243 / 2022-03-28 12:34:59

Provenance implications of quartz grain microtextures in the Salina Cruz and Bachoco beaches, Oaxaca state, Mexican Pacific

SEM,Quartz grains,Coastal sediments,Active margin,Slickenside surface,Shock melted grains

Oaxaca coast, located at the edge of the Sierra Madre mountains cover nearly 35 km of the Mexican Pacific coastline. Based on SEM images, we studied the microtextures of quartz grains recovered from the Salina Cruz (16°10’05.79’’N and 95°10’53.52’’W) and Bachoco (15°51’57.25’’N and 97°05’33.58’’W) beach areas in the Oaxaca State, Mexican Pacific Ocean. The quartz grains are angular to sub-rounded, suggesting its derivation from different source terranes with short and long transport. We inferred microtextures of mechanical, chemical, and mechanical/chemical origin. Microtextures in both beaches are abundant in mechanical origin with meandering ridges, percussion marks, abrasion fatigue, impact scars, and the sock-melted grains indicating high energy subaqueous beach environment, while slickenside surfaces reflect shear zones adjacent to faults that result from shrink and swell cycles or by the crushing of peds against one another during collision impact.  

The microtextures of chemical origin such as silica globules, solution pits and crystal overgrowth indicate the diagenetic environment in a silica saturated zone. Finally, the high influence of mechanical/chemical origin is represented by elongated depression, adhering particles and medium relief. The new microtextures observed in quartz grains are sock lamellae, arc shaped steps, slickenside surfaces, crescentic gouges, and shock-melted feature.

The rivers that drain into the Pacific Ocean and oceanic circulation along the coast in the Gulf of Tehuantepec are strongly controlled by a series of wind events known as “Nortes” or “Tehuanos”, which confirm that the mode of transport of sediments to the beach areas was predominately by wind and marine domain, with fluvial contributions due to its proximity to rivers.