Latest Cambrian sedimentary settings and trilobite faunas from the western Cordillera Oriental, Argentina

ESTEBAN, SUSANA BEATRIZ Y TORTELLO, MARCELO FRANCO

Memoirs of the Association of Australasian Palaeontologist

Association Australasian Palaeontologist

Lugar: Sidney; Año: 2007 vol. 34 p. 29 - 58

0810-8889

The Lampazar Formation is widely distributed in the western Cordillera Oriental of Jujuy and Salta Provinces, in the Gondwanan margin of Argentina. At the Quebrada Azul, Quebrada La Llama, Yacoraite, Quebrada de Jueya, El Moreno, Angosto del Moreno and Cangrejillos sections, it is represented by six sedimentary facies: grey laminated clayey shales (1), black laminated silty shales (2), green laminated shales (3), hummocky cross-laminated clayey siltstones (4), green massive mudstones (5), and coarse-grained facies. The unit is interpreted as having formed in an outer-shelf environment with some transitions towards inner-shelf conditions, representing a transgressive-regressive cycle that was eustatically controlled. Facies 1 and 2 ("olenid biofacies") contain proportionately high contents of organic matter. The trilobite faunas belong to the lower part of the Parabolina frequens argentina Zone. Agnostoids, olenids and shumardiids [Lotagnostus (Distagnostus) shergoldi Tortello sp. nov., L. (D.) llamaensis Tortello sp. nov., Gymnagnostus, Micragnostus, Parabolinella, Plicatolina, Akoldinioidia] are especially diverse in quiet, low-oxygen, resource-rich environments, whereas some taxa [Parabolina frequens argentina (Kayser), Angelina hyeronimi (Kayser)] are not confined to particular lithofacies. The occurrence of Lotagnostus (Distagnostus) corroborates a Late Cambrian age for the Lampazar Formation and permits intercontinental correlation.Parabolina frequens argentina Zone. Agnostoids, olenids and shumardiids [Lotagnostus (Distagnostus) shergoldi Tortello sp. nov., L. (D.) llamaensis Tortello sp. nov., Gymnagnostus, Micragnostus, Parabolinella, Plicatolina, Akoldinioidia] are especially diverse in quiet, low-oxygen, resource-rich environments, whereas some taxa [Parabolina frequens argentina (Kayser), Angelina hyeronimi (Kayser)] are not confined to particular lithofacies. The occurrence of Lotagnostus (Distagnostus) corroborates a Late Cambrian age for the Lampazar Formation and permits intercontinental correlation.