Geological Evolution of the Southern Coast of the Gulf of Mexico: Geomorphological and Sedimentological Evidence from the <i>Coatzacoalcos </i><i>paleolagoon</i>

Geomorphological and sedimentological evidence and depositional ages of different geological units in the northern part of the lower Coatzacoalcos River basin suggest the existence of a previously unreported paleolagoon on the southern Gulf of Mexico coast. In this paper, we refer to it as the Coatzacoalcos paleolagoon. We developed a digital elevation model to simulate the accumulation of sand sediments that, over time, filled the paleolagoon, an event that began approximately 12,000 - 10,000 years ago. It collected 22 sediment samples to analyze their grain size distribution, percentage, and color, revealing their affinity in defining the boundaries and shape of the Coatzacoalcos paleolagoon. The grain size distribution was obtained by sieving. The volume-grain size plots revealed differences between the two sediment types: cream-colored sand and red-orange silty sand and clay. Results showed that the sand sediments originated in the Chiapas Massif, which is formed by quartz-rich intrusive igneous rocks (granite and granodiorite) that filled the paleolagoon. Silty sand and clay sediments are present at the boundaries of the paleolagoon, having a distinct origin from the sand. They originate from extrusive igneous rocks of the Sierra de Santa Martha (andesites, andesitic tuffs, and basalts).