Concentraciones fosilíferas ordovícicas en las formaciones Acoite y Sepulturas, Cordillera Oriental jujeña. Análisis tafonómico y paleoecológico

WAISFELD, B.G.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 1997 vol. 34 p. 317 - 332

0002-7014

A detailed taphonomic analysis of trilobite-dominated fossil concentrations was performedin the middle- upper part of the Acoite and Sepulturas formations at thewestern flank of the Cordillera Oriental, Jujuy Province. Based onbiostratinomic indices and fabric of the concentrations, three types ofbioclastic deposits have been recognized: (1) bidimensional bioclasticdeposits, (2) thin and closely packed bioclastic deposits, and (3) tabularbioclastic deposits with complex microstratigraphy. Bidimensional bioclasticdeposited were formed under null sedimentation rates. Two grades have beendistinguished according to the effects of physical processes: grade a inwhich primary biogenic processes were obliterated, and grade b interpreted asbiogenic concentrations subsequently reworked. Thin and closely-packed bioclastic deposits are formed under lowrates of detritial sedimentation and high rates of autochthonous hardpart input,alternating with episodic increments in clastic supply. Both types ofbioclastic deposits reflect diastemic interruptions during the aggradationalprocess of the stratigraphic record. Despite the ecological shift related tosubstrate consistency and turbidity levels, no significant faunal replacementwas achieved during the development of these deposits. The tabular bioclasticdeposit with complex microstratigraphy accounts for a shallowing-up cycle in an otherwise distal shelf environment. The complex internal nature indicates condensation of the paleontologic and sedimentologic record. The faunal turnover is interpreted as an example of community tracking in response to sea level changes. From a paleoecological viewpoint trilobite associations display low levels of time-averaging. They were only slightly affected by short term environmental fluctuations, showing a long term trend of ecologic persistence.