Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

The most popular models regarding the exhumation of the Greater Himalayan Sequence (GHS), such as extrusion, channel flow, critical taper and wedge extrusion, require prolonged activity of the two bounding shear zones and faults, the Main Central Thrust (MCT) and the South Tibetan Detachment (STD). We present the crystallization age of an undeformed leucogranite that intrudes both the GHS and the Tethyan Himalaya Sequence (THS). Zircon and monazite U‐Pb ages in the leucogranite give ages between 23 and 25 Ma constraining, at that time, the end of shearing along the STD. Our results limit the contemporaneous activity of the MCT and STD to a short period of time (~1–2 Ma) and thus argue against exhumation models requiring prolonged contemporaneous activity of the MCT and STD.     

Solar-Terrestrial Signal Record in Tree Ring Width Time Series from Brazil

This work investigates the behavior of the sunspot number and Southern Oscillation Index (SOI) signal recorded in the tree ring time series for three different locations in Brazil: Humaitá in Amaz?nia State, Porto Ferreira in S?o Paulo State, and Passo Fundo in Rio Grande do Sul State, using wavelet and cross-wavelet analysis techniques. The wavelet spectra of tree ring time series showed signs of 11 and 22?years, possibly related to the solar activity, and periods of 2–8?years, possibly related to El Ni?o events. The cross-wavelet spectra for all tree ring time series from Brazil present a significant response to the 11-year solar cycle in the time interval between 1921 to after 1981. These tree ring time series still have a response to the second harmonic of the solar cycle (5.5?years), but in different time intervals. The cross-wavelet maps also showed that the relationship between the SOI x tree ring time series is more intense, for oscillation in the range of 4–8?years.     

Benthic foraminifera as bio-indicators of trace element pollution in the heavily contaminated Santa Gilla lagoon (Cagliari, Italy)

In order to assess the response of benthic foraminifera to trace element pollution, a study of benthic foraminiferal assemblages was carried out into sediment samples collected from the Santa Gilla lagoon (Sardinia, Italy). The lagoon has been contaminated by industrial waste, mainly trace elements, as well as by agricultural and domestic effluent. The analysis of surficial sediment shows enrichment in trace elements, including Cr, Cu, Hg, Ni, Pb and Zn. Biotic and abiotic data, analyzed with multivariate techniques of statistical analysis, reveal a distinct separation of both the highly polluted and less polluted sampling sites. The innermost part of the lagoon, comprising the industrial complex at Macchiareddu, is exposed to a high load of trace elements which are probably enhanced by their accumulation in the finer sediment fraction. This area reveals lower diversity and higher percentages of abnormalities when compared to the outermost part of the lagoon.     

A prehistoric lahar-dammed lake and eruption of Mount Pinatubo described in a Philippine aborigine legend

The prehistoric eruptions of Mount Pinatubo have followed a cycle: centuries of repose terminated by a caldera-forming eruption with large pyroclastic flows; a post-eruption aftermath of rain-triggered lahars in surrounding drainages and dome-building that fills the caldera; and then another long quiescent period. During and after the eruptions lahars descending along volcano channels may block tributaries from watersheds beyond Pinatubo, generating natural lakes. Since the 1991 eruption, the Mapanuepe River valley in the southwestern sector of the volcano has been the site of a large lahar-dammed lake. Geologic evidence indicates that similar lakes have occupied this site at least twice before. An Ayta legend collected decades before Mount Pinatubo was recognized as a volcano describes what is probably the younger of these lakes, and the caldera-forming eruption that destroyed it.     

Late Pleistocene flank collapse of Zempoala volcano (Central Mexico) and the role of fault reactivation

Zempoala is an extinct Pleistocene (∼ 0.7–0.8 Ma) stratovolcano that together with La Corona volcano (∼ 0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S–SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E–W and NE–SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km² and has a total volume of 6 km³, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active.     

Studying the errors in the estimation of the variation of energy by the “patched-conics” model in the three-dimensional swing-by

The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach.     

Hydrodynamics of a headland-bay beach—Nearshore current circulation

This paper is devoted to the analysis of the hydrodynamic equilibrium of a headland or semi-elliptic shaped beach. It is shown that the state of equilibrium depends not only on the in- and outgoing sediment but also on the accommodation of the sediment within the embayment. The shape and relative depth of shoals, or settling zones, also directly affect the wave and current patterns inside the bay, within which the resultant breaker line almost stops wave-induced currents at some locations, whereas the magnitude of current increases at other locations. Several numerical tests are analytically conducted in a semi-elliptic beach with two symmetrical shoals of varying relative depth where circulatory current systems are detected and analyzed. Numerical modelling for wave climate and wave-induced current estimation is also presented in order to corroborate results and provide a tool for complicated and/or physical domains. The results lead to a redefinition of the concept of equilibrium for headland-bay beaches taking into account not only the net sediment transport but also the role of the formation and disappearance of settling zones, as well as sediment interchanges between the beach and shoals.     

Organic matter characterisation of the Selli Level (Umbria-Marche Basin, central Italy)

The Selli Level is a marker-bed in the Umbria-Marche Apennines that represents the regional sedimentary expression of the Lower Aptain Oceanic Anoxic Event 1a. This one to three-metre-thick interval shows a remarkable uniformity on a regional scale, with a green to grey marly lower part overlain by black shales. Bulk geochemical studies and an examination of palynofacies were carried out on three sections in order to characterise the distribution and nature of the organic matter in the Selli Level which has been poorly known hitherto. The organic content is medium (0.5 to 2.9% TOC) in the basal part and higher (4.5% on average, and up to 18% TOC) in the black shales. Pyrolysis and palynological data indicate that the organic matter is mainly of marine origin. The geochemical characteristics of the Selli Level are compared to other, more or less organic-rich marker-beds in the Cretaceous succession of the Umbria-Marche Apennines.

Abstract

Le Niveau Selli est un niveau-repère des Apennins d'Ombrie-Marches qui correspond à l'enregistrement régional de l'événement anoxique océanique 1a. Ce niveau, épais de un à trois mètres, présente une remarquable uniformité à l'échelle régionale avec une partie inférieure argileuse, verdâtre à grise, surmontée par des black shales. Des analyses géochimiques et l'examen des palynofacies ont été entreprises sur trois coupes afin de caractériser le contenu en matière organique du niveau Selli, jusqu'à présent mal connu. Les teneurs en carbone organique sont moyennes (0,5 à 2,9% COT) dans la partie basale et élevées (4,5% en moyenne et jusque 18% COT) dans les black shales. Les résultats de pyrolyse et des observations palynologiques indiquent que la matière organique est essentiellement d'origine marine. Les caractéristiques géochimiques du niveau Selli sont comparées aux autres niveaux repères, plus ou moins riches en carbone organique, qui émaillent la série du Crétacé du basin d'Ombrie-Marches.     

End member and Bayesian mixing models consistently indicate near-surface flowpath dominance in a pristine humid tropical rainforest

The impacts of forest conversion on runoff generation in the tropics have received much interest, but scientific progress is still hampered by challenging fieldwork conditions and limited knowledge about runoff mechanisms. Here, we assessed the runoff generation, flow paths and water source dynamics of a pristine rainforest catchment in Costa Rica using end member mixing analysis (EMMA) and a Bayesian mixing model (MixSIAR). Geochemical tracer data collected over a 4-week field campaign were combined with tritium data used to assess potential deeper groundwater flow pathways to the perennial stream. The streamflow composition was best captured using three end-members, namely throughfall, shallow (5–15 cm) and deeper (15–50 cm) soil water. We estimated the end-member contributions to the main stream and two tributaries using the two mixing approaches and found good agreement between results obtained from EMMA and MixSIAR. The system was overwhelmingly dominated by near-surface sources, with little evidence for deeper and older groundwater as tritium-derived baseflow mean transit time was between 2.0 and 4.4 years. The shallow soil flow pathway dominated streamflow contributions in the main stream (median 39% and 49% based on EMMA and MixSIAR, respectively), followed by the deeper soil (32% and 31%) and throughfall (25% and 19%). The two tributaries had even greater shallow soil water contributions relative to the main stream (83% and 74% for tributary A and 42% and 63% for tributary B). Tributary B had no detectable deep soil water contribution, reflecting the morphology of the hillslope (steeper slopes, shallower soils and lower vegetation density compared to hillslope A). Despite the short sampling campaign and associated uncertainties, this study allowed to thoroughly assess runoff generation mechanisms in a humid tropical catchment. Our results also provide a first comparison of two increasingly used mixing models and suggest that EMMA and MixSIAR yield comparable estimates of water source partitioning in this tropical, volcanic rainforest environment.