Baryte and calcite cements in the 'breccias' of Ogmore-by-Sea, South Wales     

CHRIS W. LEE 《Geology Today》1991,7(4):133-136

Each year many hundreds, if not thousands, of Earth-science students visit the coastline at Ogmore-by-Sea, mid-Glamorgan. They study the excellent exposures of Lower Carboniferous Limestone, with their well-preserved coral and other shelly faunas, together with the presumed late Triassic 'breccias'* that rest unconformably on top. A study of the cements within the breccias may give an insight into syndepositional mineralization and the formation of sedimentary basins linked to the opening of the Atlantic in early Mesozoic times.  相似文献   

Late Pleistocene glacial and lake history of northwestern Russia   总被引：1，自引：0，他引：1  

EILIV LARSEN  KURT H. KJæR  IGOR N. DEMIDOV  SVEND FUNDER  KARI GRØSFJELD  MICHAEL HOUMARK-NIELSEN  MARIA JENSEN  HENRIETTE LINGE  ASTRID LYSA 《Boreas: An International Journal of Quaternary Research》2006,35(3):394-424

Five regionally significant Weichselian glacial events, each separated by terrestrial and marine interstadial conditions, are described from northwestern Russia. The first glacial event took place in the Early Weichselian. An ice sheet centred in the Kara Sea area dammed up a large lake in the Pechora lowland. Water was discharged across a threshold on the Timan Ridge and via an ice-free corridor between the Scandinavian Ice Sheet and the Kara Sea Ice Sheet to the west and north into the Barents Sea. The next glaciation occurred around 75-70 kyr BP after an interstadial episode that lasted c. 15 kyr. A local ice cap developed over the Timan Ridge at the transition to the Middle Weichselian. Shortly after deglaciation of the Timan ice cap, an ice sheet centred in the Barents Sea reached the area. The configuration of this ice sheet suggests that it was confluent with the Scandinavian Ice Sheet. Consequently, around 70-65 kyr BP a huge ice-dammed lake formed in the White Sea basin (the 'White Sea Lake'), only now the outlet across the Timan Ridge discharged water eastward into the Pechora area. The Barents Sea Ice Sheet likely suffered marine down-draw that led to its rapid collapse. The White Sea Lake drained into the Barents Sea, and marine inundation and interstadial conditions followed between 65 and 55 kyr BP. The glaciation that followed was centred in the Kara Sea area around 55-45 kyr BP. Northward directed fluvial runoff in the Arkhangelsk region indicates that the Kara Sea Ice Sheet was independent of the Scandinavian Ice Sheet and that the Barents Sea remained ice free. This glaciation was succeeded by a c. 20-kyr-long ice-free and periglacial period before the Scandinavian Ice Sheet invaded from the west, and joined with the Barents Sea Ice Sheet in the northernmost areas of northwestern Russia. The study area seems to be the only region that was invaded by all three ice sheets during the Weichselian. A general increase in ice-sheet size and the westwards migrating ice-sheet dominance with time was reversed in Middle Weichselian time to an easterly dominated ice-sheet configuration. This sequence of events resulted in a complex lake history with spillways being re-used and ice-dammed lakes appearing at different places along the ice margins at different times.  相似文献   

Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat Sea   总被引：1，自引：0，他引：1  

JØRN BO JENSEN  KAJ STRAND PETERSEN  PETER KONRADI  ANTOON KUIJPERS  OLE BENNIKE  WOLFRAM LEMKE  RUDOLF ENDLER 《Boreas: An International Journal of Quaternary Research》2002,31(2):133-150

Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region.  相似文献   

Sustainability: A View From The Paddock   总被引：1，自引：0，他引：1  

GREG BLUNDEN  CHRIS COCKLIN  WILLIAM SMITH  WARREN MORAN 《New Zealand geographer》1996,52(2):24-34

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Late- and postglacial history of the Great Belt, Denmark   总被引：3，自引：0，他引：3  

OLE BENNIKE  JØRN BO JENSEN  WOLFRAM LEMKE  ANTOON KUIJPERS  STEEN LOMHOLT 《Boreas: An International Journal of Quaternary Research》2004,33(1):18-33

On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200–300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP.  相似文献   

CALCULATIONS ON THE THERMAL CONDITIONS AROUND A SALT DIAPIR*     

P. K. JENSEN 《Geophysical Prospecting》1983,31(3):481-489

Temperature modeling around the Vejrum salt structure in Denmark shows that the heat flow near the top is twice the regional heat flow. The temperature in the vicinity of the top of the diapir is thus anomalously high. Overlying permeable formations could therefore be attractive for geothermal energy exploitation. A negative temperature anomaly of ?20°C is calculated around the root of the salt body. Comparisons between calculated and measured temperatures are used to test the model. It is shown that measurements of heat flow (or temperature gradients) in wells penetrating the region of groundwater circulation could be used in identification of salt diapirs.  相似文献   

Crustal Contamination and Fluid-Rock Interaction during the Formation of the Platreef, Northern Limb of the Bushveld Complex, South Africa   总被引：4，自引：0，他引：4  

HARRIS  CHRIS; CHAUMBA  JEFFERSON B. 《Journal of Petrology》2001,42(7):1321-1347

The Platreef is the main platinum group element (PGE)-bearingfacies of the northern limb of the Bushveld complex, but unlikethe Merensky Reef of the eastern and western limbs, it is indirect contact with the country rock. Mineral separate  相似文献   

U-series Isotope Data on Lau Basin Glasses: the Role of Subduction-related Fluids during Melt Generation in Back-arc Basins   总被引：6，自引：2，他引：6  

PEATE  DAVID W.; KOKFELT  THOMAS F.; HAWKESWORTH  CHRIS J.; VAN CALSTEREN  PETER W.; HERGT  JANET M.; PEARCE  JULIAN A. 《Journal of Petrology》2001,42(8):1449-1470

New thermal ionization mass spectrometry U-series disequilibriumdata are presented for 24 basaltic to dacitic glasses from activespreading centres in the back-arc Lau Basin (SW Pacific), togetherwith additional inductively coupled plasma mass spectrometrytrace element analyses and Sr–Nd–Pb isotope data.Valu Fa Ridge samples, adjacent to the arc front, have highU/Th and (²³⁰Th/²³⁸U) <1, implying a recent (<<350ka) addition of a U-rich slab-derived fluid. The Valu Fa datacan be combined with existing ²³⁰Th–²³⁸U data for theCentral Tonga arc to infer a fluid addition event at  相似文献   

High-resolution stratigraphy of the northernmost concentric raised bog in Europe: Sellevollmyra, Andøya, northern Norway     

KARL-DAG VORREN  MAARTEN BLAAUW  STEFAN WASTEGÅRD  JOHANNES VAN DER PLICHT  CHRISTIN JENSEN 《Boreas: An International Journal of Quaternary Research》2007,36(3):253-277

From the Sellevollmyra bog at Andøya, northern Norway, a 440‐cm long peat core covering the last c. 7000 calendar years was examined for humification, loss‐on‐ignition, microfossils, macrofossils and tephra. The age model was based on a Bayesian wiggle‐match of 35 ¹⁴C dates and two historically anchored tephra layers. Based on changes in lithology and biostratigraphical climate proxies, several climatic changes were identified (periods of the most fundamental changes in italics): 6410–6380, 6230–6050, 5730–5640, 5470–5430, 5340–5310, 5270–5100, 4790–4710, 4890–4820, 4380–4320, 4220–4120, 4000–3810, 3610–3580, 3370–3340 (regionally 2850–2750; in Sellevollmyra a hiatus between 2960–2520), 2330–2220, 1950, 1530–1450, 1150–840, 730? and c. 600? cal. yr BP. Most of these climate changes are known from other investigations of different palaeoclimate proxies in northern and middle Europe. Some volcanic eruptions seemingly coincide with vegetation changes recorded in the peat, e.g. about 5760 cal. yr BP; however, the known climatic deterioration at the time of the Hekla‐4 tephra layer started some decades before the eruption event.  相似文献   

Last Interglacial marine environments in the White Sea region, northwestern Russia     

KARI GRØSFJELD  SVEND FUNDER  MARIT-SOLVEIG SEIDENKRANTZ  CHRIS GLAISTER 《Boreas: An International Journal of Quaternary Research》2006,35(3):493-520

Marine sediments from river sections in the Mezen River drainage, northwest Russia, have been analysed for dinoflagellate cysts, foraminifers and molluscs. The sediments were dated by pollen analysis and by reference to the local sea-level history, and are Late Saalian to late Eemian (c. 133 to 119.5 kyr in age). The Late Saalian deglaciation was characterized by Arctic conditions, but a few centuries into the Eemian the Gulf Stream system carried warm Atlantic water into the region. At 129.8 kyr BP there was a marked increase in the influx of Atlantic water, and the advection of warm Atlantic water was stronger and probably penetrated further eastwards than at present. The molluscs, dinoflagellate cysts and foraminifers reflect conditions warmer than present and that the optimum temperature occurred at the time of the early Eemian global sea-level rise. Around 128 kyr BP, the eustatic sea-level rise was curbed by isostatic rebound and accompanying regression and constriction of marine passages to the White Sea. Local, low-saline, stratified basins developed and characterized the next five to six millennia.  相似文献