Fabio Trincardi

The late-Holocene Gargano subaqueous delta, Adriatic shelf: Sediment pathways and supply fluctuations

The Gargano subaqueous delta formed on the eastern and southeastern sides of the Gargano promontory, in the western Adriatic. This subaqueous deposit represents the southernmost portion of the late-Holocene highstand systems tract (HST) growing along the western side of the Adriatic as an extensive wedge of deltaic and shallow-marine mud. The late-Holocene HST rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5.5 cal. kyr BP, at the end of the late-Pleistocene–Holocene sea-level rise. High-resolution seismic–stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5.5 and 3.7 cal. kyr BP over much of the basin. Above this unit, sediment accumulation rates increased to high values (as much as 1.5 cm yr−1) reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics. The late-Holocene mud wedge, of which the Gargano subaqueous delta is a significant component, reaches up to 35 m in thickness and has a volume of ca 180 km3. The shore-parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources (with a combined modern delivery of 51.7×106 t yr−1 of mean suspended load). In sections perpendicular to the coast the late-Holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets (typically 0.5°). The Gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25–28 m, and accounts for about 1/7th of the total volume of the late-Holocene mud wedge, despite the absence of direct river supply to the Gargano area. In the area of maximum interaction between shore-parallel currents and basin morphology, progradation occurs onto a flat and barren bedrock outcrop in about 50–80 m water depth. The rapid transition from a thickness of 30 m of late-Holocene mud to nil is a good indication of the role of southward-flowing bottom-hugging shelf currents in causing the redistribution of sediment along the Adriatic inner shelf. Additional evidence of this regime comes from: (1) the most recent sigmoid (defined at seismic–stratigraphic scale) deposited since the onset of the Little Ice Age, showing a shore-parallel thickness distribution and a main depocentre to the southeast of the Gargano promontory; (2) the maximum values of sediment accumulation rates over the last century (documented by 210Pb measurements) defining a narrow shore-parallel belt immediately seaward of the depocentre of the most recent sigmoid. The Gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones. The Gargano subaqueous delta differs from other documented late-Holocene subaqueous deltas because its growth reflects: (1) sediment transport dominated by bottom currents sub-parallel to the strike of the composing clinoforms; (2) a complex supply regime including the Po delta (350 km to the north) and several coalescing Apennine rivers acting as ‘line source’; (3) several alternating intervals of enhanced outbuilding and condensed deposition; and (4) an in-phase growth of the most recent sigmoid with the major progradation of the Po delta during the Little Ice Age.

Sub-millennial scale climatic oscillations in the central Adriatic during the Lateglacial: palaeoceanographic implications

Abstract A multi-proxy study of a sedimentary core obtained from the central Adriatic basin provides evidence of short-term events of palaeoceanographic variability during the last glacial Lateglacial period (GRIP event stages GI-1 and GS-1). Comparison of the Adriatic results with other Mediterranean records reveals a common sequence of changes in palaeoceanographic conditions. Variations in foraminiferal assemblage data and in stable isotopic compositions indicate two short-term cold oscillations, which interrupted an overall cooling trend that commenced at the beginning of the Greenland GI-1 episode (Bolling/Allerod episode). These cold events, considered to be contemporaneous with GI-1b and GI-d of the GRIP ice-core record, are indicated by distinctive foraminiferal assemblages, which reflect episodes of high productivity under relatively restricted water circulation, with (in particular) reduced vertical mixing during winter. Differences in the foraminiferal assemblages indicate that the younger of the two cold spells is characterized by reduced ventilation of bottom waters. Our results, combined with published data from neighbouring marine basins, suggest a widespread reduction in deep-water formation in the central Mediterranean which commenced during the GI-1b episode and reached its maximum effect during the onset of the GS-1 (Younger Dryas) episode. Moreover, three intervals with reduced vertical mixing correspond to the two cold spells during GI-1 and the lower phase of the GS-1 episode and show close similarities with the palaeoceanographic changes reported for the North Atlantic. This similarity indicates that the Mediterranean and North Atlantic may have been responding more-or-less synchronously to common forcing mechanisms.

Short-term climate changes during the Last Glacial–Holocene transition: comparison between Mediterranean records and the GRIP event stratigraphy

This paper presents biostratigraphical and stable isotope data obtained from core CM92–43, which was recovered from the central Adriatic as part of a comprehensive investigation of the palaeoenvironmental history of the basin. The data span the period of the Last Glacial–Holocene (LG–H) transition (ca. 18000 to 8000 GRIP ice-core yr BP). Regional biozones are defined on the basis of characteristic assemblages of planktic Foraminifera, and these are compared with other foraminiferal biostratigraphical schemes from the southern Adriatic and the Tyrrhenian Sea. Variations in relative abundance of selected planktic Foraminifera and in selected pollen types are shown alongside variations in δ18O and δ13C obtained from Globigerina bulloides and relative abundance of Globigerinoides ex. gr. ruber. The data are compared with the GRIP ice-core record and the event stratigraphy scheme based on this record, and it is concluded that the climate forcing mechanisms that controlled climate variations in the North Atlantic region during the LG–H transition also extended their influence into the Mediterranean region over the same period. Copyright

Gela submarine slide: A major basin-wide event in the plio-quaternary foredeep of Sicily

The 1,500-km2 Gela slide and associated debris flow deposits cover most of the Gela foredeep basin (Sicily channel). The head of the slide follows the tip of the arcuate Gela nappe. A basin-wide detachment surface extends from the extensional slide head to a distal, contractional zone.The slide may be the result of a gravitational collapse which affected the sediments overlaying a remarkable decollement horizon. Mass movement processes resulted in the mobilization of a sedimentary sequence already deposited within the foredeep basin.

Man made deltas

The review of geochronological and historical data documents that the largest southern European deltas formed almost synchronously during two short intervals of enhanced anthropic pressure on landscapes, respectively during the Roman Empire and the Little Ice Age. These growth phases, that occurred under contrasting climatic regimes, were both followed by generalized delta retreat, driven by two markedly different reasons: after the Romans, the fall of the population and new afforestation let soil erosion in river catchments return to natural background levels; since the industrial revolution, instead, flow regulation through river dams overkill a still increasing sediment production in catchment basins. In this second case, furthermore, the effect of a reduced sediment flux to the coasts is amplified by the sinking of modern deltas, due to land subsidence and sea level rise, that hampers delta outbuilding and increases the vulnerability of coastal zone to marine erosion and flooding.

Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene

A late Quaternary, current-lain sediment drift deposit over 30 m in thickness has been discovered on the continental shelf of East Antarctica in an 850 m deep glacial trough off George Vth Land. Radiocarbon dating indicates that a period of rapid deposition on the drift (averaging 290 cm/kyr) occurred in the mid-Holocene, between about 3000 and 5000 yr before present. Slower rates of around 10 cm/kyr, during the past 0-3000 yr and from 5000 to about 13000 yr BP, coincides with deposition of bioturbated, ice-rafted debris (IRD) rich, sandy mud under an energetic bottom current regime. In contrast, the mid-Holocene (3000-5000 yr BP) sediments are fine-grained, laminated to cross-laminated with minimal IRD content, and are contemporaneous with a period of warmer marine conditions with less sea ice production. This pattern suggests that bottom currents were weaker than present day in the mid-Holocene, and that the rate of dense bottom water production was reduced at that time. This scenario is consistent with the hypothesis of non-steady state rates of Antarctic bottom water production through the Holocene as recently proposed by Broecker and his colleagues.

Climatic cycles as expressed in sediments of the PROMESS1 borehole PRAD1‐2, central Adriatic, for the last 370 ka: 1. Integrated stratigraphy

[1] A multiproxy integrated chronological framework, based on oxygen and carbon stable isotope stratigraphy, biostratigraphy (foraminifera and nannoplankton bioevents and foraminifer assemblage-based climate cyclicity), magnetostratigraphy, sapropel stratigraphy, and (14)C AMS radiometric dates, has been achieved for borehole PRAD1-2, collected in 185.5 m water depth in the central Adriatic. This work was carried out within the European Community project Profiles across Mediterranean Sedimentary Systems (PROMESS1). The 71.2 m long borehole spans a time interval between late MIS 11 and MIS 1 (the last 370 ka), showing a chronological resolution of 500 and 250 years per cm during interglacial and glacial intervals, respectively. At present, this record is the most expanded and continuous marine record available for the Adriatic Basin. Several orbital cycles can be recognized in the PRAD1-2 record: the 100 ka glacial-interglacial fluctuations and the 23 ka precession-related cycles, which in turn control the deposition of sapropel layers. An integrated analysis of short-term oscillations within the Last Glaciation interval (MIS 4-MIS 2) allowed the identification of the Adriatic signature of Dansgaard-Oeschger events, showing the potential to achieve a more refined chronostratigraphic framework for the top part of the PRAD1-2 record. Finally, the age model obtained by this study allowed the chronological integration of the main foraminifera bioevents detected in the borehole as well as of the volcanoclastic layers present in the upper part of the record. Despite its proximal location, PRAD1-2 presents a continuous record and shows the potential to be consistently correlated both with deep-sea and continental records in the Mediterranean region and beyond.

Mediterranean bottom-current deposits: an example from the Southwestern Adriatic Margin

Abstract The identification of bottom-current deposits is a key to understanding the long-term deep-sea circulation and its changes through geological times. The Southwestern Adriatic Margin (SAM) is a small Mediterranean sub-basin that represents a key site to study bottom-current deposits in a Mediterranean context and hence to improve our knowledge of changes in Mediterranean deep-water circulation during the recent geological past. The SAM is characterized by complex stratification and circulation related to an interaction between two south-flowing bottom water masses: the cold North Adriatic Dense Water (NAdDW), formed in the shallow northern Adriatic through cold wind forcing and winter heat loss, and the highly saline Levantine Intermediate Water (LIW), generated in the Eastern Mediterranean through intense evaporation and flowing along the slope in a depth range of 200–600 m. Chirp-sonar profiles, TOBI mosaics and sediment cores acquired along the SAM reveal distinctive sediment drift types (elongated, plastered and isolated drifts) and extensive fields of sediment waves. Non-depositional and erosional features related to bottom-current activity include moats between drifts and the steep slope, widespread upper-slope erosional areas and extensive furrowed areas, which are particularly developed where change in slope orientation blocks the current circulation. The distribution, morphology and size of bottom-current features along the SAM result from an interaction between current regime and slope morphology, characterized by structural highs perpendicular to the slope contour (e.g. Dauno Seamount), multiple slope incisions (e.g. Bari Canyon and slump scars) and extensive block-slide deposits. Morphobathymetric and seismic stratigraphic data on the SAM show that bottom-current deposits are best developed where the regional slope flattens seaward of a very steep, often erosional, upper slope. The roughness of the lower slope, in particular, seems to correlate with the complexity and decreasing size of the bottom-current deposits. Like other land-locked basins, the Adriatic underwent dramatic palaeogeographical and palaeoceanographic rearrangements during the Late Quaternary sea-level oscillations. Indeed, during the Last Glacial Maximum (LGM), most of the areas where NAdDW is formed today were subaerially exposed. Concurrently, during glacial times the LIW production was probably reduced compared with the present-day conditions. The SAM slope is a key site to study the impact of changing current regime on late Quaternary slope deposits. Other Mediterranean late Quaternary contourite deposits are either in water depths compatible with the LIW, particularly in the case of shallow sill basins (e.g. Sicily, Corsica Channel), or at the slope base reflecting the flow of Mediterranean deep waters. The SAM bottom-current deposits, instead, seems to record the changing interaction between two distinctive bottom-hugging currents along the same pathway.

The combined effect of sea level and supply during Milankovitch cyclicity: Evidence from shallow-marine δ18O records and sequence architecture (Adriatic margin)

The combination of sequence stratigraphy and multiproxy chronostratigraphic data, including δ 18 O records, unravels the record of Milankovitch cyclicity through the past ~400 ka on the Adriatic margin. Chronostratigraphic data and stable isotope records from planktic and benthic foraminifera are derived from borehole PRAD1-2, a 71 m continuous core drilled on the Western Adriatic slope. The cored interval encompasses the distal parts of stacked progradational wedges that are the main building blocks of 100 ka depositional sequences. These sequences and their internal progradational units reflect a cyclic interplay between sea level and oceanographic circulation, with relevant feedbacks on sediment supply fluctuations and regional long-shore sediment dispersal. Calibration of slope units with isotope stratigraphy and direct slope-shelf correlation indicates that two types of progradational clinoforms alternate in phase with the pattern of composite climate and sea-level changes figured by δ 18 O records. Changes in clinoform geometry of the kind observed in the Adriatic are consistent with a mechanism of switching supply from dominant advection on a flooded shelf, during highstands, to overall sediment starvation on a narrowed shelf, during lowstands. Seismic and core data document that this mechanism is related to ~100 and 20 ka cyclicity reflecting rearrangement of the oceanographic setting and sediment pathways during the last four glacial-interglacial cycles.

Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf

Abstract The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form. We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20–24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.