100 research outputs found
transgressive change from shoreface to shelf-indenting channel depositional systems in the Pliocene Sua Member, Ecuador
No full textShelf-indenting canyons are fairly common constituents of Quaternary shelves, but they have been rarely reported from older successions. As a consequence, facies models for these conduits are noticeably lacking and far from complete. In this respect, the lower Pliocene
Súa Member, northwest Ecuador, is of particular interest in that it gives unprecedented documentation for the stratigraphic organization of a backstepping nearshore clastic wedge that is dissected by shelf-indenting channels and overlain by their turbiditic infill. A comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order. (i) A polygenetic, regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary (SB/wRS). (ii) A nearshore, sand-prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower-shoreface bioturbated silty sandstones, into inner-shelf sandy mudstones. (iii) Two steep, U-shaped erosional features (turbidite shelf-entrenchment surfaces), interpreted as shelf channels, deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies. (iv) A thick, fining-upward sedimentary succession laid down within the confines of the channels by turbidity currents. Shelf-entrenchment surfaces are carved by bypassing turbidite currents in shelfal settings during transgression and headward erosion of shore-connected shelf channels is proposed as the most viable mechanism for their development. In order to address for sediment bypass across the shelf and deepwater sedimentation during transgression, exhisting sequence stratigraphic models need to be extended and the turbidite shelf-entrenchment surface adequately included. this study contributes to extend the existing sequence-stratigraphic schemes, further attesting that shelf-sediment bypass and deep-water sedimentation can take place at sea levels other than lowstand
External controls on internal organization and vertical stacking pattern of Pleistocene shallow-marine and fluvial depositional sequences
No full textThe complex interaction of regional uplift, glacio-eustasy, local tectonics, and sediment supply has a significant impact on the internal
architecture and vertical arrangement of shallow-marine and fluvial depositional sequences and can be documented in well-exposed
successions of Pleistocene strata cropping out along the uplifted margins of Ecuador, northern Chile, and eastern central Italy.
The results stemming from these sediments have important implications for sequence stratigraphic models in tectonically active areas
and lead to the following general conclusions: (i) given that rates of syndepositional regional tectonic uplift were substantially less
than rates of contemporaneous eustatic changes in sea level in all of the study areas, glacio-eustasy appears to have played the main
control on development of high-frequency sequences; (ii) stratal geometries, sedimentary facies, and genetic complexity of sequence
bounding unconformities of these cyclic successions indicate that the internal organization of individual depositional sequences is
directly controlled by the rates of sediment supply and by the occurrence of intrabasinal, short-term normal faults striking obliquely
with respect to paleo-shoreline trends; (iii) the effects of the regional tectonic uplift on these eustatic sequences is on longer term, at
sequence set scale, and is responsible for their distinctive stacking pattern; owing to the progressive, tectonically driven reduction of
accommodation space, high-frequency sequences are nested within a forced regressive sequence set, where each successively younger sequence is displaced basinward and downward respect to the last
Geologic map of the Neogene deposits of Mejillones Peninsula (northern Chile)
No full textA new 1:50,000 geological map of the Mejillones Peninsula (northern Chile) displays relationships between the various Neogene units present. The Neogene evolution of the peninsula, reconstructed on the basis of distribution of these units, suggests a complex interplay between sea-level changes and tectonics and indicates that basin-bounding faults propagate from north to south
Off-shelf sedimentary record of recurring global sea-level changes during the Plio-Pleistocene: evidence from the cyclic fills of exhumed slope systems in central Italy
No full textThe markedly cyclic sedimentary successions of four late Pliocene to early Pleistocene slope turbidite systems exposed in eastern central Italy have been resolved into 31 high-frequency sequences. Chronological constraints from biostratigraphy and magnetostratigraphy indicate that these successions form a composite, partially overlapping stratigraphic record and sequence-bounding surfaces can be convincingly correlated with glacial oxygen isotope stages G2–60 (c. 2.65–1.7 Ma) inclusive. The studied successions, therefore, preserve an extraordinary and legible record of recurring, orbitally dictated glacio-eustatic sea-level fluctuations and provide an unprecedented opportunity to examine the deep-water sedimentary response to such high-frequency changes from an outcrop perspective
Sedimentary features of tsunami backwash deposits in a shallow marine Miocene setting, Mejillones Peninsula, northern Chile
No full textMiocene shoreface sandstones in the Caleta Herradura half-graben, northern Chile, contain an exceptionally coarse deposit that, based on sedimentologic and stratigraphic features, is regarded as having been laid down during a tsunami event by noncohesive and sediment-laden subaqueous density flows. Interpretations of the principal sediment-depositing mechanisms effective in the tsunami surges rely largely on field observations of deposit geometry and internal sedimentary characteristics. This example comprises two erosively based sedimentation units that were probably deposited by successive waves in the tsunami wave train. The Lower Unit consists of a clast-supported, polymodal, boulder-bearing breccia composed mostly of angular clasts and fewer well-rounded clasts. Framework components are mostly chaotic but may also exhibit either inverse-tonormal grading or crude normal grading. Laterally, changes in characters of depositional facies are common and abrupt. The sand-sized, bioclastic-rich matrix is poorly sorted and very similar to the underlying lower shoreface bioclastic sandstone, implying that soft sediments eroded at the lower erosional surface contributed to the tsunami deposit. The bulk of the Upper Unit is a poorly sorted, breccia-bearing sandstone. Pebbles and cobbles are scattered, massive or normally graded. Sporadic outsized boulders, emplaced as debris fall deposits, may occur along the erosional base. An array of signatures, such as unusually coarse grain size in comparison to the surrounding deposits, erosional bases, the mixed sources of sediments, multiple erosional and depositional events, normal size grading or massive texture, are all considered distinctive features of tsunamigenic deposits. Backwash deposition is indicated by the incorporation within the tsunami deposits of sediments derived from mixed sources, such as angular clasts from nearby subaerial settings, rounded clasts reworked from beach gravels, and bioclastic sand eroded from older, and unconsolidated, shoreface deposits. Notwithstanding the absence of soft-sediment deformation features, the marked facies change from a lower shoreface into an upper shoreface environment through the tsunamiites provides directional information about the origin of the tsunami wave. It was most likely produced by a sea floor fault displacement associated with an episode of sudden, probably coseismic coastal uplift
I depositi pliocenici dell’Unità di Ariano (Monti della Baronia, Appennino meridionale)
No full textSedimentology and high-frequency sequence stratigraphy of a forearc extensional basin: the Miocene Caleta Herradura Formation, Mejillones Peninsula, northern Chile
No full textSequence response to syndepositional regional uplift: insights from high-resolution sequence stratigraphy of late Early Pleistocene strata, Periadriatic Basin, central Italy.
No full textThis paper deals with the depositional sequences that occur within the uppermost part of the Plio–PleistocenePeriadriaticbasin fill in the southern Marche region, centralItaly. The succession is an EarlyPleistocene, easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow-marine and non-marine deposits comprising two major sequences, namely Qmb and Qmc. Analysis has provided new insights into: (i) the nature of sedimentary facies and facies associations occurring within the upper part of Qmb and Qmc; (ii) the gradual contact within Qmb between regressive littoral deposits (RLD) and underlying deep-marine blue clays; (iii) the composite origin of the Emilian surface, which is a widespread erosional unconformity separating Qmb from Qmc; (iv) the cyclothemic pattern of Qmc, composed of downstepping, small-scale depositional sequences; (v) the role played by synsedimentary uplift on the stacking pattern of small-scale sequences and their internal architecture.Up to three small-scale depositional sequences have been recognised within Qmc. They are up to 50 m thick and defined by previously unrecorded. High-frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite, tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower-rank sequence boundaries
Considerazioni sull’utilizzo delle sabbie dragate al largo di Civitanova Marche (Adriatico centrale) per il ripascimento delle spiagge.
No full textSono state analizzate le principali caratteristiche dei sedimenti dragati al largo di Civitanova Marche (Adriatico centrale), confrontandole con quelle degli arenili delle Marche meridionali al fine di evidenziare la lor compatibilità.
Particolare attenzione è stata dedicata all'analisi del sito di Marina Palmense (Comune di Fermo) in cui nel luglio 2007 il materiale dragato è stato utilizzato per un primo ripascimento.
Dallo studio è risultata l'incompatibilità dei materiali dragati con la dinamica costiera lungo quasi tutto il tratto investigato, compreso quello già sottoposto a rifluimento, dimostratosi inefficace
Syn-depositional tectonic controls on the internal architecture of a mid-Pleistocene depositional sequence (Mejillones Formation, northern Chile)
No full textThe sequence stratigraphy of north Chilean mid-Pleistocene strata (Mejillones Formation) shows that the internal architecture and nature of bounding surfaces of component sequences change systematically along-strike and are controlled, through creation and loss of accommodation space, by the syndepositional movement of small-scale normal faults. Hangingwall sections comprise both the transgressive and falling-stage systems tracts, whereas on footwall crests only the falling-stage systems tract is present
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