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Late-glacial to Holocene depositional architecture of the Ombrone palaeovalley system (Southern Tuscany, Italy): sea-level, climate and local factors control in valley-fill variability
Abstract
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.
... As a result, a series of transgression-regression sedimentary strata have developed (Peeters et al., 2019;Mestdagh et al., 2019;McHugh et al., 2018;Bentley et al., 2016;Liu et al., 2016a;Alqahtani et al., 2015). Paleochannels are important products of this process (Wang et al., 2020a;Liu et al., 2019a;Zhang et al., 2018;Amorosi et al., 2016;Breda et al., 2016;Blum et al., 2013). These paleochannels vividly record the development of sedimentary strata and contain rich information on environmental evolution. ...
The East China Sea (ECS) is characterized by a wide shelf. Since the late Pleistocene, a large number of paleochannel systems have developed, and these systems contain rich information on sedimentary evolution and record the changes in the ECS. In this study, we systematically identified the spatial distribution and filling characteristics of the paleochannels in the two stages since Marine Isotope Stage 5 (MIS 5) and investigated the mechanisms by which sea level change responds to paleochannel development and evolution by using sedimentological, geophysical, and chronostratigraphic methods based on high-precision measurements of shallow seismic profiles and borehole data. The results indicate that (1) two stages of paleochannels, named SU2 and SU4 from top to bottom, were formed in the study area in Marine Isotope Stage 2 (MIS 2) and Marine Isotope Stage 4 (MIS 4), respectively. (2) A comparison of the two paleochannel stages reveals that the main stream of SU2 extends longer, whereas that of SU4 is shorter. (3) The paleotopography shows a trend of gradually sloping from the northwestern land area to the southeastern sea area. These results suggest the following: (1) The sea level fluctuation since the late Pleistocene was the key factor controlling the development of the paleochannel systems. Understanding this influence can guide the prediction of stratigraphic distribution. (2) The rise and fall of sea level directly affects the advance and retreat of coastlines and estuaries, which in turn controls the extension of paleochannels. From this information, the migration range of the coastline can be identified. (3) The SU2 paleochannel may have originated from the Minjiang River, flowed eastward, and merged into the southern tributary of the ancient Yangtze River in the eastern portion of the study area. This study can provide a scientific basis for the southern flow of the MIS 2 ancient Yangtze River system.
... Several worldwide records show evidence of rapid transgression around 11Á5 cal kyr BP (Maddox et al., 2008;Delgado et al., 2012;Milli et al., 2013), 9Á5 to 9Á2 cal kyr BP (Hori et al., 2002;Zong et al., 2009;Amorosi et al., 2013;Tanabe et al., 2015), 8Á5 to 8Á3 cal kyr BP (Yim et al., 2006;Troiani et al., 2011;Amorosi et al., 2013;Boski et al., 2015) and 8Á0 to 7Á3 cal kyr BP (Heap & Nichol, 1997;Li et al., 2002;Abrahim et al., 2008;Trog et al., 2013;Breda et al., 2016), thus supporting the hypothesis of a dominant control of eustasy on parasequence architecture. ...
To understand the complex stratigraphic response of a coastal depositional system to rapid eustatic rise and sediment inputs, the evolution of the Adriatic coastline and Po River system, during the post-glacial (Holocene) transgression, was investigated. The landward migration and evolution of a wave-dominated estuary was mapped, based on an extensive dataset comprising 14 boreholes, 28 core descriptions and 308 piezocone tests, chronologically constrained between 11.5 and 7.0 kyr BP by 137 radiocarbon dates. Palaeogeographic maps reveal temporal differences in retrogradational geometries and mechanisms that likely underpin shoreline retreat. The Po estuary initially developed within a shallowly incised valley, and then spread onto the interfluves. Between 11.5 and 9.2 kyr BP the Po fluvial system became avulsive/distributive and wetlands developed in topographically depressed areas. The shoreline retreated at a mean rate of ca 10 m/yr, between 9.2 kyr and 7.7 kyr BP, following a stepped trajectory at the centennial scale. After 7.7 kyr BP, bayhead deltas started to prograde and partially filled the estuary. The overall stratigraphic architecture is interpreted to reflect the sedimentary response of the coastal depositional system to the main pulses of early Holocene eustatic rise. The influence of antecedent topography, partly due to local subsidence, was dominant at the time of initial transgression. Basin morphology influenced sediment dispersal and partitioning. Sediment supplied by the Po River was trapped within the estuary, whereas coastal sand bodies at the estuary mouth were fed by alongshore currents and by reworking of older barriers. High-resolution age control that ties facies evolution to independently constrained eustasy provides direct data to test models of short-term coastal retreat under conditions of relative sea-level rise, and makes this case study a useful analogue for the interpretation of ancient marginal-marine, retrogradational systems where only stratal geometries are available.
... The age distribution between 8.0 and 7.5 cal ky BP of the maximum flooding surfaces identified in four Italian coastal plains facing both the Tyrrhenian Sea and the Adriatic Sea (Amorosi et al., 2012; 2013b; 2016; Breda et al., 2016), are in agreement with the age of parasequence 3 (Fig. 6). The complete melting of the former ice caps, around 8.0–7.5 cal ky BP (Pirazzoli, 2005), drove maximum marine ingression and sea level around its present position (mwp-1d – Fig. 6). ...
Holocene deposits exhibit distinct, predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record. In this study, we examined the sedimentary response of the Po Plain coastal system to short-term (millennial-scale) relative fluctuations of sea level through high-resolution sequence-stratigraphic analysis of the Holocene succession.
... As widely documented by both outcrop and subsurface data, the late Quaternary stratigraphy of several coastal and deltaic areas was mainly controlled by the interplay between glacio-eustatic and tectonic tures (Mazzini et al., 1999; Amorosi et al., 2008a Amorosi et al., ,b, 2009 Carboni et al., 2010; Milli et al.,2013; Breda et al., in press). According to the available literature (Ludwigh et al., 1996; Waelbroech et al., 2002; Siddal et al., 2003; Ferranti et al., 2006 ) during the MIS3, the age attributed by several authors to the formation of ICS reliefs (Federici & Mazzanti, 1995; Mazzanti, 2000), the sea level was ca. ...
The Upper Pleistocene “Isola di Coltano Sands” (Arno coastal plain, Tuscany Italy): review of stratigraphic data and tectonic implications for the southern margin of the Viareggio basin. We present and discuss previously published stratigraphic and chronological (mainly archaeological remains) data about the “Isola di Coltano Sands”(ICS), with the support of unpublished core stratigraphies and taking into account the geological frame of the Arno coastal plain.
ICS outcrops in the southern portion of the extensional Viareggio Basin, forming three isolated small-sized reliefs rising up to 15 m above the present-day Arno coastal plain on both sides of the Arno River.
We document that the deposits outcropping north of the Arno River (Palazzetto site) reasonably belong to the Holocene prograding beach-ridge system to which they are physically juxtaposed. Indeed, both sedimentological and morphological characteristics indicate that the Palazzetto sands were exclusively formed by wind-related processes, likely occurred during the late Holocene according to the presence of Eneolithic artefacts.
Conversely, the common presence of Mousterian artefacts at the Castagnolo and Coltano sites, located south of the Arno River, documents an age older than 40 kyr (upper Pleistocene) for these reliefs. Moreover, new stratigraphic data show that ICS are constituted by alluvial deposits with evidences of repetitive fluvial erosion episodes. All these features, indicate that ICS can be reasonably included into the Late Pleistocene Vicarello Formation, widely outcropping along the southern margin of the Leghorn Hills. In this context, an estimated age ranging between MIS 6 and MIS 3 can be hypothesized for the ICS.
However, the occurrence of Upper Pleistocene reliefs formed by alluvial deposits (Coltano and Castagnolo sites) in the southern portion of the Arno coastal plain seems to conflict with the acknowledged interpretation of the area as an extensional, subsiding setting. Moreover, the sharp morphological boundary dividing the flat Holocene coastal plain from the Quaternary Leghorn Hills is roughly coincident with the SW-NE transpressive fault (Sillaro line) that subdivides the subsiding area (Viareggio Basin, to which the Arno plain belongs) from the uplifting area (Leghorn mounts).
Thus, our review of the available stratigraphic and chronological data strongly suggests the occurrence of a geological connection between the southern portion of the Arno coastal plain, specifically of the Castagnolo and Coltano reliefs, and the Leghorns Hills where the Vicarello Formation outcrops. This connection, which may have strong consequences on the geo-tectonic interpretation of the study area, and the formation age of ICS needs to be better investigated in the future with new high-resolution tectonic and absolute chronological data.
Keywords - Facies analysis, sea-level change, Holocene, Late Pleistocene, incised valley, Arno plain, extensional basin, subsidence, Coltano sands, Vicarello Formation.
This paper presents the results of the interpretation of a set of high‐resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North‐Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea‐level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave‐ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane‐derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.
The Upper Pleistocene to Holocene (post-last glacial maximum) succession of the Po River Plain, northern Italy, illustrates the expression of sequence-stratigraphic surfaces and stratal units in paralic and coastal-plain settings that are different from the settings of most of the mudstone units considered thus far in this book. This interval spans shallow-marine, shoreline, lagoonal, swamp, and fluvial-floodplain environments.
The Po River Plain is an excellent place to study how the stratal record of changing eustasy is mediated by sediment-supply rates (detrital and biogenic) as well as by all the components of accommodation (e.g., subsidence, compaction, and groundwater table) for four reasons:
Our study shows how applying the sequence-stratigraphic method and approach from first principles in transitional environments can provide insights into the accumulation of mud in a setting that is the critical link between continental hinterlands and marine depositional basins.
A buried paleovalley system, about 50 m deep and 2 km wide, is documented from the Pescara coastal plain. Based on stratigraphic, sedimentological, paleontological, chronological and geotechnical data, the paleovalley profile and 3D facies architecture of the paleovalley fill (PVF) were reconstructed.
The lowermost PVF is a laterally extensive fluvial gravel body, up to 13 m-thick, that represents the lowstand systems tract (LST; pre-11.3 ka cal BP). Above lowstand deposits, the transgressive systems tract (TST), 21 m-thick, shows a deepening-upward trend, from freshwater/inner-estuarine to brackish/outer-estuarine facies associations (11.3–8.0 ka cal BP). The upper part of the succession (highstand systems tract – HST) shows a shallowing-upward tendency from paludal to fluvio-deltaic deposits.
Seven millennial-scale parasequences (Ps) were identified within the Pescara Holocene (TST + HST) succession. Transgressive Ps1-3 exhibit a distinctive retrogradational stacking pattern. Highstand Ps4-7 are aggradationally-to-progradationally stacked. During the aggradational phase (P4), the estuary was gradually filled and swamp environments spread onto the valley interfluve. Because of subsequent progradation (Ps5-7), delta plain conditions established. In the research core, TST parasequences show higher accumulation rates (up to 9.4 mm/y) than HST ones (1.3–1.8 mm/y). Thus, the study area evolved from a region of sediment storage (11.3–8.0 ka cal BP) into a sector of prevalent sediment bypass (last 8.0 ky).
Major early Holocene flooding events were possibly triggered by Melt-Water Pulses (MWPs) 1B, 1C and 1D. The eustatic rise linked to MWP-1B reasonably caused the P1 flooding event (11.3 ka cal BP). Post-MWPs 1C and 1D sea-level rises likely provoked the complete drowning of the paleovalley system and the subsequent maximum landward migration of the shoreline (about 8.0 ka cal BP).
This study provides new evidences, in terms of sedimentary response, of the poorly-documented MWPs 1C and 1D, and the first documentation of MWP-1B eustatic effects in an onshore sector of the Central Adriatic.
This archaeometric research examined the structural elements of the three kilns found in the plain below the archaeological site of Rusellae, the ceramics found within this artisans’ quarter and the clayey materials on which the workshops were built. Twenty-one samples were investigated by bulk chemical and mineralogical analyses (ICP-MS, ICP-AES and XRD) and mineralogical-petrographic analyses on thin sections (optical microscopy and scanning electron microscopy). The results allowed the characterisation of the production group to be obtained. Both carbonatic and non-carbonatic clayey materials were used to make common-ware ceramics and, above all, building materials such as bricks and tiles. The production technology varied from accurately to poorly worked pastes, fired from low (about 800 °C) to very high temperatures (above 1100 °C). The compositional comparison with data previously obtained on stamped bricks and neighbouring clayey materials suggested a correlation with the producer/s known by the stamps SEX CLEMENT/PROBI and PROBI. Furthermore, the variety of raw materials used in the manufacture and product diversification also let speculate that the production site welcomed various artisans and products for the final firing.
While recent landscape changes can be usually easily read through accessible morphological features, relatively ancient processes can be difficult to detect as the associated morphologies and deposits are often buried below younger sediments. With the aim of understanding the evolution of the distal Venetian-Friulian Plain (NE Italy) after the Last Glacial Maximum (LGM), this work presents the analysis performed on a dataset of ca. 2300 mechanical and hand-made cores, which allowed a detailed reconstruction of the formation and evolution of an incised valley, now almost completely filled and with little to absent morphologic expression. Such valley, up to 1.2 km wide, with a depth of 20 m below the LGM alluvial plain and traced for a length of 25 km, is the result of the complex interplay between minor spring-fed rivers and the Tagliamento River. The detailed characterization of the infilling allowed to identify two main phases in the valley evolution. The first one is related to the activity of the paleo Tagliamento River and led to the deposition of a 10 m thick gravelly unit (ca. 19–9.5 ka cal BP). The second phase, which followed a disconnection of the Tagliamento, is linked to the Holocene marine transgression and led to the formation of a lagoon environment within the valley and to the deposition of a ca. 15 m thick unit of lagoon muds (ca. 8 ka cal BP - historic time). This latter unit lays on top of gyttja deposits, indicating for the first time in this area the presence of widespread lacustrine environments in the Early Holocene. This work presents an in-depth analysis on the evolution of a distal plain incised valley, from its formation to its final filling, providing at the same time the means to describe the development of the entire alluvial plain landscape, spanning from the end of the LGM to the middle Holocene. We present new data on the paleoenvironmental and morphologic evolution of the Venetian-Friulian Plain area as a consequence of the interplay between autogenic forces and sea-level rise. Our study allowed to understand the importance of both Alpine rivers and groundwater-fed streams in the formation of large incised valleys in the coastal sector of the whole Venetian-Friulian Plain. Finally, as during the transgressive phase the upstream sediment input in the valley was almost absent, this study provides insights into facies and architecture of a rare example of downstream-controlled filling of an incised valley.
Die kontinentale Sedimentfazies ist abhängig von der Strukturbildung des Gebirges und des Sedimentbeckens.
Morphodynamic evolution in an alluvial river is usually controlled by various boundary conditions. During the past nearly 50 years, remarkable morphodynamic evolution occurred in the Jianli reach of the Middle Yangtze River owing to the combined effects of an artificial cutoff, the upstream operation of the Three Gorges Project (TGP), and the downstream confluence of the Dongting Lake. To better understand the characteristics of morphodynamic changes in the whole study reach, variations in thalweg shifting and bankfull channel geometry were quantified using a reach-averaged approach, and the effects of upstream and downstream controls were investigated on channel geometry adjustments. Calculated results indicate that: (i) events of an artificial cutoff and high flows caused the average rate of reach-scale thalweg migration to be greater than 35 m/yr, but there was a 22% reduction in the mean migration rate after the TGP operation; (ii) channel geometry adjusted mostly in the aspect of bankfull depth under various river regulation engineering, with the reach-scale bankfull depth increasing by 0.95 m from 2002 to 2016; (iii) the reach-scale bankfull dimensions are closely associated with these accumulated effects of both the altered flow-sediment regime because of upstream dam construction, and the local base-level variation owing to the downstream confluence of the Dongting Lake. Furthermore, these bankfull variables were expressed by power functions of two key parameters, covering the previous five-year average fluvial erosion intensity during flood seasons at Jianli (upstream control), and the corresponding water level difference between Jianli and Lianhuatang (downstream control). The proposed relations were calibrated by the observed data in 2002–2014, and were further verified by measurements in 2015–2016. The proposed methodology can also be applicable to estimate channel geometry adjustments of other similar alluvial rivers controlled by both upstream and downstream boundary conditions.
Incised valleys that develop due to relative sea‐level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of incised‐valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database‐driven statistical analysis of 151 late‐Quaternary incised‐valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised‐valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied incised‐valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of incised‐valley fills, probably through effects on relative sea‐level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley‐fill geometry is positively correlated with the associated drainage‐basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on valley‐fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and valley‐margin stability. Shelves with slope breaks that are currently deeper than 120 m contain incised‐valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between valley‐fill thickness and present‐day coastal‐prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of ‘source to sink’ sediment route‐ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs. This article is protected by copyright. All rights reserved.
We reconstruct human–landscape interactions in the context of ancient bloomery smelting on Elba Island, Tyrrhenian Sea, based on sedimentological evidence. Elba was, together with Populonia, the center of iron production in antiquity (mid‐6th century B.C.E. to 1st century C.E.). The sediment sequences obtained by vibracoring in the Campo plain reveal that the Holocene transgression triggered aggradation during the Early–Middle Holocene (>5.4 ka cal BP). Nevertheless, wetland conditions prevailed in low‐lying areas during Roman times. Correspondingly, ancient smelting sites are found only on elevated areas along the edge of the plain. The palaeolandscape thus plays a key role in understanding location factors for smelting sites in antiquity. Our sediment sequences indicate that during Etrusco–Roman times (2.4–2.0 ka cal BP) morphodynamics on the island increased, as is evident from the alteration of slope deposits and slack water deposits in upstream positions, and the change from lacustrine to alluvial deposition in downstream areas. The charcoal record shows that fire dynamics increased simultaneously. The sediments that are synsedimentary to the ancient smelting period show significantly increased arsenic contents and high sediment magnetic susceptibility, whereas overall concentrations of heavy metals remain in the range of the geogenic background signal.
Un-fragmented stratigraphic records of late Quaternary multiple incised-valley systems are rarely preserved in the subsurface of alluvial-delta plains due to older valleys reoccupation. The identification of a well-preserved incised-valley fill succession beneath the southern interfluve of the Last Glacial Maximum Arno palaeovalley (northern Italy) represents an exceptional opportunity to examine in detail evolutionary trends of a Mediterranean system over multiple glacial-interglacial cycles. Through sedimentological and quantitative meiofauna (benthic foraminifera and ostracods) analyses of two reference cores (80 m and 100 m long) and stratigraphic correlations, a mid-Pleistocene palaeovalley, 5 km wide and 50 m deep, was reconstructed. Whereas valley filling is chronologically constrained to the penultimate interglacial (Marine Isotope Stage 7) by four electron spin resonance ages on bivalve shells (Cerastoderma glaucum), its incision is tentatively correlated with the Marine Isotope Stage 8 sea-level fall. Above basal fluvial-channel gravels, the incised-valley fill is formed by a mud-prone succession, up to 44 m thick, formed by a lower floodplain unit and an upper unit with brackish meiofauna that reflects the development of a wave-dominated estuary. Subtle meiofauna changes toward less confined conditions record two marine flooding episodes, chronologically linked to the internal MIS 7 climate-eustatic variability.
Exposures of multistorey, alluvial deposits from the Oligocene Gebel Ahmar Formation in the Cairo-Suez province (north Eastern Desert, Egypt) show the architecture of an up to 35. m thick continuously prograding fluvial/alluvial filling of an incised valley. The Oligocene base level fall resulted in cannibalization of the Eocene bedrock. Subsequent baselevel rise created accommodation space that was filled by deposition of four stacked storeys: lower storeys (1-2) of low sinuosity sandy braid plains and upper storeys (3-4) of gravelly braid plain. These braid plains were sourced from exposed Upper Cretaceous-Eocene and Paleozoic-Lower Cretaceous siliciclastic successions to the south. These successions dominate the Galala-Araba inverted structures. The sandy braid plain channel belts mainly downstream accretion (DA), downstream oblique accretion(DLA), lateral accretion (LA), sandy bedforms (SB), channel (CH), and Hollow (HO) elements, while the gravelly braid plain consists mainly of gravel bars and sheets (GB), gravel-sandstone foresets (GSF), gravel-sand couplets (GSC), and scour pool filling (SPF) architectures. Incised valley incision is potentially linked to a global drop of sea level caused by glaciation, although hinterland tectonism (i.e. Late Cretaceous-Paleogene tectonic inversion and Late Eocene-Oligocene crustal updoming in the source terrains) as well as Late Oligocene-Miocene rifting play a significant role in the subsequent filling. The hinterland tectonism as well as the climate controls the sediment supply. The understanding of the nature of the Oligocene incised valley fill helps in the constrain potential down depositional dip hydrocarbon reservoirs in Nile Delta, East Mediterranean basins, and similar settings in passive continental margins.
Integrated sedimentological and micropaleontological data were used for the construction of a 93 km-long stratigraphic cross-section parallel to the modern Adriatic shoreline (northern Italy). The stratigraphic panel shows, for the first time, along-strike changes in facies architecture. The Late Pleistocene succession consists of well-drained floodplain deposits. Multi-storey fluvial-channel bodies, ~ 20 m thick, are correlative with a paleosol that formed in response to sea-level fall and river incision at the onset of the Last Glacial Maximum (MIS 3/2). Another paleosol (12.5-10 kyr cal BP), associated with the Younger Dryas cold event, marks the transition to overlying Holocene coastal facies. In terms of sequence stratigraphy, the lower paleosol represents the sequence boundary and the correlative, amalgamated channel-belt deposits form the lowstand systems tract. The transgressive surface coincides with a weakly-developed paleosol (18.5-16 kyr cal BP) that marks a major phase of channel abandonment induced by early sea-level rise. The Younger Dryas paleosol allows subdivision of the transgressive systems tract (TST) into lower and upper TST. The lower TST, well developed in the south, is characterized by thin poorly-drained floodplain deposits; the upper TST, showing vertical transition to coastal and shallow-marine clays, has diagnostic ‘marine’ signature, and is laterally continuous, with no significant thickness changes. The maximum flooding surface marks the turnaround from a deepening-upward to shallowing-upward trend. The highstand systems tract includes a prograding succession of prodelta clays and overlying delta-front/beach-ridge sands, which form a laterally continuous sedimentary body. Nearshore sands accumulated in prograding delta systems characterized by wave-dominated, arcuate geometries, with transition to laterally continuous strandplains.
The Late Glacial in the Italian Alps and in the Po Plain: stratigraphy, vegetation history and human peopling The palaeoenvironmental evolution and its relationship with the human peopling of the southern side of the Alps, their foreland and the Po plain during the Lateglacial, i.e. the interval following the global Last Glacial Maximum between 19 and 11.5 ka cal BP, is reconstructed on the base of high-resolution stratigraphic successions. After the major glaciers retreat from the pedemontane amphitheatres and from the great pre-alpine lakes, a collapse of the dendritic valley glaciers occurred during the first part of the Lateglacial and well before the Bølling –Allerød interstadial. Forest vegetation was limited to the foreland and the external belt of Pre-Alps, and did not enter the inner valleys, still subjected to intense paraglacial evolution. This period records the first human occurrences at the Pre-Alpine foothills. The onset of the Bølling–Allerød interstadial, dated 14.7 – 14.3 ka cal BP, allowed the treeline to reach 1700-1800 m a.s.l., promoted productivity in the lacustrine and palustrine systems, and peat formation commenced up to an altitude of 1800 m a.s.l. Together with warming and reforestation, human settlements expanded in the Eastern Alps. As a consequence of the interstadial ecological modifications, the epigravettian colonization of the Pre-Alps and the Dolomites starts. Sites increase in number and differentiate in altitude and function. The second part of this interstadial is marked by the expansion of thermophilous broad-leaved trees, the peak of which coincided with the deposition of the Laacher See Tephra in Lago Piccolo di Avigliana, dated 13 or 12.9 ka cal BP, and anticipated the beginning of the Younger Dryas by about two centuries. The YD onset, therefore, appears to be synchronous in Northern Italy and Central Europe. The YD in the Po Plain was characterized by continental dry climate, close to the semiarid regime, with strong seasonal contrast. During the second half of YD, a renewed glacial activity (Egesen, Kartell, and Kromer stadials) is recorded in the high valleys. This glacial multiphase extends well into the early Holocene. At the present state, the archaeological data are still unsufficient for revealing the possible impact of the YD on the settlement dynamics.
This study from the southern margin of the Gulf of Corinth documents a Late Pleistocene incised valley-fill succession that differs from the existing facies models, because it comprises gravelly shoal-water and Gilbert-type deltaic deposits, shows strong wave influence and lacks evidence of tidal activity. The valley-fill is at least 140m thick, formed in 50 to 100ka between the interglacials Marine Isotope Stage 9a and Marine Isotope Stage 7c. The relative sea-level rise left its record both inside and outside the incised valley, and the age of the valley-fill is estimated from a U/Th date of coral-bearing deposits directly outside the palaeovalley outlet. Tectonic up-warping due to formation of a valley-parallel structural relay ramp contributed to the valley segmentation and limited the landward extent of marine invasions. The valley segment upstream of the ramp crest was filled with a gravelly alluvium, whereas the downstream segment accumulated fluvio-deltaic deposits. The consecutive deltaic systems nucleated in the ramp-crest zone, forming a bathymetric gradient that promoted the ultimate growth of thick Gilbert-type delta. The case study contributes to the spectrum of conceptual models for incised valley-fill architecture. Four key models are discussed with reference to the rates of sediment supply and accommodation development, and it is pointed out that not only similarity, but also all departures of particular field cases from these end-member models may provide valuable information on the system formative conditions. The Akrata incised valley-fill represents conditions of high sediment supply and a rapid, but stepwise development of accommodation that resulted from the spatiotemporal evolution of normal faulting at the rift margin and overprinted glacioeustatic signals. This study adds to an understanding of valley-fill architecture and provides new insights into the Pleistocene tectonics and palaeogeography of the Corinth Rift margin.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
This study presents pollen-based climate reconstructions of Holocene temperature and precipitation seasonality for two high-resolution pollen sequences from the central (Lake Accesa, central Italy) and eastern Mediterranean (Tenaghi Philippon, Greece) regions. The quantitative climate reconstruction uses multiple methods to provide an improved assessment of the uncertainties involved in palaeoclimate reconstructions. The multimethod approach comprises Partial Least Squares regression, Weighted Average Partial Least Squares regression, the Modern Analogues Technique, and the Non-Metric-Multidimensional Scaling/Generalized Additive Model method. We find two distinct climate intervals during the Holocene. The first is a moist period from 9500 to 7800 cal. BP characterised by wet winters and dry summers, resulting in a strongly seasonal hydrological contrast (stronger than today) that is interrupted by a short-lived event around 8200 cal. BP. This event is characterised by wet winters and summers at Accesa whereas at Tenaghi Philippon the signal is stronger, reversing the established seasonal pattern, with dry winters and wet summers. The second interval represents a later aridification phase, with a reduced seasonal contrast and lower overall precipitation, lasting from 7800 to 5000 cal. BP. Present-day Mediterranean conditions were established between 2500 and 2000 cal. BP. Many studies show the Holocene to have a complex pattern of climatic change across the Mediterranean regions. Our results confirm the traditional understanding of an evolution from wetter (early Holocene) to drier climatic conditions (late Holocene), but highlight the role of changing seasonality during this time. Our data yield new insights into the aspect of seasonality changes, and explain the apparent discrepancies between the previously available climate information based on pollen, lake-levels and isotopes by invoking changes in precipitation seasonality.
Lacustrine sedimients from Lago di Pergusa in central Sicily provide a Postglacial record of environmental change in the Mediterranean. Magnetic susceptibility measurements, lithofacies characterization and pollen analysis were carried out anid integrated to obtain a better reconstruction of the past 11000 years. The chronoogy is provided by AMS radiocarbon dates on macrofossils or bulk sediment, and by a tephra correlative with a late-Holocene explosion from the Etna volcano. The transition period related to the present interglacial reafforestation, characterized by increasing humidity, started about 10700 years BP. The onset of the wettest conditions of the Postglacial occurred at about 9000 years BP and lasted until about 7200 years BP. Then a trend towards aridification began. leading to very dry conditions at about 3000 years BP. An unquestionable human impact on vegetation is found from 2800 years BP, although earlier land use cannot be excluded. As the climate had already induced change in the vegetation, the well-known human occupancy during the last three millennia did not produce strong effects on the environment.
Until recently, sequence stratigraphic models have attributed systems tracts to periods of relative sea-level rise, highstand and lowstand. Recognition of a discrete phase of deposition during relative sea-level fall has been limited to a few studies, both in clastic and carbonate systems. Our work in siliciclastic ramp settings suggests that deposition during relative sea-level fall produces a distinctive falling stage systems tract (FSST), and that this is the logical counterpart to the transgressive systems tract. The FSST lies above and basinward of the highstand systems tract, and is overlain by the lowstand systems tract. The FSST is characterized by stratal offlap, although this is likely to be difficult or impossible to recognize because of subsequent subaerial or transgressive ravinement erosion. The most practical diagnostic criteria of the FSST is the presence of erosive-based shoreface sandbodies in nearshore areas. The erosion results from wave scouring during relative sea-level fall, and the stratigraphically lowest surface defines the base of the FSST. Further offshore, shoaling-upward successions may be abruptly capped by gutter casts filled with HCS sandstone, reflecting increased wave scour on the shelf during both FSST and LST time. The top of the FSST is defined by a subaerial surface of erosion which corresponds to the sequence boundary. This surface becomes a correlative submarine conformity seaward of the shoreline, where it forms the base of the lowstand systems tract. Differentiation of the FSST and LST may be difficult, but the LST is expected to contain gradationally-based shoreface successions because it was deposited when relative sea level was rising. Internally, the FSST may be an undifferentiated body of sediment or it may be punctuated by internal regressive surfaces of marine erosion and ravinement surfaces which record higher-frequency sea-level falls and rises superimposed on a lower-frequency sea-level fall. The corresponding higher-order sequences are the building blocks of lower-order sequences. The addition of a falling stage systems tract results in a significant reduction in the proportion of strata within a sequence that are assigned to the classical highstand and lowstand systems tracts. Many outcrop and subsurface cross-sections use an overlying ravinement, or maximum flooding surface as datum. Those surfaces might be flat, but they are not horizontal. Both dip seaward at slopes that generally are steeper than the fluvial system responsible for creating the sequence boundary. When a section is restored to such a datum, the falling stage systems tract will appear to record stratigraphic climb, whereas in fact it does not.
Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight') single channel; net sand transport is headward in these areas. -from Authors
After establishing its present location around 9.5 ka, Mustang Island aggraded, stacking over 20 m of barrier-island sand in the same location. Throughout Mustang Island's history, tidal inlets shifted within nearly the same location from 7.5 ka to the present, leaving 10–15 m thick deposits of clean, well-sorted, quartz sand deposited within only a few centuries. These deposits lack some of the sedimentary features normally associated with tidal inlets, such as tidal couplets and shell hash. The lack of such features is attributed to the uniform nature of the deposits cut by the inlets during the island's relatively long period of aggradation. Mustang Island was able to maintain an aggradation character throughout most of the Holocene due to the sediment eroded from three sources: Pleistocene headlands, the transgressive Colorado River delta of Texas, and the OIS 3 shoreline of the central-Texas shelf. Each of these sources was exposed to waves and accompanying longshore drift during the island's early history when sea level rose quickly, but was flooded or capped by transgressive muds by the time sea-level rise slowed during the middle Holocene.
The late Quaternary sedimentary architecture of the Guadiana estuary (southwestern Iberian Peninsula), a narrow, bedrock-controlled estuary with moderate sediment supply, was studied by applying concepts of high-resolution seismic stratigraphy. The estuarine sedimentary infill consists of a discontinuous basal interval overlain by five seismic units bounded by laterally continuous seismic horizons. The correlation between seismic facies and a stratigraphic section of the Guadiana valley enables the proposal of a detailed sequence stratigraphic interpretation of the estuarine infill.
During the last glacial lowstand, the Guadiana was a subaerial valley with no significant accumulation of fluvial deposits because of increased sediment bypass towards the present-day middle and outer shelf. Towards the end of the postglacial transgression, the subaerial valley was transformed into an estuary, and sediments began preferentially accumulating in structural depressions. Furthermore, flood tidal currents constrained by basement highs enhanced sand deposition in the upper part of the estuary. Wave influence was reduced and confined to the lower estuarine system. Here, the narrow morphology of the valley led to an increased sediment export to the shelf during the Holocene highstand period.
The lower part of the estuarine infill consists of four fifth-order depositional sequences, composed of regressive deposits (HST). The last glacial maximum is recorded by a distinct stratigraphic surface, representing simultaneously the sequence boundary and the transgressive surface. A tidal ravinement surface is characterized by strong erosion and channel formation in the outer estuarine zones. The maximum flooding surface is identified by change of stratal patterns between landward-prograding transgressive deposits and downlapping highstand deposits. Both transgressive (TST) and regressive tracts (HST) were deposited during the final part of the postglacial transgression and subsequent highstand.
At the time of mire initiation (c4500 BP), Pinus was by far the most important tree in the area, but was undergoing destruction at the hands of Bronze age/Copper age man. Quercus was more prominant during the subsequent recovery of the vegetation, but there is evidence of continued disturbance, both in the form of charcoal inwash into the site and in the frequency of pollen from indicators of burning (such as Cistus-type) and soil disturbance (such as Loeflingia-type, Echium, Plantago and Rumex). Evidence reveals a major episode of vegetation destruction and burning which resulted in a complete layer of mineral sediment and charcoal being deposited across the entire valley. Only in the last c100 yr has Pinus recovered fully in the area, probably the result of planting. Vitis vinifera pollen is found in a series of 3 peaks, the earliest dating from 4340 ± 80 BP. One of the peaks is associated with high values of carr taxa, such as Salix, and could be accounted for by local growth of wild vine in carr vegetation, but the other peaks are associated with evidence for soil disturbance and are likely to have resulted from viticulture. -from Authors
This paper presents a detailed description of the stratigraphic architecture of the Late Pleistocene/Holocene Tiber delta succession in order to document the passage from wave-dominated estuary to wave-dominated delta in the broader context of Late Quaternary sea level fluctuations. This succession constitutes a sequence-stratigraphic unit known as Tiber Depositional Sequence (TDS), which was deposited during the last glacial–interglacial cycle (last 120 ka). Our study is based on the examination of an enormous amount of data derived from the stratigraphy of about 300 wells, petrographical and paleon-tological data (foraminifera, ostracoda, pollen, and plant macrofossils), 14 C dating, and from the integration of geomorphological and geoarcheological data. Recently a 100 m deep core (Pesce Luna well) was studied through a multidisciplinary approach and a detailed description of sedimentary facies, foraminifer and ostra-cod assemblages, pollen and 14 C dating is presented in this paper. The new data allowed to produce three new correlation panels and to describe in more detail, with respect to previous interpretations, the stratigraphic-depositional architecture of the TDS, which internally shows the preservation of sediment de-posited during the early and late lowstand, the transgressive and the highstand systems tracts. Alluvial and coastal depositional systems characterize the early lowstand phase of the TDS, which developed during the eustatic sea-level fall between about 120 and 30–26 yr BP. During the late lowstand phase, which is charac-terized by stillstand and slow eustatic sea-level rise a prograding delta and an aggrading incised-valley fluvial fill developed. The Tiber incised valley was transformed into a wave-dominated estuary during the transgres-sive phase (TST), whereas a coastal-shelf sedimentation took place during the subsequent highstand phase (HST). This study confirms the lithofacies distribution resulting from transgression and infilling of the wave-dominated estuaries, but also shows how the transition to a wave-dominated delta, prograding at the time of sea-level highstand occurred. Changes in sediment input, climatic variations and, more recently, human activities played a major role in the development of the Tiber delta during the last 20,000 yr BP. In the last 3000 years a relationship between progradational phases of the delta and flood events of the Tiber river has been highlighted, suggesting also the formation and merging of barrier-spits to the mainland.
Some of the striking results of the papers published in the special publication "French Incised valleys, estuaries and lagoons" of the Bulletin de la Société géologique de France are presented and compared. The selection of papers within this volume focuses exclusively on the recent progress made on modern French incised valleys, estuaries and lagoons around the coasts of France. Those papers together with abundant papers recently published on modern French incised valleys provide new insights for the knowledge on these sedimentary systems. The large amount of new results obtained is indebted to an extensive exploration within a large variety of estuaries, lagoons and coastal areas, from macrotidal tide-dominated, to microtidal wave-dominated, with also meso-to macrotidal mixed tide-and wave-dominated estuaries. These data allow comparing incised valleys within the same setting of tectonically stable and sediment starved margins, but showing contrasted conditions of hydrodynamics, sediment supply and bedrock control. At a stratigraphic level, sea-level variation is the main parameter controlling incised valley formation and sediment fill. The first-order controlling factor explaining the observed variations in valley fills is hydrodynamics. Three valley-fill categories are highlighted: tide-dominated, mixed tide-and-wave and wave-dominated, that match the classification based on hydrodynamics and morphology of present-day estuaries or lagoons. The second-order controlling factor explaining the observed variations in valley fills is the antecedent morphology of the bedrock, which in turn controls hydrodynamics and sediment supply. Finally, a promising result is the demonstration of the potential of incised valley fills to record high frequency environmental changes related to climate events and human activities.
Lithofacies characteristics and depositional geometry of a sandy, prograding delta deposited as part of the Holocene valley-fill stratigraphy in the Målselv valley, northern Norway, were examined using morpho-sedimentary mapping, facies analysis of sediments in exposed sections, auger drilling and ground penetrating radar survey. Various lithofacies types record a broad range of depositional processes within an overall coarsening-upward succession comprising a lowermost prodelta/bottomset unit, an intermediate delta slope/foreset unit containing steeply dipping clinoforms and an uppermost delta plain/topset unit. Bottomset lithofacies typically comprise sand-silt couplets (tidal rhythmites), bioturbated sands and silts, and flaser and lenticular bedding. These sediments were deposited from suspension fall-out, partly controlled by tidal currents and fluvial effluent processes. Delta foreset lithofacies comprise massive, inverse graded and normal graded beds deposited by gravity-driven processes (mainly cohesionless debris flows and turbidity currents) and suspension fall-out. In places, delta foreset beds show tidal rhythmicity and individual beds can be followed downslope into bottomset beds. Delta plain facies show an upward-fining succession with trough cross-beds at the base, followed by planar, laminated and massive beds indicative of a bedload dominated river/distributary system. This study presents a model of deltaic development that can be described with reference to three styles within a continuum related primarily to water depth within a basin of variable geometry: (i) bypass; (ii) shoal-water; and (iii) deep-water deltas. Bypass and deep-water deltas can be considered as end members, whereas shoal-water deltas are an intermediate type. The bypass delta is characterized by rapid progradation and an absence of delta slope sediments and low basin floor aggradation due to low accommodation space. The shoal-water delta is characterized by rapid progradation, a short delta slope dominated by gravity-flow processes and a prodelta area characterized by rapid sea-floor aggradation due to intense suspension fallout of sandy material. Using tidal rhythmites as time-markers, a progradation rate of up to 11 m year−1 has been recorded. The deep-water delta is characterized by a relatively long delta slope dominated by gravity flows, moderate suspension fall-out and slow sea-floor aggradation in the prodelta area.
A Holocene sedimentary sequence from a coastal lake in the Mediterranean area (Lago di Massaciuccoli, Tuscany, Italy, 0 m a.s.l.) was sampled for pollen and microscopic charcoal analyses. Contiguous 1‐cm samples represent an estimated time interval of c. 13 years, thus providing a high‐resolution sequence from 6100 to 5400 cal. years bp .
Just before 6000 cal. years bp , sub‐Mediterranean and Mediterranean forests were present together with fir ( Abies alba ), a submontane species that is today absent at low altitudes in the Mediterranean. A sharp vegetational change occurred after 6000 cal. years bp involving a drastic decline of Abies alba around the site.
Time‐series analyses suggest that increased fire activity at this time caused a strong decline in Abies alba , a highly fire‐sensitive species. During 100 years of higher fire incidence, diverse (predominantly evergreen) forest communities were converted to low‐diversity fire‐prone shrub communities.
Cross‐correlations reveal that fire during the mid‐Holocene hindered the expansion of holm oak ( Quercus ilex ), the most common tree species today in Mediterranean environments. While the factors that triggered the Holocene expansion of this species in the Mediterranean area are unclear, our results do not support the hypothesis that fire was key for holm oak expansion.
Diatom analyses of the same sediment core provide an independent palaeoenvironmental proxy for palaeoclimatic reconstruction. A change in the eutrophy and salinity of the lake occurred just before 6000 cal. years bp , suggesting that a climatic shift towards aridity may have triggered the observed change in hydrology and possibly also in fire regime.
Over the millennia fire has decisively contributed to the establishment of the present fire‐adapted vegetation type (macchia). Native fire‐sensitive species were displaced or repressed, and arboreal vegetation became less diverse. Combined ecological and palaeoecological data may help to assess possible future scenarios of biosphere responses to global change. Our results imply that the forecasted global warming and fire increase may trigger irrecoverable biodiversity losses and shifts in vegetational composition within a few decades or centuries at most. In particular, fire and drought‐sensitive vegetation types, such as the relict forests of Abies alba in the Apennines, seem particularly threatened by large‐scale displacement.
The palaeoenvironmental evolution and its relationship with the human peopling of the southern side of the Alps, their foreland and the Po plain during the Lateglacial, i.e. the interval following the global Last Glacial Maximum between 19 and 11.5 ka cal BP, is reconstructed on the base of high-resolution stratigraphic successions. After the major glaciers retreat from the pedemontane amphitheatres and from the great pre-alpine lakes, a collapse of the dendritic valley glaciers occurred during the first part of the Lateglacial and well before the Bølling -Allerød interstadial. Forest vegetation was limited to the foreland and the external belt of Pre-Alps, and did not enter the inner valleys, still subjected to intense paraglacial evolution. This period records the first human occurrences at the Pre- Alpine foothills. The onset of the Bølling-Allerød interstadial, dated 14.7-14.3 ka cal BP, allowed the treeline to reach 1700-1800 m a.s.l., promoted productivity in the lacustrine and palustrine systems, and peat formation commenced up to an altitude of 1800 m a.s.l. Together with warming and reforestation, human settlements expanded in the Eastern Alps. As a consequence of the interstadial ecological modifications, the epigravettian colonization of the Pre-Alps and the Dolomites starts. Sites increase in number and differentiate in altitude and function. The second part of this interstadial is marked by the expansion of thermophilous broad-leaved trees, the peak of which coincided with the deposition of the Laacher See Tephra in Lago Piccolo di Avigliana, dated 13 or 12.9 ka cal BP, and anticipated the beginning of the Younger Dryas by about two centuries. The YD onset, therefore, appears to be synchronous in Northern Italy and Central Europe. The YD in the Po Plain was characterized by continental dry climate, close to the semiarid regime, with strong seasonal contrast. During the second half of YD, a renewed glacial activity (Egesen, Kartell, and Kromer stadials) is recorded in the high valleys. This glacial multiphase extends well into the early Holocene. At the present state, the archaeological data are still unsufficient for revealing the possible impact of the YD on the settlement dynamics.
Sediment grain-size uniformity is explained on the basis of the recent Ombrone River plain evolution, which prevented coarse sediments from reaching the outlet, and also by wave energy which attacks the beach and removes the fines even at greater depths. -from Authors
In this 2006 volume John Murray investigates the ecological processes that control the distribution, abundance and species diversity of benthic foraminifera in environments ranging from marsh to the deepest ocean. To interpret the fossil record it is necessary to have an understanding of the ecology of modern foraminifera and the processes operating after death leading to burial and fossilisation. This book presents the ecological background required to explain how fossil forms are used in dating rocks and reconstructing past environmental features including changes of sea level. It demonstrates how living foraminifera can be used to monitor modern-day environmental change. Ecology and Applications of Benthic Foraminifera presents a comprehensive and global coverage of the subject using all the available literature. It is supported by a website hosting a large database of additional ecological information (www.cambridge.org/0521828392) and will form an important reference for academic researchers and graduate students in Earth and Environmental Sciences. © Cambridge University Press, 2009 and John Murray 2006. All rights reserved.
Foraminifera are extensively used in different fields of earth and environmental sciences by virtue of several factors such as (1) a hard exoskeleton, which records fundamental environmental changes and evolutionary processes of earth history, (2) small size and, consequently, high abundance in small samples, (3) wide distribution over all marine environments, (4) high taxonomic diversity, and (5) very short reproductive cycles (month to year), which make them excellent recorders of environmental changes covering a short time span.
The main
features and the evolution of the apical part of the River Ombrone delta have been analized from a morphological and sedimentological viewpoint, using cartographic data, aerial photographs and field
evidence. The geometry and the angle between beach-ridges and the fluvial course during different ages has also been determined. Moreover, 63 samples of sediments have been collected at a depth of about one meter below the land surface, inside the thalweg and the coastal ponds (locally called «chiari»). The morphological and sedimentological results allow to distinguish three elements
represented in the enclosed map: beach-ridge delta plain, coastal ponds, and a poligenic plain area.
The evolution occurred during three thousand years B.P. and the sedimentary dynamics have been outlined as well: the River Ombrone delta is a cuspate wave dominated delta, with a single distributary
channel and two asymmetrical wings, and is a typical feature of the Tyrrhenian margin.
The progradation is function of both man’s activity and climatic events; at present the influence of both factors cannot be easily quantified.
A 50 m deep well was drilled in the delta plain o f the Ombrone river. Samples have been investigated through grain size, microfaunistic andpalinological analysis, and fou r radiocarbon ages have been calculated. Processed data pointed out that the sediments have settled in a coastal zone. It is possible to subdivide the sedimentary succession into four intervals:
-50/45m — coastal plain muddy sediments, presence o f brackish marshes and ponds, damp and cold climate. Radiocarbon age > 30ky B.P.
-45/39m - mainly gravelly deposits ascribed to lagoon-delta body built by Ombrone river.
-39 / -10 m - muddy and silty sediments, settled during the last postglacial sea level rise, into a coastal basin with variable physiographic features. We have also recognised open and restricted lagoon phases, marshy environments and marine environment conditions strongly influenced by a river mouth. Climate is variable with a general trend towards a warmer climate.
-10/0m - Sandy, silty and muddy sediments settled after the postglacial sea level still stand (last 6Ky) in a temperate or warm climate. These deposits constitute the present delta body o f the Ombrone river.
The sediments comprised between 0 and - 45 m represent the postglacial depositional sequence which can be subdivided in a trasgressive system tract (-45 / -10 m) and a high stand system tract (-10 / 0 m).
Ancient fluvial valley systems are long recognized as important features in the stratigraphic record, but emerged as a specific focus of attention with publication of first-generation sequence-stratigraphic concepts. This paper reviews current understanding of paleovalley systems from the perspective of Quaternary analogs and experimental studies.Paleovalley systems can include distinct mixed bedrock–alluvial, coastal-plain, and cross-shelf segments. Mixed bedrock–alluvial segments are long-lived, cut across bedrock of significantly older age, and have an overall degradational architecture. By contrast, coastal-plain and cross-shelf segments are non-equilibrium responses to high-frequency cycles of relative sea-level change: most coastal-plain and cross-shelf segments form as a geometric response to relative sea-level fall, as river systems cut through coastal-plain and inner shelf clinothems, and extend basinward to track the shoreline. After incision and cross-shelf extension, lateral channel migration and contemporaneous channel-belt deposition creates a valley-scale feature. Coastal-plain and cross-shelf paleovalley widths are set by the number of channel-belt sandbodies deposited during this time.Paleovalley systems play a key role in source-to-sink sediment routing. Early views included the model of incision and complete sediment bypass in response to relative sea-level fall. However, this model does not stand up to empirical, theoretical, or experimental scrutiny. Instead, there is a complex dynamic between incision, deposition, and sediment export from an evolving valley: periods of incision correspond with sediment export minima, whereas periods of lateral migration and channel-belt construction result in increased flux to the river mouth. Sediment export from evolving valleys, and merging of drainages during cross-shelf transit, play key roles in sediment transfer to the shelf-margin and genetically-linked slope to basin-floor systems. Connection between the river mouth and the shelf margin likely occurs for different periods of time depending on gradient of the river and shelf, as well as amplitude of high-frequency sea-level changes.Late Quaternary analogs and experimental studies provide an alternative sequence-stratigraphic interpretation for paleovalley systems. In coastal-plain paleovalleys, basal valley-fill surfaces meet criteria for an unconformity and a classically-defined sequence boundary: however, this surface is mostly everywhere of the same age as overlying fluvial deposits, and does not correspond to a long period of incision and sediment bypass. In cross-shelf paleovalleys, the basal contact between fluvial and deltaic or shoreface deposits is commonly interpreted as a sequence boundary, but is not an unconformity characterized by incision and sediment bypass. Instead, this surface is a facies contact that separates genetically-related fluvial and deltaic strata: the surface that correlates to the basal valley-fill surface within the coastal-plain paleovalley dips below cross-shelf prograding deltaic and/or shoreface strata, which are fed by deposition within the evolving valley itself, and should be the downlap surface.Many issues deserve attention in the future. We have stressed understanding the inherent scales and physical processes that operate during the formation and evolution of paleovalley systems. We also suggest the relative roles of allogenic forcing vs. autogenic dynamics, and the potential significance of high-frequency isostatic adjustments should be topics for future discussion.
Extensive 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 a maximum 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 shallowingupward 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 sequencestratigraphic studies.
The Gironde estuary was formed by the Holocene drowning of a fluvial valley incised during the Wuerm global sea-level fall. A depositional sequence accumulated in the valley during the eustatic lowstand, the Holocene rise, and the post-Holocene highstand. The sequence comprises a diverse assemblage of lithofacies that can be grouped into lowstand, transgressive, and highstand systems tracts. The objective of this paper is to describe the facies and stratal architecture of this incised-valley fill, and to propose a sequence-stratigraphic model for incised-valley fills in this type of mixed tide- and wave-influenced coastal setting. this study is based on a compilation of the abundant core, borehole, and hydrological data published by a number of authors. The valley fills forms regionally elongated belts of channelized sandstones and are the subject of considerable interest because they furnish potentially important new hydrocarbon play concepts.
Understanding the relative control exerted by autogenic factors, such as changes in sediment supply, local subsidence and inherited topography, is of crucial interest for a thorough comprehension of the sedimentary evolution of late Quaternary coastal systems. Through an example from the Arno coastal plain, in Tuscany, we show to what extent sedimentation of the Holocene succession, even after the time of maximum marine ingression, was influenced by the presence of a buried 5–7 km-wide incised-valley system, generated by the Arno River during the late Pleistocene in response to the last glacial sea-level fall.
Ostracoda (microscopic, aquatic Crustacea) from brackish waters have a great potential for ecological monitoring and palaeoenvironmental analyses in highly variable environments. This has been proven in many articles during recent decades but their potential has yet to be fully developed or utilised. The analysis of ostracod assemblage composition, species distributions, eco-phenotypic variability and the analysis of stable isotopes and trace elements in ostracod shells provide valuable information on present and past water salinity, temperature and chemistry, hydrodynamic conditions, substrate characteristics, climate, sea level variations, oxygen and nutrient availability. This article provides an overview on the application of ostracods from brackish waters for palaeoenvironmental reconstruction in the Quaternary and for environmental studies in present day environments.
Architecture of late Quaternary incised-valley fills is commonly attributed to the interplay between sea-level rise, sediment supply, and hydrodynamic processes. Inundation of fluvial terraces is commonly overlooked as an autocyclic mechanism for formation of parasequences. If the rate of sea-level rise and sediment supply is constant, architecture of terraced incised-valley fills will likely show backstepping parasequences. The control that variable antecedent topography has on architecture of incised-valley fills is examined in the Trinity incised valley, Texas. The Trinity valley is characterized by a series of downward-stepping terraces, and the Galveston Estuary formed above this irregular antecedent topography. Flooding surfaces, recognized in core by a decrease in sedimentation rates and a change from delta-plain to central-basin facies, formed at similar to -14 m, 8,200 cal. yr BP and similar to -10 m, 7,700 cal. yr BP, matching depths of the relatively flat fluvial terraces. Flooding surfaces formed rapidly and represent entire reorganization of the estuarine complex. Across the -10 m flooding surface, the river mouth and bay-head delta shifted landward at a rate of similar to 6.5 km per century and the associated barrier shoreline was stranded on the inner continental shelf, forming Heald Bank. Flooding surfaces formed as the rate of sea-level rise was decreasing, and are not associated with a decrease in sediment delivery to the estuary. As sea level inundates relatively flat fluvial terraces, rates of transgression rapidly increase, resulting in a sudden increase in accommodation space and an associated landward shift in coastal facies. Backstepping parasequences are inherent to the architecture of terraced incised-valley fills.
http://www.sciencedirect.com/science/article/pii/S104061821100588X
Pollen data from three off-site records and twenty-six on-site (archaeological) sites are reviewed to investigate the development of cultural landscapes through the history of the olive, walnut and chestnut trees in the Italian peninsula from the Late Glacial to late Holocene. The spread of these trees, which have been gathered or cultivated since ancient times, though not marked by high values in pollen diagrams, is an important indicator of increasing human activity and anthropization in the Mediterranean area.
The response of coastal systems to allogenic forcing factors is of interest to diverse research communities, including those interested in global change, sequence stratigraphy and modelling. Quaternary systems are of particular interest because they provide analogues for ancient rock records. To understand the processes responsible for the sedimentary evolution of estuarine systems, it is necessary to study as many fluvial systems as possible. The objective of this review of the sedimentary evolution of a coastal marsh is to describe the influence of glacial paleotopography on the record of climatic and sea-level changes. The Marais Vernier, located at the interface between the marine and fluvial parts of the estuary, is a part of the Lower Seine Valley wetland network, which formed after the Last Glacial Maximum. Previous studies have described the Holocene filling, which is composed of peat and detrital material deposited following climatic and sea-level changes. To understand the sedimentary evolution, a paleotopographical (based on drillings and electromagnetic surveys) and a chronological framework (based on radiocarbon dates) for the southern peat marsh were defined. The peat marsh paleotopography has three erosional surfaces. The S1 surface is the oldest and also the highest, topographically; the S2 surface is younger, wider, and incised below the S1 surface; the S3 surface, the youngest of the three, is narrow and deeply incised. Radiometric ages were considered on the basis of their geographical position in relation to the S3 surface. Prior to 7.5 ka cal BP, sediments accumulated only above the narrow area described by the S3 surface, at a rate of 5.5 mm yr− 1. After 7.5 ka cal BP, shortly after the flooding of the Seine estuary, sediments accumulated as peat deposits over the entire peat marsh at a rate of 3 mm yr− 1 in response to the sea-level rise. The paleotopography delimits the area of deposition during the Holocene, and thus plays a critical role in determining the vertical accretion rate expressed as a thickness: prior to 7.5 ka cal BP, the vertical accretion rate (5.5 mm yr− 1) was less than that observed for the Seine estuary (6.8 mm yr− 1). However, rate of sea-level rise and sediment supply, which also affects sediment accumulation rates, vary in northwestern Europe during the Holocene. Therefore, although the Marais Vernier is a good illustration of paleotopographic influence, the effects of autocompaction, sea level and sediment supply complicate efforts to quantify the degree to which it controls sediment accumulation.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake-level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north-central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub-millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI-1d), Intra-Allerød (GI-1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice-core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra-Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake-level record shows that the sub-millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.
The palynological study of the Vico maar lacustrine sequence (Italy) is realized from the correlation of three drillholes. The time span covers a period from the end of Oxygen Isotope Substage 5b till the beginning of Stage 1 (from ca. 90 to ca. 10 ka BP).At the base of the pollen diagram (pollen zone 0), a Younger Dryas-like fluctuation is observed. After pollen zone 1, which is a well developed forest period (Substage 5a), the forests of pollen zones 3 and 5 correspond to extensive climate improvements. These last two zones are correlated to the Ognon complex of the Grande Pile (France) and to interstadial periods 20 and 19 defined in the GRIP ice core (Greenland) (72.6−66.2 ka) before the Stage 5/4 transition. These two interstadial periods are global events found in the Greenland and Antarctica ice sheets, as well as in North Atlantic marine cores. In other pollen records from north of the Alps, changes have been recorded but they are less pronounced than in Vico.Pollen zone 7 (Stage 3) shows ca. 7 warm/humid fluctuations, that might have a link to the Dansgaard-Oeschger events (Greenland). During zone 9, the Lateglacial interstadial is recorded as well as the Younger Dryas event.The localization of Vico near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes, possibly through a link to the Atlantic Ocean via westerly winds.
The purpose of this contribution is to disentangle climate forcing and human influence in the catchment of Lago di Mezzano through the interfingering of data obtained by means of archaeological, geomorphological, sedimentological and palynological approaches. A systematic archaeological survey has been undertaken and three submerged settlement areas with piles, pottery and metal tools have so far been found. The artifacts indicate that the site was inhabited, although not continuously, during the Bronze Age. Geomorphological investigations and observations in some trenches dug out on the lake shore indicate that great variations in the lake's size and strong changes in the catchment/lake surface area ratio occurred during the second half of the Holocene. Palynological, micro-charcoal, sedimentological and geochemical analyses carried out on long cores taken from the lake centre have indicated environmental changes due to either climatic influence or human impact. Even if human presence in the area has been detected during the whole Bronze Age period, the human populations caused a strong impact only in two periods centred around 3600 and 3200 cal. years BP when they settled along the lake shore, and around 3400 cal. years BP when they caused an increase in erosion leading to the beginning of the deposition of turbidites.
The pollen diagram from Stracciacappa (Sabatini volcanic complex, Rome) provides a record of vegetational and climatic change
spanning the last 60000 years, which is the time since when volcanic activity in the crater came to an end. The chronological
framework of the sediment core is set by five AMS and three conventional radiocarbon dates; the mean sedimentation rate obtained
by radiocarbon measurements was used to extrapolate the age of the record beyond the reach of 14C dating. The sequence from Stracciacappa provides results of fundamental importance for the understanding of the vegetational
changes which occurred during the last pleniglacial period in central Italy, and it can be considered as a reference pollen
record for the regional biostratigraphic characterization of this period. The site shows a high climatic sensitivity, particularly
highlighted by the development of some pleniglacial oscillations with woodland, which interrupted the succession of steppe
and grassland vegetational formations typical of the glacial periods. Unfortunately, due to sedimentation problems and alteration
of the top level sediments, the Holocene is only recorded in part. Only for one millennium, from ca. 8300 to 7200 uncalb.p., was a real forest expansion characterized by over 90% arboreal pollen found.
The local and regional history of vegetation and climate, from the Late Glacial to the present, is represented in a new,
high-resolution pollen diagram from Pian di Gembro (1350 m asl), ten 14C dates providing a reliable time control. An open pioneer vegetation dominated by Artemisia, Gramineae, and and Chenopodiaceae followed the retreat of the glaciers after the Last Glacial Maximum. Shrub vegetation
with Juniperus, Alnus viridis, and Salix expanded soon after. Denser Betula-Pinus forests were present in Pian di Gembro around 12,320 B.P. Their extent was greatly reduced by the climatic cooling of the
Younger Dryas, when open vegetation spread again. The beginning of the Holocene was marked by a considerable expansion in
mixed oak taxa. Corylus immigrated to the site at 9,250 B.P. Picea and Abies expanded at 7,370 B.P., recording an abrupt change in the structure of the vegetational belts. A coeval climatic change is
evidenced in the GRIP records and also detectable through oscillations of the timberline. Signs of human impact are present
since late Atlantic, becoming more intense around 2,200 B.P. As pasture lands increased, Abies and Fagus slowly disappeared. The introduction of Castanea and Juglans is dated to Roman times, and Secale to the Middle Ages.