Abultamiento biodetrítico en la Formación Chachao (Valanginiano): Características y evolución ambiental, Malargüe, Mendoza

Abstract

The China Echada mud mound is a small dome-shaped structure that reaches a diameter of 5,40 m and is up to 2,5 m high. The mound consists of a non-framework net mainly composed of a large amount of micrite and fragments of infaunal pelecypods, as well as sponges, echinoderms, gastropods, serpulids and microbial crusts. Scattered remains of oysters, forams, ostracods and bryozoans are also present. The core of the mud mound is massive and homogeneous, and it is flanked by microbial crusts and pelecypods, echinoderm-rich skeletal packstone to wackestone. The small mound is embedded in a monotonous succession of well-bedded bioclastic packstone to -wackestone. The presence of homogeneous micrite and peloidal micrite suggests that the in situ accumulation and early stabilization of micrite sediments may have been favoured by microbial activity, followed by rapid marine cementation. Thallasinoides isp. on both the top and flanks of the mound provide evidence that the sedimentation was interrupted and also would indicate a low rate of sedimentation. The high amount of matrix and spicules in wackestone facies also suggests quiet and deep water conditions just below the fair weather wave base. The mound occupied the external section of a homoclinal ramp. The maximum development of its growth is related to sea level rise (transgression and early highstand), as evidenced by continuous vertical accretion and a lack of allocthonous sedimentation.