Stratigraphy of the Servino Formation (Lombardy, Southern Alps): towards a correlation with the Werfen Formation of the Dolomites.

The Servino Formation, representing the Lower Triassic in the Lombardy Southern Alps, records a major tectono-eustatic transgression that flooded the Permian alluvial plains at the onset of the Triassic. The stratigraphy of the Servino Formation in central and eastern Lombardy is here revised taking into account both recently published and newly-measured stratigraphic sections. Recognition of roughly isochronous petrologic intervals, which can be traced in all considered sections, and improved biostratigraphic control thanks to a recently acquired paleontologic datum, allowed us to subdivide the Servino Formation with greater detail than possible so far and to introduce two new members formally. The new stratigraphic scheme comprises six superposed members, from hottom to top: 1) conglomerates and sandstones deposited in fan delta settings (Prato Solaro Member), locally transgressed by hyhrid oolitic arenites (Praso Limestone); 2) quartzose sandstones with abundant interstitial dolomite (Ca’ San Marco Member, firstly introduced herein); 3) oolitic coquinoid limestones yielding iron ores and passing laterally to red calcarenites and mudrocks (“Gastropod Oolite”); 4) arkosic sandstones, displaying pebbly lags in the Lake Como area (Acquaseria Member, firstly introduced herein); 5) carbonates and marls, at places coquinoid and yielding iron ores (“Myophoria Beds”); 6) variegated siltstones and marls (“Upper Member”). This scheme is useful for detailed mapping of the Servino Formation and represents a significant step towards correlation with the long established members of the Werfen Formation. In particular, correlation between the Ca’ San Marco and Siusi Members is documented by analogous Claraia assemblages in both Lombardy and the Dolomites. Thickness of Lower Triassic sediments from the Dolomites to Lombardy appears to decrease abruptly across the Giudicarie Line, rather than gradually, probably due to an inherited Permian paleotopograph