Salt Tectonics

This study focusses on aspects related to carbonate build-ups in an upper Paleozoic succession in the south central Norwegian Barents Sea. Seismic and well data are used to map and characterize the protozoan and heterozoan carbonate build-ups in order to assess the factors that control their distribution within the Gipsdalen- and Bjarmeland Groups. The main objectives are (1) to describe, compare, and contrast geomorphological characteristics of the carbonate succession on the Bjarmeland and Finnmark Platforms, (2) to determine the controlling factors on the distribution of the carbonate build-up development, and lastly (3) examine the impact of evaporites on the distribution and development of the carbonate build-ups.

The upper section of the Gipsdalen Group consists of protozoan carbonates and evaporites with occasional carbonate build-ups that were deposited in an arid-warm marine environment in a global icehouse period. The Bjarmeland Group consists of heterozoan carbonates with build-ups deposited in post-glacial environment. Previous studies have suggested that faults play a role in the distribution of carbonate build-ups in the Norwegian Barents Sea.

The two areas on the Finnmark Platform (north and south) have been used in order to compare against two areas on Bjarmeland Platform (east and west). The carbonate build-up sequence observed on the eastern Bjarmeland Platform is comparable with the build-up sequence on the northern Finnmark Platform. The two areas share similarities as both are located on footwall uplifts. The geomorphology of these carbonate units are characterized as large build-up complexes. In contrast, the geomorphology of the western Bjarmeland Platform and the southern Finnmark Platform differs significantly. These units consist of polygonal build-up morphologies of reticulated arrangement with cellular structures of various scales; this depositional pattern is similar in architecture to modern patch and pinnacle reef systems observed in Holocene carbonate systems (e.g. Abrolhos Islands in Western Australia). The similarities defining these elements are that carbonate build-ups stack vertically above the layered evaporite sequence of the Gipsdalen Group. The layered evaporite sequences are observed on both platforms where salt pillows are a main characteristic. The carbonate build-ups deposit vertically above thin units of evaporites, opposed to laterally absent where the salt pillows are present, suggesting that salt has been displaced by the weight of the growing build-up. The result supports antecedent topography as a dominant component affecting the carbonate build-up succession in the eastern Bjarmeland Platform and the northern Finnmark Platform. Furthermore, the build-up development in the two areas on western Bjarmeland Platform, and southern Finnmark Platform, has been controlled by physical conditions influenced by a combination of biotic self-organization, fossil reef growth and karst-induced structures caused by dissolution of the underlying carbonate strata. The current geomorphology of the carbonate build-up succession has been enhanced due to remobilization of the mobile evaporite unit as a result of differential loading by the carbonate build-ups.

In the United Kingdom Permian and Triassic halite (rock salt) deposits have been affected by natural and artificial dissolution producing karstic landforms and subsidence. Brine springs from the Triassic salt have been exploited since Roman times, or possibly earlier, indicating prolonged natural dissolution. Medieval salt extraction in England is indicated by the of place names ending in “wich” indicating brine spring exploitation at Northwich, Middlewich, Nantwich and Droitwich. Later, Victorian brine extraction in these areas accentuated salt karst development causing severe subsidence problems that remain a legacy. The salt was also mined, but the mines flooded and consequent brine extraction caused the workings to collapse, resulting in catastrophic surface subsidence. Legislation was enacted to pay for the damage and a levy is still charged for salt extraction. Some salt mines are still collapsing and the re-establishment of the post-brine extraction hydrogeological regimes means that salt springs may again flow causing further dissolution and potential collapse.

The Cabo Frio region, offshore Rio de Janeiro, lies between two of the most prolific Brazilian oil provinces,
the Campos and Santos basins. Major geologic features have been identified using a multidisciplinary approach
integrating seismic, gravity, petrographic, and borehole data. The Cabo Frio frontier region is characterized by
marked changes in stratigraphy and structural style and is unique among the Brazilian marginal basins. Major
geologic features include the deflection of the coastline and pre-Aptian hinge line from northeast to east; a large
east-striking offshore graben related to salt tectonics; a northwest-trending lineament extending from oceanic
crust to the continent; basement-involved landward-dipping (antithetic) normal faults in shallow water; a stable
platform in the southern Campos Basin; a thick sequence of postbreakup intrusive and extrusive rocks; and,
near the Santos Basin, a mobilized sequence of deep-water postrift strata affected by landward-dipping listric
normal faults. These faults are unusual in salt-related passive margins in that they dip landward, apparently
detach on the Aptian salt, and show large late Tertiary offsets. Locally, the older sequences do not show substantial
growth in the downthrown blocks.
South of the Rio de Janeiro coast, a phenomenal landward-dipping fault system detaches blocks of the Albian
platform to the north and, to the south, coincides with the depositional limit of the Albian platform. This deepwater
fault system controls features that can be mapped for hundreds of kilometers along strike and forms an
Albian stratigraphic gap tens of kilometers wide.
Two end-member processes of salt tectonics in the Cabo Frio region result in either synthetic or antithetic
basal shear along the fault weld under the overburden: (1) thin-skinned processes, in which the listric faults were
caused by salt flow in response to gravity forces related to massive clastic progradation from the continent; and
(2) thick-skinned processes, in which faulting was indirectly triggered by diastrophic causes or disequilibrium
in the basement topography. The structural styles in the Cabo Frio region are compared with analogs from other
basins and with sandbox models.

Mount Sedom is the surface expression of a salt diapir that has emerged since the Pleistocene in the southwestern part of the Dead Sea basin. Milestones in the uplift history of the Sedom salt diapir since its inception were deduced from angular and erosional unconformities, thickness variations, caprock formation, chemistry and isotope composition of lacustrine aragonite, cave morphology, precise leveling, and satellite geodesy. Thickness variations of the overburden observed in transverse seismic lines suggest that signifi cant growth of the Sedom diapir may have initiated only after this thickness exceeded ~2400 m in the Late Pliocene. The formation of the caprock signifi es the arrival of the Sedom diapir from depth to the dissolution level between 300,000-100,000 yr B.P. During this period and later, angular and erosional unconformities in the upper part of the overburden near Mount Sedom are attributed to the piercing diapir. Rapid solution of rock salt from parts of Mount Sedom inundated by Lake Lisan after ca. 40,000 yr B.P. is inferred from Na/Ca ratios in aragonite and their relation to δ13C. On the mountain itself, the older parts (70,000–43,000 yr B.P.) of the lacustrine Lisan Formation are missing. The top of the preserved sediments is covered by alluvial sediments that must have been deposited when the elevation of Mount Sedom was not higher than 265 m below sea level (mbsl) at ca. 14,000 yr B.P. The present elevation of these sediments at 190 mbsl indicates an average uplift rate of ~5 mm/yr over the past 14,000 yr. Similar uplift rates of 6–9 mm/yr are inferred for the Holocene from displacement of the “salt mirror” and hanging passages of caves. The present uplift rate, calculated from precise leveling and interferometric synthetic aperture radar (InSAR), is similar to the average Holocene rate. Based on the gathered data, we reconstruct the topographic rise of Sedom diapir and its relation to lake level variations during the late Pleistocene and Holocene.

In this study we investigate the Late Cretaceous to recent tectonic evolution of the southwestern Baltic Sea based on a dense grid of seismic reflection profiles. This area covers the Baltic Sea sector of the salt influenced North German Basin and its transition to the salt free Baltic Shield across the Tornquist Zone. The Upper Cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high-resolution time-structure maps of the main horizons, i.e., the Upper Cretaceous, Tertiary and Pleistocene. The Upper Creta-ceous and Tertiary layers reveal numerous significant faults throughout the study area. Several of these faults propagate upwards across the unconsolidated Pleistocene sediments and occasionally penetrate the surface. The salt influenced North German Basin reveals three major fault trends: NW-SE, N-S and NNE-SSW. Several of these faults are located directly above basement (sub-salt) faults and salt pillows. The majority of these faults are trending N-S to NNE-SSW and parallel the direction of the Glückstadt Graben faults. In the salt free Tornquist Zone, we identify two major shallow fault trends, which are NW-SE and NE-SW. The majority of these faults are located above basement faults, following the direction of the Tornquist Zone. We conclude that generally basement tectonics controls activation and trends of shallow faults. If salt is present, the ductile salt layer causes a lateral shift between the sub-and supra-salt faults. Major plate reorganisation related to the Africa-Iberia-Europe convergence and the subsequent Alpine Orogeny caused reactivation of pre-existing faults and vertical salt movement in the Late Cretaceous. The change of stress orientation from NE-SW to a NW-SE during Neogene caused another phase of fault and salt tectonic reactivation. We explain that the ice-sheet loading and/or present day stress field may have acted in combination, causing the recent tectonics and upward extension of the faults.

In the outermost region of the southeastern Pyrenees, a suite of thrusted folds detach above an upper Eocene salt that was about 300 m thick before deformation. The foremost anticlines formed during the Oligocene and represent a small amount of shortening. In map view; they display a relay pattern slightly oblique to the margin of the salt layer, where deformation stops. The three-dimensional edge effects caused by the pinch-out of the Cardona salt play an important role in the development of the frontal structures in the southeastern Pyrenees. Fold evolution has been reconstructed by interpreting variations along the strike of the folds as an indicator of deformation sequence. Where the sedimentary pile contains an upper detachment, thrusts developed fishtail geometries in which thrusts of alternating vergence were stacked up. Where an upper detachment is lacking, a thrusted anticline formed, into whose core salt migrated during the early phases of folding. Whether or not an upper ...

Jörg Lang (1), Muayyad Al Hseinat (2), Christian Brandes (1), Andrea Hampel (1), Christian Hübscher (2), and Jutta Winsemann (1)

(1) Leibniz Universität Hannover, Institut für Geologie, Hannover, Germany (lang@geowi.uni-hannover.de), (2) Universität Hamburg, Institut für Geophysik, Hamburg, Germany

A correlation between salt structures, glacigenic features and faulting of Pleistocene deposits above salt structures has been recognized in many places of the formerly glaciated areas in northern central Europe and attributed to ice-sheet loading. Conceptual models predict that the load applied by an ice sheet will favour ice-marginal salt rise and obstruct salt rise beneath the ice sheet (e.g., Liszkowski, 1993). To test these models, we simulated the response of salt structures to ice-sheet loading using a 2D finite-element model (ABAQUS). The subsurface geometries used in our models are based on regional geological cross-sections and 2D seismic profiles of salt structures in the Central European Basin System. The model layers represent (i) sedimentary rocks of elastoplastic rheology, (ii) a viscoelastic salt structure and (iii) elastoplastic basement rocks. At the model surface a temporarily and spatially variable pressure simulates ice-sheet loading. All our simulations show a response of salt structures to ice-sheet loading, which strongly depends on the location of the ice margin relative to the salt structure. Salt structures rise in front of the ice margin (up to 4 m), if load is applied to the salt source layer. Beneath an ice sheet salt structures are pushed down (up to 36 m). Much of the subglacial downwards displacement is compensated by a reversal of the movement during ice retreat. The resulting surface displacements are therefore rather low and depend on the spatial and temporal configuration of the ice load (Lang et al., 2014). Permanent deformation is restricted to the model layers above the salt structure, which either have a low yield stress to represent the unconsolidated infill of secondary rim-synclines or are dissected by steeply dipping crestal graben faults. Ice-induced salt movements will reactivate faults above the crests of salt structures, although the resulting displacements will be low due to the repeated reversals of the sense of movement. The surface displacement due to ice-load induced salt movement will impact the pattern of glacigenic deformation, erosion and deposition. Ice-marginal uplift will provide favourable conditions for push-moraine formation, while subglacial subsidence of salt structures will enhance erosion and contribute to tunnel-valley incision.


References
Lang, J., Hampel, A., Brandes, C., Winsemann, J. (2014) Response of salt structures to ice-sheet loading: implications for ice-marginal and subglacial processes. Quaternary Science Reviews 101, 217-233.
Liszkowski, J. (1993) The effects of Pleistocene ice-sheet loading-deloading cycles on the bedrock structure of Poland. Folia Quaternaria 64, 7-23.

Two-dimensional thermal-mechanical models of thick-skinned, salt-based fold and thrust belts, such as the Zagros, SW Iran, are used to address: 1) the degree of deformation and decoupling between cover and basement rocks due to the presence of a weak salt detachment; 2) the reactivation potential of pre-existing basement normal faults due to brittle or ductile behavior of the lower crust (as related to cold or hot geothermal gradients); and 3) variations in deformation style and strain distribution. The geometry and kinematics of the orogenic wedge and the activity of pre-existing basement faults are strongly influenced by the geothermal gradient (defined by the Moho temperature, MT) and basement rheology. We infer that the MT plays a major role in how the lower and upper crust transfer deformation towards the foreland. In relatively hot geotherm models (MT = 600°C at 36 km depth), the lowermost basement deforms in a ductile fashion while the uppermost basement underlying the sedimentary cover deforms by folding, thrusting, and displacements along pre-existing basement faults. In these models, cover units above the salt detachment occur within a less deformed, wide plateau in the hinterland. In relatively cold geotherm models (MT = 400°C at 36 km depth), deformation is mainly restricted to basement imbricate thrusts that form within the orogenic hinterland. Detachment folding, thrusting and gravity gliding occur within cover sediments above uplifted basement blocks. Gravity gliding contributes to a larger amount of shortening in the cover compared to the basement.

Parts of two third-order Neoproterozoic (Marinoan) depositional sequences are documented in the Wilpena Group (Wonoka Formation and Bonney Sandstone) at Patawarta diapir, located in the central Flinders Ranges, South Australia. These sequences represent an overall regressive succession transitioning upwards from outer to middle wave-dominated shelf deposits to a tidally dominated barrier bar to coastal plain. The lower, middle, upper limestone and green mudstone informal members of the Wonoka Formation comprise the Highstand Systems Tract of the lower sequence. The Sequence Boundary is at the top of the Wonoka green mudstone member and is overlain by the Lowstand Systems Tract of the upper sequence, which includes the lower dolomite, sandstone and upper dolomite beds of the Patsy Hill Member of the Bonney Sandstone. The upper sequence Transgressive Systems Tract comprises the Bonney Sandstone. These units comprise one complete tapered composite halokinetic sequence (CHS). The lower halokinetic-sequence boundary is associated with the Maximum Flooding Surface of the lower depositional sequence and the upper halokinetic-sequence boundary is interpreted as the Transgressive Surface of the overlying depositional sequence where an angular truncation of up to 908 is documented.

Durante sua evolução, a margem brasileira foi cenário de inúmeros eventos de fluxos gravitacionais turbulentos, os quais geraram os mais importantes reservatórios petrolíferos em produção no Brasil na atualidade. Os diferentes cenários deposicionais desenvolvidos nos últimos milhões de anos na Bacia do Espírito Santo demonstram um imenso potencial para aplicação de modernas técnicas de reconhecimento de análogos de reservatórios (Hercos & Schreiner, 2007).  A crescente melhoria das ferramentas e técnicas geofísicas vem possibilitando significativos avanços na caracterização de sistemas turbidíticos, principalmente em relação às geometrias deposicionais, às dimensões dos corpos rochosos e seu empilhamento estratigráfico.  A partir de dados de sísmica de reflexão de uma região da referida bacia, diversas imagens foram compostas demonstrando a evolução de sistemas turbidíticos desenvolvidos entre o Mioceno Superior e o Holoceno. Os principais estilos arquiteturais (apud Moraes et al., 2006) reconhecidos para estes sistemas foram: a: complexos de canais sinuosos; b: complexos de canais amalgamados; c: complexos de canais discretos e d: complexos de canais distributários e lobos. Estes estilos arquiteturais são recorrentes no tempo geológico e seu desenvolvimento está estritamente relacionado com a variação relativa do nível do mar nos últimos 10 M.a. Deste modo, foi possível reconhecer quatro distintos estágios deposicionais: Estágio 1: desenvolvimento de complexos de canais sinuosos conectados a vales incisos; Estágio 2: desenvolvimento de complexos de canais amalgamados e complexos de canais discretos; Estágio 3: desenvolvimento de complexos de canais distributários e lobos conectados a ravinas; Estágio 4: desenvolvimento de complexo de canais discretos intercalados com sedimentação hemiplégica. Concomitante à sedimentação, ocorreram processos halocinéticos que influenciaram nos padrões deposicionais de todos os sistemas, principalmente em relação ao desenvolvimento e migração dos canais.

We present and discuss a set of data, mainly swath bathymetry, backscatter images and a few seismic data, that have been recently recorded over large areas of the Nile deep-sea fan between water depths of 1200 and 3000 m. These data demonstrate the presence of at least three distinct morphostructural provinces where interacting sedimentary, tectonic, and salt tectonic processes control the present day morphology and the recent evolution of the major Mediterranean deep-sea fan. The role of the ongoing collision presently occurring between the continental Eratosthenes Seamount and the Cyprus Arc may have been, and still is, a determining parameter for the development of the Nile deep-sea fan.

In this study we investigate faulting above a salt wall in the Glückstadt Graben / North German Basin. Two supra-salt faults are mapped from coast to coast over a distance of 6–9 km based on offshore and onshore seismic data. These faults form a ca. 2 km wide crestal collapse graben and pierce the seafloor. Salt wall evolution started in the early Late Triassic to Early Jurassic due to regional extension and resulting sub-salt faulting. The salt wall was eroded following exposure to costal and sub-aerial erosion by the regional Mid-Late Jurassic to Early Cretaceous uplift. Late Cretaceous to Early Paleogene compressional tectonics reactivated the vertical salt movement and shortened the salt wall, creating a salt-cored anticline with the crestal collapse graben above. The supra-salt faults were reactivated between the Late Eocene and Middle Miocene when the principal horizontal stress orientation changed from a NE-SW to a NW-SE, the present-day orientation. Stratigraphic data indicate that these faults moved mainly in the Cenozoic. Several observations strongly suggest that the faults continued developing during the Pleistocene until today: (i) the Pleistocene Unconformity is concave upwards and cut by faults; (ii) growth strata within the marine Holocene deposits above the graben imply recent tectonic movements; (iii) onshore high-resolution P-wave vibroseis data of the south-eastern Eckernförde Bay suggest about 10 m of faulted Holocene strata; and (iv) marine seismic data show the faults piercing the seafloor. We suggest that the recent salt tectonics and upward propagation of supra-salt faults resulted from differential ice-sheet loading. That effect on the salt wall stopped once ice grew over the whole structure, at which time the wall subsided because of ice loading. The salt wall and faults were reactivated again once the ice front retreated so that the ice loaded only one side of the structure.

Abstract In this study we investigate the Late Cretaceous to recent tectonic evolution of the southwestern Baltic Sea based on a dense grid of seismic reflection profiles. This area covers the Baltic Sea sector of the salt influenced North German Basin and its transition to the salt free Baltic Shield across the Tornquist Zone. The Upper Cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high-resolution time-structure maps of the main horizons, i.e., the Upper Cretaceous, Tertiary and Pleistocene. The Upper Cretaceous and Tertiary layers reveal numerous significant faults throughout the study area. Several of these faults propagate upwards across the unconsolidated Pleistocene sediments and occasionally penetrate the surface. The salt influenced North German Basin reveals three major fault trends: NW-SE, N-S and NNE-SSW. Several of these faults are located directly above basement (sub-salt) faults and salt pillows. The majority of these faults are trending N-S to NNE-SSW and parallel the direction of the Gluckstadt Graben faults. In the salt free Tornquist Zone, we identify two major shallow fault trends, which are NW-SE and NE-SW. The majority of these faults are located above basement faults, following the direction of the Tornquist Zone. We conclude that generally basement tectonics controls activation and trends of shallow faults. If salt is present, the ductile salt layer causes a lateral shift between the sub- and supra-salt faults. Major plate reorganisation related to the Africa-Iberia-Europe convergence and the subsequent Alpine Orogeny caused reactivation of pre-existing faults and vertical salt movement in the Late Cretaceous. The change of stress orientation from NE-SW to a NW-SE during Neogene caused another phase of fault and salt tectonic reactivation. We explain that the ice-sheet loading and/or present-day stress field may have acted in combination, causing the recent tectonics and upward extension of the faults.

ABSTRACT
Shortened salt-withdrawal minibasins and associated salt welds are exposed in the Mesozoic strata of the Northern Calcareous Alps fold-and-thrust belt (Austria). Geological mapping and sequential restoration of a balanced cross section have indicated that these salt and salt-related structures developed during the postrift stage of the
Neo-Tethys continental margin by evacuation and inflation/deflation of uppermost Permian to lowermost Triassic salt. Middle to Late Triassic minibasins were formed by down-building and downslope translation, flanked by megaflaps and salt walls. Salt and salt structures were rejuvenated by salt-wall fall and formation of bowl mini-
basins as a response to Penninic rifting since Rhaetian times. Complex structural styles, including younger-on-older contacts, tight folds, and kilometer-scale fully overturned panels resulted from the shortening of early salt structures upon the onset of Jurassic regional convergence. Salt tectonics can reconcile the stratigraphic development and internal structure of the long-debated Northern Calcareous Alps. Our work also provides a new line of research for understanding other fold-and-thrust belts developed from the Neo-Tethys continental margin (i.e., the Carpathian Mountains, the Southern Alps in Europe, the Dinaric Alps) and sets guidelines for other salt-influenced fold belts.