Anna Gandin

Evolution of a fault-controlled fissure-ridge type travertine deposit in the western Anatolia extensional province: the Çukurbağ fissure-ridge (Pamukkale, Turkey)

In recent decades various interpretations have been proposed to explain the evolution of fissure-ridge-type travertine deposits. In this paper, we discuss the relationships between fissure-ridges and brittle structures affecting their substratum, through a detailed analysis of an inactive fissure-ridge (near Çukurbağ) located in the Pamukkale geothermal area (western Turkey). The Çukurbağ fissure-ridge can be taken as a model as it offers an opportunity to examine its internal structure on the walls of a Roman quarry; in addition, this ridge has been studied by several researchers who have discussed the processes promoting the fissure-ridge evolution. The Çukurbağ fissure-ridge is composed of irregularly alternating travertine laminated facies (bedded travertine) crosscut into rather large lithons by subvertical crystalline veins (banded travertine). The relationships between bedded and banded travertine indicate that the banded veins are diachronous and migrated through time, suggesting a progressive fault zone enlargement in the footwall. Such a fault zone was characterized by polycyclic activity, with normal to transtensional kinematics, and was active during the latest Quaternary. We demonstrate that formation of banded veins is coeval with bedded travertine deposition and strictly depends on fault activity, therefore highlighting the fundamental role of travertine fissure-ridges in reconstructing palaeotectonic activity in a region.

Early Cambrian bioconstructions in the Zavkhan Basin of western Mongolia

The Neoproterozoic–Cambrian succession in the Zavkhan Basin of western Mongolia preserves early Cambrian bioconstructions of Nemakit-Daldynian to Botomian age. As elsewhere (Siberia, Morocco), the Nemakit-Daldynian bioconstructions in the upper Tsagaan Oloom Formation to lower Bayan Gol Formation interval were purely calcimicrobial. Spectacular calcimicrobial ‘patch reefs’ of presumed Tommotian age are present in the lower Bayan Gol Formation. In contrast, late Atdabanian–early Botomian bioconstructions are varied and well developed in the upper Salaany Gol Formation including, in addition to calcimicrobial bioherms, Gordonophyton–Razumovskia crusts, radiocyathan—archaeocyathan bioherms and thickets of the ramose archaeocyath Cambrocyathellus . These latter Zavkhan Basin buildups show some ecological and sedimentological features in common with coeval bioconstructions in South Australia, which also developed under a tectonically active regime.

Calcareous tufa as indicators of climatic variability: a case study from southern Tuscany (Italy)

Abstract A carbonate terraced succession mainly consisting of fluvial/palustrine calcareous tufa and of lacustrine limestone was deposited during recent Quaternary in a limited segment of the Valdelsa fluvial pattern (southern Tuscany, Italy). The radiometric data obtained from three carbonate terraces indicate that the depositional/erosional history of the Valdelsa succession during Late Pleistocene–Holocene, has been constrained by the same cyclic events observed in coeval detrital lacustrine successions of Central Italy. At least three of the Valdelsa carbonate Synthems and the interposed erosional phases can be correlated with the major climatic changes recognized in the European–Mediterranean area, from the Last Glacial Interstadial through the Younger Dryas to the Atlantic ‘Optimum Climatic’, the Sub-Boreal and finally at 2.5 ka the last Sub-Atlantic oscillation. This climatic correlation and the radiometric data imply that the deposition of calcareous tufa in Valdelsa was mainly dependent on rainfall availability and, consequently, was active during the milder oscillations within the cold periods.

Shelf to basin transition in the Cambrian-Lower Ordovician of Sardinia (Italy) reply

In southern and central Sardinia two different Cambrian-Lower Ordovician sedimentary belts occur. The former is exposed in southwestern Sardinia (Iglesiente and Sulcis), and is characterized by shallow-marine siliciclastic and carbonate sediments settled on a continental shelf with lowangle morphology. The latter, exposed in the Nappe Zone (central and southeastern Sardinia), consists of a thick monotonous sequence of siliciclastic deposits settled in a deeper-water basin.

Marbles and carbonate rocks from central Morocco: a petrographic, mineralogical and geochemical study

Petrographic, mineralogical, and stable isotopes (δ13C, δ18O values) compositions were used to characterise marbles and sedimentary carbonate rocks from central Morocco, which are considered to be a likely source of ornamental and building material from Roman time to the present day. This new data set was used in the frame of an archaeometric provenance study on Roman artefacts from the town of Thamusida (Kenitra, north Morocco), to assess the potential employment of these rocks for the manufacture of the archaeological materials. A representative set of samples from marbles and other carbonate rocks (limestone, dolostone) were collected in several quarries and outcrops in the Moroccan Meseta, in a region extending from the Meknes–Khenifra alignment to the Atlantic Ocean. All the samples were studied using a petrographic, mineralogical and geochemical methods. The petrographic and minerological investigations (optical microscopy, electron microscopy, X-ray diffraction) allowed to group the carbonate rocks in limestones, foliated limestone, diagenetic breccias and dolostone. The limestones could be further grouped as mudstones, wackestones–packstones, crinoid grainstones, oolitic grainstone and floatstones. Textural differences allowed to define marbles varieties. The stable carbon and oxygen isotope composition proved to be quite useful in the discrimination of marble sources, with apparently less discriminatory potential for carbonate rocks.

Tectonic control on the sedimentary architecture of Early Mesozoic mixed siliciclastic-carbonate Pseudoverrucano successions (southern Tuscany, Italy)

The mixed siliciclastic-carbonate successions of Early Mesozoic age exposed in the Pseudoverrucano tectonic units, along the coast of southern Tuscany (Montebrandoli and Punta delle Rocchette, Early Liassic) and in the Monti dell’Uccellina (Porticciolo di Cala di Forno and Salto del Cervo, Late Triassic) are characterized by fossil assemblages suggesting a close relationship with the coeval, mainly carbonate successions of the “Tuscan Series” while the depositional features are completely different. The composition of the mixed facies are similar, characterized by: i) recurring fining-upward sequences with well rounded but poorly selected white quartz-conglomerates, ii) coarse quartz sand grading to lagoonal lime-muds, or iii) thin intercalations or isolated quartz pebbles enclosed together with shell debris, within open marine although shallow carbonates. The depositional environments correspond to alluvial-fan complexes on narrow coastal plains merging with sandy beaches and lagoonal to shallow marine settings where the carbonate micritic deposition prevailed. This sedimentary style suggests that unsorted quartz debris was transported from an adjacent uplifted source area by gravity currents through very narrow coastal plains, and flowing into coastal lagoons or directly into the open sea, mixed coarse, land derived debris with open marine carbonate muds. The peculiar vertical evolution of the Pseudoverrucano facies suggests that the episodic input of siliciclastic materials was connected with storm events most probably triggered by tectonic pulses since no evidences of eustatic or climatic constrain on the sedimentation is apparent. The depositional features and fossil content of the mixed silicicla - stic-carbonate Pseudoverrucano successions argues for a coastal sedimentation on narrow shelves delimited by active, fault-bounded highs, representing the landward extension of the epicontinental/ pericontinental pelagic basins that from late Triassic in a regime of continental rifting, developed on the east-facing shelf of central Pangea.

Anatomy of the Early Cambrian ‘La Sentinella’ reef complex, Serra Scoris, SW Sardinia, Italy

Abstract All bioherms from the Early Cambrian (Botoman) Matoppa Formation of the Nebida Group in SW Sardinia were previously thought to be dominated by Epiphyton. However, at ‘La Sentinella’ (Serra Scoris Hill), they are composed of Girvanella, Razumovskia, Botomaella and Renalcis, with Epiphyton and archaeocyaths as accessory components. This association forms two unusual types of crust boundstone, consisting of stacked flat or curved crusts and saucer-like archaeocyaths delimiting shelter cavities. Dendrolitic Renalcis archaeocyath-cement boundstone caps the bioherm. Analysis of the La Sentinella reef complex and comparison with similar constructions from Mongolia (Zuune Arts, Salaany Gol), Nevada (Stewarts Mill, Battle Mountain), Mexico (Sonora) and China (Tianheban Formation) suggest that episodic deposition of fine-grained siliciclastic or carbonate sediment followed by periods of non-deposition enabled the calcimicrobial rafts and crusts to colonize the substrate and then provide synoptic relief for the development of a dendrolitic Renalcis-cement framework. ‘La Sentinella’ is one of the rare examples of Cambrian reef complex displaying community replacement, from an initial stage of thrombolitic and/or flat-stacked microbial crusts on a muddy substrate to an arched microbial crust system, to a more resistant Renalcis-cement boundstone. Such bioherms reflect an open-shelf, shallow-marine environment of increasing energy.