455 research outputs found
Pleistocene tunnel valleys in the North Sea Basin
No full textTunnel valleys were first described over a century ago from the glaciated lowlands of northern Europe (Jentzsch 1884). Landforms described as tunnel valleys constitute open, partially or fully buried palaeo-landforms. Over the past 40 years the proliferation of geophysical surveys has allowed almost complete mapping of tunnel valleys across the North Sea Basin (Huuse & Lykke-Andersen 2000; Van der Vegt et al. 2012). In the central and southern North Sea, 3D seismic surveys completely image tunnel valley systems at a resolution of tens of metres (Fig. 1) (Praeg 1996; Stewart et al. 2013; Moreau & Huuse 2014)
Dinámica de zonas de subducción y evolución tectono-estratigráfica de antearco: cuenca Talara, noroeste del Perú
Get PDFForearc basins are important archives for understanding the tectonic evolution of the plate margin and subduction zone through deep time because they preserve a tectonostratigraphic record of temporal and spatial interactions of eustasy, sediment supply, climate, basin physiography and tectonism. However, forearc basins have received less attention than rift and foreland basins, due to the limited number of exposed examples and classification traditionally restricted to accretionary margins. The Talara Basin in the northern Peruvian forearc, where the oceanic Nazca plate is being subducted beneath the continental South American plate, is a well-known example of a subduction-erosion margin, where the edge of the continental plate is consumed over time and accretionary processes play a minor role. From the Late Cretaceous to the Eocene, stratigraphic units from deep water to fluvial environments comprise a 9 km-thick basin fill that has been episodically deformed by extensional faulting due to forearc vertical movements produced by subduction. This work aims to characterise the spatial and temporal behaviour of subduction and how these processes are recorded in and affect the evolution of the forearc basin. The sequence stratigraphic approach is based on the integration of outcrop, well and seismic data sets. Sedimentology and analysis of stratal stacking patterns and key stratigraphic surfaces, integrated with tectonic studies show that the Eocene Parià ±as Formation comprises three depositional sequences of fluvio-deltaic deposits that form a highstand sequence set. The succession is capped by a previously unrecognised composite sequence boundary marked by a regional palaeosol and overlain by the transgressive sequence set of the Chacra Formation. The composite sequence boundary may indicate the presence of a lowstand sequence set offshore. This integrated PhD project identified tectonically-enhanced/driven regressions and transgressions through the Eocene. Down-dip and across-strike system asymmetry was a response to uplift and extensional collapse events related to periods of locking and release of the subduction interface. These observations highlight the importance of a close temporal and spatial relationship between plate boundary and basin - a relationship unique to forearc basins, with worldwide application.El área de estudio es la cuenca Talara, localizada en el norte del antearco peruano, en la margen convergente entre las placas de Nazca y Sudamérica. Los principales análisis realizados en este trabajo consisten en la interpretación geológica de sísmica de reflexión y sus atributos, análisis y correlación de registros de pozo, descripción de núcleos, muestreo y levantamiento estratigráfico de afloramientos, análisis bioestratigráfico, y petrografía de secciones delgadas. Estos análisis a multi-escala (cuenca–microscopio) están basados en la integración de los datos empleados, tanto en tierra como costa afuera. La motivación fundamental de este trabajo es abordar la brecha de conocimiento sobre cómo el proceso de subducción influye en la estratigrafía secuencial de antearco, especialmente en escenarios de subducción con erosión, ya que el grado de influencia de los factores que controlan la sedimentación en márgenes convergentes tectónicamente activas no está bien identificado como en otras cuencas, debido a la falta de previos trabajos. Los objetivos específicos de este estudio son tres: (i) caracterizar y clasificar los procesos de subducción de la margen continental del norte peruano; (ii) caracterizar la geodinámica de antearco en el tiempo; (iii) construir modelos estratigráfico-secuenciales y tectónicos para entender las condiciones paleoambientales de sedimentación.Perú. Programa Nacional de Becas y Crédito Educativo (Pronabec). Beca Generación del BicentenarioTesi
Introduction : Subsurface sand remobilization and injection
Get PDFAcknowledgement Thanks are due for informal information provided on the Nanaimo, Tierra del Fuego and Neoquen basins (David Hodgson), the East Carpathian Fold Belt (Alexandra Tamas) and the Paraná Basin (Gus- tavo Zvirtes). Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.Peer reviewe
Hydrothermal vent complexes offshore Northeast Greenland : A potential role in driving the PETM
No full textTGS are thanked for access to data and Dwarika Maharjan is thanked for help with Kingdom software. Andy Saunders and Mads Huuse are thanked for insightful, constructive reviews and Tamsin Mather is thanked for editorial handling.Peer reviewe
Iceberg scour shapefiles from the Naust Formation on the mid-Norwegian margin
No full textThis data contains a zipped file with digitised records of iceberg scours from five seismic units that comprise the glaciogenic stratigraphy on the mid-Norwegian shelf. These records have been used to investigate iceberg trajectories during the time period covered by each seismic unit.This provides information on the palaeo-oceanography and the dominant ocean currents on the mid-Norwegian shelf during the Pleistocene when the scours were formed
Infill of tunnel valleys associated with landward-flowing ice sheets: The missing Middle Pleistocene record of the NW European rivers?
No full textThe southern termination of the Middle and Late Pleistocene Scandinavian ice sheets was repeatedly located in the southern North Sea (sNS) and adjacent, north-sloping land areas. Giant meltwater- excavated valleys (tunnel valleys) formed at the southern termination of the ice sheets and contain a hitherto enigmatic succession of northward prograding clinoforms, comprising 1000s km3 of sediment. This study analyses 3D seismic data, covering the entire sNS, and demonstrates for the first time that the formation of these tunnel valleys was separate from their infill. The infill constitutes the postglacial record of the NW European river deltas, which had so far been considered missing
Glacial geomorphology of the central Barents Sea: implications for the dynamic deglaciation of the Barents Sea Ice Sheet
Get PDFContemporary climate change has resulted in great uncertainty in how glaciers and ice sheets around the Earth might evolve. It has long been appreciated that the contemporary West Antarctic Ice Sheet (WAIS) shares many similarities with the former Barents Sea Ice Sheet (BSIS). Therefore, an increasing number of studies have sought to investigate the Barents Sea glacial record to better understand marine-based glaciation. This paper reports the analysis of a new high-resolution bathymetric survey covering ~ 55,000 km2 in the central Barents Sea. The relative chronologies of newly-mapped glacial landforms such as mega-scale glacial lineations, grounding-zone wedges, moraines, and crevasse-squeeze ridges are used to reconstruct the ice sheet dynamics in the central Barents Sea. Our results show that the ice sheet responded dynamically with different periods of retreat, advance, and stagnation observed. These new landform records have been integrated with other geomorphological records in order to reconstruct the retreat pattern of the BSIS between 17–14 ka, when the Fennoscandian Ice Sheet is thought to have uncoupled from the BSIS. Our data shows that the dynamic drawdown of the ice sheet saddle by ice streams was probably the primary mechanism in separating the two ice sheets. After the ice sheets uncoupled, the BSIS is shown to have retreated episodically with several periods of relative stability. Geomorphological records such as those from the BSIS can be used to constrain ice sheet modelling and will help to develop a clearer understanding of marine-based glaciation and the role of ice streams in driving ice sheet evolution
Pockmark formation by porewater expulsion during rapid progradation in the offshore Taranaki Basin, New Zealand
Get PDFAfter the first discovery of seabed pockmarks in the 1960s and 1970s, many examples of both modern and ancient pockmarks have been reported from sedimentary basins around the world. The exact mechanisms and fluids involved in pockmark formation are still subject to debate with many studies inferring that pockmark formation is a direct indication of hydrocarbon expulsion. This study provides the first description of a buried Pliocene paleo-pockmark field in the offshore Taranaki Basin, New Zealand. The paleo-pockmarks are located approximately 1.2–1.3 km below the seabed and are well imaged by three-dimensional seismic data. Their spatial density and size increases towards the distal portions of the fan, and they vary in size between 45 and 580 m in diameter and 2–35 ms TWT. Pockmark size is inversely correlated with the fan thickness in the study area. Detailed analysis rules out any links with faulting, while the relationship with fan variations in the depositional thickness suggests porewater expulsion during overburden progradation as the most likely cause of the paleo-pockmarks. A model is proposed in which rapid sediment loading generated overpressure which was greatest on the proximal fan due to the lateral gradient in the sediment load imposed by clinoform progradation. Fluids were consequently forced towards the distal fan where, eventually, the pore pressure exceeded the fracture gradient of the seal. The implications of this study are that not all pockmarks can be used as evidence for hydrocarbon expulsion in frontier regions and care should be taken to examine the subsurface context, plumbing systems and any associated acoustic anomalies before concluding on the pockmark origin.</p
FERTILIZATION-INDEPENDENT SEED-Polycomb Repressive Complex 2 Plays a Dual Role in Regulating Type I MADS-Box Genes in Early Endosperm Development
Get PDFEarly endosperm development presents a unique system in which to uncover epigenetic regulatory mechanisms because the contributing maternal and paternal genomes possess differential epigenetic modi?cations. In Arabidopsis (Arabidopsis thaliana), the initiation of endosperm coenocytic growth upon fertilization and the transition to endosperm cellularization are regulated by the FERTILIZATION-INDEPENDENT SEED (FIS)-Polycomb Repressive Complex 2 (PRC2), a putative H3K27 methyltransferase. Here, we address the possible role of the FIS-PRC2 complex in regulating the type I MADS-box gene family, which has been shown previously to regulate early endosperm development. We show that a subclass of type I MADS-box genes (C2 genes) was expressed in distinct domains of the coenocytic endosperm in wild-type seeds. Furthermore, the C2 genes were mostly up-regulated biallelically during the extended coenocytic phase of endosperm development in the FIS-PRC2 mutant background. Using allele-speci?c expression analysis, we also identi?ed a small subset of C2 genes subjected to FIS-PRC2-dependent maternal or FIS-PRC2-independent paternal imprinting. Our data support a dual role for the FIS-PRC2 complex in the regulation of C2 type I MADS-box genes, as evidenced by a generalized role in the repression of gene expression at both alleles associated with endosperm cellularization and a specialized role in silencing the maternal allele of imprinted genes
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