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The upper Miocene mollusc assemblages of Monti Livornesi, used as a means to study the nature of Mediterranean benthic communities at the edge of the Messinian salinity crisis, are framed in a high-resolution stratigraphic scheme and quantitatively approached by the study of historical museum collections and modern samples. Instead of a single assemblage from either Tortonian or Messinian age, as previously thought, this fauna comes from three consecutive shallowing-upward depositional sequences bounded by regional unconformities, the Luppiano (upper Tortonian-lowermost Messinian), Rosignano and Raquese units (early Messinian). Facies analysis, taphonomy and quantitative paleoecology show that the Luppiano assemblage is characterised by aragonitic species from a eutrophic brackish-water shallow marine muddy bottom, the Rosignano assemblage by calcitic species from an oligotrophic coarse-grained seafloor close to a coral reef and the Raquese assemblage from an open-marine muddy bottom. Published comparisons between Miocene and Pliocene faunal lists should be considered only crude estimates of faunal change until more is known about the distribution of species along paleoenvironmental gradients. The analysis of Miocene and Pliocene abundance data allows us to frame the Monti Livornesi molluscs along carbonate-siliciclastic and water depth gradients and to reach a better understanding of the effects of salinity crisis on the Mediterranean biota.

This paper presents a stratigraphical and geomorphological analysis supported with geochronological dating aiming to reconstruct the Late Holocene lake-level fluctuations and paleohydrological history of Lake Hayk. This lake (23 km2 in surface) is located in the eastern side of the northern Ethiopia highlands, at an altitude of around 2000 m above sea level. Along the northern margin of the lake, which is mainly characterized by steep rocky slopes, the studied succession consists of colluvial and stromatolitic deposits. Along the southern margin, which is characterized by a wide coastal plain drained by the main watercourse feeding the lake (the Ankarka River), the study deposits are mainly palustrine, deltaic and fluvial in origin. Geomorphological and sedimentological data, integrated with a radiocarbon chronology, highlighted that during the last 3500 years the lake was affected by three main highstand phases, which occurred at about 3250–3000, 2600–950 and 650–160 cal yrs BP, respectively. These highstands are documented by aggradation of siliciclastic systems both along the southern and northern margins, whereas isotope data highlight that most of the stromatolitic deposits developed during phases of intense evaporation. This peculiar feature could be differently explained: i) stromatolite growth was triggered by rapid lacustrine rises, but mainly occurred during the long-lasting lacustrine falls; ii) stromatolite developed during tectonic-induced transgressions, which occurred during phases of intense evaporation. Despite the possible effects of local tectonics, the Lake Hayk record shows a good correlation with those of several late Holocene lakes of East Africa lakes (Naivasha, Tanganyika, Victoria, Turkana, Abhe, Ziway-Shala, Bosumtwi and Abyiata), highlighting that it can be considered as a suitable climatic proxy for late Holocene time span. In particular, by both siliciclastic and stromatolitic deposits occurring in the uppermost part of the sedimentary succession record high-frequency oscillations, which have been ascribed to three main droughts that occurred during the Little Ice Age. These droughts were previously documented only in Lake Naivasha and Lake Victoria.