Examinando por Materia "sediment core"

Mostrando 1 - 3 de 3
  • No hay miniatura disponible
    Ítem
    Improved gasoline-powered soft-sediment cutter
    (SEPM-SOC SEDIMENTARY GEOLOGY, 2013-09-01) Sierra, Gloria M.; Marin-Ceron, Maria I.; Ramirez, Jackeline; Uribe, Camilo; Sierra, Gloria M.; Marin-Ceron, Maria I.; Ramirez, Jackeline; Uribe, Camilo; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
    A device used for paleomagnetic sampling has been improved which allows sampling friable, poorly to moderate lithified sedimentary and volcanic materials. The new device attaches to a portable gasoline drill and employs two steel cutting disks with a 2 cm separation, which cuts two parallel slots in the material being sampled. A second set of cuts orthogonal to the first set produces a square pedestal over which a plastic sample box can be placed and oriented to extract a cubic sample; this procedure permits using the same orientation parameters as for conventionally drilled cylindrical samples. The method allows sampling at localities where conventional drilling fails in weak materials. To test the method, sedimentary sandstones of the Amaga' Formation (Eocene-Miocene) in the NW portion of the Central Colombian Andes were sampled. The anisotropy of magnetic susceptibility (AMS) was measured on samples using the new method and compared with results from conventionally drilled cores at the same sites. Results show better AMS within-site precision for box samples compared with the drilled cores. This device improves on previous battery-powered samplers used for sampling by the double-slot procedure. Also the new device can be used with the same gasoline-powered motor for standard core drilling. Copyright © 2013, SEPM (Society for Sedimentary Geology).
  • No hay miniatura disponible
    Ítem
    Mangrove dynamics in the southwestern Caribbean since the 'Little Ice Age': A history of human and natural disturbances
    (SAGE PUBLICATIONS LTD, 2010-09-01) Gonzalez, Catalina; Estela Urrego, Ligia; Ignacio Martinez, Jose; Polania, Jaime; Yokoyama, Yusuke; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    Relatively little is known about the long-term response of Caribbean mangroves to human and natural disturbances during the 'Little Ice Age' (LIA). We present new palynological information on the dynamics of the Bahia Honda mangrove from the eastern coast of San Andres Island in the southwestern Caribbean for the late Holocene. Major changes in the Bahia Honda pollen record show the combined effects of natural events (strong storms and sea-level rise), and human disturbances. These changes are supported by 14C dates, sedimentological and palynological information. A storm (most probably a hurricane) was recorded around AD 1600, caused sediment reworking and the subsequent loss of about 2000 years of the vegetation record. The devastation of tree vegetation by this event allowed the expansion of heliophytic vegetation (e.g. grasses and vines). Mangroves and coastal vegetation started to recover at AD 1700, reaching their maximum extent within a few decades, when microforaminifera shells became abundant at the coring site, thus suggesting a relative sea-level rise because of the geomorphic reconfiguration of the coastal plain after the storm. Furthermore, the pollen evidence indicates more humid regional climates during the late LIA (AD 1700-1850). Mangrove and coastal vegetation declined sharply as a consequence of the establishment of coconut plantations around AD 1850. The recovery of the mangroves after AD 1960 is a result of the combined effect of relative sea-level rise and drastic changes in the local economy from coconut plantations to commerce. © 2010 The Author(s).
  • No hay miniatura disponible
    Ítem
    Southwest Pacific Ocean response to a warmer world: Insights from marine isotope stage 5e
    (AMER GEOPHYSICAL UNION, 2013-09-01) Cortese, G.; Dunbar, G. B.; Carter, L.; Scott, G.; Bostock, H.; Bowen, M.; Crundwell, M.; Hayward, B. W.; Howard, W.; Martinez, J. I.; Moy, A.; Neil, H.; Sabaa, A.; Sturm, A.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    Paleoceanographic archives derived from 17 marine sediment cores reconstruct the response of the Southwest Pacific Ocean to the peak interglacial, Marine Isotope Stage (MIS) 5e (ca. 125 ka). Paleo-Sea Surface Temperature (SST) estimates were obtained from the Random Forest model - an ensemble decision tree tool - applied to core-top planktonic foraminiferal faunas calibrated to modern SSTs. The reconstructed geographic pattern of the SST anomaly (maximum SST between 120 and 132 ka minus mean modern SST) seems to indicate how MIS 5e conditions were generally warmer in the Southwest Pacific, especially in the western Tasman Sea where a strengthened East Australian Current (EAC) likely extended subtropical influence to ca. 45°S off Tasmania. In contrast, the eastern Tasman Sea may have had a modest cooling except around 45°S. The observed pattern resembles that developing under the present warming trend in the region. An increase in wind stress curl over the modern South Pacific is hypothesized to have spun-up the South Pacific Subtropical Gyre, with concurrent increase in subtropical flow in the western boundary currents that include the EAC. However, warmer temperatures along the Subtropical Front and Campbell Plateau to the south suggest that the relative influence of the boundary inflows to eastern New Zealand may have differed in MIS 5e, and these currents may have followed different paths compared to today. Key Points Oceanic conditions at 125 kyr seem to agree with recent observations/trendsEast Australian Current probably stronger and Tasman Front cooler during MIS 5eObserved oceanographic changes likely linked to increases in wind stress curl ©2013. American Geophysical Union. All Rights Reserved.