Halokinetic Activity Research Articles

Albitization evidences of Mesozoic carbonates: petrological study of authigenic albites in the northwest of the Bortziriak Cinco Villas Massif, eastern Basque-Cantabrian Basin

The presence of authigenic Na-feldspars in sedimentary carbonate rocks is unusual and its origin is controversial in terms of genesis and timing. The use of optical microscopy, cathodoluminescence and in situ semi-quantitative EDX analysis techniques, has allowed the identification and characterization of authigenic albite crystals in the Mesozoic pre- and syn-rift carbonates of the northwestern margin of the Bortziriak-Cinco Villas Massif, in the northeastern Basque-Cantabrian Basin (western Pyrenees). The euhedral habit, crystal size, spatial distribution and crosscutting relationships, together with the pure albitic composition, suggest a relatively early replacement origin. Compaction of sediments during burial, besides possible fluid migration linked to the intense syn-rift halokinetic activity, may have been decisive for the mobilisation of cations, and hence, for the albitization of the carbonate rocks.

Local radon flux maxima in the quaternary sediments of Schleswig\u2013Holstein (Germany)

This paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.

The evolution of the Dowsing Graben System: implications for petroleum prospectivity in the UK Southern North Sea

Upper Permian (Zechstein Supergroup) evaporites have a major control on structural styles and prospectivity in the UK Southern North Sea (SNS). They form the regional super-seal for the main Rotliegend Group (Leman Sandstone Formation) reservoir play fairway immediately beneath. The evaporites have highly variable thicknesses due to the syndepositional basin architecture, differential loading and post-depositional deformation through diapirism and salt withdrawal. The halokinetic activity leads to touchdown (welding) of the supra-salt section onto the sub-salt strata and the development of narrow (up to 15 km-wide) graben systems. The interpretation and depth conversion of well-calibrated, high-quality, 3D post-stack time-migrated (PSTM) seismic data along the southwestern margin of the basin show that a NW–SE-striking elongate extensional Dowsing Graben System transects the area. The graben is defined by a series of large, overlapping, en echelon listric growth faults, with oblique secondary planar faults, which sole-out on two main (deep and shallow) décollement levels in the Zechstein Supergroup and the Middle Triassic Röt Halite Member. Whilst its initial formation was related to Mesozoic extension, the graben system also displays a contractional overprint resulting from regional compression and structural inversion during the Cenozoic. Detailed mapping of the Zechstein Supergroup has revealed that the evolution of the extensional system was influenced by the ESE–WNW-striking anhydrite–carbonate Zechstein shelf-margin. The occurrence of variable-thickness, low-velocity sediments within the graben impacts seismic imaging and depth conversion, leading to prospective structures being overlooked; something that has implications for prospectivity in the SNS and other evaporite basins where similar graben occur.

Style and timing of salt movement in the Persian Gulf basin, offshore Iran: Insights from halokinetic sequences adjacent to the Tonb-e-Bozorg salt diapir

The variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt diapirs and provides insights into the style of salt movement-sedimentation interaction and the timing of halokinetic phases. Episodic movement of salt diapir is defined by wedge- and tabular-shaped salt-related sedimentary strata (halokinetic sequences) adjacent to the diapir. Detailed mapping of depositional strata on 2D seismic sections adjacent to salt diapirs on the Tonb-e-Bozorg Island (Persian Gulf, SW Iran) reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers, the Hormuz and Fars salts, respectively. The Hormuz salt deposited in the uppermost Proterozoic, mobilized in the Lower Paleozoic and then continued to move periodically to present and to create the deep salt structures in the Tonb-e-Bozorg region. The Fars salt deposited in the Lower Miocene and then started rising, and created the central salt structure, the Tonb-e-Bozorg Island, and several peripheral ring-like salt structures around the island. Our results reveal that both the salt layers within the Tonb-e-Bozorg region grew by downbuilding and continued to move periodically by passive and active diapirism to the present. Salt movement-sedimentation interaction during salt diapirism influences petroleum play and therefore is of interest in petroleum geoscience.

Weld kinematics of syn-rift salt during basement-involved extension and subsequent inversion: Results from analog models

Scaled analog models based on extensional basins with synrift salt show how basement topography exerts a control factor on weld kinematics during the extension and inversion phases. In the case of basement-involved extension, syn-rift salt thickness differences may lead to variable degrees of extensional decoupling between basement topography and overburden, which in turn have a strong impact on the development of salt structures. With ongoing extension and after welding, the basin kinematics evolves toward a coupled deformation style. The basin architecture of our experimental results record the halokinetic activity related to growing diapirs and the timing of weld formationduring extension. Moreover, the structures that result from anysubsequent inversion of these basins strongly depends on the inherited welds and salt structures. While those basins are uplifted,the main contractional deformation during inversion is absorbed by the pre-existing salt structures, whose are squeezed developing secondary welds that often evolve into thrust welds. The analysis of our analog models shows that shortening of diapirs is favored by: i) basement topography changes that induce reactivation of primary welds as thrust welds; ii) reactivation of the salt unit as a contractional detachment and iii) synkinematic sedimentation during basin inversion. Finally, in this article, we also compare two natural examples from the southern North Sea that highlight deformation patterns very similar to those observed in our analog models.

The charophytes-rich Barremian-Albian record in Jebel Ksaïra (Central Tunisia)

On the southern margin of the Tethys, Early Cretaceous sediments cover most of the Central Tunisia. As a result of a Middle Cretaceous sub-aerial exposure, the Late Barremian -Early Albian interval is mainly characterized by a major stratigraphic gap (hiatus). However in the Sidi Bouzid area a continental succession has been deposited called “Kebar Formation”.The Kebar Formation was previously studied in Jebel Kebar and Jebel Koumine and attributed respectively to the Late Aptian-Early Albian and the Late Barremian- Early Albian intervals. In the Jebel Ksaïra area, located at the East of Sidi Bouzid area and 4 km East of the Jebel Kebar, the Kebar Formation includes a rich association of charophytes that allows us to assign this Formation to the Late Barremian -Early Albian. Therefore, the Kebar Formation should have been deposited in Jebel Ksaïra earlier than in Jebel Kebar.The vertical stacking pattern and facies association of the Kebar Formation in the Jebel Ksaïra locality reflect variable depositional settings ranging from palustrine to marginal marine and infratidal environments. In fact, the sedimentary deposition in Jebel Ksaïra area was cyclic, alternating between (i) continental deposition materialized by bedded limestones rich in charophytes and limnic ostracods and (ii) marginal marine to infratidal deposition receiving episodically conglomerate inputs related to recurrent halokinetic activity (diapir of Jebel Rheouis).

Paleogeographic Reconstitution and Tangential Tectonic in the Backland of Tunisian Dorsal (Fahs Area: J. Rouas and Ruissate)

The Tunisian Dorsal backland is the Eastern Atlas side of maghrebides. Field data of Fahs area allowed us to develop new interpretations and to characterize the main structural features of the studied devices (Jebel Rouas and Ruissate). Heritage of Zaghouan accident, Triassic salt movements and strike-direction of major synsedimentary faults are the principal causes and results of the skinned and superimposed geometric architecture, generated by the reversed extensional (Jurassic-Cretaceous) tectonics. The actual geometry of Jebel Rouas and Ruissate represents a fault propagation fold, affecting Jurassic and Cretaceous sets. The backland of this thrust fault defines an imbrications structures of Barremian series. Tectonic records activities show the existence of angular unconformities (Oligocene and Eocene series on the Cretaceous sets considered as bedrock), slumps, tectonic breccias and synsedimentary faults are all of them controlled by a deep major accident; N-S to NE-SW and NW-SE. Features of the study area are probably related first; to the blockage of Zaghouan thrust oriented NE-SW in the foreland; then, to the intense halokinetic activity, which facilitates the layers displacement acting as decollment level. The detailed structural and stratigraphic study of Fahs area and its neighbors shows the presence of an intense tangential tectonic during upper Miocene, affecting Meso-Cenozoic sets, because all the structures involved are sealed by Oligocene and Miocene thinned series. This is accentuated by the existence of different sets of decollment at different depths, which are represented by a displacement to the SE through the backland of the Tunisian Dorsal. We define these features as an imbrication and thrusting Out of sequence system.

Surface sediment around the Jabuka Islet and the Jabuka Shoal: Evidence of Miocene tectonics in the Central Adriatic Sea

Abstract This paper is conceived as a contribution to understanding the tectonic setting in the Jabuka region in the Central Adriatic Sea, one of the seismically active regions within the Mediterranean. This seismicity is the result of the compressional tectonics within the Adria microplate, accompanied by halokinetic activity. The Jabuka Islet and the Jabuka Shoal appear to be Triassic igneous bodies extruded by diapir tectonics. Sedimentological, mineralogical and micropaleontological analyses of the surface sediments were done to provide insights into the depositional environment around these igneous outcrops. Coarse-grained gravelly sands surrounding the Jabuka Islet and the Jabuka Shoal are composed predominantly of biogenous detritus, containing small amounts of particles derived from igneous rocks. This highly carbonate sediment cover has been formed in the low-energy environment, below wave base and without terrigenous supply from remote areas. A peculiar finding of reworked Lower Miocene foraminiferal assemblage in the recent surface sediment accompanied with re-interpreted seismic profile was used to propose a conceptual geodynamic model for the Jabuka diapir protrusion. It suggested Miocene age for the earliest protrusion of the Jabuka diapir, followed by further Plio-Quaternary growth and shaping. Together with mostly Paleogene fossil calcareous nannoplankton, fossil foraminifera were presumed to have been weathered from the pierced and extruded overburden rocks and admixed to recent, slowly forming carbonate skeletal association, typical for cool-temperate depositional environments.

Petroleum systems in the Middle East

Abstract Since the start of the twentieth century more than 550 commercially significant oil and gas fields have been discovered in the Middle East. Most of the fields have more than one pay zone and produce from shallow-water carbonates and clastics that range in age from Infracambrian to Oligo-Miocene. A providential juxtaposition of source-reservoir-seal, migration history and trapping mechanism has lead to the entrapment of hydrocarbons throughout the Phanerozoic strata of the Middle East. Each occurrence shares some characteristics but each also has unique features. The geographic occurrence of hydrocarbons in the region reflects the original facies variations across the depositional shelf and basin and the tectonic history of basement faults and halokinetic activity. The evaluation and integration of these critical variables, together with an appreciation of the maturation, migration history and trapping mechanisms, drives the search for new fields. The continued discovery of new fields proves that the region has not yielded all its treasure and stimulates future exploration. Although evidence for orogenic deformation is lacking in the Middle East, epeirogenic warping is common. The latter is attributed to the reactivation of basement faults, and evaporite structures and flow at depth. A prominent sedimentary and erosional break, locally marked by eroded Hercynian unconformities, followed an important Late Palaeozoic epeirogenic uplift. Similarly, Mesozoic sedimentary fill is broken by a major change in tectonic and depositional regimes, and numerous unconformities thought to be primarily controlled by high-frequency fluctuations in eustatic sea level and a low uniform rate of tectonic movement. Late Cretaceous and Tertiary events followed the collision and partial subduction of the east and southeastern margin of the Arabian Plate and involved vertical epeirogenic uplift of the resulting folded and thrusted gravity features. Vast areas of the Middle East Basin have yet to be extensively drilled. Although the long-lived stability of the shelf has influenced the development of the giant oil pools, and to some extent reduced the potential for stratigraphic traps, it has not eliminated the potential for smaller structures and the exploration for new oil and gas reserves. Future exploration is expected to focus on the discovery of smaller structures and subtle traps revealed by analysis of existing geological data and special seismic processing. Exploration will involve extensive regional and local geological–sedimentological studies, 3D or 4D seismic surveys and drilling progrmmes, and proposed better petroleum system model(s) for each basin (or sub-basin).

Influence of the halokinesis on the clay mineral repartition of upper Maastrichtian–Ypresian in the Meknassy-Mezzouna basin, centerwestern Tunisia

The Meknassy-Mezzouna basin is affected by a fault system, assembling two main directions, northsouth and eastwest. The Triassic outcrops are widely noticeable at Jebel Jebbes El Meheri and the Mezzouna link. During the late Maastrichtian–Ypresian, the sedimentation in the basin is influenced by halokinetic events, which are clearly manifested either by the thickness of El Haria formation along the Triassic outcrops (rim syncline) or by an alteration surface at the top of the Abiod formation. Such events also confirm the emersion of the basin from the late Maastrichtian to the early Lutetian. However, the present work tries to highlight the effects of halokinetic uplift on the clay mineralogical variations at that area. In harmony with this halokinetic activity, the clay minerals of this time interval (during the late Maastrichtian–Ypresian) show a trend of variation which corresponds to the evolution from illite and kaolinite, indicating a strongly hydrolytic marine environment, to smectite, sepiolite, and palygorskite, reflecting a very rapid evolution from this marine environment to a lagoon environment, then to a more confined continental environment. In fact, the appearance of sepiolite and palygorskite on the top of El Haria formation and the Paleocene–Eocene transition can be explained by a transformation or neoformation mechanism in an alkaline environment, rich in silica and magnesium, under arid to semi-arid climatic conditions. Moreover, the palygorskite can be formed in continental deposits as well as in close marine environment, which displays a limited communication with the open sea. Under these conditions, the evaporation leads to high ionic concentration of alkaline pH, which is favorable to the formation and stability of this mineral.

Regional-scale structural role of Permian salt within the Central European Basin System

Abstract The Central European Basin System (CEBS) includes the former Northern and Southern Permian Basins together with superimposed Meso-Cenozoic sub-basins and contains a thick layer of Upper Permian (Zechstein) salt. This salt was mobilized in response to several post-Permian tectonic events. In order to analyse the regional relationship between the structural pattern of the Meso-Cenozoic sedimentary cover and the distribution of the Upper Permian salt, a 3D structural model of the CEBS has been constructed. In this model, the Permian salt is resolved as an extra layer for the entire basin system. According to the 3D structural model, the salt layer is strongly deformed as a result of halokinetic activity. The thickest salt is localized within salt walls and diapirs, reaching up to 9 km of thickness. A regional structural 3D analysis of the overburden in relation to underlying ductile salt demonstrates that the geometry of the sedimentary cover is strongly complicated by a variety of salt structures. The withdrawal of the Permian salt appears to have played a key role in both deposition and deformation of Meso-Cenozoic deposits in addition to tectonically forced regional subsidence.

LATE CRETACEOUS TECTONIC AND SEDIMENTARY EVOLUTION OF THE BANDAR ABBAS AREA, FARS REGION, SOUTHERN IRAN

The Upper Cretaceous succession in the SE Zagros (Bandar Abbas area) is characterized by marked changes in fades and thickness. These changes relate to sediment deposition in a foreland basin along the NE margin of the Arabian plate. The succession was measured at eight outcrop sections in the Khush, Faraghun, Gahkum, Genow and Khamir anticlines. The measured sections illustrate a transition from shallow‐water carbonate platform deposits (Cenomanian to Coniacian) to deep‐water fades (Santonian to Maastrichtian). Outcrop observations were compared to data from ten off‐ and onshore wells and to a series of seismic profiles.Four cross‐sections were constructed using well and outcrop data and illustrate fades and thickness variations within the Upper Cretaceous. Based on these regional profiles, the Late Cretaceous depositional history of the Bandar Abbas area was reconstructed and can be divided into two tectono‐sedimentary phases suggesting a transition from a passive to an active margin. Sedimentation during Phase I (late Albion to Coniacian) took place in shallow‐water carbonate platform and intrashelf basin settings (Sarvak Formation), and four third‐order sequences can be recognised. The uppermost sequence is locally capped by fresh‐water, pisolith‐bearing carbonate sand and conglomerates with local laterite and palaeosols of the Coniacian Laffan Formation. Shallow‐water facies consist mainly of wackestone to packstones with abundant benthic foraminifera. Sediments deposited in intrashelf basins are dominated by oligosteginid‐bearing fades. Eustatic variations in sea level, the creation of a foreland basin and salt tectonics most probably controlled patterns of sedimentation during this phase.During the second tectono‐sedimentary phase (Phase II: Santonian to Late Maastrichtian), sediments were dominated by pelagic marls and gravity flow deposits. Lateral thickness variations become more marked to the NE as a result of obduction processes and the creation of the foreland basin.Allochthonous ophiolitic and radiolarite‐bearing units are common in the northern part of the Fars region but are restricted to a few localities in the Bandar Abbas area. Traces of allochthonous materials occur in the SE‐most part of the Khush anticline; thrust slices in offshore seismic profiles may link to the Hawasina nappes of Oman. At the top of the Phase II succession, pelagic facies locally interfinger with Omphalocyclus and Loftusia‐bearing fades (Tarbur Formation) and evaporites (Sachun Formation). These deposits are overlain by slumped and dolomitized shallow‐water carbonates of the Paleocene – Eocene Jahrum Formation.The sedimentary sequence in the Bandar Abbas area illustrates a far‐field response to Late Cretaceous obduction processes and foreland basin development, as well as to halokinetic activity. Rapid variations in thickness and fades document the evolution of depositional processes in the foreland basin.

MULTI‐PHASE HORMUZ SALT DIAPIRISM IN THE SOUTHERN ZAGROS, SW IRAN

In the Zagros orogenic belt in SW Iran, a 14 km thick sedimentary succession is decoupled from crystalline basement by the thick Infracambrian Hormuz complex. The complex consists of evaporites (“Hormuz salt”) together with marls, sandstones, carbonates and volcanic rocks and is known from emergent salt diapirs in the Fars and High Zagros areas. In this paper, we document discrete pulses of halokinetic activity using seismic profiles, well data and recent field studies. The earliest phase of mobilization of the Hormuz salt occurred in the pre‐Silurian. Later pulses of salt movement took place during opening of Neo‐Tethys in Permo‐Triassic times and during ophiolite obduction onto the NE Arabian plate margin in the Late Cretaceous. Halokinesis was intense during the Neogene Zagros orogeny when some salt plugs breached the surface.

The formation of the south-eastern part of the Dniepr–Donets Basin: 2-D forward and reverse modelling taking into account post-rift redeposition of syn-rift salt

Forward and reverse modelling of structure and stratigraphy has been used to investigate the syn-rift (Late Devonian) and early post-rift (Carboniferous) evolution of the south-eastern part of the Dniepr–Donets Basin (DDB). Modelling was carried out with and without taking into consideration the withdrawal and surface extrusion of Devonian salt during the formation of salt diapirs. The great thickness of Carboniferous deposits can be explained by the superimposed actions of three processes: post-rift thermal subsidence, withdrawal of Devonian salt from the mother layer during phases of salt diapir activity, and regional subsidence of the East European Platform. The effects of other tectonic and/or non-tectonic processes are not required. Forward syn-rift modelling using the flexural cantilever model of sedimentary basin formation predicts the total syn-rift extension across the southeastern DDB to be approximately 65 km with a maximum β stretching factor of 2.4. Shallowing of the Moho during the syn-rift phase is estimated to be 15 km. The present-day Moho, after thermal subsidence and basin fill, is predicted to be 4–6 km shallower than surrounding regions. In the axial zone of the south-eastern DDB the thickness of the Devonian syn-rift sequence may have reached 7.5 km by the end of the rift stage. This is 3–3.5 km more than at present. The thicknesses reduction is due to the outflow of Devonian salt during post-rift periods of halokinetic activity in the early Visean, the middle Serpukhovian, and in the Early Permian. The withdrawal of salt from the mother layer produced additional accommodation space and up to 1.5–1.7 km of the total eventual thickness of the Carboniferous sedimentary succession can be explained as a result of this.

Late Jurassic plays along the western margin of the Central Graben

The distribution of the Lower Kimmeridgian Fulmar sands along the edge of the Western Platform of the Central Graben is intimately related to Triassic halokinetic activity. Withdrawal of Zechstein evaporites resulted in the development of thick packages of Triassic Smith Bank claystones, the so-called ‘Smith Bank Pods’. The crests of the Zechstein evaporite highs were later subjected to groundwater dissolution, resulting in topographic lows, which controlled the pattern of drainage during the deposition of the Triassic Skagerrak sands. The Triassic salt movements associated with this phenomenon also exercised the underlying control on later drainage patterns in the Jurassic. The relative sea-level rise in the Early Kimmeridgian flooded the margin of the Western Platform which reworked the original valley fill and, together with erosion products from the hinterland, resulted in the deposition of the shallow marine sands of the Fulmar Formation. 3D seismic can reveal the extent of these palaeovalley systems draining into the Central Graben. The Fulmar sand packages are effectively encased in shales; a lateral seal is formed by the Smith Bank Formation and the top seal consists of Kimmeridgian shales. They represent an attractive possibility for stratigraphically trapped hydrocarbons.

Petroleum geology of the Campos Basin, offshore Brazil

Abstract The Campos Basin, offshore Brazil, is the most prolific basin in the western South Atlantic, with more than thirty hydrocarbon accumulations currently accounting for about 60% of Brazilian oil production. Intensive drilling and seismic, gravity and magnetic data have contributed to the recognition of four tectono-stratigraphic units related to the rifting and break-up of Pangea. The lowest sequence consists of Neocomian clastics deposited on basalt dated at 120–130 Ma, and reflects the fault-controlled subsidence associated with the stretching that preceded the emplacement of oceanic crust. The Aptian proto-oceanic stage is characterized by a sequence of evaporitic rocks that have undergone intense diapiric activity in deep water. An open-marine environment begins with a thick sequence of Albian/Cenomanian limestones, locally with clastic input, which grades upwards and basinwards into deep water marls and shales. This section is structurally associated with detached listric normal faults that sole out on the Aptian evaporites. Finally, the marine Upper Cretaceous to Recent clastic section is characterized by a more quiescent phase of thermal subsidence, with some residual halokinetic activity that increases in intensity towards deeper waters. The hydrocarbon accumulations are distributed throughout the stratigraphic column of the basin from Neocomian to Miocene. The reservoirs range from fractured basalts and porous bioclastic limestone (coquinas) in the Lagoa Feia Formation, to limestones and sandstones in the Macaé Formation, and sandstones in the Campos Formation. Detailed geochemical analyses undertaken on cutting, core and oil samples show that almost all the hydrocarbon accumulations discovered to date are sourced mainly from lacustrine calcareous black shales deposited in a closed Upper Neocomian lake system, having saline to hypersaline waters of alkaline affinities. The extreme anoxic conditions in this lacustrine environment resulted in the deposition of fine, well laminated organic-rich (TOC up to 9%) calcareous black shales, with high-quality organic matter composed almost entirely of low-sulphur type-I kerogen, originating from lipid-rich algal and bacterially-derived material. The excellent hydrocarbon source potential of these sediments, combined with the appropriate thermal history, produced the necessary conditions to yield low-density oil (around 30° API) characterized by a low sulphur content (around 0.30%), and significant quantities of alkanes (up to 70%). Diagnostic features in the biological markers from this depositional environment include: low concentration of steranes, presence of β-carotane, gammacerane and 28,30-bisnorhopane, very high concentrations of hopanes and high relative abundances of tricyclic terpanes up to C 34 .