bluuebunny/crossref_metadata_2025 huggingface dataset:
The Palaeozoic history of the Western Desert of Egypt
Authors: Keeley MARTIN L.
Published: November 2007

Abstract A formal stratigraphical scheme is proposed for the Palaeozoic succession encountered in the subsurface of the Western Desert of Egypt, and is compared to other published schemes in North Africa. Two groups and seven formations span the interval from the Mid Cambrian to the Early Permian. The resolution between these superficially similar clastic‐dominated units is enhanced by the use of the palyno‐stratigraphical zonation devised by Gueinn & Rasul. It is apparent from an analysis of this rock sequence that two depositional regimes can be recognized. In the first of these, the Ghazalat Basin lay over the central Western Desert, and was bounded by high axes to the west and south‐east. An inversion event of Early Tournaisian age preceded a new depositional regime, centred along the Libyan border: the Tehenu Basin. A poorly understood sequence of strike‐slip movements on the Trans‐African Lineament is shown to be the most likely cause of this complex basin history. One consequence of this hypothesis is, however, to throw into question the validity of correlations made with the Gulf of Suez Palaeozoic succession, across the Trans‐African Lineament.
An examination of some uncertainties associated with estimates of sedimentation rates and tectonic subsidence
Authors: Gallagher KERRY
Published: November 2007

Abstract The sensitivity of backstripping calculations (sedimentation rates and tectonic subsidence) to uncertainties regarding porosity reduction is examined. Models simulating compaction and externally sourced cementation are considered to provide first‐order bounds on the thickness and mass changes for individual sedimentary units. These bounds can be used to estimate uncertainties in sedimentation rate and subsidence estimates. With these models, the timing of cement development can be regarded as unimportant for backstripping calculations. Calculations have been made to evaluate the effect on backstripping calculations of uncertainties in sediment porosity, density and the mechanisms of porosity reduction. Departures from theoretically predicted subsidence curves of the order of 100 m or so have been variously interpreted as the result of fluctuations or uncertainties in sea‐level, palaeobathymetry, tectonic stress, sedimentation rates and stratigraphic age. Two examples are given to illustrate that such departures may occur in some subsidence curves merely as a result of imprecise assumptions regarding porosity reduction. Consideration should be given to the uncertainties in models for porosity reduction when using subsidence curves to infer second order tectonic influence during basin evolution.
Tectono‐sedimentary analysis of alternate‐polarity half‐graben basin‐fill successions: Late Devonian‐Early Carboniferous Horton Group, Cape Breton Island, Nova Scotia
Authors: Hamblin ANTHONY P. , Rust BRIAN R.
Published: November 2007

Abstract The Devono‐Carboniferous Horton Group of Cape Breton Island was mostly deposited in two fault‐bounded asymmetric sub‐basins which were part of a large intracontinental rift system. This system lay at a palaeolatitude of about 10–15o S–a warm, semi‐arid climate. The half‐graben sub‐basins had opposed polarity, were approximately 100 times 50 km in size and were separated by a narrow zone of elevated Acadian basement. These features are common to the adjacent structural segments of known rifts, and are unlike those of transtensive pull‐apart systems. Sedimentation occurred in four successive depositional systems which reflect a tectonic evolution of increased and then decreased extensional subsidence through the 8–12 Myr interval represented. Post‐Acadian sedimentation began with System 1 bimodal volcanics and grey distal braided fluvial sediments deposited in a slowly subsiding broad linear sag basin. System 2 consists of reddened braidplain sediments near fault‐bounded margins and mudflat/playa sediments in sub‐basin centres, deposited in two discrete asymmetric sub‐basins with a general upward‐fining trend. Gradual expansion of the mudflat setting and confinement of coarse marginal fades is interpreted as a response to increasingly rapid and deep fault‐bounded subsidence. Depositional System 3, is a complex of grey lacustrine offshore, shoreline and fan delta facies deposited in two adjacent half‐graben segments with opposed polarity of asymmetry. An increased rate of tectonic subsidence allowed a large standing body of water to accumulate lacustrine sediments along the axis of each sub‐basin during this phase of maximum subsidence. System 4 consists of reddened proximal alluvial fan, medial fluvial and distal grey meandering fluvial/floodplain sediments which accumulated in sub‐basins with fault‐bounded margins and asymmetry identical to those of earlier systems, indicating a continuation of tectonic style. However, an overall coarsening‐upward trend indicates waning of active fault‐related subsidence and consequent progradation of marginal coarse wedges to fill the sub‐basins. Rapid marine transgression and deposition of Windsor Group carbonates, evaporites and elastics continued within a more extensive rift basin during renewed fault‐bounded subsidence.
The inception and early evolution of the North Alpine Foreland Basin, Switzerland
Authors: Allen Philip A. , Crampton Sarah L. , Sinclair Hugh D.
Published: November 2007

The stratigraphy of the Eocene‐Miocene peripheral foreland basin in Switzerland consists of basal deposits of Nummulitic Limestones and Globigerina Marls representing a phase of deepening, followed by two shallowing‐up megacycles culminating in fully continental sedimentation.

The onset of sedimentation was diachronous and took place on an unconformity surface with increasing stratigraphic gap to the north and west. In the Ultrahelvetic units, which were derived from the south and have a provenance between the Helvetic shelf and the Penninic ocean, the stratigraphic gap is minimal. This restricts the initiation of erosion of the southern European margin due to emersion to post‐Maastrichtian and pre‐late Palaeocene. This coincides with the final closing of the Valais trough and may therefore be interpreted as the point at which continental flexure s. s. started. In the autochthon, the subcrop map of the unconformity surface shows that the regional pattern of subcropping units is oblique to both neo‐Alpine tectonic structures and Helvetic (Mesozoic) passive margin structures. There are local zones of disruption to the broad regional pattern suggesting that the basal unconformity was corrugated. Both the paliaspastic restoration of the autochthon relative to the thrust front during the Palaeocene, and the regional pattern of erosion indicate that the basal unconformity may be due to erosion of a flexural forebulge.

Following deposition of the shallow water Nummulitic Limestones and the deeper water Globigerina Marls, clastic sediments were shed from the orogenic wedge in the south. These turbidites, the Taveyannaz Sandstones, filled both ponded basins at the contemporaneous thrust front and the frontal trench or foredeep. Evidently, early thrusts drove at a shallow level into the embryonic basin as ‘front‐runners’, whereas most shortening and uplift continued to take place within the main part of the orogenic wedge further to the south. Eventually, the frontal palaeohighs, together with the turbidite basins, were buried by the northward emplacement of surface mud‐slides, and sediment depocentres were translated northwards onto the foreland.

The most likely cause of the underfilled ‘Flysch’ stage is the rapid advance of a submarine thrust wedge over the flexed European plate which resulted in (i) low sediment fluxes and (ii) high subsidence rates associated with the rapid migration of the load and depocentre. Later, as the rate of advance slowed and the wedge became subaerially exposed, the basin rapidly filled with coarse‐grained detritus representing the ‘Molasse’ stage.
Early fill of the Western Irish Namurian Basin: a complex relationship between turbidites and deltas
Authors: Collinson John D. , Martinsen Ole , Bakken Bente , Kloster Anne
Published: November 2007

The Western Irish Namurian Basin developed in Early Carboniferous times as a result of extension across the Shannon Lineament which probably coincides with the lapetus Suture. During the late Dinantian, axial areas of the NE‐SW elongate trough became deep, whilst shallow‐water limestones were deposited on the flanks. This bathymetry persisted into the Namurian when carbonate deposition ceased. In axial areas, a relatively thick mudstone succession spans earliest Namurian to Chokierian whilst on the northwestern marginal shelf, a thin, condensed Namurian mudstone sequence, in which pre‐Chokierian sediments are apparently absent, rests unconformably on the Dinantian. From late Chokierian to early Kinderscoutian, the basin was filled by sand‐dominated clastic sediments. Sand deposition began in the axial area with deposition of a thick turbidite sequence, the Ross Formation, which is largely equivalent to the condensed mudstone succession on the flanks. Turbidity currents flowed mainly axially towards the north‐east and deposited a sequence lacking well‐defined patterns of vertical bed‐thickness change. Channels and slide sheets occur towards the top of the formation. The turbidite system seems to have lacked well‐defined lobes and stable distributary channels.

Overlying the Ross Formation, the Gull Island Formation shows a decreasing incidence of turbidite sandstones at the expense of increasing siltstones. This formation is characterized by major slides and slumps interbedded with undisturbed strata. In the flanking areas of the basin, the formation is thinner, has only a few turbidites in the sequence above the condensed mudstones and contains only one slide sheet. Overall the formation is interpreted as the deposit of a major prograding slope, the lower part representing a ramp upon which turbidites were deposited, the upper part a highly unstable muddy slope lacking any conspicuous feeder channels through which sand might have been transferred to deeper water. Progradation of the slope appears to have been increasingly from the northwestern flank of the trough which is similar to the direction deduced for the overlying deltaic Tullig cyclothem which completes the initial basin fill.

Whilst several features of the succession can be explained by envisaging the whole sequence as the product of one linked depositional system, the shifting directions of palaeocurrents and palaeoslope raise problems. The switch from axial to lateral supply casts doubt on the strict application of Walther's Law to the total sequence and seems to demand large avulsive shifts of the delta system on the shelf area to the west.
Stratigraphic record and palaeogeographical context of the Neogene basins in the Betic Cordillera, Spain
Authors: de Galdeano C. SANZ , Vera J. A.
Published: November 2007

The Betic Cordillera (Southern Spain) acquired its present configuration during the Neogene. The formation, evolution and total or partial destruction of Neogene sedimentary basins were highly controlled by the geodynamic situations and the positions of the basins in the Betic Cordillera.

It is impossible to reconstruct the geometry of basins formed during the Early and Middle Miocene, concurrently with the westward drift of the Internal Zones, because in many cases only small outcrops remain. The basins formed on the mobile substratum (the Internal Zones) are characterized by a sedimentary infill made up of synorogenic deposits, which were intensely deformed towards the end of the Middle Miocene, and which were heavily eroded before the beginning of the Late Miocene. In the External Zones, deposition mainly took place in the North Betic Strait, an area across which there was wide communication between the Atlantic and the Mediterranean, which received huge olistostromic masses in its more mobile sector (the foredeep basin), and which evolved differently in its eastern and western sectors.

The palaeogeography of the Cordillera changed radically at the beginning of the Late Miocene, when the westward drift of the Internal Zones ceased. During this time the North Betic Strait disappeared and, in what had been its northwestern half approximately, the Guadalquivir Basin became individualized. This basin, which was located between the Betic Chain and the emerged Hercynian Massif, acquired a structure similar to that of the present basin and its extension was also similar to that of the present Neogene outcrops.

Intramontane basins became individualized in the recently formed and progressively emerged mountain chain, reaching a development and size in this Cordillera much greater than in other Alpine chains. These basins are characterized by their thick infills, which are unconformable on the folded and deformed substratum, and which can be subdivided according to the different movements of the fault sets that controlled their evolution.
Forward modelling of porosity and pore pressure evolution in sedimentary basins
Authors: Audet D. M. , McConnell J. D. C.
Published: November 2007

The gravitational compaction of sediments is an important process in forward basin modelling. This paper presents a mathematical model for the one‐dimensional compaction of an accreting layer of argillaceous sediments. Realistic constitutive laws for the clay compressibility and the clay permeability, based on soil mechanics tests, were incorporated into the model. The governing equations were put in dimensionless form and the extent of abnormal pore fluid pressure development was found to depend on the sedimentation parameter, a dimensionless group representing the ratio of the sediment hydraulic conductivity to the sediment accumulation rate. The effects of clay compressibility were studied and highly colloidal clays such as montmorillonite developed higher overpressures than less compressible materials. The results also showed that overpressuring developed in shales for cases in which the clay permeability did not go to zero in the limit of zero porosity. Linear models based on simplifying assumptions inappropriate for sedimentary basins were found to give significantly different estimates for the conditions leading to overpressuring. Using reasonable parameters, the model adequately reproduced porosity and pore pressure profiles measured in the sand‐shale sequences of the South Caspian Sea.
Differential response of a Devonian‐Carboniferous platform‐deeper basin system to sea‐level change and tectonics, N. Chilean Andes
Authors: Bahlburg HEINRICH , Breitkreuz CHRISTOPH
Published: November 2007

Deposition of a 2700‐m‐thick clastic platform succession in a N‐S striking basin in northern Chile began in the Early Devonian during a global sea‐level rise. A transition to terrestrial facies took place at the Early‐Late Carboniferous boundary when the Gondwana glaciation began and global sea‐level dropped. On the platform, interbedded cross‐bedded or bioturbated sandstones, offshore tidal dunes and sand waves, and mudstones and tempestites suggest switching intertidal and shallow or deep subtidal environments. However, evidence for subaerial erosion indicates a significant regression during the Early Devonian.

In an adjacent and deeper N‐S striking sub‐basin to the W, up to 3600 m of turbidites were deposited from the Late Devonian to the Late Carboniferous by mainly southerly palaeocurrents. Turbidites accumulated in coarse‐grained proximal sand lobes in the N, and in fine‐grained lobe fringe and basin plain environments in the S, with alternating upward‐thinning and upward‐thickening cycles typical of tectonically controlled aggradational turbidite systems.

The sedimentological data indicate that the deeper basin depositional system evolved to a large extent independently from the platform system. Sediment in the deeper basin is less mature and more poorly sorted than that on the platform, suggesting that detritus bypassed the platform and was shed directly from the source areas into the western basin. The only depositional link between the platform and deeper basin systems seems to be longshore platform currents which may have funnelled minor quantities of mature sand into the deeper basin via bypass canyons. Although platform and deeper basin evolved in a common extensional tectonic setting, the platform reflects eustatic changes of sea‐level whereas deposition in the deeper basin records syndepositional tectonics.
The timing and extent of illite formation in Ordovician K‐bentonites at the Cincinnati Arch, the Nashville Dome and north‐eastern Illinois basin
Authors: Elliott W. CRAWFORD , Aronson JAMES L.
Published: November 2007

The K/Ar ages of illite/smectite (I/S) were measured from Middle Ordovician K‐bentonites both west and east of the present crest of the Cincinnati Arch and the Nashville dome to test a previous hypothesis that I/S formed by reaction with migrated saline solutions during the Alleghanian Orogeny. The K/Ar ages of I/S at the distal margin of the southern Appalachian basin and from central Indiana range from 251 to 277 Ma. However, the ages of I/S from west of the crest of the Cincinnati Arch are slightly older (286–301 Ma) and the ages of I/S from north‐eastern Indiana, on the northern edge of the Kankakee Arch and in effect in the Michigan basin, are the oldest measured in this study (315–325 Ma).

The westward decrease in the K/Ar ages of I/S from Late Pennsylvanian ages in the proximal basin (286–303 Ma) to Permian (251–277 Ma) at the distal margin suggest that I/S was formed by the westward migration of fluids during the Alleghanian Orogeny as opposed to being formed by projected deep burial by Permian sediments. Moreover, the available thermal maturation data suggest the Cincinnati Arch was not buried deeply. The ages of I/S west of the Cincinnati Arch are an enigma as they are older than the ages in the distal Appalachian basin. The ages of I/S from central Indiana within the Illinois basin suggest the possibility that I/S was formed by reaction with fluids that migrated from the Ouachita orogenic belt in Mississippi. The oldest ages of I/S from north‐eastern Indiana suggest the formation of I/S might have been influenced by the presence of potassic brines from the Michigan basin.
Seismic modeling of Tertiary sandstone clinothems, Spitsbergen
Authors: Helland‐Hansen WILLIAM , Helle HANS B. , Sunde KJELL
Published: November 2007

Two‐dimensional seismic modelling has been undertaken on an overall progradational succession of sloping mudstone and sandstone units from the Palaeogene of Spitsbergen. The modelling shows that the main geometric features of the section would be resolved at 1500 m depth (with frequencies below 60 Hz, which is common in seismic data at these depths). However, interference between the base and top of lithological units gives lateral amplitude variations and discrepancies between the seismic image and the geometrical model. This is particularly prominent in low‐frequency models. Terminations of reflectors, resembling toplap and onlap, may be interpreted, but are artefacts of the general convergence of lithological units present in the geometrical model. The geological section causes a seismic pattern resembling sigmoid progradational seismic facies. Two‐dimensional seismic modelling is an efficient tool in bridging the gap between outcrop observations and subsurface data. Hence, modelled outcrop sections are important as reference points' for improved seismic stratigraphic interpretation.
Tectonic control on sedimentary evolution of three North Atlantic borderland Mesozoic basins1
Authors: Sinclair I. K. , Shannon P. M. , Williams B. P. J. , Harker S. D. , Mooren J. G.
Published: November 2007

Multiple episodes of extensional tectonism dominated the formation of Mesozoic fault‐bounded basins on the Grand Banks of Newfoundland, the Irish Continental Shelf and the central North Sea. A range of structural and stratigraphic responses in the Jeanne d'Arc, Porcupine and Moray Firth basins support widespread synchronous tectonic controls on sedimentation during one of these episodes, the Late Cimmerian.

Rifting was preceded by a phase of related tectonism during which subsidence rates began to vary across broad areas but without significant fault block rotation. This Late Cimmerian ‘onset warp’ pattern of subsidence is considered to have been essential in the establishment of restricted anoxic basins from latest Oxfordian through Kimmeridgian (sensu gallico) time and the development of one prolific layer of organic‐rich source rocks.

The most prominent and widely recognized structural/lithostratigraphic response to Late Cimmerian rifting was the deposition of sediment wedges. Tithonian to early Valanginian strata generally thicken‐ into northerly trending faults in the Jeanne d'Arc and Porcupine basins, indicating that extensional stress was orientated WNW‐ESE across a very broad area. The misalignment of this regional Late Cimmerian extensional stress with local inherited structural fabric may be responsible for transpressional uplift of individual fault blocks in the Outer Moray Firth basin.

Sedimentological responses to Late Cimmerian rifting were varied, though a common lithofacies stacking pattern is recognized. Variably thick conglomerates and/or sandstones were widely deposited at the start of rift deformation, while palaeoenvironments ranged from alluvial and braid plain to submarine fan even within individual basins. The relatively coarse basal sediments fine upwards into a second layer of commonly organic‐rich shales and mark The widest variations in palaeoenvironments and sediment thicknesses occurred during the last phase of Late Cimmerian rift tectonism, though all three basins show evidence of decreasing water depths, increasing oxygen levels and increasing grain size. This lithofacies stacking pattern of relatively coarse to fine to coarse (reservoir/source/reservoir) and the development of bounding unconformities are largely attributable to progressive changes in rift‐controlled subsidence. Rift basin subsidence rates are interpreted to increase from a low at initiation of faulting to a mid‐rift peak, followed by slowing subsidence to the end of extension. A number of counteracting crustal mechanisms that may account for progressive variations in rift‐induced subsidence are considered.
Effect of the Cretaceous Serra Geral igneous event on the temperatures and heat flow of the Parana 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 Parana 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 abovc 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.
Brine expulsion, fluid transport and metallization spanning 2.0 Gyr in basins of southern and central Africa
Authors: Duane M. J. , Saggerson E. P.
Published: November 2007

Mineral provinces in southern and central Africa are strongly controlled by major structural trends, the alignment of sedimentary basins and metamorphically induced thermal regimes deep in the crust. Ore deposits are preferentially located on cooler margins of orogenic belts and are ultimately end‐products of fluid expulsion out of the deeper parts of orogenic axes. Metamorphic and structural vectors within orogenic belts adjacent to major cratons show a trend of high‐grade thermal overprinting in the cores of axes and lower metamorphic regimes acting on the distal margins of orogens (e.g. foreland basins). This apparent pattern is considered to have importance in the expulsion of at least three generations of mineralizing fluids beginning with exhalative migration during diagenesis and culminating much later in thrust‐controlled expulsion onto adjacent craton margins. Fluids within the hydrosphere that accumulate initially through topographic gradients in the sediments mixed with components of the mantle (CO2). After storage within the crust, migration, enforced by metamorphic processes, transferred fluids out of, and away from, high thermal regimes in the axes of belts, leading to their present preservation around the margins of the major cratonic nuclei.
Miocene‐Pliocene half‐graben evolution, detachment faulting and late‐stage core complex uplift from reflection seismic data in south‐east Arizona
Authors: Kruger J. M. , Johnson R. A. , Houser B. B.
Published: November 2007

Reflection seismic data show that the late Cenozoic Safford Basin in the Basin and Range of south‐eastern Arizona, is a 4.5‐km‐deep, NW‐trending, SW‐dipping half graben composed of middle Miocene to upper Pliocene sediments, separated by a late Miocene sequence boundary into lower and upper basin‐fill sequences. Extension during lower basin‐fill deposition was accommodated along an E‐dipping range‐bounding fault comprising a secondary breakaway zone along the north‐east flank of the Pinaleño Mountains core complex. This fault was a listric detachment fault, active throughout the mid‐Tertiary and late Cenozoic, or a younger fault splay that cut or merged with the detachment fault. Most extension in the basin was accommodated by slip on the range‐bounding fault, although episodic movement along antithetic faults temporarily created a symmetric graben. Upper‐plate movement over bends in the range‐bounding fault created rollover structures in the basin fill and affected deposition within the half graben. Rapid periods of subsidence relative to sedimentation during lower basin‐fill deposition created thick, laterally extensive lacustrine or alluvial plain deposits, and restricted proximal alluvian‐fan deposits to the basin margins. A period of rapid extension and subsidence relative to sediment influx, or steepening of the upper segment of the range‐bounding fault at the start of upper basin‐fill deposition resulted in a large downwarp over a major fault bend. Sedimentation was restricted to this downwarp until filled. Episodic subsidence during upper basin‐fill deposition caused widespread interbedding of lacustrine and fluvial deposits. Northeastward tilting along the south‐western flank of the basin and north‐eastward migration of the depocentre during later periods of upper basin‐fill deposition suggest decreased extension rates relative to late‐stage core complex uplift.
Evolution of a large Miocene growth structure in the upper plate of the Whipple detachment fault, northeastern Whipple Mountains, California
Authors: Dorsey REBECCA J. , Becker ULF
Published: November 2007

Miocene sedimentary and volcanic rocks in the north‐eastern Whipple Mountains, California, and the north‐western Aubrey Hills, Arizona, accumulated in the upper plate of the Whipple detachment fault during regional extension and slip on the detachment. Miocene rocks in this area can be divided into three sequences: (1) pre‐18.5‐Ma dominantly volcanic rocks; (2) the 18.5‐Ma Peach Springs Tuff; and (3) post‐18.5‐Ma dominantly sedimentary rocks. Important stratigraphic markers in sequence 3 include a 100‐ to 14–0‐m‐thick basalt unit and the voluminous War Eagle landslide, both of which correlate across Lake Havasu from the north‐east Whipple Mountains to the Aurbrey Hills. We divide clastic sedimentary rocks of sequence 3 into three informal members: (3a) conglomerate and sandstone stratigraphically beneath the basalt; (3b) conglomerate and sandstone above the basalt and below the War Eagle landslide; and (3c) conglomerate and sandstone that overlie the War Eagle landslide. Detailed stratigraphic analysis and field mapping reveal dramatic south‐westward thickening of member 3b strata, from about 50 m in the Aubrey Hills to over 1500 m in the north‐east Whipple Mountains. In the north‐east Whipple Mountains, this thick dipping section is overlain by the War Eagle landslide along a major angular unconformity; in the Aubrey Hills the base of the War Eagle landslide is roughly parallel to bedding dips of underlying strata.

The above stratigraphic relationships can be explained by syndepositional growth of a rollover monocline by progressive tilting of the hangingwall above a master listric normal fault (Whipple detachment fault). This phase of upper‐plate deformation began shortly after deposition of the basalt and ended prior to emplacement of the War Eagle landslide. Interbedded breccias low in member 3b, about 100 m above the basalt, record the first appearance of mylonitic detritus in the section. Growth of this upper‐plate rollover was thus initiated at about the same time (shortly after deposition of the basalt) that the lower plate of the Whipple detachment fault was first exposed at the earth's surface by tectonic denudation and large‐scale crustal uplift. These events are interpreted to record initiation of a secondary breakaway fault on the north‐east flank of the growing Whipple detachment dome shortly after deposition of the basalt at about 14.5 (±1.0) Ma.
Example of a supradetachment basin within a pull‐apart tectonic setting: Mormon Point, Death Valley, California
Authors: Burchfiel B. C. , Molnar P. , Zhang P. , Deng Q. , Zhang W. , Wang Y.
Published: November 2007

The geological features now exposed at Mormon Point, Death Valley, reveal processes of extension that continue to be active, but are concealed beneath the east side of Death Valley. Late Cenozoic sedimentary rocks at Mormon Point crop out in the hangingwall of the Mormon Point low‐angle normal fault zone, a fault zone that formed within a releasing bend of the oblique‐slip (right‐normal slip) fault zone along the east side of Death Valley. The late Cenozoic sedimentary rocks were part of the valley when the low‐angle fault zone was active, but during late Quaternary time they became part of the Black Mountains block and were uplifted. Rocks and structures exposed at Mormon Point are an example of the types of features developed in a releasing bend along the margins of a major pull‐apart structure, and in this example they are very similar to features associated with regional detachment faults.

The oldest sedimentary rocks in the hangingwall of the Mormon Point low‐angle fault zone dip steeply to moderately east or north‐east and were faulted and rotated in an extensional kinematic environment different from that recorded by rocks and structures associated with younger rocks in the hangingwall. Some of the younger parts of the late Cenozoic sedimentary rocks were deposited, faulted and rotated during movement on the Mormon Point low‐angle normal fault. Progressively, strata are less faulted and less rotated. The Mormon Point low‐angle normal fault has an irregular fault surface whose segments define intersections that plunge 18°‐30°, N10°‐40°W, with a maximum of 22°, N22°W that we interpret to be the general direction of slip. Thus, even though Death Valley trends north, movement on the faults responsible for its formation was at least locally north‐northwest. Gouge and disrupted conglomerates along the faults are interpreted to have formed either as adjustments to accommodate space problems at the corners of blocks or along faults that bounded blocks during their displacement and rotation.

The younger units of the late Cenozoic sedimentary rock sequence and the geomorphic surfaces developed on them are rarely faulted, not rotated, and overlap the Mormon Point low‐angle faults. Active faults cut Holocene alluvium north of the late Cenozoic rocks and form the present boundary between Mormon Point and the Black Mountains. The distribution of active faults defines a releasing bend that mimics the older releasing bend formed by the Mormon Point low‐angle fault zone. Rocks and structures similar to those exposed above the Mormon Point low‐angle fault zone are probably forming today beneath the east side of Death Valley north‐west of Mormon Point.
Tectonic transition from the Songpan‐Garzê Fold Belt to the Sichuan Basin, south‐western China
Authors: Chen SHE FA , Wilson CHRISTOPHER J. L. , Worley BRENTON A.
Published: November 2007

The formation of the Songpan‐Garzê Fold Belt and the initiation of the terrestrial Sichuan Basin are related to closing of the Palaeo‐Tethys during the Late Triassic Indosinian orogeny. The Songpan‐Garzê Fold Belt is composed of Triassic (T1‐‐T23) turbiditic deposits and Palaeozoic greywacke‐shale, whereas the Sichuan Basin consists of Sinian to middle Upper Triassic (T23) platform carbonates and Upper Triassic (T3X to Quaternary terrestrial elastics. Three principal deformation episodes during the Late Triassic (Norian to Rhaetian) were progressively localized towards the south‐eastern margin of the fold belt. D1 was a SW‐directed shortening event, related to continuous subduction of the Palaeo‐Tethys, and produced NW‐trending structures. Differential strain between the fold belt and the Sichuan Basin was accommodated by sinistral shearing along a NE‐trending transitional zone during D2. D3 SE‐directed compression was the result of collision between the Cimmerian and Eurasian Continents and initiated the Longmen Mountains Thrust‐Nappe Belt and terrestrial Sichuan Basin. Post‐D3 deformation, related to SE‐directed thrusting in the Longmen Mountains, then propagated from hinterland to foreland. The Indosinian orogeny closed the Palaeo‐Tethys and terminated the marine conditions that dominated the early evolution of the intracratonic Sichuan Basin. Tectonic loading from the exhumed fold belt and Thrust‐Nappe Belt induced substantial subsidence in the Sichuan Basin, especially in the Western Sichuan Foreland Basin, resulting in the deposition of a terrestrial clastic sequence during Late Triassic (T3X to Quaternary times. The foreland basin history comprises an early stage during the Late Triassic (T3x1–2), an over‐fill stage during the latest Triassic to Early Cretaceous (T3X3‐ K1J), and a shrinking stage from the Late Cretaceous to the Quaternary (K2J‐Q). These can be correlated with tectonic events in the Thrust‐Nappe Belt.
Deep‐penetrating MCS images of the South Gabon Basin: implications for rift tectonics and post‐breakup salt remobilization
Authors: Meyers J. B. , Rosendahl B. R. , Jr J. A. AUSTIN
Published: November 2007

AbstractRifted margin architecture along part of the southern Gabonese margin is interpreted from four deep‐penetration, multichannel seismic reflection (MCS) profiles. A series of synthetically faulted crustal blocks are identified, separated by dominantly seaward‐dipping fault zones formed during Cretaceous rifting between Africa and South America. Extensional strain ratios are ≅ 1.5. These faults appear either to transect the entire crustal section or are interrupted by discontinuous zones of midcrustal reflections which may represent detachments.

Outer acoustic basement highs are situated just seaward of the continental slope. On the combined basis of seismic geometry, an associated positive magnetic anomaly and an increase in free‐air gravity, these outer highs are interpreted to mark faulted transitions from rifted continental crust to ‘proto‐oceanic crust’, presumably composed of mafic volcanic rocks and possibly slivers of attenuated continental crustal blocks. The outer edge of Aptian salt lies °165 km south‐west of the edge of the continental shelf. The salt forms an° 1.5‐km‐thick horizon overlying the outer highs, and it may be autochthonous there, suggesting salt was deposited contemporaneously with emplacement of proto‐oceanic crust.

Differential subsidence and tilting between continental rift‐blocks during post‐rift margin subsidence has resulted in a sympathetic terrace‐ramp geometry in overlying Aptian salt. Salt terraces form above tops of crustal blocks, where salt tends to rise vertically, creating pillows and diapirs. Ramps connecting terraces tend to form above seaward‐facing fault zones; salt flowage there has been both lateral and vertical, creating triangular diapirs along the footwalls of growth faults. Most of these growth‐faults sole within the salt base, but a few continue into the interpreted synrift succession.
The influence of spatial errors in species occurrence data used in distribution models
Authors: Graham Catherine H , Elith Jane , Hijmans Robert J , Guisan Antoine , Townsend Peterson A , Loiselle Bette A ,   The Nceas Predicting Species Distributions Working Group
Published: November 2007

Species distribution modelling is used increasingly in both applied and theoretical research to predict how species are distributed and to understand attributes of species’ environmental requirements. In species distribution modelling, various statistical methods are used that combine species occurrence data with environmental spatial data layers to predict the suitability of any site for that species. While the number of data sharing initiatives involving species’ occurrences in the scientific community has increased dramatically over the past few years, various data quality and methodological concerns related to using these data for species distribution modelling have not been addressed adequately.

We evaluated how uncertainty in georeferences and associated locational error in occurrences influence species distribution modelling using two treatments: (1) a control treatment where models were calibrated with original, accurate data and (2) an error treatment where data were first degraded spatially to simulate locational error. To incorporate error into the coordinates, we moved each coordinate with a random number drawn from the normal distribution with a mean of zero and a standard deviation of 5 km. We evaluated the influence of error on the performance of 10 commonly used distributional modelling techniques applied to 40 species in four distinct geographical regions.

Locational error in occurrences reduced model performance in three of these regions; relatively accurate predictions of species distributions were possible for most species, even with degraded occurrences. Two species distribution modelling techniques, boosted regression trees and maximum entropy, were the best performing models in the face of locational errors. The results obtained with boosted regression trees were only slightly degraded by errors in location, and the results obtained with the maximum entropy approach were not affected by such errors.

Synthesis and applications. To use the vast array of occurrence data that exists currently for research and management relating to the geographical ranges of species, modellers need to know the influence of locational error on model quality and whether some modelling techniques are particularly robust to error. We show that certain modelling techniques are particularly robust to a moderate level of locational error and that useful predictions of species distributions can be made even when occurrence data include some error.
The ECF sigma factor σT is involved in osmotic and oxidative stress responses in Caulobacter crescentus
Authors: Alvarez‐Martinez Cristina E. , Lourenço Rogério F. , Baldini Regina L. , Laub Michael T. , Gomes Suely L.
Published: November 2007

Sigma factors of the ECF subfamily are important regulators of stress responses in bacteria. Analysis of Caulobacter crescentus genome sequence has indicated the presence of 13 members of the ECF (extracytoplasmic function) subfamily, suggesting that these regulators play an important role in C. crescentus physiology. This work describes the characterization of two highly similar C. crescentus ECF sigma factors, σU and σT. The corresponding genes are not essential under normal growth conditions and absence of σU does not impair bacterial resistance to the environmental stresses tested. However, absence of σT significantly affects the ability of C. crescentus cells to survive osmotic and oxidative stress. Using transcription fusions to sigT and sigU upstream regions we demonstrate that both genes are induced by osmotic stress in a σT‐dependent manner. Determination of sigU and sigT transcription start sites revealed an identical promoter motif, typical of ECF‐dependent promoters. Transcriptome analysis revealed 40 putative members of the σT regulon, including sigU and sigR, encoding another ECF subfamily member, and genes involved in general stress responses and cell envelope functions. Twenty of those genes exhibit the sigT/sigU promoter motif in their upstream regions. Our data indicate a role of σT in distinct stress responses in C. crescentus.
Response of winter wheat (Triticum aestivum L.) and weeds to tank mixtures of 2,4‐D plus MCPA with clodinafop propargyl
Authors: BAGHESTANI MOHAMMAD ALI , ZAND ESKANDAR , SOUFIZADEH SAEID , MIRVAKILI MOHAMMAD , JAAFARZADEH NASER
Published: November 2007

Field and greenhouse experiments were conducted in 2004 and 2005 to study weed control and the response of winter wheat to tank mixtures of 2,4‐D plus MCPA with clodinafop propargyl. The field experiments were conducted at Yazd and Oroumieh, Iran, with factorial combinations of 2,4‐D plus MCPA at 0, 975, and 1300 g ai ha−1 and with clodinafop propargyl at 0, 64, 80, 96, and 112 g ai ha−1 in four replications. The greenhouse experiments further evaluated the effect of these tank mixtures on weed control, where each herbicide mixture was considered as one treatment and the experiment was established in a randomized complete block design with four replications. In the field experiments, the herbicides were applied at wheat tillering, while in the greenhouse experiments they were applied at the beginning of the tillering stage and at the four‐leaf stage of the grass and broadleaf weeds, respectively. The results indicated antagonistic effects between 2,4‐D plus MCPA and clodinafop propargyl. The best tank mixture with regard to weed control efficacy was 2,4‐D plus MCPA at 975 g ai ha−1 with clodinafop propargyl at 96 g ai ha−1. The wheat grain yield was also increased by the tank mixture of clodinafop propargyl with 2,4‐D plus MCPA. Generally, to inhibit clodinafop propargyl efficacy reduction due to tank‐mixing with 2,4‐D plus MCPA, it is recommended that the application dose of 64 g ai ha−1 should be increased to 96 g ai ha−1.
Effects of two surfactant series on the absorption and translocation of 14C‐glyphosate in sicklepod and prickly sida
Authors: SHARMA SHIV D. , SINGH MEGH
Published: November 2007

The weed species, prickly sida (Sida spinosa L.) and sicklepod (Senna obtusifolia L.), were treated with 14C‐glyphosate alone and formulated with different polyethlylane oxide (PEO) surfactants in tallow amine ethoxylate and non‐ionic alkoxylate series to determine the amount of 14C‐glyphosate absorption and translocation. The surface tension, contact angle, and 14C‐glyphosate distribution were significantly affected by both the presence of different waxes on the plants and by the addition of surfactants to the glyphosate. The surface and contact angle values of the surfactants, with and without glyphosate, showed a significant increase as the PEO number increased in both surfactant series. A higher absorption of the 14C‐glyphosate was recorded for S. spinosa compared with S. obtusifolia. The absorption and translocation of the 14C‐glyphosate increased with the increase in the PEO number of tallow amine ethoxylate. In the case of the non‐ionic alkoxylate surfactant series, an increase in the absorption of 14C‐glyphosate was recorded when the surface tension and contact angle values decreased. There was no significant difference in the translocation values obtained in the two species after the addition of the surfactants. The amount of 14C‐glyphosate absorbed by the treated leaf was significantly higher in the case of S. spinosa compared with S. obtusifolia. A linear relationship was observed with the physical properties, 14C absorption, and the efficacy of glyphosate with the addition of the non‐ionic alkoxylate surfactant series. The percentage control was higher with the higher PEO surfactant in the tallow amine ethoxylate surfactant series and with the lower PEO surfactant in the non‐ionic alkoxylate surfactant series as the two series are chemically different.
Formulation and adjuvant effects on the absorption and translocation of 14C‐clethodim in wheat (Triticum aestivum L.)
Authors: NANDULA VIJAY K. , POSTON DANIEL H. , REDDY KRISHNA N. , KOGER CLIFFORD H.
Published: November 2007

A new formulation of clethodim {(E,E)‐(±)‐2‐(1‐[([3‐chloro‐2‐propenyl]oxy)imino]propyl)‐5‐(2‐[ethylthio]propyl)‐3‐hydroxy‐2‐cyclohexen‐1‐one} is labeled for the control of grasses and volunteer grass crops, including glyphosate‐resistant corn. The effects of the formulation (new: 0.12 kg L−1 and current: 0.24 kg L−1) and adjuvants (ammonium sulfate [AMS], crop oil concentrate [COC] or both) on the absorption and translocation of the 14C‐clethodim was determined at 1, 4, 12, 24, 48, and 72 h after treatment (HAT) in wheat under greenhouse conditions. The absorption of the 14C‐clethodim with the 0.12 kg L−1 formulation was higher than that with the 0.24 kg L−1 formulation, especially at 24 HAT and beyond, regardless of the presence or absence of an adjuvant. The addition of an adjuvant increased the absorption of the 14C‐clethodim with the 0.12 kg L−1 formulation at all harvest times, except at 72 HAT. However, there were no differences in the 14C‐clethodim absorption among the adjuvants added to the 0.12 kg L−1 formulation, except at 48 and 72 HAT. Most of the 14C‐clethodim remained in the treated leaf independent of the formulation or adjuvant. The formulation did not have an impact on the distribution of the absorbed 14C‐clethodim; however, the presence of an adjuvant increased the movement of the 14C‐clethodim out of the treated leaf. Most of the absorbed 14C‐clethodim remained in the treated leaf and a negligible amount translocated to the root. These results demonstrated the improved absorption of clethodim with a formulation containing half of the active ingredient (0.12 kg L−1) and the inclusion of both AMS and COC.