Extensional development and contractional reactivation of salt walls: examples from the southeastern Paradox Basin (SW Colorado) and the Eastern Prebetic Zone (SE Spain)
[eng] This thesis uses a field-based approach complemented with geophysical and well data to investigate the controlling factors on the geometry and kinematics of salt walls developed above extensional faults whose movement occurs during or after the deposition of salt; and the behavior of these pre...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2019 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/149348 |
| Acceso en línea: | https://hdl.handle.net/2445/149348 http://hdl.handle.net/10803/668455 |
| Access Level: | acceso abierto |
| Palabra clave: | Falles (Geologia) Estratigrafia Jumella (Múrcia) Faults (Geology) Stratigraphy Colorado Utah Jumilla (Murcia) |
| Sumario: | [eng] This thesis uses a field-based approach complemented with geophysical and well data to investigate the controlling factors on the geometry and kinematics of salt walls developed above extensional faults whose movement occurs during or after the deposition of salt; and the behavior of these precursor diapiric structures when are involved in a subsequent thin-skinned contractional deformation. This is an investigation that has been carried out by defining the geometric and temporal relationships between the structure of the salt walls and their adjacent strata in two distinct field-work areas: the southeastern Paradox Basin (SW Colorado) and the Eastern Prebetic Zone at the Jumilla region (SE Spain). At the SE Paradox Basin, the analyzed salt wall is the Gypsum Valley Diapir, which was mostly driven by differential sedimentary loading and developed above a pre-existing subsalt fault without significant regional extension or contraction. The early style of diapirism was that of single-flap active NW-trending salt wall, with a thinned roof bounded by a suprasalt counterregional fault over its northeastern edge. Erosion of the thinned diapiric roof triggered the salt breakthrough and the onset of passive diapirism. Subsequent evacuation of deep salt into the growing diapir generated diapir-flanking depocenters with progressive rotation of the southwestern flank into the megaflap geometry and consequent widening of the diapir. Therefore, the present-day structure of the salt wall is characterized by a highly asymmetric stratal architecture on its northeastern and southwestern flanks, with thicker, deeper, gently dipping strata in the depositionally proximal (NE) minibasin and thinned older strata rotated to near-vertical in a megaflap on the distal (SW) side. The megaflap terminates to the SE through a progressive decrease of the bedding dip and ultimately truncation by a pair of radial faults bounding a down-dropped block with lower dips. East of these faults, the salt wall termination is a moderately plunging nose of salt overlain by a gently southeast-dipping strata separated from the down-dropped NE minibasin by a counterregional fault. At the Jumilla region instead, the studied salt walls and salt-related structures correspond to diapirs, made up of pre-kinematic salt, triggered by thick-skinned extension during the development of a passive margin (i.e. the Mesozoic Iberian margin of the Maghrebian Tethys), which was later incorporated into the external part of the eastern Betic foreland fold-and- thrust belt. In this scenario, the initial extension led to a major decoupling of the deformation with planar subsalt extensional faults overlain by monoclinal drape folds and suprasalt faults and extensionally triggered diapirs (salt walls). After extension, this inherited sub- and suprasalt structure together with the formed diapirs controlled the subsequent contractional deformation 3 in such a way that: 1) determined a stepped geometry for the salt and therefore for the future décollement level where the thin-skinned contractional deformation is propagated; and 2) allowed the development of a series of fault-bend folds where the salt walls and salt-related structures concentrated the major part of the thin-skinned contractional deformation. This deformation was resolved first by narrowing and squeezing of the preexisting salt structures (i.e. cryptic shortening) and then, when secondary welds were developed, by the formation of thrust faults at their pedestals. The results of these investigations have permitted to propose a series of simple end- member models addressing the extensional formation and later contractional reactivation of the studied salt walls developed above a thick-skinned extended basement. These simple models together with the discussion conducted in this thesis suggest that the geometry and kinematics of salt walls triggered by thick-skinned extension are strongly controlled by: 1) the geometry of the subsalt faults; 2) the spatial and temporal thickness variations of the overburden; 3) the salt thickness variations and the available deep salt budged to flow into the forming salt walls; 4) the lateral changes in the syn-kinematic sedimentary loading induced by the subsalt fault motion; and, 5) the position of the salt breakthrough and the pre-kinematic salt wall piercement geometry. And, in relation to a later thin-skinned contractional reactivation of these salt walls, this investigation points out that the resulting structure is largely determined by: 1) the subsalt structure defined by the dip, dip direction and the displacement magnitude of the subsalt faults; 2) the thickness/strength and 3) the structure of the pre-contractional overburden adjacent to the contractionally reactivated salt wall; 4) the ratio between amount of shortening and the initial width of the diapir; and finally, 5) other factors like the length, shape and orientation of the precursor salt wall, the possible linkage between adjacent diapiric structures and the lithological composition of the evaporitic sequence |
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