bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of the continental margins of the Labrador Sea: a review
Authors: Chalmers James A. , Pulvertaft T.C.R.
Published: April 2008

The Labrador Sea is a small oceanic basin that developed when the North American and Greenland plates separated. An initial period of stretching in Early Cretaceous time formed sedimentary basins now preserved under the continental shelves and around the margins of the oceanic crust. The basins subsided thermally during Late Cretaceous time and a second episode of tectonism took place during latest Cretaceous and early Paleocene time, before the onset of sea-floor spreading in mid-Paleocene time. Around the northern Labrador Sea, Davis Strait and in southern Baffin Bay, voluminous picrites and basalts were erupted at and shortly after the commencement of sea-floor spreading. Volcanism occurred again in early Eocene time at the same time as sea-floor spreading commenced in the northern North Atlantic. Farther southeast, along the Labrador and southern West Greenland margins, oceanic crust is separated from continental crust by highly stretched but non-magmatic transition zones which developed before sea-floor spreading. A complex transform zone, which developed during sea-floor spreading in late Paleocene and early Eocene time, separates continental and oceanic crust along the Baffin Island margin. The Greenland and Labrador ocean-continent transitions are asymmetric across the only available conjugate cross-sections. However, a cross-section through the Labrador margin farther north resembles the Greenland cross-section in the conjugate pair more than it does the Labrador cross-section of this pair. Consideration of the geological history of the area suggests that the non-magmatic transition zones may have formed by slow extension of a few millimetres per year through a period of 53 Ma during Cretaceous and early Paleocene time.
Rifting along non-volcanic passive margins: stratigraphic and seismic evidence from the Mesozoic successions of the Alps and western Iberia
Authors: Wilson R.C.L. , Manatschal G. , Wise S.
Published: April 2008

The paper examines aspects of the sedimentology and stratigraphy of rift basins that evolved in deep marine settings near the ocean-continent transition. It focuses on the applicability of a low-angle extensional detachment model developed in the Alps to the West Iberian margin, and on difficulties of objectively identifying syn-rift stratigraphic intervals in both areas. The paper examines evidence obtained from Ocean Drilling Program holes drilled in the Iberia Abyssal Plain. Despite the fact that all the holes were sited above highs in the acoustic basement and so did not penetrate a complete sedimentary record of rifting, they do provide some constraints on the age and mechanism of rifting. We suggest that published identifications of syn-rift intervals in distal basins off West Iberia and in the Southern Alps have not demonstrated, using objective criteria, the occurrence of syn-rift stratigraphic intervals. They have, therefore, probably overestimated the duration of rifting by as much as 20 Ma. The absence of syn-rift related stratal divergence towards fault footwalls may be due to resedimentation of syn-rift sediments towards basin centres, lack of significant hanging-wall rotation along flat detachment faults, or the syn-rift interval being too thin to resolve on seismic data. The syn-rift episode beneath the deep Galicia margin postdates Tithonian-Berriasian shallow-water carbonates, and predates Late Valanginian turbiditic sediments. Drilling results from the Iberia Abyssal Plain suggest a similar age because Tithonian siliciclastic mudrocks are overlain by Berriasian pelagic chalks. It seems likely that in both regions rifting lasted for <5 Ma, probably from late Berriasian to early Valanginian. At Site 1068 in the Iberia Abyssal Plain, the interpretation from seismic reflection data, of a low-angle detachment dipping about 10° west, was confirmed by drilling, which revealed sedimentary and tectonic breccias containing clasts of lower-crustal rocks overlying a fault zone below which occurs serpentinized periodotite showing a downward decrease in deformation. At least 20.5 km of displacement is interpreted to have occurred along this fault, but it is not accompanied by large-amplitude, rift-related topography. This paradox is resolved if the detachment developed as a deepening-downwards, rolling-hinge fault.
Serpentinization and magmatism during extension at non-volcanic margins: the effect of initial lithospheric structure
Authors: Pérez-Gussinyé M. , Reston T.J. , Phipps Morgan J.
Published: April 2008

At several non-volcanic margins serpentinized peridotites occur within a wide continent-ocean transition (COT) and beneath the edge of the thinned continental crust. However, other margins such as the Woodlark Basin appear to have a sharp COT and no reported serpentinites. We investigate the thermal, magmatic and rheological evolution of margins during extension as a function of initial lithospheric structure, rift duration and stretching factor. For cratonic and old orogen models, the entire crust should become brittle at stretching factors
c.
3–4. The resultant crust-cutting faults allow water to reach and serpentinize the mantle, leading to the development of serpentinite décollements at the crust-mantle boundary and exhumation of mantle at the COT. Our predictions are consistent with the spatial limit and thickness of serpentinites at the SW Greenland and West Iberia margins, and the Rockall Trough. They also explain the absence of a broad zone of unroofed, serpentinized mantle at the COT of the Woodlark Basin: here the crust was too thick and hot for serpentinites to form before break-up. Larger melt production than in the West Iberia type margins and concentration of the lithospheric strength in the crust leads to synchronous crustal separation and lithospheric failure, yielding a sharp COT.
Three-dimensional GPR analysis of various Quaternary gravel-bed braided river deposits (southwestern Germany)
Authors: Heinz J. , Aigner T.
Published: April 2008

Closely spaced (1 m) ground penetrating radar (GPR) profiles were used for a three-dimensional characterization and comparison of glaciofluvial gravel-bed deposits in palaeodischarge zones of the Würmian Rhine glacier (southwestern Germany). Previous sedimentological outcrop investigations revealed three regionally reoccurring architectural styles of gravel bodies. For each of these styles a three-dimensional GPR dataset has been acquired in active gravel pits in order to calibrate the radar profiles with outcrop walls and to analyse, in three dimensions, the depositional elements and their stacking pattern in the subsurface.

The GPR data were interpreted by mapping reflection terminations in order to delineate genetically related units. In particular, radar facies types and radar sequence boundaries were used to define and map depositional elements. Both accretionary and cut-and-fill depositional elements could be identified. Accretionary elements are characterized by horizontally to low-angle inclined (1–3°) and moderately continuous reflections (5–30 m) terminating on flat sequence boundaries; they represent the deposits of gravel sheets and traction carpets. In contrast, cut-and-fill elements are characterized by low to steeply inclined (3–25°), often discontinuous reflections terminating on concave to trough-shaped lower truncation boundaries; these are interpreted as scour-pool fills and small dissection elements (e.g. chutes and lobes).

The three basic architectural styles of gravel bodies can be distinguished on the basis of the size and proportion of cut-and-fill elements mapped within the radar images. One type of gravel body is composed of an amalgamation of large cut-and-fill elements whereas the other two types are dominated by accretionary elements and differ by the proportion of smaller cut-and-fill elements.

The results show that GPR is an adequate technique to illuminate the sedimentary architecture of the various types of gravel bodies. GPR data allow detailed three-dimensional reconstruction of depositional elements and their stacking pattern in the subsurface.
Cenozoic sedimentation and tectonics in Borneo: climatic influences on orogenesis
Authors: Hall Robert , Nichols Gary
Published: April 2008

The volume of sediment deposited in the basins around Borneo indicates that at least 6 km of crust has been removed by erosion during the Neogene. The amount of tectonic uplift implied by this is not reflected in a large area of high mountains on the island, which has an average elevation much lower than that of the Alps or Himalayas. High weathering and erosion rates in the tropical climate of SE Asia are likely to have been an important factor governing the formation of relief in Borneo, and consequently, controlled the structural development of the orogenic belt. Very rapid removal of material by erosion prevented tectonic denudation by fauling: around Borneo there was no lithospheric flexure due to thrust loading and no true foreland basins were developed. The sediment was deposited adjacent to the orogenic belt in older, deep oceanic basins. In terms of sediment yield, the Borneo mountains are comparable in importance to mountain ranges such as the Alps or Himalayas. However, the differences in elevation and structural style suggest that mountain belts formed in regions of high erosion rates may be different from those formed in other settings and the effects of climate need to be considered to understand orogenic evolution.
Filling and cannibalization of a foredeep: the Bradanic Trough, Southern Italy
Authors: Tropeano Marcello , Sabato Luisa , Pieri Piero
Published: April 2008

The Bradanic Trough (southern Italy) is the Pliocene-present-day south Apennines foredeep. It is a foreland basin as subsidence due to westward subduction of the Adria Plate involves the continental crust of the Apulian domain. The infill succession of the Bradanic Trough is characterised by the presence of a long thrust sheet system (the so called ‘allochthon’) that occupied part of the accommodation space created on the foreland by subduction. The upper part of the infilling succession crops out along numerous sections. About 600 m of the 3–4 km basin-fill succession is exposed as the Bradanic Trough has experienced uplift during Quaternary times.

Outcropping successions are mainly characterized by shallow-marine deposits comprising carbonates of the Calcarenite di Gravina Formation, silty clay hemipelagites of the Argille subappennine Formation and coarse-grained bodies of the ‘Regressive coastal deposits’.

The Calcarenite di Gravina Formation (Middle-Late Pliocene-Early Pleistocene in age) crops out in a backstepping configuration onto the flanks of the Apulian Foreland highs. It displays evidence of strong transgression onto a karstic region previously dissected in a complex horst and graben system.

The Argille subappennine Formation (Late Pliocene-Middle Pleistocene in age) succeeds the carbonate sedimentation on the foreland side of the basin and represents the shallowing of the basin in the other sectors of the Bradanic Trough. Toward the Apennines chain, in the wedge-top area of the foredeep, the Argille subappennine Formation covers the allochthon, while in the depocentre (in the foredeep
sensu stricto
) the same formation overlays turbidite deposits. The latter characterize the deeper part of the successions, and are mainly buried below the allochthon.

The Regressive coastal deposits (Early-Late Pleistocene in age) represent the upper part of the succession. They consist of coarse-grained wedges that lie on the hemipelagites of the Argille subappennine Formation in, alternatively, conformable or erosional contact. The wedges of the Regressive coastal deposits stack in a downward-shifting configuration, which indicates deposition during uplift.

The Quaternary development of the Bradanic Trough differs from that of the central and northern Appennines foredeep. The latter is characterized by aggradation of shallow-marine and alluvial sediments in a subsiding remnant basin, whose filling records a basin-scale depositional regression. In contrast, the Bradanic Trough is characterized by a basin-scale erosional regression and the last evolutive phase of this sector of the Apennines foredeep is best defined as a cannibalization phase rather than a filling or overfilling phase.
Fluviatile sediment fluxes to the Mediterranean Sea: a quantitative approach and the influence of dams
Authors: Poulos S. E. , Collins M. B.
Published: April 2008

The Mediterranean drainage basin incorporates more than 160 rivers with a catchment >200 km
2
, of which only a few are larger than 50 × 10
3
km
2
: this observation emphasizes the role of the smaller rivers. The present investigation, incorporating the analysis of data sets from 69 rivers, has estimated a total sediment flux of some 1 × 10
9
tonnes (t) year
−1
; of this, suspended sediment contributes some two-thirds of the load, with the remaining third supplied by the combined dissolved and bed-load components. The magnitude of the sediment supply is best demonstrated by various observations: (i) some 46% of the total length of the Mediterranean coastline (46 133 km) has been formed by sediment deposition; (ii) many Mediterranean deltas have prograded in recent times by, at least, several metres per year; and (iii) Holocene coastal (inner shelf) deposits are some tens of metres in thickness. The construction of hundreds of dams around the Mediterranean Sea, especially over the last 50 years, has led to a dramatic reduction in the sediment supply- to approximately 50% of the potential (natural) sediment supply. Such a reduction is considered to be the primary factor responsible for the loss of coastal (mainly deltaic) land, with annual rates of erosion ranging from tens (Ebro, Po) to hundreds of metres (Nile).
Sedimentology: from single grains to recent and past environments: some trends in sedimentology in the twentieth century
Authors: Eugen  , Seibold Ilse
Published: April 2008

Before 1900, Henry Clifton Sorby, the ‘founder of sedimentary petrography’, covered many aspects of the study of sedimentary rocks. During the first half of the twentieth century, there followed numerous detailed descriptions of such rocks and actualistic ideas were increasingly introduced. Specialization began between the two World Wars. The use of single grains and their statistical evaluation, especially of heavy minerals, and the investigation of clay minerals, were stimulated by the needs of the oil industry, together with regional descriptions, including facies studies on land and on the sea bottom. Specialization further increased between 1945 and 1968, with an explosion of publications. Ongoing field and laboratory studies, and new concepts such as the origin of turbidites, or diagenesis — especially in carbonate rocks — were treated in much greater detail. Again the oil industry was one of the major driving forces. Since 1968, global aspects gained greater attention, as for example with the Deep-sea Drilling Project. Geophysics contributed to facies and basin analysis. Extraterrestrial factors such as variation in Earth’s orbit or bolide impacts, and their indications in sediments, came to be considered important for understanding world climates, and also evolution. Cross-disciplinary and international approaches have become, and continue to be, of growing importance.
Sequence stratigraphy of the southern Kirthar Fold Belt and Middle Indus Basin, Pakistan
Authors: Smewing John D. , Warburton John , Daley Tim , Copestake Philip , Ul-Haq Nazir
Published: April 2008

The southern Kirthar Fold Belt (KFB) and the contiguous Middle Indus Basin (MIB) constitute a major oil and gas province on the southern Pakistan foreland. In the Middle Indus Basin, gas is reservoired in Early Cretaceous marginal marine sandstones sealed by Paleocene shales. Reservoir quality of the Early Cretaceous sediments deteriorates towards the fold belt, but recent discoveries of gas in Upper Cretaceous sandstones sealed by Paleocene shales have highlighted its potential. To understand better the petroleum systems of this region and provide a potential correlation scheme for comparison with other areas of the country, a sequence stratigraphic interpretation was carried out on the Jurassic to Recent sediments of the KFB and MIB. On the basis of outcrop and well data, 23 depositional sequences have been identified: five in the Jurassic units, 10 in the Cretaceous units and eight in the Tertiary units. Sequence boundaries have been defined according to the Exxon method of identifying unconformities and their correlative conformities. However, equal importance has been given to indentifying the potentially more chronostratigraphically significant maximum flooding surfaces between these sequence boundaries so as to define accurately the component systems tracts of each sequence. The depositional systems are described in terms of their relationship to the existing lithostratigraphic framework and interpreted in terms of sedimentary responses to external (eustatic) or local (tectonic) events. Notwithstanding the presence of a eustatic signature on some sequences, the majority appear to be tectonically driven and can be related to plate margin events affecting the NW margin of the Indo-Pakistan Plate during its rift-drift-collision history.
Along-slope variation in the late Neogene evolution of the mid-Norwegian margin in response to uplift and tectonism
Authors: Evans D. , McGiveron S. , Harrison Z. , Bryn P. , Berg K.
Published: April 2008

As part of the Norwegian Deep Water Programme, a regional geological and geophysical interpretation of the mid-Norwegian margin resulted in the establishment of a late Paleogene to Holocene stratigraphic framework for the margin, and identification and mapping of a range of possible geohazards, including slides. At the Vøring margin in the north, there has been the build-out of a huge prograding wedge of sediment in Plio-Pleistocene times. The sediments of the wedge are assigned to the Naust Formation, which has been subdivided into eight units (A-H), and includes only a few palaeoslides. To the south of the Vøring margin lies the Storegga Slide Complex and the North Sea Fan, and the whole of this southern region shows evidence of several major palaeoslides. The sediments are also referred to the Naust Formation, which here are subdivided into nine units (O-W) that have been partly correlated with equivalent Naust units to the north. The oldest Naust unit in the south, Naust Unit W, is largely made up of slide deposits that provide evidence for the earliest identified large-scale slope instability in the Storegga Slide Complex. This instability was penecontempooraneous with the initiation of the prograding wedge to the north, and both features are postulated to be the result of uplift of the Norwegian mainland. In the case of the Storegga Slide Complex, which lies close to the main area of uplift, oversteepening of the margin, together with seismicity associated with the Jan Mayen Fracture Zone and Møre-Trønderlag Fault Complex, may have initiated sliding that has since occurred intermittently up to Holocene times, over a time interval when there has additionally been much glacio-isostatic movement.
Prediction of the hydrocarbon system in exhumed basins, and application to the NW European margin
Authors: Doré A. G. , Corcoran D. V. , Scotchman I. C.
Published: April 2008

Uplift, erosion and removal of overburden have profound effects on sedimentary basins and the hydrocarbon systems they contain. These effects are predictable from theory and from observation of explored exhumed basins. Exhumed basins are frequently evaluated in the same way as ‘normal’ subsiding basins, leading to errors and unrealistic expectations. In this paper we discuss the consequences of exhumation in terms of prospect risk analysis, resource estimation, and overall basin characteristics.

Exhumation should be taken into account when assigning risk factors used to estimate the probability of discovery for a prospect. In general, exhumation reduces the probability of trapping or sealing hydrocarbons, except where highly ductile seals such as evaporites are present. Exhumation modifies the probability of reservoir in extreme cases; for example, where a unit may have been buried so deeply before uplift that it is no longer an effective reservoir, or where fracturing on uplift may have created an entirely new reservoir. The probability of sourcing or charging is affected by multiple factors, but primarily by the magnitude of the post-exhumation hydrocarbon budget and the efficiency of remigration. Generally gas will predominate as a result of methane liberation from oil, formation water and coal, and because of expansion of gas trapped before uplift. These factors in combination tend to result in gas flushing of exhumed hydrocarbon basins.

Compared with a similar prospect in a non-exhumed basin, resource levels of a prospect in an exhumed basin are generally lower. Higher levels of reservoir diagenesis influence the standard parameters used to calculate prospect resources. Porosity, water saturation and net-to-gross ratio are adversely affected, and (as a consequence of all three) lower recovery factors are likely. Hydrostatic or near-hydrostatic fluid pressure gradients (as observed in exhumed NE Atlantic margin basins) will also reduce the recovery factor and, in the case of gas, will adversely affect the formation volume factor.

Hydrocarbon systems in exhumed settings show a common set of characteristics. They can include: (1) large, basin-centred gas fields; (2) smaller, peripheral, remigrated oil accumulations; (3) two-phase accumulations; (4) residual oil columns; (5) biodegraded oils; (6) underfilled traps. Many basins on the NE Atlantic seaboard underwent kilometre-scale uplift during Cenozoic time and contain hydrocarbon systems showing the effects of exhumation. This knowledge can constrain risk and resource expectation in further evaluation of these basins, and in unexplored exhumed basins.
Evolution of Paleocene sediment dispersal systems in the Foinaven Sub-basin, west of Shetland
Authors: Morton Andrew C. , Boyd J. Douglas , Ewen David F.
Published: April 2008

Heavy mineral assemblages in deepwater Paleocene sandstones of the Foinaven Sub-basin (west of Shetland) reflect the influence of three main provenance and dispersal systems. The Schiehallion system has relatively uniform characteristics and persisted through much of the early-mid Paleocene. Its sphere of influence was centred on the Schiehallion Field, but it progressively encroached into the Foinaven area with time. Its main source was the Triassic Foula Formation, with minor supply from Lewisian and Moine basement rocks. The Foinaven system shows marked changes in character, related to evolution of the source area. The earliest sands were derived from a heavily weathered late Cretaceous regolith, and represent the onset of uplift and exhumation of the Shetland Platform. Progressive unroofing led to the incorporation of increasing amounts of Lewisian- and Moine-sourced detritus. Following deposition of the main reservoir sandstones in Foinaven and Schiehallion, there was a progressive change in provenance, with a gradual increase in the amount of sediment shed directly from metamorphic basement. Pulsing of the proto-Icelandic plume has been proposed as the mechanism for repeated influx of sand to the basins around Scotland. However, on the basis of available geochronological data, there does not appear to be a direct link between events in the British Tertiary Igneous Province (BTIP) and changes in provenance in the Foinaven Sub-basin. The initial influx of sediment from a weathered land surface may have been coeval with the onset of magmatism in the BTIP, but the cessation of supply through the Foinaven system at
c.
59 Ma does not appear to be related to magmatic events in the BTIP. The waning of magmatism in the BTIP around 58 Ma is broadly coincident with a gradual increase of first-cycle basement detritus.
A new biostratigraphic scheme for the Paleocene onshore West Greenland and its implications for the timing of the pre-volcanic evolution
Authors: Nøhr-Hansen H. , Sheldon E. , Dam G.
Published: April 2008

Based upon dinoflagellate cyst and nannofossil data, a detailed zonation of the Lower Paleocene succession in the Nuussuaq Basin, onshore West Greenland has been established. The succession is divided into the five dinoflagellate cyst zones:
Trithyrodinium evittii, Cerodinium pannuceum, Senegalinium iterlaaense, Palaeocystodinium bulliforme
and
Alisocysta margarita
. The dinoflagellate cyst zones are correlated with nannoplankton zones. The stratigraphically most important nannofossils recorded include
Chiasmolithus
cf.
bidens, Neochiastozygus modestus, N. perfectus, N. saepes, Prinsius martinii
and
Zeugrhabdotus sigmoides
. A new zonal scheme has been erected and resolves previous problems relating biostratigraphic and
40
Ar/
39
Ar data in the region.

The Upper Maastrichtian-Lower Paleocene succession records faulting and valley/submarine canyon incision resulting from pre-volcanic rifting and regional uplift of the basin. Two Early Paleocene tectonic phases have been recognized during NP1–NP3. These uplift phases were followed by rapid subsidence during NP4. Initiation of volcanism onshore West Greenland is broadly concurrent with the
Alisocysta margarita
Zone indicating that volcanism began during late NP4, in accordance with recent palaeomagnetic results and
40
Ar/
39
Ar dating of the volcanics. On the basis of the first occurrence datum of the dinoflagellate cyst species
Cerodinium kangiliense
and
Alisocysta margarita
, it is possible to correlate the lowermost volcanic Anaanaa Member hyaloclastites from the southwestern part of Nuussuaq with sediments of the Eqalulik Formation from the northern coast of Nuussuaq.
On the emplacement of sill complexes: evidence from the Faroe-Shetland Basin
Authors: Bell Brian , Butcher Helen
Published: April 2008

The North Faroe-Shetland Basin (NFSB) Sill Complex is of late Paleocene/earliest Eocene age and was emplaced within Cretaceous and Paleocene sedimentary rocks, in places to depths as shallow as a few hundred metres below the contemporaneous basin floor. Intersections of the Complex occur in exploration wells drilled by the oil industry and indicate tholeiitic basaltic compositions. High quality 3D seismic data, obtained during hydrocarbon exploration along the NE Atlantic Margin, provide a unique view of an uneroded suite of these sheet-like intrusions in UK Quadrants 218 and 219 and indicate the multi-centred nature of the NFSB Sill Complex, with upward-fingering terminations from broad bowlshaped foci of intrusion. Where the intrusion depth is very shallow, depending upon the host lithology, sill emplacement has lead to the development of structures on the contemporaneous basin floor interpreted as submarine hyaloclastite-dominated vents, up to
c.
2 km across and with heights of up to
c.
100 m. Where intrusion depth is greater, ‘seismic chimney’ structures are interpreted as the fluidescape feeders of sedimentary-hydrothermal mounds. Subsequent differential compaction of sedimentary sections, with and without shallow-emplaced sills, has given rise to distinctive ‘eye’ structures, as seen in seismic sections.
Challenges in the characterization and prediction of the hydrogeology and geochemistry of mined ground
Authors: Younger P. L. , Robins N. S.
Published: April 2008

Although mining is no longer a key industry in the UK, the international mining industry continues to expand. One of the principal legacies of past mining in Britain is water pollution emanating from abandoned mine voids and waste rock depositories. This has necessitated many expensive technical evaluations and remedial programmes in recent years, from which important lessons may be drawn for the still-growing mining industry overseas. Perhaps the single most important lesson is that there can never be too much information on mine hydrogeology and geochemistry available at the post-closure phase. As this phase is also the longest in the overall life cycle of any mine, it should be given appropriate consideration from the outset. The post-closure studies described in this paper and in this volume (as well as elsewhere) highlight the dearth of hydrological data that are usually available when compared with the wealth of geometric information available from mine abandonment plans. It is advocated that the collection of appropriate environmental data is built into the initial mine development plan and that monitoring commences from the green field site onwards. The uncertainties related to predictive modelling of mine water arisings are considerable, whilst those of predicting mine water quality are even greater. Numerous pointers towards robust mine water management strategies are identified, and a call for ‘defensive mine planning’ is made, in which relatively modest investments in hydrogeochemical control measures during the exploration and exploitation phases of the mine life cycle will yield dividends in the post-closure phase. With such measures in place, and enhanced monitoring data to hand, the conjunctive application of physical and geochemical evaluations will eventually provide much-needed predictive tools to inform site management decisions in the future.
Deflection of mantle plume material by cratonic keels
Authors: Sleep N. H. , Ebinger C. J. , Kendall J.-M.
Published: April 2008

Lithosphere that formed in Archaean and possibly early Proterozoic time is thicker, more buoyant, and geochemically distinct from lithosphere that formed after about 2.3 Ga. Mantle xenolith and seismic data indicate that some cratonic roots, or ‘keels’, extend to depths of
c.
250 km, compared with normal continental lithosphere of thickness 150 km or less; yet many cratons have experienced uplift, dyking and kimberlite emplacement, suggesting interactions with hot, rising asthenosphere referred to as mantle plumes. Plumes supply additional heat to the base of the lithospheric plates, whose base can be heated and entrained in the flow (thermal erosion). How have these cratonic keels persisted despite their interactions with mantle plumes? The geometry of cratonic keels during their interactions with mantle plumes is a critical factor controlling keel preservation. To a laterally spreading plume head, cratonic keels appear as major obstacles, and the hot, buoyant plume material ponds beneath thinner lithosphere. Our model simulations show that deep keels deflect mantle plume material and that steep gradients at the lithosphere-asthenosphere boundary between Archaean keels and ‘normal’ lithosphere will focus flow, leading to localized adiabatic decompression melting. Plume processes can lead to a reduction in the breadth of a cratonic root where the plume rises beneath the craton, regardless of the initial breadth of the craton. Where the plume rises beneath a craton the hot plume material will spread laterally beneath the keel and attain thicknesses of tens of kilometres. This transfers heat to the base of the lithosphere and could generate small volumes of melt at considerable depth, depending on the composition of the lower lithosphere. We have used model simulations of plumes beneath Africa to predict the magnitude and direction of seismic anisotropy caused by lateral flow of hot plume material beneath and around a cratonic keel. The shear-wave splitting in our models is greatest at the edge of the cratonic keel, and its azimuth is parallel to the plume flow direction.
Accretion of first Gondwana-derived terranes at the margin of Baltica
Authors: Belka Z. , Valverde-Vaquero P. , Dörr W. , Ahrendt H. , Wemmer K. , Franke W. , Schäfer J.
Published: April 2008

In central Europe, three crustal units, i.e. the Małopolska, the Łysogóry and the Bruno-Silesia, can be recognized by basement data, faunas and provenance of clastic material in the Cambrian clastic rocks. They are now situated within the Trans-European Suture Zone, a tectonic collage of continental terranes bordering the Tornquist margin of the palaeocontinent of Baltica, but during the Cambrian their position in relation to each other and to Baltica was different from today. These units are exotic terranes in respect to Baltica and are interpreted as having been derived from the Cadomian margin of Gondwana. Their detachment is probably related to the final break-up of the supercontinent Rodinia at
c.
550–590 Ma.

New detrital zircon and muscovite age data provide evidence that Małopolska was derived from the segment of the Cadomian orogen that bordered the Amazonian Craton. It must have already separated from Gondwana in Early Cambrian time (some 40–50 Ma before Avalonia became detached and began its rapid drift). The accretion of Małopolska to Baltica occurred between late mid-Cambrian and Tremadocian times. Both palaeontological and provenance evidence demonstrate that Małopolska and not Avalonia was the first terrane to join the Baltica palaeocontinent. This event initiated the progressive crustal growth of the European lithosphere, which continued during Phanerozoic times and led to the formation of modern Europe.
Seismic refraction evidence for crustal structure in the central part of the Trans-European Suture Zone in Poland
Authors: Grad M. , Guterch A. , Mazur S.
Published: April 2008

The results of seismic investigations obtained for the Trans-European Suture Zone (TESZ) show the presence of relatively low velocity rocks (V
p
< 6.1 kms
−1
), of sedimentary, metamorphic or volcanic origin, down to a depth of 20 km; high velocity (V
p
= 6.8–7.3 kms
−1
) lower crust, the Moho at a depth of approximately 30–33 km; and a high-velocity (V
p
> 8.3 kms
−1
) uppermost mantle. The transition of the crustal structure is seen across a 200 km wide zone. The three-layered crystalline crust of Baltica changes over this distance into the two-layered crust of Palaeozoic (Variscan) Europe, due to the disappearance of the lowest layer (V
p
∼ 7.1 kms
−1
) and tapering off of the Baltican/cratonic wedge. The seismic profiles suggest that the lower crust (V
p
∼ 7.1 kms
−1
) in the transition zone represents the attenuated Baltica margin underthrust towards the SW beneath the Avalonian accretionary wedge. The latter corresponds to the low-velocity upper crust (V
p
< 6.1 kms
−1
) characteristic of the German-Polish Caledonides. Consequently, the high-velocity reflective lower crust of Baltica affinity extends approximately 200 km to the SW of the Teisseyre-Tornquist Zone within the basement of the Palaeozoic Platform. The Avalonian upper/middle crust is confined in the SW against the WNW-ESE trending Dolsk Fault. To the SW of the Odra Fault, a typical Variscan crust is detected which shows two-layer structure and relatively low P-wave velocities. The WNW-ESE Odra Fault, approximately parallel to the Dolsk Fault, splits the Variscan domain into the Variscan externides buried beneath the Palaeozoic Platform in the NE and the Variscan internides of the Sudetes in the SW. We interpret both the Odra and Dolsk Faults as dextral strike-slip features that cross cut the NE termination of the Variscan Orogen parallel to the Teisseyre-Tornquist Zone. In a relatively small area, they juxtapose three crustal domains representing, successively, the Variscan internides, externides and the Variscan foreland.
Large-scale morphology of Arctic continental slopes: the influence of sediment delivery on slope form
Authors: O’Grady Damian B. , Syvitski James P. M.
Published: April 2008

The continental slopes of the pan-Arctic region exhibit a range of morphological expression inherently related to different styles of glaciation and sediment delivery to the slope. This study examines the basic associations between glacial processes and morphology at the regional scale. A Geographical Information System (GIS) is applied to a new bathymetric grid of the Arctic Ocean in order to compare the slope angle and sea-floor roughness of 70% of Arctic continental slopes. We also subdivide the circum-Arctic continental slope with respect to parameters likely to influence sediment delivery to the slope. These include proximity to Late Quaternary glacial advance, convergent versus divergent ice termini, and the presence or absence of glacial shelf troughs. Comparison shows that those continental slopes that experience higher sediment input dip more gently than slopes with less sediment input. On glaciated margins where the expanding ice sheet would have produced convergent (faster) ice flow, continental slopes have mean slopes of 1.3° on average. This is in contrast with margins that have experienced divergent (slower) ice flow which tend to have steeper slopes (mean of 2.2°). There is a direct relationship between morphological variability among trough-mouth fans and the width of the adjacent continental shelf (i.e. size of the trough). Longer troughs give rise to slope fans with a more gentle profile geometry. This finding, though simple, suggests a dependency of slope morphology on sediment input to the slope through basal ice sheet erosion. Published values for sediment discharge to several trough mouth fans support this concept. A model is proposed for fan development that relates a fan’s geomorphic state to its stage of stratigraphic development.
Submarine mass-wasting on glacially-influenced continental slopes: processes and dynamics
Authors: Elverhøi Anders , de Blasio Fabio V. , Butt Faisal A. , Issler Dieter , Harbitz Carl , Engvik Lars , Solheim Anders , Marr Jeffrey
Published: April 2008

Submarine slides and debris flows are common and effective mechanisms of sediment transfer from continental shelves to deeper parts of ocean basins. They are particularly common along glaciated margins that have experienced high sediment flux to the shelf break during and after glacial maxima. During one single event, typically lasting for a few hours or less, enormous sediment volumes can be transported over distances of hundreds of kilometres, even on very gentle slopes. In order to understand the physics of these mass flows, the process is divided into a release phase, followed by break-up, flow and final deposition. Little is presently known regarding release and break-up, although some plausible explanations can be inferred from basic mechanics of granular materials. Once initiated, the flow of clay-rich or muddy sediments may be assumed to behave as a (non-Newtonian) Herschel-Bulkley fluid. Fluid dynamic concepts can then be applied to describe the flow provided the rheological properties of the material are known. Numerical modelling supports our assertion that the long runout distances observed for large volumes of sediments moving down gentle slopes can be explained by partial hydroplaning of the flowing mass. Hydroplaning might also explain the sharp decrease of the friction coefficient for submarine mass flows as a function of the released volume. The paper emphasizes the need for a better understanding of the physics of mass wasting in the submarine environment.
Multiple generations of extensional detachments in the Rhodope Mountains (northern Greece): evidence of episodic exhumation of high-pressure rocks
Authors: Krohe Alexander , Mposkos Evripidis
Published: April 2008

An integrated structural and petrological study shows that exhumation of high-Procks of the Rhodope occurred in several pulses. The structurally uppermost Kimi Complex recording an Early Cretaceous high-Pmetamorphism was exhumed between about 65 and >42 Ma. The Sidironero, Kardamos and Kechros Complexes that record Early Tertiary high-Pmetamorphism (at least 19 kbar at 700 °C) were exhumed at >42–30 Ma. Exhumation occurred with isothermal decompression. Strain episodes depict thrusting of medium/high grade above lower grade high-Procks, syn-thrusting extension and post-thrusting extension. Polyphase extension created several generations of detachment zones, which, in sum, excise about 20 km of material within the crustal profile. This reduction in crustal thickness is consistent with a reduction of the present crustal thickness from more than 40 km to less than 30 km in the eastern Rhodope. We mapped the post-thrusting Xanthi low-angle detachment system over 100 km, from its break up zone above the Sidironero Complex (Central Rhodope) into the eastern Rhodope. This detachment shows an overall ESE-dip with a ramp and flat geometry cutting across the earlier thrust structures. The Kimi Complex is the hanging wall of all syn- and post-thrusting extensional systems. On top of the Kimi Complex, marine basins were formed from the Lutetian (c.48–43 Ma) through the Oligocene, during extension. Successively, atc.26 to 8 Ma, the Thasos/Pangeon metamorphic core complexes were exhumed. In these times representing the early stages of Aegean back-arc extension, the Strymon and Thasos detachment systems caused crustal thinning in the western Rhodope. Renewed heating of the lithosphere associated with magmatism and exhumation of hot middle crust from beneath the Sidironero Complex occurred. We focus on the geometry, timing and kinematics of extension and contraction structures related to the >42–30 Ma interval and how these exhumed high-Procks. We interpret high-Procks exhumed in this interval as a window of the Apulian plate beneath the earlier (in the Cretaceous) accreted Kimi Complex.
Models of Rodinia assembly and fragmentation
Authors: Pisarevsky Sergei A. , Wingate Michael T. D. , Powell Chris McA. , Johnson Simon , Evans David A. D.
Published: April 2008

Amongst existing palaeogeographic models of the Rodinia supercontinent, or portions thereof, arguments have focused upon geological relations or palaeomagnetic results, but rarely both. A new model of Rodinia is proposed, integrating the most recent palaeomagnetic data with current stratigraphic, geochronological and tectonic constraints from around the world. This new model differs from its predecessors in five major aspects: cratonic Australia is positioned in the recently proposed AUSMEX fit against Laurentia; East Gondwanaland is divided among several blocks; the Congo-São Francisco and India-Rayner Cratons are positioned independently from Rodinia; Siberia is reconstructed against northern Laurentia, although in a different position than in all previous models; and Kalahari-Dronning Maud Land is connected with Western Australia. The proposed Rodinia palaeogeography is meant to serve as a working hypothesis for future refinements.
Time, place and mode of propagation of foreland basin systems as recorded by the sedimentary fill: examples of the Late Cretaceous and Eocene retro-foreland basins of the north-eastern Pyrenees
Authors: Christophoul F. , Soula J.-C. , Brusset S. , Elibana B. , Roddaz M. , Bessiere G. , Deramond J.
Published: April 2008

The relationship between tectonics and sedimentary fill has been studied in two syncontractional basins of the western Corbières (eastern North Pyrenean retro-foreland basin). The Late Cretaceous basin formed during
c.
10–12 Ma as a result of left-lateral transpressional deformation, and is composed of forward-younging sub-basins characterized by reworking of the forelimbs of growing fold-propagation folds. Thrust-wedge advance and cratonward migration of the platform are recorded by a deepening-upward stacking pattern indicating increased regional subsidence with a limited contribution of the submarine orogen. Tectonic quiescence and erosional unloading lasting 29–30 Ma are recorded by a shallowing-upward stacking pattern, and fluvial sedimentation issued from widespread sources in the emerging inner orogen. The Early to Middle Eocene basin formed as a result of pure shortening normal to the range. The marine Early Eocene basin developed during
c.
2 Ma by widening of a single basin provoked by the two-step propagation of a basement duplex. This is recorded by growth-stratal patterns and coarsening-upward depositional sequences indicating the increasing contribution of the emerged orogen. The Middle Eocene continental deposits infilled two sub-basins working synchronously and were transported by alluvial fans with a provenance in the inner orogen, during decreasing thrust-wedge advance and increasing erosional unloading.
Active intraplate strike-slip faulting and transpressional uplift in the Mongolian Altai
Authors: Cunningham D. , Dijkstra A. , Howard J. , Quarles A. , Badarch G.
Published: April 2008

The Mongolian Altai is a Late Cenozoic intraplate strike-slip deformation belt which formed as a distant strain response to the Indo-Eurasian collision over 2000 km to the south. We report results from 5 weeks of detailed fieldwork carried out during summer 2000 in northwestern Mongolia investigating the crustal architecture of the Altai at latitude 48°N. The region can be divided into discrete Cenozoic structural domains each dominated by a major dextral strike-slip fault system or range-bounding thrust fault. Gentle bends along the major strike-slip faults are marked by transpressional uplifts including asymmetric thrust ridges, restraining bends, and triangular thrust-bounded massifs. These transpressional uplifts (Tsambagarav Massif, Altun Huhey Uul, Sair Uul, Hoh Serhiyn Nuruu, Omno Hayrhan Uula, Mengildyk Nuruu) comprise the highest mountains in the Mongolian Altai and are structural and metamorphic culminations exposing polydeformed greenschist-amphibolite grade basement recording at least two phases of Palaeozoic ductile deformation overprinted by Cenozoic brittle structures. Cenozoic thrust faults with the greatest amounts of displacement bound the W and SW sides of ranges throughout the region and consistently verge WSW. Each major range is essentially a NE-tilted block and this is reflected by asymmetric internal drainage patterns. Many faults are considered active because they deform surficial deposits, form prominent scarps, and define range fronts with low sinuosity where active alluvial fan deposition takes place. Reactivation of the prevailing NW-striking, NE-dipping Palaeozoic basement anisotropy is a regionally important control on the orientation and kinematics of Cenozoic faults. At first order, the Altai is spatially partitioned into a low-angle thrust belt that overthrusts the Junggar Basin on the Chinese side and a high-angle SW-vergent dextral transpressional belt on the Mongolian side. The mechanically rigid Hangay craton and Junggar basement block which bound the Altai on either side have played a major role in focusing Late Cenozoic deformation along their boundaries and within the Altai. The geometric relationship between rigid block boundaries, Palaeozoic basement structural anisotropy, and the dominantly NE SHmax (derived from India’s continued NE indentation) has dictated the kinematics of Late Cenozoic deformation in the Altai, Gobi Altai, and Sayan regions.
Relationships between Cenozoic strike-slip faulting and basin opening in northern Thailand
Authors: Uttamo Wutti , Elders Chris , Nichols Gary
Published: April 2008

Northern Thailand is located in a structurally complex area between three major tectonic regimes, a region of extensional tectonics to the south and two major strike-slip zones, the Sagaing fault zone to the west and the Red River fault zone to the northeast. Cenozoic tectonics in northern Thailand resulted from the collision between the Indian plate and Eurasia. The continued indentation of the Indian plate into Eurasia caused polyphase extrusion of Sundaland and the movement of major strike-slip faults. The movement of these faults accompanying the regional east-west extension during Late Oligocene to Early Miocene initiated the formation of the Tertiary basins.

Thirty-six major faults and forty-two intra-cratonic depositional basins in northern Thailand have been recognized and delineated using Landsat TM images. More than 70% of these basins are related to strike-slip tectonics. Five basin types have been recognized on the basis of geometric and kinematic considerations. These are fault-tip basins, pull-apart basins, fault-wedge basins, fault zone basins, and extensional basins. The opening and development of these basins was influenced by the movement of NW-trending dextral faults and NE-trending sinistral faults associated with north-south shortening and east-west extension.