Microtextures on quartz grains in the beach sediments of Puerto Peñasco and Bahia Kino, Gulf of California, Sonora, Mexico

Abstract

Beach sand samples collected from two localities of the Gulf of California (Puerto Peñasco and Bahia Kino, Sonora) were analyzed in order to identify their provenance and depositional history on the basis of the different microtextures on the quartz grains. The quartz grains were examined under a scanning electron microscope which brought out thirty two distinct microtextures that can be grouped into three modes of origin, i.e., mechanical (eighteen features), mechanical and/or chemical (five features) and chemical (seven features) origin. Among nine microtextures of chemical origin, two features are of dissolutional origin, whereas five features are characteristic of precipitational origin. Most of the microtextures are common in both areas (Puerto Peñasco and Bahia Kino) but frequency of occurrence slightly varies. Quartz grains from Puerto Peñasco and Bahia Kino show conchoidal fractures, straight steps and arcuate steps, which are characteristic features of quartz grains derived from crystalline source rocks. The presence of angular to subangular outline together with straight and arcuate steps indicates that these sediments have undergone short transportation and rapid deposition. V-shaped patterns, straight scratches and curved scratches, which are characteristic features of marine environments, are common on the quartz grains of the analysed samples. Many quartz grains show subrounded outline with bulbous edges that are considered to be the product of fluvial transport. In addition, many quartz grains show subrounded to rounded outline, upturned plates and meandering ridges, which indicate that aeolian mechanisms controlled the transport of these grains. Some quartz grains show chemical precipitational features such as silica globules, silica flower, silica pellicle and trapped diatoms, which suggest that these quartz grains were derived from the silica saturated environments of intertidal zones. The present study reveals the following inferences: 1) the beach sediments in Puerto Peñasco area were transported to the area by fluvial and aeolian processes and subsequently deposited in the marine environment, and 2) the beach sediments in the Bahia Kino area were dominantly transported by fluvial processes, whereas subordinate quantity were contributed by aeolian processes and subsequently deposited in the marine environment.