Estratigrafía y análisis tafonómico de Bonitasaura salgadoi Apesteguía, en el sitio “La Bonita” (Cretácico superior, Río Negro, Argentina)

LEANDRO M. PÉREZ; ALEJANDRO OTERO; SEBASTIÁN APESTEGUÍA; PABLO A. GALLINA

Rev. Mus. Argentino Cienc. Nat., n.s.

Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"

Lugar: Buenos Aires; Año: 2009 p. 39 - 48

1514-5158

“La Bonita” is a fossiliferous locality close to the Cerro Policía town, Río Negro Province, Argentina. It outcrops there continental siliceous rocks belonging to the Bajo de la Carpa and Anacleto Formations (Santonian-Campanian) and unconformably to the Rentería Formation (Upper Pliocene-Pleistocene). The Bajo de la Carpa Formation is composed of sandstones, fine levels of conglomerates, alternate with pelites and wackestone levels. The Anacleto Formation is composed of sandy to pelitic levels. The Rentería Formation is dominated by conglomerates with clasts that reach 15 cm in length, included in a sabullitic matrix. The facial analysis suggests that the sedimentation environment began with a fluvial regime. The fine to coarse level alternance from the base would indicate a clear subacuatic control with energy flow changes from mid to low energy. The lenticular-shaped sandy cannals with crossed stratification point to an unidirectional flow in the transporting agent and bioclasts. The taphonomical analysis suggested that the animal dies close to the river margins, being rapidly incorporated to the fluvial sediments that sepulted the specimen in successive events. The spatial distribution and bone relations suggest a very short transport from the source area, with a slight northward movement. The presence of two caudal vertebrae series with an opisthotonous articulation pattern, suggests that the animal was exposed long enough to permitt the rigor mortis and dissecation. The disarticulation degree also point to some amount of weathering of the skeleton before being sepulted. However, the exceptional periostium preservation in many cases suggests a very short subaerial exposure.