El depocentro triasico de Santa Clara, Cuenca Cuyana, se caracteriza por espesos depositos generados en ambiente lacustre. Uno de ellos, con un registro de mas de 345 m, corresponde a la Formacion Mollar. El tramo inferior a medio esta caracterizado por una monotona sucesion de lutitas bituminosas acumuladas por decantacion suspensiva en el 'off shore' anoxico de un cuerpo lacustre hidrologicamente cerrado y que muestra alto contenido de materia organica amorfa de origen algal y de restos de plantas terrestres muy degradadas junto a sulfuros de hierro autigenos. Intercalan areniscas finas debidas a corrientes de turbidez diluidas y carbonatas estromatoliticos. En esta sucesion se definen ciclos granocrecientes de pequena escala (PACs) que se atribuyen a episodios de expansion-retraccion lacustre controlados por cambios climaticos. Asociaciones de facies heteroliticas representan los depositos de la transicion entre los ambientes de 'nearshore' y 'offshore' lacustre. La seccion superior de la Formacion Mollar se compone de sucesiones peliticas con profusa bioturbacion que sugieren mayor oxigenacion del sustrato y se asignan a ambiente de costa afuera de un sistema lacustre holomictico hidrologicamente abierto. Intercalan areniscas producto de flujos hiperpicnales. Depositos de areniscas con abundantes trazas fosiles y estructuras de olas y flujos unidireccionales, representan a sectores marginales del ambiente lacustre. Ademas de los ciclos de alta frecuencia, en la Formacion Mollar se definen tres secuencias asimetricas de mayor escala atribuidas a episodios mayores de expansion-contraccion lacustre debidos a la interaccion entre factores climaticos y tectonicos. El diseno de superposicion granocreciente de la Formacion Mollar y la gradual transicion a depositos fluviales de la sobreyacente Formacion Montana refleja asimismo una constante reduccion del espacio de acomodacion sedimentaria en el depocentro de Santa Clara a medida que se produjo la acumulacion de los depositos estudiados.The Triassic Santa Clara depocenter, Cuyo Basin, is characterised by thick fine-grained deposits formed in lacustrine systems. One of them, represented by the Mollar Formation, exceeds the 345 m. The lower to middle section of this unit is dominated by a monotonous succession of black shales having a high content of amorphous organic matter produced by algae and highly degraded plant remains. These deposits were formed by suspension fallout in the anoxic ‘offshore’ sector of a hydrologically closed lake. Thin and fine-grained turbiditic beds and stromatolitic carbonates are intercalated in the fine-grained succession. Small-scale coarsening-upward cycles (PACs) are attributed to episodes of lake expansion-retraction driven by climate change. A facies association composed of an heterolithic package represents the deposits of the transition between ‘nearshore’ and ‘offshore’ settings. The upper section of the Mollar Formation essentially consists of bioturbated mudstones suggesting a greater oxygenation of the substrate. They are assigned to the ‘offshore’ environment of a holomictic hydrologically open lake system. Sporadic hyperpycnal flows are documented by intercalations of sandy turbidites. Bioturbated sandstone beds with primary structures indicative of both normal and storm wave action and unidirectional flows, represent the marginal deposits of the lacustrine system. In addition to the high-frequency cycles, three larger scale asymmetrical sequences are identified in the Mollar Formation. These sequences suggest episodes of major expansion-contraction of the lake system due to the interaction between climatic and tectonic factors. The overall shallowing up stacking pattern of the Mollar Formation and the gradual transition to fluvial deposits of the overlying Montaña Formation reflects a steady reduction of accommodation space in the Santa Clara depocenter during the accumulation of the studied succession.