Marco Brandano

Aphotic zone carbonate production on a Miocene ramp, Central Apennines, Italy

The lower Miocene Latium–Abruzzi platform was a low-angle ramp that developed under tropical-to-subtropical conditions, but was dominated by bryomol and rhodalgal sediment associations. The Aquitanian to Serravallian sequence described here paraconformably overlies the Cretaceous limestones. It consists of a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Based on facies analysis and on the light dependence of biotic associations, the ramp is divided into three parts: an inner ramp, a middle ramp and an outer ramp. The inner ramp facies are represented by a few metres of coral framestone, rhodolith floatstone–rudstone and balanid macroids floatstone without wave-related structures. The middle ramp consists of structureless bioclastic grainstone to packstone, floatstone and rudstone with rhodoliths and larger foraminifera. The outer ramp facies—proximal sector—are composed of crudely stratified bryozoan-dominated packstone to floatstone which extend over the whole platform. The outer ramp facies—intermediate sector—are represented by wackestone, packstone and rarely grainstone with foraminifera and echinoid fragments. The final depositional profile of the ramp was strongly influenced by the main organisms producing sediment. During the lowstand, the resulting profile is a ramp type. During the transgressive phase, the rapid spreading of the outer ramp facies belt, as a consequence of the enhanced productivity of the light-independent biota, is believed to be promoted by a change from oligotrophic to eutrophic conditions. Climate and/or tectonics are presumed to have played an important role in continental runoff and then in the nutrients delivery. During the highstand phase, the system returns to rates of production uniform throughout the platform. The high rates of carbonate production occurring in the aphotic zone are quite unusual in tropical settings and represent a provocative trend in apparent contrast with the common idea about the locus of the most significant carbonate production, as derived from the ‘‘tropical model’’. The example described here shows that carbonate production and accumulation below the photic zone might be higher than in the shallow euphotic zone even in tropical conditions. D 2003 Elsevier Science B.V. All rights reserved.

A DEPOSITIONAL MODEL AND PALEOECOLOGICAL RECONSTRUCTION OF THE LOWER TORTONIAN DISTALLY STEEPENED RAMP OF MENORCA (BALEARIC ISLANDS, SPAIN)

Abstract In carbonate depositional environments, sediment is mostly produced by different groups of organisms. Ecological parameters, thus, play a major role controlling carbonate production. In the present work, carbonate-producing biota, especially foraminifers, are studied to construct a depositional model and paleoecological interpretation of the lower Tortonian distally steepened ramp of Menorca (Balearic Islands, Spain). This carbonate platform corresponds to a highstand systems track prograding and aggrading over a Paleozoic, Mesozoic, and, locally, lower Tertiary basement. Outcrops are excellently exposed in the southern part of the island. Five facies associations are observed, which, in downdip direction, correspond to inner ramp, middle ramp, ramp slope, toe of the slope, and outer ramp. Samples have been studied using point counting of 102 thin sections. Six foraminiferal assemblages have been distinguished. Eight microfacies are identified (IR.1, IR.2, MR, URS, LRS, TS.1, TS.2, and OR), based on the abundance and ecological significance of the foraminifers (large benthic foraminifers, epiphytics, low-oxygen indicators, and planktonics) and other carbonate-producing organisms (echinoids, mollusks, barnacles, bryozoans, serpulids, coral genus Porites, and green and red algae). Seagrass meadows in the inner ramp correspond to the euphotic carbonate factory, whereas red algae and large benthic foraminifers dominate the oligophotic carbonate factory in the middle ramp and upper ramp slope. Microfacies composition verified intense sediment-transport processes from inner and middle ramp down to lower ramp slope, toe of the slope, and outer ramp. Finally, microfacies analysis also indicates that carbonate-production took place in warm-water conditions, in oligotrophic-to-mesotrophic waters.

Mixed carbonate-siliclastic sediments and benthic foraminiferal assemblages from Posidonia oceanica seagrass meadows of the central Tyrrhenian continental shelf (Latium, Italy)

Sedimentological and micropaleontological characterisation of bottom sediments from two Latium continental platform areas (central Tyrrhenian Sea) was carried out. The two studied areas are Santa Marinella in northern Latium and Ponza Island in southern Latium (Pontine Archipelago), characterised by the presence of Posidonia oceanica seagrass, but with different sediment inputs. In the Santa Marinella area, where seagrass ends at 15 m water depth, there are both siliciclastic sediments from fluvial run-off and carbonate lithoclasts originated by coastal erosion. In the Pontine Archipelago, in which P. oceanica meadows end at 35-40 mwd, terrigenous clasts originate only from coastal erosion and, consequently, carbonate production prevails. On the whole, grain size analysis shows a strong predominance of sandy fraction, whereas mud and gravel are subordinate. The very low frequencies of muddy fraction can be attributable to re-suspension processes and the lack of aragonitic components that produce mud-sized particles. The better sorting of Santa Marinella seagrass substrate with respect to Ponza Island is related to the origin of terrigenous sediments, which are mainly provided by rivers and so are previously sorted. Facies analysis was performed using component analyses, grain size percentage, sorting and carbonate content, complemented with the observations obtained from artificially-hardened sediments and, finally, tested with a Q-mode cluster analysis. Consequently, 4 sedimentary facies have been recognised. Facies F1, limited to the Santa Marinella area (7.5-13.5 mwd), is characterised by sand-sized wellsorted sediments, and dominated by the terrigenous fractions. Facies F2 represents the shallowest seagrass environment (5-7 mwd), and it is restricted to the Ponza area. In this environment the sedimentation is still dominated by terrigenous components, while the carbonate sediment contribution is due principally to red algae. Facies F3 has the widest water depth interval (8-34 mwd), and principally occurs in the Ponza site, while only two samples are from the Santa Marinella. The terrigenous fraction is conspicuous, however there is an increase of carbonate sediment produced mainly by the epiphytes (foraminifera, bryozoans) and, subordinately, by benthic organisms (foraminifera, molluscs). Facies F4, occurring in the Ponza site (17-29 mwd), is the most carbonate rich facies with a carbonate sediment produced by epiphytic (foraminifera, bryozoans, serpulids, red algae) as well as benthic (foraminifera, red algae, molluscs) biota. Q-mode cluster analysis performed on the most abundant benthic foraminiferal species led to the identification of 4 assemblages, dominated by epiphytic foraminifera. The A1 assemblage was found only in the Ponza site (5-12 mwd) and is dominated by Lobatula lobatula, Peneroplis pertusus and Miliolinella subrotunda. The A2 assemblage (10-34.5 mwd), characterised by L. lobatula and Rosalina bradyi, is mainly limited to Ponza Island, with only one sample from Santa Marinella. The B1 (7.5-9 mwd) and B2 (8-13.5 mwd) assemblages were found only in the Santa Marinella area and are dominated by L. lobatula, R. bradyi and Conorbella hexacamerata and by Asterigerinata mamilla and R. bradyi, respectively. The calculated diversity indices (α-Fisher and Shannon index) are very similar in both areas, whereas the dominance percentage is higher in the Santa Marinella site. The lack of the symbiont-bearing foraminifer P. pertusus in the Santa Marinella samples may be linked to less favourable environmental conditions. In this area, the prevalent siliciclastic sedimentation and the water turbidity, which decreases the light penetration, are the limiting factors also for the seagrass growth. The comparison between the foraminiferal assemblages of two areas may be used to estimate the health of present-day and fossil seagrass.

Rhodolith-rich lithofacies of the Porto Badisco Calcarenites(upper Chattian, Salento, southern Italy)

This study describes the rhodolith-rich lithofacies of the Porto Badisco Calcarenites, an upper Chattian rhodalgal/larger foraminiferaldominated unit exposed in the southern part of the Apulia Carbonate Platform (Salento Peninsula, Italy). The lensoid rhodolith-rich lithosome at the base of the studied section is made of rhodolith rudstone and floatstone which infill a channel-like depression inherited from the substrate. Changes in the texture of the rhodolith facies and in the inner structure of the rhodoliths reflect variations in submarine current velocity across the section of the channel. Inherited topography controlled both the locus and the mode of rhodolith accumulation. The rhodolith lithosome is bounded by a flat surface above which rhodoliths are notably absent and beds are tabular. This implies that rhodolith accumulation ended as soon as substrate topography was completely levelled off. The taxonomic composition of the red algal and larger foraminiferal assemblages suggests that the rhodolith-rich unit deposited in the oligophotic zone. The abundance of tropical genera among the coralline algae (Lithoporella and Sporolithon) and the high diversity of larger foraminiferal assemblages indicate that the deposition of the Porto Badisco Calcarenites took place in the warm waters of the tropical to subtropical zone

Depositional processes of the mixed carbonate–siliciclastic rhodolith beds of the Miocene Saint-Florent Basin, northern Corsica

Many sedimentary processes can lead to the formation of mixed carbonate–siliciclastic sediments in shallow shelf environments. The Miocene Saint-Florent Basin (Corsica), and in particular the Monte S. Angelo Formation, offers the possibility to analyze coarse mixed sediments produced by erosion of a rocky coast, ephemeral stream input, and shallow-water carbonate production dominated by red algae. The Monte S. Angelo Formation was deposited during the Burdigalian to Langhian interval. During this interval, the island of Corsica experienced increased subsidence related to the development of the Ligurian-Provençal Basin and associated Sardinia-Corsica block rotation. Four main rhodolith-rich subfacies have been recognized: conglomerate with rhodoliths, massive rhodolith rudstone, well-bedded rhodolith rudstone, and rhodolith floatstone. The four facies have been interpreted as having been deposited in different environments of a gravel-dominated, nearshore to offshore prograding wedge. Deep-water melobesioids dominate the red algal assemblage from shoreface to offshore. Shallow-water subfamilies of lithophylloids and mastophoroids occur in only accessory amounts. Poor illumination is believed to be due to terrigenous input by ephemeral streams and wave- and current-resuspension. Resuspension processes are favored by the limited occurrence of seagrasses. Two types of siliciclastic–carbonate mixing processes characterize the investigated rhodolith-rich deposits: (1) punctuated mixing, produced by the re-deposition of terrigenous sediments by debris-flow processes during flooding events onto carbonate sediments together with rhodoliths of the shoreface environments, and (2) in situ mixing, produced by growth of coralline algae on siliciclastic pebbles to form the rhodoliths.

Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation, Central Apennines, Italy

Convolute bedding—pillow horizons—of likely seismic origin are identified in a bioclastic carbonate succession, the Guadagnolo Formation, in the central Apennine Mountains of Italy. These sediments, which were deposited in a carbonate-ramp environment, are from Burdigalian to Langhian (Relizian) in age. The lower part, about 500 m thick, consists of marlstones, marly limestones, and calcarenites, representing cyclic, shallow-water, coarsening-upward sequences. The second part, about 100 m thick, is dominated by prograding bodies of calcarenites. The horizons containing the pillow beds are in the topmost of the lower part, about 30 m below the base of the overlying calcarenites. They are present at the same stratigraphic position from the Prenestini to the Ruffi Mountains across a distance of about 20 km. Pillows, 20 cm to more than 1 m thick, are present in all the deformed layers and consist of marly calcarenites, which differ texturally from the enclosing matrix. They are regarded as the product of deformation ensuing from liquefaction of a denser layer overlying a lighter, silty layer that is richer in clay. These structures are interpreted to reflect liquefaction processes induced by seismic shocks, and they correlate well with coeval Miocene tectonism in this sector of the Apennines. Mariotti, G., Corda, L., Brandano, M., and Civitelli, G., 2002, Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation, central Apennines, Italy, in Ettensohn, F.R., Rast, N., and Brett, C.E., eds., Ancient seismites: Boulder, Colorado, Geological Society of America Special Paper 359, p. 87–98.

Coralline algae as environmental indicators: a case study from the Attard member (Chattian, Malta)

ABSTRACT We investigated the distribution of the red algae assemblages along the depositional profile of the Attard carbonate ramp of Malta (Chattian). The Attard member is ascribed to the Lower Coralline Limestone Formation characterized by 4 members: Maghlaq, Attard, Xlendi and Il Mara. Coralline algae are present in the inner and middle ramp environments of the Attard member. Sporolithaceans and melobesioids dominate the inner ramp, while mastophoroids and peyssonneliaceans are subordinate. In the middle ramp the association of red algae is characterized by an increase of sporolithacenas and a decrease of melobesioids, mastophoroids and peyssonneliaceans. These assemblages are related to the depth gradient existing from the inner relatively shallow to the progressively deeper middle ramp. However, transportation of red algae down slope may have had an effect on the red algae associations. The shape, morphology and structure of rhodoliths in the inner ramp environment are indicative of high-energy conditions. Nevertheless localized sectors of inner ramp are characterized by morphologies typical of low energy probably related to the presence of areas colonized by seagrass. Rhodoliths from the middle ramp have characteristics of moderately highenergy. The presence of Sporolithon Heydrich and Lithoporelk (Foslie) Foslie indicates that the production of carbonate took place under tropical conditions. We suggest that the Mg/Ca ratios may had a control on the flourishing of coralline algae in the Oligocene carbonate factories situated in oligo- to mesotrophic conditions, whereas during Early to Middle Miocene times the trophic conditions were one of the main controlling factor.

Growth and demise of a Burdigalian coral bioconstruction on a granite rocky substrate (Bonifacio Basin, southeastern Corsica)

During the Early Miocene, coincident with the Sardinia–Corsica block rotation, mixed carbonate–siliciclastic sediments of the Cala di Labra Formation were deposited on the southern margin of the Bonifacio Basin (southeastern Corsica, France). The Burdigalian marine transgression is spectacularly represented by a peculiar coral bioconstruction, unconformably lying on the eroded Variscan granitic basement. Superb exposures allowed detailed, three-dimensional field mapping, lithofacies analysis, and characterization of the Cala di Labra coral bioconstruction. As a result of the extremely irregular and articulated substrate, the coral buildup appears as an organized lens-shaped structure, and its core is constituted by a relatively dense coral domestone with a moderate increase of platy corals in the upper part. A coral rubble associated with granitic cobbles and pebbles is locally present at the base. The inter-coral sediment consists of poorly sorted bioclastic wackestone to packstone. Results from this study clearly show evidence for the occurrence of a former submerged granitic substrate that, as very rarely documented in the geological record, is here interpreted as the subtidal substrate for growth of a small bioconstruction under relatively high energy and clear water conditions. The Cala di Labra bioconstruction is overlain by a fining-upward quartzose conglomerate and sandstone succession interpreted as deposited in a coastal setting near fluvial point sources. The demise of coral growth was caused by a regressive event and by the consequent quite-sudden burial and related changes of trophic conditions.

PROGRESSIVE DETERIORATION OF TROPHIC CONDITIONS IN A CARBONATE RAMP ENVIRONMENT: THE LITHOTHAMNION LIMESTONE, MAJELLA MOUNTAIN (TORTONIAN–EARLY MESSINIAN, CENTRAL APENNINES, ITALY)

Abstract The Lithothamnion Limestone constitutes the uppermost carbonate unit of the Bolognano Formation outcropping in the Majella structure (Central Apennines, Italy). It represents the northern extension of the large Apulia Carbonate Platform and preserves an excellent record of the progressive decay of trophic conditions due to the approach of foredeep systems characterized by turbiditic siliciclastic sedimentation during the early Messinian. Sedimentological and compositional analyses were used to reconstruct the depositional model and evolution of platform environmental conditions. The profile is consistent with a homoclinal carbonate ramp, with a wide middle-ramp environment in which coralline algae, mainly forming the maërl facies, dominated carbonate production. This facies was associated with seagrass meadows colonizing the inner ramp. The outer ramp was characterized by bioturbated hemipelagic marl with planktonic foraminifera and pectinids in the aphotic zone. Three main stages of ramp evolution have been identified. During the first stage, the ramp was subjected to high-energy wave-dominated conditions, which favored the development of deep rip channels in which accumulations of vertebrate bones have been identified. In the second stage, maërl facies and seagrass meadows developed, initially in an oligotrophic setting, later followed by a slight reduction in light penetration. The third stage involved a general increase in fine terrigenous sediments, together with a further decrease in light and also by the spread of coralline algal bindstone facies. This elevated terrigenous input was associated with increased trophic conditions, as also shown by the occurrence of abundant plankton and low-oxygenated foraminiferal assemblages.

Oligocene Rhodolith Beds in the Central Mediterranean Area

During the Oligocene, extensive carbonate platforms developed in the central Mediterranean. These areas were colonized by different organisms, being the coralline algae one of the most important contributors to the carbonate production. Red algae produced sediments in shallow seagrass environments, however dominate the mesophotic and oligophotic zones where produced rhodolith beds. The diffusion of red algae during the Oligocene was favoured by reduction in atmospheric CO2, a rise in seawater alkalinity and increasing Mg/Ca ratios. This chapter deals with these deposits analyzing the depositional models and the controlling factors accounting for the origin of rhodolith beds.