On the peritidal cycles and their diagenetic evolution in the Lower Jurassic carbonates of the Calcare Massiccio Formation (Central Apennines)

This paper shows the environmental changes and high-frequency cyclicity recorded by Lower Jurassic shallow- water carbonates known as the Calcare Massiccio Formation which crop out in the central Apennines of Italy. Three types of sedimentary cycle bounded by subaerial erosion have been recognized: Type I consists of a shallowing upward cycle with oncoidal floatstones to rudstones passing gradationally up into peloidal packstone alternating with cryptoalgal laminites and often bounded by desiccation cracks and pisolitic-peloidal wackestones indicating a period of subaerial exposure. Type II shows a symmetrical trend in terms of facies arrangement with peloidal packstones and cryptoalgal laminites present both at the base and in the upper portion of the cycle, separated by oncoidal floatstones to rudstones. Type III displays a shallowing upward trend with an initial erosion surface overlain by oncoidal floatstones to rudstones that, in turn, are capped by pisolitic-peloidal wackestones and desiccation sheet cracks. Sheet cracks at the top of cycles formed during the initial phase of subaerial exposure were successively enlarged by dissolution during prolonged subaerial exposure. The following sea-level fall produced dissolution cavities in subtidal facies, while the successive sea-level rise resulted in the precipitation of marine cements in dissolution cavities. Spectral analysis revealed six peaks, five of which are consistent with orbital cycles. While a tectonic control cannot be disregarded, the main signal recorded by the sedimentary succession points toward a main control related to orbital forcing. High frequency sea-level fluctuations also controlled diagenetic processes

Sedimentary facies and foraminiferal assemblages from Posidonia oceanica meadows of western Mediterranean Sea

Sedimentary facies and foraminiferal assemblages of sediments sampled into seven Posidonia oceanica meadows from Western Mediterranean Sea were investigated. Six sampling sites are localised in Italy (Maratea, Ponza Island, Santa Marinella, Giglio Island, Osalla and Alghero), and one in France (Argentella, Crovani Bay, Corsica). The role of P. oceanica meadows in the sedimentary processes was investigated in different contexts: sampled meadows are set up both on soft and hard substrates, often forming “mattes”, in geographical areas subject to different wind and sea conditions (waves and longshore currents) and characterised by various coastal landforms and terrigenous inputs derived from costal erosional processes and/or fluvial contributions. A sedimentological, compositional, micropaleontological and geochemical characterisation of 111 bottom sediment samples, collected by SCUBA diving between 0 and 35 mwd, was carried out and finally tested with a Q-mode cluster analysis. Five sedimentary facies have been recognised, from terrigenous to mixed siliciclastic-carbonate and carbonate. Facies (and subfacies) are distinguishable by sorting, gravel content, abundance and maturity of clastic sediments, and weighted average of carbonate content. In all facies, foraminifers and red algae dominate the bioclastic fraction, whereas other bioclastic components are very subordinate and show a variable distribution. In all the investigated sites, benthic foraminiferal assemblages are generally dominated by typical epiphytic species, such as Asterigerinata mamilla, Lobatula lobatula, Peneroplis pertusus, Planorbulina mediterranensis, Rosalina spp. and miliolids. Nevertheless, these assemblages show some differences in the different sites according to the presence or absence of terrigenous contributions and, consequently, to the water turbidity. This parameter influences symbiont-bearing foraminifer as P. pertusus. Moreover, the samples from Argentella (Crovany Bay) are characterised by a peculiar assemblage, in which Miniacina miniacea dominates with very high frequencies.</jats:p

Evaluating the role of seagrass in Cenozoic CO2 variations

Marine seagrass angiosperms play an important role in carbon sequestration, removing carbon dioxide from the atmosphere and binding it as organic matter. Carbon is stored in the plants themselves, but also in the sediments both in inorganic and organic forms. The inorganic component is represented by carbonates produced by calcareous organisms living as epiphytes on seagrass leaves and rhizomes. In this paper, we find that the rate of seagrass epiphyte production (leaves and rhizomes) averages 400 g m−2 yr−1 , as result of seagrass sampling at seven localities along the Mediterranean coasts, and related laboratory analysis. Seagrasses have appeared in the Late Cretaceous becoming a place of remarkable carbonate production and C sequestration during the whole Cenozoic era. Here, we explore the potential contribution of seagrass as C sink on the atmospheric CO2 decrease by measuring changes in seagrass extent, which is directly associated with variations in the global coastal length associated with plate tectonics. We claim that global seagrass distribution significantly affected the atmospheric composition, particularly at the Eocene-Oligocene boundary, when the CO2 concentration fell to 400 ppm, i.e., the approximate value of current atmospheric CO2

The Eocene–Oligocene transition in the C-isotope record of the carbonate successions in the Central Mediterranean

The Eocene-Oligocene transition marks a fundamental step in the evolution of the modern climate. This climate change and the consequent major oceanic reorganisation affected the global carbon cycle, whose dynamics across this crucial interval are far from being clearly understood. In this work, the upper Eocene to lower Oligocene δ13CCarb and δ13CTOC records of a shallow-water and a hemipelagic carbonate settings within the Central Mediterranean area have been studied and discussed. The shallow-water carbon isotope signal has been analysed in the northern portion of the Apula Platform, cropping out in the Majella Mountain, Central Apennines (Santo Spirito Formation). A coeval Umbria-Marche basinal succession has been investigated in the Massignano section (Conero area, Central Italy). The purposes of this work are: to discriminate between the global and the local (Mediterranean) signature of C-isotope record during the Oi-1 event, to correlate the regional C-isotope signal with the global record, and to evaluate the carbon cycle dynamics across the greenhouse-icehouse transition through the integration of complementary records (shallow-water vs pelagic settings, δ13CCarb vs δ13CTOC). The upper Eocene carbon isotope record of the analysed successions matches with the global signal. The overall trend shows a decrease of the δ13CCarb and a contemporary increase of the δ13CTOC. The decoupling of the two curves is consistent with a reduced fractionation effect by primary producers that characterised the interval between the Middle Eocene Climatic Optimum and the onset of the Oi-1 event. However, regional factors superimposed the global signal. In fact, the upper Eocene basinal δ13CTOC record is marked by short-term negative spikes, which possibly represent times of higher productivity triggered by the westward subtropical Eocene Neotethys current entering from the Arabian-Eurasian gateway. On the contrary, the shallow-water record does not display these short-term productivity pulses. A change in the carbonate factory is only recorded at the Eocene-Oligocene transition, marked by a reduction of the larger benthic foraminifera and the spread of seagrass and corals. Moreover, in the shallow-water record of the Santo Spirito Formation, no major carbon isotope shift related to the Oi-1 event is recorded due to the presence of extensive slumps that disrupt the bedding. These slumps are the main evidence of the sea-level drop that occurred concomitantly with the onset of the Antarctica ice-sheet, which caused the deepening of the storm wave base and increased the instability over the entire ramp

Stratigraphical and sedimentological relationships of the Bolognano Formation (Oligocene–Miocene, Majella Mountain, Central Apennines, Italy) revealed by geological mapping and 3D visualizations

The characterization and comprehension of buried reservoirs receive remarkable benefits from detailed studies of outcropping analogues which help to define the architecture of the buried sedimentary units and their petrophysical features. In particular, modern 3D techniques of geological data analysis can better constrain the geological mapping process and reveal the geometry of the sedimentary units with complex lateral and vertical relationships. By means of the 3D Move software, we define the sedimentological and stratigraphical relationships between lithostratigraphic units of the Bolognano Formation, outcropping in the northernmost sector of the Majella Mountain (Central Apennines, Italy). The study area belongs to the Apulian carbonate platform and the Majella Mountain represents the northward outcropping portion of its margin. The sedimentary succession of the Majella Mountain consists of Upper Jurassic to upper Miocene limestone and dolostone deposits. In the investigated area, outcropping deposits mainly belong to the Oligo-Miocene Bolognano Formation characterized by five lithofacies associations and representing a carbonate ramp developed in a warm subtropical depositional environment within the oliaophotic to aphotic zone. The Bolognano Fm. represents, due to its specific hydraulic properties (e.g. porosity and permeability), an outcropping analogue of worldwide common reservoirs (i.e. porous calcarenite deposits of a carbonate ramp formed by benthic foraminifers such as lepidocyclinids, nummulitids, red algae, corals). In the study area, several geological units of the Bolognano Fm. are characterized by abundant hydrocarbon (bitumen) occurrences infilled within the high-porosity of the cross-bedded calcarenites ascribed to the Chattian and Burdigalian interval. The geological field mapping of the area and the visualization of the geological data in a 3D environment show that the unit formed by mid-ramp calcarenites (Lepidocyclina calcarenites 2 unit, Chattian-Burdigalian) increases in thickness towards the NE (basinward) direction as a consequence of sediment shedding from inner ramp. Our study illustrates how the geological mapping and the visualization and analysis of geological data in a 3D environment of the northernmost sector of the Majella Mountain confirms depositional models of the Bolognano Formation and represents a valid tool for the characterization of the lateral stratigraphic relationships within this formation, and hence of its potential hydrocarbon occurrences

Using stable isotopes in deciphering climate changes from travertine deposits. The case of the Lapis Tiburtinus succession (Acque Albule Basin, Tivoli, Central Italy)

Quaternary stable isotope records of marine and lacustrine carbonate deposits as well as speleothems were extensively studied to reconstruct global and regional climatic evolution. This study demonstrates how stable isotope records of travertine provide fundamental information about climate and the consequences of its evolution on groundwater level fluctuations. The deposition of the Lapis Tiburtinus travertine succession occurred during the Late Pleistocene (150–30 ka), coeval with the last activity of the Colli Albani volcanic complex. Two boreholes (Sn1 and Sn2) were drilled into the Acque Albule Basin (23 km E of Rome), crossing the entire Lapis Tiburtinus succession. The Sn1 borehole in the central part of the basin crosscuts a travertine succession of 62.1 m in thickness, while the Sn2 borehole in the southern part of the basin is characterized by a travertine succession 36.3 m in thickness. Carbon and oxygen stable isotope ratios were analysed on 118 samples (59 samples both for Sn1 and Sn2 boreholes) representative of the entire Lapis Tiburtinus travertine succession crossed by the boreholes. Values, measured and correlated in the two drilled boreholes, permitted determination of the sensitivity of the travertine depositional system to glacial and interglacial cycles, unravelling the complex oxygen and carbon cycle dynamic recorded in such sedimentary succession. Moreover, the results obtained correlated with available pollen curves of the Mediterranean area (from the Castiglione crater, 25 km E of Rome). Regional and global oxygen isotope continental and marine curves, calibrated with the stratigraphy of the Acque Albule Basin, and available U/Th dating allow the identification of at least three phases of the last interglacial (Marine Isotope Stage 5-MIS5). The carbon isotope record, compared with CO2 flux reconstructed and associated with the volcanic activity of the Colli Albani volcanic complex, instead shows an influence from groundwater level changes. In particular, positive shifts that occurred during arid phases are associated with a lower humid periods indicate the inhibition of CO2 degassing and increase in pressure, attesting to a rise in groundwater level. In this view, travertine deposits, frequently studied to define the tectonic setting and activity of the area where they develop, can thus also be used as a tool to understand climate changes and groundwater variations apparent in their stable oxygen and carbon isotope signature. groundwater level and increased CO2 degassing, inducing a major fractionation effect on carbon isotopes. Instead, the negative shifts occurring during mor

Geometry and stratigraphic relationships of lower Oligocene coral reefs in Lumignano (Berici Hills, northern Italy)

The Cliffs of Lumignano (Northern Italy) are a renowned climbing area, set on the steep walls of lower Oligocene limestones of the Castelgomberto formation which are made mainly of coral boundstone. Lumignano lies approximately on the south-eastern margin of a Cenozoic carbonate platform known as the Lessini Shelf, but the depositional environment of coral reefs is still debated, and it is unclear whether it was a Caribbean-type carbonate platform with a lagoon and steep slope, or a carbonate ramp with coral reefs on the mid ramp. We produced a geological map of the Lumignano area, in which five lithofacies are distinguished and mapped within the Castelgomberto formation. Their spatial distribution and main sedimentological characters outline that landward of coral reefs, a high-energy environment was present and was shallower than the reefs. Seaward of coral reefs, coralline algae and marlstones with bryozoans occur, while no evidence of a slope made of coral rubble was found. Hence, the detailed geological mapping and the documentation of the stratigraphic relationships between lithofacies provided a valuable contribution to the understanding of depositional environments of the lower Oligocene Lessini Shelf. This work also suggests elements for a better definition of the Castelgomberto formation, which could be split in members or lithofacies that can be mapped at a reasonably large scale (1:10000). The coralline algal lithofacies of the Castelgomberto formation is locally indistinguishable from the analogous facies of the underlying Priabona formation, but the boundary between these two units is always marked by an unconformity, which is easy to identify and may be used for the lithostratigraphic definition of the Castelgomberto formation

Depth diagnostic mesophotic assemblages in the Northern Red Sea (Saudi Arabia) as analog to the Cenozoic fossil record

[eng] While mesophotic assemblages in the Gulf of Aqaba have been described in some detail, in the Red Sea proper, data are rare. Here we present a first report on a detached carbonate platform fragment from the Northern Red Sea off Al Wajh that stretches over a water depth range of 25 to 130 m. The assemblages observed comprise depthtypical large benthic foraminifers, crustose coralline algae, and mesophotic scleractinian corals (e.g., Leptoseris spp.).Encrusting bryozoans and foraminifers are abundant. A soft sediment cover in the deeper areas indicates the absence of strong currents. Radiocarbon ages confirm that this community is currently thriving. This example resembles the previously known occurrences of mesophotic reefs in the Gulf of Aqaba with respect to assemblage despite different oceanographic conditions. At the same time, it reminds of Cenozoic, in particular pre-Upper Miocene (i.e., before 8.5 million years ago), coral-associated assemblages, when coral bioherms preferentially occurred in mesophotic rather than euphotic settings. The present study thus contributes to improving the interpretation of those fossil bioherms with respect to their ecosystem dynamics and environmentalsignificance