Full-glacial — late-glacial palaeoclimate of the Southern Andes: evidence from pollen,beetle and glacial records

Palaeoecological studies carried out in the Chilean Lake District and Chilotan Archipelago (41°–43°S) record full-glacial and late-glacial pollen assemblages beginning just after 21000 and beetle assemblages after 18000, both sets extending until 10000 ¹⁴C yr BP. Pollen records indicate that Subantarctic Parkland, the vegetation of the early millennia of record, changed after about 14000 yr BP to become open woodland and later North Patagonian Evergreen Forest. Assemblages of plants and beetles, responding more or less in unison to a strong rise in temperature (≥ 6°C), behaved in accord at around 14000 until 13000–12500 yr BP, the beetle fauna displaying a marked increase in obligate forest types. During full-glacial conditions (17400–16100 and 15300 and 14400 yr BP) and in the late-glacial interval (after about 13000 yr BP), however, climate evidently coerced populations dissimilarly, the pollen sequence showing an increase in plant taxa indicative of colder climate, whereas the beetle fauna underwent little or no variation. Contrasting climate modes implied by plants and beetles may be attributed to differential responses to apparent low-order temperature changes (≤ 2–3°C).     

Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya

Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.     

Plate Tectonics and mineralization in the Tethyan region

The association between mineralization and plate movements is becoming evident in the American Cordillera and the Pacific Island Arcs. This paper attempts to show how these ideas apply to the zone along which the Eurasian and Afro-Arabia plates collided during the late Mesozoic, between the Alps and the Himalayas. The study highlights some of the outstanding problems concerned with plate collision and the important question of the origin of ophiolite complexes. Some of the major mineralized districts in Greece, Turkey and Iran can be related to active plate edges, to island arc development and to related tectonism around pre-Mesozoic crystalline massifs. The study reinforces the view that the younger tectonic zones traversing the Middle East will become major mineral-producing areas in the future.     

Model-based covariance mean variance classification techniques:algorithm development and application to the acoustic classification ofzooplankton

For inversion problems in which the theoretical relationship between observed data and model parameters is well characterized, a promising approach to the classification problem is the application of techniques that capitalize on the predictive power of class-specific models. Theoretical models have been developed for three zooplankton scattering classes (hard elastic-shelled, e.g., pteropods; fluid-like, e.g., euphausiids; and gas-bearing, e.g., siphonophores), providing a sound basis for model-based classification approaches. The covariance mean variance classification (CMVC) techniques classify broad-band echoes from individual zooplankton based on comparisons of observed echo spectra to model space realizations. Three different CMVC algorithms were developed: the integrated score classifier, the pairwise score classifier, and the Bayesian probability classifier; these classifiers assign observations to a class based on similarities in covariance, mean, and variance while accounting for model spare ambiguity and validity. The CMVC techniques were applied to broad-band (~350-750 kHz) echoes acquired from 24 different zooplankton to invert for scatterer class and properties. All three classification algorithms had a high rate of success with high-quality high SNR data. Accurate acoustic classification of zooplankton species has the potential to significantly improve estimates of zooplankton biomass made from ocean acoustic backscatter measurements     

Analysis of seabed instability using element free Galerkin method

Wave-induced seabed instability, either momentary liquefaction or shear failure, is an important topic in ocean and coastal engineering. Many factors, such as seabed properties and wave parameters, affect the seabed instability. A non-dimensional parameter is proposed in this paper to evaluate the occurrence of momentary liquefaction. This parameter includes the properties of the soil and the wave. The determination of the wave-induced liquefaction depth is also suggested based on this non-dimensional parameter. As an example, a two-dimensional seabed with finite thickness is numerically treated with the EFGM meshless method developed early for wave-induced seabed responses. Parametric study is carried out to investigate the effect of wavelength, compressibility of pore fluid, permeability and stiffness of porous media, and variable stiffness with depth on the seabed response with three criteria for liquefaction. It is found that this non-dimensional parameter is a good index for identifying the momentary liquefaction qualitatively, and the criterion of liquefaction with seepage force can be used to predict the deepest liquefaction depth.     

Interstitial water chemistry of villefranche bay sediments: Trace metal diagenesis

Pore water aliquots were taken with an in situ close interval sampler: the “Peeper”.We report here the pore water concentration profiles of TCO₂, SO₄, TH₂S, Ca and the trace metals Mn, Cu, Pb, Cd and Cr from sediments of a relatively polluted area, the Villefranche Bay, on the French Riviera (close to Nice).We investigated the major ion concentrations in order to establish geochemical mass balances of organic matter oxidation. ΔTCO₂/ΔSO₄ was <−2.0, reflecting the precipitation of calcite as confirmed by the calcium profile. Reduction of sulfate led to increasing sulfide concentrations with depth.Trace metal interstitial water concentrations decreased from 63 to 5 nM, 18 to 4 nM and 6.6 to less than 2 nM for Cu, Pb and Cr, respectively. Cd showed a different pattern with top and deep values of 0.7 nM and a minimum of 0.27 nM.Thermodynamic calculations were performed which suggest the potential formation of mineral phases such as sulfides.     

Dispersal of the Zhujiang River (Pearl River) derived sediment in the Holocene

High-resolution Chirp profiling and coring reveals an elongated(ca. 400 km) Holocene Zhujiang River(Pearl River)-derived mud area(maximum thickness 20 m) extending from the Zhujiang River Delta, southwestward off the Guangdong coast, to the Leizhou Peninsula. Two depo-centers, one proximal and one distal, are identified. On the continental shelf off the west Guangdong Province, the mud is deposited in water depth shallower than 50 m; while to the southeast of the Zhujiang River Estuary, the mud area can extend to the-120 m isobath. A combined analysis with the stratigraphic sequences of other muddy deposits in the Western Pacific marginal seas(mainly Changjiang(Yangtze) and Huanghe(Yellow) Rivers derived) indicates that the initiation of the Zhujiang River muddy deposit can be further divided into two stages: Stage 1 is before the mid-Holocene sea-level highstand(ca. 7.0 cal. ka BP), the proximal mud was mostly deposited after 9.0 cal. ka BP, when the sea-level rose slowly after the Meltwater Pulse-1C; Stage 2, after the mid-Holocene sealevel highstand, clinoform developed on the continental shelf off the west Guangdong Province, extending ca. 400 km from the Zhujiang River Estuary. The proximal clinoform thins offshore, from ca. 10 m thickness around 5–10 m water depth to less than 1–2 m around 20–30 m water depth. In addition, we also find a developed distal clinoform in the east of the Leizhou Peninsula.     

A record of long-time rift activity and earthquake-induced ground effects in Pleistocene deposits of southern Tenerife (Canary Islands,Spain)

Faults with a well-defined strike direction that precisely coincides with the southern rift fault system occur in the study area in southern Tenerife. This fault system was generated contemporaneously with a chain of cinder cones ~948 ka. Open fractures in ignimbrites (~668 ka) and fossil beach deposits (~42 ka) of the El Médano area suggest that the rift-associated fault system was seismically active in the aftermath of the initial volcanic activity (~948 ka) and is probably still active. A second fault system striking perpendicular to the rift-related faults probably originates from a Holocene paleoearthquake of moderate intensity. Earthquake-induced ground effects in fossil beach deposits within the study area are consistent with seismically induced ground effects of several recent and well-documented earthquakes, as well as gravitational sliding triggered by an intense earthquake in the Nicoya Peninsula of Costa Rica in 1990. Both, the rift-associated and the earthquake-induced fault system, initially produced open fractures that were occupied by plants and subsequently stabilized by cementation, forming conspicuous sediment structures in fossil beach deposits of the El Médano site in southern Tenerife.