Sequence stratigraphy of a late Pliocene lignite seam (Upper Valdarno Basin, Northern Apennines, Italy)

Ielpi A. (*)
(*) Earth Sciences Department, University of Siena, Via Laterina 8, 53100 Siena. E-mail: ielpi@unisi.it

We examine a major lignite seam occurring in the lower portion of the Castelnuovo Synthem, the oldest unconformity bounded stratigraphic unit of the Upper Valdarno Basin (Northern Apennines, Italy). The lignite seam crops out at the top of an alluvial fan to fluvial succession and is capped by lacustrine strata. Facies analysis performed on field logs has been integrated with borehole logs, implementing a stratigraphic transect representative of the whole basin. Architectural analyses have been carried on with a sequence stratigraphic approach, depicting the stacking of several high-frequency depositional sequences. Sequences register the progressive basin drowning, testified by the fluvial systems shutdown and subsequent lacustrine expansion. An anomalous sequence internal architecture comes to light, as from the bottom to the top of the lignite seam, lowstand and highstand system tracts progressively thin, against a gradual thickening of the transgressive system tracts.

sequence, synthem, Pliocene, lignite, Valdarno, Apennines