Repositorio Digital Sernageomin
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Minuta técnica : Remoción en masa en ladera de cuesta Santa Teresa, comuna de Puerto Montt
No full textMinuta técnica3 p
Fossil vertebrates of the early-middle Miocene Cerro Boleadoras Formation, northwestern Santa Cruz Province, Patagonia, Argentina
No full textThe early-middle Miocene continental Cerro Boleadoras Formation (CBF) crops out in the area of Cerro Boleadoras and Cerro Plomo on the western slope of the Meseta del Lago Buenos Aires, northwestern Santa Cruz Province, Argentina. The lower levels of the CBF consist of laterally extensive medium to pebbly sandstone beds with trough cross-bedding, interpreted as fluvial channel deposits, interbedded with tabular fine-grained floodplain deposits. Recent fieldwork provided fossil vertebrates from these levels with an estimated age between ~16.5 Ma and 15.1 Ma(late Burdigalian-early Langhian). The studied section temporally overlaps with the middle or upper sections of the Santa Cruz Formation (SCF) in the Austral-Magallanes Basin of southern Patagonia, the Río Frías Formation in Chile, and the lower Collón Curá Formation of northern Patagonia. We compile an integrated faunal list for this locality, including specimens from previous collections, and discuss its chronological and paleoenvironmental implications. The taxa list includes most of the groups recorded in the SCF: one anuran, three birds, and at least 33 mammals (metatherians, xenarthrans, litopterns, notoungulate typotheres and caviomorph rodents), indicating a Santacrucian age sensu lato. We also recorded a testudine, which constitutes the southernmost record of tortoises in South America and worldwide. Faunal dissimilarities between the vertebrate fossil content of the CBF and the mentioned sections of the Santa Cruz, Río Fríasand Collón Curá formations may reflect ecologic, climatic and geographic differences rather than temporal ones. The co-occurrence of arboreal or semiarboreal, browsing, frugivorous, and grazing mammals suggests the presence of both forested and open environments for the area occupied by the CBF rocks. However, it is not possible to discern whether these two environments coexisted or alternated, and whether one environment predominated over the other. Marker taxa, such as the chinchillid rodents Prolagostomus and Pliolagostomus, and the typothere Pachyrukhos indicate a trend to aridification during the Miocene in southern Patagonia, as previously reported for the upper part of the SCF along the Río Santa Cruz and south to the Río Coyle, along the Atlantic coast and the Río Gallegos.pp.382-42
Historia de la vegetación del sitio Huapilacuy II durante el Holoceno Medio a partir del análisis polínico y de macrofósiles vegetales, isla Grande de Chiloé, Chile
No full textEn este estudio se examina el sitio fosilífero Huapilacuy II de edad del Holoceno Medio (7.344±51-6.865±58 años cal. AP), situado en la costa noroccidental de la isla Grande de Chiloé. Esta área no fue afectada directamente por las sucesivas glaciaciones del Pleistoceno, lo que le otorga relevancia biogeográfica como potencial área de refugio y estabilidad para la vegetación. La presencia de macrofósiles vegetales, contenidos en una secuencia sedimentaria de alrededor de 300 cm de espesor, confiere un especial interés al depósito, debido a la escasa información disponible sobre este tipo de indicadores en los estudios paleoambientales del sur de Chile. Aunque numerosos registros polínicos de la región de Los Lagos (40-44˚ S) documentan, a partir del Holoceno, la recolonización de los distintos bosques templado-lluviosos que hoy ocupan este territorio, no existen registros para el Holoceno en el litoral pacífico de esta región. El objetivo deeste trabajo es reconstruir las condiciones ambientales y paleoecológicas locales con base en el contexto estratigráfico y elanálisis de los macrofósiles vegetales del sitio Huapilacuy II. Adicionalmente, a partir del análisis polínico del depósito, aportar nuevos antecedentes para la reconstrucción de las características regionales de la vegetación durante el HolocenoMedio. El registro de macrofósiles de especies palustres contenidos en los sedimentos de la parte inferior de la secuenciasedimentaria estudiada, junto con el análisis polínico de la misma, documentan una primera fase de colonización vegetal fechada en 7.344±51 años cal. AP, con predominio de Poaceae, helechos y árboles con capacidad de regeneración en áreas abiertas, como Embothrium coccineum y Drimys winteri. El análisis de los macrofósiles foliares contenidos en varias capasintercaladas en la parte media de la secuencia sedimentaria y el registro polínico del depósito evidencian el desarrollo local/regional de bosques densos, muy húmedos dominados por Aextoxicon punctatum, asociado a varias especies de Myrtaceae.Destaca la presencia de especies indicadoras de humedad edáfica, como Luma chequen, Myrceugenia sp. y Myrtaceae tipo Blepharocalyx, ensamble concordante con las condiciones de sedimentación y desarrollo local de bosques pantanosos oribereños. Este ambiente de bosque higrófilo es, además, consistente con el ensamble de los musgos fósiles del sitio, en el que predominan taxa correspondientes a los géneros Weymouthia, Ptychomnium, Rigodium, Porothamnium y Eucamptodon,característicos de bosques densos con dosel cerrado. La correlación regional del espectro polínico del sitio Huapilacuy IIcon otros registros de la región de Los Lagos permite establecer diferencias latitudinales y longitudinales en la composiciónarbórea de los bosques templado-lluviosos que se expandieron durante el Holoceno Temprano a Medio. En particular, para la costa noroccidental de la isla Grande de Chiloé se establece la presencia de la asociación costera del bosque valdiviano(As. Lapagerio-Aextoxiconetum), distribuida actualmente en el litoral chileno entre los 30 y 43˚ S. En contraste, para otras áreas de la región las asociaciones valdivianas registradas exhiben dominancia de Eucryphia cordifolia, Caldcluvia paniculata, Weinmannia trichosperma y distintas especies de Nothofagus. No obstante, las diferencias en la composiciónarbórea, las especies de briófitas fósiles registradas en varios de los sitios comparados son comunes con las reseñadas paralos bosques de la costa noroccidental de Chiloé, lo que muestra la amplitud ecológica de las briófitas chilenas asociadas abosques templado-lluviosos perennes con dosel cerrado.pp.123-14
The hydrocarbon potential of the offshore Talara Basin, Peru
No full textThe offshore Talara Basin is the western extension of the hydrocarbon producing onshore fields since the mid-1800s area of Peru and is also located above the subduction zone of the active continental margin of South America. The offshore portion was evaluated using high quality 3D seismic where mapping horizons are all unconformities within the Eocene as well as the unconformities at the top Paleocene and top Cretaceous. Possible source rocks are the Cretaceous black marine shales of the Campanian Redondo Formation, the limestones of the Albian Muerto Formation, and the marine shales of the Paleogene. The primary target offshore is expected to be deep-water turbidites of Paleocene/Eocene age with a depositional source from the northeast from highlands created by the compressional uplift of the Andes. The main seals offshore are expected to be shales of the upper Eocene Lagunitos Formation and shales in the Chacra Formation, which are also seals in the onshore Litoral field. Thermal maturation modeling shows that two hydrocarbon kitchens exist in the offshore portion of the Talara basin, one in the north and another in the south. The probable Cretaceous source rocks reached the onset of maturity (VR=0.63%) at a depth of 3,250 to 3,285 m (10,663-10,778 ft) between 30 and 39 Ma (Late Eocene to Oligocene). Importantly, the Cretaceous source rocks stay within the oil window once they enter it in the late Eocene.Satellite studies show a large offshore present-day oil seep in the southern part of the basin and 3D seismic shows directhydrocarbon indicators (DHIs) imaged as flat spots and bottom simulating reflectors (BSR). Basin modeling suggestshydrocarbon migration pathways would have been updip (to the east) into the onshore traps and would therefore havefirst filled the offshore traps along the migration pathway. We conclude that the Talara Basin offshore offers excellentexploration opportunities in a proven productive area where multiple prospects have been mappedpp.1-1
Pliocene-Pleistocene ash-fall tuff deposits in the intermountain Humahuaca and Casa Grande basins, northwestern Argentina : Tracers in chronostratigraphic reconstructions and key to identify their volcanic sources
No full textAsh-fall tuffs of the Pliocene-Pleistocene deposits of Humahuaca and Casa Grande intermountain basins, northwestern Argentina, have been differentiated into two groups based on new geochemical and geochronological data which correspond to the tuffs of the Pliocene-Lower Pleistocene alluvial fan deposits dominated by debris flow, deep sandy gravel braided, and shallow ephemeral lake deposits (Uquia and Mal Paso formations), and those recorded in Pleistocene alluvial fans sheet flood deposits. The two clusters of ages recognized: 4.3 to 2.6 Ma, and 2.2-pre 0.8 Ma, corresponding to these tuff groups, are in agreement with pulses of ignimbrite eruptions in the Altiplano Puna Volcanic Complex (APVC), and Southerm Puna calderas located west of the study region. The ash-fall tuffs of both groups are mainly vitreous to phenocryst-poor of rhyodacite-dacite composition with minor andesites to trachyandesites, characterized by 58-69% SiO2 contents, A/CNK 1-1.4, FeO/MgO (0.8-2.8), which plot in the calc-alkaline range. They can be differentiated based on its immobile trace elements ratios as indicated by a slight enrichment in LREE, higher arc affiliation and somewhat higher Sm/Yb ratios in the case of the younger group, although in both Sm/Yb ratios are indicative of sequestration of HREE in residual hornblende. The new geochemical and geochronological data of those ash fall tuffs point to these as chrono-stratigraphic tracers of the Humahuaca and Casa Grande intermountain basins stratigraphy, during the Pliocene-Pleistocene, also as the key to identify their volcanic sources.pp.208-23
Observaciones geológicas respecto a caídas de rocas en el río Maipo, sector de puente el Jaboncillo, comuna de San José de Maipo, región Metropolitana de Santiago
No full textRevisor: Alejandro Alfaro S. y Carolina Jara I.29 p
Visita técnica a sectores de la comuna de Talcahuano Región del Biobío, afectados por remociones en masa durante Julio del año 2022
No full textRevisores: Mónica Marín y Carolina Jara. ; Informe Técnico27 p
Peligro de remociones en masa de tipo flujo en la cuenca alta del río Mapocho, región Metropolitana de Santiago
Get PDFInforme Registrado IR-22-982 p
Remotely sensed time series of rapid terrace formation : Laguna del Viedma valley (Patagonia)
No full textThe Patagonian Andes were affected by a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene. Deciphering drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern terrace formation is investigated from the Laguna del Viedma valley as a modern analogue of Late Quaternary landscape evolution in Patagonia. The aim of the research was to constrain the timing of terrace formation following lake level fall of the Laguna del Viedma over a 35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from 1985-2019 to document glacier and lake changes in the study area; 2) map landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations. In total seven terrace surfaces were distinguished, with the oldest four pre-dating the ALOS PALSAR DEM (February 2000) used. Landform evidence shows the highest, and vegetated, T1 terrace surface (+40-75 m) grades to the highest lake level and was likely the elevation of the valley floor during Holocene neoglacials. Viedma glacier recession then led to a phase of lake regressions/transgressions with an overall trend of lake level fall. The DEM shows ~20 m incision from the 1985 floodplain level (T3) to the T4 level floodplain by 2000. This constrains a minimum rate of incision of 1.33 m/yr, however, the satellite time series demonstrates rapid T3 terrace formation, with evidence for mass movements contributing to lateral terrace erosion by 1986. The implications of the data are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within many large river systems of the Patagonian Andes from 42-52⁰ S. The data herein demonstrate that base level falls from sudden lake drainage events were likely a major driver of rapid landscape change in Patagonia during deglaciation.pp.169-18
