Variation in terrigenous supplies in the Upper Pliocene to Recent deposits of the Venice area

Abstract

The subject of this work is a gross composition and rock fragment analysis of sands drilled by the Venice 1 and 1 bis wells from the depth of 947.70 to 19.33 m. The obtained data allow the delineation of Upper Pliocene to Pleistocene terrigenous supplies in an area of great environmental interest. From the bottom until about 513 m in depth, the sands are litharenitic, characterised by a high amount of carbonate rock fragments and are considered indicative of an eastern South Alpine provenance. From 512.59 to 438.43 m, the sand composition is quartzolithic with large amounts of quartz and metamorphic rock fragments, indicating a provenance from the western Alps/northern Apennines. This quite abrupt change in composition is thought to reflect either the progressive infill of the Apennine foredeep and the consequent northward migration of the Po fluvial system, or tectonic movements affecting the Apennine chain and/or the eastern Southern Alps during the Middle Pleistocene. In the shallowest interval, 438.43 to 19.33 m below the surface, the sand composition results from the mixing of these two kinds of sediments. This reflects both a persistence and simultaneous activity of the sources, and reworking by marine littoral processes related to repeated sea-level oscillations.