tithonian. The simple completeness metric (SCM) displays a quite good fossil record of neoselachians in the Late Jurassic with a peak in the Kimmeridgian. The origination, extinction, diversification and turnover rates were calculated for every stage and indicate that background origination occurred in the Oxfordian and Kimmeridgian with no disappearance of genera. In the Tithonian, background extinction is the main factor for neoselachian diversity decline. The decline in neoselachian diversity at the end of the Jurassic is most probably related to reduced habitats in the course of major regression events, establishment of physical barriers, and climatic changes. Faunal assemblages are quite uniform and mostly agree well with the contemporaneous palaeogeographic situation. Our analyses indicate that both vicariance and dispersal were important processes in the biogeographic pattern of Late Jurassic neoselachians.

Holocene Paleoinlet of the Bojuru Region, Lagoa dos Patos, Southern Brazil

Abstract The Holocene environmental evolution of the Bojuru region, Rio Grande do Sul state, southern Brazil, was inferred from seismic, geochronologic, sedimentologic, and paleontologic data. The absolute ages of two samples, determined by the 14C method, are 9400 ± 140 Cal BP and 7370 ±150 Cal BP. On the basis of lithology and palynomorph and diatom data, the six stages of paleoenvironmental development of this region were chosen. Layers of muddy sediments characterized by a significant incidence of marine palynomorphs and marine and estuarine diatoms were deposited during the Early and Middle Holocene. Seismic records (3.5 kHz) revealed a prominent buried paleochannel that can be correlated to the present Barra Falsa channel. The main period of the channel incision was related to the last regressive event of the Late Pleistocene. During the last Holocene transgression, this paleochannel was filled up by fluvial, estuarine, and marine sediments. The integrated analysis of data reveals that the Barra Fal...

Cenomanian Turonian Coastal Record in SW Utah, U.S.A.: Orbital-Scale Transgressive Regressive Events During Oceanic Anoxic Event II

Abstract The Cenomanian–Turonian interval of the Sevier foredeep, western U.S.A., is examined in order to (1) establish a high-resolution stratigraphic framework for marginal-marine strata of this interval and (2) test for the existence of high-frequency (tens of kyr-scale) cycles of continental runoff or sea-level change predicted by the hemipelagic record and climate models. High rates of sediment accumulation in marginal-marine environments of southwestern Utah (up to 210 m/Myr, compacted) and a northward translation of the major Sevier thrusting made possible the preservation of a highly detailed record of shoreline movements. The coeval Bridge Creek Limestone, linked with the study interval using biostratigraphic and bentonite-stratigraphic data of previous authors, provides an unprecedented, high-resolution orbital time scale. Three orders of transgressive–regressive cycles defined as genetic sequences are identified in the upper Cenomanian (S. gracile and N. juddii Zones) through lower Turonian (W. devonense through M. nodosoides Zones). The longest sequence (S. gracile Zone through V. birchbyi Zone) spans approximately 800 kyr and is penecontemporaneous with the δ13Corg positive excursion that defines Oceanic Anoxic Event II (OAE II). Medium-term and short-term sequences show durations of c. 65–160 kyr and c. 20–40 kyr, respectively. Features suggesting regression due to relative sea-level fall are described from some of the 20–40 kyr cycles in the lowermost S. gracile Zone (possibly including the uppermost M. mosbyense Zone). The data provide the first physical evidence globally of Cenomanian–Turonian changes in shoreline position and relative sea level, whose recurrence interval was as short as a few tens of kyr. These processes provide a viable depositional link between the rhythmic deposition of the Bridge Creek Limestone and the primary orbital forcing of insolation and climate. Although the possible tectonic influence is difficult to unravel, the study area represents an important reference point for climate and oceanographic modeling of the Cenomanian–Turonian greenhouse and OAE II.

PHYLOGENY OF THE LATE JURASSIC-EARLY CRETACEOUS SUBGENUS ESELAEVITRIGONIA (BIVALVIA) OF KUTCH, INDIA, AND PALEOBIOGEOGRAPHIC CONSTRAINTS

Three of Kitchin's (1903) trigoniid species, Trigonia trapeziformis, T. spissicostata, and T. cardiniiformis, have been frequently examined taxonomically, but their phylogenetic relationships remain uncertain. Taxonomic designations have ranged from grouping them within a single subgenus to separating them into different subfamilies. Principal factors affecting the previous studies include: excessive weighing of certain features from a typological perspective; phylogenetic relationships established on the basis of plesiomorphic characters which are applicable even at the family level. Although they are endemic to Kutch, India, species' ancestries were rarely sought from the regional taxa, a situation exacerbated by inadequate stratigraphic information. This study reveals that all the three species are both geographically and stratigraphically distinct, and their distribution is linked to major regression events. Since the latest Jurassic, the Kutch Basin experienced shallowing. The unstable environment triggered a substantial diversification of new forms. The present species are close morphologically to some endemic species of different genera. Detailed morphologic, morphometric, and cladistic analyses reveal affinities between ‘Eselaevitrigonia’ trapeziformis and Indotrigonia smeei, as well as ‘E.’ spissicostata and Opisthotrigonia retrorsa. It is believed that E. cardiniiformis evolved from ‘E.’ spissicostata. In each case, speciation took place in a very shallow, high-energy, nearshore environment and proceeded through various heterochronic processes. The pattern is consistent with a punctuated model of evolution. Gondwana fragmentation and rise of eustatic sea level during the Aptian opened up the central Indian oceanic corridor, prompting the spread of ‘Eselaevitrigonia’ to the Austral Province.

Sea‐level changes, river capture and the evolution of populations of the Eastern Cape and fiery redfins (Pseudobarbus afer and Pseudobarbus phlegethon, Cyprinidae) across multiple river systems in South Africa

AbstractAim The phylogeography of the two closely related species Pseudobarbus afer and Pseudobarbus phlegethon was investigated to assess the association of evolutionary processes, inferred from mitochondrial DNA (mtDNA) sequence variation, with hypothetical palaeoriver systems and other climatic and landscape changes.Location One western and several southern river systems in South Africa.Methods We sampled known populations and confirmed known distribution gaps. This was followed by an assessment of mtDNA control region sequence variation for 31 localities across 17 river systems across the range of the species complex. A map of possible offshore drainage patterns during the last major regression event was constructed based on bathymetry and geological studies.Results The genetic distinction of four major lineages of P. afer strongly correspond with proposed palaeoriver systems. However, a western ‘Forest’ lineage, is widespread across two such proposed systems and is closely related to P. phlegethon on the west coast of South Africa. Both the ‘Krom’ and ‘St Francis’ lineages were identified in the single palaeoriver system proposed for St Francis Bay. A fourth ‘Mandela’ lineage is restricted to the one or two palaeoriver systems proposed for Nelson Mandela Bay. Four minor lineages were identified within the Forest lineage and two within the Mandela lineage.Main conclusions The close relationship between P. phlegethon and the Forest lineage of P. afer can only be explained by a series of river captures. We suggest the Gourits River system as a historical link that could account for this relationship. On the south coast, lower sea levels than at present allowed confluence between currently isolated river systems, offering opportunities for dispersal among these populations. At present, isolation between different river systems rather than dispersal appears to have a dominant influence on mtDNA diversity.

Morphological properties of mouse retinal ganglion cells during postnatal development

Quantitative methods were used to assess dendritic stratification and other structural features of developing mouse retinal ganglion cells from birth to after eye opening. Cells were labeled by transgenic expression of yellow fluorescent protein, DiOlistics or diffusion of DiI, and subsequently imaged in three dimensions on a confocal microscope followed by morphometric analysis of 13 different structural properties. At postnatal day 1 (P1), the dendrites of all cells ramified across the vertical extent of the inner plexiform layer (IPL). By P3/4, dendrites were largely confined to different strata of the IPL. The stratification of dendrites initially reflected a retraction of widely ramifying dendritic processes, but for the most part this was due to the subsequent vertical expansion of the IPL. By P8, distinct cell classes could be recognized, although these had not yet attained adult-like properties. The structural features differentiating cell classes were found to follow three different developmental trends. The mean values of one set of morphological parameters were essentially unchanged throughout postnatal development; another set of measures showed a rapid rise with age to adult values; and a third set of measures first increased with age and later decreased, with the regressive events initiated around the time of eye opening. These findings suggest that the morphological development of retinal ganglion cells is regulated by diverse factors operating during different but overlapping time periods. Our results also suggest that dendritic stratification may be more highly specified in the developing mammalian retina than has been previously realized.

Sequence-stratigraphic frameworks and their palaeogeographic patterns for the Permian Lopingian of the Dianqiangui Basin and its adjacent areas of Southwestern China

The Permian Lopingian in the Dianqiangui Basin and its adjacent areas is marked by the coal measures of the Wuchiapingian and the carbonate strata of the Changhsingian stages. For the Lopingian of the Dianqiangui Basin and its adjacent areas, the diversity of sedimentary facies and the obviousness of facies change provide an advantaged condition on a study of sequence stratigraphy. Approximately, the Wuchiapingian stage constitutes a third-order sequence and the Changhsingian stage forms another. For the Wuchiapingian stage in the study area, coal-measures were developed on the attached platform and, in addition, a special coal-measure that is composed of both limestone beds and coal beds was also developed in the central part of some isolated platforms. Grain-bank grainstones and packstones were formed on the margin of the attached platform as well as in the windward part of isolated platforms. For the Changhsingian stage in the study area, open-platform limestones were formed on the attached platform, while sponge-reef limestones were developed both on the margin of the attached platform and on the isolated platforms. The Lopingian Series is a set of basin-facies muddy shales with interbeds of silicalites in the inter-platform basin, which appears a set of the large-thick coarse clastic strata of molasses covering direct the deep-water strata from the Devonian to the Permian Yangsingian in the Qinzhou-Fangcheng region in the southern part of the study area. All of these features indicate the complexity of temporal-spatial facies-changes. Sequence-stratigraphic frameworks could be established, which would illustrate two types of facies-changing surfaces and diachronisms in the stratigraphic records, based on the combination of both biostratigraphic and chronostratigraphic materials and the regularity reflected by temporal evolutionary succession of sediments as well as spatial distributional patterns of sedimentary facies. Ultimately, features of sedimentary succession and palaeogeographical evolution of the Permian Lopingian in the study area are revealed clearly in a series of the panel diagrams of sequence-stratigraphic frameworks and the outline maps showing the sedimentary-facies and palaeogeography. The Permian Lopingian formed by two third-order sequences differs from the stratigraphy of the same era characterized by the constant regression along Euramerica. Most specially, if the end-Guadalupian mass-extinction event is genetically related to a regressive event represented by the unconformity of the first episode of the Dongwu movement in the study area, the mass-extinction event at the turn from the Permian to the Triassic is genetically related to a rapid transgressive event reflected by the drowning unconformity in the study area. These phenomena might reveal a complex relationship between mass-extinction events and transgressive-regressive events.

Palynological analysis of a sediment core obtained in Guanabara Bay, Rio de Janeiro, Brazil

The sediment of a core collected about 2 km north of Paquetá Island, Guanabara Bay, was submitted to pollen analysis, in order to recognize the dynamics of the regional vegetation, and the anthropic influence. Radiocarbon dating of a sample next to the bottom of the core indicates an age of 4.210+/-40 14C yrs B.P (calibrated age). It was possible to establish four palynological zones. Starting at the bottom of the core, a decrease in palynomorph concentration, the presence of degraded pollen grains and spores, and the predominance of ombrophilous forest pollen grains were observed in the basal portion of Zone I. These data may indicate the presence of an exuberant Atlantic Forest, dominated by a marine regressive event. The concentration of well-preserved palynomorphs increased in Zone II, with the predominance of the ombrophilous forest vegetation also, and an expressive increase of hygrophytes, indicating more humid environmental conditions. Palynomorph concentration decreased again toward the top of Zone III, and the field vegetation was predominant. In the upper Zone IV occurred a strong decrease in pollen and spore concentration, with predominance of field vegetation also, and the appearance of exotic pollen grains, showing the anthropic influence at this time.

Sub-orbital sea-level change in early MIS 5e: New evidence from the Gulf of Corinth, Greece

New evidence from uplifted marine isotope stage (MIS) 5e carbonate deposits in the Gulf of Corinth demonstrate two rapid, sub-orbitally forced, sea-level oscillations in the early part of MIS 5e. Microbial bioherms with inter-grown marine coralline algae are interpreted as early highstand deposits. Presence of thin vadose flowstone (speleothem) coating inter-bioherm surfaces mark a short-lived regression of > 10 m, followed by sea-level recovery and re-establishment of the highstand, marked by coralline algae coating inter-bioherm cavity surfaces. These marine algae are then coated by a younger vadose flowstone, thick enough to provide an uncontaminated U/Th date of 134.8 ± 2.0 ka. The dated flowstone is itself encrusted by marine fauna and the entire sequence overlain by highstand marine sediments and marine aragonite cements dated to 114–118 ka, part of the sustained MIS 5e highstand. The age of the younger flowstone demonstrates that the early highstand occurred before 134.8 ± 2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than ∼ 136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (± 4) m below present sea-level, 6–18 (± 4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of > 10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr. The flowstone dated at 134.8 ± 2.0 ka is interpreted to record the early part of the ‘Aladdin's Cave' regressive event from Papua New Guinea, although in Greece only the first 16 m of the event is recorded. The new data presented here support a recently published Red Sea TII sea-level curve: they also highlight minor discrepancies in the absolute dating of these early MIS 5e sea-level events worldwide.

ANATOMICAL REVISION OF THE GENUSMERYCOPOTAMUS(ARTIODACTYLA; ANTHRACOTHERIIDAE): ITS SIGNIFICANCE FOR LATE MIOCENE MAMMAL DISPERSAL IN ASIA

Abstract: New fossil remains of the anthracothere genusMerycopotamusFalconer and Cautley, are described. Most of them were discovered by the Harvard University and Geological Survey of Pakistan joint research project (Y‐GSP) in the well‐dated Middle and Late Miocene deposits of the Potwar Plateau in northern Pakistan. This new material led us to revise the systematics of the genus with the validation of three species,M. nanusFalconer (M. pusillusLydekker),M. dissimilisFalconer and Cautley, andM. medioximusLihoreauet al., and allowed us to determine precisely their chronological distributions in a continuous Neogene sequence. Other specimens reported from the late Miocene deposits of the Khorat Plateau in north‐east Thailand by the Department of Mineral Resources are the first remains ofMerycopotamusto have been discovered in that region and are attributed toM. medioximus. These discoveries indicate a wider geographical distribution of the genus in the early Late Miocene. Anatomical investigations highlight the evolution ofMerycopotamusthrough the Miocene towards more amphibious habits. Palaeobiogeographical and palaeoecological information forMerycopotamusstress the role of the Himalayan orogenesis as a dispersal barrier and the impact of a major global regression event on the evolution of Indian Subcontinent faunas from the Middle Miocene to the Late Pliocene.

Discrimination of Seafloor Sediment Properties by VWA

Analytical results of sound velocity and spectrum for seafloor sediment ore obtained by VWA (velocity-wave-amplitude) discrimination technique. Based on velocity-wave-amplitude, an understanding is gained of the physical condition and structural characteristics of seafloor sediment, which is combined with other geological information of the sedimentary layer to synthetically discriminate the properties of seafloor sediment. Experimental results show that, by using the relationship between sound velocity, wave form envelope, amplitude shape and size, and such parameters as sedimentary structure, microstructure, bedding, grain composition, mineral composition, and physical-mechanics, etc., the basic properties of the shallow surface seafloor sediment in the experimental sea area can be discriminated and the burial depth of traces of ancient marine transgression and regression events in the borehole cores of seafloor sediment can be divided, thus making an attempt of and contribution to the practice of acoustically remote-sensing and telemetering seafloor sediment.

Depositional framework and sequence stratigraphic aspects of the Coniacian–Santonian mixed siliciclastic/carbonate Matulla sediments in Nezzazat and Ekma blocks, Gulf of Suez, Egypt

Superb outcrops of mixed siliciclastic/carbonate rocks mark the Coniacian–Santonian Matulla Formation exposed in Nezzazat and Ekma blocks, west central Sinai. They are built up of various lithofacies that reflect minor fluctuations in relative sea-level from lower intertidal to slightly deep subtidal settings. Relying on the facies characteristics and stratal geometries, the siliciclastic rocks are divided into seven depositional facies, including beach foreshore laminated sands, upper shoreface cross-bedded sandstone, lower shoreface massive bioturbated and wave-rippled sandstones, shallow subtidal siltstone and deep subtidal shale/claystone. The carbonate rocks comprise lower intertidal lime-mudstone, floatstone and dolostone, shallow subtidal skeletal shoal of oyster rudstone/bioclastic grainstone, and shoal margin packstone. Oolitic grain-ironstone and ferribands are partially intervened the facies types. Deposition has taken place under varied conditions of restricted, partly open marine circulation, low to high wave energy and normal to raised salinity during alternating periods of abundant and ceased clastic supply. The facies types are arranged into asymmetric upward-shallowing cycles that record multiple small-scale transgressive–regressive events. Lime-mudstone and sandstone normally terminate the regressive events. Four sequence boundaries marking regional relative sea-level falls divide the Matulla Formation into three stratigraphic units. These boundaries are Turonian/Coniacian, intra-Coniacian, Coniacian/Santonian and Santonian/Campanian. They do not fit with those sequence boundaries proposed in Haq et al.’s global eustatic curves (1988) except for the sea-level fall associated with the intra-Coniacian boundary. Other sequence boundaries have resulted from regional tectonic impact of the Syrian Arc Fold System that has been initiated in north Egypt during the Latest Turonian–Coniacian. These boundaries enclose three well-defined 3rd order depositional sequences; their enclosing shallowing-upward cycles (i.e. parasequences) record the 4th order relative sea-level fluctuations. 34 and 20 parasequence sets, in the order of a few meters to tens of meters thick, mark the Matulla sequences in Nezzazat and Ekma blocks respectively. Each sequence shows an initial phase of rapid sea-level rise with retrogradational sets, followed by lowering sea-level and progradation/aggradation of the parasequence sets. The transgressive deposits display predominance of deep subtidal lagoonal facies, while highstand deposits show an increase in siliciclastic and carbonate facies with the progressive decrease of lagoonal facies. The sedimentary patterns and environments suggest that the regional, partly eustatic sea-level (i.e. intra-Coniacian) changes controlled the overall architecture of the sequence distribution, whereas changes in the clastic input controlled the variations in facies associations within each depositional sequence.

Palaeomagnetic Results from the Sarmatian/Pannonian Boundary in North-Eastern Croatia (Vranovi? Section, Našice Quarry)

The Sarmatian/Pannonian boundary in the Central Paratethys basin is marked by a major regressive event, which isolated the basin from the open sea and resulted in a palaeoenvironmental change from restricted marine to brackish water ecosystems. The exact age of this environmental change is still ambiguous since direct age control on the boundary interval is lacking, mainly due to the scarcity of suitable sections. The Vranovi? section in the Našice Quarry in Croatia, however, is relatively long and continuously exposed. A detailed sedimentological and biostratigraphic study indicates that it contains the Sarmatian/Pannonian boundary and that it reflects the same palaeoenvironmental trend as other Paratethyan sequences. Here, we present palaeomagnetic and rock magnetic results from the Vranovi? section, based on 183 sampled levels distributed along 55 m of cyclically bedded limestones and marls. Rock magnetic data indicate the presence of maghemite or haematite in the Sarmatian deposits and low contents of magnetite in the Pannonian rocks. Thermal demagnetization results indicate dominantly normal polarities, and the mean direction closely coincides with the present-day field direction at Našice. We conclude that magnetostratigraphic age control cannot be derived for the Vranovi? section because of a dominant secondary (post-tilt) magnetization. Consequently, a firm numerical age based on magnetostratigraphy cannot be assigned to Sarmatian/Pannonian boundary events from this section.

Axonal regressive events in rat corticospinal slice coculture studied with time-lapse confocal imaging of single axons

Axonal regressive events in rat corticospinal slice coculture studied with time-lapse confocal imaging of single axons

Upper Ordovician mudrock facies and trace fossils in the northern Holy Cross Mountains, Poland, and their relation to oxygen- and sea-level dynamics

The bulk of the Ordovician sedimentary record in the northern Holy Cross Mts., Poland, is composed of dark claystones, which record the long-term dysoxic conditions lasting throughout the entire Caradoc. However, a relatively short-term oxygenation event corresponding to the middle Caradoc sea-level lowstand interrupts this monotonous succession. Termination of the low oxygen environment was triggered by a major change in oceanic circulation due to onset of polar cooling. It resulted in the progressive benthic oxygenation and increase of colonization of the highly enriched sediment by soft-bodied burrowers as can be envisaged from ichnofabric of the lower to middle Ashgill sedimentary record. The rapid but gradual upward progradation of the Upper Ordovician mudrock facies into the coarse-grained deposits appears to be closely related to the late Ashgill glacio-eustatic regressive event.

Biogeography: An Emerging Cornerstone for Understanding Prokaryotic Diversity, Ecology, and Evolution

New questions about microbial ecology and diversity combined with significant improvement in the resolving power of molecular tools have helped the reemergence of the field of prokaryotic biogeography. Here, we show that biogeography may constitute a cornerstone approach to study diversity patterns at different taxonomic levels in the prokaryotic world. Fundamental processes leading to the formation of biogeographic patterns are examined in an evolutionary and ecological context. Based on different evolutionary scenarios, biogeographic patterns are thus posited to consist of dramatic range expansion or regression events that would be the results of evolutionary and ecological forces at play at the genotype level. The deterministic or random nature of those underlying processes is, however, questioned in light of recent surveys. Such scenarios led us to predict the existence of particular genes whose presence or polymorphism would be associated with cosmopolitan taxa. Furthermore, several conceptual and methodological pitfalls that could hamper future developments of the field are identified, and future approaches and new lines of investigation are suggested.

Palaeogeography of Neogene red bed sequences along the Aksa-Ata River in the Parkent–Nurekata intermontane basin (Tien Shan Mountains, Uzbekistan): With special reference to the magnetic susceptibility of siliciclastic rocks

Siliciclastic red beds formed by stream action in the Parkent–Nurekata intermontane basin of the Tien Shan Mountains, E Uzbekistan. The sedimentary rocks were cross-sectioned in the field and subject to heavy mineral, clay mineral and thin section analyses in the laboratory. In addition to these conventional methods, a survey into the variation of the magnetic susceptibility was conducted. During the Paleogene, calcareous rocks (unit A) developed in a subtidal through supratidal environment of deposition. Subsequently, tectonic disturbances tilted the Paleogene carbonate rocks and triggered the formation of an unconformity during the Oligocene. The Miocene to Pliocene red beds have the hallmarks of a delta-like wedge actively prograding over near-shore marine deposits. Two progradational stages (units B and C) were substituted for by a more regressive event (unit D). During deposition and burial the siliciclastics were percolated by strongly alkaline pore fluids under semi-arid climatic conditions. The joint action of rapid uplift in the hinterland and the afore-mentioned hydrological processes were instrumental for heavy minerals such as epidote and staurolite to survive and some peculiar phyllosilicates such as smectite and palygorskite to precipitate. Debris from metamorphic and igneous rocks were delivered from the rising hinterland. The petrographic and magnetic records of red beds are a mirror image of the unroofing of a magmatic edifice in the provenance area between 11 and 3 Ma.

PALEOAMBIENTES E ICNOFÁCEIS DA SEQÜÊNCIA CARBONÁTICA DA BACIA DA PARAÍBA (CRETÁCEO-PALEOGENO), NORDESTE DO BRASIL

This work deals an investigation of the stratigraphic, sedimentological and paleontological aspects, mainly ichnologic, in outcrops of carbonate deposits of the Gramame and Maria Farinha formations in the Paraiba Basin, northeast Brazil. The objective of the investigation was to obtain detailed information on the depositional environments of these units. The Gramame Formation was deposited in a regime of highstandstand system tract, belowstand the base level of fair weather waves where prevailed conditions of soft bottom and lowstand energy, but often reached by storm events, correlated to the Cruziana ichnofacies. The Maria Farinha Formation was deposited during a regressive event, with the increase of energy and siliciclastic input, important lateral facies variation and Cruziana-Skolithos ichnofacies . The eocenic carbonate rocks, that occur in the south coast of Paraiba state, present s expressive difference from the deposits of the typical Maria Farinha Formation, and it could represent another unit. These reefal carbonates was deposited in reef-lagoon s complexes and arc se pa rated from the Maria Farinha Formation by an unconformity and, probably indicate the establishment of a lowstand system tract . The ichnofacies interpreted for them was Trypanites?. The data integration suggests a paleobathymetry of middle to inner platform (150-80m), for the Gramame Formation, and inner platform to infralitoral (60-20m), including proximity of estuaries, for the Maria Farinha Formation.