DEFORMATION OF THE TEPOSCOLULA FORMATION BETWEEN CHILA DE LAS FLORES, PUEBLA, AND HUAJUAPAN DE LE"N, OAXACA

Between the towns of Chila de las Flores, Puebla (north) and Huajuapan de Leon, Oaxaca (south) there are many outcrops of the Cretaceous Teposcolula Formation which is a thickly bedded (1 m) carbonate unit, with local reef facies at the base and a transition to more thinly bedded strata (10 to 20 cm) toward the top. The Teposcolula Fm. is unconformably underlain by the Mapache Fm (in the north), Chimeco Fm (in the center) and Solano Fm (in the south of the area). It is unconformably overlain by the Paleocene Huajuapan Formation red beds. In general the rocks of the Teposcolula Formation belong to a carbonate platform established on the Mixteco Terrane (SW of Mexico) during the late Mesozoic.

The structure of the area has previously been attributed to the Laramide orogeny and interpreted as a homoclinal structure (Petlalcingo-Huajuapan homocline), which characterizes the Teposcolula Formation without evidence of significant internal strain (Caballero-Miranda, 1990). In this study we investigated the strain distribution of the limestone rocks in the area between Huajuapan and Chila, conducting systematic field observations and detailed structural analysis at various locations where the Teposcolula Formation is exposed.

The results of our analysis indicate that the Teposcolula Fm. Is folded and thrust faulted at various scales and accomodates a considerable amount of strain with a systematic variation from the base to the top of the unit.. Deformation at the base is dominated by imbricate thrust faults with flat-roofed duplex structures at the outcrop scale. Further up the section folds are broader and typically include fault bend and fault propagation folds. Finally, toward the top of the unit there are open folds with a general strike of axial plane towards the NW. All this structures have a vergence the SW, which is very interesting in the regional context.

References.

Caballero-Miranda, C. 1990. Geología y Anisotropía del Jurásico Continental del área de Huajuapan de León-Petlalcingo Estados de Oaxaca y Puebla: Facultad de Ciencias, UNAM, Tesis de Maestría, 142 p.