bluuebunny/crossref_metadata_2025 huggingface dataset:
The Cenozoic and Late Cretaceous evolution of the Indian Ocean Basin: uncertainties in the reconstructed positions of the Indian, African and Antarctic plates
Authors: Molnar PETER , Pardo‐Casas FEDERICO , Stock JOANN
Published: November 2007

Abstract Reconstructions of the relative positions of the Indian, African, and Antarctic plates and their uncertainties are given for the times of selected magnetic anomalies that could be identified on adjacent pairs of these plates. Among the most certain reconstructions are those for the Antarctic and African plates, which can be determined directly from recently published magnetic anomalies from both sides of the Southwest Indian Ridge. As Patriat and his colleagues reported, there was an important change in direction and a decrease in rate of separation between Africa and Antarctica between the times of anomalies 33 and 20. India moved rapidly away from both Africa and Antarctica in the Late Cretaceous and early Tertiary periods, but slowed markedly near the time of anomaly 20 (≅ 45 Myr). The positions of the Indian plate with respect to the others are poorly constrained between the times of anomaly 5 (≅ 10 Myr) and anomaly 23 (≅ 54 Myr), but using the reconstructions of the African and Antarctic plates, the uncertainties can be reduced. Despite the relatively large uncertainties, the positions of anomalies 5, 6, and 13 on the Antarctic and Indian plates apparently cannot be described by the same parameters that describe the history of separation of Australia and Antarctica. Therefore, Stein and Okal's contention that Australia and India lie on separate plates appears to be valid not only for the present, but for the last 35 Myr.
The nature and evolution of deep‐sea channel systems
Authors: Carter R. M.
Published: November 2007

Abstract A distinction is drawn between sea‐floor canyons, which are incised into bedrock, and fan valleys and deep‐sea channels, which are cut in unconsolidated sediment. The formation of continental margin canyons/fans and deep‐sea channels is an inevitable consequence of continental margin rifting and sea‐floor subsidence. Such submarine sediment transport systems are amongst the longest‐lived physiographic features on earth, with the Bounty Channel system being more than 50 Myr old. Many deep‐sea channels form the distal part of ocean‐margin sediment transport systems, being incised 100–350 m into ocean‐floor sediments, traversing great distances over the ocean‐basin floor, and generally terminating on an abyssal plain. The course of each deep‐sea channel is, however, unique. Channel locations are controlled primarily by inherited basement relief, and, during their evolution, by rates and patterns of lithospheric subsidence and sedimentation. In the early stages of ocean‐basin formation, deep‐sea channels may issue from the axial parts of marginal rifts, or directly from slope canyon‐fan systems. As an ocean basin widens, margin‐connected channels may become trapped within the strip of oldest (and therefore deepest) oceanic crust at the continent/ocean interface, and will therefore be margin‐parallel features. In some cases, as for the Cascadia Channel, channels may escape from the ocean‐margin deep, bypassing the spreading ridge via a fracture zone. Deep‐sea channels and their associated sediments are influenced also by global sea‐level change, by rate of turbidity current generation from the headward continental margin, by rates of pelagic sediment supply, by differential levee development consequent upon the Coriolis effect, and by the operation of deep‐sea current systems with their associated sediment drifts. The survival of deep‐sea channels as long‐lived features necessitates that rates of long‐term subsidence at the channel terminus exceed sediment accumulation.
Mid‐Jurassic through mid‐Cretaceous extension in the Central Graben of the North Sea ‐ part 1: estimates from subsidence
Authors: Hellinger STEVEN J. , Sclater JOHN G. , Giltner JOHN
Published: November 2007

Abstract The post early Carboniferous subsidence history of the Central North Sea basin can be separated into three major periods: Permian, Triassic and post Mid‐Jurassic. Prior efforts to account for this subsidence within an extensional framework have concentrated on the post Mid‐Jurassic. These efforts have assumed that the effects of the previous periods of extension necessary to create the Permian and Triassic subsidence are negligible. We consider the 80‐km value for the Mid‐Jurassic‐mid‐Cretaceous extension from these efforts a reasonable upper estimate of the likely amount of extension. This value has received considerable criticism as it is almost four times as great as that determined by summing the horizontal displacement (heave) on faults observed on industry seismic lines in the area.

We treat the two earlier phases of extension as one phase and develop a method to estimate the maximum value of this extension. We use this value, with estimates of the total extension from the early Carboniferous to Present, to determine a likely minimum value for the mid‐Mid‐Jurassic through mid‐Cretaceous extension. After justifying the use of Airy isostasy for the loading response of the lithosphere we show that the observed unloaded basement subsidence history is compatible with the parameters we derive for the pre and post Mid‐Jurassic extension. Our minimum estimate of 38 km is still significantly higher than that: made by summing the heave on the faults active throughout the Upper Jurassic and lower Cretaceous.
Scientific applications of downhole measurements in the ocean basins
Authors: Worthington PAUL F. , Anderson ROGER N. , Jarrard RICHARD D. , Becker KEIR , Bell J. SEBASTIAN , Salisbury MATTHEW H. , Stephen RALPH A.
Published: November 2007

Abstract The well logging activity of the Ocean Drilling Programme, which deploys the most technically advanced suite of downhole measurements available for routine use, is providing new opportunities for advancement in marine geoscience. Particular examples are cited of the application of wireline data to problems associated with global environmental changes, crust/ mantle interactions, crustal fluid circulation in the context of a global geochemical budget, lithospheric stress and deformation, and evolutionary processes in oceanic communities. Further technological developments will expand the scientific role of downhole measurements still further, especially in terms of the integration of geophysical data at different scales of measurement, and the interpretation of these data in accordance with; global scientific themes.
Compaction‐induced subsidence in the margin of a carbonate platform
Authors: Doglioni C. , Goldhammer R. K.
Published: November 2007

AbstractThe Late Carnian Raibl Formation of the Sella Group (Dolomites, N Italy) forms a sedimentary wedge which thins progressively toward the core of a stratigraphically underlying Middle Carnian carbonate platform (Cassian Dolomite). The platform is composed largely of megabreccia clinoforms displaying progradation above the coeval basinal sequence (San Cassiano Formation). These basinal sediments thin from a maximum in a basinward direction to a pinchout towards the central core of the Sella buildup. The progradational foreslopes thin in an antithetic fashion, from a maximum immediately adjacent to the central core of the Sella to a minimum in a basinward direction. The wedge geometry and onlap of the Raibl Formation atop the Sella platform margin is interpreted as the result of compaction‐induced differential subsidence and tilting of the platform top. Basinward increase in subsidence of the platform top resulted from a basinward increase in compaction of basinal San Cassiano sediments. Decompaction calculations and stratigraphic/geometric restoration of Carnian strata support this conclusion.
Reconstructing basin evolution from sedimentary thickness; the importance of palaeobathymetric control, with reference to the North Sea
Authors: Bertram G. T. , Milton N. J.
Published: November 2007

Abstract The structural evolution of a basin cannot be reconstructed from sedimentary thicknesses alone without data on palaeobathymetry. Two classes of geological horizons, are defined, profiles and traces. Profiles are time‐lines and bound depositional units. Traces were formed at a known water depth and contain implicit palaeobathymetric data.

Rock units bounded by traces are diachronous lithostratigraphic units, and the thicknesses of such units are controlled directly by subsidence, while the thicknesses of profile‐bounded units may be unaffected by the subsidence or even the palaeotopography of the basin.

Dating fault movement from thickness variations in profile‐bounded units is difficult without prior knowledge of the palaeobathymetry, and it is impossible to distinguish between synsedimentary fault movement and onlap to a pre‐existing fault scarp from thickness alone.

Reconstruction of the basin history of the North Sea is difficult due to the lack of trace‐bounded units in the post‐Jurassic. The validity of previously published studies depends largely on the quality and quantity of palaeobathymetric data included. An alternative basin history is proposed based on the few trace‐bounded units in the North Viking Graben. This includes rifting episodes in the Triassic and Late Jurassic, and a period of uplift in the Palaeocene.
Interplay of tectonics and sea‐level changes in basin evolution: an example from the intracratonic Amadeus Basin, central Australia
Authors: Lindsay JOHN F. , Korsch R. J.
Published: November 2007

Abstract The Amadeus Basin, a broad intracratonic depression (800 times 300 km) in central Australia, contains a complex Late Proterozoic to mid‐Palaeozoic depositional succession which locally reaches 14 km in thickness. The application of sequence stratigraphy to this succession has provided an effective framework in which to evaluate its evolution. Analysis of major depositional sequences shows that the Amadeus Basin evolved in three stages. Stage 1 began at about 900 Myr with extensional thinning of the crust and formation of half‐grabens. Thermal recovery following extension was well advanced when a second less intense crustal extension (stage 2) occurred towards the end of the Late Proterozoic. Stage 2 thermal recovery was followed by a major compressional event (stage 3) in which major southward‐directed thrust sheets caused progressive downward flexing of the northern margin of the basin, and sediment was shed from the thrust sheets into the downwarps forming a foreland basin. This event shortened the basin by 50–100 km and effectively concluded sedimentation.

The two stages of crustal extension and thermal recovery produced large‐scale apparent sea‐level effects upon which eustatic sea‐level cycles are superimposed. Since the style of sedimentation and major sequence boundaries were controlled to a large degree by basin dynamics, depositional patterns within the Amadeus and associated basin are, to a large degree, predictable. This suggests that an understanding of major variables associated with basin dynamics and their relationship to depositional sequences may allow the development of generalized depositional models on a basinal scale.

The Amadeus Basin is only one of a number of broad, shallow, intracratonic depressions that appeared on the Australian craton during the Late Proterozoic. The development of these basins almost certainly relates to the breakup of a Proterozoic supercontinent and in large part, basin dynamics appears to be tied to this global tectonic event. Onlap and apparent sea‐level curves derived from the sequence analysis appear to be composite curves resulting from both basin dynamics and eustatic sea‐level effects. It thus appears likely that sequence stratigraphy could be used as a basis for inter‐regional correlation; a possibility that has considerable significance in Archaean and Proterozoic basins.
Gravity studies of the Rockall and Exmouth Plateaux using SEASAT altimetry
Authors: Fowler SUE , McKenzie DAN
Published: November 2007

Abstract SEASAT altimetric measurements are used to determine the gravity anomalies across two passive continental margins: the western margin of the Rockall Plateau, UK, and the Exmouth Plateau off north‐west Australia. The small gravity anomalies observed over the starved western margin of the Rockall Plateau require the existence of a major density contrast within the crust, as well as the Moho, and show that the elastic thickness is less than 5 km at the time of rifting. The gravity anomaly over the Exmouth Plateau is compared with the gravity anomaly calculated from the sediment loading of a thin elastic plate, taking account of the variation in crustal thickness. This comparison shows that the Exmouth Plateau also has a small effective elastic thickness of 5 km, even for loads emplaced between 60 and 120 Myr after rifting. Elastic thicknesses of about 5 km have also been reported for other sedimentary basins, and are to be expected if the rheological properties of the crust and mantle depend on the ratio of the present temperature to the melting temperature. Flexural effects are therefore likely to be of minor importance in sedimentary basins.
Simple equations of sedimentation: applications to sequence stratigraphy
Authors: Cant DOUGLAS J.
Published: November 2007

Abstract An equation to relate the thickness of sediment deposited (ΔSed), eustatic sea‐level change (ΔE), and subsidence (ΔSub), to changes in depth of water (ΔD) is: ΔSub +ΔE‐ΔSed =ΔD.

Using existing sea‐level curves, the equation shows that some transgressive‐regressive sequences in a foreland basin and a composite seismic facies sequence on a passive margin cannot result solely from eustatic variation. In each case, the space created by subsidence is greater than that provided by eustatic rise. However, eustatic variation could have triggered sequence development if superimposed on a basin with relatively constant values of the other parameters. Short‐period sea‐level fluctuations with high rates of change, exceeding 70–100 m Myr‐1 for periods less than 2–3 Myr, affect the stratigraphy and sedimentology more than longer period, higher amplitude variations.

Clinoforms are generated because of lateral variations in sedimentation rate compared to the rate of creation of accommodation space. These variations may result from differing sedimentation rates, subsidence rates, or rates of eustatic change, superimposed on a basin with lateral sediment supply. Clinoform slopes and curvatures are interpre table in terms of these variables as well as the type of sediment supplied and the energy distribution in the basin.

These equations put some well‐known geological principles on a simple quantitative basis. They force precision in definition of variables, and may lead to further development of quantitative techniques in stratigraphy and sedimentology.
Stratal patterns: a proposal of classification and examples from the Dolomites
Authors: Doglioni CARLO , Bosellini ALFONSO , Vail PETER R.
Published: November 2007

Abstract A classification of stratal patterns is proposed from outcrop analysis of the Middle‐Upper Triassic succession of the Dolomites (northern Italy). Stratal patterns are classified into two groups: stratal discontinuities and internal geometries. The stratal discontinuities are further subdivided into unconformities and synsedimentary stratal discontinuities on the basis of whether significant time is missing at the discontinuity. Internal geometries are further subdivided into planes and internal patterns.
Subsidence, sedimentation and sea‐level changes in the Eromanga Basin, Australia
Authors: Gallagher KERRY , Lambeck KURT
Published: November 2007

Abstract The Jurassic‐Cretaceous subsidence history of the Eromanga Basin, a large intracratonic sedimentary basin in central eastern Australia, has been examined using standard backstripping techniques, allowing for porosity reduction by compaction and cementation. Interpretation of the results suggests that during the Jurassic the basin was subsiding in a manner consistent with the exponentially decreasing form predicted by simple thermally based tectonic models. By the Early Cretaceous, the rate of subsidence was considerably higher than that expected from such models and nearly half of the total sediment thickness was deposited over the final 20 Myr of the basin's 95 Myr Mesozoic depositional history. The Early Cretaceous also marks the first marine incursion into the basin, consistent with global sea‐level curves. Subsequently, however, the sediments alternate between marine and non‐marine, with up to 1200 m of fluvial sediments being deposited, and this was followed by a depositional hiatus of about 50 Myr in the Late Cretaceous. This occurred at a time when global sea‐level was rising to its peak. A model is presented which is consistent with the rapid increase in tectonic subsidence rate and the transgressive‐regressive nature of the sediments. The model incorporates a sediment influx which is greater than that predicted by the thermally based tectonic models implied by the Jurassic subsidence history. The excess sedimentation results in the basin region attaining an elevation which exceeds that of the contemporary sea‐level, and thereby giving the appearance of a regression. The present day elevation of the region predicted by the model is about 100–200 m above that observed. This discrepancy may arise because the primary tectonic subsidence is better represented by a linear function of time rather than an exponentially decreasing form.
Lithospheric flexure due to prograding sediment loads: implications for the origin of offlap/onlap patterns in sedimentary basins
Authors: Watts A. B.
Published: November 2007

Abstract Simple elastic plate models have been used to determine the stratigraphic patterns that result from prograding sediment loads. The predicted patterns, which include coastal offlap/onlap and downlap in a basinward direction, are generally similar to observations of stratal geometry from Cenozoic sequences of the U.S. Atlantic and Gulf Coast margins. Coastal offlap is a feature of all models in which the water depth and elastic thickness of the lithosphere, Te (which is a measure of the long‐term strength of the lithosphere), are held constant, and is caused by a seaward shift in the sediment load and its compensation as progradation proceeds. The coastal offlap pattern is reduced if sediments prograde into a subsiding basin, since subsidence causes an increase in the accommodation space and loading landward of a prograding wedge. The stratal geometry that results is complex, however, and depends on the sediment supply, the amount of subsidence, and Te. If the sediment supply to a subsiding basin proceeds in distinct ‘pulses’ (due, say, to different tectonic events in a source region) then it is possible to determine the relationship between stratal geometry and Te. Coastal offlap and downlap are features of most models where the lithosphere either has a constant Te slowly increases Te with time, or changes Te laterally; however, in the case where sediments prograde onto lithosphere that rapidly increases Te with rime, the offlap can be replaced by onlap. Lithospheric flexure due to prograding sediment loads is capable of producing a wide variety of stratal geometries and may therefore be an important factor to take into account when evaluating the relative role of tectonics and eustatic sea‐level changes in controlling the stratigraphic record.
Mesozoic sedimentation rates in the Western Canada Basin as indicators of the time and place of tectonic activity
Authors: Chamberlain V. E. , Lambert R. ST J. , McKerrow W. S.
Published: November 2007

Abstract The Mesozoic stratigraphy of the westernmost part of the Western Canada Basin is used to estimate sedimentation and relative crustal subsidence rates in the region between 49oN and 60oN, immediately to the east of the disturbed belt. Average rates of subsidence varied from zero to 120 m/Myr, with prominent maxima occurring three times during the Mesozoic. The first occurred during the Tithonian, when rates rose to 100 m/Myr; the second during the Albian to early Santonian, when rates rose to 120 m/Myr in the north and to 70 m/Myr in the south, with subsidence occurring earlier in the north than in the south. The third period of rapid subsidence occurred during the Campanian and Maastrichtian, with rates rising to 120 m/Myr in the southern part of the basin. During non‐peak periods, average rates of subsidence ranged from 3.5 m/Myr to 35 m/Myr in the Triassic, from zero to 20 m/Myr in the Jurassic and from zero to 30 m/Myr in the Cretaceous.

Tectonic loading of the lithosphere is considered to be the most probable cause for all three of these periods of rapid subsidence. The three separate episodes are correlated with the separate arrivals of accreted terranes; the first in north‐east Oregon and central west Idaho during the Late Jurassic, the second in the central Yukon during the late Early Cretaceous and the third in south‐east British Columbia during the Late Cretaceous.
The interaction of eustacy and tectonism from provenance studies of the Eocene Hecho Group Turbidite Complex (South‐Central Pyrenees, Spain)
Authors: Fontana DANIELA , Zuffa GIAN GASPARE , Garzanti EDUARDO
Published: November 2007

Abstract Using a detailed petrographical procedure conceived for arenites rich in carbonate clasts, the influence of tectonism and eustacy on silicate/carbonate cycles of the Eocene Hecho Turbidite Complex has been tested, and the palaeogeography of the source/basin system outlined.

Both extrabasinal and intrabasinal sources of sediments were active during basin filling. The extrabasinal source terrains, located in the southern sector of the basin, were made of the Pyrenean crystalline basement (granites, gneisses and phyllites) overlain mainly by carbonate rocks (Cretaceous limestones and dolostones, minor chert and siltstones). The intrabasinal sources, represented by foramol shelf carbonate factories, provided penecontemporaneous carbonate bioclasts, intraclasts and peloidal grains.

Foreland thrusting in the South‐Central Pyrenees has acted as the major control on the composition and architecture of the Hecho Turbidite Complex. Strong uplift of old silicate and carbonate source terrains during southward thrust propagation was responsible for erosion, swamping and/or reduction of shelfal areas, and gave rise to siliciclastic and carbonate basinal sequences (silicate arenites and calclithites) during lowstand stages. Conversely, hybrid arenites (mixture of extrabasinal and intrabasinal grains) originated from resedimentation of marginal shelf sediments produced in carbonate factories active during the initial phase of sea‐level rise. Hybrid arenites with minor intrabasinal content also formed during one stage of relative sea‐level fall from the erosion of previously accumulated highstand complexes.

During resedimentation processes, hybrid sands underwent marked hydraulic selection documented by deposits depleted in carbonate grains in the channel area, and by thin‐bedded turbidites rich in platy‐skeletal fragments, low‐density peloids and void‐rich bioclasts down‐basin.
Half‐graben basin filling models: new constraints on continental extensional basin development
Authors: Schlische Roy W.
Published: November 2007

Three end‐member models of half‐graben development (detachment fault, domino‐style, and fault growth) evolve differently through time and produce different basin‐filling patterns. The detachment fault model incorporates a basin‐bounding fault that soles into a subhorizontal detachment fault; the change in the rate of increase in the volume of the basin during uniform fault displacement is zero. Younger strata consistently pinch out against older synrift strata rather than pre‐rift rocks. Both basin‐bounding faults and the intervening fault blocks rotate during extension in the domino fault block model; a consequence of this rotation is that the change in the rate of increase of the volume of the basin is negative during uniform extension. Basin fill commonly forms a fanning wedge during fluvial sedimentation, whereas lacustrine strata tend to pinch out against older synrift strata. In the fault growth models, basins grow both wider and longer through time as the basin‐bounding faults lengthen and displacement accumulates; the change in the rate of increase in basin volume is positive. Fluvial strata progressively onlap pre‐rift rocks of the hanging wall block, whereas lacustrine strata pinch out against older fluvial strata at the centre of the basin but onlap pre‐rift rocks along the lateral edges. These fundamental differences may be useful in discriminating among the three end‐member models. The transition from fluvial to lacustrine deposition and hanging wall onlap relationships observed in numerous continental extensional basins are best explained by the fault growth models.
Tectonic loading, sedimentation, and sea‐level changes in the foreland basin of north‐west Alberta and north‐east British Columbia, Canada
Authors: Underschultz J. R.
Published: November 2007

By calculating mass accumulation rates for foreland basin sediments, the changing capacity of the basin can be monitored through time. It has often been assumed that there was a direct link between foreland basin sedimentation and tectonic deformation and lithospheric loading in the adjacent orogenic belt. The results of this study suggest that tectonic deformation is most likely associated with the changing capacity of the basin and the rate at which sediments accumulate within it, However, there appears to be no relation between tectonic deformation and the lithology of sediment which accumulates in the foreland basin. Instead, eustatic sea‐level fluctuations appear to have significant control, through their impact on water depth, on the lithology of sediments accumulating in the foreland basin. These relations are evidenced by mass accumulation rates calculated for foreland basin strata in north‐west Alberta and north‐east British Columbia, Canada.
Tectonic brines and sedimentary basins: further applications of fission track analysis in understanding Karoo Basin evolution (South Africa)
Authors: Duane Michael J. , Brown Roderick W.
Published: November 2007

Fission track analyses of detrital components in the Permo‐Triassic Karoo Basin (South Africa), highlight the potency of tectono‐magmatically driven fluids to penetrate wide and far in foreland basins. The data, together with the data published on Karoo tectonics and magmatism, support a model which requires that fluids were driven north out of the Cape‐Karoo orogen during the Cape Orogeny (270–200 Ma). Later fluids were redistributed and aquifers rejuvenated during (and after) the final break‐up of Gondwana (<200 Ma). The fission track data indicate that thermal annealing of fission tracks in zircon occurs non‐uniformly between individual zircon grains. This model is in agreement with recent models applied to deformed foreland basins and implicates tectonic fluids in U metallogenesis.
Tectonic development of the Drummond Basin, eastern Australia: backarc extension and inversion in a Late Palaeozoic active margin setting
Authors: Johnson S. E. , Henderson R. A.
Published: November 2007

Detailed seismic reflection data combined with regional magnetic, gravity and geological data indicate that the Drummond Basin originated as a backare extensional basin associated with Late Devonian and Early Carboniferous active margin tectonism in the northern New England Fold Belt. Seismic reflection data have been used to generate a two‐way time map of seismic basement, providing a clear view of the basinal geometry and structural development. Broadscale structural asymmetry of the basin implies that simple shear along a deep, upper‐crustal detachment provided the extensional mechanism and generated an inter‐related set of listric normal faults and associated transfer faults, as well as steeply‐dipping planat normal faults. The orientation of normal faults near the basin margins appears to have been controlled by regional basement structural trends. Transfer‐fault trends were approximarely orthogonal to the line of plate convergence as assessed from the orientation of coeval are, forcare and subduction complex stratorectonic elements. Three distinct phases of infill are represented in the basinal stratigraphic succession. The first consists largely of volcanics and volcaniclastics, indicating that effusive magmatism and extension were closely associated in space and time. The second is quartzose and of basement derivation, but was not derived from footwall blocks at the faulted basinal margins to the east and north. Uplifted hanging‐wall crust beyond the western basinal margin, a product of west‐directed simple shear detachment, was the likely source terrain. The final infill phase consisted of volcaniclastics considered to have been derived from a coeval volcanic are to the east. Major faults at the basin margins provided conduits for magmatism during extensional basin development, and long after the basinal history was complete. During the Late Carboniferous and mid‐Triassic, the basin was affected by two discrete episodes of compressional deformation. This led to inversion with the development of folds, and reverse and wrench faults now seen at the surface.
Purana basins of peninsular India: a review
Authors: Kale Vivek S. , Phansalkar V. G.
Published: November 2007

Seven supracratonic, Proterozoic basins, occupying more than a fifth of the Precambrian exposures in the Indian Peninsula, comprise the Purana basins. A comprehensive review of the current status of knowledge of these voluminous orthoquartzite‐carbonate‐shale suites in the context of their contemporary lithostratigraphy, depositional environments and structural disposition is presented. Stromatolite biostratigraphy and available geochronological data are compared, to discern their age limits.

These basins contain perhaps one of the most elaborate records of Middle to Late Proterozoic (Riphean‐Vendian) sedimentation preserved in an unmetamorphosed and only slightly deformed state. Further sedimentological and structural studies could lead to a better understanding of the Proterozoic craton‐margin processes. Their close association with the Middle Proterozoic Mobile Belt of peninsular India is that of two contrasting tectonic regimes, contemporaneously adjoining each other. The existing lithostratigraphic classifications of many of these sequences may not stand the test of process ‐ response considerations as demonstrated by the recent revisions in the stratigraphy of the Cuddapah and Bhima basins. The prolific stromatolitic, micro‐organic and trace‐fossil communities preserved in them require much more detailed, but cautious study, and may yield information on the Riphean‐Vendian biota. However, these studies must be undertaken in association with elaborate geochronological determinations which are sparse at present.

Inadequacy of the existing knowledge of these basins is highlighted, with the view of inviting the attention of the geological community to these unique basins from peninsular India.
Structure of the Central North Aegean Trough: an active strike‐slip deformation zone
Authors: Roussos Nicolas , Lyssimachou Triantafyllos
Published: November 2007

Detailed interpretation of marine seismic data shows the presence of an extending, active, dextral strike‐slip fault zone at the south edge of the Mount Athos Peninsula. The zone is over 100 km long and has both transtensional and transpressive features observable on the seismic lines. We suggest that dextral strike‐slip displacement along the zone is on the order of 5–7 km. The structure and fault patterns of Recent deformation in the Central North Aegean Trough is typical of strike‐slip tectonism.
Application of a dual‐lithology, depth‐dependent diffusion equation in stratigraphic simulation
Authors: Rivenæs Jan C.
Published: November 2007

A process‐based dynamic‐slope approach is incorporated in a two‐dimensional (2D) stratigraphic basin simulation software. It is based on the classical topographical diffusion concept, but in contrast to previous models it predicts down‐slope sorting of two grain‐size classes (here sand and mud). The effect of compaction is included in the mass balance, as well as arbitrary depth‐dependent transport coefficients (difrusivities). Each lithology will have its own transport‐coefficient function, which can be tuned to predict realistic lithology dispersion (e.g. trapping of sand in shallow‐marine environments). The set of partial‐differential equations is solved numerically by using a fully implicit finite difference method, applying a Newton iteration scheme on the non‐linear equations.

Simulations show that the mass balance due to compactional effects is taken care of. A case from a technically quiescent margin demonstrates, as commonly observed in nature, that the sand fraction increases on the alluvial plain when accommodation space is limited. In the marine part, sand‐rich coarsening‐upward sequences form during progradation, while a condensed and partly erosional maximum flooding surface (MFS) forms during transgression. The MFS is associated with very shaly lithology, a feature that is observed both in field work and on geophysical well logs. If compaction and isostasy modelling are included in this case, the overall architecture is altered. The deposits become proximal, and the timing of maximum regression, etc. is modified. Alternatively, if the time span of simulation is doubled, the result is lower slope angles and increased penetration distance of the sediment wedge into the ljasin. Thus, it is demonstrated that a process‐based dynamic‐slope approach with lithology sorting is a rich alternative to more geometrically based models when the formation of large‐scale stratigraphic architecture is investigated.
Volcanism and sedimentation in part of a Late Archaean rift: the Hartbeesfontein basin, Transvaal, South Africa
Authors: Karpeta W. P.
Published: November 2007

The Hartbeesfontein basin is one basin within the Late Archaean rift system of South Africa. This rift system has been recently compared to the Basin and Range province in western North America and may therefore be an ensialic extensional back‐arc basin. Structurally, the Hartbeesfontein basin is a half‐graben structure bounded to the south‐east by a major, normal, listric fault and to the north‐east and south‐west by strike‐slip (transfer?) fault zones. It is infilled by over 2000 m of diamictites, shales, lavas and chemical sediments. Initial basin formation appears to be accompanied by phreatomagmatic volcanic activity caused by the interaction between basic tholeiitic magmas rising along fractures and groundwater. Volcaniclastic debris from these eruptions was incorporated into laharic debris flows and deposited on basin marginal alluvial fans. At the same time a deep, permanent lake formed within the basin in which silts and muds accumulated. Major fissure eruptions of basic, tholeiitic lavas followed, their eruptive centres being apparently located along the strike‐slip (transfer?) fault /ones. Initially, these fissure eruptions had high rates of magma discharge accompanied by intense fire fountaining that resulted in the rapid accumulation of aa type flows. Later lava discharge rates decreased and more quiescent pahoehoe type flows were erupted. Localized centres of acid volcanism within the basic lava pile were located along the south‐western strike‐slip fault zone. These acid volcanic rocks are interpreted as co‐ignimbrite lag breccias and pyroclastic flow deposits and tuffs produced by the repeated formation and collapse of Plinian eruption columns. Towards the top of the basic lava pile, two breaks in volcanism permitted the formation of dolomitic playa lakes. Sedimentation in these lakes was terminated by further basic lava flows. At the top of the basin fill sequence is a thick, bedded chert interpreted as a magadiitic, alkaline playa lake fed by silica‐rich hot springs located along the south‐eastern edge of the basin. Quartzites and conglomerates deposited by braided rivers unconformably overlie the basin‐fill sequence and probably represent a through flowing river system signifying termination of the Hartbeesfontein basin as a separate basin. The Hartbeesfontein basin and its fill demonstrate that a close relationship exists between fissure volcanism, sedimentation and basin evolution and that the strike‐slip, transfer faults acted as the loci of volcanic activity.
Structural evolution of African basins: stratigraphic synthesis
Authors: Sahagian DORK L.
Published: November 2007

The structural and stratigraphic character of African interior sedimentary basins is highly variable, indicating contrasting basin‐forming mechanisms and subsequent subsidence histories. A stratigraphic database has been compiled for African interior depositional basins for the purpose of better understanding basin thermal and structural development. Data are recorded in the form of stratal age, lithology, thickness and elevation of top with respect to present sea level. The data are obtained from published structure contour maps, well sections, and outcrop geology and elevation. There are various degrees of data coverage of the basins, proportional to the amount of water and oil drilling activity. Consequently, there is excellent coverage of North African basins such as the Algerian basin and the Sirte basin, while there is little known about the subsurface of the Congo basin. The stratigraphic data are used to reconstruct the depositional history of the basins, while backstripping leads to the quantification of the thermo‐tectonic component of basin subsidence. The nature of basement subsidence can provide constraints on lithospheric flexural rigidity. In addition, the depositional and thermo‐tectonic history of each basin bears upon the mechanisms of basin formation and subsidence. Virtually all types of basins are represented in interior Africa, including thrust‐loaded basins (Algerian), passive‐margin rift basins (Algerian, Sirte), modern active rift basins (East African), ancient rift basins (Benue, Abu Gabra), basins caused by uplift of their margins (Congo, Chad, Illumeden) and even basins that may be related to thermal subsidence of hot‐spot domes (Algerian, Sirte).
Pseudo‐toplap in seismic models of the Schlern‐Raibl contact (Sella platform, northern Italy)
Authors: Stafleu JAN , Schlager WOLFGANG
Published: November 2007

In the Sella platform of the Dolomite Alps, the horizontal beds of the Raibl Formation directly overlie the Upper Schlern Dolomite (Cassian Dolomite of some authors). The Schlern Dolomite comprises steep clinoforms, together with a few tens of metres of horizontal topset beds in the platform interior.

Two‐dimensional seismic modelling techniques were used to determine the seismic‐response of this interesting situation. To perform this, two different lithological models were constructed based on outcrops of the Sella south face. The first model is that of a rapidly prograding platform with slow aggradation in the platform interior. The second model shows clinoforms toplapping against the topset beds of the platform interior.

P‐wave velocities and bulk densities were assigned to the lithostratigraphical units in accordance with values from a similar study, involving the same formations. The vertical‐incidence method was used to construct perfectly migrated time sections and depth sections of reflectivity. These were convolved with zero‐phase Ricker wavelets of different peak frequencies to produce the final synthetic seismic sections.

Using conventional, low frequencies (e.g. 25 Hz), the seismic response of the two models is almost identical. The topset beds and the Schlern‐Raibl contact appear as one event. In a real seismic survey, both sections would be interpreted as toplap of Schlern clinoforms against the Raibl Formation. At higher frequencies (75 Hz), however, differences are revealed. The angle of progradation in the progradation & aggradation model becomes visible, as opposed to the horizontal surface in the progradation & toplap model. Topset beds are resolved separate from the Raibl Formation, but still appear to form a single dipping pseudo‐toplap surface.

Another modelling technique, simulating unmigrated sections, shows few differences between the two models even at high frequencies. In addition, the clinoforms are disturbed by the refraction of rays. This study demonstrates that, even under ideal acquisition and processing conditions, the seismic tool can introduce a pseudo‐toplap. This implies that toplap in a seismic section is not necessarily toplap in outcrop.
The interaction between normal faulting and drainage in active extensional basins, with examples from the western United States and central Greece
Authors: Leeder M. R. , Jackson J. A.
Published: November 2007

Faulting exerts an important control upon drainage development in active extensional basins and thus helps determine the architecture of the sedimentary infill to a synrift basin. Examples of the interaction between faulting and drainage from the western United States and central Greece may be grouped into a relatively small number of classes based upon the structural position of a drainage catchment: footwall, hangingwall, fault offset and axial. Our examples illustrate the diversity of erosional effects that might arise because of variations in the spacing, orientation and segmentation of faults and their interactions. Where basement lithology is similar, footwall catchments are generally smaller, shorter and steeper than those of the hangingwall. Footwall‐sourced alluvial fans and fan deltas are: generally smaller in area than those sourced from similar lithologies in the hangingwall. Wide fault offsets often give rise to large drainage catchments in the footwall. The development of axial drainage depends upon the breaching of transverse bedrock ridges by headward stream erosion or by lake overflow. Once breaching has occurred the direction of axial stream flow is controlled by the potential developed between basins of contrasting widths. Fault migration and propagation leads to the uplift, erosion and resedimentation of the sedimentary infill to formerly active basins, leading to the cutting of footwall unconformities. The outward sediment flux from structurally controlled catchments is modulated in an important way by lithology and runoff. The greatest contrasts in basement lithology arise when fault migration and propagation have occurred, such that the sedimentary fill to previously active basins is uplifted, incised and eroded by the establishment of large new drainage systems in the footwalls of younger faults. Drainage patterns in areas where faults interact can shed light on the relative timing of activity and therefore the occurrence of fault migration and propagation. Facies and palaeocurrent trends in ancient grabens may only be correctly interpreted when observations are made on a length scale of 10–20 km, comparable to that of the largest fault segments.
Architecture and sedimentary facies evolution of a marine, expanding outer‐arc half‐graben (Crete, late Miocene)
Authors: Postma GEORGE , Drinia HARA
Published: November 2007

Vertical trends in architecture and facies of delta systems are preserved in a clastic wedge of an expanding marine half‐graben in which tectonics, eustatic sea‐level change and climatic change are roughly known from independent evidence. The studied half‐graben is situated on Crete (Greece) and part of a larger, E‐W‐trending extensional domain situated north of the Hellenic subduction zone. The extension seems to be related to the southward migration of the trench (roll‐back) in early Late Miocene times. The infill pattern is discussed in the light of theoretical fault‐growth models for expanding half‐grabens.

The geometry of the half‐graben fill is typically wedge shaped, with a thickness of nearly 1000 m near the fault scarp thinning to c. 50 m about 20 km away from the scarp. The lower part of the wedge (Stratified Prina Series) contains coarsening‐upward units representing progradational, shallow‐marine deltas. At the base of the wedge these units are thin and retrogradationally stacked. Upwards in the succession, the units become composite (coarsening‐upward subunits), thicker and finer grained. The composite structure, the thickening and the fining trend is related to progressive increase in accommodation space inherent in fault growth.

Rapid deepening of the basin from the photic zone (evidenced by intercalated coral and stromatolite beds) up to a depth of 900 m started at the top of the Stratified Prina Series. The deepening continued over some tens of metres of marly sediments of the base of the Kalamavka Formation and may be related to structural collapse of the fault block. After the structural collapse, basin depth remained more or less constant and basin infilling occurred by progradation of deep‐water delta systems. These systems are characterized by a muddy delta slope with channelized conglomerates, and by mainly aggradation of prodelta turbidites deposited in small lobes at the base of slope.
Tectonic controls on base‐level variations and depositional sequences within thrust‐top and foredeep basins: examples from the Neogene thrust belt of central Sicily
Authors: Butler ROBERT W. H. , Grassot MARIO
Published: November 2007

Tectonic subsidence and uplift may be recorded by concomitant sedimentation, not only from decompacted accumulation curves but also from the evolving depositional environment relative to sea level at the time. In thrust belts there are two types of processes capable of generating vertical movements, each with different wavelengths and amplitudes. Regional subsidence is driven by flexural loading by the orogenic hinterland, the thrust belt and accumulated sediments of the underlying foreland lithosphere. Within this flexure, the foreland thrust belt will generate areas of local uplift, notably at the crests of thrust anticlines. In this contribution we examine how these processes have interacted to influence relative sea level as recorded by late Neogene sediments in an array of basins developed above and adjacent to the Maghrebian thrust belt of central Sicily. Two particular periods are addressed, the late Tortonian to early Messinian (Terravecchia Formation) and early to early late Pliocene. The earlier of these is characterized by a deltaic complex that formed prograding depositional geometries, migrating into perched basins. Collectively, however, these units are transgressive and migrate back towards the orogen. A depositional model is presented that links the migration of facies belts to subsidence caused by accentuated tectonic loading in the hinterland and break‐back thrust sequences across the basins. We infer that a palaeobathymetric profile of underfilled sub‐basins resulted and that this influenced the pattern of evaporite accumulation during Mediterranean desiccation in Messinian times. The Pliocene sediments, accumulated under renewed global sea levels, prograded towards the foreland. A waning tectonic load in the hinterland driving isostatic rebound, uplift and coastal offlap is the proposed explanation. This contribution is a case history for the depositional evolution of dominantly submarine thrust systems and their record of relative sea‐level changes.