Sedimentology and composition of sands injected during the seismic crisis of May 2012 (Emilia, Italy): clues for source layer identification and liquefaction regime

InMay 2012widespread sand blows formed along buried channels in the eastern sector of the Po Plain (Northern Italy) as a consequence of a series of seismic eventswith main shocks ofMw6.1 and 5.9. At San Carlo (Ferrara) a trench dug a few week after the earthquakes exposed sand dikes cutting through an old Reno River channel– levee system that was diverted in the 18th century and was deposited starting from the 14th century (unit A). This sequence overlies a Holocene muddy floodplain deposits and contains scattered sandy channel deposits (unit B) and a Pleistocene channel sand unit (unit C). Sands with inverse and normal grading, concave layering and vertical lamination coexisting along the dikes suggest multiple rhythmic opening and closing of the fractures that were injected and filled by a slurry of sand during the compression pulses, and emptied during the extension phase. The pulse mechanism may have lasted for several minutes and formed well stratified sand volcanoes structures that formed at the top of the fractures. Sands fromdikes and fromthe various units showwell defined compositional fields from lithoarenitic to quartz-feldspar-rich compositions. Sands from the old Reno levee and channel fill (unit A) have abundant lithic fragments derived fromthe erosion of Apennine sedimentary carbonate and terrigenous successions. Composition of the sand filling the dikes showclear affinities with sand layers of the old Reno River channel (Unit A) and clearly differ from any sand from deeper Holocene and Pleistocene layers (Unit B and C),which are richer in quartz and feldspar and poorer in sedimentary lithic fragments. Sorting related to sediment flux variations did not apparently affect the sand composition across the sedimentary structures. Textural and compositional data indicate that the liquefaction processes originated from a relatively shallow source consisting of channel sands located within Unit A at 6.8.to 7.5 m depth

AMS radiocarbon dating of mortar: The case study of the medieval UNESCO site of Modena

The carbon dioxide contributing to binder formation during the set of a lime mortar reflects the atmospheric 14C content at the time of construction of a building. For this reason, the 14C dating of mortars is used with increasing frequencies in archaeological and architectural research. Mortars, however, may also contain carbonaceous contaminants potentially affecting radiocarbon dating. The Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE) of the Second University of Naples (SUN) has recently obtained some promising results in mortar radiocarbon dating thanks to the development of a procedure (i.e. CryoSoniC/Cryo2SoniC) aiming to eliminate exogenous C contamination that may occur in a mortar. The construction history of the UNESCO World Heritage Site of Modena (Italy) is still controversial and represents a challenging case study for the application of absolute dating methodologies for different reasons. From the point of view of 14C dating, for example, given the high percentage of carbonate aggregates composing these samples, Modena mortars represent an experimental test particularly indicative of exogenous carbon sources suppression ensuring methodology accuracy. In this paper several AMS Radiocarbon dates were carried out on lime lumps with the aim to: (i) verify procedure accuracy by a comparison of the results obtainable from lime lumps dated after different treatments (i.e. bulk lime lumps vs. CryoSoniC purified lime lumps); (ii) compare different building phases absolute chronology for the medieval UNESCO site of Modena, with that assumed by historical sources in order to assess preliminary the 14C dating feasibility for of the site. Historical temporal constraints and mortar clustering, based on petrography, have been applied to define a temporal framework of the analyzed structure. Moreover, a detailed petrographic characterization of mortars was used both as a preliminary tool for the choice of samples and to infer about the lack of accuracy (when verified) of the applied mortar 14C dating procedure

Studio composizionale delle sabbie della cava di via Macchioni, Spilamberto

Guida alla escursione pre-congress

Geoarcheologia degli scavi nelle aree di Spilamberto e Poviglio

Guida alla escursione pre-congresso GeoSed 2006, Modena, 25-29 settembre 200

Reconstructing the sedimentation history of an alluvial plain by sand composition investigations: the Modena case study

The Modena alluvial plain area examined for this study has an approximate extent of 150 km2 and is located at the northern side of the Northern Apennines thrust- and fold-belt, where streams draining the chain flow toward the north-east into the Po river. Detailed modal analyses by point-counting in thin sections show that modern stream sands in the Modena plain show similar overall compositional fields, but can be discriminated on the base of key-components, such as quartz, feldspar, carbonate and ophiolitic fragments.The spectacular abundance of archaeological sites of various age along the main rivers allowed us to reconstruct the variation through time of the sand composition. The study of sand sediments that buried Neolithic, Iron Age, Bronze Age, Roman and Longobardian sites indicates that the compositional fields have not varied significantly since the Neolithic. These results clearly indicate that the bedrock lithology of the source area has not changed in the considered time interval and that diagenesis has not obliterated the sediment provenance signature in such a relatively short time span. The only major diagenetic process is the formation of carbonate concretions (caliche), which can be easily recognized as secondary particles during point counting of thin sections.These results indicate that the reconstruction of the recent evolution of the local drainage system is possible simply by comparing ancient with modern fluvial sand compositions.On the other, the sand sediments older than the Neolithic, and approximately older than 10.000 years, show a significant shift in composition from the modern ones, with an overall increase of quartz and feldspar components. These compositional variations can be explained by the combination of various factors: a significant change in the bedrock lithology (neotectonic effect), climate changes related to glacial-interglacial phases which induced a variation in bedrock alteration, erosion and sand deposition rates (climate effect), and the post-depositional changes that may have varied the sand composition (diagenetic effect). Further studies, now in progress, will permit a better characterization of the sediment supply through space and time, possibly allowing the reconstruction of the sand composition in the older local drainage system as response and interplay among neotectonics, climate changes and diagenesis

Composizione dei sedimenti sabbiosi nelle perforazioni lungo il tracciato ferroviario ad alta velocit\ue0: indicazioni preliminari sull'evoluzione sedimentaria della media pianura modenese

The Modena alluvial plain has been geologically investigated in great detail and is characterized by a spectacular abundance of archaeological sites of various age. For this reasons the area may be considered a natural laboratory for the reconstruction of the recent sedimentary evolution of the Po Plain. The alluvial plain area examined for this study has an approximate extent of 150 km2 and is located at the northern side of the Northern Apennines thrust- and fold-belt, where streams draining the chain flow toward the north-east into the Po river. Detailed modal analyses by point-counting of thin sections show that modern stream sands in the Modena plain show similar overall compositional fields, but can be discriminated on the base of key-components, such as quartz, feldspar, carbonate and lithic fragments. The study of sand sediments indicates that the compositional fields have not varied significantly since the Neolithic. The only major diagenetic process is the formation of carbonate concretions (caliche), which can be easily recognized as secondary particles during point counting of thin sections. These results indicate that the reconstruction of the recent evolution of the local drainage system is possible by comparing ancient with modern fluvial sand compositions.The drilling of numerous wells along the new high speed train tract (TAV) provided us with new insight on the sedimentary evolution of the plain through time. The samples recovered from 6 wells reaching depths up to -50 m show that the sand sediments older than 10-12 kyr, have a significant shift in composition from the modern ones. This compositional change consists in a marked overall increase of quartz and feldspar components. The compositional variations can be explained by the combination of various factors: a) significant change in the bedrock lithology through time induced by tectonics and/or change in the local drainage pattern, and b) recycling of older fluvial sediments enriched in feldspar. Because the sands older than 10-12 kyr compared to the overlaying olocenic and modern sediments are enriched in feldspar, which is considered a particularly alterable component, the compositional differentiation can not be related to effects induced to glacial-interglacial climate changes and post-depositional diagenetic processes.The considerable change in sand composition and the stratigraphy of the deposits suggest dramatic geographical, environmental and depositional variations supporting the observation that a regional unconformity separates the Late Pleistocene from the Olocene sediments