Contourite porosity, grain size and reservoir characteristics

Acknowledgements Many people are to thank for the collection and release of the data used in this study. In particular, we thank the captain, officers and crew, and the scientific and technical shipboard parties of the different IODP expeditions utilised. We each thank our respective institutes for their ongoing support. Xiaohang Yu acknowledges financial support from the National Natural Science Foundation of China (No. 41976067).Peer reviewedPostprin

Contourites along the Iberian continental margins:conceptual and economic implications

34 pages, 14 figures, 3 tablesThis work uses seismic records to document and classify contourite features around the Iberian continental margin to determine their implications for depositional systems and petroleum exploration. Contourites include depositional features (separated, sheeted, plastered and confined drifts), erosional features (abraded surfaces, channels, furrows and moats) and mixed features (contourite terraces). Drifts generally show high- to moderate-amplitude reflectors, which are cyclically intercalated with transparent layers. Transparent layers may represent finer-grained deposits, which can serve as seal rocks. High-amplitude reflectors (HARs) are likely to represent sandier layers, which could form hydrocarbon reservoirs. HARs occur on erosive features (moats and channels), and are clearly developed on contourite terraces and overflow features. Most of the contourite features described here are influenced by Mediterranean water masses throughout their Pliocene and Quaternary history. They specifically record Mediterranean Outflow Water, following its exit through the Gibraltar Strait. This work gives a detailed report on the variation of modern contourite deposits, which can help inform ancient contourite reservoir interpretation. Further research correlating 2D and 3D seismic anomalies with core and well-logging data is needed to develop better diagnostic criteria for contourites. This can help to clarify the role of contourites in petroleum systemsThis contribution is a product of the IGCP-619 and INQUA-1204 projects, and is partially supported through the CTM 2008-06399-C04/MAR (CONTOURIBER), CGL2011-16057-E (MOW), CTM 2012-39599-C03 (MOWER), CGL2016-80445-R (SCORE), FCT-PTDC/GEO-GEO/4430/2012 (CONDRIBER), CTM2016-75129-C3-1-R and CGL2015-74216-JIN projectsPeer Reviewe

Onset of Mediterranean outflow into the North Atlantic

Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics

Melting and crystallization of ice in partially filled nanopores

We investigate the melting and formation of ice in partially filled hydrophilic and hydrophobic nanopores of 3 nm diameter using molecular dynamics simulations with the mW water model. Above the melting temperature, the partially filled nanopores contain two water phases in coexistence: a condensed liquid plug and a surface-adsorbed phase. It has been long debated in the literature whether the surface-adsorbed phase is involved in the crystallization. We find that only the liquid plug crystallizes on cooling, producing ice I with stacks of hexagonal and cubic layers. The confined ice is wetted by a premelted liquid layer that persists in equilibrium with ice down to temperatures well below its melting point. The liquid-ice transition is first-order-like but rounded. We determine the temperature and enthalpy of melting as a function of the filling fraction of the pore. In agreement with experiments, we find that the melting temperature of the nanoconfined ice is strongly depressed with respect to the bulk Tm, it depends weakly on the filling fraction and is insensitive to the hydrophobicity of the pore wall. The state of water in the crystallized hydrophilic and hydrophobic pores, however, is not the same: the hydrophobic pore has a negligible density of the surface-adsorbed phase and higher fraction of water in the ice phase than the hydrophilic pore. The widths of the ice cores are nevertheless comparable for the hydrophobic and hydrophilic pores, and this may explain their almost identical melting temperatures. The enthalpy of melting ΔHm, when normalized by the actual amount of ice in the pore, is indistinguishable for the hydrophobic and hydrophilic pores, insensitive to the filling fraction, and within the error bars, the same as the difference in enthalpy between bulk liquid and bulk ice evaluated at the temperature of melting of ice in the nanopores. © 2011 American Chemical Society.Fil: Gonzalez Solveyra, Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: de la Llave, Ezequiel Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Molinero, Valeria. University of Utah; Estados Unido

Along-slope oceanographic processes and sedimentary products around the Iberian margin

This contribution to this special volume represents the first attempt to comprehensively describe regional contourite (along-slope) processes and their sedimentary impacts around the Iberian margin, combining numerically simulated bottom currents with existing knowledge of contourite depositional and erosional features. The circulation of water masses is correlated with major contourite depositional systems (CDSs), and potential areas where new CDSs could be found are identified. Water-mass circulation leads to the development of along-slope currents which, in turn, generate contourite features comprising individual contourite drifts and erosional elements forming extensive, complex CDSs of considerable thickness in various geological settings. The regionally simulated bottom-current velocities reveal the strong impact of these water masses on the seafloor, especially in two principal areas: (1) the continental slopes of the Alboran Sea and the Atlantic Iberian margins, and (2) the abyssal plains in the Western Mediterranean and eastern Atlantic. Contourite processes at this scale are associated mainly with the Western Mediterranean Deep Water and the Levantine Intermediate Water in the Alboran Sea, and with both the Mediterranean Outflow Water and the Lower Deep Water in the Atlantic. Deep gateways are essential in controlling water-mass exchange between the abyssal plains, and thereby bottom-current velocities and pathways. Seamounts represent important obstacles for water-mass circulation, and high bottom-current velocities are predicted around their flanks, too. Based on these findings and those of a selected literature review, including less easily accessible “grey literature” such as theses and internal reports, it is clear that the role of bottom currents in shaping continental margins and abyssal plains has to date been generally underestimated, and that many may harbour contourite systems which still remain unexplored today. CDSs incorporate valuable sedimentary records of Iberian margin geological evolution, and further study seems promising in terms of not only stratigraphic, sedimentological, palaeoceanographic and palaeoclimatological research but also possible deep marine geohabitats and/or mineral and energy resources

Pliocene-Quaternary contourites along the northern Gulf of Cadiz margin:sedimentary stacking pattern and regional distribution

14 pages, 9 figuresThis study reports novel findings on the Pliocene–Quaternary history of the northern Gulf of Cadiz margin and the spatiotemporal evolution of the associated contourite depositional system. Four major seismic units (P1, P2, QI and QII) were identified in the Pliocene–Quaternary sedimentary record based on multichannel seismic profiles. These are bounded by five major discontinuities which, from older to younger, are the M (Messinian), LPR (lower Pliocene revolution), BQD (base Quaternary discontinuity), MPR (mid-Pleistocene revolution) and the actual seafloor. Unit P1 represents pre-contourite hemipelagic/pelagic deposition along the northern Gulf of Cadiz margin. Unit P2 reflects a significant change in margin sedimentation when contourite deposition started after the Early Pliocene. Mounded elongated and separated drifts were generated during unit QI deposition, accompanied by a general upslope progradation of drifts and the migration of main depocentres towards the north and northwest during both the Pliocene and Quaternary. This progradation became particularly marked during QII deposition after the mid-Pleistocene (MPR). Based on the spatial distribution of the main contourite depocentres and their thickness, three structural zones have been identified: (1) an eastern zone, where NE–SW diapiric ridges have controlled the development of two internal sedimentary basins; (2) a central zone, which shows important direct control by the Guadalquivir Bank in the south and an E–W Miocene palaeorelief structure in the north, both of which have significantly conditioned the basin-infill geometry; and (3) a western zone, affected in the north by the Miocene palaeorelief which favours deposition in the southern part of the basin. Pliocene tectonic activity has been an important factor in controlling slope morphology and, hence, influencing Mediterranean Outflow Water pathways. Since the mid-Pleistocene (MPR), the sedimentary stacking pattern of contourite drifts has been less affected by tectonics and more directly by climatic and sea-level changesWe thank the TGS-NOPEC Geophysical Company and Repsol-YPF for facilitating usage of an unpublished seismic dataset and borehole data from the Gulf of Cadiz. This work was supported through projects CTM 2008-06399-C04/MAR (CONTOURIBER), CTM2009-14157-C02 and CONSOLIDER-INGENIO 2010 CSD2006-0041-TOPOIBERIA, and has been partially carried out during research stages of F.J. Hernández-Molina at Heriot-Watt University (PR2009-0343)Peer reviewe

Bedform-velocity matrix: The estimation of bottom current velocity from bedform observations

A wide variety of bedforms, both depositional and erosional in origin, has been recognized on the deep seafloor and attributed to the influence of bottom currents. These range in scale from those visible in bottom photographs (centimeter to decimeter), to those recorded with seafloor bathymetric imaging (meter to kilometer). In many cases it has been possible to provide some quaication of substrate grain size and flow velocity responsible for each bedform type. We have synthesized both our own and published data in order to present a bedform-velocity matrix, which facilitates the estimation of bottom current velocity based on bedform type. Despite imperfections, we believe this to be a valuable model for assessing strength and variability of bottom currents that can have a significant influence on the siting of submarine cables, pipelines, and other seafloor installations

Echo-character of the NW Iberian continental margin and the adjacent abyssal plains

<p>The acoustic facies analyses have provided an important basis for sedimentary processes in the deep-sea environments. The echo-character mapping, through the interpretation and correlation of very high-resolution seismic profiles, is a very useful tool for the characterization of the recent sedimentary processes and their distribution. This work presents the first echo-character map at 1:800,000 scale of the Galicia Continental Margin and the adjacent abyssal plains elaborated by the Geological Survey of Spain. The map was carried out on the basis of the analysis and interpretation of the bathymetry and reflectivity data from the SIMRAD EM12, EM120 and EM1002 echosounders, and the high-resolution seismic profiles from the SIMRAD TOPAS PS18 parametric echosounder. On the basis of seafloor morphology, surface bedforms, backscatter and sub-bottom acoustic echo-characters, 26 echo-types were identified in the uppermost sedimentary sequence. These echo-types have been grouped into four main echoes: Distinct, Irregular, Hyperbolic and Undulated, according to their main acoustic characteristics. This information has been acquired in the framework of the ‘Scientific Research Program of the Economic Exclusive Zone of Spain’, which is coordinated and leaded by the Defense Ministry of Spain, during the oceanographic cruises carried out on board of the R/V Hesperides in 2001–2003 and 2006–2009.</p