GEOLOGIC AND DEPOSITIONAL SETTING

The lower Paleozoic Northwest Argentina Basin is a retroarc foreland basin developed along the margin of western Gondwanaland (Ramos 1999; Astini 2003) (Figure 2). The volcanic arc is known as the Faja Eruptiva de la Puna Occidental (Coira et al. 1982; Moya et al. 1993; Ramos 1999). Eastward prograding fan deltas fed turbidite systems that developed in the foredeep region (Astini 2003). The peripheral bulge and the back-bulge were dominated by a wave-dominated shallow-marine ramp punctuated by tide-dominated valley incisions and deltaic progradation (Astini 2003; Buatois and Mángano 2003; Buatois et al. 2006). This wave-dominated ramp is exposed along Cordillera Oriental and includes deposits ranging from the Furongian to the Ashgillian (see biostratigraphic information in Brussa et al. 2003; Waisfeld and Vaccari 2003). Wave-dominated shallow-marine successions comprise regionally extensive parasequences. Deposits commonly encompass shelf, lower- to upper-offshore, offshore-transition, and lower- to upper-shoreface settings (Buatois and Mángano 2003; Buatois et al. 2003a, 2006; Astini et al. 2004).

For this study, integrated sedimentologic and ichnologic analyses were undertaken in the following units: (1) the Furongian Lampazar Formation; (2) the Furongian Casa Colorada Member of the Santa Rosita Formation; (3) the Furongian-lower Tremadocian Alfarcito Member of the Santa Rosita Formation; (4) the upper Tremadocian Rupasca Member of the Santa Rosita Formation; (5) the upper Tremadocian Humacha Member of the Santa Rosita Formation; (6) the lower to middle Arenigian Acoite Formation, and (7) the upper Llanvirnian to lower Caradocian Santa Gertrudis Formation.