Antonietta Cherchi

Benthic foraminifera as bio-indicators of trace element pollution in the heavily contaminated Santa Gilla lagoon (Cagliari, Italy)

In order to assess the response of benthic foraminifera to trace element pollution, a study of benthic foraminiferal assemblages was carried out into sediment samples collected from the Santa Gilla lagoon (Sardinia, Italy). The lagoon has been contaminated by industrial waste, mainly trace elements, as well as by agricultural and domestic effluent. The analysis of surficial sediment shows enrichment in trace elements, including Cr, Cu, Hg, Ni, Pb and Zn. Biotic and abiotic data, analyzed with multivariate techniques of statistical analysis, reveal a distinct separation of both the highly polluted and less polluted sampling sites. The innermost part of the lagoon, comprising the industrial complex at Macchiareddu, is exposed to a high load of trace elements which are probably enhanced by their accumulation in the finer sediment fraction. This area reveals lower diversity and higher percentages of abnormalities when compared to the outermost part of the lagoon.

Chlorozoan versus foramol lithofacies in Upper Cretaceous rudist limestones

Abstract The study of Upper Cretaceous limestones of the Nurra region (northwestern Sardinia, Italy) that crop out with open shelf, rudist-rich deposits has shown that during the early Senonian (Coniacian-Santonian interval) sediments characterized by assemblages dominated by molluscs, with variable amounts of red algae, bryozoa and echinoids, replaced sediments including hermatypic corals, green algae and variable amounts of non-skeletal grains. These latter components were largely dominant in the previous carbonate-shelf contexts of the Nurra during Jurassic-early Cretaceous times, becoming less numerous until they disappeared in the transgressive deposits that followed the tectonically induced middle Cretaceous emersion phase. A rhodalgal association (typical of anomalous tropical areas or transitional ones) has been recognized in the replacing limestones that may be more generically considered foramol-type deposits. This seems to document conditions of stress in the waters impinging on the Nurra carbonate platform during the Coniacian-Santonian transition. The observation that, in the late Cretaceous, a similar evolutionary trend seems to have characterized many shallow neritic successions, from many different areas, leads us to hypothesize more general causes of stress (e.g. induced upwellings on the marginal sectors of the shelves, increased oceanic overturns and hyperproductivity due to terrestrial runoff on post-emersive transgressed substrata). Peculiar oceanic conditions were able to create depositional contexts that were considerably changed with respect to the previous ones, such that the more opportunistic forms of the foramol assemblages flourished. The change in dominant assemblages resulted in a different organization of the sediment as a response to the different producing communities. The resulting temperate-type carbonate shelves were characterized by a low growth potentiality essentially due to a higher dispersion rate and this could have facilitated their drowning.

Miocene carbonate factories in the syn-rift Sardinia Graben Subbasins (Italy)

SummaryMiocene syn-rift carbonate production areas are exposed in south-eastern Sardinia (Italy) along the eastern side of the Plio-Pleistocene Campidano Graben. Here the downfaulted margins of the Oligo-Miocene Sardinia rift-basin crop out with a complex alignment of smaller subbasins. Carbonate factories developed during the Aquitanian times in these tectonically controlled small depositional subbasins, where terrigenous input might be high due to the erosion of the uplifted pre-Neogene substrata. Terrigenous deposits generally acted as passive substratum for pioneer communities of rhodalgal-type (red algae, ostreids, bryozoans) and locally evolved into coral-dominated assemblages.Carbonate production areas occur on tilted, uplifted blocks as well as along basement margins. These have varying organic communities and facies characteristics strongly dependent on different environmental conditions. In footwall areas, devoid of (or with a very reduced) terrigenous supply, open foramol carbonate factories occur with aggradational-progradational stratigraphic geometries. The resulting pure calcareous successions are organized in sequences, bounded by tectonically driven discontinuity surfaces.In sectors close to the hinterland area, with a higher freshwater input and a consequent significant clastic input, coral-dominated assemblages grew during long periods of quiescence between flash floods. Repeated coral-rich communities developed on thick wedges of terrigenous debris.Carbonate facies composition and distribution were mainly controlled by local syn-sedimentary tectonics and eustasy as well as by climate. However, although the inception of the carbonate factories was presumably not synchronous, their growth represented the response to a relative regional sea level rise subsequent to episodes of significant clastic supply: the expression of an early syn-rift stage.During the Burdigalian (N6 zone) a hemipelagic cover uniformly sealed the neritic successions. This basin wide drowning event appears to correspond to the transgressive system tract of the TB2.1 cycle ofHaqet al. (1987) but it can also be interpreted as the expression of an evolved syn-rift stage passing to late syn-rift and quiescence stages.Beneath the hemipelagic cover in some areas, ?late Aquitanian-early Burdigalian deep erosive surfaces, terrigenous clastics and paleosoils have been recognized. These suggest a relative sea level fall and may relate to the global sea level drop at the TB1-TB2 boundary (seeHaqet al., 1987) or to diacronous uplift of different fault blocks.

Interpretation of coastal sediment quality based on trace metal and PAH analysis, benthic foraminifera, and toxicity tests (Sardinia, Western Mediterranean)

An integrated approach for the assessment of coastal sediment quality was utilised in three areas of Sardinia (Western Mediterranean, Italy). Sediments were analysed for trace metals and polycyclic aromatic hydrocarbons (PAHs), while benthic foraminifera were used as bioindicators. Furthermore, the embryo-toxicity test was used to provide ecologically relevant information using rapid and cost-effective screening tools. The aim was to evaluate the usefulness of coupling different analytical tools. The results revealed the presence of polluted sediments in areas exposed to petrochemical industries, smelters or military settlements. However, while foraminifera have presented similar indications for chemical analysis of contamination levels in the different areas, the toxicity test exhibited a poor relationship with the contaminants measured individually. The results raise questions concerning the bioavailability of contaminants released by sediments in the water column. Overall, the toxicity rate was significant in many samples in comparison with other sites studied in other Mediterranean regions.

Heavy metal accumulation in surface sediments at the port of Cagliari (Sardinia, western Mediterranean): Environmental assessment using sequential extractions and benthic foraminifera

Superficial sediments were taken at the port of Cagliari (Sardinia, Italy), which includes the oil terminal of one of the largest oil refineries in the Mediterranean. Significant trace metal concentrations were found in the whole port area. Sequential extraction of metals from the different sediment fractions (BCR method) showed a higher risk of remobilisation for Cd, which is mostly bound to the exchangeable fraction. Foraminiferal density and richness of species were variable across the study area. The living assemblages were characterized by low diversity in samples collected close to the port areas. Ammonia tepida and bolivinids, which were positively correlated with concentrations of heavy metals and organic matter content, appeared to show tolerance to the environmental disturbance. The sampling sites characterized by the highest values of biotic indices were located far from the port areas and present an epiphytic and epifaunal biocoenosis.

Revision of the holotype of Lithocodium aggregatum Elliott, 1956 (Lower Cretaceous, Iraq): new interpretation as sponge–calcimicrobe consortium

The encrusting microorganism Lithocodium (type species: Lithocodium aggregatum Elliott), widespread in Late Triassic–Middle Cretaceous shallow-marine carbonates of the Tethys realm, was interpreted in the past as a codiacean green alga, a lituolid foraminifer, calcimicrobial colonies, ulotrichalean green algae, or chambers of boring sponges. A re-study of the type material of L. aggregatum (in the sense of Elliott), stored in the British Museum (Natural History), revealed that this “species” has to be regarded as a calcimicrobial crust, infested by boring sponges (ichnotaxon Entobia).

Rudist-bearing rhodalgal facies in the post-Turonian recovery of peri-Tethyan carbonate systems: a case history from the Nurra region (northwestern Sardinia, Italy)

ABSTRACT The presence of non-geniculate coralline red algae and bryozoans (rhodalgal lithofacies) in association with rudists has been mentioned only rarely in the literature. Nevertheless, because of the significance of rhodalgal facies in the characterization of shallow-water carbonate factories, a correct interpretation of the related ecological factors may improve the palaeo-environmental reconstruction of some rudist-bearing carbonate depositional systems. Uppermost Coniacian-Santonian rhodolith-rich rudist-bearing carbonate successions in the Nurra region (northwestern Sardinia, Italy) record several discrete depositional settings, from autochthonous shallow-water mobile skeletal deposits including coralline algal fragments and rhodoliths, to re-mobilized deposits rich in skeletal components with rhodoliths. The rudist-bearing rhodalgal limestone studied is part of an uppermost Turonian-Campanian transgressive sequence that covers a tectonically-modelled Lower Cretaceous substrate. The recovery of the Upper Cretaceous carbonate factories followed an interval of time during which the Lower Cretaceous carbonate systems, dominated by chlorozoan assemblages and non-skeletal grains, had experienced “Mid-Cretaceous” worldwide crises presumed to have been caused by global climatic/oceanographic perturbations. In particular, Early-Middle Turonian times, characterized by the hyper-greenhouse conditions then prevailing, witnessed a significant reduction or even complete demise of highly productive carbonate factories. In carbonate settings, biotic assemblages grew in mesotrophic/eutrophic environments. Cyanobacterial consortia, with variable contributions from rudists, largely prevailed in shallow-water domains. Thus far, the latest Turonian-Coniacian recovery of Sardinian carbonate factories with “impoverished chlorozoan assemblages” might be considered as an indication of ameliorated environmental conditions. However, ecological constraints did not allow the tropical “chlorozoan assemblages” to thrive in the Late Cretaceous low-latitudinal carbonate shelves of Sardinia. A Santonian shift toward foramol/rhodalgal depositional systems occurred with sciaphile- (shadow preferring), and mesotrophic-adapted (“rudist-bearing rhodalgal”) assemblages flourishing in the new shallow-water domains. In Santonian times relatively cool and mesotrophic to eutrophic conditions are presumed to have become dominant in the water mass impinging on the marginal sectors of the shelf or distal ramp of the Nurra carbonate system. Deterioration in the quality of water presumably caused the demise of large sectors of the Nurra carbonate factory, which underwent local drowning episodes controlled by tectonic activity.

Remarks on Spiraloconulus giganteus Cherchi & Schroeder, 1982 and Limognella dufaurei Pelissié & Peybernès, 1982 (Foraminifera, Lituolidae)

Abstract The lituolid foraminifera Limognella dufaurei Pelisssie & Peybernes , 1982 and Spiraloconulus giganteus Cherchi & Schroeder , 1982 are identical and published at the same time. Therefore we decide that S. giganteus should be the usual name of this taxon.

BORING SPONGES (ICHNOGENUS ENTOBIA ) IN MESOZOIC LITHOCODIUM CALCIMICROBIAL CRUSTS

Globular cavities in calcimicrobial Lithocodium crusts are interpreted as trace fossils of boring sponges belonging to the ichnogenus Entobia . Two informal groups can be differentiated: a Norian-Rhaetian group from Tabas area(NE Iran) and Adnet (near Salzburg, Austria), characterized by large chambers and broad bifurcating apertural canals, and a second group from the Aptian of central Italy presenting smaller chambers and canals. The distal ends of these canals are closed by alveolar structures, preventing water circulation and leading to the death of the sponge.

Praedictyorbitolina busnardoi n. sp. (Foraminiferida) et évolution de la lignéePraedictyorbitolina — Dictyorbitolina (Hauterivien supérieur — Barrémien basal)

KurzfassungDie Vertreter der Orbitoliniden-GattungenPraedictyorbitolinaSchroeder, Clavel &Charollais undDictyorbitolinaCherchi &Schroeder gehören einer einzigen, vom oberen Hauterive bis in das basale Barrême reichenden phylogenetischen Reihe an, die aus folgenden Arten zusammengesetzt ist (in stratigraphischer Reihenfolge):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais undDictyorbitolina ichnusaeCherchi &Schroeder. Die Aufstellung dieser Linie gründet sich — unter Berücksichtigung der stratigraphischen Position der einzelnen Arten — vor allem auf drei Entwicklungstendenzen: (1) Größenzunahme der Gehäuse und Veränderung der äußeren Form, (2) Verlagerung des Embryos und Komplizierung seiner Struktur und (3) Entwicklung des Septulen-Systems innerhalb der Marginalzone.-Praedictyorbitolina busnardoi n. sp. wird ausführlich beschrieben.SummaryThe representatives of the orbitolinid generaPraedictyorbitolinaSchroeder, Clavel &Charollais andDictyorbitolinaCherchi &Schroeder belong to a monophyletic lineage ranging from the late Hauterivian to the basal Barremian and comprising the following species (in stratigraphic order):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais andDictyorbitolina ichnusaeCherchi &Schroeder. Considering the stratigraphic range of the different species, the establishment of this lineage is based on three evolutionary trends: (1) increase of the size of the tests and change of their morphology, (2) shift of the embryo and development of a subepidermic cellular layer within the deuteroconch, and (3) evolution of the network of septula within the marginal zone.-Praedictyorbitolina busnardoi n. sp. is described in detail.RésuméLes représentants des genres d’OrbitolinidésPraedictyorbitolinaSchroeder, Clavel &Charollais etDictyorbitolinaCherchi &Schroeder appartiennent à une seule lignée phylétique d’âge Hauterivien supérieur — Barrémien basai, qui comprend les espèces suivantes (par ordre stratigraphique):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais etDictyorbitolina ichnusaeCherchi &Schroeder. L’établissement de cette lignée, examinée dans le cadre de sa répartition stratigraphique, se base sur trois tendances évolutives: (1) agrandissement du test et changement de leur forme extérieure, (2) déplacement de l’embryon et complication de sa structure, et (3) évolution du système de cloisonnettes dans la zone marginale.-Praedictyorbitolina busnardoi n. sp. est décrite en détail.