The oligo-miocene sediments of the Maltese Islands

The Maltese Islands are situated at the south-western end of the Malta-Ragusa Rise, an area characterised by high gravity anomaly values and a ridge-like bathymetrical profile. The Islands lie 50-80km. south of Sicily and 282km. away from the north African coastline.The sedimentary sequence is entirely composed of shallow water carbonates, dominantly marine, and with biohermal developments in the upper and lower exposed formations. The intermediate formations accumulated in somewhat deeper water and are characterised by planktonic foraminifera.Subdivision of the Upper and Lower Coralline Limestone Formations into 7 new members and 11 new beds was found necessary, in order to appreciate fully the local environments represented in these shallow water units. The Globigerina Limestone and Blue Clay Formations are now considered as fairly shallow water deposits, the analysis of the associated phosphorite conglomerate beds of the former indicating that dominant transport of clasts was from the west, in an area of primary phosphorite and glauconite development. The Greensand Formation is re-defined on the basis of sedimentology, and the upper part of previous classifications is now included in the Upper Coralline Limestone Formation.For each of the Formations a total of 15 biofacies are proposed on the basis of faunal variation. The probable depth ranges of each are used to refine conclusions drain from the sedimentological interpretations, in order that the palaeoenviromnents may be reconstructed. The study of a newly defined brachiopod marker horizon within the Upper Corailine Limestone has resulted in the prediction of the ecology of the four species involved, primarily with the aid of bryozoan growth-form studies. A new fossil fish horizon in western Malta is also discussed.A number of tectonic structures previously referred to as "sinks" are re-defined, and a prolonged episode of Cainozoic cavern development, associated with subaerial and submarine subsidence is postulated on the basis of structural and sedimentological interpretations

The Ghar Lapsi limestones : sedimentology of a Miocene intra-shelf graben

The Gnar Lapsi succession of west Malta developed during a Late Tortonian Early Messinian episode of tectonism associated with the Maghlaq Fault Zone. These syntectonic strata, Porites coral bioherms bioclastic packstones and wackestones, debris flow deposits and calciturbidites form a prism banked against the southwest- facing fault-line but are absent from the island of Filfla which lies about 4.5km to the west. Faunal correlation is imprecise; however, the macro faunas and general foraminiferal micro faunas of the Porites bioherm show it to be correlated with the Tal-Pitkal Member (Late Tortonian). The overlying calciturbidites and debris flow deposits are part of the Gebel Imbark Member (Early Messinian). These strata are part of a half-graben fill which cuts the Miocene shelf between Filfla and the present Magnlaq cliffs of Malta. The absence of planktonic Foraminifera from the graben fill sequence and low percentages recorded from strata on Filfla island confirm that this structure was intra-shelf in origin rather than a shelf edge feature. Calciturbidite laminites and debris flow deposits, developed during the Lower Messinian, were deposited during a eustatic fall of Mediterranean sea-level concomitant with the Lower Evaporite Complex of Sicily.peer-reviewe

Connecting chert sources of Sicily with the Neolithic chert artefacts of Malta.

This article presents the results of a provenance study between late-Neolithic chert artefacts from Malta and chert sources of Sicily. It is part of a larger geoarchaeological research dedicated to investigate whether the cherts used for stone artefacts represent indigenous exploitation or results from longer-distance networks. Chert is a raw material commonly used in prehistory for tool crafting and with abundant geological sources in the broader Mediterranean region. However, the features of most of these sources are unknown and no detailed data regarding their geochemical characteristics and composition are available. The lithic assemblages of late Neolithic Malta are abundant with non-local chert finds and their origin will contribute to inferences about the role of Malta within the broader Mediterranean social landscape and raw-material network of this period. The paper uses macroscopic examination to distinguish the different chert varieties in the assemblages and the non-destructive LA-ICP-MS technique to identify groups with specific geochemical characteristics/signature. The field and lab-based work suggest multiple sources for the chert artefacts and most significantly, presents strong evidence of artefacts having almost identical geochemical signature with specific chert sources from southeast Sicily. These are the first highly reliable results confirming a connection between these two locations and strongly suggests the existence of seafaring in this area during the late Neolithic.ER

The geology of the Pelagian Islands and their structural setting related to the Pantelleria rift (central Mediterranean Sea)

The Pelagian islands of Lampedusa, Lampione and Linosa form a natural laboratory in which, through the analysis of synsedimentary patterns and fault kinematics, to model the history of compressional and tensional structures from Upper Miocene to recent times'. This information correlates remarkably well and compliments recent detailed studies on the Maltese Islands lying on the opposite shoulder of the Pantelleria Rift. The upper Miocene onset of rifting is deduced from synsedimentary faulting on Lampedusa. The continuation of the same tectonic regime up to the present time can be recognized on the Quaternary volcanic island of Linosa where volcanic activity is related to structures paralleling the Lampedusa trend. In the central Mediterranean area, NW-SE trending structures are characterized by normal faulting and are present from the Ionian side of the Hyblean Plateau (SE Sicily) through Malta and into central Tunisia. A second NNW-SSE trending fault pattern reveals evidence of sinistral motion as can be demonstrated in Lampedusa. This activity commenced in Upper Miocene and continues to recent time. The movements associated with the two fa ult trends a re consistent with a northwestward directed maximal horizontal compressive stress.peer-reviewe

NEOGENE AND QUATERNARY SEDIMENTATION PATTERNS IN THE NORTHWESTERN HYBLEAN PLATEAU (SE SICILY): THE EFFECTS OF A COLLISIONAL PROCESS ON A FORELAND MARGIN

Miocene carbonates and marls in the northwestern margin of the Hyblean Plateau (SE Sicily) exhibit considerable thickness variations consistent with synsedimentary tectonism. In the Early-Middle Mio­cene carbonates (Ragusa Formation) a series of parallel swells dose to the platform edge encouraged the development of a coarse-grained bioclastic facies. The overlying Middle-Late Miocene marls (Tellaro Formation) thin over these seafloor highs and associated mafie Tortonian volcanics are particularly developed along the hinge zones between swells and local sea-floor depressions. The basic extrusives appear to have followed in­cipient NE-SW fault lines propagated from deeper basement fractures. During the succeeding Messinian these faults were activated to produce horst structures (Vallone Lamia horst, Monte Caratabia horst and Cameme horst). These separate locai NE-SW oriented narrow grabens in which thick Messinian evaporites were deposited, probably connected with the main Centrai Sicilian Basin. Further subacrial deposits and volcanics levelled the Hyblean horst and graben topography prior to the major Early Pliocene marine high-stand. The ensuing transgression covered the study area with a thick pelagic Early Pliocene chalk. Local regressions, the product of Middle Pliocene and Early Pleistocene major tectonic activity along the margins of the plateau, are associated with local unconformities. Final emergence along the margins of the plateau occurred at the close of Early Pleistocene times when the emplacement of the Gela Nappe, from the NE, partly filled the foredeep basin. The withdrawal of the sea from the foredeep occurred shortly afterwards

Interaction of temperature, salinity and extracellular polymeric substances controls trace element incorporation into tufa calcite

The influence of extracellular polymeric substances on carbonate mineral growth in natural settings remains one of the most poorly understood contributors to the growth of non-marine carbonate sediments. The influences of these materials are complicated by their association with living cells creating local microenvironments via metabolism and enzyme production, and by our uncertainty about the extracellular polymeric substances materials themselves. Different mixtures of extracellular polymeric substance molecules may behave in different ways, and differences in the local physical environment may alter how the mixtures influence mineral formation, and even result in different patterns of polymerization. Here, the influence of extracellular polymeric substances on calcite precipitation rate and Mg/Cacalcite in the absence of cells is investigated using extracts of extracellular polymeric substances from temperate fluvial tufa biofilm. The influence is complex, with the concentration of extracellular polymeric substances in solution altering deposition rate and trace element incorporation. Moreover, the results show interaction of the presence/absence of extracellular polymeric substances and both temperature and salinity. However, despite extracting extracellular polymeric substances from the same parent sample, a uniform influence was not found in these experiments, implying that the mixture is sufficiently variable within a sample for microenvironments within the biofilm to either promote or inhibit mineralization. As sedimentologists, we can no longer take the view that extracellular polymeric substances are a bystander material, or that they have a single set of coherent and predictable or intuitive influences. Rather, the emphasis must be on investigating the specific mixtures present in nature, and their complex and dynamic interaction with both mineral surfaces and hydrochemical conditions

A depositional model for spherulitic carbonates associated with alkaline, volcanic lakes

The South Atlantic Aptian ‘Pre-salt’ reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcrop analogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of spherulitic calcitic components were formed, including coated grains, crusts, and build-ups. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the ‘Pre-Salt’ subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) Ca-Mg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spherulitic grainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex ‘microbe-solution’ interactions before any reliable facies model is envisaged

Are spherulitic lacustrine carbonates an expression of large-scale mineral carbonation? : A case study from the East Kirkton Limestone, Scotland

BP Exploration Co. is thanked for funding, and particularly the Carbonate Team for supporting this research and for fruitful discussions. West Lothian Council and Scottish Natural Heritage are thanked for allowing access and permission for sampling the site. The Core Store Team at BGS Keyworth is particularly acknowledged for their assistance. Mark Anderson, Tony Sinclair (University of Hull), and Bouk Lacet (VU University Amsterdam) are thanked for technical support. Anne Kelly (SUERC) for carrying out the Strontium Isotope analyses. Mark Tyrer is thanked for his advice on PHREEQC modelling.Peer reviewedPostprin

A model for the Late Miocene reef-Tripolaceous associations of Sicily and its relevance to aberrant coral growth-forms and reduced biological diversity within the Palaeomediterranean

A detailed study of the latest Tortonian and earliest Messinian (Miocene) strata of North Central Sicily reveals the presence of a trans -gressive episode immediately prior to the "salinity crisis". In detail two reef events are present, an earlier one (Late Tortonian) with diverse coral faunas, and a second (Early Messinian) reef episode containing both relatively diverse Porites-Tarbellastraea dominated reefs and monogeneric Porites reefs, together with the earliest diatomite deposits (Tripoli Formation). The diatomites are associated with partly isolated embayments which were the sites of algal and bacterial blooms. These probably periodically generated toxic conditions. Leakage from the diatom aceou s embayment waters into the open marine, but virtually static water, reefal areas during the Early Messinian is believed to have given a selective advantage to stromatolitic microbial mat growth. Only the rod-like growth-form of Porites ultimately was able to thrive under increasingly tranquil water conditions and strong competition from microbial mats. This was achieved by a growth strategy involving rapid apical growth of slender vertical orientated branches. The juxtapositioning of algal dominated diatom basins and coral reef basins by Late Miocene times was due to a combination of plate margin synsedimentary tectonic deformation associated with Afro-European plate collision, and normal marine eustatic events connected with the initiation of dessication of the Palaeomediterranean Basin. The model presented is applicable to all Mediterranean, late Miocene coral reef ares flanking the alpine chain affected by synsedimentary tectonism.Un modèle pour les associations récif-faciès Tripoli dans le Miocène supérieur de Sicile. Application aux croissances coralliennes aberrantes et à la réduction de la diversité biologique dans la Paléoméditerranée. Une étude détaillée des terrains du Tortonien terminal et du Messinien basai de Sicile nord-centrale permet de mettre en évidence un épisode trans gressif précédent immédiatement la "crise de salinité". Dans le détail, deux épisodes récif aux sont identifiés : le premier (Tortonien terminal) est caractérisé par des faunes coralliennes diversifiées : le second (Messinien inférieur) est représenté par des récifs relativement diversifiés à Porites-Tarbellastraea et des récifs monogénériques à Porites, contemporains des plus anciens dépôts diatomitiques (formation des Tripoli). Les diatomites sont associées à des bassins partiellement isolés qui ont été le siège d'explosions algaires et bactériennes probablement provoquées par des conditions toxiques périodiques. Le passage des eaux des bassins diatomitiques vers les zones récifales de mer ouverte durant le Messinien inférieur est considéré comme un phénomène qui a favorisé la croissance des mattes microbiennes stromatolitiques. Seules les formes coloniales de Porites en bâtons ont pu survivre dans un milieu où les eaux étaient de plus en plus calmes et où la compétition avec les mattes microbiennes était forte. Ceci entraîne une stratégie de croissance finale marquée par une croissance apicale rapide de branches grêles orientées verticalement. La juxtaposition de bassins à récifs coralliens au Miocène supérieur est le résultat de la combinaison de deux phénomènes : des déformations tectoniques synsédimentaires de bordures de plaques lors de la collision entre les plaques africaines et européennes ; des événements eustatiques normaux liés au début de la dessication de la Palaéoméditerranée. Le modèle est applicable à toute la Méditerranée, dans la mesure où les récifs coralliens du Miocène supérieur frangent la chaîne alpine affectée de tectonique synsédimentaire.Pedley Martyn, Grasso M. A model for the Late Miocene reef-Tripolaceous associations of Sicily and its relevance to aberrant coral growth-forms and reduced biological diversity within the Palaeomediterranean. In: Géologie Méditerranéenne. Tome 21, numéro 1-2, 1994. Récifs et plates-formes carbonatées miocènes de Méditerranée / Miocene reefs and carbonate platforms of the Mediterranean. Interim colloquium R.C.M.N.S. (Marseille 3-6 mai 1994) sous la direction de Jean-Paul Saint-Martin et Jean-Jacques Cornée. pp. 109-121