No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Vertically stacked Gilbert-type deltas of Ventimiglia (NW Italy): The Pliocene record of an overfilled Messinian incised valley
Abstract
Overfilled incised valleys develop when the rate of sediment supply outpaces the rate of accommodation. An overfilled incised valley presents simple or compound valley-fill architecture, depending on the depth of the valley incision, compared with the height reached by the following sea-level rise.The Ventimiglia incised valley, exposed on the Ligurian coast, north-western Mediterranean margin, presents a spectacular example of compound incised-valley fill, developed in perennial “overfill” conditions. The valley was subaerially incised during the Messinian Salinity Crisis and rapidly flooded by the sea at the beginning of Pliocene, then filled by eleven coarse-grained Gilbert-type deltas during Early–Middle Pliocene time.The basal Messinian unconformity is locally paved with subaerial scree breccias and bioclastic shallow-marine sandstones, and blanketed by bathyal marls. These deposits record the lowstand, transgressive and early-highstand systems tracts of the first valley-fill sequence. The subsequent progradation of Gilbert-type deltas occurred in four stages, or depositional sequences, separated by transgressive marine-marl intervals. Within each depositional sequence, the deltaic bodies display offlapping architecture, recording falling shoreline trajectory, downward shifts in facies, and overall forced regression. The water depth and accommodation in the inundated coastal valley was gradually decreasing with time. The reduced accommodation allowed the youngest deltas to prograde out to the shelf edge, triggering mass collapses and subsequent filling into the newly created slump scars. Some of the deltas probably acted as “canyon-perched deltas” and supplied sediment to the deep-water slope and floor of the Ligurian Basin.The vertical stacking of Gilbert-type deltas is usually attributed, in tectonically active basins, to fault-related subsidence pulses. In Ventimiglia, the accommodation was created by high-frequency eustatic sea-level rises that, probably accompanied by climate controlled reductions in sediment supply, temporarily outpaced uplift, leading to the development of multiple cycles of infill.
... Overall, FA1 represents the subaqueous deposition of generally sand-sized sediment within a low-energy setting, potentially resulting from distal waning of gravity-driven currents (e.g., Breda et al., 2009;Nemec, 1990a and references therein). These facies suggest distal turbidity currents near the base of the delta slope within a prodeltaic lacustrine setting (e.g., Postma, 1986). ...
... The presence of individual beds of locally graded, coarser-grained pebble conglomerate interbedded within the sandstone suggests episodic increases in the local energy that could be linked to flood events across the delta (e.g., Bardaji et al., 1990). This hypothesis is also supported by the presence of localized cross-stratification, scour surfaces, and restricted examples of backset beds (e.g., Breda et al., 2009;Postma, 1984). The latter, in particular, are produced by "hydraulic jumps," a sudden change in flow velocity of the density current responsible for the deposition of the strata (e.g., Longhitano, 2008;Rohais et al., 2008). ...
... Overall, the variety of structural and textural elements described here are most consistent with the sedimentary record of a steep-fronted Gilbert delta system (e.g., Breda et al., 2009;Clauzon et al., 2015;Longhitano, 2008;Postma, 1984Postma, , 1990Sztanó et al., 2010). This interpretation is preferred over alternative hypotheses, such as the inclined bedding resulting from subaqueous dunes or lateral accretionary bars in a fluvial setting in the absence of conspicuous scouring surfaces or grading across the interval (cf. ...
High‐resolution 2D and 3D data remotely acquired by SuperCam's Remote Micro‐Imager and Mastcam‐Z aboard the Perseverance rover enabled us to characterize the stratigraphic architecture and sedimentary record of the Kodiak butte, an isolated remnant of the western delta fan of Jezero crater. Using these data, we build up on previous interpretations of the butte interpreted as a prograding Gilbert‐type deltaic series. We characterize three individual stratigraphic Units 0 to 2 on the eastern and northern faces of the butte. Each Unit displays the same vertical succession of prodeltaic/lacustrine bottomsets, delta slope toesets and foresets, and fluvially influenced topsets of a deltaic plain with a braided river pattern, shown by 11 individual sedimentary facies. We infer that these individual Units record the formation of three distinct deltaic mouth bars successively across time and space. For the first time on another planet than Earth, we are able to construct a precise sequence stratigraphic framework to highlight lake‐level fluctuations at the time the Kodiak butte was emplaced, during the latest stages of deltaic activity. We identify four hydrogeological cycles indicated by alternating rises and falls of the lake‐level on the order of 5–10 m. These were most probably linked to climatic events and variations controlling lake water inputs in probable relation to an astronomical control.
... During the earliest Pliocene, the valley was flooded by the sea, becoming a coastal embayment (ria). After transgression culminated in the earliest Pliocene, the ria was filled by stacked coarse-grained Gilbert-type deltas (Breda et al., 2007(Breda et al., , 2009). This deltaic deposition was controlled by transgressive-regressive cycles, in which conglomeratic intervals mark the regressive stages and marly intervals mark the transgressive ones ( Fig. 2A) (Giammarino and Tedeschi, 1975;Giammarino et al., 1984;Marini, 2000Marini, , 2001Foeken et al., 2003Foeken et al., , 2006Breda et al., 2009). ...
... After transgression culminated in the earliest Pliocene, the ria was filled by stacked coarse-grained Gilbert-type deltas (Breda et al., 2007(Breda et al., , 2009). This deltaic deposition was controlled by transgressive-regressive cycles, in which conglomeratic intervals mark the regressive stages and marly intervals mark the transgressive ones ( Fig. 2A) (Giammarino and Tedeschi, 1975;Giammarino et al., 1984;Marini, 2000Marini, , 2001Foeken et al., 2003Foeken et al., , 2006Breda et al., 2009). Since the studied system consists of multiple, stacked Gilbert-type deltas, it is here referred to as 'delta complex' and 'delta system'. ...
... Minor siltstone-sandstone interbeds are also documented. The Ortovero Clay is occasionally rich in fossils (gastropods, otoliths and bivalves) and was deposited in the Zanclean-Piacenzian interval Tedeschi, 1970, 1982;Breda et al., 2009;Dallagiovanna et al., 2012). The Ortovero Clay, informally known as 'Lower Shales' (Foeken et al., 2006), was deposited on the continental slope, close to the boundary of the epibathyal zone (Breda et al., 2009;Dallagiovanna et al., 2012). ...
... During the Messinian Salinity Crisis, the Mediterranean Basin saw a remarkable sea-level drop, likely inducing an intense erosive phase resulting in the formation of deep and long canyons (Hsü et al. 1973;Adams et al. 1977;Ryan & Cita 1978;Clauzon et al. 1995;Krijgsman et al. 1999;Roveri et al., 2014;Madof et al. 2019;Meilijson et al. 2019). During the ensuing Zanclean transgression, the Messinian canyons were rapidly flooded by the sea and became rias (flooded valleys), thus providing the Western Ligurian coastline with a physiography somewhat similar to that of the modern Scandinavian region (Boni 1984;Breda et al. 2007Breda et al. , 2009). The Western Ligurian Pliocene coast was bounded to the north by the rising Alpine massif and to the south by the subsiding Ligurian-Provençal Basin (Giammarino 1984;Chaumillon et al. 1994;Clauzon et al. 1995;Breda et al. 2007Breda et al. , 2009 (Fig. 1A, B). ...
... During the ensuing Zanclean transgression, the Messinian canyons were rapidly flooded by the sea and became rias (flooded valleys), thus providing the Western Ligurian coastline with a physiography somewhat similar to that of the modern Scandinavian region (Boni 1984;Breda et al. 2007Breda et al. , 2009). The Western Ligurian Pliocene coast was bounded to the north by the rising Alpine massif and to the south by the subsiding Ligurian-Provençal Basin (Giammarino 1984;Chaumillon et al. 1994;Clauzon et al. 1995;Breda et al. 2007Breda et al. , 2009 (Fig. 1A, B). The uplift started in the late Miocene, with a major phase around 3.5 Ma (Bigot-Cormier et al. 2000;Foeken et al. 2003). ...
... Both hinterland uplift and basin subsidence contributed to increase coastal steepness, leading to a physiography similar to the current one, characterised by an extremely narrow continental shelf and a steep slope (Rehault et al. 1984(Rehault et al. , 1985. Along the coast, these movements were accommodated by reactivated Oligocene-Miocene normal faults originally related to the opening of the Ligurian-Provençal Basin (Biju-Duval et al. 1978;Speranza et al. 2002;Chaumillon et al. 1994;Breda et al. 2007Breda et al. , 2009. These faults exerted a strong control over Pliocene sediment deposition, as testified by the fault-bounded nature of most Pliocene basins (Giammarino 1984;Fanucci et al. 1978Fanucci et al. , 1980Marini 1984Marini , 2000. ...
... During the earliest Pliocene, the valley was flooded by the sea, becoming a coastal embayment (ria). After transgression culminated in the earliest Pliocene, the ria was filled by stacked coarse-grained Gilbert-type deltas (Breda et al., 2007(Breda et al., , 2009). This deltaic deposition was controlled by transgressive-regressive cycles, in which conglomeratic intervals mark the regressive stages and marly intervals mark the transgressive ones ( Fig. 2A) (Giammarino and Tedeschi, 1975;Giammarino et al., 1984;Marini, 2000Marini, , 2001Foeken et al., 2003Foeken et al., , 2006Breda et al., 2009). ...
... After transgression culminated in the earliest Pliocene, the ria was filled by stacked coarse-grained Gilbert-type deltas (Breda et al., 2007(Breda et al., , 2009). This deltaic deposition was controlled by transgressive-regressive cycles, in which conglomeratic intervals mark the regressive stages and marly intervals mark the transgressive ones ( Fig. 2A) (Giammarino and Tedeschi, 1975;Giammarino et al., 1984;Marini, 2000Marini, , 2001Foeken et al., 2003Foeken et al., , 2006Breda et al., 2009). Since the studied system consists of multiple, stacked Gilbert-type deltas, it is here referred to as 'delta complex' and 'delta system'. ...
... Minor siltstone-sandstone interbeds are also documented. The Ortovero Clay is occasionally rich in fossils (gastropods, otoliths and bivalves) and was deposited in the Zanclean-Piacenzian interval Tedeschi, 1970, 1982;Breda et al., 2009;Dallagiovanna et al., 2012). The Ortovero Clay, informally known as 'Lower Shales' (Foeken et al., 2006), was deposited on the continental slope, close to the boundary of the epibathyal zone (Breda et al., 2009;Dallagiovanna et al., 2012). ...
... They are also common in high-relief physiographic settings where accommodation is not primarily created by tectonics, such as incised valleys, fjords, or proglacial lakes; they can even form in lakes inside volcanic craters (Nemec et al., 1999;Németh et al., 2001;Gutsell et al., 2004;Kostic et al., 2005;Eilertsen et al., 2011;Gobo et al., 2014a;Leszczyński and Nemec, 2015;Winsemann et al., 2018). These deltas form important nodes in sediment-delivery pathways linking continental hinterlands to subaqueous lacustrine (Bowman, 1990;Bestland, 1991;Lee and Chough, 1999;Ilgar and Nemec, 2005;Sztanó et al., 2010) and marine depocentres (Colella, 1988;Mortimer, 2004, Mortimer et al., 2005García-García et al., 2006a;Breda et al., 2009;Ciampalini and Firpo, 2015;Rees et al., 2018). ...
... All these factors can influence the geometry of the prograding deltas and their architectural elements. They can also influence the predominance of different depositional processes, themselves determining distributions of grainsize and sedimentary structures, and thereby lithofacies (Colella, 1988;Postma, 1995;Gupta et al., 1999;Breda et al., 2009;Gobo et al., 2014a, Sedimentary Geology 426 (2021) 106022 2014b, 2015Martini et al., 2017;Winsemann et al., 2018Winsemann et al., , 2021. The role of autogenic mechanisms in shaping the evolution and stratigraphic record of these deltas is also recognized. ...
... Winsemann et al., 2018). The gradual, tangential transition from foreset to bottomset defines a physiographic element that is commonly referred to as a toeset (Breda et al., 2007(Breda et al., , 2009Ghinassi, 2007;Gobo et al., 2014b;Rubi et al., 2018). In some cases, bottomsets may be lacking altogether, for example during the early stages of delta evolution (Colella, 1988;Mortimer, 2004;Mortimer et al., 2005) (Fig. 1), or through progradation in sub-basins confined by topographic highs (Zelilidis and Kontopoulos, 1996). ...
Steep-fronted Gilbert-type deltas are common features of tectonically active settings, as well as of physiographic settings where accommodation is dictated by landforms with steeply inclined margins, such as incised valleys, fjords, and proglacial lakes. Existing facies models for Gilbert-type deltas are largely qualitative; this study presents a quantitative analysis of the variability in facies architectures of such deltas. A database approach is used to characterize the preserved sedimentary architecture of 62 Gilbert-type deltas of Cretaceous to Holocene ages developed in various basin settings worldwide. Data on 706 architectural elements and 12,872 facies units are used to develop quantitative facies models that describe the variability in architecture and facies of Gilbert-type deltas at multiple scales of observation, and to account for the possible controls exerted by allogenic and autogenic factors.
The analysed data reveal high variability in the geometry and facies of Gilbert-type deltas. The thickness of the examined deltas varies from 2 to 650 m, yet positive scaling between delta thickness and length is consistently recognized across the studied examples, which is interpreted in terms of relationships between accommodation, sediment supply and delta lifespan. Based on their facies character, the deltas are classified into gravel- and sand-dominated types, with contrasting facies organizations of topset, forest and bottomset elements, and by different relationships between facies and dimensions; yet, both types exhibit significant spatial variability in the distribution of sediments linked to debris flows or turbidity currents, and in vertical stratal trends. Changes in allogenic (e.g., changes in base-level or, rate of sediment influx) and autogenic mechanisms (e.g., channel avulsion) are inferred as causes for significant differences in facies organization, both across distinct deltas and within individual deltaic edifices.
The study highlights the marked variety of architectural and sedimentological (e.g., grain size, depositional processes) properties of Gilbert-type deltas. Findings allow the relation of outcrop observations to a general template and the quantitative determination of potential analogues with which to assist the prediction of the dimensions and facies of deltaic sedimentary bodies in the subsurface. Information on facies relationships and basinward variability of Gilbert-type deltas is valuable for the recognition and correlation of deltaic bodies in the subsurface.
... During the Messinian Salinity Crisis, the Mediterranean Basin saw a remarkable sea-level drop, likely inducing an intense erosive phase resulting in the formation of deep and long canyons (Hsü et al. 1973;Adams et al. 1977;Ryan & Cita 1978;Clauzon et al. 1995;Krijgsman et al. 1999;Roveri et al., 2014;Madof et al. 2019;Meilijson et al. 2019). During the ensuing Zanclean transgression, the Messinian canyons were rapidly flooded by the sea and became rias (flooded valleys), thus providing the Western Ligurian coastline with a physiography somewhat similar to that of the modern Scandinavian region (Boni 1984;Breda et al. 2007Breda et al. , 2009). The Western Ligurian Pliocene coast was bounded to the north by the rising Alpine massif and to the south by the subsiding Ligurian-Provençal Basin (Giammarino 1984;Chaumillon et al. 1994;Clauzon et al. 1995;Breda et al. 2007Breda et al. , 2009 (Fig. 1A, B). ...
... During the ensuing Zanclean transgression, the Messinian canyons were rapidly flooded by the sea and became rias (flooded valleys), thus providing the Western Ligurian coastline with a physiography somewhat similar to that of the modern Scandinavian region (Boni 1984;Breda et al. 2007Breda et al. , 2009). The Western Ligurian Pliocene coast was bounded to the north by the rising Alpine massif and to the south by the subsiding Ligurian-Provençal Basin (Giammarino 1984;Chaumillon et al. 1994;Clauzon et al. 1995;Breda et al. 2007Breda et al. , 2009 (Fig. 1A, B). The uplift started in the late Miocene, with a major phase around 3.5 Ma (Bigot-Cormier et al. 2000;Foeken et al. 2003). ...
... Both hinterland uplift and basin subsidence contributed to increase coastal steepness, leading to a physiography similar to the current one, characterised by an extremely narrow continental shelf and a steep slope (Rehault et al. 1984(Rehault et al. , 1985. Along the coast, these movements were accommodated by reactivated Oligocene-Miocene normal faults originally related to the opening of the Ligurian-Provençal Basin (Biju-Duval et al. 1978;Speranza et al. 2002;Chaumillon et al. 1994;Breda et al. 2007Breda et al. , 2009. These faults exerted a strong control over Pliocene sediment deposition, as testified by the fault-bounded nature of most Pliocene basins (Giammarino 1984;Fanucci et al. 1978Fanucci et al. , 1980Marini 1984Marini , 2000. ...
The lower Pliocene deposits of Pairola (Liguria, Italy) display the otherwise rare occurrence of rock-forming amounts of barnacles (mostly belonging to the extinct Euromediterranean species Concavus concavus). Three main facies are recognised in the investigated succession: a barnacle-dominated facies, which formed along a shallow (<15 m deep) nearshore environment, a foraminifera-dominated facies from relatively deeper waters (40-100 m), and an intermediate facies forming at the boundary of the other two. These facies and their relationships suggest deposition in a flooded valley – a kind of setting that was common in the Mediterranean after the Messinian Salinity Crisis.Differing from other rias, the Pairola basin was exposed to strong waves, resulting in conditions favourable to barna-
cles. Sedimentological and stratigraphic observations indicate that the Pairola succession formed within a timespan covering both cold and warm phases. This is relevant because the sub-tropical foraminifer Amphistegina is ubiquitous throughout the succession. Amphistegina occurs in the Pliocene and lower Pleistocene (Gelasian) of Northern Italy, but not in the remainder of the Pleistocene, not even its warm portions. This genus is currently recolonizing the Mediterranean and is projected to reach the northern coast of the basin soon, foretelling that Anthropocene temperatures are going to overcome those of the late Pleistocene warm periods and reach those of the Pliocene.
... Here, it is observed as well in the fine-grained facies F18 than in F22 (reworked shells into sub-marine lobe). All these remarks led to interpret F22 as a distal sub-marine lobe deposited, in lower-shoreface conditions (Breda et al., 2007(Breda et al., , 2009). Finally, we interpreted this association as lower shoreface facies (Galloway and Hobday, 1996;Coe, 2003;Bullimore et al., 2008) formed on the outer delta-front. ...
... In the Roussillon basin (southwest of France), Clauzon et al. (2015) proposed that immediately after a sudden return of marine waters, some debris flows were emplaced prior to Zanclean Gilbert-type delta systems. In the Ventimiglia canyon, Breda et al. (2007Breda et al. ( , 2009) described a different sedimentary organization in the first sedimentary sequence deposited in the paleo-ria. From bottom to top are: 1/local scree breccias interpreted as a LST; 2/15 m thick shoreface bioclastic sandstones interpreted as an early TST; 3/150 m thick onlapping deep-marine marls dating Zanclean (MPl1 and MPl2) and interpreted as a TST; 4/a Zanclean Gilbert-type delta that was deposited during a HST. ...
... Consequently, all along the onshore southern margin of the Alboran Sea the post-MSC base level rise and the marine drowning were progressive and very probably lasted few hundreds of thousand years. Moreover, our results fit with the sedimentary organization described for the first infilling sequence of the Bajo Segura basin (Caracuel et al., 2011) and of the Ventimiglia canyon (Breda et al., 2007(Breda et al., , 2009). This questions the catastrophic hypothesis of the reflooding in the western Mediterranean. ...
... However, recent acquisition of high-resolution multibeam seafloor images, coupled with outcrop analogue data on canyonized shelves and upper slopes, show that depositional elements are also a common trait of canyon heads (Postma, 1984;Morris and Busby-Spera, 1988;Mellere et al., 2003;Breda et al., 2007Breda et al., , 2009). Highresolution data from the modern seafloor provide planform and 3D insights into canyon head geomorphological elements, but usually lacks lithological information, particularly in coarsegrained systems where core recovery is poor. ...
... During the subsequent Pliocene sea-level rise, the river valleys were flooded and transformed into submarine canyons. Their heads, at the re-adjusted shelf-slope break, were gradually infilled by mass flow deposits and subsequently by coarse-grained shelfedge delta systems (Breda et al., 2007(Breda et al., , 2009Carbone et al., 2011). During late Pleistocene and Holocene times, the newly created shelf and the canyonized upper slope underwent alternating processes of erosion and deposition caused by tectonic movements and eustatic fluctuations (Dallagiovanna et al., 2012;Gamberi et al., 2013Gamberi et al., , 2014. ...
... The canyon fill-architecture is compound and formed by repetitive phases of offlapping conglomeratic wedges separated by epibathyal marl intervals deposited during high-frequency eustatic sea-level rises when rate of sea level rise outpaced rate of hinterland uplift (Breda et al., 2007(Breda et al., , 2009). The first marl interval, just above the Messinian erosional surface, records the regional marine reflooding of the Mediterranean Basin during Earliest Pliocene. ...
Marine geology data show that canyon heads can be the site of depositional processes and furnish the details of the geometry of their geomorphic elements. Canyon heads are usually floored by sediment with a prevailing coarse-grained nature and their sampling is very difficult thus preventing the characterization of the facies of their infill. Lithological and facies information is however available through outcrop studies. In this paper, we integrate modern seafloor and outcrop data to characterize the architecture of depositional canyon heads in tectonically active continental margins with a narrow shelf. The modern examples are located along the northeastern Sicilian margin (Milazzo and Niceto canyon-head systems), whereas the ancient one, Pliocene in age, is located onshore, along the Ligurian coast (Ventimiglia canyon-head system). The modern Milazzo canyon head is located at the coastline and has a steep slope. The flanking deposits are equivalent to the oldest Gilbert delta foresets of the Ventimiglia canyon head as the delta progrades directly into the upper slope. A deeply entrenched channel and a large chute mark the mostly erosional area directly facing the mouths of the rivers that enter the Milazzo canyon head. Laterally, the upper part of the foresets slope is characterized by a bulge with swales and ridges topography. These geomorphic elements are interpreted to be formed by debris flows and turbidity currents as suggested by the upper part of the Ventimiglia foresets, where chaotic, massive or graded deposits are observed. The swales and ridges topography gradually disapper downslope; this area is dominated by turbulent processes due to flow expansion from a confined to a more unconfined setting. An high turbulent flow environment is also confirmed by the formation of plunge pools, due to hydraulic jump, at the foresets-toesets transition. Similar features in the outcrop are infilled by bedsets facies with grain-size coarser than the eroded surroundings. The modern Niceto canyon head is connected landwards to a delta system that stretches across a 1 km wide shelf. Channelized delta distributaries are similar to the topset strata of the youngest deltas of the Ventimiglia canyon head. Channels are up to 200 m wide and 50 m deep and show axial bedform trains confirming that large scale trough cross beds are an important facies of channel infill. Wave reworking in the upper part of the topsets is also suggested by both the modern and outcrop data.
... Our purpose is to disentangle the stratigraphic relationship between the marine Pliocene strata to the south of Lyon and the continental counterpart, i.e., alluvial and lacustrine deposits, in the Bresse and Dombes basins to the north of Lyon (Fig. 1). More specifically, the present study is about checking whether the valley-fill models that have been established for the Messinian incised valleys around the Western Mediterranean (e.g., Clauzon et al., 1996Clauzon et al., , 2015aClauzon et al., , 2015bBreda et al., 2009) apply to a very upstream portion of the valley. Ultimately, the upper Pliocene ria which bounds the Massif Central epeirogeny and the western Alps orogen, presents an unparalleled opportunity to understand relationships between tectonics and surface processes in context of a regional transition from a Miocene active thrust belt to a Pleistocene vertical uplift of the collisional orogen. ...
... A variety of depositional subsystems are tentatively recognized throughout the valley fill: (i) an anastomosed river system with floodplain lakes, over the Plaine-de-la-Saône area; (ii) Gilbert-type deltas of two distinct forms: Reyrieux to the north, and Vaise M122 BH in the Central Lyon area; (iii) deep-water lacustrine settings, in the forms of varved and black shale facies in Vaise and Gerland localities, respectively; (iv) marginal alluvial fans which flank the side of the valley at the outlet of tributaries, e.g., Cailloutis de Gerland; (v) marginal marine swamps which top the valley fill, e.g., in Oullins. Such an assemblage of subsystems is not consistent with the model of the Messinian valley fills around the Northwestern Mediterranean coast which consists either of a single Gilbert-type delta prograding down the incised valley right after the initial marine reflooding, e.g., the Var Valley (Ligurian Sea; Clauzon et al., 1990), or followed a series of vertically stacked Gilbert-type deltas, e.g., the Roya Valley (Ligurian Sea; Breda et al., 2009) and the Têt Valley (Roussillon Basin; Clauzon et al., 2015a). Instead, sedimentological and stratigraphic data, here about 300 kms inland, seem best interpreted in terms of a chain of lakes dammed by locallysourced alluvial fans, and in which distinct Gilbert-type fan deltas prograded. ...
The Pliocene ria, a narrow seaway running up the Rhône Valley, has been mapped for a while by field geologists. Only much later, after the DSDP Leg 13 in 1970, a consensus was reached that this unique geological feature of the Rhône Valley was created by the major Mediterranean sea-level drop associated with the Messinian Salinity Crisis, followed by a sudden sea-level rise caused by the breach of the Strait of Gibraltar and the invasion of the Mediterranean Basin by the Atlantic waters. At the regional level of the Lyon Metropolis in the upper Rhône Valley, main issues were however remaining about the course and depth of the Messinian valley, and about the valley fill, namely where and how do the Pliocene marine strata of the Rhône Valley pass to the continental deposits of the Bresse Basin to the north? These are key-questions in that the Plio-Pleistocene makes up a large fraction of the basement that holds up a large city, not free from potential geological hazards and subject to problems of groundwater management, high-cost tunneling projects, etc. Our survey reviews first the historical researches − descriptions of the outcrops and fossil assemblages. It is followed by an unprecedented analysis and correlation of a thousand boreholes, which makes it possible to physically link and reconcile ancient local observations. Sections across the Messinian valley reveal a proper canyon morphology for the segments that cut the crystalline basement. The magnitude of the incision has been calculated as 335 m to a minimum, three hundred kilometers away from the river mouth. Three major depositional systems are distinguished for the Pliocene − Lower Pleistocene succession. The valley that initially ran much farther north of Lyon was occupied in the Zanclean by a series of pounded lakes, dammed by transverse local alluvial fans, filled by minor Gilbert-type deltas, and repeatedly flooded by marine ingressions. The valley wings were then encroached during the Piacenzian by a major, Alps-rooted alluvial sheet. At the level of Lyon, the fluvial deposits were deflected to the north (Sables de Trévoux) and to the south (Alluvions jaunes) as a dichotomy. The succession was then capped by a gravel-dominated fluvio-glacial fan (Alluvions jaunes sommitales) at the Plio-Pleistocene transition. It spread out from the north-east to the south, and intersected the previous valley overfill due to the shift to the north, i.e., South Jura, of the feeder stream. The depositional and current elevations of the marine-influenced episodes, i.e. marker bands that punctuate the regional Neogene succession, are used to bring out successive uplift and subsidence phases of the region. Finally, we tentatively link the major shifts in the depositional patterns of the Late Neogene succession in the Lyon area to major changes in the thrust belt activity, exhumation story, and outset of glaciers in the western Alps.
... Accordingly, during the relative sea-level fall and lowstand, an erosive surface is believed to originate from subaerial erosion, i.e., deep river erosion chiefly along the Raganello River valley, filled during relative sea-level rise by incised-valley systems [60,61]. Only for the T7 terrace is the first early phase of relative sea-level fall represented by erosive-based, fluvial conglomerates resting erosively on delta-slope deposits of FA3a (Figures 3F and 5B). ...
... The incised valley system wasthen flooded by the sea and formed a coastal embaymentlike ria. Although most of the valleys are backfilled during the successive transgressive phase, deltas may develop at times when sediment supply exceeds the rate of relative sea-level rise [60,61]. Unfortunately, no evidence of in-valley transgressive marine deposits has been documented, but transgressive stages may be supported by the stratal geometry of Gilbert-type deltas. ...
The Sibari Plain (northeastern Calabria) shows a well-developed stair of late Quaternary marine/coastal terraces resulting from the interaction between sea level fluctuations and tectonic uplift. This paper (i) provides a stratigraphic description of terraced deposits between the Raganello and Coscile rivers, (ii) assesses the relative controls of eustacy and uplift on the staircase formation, and (iii) unravels the Quaternary morphosedimentary evolution of the study area. A geomorphological approach was coupled with stratigraphic field surveys. Photo interpretation, topographic map analyses, and field surveys allowed us to map ten orders of terraces forming telescopically incised valley-fills. Based on the uppermost position of foreshore deposits on inner margins and an average uplift rate of ~1 mm/y, inferred from the Marine Isotope Stage (MIS) 5.5, terraces were correlated with highstands. Sedimentological and stratigraphic analyses allowed us to recognize four assemblages of genetically associated sedimentary facies related to superimposed and juxtaposed coastal and alluvial systems, showing a seaward-stepping architecture. Based on stratal geometry and facies association, we argue that alluvial/fluvial sediments and coastal depositional systems formed contemporaneously along the same terrace. Terrace arrangement resulted from repeated cycles of valley incision (sea level fall) and aggradational to progradational stacking pattern (sea level rise and highstands) in a framework of sustained uplift.
... A variety of sediment-gravity flows occur on the steeply dipping foreset slopes of deltas, including debris flows, debris falls, and density flows (e.g., Colella, 1988;Prior and Bornhold, 1988;Massari and Parea, 1990;Sohn et al., 1997;Breda et al., 2009;Gobo et al., 2014). Density flows on steep slopes are commonly supercritical flows; therefore, sedimentary structures formed by supercritical flows should be preserved on steep delta-foreset slopes (Nemec, 1990). ...
... The steep slopes of delta fronts are sensitive to changes in environmental factors around the delta such as river discharge, wave energy, tidal range, and baselevel change. For instance, changes in base level caused by eustatic sea-level changes and regional tectonic movements result in vertically stacked clinoforms of successive deltas during times of increasing accommodation (e.g., Gawthorpe and Colella, 1990;Breda et al., 2009;Eilertsen et al., 2011). Some architectural changes in delta foresets due to transition of flow have been suggested to be linked to river-derived hyperpycnal flows or tide-driven gravity flows on foresets (Ayranci et al., 2012;Turmel et al., 2015;Ventra et al., 2015;Dietrich et al., 2016). ...
Bedforms related to supercritical flows and hydraulic jumps have been increasingly recognized in various depositional environments. However, few ancient examples have been investigated in terms of the variations and transitions of supercritical-flow deposits. We present a detailed analysis of the sedimentary facies and stacking patterns of cyclic step, chute-and-pool, and antidune deposits of a coarse-grained Gilbert-type delta in the middle Pleistocene Kamiizumi Formation, Shimosa Group, central Japan. The Kamiizumi Formation was deposited during marine isotope stages 8–7.5 in the paleo-Tokyo Bay basin. We describe the following four facies and two facies successions in the foreset beds exposed at the study site. Planar-parallel stratification represents antidune to subcritical deposits from high-density flows. Deep scours infilled by steeply dipping backsets are interpreted as chute-and-pool deposits. Shallow, lenticular troughs infilled with backsets and foresets are interpreted as chute-and-pool and unstable antidune deposits. Lenticular units of fine sand with low-angle backsets of considerably greater wavelength than the other three facies are indicative of cyclic step deposits. One facies succession is characterized by chute-and-pool deposits alternating antidune to subcritical deposits formed during progradation of foresets. The lateral cyclicity of coarser-grained chute-and-pool deposits and finer grained antidune to subcritical deposits is characteristic of autogenic flow changes on progradational steep delta slopes. The other facies succession represents an aggradational delta succession from cyclic step deposits, to chute-and-pool deposits, to antidune to subcritical deposits. The vertical changes indicate decreasing flow velocity and may be the result of autogenic flow transitions during rapid aggradation. These facies changes resulted from the intrinsic instability of supercritical flows on steep foreset slopes at high depositional rates.
... Dans le bassin du Roussillon (Sud-Ouest de la France), Clauzon et al. (2015) proposent qu'immédiatement après un retour soudain des eaux marines, quelques écoulements de débris ont été mis en place avant les systèmes de Gilbert deltas zancléens. Dans le canyon de Ventimiglia, Breda et al. (2007Breda et al. ( , 2009 (Breda et al. 2007(Breda et al. , 2009, qui ont également mis en question l'hypothèse du réennoiement catastrophique de la Méditerranée occidentale. ...
... Dans le bassin du Roussillon (Sud-Ouest de la France), Clauzon et al. (2015) proposent qu'immédiatement après un retour soudain des eaux marines, quelques écoulements de débris ont été mis en place avant les systèmes de Gilbert deltas zancléens. Dans le canyon de Ventimiglia, Breda et al. (2007Breda et al. ( , 2009 (Breda et al. 2007(Breda et al. , 2009, qui ont également mis en question l'hypothèse du réennoiement catastrophique de la Méditerranée occidentale. ...
The Neogene geodynamics evolution of the south-Alboran realm in western Mediterranean has been clarified, based on sedimentological and chronostratigraphical studies. This work focuses on three main themes of research, the first is to establish the moments for the opening and closing of the North Rifian Corridor by studying two Neogene basins of the southern edge of the Alboran sea. The second, aims to understand the behavior of these two basins face a major event in the history of the Mediterranean: The Messinian Salinity Crisis. Finally, the third theme aims to understand the modalities Post-MSC reflooding in the southern part of the Alboran realm.
The late Miocene evolution of the North Rifian Corridor is clarified on the basis of chronostratigraphic studies of the Neogene Boudinar and Arbaa Taourirt basins (northeastern Morocco). The marine sediments deposited in the Boudinar basin between the early Tortonian and the late early Messinian (10 Ma to 6.1 Ma) and in the late Tortonian-earliest Messinian interval in the Arbaa Taourirt basin. Palaeoenvironmental data record a major drowning in association with extensive tectonics in the Boudinar basin during the early Messinian at ~7.2 Ma. At the same time, prograding conglomerates and sandstones developed over the late Tortonian marls in the Arbaa Taourirt basin. During the late-early Messinian, a shallowing trend occurred in the Boudinar basin. Thus, the North Rifian Corridor opened at ~7.2 Ma ensuring Atlantic-Mediterranean connections, then was progressively restricted during the late-early Messinian and totally closed at ~6.1 Ma.
New sedimentological and paleontological studies of the late Messinian-early Pliocene deposits in the Boudinar basin provide new information on the Messinian Salinity Crisis (« MSC ») and the Zanclean reflooding in the Alboran sea. The Messinian erosional surface « MES » is of late Messinian age and was emplaced in subaerial settings. It is polygenic, its original geometry is locally preserved and was re-shaped by the Pliocene transgressive surface.
Above the « MES », the Boudinar basin infill is characterized by a wide variety of facies from continental settings to lower offshore conditions. Two major sets are recognized: a latest Messinian-Zanclean set that constitutes a transgressive-regressive megasequence interrupted at the top by a tectonic unconformity, and an Plio-Quaternary regressive set. During the late Messinian Zanclean interval, four successive depositional models were documented. They record major changes in palaeoflow and paleogeography related to base-level fluctuations. No Gilbert-type delta has ben identified at Boudinar. the beginning of base-level rise is marked by normal regressions and by the formation of several lacs and fan-delta complexes on the margins of the basin in the late Messinian and befor the marine reefloding in the early Zanclean. The marine reflooding of the basin appears later, with a transgressive surface of ravinment and a thick package of transgressive deposits. These transgressive deposits onlap over all previous deposits. The major part of the basin infill did not issue from an inner landward position (south of the basin) but from the northwestern side of the basin, i.e. near the Mediterranean. Sediments were subsequently reworked by storms and transported by longshore-drift towards the south. a maximum flooding surface is found several tens of metres above the « MES ». This fiding is consistent with a progressive and not a catastrophic early Zanclean flooding of the westernMediterranean after the Mediterranean base-level fall.
... Interpretación: esta asociación representa flujos no canalizados (sheetflood deposits) generados durante episodios de baja frecuencia y gran magnitud de descarga de agua y sedimentos. (Massari y Parea, 1990;Breda et al., 2009). El conjunto de facies agradacionales del topset puede ser interpretado como el resultado de la sedimentación en una extensa planicie, donde el suministro pulsatorio repetitivo y el depósito de carga de lecho arenosa del río produjo acreción vertical (Bridge, 2003). ...
... Durante la disminución progresiva de la fase de inundación y depósito del foreset corriente arriba se generan estructuras de corte y relleno (Figura 4c; Siegenthaler y Huggenberger, 1993), que se presentan como pequeñas unidades de canal subhorizontales o intersecciones de canales menores (Ashmore, 1982). La estructura interna de los depósitos del topset, en general, sugiere el desarrollo de una sistema fluvial con una dinámica inestable y canales con patrones de baja sinuosidad (Breda et al., 2009), rellenados durante periodos de alta descarga de agua y sedimentos (Figura 3c y 3d) donde el flujo, cuando se supera el valor crítico del gradiente del piso del canal, se extiende sobre la planicie y genera depósitos no canalizados en condiciones de alta energía. ...
The geometry of a foreland basin is mainly a product of a complex dynamic balance between orogenic loading, erosion and sedimentation, and lithospheric flexural response. To improve our understanding of the relationships between these processes and the Andean foreland basin stratigraphy, a detailed stratigraphic and sedimentologic study of the Late Cenomanian - Early Turonian Cerro Lisandro Formation in the surface and subsurface of western Neuquen basin is presented in this paper. The Cerro Lisandro Formation shows a cyclic alternation of lacustrine and Gilbert-type delta deposits, with lacustrine-dominated intervals up to 152 m thick. Flood-dominated Gilbert-type deltas represent a volumetrically significant component of the Cerro Lisandro Formation, on a foreland basin margin that developed during the Late Cenomanian - Early Turonian in central-western Neuquen basin (Argentina). Excellent exposures of the vertical and lateral relationships among facies assemblages reveal a suite of deltaic and lacustrine depositional environments within elongate, highly subsiding troughs (foredeeps) that developed in front of the advancing Andean thrust systems. The entire succession is around 370 m thick and consists mainly of lacustrine clay and siltstone, and deltaic clinostratified and mouth bar lobe sandstone. The Gilbert-type deltas are organized into numerous vertically-stacked successions that display well-developed tangential foresets, poorly-preserved topsets, toesets and bottomset. The internal depositional architectures consisting of alternating progradational, aggradational-progratacional and retrogradational geometries were controlled by high-frequency, climatic events in a relatively rapidly subsiding basin. The common element that characterizes all the depositional architectures detected within the main studied sections is the constant influence of high rates of subsidence and sediment supply, associated with orogenic uplift and loading on the deltaic systems during sediment accumulation. The tectonic control of the basin margin from which the deltas were sourced forced a forward-stepping (basinward) arrangement of stacked Gilbert-type deltas, and these produced clinoforms that become progressively younger toward the basin depocentre. The concept of stratigraphic base level, or the ratio between accommodation and sediment supply (A/S ratio), has been used to analyse the Cerro Lisandro Formation. The lacustrine/Gilbert-type deltas cyclicity is interpreted as recording repeated uplift of the Agrio fold and thrust belt to the west, and a subordinate influence of paleoclimate. Cerro Lisandro Formation was deposited in underfilled conditions; during the early underfilled basin period, the basin geometry is mainly controlled by the orogenic loading, and a forebulge zone with an approximately fixed location is formed. A qualitative model for the migration and stratigraphic fill of an underfilled Andean foreland basin is proposed. This model provides a qualitative pattern of the cratonward migration of the forebulge zone within a several-million-year tectonically-driven cycle. It is demonstrated that the uplifting forebulge zones migrated toward the craton during the Cenomanian - early Turanian.
... Interpretación: esta asociación representa flujos no canalizados (sheetflood deposits) generados durante episodios de baja frecuencia y gran magnitud de descarga de agua y sedimentos. (Massari y Parea, 1990;Breda et al., 2009). El conjunto de facies agradacionales del topset puede ser interpretado como el resultado de la sedimentación en una extensa planicie, donde el suministro pulsatorio repetitivo y el depósito de carga de lecho arenosa del río produjo acreción vertical (Bridge, 2003). ...
... Durante la disminución progresiva de la fase de inundación y depósito del foreset corriente arriba se generan estructuras de corte y relleno (Figura 4c; Siegenthaler y Huggenberger, 1993), que se presentan como pequeñas unidades de canal subhorizontales o intersecciones de canales menores (Ashmore, 1982). La estructura interna de los depósitos del topset, en general, sugiere el desarrollo de una sistema fluvial con una dinámica inestable y canales con patrones de baja sinuosidad (Breda et al., 2009), rellenados durante periodos de alta descarga de agua y sedimentos (Figura 3c y 3d) donde el flujo, cuando se supera el valor crítico del gradiente del piso del canal, se extiende sobre la planicie y genera depósitos no canalizados en condiciones de alta energía. ...
The geometry of a foreland basin is mainly a product of a complex dynamic balance between orogenic loading, erosion and sedimentation, and lithospheric flexural response. To improve our understanding of the relationships between these processes and the Andean foreland basin stratigraphy, a detailed stratigraphic and sedimentologic study of the Late Cenomanian - Early Turonian Cerro Lisandro Formation in the surface and subsurface of western Neuquen basin is presented in this paper. The Cerro Lisandro Formation shows a cyclic alternation of lacustrine and Gilbert-type delta deposits, with lacustrine-dominated intervals up to 152 m thick. Flood-dominated Gilbert-type deltas represent a volumetrically significant component of the Cerro Lisandro Formation, on a foreland basin margin that developed during the Late Cenomanian - Early Turonian in central-western Neuquen basin (Argentina). Excellent exposures of the vertical and lateral relationships among facies assemblages reveal a suite of deltaic and lacustrine depositional environments within elongate, highly subsiding troughs (foredeeps) that developed in front of the advancing Andean thrust systems. The entire succession is around 370 m thick and consists mainly of lacustrine clay and siltstone, and deltaic clinostratified and mouth bar lobe sandstone. The Gilbert-type deltas are organized into numerous vertically-stacked successions that display well-developed tangential foresets, poorly-preserved topsets, toesets and bottomset. The internal depositional architectures consisting of alternating progradational, aggradational-progratacional and retrogradational geometries were controlled by high-frequency, climatic events in a relatively rapidly subsiding basin. The common element that characterizes all the depositional architectures detected within the main studied sections is the constant influence of high rates of subsidence and sediment supply, associated with orogenic uplift and loading on the deltaic systems during sediment accumulation. The tectonic control of the basin margin from which the deltas were sourced forced a forward-stepping (basinward) arrangement of stacked Gilbert-type deltas, and these produced clinoforms that become progressively younger toward the basin depocentre. The concept of stratigraphic base level, or the ratio between accommodation and sediment supply (A/S ratio), has been used to analyse the Cerro Lisandro Formation. The lacustrine/Gilberttype deltas cyclicity is interpreted as recording repeated uplift of the Agrio fold and thrust belt to the west, and a subordinate influence of paleoclimate. Cerro Lisandro Formation was deposited in underfilled conditions; during the early underfilled basin period, the basin geometry is mainly controlled by the orogenic loading, and a forebulge zone with an approximately fixed location is formed. A qualitative model for the migration and stratigraphic fill of an underfilled Andean foreland basin is proposed. This model provides a qualitative pattern of the cratonward migration of the forebulge zone within a several-millionyear tectonically-driven cycle. It is demonstrated that the uplifting forebulge zones migrated toward the craton during the Cenomanian - early Turonian.
... Interpretación: esta asociación representa flujos no canalizados (sheetflood deposits) generados durante episodios de baja frecuencia y gran magnitud de descarga de agua y sedimentos. (Massari y Parea, 1990;Breda et al., 2009). El conjunto de facies agradacionales del topset puede ser interpretado como el resultado de la sedimentación en una extensa planicie, donde el suministro pulsatorio repetitivo y el depósito de carga de lecho arenosa del río produjo acreción vertical (Bridge, 2003). ...
... Durante la disminución progresiva de la fase de inundación y depósito del foreset corriente arriba se generan estructuras de corte y relleno (Figura 4c; Siegenthaler y Huggenberger, 1993), que se presentan como pequeñas unidades de canal subhorizontales o intersecciones de canales menores (Ashmore, 1982). La estructura interna de los depósitos del topset, en general, sugiere el desarrollo de una sistema fluvial con una dinámica inestable y canales con patrones de baja sinuosidad (Breda et al., 2009), rellenados durante periodos de alta descarga de agua y sedimentos (Figura 3c y 3d) donde el flujo, cuando se supera el valor crítico del gradiente del piso del canal, se extiende sobre la planicie y genera depósitos no canalizados en condiciones de alta energía. ...
The geometry of a foreland basin is mainly a product of a complex
dynamic balance between orogenic loading, erosion and sedimentation,
and lithospheric flexural response. To improve our understanding of the
relationships between these processes and the Andean foreland basin
stratigraphy, a detailed stratigraphic and sedimentologic study of the
Late Cenomanian - Early Turonian Cerro Lisandro Formation in the
surface and subsurface of western Neuquen basin is presented in this
paper. The Cerro Lisandro Formation shows a cyclic alternation of
lacustrine and Gilbert-type delta deposits, with lacustrine-dominated
intervals up to 152 m thick. Flood-dominated Gilbert-type deltas
represent a volumetrically significant component of the Cerro Lisandro
Formation, on a foreland basin margin that developed during the Late
Cenomanian - Early Turonian in central-western Neuquen basin
(Argentina). Excellent exposures of the vertical and lateral relationships
among facies assemblages reveal a suite of deltaic and lacustrine
depositional environments within elongate, highly subsiding troughs
(foredeeps) that developed in front of the advancing Andean thrust systems. The entire succession is around 370 m thick and consists mainly
of lacustrine clay and siltstone, and deltaic clinostratified and mouth bar
lobe sandstone. The Gilbert-type deltas are organized into numerous
vertically-stacked successions that display well-developed tangential
foresets, poorly-preserved topsets, toesets and bottomset. The internal
depositional architectures consisting of alternating progradational,
aggradational-progratacional and retrogradational geometries were
controlled by high-frequency, climatic events in a relatively rapidly
subsiding basin. The common element that characterizes all the
depositional architectures detected within the main studied sections is
the constant influence of high rates of subsidence and sediment supply,
associated with orogenic uplift and loading on the deltaic systems
during sediment accumulation. The tectonic control of the basin
margin from which the deltas were sourced forced a forward-stepping
(basinward) arrangement of stacked Gilbert-type deltas, and these
produced clinoforms that become progressively younger toward the
basin depocentre. The concept of stratigraphic base level, or the ratio
between accommodation and sediment supply (A/S ratio), has been
used to analyse the Cerro Lisandro Formation. The lacustrine/Gilberttype
deltas cyclicity is interpreted as recording repeated uplift of the
Agrio fold and thrust belt to the west, and a subordinate influence of
paleoclimate. Cerro Lisandro Formation was deposited in underfilled
conditions; during the early underfilled basin period, the basin geometry
is mainly controlled by the orogenic loading, and a forebulge zone with
an approximately fixed location is formed. A qualitative model for
the migration and stratigraphic fill of an underfilled Andean foreland
basin is proposed. This model provides a qualitative pattern of the
cratonward migration of the forebulge zone within a several-millionyear
tectonically-driven cycle. It is demonstrated that the uplifting
forebulge zones migrated toward the craton during the Cenomanian
- early Turonian
... Importantly, Gilbert-type deltas are highly sensitive recorders of baselevel changes (sensu Catuneanu 2002Catuneanu , 2006. Long-term large changes result in vertical stacking of successive deltas (Colella 1984(Colella , 1988a(Colella , 1988bGawthorpe and Colella 1990;García-García et al. 2006;Breda et al. 2009) or cause incision of deep fluvial valleys that are filled by younger bayhead deltas (Dart et al. 1994;Ford et al. 2007Ford et al. , 2013Rohais et al. 2008;Backert et al. 2010;Gobo et al. 2014a). Short-term smaller changes result in alternation of oblique and sigmoidal topset-foreset clinoform architecture in the prograding delta (Massari 1996;García-García 2004;Breda et al. 2007;Gobo et al. 2014a, in review). ...
... These short-term morphodynamic changes in the delta-front brink zone have been linked by Gobo et al. (in review) to coeval changes in the delta-slope processes, with an alternating dominance of turbidites and debrisflow deposits (Fig. 1B). Little attempt has thus far been made to study the impact of these coupled brink and slope changes on the delta toeset and bottomset processes, as the modern ''snapshot'' observations are few and lack stratigraphic perspective (Kostaschuk and McCann 1987;Prior and Bornhold 1989;Bornhold and Prior 1990), whereas the transition from foreset to coeval bottomset deposits in ancient deltas is seldom well exposed (Sohn et al. 1997;Breda et al. 2007Breda et al. , 2009. ...
Results of a detailed sedimentological study of the mid-Pleistocene Gilbert-type Ilias delta at the southern coast of the Corinth Rift, Greece, are reported. The study indicates that the development of a turbidite-dominated facies assemblage (TFA) of delta foreset deposits is associated with an oblique delta-brink geometry, which signifies a deficit of delta-front accommodation due to the falling or stable base level. A debrite-dominated assemblage (DFA) of foreset deposits forms when the base level is rising and the delta-brink geometry becomes sigmoidal, signifying an increase in delta-front accommodation. The comparison of coeval foreset and toeset to bottomset deposits in the delta indicates a reverse pattern of reciprocal changes in facies assemblages, with the foreset TFA deposits corresponding to delta-foot DFA deposits, and with the foreset DFA deposits corresponding to delta-foot TFA deposits. This reciprocal alternation of TFA and DFA facies assemblages is attributed to changes in the delta-front accommodation driven by short-term base-level changes, with a degree of ''noise'' in the facies record due to the system autogenic variability and regional climatic fluctuations. The study sheds a new light on the changing pattern of subaqueous sediment dispersal in Gilbert-type deltaic systems in response to base-level changes. It also indicates a new possibility for the recognition of a hidden record of such changes in other similar ancient deltas on the basis of their detailed facies analysis. INTRODUCTION
... The eustatic rise in sea level and the tectonic subsidence led to increased accommodation in the incised valley. Although the lagoonal mudstones were deposited in the middle of the succession, the thick fluvial deposits at the base of the incised valley and the normal regressive deltaic successions make up the bulk of the valley fill, which may be an example of "overfilled" incised valley (Breda et al. 2009). All these sedimentary records indicate that the Early Tortonian sedimentation in the Mut Basin, especially in the incised valleys, is the product of the interplay of eustatic sea-level rise, tectonic subsidence and sediment supply. ...
The Mut Basin in Southern Türkiye formed as a post-orogenic intramontane collapse depression and a thick carbonate succession consisting mainly of platform carbonates and reefal limestones deposited in the basin during the Late Burdigalian–Late Tortonian. These shallow marine carbonates provide a high-resolution sedimentary record of several relative sea-level changes. Through sedimentological and biostratigraphical analyses, we have identified four major relative sea-level changes in the stratigraphic succession during the Late Burdigalian, Late Serravallian, Early Tortonian and the Late Tortonian. The first marine transgression, during the Late Burdigalian, flooded the basin and led to carbonate sedimentation, which continued without significant interruption until the Late Serravallian, causing the greatest amount of extension and deepening of the Mut Basin. However, the relative fall in sea level during the Late Serravallian interrupted marine sedimentation at the basin margin, causing subaerial exposure and fluvial erosion of carbonate sediments. As a result, the sediments eroded during this period were initially deposited in the shoreface and foreshore zones as sharp-based, forced regressive depositional units. The continued fall in base level was manifested by incised fluvial palaeovalleys; these formed on the reefal limestones of the Mut Formation, representing forced regression and unconformity. The latest sea-level lowering and early base-level rise resulted in the deposition of fluvial successions at the base of the incised valleys during the Early Tortonian. The rising sea level inundated the incised valleys and turned them into embayments. Gilbert-type delta, shoal-water delta, shoreface, foreshore, lagoonal sediments and platform carbonates were deposited within the incised valleys. These sediments reflect the interplay of marine flooding and sediment supply within the incised valley. The transgression associated with the Early Tortonian eustatic rise in sea level and the basin subsidence resulted in the deposition of a second generation of reefal limestones along the basin margin, namely the Tırtar Formation, which is directly superimposed on the limestones of the Mut Formation. The Late Tortonian forced regression was associated with the tectonic uplift of the Mut Basin and resulted in subaerial exposure and fluvial erosion along the basin margin. The sediments eroded from the Tırtar Formation formed Gilbert-type delta deposits on the lowstand shoreline.
... All these factors can influence the geometry of fan deltas and their architectural elements. They can also impact the predominance of different depositional processes, determining distributions of grains and sedimentary structures, and thereby lithofacies [1][2][3][4][5][6][7][8][9][10][11][12][13]. Previous studies indicate that strong tectonic activities, arid-semiarid climate, sufficient material supply, and rapid accumulation account for fan deltas, which are usually composed of fan delta plain, fan delta front, and prodelta [14][15][16][17]; tectonic activities in continental rift basins generate accommodation and dominate fan delta sedimentary architectures [18][19][20][21] and sequence evolution [22][23][24][25], and variations in the fault activity bring about changes of the depocenter location in space and time [26]; climate changes influence the accommodation by varied lake depths, and thus stratigraphic architectural patterns [19,25,27,28]. ...
Fan deltas of the Lower Cretaceous area in Saihantala sag, Erlian Basin have been identified as major petroleum exploration opportunities. The sedimentary evolution is, however, still debatable, which hinders insights into its controlling factors. This research employed new core observations, thin section observations, and grain size analyses of 28 wells in the Saidong sub-sag, together with numerous borehole and seismic data points, to explore lithofacies types, subfacies, and microfacies characteristics, thus leading to a further investigation of the sedimentary facies evolution of the sag and its controlling factors. The findings showed there are 3 categories, 12 sub-categories, and 20 fine lithofacies types in the Saidong sub-sag. Additionally, various sand-conglomerate lithofacies were characterized by lower composition and texture maturity. With dentate-shaped, box-bell-shaped, and other morphological well-logging responses, fan deltas were mostly developed in the A’ershan Formation and the Tengge’er Formation, which could be subdivided into three subfacies and eight microfacies. Given the sedimentary features and lithofacies characteristics of each microfacies, it can be determined that three main stages occurred in formations from the A’ershan to the Tengge’er: the water transgression, the water oscillation, and the water regression. Moreover, fan delta deposits were regulated primarily by semi-arid hygrothermal and semi-arid paleoclimate and paleotectonic factors.
... This led to the opening of the Liguro-Provençal Basin (late Oligocene to early Miocene, e.g., [1,5,19,57]) and the Tyrrhenian Sea (Late Miocene to Pliocene; [58,59]) due to southeasternward roll-back of the Apennines-Maghrebides subduction zone (e.g., [1] and references therein). In this framework, vertical movements in the Ligurian Alps were not limited to the orogenic stage, but protracted during the Miocene to Present, as shown by the low-temperature apatite (U-Th)/He and fission track studies [31,60] and the morphostratigraphic reconstructions of the Plio-Pleistocene sedimentary sequences [61][62][63]. These latter, locally exposed (e.g., in the Ventimiglia area: [62,64]), witness a post-Pliocene uplift of about 500 m [31]. ...
The review of recent bathymetric and geophysical data collected in the framework of several research and cartographic projects have allowed a detailed reconstruction of the morpho-structural setting and the (neo)tectonic evolution for both the Alpine and Apennine margins of the Ligurian Sea (Italy). The widespread occurrence of erosional processes and sediment mass movements along the steep continental slope and within the system of submarine canyons reflect the close correlation between the active tectonics and the recent morpho-dynamic evolution of the Ligurian Margin. This
relation is better constrained in the western sector (Alpine) of the Ligurian Sea, where the recent uplift of the continental margin is associated to a well-developed system of inherited structures reactivated under a compressive/transpressive regime and widespread seismicity. In the eastern sector, where the seismicity is lower or absent, the mass movements are limited to few areas (e.g., the Portofino slope) coinciding with seismic clusters. Additionally, this sector is characterized by moderate and
episodic fault reactivations under a compressive regime. The evidence of compressive deformation along the inherited fault systems has been revealed in some areas of the Ligurian Sea where the post-drifting extensional tectonics is interrupted by episodic tectonic inversion (at least) during the Middle–Upper Miocene and the Plio–Pleistocene until present.
... 10,13,14,16 and 20). This outcome confirms that steep slopes and relatively high sediment supply at the shelf-edge promote the condition for sediment instability and landslide processes (Coleman et al., 1983;Breda et al., 2009;Ryan et al., 2009;Wild et al., 2009;Oliveira et al., 2011;Dixon et al., 2013;Gomis-Cartesio et al., 2017). Fig. 5h). ...
Systems Supplying Sediment to Canyon or Slope Channel Heads (SSSCHs) initiate sediment transfer from the shallow water areas to the deep sea. SSSCHs are very sensitive to sea-level variations, to perturbations in sediment production and redistribution and to variations in accommodation in the shelf. Through the analysis of bathymetric and subbottom data, I review the variability in time and space of SSSCHs in the eastern Sardinian and northeastern Sicilian margins of the Tyrrhenian Sea. I distinguish three main types of SSSCHs: type I corresponds to shelf-edge deep-water coastal systems; type II corresponds to continental shelf, shoal-water coastal systems; type III is coast-disconnected. Further subdivisions involve the degree of confinement and the process-regime at the shelf-edge for Type I SSSCHs, and the distance from the canyon head and the process-regime for type II SSSCHs. Coast-disconnected type III SSSCHs consist of shelf-wide depositional belts, both un-channalised and channalised, as well as of landslide complexes.
Each of the different SSSCHs has its distinct process-regime, which regulate its capability of sediment transfer to the canyon or channels and eventually to the deep-sea. SSSCHs of type IA and IB develop coastal bodies at the shelf-edge, which store part of the sediment budget. Type IC SSSCHs exhibit a direct connection between a river and a canyon, leading to shelf-edge sediment bypass; direct hyperpycnal discharge and landslides result in the largest efficiency in transferring sediment to the deep sea. The efficiency of type II SSSCHs depends mainly on their distance from the canyon head and on the ability of hyperpycnal flows, both from plunging river-floods and from wave resuspension, and storm waves, in transporting sediment offshore. Type IIC SSSCHs, consisting of tide-dominated shorelines, play a minor role in the study area due to the microtidal regime of the Mediterranean Sea. Type IIIA SSSCHs are also rare, since they correspond to shelf-wide depositional belts, that in the study area only seldom are able to reach the canyon heads. Type IIIB SSSCHs, corresponding to landslide complexes, also have a restricted frequency but can contribute a large amount of sediment to the deep-sea.
Sea-level variations have the largest influence on SSSCH evolution along the two margins of the study area. Type I prevails during the falling-stage and the lowstansd of sea level. They are however, also active during the present sea-level highstand in the tectonically active Sicilian margin. Type II SSSCHs dominate the TST but their activation is diachronous, being dependent also on inherited margin physiography.
The present review highlights the large spectrum of processes that contribute to sediment supply to canyon or slope channels heads. As a result, the complexity of the initial part of the marine tract of the source to sink system that transports sediment from the shallow-to the deep-sea is uncovered. While stressing the role of the previous evolution of a margin, of tectonic activity, and of climate variations, the present review acknowledges the importance of sea-level variations as a control on SSSCH development. It however shows that the complexity of the sedimentary processes that rules the transfer of sediment to the deep-sea results in times of activity during a cycle of sea-level variations, and consequent depositional histories that do not conform with those predicted by the sequence stratigraphic models.
... For example, based on DSDP sites 121-139, K. J. Hsü et al. (1973a) speculated about a refill of the Mediterranean lasting "probably less than 1000 years". Onshore evidence for a rapid Mediterranean Sea level rise at the end of the MSC came from the abundance of Giberttype deltas in the Gulf of Lyons and the Tyrrhenian Sea (Clauzon, 1978(Clauzon, , 1982Breda et al., 2009) and from the abrupt transit from paleosol to foraminifera-rich, deep marine laminites in the M/P contact in Pissouri (Orszag-Sperber et al., 2000). These observations suggested that the sea level rise was rapid in sedimentological terms and that the Strait of Gibraltar was the scenario for the reconnection between the Atlantic Ocean and the Mediterranean Sea, reestablishing the normal marine conditions ca. 5.3 million years ago. ...
About six million years ago, the Mediterranean Sea underwent a period of isolation from the ocean and widespread salt deposition known as the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km 3 of Miocene sediment and bedrock. Based on the understanding obtained from Pleistocene onshore megaflooding events and using ad-hoc hydrodynamic modeling, here we explore two predictions of the Zanclean outburst flood hypothesis: 1) The formation of similar erosion features at sills communicating sub-basins within the Mediterranean Sea, specifically at the Sicily Sill; and 2) the accumulation of the eroded materials as megaflood deposits in areas of low flow energy. Recent data show a 6-km-wide amphitheater-shaped canyon preserved at the Malta Escarpment that may represent the erosional expression of the Zanclean flood after filling the western Mediterranean and spilling into the Eastern Basin. Next to that canyon, a ~1600 km 3 accumulation of chaotic, seismically transparent sediment has been found in the Ionian Sea, compatible in age and facies with megaflood deposits. Another candidate megaflood deposit has been identified in the Alborán Sea in the form of elongated sedimentary bodies that parallel the flooding channel and are seismically characterized by chaotic and discontinuous stratified reflections, that we interpret as equivalent to gravel and boulder megabars described in terrestrial megaflood settings. Numerical model predictions show that sand deposits found at the Miocene/Pliocene (M/P) boundary in ODP sites 974 and 975 (South Balearic and Tyrrhenian seas) are consistent with suspension transport from the Strait of Gibraltar during a flooding event at a peak water discharge of ~10 8 m 3 s −1 .
... Thick fl uvial and delta deposits alternating with lagoon and shoreface deposits within the Dağpazarı incised valley were interpreted as an "overfi lled incised valley" as a whole (Breda et al., 2009). The continuing transgression in the basin caused the drowning of the incised valley and fl ooding of very large areas of the Mut Basin. ...
Early–middle Miocene reefal limestones are overlain disconformably by late Serravallian–
early Tortonian incised valley-fi ll deposits of Dağpazarı formation in the Mut Basin. Dağpazarı
formation is composed of mudstone, siltstone, sandstone and conglomerates. Facies associations of
the formation are: fl uvial, lagoon, shoal-water delta, shoreface, beach and barrier island deposits.
Loxoconcha tumida Brady and Loxoconcha sp. in the gray mudstones indicate the freshwater
infl uence and decrease in salinity. Hemicyprideis sp. documents brackish water conditions. The
shoreface sandstones alternating with the lagoonal mudstones, and oyster-rich beach deposits in
different levels of the sequence indicate episodes of marine connections. The age of the Dağpazarı
formation is provided by the planktonic foraminifera from the marine mudstones and marls below
and above the formation, and corresponds to the MMi8–MMi10 biostratigraphic interval, which
spans the late Serravallian–early Tortonian. Late Serravallian eustatic sea-level fall caused to the
quick shallowing of the Mut Basin and subaerial exposure of the reefal limestones at the basin
margin. Thus, the incised valley, formed upon the reefal limestones of the Mut formation. This
incised valley refl ects a regional forced regression and unconformity. The Dağpazarı formation was
deposited within this incised valley following an early Tortonian relative sea-level rise.
... Thick fl uvial and delta deposits alternating with lagoon and shoreface deposits within the Dağpazarı incised valley were interpreted as an "overfi lled incised valley" as a whole ( Breda et al., 2009). The continuing transgression in the basin caused the drowning of the incised valley and fl ooding of very large areas of the Mut Basin. ...
... Thick fl uvial and delta deposits alternating with lagoon and shoreface deposits within the Dağpazarı incised valley were interpreted as an "overfi lled incised valley" as a whole ( Breda et al., 2009). The continuing transgression in the basin caused the drowning of the incised valley and fl ooding of very large areas of the Mut Basin. ...
Early-middle Miocene reefal limestones are overlain disconformably by late Serravallian-early Tortonian incised valley-fill deposits of Dağpazarı formation in the Mut Basin. Dağpazarı formation is composed of mudstone, siltstone, sandstone and conglomerates. Facies associations of the formation are: fluvial, lagoon, shoal-water delta, shoreface, beach and barrier island deposits. Loxoconcha tumida Brady and Loxoconcha sp. in the gray mudstones indicate the freshwater influence and decrease in salinity. Hemicyprideis sp. documents brackish water conditions. The shoreface sandstones alternating with the lagoonal mudstones, and oyster-rich beach deposits in different levels of the sequence indicate episodes of marine connections. The age of the Dağpazarı formation is provided by the planktonic foraminifera from the marine mudstones and marls below and above the formation, and corresponds to the MMi8-MMi10 biostratigraphic interval, which spans the late Serravallian-early Tortonian. Late Serravallian eustatic sea-level fall caused to the quick shallowing of the Mut Basin and subaerial exposure of the reefal limestones at the basin margin. Thus, the incised valley, formed upon the reefal limestones of the Mut formation. This incised valley refl ects a regional forced regression and unconformity. The Dağpazarı formation was deposited within this incised valley following an early Tortonian relative sea-level rise.
... Thick fl uvial and delta deposits alternating with lagoon and shoreface deposits within the Dağpazarı incised valley were interpreted as an "overfi lled incised valley" as a whole (Breda et al., 2009). The continuing transgression in the basin caused the drowning of the incised valley and fl ooding of very large areas of the Mut Basin. ...
... They overlie the basal unconformity and show scoop-shaped scours (about 1 m deep and about 10 m wide). These structures resemble "spoon-shaped depressions" (Breda et al. 2007(Breda et al. , 2009Leszczyński & Nemec 2015) formed by turbidity currents descending a steep subaqueous slope and undergoing a hydraulic jump at its toe. However, sharp contact of gravels and underlying offshore mudstones of FA 4 is very common in the surrounding drill holes. ...
Two coarse-grained Gilbert-type deltas in the Lower Badenian deposits along the southern margin of the Western Carpathian Foredeep (peripheral foreland basin) were newly interpreted. Facies characterizing a range of depositional processes are assigned to four facies associations — topset, foreset, bottomset and offshore marine pelagic deposits. The evidence of Gilbert deltas within open marine deposits reflects the formation of a basin with relatively steep margins connected with a relative sea level fall, erosion and incision. Formation, progradation and aggradation of the thick coarse-grained Gilbert delta piles generally indicate a dramatic increase of sediment supply from the hinterland, followed by both relatively continuous sediment delivery and an increase in accommodation space. Deltaic deposition is terminated by relatively rapid and extended drowning and is explained as a transgressive event. The lower Gilbert delta was significantly larger, more areally extended and reveals a more complicated stratigraphic architecture than the upper one. Its basal surface represents a sequence boundary and occurs around the Karpatian/Badenian stratigraphic limit. Two coeval deltaic branches were recognized in the lower delta with partly different stratigraphic arrangements. This different stratigraphic architecture is mostly explained by variations in the sediment delivery and /or predisposed paleotopography and paleobathymetry of the basin floor. The upper delta was recognized only in a restricted area. Its basal surface represents a sequence boundary probably reflecting a higher order cycle of a relative sea level rise and fall within the Lower Badenian. Evidence of two laterally and stratigraphically separated coarse-grained Gilbert deltas indicates two regional/basin wide transgressive/regressive cycles, but not necessarily of the same order. Provenance analysis reveals similar sources of both deltas. Several partial source areas were identified (Mesozoic carbonates of the Northern Calcareous Alps and the Western Carpathians, crystalline rocks of the eastern margin of the Bohemian Massif, older sedimentary infill of the Carpathian Foredeep and/or the North Alpine Foreland Basin, sedimentary rocks of the Western Carpathian/Alpine Flysch Zone).
... The large-scale sets of cross-bedded conglomerates and sandstones also resemble the coarse-grained Gilbert-type deltas or tidal deltas (e.g. Limarino et al., 2002;Longhitano, 2008;Breda et al., 2009;Leren et al., 2010), although these show slightly thinner cross-bedded sets than tidal dunes, they are in the range of the beds described in this paper. ...
The Utrillas Formation represents clastic wedges that accumulated in relation to continental-coastal areas of Iberian Basin during the worldwide Late Cretaceous sea-level rise. At the Tamajón outcrop the Late Cenomanian Utrillas wedges are composed of four facies associations (FA1 to FA4), which unconformably overlay Triassic deposits. Basal sediments (FA1) are interpreted as high energy, braided fluvial deposits, characterized by coarse-grained (conglomerate–sandstone) facies; which grade upwards to tide-influenced, estuarine sedimentation (sandstones and mudstones with inclined heterolithic stratification, FA2), and then to high-energy, coastal sheet and channelled sandstones with different tidal features (FA3); and finally, to fine-grained (mudstones and minor burrowed sandstones) of an offshore marine associations (FA4). The depositional architecture based in the presence and hierarchy of several ranks of bounding surfaces and the overall upward-fining succession show the long term retrogradational trend of these facies associations. Peculiar sedimentary features of these sediments are 1) the presence of large-scale, single sets of cross beds infilling large erosive channels, which are tidal in origin. 2) The size and length of the cross-bedding defined by couplets of different grain size; here interpreted as originated by flow unsteadiness in relation to changing tides. And 3) an unusual association of ironstones, wrinkle structures and vertebrate tracks with microbial mats and penecontemporaneous iron encrusting allowing track preservation in the sedimentary record. © 2016, Universidad Complutense de Madrid. All rights reserved.
... It thus corresponds to the fluvial erosion related to the peak of the MSC. The Messinian erosion affected the Sorbas Basin even if its impact was relatively weak in comparison to other peripheral regions such as the Roussillon or the French and Italian Rivieras Breda et al., 2007Breda et al., , 2009. This difference may be explained by the character of the Sorbas Basin, an inner basin. ...
... It thus corresponds to the fluvial erosion related to the peak of the MSC. The Messinian erosion affected the Sorbas Basin even if its impact was relatively weak in comparison to other peripheral regions such as the Roussillon or the French and Italian Rivieras Breda et al., 2007Breda et al., , 2009. This difference may be explained by the character of the Sorbas Basin, an inner basin. ...
The Sorbas Basin is the land reference of the Messinian Salinity Crisis (MSC) that affected the Mediterranean
Sea in the latest Miocene. Its stratigraphy has been re-visited using calcareous nannofossils and
planktonic foraminifers, which provide a reliable biostratigraphic frame and lead to particularly specify
the relationships between the Sorbas and Zorreras members with Yesares evaporites.
The evaporites overlie a shallowing upward sequence ending with the deposition of the Reef Unit and
Terminal Carbonate Complex (TCC) on the periphery of the basin. The reefal carbonates of the TCC are
overlain by clastic deposits that are foreset beds of post-MSC Gilbert-type fan deltas developed on the
northern edge of the basin. These sedimentary structures are separated from reefal carbonates and the
Reef Unit by the Messinian Erosional Surface (MES). The various facies of the Sorbas Member have been
correlated with the bottomset beds of the Gilbert-type fan deltas despite some differences in palaeobathymetry.
In the southeastern periphery of the basin, the MES separates the Sorbas Member from the
Yesares gypsums. In the central part of the basin, a hiatus characterizes the contact between these
members. The Zorreras Member postdates the MSC and entirely belongs to Zanclean. Its white “Lago
Mare” layers are lagoonal deposits, the fauna of which is confirmed to result from Mediterranean
eParatethys high sea-level exchange after the post-MSC marine reflooding of the Mediterranean Basin.
... It thus corresponds to the fluvial erosion related to the peak of the MSC. The Messinian erosion affected the Sorbas Basin even if its impact was relatively weak in comparison to other peripheral regions such as the Roussillon or the French and Italian Rivieras Breda et al., 2007Breda et al., , 2009. This difference may be explained by the character of the Sorbas Basin, an inner basin. ...
... Similar sandy deposits form toesets in other gravelly Gilbert-type deltas, with the scoop-like scours referred to as 'spoon-shaped depressions' (Breda et al., 2007(Breda et al., , 2009). Analogous scours have been reported as 'large flutes' from the toes of modern Gilbert-type deltas (Bornhold & Prior, 1990, fig. 5). ...
This study employs facies analysis and basic principles of sequence stratigraphy to correlate isolated outcrop sections and reveal depositional history of the Chmielnik Formation – a prominent mid-Serravalian clastic wedge formed on the basinward forebulge flank of the Polish Carpathian Foredeep. The coarse-grained clastic wedge, up to 30 m thick and spanning ca 1.1 Ma within biozone NN6, consists of fluvio-deltaic, foreshore and shoreface deposits with a range of large littoral sand bars, all enveloped in muddy offshore-transition deposits. Its dynamic stratigraphy indicates rapid shoreline shifts and environmental changes due to the interplay of forebulge tectonism, sediment supply and third-order eustatic cycles. A similar interplay of tectonism and eustasy is recognizable in the whole middle Miocene sedimentary succession deposited on the forebulge flank, demonstrating an extreme case of an accommodation-controlled shelf and indicating tectonic cycles of the forebulge uplift and subsidence spanning ca 800 to 900 ka. The episodes of forebulge uplift correlate with the main pulses of orogen thrusting. The resulting composite peripheral unconformity differs markedly from the idealized model of a ‘steady-state’ stepwise onlap driven by forebulge continuous retreat. It is concluded that the foredeep peripheral unconformities, instead of being simplified in accordance to this idealized model, should rather be studied in detail because they bear a valuable high-resolution record of regional events and give unique insights into the local role of tectonics, eustasy and sediment supply.This article is protected by copyright. All rights reserved.
... In a transverse outcrop section, the delta-toe pebbly sandstones show multiple scoop-shaped scour-and-fill features, 40-70 cm deep and a few metres wide, cross-cutting one another ( Fig. 19B). Similar features, resembling trough crossstratification and referred to as 'spoon-shaped depressions', were recognized at the toes of many modern and ancient Gilbert-type deltas (e.g., Breda et al., 2007Breda et al., , 2009 The small outcrops here -lateral to that at stop A1.7 -show a regressive shoreface to foreshore succession corresponding to the shoal-water delta and subsequent lowstand phase at the previous locality. The succession shows further the record of a brief marine transgression, coeval with the drowning of the incised valley at locality A1.7, followed by rapid shoreline progradation coeval with the advance of Gilbert-type bayhead delta at this A1 -Sedimentation on Serravalian forebulge shelf Outcrop photograph and a corresponding interpreted log of the deposits exposed at stop A1.9 (Figs 1B, 17). ...
Guidebook is available online at www.ing.uj.edu.pl/ims2015
... It thus corresponds to the fluvial erosion related to the peak of the MSC. The Messinian erosion affected the Sorbas Basin even if its impact was relatively weak in comparison to other peripheral regions such as the Roussillon or the French and Italian RivierasBreda et al., 2007Breda et al., , 2009). This difference may be explained by the character of the Sorbas Basin, an inner basin. ...
The Sorbas Basin is the land reference of the Messinian Salinity Crisis (MSC) that affected the Mediterranean Sea in the latest Miocene. Its stratigraphy has been re-visited using calcareous nannofossils and planktonic foraminifers, which provide a reliable biostratigraphic frame and lead to particularly specify the relationships between the Sorbas and Zorreras members with Yesares evaporites.
The evaporites overlie a shallowing upward sequence ending with the deposition of the Reef Unit and Terminal Carbonate Complex (TCC) on the periphery of the basin. The reefal carbonates of the TCC are overlain by clastic deposits that are foreset beds of post-MSC Gilbert-type fan deltas developed on the northern edge of the basin. These sedimentary structures are separated from reefal carbonates and the Reef Unit by the Messinian Erosional Surface (MES). The various facies of the Sorbas Member have been correlated with the bottomset beds of the Gilbert-type fan deltas despite some differences in palaeobathymetry. In the southeastern periphery of the basin, the MES separates the Sorbas Member from the Yesares gypsums. In the central part of the basin, a hiatus characterizes the contact between these members. The Zorreras Member postdates the MSC and entirely belongs to Zanclean. Its white “Lago Mare” layers are lagoonal deposits, the fauna of which is confirmed to result from Mediterranean–Paratethys high sea-level exchange after the post-MSC marine reflooding of the Mediterranean Basin.
This study allows to re-assert the two-step scenario of the MSC (Clauzon et al., 1996) with the following events:
- at 5.971–5.600 Ma, minor sea-level fall resulting in the desiccation of this peripheral basin with secondary fluctuations;
- at 5.600–5.460 Ma, significant subaerial erosion (or lack of sedimentation) caused by the almost complete desiccation of the Mediterranean Sea;
- instantaneous marine reflooding, accepted at 5.460 Ma, followed by continuing sea-level rise.
... Sequence stratigraphy is a powerful tool to understand the history and the evolution of depositional systems and sedimentary basins (e.g., Vail et al., 1991;Catuneanu, 2006;Catuneanu et al., 2011). It has been successfully applied in a variety of geodynamic settings to both siliciclastic (Galloway and Williams, 1991;Helland-Hansen, 1992;Mellere and Steel, 1995;Miall and Arush, 2001;Catuneanu et al., 2002;Cantalamessa et al., 2005;Breda et al., 2009a;Galloway, 2008;Miall et al., 2008;among others) and carbonate systems (Sarg, 1988;De Zanche et al., 1993;Pasquier and Strasser, 1997;Gianolla and Jacquin, 1998;Pomar and Tropeano, 2001;Mateu-Vicens et al., 2008;among others). However, the sequence stratigraphic interpretation of carbonate systems still has significant limitations, related to the capability of some carbonate platforms to produce sediment in situ, at a rate that is influenced by oceanographic and climatic parameters more than by sea-level change (Schlager, 1991(Schlager, , 1993Schlager et al., 1994;Pomar, 2001a,b). ...
Sedimentary facies analysis aided by quantitative 3D georeferenced field data are applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the Late Triassic of the Dolomites. This multidisciplinary approach was the key to disentangle the timing of climatic change vs. sea-level fluctuation and their effects on shallow water carbonate depositional systems. The “Carnian Pluvial Event”, a global episode of climate change worldwide documented at low latitudes, involved increased rainfall and possibly global warming. This climatic event begins before a drop of sea-level and caused the demise of microbial-dominated high-relief carbonate platforms that dominated the Dolomites region, and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal-oolitic grainstones. A subsequent sealevel fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic-bioclastic grainstones. The crisis of early Carnian shallow water carbonate systems of the Dolomites generated a geological surface similar to a drowning unconformity, although no transgression occurred. As the high-relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic-skeletal-siliciclastic ramps, basins were rapidly filled. The change of carbonate depositional systems was associated with an increase in siliciclastic input, in turn triggered by the onset of a humid climatic event and only later to a sealevel drop. This evolution of carbonate systems cannot be interpreted in the light of sea-level changes only: climate change, and consequent ecological changes in the main carbonate producing biotas, induced significant modifications in depositional geometries. This case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because, despite a drop in shallow water carbonate production, a combination of low subsidence and/or sea level drop maintains the platform top at shallow depth.
... Sequence stratigraphy is a powerful tool to understand the history and the evolution of depositional systems and sedimentary basins (e.g., Vail et al., 1991;Catuneanu, 2006;Catuneanu et al., 2011). It has been successfully applied in a variety of geodynamic settings to both siliciclastic (Galloway and Williams, 1991;Helland-Hansen, 1992;Mellere and Steel, 1995;Miall and Arush, 2001;Catuneanu et al., 2002;Cantalamessa et al., 2005;Breda et al., 2009a;Galloway, 2008;Miall et al., 2008;among others) and carbonate systems (Sarg, 1988;De Zanche et al., 1993;Pasquier and Strasser, 1997;Gianolla and Jacquin, 1998;Pomar and Tropeano, 2001;Mateu-Vicens et al., 2008;among others). However, the sequence stratigraphic interpretation of carbonate systems still has significant limitations, related to the capability of some carbonate platforms to produce sediment in situ, at a rate that is influenced by oceanographic and climatic parameters more than by sea-level change (Schlager, 1991(Schlager, , 1993Schlager et al., 1994;Pomar, 2001a,b). ...
Sedimentary facies analysis aided by quantitative 3D georeferenced field data are applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the Late Triassic of the Dolomites. This multidisciplinary approach was the key to disentangle the timing of climatic change vs. sea-level fluctuation and their effects on shallow water carbonate depositional systems. The “Carnian Pluvial Event”, a global episode of climate change worldwide documented at low latitudes, involved increased rainfall and possibly global warming. This climatic event begins before a drop of sea-level and caused the demise of microbial-dominated high-relief carbonate platforms that dominated the Dolomites region, and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal-oolitic grainstones. A subsequent sea-level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic-bioclastic grainstones. The crisis of early Carnian shallow water carbonate systems of the Dolomites generated a geological surface similar to a drowning unconformity, although no transgression occurred. As the high-relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic-skeletal-siliciclastic ramps, basins were rapidly filled. The change of carbonate depositional systems was associated with an increase in siliciclastic input, in turn triggered by the onset of a humid climatic event and only later to a sea-level drop. This evolution of carbonate systems cannot be interpreted in the light of sea-level changes only: climate change, and consequent ecological changes in the main carbonate producing biotas, induced significant modifications in depositional geometries. This case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because, despite a drop in shallow water carbonate production, a combination of low subsidence and/or sea level drop maintains the platform top at shallow depth.
... The temporal variation of the bayhead shoreline system from deltaic to non-deltaic (Fig. 11) most probably reflects regional climatic fluctuations and related major changes in the intensity of fluvial sediment supply. The changes from predominating shoal-water deltas to occasional Gilbert-type deltas in the valley-fill succession reflect the bathymetric magnitude of marine-flooding events (see Breda et al., 2009;Gobo et al., 2013). ...
... By contrast, upstream and fluvial-dominated valley reaches have received far less attention (Gibling et al., 2011). Most downstream valley reaches are arguably cut and filled in response to sea-level changes (Allen & Posamentier, 1993;Dalrymple et al., 1994;Li et al., 2006;Simms et al., 2006;Breda et al., 2009), with inland expressions of such control extending tens to a few hundred kilometres upstream (Blum & T€ ornqvist, 2000;Gibling et al., 2011). The great majority of upstream valley reaches experience sedimentation solely characterized by fluvial deposition Zaitlin et al., 1994;Vincent, 2001) which, in most cases, is not influenced by relative sea-level oscillation (Currie, 1997;Legarreta & Uliana, 1998;Martinsen et al., 1999). ...
Sedimentation in the upstream reaches of incised valleys is predominantly of alluvial origin and, in most cases, independent from relative sea-level or lake-level oscillations. Preserved facies distributions record the depositional response to a combination of allogenic factors, including tectonics, climate and landscape evolution. Tectonics drives fluvial aggradation and degradation through local changes in gradient, both longitudinal and transverse to the valley slope. This article deals with a Pliocene – Pleistocene fluvial valley fill developed in the north-eastern shoulder of the Siena Basin (Northern Apennines, Italy). Evolution of the valley was not influenced by sea-level or lake-level changes and valley morphological and depositional evolution resulted from extensional tectonics that gave rise to normal and oblique-slip faults orthogonal and parallel to the valley axis. Data from both field observations and geophysical study are interpreted to develop a comprehensive tectono-sedimentary model of coeval longitudinal and lateral tilting of the developing alluvial plain.Longitudinal tilting was generated by a transverse, upstream-dipping normal fault that controlled the aggradation of fining-upward strata-sets. Upstream of the fault zone, valley back-filling generated an architecture similar to that of classic, sea-level-controlled, coastal incised valleys. Downstream of the fault zone, valley down-filling was related to an overwhelming sediment supply sourced and routed from the active fault zone itself. Lateral tilting was promoted by the activity of a fault oriented parallel to the valley axis, as well as by different offsets along near orthogonal faults. As a result, the valley trunk system experienced complex lateral shifts, which were governed by interacting fault-generated subsidence and by the topographic confinement of progradational, flank-sourced alluvial fans.This article is protected by copyright. All rights reserved.
The Permian strata in southern Zhongguai Rise are famous for their abundant petroleum reservoirs. The depositional evolution of the Upper Urho Formation has been studied analyzing the interactions between the sedimentary environments and the diagenetic evolution based on the comprehensive analysis of geological and geophysical datasets. The obtained results have shown that fan delta deposits, overlain by lacustrine deposits, were deposited. Proceeding upwards, the fan delta succession is characterized by retrogradational patterns, including both sandstone facies and conglomeratic facies. These facies have shown different clay mineralogic composition, porosity and physical properties. The sandstone facies shows well-sorted and well-rounded sedimentological textures, with good physical properties. In contrast, the conglomeratic facies shows poorly-sorted and poorly-rounded sedimentological textures, with poor physical properties. All these characteristics leading to reservoir heterogeneity result from sedimentary facies and diagenesis.
Palaeoenvironmental data are fundamental in determining the manifold impacts of climate change. This paper argues that sessile barnacles are an excellent palaeoenvironmental proxy: they are present in nearly all nearshore environments, and their shell consists of diagenetically stable low-magnesium calcite and grows fast enough to record short-term variations. To demonstrate their utility, specimens from several Western Mediterranean Pliocene-Pleistocene barnacle-rich deposits are analysed herein, using for the first time a combination of sedimentology, taphonomy, stable isotope geochemistry and detailed comparisons with modern counterparts. Within shelf carbonate systems, barnacle diversity is highest in the shallow, nearshore waters and decreases moving offshore, thus providing a good proxy for the reconstruction of water depth and distance from the coastline. Barnacle taphonomy is also informative. Well-preserved complete specimens are characteristic of protected areas, whereas less well-preserved specimens occur in high-energy areas. The presence/absence of opercular plates is also particularly relevant for evaluating hydrodynamic conditions. As regards the C and O stable isotope ratios, due to the porous and coarse-grained nature of the deposits in which barnacle remains are usually found, the shells are often exposed to meteoric water percolation during diagenesis. Among the analysed specimens, only those collected from fine-grained deposits displayed no evidence of alteration and had isotopic ratios in line with those of their modern counterparts. These fossils display intra shell variations that in modern barnacles have been related to short-term environmental changes (e.g., seasonal cycles). These results demonstrate that barnacles can always be useful for detailed paleoenvironmental reconstructions based on skeletal assemblages. Furthermore, with further research aimed at gathering more data and assessing potentially interfering signals, they could become useful proxies for paleoseasonality.
We report the first description of a ~ 15 km long NE-SW-striking transtensive fault network crosscutting the metamorphic units of the Ligurian Alps. The main fault zone, hereby named Horse Head Fault Zone, is up to 250 m thick, involves quarzite, metarhyolite, marble and alternation of dolostone and limestone and minor pelite. Relatively narrow (~ 1–3 m-thick) fault cores are characterized by gouge and cataclasites, surrounded by brecciated damage zones as thick as tens to hundreds of meters. Damage zones show widespread evidence for dilation in the form of dilation breccia, large calcite crystals and aggregates, and centimeter- to meter-thick veins. Moreover, the fault zone contains a multitude of polished slip surfaces with multiple sets of slickensides and slickenfibers. Oblique to strike-slip kinematics dominates over the large part of the fault mirrors and both overprint and are overprinted by down-dip slip surfaces. The fault network includes dominant NE-SW right-lateral faults with a minor normal component and NW–SE left-lateral steep faults with a negligible reverse component, consistent with a km-size dextral NE-SW-striking Riedel shear zone, in turn representing an antithetic R’ of the regional sinistral shear zone constituted by the Ligurian Alps after the nappe stacking. The Horse Head Fault Zone accommodated km-scale displacement before the Early Miocene, as it is sealed by the sedimentary deposits of the Finale Ligure Basin, thus predating the Corsica-Sardinia drifting. Results of this work constraint the bending of the Ligurian Alps as part of the Western Alpine arc as accomplished through two consecutive, late Oligocene and Early Miocene, stages driven by the combination of Adria rotation and the rollback of the Apennine subduction.
La Crisi di Salinità del Messiniano dal suo “esordio” nella letteratura geologica a inizio Anni ‘60 e ancora oggi costituisce uno degli “enigmi” geosedimentari e geopaleontologici più sugge-stivi e avvincenti per i numerosi indizi che ci “parlano” della scomparsa di un intero bacino di acque marine, il Mar Mediterraneo, per coinci-denze di processi geodinamici e fattori climatici. Studi geologici, sedimentologici, oceanografici e paleontologici hanno dato inizio ad un lungo dibattito allora e tuttora molto acceso su cause, tempi e scenari paleoambientali dell’Evento Messiniano. Il libro in tre volumi “La Crisi di Salinità del Messiniano - Il Mistero del Mare Scomparso”, pubblicato online nel 2018 all’indirizzo http://danilobonanni.weebly.com/il-mistero-del-mare-scomparso.html, costituisce il mio personale contributo alla divulgazione di questo straordinario evento geologico. Ne “Il Mistero del Mare Scomparso” la Crisi di Salinità del Messiniano viene “raccontata” nei suoi molteplici aspetti geologici e paleontologici, con notazioni, osservazioni, inferenze e deduzioni logico-scientifiche mie personali relative a cronostrati-grafia, correlazioni stratigrafiche e ricostruzione paleoambientale in una sintesi multidisciplinare dei numerosi studi sul tema.
Dalla pubblicazione online de “Il Mistero del Mare Scomparso” nuovi studi geologici hanno di recente apportato contributi di conoscenza al tema “Crisi di Salinità del Messiniano”, alcuni proponendo un aggiornamento del modello cronostratigrafico dell’evento con propensione verso lo scenario “bacino profondo disseccato”. L’aspetto maggiormente interessante come ricercatore scientifico libero è che nelle risultanze di questi recenti studi le mie osservazioni contenute nei tre volumi “Il Mistero del Mare Scomparso” hanno trovato pieno riscontro e validazione, motivo per me di soddisfazione e ulteriore stimolo a portare avanti studi e ricerche su questo affascinante evento nella Storia Naturale della Regione Mediterranea.
The deposits of transgressive and highstand systems tracts have the highest preservation potential in incised valleys, which suffer little erosion from storms and are virtually free of sediment removal by alongshore drift. Incised valley-fill successions, therefore, provide a valuable record of the relative rates of base-level rise (accommodation-space creation) and terrestrial sediment supply (accommodation-space infilling). In terms of these two parameters, four scenarios for an incised valley-fill are suggested by previous studies (Fig. 1): (A) a rapid sea-level rise combined with relatively low coarse-sediment supply, resulting in a Gilbert-type bayhead delta prograding slowly in a rapidly aggrading and shallowing prodelta environment (e.g., many postglacial fjord-head deltas); (B) a rapid sea-level rise combined with relatively high coarse-sediment supply, resulting in a quickly prograding Gilbert-type delta; (C) a gradual sea-level rise combined with relatively low coarse-sediment supply, resulting in the classical estuary with a bayhead delta, muddy central basin and an outer barrier/tidal-inlet complex; and (D) a gradual sea-level rise combined with relatively high coarse-sediment supply, resulting in a fluvial-dominated valley-fill. Considering the additional controlling role of climate, syndepositional tectonics and marine regime, it is rather obvious that this range of basic scenarios may be far from exhausting the natural spectrum of incised valley-fill cases. It is suggested that, in particular case studies, instead of pigeonholing the case into one of the four categories (Fig. 1A−D)-an attempt should rather be made to distinguish it from these end-members and recognize its own specific formative conditions. A case study from the southern margin of the Corinth Rift, Greece, is presented to show an 'intermediate' type of valley-fill, additionally influenced by syndepositional tectonics (Fig. 1E).
Mut Havzası’nda erken–orta Miyosen yaşlı resifal kireçtaşları geç Serravaliyen–erken Tortoniyen
yaşlı Dağpazarı formasyonunun kazınma vadi dolgusu çökelleri tarafından aşınmalı uyumsuzlukla
üzerlenir. Dağpazarı formasyonu çamurtaşı, silttaşı, kumtaşı ve çakıltaşından oluşur. Formasyon
içinde akarsu, lagün, sığ su deltası, kıyıyüzü, plaj ve set adası fasiyes toplulukları tanımlanmıştır.
Formasyona ait gri renkli çamurtaşlarında saptanan Loxoconcha tumida Brady ve Loxoconcha sp.
gibi ostrakod türleri çökelme ortamına tatlı su girdilerinin bulunduğunu ve tuzluluktaki azalmayı,
Hemicyprideis sp. ise acısu ortam koşullarını yansıtmaktadır. Lagüner çamurtaşları ile ardalanan
kıyıyüzü kumtaşları ve bol Ostrea fosilli plaj çökelleri ise zaman zaman kurulan denizel bağlantıyı
gösterir. Dağpazarı formasyonunun yaşı, formasyonu altta ve üstte sınırlayan denizel çamurtaşı ve
marnlardan elde edilen planktonik foraminifer biyostratigrafi si ile elde edilmiştir. Bu yaş MMi8–
MMi10 planktonik foraminifer zonları içinde yer almakta olup, geç Serravaliyen–erken Tortoniyen
olarak saptanmıştır. Geç Serravaliyen östatik deniz düzeyi düşmesi Mut Havzası’nın sığlaşmasına
resifal kireçtaşlarının havza kenarında yüzeylenmesine neden olmuştur. Böylece Mut formasyonunun
resifal kireçtaşları üzerinde bir akarsu kanalından daha büyük ölçekte kazınma vadileri oluşmuştur.
Bu kazınma vadileri bölgesel ölçekte görülen zorunlu regresyonu ve uyumsuzluğu yansıtmaktadır.
Dağpazarı formasyonuna ait sedimanter fasiyesler bu kazınma vadisi içinde erken Tortoniyen
döneminde gelişen yeni bağıl deniz düzeyi yükselmesine bağlı olarak çökelmiştir.
Mut Havzası’nda erken–orta
Miyosen yaşlı resifal kireçtaşları geç Serravaliyen–erken Tortoniyen yaşlı
Dağpazarı formasyonunun kazınma vadi dolgusu çökelleri tarafından aşınmalı
uyumsuzlukla üzerlenir. Dağpazarı formasyonu çamurtaşı, silttaşı, kumtaşı ve
çakıltaşından oluşur. Formasyon içinde akarsu, lagün, sığ su deltası, kıyıyüzü,
plaj ve set adası fasiyes toplulukları tanımlanmıştır. Formasyona ait gri
renkli çamurtaşlarında saptanan Loxoconcha tumida Brady ve Loxoconcha sp. gibi
ostrakod türleri çökelme ortamına tatlı su girdilerinin bulunduğunu ve
tuzluluktaki azalmayı, Hemicyprideis sp. ise acısu ortam koşullarını
yansıtmaktadır. Lagüner çamurtaşları ile ardalanan kıyıyüzü kumtaşları ve bol Ostrea
fosilli plaj çökelleri ise zaman zaman kurulan denizel bağlantıyı gösterir.
Dağpazarı formasyonunun yaşı, formasyonu altta ve üstte sınırlayan denizel
çamurtaşı ve marnlardan elde edilen planktonik foraminifer biyostratigrafisi
ile elde edilmiştir. Bu yaş MMi8– MMi10 planktonik foraminifer zonları içinde
yer almakta olup, geç Serravaliyen–erken Tortoniyen olarak saptanmıştır. Geç
Serravaliyen östatik deniz düzeyi düşmesi Mut Havzası’nın sığlaşmasına resifal
kireçtaşlarının havza kenarında yüzeylenmesine neden olmuştur. Böylece Mut
formasyonunun resifal kireçtaşları üzerinde bir akarsu kanalından daha büyük
ölçekte kazınma vadileri oluşmuştur. Bu kazınma vadileri bölgesel ölçekte
görülen zorunlu regresyonu ve uyumsuzluğu yansıtmaktadır. Dağpazarı
formasyonuna ait sedimanter fasiyesler bu kazınma vadisi içinde erken Tortoniyen
döneminde gelişen yeni bağıl deniz düzeyi yükselmesine bağlı olarak
çökelmiştir.
Different base level scenarios have been imposed to a sand-gravel laboratory Gilbert delta to gain insight on its dynamics under varying base level. Base level rise results in intensified aggradation over the topset, as well as a decrease in topset slope and topset surface coarsening, the signals of which migrate in an upstream direction. Preferential deposition of coarse sediment in the topset results in a finer load at the topset-foreset break, which creates a fine signature in the foreset deposit. Base level fall has the opposite effects. Entrainment of the topset mobile armor causes a coarsening of the load at the topset-foreset break and so a coarse signature in the foreset deposit. The entrainment of the topset substrate and fine top part of the foreset may follow which causes a fining of the load and a fine signature in the foreset deposit. The fact that the upstream sediment supply requires a certain slope and bed surface texture to be transported downstream under quasi-equilibrium conditions counteracts the effects of base level change. This information travels in the downstream direction. In nature base level change is likely so slow that the upstream sediment load maintains the topset slope and bed surface texture and so keeps the topset in a quasi-equilibrium state. Base level change is therefore not expected to leave a clear signal in a mixed-sediment Gilbert delta other than a change in elevation of the topset-foreset interface.
下切谷的形成是海(湖)平面相对变化的结果，气候和构造运动的变化可以导致海(湖)平面相对变化。下切谷受形成机制和沉积环境特殊性的影响，具有独特的“U”字型或“V”字型几何特征，独特的形态导致其内沉积物在垂直于下切谷的地震剖面中表现为上超充填型和发散充填型反射结构特征，而在平行或近于平行下切谷走向的地震剖面上，谷内沉积主要表现为斜交型前积反射特征。由于影响下切谷形成与充填的因素众多，导致其一直以来没有一个令人满意的充填模式。下切谷作为一种特殊的层序内部组成要素，其侵蚀–充填演化模式对于层序划分、地层对比、恢复陆架区古环境及确定古海平面位置具有重要的意义。此外，下切谷在油气藏形成过程中既是良好的油气运移通道，又是良好的油气储集场所，对油气勘探均具有重要意义。 The formation of incised valley is the result of relative change of sea (lake) level, which can be affected by the change of climate and tectonic movement. The incised valley is influenced by formation mechanism and sedimentary environment particularity, and it is characterized by symmetric or asymmetric “U” or “V”. Unique shape led that the interior sediment filling has a reflection character of onlap and divergent types in seismic section perpendicular to the incised valley. In parallel or nearly parallel to the incised valley, the interior sediment filling mainly reflects oblique type progradation characteristics. Because of many factors influencing the formation and filling of the incised valley, it has been without a satisfactory filling pattern. Incised valley as a special sequence of internal elements, the erosion-filling evolution model is important for sequence stratigraphy division, stratigraphic correlation, restoration for the ancient environment of continental shelf and determination for the ancient sea level position. In addition, the incised valley is an important migration channel and good reservoir of oil and gas in the process of reservoir formation, and it is of great significance for oil exploration.
A numerical model that predicts the stratigraphy of a prograding Gilbert delta is presented. Such a Gilbert delta is formed when a river is flowing into a deep basin and the sediment transported by the river downstream avalanches downa steep slope.These deltas are characterized by thin and relatively low-slope topsets, steep foresets (the prograding slip faces), and thin, fine-grained bottomsets. Bedforms such as dunes, bars and Gilbert deltas prograde through avalanching of sediment down the slip face, in which a vertical sorting pattern develops, with the coarser sediment preferentially deposited at lower elevations. We describe the stratigraphy formed by such a prograding delta in case of a variable base level by coupling the Hirano active layer model for the topset to a lee face-sorting model for the foreset. Numerical simulations are performed at laboratory scale. Base level varies as a cosine function with constant amplitude and variable frequency, so representing cycles of base level. The main result is that low-frequency oscillations of base level are recorded in the stratigraphy of a Gilbert delta, which offers possibilities for future interpretations of base level variations from measured stratigraphy.
The Ombrone palaeovalley was incised during the last glacial sea-level fall and was infilled during the subsequent Late-glacial to Holocene transgression. A detailed sedimentological and stratigraphic study of two cores along the palaeovalley axis led to reconstruction of the post-Last Glacial Maximum valley-fill history. Stratigraphic correlations show remarkable similarity in the Late-glacial to early-Holocene succession, but discrepancy in the Holocene portion of the valley fill. Above the palaeovalley floor, about 60 m below sea-level, Late-glacial sedimentation is recorded by an unusually thick alluvial succession dated back to ca 18 cal kyr bp. The Holocene onset was followed by the retrogradational shift from alluvial to coastal facies. In seaward core OM1, the transition from inner to outer estuarine environments marks the maximum deepening of the system. By comparison, in landward core OM2, the emplacement of estuarine conditions was interrupted by renewed continental sedimentation. Swamp to lacustrine facies, stratigraphically equivalent to the fully estuarine facies of core OM1, represent the proximal expression of the maximum flooding zone. This succession reflects location in a confined segment of the valley, just landward of the confluence with a tributary valley. It is likely that sudden sediment input from the tributary produced a topographic threshold, damming the main valley course and isolating its landward segment from the sea. The seaward portion of the Ombrone palaeovalley presents the typical estuarine backfilling succession of allogenically controlled incised valleys. In contrast, in the landward portion of the system, local dynamics completely overwhelmed the sea-level signal, following marine ingression. This study highlights the complexity of palaeovalley systems, where local morphologies, changes in catchment areas, drainage systems and tributary valleys may produce facies patterns significantly different from the general stratigraphic organization depicted by traditional sequence-stratigraphic models.
Upper Cretaceous deposits included in Río Colorado Subgroup crop out in Neuquén city and surrounding areas. This work shows the results of the sedimentogical and paleoenvironmental analysis of Bajo de la Carpa (Santonian) and Anacleto (Lower Campanian) Formations. The studies allowed defining four conglomeratic lithofacies, nine sandy and two pelitics, which were grouped into nine lithofacies associations, being two of them eolian and the other fluvial. Bajo de la Carpa Formation is represented by an ephemeral fluvial system at its base, and fluvio-eolian interactions deposits on the top. Fluvial deposits belong to channalized flows during maximum discharge events. Then a transverse dune field affected by ephemeral currents that invaded interdune areas, and parabolic dunes, were the result of the remobilization of the underlying system, with periodic flood events by sheet ephemeral flows were also identified. The extension and geometry of the dune fields responded to short term climatic variability, fluvial system interference, water table fluctuations, low supply and/or availability of sediments and tectonic factors. Stabilization surfaces, suggested by truncated paleosoils, and a super bounding surface, have been recognized and both responded to climatic and tectonic factors. At its base, Anacleto Formation is bounded by a flood surface and is made of fluvial deposits of low sinuosity, high energy and quickly aggradation systems, controlled by low accommodation space and strong seasonal climatic conditions. Towards the top an anastomosed fluvial system were identified and reflects climatic variations and an increasing subsidence rate accompanied by a slow rise base level related to Maastrichtian atlantic ingression.
In the Early - Middle Pliocene, a conglomeratic fan-delta (Abrioja Formation) prograded approximately 15 km southeastwards in a confined canyon in the Almeria Basin. The canyon was 2 - 4 km wide and 100 - 200 m deep. It probably originated from rifting of the area between the metamorphic basement blocks of the Sierra de Gador and the Sierra Alhamilla.
The Abrioja fan-delta sequence, which filled the canyon is as follows (from top to bottom): 1) Alluvial fan and coastal plain deposits with paleosols; 2) Sediments of a transition zone (beach, nearshore and delta front); 3) Upper delta slope sediments, with tangential foresets of pebbly sandstones; 4) Lower delta slope sediments, with parallel bedded conglomerates, sandstones and pebbly mudstones; 5) Pro-delta sediments, with heavily bioturbated muds. Detailed study of the subaqueous part of the fan-delta has shown that the gravel and sand were transported mainly by sediment gravity flows. The various facies described from the subaqueous fan-delta reflect different kinds of mass flow behaviour. Slumping in the upper part of the delta slope was probably the main sediment source for the conglomeratic beds of the lower delta slope, which were deposited in troughs downslope from the slump scar. The slump scars have been filled again with sediment from the transition zone. From several conglomerate beds, some important structures have been described: a) Asymmetric conglomerate beds show a type of back-set bedding. These 'backsets' are indicated by either a diffuse, centimetre thin sandy zone or by a preferred pebble alignment. They are interpreted as shear zones due to downslope transmitted compression. The compression is probably due to resedimentation at the
upslope-side of the gravel body, b) The head of a structureless, polymict gravel flow deposit shows straight troughs, of ca. 50 cm in cross-section filled with pebbly sandstone, issuing from this body, c) At the base and on the top of some conglomerate beds, evenly stratified sandstones may have originated from flow surges, rather than from (basal) shearing.
The sediment for the flow surges may have been progressively winnowed by liquefaction and gravity from the margins of a gravel flow, a process which was studied from experiments described here, and has been named gravity-winnowing. Conglomerate beds in the canyon are covered by (pebbly) mudstones which were probably deposited during periods of 'normal' sedimentation conditions.
Numerous single-channel seismic profiles recorded in the northern Ligurian margin allow deposition of a Plio-Quaternary tectonic activity along a steep normal fault system at the foot of the passive margin, associated with local subsidence. Deformation increases towards the east, where the upper margin was uplifted by about 700m during the Quaternary. At depth, earthquakes reveal reverse and transcurrent faulting. To explain these observations, a flexural response of the two converging lithospheres which takes place along an old inherited zone of weakness is invoked. -English summary
Four sediment-rich incised-valley systems in China, which underlie the Luanhe fan delta, the Changjiang delta, the Qiantangjiang estuary, and the Zhujiang delta, are examined based on over 800 drill cores. These four systems are of different shapes and sizes, and are located in different tectonic zones with different tide regimes ranging from microtidal to macrotidal. Because of the abundant fluvial sediment supply and relative dominance of river forcing, sediments in the modern Qiantangjiang and paleo-Changjiang estuaries display a fining-seaward trend. This is different from the classical estuarine facies model of coarse bay-head delta, fine central basin, and coarse bay-mouth deposits. The abundant sediment supply also results in the presence of relatively thick transgressive successions in the overall incised-valley fill. The transgressive succession constitutes more than 50% of the total strata thickness and approximately 60–70% of the total sediment volume within the valley. The river-channel facies in the transgressive succession was formed by retrogressive aggradation during postglacial sea-level rise. Retrogressive aggradation extends far inland beyond the reach of flood-tidal currents, and, therefore, no marine signatures were found at the lower portion of the incised-valley fill. The regressive succession in the incised-valley systems consists of fluvial facies or tidal facies and deltaic facies, and was developed as the estuary filled and evolved into a progradational delta. The tide-dominated facies tends to be developed in the apical areas of funnel-shaped estuaries, such as the modern Qiantangjiang and paleo-Changjiang estuaries.
The Oligo-Miocene extension phase of the Mediterranean basins rifting (30-25 Ma) [Jolivet and Faccenna, 2000] followed by the Ligurian basin oceanic crust formation (21-18 Ma) [Le Pichon et al., 1971 ; Réhault et al., 1984 ; Carminati et al., 1998 ; Gueguen et al., 1998] occurred during the western Alps compression phase. The deformations were characterised during the Miocene by the southwestward structuration of the Castellane Arc [Fallot and Faure-Muret, 1949 ; Laurent et al., 2000] and during the Mio-Pliocene by the southward structuration of the Nice Arc. This latter arc is bounded on its western side by a dextral strike-slip fault and on its southern side by a thrust inducing an uplift of this arc [Ritz, 1991 ; Guglielmi and Dubar, 1993 ; Clauzon et al., 1996 ; Guardia et al., 1996 ; Schroetter, 1998]. Fission tracks thermochronology data [Bigot-Cormier et al., 2000] suggest a general uplift at ∼3.5 Ma of the Argentera massif. Stratigraphical [Irr, 1984 ; Hilgen, 1991 ; Hilgen and Langereis, 1988, 1993] and geomorphological studies [Clauzon et al., 1996 b ; Dubar and Guglielmi, 1997] show evidences for an uplift of the Ligurian coast increasing east of the Var river. The analysis of 70 seismic-reflection profiles allows us to better characterise and quantify the deformation from Antibes to Imperia. We then reconstruct vertical motions in space and time since the Messinian crisis in order to propose a deformation model of the margin related to crustal thickening. Morpho-structural and sedimentary characteristics of the margin. - The morphology of the margin results both from the Oligocene rifting and the Messinian crisis (5.8-5.3 Ma) characterised by a sea level fall of ∼1500 m. At the surface, the margin, with a steep mean slope of 6-8° near Antibes [Réhault, 1981] to 12° near Imperia [Savoye and Piper, 1991], is cut by several canyons. At depth, there are two or three tilted blocks covered by Mesozoic sediments and in the Imperia area by the Helminthoïd Flyschs [Sosson et al., 1998]. In the basin, above the Miocene units, we observe some lower evaporites at the bottom, the Messinian salt in the middle and upper evaporites (E) marking the end of the low sea level 5.32 Ma ago [Ryan et al., 1973 ; Mauffret et al., 1973 ; Réhault 1981 ; Savoye and Piper, 1991]. The sedimentary series ends with 1500 m thick of Plio-Quaternary units [Gennesseaux and Le Calvez, 1960 ; Sosson et al., 1998]. At the top of the margin, we observe an erosion surface while toward the basin, two units are evidenced : the Messinian fan (CYL 30-05,) unconformity, covered by a seismic facies similar to the one of the upper evaporites in the basin. The "M" surface, that relates the erosional surface of the margin and the upper evaporites of the basin, has a regular slope toward the basin. We will use this surface as a stratigraphic and structural reference for this work. Acquisition and methodology. - We analysed 12 profiles from the MALIGU cruise (1993-1994) [Chaumillon et al., 1994] and ∼60 from several cruises (1992-2001) with the "Tethys" oceanographic ship to synthesize all stratigraphic and structural observations along the margin. In this paper, we only present 12 of them. We quantify the deformation at the margin/basin limit with a velocity gradient [Le Douaran et al., 1984 ; Rollet, 1999 ; Contrucci et al., 2001] on 50 profiles and we propose a deformation chronology using the "M" surface. Evidence for Pliocene deformation. - Between Antibes and the east of Nice : there is no deformation of the "M" surface. - Between the east of Nice and the west of Menton : we observe a deformation at the top of the margin characterised by tilted seismic reflectors. According to the micro-paleontology study, this deformation is dated at the Lower-Upper Pliocene limit. - From the west of Menton to San Remo : the deformation, observed in the middle of the margin, is characterised by a tilted Messinian fan and the formation of small basins. We note that this deformation increases when the margin strikes ENE-WSW. - From San Remo to Imperia : the deformation increases from the middle to the base of the margin. The apparent normal throw estimated at ∼ 500 m near Antibes increases up to more than 2000 m near Imperia since ∼ 5 Ma. This deformation induced (i) the formation of a piggy-back basin located near Imperia, (ii) a decrease of the "M" surface slope with at places a slope inversion compared with the Antibes area. Space and time reconstitution of vertical motions. - In order to better visualise the geometry of the structure of the margin, we drew seismic profiles with no exaggeration. We interpret the observations seen above and the fact that normal faults on the rifted tilted blocks show a slope between 45-30° as the occurrence of a blind thrust. Motion along the thrusting plane induces the rotation of tilted blocks and is responsible for the margin uplift during the Lower-Upper Pliocene limit following a book-shelf mechanism [Mandl, 1987 ; Jackson and McKenzie, 1983]. At the bottom of the margin, we therefore interpret the apparent normal fault as a gravitary sliding which enhances the front of the thrust vanishing in the Messinian salt unit. Discussion. - Comparison between this model and others previously proposed : contrary to the model proposed by Chaumillon et al. [1994], we can explain the uplift of the margin and the presence of the "normal" faults at the limit margin/basin, only with one mechanism of crustal compression. This mechanism clearly comes from onshore and not from offshore as suggested by Béthoux et al. [1992]. The thrust, dipping toward the continent, can be observed on multichanel seismic reflection profiles [Rollet, 1999]. - The compression of the margin since the end of the lower-Pliocene : our results are chronologically and geometrically in agreement with reversal faults dipping toward the continent, observed along Cap Mele at the bottom of the Pliocene units [Réhault, 1981]. Both, the important thickness of the Plio-Quaternary sediments near Imperia, far away from the Var river, and the many salt diapirs in the NE area, are consistent with a thrust motion. - The area Argentera massif-Ligurian margin : according to fission track data [Bigot-Cormier et al., 2000] a major uplift was detected at ∼3.5 Ma. At the same time, the Ligurian margin recorded a compressive phase with a structural geometry consistent with the deformation onshore. The deformation on the thrust front is the most important at the axis of the main structures of the Argentera. This thrust front is located at the base of the margin near Imperia and propagated toward the top close to the western edge of the Nice arc. Our observations suggest that the deformations propagate offshore in relation with the advance of the Alpine front toward the south. Conclusion. - The analysis of 70 seismic reflection profiles based on stratigraphic and structural studies allows us to quantify and date the deformation of the Ligurian margin increasing eastward. This deformation dated at the Lower-Upper Pliocene limit is due to the propagation of a blind thrust front consistent with the basement tectonic deformation of this period reactivating the Oligocene rifting structures.
Bulletin de la Société Géologique de France, v. 175, n. 2, p. 197-211, 2004
Duration and chronologic location of the Messinian salinity crisis are still unknown. Because the
paleontological approach is inadequate, palaeomagnetism has been used on several sections from the
Sorbas (Andalusia) and Caltanissetta (Sicily) basins.The crisis occurred later and was shorter (about
0.4Ma) than considered until now; It entirely belongs to the first reverse Chron (3r) in the Gilbert Epoch
Duration and chronologic location of the Messinian salinity crisis are still unknown. Because the palaeontological approach is inadequate, palaeomagnetism has been used on several sections from the Sorbas (Andalusia) and Caltanissetta (Sicily) basins. The crisis occurred later and was shorter (about 0.4 Ma) than considered until now; it entirely belongs to the first reverse Chron (3r) in the Gilbert Epoch. There is an abridged English version. -English summary
Ichnofacies stand today as one of the more elegant but widely misunderstood concepts in ichnology, especially where paleobathymetry is concerned. Marine ichnofacies are not intended to be paleobathometers, as some workers continue to imply (e.g., Lockley et al., 1987; Ekdale, 1988); rather, they are archetypical facies models based upon recurring ichnocoenoses (Frey and Pemberton, 1984, 1985, 1987). If a particular ichnocoenose tends to occur repeatedly within a given bathymetric setting, so much the better; but water depth per se is rarely, if ever, a governing factor. Ichnocoenoses and ichnofacies, therefore, are best viewed in the context of actual depositional conditions or environmental gradients, wherever they occur (Figure 1).
Crystal field in the Albian Viking Formation represents the fill of a lowstand incised valley at least 55 km long, 7-12 km wide, and up to 32 m deep. The valley trends south-north, with a smaller arm trending east-west; the open sea lay to the north and east. The valley cuts into five regionally extensive sandier-upward successions of open marine bioturbated mudstones and sandstones. There were two separate episodes of valley filling. The base of Valley 1 represents an original fluvially formed sequence boundary completely modified by marine transgression, whereas the base of Valley 2 is a fluvial cut sequence boundary in the south and a marine-modified sequence boundary in the north. The sandbodies within the valley are poorly connected as reservoirs. -from Authors
The deltaic complexes consist of very thick (up to 700 m) foreset packages that pass into bottomset strata, which, in turn, pass into thin-bedded turbidites. The geometric pattern is discussed in terms of accommodation, that is the vertical space made available for the sedimentation. Where there is no accommodation, the topset environment is bypassed and, geometrically, toplap boundaries occur. With increasing accommodation, fluvial topset strata are formed: they pass downdip into the foreset beds. -from Authors
Paleovalley systems preserved in the stratigraphic record provide useful information on the evolution of ancient landscapes. I investigate the controls on erosion of a set of bedrock-confined paleovalleys at the distal margin of the early Tertiary Alpine foreland basin in southeastern France. The paleovalleys are incised into pre-Tertiary subcrop along the basal unconformity of the foreland basin. They have been identified on the basis of: (i) they form incised paleotopographic features that erosionally truncate bedrock; (ii) they comprise a basal erosion surface that is locally characterized by paleosols along valley margins; (iii) valley-fill strata onlap the margins of the paleo-erosional features; (iv) they show abrupt lateral thickness and facies variations. Paleosol remnants and erosional scour indicate subaerial exposure and erosion of the foreland plate bedrock. The paleovalleys are located adjacent to or on the hanging wall of a set of pre-late Eocene reverse faults that bound a major basement massif. Provenance studies indicate that paleovalley-fill conglomerates were locally derived from erosion of paleo-fault scarps. Incision of the paleovalleys is linked to fluvial erosion of bedrock during surface uplift and tilting related to growth of basement-cored fault-propagation anticlines. The pre-Priabonian paleodrainage drained hanging-wall uplands created by uplift of these structures. Catchment basins were small and stream lengths relatively short. Paleovalley incision in response to growth of intraforeland uplifts contrasts with flexural forebulge uplift and eustatic sea-level fall as an explanation for development of paleodrainage at the distal margin of foreland basins.
Reveals two types of shelf-to-shoreface sequences: 1) gradational-based sequences that steadily coarsen upward from thin-bedded, wave-rippled sandstone and mudstone through hummocky cross-stratified (HCS) sandstone and mudstone into mud-free, swaley cross-stratified (SCS) sandstone capped by a root bed, and 2) sharp-based sequences that consist of SCS sandstone which, near the base, may contain large mudstone intraclasts, sharply overlying thin-bedded sandstone and mudstone. -from Author
Data from 11 wells, a dense seismic grid, and the ECORS deep seismic profiles provide a precise picture of the geological history of the Gulf of Lions. Four sequences are identified from the late Oligocene-early Miocene synrift to the Pliocene-Quaternary progradational shelf. The middle Miocene is characterized by a highstand system tract established on a paleoself. These seismic-stratigraphical observations can be placed into their tectonic framework. The Gulf of Lions area first underwent a compressional phase related to the Pyrenean orogeny, then a later extensional phase caused by the opening of the Provencal basin. When suitably oriented, the former thrusts are reactivated as detachment due to subsequent extension. -Authors
Two vertically stacked shelf-ridge (bar) complexes in the Shannon Sandstone member of the Cody Shale crop out in the Salt Creek anticline of the Powder River Basin. The shelf-ridge complexes are composed primarily of moderately to highly glauconitic, fine- to medium-grained lithic sandstone and attain thicknesses of over 70 ft. The complexes were deposited at least 70 miles from shore at middle to inner shelf depths by S to SW-flowing shore-parallel currents intensified periodically and frequently by storms. Ridges in each sequence trend N-S, slightly oblique to current flow. A possible source of sediments was the Eagle Sandstone shoreline and deltaic deposits of S Montana 200 miles to the NW. Eleven facies were defined in outcrop on the basis of physical and biologic sedimentary structures and lithology. Vertical and lateral changes in facies are relatively abrupt where observed in closely spaced outcrop sections, and, in general, facies are stacked in coarsening-upward sequences with Central Bar Facies commonly immediately overlying Interbar Sandstone Facies.-from Authors
Au Sud-Est du massif de l'Argentera-Mercantour qui est le plus méridional des massifs externes des Alpes, se développe un pays de flysch de forme triangulaire. Il sépare le domaine des enveloppes sédimentaires du massif de l'Argentera-Mercantour de celui des massifs ligures. L'étude abordée ici intéresse essentiellement ce pays de flysch. Elle veut en dégager d' une part sa constitution, d'autre part les relations de ses différents termes constitutifs avec le domaine du massif de l'Argentera-Mercantour et de ses enveloppes sédimentaires et avec le domaine des massifs ligures. La région étudiée ne correspond en réalité, ni à une distinction morphologique, ni à une distinction géographique définie. Il s'agit de la partie orientale des Alpes Maritimes françaises correspondant au bassin de la Roya et de la Bevera, et de la partie occidentale des Alpes Maritimes ligures, limitée au Nord et à l'Est par une ligne qui joint Limone Piemonte à Albenga. Le présent travail comporte deux volumes. Un premier volume est consacré aux introductions géographique et bibliographique et à l'étude stratigraphique raisonnée des séries des différentes unités tectoniques (2ème partie)., Dans cette deuxième partie sont envisagées d'abord la stratigraphie du domaine externe. Un second volume comprend trois parties : Une partie est consacrée à la Paléogéographie d'ensemble. On a ainsi envisagé d'une part (chapitre 1) l'évolution paléogéographique de l'ensemble Autochtone-Parautochtone-Subbriançonnais - Briançonnais, d'autre part la paléogéographie de la formation du Flysch à Helminthoides dans le contexte paléogéographique alpino -a penninique ). L'autre partie intéresse ,la tectonique. Le ohapitre l comporte l'étude des dislocations de l'Autochtone; le chapitre II est consacré à celles affectant le Parautochtone; l'étude tectonique de la zone des Klippes est faite au chapitre III; le chapitre IV traite de la tectonique de la nappe du Flysch à Helmintholdes (tectonique intime et tectonique de nappe); le chapitre V envisage la tectonique d'ensemble du domaine étudié et sa position structurale dans l'ensemble des Alpes occidentales. La dernière partie (Vème partie) clôturant le travail correspond aux conclusions générales. On y envisage en fonction des problèmes posés par l'origine interne vraisemblable de la nappe du Flysch à Helminthoides, la question de la liaison Alpes-Apennins.
Rift basins (extensional and transtensional) commonly have an asymmetric, half-graben form that results from the throw on one border fault zone being much greater than on the other basin margin. This structural geometry, the detailed linkages between fault segments and the episodic nature of fault activity have a pronounced effect on coarse-grained delta depositional systems. A clear tectonic control can be observed on the location, form and basin-fill architecture and on the internal geometry of individual coarse-grained delta sequences in both modern and ancient rift basins. Delta location is related to structurally controlled topography and bathymetry; lateral (footwall- and hanging-wall-derived) and axial coarse-grained deltas may develop. However, the lower gradients of the hanging wall, and particularly the axial slopes, tend to promote the development of finer-grained deltaic systems. Transfer zones linking major fault segments act as loci for drainage entering the rift basin and hence are commonly the sites of coarse-grained delta deposits.
Sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level. On the shelf, low-stand deposits, which form during falls and subsequent stillstands of relative sea level, can be recognized by the presence of an unconformity at the base, the isolated and basinward position relative to the previous shoreline, and the abrupt seaward translation of shallow-water and shoreline facies into the basin across an unconformity surface. This seaward translation of facies and shoreline regression in a response to relative sea level lowering is termed a "forced regression'. Certain shelf sands, previously interpreted as offshore or mid-shelf sand bodies, can be reinterpreted as stranded lowstand shorelines associated with forced regressions. This alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries. Examples of forced regression are described. -from Authors
Quantitative analysis of planktonic foraminiferal assemblages from Mediterranean Pliocene sections evidenced several fluctuations in abundance which for four taxonomic units (Globorotalia inflata group, Globigerinoides ruber, Globigerinoides obliquus and Globigerinoides quadrilobatus) occur cyclically. Estimate of cycle periodicity, using paleomagnetically or biochronologically absolute dated calibration points, proves that abundance fluctuations display a periodicity of about 20 kyr in the lower part of the Pliocene and of about 40 kyr in the upper part of the Pliocene, thus correlatable to the precession and obliquity astronomical cycles respectively. Based on the sequence of abundance fluctuations a precise age estimate was obtained for several biostratigraphic events. -from Author
The Western Mediterranean Sea is viewed as a marginal basin, generated by a north-northwest subduction of the Africa-Apulia plates beneath the European plate. Succeeding an Oligocene rifting phase, oceanic accretion occurred between 21 and 18 m.y. (million years) ago along three main spreading axes trending northwest-southwest in the Liguro-Provençal Basin, northwest-southeast in the southern Sardo-Balearic Basin, and east-west in the North Algerian Basin. Such kinematics and chronology are consistent with pa-leomagnetic data supporting the Sardinian rotation, basin and margin structure, subsidence since 21 m.y, (especially during Messinian time), and heat flow measurements.
Extended sedimentary sequences encompassing the Miocene/Pliocene boundary were continuously cored in the Tyrrhenian Sea (Hole 974B) and Balearic Basin (Hole 975B) during Ocean Drilling Program Leg 161, and investigated in terms of foraminifer (planktonic and benthic) high-resolution biostratigraphy. The interval studied includes the earliest part of the Zanclean (Zone MP11) and the Miocene/Pliocene boundary. The lower Zanclean (Sphaeroidinellopsis Acme Zone or MP11) is characterized by pelagic sediments in both holes. Within the lower part of MP11 Zone, cyclically repeated changes in abundance of Globigerinoides population have been recognized at both sites and interpreted as caused by astronomical forcing precession cycles. The calibration of these cycles with bioevents like the acme interval of Sphaeroidinellopsis, two intervals of Neogloboquadrina acostaensis sinistrally coiled, and the first common occurrence (FCO) of Globorotalia margaritae led to the identification of five cycles in Hole 974B and six cycles in Hole 975B. Such data indicate that the Hole 975B sequence is more complete than that recorded in Hole 974B, where the first cycle is missing. The MP11/MP12 boundary, which is based on the FCO of Globorotalia margaritae at 5.07 Ma, represents the top of the sequence investigated. The repopulation of the Mediterranean basin floor by benthic foraminifers is stepwise. The first immigrants were small in size (Eponides pusillus and bolivinids) and were found only in Hole 975B. They were followed by Oridorsalis stellatus, Cassidulina subglobosa, and Uvigerina peregrina, which occur at both sites. Such assemblages suggest water masses partially depleted of oxygen at the very base of the Pliocene sequence.
The stratigraphic profile along a 100 km section of the Lake Calcasieu incised-valley fill was reconstructed from 87 bridge borehole records at four sites along the tidal reaches of the Calcasieu River, an additional 18 boreholes aligned along the chenier plain near the estuary mouth, and shallow seismic data collected along 160 km of track line within the Lake Calcasieu central basin. Valley incision occurred during the δ 18O stage 2 sea-level lowstand, when the paleo-Calcasieu River flowed across the inner continental shelf and incised into older fluvial terraces of the Prairie Formation. The valley floor is 57 m deep beneath the modern chenier plain and rises to -30 m along the upper reaches of the modern estuary. Sea-level rise commenced about 20 ka and has continued episodically throughout the Holocene. Shoreline transgression has proceeded at varying rates in response to sea-level rise, and the incised valley is now occupied by a wave-dominated estuary, fringed by the chenier plain of western Louisiana. Lowstand deposits are poorly preserved within the Calcasieu incised valley. Deposits constituting the transgressive systems tract (TST) lie directly above the lower sequence boundary at the top of the Prairie Formation. The TST shows greatest facies diversity and clearest separation of bounding surfaces toward the present seaward end of Lake Calcasieu. Here, the TST comprises three parasequences that include fluvial, bayhead-delta, and central-basin (estuarine) deposits. Multiple flooding surfaces within the TST relate to the episodic style of sea-level rise. Highstand infilling of the valley has been characterized by near-shore marine deposition and chenier-plain progradation. Along the lower reaches of the modern Calcasieu River, the valley fill comprises transgressive central-basin and landward-stepping bayhead-delta fades, overlain by the highstand bayhead-delta complex. This study documents the most recent phase of deposition within the compound fill of a coastal-plain incised valley and demonstrates the potential importance of fluvial controls on facies within incised-valley systems.