The use of the slope–area function to analyse process domains in complex badland landscapes

This paper explores the effectiveness of the widely-used functional relationship between drainage area (A in m²) and slope (S in m/m) to identify local process domains and aid interpretation of process interactions in a complex badland landscape. In order to perform this investigation, a series of sub-basins tributary to the Formone River in the Orcia catchment (central Italy) were selected as a suitable study area within which to explore our questions, given these basins' general representativeness of local terrain, the availability of a high resolution digital terrain model and previous extensive geomorphological research. Eroding basins containing both calanchi and landslides are common in the sub-humid badland landscape of central Italy, where field observation identifies a complex pattern of erosive processes associated with a history of uplift, despite which parts of the local landscape appear disconnected. Results reveal that the shape of all S–A curves (plotted using S data binned on log A) is comparable with that described in the literature, although sub-basins containing calanchi generally plot with higher S values than non-calanchi ones, except in the ‘fluvial’ section of the plots. Second, when viewed on total data (non-binned) S–A plots, landslide source area domains and calanchi domains are entirely coincident in all basins, supporting a cause–effect relationship. Additional plotting of the frequency characteristics of the raw data in a new way supports the interpretation that calanchi frequently initiate in landslide scars. In general though, although the S–A plots can contribute to the disentanglement of geomorphological behaviour in some complex erosional landscapes, it became apparent that in this landscape, process domains do not separate out with clarity along the A axis as suggested by theory. Despite this, an alternative, broader-scale morphoevolutive model can be proposed for the development of within-landslide calanchi, driven by changes to basin connectivity to the base channel. © 2018 John Wiley & Sons, Ltd.     

Strike-slip systems as the main tectonic features in the Plio-Quaternary kinematics of the Calabrian Arc

The oblique and diachronous collision of the Apennine-Maghrebian Chain with the Apulian (in the north-east) and Pelagian (in the south) continental forelands, has determined the characteristic arcuate structure of this orogen. The effects of Plio-Pleistocene deformation of the Calabrian Arc have been analysed on the basis of available reflection seismic profiles and using local time-structural maps reconstructed along the main structures. During this period, internal sectors of the Tertiary chain migrated forward on the oceanic Ionian foreland, and were cut by important strike-slip systems. These last have an orientation approximately coincident with that of the migration of the front, allowing differential movement of the different sectors of the arc, towards the weakly buoyant Ionian oceanic domain. The dataset suggests a clear connection between the development of the strike-slip systems cutting the chain and the direction of tectonic transport, towards the East during Late Messinian/Early Pliocene time, to the ESE during Late Pliocene/Early Pleistocene time, finally to the SSE during the Middle/Late Pleistocene to Present, showing a clockwise rotation in well defined stages during the kinematic evolution of the chain. The origin of the Strait of Messina during the different phases is also interpreted in the context of the analysed regional tectonic setting.     

Diel microbial variations at a coastal Northern Adriatic station affected by Po River outflows

Diel sampling was performed during an early spring survey in the Northern Adriatic Sea at a coastal station off the Po River delta. Samples were taken every 6 h at spring tide maxima and minima in the sub-superficial layer, at the maximum fluorescence depth (∼3 m). Variations in microbial community structure and its processes were assessed by considering heterotrophic bacteria, picocyanobacteria, viruses, exoenzymatic activities, microphytoplankton, nanoplankton and bacterial/cyanobacterial Denaturing Gradient Gel Electrophoresis (DGGE) profiles. A considerable diatom bloom, mostly supported by Skeletonema marinoi was detected. All microbial parameters except viruses, showed a sinusoidal trend with a 12 h period; only picocyanobacteria expressed relative maxima during high tide, showing a phase in opposition to the other parameters. No substantial changes in DGGE band patterns were detected. Even though the results showed bacterial activities to be influenced by the phytoplankton bloom, all microbial parameters' diel trends (except viruses) preferentially followed the tidal fluctuation rather than the light:dark cycle.     

“21·11”极端暴雪过程多系统结构演变及热动力机制

利用多种实时观测资料和ERA5再分析资料,对造成2021年11月6—8日华北、东北极端暴雪过程多系统的结构特征及热动力机制进行分析。结果表明:此次过程先后由500 hPa高空横槽、河套西风槽及高空冷涡接力影响,其上空的高空急流不断加强并呈现“S”型弯曲,同时低空偏南风急流形成与加强,并在东北地区与高空急流耦合。此次过程阶段性特征明显,其影响系统的结构特征和水汽输送存在差异。回流冷锋形成的冷垫锋面较为浅薄,暖湿气流在其上倾斜上升。寒潮冷锋则较为陡立,上升气流随高度西倾。而锋面气旋结构较为深厚直立,使得气流呈垂直上升运动。随着斜压强迫的不断增强,850 hPa切变线由准东西向分布转为南北向分布,再演变为低涡切变结构。对应的水平涡度由弱转强,其上空正涡度垂直分布也逐渐加强,由弱倾斜上升运动逐步演变为较强垂直上升运动区,并在系统东侧形成次级环流下沉支。此次过程的发生发展与锋生作用密切相关,降雪落区和强度与锋区走向及锋生函数大小较为一致。假相当位温锋区在降雪3个阶段逐渐加强,垂直锋区和低层锋生函数由倾斜状态演变为近乎直立结构;湿位涡诊断表明,3个阶段降雪落区均发生在湿位涡正压项>0而斜压项...     

Positive fault inversion triggering 'intrusive diapirism': an analogue modelling perspective

Understanding the formation and the development of salt structures is very important especially because they are of significant economical interest for hydrocarbon trapping and for long-term storage of radioactive waste and energy reserves. Generally, the activity of normal faults developed in extensional regimes is considered the most efficient mechanism for salt diapirs. The results of analogue models reported in this paper suggest a new triggering mechanism for the rise of salt structures during basin inversion. This mechanism relates the localization of ductile diapirs to early normal faults only after their inversion during later shortening. In this case, diapiric growth is related to the strong dip-slip reactivation component along the fault extruding the silicone-simulating salt upward. Some natural cases, in which the timing and the mechanism of diapiric growth is not clear, can be re-interpreted in the light of these analogue model results.     

Modelling of ground deformation and gravity fields using finite element method: an application to Etna volcano

Elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources. Changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source. Contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source. Both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities. Numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions, which disregard topography, elastic heterogeneities and density subsurface structures. With this in mind, we reviewed the expected gravity changes accompanying the 1993–1997 inflation phase on Mt Etna by setting up a fully 3-D finite element model in which we used the real topography, to include the geometry, and seismic tomography, to infer the crustal heterogeneities. The inflation phase was clearly detected by different geodetic techniques (EDM, GPS, SAR and levelling data) that showed a uniform expansion of the overall volcano edifice. When the gravity data are integrated with ground deformation data and a coupled FEM modelling was solved, a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations.     

Interplay between geochemistry and magma dynamics during magma interaction: An example from the Sithonia Plutonic Complex (NE Greece)

Orogenic granitoids often display mineralogical and geochemical features suggesting that open-system magmatic processes played a key role in their evolution. This is testified by the presence of enclaves of more mafic magmas dispersed into the granitoid mass, the occurrence of strong disequilibrium textures in mineralogical phases, and/or extreme geochemical and isotopic variability.

In this contribution, intrusive rocks constituting the Sithonia Plutonic Complex (Northern Greece) are studied on the basis of mineral chemistry, whole-rock major, trace element geochemistry, and Sr and Nd isotopic composition. Sithonia rocks can be divided into a basic group bearing macroscopic (mafic enclaves), microscopic (disequilibrium textures), geochemical, and isotopic evidence of magma interaction, and an acid group in which most geochemical and isotopic features are consistent with a magma mixing process, but macroscopic and microscopic features are lacking.

A two-step Mixing plus Fractional Crystallization (MFC) process is considered responsible for the evolution of the basic group. The first step explains the chemical variation in the mafic enclave group: a basic magma, represented by the least evolved enclaves, interacted with an acid magma, represented by the most evolved granitoid rocks, to give the most evolved enclaves. The second step explains the geochemical variations of the remaining rocks of the basic group: most evolved enclaves interacted with the same acid magma to give the spectrum of rock compositions with intermediate geochemical signatures. A convection–diffusion process is envisaged to explain the geochemical and isotopic variability and the lack of macroscopic and petrographic evidence of magma interaction in the acid group.

The mafic magma is presumably the result of melting of a mantle, repeatedly metasomatized and enriched in LILE due to subduction events, whereas the acid magma is considered the product of partial melting of lower crustal rocks of intermediate to basaltic composition.

It is shown that Sithonia Plutonic Complex offers the opportunity to investigate in detail the complex interplay between geochemistry and magma dynamics during magma interaction processes between mantle and crustal derived magmas.