7-1 Lithified Thrombolites Discovered in the Municipality of Loreto, Baja California Sur.

Session: Earth Life Sciences across the Cordillera (Posters)

Presenting Author:

Authors:

Abstract:

Thrombolites are lithified microbial structures formed by benthic cyanobacterial and microbial communities that precipitate carbonate, producing accretionary, clotted microbialites. These formations represent some of the most ancient biological structures on Earth and provide critical insight into early biospheric evolution and modern extremophile ecosystems. In Mexico, thrombolites have historically been considered rare and poorly documented. In 2006, Siqueiros-Beltrones et al. reported the first confirmed occurrence of lithified thrombolites in Mexico, documenting well-developed microbialite platforms in the Bay of La Paz, Baja California Sur. These formations occur in shallow, sheltered, hypersaline environments and represent rare modern analogues of ancient microbial reef systems. In 2021, during mangrove surveys in a small closed estuary near Loreto, Baja California Sur, an additional site of lithified microbial structures was identified. The microbialite platforms show strong morphological, environmental, and lithological similarities to the thrombolites described from the Bay of La Paz, approximately 100 km to the south. The Loreto site is located within a small saline estuary isolated behind a sand barrier. Preliminary observations suggest active accretion under hypersaline, low-energy conditions comparable to those of the La Paz thrombolites. Ongoing work focuses on formal documentation, geomorphological characterization, and taxonomic identification of the microbial communities responsible for carbonate accretion. Recent hydrological changes have raised immediate conservation concerns. A notable decline in estuarine water levels has occurred over the past several years, and by 2025 a substantial portion of the thrombolite platform has become subaerially exposed. These exposed structures show signs of desiccation and apparent mortality, suggesting that a significant fraction of the living microbial structure may already have been lost. Given the extreme rarity of confirmed modern thrombolite systems in Mexico, the Loreto microbialite platform represents a site of high scientific and conservation value. Its vulnerability to minor hydrological shifts highlights the need for urgent baseline documentation, species-level microbial characterization, and assessment of hydrological drivers, as well as evaluation of potential habitat stabilization strategies. This newly recognized platform expands the known distribution of modern microbialite systems in the southern Gulf of California and provides a valuable opportunity to examine early reef analogues under contemporary environmental stressors.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.