SEDIMENTOLOGY, ICHNOLOGY, BIOSTRATIGRAPHY, AND SEQUENCE STRATIGRAPHY OF THE MIDDLE MIOCENE OFICINA FORMATION, ORINOCO OIL BELT, VENEZUELA

Although the middle Miocene Oficina Formation of the Orinoco Oil Belt represents most of Venezuela’s hydrocarbon resource, a comprehensive and detailed sedimentary facies model for the whole belt has never been put forward. Nine facies (FA-FI), grouped in five facies assemblages (FA1-5), have been identified in the Oficina Formation in the Orinoco Oil Belt. FA1 occurs in the lower member, encompassing fluvial braided channels (FB), floodplains (FG2), swamps (FH1) and paleosols (FG3). FA2 occurs in the middle member and consist of meandering estuarine-channel deposits (FA, FC, FD, FE, and FI). FA3 occurs in the middle member, including tidal flats and tidal creeks (FC, FD, FE, FF, and FG2), swamps (FH1 and FH2), and paleosols (FG3) formed in tide-dominated estuarine systems. FA4 is present in the uppermost part of the middle members, including sandbars (FC, FD, FG1), paleosols (FG3), and swamps (FH2) formed in the outer part of estuaries. FA5 occurs in the upper member and consists of deltaic distributary channel (FC and FD), floodplain and interdistributary bay (FG2) and swamp (FH1) deposits of the lower delta plain of tide-dominated deltas. The sedimentary succession in the Oritupano Field represents the upper member of the Oficina Formation, therefore correlating with the deltaic deposits identified in the Orinoco Oil Belt. Eleven facies (FJ-FS), grouped in four facies assemblages (FA6-9), have been recognized in the Oritupano Field. FA6 is present in the lower part and consists of deltaic distributary-channel (FJ) and interdistributary-bay (FK) deposits of the delta plain of a wave-dominated delta. FA7 is present in the middle part and consists of sandy mouth-bar (FL), proximal delta-front (FM1), storm-dominated distal delta-front (FM2), and prodelta (FN) deposits formed in an area encompassing the delta front and the prodelta of a wave-dominated delta. FA8 is present in the upper part, including upper- to middle-shoreface (FO) and lower-shoreface (FP) deposits formed in a wave-dominated shoreface. FA9 is present in the upper part, including deposits of the upper offshore (FQ), lower offshore (FR) and shelf (FS) formed in an offshore-shelf complex. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). The Oficina Formation in the Orinoco Oil Belt and Oritupano areas provides an ideal opportunity to study faunal distribution and ichnofacies because it comprises a wide range in depositional environments formed under variable salinity conditions within a single stratigraphic unit. Freshwater conditions in the fluvial deposits, as well as in the inner portions of the estuary and delta plain, are further supported by the presence of Scoyenia Ichnofacies, whereas brackish-water segments of the estuarine and delta-plain deposits are characterized by the Skolithos and depauperate Cruziana Ichnofacies. Rapid ichnofaunal changes are distinctive of delta-front and prodelta deposits, where archetypal marine ichnofacies (i.e. Skolithos and Cruziana) alternate with stressed expressions of marine suites (i.e. depauperate Cruziana Ichnofacies), indicating rapid changes in salinity conditions due to times of freshwater discharge and return to fully marine conditions. Shoreface, offshore and shelf are characterized by the Skolithos and archetypal Cruziana Ichnofacies, indicating persistence of normal-marine salinity conditions. Salinity is a crucial factor in the development of benthic organisms and is independent of physical sedimentological processes. Therefore, understanding ichnofaunal distribution is very important for paleoenvironmental characterization of marginal-marine settings. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of coastal-plain deposits, providing insights into sequence-stratigraphic interpretations. The Oficina Formation (15.97-12.7 Ma) in the Orinoco Oil Belt comprises a single 2nd-order sequence, which is divided into two third-order depositional sequences (DS1-2). Third-order sequences provide a better understanding of reservoir distribution and are associated with sea-level changes. DS1 is bounded by sequence boundaries U-1 (15.97 Ma) and U-2 (13.82 Ma) and includes maximum flooding surface MFS-1 (14.91 Ma). It consists of thick lowstand systems tract (LST) and transgressive systems tract (TST) strata, and a thin highstand systems tract (HST) package. DS1 is associated with incised-valley systems formed during a relative sea-level fall. Fluvial valley-fill is recorded by FA1. The fluvial valleys were replaced by estuarine valleys during the Langhian relative sea-level transgressive episode. The estuarine valley-fill displays a retrogradational stacking pattern, comprising FA2, FA3 and FA4. Thin deltaic deposits also occur in the uppermost interval of DS1, forming a thin HST. DS2 is bounded by U-2 (13.82 Ma) and U-3 (12.7 Ma) and includes MFS-2 (13.53 Ma). It consists of a thin TST and a thick HST formed during the Serravallian sea-level highstand. In DS2, transgressive deposits in the lower part form a thin TST interval reflecting delta abandonment, which rests directly on top of the underlying highstand systems tract (HST) deposits of DS1, therefore mantling a flooding surface/sequence boundary. The bulk of DS2 is represented by FA5, displaying a progradational stacking pattern. The Oficina Formation of the Orinoco Oil Belt shows similarities in sedimentologic, ichnologic and sequence-stratigraphic aspects to other marginal-marine units worldwide (most notably the Cretaceous McMurray Formation of Alberta), representing a broad spectrum of latitudinal contexts. These similarities therefore stress the importance of tidal dominance and relative sea-level changes as main controls on deposition, regardless of latitudinal controls. However, latitude may have played some role in controlling the establishment of extensive coastal wetland systems, the abundance of tidal channels and the types of burrowing organisms

The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies

We present the result obtained from a study, based on long-slit spectroscopy, of the kinematics and ionization mechanisms of the line-emitting gas for a sample of four high/intermediate-redshift radio galaxies. In two of the galaxies (3C352 and 3C435A) the radio sources are of the same scale as the emission-line regions, whereas in the other two (3C34 and 3C330) the radio sources are extended on a larger scale than the emission-line structures. We see evidence for shock-acceleration of the emission-line gas in the extended regions of all the galaxies, even in the largest radio sources of our sample, in which the radio hot spots have passed the extended gas of the galaxies. The extended regions present highly disturbed kinematics (line-splitting and/or underlying broad components), which are difficult to explain if we do not consider a strong interaction between the radio-emitting components and the ambient gas. However, the dominant ionization mechanism of the line-emitting gas remains uncertain. We have compared the optical diagnostic line ratios of the galaxies in our sample with both AGN-photoionization and shock-ionization models. We find a lack of consistency in explaining the main ionization mechanism of the emission-line gas. This suggest that, if the extended regions are shock-ionized, some of the assumptions implicit in the shock models may need to be reconsidered. In addition, we have investigated the nebular continuum cointribution to the UV excess in the galaxies of our sample. We find a substantial nebular emission contribution to the UV continuum in all the cases. However, after the subtraction iof the nebular component, a significant UV excess remains in the extended nebulae of most of the objects.Comment: 33 pages, 24 figures, accepted for publication in MNRAS. (Abstract shortened for astro-ph

CFD modeling of a road tunnel with multiple sources of Co. case of study: boqueron-I tunnel

This work aims to the modeling of CO transport in one section considered critical of the Boqueron I tunnel, located on the outskirts of Caracas, the capital city of Venezuela, with a scenario where vehicles are stopped by an interruption of traffic. This scenario considers a relationship between the number of large-sized vehicles (buses or trucks) and small-sized vehicles (passenger cars) reported by transit statistics and also, it considers the semi-transverse ventilation system in the tunnel. It is explored the influence of the ventilation on the flow patterns and its relationship to the regions with the highest CO concentration. The finite-volume based finite element method is used for the discretization of the computational domain and the integration of the governing equations. The transient 3D-incompressible Navier-Stokes, energy, mass and species conservation equations, along with the k-e turbulence equations, were discretized, using higher-order numerical schemes in space. The numerical simulation is performed using a fully implicit coupled treatment of the set of resulting discrete transport equation

Numerical simulation of slurry flows in heterogeneous and saltation regimes in horizontal pipelines

In this work, the simulation of a two-phase liquid-particles flow is performed using an Eulerian- Eulerian model to predict the complex flow behavior where both particle concentration and particle velocity profile are shown and compared with experimental data. One of the main concerns during implementation of pipeline transportation of multiphase mixtures the is assurance of the flow, where the formation of particle fixed beds should be strongly avoided due to its disadvantageous and damaging effects on the flow, which mostly occur at the bottom sides of the pipeline walls

Numerical simulation of slurry flows in heterogeneous and saltation regimes in horizontal pipelines

In this work, the simulation of a two-phase liquid-particles flow is performed using an Eulerian- Eulerian model to predict the complex flow behavior where both particle concentration and particle velocity profile are shown and compared with experimental data. One of the main concerns during implementation of pipeline transportation of multiphase mixtures the is assurance of the flow, where the formation of particle fixed beds should be strongly avoided due to its disadvantageous and damaging effects on the flow, which mostly occur at the bottom sides of the pipeline walls

Neutron background at the Canfranc Underground Laboratory and its contribution to the IGEX-DM dark matter experiment

A quantitative study of the neutron environment in the Canfranc Underground Laboratory has been performed. The analysis is based on a complete set of simulations and, particularly, it is focused on the IGEX-DM dark matter experiment. The simulations are compared to the IGEX-DM low energy data obtained with different shielding conditions. The results of the study allow us to conclude, with respect to the IGEX-DM background, that the main neutron population, coming from radioactivity from the surrounding rock, is practically eliminated after the implementation of a suitable neutron shielding. The remaining neutron background (muon-induced neutrons in the shielding and in the rock) is substantially below the present background level thanks to the muon veto system. In addition, the present analysis gives us a further insight on the effect of neutrons in other current and future experiments at the Canfranc Underground Laboratory. The comparison of simulations with the body of data available has allowed to set the flux of neutrons from radioactivity of the Canfranc rock, (3.82 +- 0.44) x 10^{-6} cm^{-2} s^{-1}, as well as the flux of muon-induced neutrons in the rock, (1.73 +- 0.22(stat) \+- 0.69(syst)) x 10^{-9} cm^{-2} s^{-1}, or the rate of neutron production by muons in the lead shielding, (4.8 +- 0.6 (stat) +- 1.9 (syst)) x 10^{-9} cm^{-3} s^{-1}.Comment: 17 pages, 8 figures, elsart document class; final version to appear in Astroparticle Physic

Using Wavelets to reject background in Dark Matter experiments

A method based on wavelet techniques has been developed and applied to background rejection in the data of the IGEX dark matter experiment. The method is presented and described in some detail to show how it efficiently rejects events coming from noise and microphonism through a mathematical inspection of their recorded pulse shape. The result of the application of the method to the last data of IGEX is presented.Comment: 14 pages, 8 figures. Submitted to Astrop. Phy