The rift history of the Salta basin is related to the evolution of the Central Andes and to the activity of the Pacific margin, owing to its geographic location. Sedimentation occurred from the Neocomian to the Paleogene, with deposits reaching up to 5,000 m in thickness. Paleoenvironmental analysis reveals an evolutionary history controlled by tectonic and climatic changes. Isolated grabens characterized the early synrift stage; differential subsidence provoked distinct environments in the southern and northern subbasins. In the southern subbasins, alluvial-fan, fluvial-fan and lacustrine deposits prevail, whilst in the northern subbasins eolian and fluvial environments dominate. During the Maastrichtian, two major factors controlled the basin fill: the decrease in tectonic subsidence and a relative sealevel rise as recorded in South America. An extensive and shallow Atlantic marine ingression installed a carbonate system coincident with mainly humid conditions until the Danian. Until the Middle Eocene, the fluvial and lacustrine environmental evolution of the sag basin was controlled especially by the alternation of temperate with dry and humid periods. Paleontological records reflect these climatic changes and show their relationship to the sedimentation regime.

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The Maastrichtian-Danian limestones of the Yacoraite Formation (northwestern Argentina) show carbon and oxygen isotopic values consistent with shallow marine conditions. The members of the formation respond to different sedimentary environments and are characterised by distinctive stable isotopes and geochemistry. The basal Amblayo Member is composed of high-energy dolomitic limestones and limestones with positive isotopic values (+2& d 13 C, +2& d 18 O). The top of the member reveals an isotopic shift of d 13 C (À5&) and d 18 O (À10&), probably related to a descent in the sea level. The sandy Gü emes Member has isotopically negative (À2& d 13 C, À1& d 18 O) limestones, principally controlled by water mixing, decreased organic productivity, and compositional changes in the carbonates. The isotopically lighter limestones are calcitic, with a greater terrigenous contribution and different geochemical composition (high Si-Mn-Fe-Na, low Ca-Mg-Sr). These isotopic and lithological changes relate to the Cretaceous-Palaeogene transition. The Alemanía Member, composed of dolomitic limestones and pelites, represents a return to marine conditions and shows a gradual increase in isotopic values, reaching values similar to those of the Amblayo Member. The Juramento Member, composed of stromatolite limestones, shows isotopic variations that can be correlated with the two well-defined, shallowing-upward sequences of the member. ResumenLas calizas maastrichtiano-danianas de la Formació n Yacoraite del noroeste argentino revelan valores de isó topos estables coherentes con el ambiente marino somero predominante del depó sito. Los miembros de la Formació n, que responden a variaciones ambientales, quedan caracterizados por valores isotó picos y geoquímicos. El Miembro Amblayo basal está compuesto por calizas dolomíticas y calizas de alta energía con valores isotó picos positivos (+2& d 13 C, +2& d 18 O). En el techo del miembro se observa un salto isotó pico del d 13 C (À5&) y del d 18 O (À10&) probablemente vinculado con un descenso del nivel del mar. El Miembro Gü emes, arenoso, posee calizas con valores isotó picos negativos (À2& d 13 C, À1& d 18 O) controlados principalmente por mezcla de aguas, descenso en la productividad orgánica y cambios composicionales del carbonato. Las calizas isotó picamente más livianas son calcíticas, poseen mayor contenido de elementos terrígenos y composició n geoquímica diferente (alto Si-Mn-Fe-Na, bajo Ca-Mg-Sr). Estos cambios estarían relacionados con la transició n Cretácico-Paleó geno. El Miembro Alemanía, compuesto por calizas dolomíticas y pelitas, representa un regreso a las condiciones marinas y muestra un paulatino aumento isotó pico hasta asemejarse a los valores del Miembro Amblayo. El Miembro 0895-9811/$ -see front matter Ó Juramento, compuesto por calizas estromatolíticas, muestra variaciones isotó picas que serían correlacionables con los dos ciclos de somerizació n bien definidos del miembro.