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Based on scanning electron microscopy (SEM) images, we studied the microtextures of quartz grains recovered from the Boca del Cielo and Chocohuital beach sediments in the Chiapas state, Mexico. Microtextures of mechanical, chemical, and mechanical/chemical origins were identified. Quartz grains in both beaches were sub-angular to sub-rounded in shape, indicating high energy, short transport, and nearby source. The microtextures of mechanical origin like percussion marks, conchoidal fractures, and V-shaped marks were abundant in the Chocohuital beach, which revealed high energy subaqueous beach environment. Large-scale conchoidal fractures are characteristic of crystalline rocks, and abrasion features are due to energetic grain-to-grain collision during eolian transport. However, quartz grains in the Boca del Cielo beach were dominated with microtextures of chemical origin such as adhered particles, solution pits, and crystal overgrowth, and are abundant with trapped diatoms, which indicated the diagenetic processes in a silica saturated environment. Two diatoms Navicula incertata and Cyclotella bodanica of 15-μm size are identified in Boca del Cielo quartz grains. [ABSTRACT FROM AUTHOR]

The study area is northwest part of Sanandaj-Sirjan or Esfandegha-Marivan zone in the northwest of Iran. The oldest rocks which are limestone, sandstone, tuff, and lava belong to the Jurassic which have deformed during the Late Cimmerian orogeny. This complex is unconformably overlain by Cretaceous volcano sedimentary. The dominantly Cretaceous outcrops are limestone, shale, tuff, and basic to intermediate volcanic rocks. The Jurassic complex was locally metamorphosed by granitoid intrusions during the Cretaceous. Geochemical interpretations show some differences in magmatic activity in the Jurassic and Cretaceous periods. Furthermore, the chemical composition confirms the alkaline to calc alkaline trend for these two major groups. In petro-tectonic diagrams, they plot in the extensional and active margin tectonic regime. The existence of a few hundred meters of Jurassic lava with interbeded sediments, which have deformed in the Late Cimmerian orogeny infer the simultaneous existence of extension and subsidence during the Jurassic and so a compression regime in the late Jurassic (Late Cimmerian). Based on our findings, this area shows sporadically occurring extension and compression tectonic regimes over the subduction zone in the Jurassic and Cretaceous such as Cordilleran belt. [ABSTRACT FROM AUTHOR]