1,721,024 research outputs found
The relationship between flood hydrograph and facies sequences of delta-front sandstone lobes produced by hyperpycnal flows
No full textRelazione tra l'idrogramma di piena e le sequenze di facies di foce (barre) e di piattaforma (lobi)
No full textCombined flow sedimentary structures and the genetic link between sigmoidal- and hummocky-cross stratification
No full textThis work is based on the comparison between facies tracts of flood-dominated fluvio-deltaic systems and basin-
plain turbidites to the main combined flow experimental data available in literature; it discusses the possibility
of a genetic link between sigmoidal and hummocky structures and their significance in facies analysis. Sigmoidal
and hummocky-cross stratifications are large-scale sedimentary structures, usually considered indicative of tidal and
storm deposits, respectively. However, facies analysis of flood-dominated fluvio-deltaic systems in tectonically active
settings shows that these two types of structures are also typical of these depositional systems. In flood-dominated
river-delta systems, coarse-grained mouth bars, which can be characterized by different types of sigmoidal-cross stratifications
deposited by sediment-laden stream flows entering seawater, pass down-current into fine-grained delta-front
sandstone lobes. That is to say, sharp based normally graded beds with hummocky-cross stratifications, deposited by
flood-related hyperpycnal flows characterized by an oscillatory component, whose origin can be related to different
processes. At a small scale, biconvex and rounded ripples and megaripples with sigmoidal-cross laminae are related
to small- and medium-scale hummocky structures in basin plain turbidites, where ponding and rebound processes can
transform the turbidity currents into combined flows. These field observations suggest a genetic link, at different scales,
between these two types of structures, especially in terms of combined flows. This study, therefore, has prompted
a re-examination of the combined-flow sedimentary structures produced in laboratory experiments, and has led to the
proposal and discussion of some facies schemes (small- and large-scale) based not only on the ratio of Uu (unidirectional
velocity) to Uo (oscillatory velocity) but also upon grain sizes, rates of fallout and frequency of oscillatory
component (i.e. the period T)
Stratigraphy, facies and processes of Roda Sandstone: a river-delta system dominated by hyperpycnal flows (Lower Eocene, south-central Pyrenees)
No full textProposal for a classification scheme for combined flow sedimentary structures and the meaning of sigmoidal- and hummocky-cross stratification in facies analysis
No full textTHE LOWER EOCENE RODA SANDSTONE (SOUTH-CENTRAL PYRENEES):AN EXAMPLE OF A FLOOD-DOMINATED RIVER-DELTA SYSTEMIN A TECTONICALLY CONTROLLED BASIN
No full textThe lower Eocene Roda Sandstone (Figols Group, south-central Pyrenees) mainly consists of mouth bars and delta-front sandstone lobes deposited in a flood-dominated river-delta system. The deposition of these bodies was strongly controlled by an interaction between flood-dominated gravity flows entering seawater, topographic confinement and tidal currents. The Roda Sandstone is made up of six depositional sequences of different hierarchical order each of which is characterized by a basal deltaic sandstone wedge (R1 to R6) that passes upward into a siltstone and mudstone interval. Each basal deltaic sandstone wedge is composed of three types of facies association and respective facies tract (sensu Mutti 1992) that, from proximal to distal zones, are indicated as T1, T2 and T3. These three facies tracts are created by the downcurrent evolution of different types of sediment-laden stream flows entering seawater and related hyperpycnal flows. Their deposits are constituted by three different types of coarse-grained mouth bars and corresponding fine-grained delta-front sandstone lobes. The tidal influence is present in facies tract T3 in the R5 and R6 sandstone units, where the passage between flood-dominated mouth bars and the delta-front sandstone lobes occurs through intermediate facies characterized by different types of sigmoidal-cross stratification whose meaning will be discussed. The basal deltaic sandstone wedges of Roda sandstone are characterized by a progressive forestepping culminating in the R6 unit that erodes the underlying R5 unit and by an overlying backstepping unit indicated as R7. The erosive surface at the base of R6 unit is interpreted as a sequence boundary that divides the Roda Sandstone into two parts: 1) an underlying highstand system tract (HST) and falling stage system tract (FSST) (units R1 to R5) and 2) an overlying low-stand delta (the R6 unit) that passes upward into highstand mudstone through a transgressive system tract represented by the R7 unit. Pd
Submarine orogenic front forming inside turbiditic foredeep basin: the case of the middle Miocene Salsomaggiore frontal fault-related anticline (Northern Apennines, Italy)
No full textCross-stratified sandstones and multiple beds: Evidence of internal flow divergence in turbidity currents caused by submarine topography
No full textBalls-and-pillows structures and hummocky-cross stratification (HCS) in delta-front sandstone lobes
No full textThe syntectonic evolution of foredeep turbidites related to basin segmentation: Facies response to the increase in tectonic confinement (Marnoso-arenacea Formation, Miocene, Northern Apennines, Italy)
No full textThe Marnoso-arenacea Formation (MAF) records the progressive closure of the foredeep due to the north-eastward propagation of thrust fronts. The latter produced a complex foredeep characterized by the uplift of the basin inner portions and by the north-eastward shifting of the main depocentres. This work discusses the evolution of the MAF inner basin and the first deposits of the outer basin in a transect perpendicular to the paleocurrents and the main tectonic structures that are NW-SE-oriented. Specifically, this study focuses on the upper Serravallian transitional stage, which records the closure of the inner basin and the deposition shifting to an outer basin due to the growth of an important regional structure represented by the NW-SE-oriented M. Castellaccio thrust-related fold (CTRF). The growth of this structure produces progressive segmentation of the foredeep through the progressive isolation of the inner basin that becomes, in the upper Serravallian phase of basin narrowing, a ponded piggyback basin. During this evolution, the structural control and associated morphologic confinement increased over time, controlling the lateral and vertical distribution of turbidite facies that is very similar to that of intra-slope minibasins. In such a situation, vertical and lateral facies changes, associated with evident stratigraphic pinchings and onlap relationship, have played a key role in showing this phase of strong foredeep segmentation and basin confinement. This phase is marked by a well-determined vertical facies variation: contained-reflected beds pass upward into huge accumulations of sandstone lobes featuring the appearance of Ophiomorpha trace fossils and coarse-grained massive sandstone beds often overlain by mud-draped scours and tractive structures (megaripples and traction carpets). These beds are interpreted as related to flow decelerations induced by structurally-controlled basin confinement that favour the deposition of massive sandstones through hydraulic jumps and flow decoupling with bypass of upper turbulent flows that can produce well-developed tractive structures
- …
