Hybrid coastal edges in the Neuquén Basin (Allen Formation, Upper Cretaceous, Argentina)

The Allen Formation records the first Ingression Atlantic to the Neuquén Basin during the Late Cretaceous. The definition of lithofacies and facies associations interpretation for stratigraphic sections in Paso Córdoba and Salitral Moreno area, Río Negro, Argentina allowed to establish the depositional system that characterized this transgression in the northeastern edge of the Basin. In this paper we present sedimentological analysis of conglomeratic, sandstone, heterolithic and pelitic facies, which allowed the interpretation of tidal channels (CM), intertidal flats (PI), tidal flat influenced by storms (PT), subtidal flat (PS) and shoreface deposits (CP) parts of the depositional environment. These deposits represent a sedimentary records preserved example of hybrid systems, in which, the base of the sequence has greater tidal influence, while the upper portion is dominated by wave action. The paleocurrent data indicating a NNW-SSE direction to the shore and correlations and spatial distribution of facies associations propose paleogeographic and paleoenvironmental interpretations to Malargüe Group base. Then in this paper the relationship of this coastal environment presents with wind systems previously defined in this area for the Allen Formation.Fil: Armas, María Paula. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente.; ArgentinaFil: Sanchez, Maria Lidia. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales; Argentin

Glacial and Postglacial Deposits of Northeastern Ohio

Author Institution: Department of Geology, University of AkronRecent high levels of Lake Erie have produced severe erosion and mass wasting along the shore. At the same time they have created excellent exposures of glacial and postglacial deposits east of Cleveland, Ohio. Glacial deposits consist of an older Coastal till and the Late Wisconsinan Ashtabula Till, whereas postglacial deposits generally are gravels, sands and silts. Lithofacies of the Ashtabula Till exposed at Sims Park in Euclid, Ohio, include sheared, massive diamicts and resedimented diamicts. The lowest sheared massive diamict previously identified as the Coastal till possibly represents a lodgement till deposited by Ashtabula ice. Beach deposits at Mentor Headlands resulted from construction of manmade structures. At Camp Isaac Jogues, deltaic sands overlie a sequence of diamicts, which has an unusually high carbonate content when compared to other sections along the shore. The geometry of the overlying sands and the facies sequence strongly suggest a river-dominated deltaic system. Two sand pits in beach ridges (one at the Warren level and the other at the Arkona level) farther inland contain coarse-grained facies that may represent an outwash plain or coastal barrier overlain by dune sand. A log dated at 13-4 ka was found at the Arkona level, 1 km south of the second pit

Hydrodynamic-Driven Stability Analysis of Morphological Patterns on Stalactites and Implications for Cave Paleoflow Reconstructions

A novel hydrodynamic-driven stability analysis is presented for surface patterns on speleothems, i.e., secondary sedimentary cave deposits, by coupling fluid dynamics to the geochemistry of calcite precipitation or dissolution. Falling film theory provides the solution for the flow-field and depth perturbations, the latter being crucial to triggering patterns known as crenulations. In a wide range of Reynolds numbers, the model provides the dominant wavelengths and pattern celerities, in fair agreement with field data. The analysis of the phase velocity of ridges on speleothems has a potential as a proxy of past film flow rates, thus suggesting a new support for paleoclimate analyse

Large-scale displacement along the Altyn Tagh Fault (North Tibet) since its Eocene initiation: Insight from detrital zircon U–Pb geochronology and subsurface data

International audienceMarking the northern boundary of the Tibetan plateau, the Altyn Tagh fault plays a crucial role in accommodatingthe Cenozoic crustal deformation affecting the plateau. However, its initiation time and amount of offset are stillcontroversial despite being key information for the understanding of Tibet evolution. In this study, we present1122 single LA-ICP-MS detrital zircon U–Pb ages obtained from 11 Mesozoic to Cenozoic sandstone samples, collectedalong two sections in the northwestern Qaidam basin (Eboliang and Huatugou). These data are combinedwith new3D seismic reflection profiles to demonstrate that: (1) fromthe Paleocene to early Eocene, the Eboliangsection was approximately located near the present position of Anxi, 360 ± 40 km southwest from its currentlocation along the Altyn Tagh fault, and sediments were mainly derived from the Altyn Tagh Range. At thesame period, the Huatugou section was approximately located near the present position of Tula, ca. 360 kmsouthwest from its current location along the Altyn Tagh fault, and the Eastern Kunlun Range represented a significantsediment source. (2) Left-lateral strike-slip movement along the Altyn Tagh fault initiated during theearly-middle Eocene, resulting in northeastward displacement of the two sections. (3) By early Miocene, the intensivedeformation within the Altyn Tagh Range and northwestern Qaidam basin strongly modified the drainagesystem, preventing the materials derived fromthe Altyn Tagh Range to reach the Eboliang and the Huatugousections. The post-Oligocene clastic material in the western Qaidam basin is generally derived fromlocal sourcesand recycling of the deformed Paleocene to Oligocene strata. From these data, we suggest enhanced tectonic activitywithin the Altyn Tagh Range and northwestern Qaidam basin since Miocene time, and propose an earlymiddleEocene initiation of left-lateral strike-slip faulting leading to a 360 ± 40 km offset along the Altyn Taghfaul

Geomorphological mapping of granite caves

[Abstract] The aim is to develop a mapping which represents the relief and the form (morphology) of granite caves and associated superficial structures

Discovery of sediment indicating rapid lake-level fall in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal: implication for terrace formation

Sediment indicating a rapid fall in lake level has been discovered in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal. The indicator is observed along a widely traceable erosional surface in this formation, and is characterized by (1) gently inclined (ca. 10°) tabular cross-stratified sand beds of delta front origin consisting of coarser material and showing gradual decrease in elevation of its top to the progradation direction, (2) an antidune cross-laminated sand bed that interfingers with the delta front deposit, and (3) an approximately 5 m-deep erosional depression filled with convolute laminated sand beds and recognized at a location distal to that where deposits (1) and (2) were found. The early phase of rapid lake level fall caused minor erosion of the delta plain deposits by fluvial processes, introducing a higher rate of progradation of the delta front and resulting in the accumulation of deposit (1). The delta emerged as dry land due to further lowering of the lake level. The antidune cross-laminated sand bed shows evidence of having accumulated from a high-velocity stream that may have formed as the lake water drained from the delta front during the lowering of lake level. When the lake level fell below the level of the topographic high created by delta accumulation, incised valleys may have formed and part of them may have been filled with sediment at that time. The rapid fall in lake level is interpreted to have been the result of lake-wall failure, which would have occurred at the gorge outlet as the only discharge path for the basin. The initial rise of lake level causing accumulation of terrace sediments may have been due to the formation of a plug at this outlet, attributable to mass movement along the gorge

Stratigraphic Architecture and Sediment Facies of the Western Oak Ridges Moraine, Humber River Watershed, Southern Ontario

The Oak Ridges Moraine in southern Ontario is a ca. 160 km long east-west trending ridge of sand and gravel situated north of Lake Ontario. Study of the Oak Ridges Moraine in the Humber River watershed was undertaken to assess its role in the groundwater system of the buried Laurentian Valley. The Oak Ridges Moraine is interpreted to have been deposited in three stages. Stage I records rapid deposition from hyperconcentrated flows where tunnel channels discharged into a subglacial lake in the Lake Ontario basin. Low-energy basin sedimentation of Stage II was in a subglacial and ice-contact setting of a highly crevassed ice sheet. Stage III sedimentation is characterized by rapid facies changes associated with esker, subaqueous fan, and basinal sedimentation. Detailed sediment analysis challenges the concept that the Oak Ridges Moraine was deposited principally from seasonal meltwater discharges, climatic modulated ice-marginal fluctuations, or in an interlobate position. Instead it is interpreted to have formed in response to late-glacial ice sheet events associated with subglacial meltwater ponding, episodic and catastrophic subglacial meltwater discharge, and subsequent seasonal meltwater discharge. The moraine probably formed as the glacial-hydraulic system re-equilibrated to the presence of a thinned, grounded ice shelf and a subglacial lake in the Lake Ontario basin.La moraine de Oak Ridges, sud de l’Ontario, est une crête de sable et de gravier orientée est-ouest d’une longueur de 160 km au nord du lac Ontario. L’étude de la moraine de Oak Ridges dans le bassin de la rivière Humber permet de comprendre son rôle dans le système de drainage de la vallée Laurentienne. La moraine de Oak Ridges a été édifiée en trois phases. La phase I consiste en une sédimentation rapide par hyperconcentration des écoulements, où les chenaux en tunnel se déversent dans un lac sous-glaciaire du lac Ontario. Le bassin de sédimentation de faible énergie de la phase II est sous-glaciaire et touche à un inlandsis ayant d’importantes crevasses. La phase III se caractérise par un changement de faciès très rapide, par la présence d’eskers, de cônes aquatiques et de bassins sédimentaires. Les analyses sédimentaires détaillées ébranlent l’hypothèse que la moraine de Oak Ridges ait été formée par la fonte des glaces saisonnière, les fluctuations climatiques près des marges glaciaires, ou dans une position interlobaire. Notre interprétation indique plutôt qu’elle a été mise en place en réponse à des événements de fonte sous-glaciaire de nature épisodique et catastrophique, et par des apports subséquents d’eau de fonte saisonnière. La moraine s’est probablement formée lors de la ré-équilibration du système glacio-hydraulique en présence d’un inlandsis mince, en contact avec le substrat et alimentant un lac sous-glaciaire dans le bassin du lac Ontario

Pampa del Palo : an anomalous composite marine terrace on the uprising coast of Southern Peru

Quaternary sediments along the southern Peruvian coast occur as staircase terraces of coastal and shallow-marine deposits in response to continuous uplift related to the active boundary between the Nazca and South-American plates. However, near Ilo (in the same coastal stretch) the emergent Pampa del Palo terrace consists of a relatively-thick, vertical stack of shallow-marine, coastal and lagoonal deposits that indicate a rather different geodynamic behaviour. Coastal deposits are correlatable with the successive marine highstands of isotopic stages 7 (?) and 5 (substages 5e and 5c). Combining aerial photo-interpretation, geomorphological mapping, sedimentological analysis, chronostratigraphical data, and structural observations, the Pampa del Palo feature is interpreted as a faulted block that moved independently of the remaining southern Peruvian coast and, for some time between the end of Middle Pleistocene (before ca. 220 ka) and the early Late Pleistocene (ca. 120 ka), it rose more slowly or was even down-faulted relative to the rest of the southern Peruvian margin. The independent block movements ceased after substage 5e, when the Pampa del Palo "terrace" was incorporated into the regional uplift of the area. Since ca. 100 ka, measured uplift rate in the Ilo area amounted up to 160 mm/1000 y when the area has been affected by a few active, NE-SE trending faults only. (Résumé d'auteur

Estratigrafía y arquitectura depositacional de la Formación Viamonte, Mioceno, Tierra del Fuego, Argentina: interacción entre sistemas depositacionales marinos profundos transversales y longitudinales

Los depósitos miocenos de la Formación Viamonte, cuenca de antepaís Austral, costa atlántica de Tierra del Fuego, fueron interpretados como complejos de canal-albardón marinos profundos. Nuevos datos de facies sedimentarias, paleocorrientes y relaciones estratigráficas evidencian, sin embargo, paleoambientes más complejos. En este trabajo se reconocen en la Formación Viamonte tres elementos arquitecturales mayores: 1) un sistema transversal, cárcavas (gullies) y otros depósitos de talud depositacional (clinoformas), que incluye depósitos axiales, laterales/marginales y abandono de cárcava, como sub-elementos; 2) un sistema axial, faja de canales, que incluye depósitos de relleno de canal, acreción lateral, albardones internos/terrazas, y depósitos de deslizamientos basales, como sub-elementos; y 3) otro sistema axial, albardón externo. Las cárcavas del sistema transversal están incisas en albardones externos de la Formación Viamonte o en depósitos de lóbulos más antiguos. Las facies sedimentarias más comunes son depósitos de remoción en masa en el relleno de cárcavas; turbiditas delgadas en los albardones externo, interno y terrazas; y turbi ditas arenosas de alta densidad en el relleno de canales. Las paleocorrientes están dirigidas hacia el NO-NE, pendiente abajo de las clinoformas, en el sistema transversal y hacia el SE, paralelas a la antefosa, en el sistema axial. Los sistemas axiales se localizan en la base o en quiebres de pendiente de las clinoformas transversales. La arquitectura depositacional interpretada para estos sistemas transversales y axiales constituye un excelente análogo en depósitos turbidíticos semejantes del Cretácico Superior-Paleógeno de la Cuenca Austral y puede facilitar la interpretación del origen y dispersión sedimentaria de depósitos arenosos en la adyacente cuenca de antepaís Malvinas.Miocene, foreland Austral basin strata of the Viamonte Formation in the Atlantic coast of Tierra del Fuego are currently interpreted as deep marine channel-levee complexes. New data on sedimentary facies, paleocurrents, and stratigraphic relationships documents, however, more complex settings. We recognize in the Viamonte Formation three higher-rank architectural elements: 1) a transverse system of gullies and other slope deposits, including gully axis, gully off-axis/gully margin, and slope-gully abandonment sub-elements; 2) an axial system, the channel belt, including channel fill, lateral accretion, internal-levee/terrace, and basal slumps sub-elements; and 3) another axial system, the external levee. Gullies in the transverse system are carved into external-levee deposits of the Viamonte Formation or older lobe deposits. Dominant sedimentary facies are mass transport deposits in the gully fill; thin-bedded turbidites in the external levee, internal levee, and terraces; and thick, high-density turbidite sandstones in the channel fill. In the transverse system, paleocurrents are directed to the NW-NE, down dip high-relief progradational clinoforms, and in the axial systems to the SE, parallel to the basin foredeep. Axial systems are located either at the base, or at subtle slope-breaks of transverse clinoforms. The envisaged depositional architectures of these axial and transverse systems offer excellent analogues for similar, poorly exposed Upper Cretaceous-Paleogene Austral basin turbidites and may help to interpret the source and routing of sand-rich deposits in the adjacent Malvinas foreland basin.Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; ArgentinaFil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin

Changes in the architecture of fluvial deposits in the Paganzo Basin (Upper Paleozoic of San Juan province) : an example of sea level and climatic controls on the development of coastal fluvial environments

Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for assessing the role of sea level and climatic changes on the morphology and nature of coastal fluvial systems deposited in areas of limited tectonic activity. The paleogeographic position of Huaco, close to a coastal region within the Paganzo Basin, allows identification of the effects of sea level change on fluvial architecture. Despite the fact that the Huaco area was dominated by coastal fluvial systems, three marine incursions flooded this part of the basin during the Namurian, Early Pennsylvanian and Late Pennsylvanian respectively. During deposition of the Paganzo Group, climatic conditions evolved from glacial (Namurian) to hot and dry (Late Cisuralian). Five types of fluvial deposits were recognized on the basis of architectural element analysis, lithofacies distribution and type of fluvial bounding surfaces present. Fluvial system 1 (FS1) constitutes the lower part of the Tupe Formation and consists of stacked multi-storey channel-fill complexes formed on large braided alluvial plains dominated by channel-avulsion processes. FS2 consists of multi-storey channels alternating with floodplain deposits including coal beds and organic-rich mudstones. This fluvial system is interpreted as the deposit of an anastomosed network of sandy channels. FS3 occurs between the Early Pennsylvanian and Late Pennsylvanian marine transgressions and consists of sandstones and some conglomerates that form stacked channel complexes. Sporadically, very fine-grained sandstone and mudstone floodplain deposits appear as thin intercalations. FS3 likely formed on braided alluvial plains with channels dominated by transversal bars. FS 4 corresponds to an anastomosed fluvial system that was dominated by two types of braided channel belts that were separated by narrow floodplains. Finally, FS5 is composed of fining-upward cycles ranging from gravely sandstones at the bottom of channels to muddy floodplain deposits at the top. The whole FS5 succession was deposited by high-sinuosity meandering rivers. Detailed stratigraphic analyses clearly suggest that both, sea level and climate changes were first-order controls on fluvial system configurations. In this way, braided systems belonging to FS1 correspond to a low-accommodation system tract. Whereas, coal beds of FS2, which resulted from high water-tables, correspond to a high accommodation system tract that was likely associated with advanced stages of the Late Pennsylvanian transgression. A significant change in the nature of fluvial deposits took place prior to the Late Pennsylvanian sea level rise when braided fluvial systems (FS3) with very scarce floodplain deposits prevailed. Towards the top of the Late Pennsylvanian transgressive deposits, a high relief fluvial incision surface was carved into the underlying marine deposits. This surface was later mantled by anastomosed rivers (FS4) corresponding to low-accommodation deposits formed in a lowstand or during the early stages of the ensuing sea level rise. In later phases of this transgression, high accommodation conditions prevailed and fluvial sedimentation was dominated by high-sinuosity rivers (FS5). These fluvial deposits are considered as an inland equivalent to the shallow-marine deposits exposed in the neighboring Agua Negra Formation located to the west