The Senio River drainage basin (northern Apennines, Italy) provides a good opportunity to study the effects of sedimentary recycling in a temperate climate. In fact, the bedrock of its upper portion is made of a single and homogeneous sedimentary unit, the Marnoso-arenacea Formation (Miocene), which consists of graded beds composed each of sandstone, siltstone, and mudstone.
Composition of the soil sand-fraction within the upper portion of the Senio River drainage basin reflects the sandstone/siltstone composition of the underlying Marnosoarenacea Formation. Thus, pedogenic processes are generally not strong enough to affect siliciclastic sand grains formed by the alteration of the corresponding source lithology. Carbonate bioclasts are virtually the only sand-size detritus released from the poorly indurated mudstone of the Marnoso-arenacea Formation (i.e., Te divisions of turbidite beds and hemipelagic beds).
Siliciclastic sand-fractions of fluvial sediments and soils are very similar, indicating that only minor modifications occurred during transport. On the other hand, a large population of carbonate clasts (as much as 35% of the sand fraction) is produced by the breakage of penecontemporaneous carbonate concretions generated mostly by vegetal activity along the upper reaches of the Senio River and its tributaries. In spite of their abundance, these carbonate grains are rapidly lost during transport because of their fragile and chemically labile nature; this implies that their preservation potential in the rock record is low.
Marnoso-arenacea-derived sandstone and siltstone rock fragments are the only siliciclastic components of the detritus present along the Senio River which are modified during transport, decreasing progressively downstream probably because of breakage.
The most useful indicators of sedimentary recycling within the sediments of the Senio River are the siltstone/sandstone lithic fragments, mono- and polycrystalline calcite grains due to breakage of the Marnoso-arenacea sandstone cement, and the mostly unworn fossil tests derived from the Marnoso-arenacea mudstones.
This study confirms that composition of the sand shed off tectonically active source-areas composed of sedimentary rocks in conditions of temperate climate and high/moderate relief and short transport reflects the sediment source-rock, except for poorly indurated mudstone source rocks.
