Showing papers on "Sea-level curve published in 2001"

Tectonic and eustatic signals in the sequence stratigraphy of the Upper Devonian Canadaway Group, New York state

Abstract: We have refined the late Frasnian to early Famennian relative sea level curve based on detailed stratigraphic data from more than 1200 outcrops in the Appalachian basin of western New York. This curve is constructed from considerations of lithologies, bedforms, and ichnofacies. We document 3 sequences and 48 parasequences in the Canadaway Group, part of the marine component of the Catskill delta complex. Several apparent lowstands and one transgression are localized along the syndepositionally active Clarendon-Linden fault system; we infer that these systems tracts are forced, and result from interaction between fault-block motion and eustatic sea level changes. This detailed study thus demonstrates that sea level curves inferred from local foreland basins may have a stronger tectonic signal than formerly perceived.

Evolução paleogeográfica da planície costeira de Itapoá, litoral norte de Santa Catarina

Abstract: The paper aims to characterize the paleogeographical evolution of the Itapoa coastal plain during the Quaternary and to compare this evolution with other proposed models. To reach the objectives the area was mapped in scale 1:50.000, sub-surface information were obtained from geotechnical drillings and paleosca-levels were inferred by radiocarbon dating performed on vermetids tubes, woodfragments and shells of Anomalocardia brasiliana samples. The paleosea-level reconstructions are consistent with the sea level curve proposed in previous works. The evolution model for the Itapoa coastal plain proposed in this work is similar to the model proposed for the coastal plain of Paranagua. The paleogeographical evolution of the Itapoa coastal plain can be summarized as: (I) formation of fans during Lower Miocene, with sea level similar or lower than the present one; (II) island-barrier formation during the Upper Pleistocene transgression maximum; (III) formation of extensive regressive barriers and later dissection by a rectangular pattern drainage system, during sea level low stand; (IV) islandbarrier formation during the Holocene transgression maximum, with inlets associated to the present mouth of Sai-Mirim and Sai-Guacu rivers; (V) formation of extensive regressive barriers during falling sea level period. During the Holocene regression, spits grew northward, moving northward the estuarine inlets as well. This drift direction is the same that was suggested for Parana and Santa Catarina north coast. During regression until present the Sai-Mirim River has eroded the Holocene barrier inland portion, that probably caused the erosion of most of the Holocene transgressive barrier-islands.

Les Sillons: a relict foredune plain

Abstract: `Les Sillons' (meaning `furrows') is the local name given to an outstanding example of a relict foredune plain on Les Iles de la Madeleine, Quebec. This series of shore-parallel dune ridges was built seaward during a period of post-glacial sea level rise, an indication of moderate to high sediment supply. Sea level has continued to rise; on the seaward side of the complex, wave erosion is now reactivating sand and active dunes are burying relict foredune ridges. Other similar features exist in Atlantic Canada (King 2000), but Les Sillons is the largest, having a maximum width of 2250 m and covering an area of 10.6 [km.sup.2]. The objectives of this article are to describe the setting and morphology of Les Sillons, and to explain its development based on regional Holocene history. Relict Foredune Plains Prograding coastlines are often associated with conditions of falling or stable sea level; however, progradation may also occur with rising sea level if there is a sufficient rate of sediment supply (Thompson and Baedke 1995; Hesp and Short 1999). Repeated construction of new foredune ridges at the back of the beach causes the shoreline to advance, or prograde, seaward. More widely spaced, lower ridges indicate more rapid progradation (Hesp 1984; Shepherd 1987). Examined closely, the `parallel' nature within a relict foredune plain is usually an approximation, as individual ridges are frequently a few degrees off parallel and merge into adjacent ridges. Genesis of foredune ridges is a subject of some controversy (Hesp 1984; Trenhaile 1997). The terms `beach ridge' and `foredune ridge' have been used both interchangeably and with differing meanings (Hesp 1984). The distinction is preferred- foredune ridges are characterized by the establishment of pioneer vegeration and can attain greater heights (swale to crest) than beach ridges. A series of arcuate shore-parallel progradational foredune ridges forms in a low wave energy sediment sink that is protected from significant prevailing longshore currents; an ideal location for these conditions is between two headlands (Komar 1998). In a higher energy coastal environment, the preservation potential of long, continuous ridges is lower; and with prevailing currents a prograding spit is more likely to form, such as Buctouche Spit, N.B. (Ollerhead and Davidson-Arnott 1995) or Long Point, Ontario (Davidson-Arnott and Conliffe Reid 1994). Regional Setting Les lies de la Madeleine are located in the southern Gulf of St. Lawrence (Figure 1). Two effects of the Laurentide ice sheet in the region during the last glacial period were depression of the crust, and provision of large quantities of sediment that were later moved onshore and used in the development of coastal landforms (Loring and Nora 1973). Deglaciation was accompanied by isostatic rebound that varied according to the thickness of ice and the passing of a forebulge, and by concurrent rising eustatic sea level (Quinlan and Beaumont 1981). Thus, the timing and magnitude of relative sea level changes in Atlantic Canada was variable. Evidence of past sea levels on Les Iles de la Madeleine is limited, and a specific sea level curve for the islands has not been produced. However, the general pattern for the southern Gulf of St. Lawrence is that the combination of isostatic rebound and eustatic sea level rise resulted in coastal emergence followed by submergence (Quinlan and Beaumont 1981; Scott et al. 1987; Grant 1989). Observations of modern sea level rise in the region are approximately 0.35 m per century (Shaw and Forbes 1990). [FIGURE 1 OMITTED] Barriers on Les Iles de la Madeleine Les Iles de la Madeleine consist of seven major bedrock islands and six major sandy depositional barriers connected to the islands (Figure 1). Two of the sandy barriers are terminal spits, and the other four comprise two double tombolo systems, separated by shallow lagoons, that extend between six of the islands. …

Geochemistry of shelf sediments off mulki on the southwestern coast of india and their palaeoenvironmental significance

Abstract: A sediment core collected from the shelf (50 m water depth) off the Mulki-Pavanje river mouth has been studied for down-core variations of base metals, magnetic susceptibility (x m ) and partitioning of metals in various accumulative phases of sediment, to understand the impact of late Quaternary sea level fluctuations on shelf sedimentation processes. The 192 cm-long core may be demarcated into two zones: the lower (140 to 192 cm) dark green to greenish black clayey silt with abundant plant debris; and the upper (0 to 140 cm) light green to dark green silty sand. Sediments of the lower zone are characterised by higher Cu, Zn, Pb, Co, Mn, Fe, Al, x m and organic matter contents and higher metal/Al ratios, but lower Ca, and Pb/Al and Mn/Al ratios when compared to the upper zone indicating textural control on the geochemistry of sediments. Although Mn is high in the lower zone, the low Mn/Al ratios suggest that a part of Mn has been remobilised under anoxic-sulphidic conditions. Higher Pb/Al ratios in the upper zone may not imply mobilisation of Pb, but may be suggestive of anthropogenic input of this element from the use of leaded petrol in modern times. Geochemical and textural variations of these sediments suggest changes in the depositional environments: Sediments of the lower zone were deposited in a marshy environment when the core site was close to the shore during the late Pleistocene low stand of sea level. The late Quaternary sea level rise led to a shift in the depositional environment - from marsh to a still stand beach environment- when silty sands were deposited. Although the core site has been in the shelf since the beginning of Holocene, there has not been much sedimentation not only because of the negligible quantity of sediment supplied by the small west-flowing rivers but also due to the rapid rise in sea level during early Holocene. The reconstructed depositional history of the core is in consonance with the recently proposed sea level curve for the western continental margin of India.

Determination of Late Pleistocene and Holocene sea level changes in the Adriatic - A review and new attempts

Abstract: The paper presents a short review of previous research of the Adriatic Sea level changes accomplished by geomorphologic, biostratigrafic, historiographic and mareographic methods, and recent attempts of reconstructing the Late Pleistocene – Holocene sea level curve of the Adriatic Sea by radiometric dating of submerged speleothems. The data for the curve will be obtained by radiocarbon dating of submerged speleothems, particularly the last stratum of the speleothems as the last upper limit when the speleothems were still growing, and marine biogenic deposits covering the speleothems, as the lower time limit when the sea flooded the caves and marine organisms started to grow over the speleothems.