Sedimentary facies, depositional environments and stratigraphy of the Cambrian - Tremadocian Santa Rosita Formation at the Alfarcito area, Cordillera Oriental, Argentina

BUATOIS, L.A.; ZEBALLO, F.J.; ALBANESI G.L; ORTEGA G.; VACCARI, N.E.; MÁNGANO, M.G.

Latin American Journal of Sedimentology and Basin Analysis

Asociación Argentina de Sedimentología

Año: 2006 vol. 13 p. 1 - 29

1669 7316

The Upper Cambrian-Tremadocian rocks exposed in the Alfarcito area of CordilleraOriental, northwest Argentina reveal a series of transgressive-regressive cycles punctuated by incisionof fluvio-estuarine valleys. An integrated sedimentologic, biostratigraphic and sequence stratigraphicstudy permits characterization of the sedimentary facies and stratal stacking patterns, and a revisionof the stratigraphic framework of this succession. The Upper Cambrian-Tremadocian succession isincluded within the existing Santa Rosita Formation, which is formally subdivided here into sixunits, the Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Rupasca and Humacha members. Thisscheme recognizes the internal complexities of the formation, in that the Tilcara and Pico de Halcónmembers record sedimentation in areally-restricted incised valleys and contain structures indicativeof tidal dominance, whereas the Casa Colorada, Alfarcito and Rupasca members typify wavedominatedopen-marine environments, where background suspension-fallout was punctuated byoscillatory flows during storms. The Tilcara Member is incised into the underlying Mesón Group.The Casa Colorada Member reflects a basinwide Late Cambrian transgression and subsequentprogradation and consists of lower to upper offshore deposits. The Pico de Halcón Member isincised into the Casa Colorada Member. The Alfarcito Member is divided into three distinctlyupward-coarsening and-thickening intervals. The sandstone-dominated intervals are composed oflower to middle shoreface deposits with minor amounts of offshore transition and upper shorefacedeposits. The heterolithic, fine-grained intervals record more distal deposition, ranging from thelower offshore to the offshore transition. The Rupasca Member is a dominantly fine-grained unitthat records a major late early to early late Tremadocian transgression. The lower interval of thismember consists of lower offshore to offshore-transition deposits, while the upper part is made upof shelf to lower offshore deposits. The Humacha Member is not well exposed in the study area.The importance of integrating biostratigraphy within a sedimentologic and sequence-stratigraphicframework is underscored here, in that it enables us to construct a more accurate stratigraphicframework which permits a clear understanding of the sedimentary dynamics of this system.