PRELIMINARY INTERPRETATION OF A STROMATOLITE FIELD IN LAGUNA BACALAR, QUINTANNAROO MEXICO

A field of fifty “mushroom-shaped” stromatolites has been mapped in Laguna Bacalar, Mexico. The field rims a cenote with pillar-formed stromatolites flanking the slopes indicating contemporaneous formation. Mapping suggests the field is geoographically more widespread. The fauna and flora is low diversity on the “living surface”. Paleodiversity is poorly understood, but coring indicates stable biota during growth. Stromatolites heads are "marine shaped", consist of isolated and coalesced heads within 2 m of lagood floor, in less than 2m water depth. The immediate shore proximity and 5cm peat horizon above some of the heads indicates a progradation of sediment, suggesting the stromatolites may be relict exhumations. A field of likely reworked "oncolites", or lithoclasts, occurs 30 meters offshore. Radiocarbon dating indicates stromatolites formed began 8-9 KYA. The initial environment of formation is still uncertain and several questions remain unanswered, including: was the initial environment a restricted lagoon/lake (i.e., has the salinity of Laguna Bacalar changed during the Holocene), does salinity of Laguna Bacalar shift through time, is the stromatolite trend structually controlled with cenotes along the trend as reflected by linear lake shape, what is the relationship to known regional elevated carbonate-saturation setting, and why are no macro-grazers present?