18-19 m thick Renalcis-archaeocyath reefs.
Typified as type 1 reef with abundant cement.
Abstract ref. 1070:
 I - Framework reefs occurring at the base of the carbonate interval of the Puerto Blanco Formation. These consist of an archaeocyathan framework with encrusting renal acids and abundant fibrous cements. Cavities are filled with mudstone and contain rare sponge spicules. Cements are well developed upon internal sediments. The archaeocyathan fauna is dominated by colonial Paranacyathus along with Batenevia and Claruscoscinus with taeniae and curved tabulae. A few regular archaeocyaths are present, including Palmericyathus and Aulocricus. Lateral to the reef facies the lime mud sediment contains abundant skeletal fragments of trilobites, echinoderms, Chancelloria, hyoliths, and archaeocyaths. These buildups are interpreted to have formed as wave-resistant, framework reefs in a tidally dominated, shelf-margin setting seaward of a carbonate barrier. II - Girvanella-dominated buildups located in the upper part of the carbonate interval of the Puerto Blanco Formation and associated with oolites. These are built by stacked Girvanella crusts, with an important contribution of Renalcis and a less important presence of Epiphyton. Shelter cavities are filled by mudstone often rich in siltsize quartz. Cements are poorly developed and confined to the intraskeletal cavities. Archaeocyaths are scattered in the Girvanella frame either as isolated individuals or as clusters of solitary or colonial forms. Regular archaeocyaths are here abundant, represented by several taxa with an ethmophylloid inner wall, including Palmericyatbus and Cordilleracyathus. The dominant genus is Aulocricus. Colonial species of Archaeocyathus and Arrythmocricus are well developed. These latter two genera are now recorded from Mexico to northern Canada. The internal and lateral sediment contains a rich fauna represented by trilobites, Chancelloria, echinoderm plates, hyoliths, brachiopods, and helcionellacean mollusks. We interpret these buildups to have formed in a back-shoal setting as isolated patch reefs and laterally continuous biostromes. Samples of float from the Buelna Formation contain cryptalgal boundstones consisting of isolated and rare archeocyathan cups in a homogenous micritic tissue interpreted to have resulted from cyanobacterial activity. There are abundant cavities filled with internal sediments that contains scarce skeletal remains. cements are poorly developed. Marine cements are lacking, possibly because they have been replaced by blocky calcite of meteortic origin. Rather large specimens of Claruscoscinus and Archaeocyathus are present. The bioconstructions probably formed subtidally above storm wavebase. Twenty-two taxa of Archaeocyatha are recognized. Two new genera and eleven new species are described. The fauna from the Puerto Blanco Formation is Botomian in age. The fauna from the Buelna is probably Toyonian. 