Basin Research - Volume 19, Issue 1, 2007

This paper presents a detailed analysis of the top of the Messinian evaporites (Horizon M) in the Levant region, offshore Israel, based on the integration of three‐dimensional (3D)/2D seismic and well data. 3D mapping of a series of intra‐evaporite horizons and their termination against Horizon M provides new insights into the depositional setting and structural evolution of this saline giant system. New evidence of a discordant relationship between the intra‐evaporite horizons and the top of the Messinian evaporites (Horizon M) is given by the seismic stratigraphic analysis. This confirms that the top of the Messinian evaporites represents an erosional unconformity of semiregional extent in the Levant region. The truncation of the folded and faulted intra‐evaporite horizons indicates for the first time a Messinian phase of evaporite deformation, i.e. pre‐dating the well‐documented Plio‐Pleistocene thin‐skinned tectonic phase in the region. This major erosional unconformity is interpreted as subaerial in origin, documenting the exposure of the evaporitic system at the end of the Messinian Salinity Crisis. These results give new evidence for the understanding of the events occurring during the last stages of the Messinian Salinity Crisis in the region.

Natural sediment compaction in deltaic plains influences subsidence rates and the evolution of deltaic morphology. Determining compaction rates requires detailed knowledge of subsurface geotechnical properties and depositional history, neither of which is often readily available. To overcome this lack of knowledge, we numerically forward model the incremental sedimentation and compaction of stochastically generated stratigraphies with geotechnical properties typical of modern depositional environments in the Mississippi River delta plain. Using a Monte Carlo approach, the range of probable compaction rates for stratigraphies with compacted thicknesses <150 m and accumulation times <20 kyr. varies, but maximum values rarely exceed a few mm yr⁻¹. The fastest compacting stratigraphies are composed primarily of peat and bar sand, whereas the slowest compacting stratigraphies are composed of prodelta mud and natural levee deposits. These results suggest that compaction rates can significantly influence vertical and lateral stratigraphic trends during deltaic evolution.

Methods for detection of pore fluid overpressures in shales from seismic data have become widespread in the oil industry. Such methods are largely based on the identification of anomalous seismic velocities, and on subsequent determination of pore pressures through relationships between seismic velocities and the vertical effective stress (VES). Although it is well known that lithology variations and compaction mechanisms should be accounted for in pore pressure evaluation, a systematic approach to evaluation of these factors in seismic pore pressure prediction seems to be absent. We have investigated the influence of lithology variations and compaction mechanism on shale velocities from acoustic logs. This was performed by analyses of 80 wells from the northern North Sea and 24 wells from the Haltenbanken area. The analyses involved identification of large‐scale density and velocity variations that were unrelated to overpressure variations, which served as a basis for the analyses of the resolution of overpressure variations from well log data. The analyses demonstrated that the overpressures in neither area were associated with compaction disequilibrium. A significant correlation between acoustic velocity and fluid overpressure nevertheless exists in the Haltenbanken data, whereas the correlation between these two parameters is weak to non‐existing in the North Sea shales. We do not presently know why acoustic velocities in the two areas respond differently to fluid overpressuring. Smectitic rocks often have low permeabilities, and define the top of overpressures in the northern North Sea when they are buried below 2 km. As smectitic rocks are characterized by low densities and low acoustic velocities, their presence may be identified from seismic data. Smectite identification from seismic data may thus serve as an indirect overpressure indicator in some areas. Our investigations demonstrate the importance of including geological work and process understanding in pore pressure evaluation work. As a response to the lack of documented practice within this area, we suggest a workflow for geological analyses that should be performed and integrated with seismic pore pressure prediction.

The Upper Devonian Rhinestreet black shale of the western New York state region of the Appalachian Basin has experienced multiple episodes of overpressure generation manifested by at least two sets of natural hydraulic fractures. These overpressure events were thermal in origin and induced by the generation of hydrocarbons during the Alleghanian orogeny close to or at the Rhinestreet's ∼3.1 km maximum burial depth. Analysis of differential gravitational compaction strain of the organic‐rich shale around embedded carbonate concretions that formed within a metre or so of the seafloor indicates that the Rhinestreet shale was compacted ∼58%. Compaction strain was recalculated to a palaeoporosity of 37.8%, in excess of that expected for burial >3 km. The palaeoporosity of the Rhinestreet shale suggests that porosity reduction caused by normal gravitational compaction of the low‐permeability carbonaceous sediment was arrested at some depth shy of its maximum burial depth by pore pressure in excess of hydrostatic. The depth at which the Rhinestreet shale became overpressured, the palaeo‐fluid retention depth, was estimated by use of published normal compaction curves and empirical porosity‐depth algorithms to fall between 850 and 1380 m. Early and relatively shallow overpressuring of the Rhinestreet shale likely originated by disequilibrium compaction induced by a marked increase in sedimentation rate in the latter half of the Famennian stage (Late Devonian) as the Catskill Delta Complex prograded westward across the Appalachian Basin in response to Acadian tectonics. The regional Upper Devonian stratigraphy of western New York state indicates that the onset of overpressure occurred at a depth of ∼1100 m, well in advance of the Rhinestreet shale's entry into the oil window during the Alleghanian orogeny.

A series of analogue models are used to demonstrate how the multistage development of the Mid‐Polish Trough (MPT) could have been influenced by oblique basement strike–slip faults. Based on reinterpretation of palaeothickness, facies maps and published syntheses of the basin development, the following successive stages in the Mesozoic history of the south eastern part of the MPT were simulated in the models: (1) Oblique extension of the NW segment of the MPT connected with sinistral movement along the Holy Cross Fault (HCF, Early Triassic–latest Early Jurassic). (2) Oblique extension of both NW and SE segment of the MPT, parallel to the HCF (latest Early and Middle Jurassic). (3) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the HCF (Early Oxfordian–latest Early Kimmeridgian). (4) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the Zawiercie Fault (ZF, latest Early Kimmeridgian–Early Albian). (5) Oblique inversion of the NW segment of the MPT connected with dextral movement along the HCF (Early Albian–latest Cretaceous). (6) Oblique inversion of the SE segment of the MPT along the W–E direction (latest Cretaceous–Palaeogene). The different sense of movements of these two basement strike–slip faults (HCF and ZF) resulted in distinct segmentation of the basin and its SW margin by successive systems of extensional en‐echelon faults. The overall structure of this margin is controlled by the interference of the border normal faults with the en‐echelon fault systems related to successive stages of movement along the oblique strike–slip faults. This type of en‐echelon fault system is absent in the opposite NE‐margin of the basin, which was not affected by oblique strike–slip faults. The NE‐margin of the basin is outlined by a typical, steep and distinctly marked rift margin fault zone, dominated by normal and dip–slip/strike–slip faults parallel to its axis. Within the more extended segment of the basin, extensive intra‐rift faults and relay ramps develop, which produce topographic highs running across the basin. The change in the extension direction to less oblique relative to the basin axis resulted in restructuring of the fault systems. This change caused shifting of the basin depocentre to this margin. Diachronous inversion of the different segments of the basin in connection with movement along one of the oblique basement strike–slip faults resulted in formation of a pull‐apart sub‐basin in the uninverted SE‐segment of the basin. The results of the analogue models presented here inspire an overall kinematic model for the southeastern segment of the MPT as they provide a good explanation of the observed structures and the changes in the facies and palaeothickness patterns.

Imbricate reflections commonly occur in the glacigenic section of seismic profiles from the Bjørnøya Trough. This was the main drainage pathway for fast‐flowing ice‐streams from the former Barents Sea and Scandinavian ice sheets. Industry three‐dimensional (3D) seismic data from the southern flank of the Bjørnøya Trough are used here to investigate these imbricate reflections. Integration of vertical seismic sections with 3D plan view images and attribute maps reveal that imbricate reflections at the SW Barents Sea Margin are mega‐scale sediment blocks with a glacigenic origin. Imbricate reflections in two regions to the east of the survey appear on plan‐view as well‐developed lineations of U‐shaped crescents; however, following detailed analysis of their location, geometry and relation to sailing direction during data acquisition, we can demonstrate that these are seismic artefacts. These artefacts are related to the straight parts of east–west‐trending plough marks on the sea floor, having a dip direction that is directly related to the sailing direction of the ship during seismic acquisition. By analysing both real glacigenic imbrications and false imbrications or artefacts, we are able to demonstrate the critical distinguishing criterion.

Integrated geohistory analysis performed on high‐resolution stratigraphy of Venezia 1 and Lido 1 wells (Quaternary–Pliocene interval) and low‐resolution stratigraphy of a simulated well extending Lido 1 down to the base of Cenozoic (Palaeocene–Miocene interval) is used to reconstruct the interplay between subsidence and sedimentation that occurred in the Venice area (eastern Po Plain) during the last 60 Myr, and to discuss the relationships between calculated subsidence rates and time resolution of stratigraphic data. Both subsidence and sedimentation are mostly related to the tectonic evolution of the belts that surround the Venice basin, influencing the lithosphere vertical motions and the input of clastic sediments through time. In particular, two subsidence phases are recorded between 40–33.5 and 32.5–24 Myr (0.13 and 0.14 mm year⁻¹, respectively), coeval with tectonic phases in the Dinaric belt. Vice versa, during the main South‐Alpine orogenic phase (middle–late Miocene), quiescence or little uplift (−0.03 mm year⁻¹) reflects the location of the Venice area close to the peripheral bulge of the South‐Alpine foreland system. Early Pliocene evolution is characterised by a number of subsidence/uplift events, among which two uplifts occurred between 5–4.5 and 3–2.2 Myr (at −0.4 and −0.2 mm year⁻¹, respectively) and can be correlated with tectonic motions in the Apennines. During the last million years, the Venice area was initially characterised by uplift (−0.6 mm year⁻¹ rising to −1.5 mm year⁻¹ between 0.4 and 0.38 Myr), eventually replaced by subsidence at a rate ranging between 1.6 and 1.0 mm year⁻¹ up to 0.12 Myr and then decreased to 0.4 mm year⁻¹, as an average, up to present. Our results highlight that time resolution of the stratigraphic dataset deeply influences the order of magnitude obtained for the calculated subsidence rate. This is because subsidence seems to have worked through short‐lived peaks (in the order of 10⁵ years), alternating with long relatively quiescent intervals. This suggests caution when components of subsidence are deduced by subtracting long‐term to short‐term subsidence rate.

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).

We describe the internal structure of a multi‐kilometre scale mud volcano edifice from the South Caspian Sea using three‐dimensional (3D) seismic reflection data leading to a reconstruction of the volcano system's eruptive history. By adapting elements of classic seismic stratigraphy to the study of this volcano, we have found its edifice to consist of a series of stacked mud cones. This internal architecture is most likely to have formed as a result of repeated episodes of expulsion of a fluid‐mud mix. Underlying the stack of cones is an asymmetric fault‐bounded caldera measuring approximately 2 km in diameter. This caldera shows close structural similarity to the trapdoor type of magmatic caldera. Based on the geometrical relationships of individual mud cones to this caldera, we conclude that caldera‐like collapse of the edifice floor initiated following the deposition of the first mud cone (the pioneer cone). Growth of the caldera continued until the later stages of edifice evolution when it eventually abated. This eruptive history shows strong similarities to recent models for magmatic caldera eruption cycles. The study therefore highlights the potential analogue value of mud volcano systems to the study of igneous volcanism. Furthermore, it identifies 3D seismic data as a potentially useful tool in reconstructing the history of mud volcanic eruption and fluid and sediment expulsion from sedimentary basins.

Scaled sandbox models simulated primary controls on the kinematics of the early structural evolution of salt‐detached, gravity‐driven thrust belts on passive margins. Models had a neutral‐density, brittle overburden overlying a viscous décollement layer. Deformation created linked extension–translation–shortening systems. The location of initial brittle failure of the overburden was sensitive to perturbations at the base of the salt. Salt pinch‐out determined the seaward limit of the thrust belt. The thrust belts were dominated by pop‐up structures or detachment folds cut by break thrusts. Pop‐ups were separated by flat‐bottomed synclines that were partially overthrust. Above a uniformly dipping basement, thrusts initiated at the salt pinch‐out then consistently broke landward. In contrast, thrust belts above a seaward‐flattening hinged basement nucleated above the hinge and then spread both seaward and landward. The seaward‐dipping taper of these thrust belts was much lower than typical, frictional, Coulomb‐wedge models. Towards the salt pinch‐out, frictional resistance increased, thrusts verged strongly seawards and the dip of the taper reversed as the leading thrust overrode this pinch‐out. We attribute the geometry of these thrust belts to several causes. (1) Low friction of the basal décollement favours near‐symmetric pop‐ups. (2) Mobile salt migrates away from local loads created by overthrusting, which reduces the seaward taper of the thrust belt. (3) In this gravity‐driven system, shortening quickly spreads to form wide thrust belts, in which most of the strain overlapped in time.