bluuebunny/crossref_metadata_2025 huggingface dataset:
Tectonic evolution of the Alboran Sea basin
Authors: Watts A. B. , Piatt J. P. , Buhl P.
Published: November 2007

The Alboran Sea is an extensional basin of Neogene age that is surrounded by highly arcuate thrust belts. Multichannel seismic (MCS) reflection profile data suggest the basin has a complex tectonic fabric that includes extensional, compressional and strike‐slip structures. The early Miocene history appears to be dominated by graben formation with border faults that are in large part contemporaneous with thrust movements in the external zones of the Betic and Rif mountains. Extension appears to have continued into the late Miocene although the main movements were probably completed by the time of the Messinian ‘salinity crisis’. The Pliocene and younger history of the basin is dominated by infilling of the Messinian topography, gentle subsidence, and extensional, compressional and strike‐slip movements. There is evidence from the sea‐floor morphology and seismicity patterns that the basin is actively deforming in response to present‐day plate motions. Backstripping of well data in the basin margin suggests that the initial extensional event was accompanied by crustal and lithospheric thinning. The depth to Moho inferred from backstripping is greater than the depth expected based on seismic and gravity modelling, suggesting that backstripping underestimates the true amount of thinning. One explanation is that some of the thinning occurred while the crust was above sea level, perhaps as a result of either crustal thickening, or a period of lithospheric heating and thinning, prior to rifting. We found that a model with a ‘normal’ crustal thickness of 31.2 km, a lithospheric thickness of 50 km, and β= 1.4 predicts 0.8 km of initial uplift. These parameters fit the well subsidence data and bring the backstripped Moho into better agreement with the seismic and gravity Moho. The origin of such a thin lithosphere is not constrained by the data, but we believe that it may be a result of the detachment of a cold lithospheric ‘root’ that formed during pre‐Neogene collisional orogeny in the region.
Geometry of trapezoidal fan deltas and their relationship to extensional faulting along the southwestern active margins of the Corinth rift, Greece
Authors: Poulimenos G. , Zelilidis A. , Kontopoulos N. , Doutsos T.
Published: November 2007

A new subtype of Gilbert‐type fan deltas, ‘the trapezoidal fan delta’, characterized by the absence of bottomset deposits, is recognized in the south‐western active margins of the Corinth rift in central Greece. They are formed adjacent to master extensional listric faults and developed by progradation either onto a subaqueous basin escarpment or across a subaerial platform where alluvial fans have accumulated. Simultaneously with master fault activity, displacements on counter faults along intrabasinal basement highs produced fan delta foreset deposits. Furthermore, footwall imbrication and uplift along the listric faults, as well as transfer fault displacement, have strongly influenced the pattern of fan delta sedimentation.
Anomalous thermal maturities caused by carbonaceous sediments
Authors: Pollack HENRY N. , Cercone KAREN ROSE
Published: November 2007

Sedimentary rocks such as coal and carbonaceous mudstone which contain abundant carbonaceous matter are characterized by thermal conductivity much lower than that exhibited by other common rock types, by a factor of 5–10. As a result, temperature gradients in such sediments can range up to 0.25 °Cm‐1 even under conditions of average heat flow. When such steep gradients extend over a significant sedimentary thickness, temperatures of underlying rock units are elevated, causing both organic and inorganic phases to record what seem to be anomalously high levels of thermal maturity. This carbonaceous blanket insulating effect may help to explain unusual levels of maturity observed at shallow depths in the Appalachian Basin, Michigan Basin and other regions of the world with significant carbonaceous strata.
Overpressures and hydrocarbon generation in the Sable sub‐basin, offshore Nova Scotia
Authors: Williamson MARK A.
Published: November 2007

One of several interconnected depocentres lying offshore eastern Canada, the Sable sub‐basin preserves a thick sequence of Mesozoic‐Cenozoic clastic sediments, significant gas accumulations and an extensive development of abnormal pressures. In order to understand the basin's hydrocarbon generation, migration and accumulation history it is necessary to quantify the interplay between its burial, thermal, and maturation history, and to determine the influence on these of the basin's excess pressure history. Simple, one‐dimensional reconstructions of maturity and pore pressure histories are derived for exploration well and pseudo‐well locations on a seismic line running from the basin's structural high to its depocentre. Calibrated, where possible, by reference to measured maturity, temperature and pressures, these models provide a basic dynamic framework within which it is possible to consider the generation history of the basin's source rocks. Late Jurassic to Early Cretaceous sediments underwent an initial rapid, rift‐related subsidence. The thermal/maturation models suggest that source rocks lying within these intervals quickly matured and began generating gas and condensates. Similarly, this rapid burial was translated, through sediment compaction disequilibrium processes, into an early expression of abnormal pressures.

The pore pressure/time reconstructions in the modelling assume that sediment compaction disequilibrium and gas generation are the principal causal mechanisms. Matching pore pressure reconstructions with present‐day pressure‐depth profiles is particularly sensitive to assumed seal permeability profiles. Although the seal permeabilities used as model input are based on actual measured permeabilities at the present day, this does not mean that the permeability‐time curves derived through the model's decompaction assumptions accurately reflect seal permeability evolution.
Modelling of pore pressure evolution associated with sedimentation and uplift in sedimentary basins
Authors: Luo XIAORONG , Vasseur GUY
Published: November 2007

Unconformities, which represent either periods of interruption of sedimentation or, in most cases events characterized by deposition and subsequent erosion, are commonplace geological phenomena in sedimentary basins, and will affect the pore pressure evolution of the basin fill. The effect of unconformities on pore pressure, as well as on sediment compaction and on burial processes is studied using a numerical basin model. For coarse sediments, which are permeable so that their pore pressure always remains nearly hydrostatic, the effects of both pure deposition interruption (hiatus) and deposition‐erosion events are negligible for pore pressure evolution. However, for fine‐grained sediments, unconformities can modify the pore pressure and the stress state to varying degrees. The results show that the rate of removal of overlying sediments, the permeability of sediments and time play important roles in the pore pressure evolution. In the East Slope of the Ordos Basin (China), in which overpressure has not been detected in deep wells, the modelling results suggest that the large‐scale erosion occurring in the Late Cretaceous and in the Tertiary may have removed high overpressure existing in the basin before the erosion.
Cross formational flow in the Paris Basin
Authors: Worden R. H. , Matray J.‐M.
Published: November 2007

Cross formational flow of water has occurred across several hundred metres of Liassic mudstone from the Triassic Chaunoy Formation sandstone to the Middle Jurassic Dogger Formation carbonate in the Paris Basin, France. This has been demonstrated by chemical and isotopic data from rocks and formation waters, sampled on a basin scale, from the Dogger and Chaunoy formations. Present‐day and palaeoformation waters in the Dogger record input of exotic water in terms of salinity and carbon and strontium isotopes. The exotic water was highly saline and contained isotopically light carbon and 87Sr‐enriched strontium in comparison to the indigenous Dogger Formation water. The source of the exotic water can only have been the Chaunoy Formation. Salinity and isotope data show that present‐day Dogger Formation water contains 10–15% invasion Chaunoy water. Modelling strontium isotope ratio and concentration data from mineral cements shows that over the duration of Dogger cementation, Dogger palaeoformation waters were replaced by 1–5% Chaunoy water. Cross formational flow of water must have occurred by convective mass flow, rather than diffusion, in order to preserve the characteristics of water input from the Chaunoy. Flow probably occurred via the major Hercynian fault and fracture systems that run through the centre of the Paris Basin. Upward flow in this setting is most likely in a compressional tectonic regime, the situation during much of the Tertiary in the Paris Basin. Thermodynamic modelling indicates that cross formational flow from the Chaunoy has probably caused carbonate cementation in the Dogger.
Convective and conductive heat transfer in sedimentary basins
Authors: Vasseur G. , Demongodin L.
Published: November 2007

In the Earth's crust the temperature is largely controlled by heat conduction. However, under some circumstances, the thermal state is disturbed by advection of heat associated with groundwater flow. The corresponding thermal disturbance depends on the water flow velocity (modulus and direction) and therefore thermal data may be used to constrain the pattern of natural fluid flow. In this paper, some models of thermal disturbance induced by convective heat transfer are presented. They are based on the assumption that the water flow is concentrated in thin permeable structures such as aquifer or fault zones. The steady‐state and transient thermal effects associated with such scenarios are computed using a somewhat idealized model which depends on a small number of parameters: flow rate, time, aquifer geometry and thermal parameters of surrounding rocks. In order to extract the conductive and convective components of heat transfer from temperature data and to estimate the corresponding fluid flow rate, it is first necessary to estimate the thermal conductivity field. The problem of the estimation of thermal conductivity in clay‐rich rocks, based on laboratory andin‐situmeasurements, is emphasized. Then a method is proposed for the inversion of temperature data in terms of fluid flow. Vertical and lateral variations of thermal conductivity are taken into account and the fluid flow is assumed to be concentrated on a specified surface (2‐D quasi‐horizontal pattern). Thermal effects of the flow are simulated by a distribution of surface heat production which can be calculated and then inverted in terms of horizontal fluid flow pattern.
Rift basins and supradetachment basins: intracontinental extensional end‐members
Authors: Friedmann S. JULIO , Burbank DOUGLAS W.
Published: November 2007

Two end‐members characterize a continuum of continental extensional tectonism: rift settings and highly extended terrains. These different styles result in and are recorded by different extensional basins. Intracontinental rifts (e.g. East Africa, Lake Baikal) usually occur in thermally equilibrated crust of normal thickness. Rift settings commonly display alkali to tholeiitic magmatism, steeply dipping (45–60°) bounding faults, slip rates <1 mm yr‐1 and low‐magnitude extension (10–25%). Total extension typically requires > 25 Myr. The fault and sub‐basin geometry which dominates depositional style is a half‐graben bounded by a steeply dipping normal fault. Associated basins are deep (6–10 km), and sedimentation is predominantly axial‐ or hangingwall‐derived. Asymmetric subsidence localizes depocentres along the active basin‐bounding scarp.

Highly extended continental terrains (e.g. Colorado River extensional corridor, the Cyclade Islands) represent a different tectonic end‐member. They form in back‐arc regions where the crust has undergone dramatic thickening before extension, and usually reactivate recently deformed crust. Volcanism is typically calc‐alkalic, and 80–90% of total extension requires much less time (<10 Myr). Bounding faults are commonly active at shallow dips (15–35°); slip rates (commonly > 2 mm yr‐1) and bulk extension (often > 100%) are high.

The differences in extension magnitude and rate, volcanism, heat flow, and structural style suggest basin evolution will differ with tectonic setting. Supradetachment basins, or basins formed in highly extended terrains, have predominantly long, transverse drainage networks derived from the breakaway footwall. Depocentres are distal (10–20 km) to the main bounding fault. Basin fill is relatively thin (typically 1–3 km), probably due to rapid uplift of the tectonically and erosionally denuded footwall. Sedimentation rates are high (˜ 1 m kyr‐1) and interrupted by substantial unconformities. In arid and semi‐arid regions, fluvial systems are poorly developed and alluvial fans dominated by mass‐wasting (debris‐flow, rock‐avalanche breccias, glide blocks) represent a significant proportion (30–50%) of basin fill. The key parameters for comparing supradetachment to rift systems are extension rate and amount, which are functions of other factors like crustal thickness, thermal state of the lithosphere and tectonic environment. Changes in these parameters over time appear to result in changes to basin systematics.
Effect of the Cretaceous Serra Geral igneous event on the temperatures and heat flow of the Paraná Basin, southern Brazil
Authors: Hurter SUZANNE J. , Pollack HENRY N.
Published: November 2007

We investigate the effects of the cooling of intrusive and extrusive igneous bodies on the temperature history and surface heat flow of the Paraná Basin. The Serra Geral igneous event (130–135 Ma) covered most of this basin with flood basalts. Associated with this event numerous sills and dykes intruded the sediments and basement, and extensive underplating may have occurred in the lower crust and upper mantle beneath the basin. We develop an analytical model of the conductive cooling of tabular intrusive bodies and use it to calculate temperatures within the sediments as a function of time since emplacement. Depending on the thickness of these igneous bodies and the timing of sequential emplacement, the thermal history of a given locus in the basin can range from a simple extended period of higher temperatures to multiple episodes of peak temperatures separated by cooling intervals. The cooling of surface flood basalts, sills and dykes is capable of maintaining temperatures above the normal geothermal gradient temperatures for a few hundred thousand years, while large‐scale underplating may influence temperatures for up to 10 million years. We conclude that any residual heat from the cooling of the Serra Geral igneous rocks has long since decayed to insignificant values and that present‐day temperatures and heat flow are not affected. However, the burial of the sediments beneath the thick basalt cap caused a permanent temperature increase of up to 50°C in the underlying sediments since the beginning of the Cretaceous.
Experimental modelling of forearc basin development during accretionary wedge growth
Authors: Larroque CHRISTOPHE , Calassou SYLVAIN , Malavieille JACQUES , Chanier FRANK
Published: November 2007

We present results of three sand‐box experiments that model the association between tectonic accretion and sedimentation in a forearc basin. Experimental sedimentation occurs step by step in the forearc basin during shortening of the sand wedge.

In each experiment, the development of the accretionary wedge leads to the formation of a major backthrust zone. This major deformation zone accounts for the thickening in the rear part of the wedge. In natural settings this tectonic bulge dams sediments that are transported toward the trench from mountainous terrain behind the forearc.

We test the variation of friction along the déollement and note the following: (1) shortening of a low‐friction wedge involves a mechanical balance between forethrusts and backthrust propagation and this balance is recorded by the sedimentary sequence trapped in the forearc basin. Indeed, if most of the movement occurs along the backthrust, the deepening of the basin will be larger and consequently the thickness of the sedimentary sequence will be greater. (2) Such balance does not exist in the case of a high‐friction wedge. (3) Variation of friction along the décollement during shortening of the sand wedge leads to modification in the forearc basin filling. Thus, for similar increments of convergence, the sequence deposited in the forearc basin shows relatively larger thickness when the wedge is shortened above a high‐friction décollement.

We suggest that contraction and thickening in the rear part of the wedge is an efficient mechanism to, initiate and develop a forearc basin. Thus, this kind of basin occurs in convergent settings, without collapse related to local extension or tectonic erosion. They represent a sedimentary trap on a passive basement, bounded by a tectonic bulge.

The Quaternary Hikurangi forearc basin, southeast of the North Island of New Zealand, is bounded by two actively uplifting ridges. Thus, this basin is considered to be a possible example of the basins modelled in our experiments, and we suggest that the limit between the basin and the wedge could be a complex backthrust zone.
The blanketing effect in sedimentary basins
Authors: Wangen Magnus
Published: November 2007

The deposition of cold sedimerlts, called thermal blanketing, is studied when the sedimentary basin is considered as part of the lithosphere. A general one‐dimensional temperature equation is obtained which accounts for blanketing, the movement of the lower boundary of the lithosphere, and the eventual stretching of the sediments and the lithosphere. These processes appear explicitly as convective terms in the model, which is a generalization of a previous temperature equation. The description of these processes b!‐means of convective terms is a major result in the paper; it makes these processes more amenable to quantitative investigations. The temperature equation is studied in two different settings; one where the lithosphere remains unstretched, and another where the lithosphere is subjected to constant strain rate stretching. The parameter controlling thermal blanketing in these models is the Peclet number. The transient period towards a stationary state, and the stationary state representing maximal blanketing are studied. Analytical expressions for various stationary states are obtained. When the lithosphere remains unstretched it is concluded that a necessary condition for strong blanketing is a sedimentation rate of the order of 250mMyr‐1. Where the sediments contribute to the heat flow by decay of radioactive isotopes, the radioactive heat production divided by the sedimentation rate should be at least 10‐9 (Wm‐3)/(mMyr‐1) for the heat production to compete with blanketing. During stretching of the lithosphere it is shown that for stretching factors (p) larger than 2, the convective effect of stretching the sediments contributes more to the reduction of the heat flow than the blanketing effect. Blanketing counteracts the increased heat flow caused by the stretching of the lithosphere, and the upwelling hot asthenosphere. With sedimentation rates inferred from isostatic calculations it is found that the strain rate times the initial crust thickness should be more than 0.25 km Myr‐1 for the blanketing effect to be noticeable. It is also shown that sediment infill which follows thermal subsidence, after a period of stretching, is not capable of blanketing.
Oligocene to early Miocene tectono‐sedimentary history of the Alicante region (SE Spain): implications for Western Mediterranean evolution
Authors: Geel T.
Published: November 2007

The Alicante region, situated at the intersection of major Western Mediterranean structural units, is unique in possessing a complete marine Oligocene to early Miocene record of both platform and slope deposits. Detailed analysis of three selected platform areas in the north of the region, each showing a different tectono‐sedimentary history, and comparison with coeval slope deposits in the south of the region shows that: (a) during the Rupelian to early Chattian the region formed part of the Iberian microplate and can be considered the south‐eastern continuation of the NW‐SE‐trending Iberian Chain (folding phase between 36 and 33 Ma, updoming event at 31–29 Ma, both induced by Pyrenean collision); (b) during the late Chattian to Aquitanian it was linked to the extensional, SW‐NE‐orientated Valencia Trough forming part of its western margin (rifting phases at 28 and 25 Ma); (c) from the Aquitanian‐Burdigalian boundary (20 Ma) onward, the region underwent NW‐directed compression due to Betic collision (folding phases at 20 and 17 Ma); (d) a foreland basin formed in the late Burdigalian (18–17 Ma), continuous from the Betic Cordilleras over the Alicante region to the Balearics; (e) a purely compressive regime was superseded by strike‐slip tectonics at the Langhian—Serravallian boundary.

The previously formulated hypotheses of coeval compression and extension with inferred hypothetical strike‐slip or other faults in or near the Alicante region is rejected on the basis that compress ional and extensional tectonics are separated in time in the Alicante region.
The interior rifts of the Yemen ‐ analysis of basin structure and stratigraphy in a regional plate tectonic context
Authors: Redfern Phillip , Jones Julie A.
Published: November 2007

The full extent of Mesozoic rift basins within interior Yemen has only recently been established. This work presents a detailed documentation of the stratigraph)., structure and basin development of the Marib‐Shabwa and Sirr‐Sayun basins, and the Jeza Trough.

Yemen is located at the south‐western margin of the Arabian Plate, which for most of its early geological history formed part of the northern passive margin of Gondwanaland. Mesozoic break up of the super‐continent was associated with major rifting in the Late Jurassic (main phase) and Early Cretaceous. Orientation of the rift basins reflects an inheritance from deep‐seated Precambrian structural trends which cross the Arabian Plate.

The resultant structure of basement highs, tilted fault blocks, marginal terraces and central graben highs is illustrated in a series of detailed cross‐sections. A comprehensive stratigraphic framework has also been established for the Jurassic and Cretaceous basin‐fill, enabling thickness and facies variations to be analysed. This reveals a clear shift in the main period of fault‐related, high sediment accumulation rates, both within and across the three interior basins of Yemen.

In the western Marib‐Shabwa Basin, the fill is dominantly Late Jurassic, whilst the eastern Shabwa Basin and Sirr‐Sayun Basin exhibit a progressively increased, and younger, Early Cretaceous fill. The main period of fault‐related sedimentation in the most easterly basin, the Jeza Trough, is wholly Cretaceous.

Plate tectonic reconstructions of the area for this period have documented the separation and subsequent north‐eastward movement of the Indian Plate, away‐ from Africa‐Arabia. We believe this may have been the causal mechanism in the progressive eastward migration of rift activity in the Yemen.
New seismic stratigraphy and Late Tertiary history of the North Tanganyika Basin, East African Rift system, deduced from multichannel and high‐resolution reflection seismic data and piston core evidence
Authors: Lezzar K. E. , Tiercelin J.‐J. , Batist M. DE , Cohen A. S. , Bandora T. , Rensbergen P. VAN , Turdu C. LE , Mifundu W. , Klerkx J.
Published: November 2007

AbstractWe present here the initial results of a high‐resolution (sparker) reflection seismic survey in Northern Lake Tanganyika, East African Rift system. We have combined these results with data from earlier multichannel reflection seismic and 5‐kHz echosounding surveys. The combination of the three complementary seismic investigation methods has allowed us to propose a new scenario for the late Aliocene to Recent sedimentary evolution of the North Tanganyika Basin. Seismic sequences and regional tectonic information permit us to deduce the palaeotopography at the end of each stratigraphic sequence. The basin history comprises six phases interpreted to be responses to variations in regional tectonism and/or climate. Using the reflection seismic‐radiocarbon method (RSRM), the minimum ages for the start of each phase (above each sequence boundary) are estimated to be: ?7.4 Ma, ? 1.1 Ma, ?393–363 ka, ?295–262 ka, ? 193–169 ka, ?40–35 ka. Corresponding lowstand lake elevations below present lake level for the last five phases are estimated to have been: ?650–700 m, ?350 m, ?350 m, ?250 m and ? 160 m, respectively. The latest phase from ?40–35 ka until the present can be subdivided into three subphases separated by two lowstand periods, dated at ?23 ka and ? 18 ka. From the late Miocene until the mid Pleistocene, large‐scale patterns of sedimentation within the basin were primarily controlled by tectonism. In contrast, from the mid Pleistocene to the present, sedimentation in Lake Tanganyika seems to have responded dramatically to climatic changes as suggested by repeated patterns of lake level fluctuations. During this period, the basin infill history is characterized by the recurrent association of three types of deposits: ‘basin fill’ accumulations; lens‐shaped ‘deep lacustrine fans’; and ‘sheet drape’ deposits. The successive low‐lake‐level fluctuations decreased in intensity with time as a consequence of rapid sedimentary filling under conditions of declining tectonic subsidence. The climate signal has thus been more pronounced in recent sedimentary phases as tectonic effects have waned.
Regular spacing of drainage outlets from linear mountain belts
Authors: Hovius NIELS
Published: November 2007

Abstract Straight sections of many actively uplifting mountain belts have simple patterns of drainage, transverse to their main structural trend. Streams rising near or beyond the topographic ridgepole of these sections are spaced at seemingly regular intervals. To test whether this regularity exists, morphometric aspects of drainage networks were measured in 11 mountain belts. The spacing of drainage basins can be expressed using a spacing ratio, which in effect is the ratio of the length and the width of the catchments under consideration. Average spacing ratios for most linear mountain belts are within a narrow range of values between 1.91 and 2.23. A linear relationship exists between the spacing of catchment outlets and the distance between the main divide and the front of the mountain belt in which they have developed. The Nepalese Himalaya form an exception to this regular pattern. In this mountain belt drainage is blocked and diverted by structures that have developed in relation to the Main Boundary Thrust. Structural complications cause drainage patterns to become less regular, introducing important non trans verse components.

The linear relationship between spacing of catchment outlets and half‐width of the mountain belt may be expressed in an equation of the same general form as Hack's law of stream length and drainage basin area. It seems likely that the mechanism underlying Hack's law also explains the consistent regularity of drainage spacing in active mountain belts. However, no generally accepted explanation for Hack's law has been offered. The narrow range of spacing ratios found for drainage networks in active orogens may represent an optimal catchment geometry that embodies a ‘most probable state’ in the uplift‐erosion system of a linear mountain belt.

The linear relationship between the half‐width of a mountain belt and spacing of catchment outlets has profound implications for the modelling of erosion of orogenic topography, and for the formation and filling of foreland basins.
The relationship between basin and margin thermal evolution assessed by fission track thermochronology: an application to offshore southern Norway
Authors: Rohrman MAX , Andriessen PAUL , van der Beek PETER
Published: November 2007

Abstract We use a quantitative model of apatite fission track (AFT) annealing to constrain the thermal evolution of a sedimentary basin and its margin. Apatites deposited in a basin contain several types of information. Provided temperatures remained below ≅70°C, they retain much of their provenance thermal signatures and mainly record the thermal evolution of their source area. Above 70°C, the fission tracks in apatite rapidly fade, reflecting the thermal evolution of the basin. Therefore, downhole AFT dates in a well section can in principle be used to assess both the provenance detail (from shallow/cool samples) and the subsequent thermal history in the basin (from the deeper samples).

We apply this concept to the south Norwegian offshore and onshore using AFT and ZFT (zircon fission track) data; the latter constrain maximum palaeotemperatures and provide additional provenance information. AFT and ZFT data from three offshore wells in the northern North Sea are shown to contain a record of palaeogeographical and tectonic evolution, closely associated with the Norwegian basement. ZFT data from Middle Triassic sediments suggest a Permian volcanic source. Modelling of AFT data from Jurassic sediments presently residing at temperatures below 70°C indicate rapid cooling during the Late Triassic to Early Jurassic, similar to onshore AFT data. During the Cretaceous minor sediment supply was derived from the Norwegian basement, as evidenced by ZFT ages that do not correlate to the onshore, suggesting that parts of southern Norway were covered with sediments at this time. At the end of the Palaeogene and during the Neogene, the south Norwegian basement again became a major source of elastics.

AFT and ZFT data indicate that all wells are presently at maximum temperatures. No significant (> 500 m) erosion events are indicated in the three wells since the Jurassic. AFT data have not yet effectively equilibrated to present‐day temperatures as nonzero fission track ages are maintained in sediments currently at temperatures of > 120°C. This implies that the present‐day thermal regime has only recently been installed. Probable causes include rapid subsidence and an increase in the geothermal gradient during the last 5 Myr.
Modelling sedimentation in ocean trenches: the Nankai Trough from 1 Ma to the present
Authors: Mountney NIGEL P. , Westbrook GRAHAM K.
Published: November 2007

Abstract Sediment accumulation within ocean trenches located at actively accreting convergent margins is determined by an interplay between sediment supply, sediment subduction/accretion at the toe of the overriding accretionary complex and the rate of subduction. Modelling trench sedimentation provides insight into the principal controlling factors, and a means of deriving, from the pattern of sedimentation, how factors, such as the rates of sediment supply and subduction, have varied over the period of accumulation of the trench sediments. Two DSDP‐ODP drill sites within the Nankai Trough reveal a coarsening‐upward megasequence, indicating a progressive facies transition from abyssal muds to outer‐trench silts to inner‐trench sands. The changing geometry of the trench‐wedge over the past 1 Myr has been determined by modelling variations in net sediment flux for two trench‐perpendicular profiles. The models were constrained to fit the stratigraphy at the drill sites, and the simulated present‐day geometries of the trench were matched with those shown on seismic reflection profiles by successive adjustment of the model. Results from both sites confirm a ‘slow’ subduction rate of <20 km Myr‐1. At the south‐western site (582), the width of the trench‐wedge has ranged from 13 to 21 km over the past 1 Myr. To the north‐east, at Site 808, the width has ranged from 7 to 13 km over the past 0.5 Myr. These changes in trench‐wedge width are primarily the result of large changes in sediment supply rate. The subduction of the Shikoku Ridge, a fossil spreading centre adjacent to Site 808, has had a major influence on the style of sedimentation within the trench.

The style of accretion from the trench to the toe of the accretionary complex has important implications for geometrical adjustment of the trench‐wedge. Thrust displacement lifts the protothrust region out of the trench, resulting in a decreased width. This is followed by a phase of increasing width as the trench‐wedge adjusts towards a new equilibrium. The cyclical, episodic accretion process results in a periodic second‐order variation in trench‐fill size that is superimposed on primary trends determined by variations in sediment supply rates and subduction rates over time.
Molecular mechanisms of virstatin resistance by non‐O1/non‐O139 strains of Vibrio cholerae
Authors: Shakhnovich Elizabeth A. , Sturtevant Derek , Mekalanos John J.
Published: November 2007

Virstatin is a previously described small molecule inhibitor of Vibrio cholerae virulence. We have demonstrated that the molecule inhibits the activity of the transcriptional activator ToxT, thereby preventing elaboration of the toxin co‐regulated pilus (TCP) and cholera toxin in vitro and in vivo in O1 strains of V. cholerae. While strains of the O1 and O139 serogroups are the cause of most epidemic and endemic cholera currently seen globally, sporadic disease caused by strains of non‐O1/non‐O139 serogroups suggests that understanding the pathogenic mechanisms of these unusual strains is relevant for disease. Although some non‐O1/non‐O139 strains have acquired the pathogenicity island that encodes the TCP, the role that this essential colonization factor of O1/O139 strains plays in the virulence of non‐O1/non‐O139 strains has not been determined. In this study, we utilize virstatin in a ‘chemical genetic approach’ to examine the role of ToxT, and thus by inference TCP, in the colonization of a panel of predominantly non‐O1/non‐O139 tcp+ strains. We identified nine strains whose colonization was resistant to virstatin inhibition in the infant mouse model. These strains presumably colonize by a TCP‐independent mechanism or contain a naturally occurring virstatin‐resistant ToxT. Four strains contained the typical toxT gene found in O1/O139 strains (toxTEPI) isolated from cholera epidemics. Interruption of toxT in one of these strains did not affect colonization of the infant mouse small intestine. The remaining five strains were found to contain a sequence divergent toxT gene that has been previously designated toxTENV because of its occurrence in isolates of V. cholerae from the environment. We show that ToxTENV is resistant to virstatin in two separate heterologous systems and is necessary for efficient colonization of the infant mouse small intestine. These results support the new concept that chemical genetic probes for the in vivo function or expression of virulence genes can be used to identify strains that express alternative virulence factors or novel regulatory systems that are functional in vivo.
Solution structure of the novel dispersin protein of enteroaggregative Escherichia coli
Authors: Velarde Jorge J. , Varney Kristen M. , Inman Keith G. , Farfan Mauricio , Dudley Edward , Fletcher Jonathan , Weber David J. , Nataro James P.
Published: November 2007

Enteroaggregative Escherichia coli (EAEC), increasingly recognized as an important cause of infant and travelers' diarrhoea, exhibits an aggregative, stacked‐brick pattern of adherence to epithelial cells. Adherence is mediated by aggregative adherence fimbriae (AAFs), which are encoded on the pAA virulence plasmid. We recently described a highly prevalent pAA plasmid‐borne gene, aap, which encodes a protein (nicknamed dispersin) that is secreted to the bacterial cell surface. Dispersin‐null mutants display a unique hyper‐aggregating phenotype, accompanied by collapse of AAF pili onto the bacterial cell surface. To study the mechanism of this effect, we solved the structure of dispersin from EAEC strain 042 using solution NMR, revealing a stable beta‐sandwich with a conserved net positive surface charge of +3 to +4 among 23 dispersin alleles. Experimental data suggest that dispersin binds non‐covalently to lipopolysaccharide on the surface of the bacterium. We also show that the AAF organelles contribute positive charge to the bacterial surface, suggesting that dispersin's role in fimbrial function is to overcome electrostatic attraction between AAF and the bacterial surface.
Dissection of a type VI secretion system in Edwardsiella tarda
Authors: Zheng Jun , Leung Ka Yin
Published: November 2007

Bacterial pathogens use different protein secretion systems to deliver virulence factors. Recently, a novel secretion system was discovered in several Gram‐negative bacterial pathogens, and was designated as the type VI secretion system (T6SS). In Edwardsiella tarda, a partial E. tardavirulent protein (EVP) gene cluster was implicated in protein secretion. Here, we identified the entire EVP cluster as a T6SS and two additional secreted proteins (EvpI, a homologue of VgrG, and EvpP) were found. We systematically mutagenized all the 16 EVP genes and found that the secretion of EvpP was dependent on 13 EVP proteins including EvpC (a homologue of Hcp) and EvpI but not EvpD and EvpJ. All EVP mutants except ΔevpD were attenuated in blue gourami fish. The 16 EVP proteins can be grouped according to their functions and cellular locations. The first group comprises 11 non‐secreted and possibly intracellular apparatus proteins. Among them, EvpO, a putative ATPase which contained a Walker A motif, showed possible interactions with three EVP proteins (EvpA, EvpL and EvpN). The second group includes three secreted proteins (EvpC, EvpI and EvpP). The secretion of EvpC and EvpI is mutually dependent, and they are required for the secretion of EvpP. The interaction between EvpC and EvpP was demonstrated. Lastly, two proteins (EvpD and EvpJ) are not required for the T6SS‐dependent secretion.
Dimerization or oligomerization of the actin‐like FtsA protein enhances the integrity of the cytokinetic Z ring
Authors: Shiomi Daisuke , Margolin William
Published: November 2007

In bacteria, the actin‐like FtsA protein interacts with the tubulin‐like FtsZ protein, helping to assemble the cytokinetic Z ring, anchor it to the cytoplasmic membrane and recruit other essential divisome proteins. FtsA also interacts with itself, but it is not clear whether this self‐interaction is required for its full functionality. Here we describe new dominant negative missense mutations in Escherichia coli ftsA that specifically inhibit FtsA homodimerization and simultaneously cause disruption of Z rings. The negative effects of one mutation, M71A, were suppressed by altering levels of certain division proteins or by additional mutations in ftsA that promote increased integrity of the Z ring. Remarkably, when FtsA, FtsA‐M71A, and other mutants of FtsA that compromise self‐interaction were connected in a tandem repeat, they were at least partially functional and suppressed defects of an ftsZ84(ts) mutation. This gain of function by FtsA tandems further suggested that FtsA monomers cause deleterious interactions with FtsZ and that increased dimerization or oligomerization of FtsA enhances its ability to promote Z‐ring integrity. Therefore, we propose that FtsZ assembly is regulated by the extent of FtsA oligomerization.
The ClpPX protease is required for radioresistance and regulates cell division after γ‐irradiation in Deinococcus radiodurans
Authors: Servant Pascale , Jolivet Edmond , Bentchikou Esma , Mennecier Samuel , Bailone Adriana , Sommer Suzanne
Published: November 2007

Protein degradation in bacteria is involved in diverse cellular responses to environmental stimuli and in removing potentially toxic damaged proteins or protein aggregates. ATP‐dependent proteases play a key role in these processes. Here, we have individually inactivated all the ATP‐dependent proteases belonging to the Clp or Lon families in Deinococcus radiodurans. The mutants were tested for survival after γ‐irradiation and for sensitivity to the tRNA analogue puromycin in order to assess the impact of each disruption on radioresistance, as well as on proteolysis of misfolded proteins. We found that inactivation of the ClpPX protease significantly decreased cell survival at elevated γ‐irradiation doses, while inactivation of Lon1 and Lon2 proteases reduced resistance to puromycin, suggesting that they play a role in eliminating damaged proteins. Mutants devoid of ClpPX protease displayed altered kinetics of DNA double‐strand break repair and resumed cell division after an exceedingly long lag phase following completion of DNA repair. During this stasis period, most of the ΔclpPX irradiated cells showed decondensed nucleoids and abnormal septa and some cells were devoid of DNA. We propose that the ClpPX protease is involved in the control of proper chromosome segregation and cell division in cells recovering from DNA damage.
Campylobacter sialyltransferase gene polymorphism directs clinical features of Guillain–Barré syndrome
Authors: Yuki Nobuhiro
Published: November 2007

Progress has been made in Guillain–Barré syndrome, a post‐infectious autoimmune neuropathy, especially on identifying Campylobacter jejuni genes responsible for the development and determinant of clinical features. C. jejuni strains carrying a sialyltransferase gene (cst‐II), which is essential for the biosynthesis of ganglioside‐like lipo‐oligosaccharides (LOSs), are associated with the development of Guillain–Barré syndrome. The C. jejuni sialyltransferase (Cst‐II) consists of 291 amino acids, and the 51st determines its enzymatic activity. Strains with cst‐II (Thr51) expressed GM1‐like and GD1a‐like LOS, whereas strains with cst‐II (Asn51) expressed GT1a‐like and GD1c‐like LOS. Patients infected with the cst‐II (Thr51) strains had anti‐GM1 or anti‐GD1a IgG antibodies, and showed limb weakness. Patients infected with the cst‐II (Asn51) strains had anti‐GQ1b IgG antibodies, and showed ophthalmoplegia and ataxia. The cst‐II gene is responsible for the development of Guillain–Barré and Fisher syndromes, and the polymorphism (Thr/Asn51) determines which syndrome develops after C. jejuni enteritis.
The function of sphingolipids in the nervous system: lessons learnt from mouse models of specific sphingolipid activator protein deficiencies
Authors: Matsuda Junko , Yoneshige Azusa , Suzuki Kunihiko
Published: November 2007

We have generated specific saposin A and D deficient mouse mutants by the gene targeting technology. Saposin A deficient mice showed the clinical, biochemical and pathological phenotype of a chronic form of globoid cell leukodystrophy (Krabbe disease) establishing that saposin A is essential for in vivo degradation of galactosylceramide. Saposin D deficient mice showed an accumulation of ceramides containing α‐hydroxy fatty acids (HFA/d18:1) in the brain and kidney and showed renal tubular degeneration and cerebellar Purkinje cell loss. Here we review the current information which we have learnt from these mouse models of specific sphingolipid activator protein deficiencies. Collectively, the information provides support for the potential importance of sphingolipids in the function of the nervous system.
Glycosignaling in neural stem cells: involvement of glycoconjugates in signal transduction modulating the neural stem cell fate
Authors: Yu Robert K. , Yanagisawa Makoto
Published: November 2007

The mammalian CNS is organized by a variety of cells, such as neurons and glia, which are generated from neural stem cells (NSCs), undifferentiated neural cells characterized by their high proliferative potential while retaining their capacity for self‐ renewal and multipotency. Various signals from the environment, such as the ‘niche,’ modulate the fate of NSCs in their ability for self‐renewal, proliferation, differentiation, and survival. There is increasing evidence that glycoconjugates, including proteoglycans, glycoproteins, and glycolipids, which are part of the plasma membrane glycocalyx network, are involved in mediation of these signals. In the present review, we discuss the roles of glycoconjugates in regulating the fate of NSCs and in supporting the underlying signal transduction mechanisms.
Experimental approaches to interfere with the polysialylation of the neural cell adhesion molecule in vitro and in vivo§
Authors: Bork Kaya , Gagiannis Daniel , Orthmann André , Weidemann Wenke , Kontou Maria , Reutter Werner , Horstkorte Rüdiger
Published: November 2007

Sialic acid (Sia) is expressed as terminal sugar in many glycoconjugates and plays an important role during development and regeneration. Addition of homopolymers of Sia (polysialic acid; polySia/PSA) is a unique and highly regulated post‐translational modification of the neural cell adhesion molecule (NCAM). The presence of polySia affects NCAM‐dependent cell adhesion and plays an important role during brain development, neural regeneration, and plastic processes including learning and memory. PolySia‐NCAM is expressed on several neuroendocrine tumors of high malignancy and correlates with poor prognosis. Two closely related enzymes, the polysialyltransferases ST8SiaII and ST8SiaIV, catalyze the biosynthesis of polySia. This review summarizes recent knowledge on Sia biosynthesis and the correlation between Sia biosynthesis and polysialylation of NCAM and report on approaches to modify the degree of polySia on NCAM in vitro and in vivo. First, we describe the inhibition of polysialylation of NCAM in ST8SiaII‐expressing cells using synthetic Sia precursors. Second, we demonstrate that the key enzyme of the Sia biosynthesis (UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase) regulates and limits the synthesis of polySia by controlling the cellular Sia concentration.
Modulation of cell functions by glycosphingolipid metabolic remodeling in the plasma membrane
Authors: Prinetti Alessandro , Chigorno Vanna , Mauri Laura , Loberto Nicoletta , Sonnino Sandro
Published: November 2007

The endoplasmic reticulum and the Golgi apparatus are the subcellular sites for glycosphingolipid neobiosynthesis. In addition to this very well‐established knowledge, it is now emerging that post‐Golgi changes in glycosphingolipid structures occurring at the plasma membrane are an important opportunity to modulate cell glycosphingolipid composition and to affect consequently a number of signaling processes. In fact, it is possible to modify very rapidly the membrane organization by the modulation of plasma membrane‐associated enzymes through external stimuli, thus affecting the membrane environment and the functional properties of plasma membrane proteins involved in cell signaling.

The number of enzymes for glycosphingolipid metabolism that have been shown to be associated with the plasma membrane and the information on their features are growing very rapidly, and today some of these enzymes have been deeply characterized. In this review, we focus on the possible role and on the involvement of these plasma membrane‐associated enzymes in modulating cell functions.