Global and continental-scale glaciations on the Precambrian earth

Earth’s climate during the Proterozoic Eon was marked by major glacial events with evidence for large continental ice sheets on many cratons, and with sedimentological data indicating that glaciers had extended to sea-level. This paper emphasizes the sedimentological and sequence stratigraphic responses to glaciations and evaluates the major driving forces of glaciations during the Precambrian. First- and second-order sequences are recognized related to continental-scale fragmentation and formation of marine rift basins wherein sedimentary rocks indicate glacial influences and pronounced tectonic-climatic linkages. Coarse syn-rift deposits are typically characterized by mass flow diamictites and conglomerates. It is important to undertake sedimentological facies and sequence stratigraphic analysis of these syn-rift and capping passive margin sequences, as well as of slope turbidite deposits which formed if enhanced subsidence of the basins was occurring. More generally, latitude and syn-rift tectonic uplift can cause formation of glacial ice and enhance distinctive glacial influences on extensional basin sedimentation, thus supporting a causal relationship between thermal subsidence and the formation of glacier ice on inland areas. During the Precambrian, however, it is suggested that long-lived marine-terminated glaciers also situated at low paleolatitudes, were related to an extensional tectonic setting. In such settings, glacial deposits associated with sedimentary sequences of distinctively different origin, e.g. carbonate and chemically mature siliciclastic sequences, can well be used to detect the prominent sequence boundaries to verify depositional systems tracts. Internal sediment stacking patterns in sequences are indicative of dynamic processes along glaciated continental margins and without always having the need for global synchroneity. In glacially influenced rift basins and continental margins it is important to recognize the sequence boundaries of significant subaerial unconformities and their correlative conformities. A sequence boundary is a chronostratigraphically significant surface always produced as a consequence of a change in relative sea-level. These can then be well related to initiation and decay of glaciations, however on-land glacial deposits in a very few cases are prevented from later erosion. Attenuation of continental crust during rifting and breakup of the continent raises relative sea-level and also many of the shallow intra-cratonic basins subsided below sea-level, in favourable conditions being affected by major continental glaciations.Paleoproterozoic and Neoproterozoic glacial deposits are known in North and South America, South Africa, India, Western Australia and Fennoscandia. Against this background, continental-scale to global glaciations in the Precambrian appear to be possible, however views on the causes and timing of these glaciations, as well as on planetary extent of ice cover are still contradictory. There is a need to continue detailed sedimentological studies of pre-glacial and post-glacial deposits as well as to interpret syn-glacial lithofacies for their inferred transportation and depositional processes. Pre-glacial deposits, especially, should provide a new target to help us understand the processes that initiated these Precambrian glaciations. The sequence stratigraphic approach with understanding of the stacking pattern of depositional systems could prevent oversimplification and use of just single events to explain the complexity of evolution of glacially influenced Precambrian continental margin sediments.     

Quantitative bathymetric analyses of selected deepwater siliciclastic margins: receiving basin configurations for deepwater fan systems

Comparative bathymetric analyses of four siliciclastic continental margins reveal important distinguishing characteristics in deepwater receiving basin configurations. These characteristics have potential impact on deepwater sedimentation patterns and associated fan development. Present-day bathymetry was analysed quantitatively, using advanced software and digital bathymetry data. Various physical attributes of dip, basin geometry, and accommodation were quantified and mapped in 3D. Results show significant differences in receiving basin configurations between salt-based and shale-based continental margins in the Gulf of Mexico, Angola, Nigeria, and NW Borneo, especially in the type, amount, and distribution of accommodation. Salt-based systems have more ponded accommodation than shale-based systems; however, all the margins have a relatively small percentage of ponded to total accommodation. Two exceptions to this are the central portion of the Northwest Gulf of Mexico where ponded accommodation constitutes 55% of the total accommodation and the Kwanza Basin of Offshore Angola with 39% ponded accommodation. Shale-based systems may be more prone to bypass on the upper to mid slope than salt-based systems. Evidence for this is found in the linear grade trend analyses where large below-grade areas (sinks) are pervasive on the upper and mid slope of salt-based systems for deepwater sediment to accumulate, while shale-based systems show extensive above-grade highs across the entire slope. Ponded accommodation trends and drainage analyses also demonstrate that shale-based systems are more susceptible to extensive bypass than salt-based systems. The tectonically active margin of NW Borneo has steeper slope profiles than the passive margins, with areally small ponded accommodation largely restricted between active toe-thrusts on the lower slope and locally distributed on the shelf. These and other quantitative analyses suggest that the type of substrate and overall tectonic setting are important factors to consider for receiving basin configuration and its potential impact on deepwater sedimentation patterns.     

Relating petroleum system and play development to basin evolution: West African South Atlantic basins

Sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development. We propose an approach in which we use the established concepts in a new way: breaking basins down into their natural basin cycle division, then defining the characteristics of each basin cycle (including the type of petroleum systems and plays they may contain) and comparing them with similar basin cycles in other basins, thereby providing a means to learn through a greater population of (perhaps not immediately obvious) analogues. Furthermore, we introduce the use of the trajectory plot as a new tool in such an analysis. This methodology has been applied to the West African South Atlantic marginal basins between Cameroon and Angola, and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play (level)s. Consequently, we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential, yet undiscovered, hydrocarbon accumulations in less well explored parts of the margin.     

Study on the slope break belts in the Jurassic down-warped lacustrine basin in western-margin area, Junggar Basin, northwestern China

The Junggar Basin is one of the large-scale petroliferous basins in northwestern China. During the Jurassic Age it was a down-warped continental basin. Different types of slope break belts with different origins have been identified in the basin, including the fracture, flexure, erosional and depositional slope break belts. Fracture and flexure slope break belts were mainly developed in the western-margin area of the Junggar Basin. Slope break belts can be further divided into two types, which are basin margin and inner basin according to their geographical locations. Tectonic movements are the important origin mechanisms controlling the development of the slope break belts, such as deep-seated thrust structure, inherited paleouplift and secondary fracture movement in the basin. Obviously slope break belts are developed in episodes, developed in multi-stages and are differential in movements and can be inherited and transformed due to the changes of tectonic movements in different periods and different areas. Detailed studies indicate that slope break belts obviously control the strata onlap, the vertical lithologic succession and the vertical and lateral distribution of depositional systems. Slope break belts can control the distribution of different non-structural traps.     

4D analogue modelling of transtensional pull-apart basins

Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above underlapping releasing stepovers in both pure strike-slip and transtensional basement fault systems. Serial sectioning and 3D volume reconstruction permitted analysis of the full 3D fault geometries. Results show that very different pull-apart basins are developed in transtension compared to pure strike-slip. Both types of models produced elongate, sigmoidal to rhomboidal pull-apart systems, but the transtensional pull-apart basins were significantly wider and uniquely developed a basin margin of en-echelon oblique-extensional faults. Dual, opposing depocentres formed in the transtensional model whereas a single, central depocentre formed in pure strike-slip. In transtension, a distinct narrow graben system formed above the principal displacement zones (PDZs). Cross-basin fault systems that linked the offset PDZs formed earlier in the transtensional models.Sequential model runs to higher PDZ displacements allowed the progressive evolution of the fault systems to be evaluated. In cross-section, transtensional pull-aparts initiated as asymmetric grabens bounded by planar oblique-extensional faults. With increasing displacement on the PDZs, basin subsidence caused these faults to become concave-upwards and lower in dip angle due to fault block collapse towards the interior of the basin. In addition, strain partitioning caused fault slip to become either predominantly extensional or strike-slip. The models compare closely with the geometries of natural pull-apart basins including the southern Dead Sea fault system and the Vienna Basin, Austria.     

Classification of rifted sedimentary basins of the Pannonian Basin System according to the structural genesis, evolutionary history and hydrocarbon maturation zones

We apply the concept that sedimentary basins can be classified according to their structural genesis and evolutionary history to the Tertiary rifts of the Pannonian Basin of Eastern Europe.We have approached the classification by breaking the basins down into the cycles or stages that they comprise. This approach helps us to understand the basin evolution better and allows us to compare the basins more easily. The drivers that define the cycles of basin history are (1) basin-forming tectonics, (2) sedimentary processes, and (3) basin-modifying tectonics.We link common elements of petroleum systems and plays to these natural cycles or stages in basin evolution to improve the prediction of which plays could be expected to occur in a particular basin or region.This concept is constructed through several steps. These steps are (1) to identify standard evolutionary patterns related to geodynamic drivers, (2) to group the basins with similar tectono-stratigraphic evolution and correlate these with petroleum system development, (3) to relate basin trap types to basin history and (4) to calculate characteristic hydrocarbon maturation zones by thermal modeling.We present an application to the Pannonian Basin System of Eastern Europe, an area formed by Miocene back-arc extension and affected by compressional reactivation during its late-stage evolution. The sub-basins of the Pannonian Basin System appear to have experienced comparable magnitudes of deformation, to have developed similar trap types and to have experienced a characteristic hydrocarbon maturation history in a way that supports play prospectivity.     

The impact of syn- and post-extension prograding sedimentation on the development of salt-related rift basins and their inversion: Clues from analogue modelling

Various studies have demonstrated the intrinsic interrelationship between tectonics and sedimentation in salt-related rift basins during extension as well as during their inversion by compression. Here, we present seven brittle–ductile analogue models to show that the longitudinal or transverse progradation of sediment filling an elongate extensional basin has a substantial impact on the growth of diapirs and their lateral geometrical variations. We use five extensional models to reveal how these prograding systems triggered diapir growth variations, from proximal to distal areas, relative to the sedimentary source. In the models, continuous passive diapir walls developed, after a short period of reactive–active diapiric activity, during syn-extensional homogeneous deposition. In contrast, non-rectilinear diapir walls grew during longitudinal prograding sedimentation. Both longitudinal and transverse post-extensional progradation triggered well-developed passive diapirs in the proximal domains, whereas incipient reactive–active diapirs, incipient roller-like diapirs, or poorly developed diapirs were generated in the distal domains, depending on the modelled sedimentary pattern. Two models included final phases of 6% and 10% shortening associated with basin inversion by compression, respectively, to discriminate compressional from purely extensional geometries. With the applied shortening, the outward flanks of existing diapir walls steepened their dips from 8°–17° to 30°–50°. Likewise, 6% of shortening narrowed the diapir walls by 32%–72%, with their fully closing (salt welds) with 10% of shortening. We compare our results with the distribution of salt walls and minibasins of the Central High Atlas diapiric basin in Morocco, which was infilled with a longitudinally prograding mixed siliciclastic and carbonatic depositional sequence during the Early–Middle Jurassic with a minimum thicknesses of 2.5–4.0 km.     

Neogene igneous intrusions in the northern South China Sea: Evidence from high-resolution three dimensional seismic data

Igneous intrusions emplaced within the prospective intervals of sedimentary basins can exert a significant impact on petroleum systems and hence are of considerable interest particularly when risking exploration plays. A number of discordant high amplitude seismic anomalies (DSAs) with a range of geometries are documented in high resolution 3D seismic data in the northern South China Sea. Their distribution and seismic characteristics are analysed and compared with similar seismic anomalies documented within sedimentary basins in the Atlantic margins and other locations. The DSAs occur mainly within Early Miocene strata and are interpreted as igneous intrusions that were emplaced close to the palaeo-seabed and are dated as early Middle Miocene using seismic-stratigraphic methods. A number of vents are also identified above the intrusions within early Middle Miocene strata. Several geometrical forms are observed, referred to here as saucer-shaped, lensoid-shaped, stacked and composite intrusions. The seismic expression of these is increasing complex towards the palaeo-seabed, with a tendency for the saucer-shaped sills to be the deepest intrusive forms. The igneous intrusions observed in this study only could be identified using 3D seismic data and they are important for the future evaluations of petroleum systems, basin evolution and tectonic analysis in the Pearl River Mouth Basin.     

Morphologic signatures in submarine canyons and gullies,central USA Atlantic continental margins

The accumulation of bathymetric and seismic data on many continental margins has provided valuable new insights into variability of seascape morphology. The present challenge is in finding appropriate manners to characterise that morphology so that variations between areas and between potential influences can be recorded. In this paper, we employ hypsometry (area-elevation analysis) and present parameters derived from 65 hypsometric curves which represent distinct slope-basin shapes, based on data from the central USA Atlantic continental slope. The distinction of morphologic signatures has derived from the statistical moments, such as skewness and kurtosis, in describing the hypsometric curves of the submarine basins. Moreover, basin geometry in planview and network structure, have shown to be remarkably well reflected in the shape of the hypsometric curve. Based on the combined analysis of morphology and submarine processes and scenarios, we propose that concave hypsometry is characteristic of trellis networks that probably initiated by sporadic erosion by sedimentary flows, spilling over the shelf edge. The convex hypsometry that characterises poor- to well- developed dendritic networks, heading at or below the shelf break, is attributed to retrograde erosion and sediment fallout events, respectively. These results present initial step in helping to infer submarine processes from morphology, and provide initial information about the environmental scenarios for areas where the erosional record is unknown.     

Contrasting sedimentary processes along a convergent margin: the Lesser Antilles arc system

Sedimentation processes occurring in an active convergent setting are well illustrated in the Lesser Antilles island arc. The margin is related to westward subduction of the North and/or the South America plates beneath the Caribbean plate. From east to west, the arc can be subdivided into several tectono-sedimentary depositional domains: the accretionary prism, the fore-arc basin, the arc platform and inter-arc basin, and the Grenada back-arc basin. The Grenada back-arc basin, the fore-arc basin (Tobago Trough) and the accretionary prism on the east side of the volcanic arc constitute traps for particles derived from the arc platform and the South American continent. The arc is volcanically active, and provides large volumes of volcaniclastic sediments which accumulate mainly in the Grenada basin by volcaniclastic gravity flows (volcanic debris avalanches, debris flows, turbiditic flows) and minor amounts by fallout. By contrast, the eastern side of the margin is fed by ash fallout and minor volcaniclastic turbidites. In this area, the dominant component of the sediments is pelagic in origin, or derived from South America (siliciclastic turbidites). Insular shelves are the locations of carbonate sedimentation, such as large platforms which develop in the Limestone Caribbees in the northern part of the margin. Reworking of carbonate material by turbidity currents also delivers lesser amounts to eastern basins of the margin. This contrasting sedimentation on both sides of the arc platform along the margin is controlled by several interacting factors including basin morphology, volcanic productivity, wind and deep-sea current patterns, and sea-level changes. Basin morphology appears to be the most dominant factor. The western slopes of the arc platform are steeper than the eastern ones, thus favouring gravity flow processes.     

Cenozoic tectonic and stratigraphic development of the Central Vietnamese continental margin

The East Vietnam Boundary Fault Zone (EVBFZ) forms the seaward extension of the Red River Shear Zone and interacted with the extensional rift systems in basins along the Central Vietnamese continental margin. The structural outline of the central Vietnamese margin and the timing of deformation are therefore fundamental to understanding the development of the South China Sea and its relation to Indochinese escape tectonism and the India-Eurasia collision. This study investigates the structural and stratigraphic evolution of the Central Vietnamese margin in a regional tectonic perspective based on new 2-D seismic and well data. The basin fill is divided into five major Oligocene to Recent sequences separated by unconformities. Deposition and the formation of unconformities were closely linked with transtension, rifting, the opening of the South China Sea and Late Neogene uplift and denudation of the eastern flank of Indochina. The structural outline of the Central Vietnamese margin favors a hybrid tectonic model involving both escape and slab-pull tectonics. Paleogene left-lateral transtension over the NNW-striking EVBFZ, occurred within the Song Hong Basin and the Quang Ngai Graben and over the Da Nang Shelf/western Phu Khanh Basin, related to the escape of Indochina. East of the EVBFZ, Paleogene NE-striking rifting prevailed in the outer Phu Khanh Basin and the Hoang Sa Graben fitting best with a prevailing stress derived from a coeval slab-pull from a subducting proto-South China Sea beneath the southwest Borneo – Palawan region. Major rifting terminated near the end of the Oligocene. However, late stage rifting lasted to the Early Miocene when continental break-up and seafloor spreading commenced along the edge of the outer Phu Khanh Basin. The resulting transgression promoted Lower and Middle Miocene carbonate platform growth on the Da Nang Shelf and the Tri Ton High whereas deeper marine conditions prevailed in the central part of the basins. Partial drowning and platform retreat occurred after the Middle Miocene due to increased siliciclastic input from the Vietnamese mainland. As a result, siliciclastic, marine deposition prevailed offshore Central Vietnam during the Pliocene and Pleistocene.     

Deltaic,mixed and turbidite sedimentation of ancient foreland basins

The marine fill of ancient foreland basins is primarily recorded by depositional systems consisting of facies and facies associations deposited by a variety of sediment gravity flows in shallow-marine, slope and basinal settings. Tectonism and climate were apparently the main factors controlling the sediment supply, accommodation and depositional style of these systems. In marginal deltaic systems, sedimentation is dominated by flood-generated hyperpycnal flows that build up impressive accumulations of graded sandstone beds in front of relatively small high-gradient fan-deltas and river deltas. During periods of tectonically forced lowstands of sealevel, these systems may commonly shift basinward to shelfal and slope regions. Instability along the edges of these lowstand deltas and sand-laden hyperpycnal flows generate immature and coarse-grained turbidite systems commonly confined within structural depressions and generally encased in distal delta-front and prodeltaic deposits. Because of the close vertical and lateral stratigraphic relations between deltaic and turbidite-like facies, these marginal systems are herein termed ‘mixed depositional systems’. They are very common in the fill of foreland basins and represent the natural link between deltaic and basinal turbidite sedimentation.Basinal turbidite systems form in deeper water elongate highly subsiding troughs (foredeeps) that developed in front of advancing thrust systems. The impressive volumes of sheet-sandstones that form the fill of these troughs suggest that basinal turbidite systems are likely to form following periods of dramatic tectonic uplift of adjacent orogenic wedges and related high-amplitude tectonically-forced sealevel lowstands. In such deep basinal settings, sediment flux to the sea is dramatically increased by newly formed sediment in fluvial drainage basins and the subaerial and submarine erosion of falling-sealevel deltaic deposits generated during the uplift. Turbidity currents are very likely to be mainly triggered by floods, via hyperpycnal flows and related sediment failures, but can fully develop only in large-scale erosional conduits after a phase of catastrophic acceleration and ensuing bulking produced by bed erosion. This process leads to deepening and widening of the conduits and the formation of large-volume highly efficient bipartite currents whose energy dissipation is substantially reduced by the narrow and elongate basin geometry. These currents can thus carry their sediment load over considerable distances down the basin axis.     

Geochemical assessment of the Colombian oils based on bulk petroleum properties and biomarker parameters

This geochemical survey defines the typical features of representative oils from the major Colombian basins, and proposes a classification scheme useful for hydrocarbon exploration. This work is based on properties of whole oils such as API gravity, sulfur, vanadium and nickel concentrations, and gas chromatography fingerprints. The framework is completed by inclusion of biomarker parameters derived from GCMS and GCMSMS analysis.Oils from the basins of the Middle Magdalena Valley, Upper Magdalena Valley, Sinú - San Jacinto, Putumayo-Caguan, Lower Magdalena Valley and Catatumbo were assessed. Conclusions were drawn regarding possible sources of origin, oil families, degree of thermal evolution, biodegradation, mixing and refreshing, and inferences regarding exploration implications.The oils from the Middle Magdalena Valley and Upper Magdalena Valley (intermontane basins) and Putumayo (foreland basin), except those from the Caguan area, are oils with similar characteristics. In these three cases the oils are probably coming from source rocks intervals deposited in a marine Cretaceous platform, with variable carbonate/siliciclastic features. In these basins there are no oils derived from Tertiary source rocks.In Sinú-San Jacinto and Lower Magdalena Valley basins the main proportions of oils comes from very proximal environments, probably deltaic type, of Tertiary age with a minor proportion of oils coming from Cretaceous source rocks of marine anoxic environment (the only marine Cretaceous oils discovered so far in the Sinú-San Jacinto and Lower Magdalena Valley basins).The oils from Eastern Foothills of the Eastern Cordillera, look to be derived mainly from proximal Cretaceous source rocks with some mixing of oils derived from Tertiary strata. In the Catatumbo basin there are oils derived mainly from Cretaceous source rocks and some from Tertiary source rocks.Regarding the processes after entrapment, in all of the basins, the biodegradation effects were observed in varying degrees. These processes are dominant toward more quiescent regions, beyond the areas with more tectonic activity, far from the foothills of the Eastern Cordillera. Instead, close to the Eastern Cordillera are more common the paleobiodegradation processes due to reburial of younger molasses. The effects of mixing or refreshing are remarkable close to the Eastern Cordillera foothills in Llanos, Middle Magdalena Valley, and Upper Magdalena Valley basins.     

Triassic platform-margin deltas in the western Barents Sea

The Early to Middle Triassic in the Barents Sea was dominated by prograding transgressive-regressive sequences. Internal clinoform geometries indicate that sediments were derived from the Baltic Shield in the south and the Uralian Mountains in the east and southeast. These systems were formed in a large, relatively shallow epicontinental basin, where modest variations in relative sea-level relocated the shoreline significantly. This study shows the development of strike elongated depositional wedges that thicken just basinward of the platform-edge. Seismic facies and time-thickness maps show the position and development of platform-margin delta complexes within each sequence. Seismic clinoforms and trajectory analysis show significant lateral variation from the axis of the delta complex to areas adjacent to the main delivery system. Frequent toplap geometries are observed in proximity to coarse-grained deposits, while aggradation of seismic clinoforms characterizes areas laterally to the platform-margin deltas. Complex shifts in depocenters are revealed by large-scale compensational stacking pattern and relict platform breaks. Locally, relict breaks are created due to pre-existing paleo-topography. Platform-margin deltas can be identified by careful mapping of clinoform geometries, clinoform angles and trajectories. However, seismic analysis of prograding clinoform units indicate that the shoreline and delta complexes commonly are positioned landward of the platform-edge. Deposition of platform-margin deltas is sometimes caused by locally increased sediment supply during slightly rising relative sea-level, and occasionally caused by a regional drop in relative sea-level with significant shelf bypass.Development, position, thickness and facies distribution of platform deltas and platform-margin deltas of very broad low-relief basins, like the Triassic of the epicontinental Barents Sea basin, are strongly sensitive to changes in relative sea-level due to rapid emergence and submergence of wide areas, and to changes in position of major rivers supplying sand to the delta systems. In this respect, the depositional model of the present study deviates from models of clinoform successions obtained from small and narrow basins or siliciclastic platforms with high coarse-clastic sediment supply.     

陆相断陷盆地沉积可容空间变化与油气汇聚体系关系探讨

陆相断陷盆地的沉积可容空间变化规律控制着盆地的层序地层充填样式和生储盖发育规律,根据目前我国陆相断陷盆地的层序地层响应特征,将沉积可容空间的变化频率分为低频和高频两种类型。油气汇聚体系是陆相断陷盆地油气勘探的研究对象,根据油气聚集规模将其划分为大型、中型和小型等三种规模类型。具备不同层序地层充填样式的陆相断陷盆地一般发育不同规模类型的油气汇聚体系和相应的空间展布规律：低频率沉积可容空间变化的陆相断陷盆地可以发育大型、中型规模的油气汇聚体系;高频率沉积可容空间变化的陆相断陷盆地一般发育中型或者小型规模的油气汇聚体系,大型规模的油气汇聚体系欠发育。我国陆区陆相断陷盆地中的东营凹陷是低频率沉积可容空间变化的典型代表,东濮凹陷是高频率沉积可容变化的典型代表;海区陆相断陷盆地中的涠西南凹陷属于低频率可容空间变化的类型,海中凹陷属于较高频率可容空间变化的类型。     

The development of polygonal fault systems by syneresis of colloidal sediments

Polygonal fault systems occur in numerous sedimentary basins worldwide, are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting. These fault systems have been most thoroughly described in the central North Sea basin and the detailed structure shows a significant correlation with lithological variations, both vertically and laterally. Extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content. Lateral facies variations are also observed and indicate that time-equivalent sequences upslope from the smectite-rich polygonally faulted sediments are coarse-grained, clay-poor and undeformed. This leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments, and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction. Syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid. This process occurs due to the domination of interparticle attractive forces in marine clays, dependent on environment, and is governed by the change of gel permeability and viscosity with progressive compaction. The process of syneresis can account for a number of structural features observed within the fault systems, such as tiers of faults, the location of maximum fault throw and growth components at upper fault tips. As such, this paper represents the first attempt to correlate microscale properties of clay-rich sediments to their macroscale seismic character.     

Probabilistic tectonic heat flow modeling for basin maturation: Assessment method and applications

Tectonic modeling is often neglected in the basin modeling workflow and heat flow is most times considered a user input. Such heat flows can, therefore, result in erroneous basin modeling outcomes, resulting in false overoptimistic identification of prospective areas or failure to identify prospects. This is particularly true for areas with limited data control such as frontier basin areas, or deep unexplored plays in mature basins.     

Rift sequence stratigraphy

Conventional sequence stratigraphy has been developed primarily for passive-margin basins. Despite the conceptual advances within the last 30 years, a suitable model for rift basins has not yet been devised. Many authors have attempted to adapt the passive-margin model to all other tectonic settings, including rifts, despite the fundamental differences in terms of the mechanisms controlling the formation and evolution of these sedimentary basins. Passive margins have their stratigraphic framework controlled largely by cyclic sea-level fluctuations superimposed on long-term thermal subsidence. By contrast, rift basins have their accommodation history strongly related to their mechanical subsidence regime, with episodic pulses of extension that create space for sediment accumulation at very fast rates. Stages of rapid mechanical subsidence are typically followed by longer periods of tectonic quiescence, when sediment supply gradually consumes and fills the available accommodation. This cyclicity results in depositional sequences that display overall progradational trends and coarsening-upward vertical stacking patterns. Sequence boundaries are often marked by sharp flooding surfaces related to the transgression of lacustrine or marine systems in response to rapid tectonic subsidence and the consequent ‘instantaneous’ generation of accommodation. As such, a typical rift depositional sequence starts with a flooding surface overlain by a relatively thin transgressive systems tract and a much better developed highstand systems tract. A renewed subsidence pulse leads to the drowning of the previous deposits and the start of a new depositional sequence. The strong asymmetry of the base-level curve resembles the shape of glacio-eustatic cycles, with fast transgressions followed by longer term regressions, although at potentially different temporal scales.     

Tectonism: the dominant factor in mid-Cretaceous deposition in the Jeanne d'Arc Basin, Grand Banks

The development of stratigraphic sequences has been demonstrated to be controlled by a set of factors including variations in subsidence, sediment input, eustatic sea level and physiography. Well and seismic data from the Jeanne d'Arc Basin, Grand Banks indicate that mid-Cretaceous tectonism controls at least three of these factors, namely subsidence, sediment input and physiography. North Atlantic rift tectonism was therefore the dominant factor in controlling the migration of coastal to shallow marine environments and the development of sequence stratigraphy in this basin during the mid-Cretaceous. The Avalon Formation respresents a mainly Barremian to Early Aptian regressive phase of clastic, marine to marginal marine sedimentation. This followed the deposition of a thick sequence of mainly marine limestones and shales of the Whiterose Formation above a mid-Valanginian sequence-bounding unconformity. The increased clastic input and northward progradation of coastal environments represented by the Avalon Formation occurred during uplift of a basement arch to the south with subsidence of the basin increasing to the north, accompanied by only relatively minor faulting. These features indicate that a period of epeirogenesis was initiated during the Barremian. Continuing uplift over an expanding area at the southern end of the basin is interpreted to have resulted in the development of an angular unconformity with incised valleys. This mid-Aptian unconformity defines the top of the Whiterose/Avalon sequence. Initiation of brittle fracturing of the sedimentary package and underlying basement (i.e. rifting) in mid-Aptian times resulted in rapid fault-controlled subsidence and fragmentation of the Jeanne d'Arc Basin. This great increase in subsidence rate caused retrogradation of coastal environments across the previously developed sequence-bounding unconformity, despite continuing high rates of sediment input from the uplifted basin margins. The transgressive, siliciclastic Ben Nevis Formation comprises two separate but related facies associations. A locally preserved basal association represents interfingering back-barrier environments and is herein defined as the Gambo Member. An upper, ubiquitous facies association comprises tidal-inlet channel, shoreface and lower shoreface/offshore transition sandstones. This upper facies association onlapped marine ravinement diastems above the laterally equivalent back-barrier facies. The rapid fault-controlled subsidence and high sediment input rate of this mid-Aptian to late Albian rift period resulted in the accumulation and preservation of very thick shoreface sandstones. The transgressive sandstones were buried by laterally equivalent offshore shales of the Nautilus Formation. Flooding of the basin margins induced by the onset of thermal subsidence in latest Albian or early Cenomanian times marks the top of the Ben Nevis/Nautilus syn-rift sequence.     

Chaotic magnetic patterns in marginal seas and small ocean basins have similar origin to structural magnetic quiet zones in deep oceans

The empirical observation is made that marginal seas which have spread orthogonal to their margins have clearly defined lineated magnetic anomaly patterns, while marginal seas which have spread at acute angles to their margins have chaotic or subdued magnetic anomaly patterns.Deep ocean basins which have acute angles between their margins and their spreading directions generate magnetic patterns that are also chaotic (magnetic quiet or smooth zones), due to a geometrically controlled MOR structure consisting of many small spreading-segments connected by many small-offset FZ. Magnetization of such a complex structure by reversals of the Earth's magnetic field produces a magnetic pattern having many small magnetic domains juxtaposed, half with normal and half with reversed polarity. The FZ offsets cause blocks of one polarity to be surrounded on all sides by blocks of opposed polarity, and both their small size and close proximity results in sea-surface magnetometers recording magnetically subdued or chaotic area.Marginal sea basins having margins acutely angled to the spreading direction, can also be explained as structural magnetic quiet zones.