Miocene Phase Research Articles

Fault leakage and reservoir charging in the Upper Rhine Graben, Germany – Assessment of the Leopoldshafen fault bend

Faults control subsurface fluid flow in sedimentary basins worldwide, often affecting hydrocarbon migration as well as geothermal fluid circulation. Since the Upper Rhine Graben hosts geothermal, lithium brine, and hydrocarbon resources, the role of faults on fluid flow in the basin is of great interest. To better understand structurally controlled fluid flow in the central Upper Rhine Graben, this study investigates the hydrocarbon migration of the fault-related Leopoldshafen oil field. As fault geometry can change along-strike, fault conductivity might also vary spatially as it depends on, among others, the fault orientation relative to the active stress field. Therefore, slip and dilation tendencies are used as proxies for stress-controlled fault conductivity, computed for a strike-slip faulting regime with NW to NNW oriented σHmax. Fault Response Modelling is applied to derive subsurface strain distributions, associated with fault activity during the Miocene phase of basin development. The Leopoldshafen fault, as a fundamental element of the fault-related three-way dip closure trap structure, is characterized by a changing along-strike geometry with NNE-SSW trending fault segments linked by a NNW-SSE trending left-stepping fault bend. Slip and dilation tendencies are highest around the fault bend segment, with a range of considered σHmax orientations. As Expansion Index analysis indicates across-fault thickening and thus fault activity of the Leopoldshafen fault during the main phase of graben rifting (Late Eocene to Oligocene), subsurface strain distribution pattern associated with Miocene fault activity highlight strain concentrations around the fault bend segment, which has acted as a releasing bend. Thus, based on slip and dilation tendency analyses, as well as Fault Response Modelling, the fault bend segment is identified as the up-fault fluid migration zone along the Leopoldshafen fault. This underscores the importance of comprehending the structural inventory of the Upper Rhine Graben for the prospect of future subsurface exploration and alternative post-oil utilization.

The Rossano–San Nicola Fault Zone evolution impacts the burial and maturation histories of the Crotone Basin, Calabrian Arc, Italy

This work addresses the tectonic significance of a NW–SE-trending strike-slip fault zone in the Calabrian Arc of southern Italy, the Rossano–San Nicola Fault Zone (RSFZ). High-quality seismic reflection and 1D forward models of exploration boreholes and pseudo-wells show that the RSFZ experienced multiple Miocene phases of contractional/transpressional tectonics. These were followed by crustal extension during the Pliocene, which occurred in association with the oceanization of the Tyrrhenian Sea, Apennine orogenesis, and collision between the Calabrian Arc and adjacent tectonic plates. Such a setting had a profound influence on the Crotone Basin and its economic potential: (1) tectonic reactivation allowed reservoir units of the Crotone Basin to be charged by gas derived from Triassic/Lower Jurassic source rocks; and (2) source rocks reached their maximum depth and remained in the gas generation window after the emplacement of a large mass-transport complex in the Pliocene. In the surrounding areas, tectonic activity near the RSFZ contributed to source-rock maturation by enhancing local sedimentation rates, particularly during Langhian (Middle Miocene) and Zanclean (early Pliocene) tectonics. This work is important as it demonstrates that the tectonostratigraphic evolution of the Crotone Basin was closely related to the structural evolution of the RSFZ. Crucially, the study area reveals the first example of a gas field fully sealed by a large mass-transport complex. As a corollary, we tie the Late Cenozoic geological history of the Crotone Basin to the geodynamic evolution of the central Mediterranean region, namely the Ionian and Tyrrhenian seas. We identify new prospects in the Crotone Basin, and provide a time frame for gas generation and accumulation in southern Italy.

Red Sea rifting in central Egypt: constraints from the offshore Quseir province

The formation of oceanic crust in the southern and central Red Sea is generally accepted to have started at c. 5 Ma. However, the nature of the crust in the northern Red Sea is still debated. This paper describes the rift architecture, dynamics and evolution of the northern Red Sea and identifies domains that relate to first-order geodynamic processes. The proximal margin domain is located onshore and is characterized by latest Oligocene–Miocene half-graben basins. New seismic interpretations show that the offshore region is a necking domain dominated by low-angle, high-offset extensional faults, which led to the exhumation of lower crustal gabbros at Brothers Islands. Two-dimensional forward models suggest that the necking domain passes into a distal margin domain, where the continental crust thins to <10 km at 120 km from the coast. Sensitivity testing of interpretations for the distal domain indicates a probable scenario where exhumed lower continental crust or serpentinized mantle is present. A comprehensive rift model for the northern Red Sea in the Quseir province accounts for magmatic underplating accompanied by half-graben development at c. 25 Ma, followed by Early Miocene crustal thinning accommodated by an east-dipping detachment fault. A Late Miocene phase with a flip of the detachment geometry led to the present day configuration.

Growth of the southern Tian Shan-Pamir and its impact on central Asian climate

Uplift and amalgamation of the high-elevation (>3000 m) Tian Shan and Pamir ranges in Central Asia restricts westerly atmospheric flow and thereby limits moisture delivery to the leeward Taklimakan Desert in the Tarim Basin (<1500 m), the second largest modern sand dune desert on Earth. Although some research suggests that the hyper-arid conditions observed today in the Tarim Basin developed by ca. 25 Ma, stratigraphic evidence suggests the first erg system did not appear until 12.2 Ma. To address this controversy and to understand the tectonic influences on climate in Central Asia, we studied a continuous, 3800-m-thick stratigraphic section deposited from 15.1 to 0.9 Ma now exposed within the western Kepintagh fold-and-thrust belt in the southern Tian Shan foreland. We present new detrital zircon data (n = 839), new carbonate oxygen (δ18Oc) and carbon (δ13Cc) stable isotope compositions (n = 368), structural modeling, and stratigraphic observations, and combine these data with recently published magnetostratigraphy and regional studies to reconstruct the history of deposition, deformation, and climate change in the northwestern Tarim Basin. We find that basins along the southern (this study) and northern (i.e., Ili Basin) margins of the Tian Shan were likely receiving similar westerly precipitation by 15 Ma (δ18Oc = ∼−8‰) and had similar lacustrine-playa environments at ca. 13.5 Ma, despite differences in sedimentary provenance. At ca. 12 Ma, an erg desert formed adjacent to the southern Tian Shan in the northwestern Tarim Basin, coincident with a mid- to late Miocene phase of deformation and exhumation within both the Pamir and southern Tian Shan. Desertification at ca. 12 Ma was marked by a negative δ18Oc excursion from −7.8 ± 0.4‰ to −8.7 ± 0.7‰ in the southern Tian Shan foreland (this study), coeval with a negative δ18Oc excursion (∼−11 to −13‰) in the Tajik Basin, west of the Pamir. These data suggest that only after ca. 12 Ma did the Pamir-Tian Shan create a high-elevation barrier that effectively blocked westerly moisture, forming a rain shadow in the northwestern Tarim Basin. After 7 Ma, the southern Tian Shan foreland migrated southward as this region experienced widespread deformation. In our study area, rapid shortening and deformation above two frontal foreland faults initiated between 6.0 and 3.5 Ma resulted in positive δ13Cc excursions to values close to 0‰, which is interpreted to reflect exhumation in the Tian Shan and recycling of Paleozoic carbonates. Shortening led to isolation of the study site as a piggy-back basin by 3.5 Ma, when the sediment provenance was limited to the exhumed Paleozoic basement rocks of the Kepintagh fold belt. The abrupt sedimentologic and isotopic changes observed in the southern Tian Shan foreland appear to be decoupled from late Cenozoic global climate change and can be explained entirely by local tectonics. This study highlights how tectonics may overprint the more regional and global climate signals in active tectonic settings.

40Ar/39Ar ages and geochemistry of the Intersalar Range of the Bolivian Altiplano: A volcanological transect spanning the arc and reararc of the Central Andean Plateau

The volcanic Intersalar Range of western Bolivia provides a unique opportunity to examine geochemical variations spanning the arc and reararc regions of the Central Andean Plateau. In this study we report 23 new 40Ar/39Ar ages, 15 whole-rock Sr-Nd-Pb isotope analyses, and 50 whole-rock major and trace element analyses from samples collected across ∼115 km of the Intersalar Range. Most samples are classified as trachyandesites and trachydacites, with the most mafic lavas (slightly alkaline, basaltic trachyandesites) erupting from the Pliocene Coracora volcano in the central Altiplano. We identify two distinct pulses of reararc magmatism: a Miocene phase between 20 Ma and 14 Ma that corresponds with local compressional shortening, and a Plio-Pleistocene phase between 5 and 1 Ma that postdates observed structural deformation in the region. 87Sr/86Sr values (0.70512–0.70600) and 143Nd/144Nd values (0.51226–0.51255) are generally higher, and lower, respectively, in the younger phase, whereas Pb isotopes (206Pb/204Pb = 17.7315–18.5095; 207Pb/204Pb = 15.5714–15.6279; 208Pb/204Pb = 37.7862–38.6156) show little variation with age. Isotope values are only loosely correlated with distance from the modern Central Volcanic Zone. Higher Sr/Y, Dy/Yb, and [La/Yb]N values in the Plio-Pleistocene samples are consistent with homogenization at the base of a thicker continental crust compared to the Miocene samples. Nb concentrations show the strongest correlation with distance into the reararc compared to all other trace elements (arc Nb = 6–16 ppm; reararc Nb = 12–26 ppm). Nb/Nb* values (a measurement of the depth of the negative Nb anomaly) correspondingly increase into the reararc (indicating smaller anomalies), reaching a maximum at Coracora volcano before decreasing in the far rear arc region. Compiled data across the Central Andean Plateau reveal a strong correlation between Nb/Nb* and the presence of intact mantle lithosphere beneath the central Altiplano. We interpret this distinct Nb signal to reflect melting triggered by the breakdown of Nb-rich hydrous minerals within foundering (delaminating) mantle lithosphere. In conjunction with spatiotemporal data, Nb systematics provide the clearest indication of mantle lithosphere in regions where mafic samples are not present.

Middle to late Miocene growth of the North Pamir

AbstractHow and when the Pamir formed remains an open question. This study explores Pamir tectonics recorded in a sedimentary section in the eastern Tajik Basin. A prominent lithofacies change that has been recognised regionally is assigned to the middle Miocene (13.5 Ma based on preferred magnetostratigraphic correlation). Closely following this change, detrital zircon U‐Pb age spectra and mudstone bulk‐rock εNd values exhibit a sediment source change from the Central to the North Pamir estimated ca. 12 Ma. At the same time, the stable oxygen and carbon isotopic values of carbonate cements show negative and positive shifts, respectively. Combined with previous studies in both the Tajik and Tarim basins, these results suggest that the North Pamir experienced a middle–late Miocene phase of deformation and surface uplift. This supports models proposing middle–late Miocene Pamir tectonism, and climate models implying that coeval Pamir orogenesis deflected Westerly moisture and affected Asian environments.

Oligocene-Early Miocene exhumation and shortening along the Anninghe fault in the southeastern Tibetan Plateau: insights from zircon and apatite (U-Th)/He thermochronology

ABSTRACT The growth mechanisms of the southeastern Tibetan Plateau are debated between models of Oligocene shortening and lateral extrusion of coherent crustal blocks versus Late Miocene flow of low-viscosity lower crust. To test these models, we examine brittle deformation of the north-striking Anninghe fault, which has been acting as a left-lateral strike-slip fault since Late Miocene time, using structural and bedrock low-temperature thermochronologic methods. Different from previous interpretations of Late Miocene strike-slip motion, our structural observations indicate westward contractional dip-slip along the southern segment of the fault. New zircon and apatite (U-Th)/He thermochronologic data along a vertical profile of Precambrian volcanoclastic cover both sides of the Anninghe fault. The age-elevation relationships and inverse thermal modelling suggest a phase of Oligocene-Early Miocene (~24-18 Ma) differential rock exhumation and cooling across the fault, with a mean erosion rate of ~0.30 ± 0.12 km/m.y. and ~0.007 ± 0.007 km/m.y. in the hanging wall and footwall, respectively. Consistent with the structural observations, the higher rate of rock exhumation in the hanging wall indicates an Oligocene-Early Miocene phase of west-verging reverse faulting. Combined with previously published data from adjacent sites, we suggest that the Anninghe fault has experienced a tectonic transition from Oligocene-Early Miocene east-west contraction to Late Miocene strike-slip motion. The early to Mid-Cenozoic crustal shortening contributed to the uplift of the southeastern Tibetan Plateau, supporting the crustal shortening and extrusion model.

Detrital record of the late Oligocene – early Miocene mafic volcanic arc in the southern Patagonian Andes (∼51°S) from single-clast geochronology and trace element geochemistry

Retroarc foreland basins are important archives of continental arc magmatism and upper plate deformational processes that control the evolution of continental lithosphere. However, resolving source areas in foreland basin infill dominated from mixed mafic and recycled sediment using conventional methods such as detrital zircon geochronology poses a challenge to thorough analysis due to lower zircon fertility and the higher susceptibility to weathering of mafic lithologies. Here, we integrate whole rock 40Ar/39Ar geochronology and major and trace element geochemistry data from volcanic clasts from the lower Miocene infill of the Magallanes-Austral Basin and local Sierra Baguales intrusive rocks to understand the distribution of mafic sources and Neogene changes in arc magmatism in between multiple ridge subduction events in the southern Patagonian Andes. Potential source areas for the coarse-grained mafic detritus include the Eocene plateau lavas, the Late Jurassic-Miocene Southern Patagonian batholith, and the Late Jurassic Sarmiento Ophiolitic Complex. Published detrital zircon U-Pb age spectra suggest that all three sources are viable contributors to the basin, though the paucity of Jurassic and Eocene zircons preclude these as major sources. Here, new 40Ar/39Ar dating of the volcanic clasts from the early Miocene Río Guillermo Formation reveals latest Oligocene to early Miocene eruptive ages (∼25-22 Ma), indicating syndepositional eruption with the ancestral Río Guillermo fluvial sedimentation. A single dated clast yields a Late Cretaceous age (∼102 Ma). The clasts are dominantly basaltic andesite with Ba/Ta ∼500-1000, La/Ta >20, and Ba/La >15, indicating an arc-derived melt source. We propose that the clasts record a Miocene mafic continental arc source area in the Patagonian Andes, which has since been removed by erosion and is thus sparsely represented in the batholith. Furthermore, we suggest that this early Miocene phase of arc volcanism, which postdates Eocene and Oligocene backarc magmatism and pre-dates middle Miocene to recent Chile Ridge backarc magmatism, reflects a return to normal arc volcanism along the Patagonian margin following a cessation due to ridge subduction and subsequent slab window migration. New geochemistry and 40Ar/39Ar data from a basaltic dike in the Sierra Baguales, which crosscuts the Cenozoic stratigraphic section, records plateau magmatism ∼16 Ma associated with incipient Chile Ridge slab window volcanism.

Two phases of post-onset collision adakitic magmatism in the southern Lhasa subterrane, Tibet, and their tectonic implications

AbstractAbundant Neogene adakitic magmatism occurred in the southern Lhasa subterrane after the onset of the India–Asia collision while convergence continued. However, the tectonic setting and magmatic evolution of the adakitic rocks are still under discussion. This study includes new mineral chemical and whole-rock geochemical data as well as zircon U-Pb and Lu-Hf isotopes of adakitic intrusive rocks from the Gyaca and Nyemo locations in the southern Lhasa subterrane. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U-Pb dating yielded crystallization ages of ca. 30 Ma for the Gyaca and Nyemo monzogranite and ca. 15 Ma for the Nyemo granodiorite. Both have common chemical signatures such as low MgO and heavy rare earth element contents as well as low compatible element abundances, indicating that these rocks result from partial melting of thickened lower crust with residual eclogite and garnet amphibolite. Furthermore, these rocks are characterized by variable positive zircon εHf(t) values, suggesting a juvenile magma source with variable ancient crustal contributions. Taking previous data into account, the adakitic magmatism concurs with an early late Eocene to Oligocene (ca. 38–25 Ma) and a late Miocene (ca. 20–10 Ma) phase. The adakitic rocks of the two phases are characterized by different fractionation evolutions of light and medium rare earth elements. We propose that the early-phase adakitic rocks were generated by the anatexis of Lhasa terrane lower crust owing to crustal shortening and thickening subsequent to the onset of the India–Asia collision and the upwelling of hot asthenosphere beneath the Lhasa terrane caused by the break-off of the Neo-Tethyan oceanic slab. The latest phase of adakitic rocks, however, relates to upwelling asthenosphere following the delamination and/or break-off of the subducting Indian continental slab.

A „Kapos-vonal” középső szakaszának szerkezeti-mélyföldtani viszonyai és neotektonikai jellegei a legújabb geofizikai vizsgálatok tükrében

Tanulmányunkban a Kapos-vonal középső szakaszának legújabb geofizikai vizsgálatainak eredményeit tekintjük át. Munkánkkal tavaly ősszel elhunyt Kollégánk, Barátunk, Tanárunk és Mesterünk — Prof. Dr. Horváth Ferenc — emléke előtt tisztelgünk. A kutatási területen elérhető korábbi és újonnan mért 2D/3D reflexiós szeizmikus és fúrási adatok integrációjával komplex adatbázist alakítottunk ki, amelynek értelmezésével földtanilag és geometriailag egyaránt konzisztens, új 3D földtani-tektonikai modellt hoztunk létre. A modell a vizsgált terület földtani felépítésének alapvonásait szem előtt tartva öt meghatározó jelentőségű földtani horizont (prekainozoos aljzat-tető, alsó-miocén tető, középső-miocén tető, Endrődtető, Algyő-tető) és az értelmezett vetők téradatrendszerét tartalmazza. A kialakított 3D modell alapján elvégeztük a korábbi vizsgálatokkal nyert földtani-szerkezeti kép felülvizsgálatát, és azt szükség szerint módosítottuk, illetve pontosítottuk/kiegészítettük.A kutatás mélyföldtani szempontból legfontosabb eredményei közé tartozik a kristályos és mezozoos aljzat képződmények szerkezeti, elterjedési és kifejlődési viszonyainak reambulációja a lemélyült új szerkezetkutató fúrások és a szeizmikus adatrendszer integrált értelmezése alapján. Ugyancsak alapvető jelentőségű a markáns kora-miocén riftesedés kimutatása, amely során intenzív, többfázisú mészalkáli vulkáni működés, illetve egyidejű kontinen tális üledékképződés zajlott a létrejött, helyenként akár 2 km mélységű süllyedékekben. Mindez tágabb kontextusban a Pannon-medence korábban kevésbé ismert (és hangsúlyozott) kora-miocén kialakulási szakaszának jelentőségére hívja fel a figyelmet. A vetőtérképezés eredményei alapján a szűkebb kutatási terület meghatározó vetőzónái a KÉK–NyDNy-i csapású „Kapos-vonal”, továbbá az ÉK–DNy-i csapású Dunaszentgyörgy–Harta és az ezen kutatás során először térképezett Bonyhádi vetőzóna, amelyeket mind meredek dőlés (≥60–70°) jellemez. A Bonyhádi vetőzóna délnyugati irányban a Mecsek északi pikkelyzónájához csatlakozik. A terület szerkezeti képét összességében a fentiekkel többnyire (közel) párhuzamos törések uralják, míg az előbbiekre kb. merőleges ÉÉNy–DDK-i csapású, szerkezetileg kevésbé jelentős törések főként a Kapos-vonaltól délre jelentkeznek.Eredményeink alapján geometriai-szerkezeti értelemben egységes Kapos-vonal nem létezik: e vetőzóna a kutatási területen ugyanis egy nyugati („Kapos-Ny”) és egy keleti szegmensre („Kapos-K”) bontható, amelyek mind dőlés irányban, mind az észlelt neotektonikus aktivitásban — összhangban a korábbi szakirodalmi adatokkal — markánsan különböznek. A vizsgált területen élénk neotektonikus aktivitást mutató Kapos-K, Dunaszentgyörgy–Harta és Bonyhádi vetőrendszerek regionális léptékben egy ÉK–DNy-i és KÉK–NyDNy-i csapású elemekből felépülő, széles nyírási zónát körvonalaznak, amely a neotektonikus fázisban balos eltolódásként működött. Ezt igazolja az egyes vetőzónákban megfigyelt tipikus „virágszerkezetet” mutató belső struktúra, továbbá a kapcsolódó másodlagos formaelemek (Riedel-törések) is.A kialakított 3D modell eredményeinek figyelembevételével telepített nagyfelbontású 2D és pszeudo-3D sekélygeofizikai vizsgálatok, valamint az ezek eredményei alapján kijelölt árkolás és sekélyfúrások adatai bizonyították a Dunaszentgyörgy–Harta vetőzóna negyedidőszaki, sőt az árkolás eredményei szerint késő-negyedidőszaki aktivitását, hiszen a kutatóárokban feltárt késő-pleisztocén végi futóhomok tektonikus eredetű deformációja jelentkezett. A fiatalnegyedidőszaki tektonikai aktivitást a kutatási területen számos további korábbi, illetve a jelen kutatáshoz kapcsolódó, de e tanulmányban nem részletezett neotektonikai megfigyelés is alátámasztja. Mindezen eredmények a szak irodalomban a Kapos-vonal keleti szakaszáról (Duna–Tisza köze és Tiszántúl) közölt tektonikai adatokkal és értelmezésselteljes összhangban állnak.A tanulmányunkban ismertetett eredmények a Paks II földtani kutatási programjának (FKP) keretében 2015–2016 során elvégzett földtani-geofizikai kutatásokhoz kapcsolódnak.

Mesozoic – Cenozoic evolution of the Southern Patagonian Andes fold and thrust belt (47°–48°S): Influence of the Rocas Verdes basin inversion and onset of Patagonian glaciations

The Southern Patagonian Andes (SPA) between 47°–48°S are characterized by relatively high elevations (1500–4000 m) and a 200-km-wide, largely exhumed, basement domain along the backbone of the Cordillera, bounded by a narrow 30-km-wide fold and thrust-belt to the east. The tectonic evolution of the SPA includes widespread Jurassic extension during the opening of the Austral-Magallanes basin and the Rocas Verdes back-arc oceanic basin (RVB), followed by Cretaceous to Cenozoic shortening. Although the main phases of deformation that affected this Andean segment have been the focus of previous studies, its finite geometry and step by step structural and kinematic evolution have not been quantitatively determined. In this work, we present kinematically restored cross sections, showing the variable geometry, trough time, of the eastern basement domain and the fold and thrust-belt. A regional westward-dipping listric decollement, interpreted as formed during the Jurassic extensional event, was reactivated during the Andean deformation constituting the main detachment surface of basement structures and the fold and thrust belt. West verging faults systems are considered a consequence of inversion of north-south trending extensional features as passive roof high-angle west-vergent faults. Using regional data such as field relations, unconformities, and existing ages to differentiate deformational stages, three main phases of contractional deformation are proposed for the area, starting with an Aptian - Cenomanian? phase related to inversion of the extensional depocenter in inmediate response to the closure of northernmost RVB. A second, Miocene phase responsible for most of the shortening occurred between 18 Ma and 10 Ma. Finally, the onset of glaciations and glacial erosion might have triggered out-of-sequence thrusting in the interior of the orogen after 7 Ma.

Salt tectonics in the Bend Zone segment of the Carpathian fold and thrust belt, Romania

The Carpathian Bend Zone is part of the Eastern Romanian Carpathians. The stratigraphic profile contains two levels of salt: Lower Miocene (Lower Burdigalian) and Middle Miocene (Badenian). The studied segment of the fold belt was deformed during the Middle Miocene (Badenian-to-Middle Sarmatian phase) and during the Late Miocene to present (Wallachian phase). During this latter phase, the Lower Burdigalian salt was remobilized and reached the surface on several locations piercing through 2–3 km-thick post-tectonic deposits. The salt outcrops and contractional structures now form a 30 km long, NE–SW lineament at the surface. This contribution proposes kinematic models for the Lower Burdigalian salt movement during both tectonic phases. The lineament was a detachment fold in the Middle Miocene phase. Thickened Burdigalian salt and Oligocene s.l. duplex filled the core of the detachment fold. The detachment fold was subsequently peneplained with the Burdigalian salt exposed on the paleo-surface that locally redeposited during the Badenian. The Wallachian evolution is less clear and we propose two viable kinematic models. It is possible that the salt rise kept up with sedimentation and halokinetic sequences formed at the salt–sediment interface. Alternatively, the area was reactivated in a thin-skinned, right-lateral strike–slip manner with local pull-apart basins (1–2 km across) providing space for salt plugs. Currently available data do not allow us to pick a preferred model for the kinematics during the Wallachian phase. Both kinematic models are novel and are in contrast with earlier ideas.

Impact of pre-existing fabrics and multi-phase oblique extension on Cenozoic fault patterns, Wichianburi sub-basin of the Phetchabun rift, Thailand

Cenozoic fault patterns associated with rift development in the Wichianburi Sub-Basin show a wide range of controls at different scales including influence by the margin of a Permian basin, and NW-SE to NE-SW trending Triassic folds and faults. During the Late Oligocene-Early Miocene phase 1 normal faults (NNW-SSE to NNE-SSW trends) developed in response to ∼ E-W extension. Faults predominantly trend NNW-SSE to N-S during this phase. During the Middle Miocene-Pliocene the extension direction rotated to a more NW-SE orientation. The old fault orientations were reactivated, and new faults also developed with predominantly NNE-SSW to NE-SW orientations. Many new faults nucleated within the syn-rift section and were not directly influenced by pre-existing fabrics in the pre-rift section. Four types of phase 2 fault can be identified: Type 1 = newly formed faults that strike sub-orthogonal to the phase 2 extension direction, Type 2 = newly formed faults that strike between the phase 1 fault orientations and Type 1 faults. Type 3 = newly formed faults that strike at angles greater than 90° with respect to the phase 2 extension direction. Type 4 = reactivated phase 1 faults. Local stress rotations, and fault linkage rotations explain many of the Type 2 and 3 fault orientations. The stress rotation in the Middle Miocene is observed in other basins in Central Thailand, notably the Suphan Buri and Phitsanulok Basins, where a range of fault patterns are produced by the effects of inherited fabrics plus multi-phase rifting.

Tectonostratigraphy, structural geometry and kinematics of the NW Iranian Plateau margin: Insights from the Talesh Mountains, Iran

The structural geometry and kinematic variations along curved fold and thrust belts and their interaction with neighboring rigid basement blocks are not well understood. In this study, we present a structural mapping and stratigraphic analysis of the Talesh Mountains, Iran, to document the timing and evolution of this curved orogen due to collision with the South Caspian Block. NE and SW verging oblique slip thrust faults are the main structural features in the northern and southern parts of the mountains. The N-trending central part of the range is connected to the curved ends of the Talesh Mountains by a system of high angle reverse faults with right lateral strike-slip sense of motion. Restored cross sections indicate greater horizontal shortening (25–30%) in the southern parts which gradually decreases toward the center (13–16%), and then increases to the north (22%). A compilation of stratigraphic sections across the region indicates three major phases of regional deformation in the early Oligocene, middle Miocene and early Pliocene. The middle Miocene phase, in good agreement with other data sets across the Iranian Plateau, is the onset time of deformation for the Talesh Mountains. The regional convergence direction has changed during this major phase of deformation in the NW margins of the Iranian Plateau. The observed kinematic variation along the major faults across the Talesh Mountains is likely resulted from a regional change in the shortening direction in middle Miocene. Variations on the measured Late Cenozoic horizontal shortening across the northern, central and southern parts of the Talesh Mountains resulted from their different orientations with respect to the regional convergent direction as well as interaction with the rigid south Caspian block. These results highlight that the orientation and timing of deformation was strongly influenced by the neighboring Caspian block and regional variations in the convergence direction associated with evolution of the Iranian Plateau.

Determining of a complex structure consisting of detachment, fault-bend and fault propagation folds in the collapse structure of Zaghouan-Bouficha (Bouficha region, north eastern Tunisia)

The structural study in Bouficha region based on subsurface investigation has allowed determining the geometry of deformations. These deformations are represented by faults of NE–SW and NW–SE directions and folds of NE-SW mean orientation. The aim of the present paper is to demonstrate the structural style of these folds and reconstruct their evolution. Data obtained from a seismic profile that cross longitudinally the collapse structure of Zaghouan-Bouficha, have revealed the structure of fault-related folds. The interpretation of the NW-SE seismic profile revealed two fault-propagation folds, a detachment fold and two fault-bend folds in the Zaghouan-Bouficha collapse structure. From the South-east to the North-west, the seismic profile shows: (1) a fault-propagation fold built on a horizontal detachment level situated in the Triassic series linked to a ramp, (2) a detachment fold formed on a detachment level in the Triassic series, (3) a second fault-propagation fold formed on a horizontal detachment in the Triassic series and a ramp, (4) a fault-bend fold overcomes the second fault-propagation fold. It formed over two detachment levels which are connected to a ramp of a dip towards the SE indicating a displacement to the North-west, (5) a second fault-bend fold formed over two detachment levels which are connected to a ramp of a dip towards the NW indicating a displacement to the South-east. The evolution reconstruction of these fault-related folds shows that they formed during the Late Miocene and Plio-Quaternary compressive phases. This study shows also an analogical modeling that explains some evolutionary steps of the determined deformations.

Middle to Late Miocene Contractional Deformation in Costa Rica Triggered by Plate Geodynamics

AbstractContractional deformation in Costa Rica is usually attributed to the subduction of the aseismic Cocos Ridge. In this work, we review the evidences for contraction in the middle to late Miocene, prior to the arrival of the Cocos Ridge at the Middle America Trench. We find that the Miocene phase of contractional deformation is found in all of Costa Rica, probably extending to Nicaragua as well. The widespread distribution of this event requires a regional or plate geodynamic trigger. We analyze the possible mechanisms that could produce the onset of contractional deformation, using the better known case of subduction orogeny, the Andes, as an analog. We propose that a change in the direction of the Cocos plate since ∼19 Ma led to a change from oblique to orthogonal convergence, producing contractional deformation of the upper plate.

Basalt Intrusions in Palaeokarst Caves in the Central Lessini Mountains (Venetian Prealps, Italy)

The Lessini Mountains carbonate plateau (Venetian Prealps, Italy) is one of the most important karst areas in Italy. Along with alpine-type caves and well-developed karst landscapes, palaeokarst features are also common. In most cases, palaeokarst is represented by caves and fissures filled by limonitic-haematitic palaeosols (ochres) in which fossiliferous arenite layers are sometimes embedded. These features developed and fossilised during a late Eocene-middle Miocene phase of emersion. Between the Palaeocene and the Oligocene, over a time span partially overlapping the development of palaeokarst, basaltic volcanism took place in the Lessini Mountains. Along with ochre fills, cave passages that were intruded by basalt provide further evidence that a well developed karst network existed in the Lessini Mountains area in the middle-late Palaeogene. Moreover, basalt intrusions provide the only available data for the dating of palaeokarst in the central Lessini Mountains, where fossiliferous layers in ochre beds have not been found. We have started a new survey on palaeokarst in the Lessini plateau, with the aim of identifying ancient features on the basis of unusual fills (namely, ochre and basalt) and morphologies. New instances of basalt intrusions in three caves, Spigola di Canova, Covoli di Velo, and Covolo della Croce, have been recognised; evidence of pre-existing karst features filled by basalt in a previously studied cave (Grotta A Veja) has been identified, and an unusual basalt outcrop that might relate to palaeokarst has also been observed. This paper aims to document the new findings and to discuss previous ones. At the same time, we would like to point out some cautionary observations to prevent a “basalt = palaeokarst” misunderstanding. Key words: palaeokarst, basalt intrusion, cave fills, Lessini Mountains.

Balanced geological cross-section of the outer ukrainian carpathians along the pancake profile

The Outer Ukrainian Carpathians (OUC) are part of the Eastern Carpathians, which is a segment of the European Alpine belt. The OUC is crossed by recently acquired WARR (wideangle reflection and refraction) PANCAKE profile (Starostenko et al., 2013). To study the basin architecture of the OUC along the profile a balanced geological cross-section was onstructed. Reconstruction of the balanced geological cross-section has shown that the present day fold-and-thrust belt of the Outer (Flysch) Carpathians was formed in the Miocene from the deposits of the sedimentary basin∼460km in width. Evolution of the sedimentary basin to the present fold-and-thrust belt 70km in width occurred in two stages, characterized by accelerating the shortening rate of the basin from 11.5km/Ma between∼32 and 22 Ma to 22.5km/Ma between∼22 and 12 Ma. The detachment of the flysch complexes of the OUC occurred on the top of the basement located at a depth of 10−12km. The main phase of Miocene thrusting was followed by significant exhumation and erosion during the period of 12−2 Ma related to isostatic uplift in the OUC, which reached a maximum (up to 7km) in the central nappes (Krosno and Dukla-Chornohora). The collision regime, obviously, followed the subduction one; this could happen approximately at 22 Ma which is evident after changing the shortening rate of the basin.

Mapping geology in Djelfa District (Saharan Atlas, Algeria), using Landsat 7 ETM+ data: an alternative method to discern lithology and structural elements

Djelfa area in the central Saharan Atlas is characterized by its high lithological diversity with different facies from the Triassic to the Tertiary. The lack of published geological maps of the region (Djelfa) prompted us to test specific processing of satellite images (ratio bands, principal component analysis) in order to establish a lithological discrimination of the region. Several treatments allowed us to map the lineaments highlighting the various tectonic structures of the region. The combination of field and remote sensing data pointed out the double influence of the E-W Eocene and N-S Miocene phases in the structuration of these regions. As a large part of the Djelfa area is inaccessible, the obtained results undeniably contribute to a better understanding of the local geology.

Mid-Late Miocene deformation of the northern Kuqa fold-and-thrust belt (southern Chinese Tian Shan): An apatite (U-Th-Sm)/He study

The Kuqa fold-and-thrust belt developed in response to Cenozoic southward shortening between the Chinese Tian Shan and the Tarim Basin. This study aims to constrain the timing of the Late Cenozoic deformation by determining the onset time of enhanced rock cooling using apatite (U-Th-Sm)/He thermochronometry. Eight sedimentary samples were collected from Triassic to Cretaceous strata exposed along a 17km N-S transect, cross-cutting the northern Kuqa fold-and-thrust belt. Single-grain AHe ages from these samples mostly cluster around 8–16Ma and are younger than their depositional ages. Older AHe ages show a positive relationship with [eU], a proxy for radiation damage. Modelling of the observed age-eU relationships suggest a phase of enhanced cooling and erosion initiated at Mid-Late Miocene time (10–20Ma) in the northern Kuqa fold-and-thrust belt. This result is consistent with a coeval abrupt increase of sedimentation rate in the foreland Kuqa depression, south of the study area, indicating a Mid-Late Miocene phase of shortening in the northern Kuqa fold-and-thrust belt.