Chapter 4 – Peat Fires in Northeastern Mexico: Geochemistry, Chronology, and Paleoreconstruction

This chapter presents the geomorphological features associated with a peat fire occurring in one of the sedimentary basins of northeastern Mexico along with the chemical composition and radiocarbon chronology of one peat horizon. The peat fire has caused the formation of a semicircular sinkhole, vertical ground fissure, and subsidence in the basin. Chemical and chronological characteristics estimated the amount of carbon storage, identified the source of biomass, and presented a conceptual model of different depositional environments up to the initiation of a peat fire. The peat horizon was deposited between 19,100 and 12,200 cal yr BP and comprises different amounts of quartz, gypsum, and rosickýite. The lower part of the peat (19,100–15,600 cal yr BP) has more carbon storage (81–167 mgC/cm3) compared to the upper part (15,600–12,200 cal yr BP; 18–59 mgC/cm3). Chemical and mineralogical compositions and stratigraphy suggest that plants growing in a fresh water marshy environment provided biomass for the lower part. The biomass for the upper part was mainly sourced from lacustrine algae and phytoplankton in a deeper and perennial lake condition. Over the last 12,200 cal yrs, the amount of carbon storage was reduced to 0–23 mgC/cm3 as the basin experienced several intervals of desiccation. The unregulated exploitation of ground water for agricultural activities during AD 1980–2004 has caused a fall in the water table and expansion of the desiccation fissures into the subsurface and has led to the initiation of a peat fire in the basin.