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Thijs R. A. Vandenbroucke Jan Hennissen Jan A. Zalasiewicz Jacques Verniers 《Geological Journal》2008,43(4):397-414
The type locality for several core elements of the Hirnantia brachiopod fauna is a small disused quarry on the western slopes of Cwm Hirnant. There, the Hirnant Limestone Member of the Foel‐y‐Ddinas Mudstone Formation yields a new, well‐preserved chitinozoan assemblage, attributed to the Spinachitina taugourdeaui Biozone. This allows tight correlation with the Hirnantian of Baltica and Laurentia and neatly ties the chitinozoan zonation with the classical brachiopod fauna. Nearby, the chitinozoan assemblage from the Caradoc Cymerig Limestone Member at Gelli‐grîn belongs to the Spinachitina cervicornis Biozone?, and is identical to that recovered from the Burrellian in the Onny Valley, Welsh Borderland. A Silurian assemblage higher up section, discovered in the Cwm‐yr‐Aethnen Formation, is attributed to the globally recognized Eisenackitina dolioliformis Biozone. Attempts to integrate the chitinozoan and graptolite biozonation, in the central Welsh Rhayader area, were less successful. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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The occurrence of organic-walled dinoflagellate cysts (dinocysts) in the Diest Formation, a largely decalcified succession with a poor fossil content, and in the adjacent strata of Lower Miocene and Lower Pliocene formations, allowed a biostratigraphic evaluation of these deposits and an assessment of the hiatus between the lithostratigraphic units. The Diest Formation was deposited during Tortonian – Messinian times. Dinocyst biozones defined in the North Sea region and the U.S.A. East Coast are recognised within the Diest Formation, although environmental factors seem to have influenced the presence of some key zonal species in the shallow-marine deposits of northern Belgium. The two members of the Diest Formation studied, i.e., the Dessel Sands and the Diest Sands, appear to be strongly diachronous. The depocentre was located in the Campine area during the early Tortonian and shifted to the area north of Antwerp during late Tortonian to Messinian times. The age assessment provides a correlation of the sequence boundaries of Haq et al. (1987) at the top of the Diest Formation with SB 5.5. 相似文献
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Jiayu Rong Michael Melchin S. Henry Williams Tatyana N. Koren Jacques Verniers 《《幕》》2008,31(3):315-318
The Global Stratotype Section and Point （GSSP） for the base of the Silurian System was defined in 1985. Since that time, a number of researchers have suggested that this section has serious deficiencies for use as a GSSP. As a result, in 2000, the Subcommission on Silurian Stratigraphy （SSS） proposed undertaking a formal restu@ of this GSSP, which was subsequently approved by the International Commission of Stratigraphy （ICS）. The result of this restudy was the formal proposal that the current GSSP, at 1.6 m above the base of the Birkhill Shale, at Dob＇s Linn, Scotland, should be maintained as the same locality and stratigraphic level, but the bios- tratigraphical definition of the boundary should be revised. The previously defined, basal Silurian grapto- lite zone, the Parakidograptus acuminatus Zone, should be subdivided into a lower Akidograptus ascensus Zone and a higher E acuminatus Zone. The base of the A. ascensus Zone, marked by the first appearance of A. ascensus, should be regarded as the biostratigraphic mark for the base of the Silurian. This proposal has now been formally approved by the SSS and ICS, and ratified by International Union of Geological Sciences. This is the first GSSP to undergo formal restudy and redefini- tion, and the proposal also included a recommended procedure for restudy of GSSPs. 相似文献
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Identification of palaeocontinental affinities is important to place Moesia in the global context of palaeogeographical reconstructions. In the absence of palaeomagnetic data and relevant macrofauna, palynological data and especially chitinozoans represent an important tool, recently used to unravel palaeogeographical affinities. Chitinozoans from three main boreholes (Călăraşi 2881, Zăvoaia 2581 and Ţăndărei 1052) located in East Moesia have been studied. They indicate a predominant palaeogeographical affinity with northern Gondwana. 相似文献
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Ann Zwertvaegher Peter Finke Jeroen De Reu Alexander Vandenbohede Luc Lebbe Machteld Bats Wim De Clercq Philippe De Smedt Vanessa Gelorini Joris Sergant Marc Antrop Jean Bourgeois Philippe De Maeyer Marc Van Meirvenne Jacques Verniers Philippe Cromb 《Geoarchaeology》2013,28(2):170-189
The complex debate on prehistoric settlement decisions is no longer tackled from a purely archaeological perspective but from a more landscape‐oriented manner combined with archaeological evidence. Therefore, reconstruction of several components of the former landscape is needed. Here, we focus on the reconstruction of the groundwater table based on modeling. The depth of the phreatic aquifer influences, for example, soil formation processes and vegetation type. Furthermore, it directly influences settlement by the wetness of a site. Palaeogroundwater modeling of the phreatic aquifer was carried out to produce a series of full‐coverage maps of the mean water table depth between 12.7 ka and the middle of the 20th century (1953) in Flanders, Belgium. The research focuses on the reconstruction of the input data and boundary conditions of the model and the model calibration. The model was calibrated for the 1924–1953 time period using drainage class maps. Archaeological site data and podzol occurrence data act as proxies for local drainage conditions over periods in the past. They also served as a control on the simulated phreatic palaeogroundwater levels. Model quality testing on an independent validation data set showed that the model predicts phreatic water table levels at the time of soil mapping well (mean error of 1.8 cm; root mean square error of 65.6 cm). Simulated hydrological conditions were in agreement with the occurrence of archaeological sites of Mesolithic to Roman age at 96% of the validation locations, and also with the occurrence of well‐drained podzols at 97% of the validation locations. 相似文献
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Summary The Brabant Massif is the southeastern part of the Caledonian fold belt known as the Anglo-Brabant Massif, which extends from East Anglia to central Belgium and is a major constituting part of the Eastern Avalonia microcontinent. Recent research in Lower Palaeozoic stratigraphy and in geophysical interpretation led to a new subcrop map of the Brabant Massif. Palaeogeographical analysis supports the rapid movement of this Massif to lower latitudes and towards Baltica in Ordovician times. Structurally, the Brabant Massif appears as a faulted antiform, flanked longitudinally to the southwest by a magmatic arc of late Ordovician to early Silurian age. An elongated gravity low points to concealed granitic intrusions below a part of the magmatic arc. 相似文献
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The presence of convergent cleavage fans in folded Silurian pelitic deposits along the southern extremity of the Brabant Massif has commonly been considered as an indication for a polyphase deformation history. Recent field work on the classic section at Ronquières shows, however, that all the structural elements can be explained by a single progressive deformation, taking place at gradually higher structural levels. This deformation is considered to have occurred at the time of the Acadian orogeny. The section under study contains a fold train of five gentle to open first-order folds, unconformably overlain by gently S-dipping Givetian rocks. Although the Silurian turbidite deposits are predominantly pelitic, the folds are characterized by convergent cleavage fans. The trend of the cleavage fan axes remains constant in the various folds throughout the section. In contrast, the trend of the folds hinge lines gradually changes along the section from a clockwise relation with the cleavage fan axis in the northern part (anticlockwise cleavage transection) towards an anticlockwise relation in the southern part (clockwise cleavage transection). Individual fault/fault intersections have a constant trend throughout the section, parallel to the cleavage fan axes and the mean fold hinge line. Small kink bands and small transverse joints reflect the same structural trend. The coaxial disposition of the structural elements seems at first sight incompatible with the presence of both clockwise and anticlockwise cleavage-transected folds. This disposition may, however, be explained by an en-echelon periclinal nature of the fold train, possibly formed in a slightly constrictional deformation environment. 相似文献
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