scholarly journals Micro-tectonic constraints on the evolution of the Barles half-window (Digne nappe, southern Alps). Implications for the timing of folding in the Valensole foreland basin

2008 ◽  
Vol 179 (6) ◽  
pp. 551-568 ◽  
Author(s):  
Marc Fournier ◽  
Philippe Agard ◽  
Carole Petit
Keyword(s):  
Late Miocene ◽  
Tectonic Setting ◽  
Regional Scale ◽  
Foreland Basin ◽  
Structural Data ◽  
Late Eocene ◽  
Rift System ◽  
Late Cenozoic ◽  
Northern Margin ◽  
Two Phases

Abstract The “Vélodrome” overturned syncline, at the northern margin of the Cenozoic foreland basin of Valensole in SE France, was formed during the Late Cenozoic at the front of the Digne nappe. Microstructural analyses reveal that mesoscale faulting in the molassic series, from the Oligocene “Molasse Rouge” at the base to the middle to late Miocene “Valensole Conglomerates” at the top, partly occurred before the folding, as layer-parallel shortening: the NNE-SSW-directed compression is recorded by two systems of reverse and strike-slip faults, which formed when the strata were still horizontal and were passively tilted as folding occurred. These data suggest that the Vélodrome folding postdates the deposition of the Valensole Conglomerates and occurred in late Miocene-Pliocene times during the emplacement of the Digne nappe. These results are difficult to reconcile with the interpretation of the Vélodrome as a growth fold progressively formed in 10–15 m.y. during the deposition of the Miocene molasses. Structural data collected in the Barles tectonic half-window enable to reconstruct the evolution of the deformation since the Jurassic. The two main phases of shortening, the pre-Oligocene Pyrenean-Provençal and the Mio-Pliocene Alpine phases, are almost homoaxial with a direction of compression trending N-S for the former and NNE-SSW for the later. A late Eocene-basal Oligocene N-S extensional episode is documented between these two phases, probably in relation with the formation of the western European rift system. The direction of extension of the Liassic rifting of the Alpine Tethys is roughly constrained in the NW-SE quadrant. Paleo-stress field reconstruction brings consistent results at the regional scale and proves to be a powerful tool to decipher the evolution of the deformation in a remarkably complicated tectonic setting.

scholarly journals Mid-Cenozoic succession on the northeast limb of the Mount Diablo anticline, California—A stratigraphic record of tectonic events in the forearc basin

2021 ◽  
Author(s):  
Raymond Sullivan ◽  
Morgan D. Sullivan ◽  
Stephen W. Edwards ◽  
Andrei M. Sarna-Wojcicki ◽  
Rebecca A. Hackworth ◽  
...  
Keyword(s):  
North America ◽  
Late Miocene ◽  
Plate Boundary ◽  
Leading Edge ◽  
Late Eocene ◽  
Late Cenozoic ◽  
Forearc Basin ◽  
Late Mesozoic ◽  
The North ◽  
Silicic Volcanic

ABSTRACT The mid-Cenozoic succession in the northeast limb of the Mount Diablo anticline records the evolution of plate interactions at the leading edge of the North America plate. Subduction of the Kula plate and later Farallon plate beneath the North America plate created a marine forearc basin that existed from late Mesozoic to mid-Cenozoic times. In the early Cenozoic, extension on north-south faults formed a graben depocenter on the west side of the basin. Deposition of the Markley Formation of middle to late? Eocene age took place in the late stages of the marine forearc basin. In the Oligocene, the marine forearc basin changed to a primarily nonmarine basin, and the depocenter of the basin shifted eastward of the Midland fault to a south-central location for the remainder of the Cenozoic. The causes of these changes may have included slowing in the rate of subduction, resulting in slowing subsidence, and they might also have been related to the initiation of transform motion far to the south. Two unconformities in the mid-Cenozoic succession record the changing events on the plate boundary. The first hiatus is between the Markley Formation and the overlying Kirker Formation of Oligocene age. The succession above the unconformity records the widespread appearance of nonmarine rocks and the first abundant appearance of silicic volcanic detritus due to slab rollback, which reversed the northeastward migration of the volcanic arc to a more proximal location. A second regional unconformity separates the Kirker/Valley Springs formations from the overlying Cierbo/Mehrten formations of late Miocene age. This late Miocene unconformity may reflect readjustment of stresses in the North America plate that occurred when subduction was replaced by transform motion at the plate boundary. The Cierbo and Neroly formations above the unconformity contain abundant andesitic detritus due to proto-Cascade volcanism. In the late Cenozoic, the northward-migrating triple junction produced volcanic eruptive centers in the Coast Ranges. Tephra from these local sources produced time markers in the late Cenozoic succession.

scholarly journals Magnetostratigraphic dating of the Paleogene synorogenic sediments of the NE sector of the Ebro Foreland Basin (Spanish Pyrenees)

2021 ◽  
Author(s):  
Charlotte Peigney ◽  
Elisabet Beamud ◽  
Òscar Gratacós ◽  
Eduard Roca ◽  
Alberto Sáez ◽  
...  
Keyword(s):  
Regional Scale ◽  
Foreland Basin ◽  
Late Eocene ◽  
Tectonic Activity ◽  
Orbital Eccentricity ◽  
The South ◽  
Drainage Pattern ◽  
Ebro Basin ◽  
Alluvial Deposits ◽  
Thrust Sheets

<p>In foreland settings at the front of active orogens, the aggradation/progradation of fluvial fans and sedimentary changes in lacustrine systems depends greatly on the tectonic activity and the derived drainage pattern changes in the hinterland. As a result of the emplacement and erosion of the South-Pyrenean thrust sheets, a system of N-S fluvial fans prograded into the Ebro foreland basin from late Eocene to Oligocene times. After the synorogenic deposition of the Priabonian (late Eocene) marine evaporites of the Cardona Fm, the Ebro Basin was characterized by internal drainage, with the fluvial fans grading to lacustrine systems at the center of the basin, which developed and migrated in response to subsidence changes. All these deposits were deformed by variably oriented salt-detached folds, evidencing the basinwards propagation of the deformation. In this work, we study the Solsona-Sanaüja fluvial fan system by means of litostratigraphy and magnetostratigraphy aiming to determine the age of the transition from fluvial fan to lacustrine systems in the NE sector of the Ebro Basin. The precise dating of this succession reveals causal relationships between tectonic and climatic processes affecting the source-to-sink system, including changes in the depositional style linked to the evolution of the Pyrenean fold and thrust belt.</p><p>Our new magnetostratigraphic study consisted in the sampling and analysis of 195 samples along a ca. 1800m thick stratigraphic section of the late Eocene-Oligocene succession in the northern limb of the NW-SE oriented Sanaüja Anticline. Our results show overall Priabonian to Rupelian ages for the succession, considering an age of 36 Ma. (C16n) for the top of the Cardona Fm from previous magnetostratigraphic studies. This allows dating the end of the evaporitic sedimentation (top of the Barbastro Fm) as Priabonian and establishing a late Priabonian to early Rupelian (C13r) age for the transition from the younger lacustrine deposits (Torà Fm) to the continuous and most important fluvial fan episode of progradation in the study area. The final progradation of the fluvial fan system was coeval to a tectonically controlled reorganization of the drainage pattern of the basin responding to the emplacement of the South-Pyrenean thrust sheets. Meanwhile, smaller scale (hectometric-decametric) alternation between lacustrine and alluvial deposits was possibly driven by climatic changes related to orbital eccentricity cycles. The correlation and integration of these results with previous magnetostratigraphic studies in the area can help analyzing sedimentation patterns and architectural changes in the basin margins at a regional scale.</p>

Geochronology of the Nabwal Hills: a record of earliest magmatism in the northern Kenyan Rift Valley

2005 ◽  
Vol 143 (1) ◽  
pp. 25-39 ◽  
Author(s):  
IAN McDOUGALL ◽  
RONALD T. WATKINS
Keyword(s):  
Late Miocene ◽  
Alkali Feldspar ◽  
East African Rift ◽  
Late Eocene ◽  
Rift System ◽  
Crustal Extension ◽  
East African Rift System ◽  
East African ◽  
Metamorphic Basement ◽  
African Rift

The Nabwal Hills, northeast of Lake Turkana, contain a record of magmatism associated with the initiation and early development of the East African Rift System in northernmost Kenya. The predominantly volcanic Asille Group, 1400 m thick, directly overlies metamorphic basement and comprises a sequence of basaltic lava flows with significant intervals of rhyolitic pyroclastic units, and minor intercalations of fluviatile sediments. The basement gneisses yield K–Ar cooling ages on biotite of 510 and 522 Ma, typically Pan-African. The 40Ar–39Ar ages on alkali feldspar crystals from the rhyolitic units are concordant and show that the Asille Group spans an interval from at least 34.3 to 15.8 Ma, continuing to at least as young as 13 Ma based on previous measurements. Vertebrate fossil sites, containing primate remains, at Irile and Nabwal are shown to be 17 ± 2 Ma old, Early Miocene, based upon K–Ar age measurements on immediately overlying basalts. Variably reliable whole rock K–Ar ages, determined on basalt samples from low in the sequence, indicate that volcanism commenced as early as 34.8 Ma ago. The overall geochronological results show that magmatism in the Nabwal Hills began about 35 Ma ago in Late Eocene times, interpreted as the time of initiation of crustal extension that led to the development of this segment of the East African Rift System. The Asille Group is tilted about 6° to the SSW. This tilting occurred later than 13 Ma ago, and prior to the eruption of the flat-lying Gombe Group basalts. These basalts may have begun erupting about 6 Ma ago in Late Miocene times, although much of this volcanism occurred between about 3.9 and 4.2 Ma ago in Pliocene times. It is suggested that the main rifting, which continues today, commenced in Late Miocene times, less than 13 Ma ago, and is partly reflected in the tilting of the Asille Group.

scholarly journals Cenozoic tectonic evolution of the Ecemiş fault zone and adjacent basins, central Anatolia, Turkey, during the transition from Arabia-Eurasia collision to escape tectonics

Geosphere ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1358-1384
Author(s):  
Paul J. Umhoefer ◽  
Stuart N. Thomson ◽  
Côme Lefebvre ◽  
Michael A. Cosca ◽  
Christian Teyssier ◽  
...  
Keyword(s):  
Fault Zone ◽  
Tectonic Evolution ◽  
Tectonic Setting ◽  
Structural Data ◽  
Late Eocene ◽  
Central Anatolia ◽  
Normal Faults ◽  
Profound Change ◽  
Escape Tectonics ◽  
Lateral Offset

Abstract The effects of Arabia-Eurasia collision are recorded in faults, basins, and exhumed metamorphic massifs across eastern and central Anatolia. These faults and basins also preserve evidence of major changes in deformation and associated sedimentary processes along major suture zones including the Inner Tauride suture where it lies along the southern (Ecemiş) segment of the Central Anatolian fault zone. Stratigraphic and structural data from the Ecemiş fault zone, adjacent NE Ulukışla basin, and metamorphic dome (Niğde Massif) record two fundamentally different stages in the Cenozoic tectonic evolution of this part of central Anatolia. The Paleogene sedimentary and volcanic strata of the NE Ulukışla basin (Ecemiş corridor) were deposited in marginal marine to marine environments on the exhuming Niğde Massif and east of it. A late Eocene–Oligocene transpressional stage of deformation involved oblique northward thrusting of older Paleogene strata onto the eastern Niğde Massif and of the eastern massif onto the rest of the massif, reburying the entire massif to >10 km depth and accompanied by left-lateral motion on the Ecemiş fault zone. A profound change in the tectonic setting at the end of the Oligocene produced widespread transtensional deformation across the area west of the Ecemiş fault zone in the Miocene. In this stage, the Ecemiş fault zone had at least 25 km of left-lateral offset. Before and during this faulting episode, the central Tauride Mountains to the east became a source of sediments that were deposited in small Miocene transtensional basins formed on the Eocene–Oligocene thrust belt between the Ecemiş fault zone and the Niğde Massif. Normal faults compatible with SW-directed extension cut across the Niğde Massif and are associated with a second (Miocene) re-exhumation of the Massif. Geochronology and thermochronology indicate that the transtensional stage started at ca. 23–22 Ma, coeval with large and diverse geological and tectonic changes across Anatolia.

Petrogenesis and tectonic significance of the middle Neoproterozoic highly fractionated A-type granite in the South Qinling block

2021 ◽  
pp. 1-20
Author(s):  
Xiao-Fei Qiu ◽  
Qiong Xu ◽  
Tuo Jiang ◽  
Shan-Song Lu ◽  
Long Zhao
Keyword(s):  
Tectonic Setting ◽  
Eastern China ◽  
Continental Rift ◽  
The South ◽  
Yangtze Craton ◽  
Dabie Orogen ◽  
Northern Margin ◽  
South Qinling ◽  
Type Granite ◽  
High Alkali

Abstract The South Qinling block, a segment of the Yangtze craton involved in the Qinling–Dabie orogen, is critical for understanding the tectonic evolution of eastern China. However, the tectonic setting of the South Qinling block and the northern margin of the Yangtze block during middle Neoproterozoic time has long been the subject of debate, with two distinctly different models (continental rift or volcanic arc) proposed. Here, a comprehensive study of zircon U–Pb geochronology and geochemistry has been carried out on the Chengwan granitic pluton from the Suizao terrane in the South Qinling block. The granites are monzogranite and syenogranite in lithology, and are mainly composed of potash feldspar, quartz, plagioclase and biotite. This suite has long been regarded as a Palaeozoic magmatic pluton, but zircon U–Pb ages of 809 ± 9 Ma and 816 ± 4 Ma are obtained in this study. The granites are metaluminous to strongly peraluminous with high alkali contents, and exhibit highly fractionated features, including high SiO2, low Zr/Hf ratios, rare earth element tetrad effects and enrichment of K and Rb. They show Hf–Nd isotopic decoupling, which may be genetically related to their petrogenetic process. Based on the geochemical features and the positive εHf(t) values of the zircons, it is indicated that the granites may have been derived from partial melting of juvenile tonalitic rocks by biotite breakdown under fluid-absent conditions. The Chengwan granite geochemically belongs to the A2-subtype granites, suggesting that it might have formed in a post-orogenic tectonic setting. The highly fractionated A-type granite in this study may represent extensional collapse shortly after the collisional events in the South Qinling block, and thus indicate a tectonic regime switch, from compression to extension, as early as middle Neoproterozoic time. Integrating our new data with documented magmatic, metamorphic and sedimentary events during middle Neoproterozoic time in the region may support a continental rift model, and argues against arc models.

The Neogene transition from C3 to C4 grasslands in North America: assemblage analysis of fossil phytoliths

Paleobiology ◽  
2011 ◽  
Vol 37 (1) ◽  
pp. 50-71 ◽  
Author(s):  
Caroline A. E. Strömberg ◽  
Francesca A. McInerney
Keyword(s):  
North America ◽  
Great Plains ◽  
Late Miocene ◽  
Vegetation Change ◽  
Stable Carbon Isotopes ◽  
Fire Regime ◽  
Tooth Enamel ◽  
Regional Scale ◽  
Grassland Ecosystems ◽  
Isotopic Records

The rapid ecological expansion of grasses with C4 photosynthesis at the end of the Neogene (8–2 Ma) is well documented in the fossil record of stable carbon isotopes. As one of the most profound vegetation changes to occur in recent geologic time, it paved the way for modern tropical grassland ecosystems. Changes in CO2 levels, seasonality, aridity, herbivory, and fire regime have all been suggested as potential triggers for this broadly synchronous change, long after the evolutionary origin of the C4 pathway in grasses. To date, these hypotheses have suffered from a lack of direct evidence for floral composition and structure during this important transition. This study aimed to remedy the problem by providing the first direct, relatively continuous record of vegetation change for the Great Plains of North America for the critical interval (ca. 12–2 Ma) using plant silica (phytolith) assemblages.Phytoliths were extracted from late Miocene-Pliocene paleosols in Nebraska and Kansas. Quantitative phytolith analysis of the 14 best-preserved assemblages indicates that habitats varied substantially in openness during the middle to late Miocene but became more uniformly open, corresponding to relatively open grassland or savanna, during the late Miocene and early Pliocene. Phytolith data also point to a marked increase of grass short cells typical of chloridoid and other potentially C4 grasses of the PACMAD clade between 8 and 5 Ma; these data suggest that the proportion of these grasses reached up to ∼50–60% of grasses, resulting in mixed C3-C4 and highly heterogeneous grassland communities by 5.5 Ma. This scenario is consistent with interpretations of isotopic records from paleosol carbonates and ungulate tooth enamel. The rise in abundance of chloridoids, which were present in the central Great Plains since the early Miocene, demonstrates that the “globally” observed lag between C4 grass evolution/taxonomic diversification and ecological expansion occurred at the regional scale. These patterns of vegetation alteration imply that environmental change during the late Miocene-Pliocene played a major role in the C3-C4 shift in the Great Plains. Specifically, the importance of chloridoids as well as a decline in the relative abundance of forest indicator taxa, including palms, point to climatic drying as a key trigger for C4 dominance.

scholarly journals Coal petrology analysis and implications in depositional environments from upper Cretaceous to Miocene: a study case in the Eastern Cordillera of Colombia

2021 ◽  
Author(s):  
Clara Guatame ◽  
Marco Rincón
Keyword(s):  
Late Cretaceous ◽  
Foreland Basin ◽  
Late Eocene ◽  
Depositional Environments ◽  
Estuarine System ◽  
Eastern Cordillera ◽  
Stratigraphic Position ◽  
San Fernando ◽  
Coal Facies ◽  
Oil Sector

AbstractThe Piedemonte Llanero Basin is located on the eastern side of the Eastern Cordillera of the Colombian Andes. It has been the subject of numerous geological studies carried out for the oil sector, mainly. This study presents the coal-petrographical features of 15 coal seams of four geological formations from Late Cretaceous to Middle Miocene (Chipaque formation, Palmichal group, Arcillas del Limbo formation, and San Fernando formation). Analysis of 33 samples indicates enrichment in vitrinite, while liptinite and inertinite concentrations vary according to the stratigraphic position. Reflectance indicates that the coal range gradually decreases from highly volatile bituminous C (Chipaque formation) to subbituminous C (San Fernando formation). The microlithotypes with the highest concentrations are clarite and vitrinertoliptite. Maceral composition and coal facies indicate changes in the depositional conditions of the sequence. The precursor peat from Late Cretaceous to Late Paleocene accumulated under limnic conditions followed by telmatic in Late Eocene–Early Miocene. The coal facies indices show wet conditions in forest swamps with variations in the flooding surface, influxes of brackish water and good tissue preservation. The tectonic conditions along the Piedemonte Llanero basin is evident, from post-rift to foreland basin, evidenced by oxic and anoxic periods reflected in the maceral composition and its morphology. The coal environment corresponds to an estuarine system started in the Chipaque formation evolving to the lacustrine conditions in the San Fernando formation.

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