bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen-isotope studies of clastic diagenesis in the Lower Cretaceous Viking Formation, Alberta: implications for the role of meteoric water
Authors: Longstaffe Fred J. , Ayalon Avner
Published: April 2008

The oxygen-isotope compositions and paragenetic sequence of diagenetic minerals from the Lower Cretaceous Viking sandstone and conglomerate from south-central Alberta, Canada have been used to identify changes in porewater composition during diagenesis and to relate these changes to major geological events within the western Canada sedimentary basin. Large-scale influx of meteoric water has played an important role in diagenesis of this unit, especially following uplift of the basin in early Eocene time.

Diagenetic phases include early kaolinite (
δ
18
O SMOW = + 24.9 to +28.2 ‰), siderite (
δ
18
O SMOW = + 22.0 to + 23.9 ‰;
δ
13
C PDB = −6.3 to −1.3 ‰), calcite (
δ
18
O SMOW = + 26.0 ‰;
δ
13
C PDB = −0.4 ‰) and chlorite (
δ
18
O SMOW = + 10.7 − + 13.4 ‰), followed in order by dolomite (
δ
18
O SMOW = + 19.3 − + 22.1 ‰;
δ
13
C PDB = −5.9 to −2.6 ‰), calcite (
δ
18
O SMOW = + 13.9 − + 15.9 ‰;
δ
13
C PDB = −8.4 to −6.1 ‰), ankerite (
δ
18
O SMOW = + 16.3 − + 17.9 ‰;
δ
13
C PDB = −12.4 to −3.5 ‰), kaolin group minerals (
δ
18
O SMOW = + 12.0 − + 15.7 ‰), and illite (
δ
18
O SMOW = + 14.2 − + 15.7 ‰) and illite/smectite (
δ
18
O SMOW = + 13.8 − + 16.5 ‰). Quartz overgrowths (
δ
18
O SMOW = + 16.2 − + 27.4 ‰) began crystallizing relatively early during burial diagenesis and continued to form at least up to the onset of late diagenetic formation of clay minerals.

The interpretation of these results is that shallow diagenesis, early in the burial history (glauconite, pyrite, calcite, chlorite), occurred largely in the presence of seawater-derived fluids, although a freshwater influence is indicated where siderite and(or) early kaolinite cements are abundant. As compaction and burial diagenesis proceeded (diagenetic chlorite, quartz overgrowths, dolomite), the porewaters became enriched in
18
O due to water/rock interaction. Burial diagenesis was terminated in the early Eocene by uplift related to the major Laramide Orogeny. Recharge of the basin by low
18
O meteoric water occurred at this time. The meteoric water then became involved in the formation of diagenetic quartz, calcite and ankerite (and the dissolution and albitization of feldspar) at or near maximum burial temperatures, and in the crystallization at lower temperatures of kaolin group minerals, illite and illite/smectite as the post-Eocene erosion progressed.
Distribution, crustal properties and significance of seawards-dipping sub-basement reflectors off E Greenland
Authors: Larsen H. C. , Jakobsdóttir S.
Published: April 2008

We report in this paper the existence of seawards-dipping sub-basement reflectors along the entire E Greenland margin. The study is based on 8000 km of multichannel seismic data and a sonobuoy refraction seismic study providing information on the geographical and stratigraphical extension, internal geometry and crustal structure of the E Greenland dipping reflector sequence. A basaltic, subaerial seafloor-spreading origin of the reflector sequence is concluded from seismic stratigraphic analysis, including well information from the Rockall Plateau and the Vøring Plateau. Formation of the basaltic dipping reflector sequence off E Greenland took place within a period of a few million years along the axis of opening within the NE Atlantic. Duration of spreading above sea-level was relatively short (2 My) in areas of present-day deep basement, as opposed to 5–8 My in areas of present-day more shallow basement. On the highly elevated Iceland-Greenland Ridge, subaerial seafloor spreading continued into the Neogene and most likely into present-day subaerial spreading in Iceland. Following the mid-Tertiary westward shift of spreading towards Greenland, N of Iceland, spreading again took place above sea-level along this part of the Greenland margin until late Miocene, but this development only caused an erratic and shallow development of seawards-dipping reflectors.

Application of the kinematic model for crustal formation in Iceland (Pálmason 1980) onto the E Greenland dipping reflector sequence demonstrates a striking similarity between the two structures. However, volcanic productivity rate within the oldest part of the E Greenland dipping reflector sequence may be as much as three times the volcanic productivity rate recorded in Iceland with an original rift width equal to, or somewhat less than, that in Iceland. The high volcanic productivity rate caused the development of a thick extrusive upper crust (> 5–6 km) dominated by seawards-dipping reflections arising from lava flows or groups of flows which acquired their dip through postdepositional differential subsidence towards the rift zone. Refraction seismology defines a fairly flat-lying velocity zonation of the igneous crust with an anomalously thick layer 2 (3–5.5 km) in areas of well-developed dipping reflectors. The layer 2/3 boundary is seen to cut strongly across the dipping reflectors suggesting a metamorphic origin of this boundary. Initiation of seafloor spreading above sea-level is seen as a result of early upwelling of anomalously hot asthenospheric material that was able to ascend through a relatively mechanically unstretched crust and lithosphere and create a thick extrusive upper crust. Formation of a thick extrusive upper crust above sea-level only continued beyond the early spreading phase in the area of the Icelandic hot-spot (Iceland-Greenland Ridge).
Some properties of basalt lava sequences and volcanic centres in a plate-boundary environment
Authors: Kristjansson L. , Helgason J.
Published: April 2008

This paper discusses the implications that two current studies in Iceland may have in the interpretation of results from marine deep drilling and geophysical surveys in marginal volcanic areas of the N Atlantic. One study, concerning the magnetic remanence of lava flows, shows that the rate of geomagnetic reversals in the Tertiary is higher than is generally expected, and that caution must be exercised in tracing magnetic lineations between coeval submarine and subaerial formations. The other study, which deals with the distribution of major volcanic complexes within the Icelandic lava pile, demonstrates that this distribution is dependent upon various tectonic factors, especially any lateral shifts or direction changes of the active plate boundary that may have occurred.
Volcanic ash in a cored borehole W of the Shetland Islands: evidence for Selandian (late Palaeocene) volcanism in the Faeroes region
Authors: Morton A. C. , Evans D. , Harland R. , King C. , Ritchie D. K.
Published: April 2008

A volcanic ash layer, containing basic glass shards compositionally comparable to the basalts of the Faeroe-East Greenland Province, has been discovered in early Selandin sediments from a borehole W of the Shetland Isles. The available magnetostratigraphical, biostratigraphical and tephrachronological information indicates that basaltic volcanism in the province began during magnetic anomaly chron C26R, earlier than the currently accepted C24R interval, but correlating with the main period of basaltic volcanism in the British Tertiary Igneous Province.
Distribution of early Tertiary lavas in the NE Rockall Trough
Authors: Wood M. V. , Hall J. , Doody J. J.
Published: April 2008

A study of lavas of early Tertiary age in NE Rockall Trough has revealed that they can be classified on the basis of their seismic reflection character and their relationship with the overlying Tertiary sediments. The lavas have been mapped using commercial seismic reflection data. Our interpretation of the areal distribution of the subaerial flows has major implications for the subsidence history of the area. Three seismic facies are recognized:

(1)

High amplitude parallel reflections in laterally continuous sheets with steep edges.

(2)

Basinward-thinning wedges of high-amplitude discontinuous reflections.

(3)

A single high-amplitude reflection underlain by a zone of small diffractions.

These are interpreted respectively as subaerial flows, hyaloclastite deposits derived from the basalts, and tuffs.

Throughout the sedimentary sequence below the lavas, high amplitude, subhorizontal reflection packages occur. These are interpreted as sills of early Tertiary age intruding Mesozoic sediments. In places, the lavas themselves are intruded by seismically translucent bodies of up to a few kilometres across. These may represent small centres of lava extrusion.
Significance of lacustrine cherts for the environment of source-rock deposition in the Orcadian Basin, Scotland
Authors: Parnell J.
Published: April 2008

Middle Old Red Sandstone lacustrine sequences in the Orcadian Basin include rocks of petroleum source-rock potential, most extensively exposed onshore in Orkney and Caithness. The richest source rocks are carbonate laminites, in which carbonate and carbonaceous laminae are believed to be the deposits of algal blooming and mortality in a stratified lake (Donovan 1980). Many carbonate laminites and some other organic-rich laminites contain chert nodules, interpreted as magadi-type chert enclosing pseudomorphs after (?) trona. The cherts and evaporites were precipitated in sub-lacustrine sediment from groundwaters rich in dissolved sodium carbonate/bicarbonate. This implies that the source rocks were deposited from saline, alkaline lake waters.
Biological markers in lacustrine Chinese oil shales
Authors: Brassell S. C. , Eglinton G. , Sheng Guoying , Fu Jiamo
Published: April 2008

A major objective in molecular organic geochemistry is the assessment and characterization of sedimentary depositional environments from the occurrence of specific biological marker compounds related to particular source organisms. The aliphatic hydrocarbon distributions of petroleums and/or sediments from Chinese freshwater and hypersaline lacustrine environments are described and contrasted in the search for diagnostic features among their biological marker distributions. The Eocene Maoming oil shale, which crops out in Guangdong Province, shows major differences in hydrocarbon composition through its stratigraphic succession. These variations reflect changes in lithology and in the origins of the sedimentary organic matter, as seen from petrographic examination. The lower lignite and vitrinite layers contain significant contributions of biological markers from bacterial sources, plus components derived from terrigenous higher plants, such as C
29
steroids. In contrast, the overlying shales show a dominance of dinoflagellate-derived 4-methylsteroids and culminate in an horizon with botryococcane homologues as their dominant alkanes. Thus, the geochemical profile suggests that a swampy environment, in which peats accumulated, deepened to support populations of dinoflagellate and, finally, blooms of
Botryococcus
green algae. The aliphatic hydrocarbons of a series of sediments and petroleums from the Eocene hypersaline sequence of the Jianghan Basin in southern Hubei Province shows various features that may be typical of such facies. These include a dominance of even-numbered n-alkanes, high amounts of phytane and gammacerane, and an abundance of C
35
-hopanes. Similar characteristics are observed in shales from the Eocene Green River Formation and in Rozel Point crude oil, a petroleum thought to originate from sediments deposited under hypersaline conditions. The same features also appear in a lower Tertiary evaporitic mudstone from south of the Renqui oil field in Hebei Province, together with 4-methylsteranes, β-carotane and 18α(H)-oleanane, a marker for terrigenous higher plants. These data illustrate the potential of biological markers in the differentiation of different lacustrine environments and suggest that such characteristics may provide signatures for environmentally similar, but geographically distant, deposits.
Upper Proterozoic passive margin deltaic complex, Finnmark, N Norway
Authors: Siedlecka A. , Pickering K. T. , Edwards M. B.
Published: April 2008

The Upper Proterozoic Båsnaering Formation in the 9000 m thick Barents Sea Group is a succession of deltaic siliciclastics, 2500–3500 m thick, with an exposed extent covering an area of 3000 km
2
. The Båsnaering Formation is underlain by up to 3200 m of deep-marine submarine fan deposits, while above the deltaics there are up to 1500 m of shallow- and marginal-marine (intertidal and supratidal) carbonates and siliciclastics. The lower part of the Båsnaering Formation records the change from deep- to shallow-marine, slope and prodelta environments to delta-front and delta-top environments. The middle and upper parts of the formation comprise delta-top, fluvial, marginal-marine, interdistributary bay and related environments. The Båsnaering Formation appears to record the northeastward progradation of a fluvially dominated wave-modified deltaic system. Tidal processes influenced the delta development, but the importance and magnitude of such tides remains uncertain. Gravity-controlled sediment instability was prevalent in the prodelta and delta-front environments.
Reservoir geology of the Sirikit oilfield, Thailand: lacustrine deltaic sedimentation in a Tertiary intermontane basin
Authors: Flint S. , Stewart D. J. , van Riessen E. D.
Published: April 2008

The Sirikit oilfield, situated some 400 km N of Bangkok, Thailand, is a fault-bounded structure within a major half-graben basin, comprising a relatively undeformed eastern sector and a western area characterized by a complex pattern of isolated fault blocks. The 8 km thick basin-fill succession includes alluvial fan-fluvial deposits overlain by the fluvio-deltaic Lan Krabu Formation, which contains two main oil reservoirs.

A reservoir geological model has been produced based on cores and wireline log suites from some 45 wells. The geology is characterized by cycles of regressive coarsening-upward sequences, up to 15 m thick, which reflect cyclic progradation of fluvial-dominated deltas into a large relatively shallow lake in a humid tropical climatic regime. The cycles are commonly topped by subaerial flood-plain claystones. Distributary channel sandstones show evidence of stage fluctuation and intermittent abandonment. Individual mouth-bar reservoir sandstones range in thickness from 1 to 5 m and form complex sheet-like bodies of lateral extent up to 20 km
2
. Thus the Sirikit deltas have little inferred geometrical similarity with contemporary bar-finger models postulated for river-dominated lacustrine deltas. The sheet-delta geometry may be due to a combination of high frictional forces related to similar river and lake water densities, shallow lake depth and a large but variable fluvial sediment load. This combination of factors resulted in rapid dumping of sediment, the plugging of channel mouths and subsequent channel bifurcation.
Partial melting of a lithologically heterogeneous mantle: inferences from crystallization histories of magnesian abyssal tholeiites from the Siqueiros Fracture Zone
Authors: Natland James H.
Published: April 2008

Complex processes of magma mixing are revealed by the crystallization histories of several magnesian, porphyritic abyssal tholeiites dredged from the Siqueiros Fracture Zone at about 8°30′ N near its intersection with the East Pacific Rise. The compositions of chromian spinels, olivines, plagioclases and glass inclusions in these rocks indicate that polybaric crystallization and mixing occurred at high temperatures involving a range of refractory (low-TiO
2
, low-Na
2
O) melts. These later coalesced with cooler much less refractory components to produce the bulk rocks.

The crystallization histories and comparisons with experimental data indicate that mantle sources of these basalts were lithologically heterogeneous, ranging from fertile (lherzolitic) to refractory (in the extreme, harzburgitic) with respect to a basaltic melt fraction. The separate magma strains going into a typical magnesian abyssal tholeiite were produced by simultaneous partial melting of the different lithofacies, after which they coalesced and mixed. Such mixing is more likely than batch melting to explain the ranges in CaO/Al
2
O
3
, and abundances of Na
2
O and TiO
2
, within the fairly small range and low (non-picritic) magnesium numbers (0.75–0.64) exhibited by all liquids including those inferred from mineral compositions.

The early crystallization of minerals from refractory magma strains suggests that melting domains beneath spreading ridges consist of cores of refractory peridotite surrounded by cooler, more fertile peridotite. Sequential mixing of refractory and fertile magma strains is an unavoidable consequence of the ascent of magma batches from the interiors of complex melting regimes (diapirs) in the mantle. The diapirs may have been triggered into ascent by the buoyancy of low-density (low-iron) refractory peridotite.

Several of the Siqueiros magnesian abyssal tholeiites are among the most depleted basalts ever obtained from the eastern Pacific, and yet alkalic basalt was also dredged from the fracture zone a few kilometres away. The tholeiites are even more depleted than typical, more fractionated, summit eruptives of the East Pacific Rise. The contrast may arise because of the homogenizing effects of axial magma chambers, within which truly depleted tholeiites are mixed with enriched alkalic magmas instead of erupting separately, as they do in the fracture zone. Mantle in this region thus appears to be segregated into strongly contrasting depleted and enriched peridotites, with depleted peridotite also ranging from refractory to fertile lithofacies. Primary lithological variability in the mantle thus was probably imposed by one or more ancient melting events that left distinctively enriched and depleted reservoirs in their wake.
Mineral relationships in gabbroic rocks from fracture zones of Indian Ocean ridges: evidence for extensive fractionation, parental diversity and boundary-layer recrystallization
Authors: Bloomer Sherman H. , Natland James H. , Fisher Robert L.
Published: April 2008

Evolved two-pyroxene gabbros and ferrogabbros predominate in gabbroic suites dredged from five fracture zones on the SW and Central Indian Ridges. Compositions of olivines (Fo
56
-Fo
85
) and plagioclases (An
10
-An
80
) and the generally low magnesium numbers of orthopyroxene (0.58–0.84) and clinopyroxene (0.50–0.89) indicate that most gabbros crystallized from liquids more fractionated than those represented by basalts from adjacent ridge segments and the fracture zones themselves. This disparity, the paucity of diabases and gabbros, the absence of more magnesian gabbros and olivine-spinel cumulates, and the abundance of serpentinite in the dredge collections suggest that the fracture-zone gabbros crystallized in small magma bodies such as dykes or sills. These were emplaced laterally from large central magma chambers along ridge axes towards the fracture zones beneath a carapace of less fractionated basalt.

Rare olivine gabbros, however, contain magnesian clinopyroxene (magnesium number >0.84) and orthopyroxene (magnesium number >0.70), compositions which are more magnesian than those of pyroxenes that have been crystallized experimentally from certain ocean-ridge basalts at 1 atm. It has been suggested that such high-magnesium pyroxenes result from moderate- to high-pressure fractionation. However, the magnesian pyroxenes in the Indian Ocean samples follow olivine and plagioclase in the crystallization sequence and have compositions appropriate for crystallization at low pressure. For example, they match compositions of phenocrysts in refractory (low-Na
2
O, low-TiO
2
) siliceous (51–53% SiO
2
) basalts from Deep Sea Drilling Project sites in Eocene-Cretaceous portions of the Indian Ocean. Such refractory basalts have not been studied experimentally, but the early crystallization of bronzite at low pressure in one of them is consistent with the siliceous and magnesian composition of the host glass.

Alternatively, the more magnesian pyroxenes in the gabbros may have resulted from a process of
in situ
boundary-layer recrystallization (resorption and recrystallization) of minerals on the walls of small magma bodies as high-temperature magmas were repeatedly injected along them. This mechanism is suggested by phase relationships in simplified basaltic systems at low pressure and by the compositions of rounded (resorbed) mega-crystal minerals which occur in many tholeiites from the Indian Ocean and elsewhere.
The Fjallgardar volcanic ridge in NE Iceland: an aborted early stage plate boundary or a volcanically dormant zone?
Authors: Helgason Johann
Published: April 2008

The extinct Fjallgardar volcanic ridge (FVR) in NE Iceland is approximately 15–20 km wide and extends for about 190 km from the Vatnajökull glacier toward the Slétta peninsula in the far N. The FVR was mainly formed subglacially and strikingly parallels the curvature of the present median line (Askja to Theistareykir centres) of the neovolcanic zone (NVZ) which lies about 40 km to the W.

The basalts from the Fjallgardar and Slétta regions are dominantly evolved tholeiites as shown by major- and trace-element compositions of 42 samples. The average magnesium number is 47 (range 37–58). 90 per cent of the samples can be grouped into either ‘low-’ potassium (0.1%–0.4% K
2
O) or ‘high-’ potassium (0.5%–0.7% K
2
O) units. The high-potassium lavas in the FVR are chemically similar to Tertiary tholeiites of eastern Iceland.

A test for temporal geochemical variations for three stratigraphic formations was carried out for the Mödrudalur area of the FVR. The oldest of the three formations (M3) consists of low-potassium basalts only, whereas the two younger formations (M4 and M5) consist predominantly of more evolved high-potassium basalts. Formation M5 is most probably fed into Mödrudalur from the Kverkfjöll volcanic system some 75 km further S.

Volcanism in the FVR S of Slétta was short-lived and lasted for perhaps 200 000–300 000 years. Subsurface lateral flow of magma from the NVZ is probably responsible for the Recent subaerial volcanism in Slétta. In the Slétta area the older subglacially formed ridges have only a low-potassium basalt composition.

The FVR may be viewed as ‘abortive’ and as the precursor to the NVZ in northeastern Iceland. During the Brunhes magnetic polarity chron (less than 0.7 Ma) a rift jump is postulated to have occurred from the FVR to the present NVZ, approximately 40 km to the W. E.-W lateral rift jumps (20–40 km) may have been common in the eastern half of Iceland in the vicinity of the Iceland hot-spot located 150–200 km E of the Reykjanes and Kolbeinsey mid-ocean ridges.
Inversion of the Kechika Trough, Northeastern British Columbia, Canada
Authors: McClay K. R. , Insley M. W. , Anderton R.
Published: April 2008

The Kechika Trough, in the western Rocky Mountains of northern Canada, is a NW-trending fold and thrust belt of Hadrynian through Mississippian strata within the telescoped passive margin of ancestral North America. The Kechika Trough underwent major crustal extension in the Mid-Late Devonian with the deposition of coarse to fine ‘Antler’ type black clastics in an asymmetrical basin consisting of a terraced half-graben system to the west and a roll-over structure to the east. Inversion and contraction of the Kechika Trough occurred during the Jurassic-Cretaceous Columbian-Laramide orogeny. The geometries of the resultant fold and thrust systems were strongly controlled by the half-graben extensional architectures and by the geometries of the synrift sediment packages. Inversion structures include contractionally reactivated extensional faults, rotated and re-utilized extensional faults, and thrust faults pinned by extensional faults as a result of buttressing against rigid sediment wedges. Inversion of the synrift sediments is associated with strongly developed chevron folding, pervasive cleavage development and imbrication by out-of-half-graben thrust faults. These thrust faults may locally climb down stratigraphic section in the direction of transport as a result of cutting through strata tilted by Mid-Late Devonian extensional faults. Major stratigraphic contrasts between adjacent thrust packages have been resolved in terms of lateral facies differences produced by extension, rather than by over-complex thrust geometries. Although syndepositional extensional faults are not preserved in the thrust belt, their position and geometry may be inferred from an analysis of structural, stratigraphic and sedimentological relationships.
Fold and fault geometry in the western Helvetic nappes of Switzerland and France and its implication for the evolution of the arc of the western Alps
Authors: Ramsay J. G.
Published: April 2008

The main features of the fold and fault geometry of the Helvetic nappes and Chaînes Subalpines of Switzerland and France have been determined by the construction of tie lines between outcropping hinge points of folds and cut-off points of strata against thrusts. Longitudinal correlation of these structures is now possible. Folds are very persistent along their hinge lines and can often be followed for tens of kilometres. Fold hinges and thrust plane cut-off lines are extremely regularly oriented. The Alpine structures developed in the external massifs are obliquely superposed on previously emplaced nappes. The overall structural pattern is attributed to a progressive change of the relative displacement directions between the northern (European) plate and southern (Apulian) plate from N-S, through NW-SE, concluding with movements in an E-W sense. The well known structural culminations and depressions are interpreted as the result of the latest shortening in an E-W direction and not to complex ramp geometry or to duplex stacking.
South-Alpine thrusting and trans-Alpine convergence
Authors: Roeder D.
Published: April 2008

The south front of the Alps in northern Italy contains a Neogene S-vergent fold-thrust belt. It affects the crust of the Adria plate, a series of shelf sediments, and S Alpine foredeep fill. The belt shows that after collision, the Alps assumed the bivergent wedge shape of an intracratonic compressional belt, notwithstanding its long prior history of N-vergent subduction and thrust imbrication.

Parts of the S Alpine fold-thrust belt are buried beneath Apennine foredeep fill. Thrust transport is about 60 km to the SE; it has produced detached foothills folds, a triangle zone of stacked blind and emergent thrusts, and a basement front with out-of-sequence thrusting above a line of duplex anticlines. The structure of the foreland can be described by the curvature of an elastic line-load deflection. Details not predicted by the load model include Mesozoic rifting, foreland upthrusts, and perhaps complex map patterns of thrust fronts.

A match between trans-Tethys convergence and Alpine kinematics suggests either that a 150 km wide oceanic gap north of the Tauern was closed in late Miocene. Or it suggests an origin of the Tauern terranes on the S margin of a sub-Apennine crustal slab. The first choice is consistent with traditional Alpine crustal data but inconsistent with Mesozoic palaeogeography. The second choice is consistent with newer, EGT-generated, crustal data from the Ligurian—Apennine area. It admits 26% compression or 80 km bulk strain within the upper crustal slab while plate convergence generates 380 km of thrust overlap.

A conceptual model of Neogene Alpine convergence, consistent with the second choice, assumes increased traction where the basal detachment of the upper crustal slab passes upward into the brittle shell. Part of the viscous overlap at plate convergence rates is translated upward into compression within a back-to-back pair of thickening and over-critical Coulomb wedges.
Deep-reaching geodynamic processes in the Alps
Authors: Mueller St.
Published: April 2008

The Alps are a deep-reaching crust-mantle structure in Europe situated at the northernmost tip of the Adriatic promontory of the African plate. In that region the contact against the Eurasian plate is presently characterized by a NW-SE oriented compressional stress regime. A detailed regional analysis of seismic surface-wave dispersion and of P-wave travel time residuals (‘seismic tomography’) as well as long-range seismic refraction measurements and the interpretation of ‘stripped’ residual gravity anomalies have revealed a rather anomalous structure within the uppermost mantle under the Alpine arc. As a result of the massive continent-continent collision, parts of the lithosphere have been delaminated — a process which has led to ‘flaking’ in the upper crust, combined with a thickening of the entire crust and the formation of a pronounced relatively cold, dense and slowly subsiding ‘lithospheric root’ beneath the mountain chain. In this still continuing plate collision the lower parts of the lithosphere apparently have penetrated into the asthenosphere to a depth of 130 to 200 km in a steep zone of ‘subfluence’ (‘Verschluckung’). On this scale the presently measurable uplift of the Alpine chain (about 0.1 cm per year) is a secondary effect due to isostatic rebound of less dense crustal masses which previously had been forced to greater depths. A configuration of this type generates regionally a compressive dynamics of its own on which — within a wider framework — rotational processes may be superimposed.
Indentation and rotation in the western Alpine arc
Authors: Vialon P. , Rochette P. , Ménard G.
Published: April 2008

The overall structural aspects of the external western Alpine arc and foreland may be consequences of NW-SE compression ahead of crustal thrusting on the northern front and of mainly sinistral wrenching along its southwestern lateral border. However such a model assumes a simple straight-line displacement which, while possibly valid on the continental scale, cannot be considered for the external arc since a model of linear translation and rotation around a distant pole is not compatible with the structural organization of the western arc of the Alps. The constant tangential stretching parallel to the curved front, the fan-ring shortening and shear directions on décollement levels, the complex nappe transport trajectories and the widespread dextral wrench-faulting around the arc, can be better explained by local rotation of a block belonging to the European margin, dragged along the western sidewall of a large indenter moving northwestwards. This laterally displaced block produces an anticlockwise ring shear about a pole of rotation within it. Consequently, the Alpine arc cannot be understood in terms of plane-strain models along local ‘transport’ directions. The deformation process corresponds instead to lateral rotation-expulsion of a deformed unit belonging to the European Plate margin, jammed against its stable foreland.
Phyllosilicate formation in berthierine peloids and iron oolites
Authors: Velde B.
Published: April 2008

Electron microprobe compositions of phyllosilicates formed in berthierine pellets and iron oolites suggest two different reaction paths which result in slightly different bulk chemical compositions.

In the case of berthierine peloids, for mineral aggregates formed and transformed at or very near the sediment—sea water interface, the starting materials seem to be most often dominated by kaolinite. The gradual incorporation of iron and magnesium produces the chlorite composition within the pellet. Systematic compositional zoning is apparent when pellet edges are compared to pellet centres. The compositions of the chlorite end-product have a rather large range of Fe/Fe + Mg (0.65–0.88). The general compositional range of the transformed berthierine peloids is less aluminous than kaolinite suggesting a high silica activity in the solutions, which is independent of the dissolution of kaolinite.

In the case of berthierine/chamosite-bearing iron oxide oolites, the system is dominated by the presence of iron, as would be expected. The range of compositions observed using the electron microprobe on oolites which still contain iron oxides gives an Al/Si ratio of one, that of kaolinite. The formation of these chlorites is through a combination of divalent iron and kaolinite. These minerals have Fe/ Fe + Mg = 0.88–1.0. The bulk composition is Si
26
Al
26
(Fe,Mg)
48
. Multiple point analyses in the same oolite or pellet indicate that the formation of chlorite occurs at various points in the mass with no specific zoning pattern.

When the iron oxide in a rock is completely reacted to form silicate and/or phosphate phases (the oolites are completely chloritized), the berthierine/chamosite mineral composition can become less aluminous due to a general chemical equilibrium established throughout the sample. In more metamorphic iron ore rocks, where the oolitic structure is absent and where new iron silicates are present (such as stilpnomelane) and iron oxides are present, the chlorite composition can be found to vary from that formed in the initial reaction, i.e. Si/Al = 1. They can be more silica-rich or more aluminous.

These analytical results indicate that the composition of the chlorites formed in high iron environments reflect the chemical system in which they form and the scale of that system, a pellet or a rock.
A depositional model for the Liassic Minette ironstones (Luxemburg and France), in comparison with other Phanerozoic oolitic ironstones
Authors: Teyssen T.
Published: April 2008

Oolitic ironstones generally mark the top of a regressive, coarsening- and shallowing-upward depositional megasequence. The iron ooids themselves are preferentially formed during sea-level lowstands or in condensed sections. This general model is valid for the Minette iron formation which was deposited in Toarcian and Aalenian times at the north-eastern margin of the Liassic Paris Basin in a near-shore, shallow marine, mostly high-energy environment. The top of the regressive sequence shows intraformational reworking. The Minette, however, is a remarkably thick unit (up to 60 metres), also internally composed of coarsening-up sequences. In many places these sequences represent large-scale subtidal sand waves, elsewhere large subtidal shoals advancing over their distal finer grained facies. Strong tidal currents building up large sand waves are preferentially active during transgressions. For the Minette base level rise events (transgressions) are therefore required at the top of a base level fall sequence (regression). This apparent discrepancy can be resolved when considering the tectonic setting. Reactivation of structures of the underlying Variscian basement led to subsidence events in syndepositionally formed troughs. This model can explain a high aggradational potential and deposition of thick ironstone deposits at the top of a regressive sequence while erosion took place laterally along the same palaeocoastline.
Late Cambrian molluscan faunas and the origin of the Cephalopoda
Authors: Webers Gerald F. , Yochelson Ellis L.
Published: April 2008

Late Cambrian gastropod and monoplacophoran faunas from western Antarctica, eastern and mid-western North America, and northern China, are diverse and provide some insight into palaeogeography and faunal distribution. The oldest of these, a well-preserved trilobite-mollusc fauna from the Ellsworth Mountains, Antarctica is dated as latest Dresbachian (Idamean); the Antarctic fauna is not unlike a slightly younger one (Franconian) from east-central Minnesota, USA. Slightly younger Franconian-age rocks from north China contain the first authentic cephalopods. A Trempealeauan fauna from eastern New York, USA, is closely comparable to another Trempealeauan fauna from north China.

Relatively high taxonomic diversity suggests tropical to sub-tropical marine environments for all these faunas. Plate tectonic position as interpreted from palaeomagnetism supports this interpretation. The occurrence of these molluscs on separate continents, and the presumed widely separated position of these continents in the Late Cambrian, makes it likely that the distribution mechanism for the molluscs was long-lived larval forms.

A key member of the Antarctic faunule is the monoplacophoran
Knightoconus
which has been considered representative of a group directly ancestral to the oldest cephalopod
Plectronoceras
. This view is reconsidered in the light of criticisms and alternatives proposed during the last 15 years; these occupy the bulk of the paper. Reaffirmation of evolution from the Antarctic
Knightoconus
is supported both by refutation of the criticisms and by ontogenetic studies of new topotypical material of the genus.
Antarctica: Cretaceous cradle of austral temperate rainforests?
Authors: Dettmann Mary E.
Published: April 2008

Although it is well known that certain Gondwanic elements of present-day austral temperate rainforests occurred on Antarctica during latest Cretaceous to early Tertiary times, there has been insufficient factual evidence for pinpointing the cradle of these forests. Fossil evidence from Antarctica and closely associated regions in the Creataceous southern Gondwanan assembly confirms that Antarctica was a Cretaceous origination and dispersal region of certain elements of today’s southern hemispheric humid and perhumid forests. Antarctic origins are indicated for the fern
Lophosoria
, the podocarp gymnosperms
Lagarostrobus
and
Dacrydium, Nothofagus, Ilex
, and several lineages of the Proteaceae; migration to their present regions of distribution was probably step-wise. Antarctica also served as a Cretaceous dispersal corridor for other angiosperms represented today in mid to low latitude austral regions. These include
Ascarina
(or its stock), Myrtaceae, Gunneraceae, and Winteraceae, all of which had earlier histories in northern Gondwana or southern Laurasia. Origination and dispersal appears to be related to changing environmental circumstances associated with fragmentation of Gondwana and opening and enlargement of the southern oceans.
Endemism and heterochroneity in the Late Cretaceous (Campanian) to Paleocene palynofloras of Seymour Island, Antarctica: implications for origins, dispersal and palaeoclimates of southern floras
Authors: Askin Rosemary A.
Published: April 2008

Late Cretaceous (Campanian) to Paleocene nearshore marine-coastal/deltaic sediments (López de Bertodano and Sobral Formations) from Seymour Island, Antarctica, contain abundant marine and terrestrial palynomorphs. Marine dinoflagellate cysts, and spores and pollen of land plants from 510 samples exhibit varying levels of provincialism: (1) Seymour Island-James Ross Island basin endemic species; (2) Antarctic endemic species; (3) Weddellian Province (southern South America-Western Antarctica-New Zealand-southeastern Australia) species; (4) Austral species; and (5) Cosmopolitan species.

A significant proportion of the Antarctic Cretaceous-Tertiary terrestrial vegetation evolved in southern polar latitudes. Almost half of the late Maastrichtian angiosperm pollen flora is apparently endemic to the Seymour Island-James Ross Island basin or Antarctica. The late Campanian-Maastrichtian dinoflagellate cyst assemblages also include a significant Antarctic or Weddellian provincial component. Climatic conditions in the Late Cretaceous were moist and equable. Many species that evolved in these polar latitudes became isolated due to various geographical, climatic or biological barriers. Other species dispersed northward, presumably following routes of similar climate. Some Seymour Island latest Cretaceous angiosperm species which subsequently appeared in the Paleocene or Eocene in New Zealand and southeastern Australia, have modern relatives living in mid- to low latitudes.
New plesiosaurs from the Upper Cretaceous of Antarctica
Authors: Chatterjee Sankar , Small Bryan J.
Published: April 2008

New plesiosaur remains from the Upper Cretaceous Lopez de Bertodano Formation (late Campanian-Maastrichtian) of Seymour Island, Antarctic Peninsula include Cryptoclididae and Elasmosauridae. The occurrence of Cryptoclididae is reported from the Antarctic region for the first time. The taxon represents a new genus and species, based on a skull and associated cervical vertebrae. The long, slender and delicate teeth may have formed a ‘trapping’ device that enabled cryptoclidids to feed on small fish and crustaceans that abound in the same deposits. The cryptoclidids had a restricted distribution, being known so far from the Middle and Late Jurassic of England, and the Late Cretaceous of Chile, Argentina, and Antarctica.

Other specimens, represented by several postcranial skeletons, are taxonomically indeterminate, but they share some features with other contemporary elasmosaurid genera such as
Hydrotherosaurus, Morenosaurus, Thalassomedon
, and
Mauisaurus
. Unlike the cryptoclidids, the elasmosaurids had a cosmopolitan distribution during the Jurassic and Cretaceous periods.

Trophic diversity within guilds of marine predators is examined in the Lopez de Bertodano palaeocommunities. Three predator guilds are recognized on the basis of tooth morphology and prey preference. The mosasaurs composed the ‘Cut guild’, and were the principal predators. The elasmosaurids constituted the ‘Pierce guild’, and the cryptoclidids formed the ‘Trap guild’. These marine reptiles exploited the various pelagic resources such as sharks, bony fish, soft cephalopods and crustaceans, and survived until the end of the Cretaceous. The plesiosaurs were excellent swimmers, and used their hyperphalangic paddles for subaqueous flight in the manner of modern sea lions.
Late Cretaceous-early Tertiary floras of King George Island, West Antarctica: their stratigraphic distribution and palaeoclimatic significance
Authors: Birkenmajer K. , Zastawniak E.
Published: April 2008

Stratigraphic positions of Late Cretaceous and Tertiary floras have been established on King George Island, West Antarctica, based on K-Ar dating of associated volcanics. The oldest dated floras, of Late Cretaceous and Paleocene ages, provide evidence for a warm climate phase preceding the early Eocene glacial event termed the Kraków Glaciation. Late Eocene through early Oligocene floras indicate another warm period termed the Arctowski Interglacial, which post-dates the Kraków Glaciation. The youngest floras, of Oligocene-Miocene boundary age, indicate a temperate (or cool-temperate) climate, corresponding to the Wawel Interglacial which separated late Oligocene glacial and interglacial epochs (Polonez Glaciation, Wesele Interglacial and Legru Glaciation) from early Miocene glaciation (Melville Glaciation).
Evolution of the Antarctic fish fauna with emphasis on the Recent notothenioids
Authors: Eastman J. T. , Grande L.
Published: April 2008

The composition of the Antarctic fish fauna has undergone remarkable changes through time. Fossil fishes are known from Devonian, Jurassic, Cretaceous and early Tertiary deposits of the region. The Recent fauna does not appear to be derived from any part of any of the known fossil faunas. The Devonian fish fauna includes agnathans, placoderms, acanthodians, chondrichthyans and osteichthyans all belonging to families now extinct. The Jurassic fauna is known by only one species, a neopterygian of the now extinct family Archaeomaenidae. Both the Palaeozoic and early Mesozoic fish faunas known from Antarctica indicate Australian biogeographic affinities based on other (
i.e.
, non-Antarctic) known Palaeozoic and Mesozoic fish faunas. Late Cretaceous and early Tertiary species from the Antarctic region (Seymour Island) belong largely to families of fishes that today live in other regions of the world, but are extinct in the Antarctic region. The Recent (extant) fish fauna is drastically different from any of the fossil faunas and is dominated by perciforms of the suborder Notothenioidei. To date the fossil record has provided no fossils identifiable as notothenioids, or even species closely related to the group. It is unlikely that low water temperatures were directly respnsible for the local extinction of the Tertiary Seymour Island ichthyofauna or for the lack of diversity in the Recent fauna. The decline of suitable substrate and trophic factors may have been more important in changing the composition of the fish fauna. There is considerable morphological, physiological and ecological diversification within the Notothenioidei. Although the emergence of this group was probably not a direct response to cooling, the subsequent radiation of notothenioids was associated with a variety of specializations related to low water temperature.
The origin of the Southern Ocean marine fauna
Authors: Clarke Andrew , Crame J. Alistair
Published: April 2008

Current knowledge of the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present. Although direct fossil evidence is sparse after the Eocene, geophysical evidence suggests that shallow waters have been present since the late Mesozoic, and possibly much longer. The break-up of Gondwana was accompanied by a more or less steady lowering of both surface and bottom temperatures in the Southern Ocean from about 15°C in the Late Cretaceous to the present range of roughly +2 to −1.8°C. Microfossils in deep-sea drilling cores indicate that temperature drops were particularly sharp in the early Oligocene (
c.
38 Ma), mid-Miocene (10–14 Ma) and Pliocene (
c.
4 Ma BP). Geological evidence suggests that the Drake Passage opened, and the present oceanographic regime established, about 25–30 Ma BP. This is now known to be about the time of full-scale development of the East Antarctic ice cap. Subsequently ice sheets extended across, and deeply eroded, the continental shelves but the effects of these glacial maxima on the marine biota are not fully understood. Late Cretaceous/early Tertiary marine fossils from the James Ross Island group indicate a diverse shallow water marine fauna, including two groups notably lacking in diversity in the living fauna: decapods and teleost fish. In several genera occurrences in this fauna predate first occurrences in lower latitudes by as much as 40 Ma, suggesting the possibility that a number of groups originated at high southern latitudes.

The living fauna exhibits a high biomass in many areas, and within-site diversity can be as high as anywhere in the world. Some individual taxonomic groups, however, (notably bivalves and gastropods) have a lower diversity than in the tropics, supporting the concept of a latitudinal cline in diversity. Studies of physiological adaptation to temperature suggest that the decline in seawater temperature during the Cenozoic has not presented a particularly severe evolutionary problem. The reasons for the absence of large decapods and the low diversity of fish in the present fauna are unclear. Most of the biological features of the modern fauna are more likely a response to the seasonality of the ecosystem rather than low temperature
per se
. Overall the evidence suggests that the present Southern Ocean shallow water marine fauna largely evolved in situ, having been present since at least the Late Cretaceous, and possibly much longer. Some groups have invaded, for example along the Scotia arc, but the isolation of the Southern Ocean by the present oceanographic regime and the limited dispersal ability of many forms means that exchange with lower latitudes is very slow.
Incorporating geological data in well log interpretation
Authors: King D. E.
Published: April 2008

A multi-step technique is presented that permits a variety of quantitative and qualitative geological data to be incorporated in the log interpretation process to derive a detailed lithological analysis. The geological data are used to develop and refine explicit tool response and interpretation models. The models include synthetic wireline log data generated from input mineralogical and fluid data. These models are used in an interpretation system together with wireline data to provide a geologically reasonable lithological solution appropriate to the stratigraphic framework of a basin. An application of this technique is presented for a lithologically complex reservoir. A full suite of conventional logs was used together with core-derived data to provide an accurate level-by-level lithological analysis. The results contribute to the refined geological interpretation of the well.