CORRELATION OF JURASSIC TECTONO-SEDIMENTARY EVENTS BETWEEN AYUQUILA AND OTLALTEPEC BASINS, MIXTECA TERRANE, MEXICO

The Ayuquila and Otlaltepec Basins are located in Oaxaca and Puebla States, about 80 km apart from each other.

Both basins are filled with subaerial, fluvial/alluvial successions characterized by their abundant sin-depositional angular unconformities. Each basin stratigraphy has been subdivided in three lithostratigraphic units. Correlation is discussed, based on their similarities in sedimentary facies, detrital zircon geochronology, paleo-flora content, and major unconformities.

La Mora Fm is the oldest unit of the Ayuquila Basin; composed of red sandstone and siltstone (flood deposits). Although The Tianguistengo Fm is the oldest unit of the Otlaltepec Basin, there are some differences in its facies and deformation. The Tianguistengo Fm is made up of fluvial sandstone, siltstone, and conglomerate, that changes laterally to fine-grained flood deposits. Both show similar U/Pb detrital zircon (DZ) ages: abundant Permian ages, and a wide range of Paleozoic and Proterozoic DZ ages. Youngest Late Triassic DZ ages suggest a Triassic-Early Jurassic depositional age. However, their correlation has not been constrained.

Ayuquila Fm, at the Ayuquila Basin, and Piedra Hueca Formation, at Otlaltepec Basin overlie La Mora Fm and Tianguistengo Fm respectively. Both formations are composed of fluvial and alluvial fan conglomerate and sandstone, finning upward to sandstone and siltstone with lesser conglomerate. DZ populations are similar in both units, with three clusters, a major one of Jurassic (178-185 Ma), a second cluster of Permian DZ ages, and a third of Proterozoic (950-1,300 Ma) ages. Bedding in both formations is tilting toward the north, and were probable associated to growth faults.

Although there are sedimentological differences between the Tecomazúchil Fm, at the Ayuquila Basin, and the Otlaltepec Fm at the Otlaltepec Basin, overall, both seem to record sedimentation in coastal plains. Both have similar DZ age populations, with youngest cluster at 165-175 Ma, a wide range of Paleozoic to Mesozoic DZ ages (300-175 Ma), some Neoproterozoic DZ ages, and a Mesoproterozoic cluster.

Regional and Tectonic significance will also be discussed.

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