Types of mixing and heterogeneities in siliciclastic-carbonate sediments

Mixed siliciclastic-carbonate deposits consist of a suite of different types of mixing between the two components, from bed (core-plug) to stratigraphic (seismic) scales, producing a high vertical and lateral lithological variability. Mixed deposits results from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and/or spatial factors. Although mixed deposits are very diffuse in the geological record, studies about these deposits are scrappy and not well encoded. Accordingly, mixed deposits represent a labyrinth for researchers who want to investigate them for the first time. In this paper, different types of mixing (compositional versus strata) controlled by different allocyclic (e.g. sea-level, climate) and/or autocyclic (e.g. depositional processes) factors that operate at different scale are documented. Mixing is recognized and described at three main scales of observation: bed/core-plug scale; lithofacies/well-log scale; and stratigraphic/seismic scale. (i) Compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time. This type of mixing is observable at lamina to bed scale, locally producing depositional structures diagnostic for particular depositional environments. (ii) Strata mixing results from the alternation of the two heterolithic fraction in time. This type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes, climatic variations and/or relative sea-level changes. A correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing (i) physical processes that control the sedimentation, (ii) environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms, and (iii) internal heterogeneity of the resulting sedimentary deposit. Furthermore, the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic-carbonate systems (e.g., porosity, permeability) and to reconstruct predictive 3D models for the related reservoirs. The correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation

Il nuovo Foglio Geologico 438 “Bari” in scala 1:50.000. Un importante contributo per la conoscenza geologica dell’area metropolitana di Bari

I risultati del rilevamento geologico del Foglio 438 “Bari” in scala 1:50.000 effettuato nell’ambito del progetto CARG (Cartografia Geologica) mostrano numerose differenze rispetto a quanto riportato nella Cartografia Ufficiale in scala 1:100.000, che rappresenta tuttora la cartografia di riferimento. Le differenze rilevate, o comunque le ulteriori informazioni ottenute dai nuovi studi, sono risultate molto significative soprattutto in corrispondenza dell’area metropolitana di Bari recentemente soggette ad intensa urbanizzazione ed espansione. Tenuto conto dei tempi necessari per poter divulgare tali dati, si è ritenuto importante, in occasione del Convegno sulla “Geologia urbana di Bari ed area metropolitana”, presentare una carta in scala 1:25.000 del territorio metropolitano barese, dove emergessero tutte le novità dei nuovi rilevamenti, al fine di poter fornire uno strumento utile a tutte le figure che operano sul territorio quotidianamente e che necessitano avere dati aggiornati

Tidal signatures in Neogene to Quaternary mixed deposits of southern Italy straits and bays

Some of the Neogene to Quaternary sedimentary successions cropping out in the southern Italy orogenic belt exhibit distinct stratigraphic intervals of mixed, silici-bioclastic arenites. These deposits represent bay- and strait-fill successions that accumulated during tectonically-driven, rapid transgressions in peripheral marine basins of the central Mediterranean, experiencing microtidal conditions similar to those presently existing in the Mediterranean Sea. The Upper Miocene to Middle Pleistocene successions of Basilicata, Calabria and NE Sicily, show laterallyaccreted, cross-strata of mixed composition, with the siliciclastic fraction derived from either sedimentary or metamorphic rocks and the bioclastic fraction produced by an in situ or near situ heterozoan factory. Tidal cyclicity of semi-diurnal and diurnal to monthly and yearly periodicities has been detected in the studied deposits, where tidal bundling is revealed by the rhythmic alternation of siliciclastic and bioclastic set of laminae, repeated according to different cycles. This rhythmic signature appears to be more evident where randomly-occurring processes, such as waves, storms and currents, were mitigated by engulfed or strait palaeo-settings. Palaeo-bays preserved short-term tidal cycles in shoreface to offshore-transition mixed deposits because hydrodynamically isolated from open marine conditions and therefore subjected to tidal influence only during fair-weather periods. On the contrary, palaeo-straits recorded tidal cyclicities of longer duration in deeper mixed deposits subjected to steady tidal currents

Depositi carbonatici infrapleistocenici di tipo foramol in sistemi di scarpata (Salento – Italia meridionale)

Along the eastern Salento coast (Southern Italy), Cretaceous to Quaternary carbonates crop out on a 100 m high escarpment that connects a wide and relatively flat area to the Otranto Strait (Ionian Sea). Along the escarpment, faulted and tilted Cretaceous and Eocene limestones record deposition in shallow-marine and marginal carbonate environments. Younger carbonates disconformably overlie this substratum and they formed when the region was partially submerged. Accordingly, Priabonian to Messinian carbonates which crop out along the escarpment were interpreted as slope deposits linked to reef systems developed on the margin of the top area, while lower Pleistocene carbonates cropping out at the base of the same escarpment were considered coastal in origin and formed during the uplift of the region. Stratigraphic and sedimentologic studies carried out on these lower Pleistocene carbonates demonstrate that also these deposits should be considered as slope deposits. The studied carbonates are foramol-type ones and discontinuously crop out along the lower part of the escarpment. They show a variable thickness (from a few meters up to several tens) and often exhibit a fan morphology; they correspond to small isolated bodies (up to a few km2 wide) developed in some indentations of the escarpment, and are composed of coarse skeletal grains mainly deposited via slumpings or grain flows. Successions are characterized by long clinobeds cut by slump scars downward passing to gullies; backsets, slumps and chaotic deposits fill these erosional features. Clinobeds are alternatively made up of molechfor and rodhalgal facies which respectively record resedimentation by grain flows of shallow marine carbonates developed on top of the region and along-slope carbonate production. Depositional systems correspond to small shallow-marine aprons whose discontinuous distribution along the escarpment (inside indentations) should be considered an original feature. The idea that these deposits record the Sicilian sea-level along the escarpment should be abandoned as they are not coastal deposits. The studied deposits should be correlated to the Calcarenite di Gravina Formation which in other areas of the Apulian Foreland (which the Salento region belongs to) are considered as the deposits linked to the subsidence induced by the estward migration of the south- Apennines orogenic system. The Quaternary uplift of the Salento region should be begun after the deposition of the studied slope deposits, as indicated also by a series of middle-upper Pleistocene marine terraces which start at heights higher than those ones of the studied deposits

Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)

We investigate the effect of external pressure on magnetic order in undoped LnFeAsO (Ln = La, Ce, Pr, La) by using muon-spin relaxation measurements and ab-initio calculations. Both magnetic transition temperature $T_m$ and Fe magnetic moment decrease with external pressure. The effect is observed to be lanthanide dependent with the strongest response for Ln = La and the weakest for Ln = Sm. The trend is qualitatively in agreement with our DFT calculations. The same calculations allow us to assign a value of 0.68(2) $\mu_B$ to the Fe moment, obtained from an accurate determination of the muon sites. Our data further show that the magnetic lanthanide order transitions do not follow the simple trend of Fe, possibly as a consequence of the different $f$-electron overlap.Comment: 16 pages, 11 figure