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Despite the large number of tsunamis that impact Mexico’s Pacific coast, stratigraphic studies focusing on geological impacts are scanty, making it difficult to assess the long-term risks for this vulnerable region. Surface samples and six cores were taken from Laguna Mitla near Acapulco to examine sedimentological and geochemical evidence for marine incursion events. Sediment cores collected from behind the beach barrier are dominated by intercalated layers of peat and inorganic sediments, mostly silt and clay, with little or no sand. Sand- and shell-rich clastic layers with high levels of sulfur, calcium, and strontium only occur adjacent to the relict beach ridge remnants near the center of the lagoon. With the exception of one thin fine sand layer, the absence of sand in the near-shore cores and the predominance of the terrigenous element titanium in the inorganic layers, evidently eroded from the surrounding hillslopes, suggests that these large-grained intervals do not represent episodic marine incursions, but rather were likely formed by the erosion and redeposition of older marine deposits derived from the beach ridge remnants when water levels were high. These results do not support the occurrence of a large tsunami event at Laguna Mitla during the Late Holocene. [ABSTRACT FROM AUTHOR]

To understand the geological processes induced by tropical cyclones, geochemical and sedimentological analyses were performed on a 3 m sediment core (basal 14C date of 940 +/- 50 years BP) extracted from a marsh adjacent to a backbarrier lake along Louisiana's Gulf of Mexico coast (USA). This study was conducted in order to identify the geologic changes within a subsiding coastal region in the light of coastal recession and past hurricane activity. Previous studies show that Bay Champagne, a semi-circular lake near Port Fourchon, Louisiana, is subjected to subsidence rates between 1.0 and 1.2 cm year-1, the highest rate of retreat within the entire northern Gulf of Mexico. Loss-on-ignition (LOI) and X-ray fluorescence (XRF) analyses, employed to generate lithological and geochemical core profiles, identified three distinct sand layers measuring up to 50 cm in thickness deposited by recent hurricanes. LOI shows large decreases in water, organic, and carbonate contents, indicating the occurrence of marine inundation. Within each marine incursion layer terrestrial elemental concentrations as determined by XRF display large depletions. Grain size analysis of a portion of the core (30-86 cm) indicates the presence of two series of sequential high-energy storm deposits followed by intense fluvial flooding within Bay Champagne. These events are attributed to Hurricanes Katrina/Rita in 2005 and Gustav/Ike in 2008. [ABSTRACT FROM AUTHOR]