Mass transport events are virtually ubiquitous on the modern continental slope, and are also frequent in the stratigraphic record. They are commonly very large (volumes >10 3 km 3 , areas >10 4 km 2 , thicknesses >10 2 m). They extensively remould sea-floor topography on the continental slope and rise. Turbidity currents are highly sensitive to topography, thus turbidite reservoir distribution and geometry can be significantly affected by subjacent mass transport deposits or their slide scars. Given the abundance of mass transport deposits, we should expect that many turbidite systems are so affected. In fact several well-known deepwater outcrops may represent examples of MTD-influenced sedimentation. Turbidites may be captured within slide scars and on the trailing edges of MTDs. They may also be ponded on and around mass transport deposits, in accommodation developed when the mass movement comes to rest, or subsequently due to compaction or creep. The filling of such accommodation depends on the properties of the turbidity currents, their depositional gradient, and how they interact with basin floor topography. The scale of supra-MTD accommodation is determined largely by dynamics of the initial mass flow and internal structure of the final deposit, and typically has a limited range of length scales. We discuss the implications for reservoir location, geometry and facies distribution, and subsurface identification.

Unique wind ripples attaining heights to 2.3 m, wavelengths to 43 m, and a crest maximum grain size of 19 mm occur on the Argentine Puna Plateau at ~4000 m altitude. These are the largest ripples reported on Earth, comparable only to Mars counterparts. They form in the presence of high proportions of low-density pumice clasts (0.91 g/cm 3 ), although crests are exclusively composed of varnished, normal-density clasts (2.43 g/cm 3 ). Mature ripple profi les are partly excavated on bedrock, so they form by a combination of defl ation, winnowing of fi ner grains, minor wind drift of fi ne gravel, and lagging of clasts >4 cm. The large ripple size appears to be related to strong winds, dense saltation layers, and a long time for evolution. Ripple sizes are smaller on obstacles, as compared to fl at terrain; there is a lack of correlation between clast size, wavelength, and the extreme ripple size (in spite of the thin atmosphere), all of which suggest that while small-scale gravel ripples may form according to a reptation model, their evolution into large-scale types may relate to aero dynamic instabilities originating at the saltation curtain-air interface.

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J.P. Milana). AbstractThe role of Mass Transport Deposits (MTD's) in redistributing sediment from the shelf-break to deep water is becoming increasingly apparent and important in the study of basins. While seismic analysis may reveal the general morphology of such deposits, it is unable to provide information on the detailed geometry and kinematics of gravity-driven transport owing to the limits of seismic resolution.Outcrop analysis of ancient MTD's may therefore provide critical observations and data regarding the internal deformation and behaviour during slope failure. One such field area where geometry and kinematics are clearly exposed is Cerro Bola in the Paganzo basin of northwestern Argentina. This 8 km strike section exposes a mid to late Carboniferous succession, comprising fluvio-deltaic sediments, turbidites and MTDs. Our work focuses on the main MTD that is up to 180 m thick and is characterized by a silty matrix, containing sandstone blocks and siltstone rafts. Although we consider a single slope failure as the most likely scenario, a possible double failure might also explain the occurrence of a folded turbidite marker in the upper zone of the MTD. The MTD is host to a variety of deformational features such as folding, boudinage, shear zones, allochthonous strata, and secondary fabrics among others. These deformational features vary in intensity, scale and style, both vertically A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT and laterally across the deposit. The vertical variation is the most notable, and the entire deposit can be subdivided into lower, middle and upper zones according to variations in texture and structures, including sandstone blocks, sand streaks and blebs in the matrix, folding on a variety of scales, and shear zones. The middle part of the MTD is characterized by the abundance of siltstone rafts. Various models are proposed for the origin of blocks and rafts within the MTD: erosion of underlying strata; fragmentation of the original protolith; or a mixture of both. Significantly, specific strain cells occur around the blocks, and so the kinematics of deformation structures in the matrix of the MTD are very largely governed by their proximity and position relative to blocks, and may not relate to the overall kinematics of the MTD. This casts serious doubt on the ability to interpret overall movement directions from core or dip-meter data in the subsurface.

This paper reports results of the application of combined refraction and geoelectric geophysical methods to the study of the El Paso rock glacier in the arid Andes of Argentina. The data allow inferences to be made upon the internal structure, and permafrost thickness of the rock glacier. The El Paso rock glacier is located in the arid to hyper‐arid Agua Negra basin. Due to its altitude, it records some of the world's highest global radiation. The active layer thickness was studied using refraction seismic methods. Seasonal monitoring of this layer showed large variations in thickness, being thicker in summer and thinner in winter. Geoelectric methods allowed detection of a wet layer underlying permafrost, thereby providing information about the character of the rock‐glacier base. The maximum inferred thickness of El Paso permafrost was 18.5 m. Three main layers were detected: an upper deposit of dry debris over a debris‐water layer, a debris‐ice‐mixture (i.e. permafrost), and a lower one composed of wet debris. The geophysical results permit a first estimate of the volume of water (6.3 hm3) enclosed in the rock glaciers of this region, indicating that locally, rock glaciers are important water resources. However the incidence of water availability to the arid lowlands is unknown. Copyright © 2002 John Wiley & Sons, Ltd.

Erosion of the seafloor is often interpreted to be the result of turbidity currents and reflects their frictional and non-cohesive nature. However, evidence of the interaction between sediment gravity-flows and the substrate forming the sea floor has been increasingly reported in the literature. Based on styles of basal interaction with the substrate, we here propose a broad classification of submarine mass movements labelled free-and no-slip flows. Three mechanisms are proposed for free-slip flows during translation of mass movements that are effectively detached from the substrate; hydroplaning, shear wetting, and substrate liquefaction. In contrast, no-slip flows occur where the mass movement is welded to the substrate, and the strain front lies within the substrate itself. In the latter case, flows can erode by pushing forward and/or ploughing into the substrate, often remobilizing sediments that are later incorporated into the flow, a common characteristic shared by many mass transport deposits (MTDs) containing blocks. Additionally, linear track features (e.g. grooves and striations) are described as a consequence of substrate tooling by rigid blocks. Using outcrops in NW Argentina as a detailed case study, we have recorded evidence for penetration of the strain profile into sediments underlying MTDs and categorised the deformation into no-slip basal deformation that may display continuous and discontinuous profiles. Continuous deformation profiles involve the complete deformation of the uppermost layers of the substrate, while discontinuous deformation profiles preserve a undeformed substrate layer between the MTD and the zone of deformed substrate. These features highlight the erosive and deformational nature of MTDs, and can be used as potential kinematic indicators.

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