During the Early Jurassic, the shallow marine carbonate platforms of the western-Tethys margins were characterized by highly diverse benthos including larger foraminifera, sponges, bivalves, ...gastropods, brachiopods, echinoderms, and dasycladalean calcareous algae. In this paper, we document examples of such assemblages within the lower Pliensbachian part of the Rotzo Formation (upper Orbitopsella Zone) of the Southern Alps, Italy. This carbonate succession was deposited in a complex mosaic of marine and brackish habitats within a tropical lagoon of the Trento Platform area. Large terebratulide brachiopod shells form autochthonous accumulations comprising exceptionally well-preserved monospecific assemblages of Lychnothyris rotzoana. These brachiopod-bearing successions were analysed in terms of biotic components, microfacies analysis, shell biofabric (three-dimensional arrangement of skeletal elements), and taphonomic signatures to understand brachiopod response to changing conditions within a highly variable lagoonal palaeoecosystem. Findings show that terebratulide shell accumulations are dominated by adult specimens and juveniles are rare. The brachiopods thrived during low energy conditions that resulted in the accumulation of highly temporally-condensed shell beds. Stabilized by microbialite encrustations, the shells were not re-oriented during the subsequent rapid burial. The abrupt demise of these communities was possibly related to rapid environmental change, and causal factors are discussed. The medium-term response of brachiopods to the relatively instable ecosystem of the tropical lagoon shows that they were not able to adapt to continuous perturbations, and that continuing stress severely compromised the resilience of benthic taxa.
•Large terebratulide brachiopods thrived in Pliensbachian lagoonal settings.•Autochthonous accumulations with abundant adults and rare juveniles.•Accumulations grew under low sedimentation rate and low hydrodynamic energy.•Stabilized by microbialites shells underwent to rapid burial and early lithification.•Unpredictable environmental changes brought about the demise of the community.
New geological and morphotectonic surface data coupled with the revision of the ENI-Exploration & Production seismic lines, made it possible to review the tectonic structure of the ...Pliocene-Quaternary front of the eastern Southern Alps in the area between the Cellina River and the Tagliamento River (central Carnic Prealps, NE Italy). The eastern Southern Alps are a SE-verging fold and thrust belt in activity from the middle Miocene to the Present. The presence of Paleogene structural inheritances influenced the current structural arrangement of the thrust-belt and the potential seismogenesis, supporting segmentation of the Neoalpine external front. In particular, the presence of the NW-SE trending Mt.Ciaurlec – Palmanova – Pozzuolo structural high, inherited from the W-ward propagation of the External Dinarides during Paleogene, generated lateral lithological facies change and influenced not only the undulation between the Neogene-Quaternary Maniago-Meduno and Toppo-Forgaria Thrusts, but also the segmentation of the outermost portion of the Neoalpine external front consisting into two segments with different geometric and structural characteristics: 1) the ENE-WSW striking Arba-Sequals segment that runs buried under the upper Pleistocene sequences of the piedmont Friuli plain; 2) the W-E Ragogna segment that shows widespread evidence of surface deformation of the Last Glacial Maximum (LGM) alluvial plain. In particular, the long-lasting activity of the Ragogna segment is testified by the late Miocene-Middle Pleistocene angular unconformities, forced drainage anomalies and tilted and uplifted Quaternary palaeosurfaces. A discussion on the seismogenic potential of the investigated structures is proposed.
•The active front of eastern Southern Alps in the carnic Prealps (NE Italy) is segmented.•The Paleogene inheritances influenced the present structural architecture of ESA Neogene-Quaternary active front.•Seismogenic potential of each active structure has been evaluated.
The Eastern Southern Alps fold‐and‐thrust belt (ESA) is part of the seismically active S‐verging retro‐wedge of the European Alps. Its temporal tectonic evolution during continental shortening has so ...far been constrained by few and low‐resolution indirect time constraints. Aiming at better elucidating the ESA spatiotemporal evolution, we gathered new structural and geochronological data from two regional thrust systems: the innermost south verging Valsugana Thrust (VT) and the more external Belluno Thrust System (BTS). Field work allowed us to constrain the geometry and kinematics of those thrusts and related folds and informed our sampling strategy to carry out fault gouge K‐Ar and tectonic carbonate U‐Pb dating from representative samples structurally associated with the VT and BTS. Our results suggest that the VT was active already in the Late Cretaceous (between ∼78 and 76 Ma) in response to far‐field stresses, with repeated reactivation continuing to the Late Miocene (∼6 Ma). The BTS recorded two distinct deformation events during the Oligocene (∼30 Ma) and at the Oligocene‐Miocene boundary (∼23 Ma). The VT was active for ∼72 Myr and partly acted during out‐of‐sequence thrusting. Based on regional correlations, we propose that the ESA share a similar spatiotemporal deformation history with the central Southern Alps farther to the west. We suggest a conceptual regional tectonic model wherein multiple, broadly coeval deformation events occurred in the entire Southern Alps during their long‐lived orogenic deformation in response to generally continuous NW‐SE shortening.
Key Points
Tectonic evolution of the Eastern Southern Alps
Long‐lived orogenic deformation in the Alps
Cretaceous far field tectonics, multiple (re)activation, and out‐of‐sequence thrusting constrained through K‐Ar and U‐Pb dating
Several parameters steer the modes of shortening of carbonate-dominated fold-and-thrust belts from incipient- (layer parallel shortening, buckle folds) to evolved deformation stages (verging folds, ...discrete thrusts). In this study, we address the spatial and temporal evolution of contractional structures within carbonate-dominated fold-and-thrust belts by documenting the geometry, kinematics and structural architecture of the San Donato-Costa Thrust Zone, a splay of the regional Belluno Thrust of the seismically active Eastern Southern Alps (Northern Italy). Deformation is there accommodated by a variety of features ranging from open and upright to tight and verging folds cut by later thrusts. An integrated structural analysis indicates inherited primary features to have effectively steered the deformation style of the thrust and its immediate hanging wall and footwall. We propose an evolving deformation scenario initially governed by the inherited lithological features and localised pressure solution, then by the geometry of folds accommodating progressive shortening and, finally, by thrusting. The folding-faulting transition occurs when fold forelimbs dip ∼80° and the ratio between the dip angle of fore- and back limbs becomes ∼3.3. These geometric boundary conditions control the mechanical behaviour of carbonate multilayer successions during orogenic shortening in fold-and-thrust belts, assisting the partitioning between seismic and aseismic deformation.
•Strain localisation in carbonate multilayers is steered by inherited primary features.•Mechanical stratigraphy governs the transition from upright to vergent folds.•Transition from folding to faulting is governed by fold geometry.•Fold geometry is key to the seismic vs aseismic character of deformation localisation.
Transverse Alpine Speciation Driven by Glaciation Wallis, Graham P.; Waters, Jonathan M.; Upton, Phaedra ...
Trends in ecology & evolution (Amsterdam),
12/2016, Letnik:
31, Številka:
12
Journal Article
Recenzirano
The allopatric model of biological speciation involves fracturing of a pre-existing species distribution and subsequent genetic divergence in isolation. Accumulating global evidence from the ...Pyrénées, Andes, Himalaya, and the Southern Alps in New Zealand shows the Pleistocene to be associated with the generation of new alpine lineages. By synthesising a large number of genetic analyses and incorporating tectonic, climatic, and population-genetic models, we show here how glaciation is the likely driver of speciation transverse to the Southern Alps. New calibrations for rates of molecular evolution and tectonic uplift both suggest a ⿼2 million-year (Ma) time frame. Although glaciation is often seen as destructive for biodiversity, here we demonstrate its creativity, and suggest a general model for speciation on temperate mountain systems worldwide.
Mountain ranges are often seen as drivers of allopatric speciation in lowland species. However, for alpine species, a range represents a long, narrow piece of available habitat. Glaciation can sever a continuously distributed population into two or more fragments.
Global climate change adds incentive to understand how distributions respond to glacial cycles.
Synthesising genetic data from hundreds of species across four major mountain ranges, transverse phylogeographic breaks are shown to be common.
Tectonic and climate modelling of the New Zealand Alps strongly implicate glaciation as a cause of this structure. Molecular and geological dating are consistent with the onset of Pleistocene glaciation. Glaciation has led to speciation in many cases, and is likely to have done so on temperate mountain ranges worldwide.
The Tolmin Basin constitutes the western part of the Slovenian Basin, a large Mesozoic interplatform basin that was bounded to the north by the Julian Carbonate Platform and to the south by the ...Dinaric Carbonate Platform. Today, it is found along the structural boundary between the Southern Alps and the External Dinarides in northwestern Slovenia. After the drowning of the Julian Carbonate Platform, the Tolmin Basin was dominated by pelagic deposits, namely the Toarcian marlstones (Perbla Formation), the Aalenian to lower Tithonian siliceous limestones and radiolarites (Tolmin Formation), and the upper Tithonian to the Berriasian Biancone Limestone Formation. In this study, a basin-scale sedimentary evolution and calpionellid biostratigraphy of the latter is presented. The Biancone Limestone Formation is a calpionellid-bearing pelagic limestone typical of all deepened segments of the Adria microplate in this time interval. It is generally monotonous but shows considerable vertical and lateral variations. The lower boundary with radiolarites is sharp, revealing a pronounced and rapid overturn in pelagic sedimentation. The lower Berriasian slumps indicate a tectonic pulse. Rare beds of resedimented limestones, assigned to the middle Berriasian, are similar in composition to those intercalated in the underlying radiolarites. They thus show that the factors that led to a significant shift in pelagic sedimentation had little or no effect on shallow-marine carbonate production. In the upper Berriasian, an increase in clay content is evident in the formation, which is explained by the uplift and erosion of the propagating thrust belt in the Neotethys area, superimposed by humidification.
Mantle xenoliths exhumed from beneath the South Island of New Zealand offer an opportunity to investigate the role of lithospheric mantle water in influencing deep lithosphere deformation and ...formation of the narrow Southern Alps mountain range during orogeny along the Australia–Pacific plate boundary. Fourier transform infrared spectrometry (FTIR) water measurements on clinopyroxene (cpx), orthopyroxene (opx) and olivine of peridotite xenoliths from seven localities across the Zealandia continent reveal a lateral variation of H2O within the Oligocene–Miocene lithospheric mantle. There is a “wet” domain beneath what is now the Southern Alps mountain range with average measured H2O concentrations of 610 ppm for cpx and 298 ppm for opx. In contrast, dominantly “dry” domains with average H2O concentrations of 110 ppm for cpx and 49 ppm for opx reside beneath East Otago, Chatham Island and Auckland Islands. Contrasting H2O concentrations within olivine (calculated to be 60 to 100 ppm for the wet domain versus <10 ppm for the dry domains) indicate a lateral gradient in mantle effective viscosity of up to one order of magnitude beneath the Southern Alps and the surrounding regions. The narrow width of the Southern Alps orogen, ∼80 km, contrasts with most of its broad counterparts worldwide, such as the North American Cordillera where the mantle was hydrated and weakened by the subduction of the Farallon plate. However, those developed orogens were often complicated by subsequent tectonic overprinting. Our findings show that the pre-existing rheologically weak zone of the mantle lithosphere, most likely resulting from hydration by the subduction of the oceanic lithosphere attached to the Australian plate beneath the South Island of New Zealand at ∼25 Ma, affects the continental deformation at or near the surface and controls the width of the developing Southern Alps orogen.
•Peridotite xenoliths show a wet mantle beneath what is now the Southern Alps orogeny.•Other Oligocene–Miocene Zealandia lithospheric mantle domains appear to be dry.•Lateral width of the Southern Alps orogen may be influenced by a narrow weak mantle.
