ABSTRACT Stratigraphic analysis of two sections of a fluvial strath terrace exposed on the left bank of the Esino River near the village of Trocchetti (province of Ancona, Marche region of central Italy), and the study of a large landslide located near the village of San Cristoforo, a few kilometers down valley from the Trocchetti fluvial terrace, provide evidence for two catastrophic environmental events, namely: (1) the aggradation on the riverbed of coarse, chaotic gravel due to a violent flashflood; and (2) the formation of a large ephemeral lake as the consequence of the landslide that barred the river channel at San Cristoforo. Archaeological and historical information about the lost Roman city of Tuficum , which was located just a kilometer upriver from the Trocchetti terrace, and ceramic artifacts found in the chaotic gravel unit, led us to the hypothesis that both the flashflood and the landslide were induced by the sudden, severe climate change of the Late Antique Little Ice Age (mid-sixth century to mid-seventh century CE).

Abstract The role of climate change in driving alluvial-fan sedimentation is hard to assess in pre-Quaternary successions, for which detailed chronologies and climate-proxy records cannot be easily established. In the Teruel Basin (Spain), high-resolution (10 4 –10 5 years) chronological and palaeoclimatic information was derived by orbital tuning of Late Miocene mudflat to ephemeral-lake deposits. The semi-arid palaeoclimate made this low-gradient, basinal environment sensitive to thresholds in the local hydrological balance. Basic facies rhythms are attributed to alternating, relatively humid/arid phases controlled by the climatic precession cycle. The lower stratigraphic interval of this reference section interfingers with distal, coarse-clastic beds from a coeval alluvial fan. The consistent interdigitation of debris-flow deposits with distal strata indicative of arid-to-humid climate transitions shows that fan sedimentation was regulated by climate cyclicity. In particular, the largest volumes of terrigenous debris were shed from the fan onto adjacent mudflats during transitions to relatively humid periods with pronounced seasonality, during precession minima. Distal to medial sections within alluvial-fan outcrops also feature prominent, laterally continuous alternations of coarse- and fine-clastic packages. This high degree of architectural organization, uncommon in fan successions, and stratigraphic relationships with the reference section suggest orbitally controlled climate change to have been the forcing mechanism.

Clinton Lake is a small ephemeral lake lying in a glacial paleomeltwater channel near Clinton, Interior British Columbia. The lake is a Mg-Na-S0 4 brine (>300 g l –1 TDS), similar to those at Basque, 50 km to the south. Like the Basque Lakes, Clinton Lake has permanent deposits of epsomite. There are six main depositional subenvironments: (1) hillslopes, (2) springs, (3) carbonate playa, (4) hummocky carbonate mudflats, (5) saline mudflats, and (6) ephemeral lake or saline pan. There is no channelled inflow, and Clinton Lake is fed mainly by groundwater, direct precipitation, and diffuse runoff. About 120 m north of the lake, at slightly higher elevation, lies a small carbonate playa. called Clinton Pond. This is fed by a series of small springs and seepages. Other springs issue from the basin margins, but most seep into the ground or evaporate before reaching the lake. Shallow brine covers Clinton Lake during spring and early summer, but most of the surface is salt encrusted by late summer and autumn. Preliminary analyses of the basin waters and sediment mineralogy suggest that Clinton Lake may be fed by at least two distinct groundwater sources. The first type has a very high Na/Cl ratio (>15); the second type is less evolved, less saline, and has a lower Na/Cl ratio (<12). Both types of groundwaters have very high Mg/Ca ratios, resulting from contact with Mg-rich bedrock and early precipitation of calcite cements in soils. Aragonite and Mg-calcite are precipitated at the spring orifices, further depleting the waters in calcium. Some spring waters flow into Clinton Pond, where aragonite and hydromagnesite precipitate. Pond waters, augmented by other springs, may seep below hummocky carbonate mudflats toward Clinton Lake. At Clinton Lake, these waters mix with other shallow, dilute seepage and possibly, artesian groundwaters discharging through the lake floor. Cores and surficial muds from the saline mudflat contain hydromagnesite, aragonite, dolomite, and magnesite, and gypsum. Most calcium and much of the carbonate are precipitated in the outer mudflat, leaving a Mg-Na-S0 4 brine. Clinton Lake is a “spotted lake,” consisting of more than 100 brine pools separated by rims of Mg-carbonate and gypsum muds. In summer, clear epsomite crystallizes in the pools as rafts and bottom-nucleated crystals. Mirabilite forms from residual brine in the autumn. Permanent epsomite deposits, showing evidence for repeated dissolution and recrystallization, underlie the pools. Clinton Lake is the successor to an earlier Mg-carbonate marl lake. Historical records suggest that evaporite precipitation could be very recent.