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Late Quaternary depositional architecture of Po and Tevere river deltas (Italy) and worldwide comparison with coeval deltaic successions
No full textPo and Tevere rivers form two of the most important deltas of the whole Mediterranean area. Detailed investigations have been carried out in the last decade beneath the present delta plains of these two river systems using borehole data correlation, With the aid of radiocarbon dates and other dating methods (pollens, archaeology) a detailed sequence stratigraphic framework has been constructed in both areas, especially for the last glacial-interglacial cycle. Regional subsidence, combined with short-term sea-level fluctuations of relatively high amplitude, played a fundamental role in creating/subtracting accommodation during the long phase of falling sea level, which followed the Tyrrhenian (substage 5e) transgressive event. A discontinuous record of this phase is present in the subsurface of the Po Plain, whereas poor or no preservation has been detected in the Tevere area. Progradational lowstand wedges accumulated during the last glacial maximum mostly in the central part of the basins, far from the present deltas, and are lacking in the study areas, where a hiatal surface is invariably recorded below the transgressive deposits. Glacioeustasy exerted a major control on sedimentation in both areas during the latest Pleistocene-Holocene sea-level rise. Infilling of fluvial valleys and rapid landward migration of barrier-lagoon systems, in the context of wave-dominated estuaries, characterized the transgressive phase in both Po and Tevere systems. In-place drowning and transgressive submergence mechanisms of barrier migration were effective predominantly between 13.5 and 9 ka Bp. In contrast, shoreface retreat was dominant in the late transgressive phase. The maximum flooding surface (MFS) can be traced physically from continental to marine deposits, and has similar characteristics in the Po and Tevere river systems, being marked by peat layers or lagoonal deposits at landward locations and by distinctive lithological characteristics and micro- and macrofossils. assemblages basinwards. Above the MFS, the early highstand systems tract records initially the filling of the lagoons, followed by the rapid progradation of wave-dominate delta systems and flanking strandplains. Autocyclic processes, such as distributary channel avulsion, delta lobe abandonment, and local subsidence due to sediment compaction were the fundamental controlling factors on sedimentation during deposition of the HST. The stratigraphic architecture of the post-glacial Po and Tevere delta complexes closely resembles the basic facies successions documented from coeval deposits of wave-dominated and wave-influenced clastic coasts, both locally within the Mediterranean area and in other parts of the world. Our study emphasizes, however, some additional features and major differences with previously published depositional models, including (i) the development of backstepping wave-dominated estuaries during transgression; (ii) consistent changes through time in the mechanism of barrier migration; (iii) a later construction of the delta systems, with respect to what traditionally considered. (C) 2001 Elsevier Science B.V. All rights reserved
Organizzazione e guida scientifica dell'escursione LATE QUATERNARY DEPOSITIONAL EVOLUTION OF THE PO DELTA AND VENICE LAGOON AREAS, Field Trip N. 8 dell'International Association of Sedimentologist Congress, Alghero 2009.
No full textStratigraphy, sedimentology, and geomorphology of Holocene sedimentary bodies in the high sediment-input Po Delta area and in the sediment starved Venice Lagoon region. The impact of the eustatic and climatic fluctuations on the depositional history will be addressed and the implications of the stratigraphic knowledge for the environmental management of these fragile coastal areas discussed. The dynamic interaction of the depositional processes with the urban growth of the historic towns of Venice and Ferrara are also examined
Benthic foraminifera as a key to delta evolution: A case study from the late Holocene succession of the Po River Delta
No full textABSTRACT: Benthic foraminifera from stratigraphically expanded, late Quaternary prodelta successions of the Po Delta plain reveal small-scale paleoenvironmental variations within lithologically homogeneous deposits formed under conditions of rapid sedimentation (ca. 6 cm/yr). A detailed paleoenvironmental reconstruction was obtained comparing benthic foraminifera with shallow-water assemblages from the modern Po Delta. The integration with sediment geochemistry and radiocarbon dates was also tested to detect short time-scale delta dynamics controlled by autogenic factors. Core 7 records the development of an inner-shelf environment (interval A), replaced by a prodelta with strong fluvial influence, shown by the sharp increase in Ammonia tepida and Ammonia parkinsoniana (interval B). These taxa are replaced by Aubignyna perlucida (interval C) which indicates a major mouth shift (Ficarolo avulsion). Subsequent abrupt increases in A. tepida and A. parkinsoniana document a step-like progradation of the Po di Goro delta lobe (intervals D and E). In the seaward Core 1, possible minor mouth shifts are recorded by a sharp increase in A. tepida and A. parkinsoniana, paralleled by Cr/Al2O3 depletion. The upper portion of both prodelta successions includes stacked flood layers formed near the river mouth, as indicated by scarce A. tepida and A. parkinsoniana
Timing and mechanisms of sediment accumulation and pedogenesis: Insights from the Po Plain (northern Italy)
Full text linkThe relationships between pedogenetic processes and fluvial-coastal dynamics in the Po Plain have been reconstructed through sedimentological analysis and correlation of ca. 170 core data chronologically constrained by 376 radiocarbon dates. Vertically stacked, weakly developed paleosols within Upper Pleistocene and Holocene mud-prone strata testify to intermittent pedogenesis, periodically interrupted by overbank sedimentation. Individual paleosols are laterally traceable for tens of km and exhibit A-Bk-Bw, A-Bk or A-Bw profiles. Strati graphically ordered 14C calibrated ages from A organo-mineral horizons testify to slow aggradation during 4-6 thousand years-long exposure periods. Burial ages, with an error of few centuries, are provided by plant debris at the top of A horizons.Millennial-scale climate oscillations and glacio-eustasy are the main drivers of the pedo-sedimentary evolution of the area during the last 50 kyr. Upper Pleistocene paleosols (P1-P3) developed in well-drained floodplain environments, during relatively warm periods.Paleosol burial occurred during colder phases. High-sediment supply during the Last Glacial Maximum hindered pedogenesis and led to the accumulation of 3-10 m-thick overbank strata. Widespread soil development (paleosol PH) occurred at the end of Last Glacial Maximum, following the retreat of Alpine glaciers and the afforestation of Apennine drainage basins. At distal locations, paleosol PH was progressively buried under estuarine sediments during the Holocene phases of post-glacial sea level rise. Beyond the area of marine influence, burial ages of paleosol PH change from a place to another without specific spatial trends and reflect upstream fluvial sedimentation dominated by avulsions and deposition of spatially restricted alluvial units. Holocene (H1-H2) paleosols show a poor correlation potential and laterally variable degree of maturity that reflect avulsive sedimentation patterns and crevassing. This paper provides insights on the timing and mechanisms of formation and burial of weakly-developed paleosols. The outcomes of this research are applicable to similar Quaternary alluvial systems, and may help interpreting ancient paleosolbearing successions
Ostracod response to delta dynamics: an example from a Holocene succession of the Po Delta
Full text linkThe detailed stratigraphic frame of the late Quaternary Po Delta deposits represents an ideal setting
to test the response of microfossil assemblages to short-time phases of delta evolution, strictly
constrained in time and space. Benthic foraminiferal studies within the Po Delta subsurface
succession have been extensively performed in the last years, whereas less attention has been paid to
ostracods.
Holocene benthic foraminiferal and ostracod assemblages were determined in the 21m-thick shallow-marine
deposits of core EM13. According to radiocarbon dates, the lower part of this fine-grained
succession was formed during the last stages of transgression and the following high-stand phase,
when a series of cuspate deltas developed in the study area. In contrast, the upper interval accumulated
after the Ficarolo avulsion (mid XII Century AD), which determined the rapid outbuilding of the
supply-dominated Po Delta. Here we test the ostracod ability to detect these evolutionary phases,
possibly recorded as palaeoenvironmental changes.
High concentration of valves and high species richness are recorded in the lowermost part of the
succession, where ostracod assemblages include abundant Semicytherura spp. and Loxoconcha spp,
indicative of a shallow-marine environment with low fluvial influence. The overlying sediments
include scarce ostracods mainly represented by Pontocythere turbida, with lower frequencies of
Palmoconcha turbida. Such low-diversity assemblage, dominated by opportunistic species, shows
the transition to more stressed environmental conditions, in accordance with a prodelta environment.
Species turnover is also recorded in the uppermost part of the succession, where Leptocythere ramosa
becomes strongly dominant. Its tolerance to salinity variations and organic matter input indicates a
very shallow and proximal prodelta with high fluvial influence. Scattered, mainly juvenile, valves of
Cyprideis torosa are encountered through the entire sediment succession and suggest transport from
coastal brackish-water environments due to the fluvial input.
The superposition of these ostracod assemblages reflects small-scale palaeoenvironmental variations
within a shallow prodelta environment, related to different phases of activity of the Po Delta. The
comparison with foraminiferal assemblages reinforces the palaeoenvironmental interpretation and
documents the combined analysis of benthic foraminifers and ostracods as a high-resolution proxy to
reconstruct delta dynamics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Benthic foraminifera and ostracoda as palaeoecological proxies from modern to fossil river-influenced shelves: the case of the North Adriatic area
No full textThe North Adriatic area represents an excellent location for the study of present-day and fossil meiofauna, since wide, detailed databases of benthic foraminifera and ostracoda are available for the modern North Adriatic Sea as well as for the nearby late Quaternary succession of the Po coastal plain. In this setting, benthic foraminifera and ostracoda were applied as facies indicators in a sequence stratigraphic perspective during the last years. However, such palaeoenvironmental reconstructions did not meet the requirements of modern palaeoecology, which aims to discriminate with quantitative methods significant abiotic factors influencing the faunal assemblages in order to quantify palaeoenvironmental changes through time. To improve the palaeoenvironmental resolution within the Holocene shallow-marine deposits of the Po coastal plain, the first step was the analysis of the most reliable modern analog: the North Adriatic shelf. We separately analyzed published databases on modern benthic foraminifera and ostracoda, focusing on the shallow (i.e. <40 m water depth) North Adriatic Sea, with the aim to find independent connections between single faunal groups and controlling factors. Through a set of multivariate statistical analyses, we identified five benthic foraminiferal biofacies mainly controlled by organic matter concentration and seven ostracod biofacies driven by grain-size (sand concentration) and bathymetry. The integration of benthic foraminiferal and ostracod biofacies allowed the distinction of five depositional environments on the modern North Adriatic shelf, determined by the relative position with respect to the Po Delta outlets. More specifically, the distribution of depositional environments from coastal to offshore locations reflects three macro-areas subject to low, moderate and high riverine inputs. In order to test the palaeoenvironmental resolution of benthic foraminifera and ostracoda, the 21 m-thick shallowmarine, fine-grained succession of core EM13 was quantitatively analyzed and its fossil content compared to the modern North Adriatic fauna by means of statistical techniques. The good chronological constraints available for the evolution of the Po Delta represent a solid framework to test the meiofaunal response to coastal and deltaic dynamics. Benthic foraminifera from the study succession clearly marks the transition from open marine to prodelta conditions linked to the coastal progradation after the last maximum marine transgression (ca. 7000 yr BP). This faunal group also highlights cycles of organic matter fluxes within prodelta sediments, chronologically in accordance with the main phases of Po Delta progradation. On the other hand, ostracoda indicate three phases of progressive increase of sediment supply: the first when the drainage system was stable until the demise of the Roman Empire (ca. 1500 yr BP), the second during the progradation of the Ariano and Volano mouths (ca. 1500-800 yr BP) and the last one after the Ficarolo avulsion (798 yr BP), when the Po Delta started to prograde very rapidly in its present-day position. This study case indicates that benthic foraminifera and ostracoda represent excellent and complementary palaeoecological indicators on river-influenced shelf settings. Nevertheless, an accurate interpretation of shallow-marine successions can be obtained exclusively through their integration
The palaeoecological record of delta dynamics: testing the faunal response of benthic foraminifers and ostracods
No full textThe mid-late Holocene subsurface succession of the Po River plain records complex delta outbuilding under a predominantly autogenic control during the sea-level high stand phase. Chronologically constrained phases of the Po Delta evolution represent a solid base to test the response of microfossils to short time-scale delta dynamics. Benthic foraminifers and ostracods from the 21m-thick shallow-marine succession of core EM13 were quantitatively analysed and statistically compared to modern North Adriatic meiofaunal assemblages, in order to assess the main palaeoecological factors that controlled the composition of assemblages, and compare the palaeoenvironmental resolution provided by these two benthic groups.
Benthic foraminifers from the lowermost shallow-marine succession indicate the transition from inner shelf to coastal conditions, marked by the gradual increase in Ammonia tepida and Ammonia parkinsoniana. Ostracods from the same stratigraphic interval are comparable to those nowadays recorded in shallow-marine settings affected by relatively low river flows. Chronologically in accordance with the development of cuspate deltas during the Roman Age, benthic foraminifers record the approach to coastal environments, subject to low fluvial inputs as evidenced by ostracods. The overlying deposits with high frequencies (ca. 50%) of A. tepida and A. parkinsoniana suggest the transition to a proximal prodelta, as confirmed by the similarity with modern assemblages at shallow depths, few km far from the river mouths. Upwards, the overwhelming dominance of the same taxa is indicative of extreme vicinity to river mouths. Within the same stratigraphic portion, ostracods indicate conditions similar to those nowadays present along the mid-Adriatic Italian coast, where the dominant action of longshore current distributes river-supplied material enriched in organic matter. Following one of the main avulsion events in the Po Delta history (XII century), the transition from wave- to fluvially dominated deltaic systems is marked by a great change in ostracod assemblages. Therefore, distinct palaeoecological information are provided by each fossil group: benthic foraminifers give indications about the distance from river mouths, whereas the dominant depositional regime is suggested by ostracods. Benthic foraminifers and ostracods are excellent palaeoenvironmental indicators in river-influenced shelves, but refined sub-environmental characterization can be achieved with their combined application only
Late Quaternary incision and deposition in an active volcanic setting: The Volturno valley fill, southern Italy
No full textExtensive illustration of depositional facies, ostracod and foraminiferal assemblages, and Late Quaternary stratigraphic architecture is offered for the first time from beneath the modern coastal plain of Volturno River, the longest river in southern Italy. Proximity to an active volcanic district, including quiescent Vesuvius Volcano, provides an easily identifiable stratigraphic marker (Campania Grey Tuff or CGT), up to 55 m thick, emplaced 39 ky cal BP by a large-volumeexplosive pyroclastic eruption. Identification of top CGT to amaximum depth of 30 mallows tracing out the shape of a 15–20 kmwide Late Quaternary palaeovalley incised by Volturno River into the thick ignimbritic unit immediately after its deposition. A terraced palaeotopography of the valley flanks is reconstructed on the basis of core data. Above the basal fluvial deposits, the early Holocene transgressive facies consist of a suite of estuarine (freshwater to brackish) deposits. These are separated from overlying transgressive barrier sands by a distinctive wave ravinement surface. Upwards, a distinctive shallowing- upward succession of middle–late Holocene age is interpreted to reflect initiation and subsequent progradation of a wave-dominated delta system, with flanking strandplains, in response to reduced rate of sea-level rise. The turnaround from transgressive to highstand conditions is identified on the basis of subtle changes in the meiofauna. These enable tracking of themaximumflooding surface into its updip (lagoonal/estuarine) counterpart,thus highlighting the role of refined palaeontological criteria as a powerful tool for high-resolution sequence-
stratigraphic studies
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