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1.
Allochthonous salt structures and associated primary and secondary minibasins are exposed in Neoproterozoic strata of the eastern Willouran Ranges, South Australia. Detailed geologic mapping using high‐quality airborne hyperspectral remote‐sensing data and satellite imagery, combined with a qualitative structural restoration, are used to elucidate the evolution of this complex, long‐lived (>250 Myr) salt system. Field observations and interpretations at a resolution unobtainable from seismic or well data provide a means to test published models of allochthonous salt emplacement and associated salt‐sediment interaction derived from subsurface data in the northern Gulf of Mexico. Salt diapirs and sheets are represented by megabreccias of nonevaporite lithologies that were originally interbedded with evaporites that have been dissolved and/or altered. Passive diapirism began shortly after deposition of the Callanna Group layered evaporite sequence. A primary basin containing an expulsion‐rollover structure and megaflap is flanked by two vertical diapirs. Salt flowed laterally from the diapirs to form a complex, multi‐level canopy, now partly welded, containing an encapsulated minibasin and capped by suprasalt basins. Salt and minibasin geometries were modified during the Late Cambrian–Ordovician Delamerian Orogeny (ca. 500 Ma). Small‐scale structures such as subsalt shear zones, fractured or mixed ‘rubble zones’ and thrust imbricates are absent beneath allochthonous salt and welds in the eastern Willouran Ranges. Instead, either undeformed strata or halokinetic drape folds that include preserved diapir roof strata are found directly below the transition from steep diapirs to salt sheets. Allochthonous salt first broke through the diapir roofs and then flowed laterally, resulting in variable preservation of the subsalt drape folds. Lateral salt emplacement was presumably on roof‐edge thrusts or, because of the shallow depositional environment, via open‐toed advance or extrusive advance, but without associated subsalt deformation.  相似文献   

2.
Salt tectonics have markedly influenced the rapid evolution of the Upper Palaeozoic Cumberland Basin of Atlantic Canada, including the ca. 5 km‐thick Mississippian – Pennsylvanian stratigraphic succession exposed along the UNESCO World Heritage coastline at Joggins, Nova Scotia. A diapiric salt wall is exposed in the Minudie Anticline to the north of the Joggins section on the Maringouin Peninsula of New Brunswick, which corresponds to the fault‐bounded northern margin of the Cumberland Basin. The salt wall is of Visean evaporites of the Windsor Gp that originally were buried by red‐beds of the Mabou Gp in the Serpukhovian, and later by fluvial and floodplain strata (Boss Point Fm, Cumberland Gp) in the Yeadonian (mid‐Bashkirian, Early Pennsylvanian). Folds and faults in the Boss Point and overlying basal Little River formations are truncated by an angular unconformity at the base of overlying red‐beds of the Grande Anse Fm. Re‐evaluation of the palynological data delimits the Grande Anse Fm as Langsettian, providing a tight constraint of less than 2 myr on the timing of deformation. Diversion of palaeoflows by the rising salt structure, noted in previous work on the upper Boss Point Fm, occurs to the north of the diapiric anticline. This is interpreted to signify the development of a mini‐basin on commencement of diapirism once a ~1.5 km‐thick succession of clastic strata had buried the salt. Faults and folds in the succession below the unconformity indicate an initial phase of dextral transpressive strike‐slip motion, which may have promoted halokinesis. Reverse faults indicate shortening associated with northward development and overturn of the Minudie Anticline during transpression; subsequent normal faulting was associated with collapse of the sediment pile and underlying salt structure.  相似文献   

3.
The northern Paradox Basin evolved during the Late Pennsylvanian–Permian as an immobile foreland basin, the result of flexural subsidence in the footwall of the growing Uncompahgre Ancestral Rocky Mountain thick‐skinned uplift. During the Atokan‐Desmoinesian (～313–306 Ma) fluctuating glacio‐eustatic sea levels deposited an ～2500 m thick sequence of evaporites (Paradox Formation) in the foreland basin, interfingering with coarse clastics in the foredeep and carbonates around the basin margins. The cyclic deposition of the evaporites produced a repetitive sequence of primarily halite, with minor clastics, organic shales and anhydrite. Sediment loading of the evaporites subsequently produced a series of salt walls and minibasins, through the process of passive diapirism or downbuilding. Faults at the top Mississippian level localised the development of linear salt walls (up to 4500 m high) along a NW–SE trend. A crosscutting NE–SW structural trend was also important in controlling the evaporite facies and the abrupt termination of the salt walls. Seismic, well and field data define the proximal Cutler Group (Permian) as a basinward prograding sequence derived from the growing Uncompahgre uplift that drove salt basinwards (towards the southwest), triggering the growth of the salt walls. Sequential structural restorations indicate that the most proximal salt walls evolved earlier than the more distal ones. The successive development of salt‐withdrawal minibasins associated with each growing salt wall implies that parts of the Cutler Group in one minibasin may have no chronostratigraphic equivalent in other minibasins. Localised changes in along‐strike salt wall growth and evolution were critical in the development of facies and thickness variations in the late Pennsylvanian to Triassic stratigraphic sequences in the flanking minibasins. Salt was probably at or very close to the surface during the downbuilding process leading to localised thinning, deposition of diapir‐derived detritus and rapid facies changes in sequences adjacent to the salt wall structures.  相似文献   

4.
Salt tectonics is typically caused by the flow of mobile evaporites in response to post-depositional gravity gliding and/or differential loading by overburden sediments. This situation is considerably more complex near the margins of salt basins, where carbonate and clastic rocks may be deposited at the same time as and be interbedded with more mobile, evaporitic strata. In these cases, syn-depositional salt flow may occur due to density differences in the deposited lithologies, although our understanding of this and related processes is relatively poor. We here use 3D seismic reflection and borehole data from the Devil's Hole Horst, West Central Shelf, offshore UK to understand the genesis, geometry, and kinematic evolution of intra-Zechstein Supergroup (Lopingian) minibasins and their effect on post-depositional salt deformation. We show that immobile, pinnacle-to-barrier-like, carbonate build-ups and anhydrite are largely restricted to intra-basin highs, whereas mobile halite, which flowed to form large diapirs, dominates in the deep basin. At the transition between the intra-basin highs and the deep basin, a belt of intra-Zechstein minibasins occurs, forming due to the subsidence of relatively dense anhydrite into underlying halite. Depending on primary halite thickness, these intra-Zechstein minibasins created topographic lows, dictating where Triassic minibasins subsequently nucleated and down-built. Our study refines the original depositional model for the Zechstein Supergroup in the Central North Sea, with the results also helping us better understand the style and distribution of syn-depositional salt flow within other layered evaporitic sequences and the role intra-salt heterogeneity and related deformation may have in the associated petroleum plays.  相似文献   

5.
The synkinematic strata of the Kuqa foreland basin record a rich history of Cenozoic reactivation of the Palaeozoic Tian Shan mountain belt. Here, we present new constraints on the history of deformation in the southern Tian Shan, based on an analysis of interactions between tectonics and sedimentation in the western Kuqa basin. We constructed six balanced cross‐sections of the basin, integrating surface geology, well data and a grid of seismic reflection profiles. These profiles show that the Qiulitage fold belt on the southern edge of the Kuqa basin developed by thin‐skinned compression salt tectonics. The structural styles have been influenced by two major factors: the nature of early‐formed diapirs and the basinward depositional limit of the Kumugeliemu salt. Several early diapirs developed in the western Kuqa basin, soon after salt deposition, which acted to localize the subsequent shortening. Where diapirs had low relief and a thick overburden they tended to tighten into salt domes 3000–7000 m in height. Conversely, where the original diapirs had higher relief and a thinner overburden they tended to evolve into salt nappes, with the northern flanks of the diapirs thrusting over their southern flanks. Salt was expelled forward, up dip along the mother salt layer, tended to accumulate at the distal pinch‐out of Kumugeliemu salt located at the Qiulitage fold belt. Furthermore, the synkinematic strata (6–8 km thick) of the Kuqa basin indicate that during the Cenozoic reactivation of the Tian Shan, shortening of the western Kuqa basin was mainly in the hinterland until the early Miocene. Then, compression spread simultaneously southwards to the Dawanqi anticline, the Qiulitage fold belt and the southernmost blind detachment fold at the end of Miocene. The western Kuqa basin has a shortening of ca. 23 km. We consider that ca. 9 km was consumed from the end of the Miocene (5.2/5.8 Ma) to the early Pleistocene (2.58 Ma) and another ca. 14 km have been absorbed since then. Thus, we obtain a ca. 3.4/2.8 mm year?1 average shortening from 5.2/5.8 to 2.58 Ma, followed by a 60–90% increase in average shortening rate to ca. 5.4 mm year?1 since 2.58 Ma. This suggests that the reactivation of the modern Tian Shan has been accelerating up to the present day.  相似文献   

6.
In salt‐detached gravity‐gliding/spreading systems the detachment geometry is a key control on the downslope mobility of the supra‐salt sequence. Here, we used regional 3D seismic data to examine a salt‐stock canopy in the northern Gulf of Mexico slope, in an area where supra‐canopy minibasins subsided vertically and translated downslope above a complex base‐of‐salt. If thick enough, minibasins can interact with, and weld to, the base‐of‐salt and be obstructed from translating downslope. Based on the regional maps of the base of allochthonous salt and the base of the supra‐canopy sequence, the key controls on minibasin obstruction, we distinguished two structural domains in the study area: a highly obstructed domain and a highly mobile domain. Large‐scale translation of the supra‐canopy sequence is recorded in the mobile domain by a far‐travelled minibasin and a ramp syncline basin. These two structures suggest downslope translation on the order of 40 km from Plio‐Pleistocene to Present. In contrast, translation was impeded in the obstructed domain due to supra‐canopy bucket minibasins subsiding into feeders during the Pleistocene. As a result, we infer that differential translation occurred between the two domains and argue that a deformation area between two differentially translating supra‐canopy minibasin domains is difficult to recognize. However, characterizing domains according to base‐of‐salt geometry and supra‐canopy minibasin configuration can be helpful in identifying domains that may share similar subsidence and downslope translation histories.  相似文献   

7.
Detachment surfaces have important implications for structural restoration, burial-history and thermal modeling, hydrocarbon migration, and diagenesis. We present criteria to distinguish salt welds from shale detachments based on geophysical data from the inner Texas shelf. Here, the Paleogene detachment has been variously interpreted as salt or shale by different people. A newly reprocessed 8200 km2 (3200 mi2) 3D seismic volume provides excellent imaging of this detachment, which separates growth-faulted Oligocene–Miocene strata from the underlying, gently folded Cretaceous–Eocene section. Key criteria to evaluate detachment origins include seismic amplitude response, geometry, and relationship to supradetachment and subdetachment reflections. We argue that the detachment is a salt weld because (a) it is imaged as a high-amplitude, discrete reflection; (b) it has a ramp-flat geometry, cutting across underlying reflections; (c) it locally forms bowl-shaped depotroughs interpreted as former diapiric salt feeders; (d) it is overlain by seismically incoherent pods having high-amplitude tops and bases interpreted as remnant salt; and (e) in the depotroughs associated with former diapiric salt feeders the detachment has hints of upturned strata just beneath (possible halokinetic sequences). The inferred weld represents the evacuated remains of a patchy salt canopy emplaced across the study area during the Late Eocene to Early Oligocene. Preliminary examination beyond our study area suggests that this discontinuous canopy may have extended across most of the modern Texas shelf. Most of the salt was expelled from the canopy by loading from prograding Oligo–Miocene deltaic deposits.  相似文献   

8.
The structure and tectonic evolution of an evaporite basin are investigated in this case study, which combines the interpretation of magnetic data with the more commonly applied seismic reflection and gravity methods. The Maritimes Basin contains up to 18 km of Upper Palaeozoic sedimentary rocks resting on the basement of the Acadian orogeny. Carboniferous rocks are intensely deformed to the southeast of the Magdalen Islands as a result of deformation of evaporites of the Viséan Windsor Group. Short‐wavelength (<5 km) magnetic lineations define NNE‐ and ENE‐trending linear belts, coincident with the mapped pattern of salt structures. Magnetic models show that these lineations can be explained by the infill of subsidence troughs by high‐susceptibility sediment and/or the presence of basaltic rocks, similar to those uplifted and exposed on the Magdalen Islands. Additional shallow, magnetic sources are interpreted to result from alteration mineralization in salt‐impregnated, iron‐rich sedimentary rocks, brecciated during salt mobilization. Magnetic susceptibility measurements of samples from the Pugwash mine confirm the presence of higher susceptibility carnallite‐rich veins within salt units. Salt tectonism and basin development were influenced by the structure of the base group, the deepest regionally continuous seismic reflections (ca. 5–11 km), associated with an unconformity at the base of the Windsor Group, sampled at the Cap Rouge well. Salt structural evolution, formation of the magnetic lineations and geometry of the base group are associated with regional dextral transpression during basin development (late Carboniferous) and/or Alleghanian Orogeny (late Carboniferous to Permian). In this and similar studies, the effective use of magnetics is dependent upon the presence of rocks of high magnetic susceptibility in contrast to the low‐susceptibility salt bodies. In the absence of high‐susceptibility rocks, magnetic lows over the salt structures may be modelled, similar to commonly applied gravity techniques, to derive the internal structure and geometry.  相似文献   

9.
Well‐calibrated seismic interpretation in the Halten Terrace of Mid‐Norway demonstrates the important role that structural feedback between normal fault growth and evaporite mobility has for depocentre development during syn‐rift deposition of the Jurassic–Early Cretaceous Viking and Fangst Groups. While the main rift phase reactivated pre‐existing structural trends, and initiated new extensional structures, a Triassic evaporite interval decouples the supra‐salt cover strata from the underlying basement, causing the development of two separate fault populations, one in the cover and the other confined to the pre‐salt basement. Detailed displacement–length analyses of both cover and basement fault arrays, combined with mapping of the component parts of the syn‐rift interval, have been used to reveal the spatial and temporal evolution of normal fault segments and sediment depocentres within the Halten Terrace area. Significantly, the results highlight important differences with traditional models of normal fault‐controlled subsidence, including those from parts of the North Sea where salt is absent. It can now be shown that evaporite mobility is intimately linked to the along‐strike displacement variations of these cover and basement faults. The evaporites passively move beneath the cover in response to the extension, such that the evaporite thickness becomes greatest adjacent to regions of high fault displacement. The consequent evaporite swells can become large enough to have pronounced palaeobathymetric relief in hangingwall locations, associated with fault displacement maxima– the exact opposite situation to that predicted by traditional models of normal fault growth. Evaporite movement from previous extension also affects the displacement–length relationships of subsequently nucleated or reactivated faults. Evaporite withdrawal, on the other hand, tends to be a later‐stage feature associated with the high stress regions around the propagating tips of normal faults or their coeval hangingwall release faults. The results indicate the important effect of, and structural feedback caused by, syn‐rift evaporite mobility in heavily modifying subsidence patterns produced by normal fault array evolution. Despite their departure from published models, the results provide a new, generic framework within which to interpret extensional fault and depocentre development and evolution in areas in which mobile evaporites exist.  相似文献   

10.
Salt tectonics in the Eastern Persian Gulf (Iran) is linked to a unique salt‐bearing system involving two overlapping ‘autochthonous’ mobile source layers, the Ediacaran–Early Cambrian Hormuz Salt and the Late Oligocene–Early Miocene Fars Salt. Interpretations of reflection seismic profiles and sequential cross‐section restorations are presented to decipher the evolution of salt structures from the two source layers and their kinematic interaction on the style of salt flow. Seismic interpretations illustrate that the Hormuz and Fars salts started flowing in the Early Palaeozoic (likely Cambrian) and Early Miocene, respectively, shortly after their deposition. Differential sedimentary loading (downbuilding) and subsalt basement faults initiated and localized the flow of the Hormuz Salt and the related salt structures. The resultant diapirs grew by passive diapirism until Late Cretaceous, whereas the pillows became inactive during the Mesozoic after a progressive decline of growth in the Late Palaeozoic. The diapirs and pillows were then subjected to a Palaeocene–Eocene contractional deformation event, which squeezed the diapirs. The consequence was significant salt extrusion, leading to the development of allochthonous salt sheets and wings. Subsequent rise of the Hormuz Salt occurred in wider salt stocks and secondary salt walls by coeval passive diapirism and tectonic shortening since Late Oligocene. Evacuation and diapirism of the Fars Salt was driven mainly by differential sedimentary loading in annular and elongate minibasins overlying the salt and locally by downslope gliding around pre‐existing stocks of the Hormuz Salt. At earlier stages, the Fars Salt flowed not only towards the pre‐existing Hormuz stocks but also away from them to initiate ring‐like salt walls and anticlines around some of the stocks. Subsequently, once primary welds developed around these stocks, the Fars Salt flowed outwards to source the peripheral salt walls. Our results reveal that evolving pre‐existing salt structures from an older source layer have triggered the flow of a younger salt layer and controlled the resulting salt structures. This interaction complicates the flow direction of the younger salt layer, the geometry and spatial distribution of its structures, as well as minibasin depocentre migration through time. Even though dealing with a unique case of two ‘autochthonous’ mobile salt layers, this work may also provide constraints on our understanding of the kinematics of salt flow and diapirism in other salt basins having significant ‘allochthonous’ salt that is coevally affected by deformation of the deeper autochthonous salt layer and related structures.  相似文献   

11.
In passive margin salt basins, the distinct kinematic domains of thin‐skinned extension, translation and contraction exert important controls on minibasin evolution. However, the relationship between various salt minibasin geometries and kinematic domain evolution is not clear. In this study, we use a semi‐regional 3D seismic reflection dataset from the Lower Congo Basin, offshore Angola, to investigate the evolution of a network of minibasins and intervening salt walls during thin‐skinned, gravity‐driven salt flow. Widespread thin‐skinned extension occurred during the Cenomanian to Coniacian, accommodated by numerous distributed normal faults that are typically 5–10 km long and spaced 1–4 km across strike within the supra‐salt cover. Subsequently, during the Santonian–Paleocene, multiple, 10–25 km long, 5–7 km wide depocentres progressively grew and linked along strike to form elongate minibasins separated by salt walls of comparable lengths. Simultaneous with the development of the minibasins, thin‐skinned contractional deformation occurred in the southwestern downslope part of the study area, forming folds and thrusts that are up to 20 km long and have a wavelength of 2–4 km. The elongate minibasins evolved into turtle structures during the Eocene to Oligocene. From the Miocene onwards, contraction of the supra‐salt cover caused squeezing and uplift of the salt walls, further confining the minibasin depocentres. We find kinematic domains of extension, translation and contraction control the minibasin initiation and subsequent evolution. However, we also observe variations in minibasin geometries associated with along‐strike growth and linkage of depocentres. Neighbouring minibasins may have different subsidence rates and maturity leading to marked variations in their geometry. Additionally, migration of the contractional domain upslope and multiple phases of thin‐skinned salt tectonics further complicates the spatial variations in minibasin geometry and evolution. This study suggests that minibasin growth is more variable and complex than existing domain‐controlled models would suggest.  相似文献   

12.
Salt-detached gravity gliding/spreading systems having a rugose base-of-salt display complex strain patterns. However, little was previously known about how welding of supra-salt minibasins to the sub-salt may influence both the downslope translation of minibasins on salt-detached slopes and the regional pattern of supra-salt strain. Using a regional 3D seismic reflection data set, we examine a large salt-stock canopy system with a rugose base on the northern Gulf of Mexico slope, on which minibasins both subside and translate downslope. Some minibasins are welded at their bases and others are not. We suggest that basal welds obstruct downslope translation of minibasins and control regional patterns of supra-canopy strain. The distribution of strain above the canopy is complex and variable. Each minibasin that becomes obstructed modifies the local strain field, typically developing a zone of shortening immediately updip and an extensional breakaway zone immediately downdip of the obstructed minibasin. This finding is corroborated by observations from a physical sandbox model of minibasin obstruction. We also find in our natural example that minibasins can be obstructed to different degrees, ranging from severe (e.g., caught in a feeder) to mild (e.g., welded to a flat or gently dipping base-of-salt). By mapping both the presence of obstructed minibasins and the relative degree of minibasin obstruction, we provide an explanation for the origin of complex 3-D strain fields on a salt-detached slope and, potentially, a mechanism that explains differential downslope translation of minibasins. In minibasin-rich salt-detached slope settings, our results may aid: i) structural restorations and regional strain analyses; ii) prediction of subsalt relief in areas of poor seismic imaging; and iii) prediction of stress fields and borehole stability. Our example is detached on allochthonous salt and where the base-of-salt is rugose, with the findings applicable to other such systems worldwide (e.g., Gulf of Mexico; Scotian Margin, offshore eastern Canada). However, our findings are also applicable to systems where the salt is autochthonous but has significant local basal relief (e.g., Santos Basin, Brazil; Kwanza Basin, Angola).  相似文献   

13.
Two end‐member models have been proposed for the Paleogene Andean foreland: a simple W‐E migrating foreland model and a broken‐foreland model. We present new stratigraphic, sedimentological and structural data from the Paleogene Quebrada de los Colorados (QLC) Formation, in the Eastern Cordillera, with which to test these two different models. Basin‐wide unconformities, growthstrata and changes in provenance indicate deposition of the QLC Formation in a tectonically active basin. Both west‐ and east‐vergent structures, rooted in the basement, controlled the deposition and distribution of the QLC Formation from the Middle Eocene to the Early Miocene. The provenance analysis indicates that the main source areas were basement blocks, like the Paleozoic Oire Eruptive Complex, uplifted during Paleogene shortening, and that delimits the eastern boundary of the present‐day intraorogenic Puna plateau. A comparison of the QLC sedimentary basin‐fill pattern with those of adjacent Paleogene basins in the Puna plateau and in the Santa Bárbara System highlights the presence of discrete depozones. These reflect the early compartmentalization of the foreland, rather than a stepwise advance of the deformation front of a thrust belt. The early Tertiary foreland of the southern central Andes is represented by a ca. 250‐km‐wide area comprising several deformation zones (Arizaro, Macón, Copalayo and Calchaquí) in which doubly vergent or asymmetric structures, rooted in the basement, were generated. Hence, classical foreland model is difficult to apply in this Paleogene basin; and our data and interpretation agree with a broken‐foreland model.  相似文献   

14.
Salt canopies are present in many of the worldwide large salt basins and are key players in the basins' structural evolution as well as in the development of associated hydrocarbon systems. This study employs 2D finite‐element models which incorporate the dynamical interaction of viscous salt and frictional‐plastic sediments in a gravity‐spreading system. We investigate the general emplacement of salt canopies that form in the centre of a large, autochthonous salt basin. This is motivated by the potential application to a mid‐basin canopy in the NW Gulf of Mexico (GoM) that developed in the late Eocene. Three different salt expulsion and canopy formation concepts that have been proposed in the salt‐tectonic literature for the GoM are tested. Two of these mechanisms require pre‐existing diapirs as precursory structures. We include their evolution in the models to assure a continuous, smooth evolution of the salt‐sediment system. The most efficient canopy formation takes place under the squeezed diapir mechanism. Here, shortening of a region containing pre‐existing diapirs is absorbed by the salt (the weakest part of the system), which is then expelled onto the seafloor. The expulsion rollover mechanism, which evacuates salt from beneath evolving rollover structures and expels it both laterally and to the surface, was not successfully captured by the numerical models. No rollover structures developed and only minor amounts of allochthonous salt emerged to the seafloor. The breached anticline mechanism requires substantial shortening of salt‐cored, pre‐weakened folds such that the salt breaches the anticlines and is expelled to the seafloor. The amount of shortening may be too large to occur in the central part of a salt basin, but may explain canopy evolution closer to the distal end of the allochthonous salt. When applying the different concepts to the northwestern GoM, none of the models adequately describes the entire system, yet the squeezed diapir mechanism captures most structural features of the Eocene paleocanopy. It is nevertheless possible that different mechanisms have acted in combination or sequentially in the northwestern GoM.  相似文献   

15.
The Plataforma Burgalesa is a partly exposed extensional forced fold system with an intermediate salt layer, which has developed along the southern portion of the Basque‐Cantabrian Basin from Malm to Early Cretaceous as part of the Bay of Biscay‐Pyrenean rift system. Relationships between syn‐ and pre‐rift strata of the supra‐salt cover sequence and distribution of intra‐cover second‐order faults are observed both along seismic sections and at the surface. These relationships indicate an along‐strike variability of the extensional structural style. After a short period of salt mobilization and forced folding, high slip rates in the central portion of the major basement faults have rapidly promoted brittle behaviour of the salt layer, preventing further salt mobilization and facilitating the propagation of the fault across the salt layer. In contrast, at the tip regions of basement faults, slower slip rates have facilitated ductile salt behaviour, ensuring its further evaporite evacuation, preventing fault propagation across the salt layer and, in essence, allowing for a long‐living forced folding process. Our results indicate the important effect of along‐strike variation in displacement and displacement rates in controlling evaporite behaviour in extensional basins. Amount of displacement and displacement rates are key factors controlling the propagation of basement faults across evaporite layers. In addition, growth strata patterns are recognized as a powerful tool for constraining the up‐dip propagation history of basement faults in extensional fault‐related fold systems with intermediate décollement levels.  相似文献   

16.
Tectonic subsidence in rift basins is often characterised by an initial period of slow subsidence (‘rift initiation’) followed by a period of more rapid subsidence (‘rift climax’). Previous work shows that the transition from rift initiation to rift climax can be explained by interactions between the stress fields of growing faults. Despite the prevalence of evaporites throughout the geological record, and the likelihood that the presence of a regionally extensive evaporite layer will introduce an important, sub‐horizontal rheological heterogeneity into the upper crust, there have been few studies that document the impact of salt on the localisation of extensional strain in rift basins. Here, we use well‐calibrated three‐dimensional seismic reflection data to constrain the distribution and timing of fault activity during Early Jurassic–Earliest Cretaceous rifting in the Åsgard area, Halten Terrace, offshore Mid‐Norway. Permo‐Triassic basement rocks are overlain by a thick sequence of interbedded halite, anhydrite and mudstone. Our results show that rift initiation during the Early Jurassic was characterised by distributed deformation along blind faults within the basement, and by localised deformation along the major Smørbukk and Trestakk faults within the cover. Rift climax and the end of rifting showed continued deformation along the Smørbukk and Trestakk faults, together with initiation of new extensional faults oblique to the main basement trends. We propose that these new faults developed in response to salt movement and/or gravity sliding on the evaporite layer above the tilted basement fault blocks. Rapid strain localisation within the post‐salt cover sequence at the onset of rifting is consistent with previous experimental studies that show strain localisation is favoured by the presence of a weak viscous substrate beneath a brittle overburden.  相似文献   

17.
The Southern Tail‐End Graben, Danish Central Graben, is characterized by a lateral variation in the thickness and mobility of pre‐rift Zechstein Supergroup evaporites, allowing investigation of how supra‐basement evaporite variability influences rift structural style and tectono‐stratigraphy. The study area is divided into two structural domains based on interpretations of the depositional thickness and mobility of the Zechstein Supergroup. Within each domain, we examine the overall basin morphology and the structural styles in the pre‐Zechstein and supra‐Zechstein (cover) units. Furthermore, integration of two‐way travel‐time (TWT)‐structure and ‐thickness maps allows fault activity and evaporite migration maps to be generated for pre‐ and syn‐rift stratal units within the two domains, permitting constraints to be placed on: (i) the timing of activity on pre‐Zechstein and cover faults and (ii) the onset, duration and migration direction of mobile evaporites. The northern domain is interpreted to be free from evaporite‐influence, and has developed in a manner typical of brittle‐only, basement‐involved rifts. Syn‐rift basins display classical half‐graben geometries bounded by thick‐skinned faults. In contrast, the southern domain is interpreted to be evaporite‐influenced, and cover structure reflects a southward increase in the thickness and mobility of the Zechstein Supergroup evaporites. Fault‐related and evaporite‐related folding is prominent in the southern domain, together with variable degrees of decoupling of sub‐Zechstein and cover fault and fold systems. The addition of mobile evaporites to the rift results in: (i) complex and spatially variable modes of tectono‐stratigraphic evolution; (ii) syn‐rift stratal geometries which are condensed above evaporite swells and over‐thickened in areas of withdrawal; (iii) compartmentalized syn‐rift depocentres; and (iv) masking of rift‐related megasequence boundaries. Through demonstrating these deviations from the characteristics of rifts free from evaporite influence, we highlight the first order control evaporites may exert upon rift structural style and the distribution and thicknesses of syn‐rift units.  相似文献   

18.
《Basin Research》2018,30(Z1):479-496
Analysis of current temperature data in the Canadian Arctic Archipelago results in the recognition of two major thermal regimes. High temperature regions are observed where salt diapirs and salt cored anticlines are present. Low temperature fields are observed along the western and southern basin margins and around Cornwall‐Amund Ringnes islands, where regional Mesozoic aquifers are exposed to surface, connected to basin boundary faults, or regional unconformities. Meteoric and Holocene sub‐glacial water recharge are inferred to be responsible for the low geothermal regime and low formation water salinity. Neither exhumation associated with the Eocene “Eurekan” orogeny nor volcanic intrusion associated with opening of Amerasia Basin in late Jurassic‐early Cretaceous have been interpreted to be a significant influence on the present day temperature field, although thermal indicators show evidence of elevated thermal alteration of organic matter pointing to earlier, but now dissipated, thermal anomalies.  相似文献   

19.
However salt has a viscous rheology, overburden rocks adjacent to salt diapirs have a brittle rheology. Evidence of deformation within the overburden has been described from diapirs worldwide. Gravity‐driven deposits are also present along the flanks of several diapirs. The well‐known example from the La Popa Basin in northern Mexico shows that such deposits may be organized into halokinetic sequences. This leads to several questions: (i) How does diapir growth contribute to overburden deformation? (ii) Are halokinetic sequence models valid for other areas beyond the La Popa Basin. The Bakio diapir and its well‐exposed overburden in Basque Country, Spain provides key elements to address these questions. The Bakio diapir consists of Triassic red clays and gypsum and is flanked by synkinematic middle to upper Albian units that thin towards the diapir. The elongate diapir parallels the Gaztelugatxe normal fault to the NE: both strike NE–SW and probably formed together during the middle Albian, as synkinematic units onlap the fault scarp. The diapir is interpreted as a reactive diapir in response to middle Albian motion on the Gaztelugatxe fault. The rate of salt rise is estimated to be about 500 m Myr?1 during this passive stage. During Late Albian, the diapir evolved passively as the Gaztelugatxe fault became inactive. Synkinematic units thinning towards the diapir, major unconformities, slumps and other gravity‐driven deposits demonstrate that most deformation related to diapir growth occurred at the sea floor. Halokinetic sequences composed of alternating breccias and fine‐grained turbidites recorded cyclic episodes of diapir flank destabilization. This work provides insights into drape fold and halokinetic sequence models and offers a new simple method for estimating rates of diapir growth. This method may be useful for outcrop studies where biostratigraphical data are available and for other passive diapirs worldwide.  相似文献   

20.
“Salt” giants are typically halite‐dominated, although they invariably contain other evaporite (e.g. anhydrite, bittern salts) and non‐evaporite (e.g. carbonate, clastic) rocks. Rheological differences between these rocks mean they impact or respond to rift‐related, upper crustal deformation in different ways. Our understanding of basin‐scale lithology variations in ancient salt giants, what controls this and how this impacts later rift‐related deformation, is poor, principally due to a lack of subsurface datasets of sufficiently regional extent. Here we use 2D seismic reflection and borehole data from offshore Norway to map compositional variations within the Zechstein Supergroup (ZSG) (Lopingian), relating this to the structural styles developed during Middle Jurassic‐to‐Early Cretaceous rifting. Based on the proportion of halite, we identify and map four intrasalt depositional zones (sensu Clark et al., Journal of the Geological Society, 1998, 155, 663) offshore Norway. We show that, at the basin margins, the ZSG is carbonate‐dominated, whereas towards the basin centre, it becomes increasingly halite‐dominated, a trend observed in the UK sector of the North Sea Basin and in other ancient salt giants. However, we also document abrupt, large magnitude compositional and thickness variations adjacent to large, intra‐basin normal faults; for example, thin, carbonate‐dominated successions occur on fault‐bounded footwall highs, whereas thick, halite‐dominated successions occur only a few kilometres away in adjacent depocentres. It is presently unclear if this variability reflects variations in syn‐depositional relief related to flooding of an underfilled presalt (Early Permian) rift or syn‐depositional (Lopingian) rift‐related faulting. Irrespective of the underlying controls, variations in salt composition and thickness influenced the Middle Jurassic‐to‐Early Cretaceous rift structural style, with diapirism characterising hangingwall basins where autochthonous salt was thick and halite‐rich and salt‐detached normal faulting occurring on the basin margins and on intra‐basin structural highs where the salt was too thin and/or halite‐poor to undergo diapirism. This variability is currently not captured by existing tectono‐stratigraphic models largely based on observations from salt‐free rifts and, we argue, mapping of suprasalt structural styles may provide insights into salt composition and thickness in areas where boreholes are lacking or seismic imaging is poor.  相似文献   

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