Resumen del producto

In the Baja California peninsula and elsewhere most studies on microbialiths have focused on understanding the processes by which stromatolites are formed and to provide clues of past microbial activity. Unlike stromatolites, thrombolithic platforms from the peninsula and their incipient predecesors are not obviously differentiated into structures that immediately catch the untrained eye. The recent discovery of pro-thrombolites the predecesors of thrombolites in the southernmost part of the peninsula gave a new perspective on the geomorphological role of microbialithic structures in the coastal zone, particularly in the formation of coastal lagoons. Pro-thrombolithic development initiates with the extensive growth of cyanophyte mats that conglomerate sediments and accrete. These evolve into platforms that accrete seaward and may continue on to lithified plate formation. However much remains as unlithified extensive platforms. More recent ones showing a cyanophytic sheet, older ones are deprived of it. Evidence shows that pro-thrombolithic growth seaward may be responsible for much coastal terrain including that serving as basement for the dune formations of sand bars in coastal lagoons. Wherever coastal lagoons have been formed by way of sand bar development, similar pro-thrombolithic processes are expected to have occurred and may still be going on. This has been confirmed in several localities in NW México including non-lacunar environments that may have shown lacunar conditions in the past. Similar formations have been recently observed in the Yucatán peninsula.

Palabras clave: lagunas costeras; protrombolitos; cianofitas; Tapetes microbianos

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