Microtextures and trapped diatoms on quartz grain surfaces in the Acapulco Beach, Mexican Pacific: An insight into palaeoenvironment

Abstract

In this study, we report Scanning Electron Microscopy (SEM) images of quartz grains in the Acapulco beach, Mexican Pacific. The morphology of quartz grains is angular, sub-angular, sub-rounded, rounded, and well-rounded. The variations in the morphology of quartz grains are indicating both nearby and distance sources. The rounded and well-rounded grains support for a long transport distance and a distal source. Microtextures of mechanical and chemical origins are identified in quartz grains. The mechanical features include, bulbous edges (ble), elongated depression (ed), parallel striations, crater, meandering ridges (mr), arcuate steps, conchoidal fractures (cf), v-shaped marks (v-s), and broken grain. These mechanical features indicate the combination of fluvial, aeolian, and subaqueous environments. The conchoidal fractures are characteristic of crystalline rocks. Arcuate steps and meandering ridges are indicating a high wave energy. The striations on grain surfaces are due to collision between two grains, probably during an aeolian transport. The chemical features include adhered particles (ap), solution pit (sp), silica globule, crystal overgrowth (crg), precipitation, and trapped diatoms. The solution pits and precipitation are indicating the diagenetic processes in a silica saturated coastal environment. A few grains are associated with both mechanical and chemical features, suggesting a dual environment, probably littoral and marine. Trapped diatoms identified in quartz grains are Cocconeis guttata and coccolith.