Francesco Latino Chiocci

Sequence Stratigraphy and Depositional Setting of the Tiber Delta: Integration of High-resolution Seismics, Well Logs, and Archeological Data

ABSTRACT Using archeological evidence, radiocarbon data, well logs, and high-resolution seismic profiles, we applied sequence-stratigraphic analysis to sediments deposited during the last glacio-eustatic cycle on the Tyrrhenian continental margin embracing the Tiber River months. These sediments form a high-frequency sequence of fifth order that has developed over the last 20,000 yr since the last lowstand, hereafter referred to as the Tiber Depositional Sequence (TDS). The TDS is still evolving and lies on a Type 1 sequence boundary that has been identified both on the shelf and below the present delta plain. This sequence consists of lowstand, transgressive, and highstand systems tracts. The lowstand deposits are not present on the shelf but are found on the continental slope, where they constitute the last progradation set of the continental margin. A network of gullies, active when the river mouth was at the shelf break, is present within the lowstand deposits. The transgressive-systems-tract (TST) deposits lie directly on the basal unconformity. Landwards the TST is represented by a retrogradational parasequence set of fluvial, coastal barrier-lagoon, and lagoonal delta facies. Seaward, on the shelf, these parasequences merge into a seismically transparent deposit that forms a condensed section. The flooding surfaces that bound the parasequences are marked by peat layers that were dated by 14C. The radiometric ages were used to draw a carve of sea-level rise for the last 11,000 yr. The top of the transgressive systems tract (maximum flooding surface) is represented by the last peat layer, which was formed about 4700-5000 yr BP and buried 4-5 m below the present upper delta plain. The highstand systems tract is made up of deposits of the present Tiber wave-dominated delta, i.e., upper and lower delta plain, delta front, and prodelta slope. The aligned beach ridges mark the position of the prograding coastline, which for the last 2500 yr can be dated by archeological and historical data. The recent very fast progradation of the Tiber delta, during the last 500 years, is consistent with historical data on floods of the city of Rome and the suspended load of the Tiber River.

Lowstand terraces on Tyrrhenian Sea steep continental slopes

Abstract Wave-built terraces formed during sea-level Stillstands at depths lower than present are found along margins with fairly steep morphology and no- to ill-developed continental shelf, for instance the margin of volcanic islands. Terraces deposits are up to 20–30 m thick and are flat-topped with well-defined edges. They extend up to 1 km in dip section. The deposits are composed of intrabasinal sediments, mainly bioclastic sand and silt and are probably due to deposition below the storm wave-base during large-scale energy episodes. Two areas of the Tyrrhenian Sea have been analysed, one in a volcanic context (the Pontine archipelago) and the other in a highly active structural context (the Calabrian Arch). Similar wave-built terraces were found in both areas, with a main terrace placed at a depth of 100–150 m, which is thought to be Wurmian. Older terraces are also present, emplaced during the preceding lowstands in the Late Pleistocene. A possible present-day terrace is found at about 20 m depth in the Pontine archipelago. A mechanism of subsequent formation below wave base-level and removal because of sea level lowering has been hypothesised during long-lasting periods of Late Pleistocene sea level falls. Terraces are thus thought to preserve only at the minimum lowstand position and to remain relict on the slope during sea level rise and highstand. The analysis of the distribution and depths of these terraces allows some neotectonic interpretation. For example, in the volcanic archipelago, whose western sector has probably risen at an average rate of 2.5 mm/yr over the last 20,000 years.

The morphology of insular shelves as a key for understanding the geological evolution of volcanic islands: Insights from Terceira Island (Azores)

Shelves from volcanic ocean islands result from the competition between two main processes, wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension. In places where erosion dominates over volcanism, shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved. In this study, new multibeam bathymetry and high-resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of Terceira Island in order to improve the understanding of its evolution. Subaerial morphological and geological/stratigraphic data were also used to establish the connection between the onshore and offshore evolution. Shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island; most of the older edifices have wider shelves than younger ones. The shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view. Its depth was also used to reconstruct vertical movements, showing that older edifices like Serra do Cume-Ribeirinha, Guilherme Moniz, and Pico Alto have subsided while more recent ones have not. The morphology of the shelf (namely the absence/presence of fresh lava flow morphologies and several types of erosional, depositional, and tectonic features) integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution.

Depositional response to Quaternary fourth-order sea-level fluctuations on the Latium margin (Tyrrhenian Sea, Italy)

Abstract More than 10 000 km of high-resolution seismic profiles permit detailed study of six fourth-order seismic stratigraphic sequences deposited during the last million years on the Latium continental shelf, Tyrrhenian Sea, Italy. Sedimentation occurred on a relatively young passive margin characterized by a narrow and relatively steep shelf where sediment storage capacity in adjacent subaerial basins was limited. The Late Pleistocene deposits are locally tilted and eroded to different levels along the sea-floor so that carefully placed seafloor gravity cores help constrain the age of the seismic sequences by the dating of micro-fauna. Correlation with a deep well located on the coast constrains the basal third-order sequence boundary on the shelf. The seismic and a limited core database make it possible to: (1) detail variability in the architecture, stratal patterns and bounding surfaces of the sequences across the shelf and adjacent continental slope; (2) define a hierarchy of seismic units and their bounding surfaces; (3) make a correlation with the published oxygen-isotope curves; (4) develop a detailed stratigraphic framework and model for the fourth-order sequences deposited during last 0.8 Ma; (5) define the effects of the long-lasting eustatic falls on margin sedimentation; (6) recognize volumetric partitioning of sedimentation between systems tracts. The seismo-stratigraphic expression of the third- and fourth-order sequence boundaries varies greatly from the inner to the outer part of the margin. Where subsidence allowed the preservation of lowstand systems tract (LST) deposits on the shelf, they are bounded by erosional unconformities interpreted to reflect fourth-order glacioeustatically-driven cycles. Relatively thin (<10 m) lens-shaped bodies mark the transition from the unconformities to their correlative conformities and are interpreted to have been deposited during the eustatic minimum. The deposits bounded between correlative conformities show an upward loss in acoustic transparency thought to indicate upward-coarsening and regression within the sequences. Downdip on the continental slope, sequence boundaries are concordant surfaces correlative with unconformities on the shelf. However, these surfaces are locally scoured by channellized features, interpreted to record slope erosion related to the discharge of river bedload during lowstands. There is marked asymmetry and volumetric partitioning between systems tracts; most of the Late Quaternary deposits that comprise the Latium continental margin are interpreted to have formed during forced regression and lowstand. Offshore of the northern and central Latium shelves forced regressive and lowstand deposits account for some 1000 km3 of shelf and slope deposition during the last eustatic cycle. In contrast, sediments attributed to the transgressive and highstand systems tracts account for approximately 37 km3. High-frequency, high-amplitude asymmetric sea-level changes driven mainly by glacioeustasy are interpreted to have controlled deposition. Following classic three-fold sequence stratigraphic models, the unconformities created by shelf subaerial exposure and erosion represent sequence boundaries at the base of depositional sequences. However, if as is the case of the Latium margin during the Late Pleistocene, where a continental margin is formed almost exclusively of forced regressive deposits, each sequence basal boundary will paradoxically be situated above the forced regressive deposits that are deposited as the subaerial exposure surface forms, i.e. above the whole of its own depositional sequence. In this respect, the incorporation of a fourth forced regressive or falling stage systems tracts specific to times of base-level fall would help avoid this inconsistency.

The Landslide Sequence Induced by the 2002 Eruption at Stromboli Volcano

The complex sequence of large-scale tsunamogenic instability phenomena occurred on the subaerial and submarine NW flank of the Stromboli Volcano soon after the beginning of the December 2002 eruption is reconstructed and its relationship with volcanic activity is evidenced. After a brief description of slope morphology and stratigraphy, geometry and kinematics of the landslides are described. Finally, instability mechanisms that controlled the subaerial and submarine slope failures are proposed with reference to the different geotechnical, hydraulic, and loading/strain conditions that characterized the different stages of the slope evolution.

The Magdalena Turbidite System (Caribbean Sea): present-day morphology and architecture model

Abstract A detailed analysis of the modern morphology, acoustic facies and architecture of the eastern Magdalena Turbidite System has been based on multibeam bathymetry and backscatter data. In spite of the fact that the Magdalena Turbidite System developed in a tectonically active setting, its present architecture model is comprised of two tecto-sedimentary provinces: deformed-constructional and undeformed-erosive. The deformed province occurs where the deformed prism developed. This prism is characterised by structural highs and associated small-scale ridges and scarps. In this province, the Magdalena Turbidite System is constructional because sediment coming from the Colombian hinterland (via the Magdalena River and from coastal erosion) and sediment remobilised from the walls of the structural highs are transported trough canyons and gullies, and emplaced as gravity deposits into the deformed prism. In the undeformed province, by contrast, the Magdalena Turbidite System displays an architecture model similar to a passive continental margin, and is characterised by large-scale mass-flow deposits, leveed channel complexes, scars of slumps, and sediment waves. This province is presently erosive because the existing leveed channels are partially or totally destroyed and cannibalised by mass-flow deposits, cut by small-scale scars of slumps, and their morphology is subdued or modified by the formation of a sediment wave field.

Effect of sea-level variation on upper-slope depositional processes offshore of Tiber delta, Tyrrhenian Sea, Italy

Abstract The upper slope and outer shelf in front of the Tiber River mouth (east-central Tyrrhenian Sea) exhibits a series of about 15 gullies that are not clearly related to present-day erosional or depositional processes. An extensive, high-resolution, seismic-reflection profiling survey of a 450 km 2 area in front of the Tiber delta shows several generations of similar features within the older depositional sequences underlying the outer continental shelf. The gully relief appears dominantly depositional, probably developed during lowstand periods when the Tiber River mouth was relatively near the shelf break. The position of the gullied intervals, including those on the modern slope relict from the last lowstand, shows a successive northward shift with time. This northward shift indicates continued tilting of this part of the eastern Tyrrhenian continental margin, probably resulting from a continued subsidence to the north.

Volcanic, tectonic and mass-wasting processes offshore Terceira Island (Azores) revealed by high-resolution seafloor mapping

Terceira Island, in the Azores Archipelago, lies at the intersection of four submarine volcanic ridges. New high-resolution bathymetric and seismic reflection data have been used to analyze the main volcanic, tectonic and mass-wasting features of the island offshore. Volcanic features such as linear volcanic centers, and pointy and flat-topped cones are mainly concentrated on the narrow western and north-western ridges, characterized by an overall rugged morphology. Fault scarps dominate mainly the broad eastern and south-eastern ridges, which are characterized by an overall smooth and terrace-like morphology. On the eastern ridge, faults form a series of horsts and grabens related to the onshore Lajes Graben. The strikes of the fault scarps, linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends, WNW–ESE and NNW–SSE, consistent with the main tectonic structures observed on the Azores Plateau. In contrast, a large variability of strike was observed in inter-ridge areas, reflecting the relative importance of regional and local stresses in producing these structures. Mass-wasting features are subordinate and mostly represented by hundred meter-wide scars that indent the edge of the insular shelf surrounding the island, apart from two large, deeper scars identified on the southern steep flank of the western ridge. Finally, the remarkable morpho-structural differences between the western and eastern ridges are discussed in the framework of the evolution of the Terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution.

New high-resolution acoustic data from the 'braided system' of the Orinoco deep-sea fan

Abstract The interpretation of approximately 100 km of EM12 multibeam bathymetry and backscatter data together with high resolution TOPAS profiles obtained during a transit over the Orinoco deep-sea fan, near the Barbados accretionary prism, shows that the braided drainage pattern seen on GLORIA images by Belderson et al. (1984) corresponds to wide (∼10 km), low relief (

Bathy-morphological setting of Terceira Island (Azores) after the FAIVI cruise

High-resolution morpho-bathymetric data at 1:200,000 scale obtained during the FAIVI cruise (2011) and the resulting geomorphologic map of the Terceira island offshore area (central Azores, Portugal) are presented for the first time. The uneven morphology around Terceira is primarily related to volcanic features, such as linear and cone-shaped eruptive centres and lava flows. Such features are mostly concentrated on volcanic ridges and are aligned along preferential axes, suggesting a strong interaction between tectonics and volcanic processes. The occurrence of active tectonics is also demonstrated by systems of faults cutting the seafloor to the north, east and south of the island. Mapped erosive-depositional features include an insular shelf located at < 150 m water depth (wd), small landslide headwalls, erosive scarps, channelized features and crescent-shaped bedforms. The presented map may represent the base for a first-order geo-hazard assessment.