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Stratigraphic Position (stratigraphic + position)
Selected AbstractsHigh-resolution seismic imaging in deep sea from a joint deep-towed/OBH reflection experiment: application to a Mass Transport Complex offshore NigeriaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010S. Ker SUMMARY We assess the feasibility of high-resolution seismic depth imaging in deep water based on a new geophysical approach involving the joint use of a deep-towed seismic device (SYSIF) and ocean bottom hydrophones (OBHs). Source signature measurement enables signature deconvolution to be used to improve the vertical resolution and signal-to-noise ratio. The source signature was also used to precisely determine direct traveltimes that were inverted to relocate source and receiver positions. The very high accuracy of the positioning that was obtained enabled depth imaging and a stack of the OBH data to be performed. The determination of the P -wave velocity distribution was realized by the adaptation of an iterative focusing approach to the specific acquisition geometry. This innovative experiment combined with advanced processing succeeded in reaching lateral and vertical resolution (2.5 and 1 m) in accordance with the objectives of imaging fine scale structures and correlation with in situ measurements. To illustrate the technological and processing advances of the approach, we present a first application performed during the ERIG3D cruise offshore Nigeria with the seismic data acquired over NG1, a buried Mass Transport Complex (MTC) interpreted as a debris flow by conventional data. Evidence for a slide nature of a part of the MTC was provided by the high resolution of the OBH depth images. Rigid behaviour may be inferred from movement of coherent material inside the MTC and thrust structures at the base of the MTC. Furthermore, a silt layer that was disrupted during emplacement but has maintained its stratigraphic position supports a short transport distance. [source] Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2006B. Wohlfarth Abstract The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution 14C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono- and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and ,realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for over-dependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age,depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright © 2006 John Wiley & Sons, Ltd. [source] A tyrannosaur jaw bitten by a confamilial: scavenging or fatal agonism?LETHAIA, Issue 2 2010PHIL R. BELL Bell, P.R. & Currie, P.J. 2009: A tyrannosaur jaw bitten by a confamilial: scavenging or fatal agonism?. Lethaia, Vol. 43, pp. 278,281. A partial dentary of an adult tyrannosaur from the Dinosaur Park Formation of Alberta, Canada, preserves the embedded tooth of another tyrannosaur within the bone. The specimen's incompleteness precludes generic identification of either the jaw or the embedded tooth, although Gorgosaurus and/or Daspletosaurus are most likely given the stratigraphic position. The absence of healing around the lesion indicates the bite took place either post-mortem or within weeks prior to the death of this animal. A post-mortem bite can be explained by confamilial or cannibalistic scavenging. Alternatively, the bite would represent a perimortem instance of intrafamilial aggression that may have resulted in the death of that animal. An estimated 6053N of bite force was required to produce the bite mark. This specimen provides the best evidence for aggressive peri- or post-mortem confamilial interaction among tyrannosaurs and corroborates previous studies based on inferred tooth marks. ,Alberta, behaviour, Campanian, Cretaceous, Dinosaur Park Formation, Theropoda, Tyrannosauridae. [source] ESR/OSL ages of long-debated subtill fossil-bearing marine deposits from the southern Kola Peninsula: stratigraphic implicationsBOREAS, Issue 2 2004ANATOLY MOLODKOV The occurrence of sandy clay deposited in a warm marine environment just below the till of the last glaciation has created controversy about its age and stratigraphic position in the sedimentary basin of the Kola Peninsula. Data on marine microfauna, diatoms, malacofauna and pollen composition indicate that during the period when the sandy clay was deposited the climate was similar or even warmer than at present. According to 14C dates, sedimentation of the sandy clay occurred around 40 ka BP. Based on these data, some researchers have attributed these marine deposits to the third Late Pleistocene Belomorian (sensu Lavrova 1960) interglacial transgression. At the same time there are geological indications suggesting re-deposition of these subtill sediments. To solve this problem we have reinvestigated the subtill interglacial marine deposits from the Varzuga section (,66.4° N and 36.6° E). Four different marine shell species and enclosing sandy clay sediments taken from the subtill marine unit of the section were dated by the electron spin resonance (ESR) and optically-stimulated luminescence (OSL) methods at about 103 and 104 ka, respectively. The results indicate that the subtill marine deposits belong to the first Late Pleistocene Boreal transgression that, according to our previous studies of the marginal areas of the Eurasian North, has occurred in the time interval from approximately 145 to 70 ka BP. [source] Paleoindian environmental change and landscape response in Barger Gulch, Middle Park, ColoradoGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2005James H. Mayer Middle Park, a high-altitude basin in the Southern Rocky Mountains of north-central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (,10,500 14C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest-Pleistocene soil and a younger mollic epipedon formed between ,6000 and 5200 14C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ,10,200 and 9700 14C yr B.P., and that the erosion is likely related to truncation of the latest-Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ,10,000 and 9700 14C yr B.P. was followed by rapid aggradation between ,9700 and 9550 14C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ,11,000,10,000 14C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ,9500 and 8000 14C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (,11,000,10,000 14C yr B.P., 76%) relative to late Paleoindian sites (,10,000,8000 14C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc. [source] Hominid Mandibular Remains from Sangiran: 1952,1986 CollectionAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2005Yousuke Kaifu Abstract Eight hominid mandibular and associated dental remains discovered between 1952,1986 from the Early Pleistocene deposits of Sangiran, Central Java, are described. Although the specimens are surface finds, their original stratigraphic positions can be reasonably inferred on the basis of coincidental sources of information. These specimens significantly increase the dento-gnathic sample available for intensive morphological investigation of the earliest Javanese hominids [Kaifu et al., 2005]. Am J Phys Anthropol, 2005. © 2005 Wiley-Liss, Inc. [source] | ||||||||||