Sedimentología de los depósitos lacustres neógenos de Castrillo del Val (Burgos), España

Abstract

Two informal lithostratigraphic units are proposed in the terrestrial Neogene deposits of the northeastern Duero Basin, including ten associations of sedimentary facies considered to be representative of lacustrine, deltaic, paludal and fluviatile sedimentary environments. Unit I (the lower one) consists of marls and gypsarenites deposited in saline lakes, topped by shallow lacustrine (paludal) fresh-water carbonates with pseudomicrokarst surfaces indicative of repeated subaerial exposure due to water-level oscilations. Unit 2 is made up of lacustrine fossiliferous marls and carbonate silts, deposited near the mouth bars of distributary deltaic channels, overlaid by paludal carbonates. The major sedimentary controls recognized in this tectonically-quiet area with semiarid seasonal climate are: (1) chemistry of lake waters, (2) lake-level fluctuations and (3) low siliciclastic input. At the time of deposition of Unit 2, the lake acted as stratified during dry seasons (or longer periods ot time) but large inflows of fresh waters during rainy seasons changed it into an open lake realm.