The main purpose of this work is to make a first evaluation of the potential of the carbonate lacustrine sediment of the Mercure Basin (Basilicata region), to preserve palaeoclimatic information during the Middle Pleistocene. For this purpose a multi-proxy analysis of the lacustrine sediments from a selected section of the basin was undertaken. The selected section contains several tephra layers, which constrains the timing of deposition to MIS 13. Stable isotopes (oxygen and carbon) and element content were tentatively interpreted as linked to climatic changes giving interesting results for this poorly studied interval

Boschi, Chiara

Chiellini, Matteo

Giaccio, Biagio

Perchiazzi, Natale

Regattieri, Eleonora

Zanchetta, Giovanni

English

Archivio della Ricerca - Università di Pisa

Palaeo-environmental reconstruction of the Mercure Basin (Basilicata region) during MIS 13, through a multi-proxy analysis of lacustrine sediments

CHIELLINI, MATTEO

Available online http://amq.aiqua.it ISSN (print): 2279-7327, ISSN (online): 2279-7335    Alpine and Mediterranean Quaternary, Vol. 31 (Quaternary: Past, Present, Future - AIQUA Conference, Florence, 13-14/06/2018), 121 - 124 PALAEO-ENVIRONMENTAL RECONSTRUCTION OF THE MERCURE BASIN (BASILICATA REGION) DURING MIS 13, THROUGH A MULTI-PROXY ANALYSIS OF LACUSTRINE SEDIMENTS  Matteo Chiellini 1, Giovanni Zanchetta 1, Eleonora Regattieri 1, Biagio Giaccio 2, Natale Perchiazzi 1, Chiara Boschi 3  1 Dipartimento di Scienze della Terra, University of Pisa, Pisa, Italy 2 IGAG-CNR, Roma, Italy 3 IGG-CNR, Pisa, Italy Corresponding author: M. Chiellini <m.chiello89@gmail.com>  ABSTRACT: The main purpose of this work is to make a first evaluation of the potential of the carbonate lacustrine sediment of the Mer-cure Basin (Basilicata region), to preserve palaeoclimatic information during the Middle Pleistocene. For this purpose a multi-proxy analysis of the lacustrine sediments from a selected section of the basin was undertaken. The selected section contains several tephra layers, which constrains the timing of deposition to MIS 13. Stable isotopes (oxygen and carbon) and element content were tentatively interpreted as linked to climatic changes giving interesting results for this poorly studied interval.   KEYWORDS: Multi-proxy, stable isotopes, palaeoenvironment, palaeoclimate, Mediterranean   1. INTRODUCTION  Apennine tectonic basins are fundamental archives for the reconstruction of past climate conditions (e.g. Giaccio et al., 2015). Mercure Basin is currently a large river basin, which extends from the S-W Basilicata to the Calabria boundary (Fig. 1). During the Middle Pleis-tocene, the Mercure Basin was entirely occupied by a lake (Schiattarella et al., 1994; Robustelli et al., 2014). The presence of some tephra layers and their direct dating and correlation with known eruptions allowed a precise chronological definition of part of the lacustrine succession (Giaccio et al., 2014). This indicates that lacustrine succession deposited during marine isotope stage (MIS) 13, ca. 533-478 ka, an interval still poorly studied in the Mediterranean area.  2. MATERIALS AND METHODS  In this study, the composite section of S. Ciriaco (between the locations of Rotonda and Viggianello) was sampled, at a constant resolution of 10 cm, for a total of 21 m. In the sampled section, there are the volcanic tephra layers of different origins (SC5, SC4, SC3, SC2 and SC1) described by Giaccio et al. (2014). Isotopic analyses (δ13C and δ18O) were performed on all the samples using a Gas Bench II (Thermo Scien-tific) coupled with an IRMS Delta XP, whereas carbon-ate content was measured at resolution of 20 cm using De Astis’ calcimeter. X-ray fluorescence analyses were made through spectrometer NITON XL3t Goldd + XRF. Finally, X-ray diffraction analyses were made using a Brucker D2 phaser Diffractometer.   3. RESULTS AND DISCUSSION  The analysed composite section is made of 5 sub-sections. Correlation among subsections was allowed during the sediment sampling thanks to the volcanic tephra layers and stratimetric criteria (Fig. 2a). Samples of conglomerate was also sampled to compare isotopic data between lacustrine and potential clastic component. The chronology of the succession was based on 40Ar/39Ar dating on SC1 and SC5 tephras, which turn out to be between, respectively, 494 ±11 ka and 517 ±3 ka (Giaccio et al., 2014), as well as on the correlation of the SC5 tephra level with the same level found in the lacus-trine basin of Ohrid, Macedonia (Francke et al., 2016). Further tuning points were obtained from comparisons with the Ohrid record (Francke et al., 2016). From the analysis, it emerges that the content of CaCO3 is vari-able: it oscillates between a minimum of 64% and a maximum of 97% (Fig. 3), with average values of ca. 83%. The isotopic record shows that δ18O and δ13C re-cords have different trends. The δ18O curve shows to be roughly consistent with the percentage variation of CaCO3 (Fig. 3). In the δ18O record, three intervals can be distinguished on the basis of the different values with respect to the average value of -4.35‰. The first interval, from 545 ka to 520 ka, exhibits more negative values than the average; the second interval, from 520 ka to about 505 ka. is characterized by less negative values than the average; the third interval, from 505 ka to 493 ka, shows similar values to the average (Fig. 3). The δ13C curve shows less congruent trend with the CaCO3 record; it can be divided into two parts with respect to the average value of -0.13‰: the first part has positive val-ues and the second has values significantly more nega-tive than the average value. Results from the X-ray fluorescence (XRF) made on fifty-nine samples were expressed as concentration curves for each element. The curves of Ca and Sr show quite congruent trends with the percentage variation of CaCO3. On the contrary, the curves of K, Ti, Sr, Rb and Zr show poor congruent trends compared to the others. X-ray diffraction (XRD) points out that the main minera-logical phase is calcite, which is associated to less rep-resented Quartz, Aragonite and Muscovite. Aragonite is possibly related to the presence of abundant freshwater shell remains.   4. DISCUSSION AND CONCLUSION  According to Leng & Marshall (2004), the content of CaCO3 can be interpreted as an indicator of primary productivity within the lake. The variation of δ18O is con-sidered as an indicator of the water recharge/evaporation ratio and of the amount effect in precipita-tion in the basin catchment, as demonstrated for other Italian lacustrine successions (Giaccio et al., 2015; Re-gattieri et al., 2015, 2016). Variation of δ13C, despite being more complex to interpret, is considered indicator of photosynthetic activity within the lake as well as inter-nal processes such as recycling of organic matter and the equilibration of the lake water with the atmospheric CO2 (Leng & Marshall, 2004).  The variation of the Ca concentration was corre-lated to the CaCO3 content and interpreted as an indica-tor of the quantity of bioinduced calcite. The variations of K, Ti, Si, Rb and Zr were considered as indicator of clastic input within the lake.  During the interval from 545 ka to 520 ka, the insta-bility of CaCO3 content and the progressive decrease of δ13C suggest a progressive decrease of primary produc-  122   Chiellini M.  et al. Fig. 1 - (a) Location of the Mercure Basin with respect to the main volcanic centers of central and southern Italy (b) Geological map of the Mercure Basin (modified from Giaccio et al., 2014)   123    Palaeo-environmental reconstruction of the Mercure basin during MIS 13  Fig. 2 - (a) Representative stratigraphic and lithological sketch of the S. Ciriaco section containing tephra layers. (b) Fieldwork of samples collection at the S. Ciriaco section, during August 2016. Fig. 3 - Variation trend of the δ18O, of the δ13C, of the % CaCO3 and the elements Ca e Ti, with highlighted the three distinct phases ex-pressed consistently by all the proxies. tivity and photosynthetic activity. In this interval, a reduc-tion of the amount of precipitation and an increase of the detrital contribution within the lake is suggested by the increasing to less negative values of δ18O and increas-ing of the amount of K, Rb, Zr, Si and Ti. In the phase between 520 ka and 505 ka, more negative CaCO3 and δ13C values point to a minimum in the primary productiv-ity and a maximum reduction of photosynthetic activity; minimum values of δ18O and increase of K, Rb, Zr, Si and Ti in this interval suggest decreasing precipitation and an increase of the detrital contribution within the lake. The phase from 505 ka to 493 ka is characterised by a continuous decrease of the primary productivity as suggested by a decrease in CaCO3 content; unstable values of δ13C depict an unstable recovery photosyn-thetic activity; unstable quantities of K, Rb, Zr, Si, Ti and Ca point to instability of the detrital contribution within the lake as well as of the rates of the bioinduced calcite precipitation.  In conclusion, the Mercure Basin turned out to be a perfect archive for palaeo-environmental and palaeo-climatic studies. Moreover, it is possible to extend this kind of analysis to successions covering longer time intervals, like those cropping out to a large extent within the basin.  REFERENCES   Francke A., Wagner B., Just J., Leicher N., Gromig R., Baumgarten H., Vogel H., Lacey J.H., Sadori L., Wonik T., Leng M. J., Zanchetta G., Sulpizio R., Giaccio B. (2016) - Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present. Biogeosciences, 13(4), 1179-1196. Giaccio B., Galli P., Peronace E., Arienzo I., Nomade S., Cavinato G.P., Mancini M., Messina P., Sottili G. (2014) - A 560-440 ka tephra record from the-Mercure Basin, southern Italy: volcanological and tephrostratigraphic implications. 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Palaeogeography, Palaeoclimatology, Pa-laeoecology, 472, 51-66 Robustelli G., Ermolli E.R., Petrosino P., Jicha B., Sardella R., Donato P. (2014) - Tectonic and cli-matic control on geomorphological and sedimen-tary evolution of the Mercure basin, southern Ap-ennines, Italy. Geomorphology, 214, 423-435. Schiattarella M., Torrente M. M., Russo F. (1994) - Ana-lisi strutturale ed osservazioni morfostratigrafiche nel bacino del Mercure (confine calabro-lucano). Il Quaternario, 7(2), 613-626.   124   Chiellini M.  et al. Ms. received: April 27, 2018 Final text received: May 23, 2018 

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Palaeo-environmental reconstruction of the Mercure Basin (Basilicata region) during MIS 13, through a multi-proxy analysis of lacustrine sediments

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