Search results

Filters

  • Journals
  • Authors
  • Keywords
  • Date
  • Type

Search results

Number of results: 10
items per page: 25 50 75
Sort by:

Abstract

Three tectonic units occur in folded stratified volcanic sequence on Barton Peninsula. Fossil flora (Del Valle et al. 1984) occurs in the basal part of the upper unit which age is not younger than Paleocene. The rocks of the middle and lower units are older, possibly Mesozoie.
Go to article

Abstract

The Upper Greensand Formation, mostly capped by the Chalk, crops out on the edges of a broad, dissected plateau in Devon, west Dorset and south Somerset and has an almost continuous outcrop that runs from the Isle of Purbeck to the Vale of Wardour in south Wiltshire. The Formation is well exposed in cliffs in east Devon and the Isle of Purbeck, but is poorly exposed inland. It comprises sandstones and calcarenites with laterally and stratigraphically variable amounts of carbonate cement, glauconite and chert. The sedimentology and palaeon- tology indicate deposition in marginal marine-shelf environments that were at times subject to strong tidal and wave-generated currents. The formation of the Upper Greensand successions in the region was influenced by penecontemporaneous movements on major fault zones, some of which are sited over E-W trending Variscan thrusts in the basement rocks and, locally, on minor faults. Comparison of the principal sedimentary breaks in the succession with the sequence boundaries derived from world-wide sea-level curves suggests that local tec- tonic events mask the effects of any eustatic changes in sea level. The preserved fauna is unevenly distributed, both laterally and stratigraphically. Bivalves, gastropods and echinoids are common at some horizons but are not age-diagnostic. Ammonites are common at a few stratigraphically narrowly defined horizons, but are rare or absent throughout most of the succession. As a result, the age of parts of the succession is still poorly known
Go to article

Abstract

Attempt of correlation of raised marine beaches and glacial episodes in West Spitsbergen is presented for the Middle and the Late Quaternary. A model of predominating Barents Sea shelf ice sheet during the Saalian and of co-existing distinct local ice domes during the Vistulian is postulated on the basis of varying land uplift. Glacial episodes in Spitsbergen are referred to the ones in continental Europe and North America. Rough prognosis of climatic trends is introduced.
Go to article

Abstract

Studies of the Quaternary evolution of the Hornsund Region in Spitsbergen focused in nine key areas, in which detailed fieldworks with mapping and sampling to radiocarbon and thermoluminescence analyses have been done. Glacial history of the Hornsund Region is known from the Torellkjegla (Holsteinian) Interglacial up to the recent times. The Wedel Jarlsberg Land (Saalian) Glaciation was the most widespread in this part of Spitsbergen and consisted of two stades(?). It was followed by considerable glacier retreat during the Bogstranda (Eemian) Interglacial, the latter being represented by development of soils. Four glacier advances (the two younger ones are the Lisbetdalen and the Slaklidalen stages) occurred during the Sörkapp Land (Vistulian) Glaciation. Three glacier advances (Gronfjorden and Revdalen stages, followed by the Little Ice Age) were recognized for the Holocene. The oldest and highest (although somewhat questionable) raised marine beaches come presumably from the Wedel Jarlsberg Land Glaciation. The beaches 80-100 m a.s.l. were formed during the Bogstranda (Eemian) Interglacial. The beaches 20-60 m a.s.l. are correlated with the Sórkapp Land Glaciation. All the lower marine beaches were formed during the Holocene.
Go to article

Abstract

The δ18O data for the last 8000 years in the Greenland NGRIP1, GRIP, DYE-3 and GISP2 ice cores have been analyzed stratigraphically in search of potentially meaningful boundaries and units. Pattern matching of the profiles is supported by using graphical display enhancements, calculating spectral trend curves and generating a compound profile. Techniques routinely used in subsurface geology have been applied in correlating the profiles. Four major stratigraphic units are identified (8.1–4.9, 4.9–3.3, 3.3–1.9 and 1.9–0.1 ka b2k), resulting in an improved understanding of the climate change after the Holocene Climate Optimum. Correlatable higher-order boundaries are identified within these units. The layers between the boundaries show δ18O patterns which generally are similar in character, the differences being ascribed to lateral variations in the factors that control the isotope content of the ice. The layering forms a series of short-lived low-amplitude aperiodic oscillations on a centennial time scale. The suggestion is that these higher-order boundaries and δ18O oscillations have climatic significance. Equivalent units are tentatively identified in ice-core data from the Agassiz and Renland ice caps. Comparison with other climate proxies or stratigraphies from the Northern Hemisphere is expected to render support for the here proposed scheme. It will then serve to guide and constrain the analysis of the dynamics of the climatic fluctuations for the study period.
Go to article

Abstract

The sedimentary environment, sediment characteristics and age−depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77 ° N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment−to−lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137 Cs, 210 Pb, AMS 14 C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. A recovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14 C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137 Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age−depth model of AMS 14 C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.
Go to article

Abstract

The lithostratigraphy, biostratigraphy, sequence stratigraphy, ammonite and inoceramid faunas of the Upper Albian, Cenomanian, and Lower Turonian Karai Formation, the highest unit of the Uttatur Group in the Pondicherry Sub-Basin of the Cauvery Basin in Tamil Nadu, south India, are documented. Detailed logs and descriptions of sections between Karai and Kulakkalnattam, Odiyam and Kunnam, and north-west of Garudamangalam are presented. They provide the evidence for an ammonite zonal scheme that can be correlated in detail with sequences developed in Europe, with successive Upper Albian zones of Pervinquieria (Subschloenbachia) rostrata and P. (S.) perinflata (the latter on slight evidence), Cenomanian zones of Mantelliceras mantelli, Cunningtoniceras cunningtoni, Calycoceras (Newboldiceras) asiaticum, Pseudo calycoceras harpax, Euomphaloceras septemseriatum and Pseudspidoceras footeanum. The Lower Turonian is represented by a Neoptychites cephalotus–Mytiloides borkari fauna. Over 120 ammonite species are described, of which Puzosia (Bhimaites) falx, Protacanthoceras parva, Watinoceras elegans, Euomphaloceras varicostatum, Kamerunoceras multinodosum, and Carthaginites multituberculatus are new. The new genus Kunnamiceras, with Ammonites tropicus Kossmat, 1865 as type species, is interpreted as a paedomorphic dwarf derivative of Pseudocalycoceras harpax (Stoliczka, 1864). Ammonite faunas from shales are dominated by feebly-ornamented taxa: leiostraca; those from sandstones by strongly ornamented taxa: trachyostraca, differences interpreted as reflecting the preferred habits of adults in life. 15 species of inoceramid bivalves, including a newly described species Inoceramus chiplonkari, are recognised, with a mixed East African–Euramerican–North Pacific affinity. On the basis of the stratigraphic framework developed, a sequence stratigraphic interpretation of the Karai Formation is proposed, and correlated with those recognised in Europe, Morocco, and the United States Gulf Coast and Western Interior.
Go to article

Abstract

Geological investigations of the 4th Polish Geodynamic Expedition to West Antarctica, summer 1990/91, covered the following topics: volcanological studies and mapping at Deception Island; stratigraphic, palaeonotological and sedimentological studies, and mapping of Tertiary glacial and glacio-marine strata on King George Island; sedimentological and mesostructural studies, and mapping at Hurd Peninsula, Livingston Island; and palaeontological sampling of Jurassic (Mount Flora Formation) and Trinity Peninsula Group deposits at Hope Bay, Trinity Peninsula.
Go to article

Abstract

Geological investigations of the 3rd Polish Geodynamic Expedition to West Antarctica, 1987—1988, covered the following topics: sedimentological and mesostructural studies of the Trinity Peninsula Group (?Carboniferous — Triassic) at Hope Bay, Cape Legoupil and Andvord Bay, Antarctic Peninsula, and at South Bay. Livingston Island (South Shetland Islands); late Mesozoic plant-bearing terrestrial sediments at Hope Bay; Antarctic Peninsula Volcanic Group, Andean-type plutons and systems of acidic and basic dykes (Upper Cretaceous and ?Tertiary) at Trinity Peninsula and around Gerlache Strait (Arctowski Peninsula, Anvers and Brabant islands); basalts and hyaloclastites within Tertiary glacigenic successions of King George Island; volcanic succession of the Deception Island caldera.
Go to article

This page uses 'cookies'. Learn more