Examinando por Autor "Martinez, J. I."
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Ítem Holocene soft-sediment deformation of the Santa Fe-Sopetrán Basin, northern Colombian Andes: Evidence for pre-Hispanic seismic activity?(ELSEVIER SCIENCE BV, 2011-04-01) Suter, F.; Martinez, J. I.; Velez, M. I.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe detailed study of four deformed intervals from the Holocene fluvio-lacustrine deposits of the Santa Fe-Sopetrán Basin in northern Colombia shows 17 types of soft-sediment deformation (SSD) structures. Evidence indicates that seismic activity was responsible for the SSD structures, a conclusion reached after considering the environmental conditions at the time of sediment deposition and shortly after, and the detailed analysis of the driving force systems. Other triggers (i.e. overloading and rapid sedimentation), however, are not discarded. Intervals showing SSD structures occurred at centennial frequencies and apparently resulted from Mw 6-7 earthquakes. The Holocene age of these major shaking events should be seriously considered when evaluating the seismic hazard and risk for the middle Cauca Valley and the nearby city of Medellín with 3. million inhabitants. © 2010 Elsevier B.V.Ítem Paleoenvironmental reconstruction for the lower Pliocene Arroyo Piedras section (Tubará - Colombia): Implications for the Magdalena River - paleodelta's dynamic(PERGAMON-ELSEVIER SCIENCE LTD, 2012-11-01) Molinares, C. E.; Martinez, J. I.; Fiorini, F.; Escobar, J.; Jaramillo, C.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe Magdalena river transports one of the largest load of sediments per basin area in the world. Its delta position has changed several times over the Neogene. The Arroyo Piedras Section (169 m) in northern Colombia, contains part of the record of the Late Miocene to Early Pliocene evolution of the Magdalena paleodelta. The section was described and sampled for sedimentological and micropaleontological analyses. Based on lithofacies and benthic foraminifera content, the section was divided in three segments, and the upper segment was dated as Early Pliocene using planktonic foraminifera. The lower segment suggests siliciclastic sedimentation in a proximal prodelta/delta plain transitional environment. The intermediate segment suggests sedimentation in a lagoon and/or coastal swamp environment, whereas the upper segment is interpreted as the result of a transgression and subsequent deposition at the foreshore/upper shoreface environment, with a considerable decrease of terrigenous input. The decrease of sediment delivery to the delta produced by permanent El Niño-like conditions coupled with autocyclic processes could explain the transgressive pattern observed in the Arroyo de Piedras section during the Early Pliocene. © 2012 Elsevier Ltd.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 MarPaleoceanographic 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.