1,720,977 research outputs found
A sedimentary model for early Palaeozoic fluvial fans, Alderney Sandstone Formation (Channel Islands, UK)
No full textStratal architecture and morphodynamics of downstream-migrating fluvial point bars (Jurassic Scalby Formation, U.K.)
No full textAn outer ramp to basin plain transect: Interacting pelagic and calciturbidite deposition in the Eocene–Oligocene of the Tuscan Domain, Adria Microplate (Italy)
No full textThe interaction of ramps, basin plains and turbidite systems on the scale of tens of km has been rarely observed in fossil examples. Deep marine Eocene-Oligocene beds are exposed in the axial zone of the Chianti Mountains, Italy, and compose a regionally continue stratigraphic succession known as the Scaglia Toscana Formation. The formation was deposited in the Tuscan Domain of the Adria Microplate. This research aims at depicting its depositional architecture and evolution in the type area. Stratigraphic and sedimentologic analyses were performed on a ca. 25. km-long transect that includes depositional systems sectioned both in the down- and along-dip directions. Shaly-carbonate deposits compose a complex of interacting ramps, basin plains and turbidite floor fan systems. Ramp deposits accumulated above the lysocline and in oxic conditions. Basin plain beds were deposited below the lysocline and were subject to episodes of oxygen depletion. Turbidity flows fed elongate fan lobes characterized by poor channelisation. The basin palaeogeography hampered the development of slope apron turbidite systems.The Eocene-Oligocene geodynamic setting of the Tuscan Domain was characterized by the evolution of a peripheral bulge and by the early structuring of a foredeep basin. Syn-sedimentary tectonism acted a primary role in the basin-scale arrangement. However other mechanisms also contributed to the local facies distribution, including the disposition of sediment-source areas and intrabasinal confinement morphologies, as well as relative oscillations of the depositional surface with respect to the lysocline and oxycline. © 2013 Elsevier B.V
Planview style and palaeodrainage of Torridonian channel belts: Applecross Formation, Stoer Peninsula, Scotland
No full textDeeply channelled Precambrian rivers: Remote sensing and outcrop evidence from the 1.2 Ga Stoer Group of NW Scotland
No full textPrecambrian snapshots: Morphodynamics of Torridonian fluvial braid‐bars revealed by three‐dimensional photogrammetry and outcrop sedimentology
No full textGeology of the late Miocene south-eastern Volterra Basin (Northern Apennines, Italy)
No full textWe present a 1:10,000 scale geological map for the south-eastern sector of the Volterra Basin
(Northern Apennines, Italy), together with supporting stratigraphic-structural data. The
Volterra Basin consists of a major structural depression within the Northern Apennines
hinterland, NNW-SSE-oriented and filled with more than 2000 m of late Miocene-
Quaternary deposits. Its south-eastern sector is classically considered as a type area for late
Tortonian non-marine strata, here mapped and refined in terms of internal stratigraphy
adopting a scheme of depositional and lithostratigraphic units. Stratigraphic assessments
helped in redefining the character of the lower boundary of the non-marine succession, as
well as in mapping a newly recognized angular unconformity. Deformation structures
affecting the basin fill include blind normal faults rooted to a deep detachment, outcropscale
transtensional faults and clusters of gentle folds. Faults and folds appear to be
kinematically linked. Our structural observations largely agree with those present in the
literature, supporting a model of post-orogenic crustal stretching
A sagging along the eastern Chianti Mts., Italy
No full textA deep-seated gravitational slope deformation (DGSD) affects the eastern side of the Chianti Mts. Ridge. It
develops in an N−S to NW−SE direction and is N10 km wide and 3-4 km long. This area corresponds to the
eastern side of a main antiform, characterised by east-verging folds and thrusts involving bedrock of the
Mesozoic−Paleogene Tuscan Units, particularly sandstones containing interlayered highly fractured and
deformed Ligurian rocks (shales and limestones with olistostromes). The foot of the slope is characterised by
tilted Plio-Pleistocene deposits unconformably sealing the bedrock structures as folds, thrusts and faults. The
most significant morphological features are a main escarpment, trenches, several secondary and counter-slope
escarpments that together indicate large-scale gravitational phenomena. The main escarpment is responsible
for the headward retreat of the slope, and is deeply segmented by numerous arcuate niches that reveal
differential movements of single blocks. The DGSD is also dissected by SW−NE trending streams that often
deepen inside the N−S trenches. Minor landslides due to local instability are also present. At the foot of the
slope, the older continental Pliocene deposits of the Upper Valdarno Basin crop out. Although tilted by tectonic
movements, the deposits have not been severely affected by gravitational deformations. This indicates that the
movement is a typical sagging, a large landslide at an embryonic stage, affecting the upper part of the slope but
not reaching the valley bottom. The deformations are absorbed in the rock mass which is also partially drained
by stream incision that prevents high pore pressure. The occurrence of down-slope and down-movement
facing escarpments and up-slope and up-movement facing counter-slope escarpments indicate a sagging
characterised by a listric spoon-shaped geometry. The DGSD has a style similar to crustal extensional tectonics
such as Morton and Black's crustal attenuation model. Although few chronological indications of movements
are present, the fact that Late Pleistocene debris deposits, widespread in the northern and central Apennines,
are not found at the contact between the escarpment and the trenches suggests a post-glacial activity for at
least part of the movements. Recognizing embryonic-stage collapse is of primary importance in assessing
geological hazard and risk because rapid evolution and collapse could follow
Vegetation changes the trajectory of river bends
No full textA primary axiom in geoscience is that the evolution of plants drove global changes in river dynamics. Notably, the apparent sinuosity of rivers, derived from the variance of sediment accretion direction measured in rocks, substantially increased when land plants evolved, around 425 million years ago. this led to the hypothesis that the rise of vegetation triggered river meandering. Recent studies of barren, meandering rivers challenge this notion, but the Paleozoic shift in the geometry of river deposits remains unexplained. Here, we suggest that it occurred because vegetation changes how river bends move through space. using satellite images to monitor river migration, we found that bank vegetation alters the orientation of point bar accretion, resulting in a 62% increase in the inferred variance of flow direction. these results explain why meandering rivers have been underrecognized in prevegetation stratigraphy
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