Estructuras de corte y relleno en secuencias de plataforma: su significado tafonómico y paleoecológico (Ordovícico de la Cordillera Oriental, Argentina)

ASTINI, R.A.; WAISFELD, B.G.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 1995 vol. 32 p. 41 - 55

0002-7014

Cut andfill (gutter-casts) and similar circular or furrow-like structures from theEarly Ordovician (Acoite Formation) of the Cordillera Oriental of NorthwesternArgentina are described and interpreted throughout a combined sedimentologic,paleoecologic, and taphonomic analyses. The Acoite Formation is about 2000 mthick and represents a storm-dominated shelf depositional  system. Gutter-cast filled with sandstonesand coquinas are dominant in muddy facies in the middle and upper parts of theunit. The analysis of the morphology and internal structure of the gutter-castssuggest a composite origin for both the erosive and depositional phasesinvolved in the formation of these structures. The erosive events areinterpreted as produced by strong storm-surge ebb currents, which drag thebottom with secondary helical flows superimposed to characteristic combinedflows present on the shelf. A detailed biostratinomic study allows thedistinction of various types of coquinas filling the furrows. Some are mainlyallochthonous and others mainly autochthonous or parautochthonous. Taking inaccount their segregation, sorting, reorientation, mechanical abrasion, and fragmentation,a variable degree of mixing has been determined. Life habits and preferences ofthe organisms colonizing the furrows account for a string habitat alteration.The paleoecologic features of autochthonous and parautochthonous concentrationsindicate a significant faunal turnover in relation to surrounding autochthonous assemblages of the muddy shelf.