Bollettino SPI Vol. 59 (1) - OPEN ACCESS!
Paleobiology in the Mediterranean
Published in June 2020
Stefano Dominici & Daniele Scarponi
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- Azzarone M., Pellegrini C., Barbieri G., Rossi V., Gamberi F., Trincardi F. & Scarponi D. (2020)
Linking benthic fauna and seismic facies to improve stratigraphic reconstructions: the case of the Mid-Adriatic Deep since the late glacial period (Central Adriatic Sea)
Direct observations from the geologic record are commonly used in conjunction with indirect seismic inferences to detail environmental settings and stratal architecture of sedimentary successions. However, examples of integration between seismic and macrobenthic insights are scarce and limited to the use of such a group as an auxiliary to other proxies. We investigated mollusc and ostracod assemblages along an onshore-offshore transect that intersects the C2 clinothem (15.6 – 14.4 ka BP) and the overlying transgressive deposits that recorded the last phase of progradation and abandonment of the Po River Lowstand Wedge (PRLW). We applied multivariate analyses to benthic data to assess the extent to which mollusc and ostracod assemblages can improve both the resolution of seismic-derived depositional environments and the sequence stratigraphic architecture of targeted sedimentary succession. Along the onshore-offshore transect, seismic reflection geometries correspond with three broad sedimentary environments: High Amplitude Continuous reflections (HAC) are interpreted as delta plain/subaqueous shelves, High Amplitude Continuous Wavy Dipping reflections (HACWDip) as prodeltas and Low Amplitude Continuous reflections (LAC) are associated to distal basin settings. The integration of quantitative palaeoecologic trends with seismicderived depositional environments allowed us to subdivide the HAC facies into a proximal (core LSD-26) and distal (cores LSD-27 and -28) area. The proximal HAC facies, in particular, encompasses lower delta plain semi-barred settings with vegetated substrates that upcore pass to nearshore settings. The distal HAC facies is distinguished by clusters that suggest ecological mixing due to strong bioturbation and wave-aided hyperpycnal flows in offshore transition/inner shelf settings. The paucity of benthic fauna for the geophysical units HACWDip (core LSD-05) and LAC (core LSD-04) hampered a complete reconstruction of the palaeoenvironmental dynamics. However, both benthic groups support a seismically derived interpretation of shelf and basinal settings, respectively, and both were subjected to high sedimentation rates. Moreover, integration of mollusc and ostracod multivariate-derived trends with grain-size data across the onshore-offshore transect reveals distinctive stratal stacking patterns that are useful in constraining the position of the Maximum Regressive Surface that marks the abandonment of the PRLW in the Central Adriatic Sea.
- Cau S., Roveri M. & Taviani M. (2020)
Palaeobiology of Pliocene-Pleistocene shallow-water biocalcarenites (Northern Apennines, Italy) and their relationship with coeval sapropels
The interplay between carbonate and siliciclastic sediment production in shallow marine environments may result in the development of mixed depositional systems showing a cyclical arrangement of sedimentary facies. The palaeoenvironmental record associated with these cyclical facies changes is not always univocally correlated with eustatic oscillations, suggesting that other forcing processes have played an additional role. The Castell’Arquato Basin (CAB: Pliocene-Pleistocene, Northern Apennines, Italy) offers the opportunity to integrate the study of small and large-scale stratigraphic architectures with that of shell beds in shelf to deep-water successions. The analysis of diversity trends allows a first insight into the structure of CAB benthic communities associated with minor and major biocalcarenites. Biofacies types are identified through a multivariate analysis of a large quantitative database including shells of all molluscs, serpulids and brachiopods. The study shows that these bio-detrital deposits and their bracketing marine mudstones developed at inner-shelf settings and that taphonomic feedback played an important role in the stratigraphic distribution of biofacies. Benthic communities from shelly bottoms depend on the winnowing of fines by bottom currents, a factor that is not related to water depth in a simple manner. Heterogeneity of the seafloor is associated to high-diversity of communities of topset strata of major biocalcarenites. Communities living in siliciclastic bottoms depend on factors that are largely depth-dependant. The study confirms the correlation of major biocalcarenite cycles with coeval deep-water sapropels, supporting the hypothesis of a more effective role of high-amplitude climatic changes driven by orbital forcing. This affects the source-to-sink dynamics of the whole basin and the biological structuring processes of shelfal depositional settings and related ecosystems.
- Bracchi V.A., Bulegato S. & Basso D. (2020)
Palaeoecology of the Pinna nobilis biofacies along the Stirone River (Early Pleistocene, Northern Italy)
The Stirone riverbanks (Northern Italy) host a famous Pliocene-Pleistocene marine succession, interpreted as a mosaic of shallow marine palaeoenvironments. One of the most remarkable occurrences is fossil Pinnidae in life position, here identified as Pinna nobilis Linnaeus, 1758. It is an endemic Mediterranean bivalve, commonly reported from within Posidonia or Cymodocea meadows, or more rarely from other unvegetated shallow sedimentary bottoms, and even under hypoxic conditions. Few reports are found in the fossil record because of the low preservation potential of this large, semi-infaunal, fragile nacreous bivalve. Although already mentioned in the literature, no detailed palaeoecological investigation has been conducted on the mollusc association of the Pinnidae biofacies outcropping at the Stirone River. Four replicas of bulk sediment (2 l each) have been collected from the Pinnidae biofacies, in order to conduct a palaeontological and palaeoecological analysis, aimed at defining the composition and structure of the mollusc fossil assemblage, for the reconstruction of the associated palaeoenvironmental setting. The associated sediment, rich in tiny plant frustules, is a poorly sorted fine to very fine sand, with a bimodal distribution of sand and mud together with a coarse bioclastic fraction. The mollusc fossil assemblage is formed by a mixing of species which are related to both infralittoral vegetated and unvegetated bottoms, together with species with an affinity for both mud and coarse detritic sediments. One of the most common and abundant species is Corbula gibba, a bivalve considered of high ecological importance due to its opportunistic nature and reported as tolerant to elevated organic mud input, bottom hypoxia and unstable sedimentation rate. The fossil assemblage and the associated sediment point to a likely colonisation by Cymodocea, although the occurrence of mosaic facies of unvegetated and vegetated bottoms, with both Cymodocea and sparse Posidonia, cannot be ruled out. The bottom was strictly infralittoral (shallower than 15 m of water depth), with pulses of mud by fluvial transport, supporting the mixing of infralittoral and mud-loving deeper species, and the ubiquitous occurrence of C. gibba.
- Dominici S., Benvenuti M., Garilli V., Uchman A., Pollina F. & David A. (2020)
Pliocene-Pleistocene stratigraphic paleobiology at Altavilla Milicia (Palermo, Sicily): tectonic, climatic and eustatic forcing
The integration of sedimentary facies analysis, ichnology and benthic mollusc quantitative paleoecology allowed interpretation of factors that have controlled the deposition of the alluvial to marine succession outcropping in Northwestern Sicily (Southern Italy) at Altavilla Milicia, near Palermo (Imerese Basin). Two main marine units are recognised, labelled CNM and ALT, separated by an angular unconformity and formed by elementary depositional sequences (CNM1-4, ALT1-5). The succession was subdivided by means of calcareous nannoplankton biostratigraphy into upper Pliocene (Piacenzian: CNM1-4 and ALT1-4) and lower Pleistocene (Gelasian, ALT4- 5), covering the onset of the Quaternary glaciation. The main asset of the succession is driven by tectonic compression and accommodation by transpressional faults, a regime that led to a change in the direction of fluvial sediment delivery, from axial (mid-Piacenzian: CNM), to transverse with respect to the basin elongation (upper Piacenzian-Gelasian: ALT). High-frequency eustatic changes drove the formation of elementary depositional sequences, the building blocks of CNM and ALT. During the late Piacenzian, a phase of gradual passage from the mid-Piacenzian warm period to the Quaternary glaciation, bioclastic production was still high, characterising the maximum flooding intervals of the two composite depositional sequences CNM and ALT. Mixed carbonate-siliciclastic lithosomes of both CNM and ALT show a good correlation with shallow marine shell-rich detrital carbonates of Northern and Southern Italy and with Mediterranean deep-water sapropel clusters, suggesting common climatic forcing. Some tropical species thought to disappear from the Mediterranean at around 3.0 Ma, including Pecten bosniasckii, Macrochlamys latissima, Spondylus crassicosta, Lucina orbicularis, Isognomon maxillatus, Crassatina concentrica, Gastrana lacunosa, Callista italica, Circomphalus foliaceolamellosus and Persististrombus coronatus, are present in the upper Piacenzian of Sicily (top of the MN16a Zone and the MN16b/17 Zone of calcareous nannofossil biostratigraphy). More data are needed to reconstruct the geographic dimension in the disappearance of the Mediterranean Pliocene macrobenthos with tropical affinities.