Search results for "processes"

Orbitally modulated black shale deposition in the upper Albian Amadeus Segment (central Italy): a multi-proxy reconstruction

2003

Abstract The upper Albian Amadeus Segment, which falls within Oceanic Anoxic Event 1c, exhibits cyclical alternations of marls/black shales and carbonate-rich beds that record evidence of orbital climate and sedimentary dynamics. A combined micropalaeontological (planktic and benthic foraminifera, and palynomorphs) and geochemical (stable isotopes, clay mineralogy, and major element distribution) investigation allowed recognition of a remarkable influence of continental material within the black shales. Moreover, the palaeoproductivity record is characterised by a non-linear response to the orbital forcing. The micropalaeontological and geochemical record suggests that upper Albian bedded c…

Zircon ages and Hf isotopic compositions of Ordovician and Carboniferous granitoids from central Inner Mongolia and their significance for early and …

2016

Abstract We present zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the evolution of central Inner Mongolia, China, in the early and late Paleozoic. Zircons of a granodiorite yielded a 206 Pb/ 238 U age of 472 ± 3 Ma that reflects the time of early Paleozoic magmatism. Zircon ages were also obtained for a tonalite (329 ± 3 Ma), quartz-diorite (320 ± 3 Ma), and granite vein (297 ± 2 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia. The dated samples are mostly granodiorite, tonalite and quartz-diorite in composition with intermediate to high-silica, high Na 2 O (3.08–4.26 w…

Serbo-Macedonian revisited: A Silurian basement terrane from northern Gondwana in the Internal Hellenides, Greece

2009

Abstract New geochronological and geochemical data on basement orthogneisses from the Vertiskos Unit of the Serbo-Macedonian Massif (SMM), Internal Hellenides, northern Greece, are used in order to constrain the pre-Alpine tectonic history of the basement units in the metamorphic hinterland of the Hellenides. The prevailing rock types in the Vertiskos crystalline basement are coarse-grained biotite augengneisses with subordinate leucocratic muscovite gneisses and two-mica gneisses. Zircon Pb–Pb and U–Pb ages on 20 samples range from 425.9 ± 4.2 Ma to 443.4 ± 5.5 Ma with a mean of 432.2 ± 3.2 Ma and are interpreted as primary crystallisation ages of the basement granites on the basis of the …

Palaeozoic arc magmatism in the Central Asian Orogenic Belt of Kazakhstan: SHRIMP zircon ages and whole-rock Nd isotopic systematics

2008

Abstract Early Palaeozoic tonalite to granodiorite intrusions in northern Kazakhstan are associated with lode gold mineralization and have SHRIMP zircon ages of 457.3 ± 6.6 Ma (Aksu), 452.9 ± 5.6 Ma and 447.4 ± 5.4 Ma (both Zholymbet). The Stepnyak intrusion contains large xenoliths with an age of 480.6 ± 5.0 Ma. One early Palaeozoic zircon from a porphyritic diorite at Stepnyak has a core with a near-concordant 207Pb/206Pb age of 3888 ± 1.5 Ma, whereas other xenocrystic grains are between 983 and 2698 Ma old. The early Archaean age is probably inherited from unexposed basement of the Kokchetav Massif and represents the oldest crustal material so far known from the Asian continent. It appea…

2021

Abstract. Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ 8, provides information on the abundance of vegetation, while the ratios C / V and S / V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the C / V and S / V ratios, and thus compli…

Peat stratigraphy and changes in peat formation during the Holocene in Latvia

2015

Mires represented by raised bogs, fens, and transitional mires cover approximately 10 % of Latvia. They started to form towards the end of the last glacial period and the beginning of the Holocene under varying geological and palaeoecological conditions. The aim of the study was to evaluate how the results of peat palaeobotanical investigation can reveal changes in the conditions of peat formation and allow a subdivision to be made of the Holocene according to the scheme suggested by the INTIMATE group (Walker et al. 2012). Records from 21 mires have been evaluated to find evidence of changes in mire vegetation and peat formation, and to discover whether these records define boundaries allo…

Tectonic beheading of fluvial valleys in the Maestrat grabens (eastern Spain): Insights into slip rates of Pleistocene extensional faults

2013

Abstract Interaction between faulting and landscape evolution in regions of active tectonics allows us to use subtle geomorphological markers for estimating fault slip rates. Geomorphic features of two valleys connected with the bottom of the Alcala de Xivert graben, at the Maestrat graben system (eastern Spain), suggest that they correspond to the lowest segments of ancient valleys whose original heads were located at the axis of the neighbouring Irta range. They were beheaded owing to displacement of the Torreblanca and Irta faults during a period of active extensional faulting in Middle Pleistocene times. These faults produced a negative inversion of the relief, sinking a narrow graben (…

Phylogeny and biogeography of fossil and extant Microtus (Terricola) (Mammalia, Rodentia) of Sicily and the southern Italian peninsula based on curre…

2011

Abstract The fossil record of the Savi vole, Microtus ( Terricola ) savii , is analyzed in terms of morphological and morphometrical variability of the first lower molar, in order to reconstruct phylogenetic relationships between insular and mainland populations and the dispersal events. The present work gives a contribution to better understand the phylogenetic history of this taxon in Sicily and Southern Italy during the interval Middle Pleistocene – Holocene, in an attempt to reconstruct the relationships between insular and continental voles and to clarify some paleobiogeographical aspects. The morphometrical data have been acquired by traditional measurements of the first lower molar a…

Vertical movements in NE Sicily and its offshore: Outcome of tectonic uplift during the last 125 ky

2013

New data in the coastal area between Acquedolci and Patti (northeastern Sicily, Italy) have been collected to calculate vertical tectonic rates in a key sector between the Kabilian-Calabrian and the Sicilian-Maghrebian chain. The comparison among marine geology data (multibeam and seismic reflection profiles) on the continental shelf-slope system and the radiocarbon ages on geomorphological markers collected during a coastal survey, provided new stratigraphic, geomorphological and biological data, contributing to the knowledge of the geological evolution of this sector for the last 125 ky.This coastal area is framed between two main structural features active during the Pleistocene in north…

Middle-Late Pleistocene marine terraces and fault activity in the Sant’Agata di Militello coastal area (north-eastern Sicily)

2012

Abstract The coastal sector of Sant’Agata di Militello (north-eastern Sicily) is characterized by a flight of raised Middle-Upper Pleistocene marine terraces occurring at different heights with respect to present sea level. In particular, the geomorphological survey and the analysis of stereo-pairs of aerial photographs allowed to recognize at least five main orders of well preserved Quaternary surfaces and relative deposits mostly located at the hanging wall and at the footwall of the Pleistocene northwest-dipping Capo d’Orlando normal fault, which controlled the geomorphological evolution of the coastal area. The marine terraces show an overall good morphological continuity and are formed…