Tyrrhenian Shelf Research Articles

Carbonate Deposition In Restricted Basins: A Pliocene Case Study From the Central Mediterranean (Northwestern Apennines), Italy

Abstract Carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness, because of their significance in petroleum geology. However, spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic-dominated or mixed carbonate–siliciclastic systems. Pliocene successions of Tuscany and the Tyrrhenian shelf (Northern Apennines, Italy) record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation. This study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves. Analyses of the extension, composition, facies, and sequence stratigraphic architecture of the studied Piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data, which document the slightly diachronous development of the carbonates within Mediterranean planktonic foraminifera Subzones MPL4b and MPL5a and magnetic polarity Chron C2An. The carbonate units are part of a regionally defined, tectonically controlled sequence, and represent the first transgressive unit overlying the basal sequence boundary, but are also found in the regressive portion of the sequence. Collectively, the units document the establishment of a shallow-marine carbonate factory, dominated by calcareous red algae, the larger benthic foraminifer Amphistegina, and heterozoan skeletal components, along the margins of a complex, archipelago-like coastal domain. A review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by: a) spatial discontinuity; b) an overall skeletal association consistent across separate basins, but with local variability in dominant skeletal components; c) preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems; d) predominance of low- to moderate-energy facies; e) preferential onset of deposition during transgression, with possible development of mixed carbonate–siliciclastic facies; and f) differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins. These observations built upon the study of mid-Piacenzian carbonate units from the central Mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis.

The role of foraminifera as indicators of the Late Pleistocene–Holocene palaeoclimatic fluctuations on the deltaic environment: The example of Tiber delta succession (Tyrrhenian margin, Italy)

The palaeoclimatic and palaeoenvironmental reconstruction of the last 39.0 kyr of the central Tyrrhenian shelf are presented in this paper. Micropalaeontological, sedimentological and stable isotopic data integrated by radiocarbon dates were determined from three cores drilled in the Tiber delta sequence (TDS), which constitutes one of the most complete Late Quaternary high-frequency depositional sequences in the Mediterranean area. Short-period climate variations that induced short-period events caused changes in the Tiber run-off and increased the sediment supply and grain size in the delta system. The three cores, with different thicknesses, record all the system tracts forming the TDS. Three intervals corresponding to the Early and Late Lowstand, Transgressive and Highstand System Tracts (TST and HST) were recognised. The first is characterised by shoreface/inner shelf deposits and corresponds to a general cooling period characterised by short warmer periods (approximately 1.0 kyr), confirming the climatic variability of MIS 3/MIS 2. A very condensed deposition affected the second interval, which is characterised by a very low sedimentation rate corresponding to the TST of TDS. The third interval, corresponding to Holocene shelf deposits, shows small climatic oscillations that mark an enhanced seasonality typical of the modern Tyrrhenian regime. At the millennial scale, two warm intervals (Copper Age and Late Bronze Age/II century AC) alternating with two cold humid intervals (Bond cycle B3/RCC: 4.2–3.8 kyr BP of Mayewski events and the Little Ice Age) have been recognised.

Seagrass-Meadow Sedimentary Facies In A Mixed Siliciclastic-Carbonate Temperate System In the Tyrrhenian Sea (Pontinian Islands, Western Mediterranean)

Abstract The paper presents the characteristics of surface sediments in a seagrass-dominated environment of the inner shelf of the Pontinian Islands (Tyrrhenian Shelf, Central Mediterranean). The aims of this work are to characterize the carbonate production and sedimentary processes of a representative high-latitude, temperate Posidonia oceanica–dominated area, to discuss the role of seagrass in the siliciclastic–carbonate mixing processes, which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record. The majority of sediments are poorly sorted siliciclastic skeletal sand. Based on grain type and abundance and carbonate content, these deposits include six subfacies. The different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions. Additionally, the seagrass facies range from purely carbonate to mixed carbonate–siliciclastic, depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate-producing biota. The type of substrate and the erosion and transport processes control the siliciclastic input. In these Pontinian seagrass meadows, sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes. This Pontinian example illustrates that in heterozoan-dominated seagrass settings, mud-producing green algae are not present or are not calcifying, and consequently, seagrass deposits are much more grainy than photozoan counterparts. Ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains.

Reconstruction of Late Pleistocene–Holocene palaeobathymetries from Ostracoda on the Tyrrhenian continental shelf

Quantitative analyses of ostracod assemblages from three cores recovered on the Tyrrhenian shelf (Gaeta and Salerno Gulfs) have been applied to construct palaeobathymetric curves. Palaeoclimatic curves obtained from planktonic foraminifera, calcareous nanoplankton, pteropods and pollen are available for the same cores, in addition to sedimentological, mineralogical, geochemical (δ 18O, 14C, C/N, CaCO 3) and volcanological data with regard to the two cores from the Salerno Gulf. The palaeobathymetric curves reflect the climatic events through the Late Pleistocene–Holocene interval. The climatic events of the Last Glacial (and within it, the Last Glacial Maximum), the Late Glacial (with Oldest Dryas, Bølling-Allerød, Younger Dryas events) and Postglacial have been recognised. The palaeobathymetric curves are also in agreement with palaeoclimatic curves of planktonic assemblages and pollen.

State of stress in southern Italy from borehole breakout and focal mechanism data

We present new wellbore breakout data from oil exploration wells drilled in southern Peninsular Italy, from the Tyrrhenian shelf through the Apenninic mountain belt and foredeep, eastward to the undeformed Adria foreland. From the analysis of 64 wells, we observe Shmin oriented around NE‐SW, perpendicular to the trend of the Apennines, both within the belt and in the eastern foredeep. Some variations are observed in the few wells analyzed on the Tyrrhenian shelf, possibly due to local tectonic structures, such as transverse NE‐SW oriented extensional basins. The Apulian platform overthrust by the Apenninic mountains at 3–4 km depth, shows a very consistent direction of Shmin oriented N40°–50°E, in agreement with the stress regime inferred from focal mechanisms of strong earthquakes at depths of 10–15 km, which show NE extension, mostly accomplished by normal faulting. The overlying sedimentary and allochthonous units of the Apenninic belt exhibit the same NE Shmin direction, but show a larger scatter. Breakout data demonstrate that Quaternary compressional tectonism has ended, as Shmin is oriented NE also in the undeformed foreland as far as 50 km NE from the seismic belt. In the easternmost sector of the Adria foreland there are suggestions of a nearly isotropic horizontal stress field, as most wells do not show significant ellipticity.

Sediment waves on the tiber prodelta slope: Interaction of deltaic sedimentation and currents along the shelf

A regressive depositional sequence has been prograding on the northeastern Tyrrhenian Shelf since the establishment of the present high stand of sea level. Thickness and distribution of this prograding sequence are chiefly controlled by the Tiber Delta sediment source and the oceanographic conditions on the shelf.

Elements for a comparison between the Tyrrhenian and Ligurian coastal currents during spring

Hydrological and current measurements effected along the western Italian coasts permit to compare the main dynamical peculiarities of the coastal circulation of the Ligurian and Tyrrhenian basins, evidencing in particular their different response to atmospheric fluctuations. While the Ligurian currents show a great energy that depends essentially on the large-scale circulation, the Tyrrhenian shelf dynamics is characterized by a low thermohaline driven velocity, largely influenced by the local wind.