Abstract
Abstract. The beach-ridge sequence of the Usumacinta–Grijalva delta borders a 300 km long section of the southern Gulf of Mexico coast. With around 500 beach ridges formed in the last 6500 years, the sequence is unsurpassed in the world in terms of numbers of individual ridges preserved, continuity of the record, and temporal resolution. We mapped and dated the most extensively accreted part of the sequence, linking six phases of accretion to river mouth reconfigurations and constraining their ages with 14C and OSL dating. The geomorphological and sedimentological reconstruction relied on lidar data, coring transects, GPR measurements, grain-size analyses, and chemical fingerprinting of volcanic glass and pumice encountered within the beach and dune deposits. We demonstrate that the beach-ridge complex was formed under ample long-term fluvial sediment supply and shorter-term wave- and aeolian-modulated sediment reworking. The abundance of fluvially supplied sand is explained by the presence of easily weatherable Los Chocoyos ignimbrites from the ca. 84 ka eruption of the Atitlán volcano (Guatemala) in the catchment of the Usumacinta River. Autocyclic processes seem responsible for the formation of ridge–swale couplets. Fluctuations in their periodicity (ranging from 6–19 years) are governed by progradation rate, and are therefore not indicative of sea level fluctuations or variability in storm activity. The fine sandy beach ridges are mainly swash built. Ridge elevation, however, is strongly influenced by aeolian accretion during the time the ridge is located next to the beach. Beach-ridge elevation is negatively correlated with progradation rate, which we relate to the variability in sediment supply to the coastal zone, reflecting decadal-scale precipitation changes within the river catchment. In the southern Mexican delta plain, the coastal beach ridges therefore appear to be excellent recorders of hinterland precipitation.
Highlights
Beach-ridge plains with long sequences holding many individual ridges consisting of coral rubble, shell hash, cobbles, gravel, and/or sand are widely distributed across the globe
During the past few decades, research on beach-ridge sequences has progressed from describing their morphology and possible origins (Taylor and Stone, 1996; Otvos, 2000) to enabling their usage for palaeoenvironmental reconstructions
Since the significant reduction in the rate of postglacial sea level rise in the mid-Holocene, hundreds of semi-parallel sandy beach ridges formed across a shore-perpendicular distance of more than 20 km
Summary
Beach-ridge plains with long sequences holding many individual ridges consisting of coral rubble, shell hash, cobbles, gravel, and/or sand are widely distributed across the globe They have developed along marine shores and lakeshores under favourable wind and wave conditions and sufficient longterm sediment supply. During the past few decades, research on beach-ridge sequences has progressed from describing their morphology and possible origins (Taylor and Stone, 1996; Otvos, 2000) to enabling their usage for palaeoenvironmental reconstructions They can be used to assess external controls of (relative) sea level rise, land subsidence, variations in storm impact, and changes in climate and upstream land use (Scheffers et al, 2012; Tamura, 2012 and references therein). We use Otvos’s (2000) broad definition of beach ridges, including all “relict, semiparallel, multiple ridges” formed by waves (berm ridges), wind (multiple ridges originating as foredunes), or a combination of both
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