Sedimentology and sequence stratigraphy within a mixed (carbonate-siliciclastic) rift to passive margin transition: The Early to Middle Cambrian of the Argentine Precordillera

GOMEZ, F.J.; ASTINI R.A.

SEDIMENTARY GEOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 316: p. 39 - 61

0037-0738

Through the analysis of facies stacking patterns, geometries and bounding surfaces,sequence stratigraphy provides a framework to better understand sedimentary facies distribution and evolution. Many published works contain noteworthy examples where a sequence stratigraphy approach was applied to Middle-Late Paleozoic, Mesozoic and Cenozoic sedimentary units. Early Paleozoic examples, however, remain relatively scarce. This article addresses the exceptionally well-exposed Cambro-Ordovician Argentine Precordillera carbonate bank. It focuses on the late Early to Middle Cambrian La Laja Formation, a carbonate siliciclastic succession outcropping at its base. Given the stratigraphic and faunitic similarities, the Precordillera is considered a Laurentia-derived allochthonous terrane, which detached from Laurentia margin during Early to Middle Cambrian and attached to the western Gondwana margin in Mid-Ordovician. This work was built upon a detailed facies and microfacies analysis of the La Laja Formation and equivalent units. Thirteen facies associations were recognized,representing a spectrum of environments ranging from deep subtidal, shallow subtidal to inter supratidal sabkha facies. This analysis allowed for the recognition of three sequences (S1, S2 and S3) separated by unconformities (D1, D2, D3 and D4). A recipirocal sedimentation model is suggested to explain coarse-grained siliciclastic intervals overlying subtidal limestones. However the fine-grained siliciclastic-rich carbonate intervals seem to represent transgressive and normal regressive highstand deposits, probably influenced by high accommodation and climatically driven siliciclastic influx. Lateral facies and thickness variations suggest that the La Laja Formation developed during the progressive margin stabilization with differential subsidence. The sequence boundary separating the La Laja Formation from the overlying Zonda Formation represents an important architectural change from mosaic heterogeneous subsidence in the Early- Middle La Laja Formation to the passive margin stage with flat-lying remarkably continuous rhythmic dolomites in the overlying Upper Cambrian Zonda Formation. Further strengthening these similarities, a similar transition has also been suggested for coeval units of the Larentia paired margin.