Examinando por Materia "Holocene"
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Ítem Assessing the effect of sea-level change and human activities on a major delta on the Pacific coast of northern South America: The Patía River(ELSEVIER SCIENCE BV, 2012-05-15) Restrepo A, Juan D.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThis paper presents the main physical and human-induced stresses that have shaped the recent evolution of the Patía River delta, the largest and best-developed delta on the western margin of South America. During the Holocene, the Patía Delta moved southward and the northern part became an estuarine system characterized by large extensions of mangrove ecosystems. However, a major human-induced water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, and shifted the active delta plain back to its former Holocene location. This discharge diversion has led to sediment starvation of the southern delta lobe and changed the northern estuarine system into an active delta plain. In addition, coastal areas of the Patía delta subsided as a result of a devastating tsunami in 1979. Morphological changes along the delta coast are evidenced by: (1) coastal retreat along the whole delta front during the period 1986-2001; (2) coastal retreat along the abandoned delta lobe for the period 2001-2008; 56% of the southern delta shoreline is retreating and only 4% of the coast shows signs of accretion; (3) progradation of the northern delta region during the period 2001-2008; the discharge diversion of the Patía River to the Sanquianga has apparently balanced the observed trends in coastal erosion and sea-level rise (5.1mmyr -1 for the period 1984-2006, after the 1979 tsunami); (4) formation of transgressive barrier islands with exposed peat soils in the surf zone; and (5) abandonment of former active distributaries in the southern delta plain with associated inlet closure. In the northern delta lobe, major geomorphic changes include: (1) distributary channel accretion by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, inter-distributary channel fill, and colonization of pioneer mangrove; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity<1psu) downstream; and (3) changes in vegetation succession; approximately 30% of mangrove forests in the current delta apex have been replaced by freshwater vegetation. Overall, the recent evolution of the Patía has been controlled by the interplay of (1) high basin-wide sediment load; (2) low discharge variability (Q max/Q min); (3) spatial switch of delta distributaries related to tectonic movements and subsidence; (4) a relative sea-level rise of 5.1mmyr -1 after the occurrence of the 1979 tsunami; (5) episodes of sea-level rise associated with the ENSO cycle; and (6) human-induced discharge diversion. The information presented here is valuable evidence for understanding the role of extreme events versus 'normal' conditions in creating and shaping deltas. © 2012 Elsevier B.V.Ítem Atlantic Multidecadal Oscillation (AMO) forcing on the late Holocene Cauca paleolake dynamics, northern Andes of Colombia(Copernicus GmbH, 2015-01-01) Martínez J.I.; Obrochta S.; Yokoyama Y.; Battarbee R.W.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe Atlantic Multidecadal Oscillation (AMO), is a major driving climate mechanism, in the eastern Caribbean Sea and the South Atlantic Ocean in relation to the dynamics of the South American Monsoon System (SAMS) for the late Holocene. Here we document the AMO signal in the San Nicolás-1 core of the Cauca paleolake (Santa Fé-Sopetrán Basin) in the northern Andes. Wavelet spectrum analysis of the gray scale of the San Nicolás-1 core provides evidence for a 70 yr AMO periodicity for the 3750 to 350 yr BP time interval, whose pattern is analogous to the one documented for the Cariaco Basin. This supports a possible correlation between enhanced precipitation and ENSO variability with a positive AMO phase during the 2000 to 1500 yr BP interval, and its forcing role on the Cauca ria lake deposits, which led to increased precipitation and to the transition from a igapo (black water) to a varzea (white water) environment ca. 3000 yr BP. © Author(s) 2015.Ítem Chenevo Lake : a late quaternary paleoecological reconstruction using diatoms(Universidad EAFIT, 2023) Jirado Barrios, Heylim Paola; Vélez Caicedo, María IsabelÍtem Foraminifera and coccolithophorid assemblage changes in the Panama Basin during the last deglaciation: Response to sea-surface productivity induced by a transient climate change(ELSEVIER SCIENCE BV, 2006-05-03) Martinez, Ignacio; Rincon, Daniel; Yokoyama, Yusuke; Barrows, Timothy; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe responses of community assemblages of planktonic and benthonic foraminifera and coccolithophorids to transient climate change are explored for the uppermost 2 m of cores ODP677B (1.2°N; 83.74°W, 3461 m) and TR163-38 (1.34°S; 81.58°W, 2200 m), for the last ~ 40 ka. Results suggest that the deglaciation interval was a time of increased productivity and a major reorganization of planktonic trophic webs. The succession in dominance between the planktonic foraminifera species Globorotalia inflata, Globigerina bulloides, and Neogloboquadrina pachyderma denote four periods of oceanographic change: (1) advection (24-20 ka), (2) strong upwelling (20-15 ka), (3) weak upwelling (14-8 ka) and (4) oligotrophy (8 ka to present). Strong upwelling for the deglaciation interval is supported by the low Florisphaera profunda/other coccolithophorids ratio and the high percentage abundance of Gephyrocapsa oceanica. Benthonic foraminifera assemblage changes are different in both cores and suggest significant regional variations in surface productivity and/or oxygen content at the seafloor, and a decoupling between surface productivity and export production to the seafloor. This decoupling is evidenced by the inverse relationship between the percentage abundance of infaunal benthonic foraminifera and the percentage abundance of N. pachyderma. The terrigenous input of the Colombian Pacific rivers, particularly the San Juan River, is suggested as a possible mechanism. Finally, the Globorotalia cultrata/Neogloboquadrina dutertrei ratio is used to reconstruct the past influence of the Costa Rica Dome-Panama Bight and cold tongue upwelling systems in the Panama Basin. A northern influence is suggested for the late Holocene (after 5 ka) and the last glacial (before 20 ka), whereas a southern influence is suggested for the 20-5 ka interval. There is a correspondence between our reconstructed northern and southern influences and previously proposed positions of the Intertropical Convergence Zone (ITCZ) after the Last Glacial Maximum (LGM). © 2005 Elsevier B.V. All rights reserved.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 Human induced discharge diversion in a tropical delta and its environmental implications: The Patía River, Colombia(ELSEVIER SCIENCE BV, 2012-03-06) Restrepo, Juan D.; Kettner, Albert; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe Patía River, the number one in terms of sediment yield ~1500tkm -2yr -1 draining the western South America, has the most extensive and well developed delta on the Pacific coast, measuring 1700km 2. During the Holocene, nature forced the Patía delta to the south; however, a major water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, the latter, a small stream draining internal lakes from the Pacific lowlands. This human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain. Overall, major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels, are evidenced by: (1) coastal retreat along the abandoned delta lobe; 63% of the southern shoreline is retreating at maximum rates of 7myr -1, with a corresponding coastal land loss of 106myr -1; (2) transgressive barrier islands with exposed peat soils in the surf zone; (3) abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas; (4) breaching events on barrier islands; and (5) distributary channel accretion in the northern delta plain by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, interdistributary channel fill, and colonization of pioneer mangrove. The Sanguianga Mangrove National Park (SMNP), the largest mangrove reserve in Colombia, measuring 800km 2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Observed environmental changes in the SMNP, include (1) seaward advance of the sub-aqueous delta front at the Sanquianga inlet evidenced by an increase in tidal flat area from 5.4Mm 2 in 1986 to 14Mm 2 in 2001; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity <1psu) downstream; (3) downstream advance of freshwater vegetation, which is invading channel banks in the lower and mixing estuarine zones; (4) die-off of approximately 5200ha of mangrove near the delta apex at Bocas de Satinga; and (5) recurrent periods of mangrove defoliation due to a warm plague. Further analysis indicate that during the past two decades, processes such as mangrove erosion in the delta shore, are the result of a short-term relative sea-level rise of 5.1mmyr -1 for the 1984-2006yr-period, after the devastating tsunami of 1979. In the Patía catchment, erosion rates have been more pronounced during the 1970-1980 and 1990-2000 decades, as a result of land degradation and deforestation. Preliminary results indicate that relative resent anthropogenic influences on the Patía River drainage basin have altered the deltaic environment and beyond significantly. © 2011 Elsevier B.V.Ítem Large-magnitude late Holocene seismic activity in the Pereira-Armenia region, Colombia(GEOLOGICAL SOC AMER INC, 2011-01-01) Lalinde, C.P.P.; Toro, G.E.; Velásquez, A.; Audemard, F.A.M.; Lalinde, C.P.P.; Toro, G.E.; Velásquez, A.; Audemard, F.A.M.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaThe Pereira-Armenia region, located west of the Colombian Central Cordillera, is crosscut by the Romeral fault system, which consists of an active north-south- trending, left-lateral, strike-slip fault system with a secondary thrust component in the Eje Cafetero zone (4°N-5°N). The terrain where the Liceo Taller San Miguel high school sits-9 km south of Pereira-is draped with an ~2-m-thick layer of volcanic ash younger than 30 k.y. in age. This locality has been affected by both N40°E- and E-W-trending faults that correspond to thrust faults or folds and normal rightlateral, strike-slip faults, respectively, in the tectonic model for the zone. Two kinds of strong fi eld evidence for the E-W faults were found at a site named Canchas: (1) the 50°N tilt of the late Quaternary interbedded sequence of volcanic ash and three paleosols, and (2) a vertical fault throw of ~1.70 m affecting the sequence (layers). A normal vertical throw of ~0.65 m at Parqueadero stands as a proof of the activity of the N40°E-trending faults. This latter faulting does not correspond with the stress tensor proposed for this region, and thus this deformation could be interpreted as being a consequence of fl exural slip induced by a NE-SW-striking blind thrust, where reverse faulting along bedding at depth is seen as normal faulting at the surface. Measured offsets could have generated seismic events of at least Mw 6.6 for the NE-trending fault that affected the paleosols and volcanic ash sequence at 13,150 ± 310 14C yr B.P., and a seismic event of Mw 6.9 for the E-W-trending fault that affected the paleosols and volcanic ash sequence at 19,710 ± 830 14C yr B.P. These two recently identifi edfaults are now named the Tribunas (NE-SW) and the Cestillal (E-W) faults. Up to now, the fault and its seismogenic potential determinations in this region have been based solely on morphologic evidence. The maximum seismic magnitude estimated for this region ranged from Mw 6.2 to Mw 6.6 for seismic sources 35 km away from the site. Seismic magnitudes like the one calculated in this work (Mw 6.9) were previously estimated only for source-site distances greater than 50 km. This work provides fi eld evidence that leads to a better understanding of the seismic activity of this region in the last 30 k.y. and confi rms the occurrence of local Mw >6.5 seismic events in this region. Although volcanic ash drapes and eventually hides the geomorphic evidence of active deformation, it turns out to be a perfect chronometer of a fault's activity whenever the deformation is revealed, as in this case. After the Armenia event of 1999, it is imperative to examine the seismic hazard assessments of this region in terms of local crustal seismicity. © 2011 The Geological Society of America. All rights reserved.Ítem Late Holocene evidence of coseismic subsidence on the San Juan delta, Pacific coast of Colombia(COASTAL EDUCATION & RESEARCH FOUNDATION, 2001-01-01) Gonzalez, JL; Correa, ID; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe San Juan delta of Colombia formed under a complex physical setting. Among the unusual factors that controlled the delta formation are: its location in an area with one of the highest precipitation rate anywhere in the world, highly variable river discharge and high sea levels of short duration, both associated with El Niño-La Niña climatic disturbance, and high mesotidal range combined with a medium to low wave energy. Of all the aspects that make the physical setting complex, the high seismicity produced by the subduction of the Nazca plate under the South American plate, has perhaps, been the most important controlling factor in the Late Holocene development of the delta. Coring on its SW island retrieved soils buried, 1.2-1.5 m by intertidal deposits; the sharp contact between the soils and the mantling deposits, implies large sudden submergence, which is most simply explained as being coseismic, associated with the high seismicity of the area. Timing of the earthquake that caused subsidence, is placed around 500 years BP. Evidence from recent earthquakes along the South central Pacific coast of Colombia indicates that - subsidence > 1 m requires a M 7.9 or greater earthquake.Ítem Late Holocene history of the floodplain lakes of the Cauca River, Colombia(SPRINGER, 2013-04-01) Velez, Maria Isabel; Martinez, Jose Ignacio; Suter, Fiore; Universidad EAFIT. Departamento de Geología; Ciencias del MarWe conducted a paleolimnological investigation of late Holocene deposits on a distal, constrained floodplain of the Cauca River, northern Colombia, i. e. the La Caimana sedimentary succession. The record starts sometime between 4,500 and 4,000 cal yr BP, when the first high-energy fluvial events inundated an ancient soil surface. From that time until about 3,260 cal yr BP, a stable and probably seasonal flooding regime was established on the floodplain. From ~3,260 to ~2,800 cal yr BP, ephemeral and shallow swamps developed on the floodplain. Their formation and duration depended on their connection with the Cauca River. From ~2,800 to ~2,400 cal yr BP, fluvial influence became more dominant, establishing a semi-permanent connection between the river and the floodplain. From ~2,400 to 1,400 cal yr BP, episodic formation of ephemeral swamps occurred. During this stage, floodplain lakes displayed high salinity and nutrient concentrations, and possibly alkaline conditions as a consequence of reduced water volume when the connection with the river was reduced or lost completely. A change in the hydrological regime occurred from ~1,400 to ~850 cal yr BP, when high-energy fluvial events were punctuated by periods of reduced flooding that enabled soil formation. Generally, connection with the Cauca River resulted in lake waters with low salinity and nutrient concentration, whereas loss of connection with the river led to lakes with greater salinity and nutrient content. Paleocurrent analyses indicate that flows came predominantly from the Cauca River, suggesting the lakes were formed by the impoundment of La Caimana Creek. The sedimentary succession of La Caimana offers a unique, high-resolution record of the evolution and dynamics of an ancient floodplain of the Cauca River and its aquatic ecosystems. © 2012 Springer Science+Business Media Dordrecht.Ítem Late Holocene marine terraces of the Cartagena region, southern Caribbean: The product of neotectonism or a former high stand in sea-level?(PERGAMON-ELSEVIER SCIENCE LTD, 2010-03-01) Ignacio Martinez, J.; Yokoyama, Yusuke; Gomez, Andres; Delgado, Adriana; Matsuzaki, Hiroyuki; Rendon, Esteban; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe detailed stratigraphic survey and paleontological study (mollusks, corals, foraminifera and ostracods) of four low-level, ~3 m, marine terrace sections: Punta Canoas, Manzanillo del Mar, Playa de Oro, and Tierra Bomba Island, from the Cartagena region, southern Caribbean, supplemented with 22 radiocarbon dates, reveals that the northern terraces were deposited as parasequences in a clastic depositional system compared to the Tierra Bomba Island succession that was deposited in a carbonate depositional system between ~3600 and ~1700 cal yrs BP. Drier conditions and the southern location of the ITCZ at about 3 ka triggered stronger easterly Trades and more dynamic southwestward sediment drift fed by the Magdalena River mouth, thus promoting the formation of sand spits that ultimately isolated the Cienaga de Tesca coastal lagoon from the Caribbean Sea. Our estimates support the hypothesis that the present position of the terraces is the product of neotectonism rather than a higher 3 ka, sea-level. Upheaval of the terraces varies between ~3.8 mmyr-1 at Punta Canoas and ~2.2 mmyr-1 at Tierra Bomba to ~1.5 mmyr-1 at Manzanillo del Mar and Playa de Oro terraces. Our study corroborates previous contentions on the role of mud diapirism and the dynamics of the Dique Fault as late Holocene upheaval mechanisms. © 2009 Elsevier Ltd. All rights reserved.Ítem Palynofacies analysis of the late Holocene San Nicolás terrace of the Cauca paleolake and paleohydrology of northern South America(ELSEVIER SCIENCE BV, 2011-01-01) Garcia, Yuri C.; Ignacio Martinez, J.; Velez, Maria I.; Yokoyama, Yusuke; Battarbee, Richard W.; Suter, Fiore D.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe detailed palynofacies analysis of the late Holocene laminated succession of the San Nicolás terrace in the middle Cauca Valley, northern Colombia, is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting. Radiocarbon analyses reveal that the succession was deposited between ~. 3500 and a few hundreds of years with sedimentary rates in excess of ~. 600. cm/ka. The milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin, i.e., the high altered ligno-cellulosic debris/amorphous organic matter ratio, together with diatoms typical of fluvial conditions, such as Aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the Cauca River, akin to a varzea lacustrine environment. Drier to wetter conditions appear to occur, moving upward in the succession. This might reflect regional precipitation conditions all along the Cauca Valley and the southern migration of the intertropical convergence zone. © 2010 Elsevier B.V.Ítem Reconstrucción paleoambiental del holoceno tardío con base en el análisis de palinofacies de la terraza de San Nicolás, registro del Paleolago Cauca, Colombia(Universidad EAFIT, 2011) García Castro, Yuri Carolina; Martínez Rodríguez, José Ignacio; Vélez, María IsabelNorthwestern South America is one area of greatest potential for the understanding of climate dynamics that affect the Neotropics and are of global impact. The body of this research shows in the irst part a synthesis of the climatic effects of the Medieval Warm Period (MWP, AD ~800-1300) and Little Ice Age (LIA, ~1300-1800 AD) in the Neotropics, where the diversity the paleoclimate responses and the gap in their documentation, especially in northern South America, are discussed. In the second part, the paleoenvironmental evolution of the Late Holocene (last 6000 years) San Nicolás succession in the Santa Fé de Antioquia Basin is presented.Ítem The San Nicolás succession of the Cauca paleolake: A late Holocene laminated ria lake record from the Neotropics(SPRINGER, 2013-02-01) Ignacio Martinez, J.; Mayr, Christoph; Yokoyama, Yusuke; Velez, Maria I.; Battarbee, Richard W.; Universidad EAFIT. Departamento de Geología; Ciencias del MarThe stratigraphic, geochemical, and organic matter study of the late Holocene San Nicolás succession of the Cauca paleolake (Santa Fé-Sopetrán pull-apart basin) in the middle Cauca Valley, northern Colombia, suggests that it was deposited in a ria lake environment, at sedimentary accumulation rates in excess of 600 cm ky-1 between ~3500 and ~500 yr BP. Laminated deposition occurred, first under igapo (black-water), and then under varzea (white-water) conditions. The transition occurred ca. 3000 yr BP, a time of major change in El Niño/Southern Oscillation (ENSO) behavior in the Cariaco Basin, thus reflecting the southern migration of the intertropical convergence zone and intensified rain upstream the Cauca Valley. A second, but less conspicuous change occurred ca. 2000 yr BP, which apparently corresponds to the intensified and/or more frequent ENSO activity in the Galapagos Islands. Our contribution describes, for the first time, a ria lake sedimentary succession from the northern Andes and demonstrates the high potential of these hitherto undervalued deposits for the reconstruction of the paleohydrological history of the northern Andes. © 2012 Springer Science+Business Media Dordrecht.