Sedimentology and palaeontology of the Upper Jurassic Puesto Almada Member (Cañadón Asfalto Formation, Fossati sub-basin), Patagonia Argentina: Palaeoenvironmental and climatic significance

CABALERI, NORA; BENAVENTE, C.A.; MONFERRAN, M.D.; NARVÁEZ, P.L. ; VOLKHEIMER, W.; GALLEGO, O.F.; DO CAMPO, M.

SEDIMENTARY GEOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 296 p. 103 - 121

0037-0738

Six facies associations are described for the Puesto Almada Member at the CerroBandera locality (Fossati sub-basin). They correspond to lacustrine, palustrine, andpedogenic deposits (limestones); and subordinated alluvial fan, fluvial, aeolian, andpyroclastic deposits. The lacustrine-palustrine depositional setting consisted ofcarbonate alkaline shallow lakes surrounded by flooded areas in a low-lyingtopography. The facies associations constitute four shallowing upward successionsdefined by local exposure surfaces: 1) a Lacustrine-Palustrine-Pedogenic faciesassociation with a ´conchostracan´-ostracod association; 2) a Palustrine faciesassociation representing a wetland sub-environment, and yielding ´conchostracans´,body remains of insects, fish scales, ichnofossils, and palynomorphs (cheirolepidiaceanspecies and ferns growing around water bodies, and other gymnosperms in moreelevated areas); 3) an Alluvial fan facies association indicating the source of sedimentsupply; and 4) a Lacustrine facies association representing a second wetland episode,and yielding ´conchostracans´, insect ichnofossils, and a palynoflora mainly consistingof planktonic green algae associated with hygrophile elements. The invertebrate fossilassemblage found contains the first record of fossil insect bodies (Insecta-Hemipteraand Coleoptera) for the Cañadón Asfalto Formation. The succession reflects a mainlyclimatic control over sedimentation. The sedimentary features of the Puesto AlmadaMember are in accordance with an arid climatic scenario across the Upper Jurassic, andthey reflect a strong seasonality with periods of higher humidity represented bywetlands and lacustrine sediments.