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This paper describes petrographically and genetically, a number of peperites, as examples of spatial and temporal coexistence of magmatism and sedimentation in Costa Rica. The cases are presented in basic igneous complexes (ophiolites), mixtures varying from incomplete (megablocks of radiolarite with diabase in the Nicoya Complex) to complete mixes in various stages of Maastrichtian-Paleocene (Golfito Formation) or Paleocene pelagic limestones with basalts (Quepos Subcomplex or Tulín Formation) to form brechoid and pillowed peperites. Within the Oligo-Miocene arc, there are examples extended along the Talamanca range and its foothills, as well as Sarapiquí's plains represented for brechoid and bulbous (fluidal) peperites in latiandesitic lavas (Pacacua Formation) or brechoid peperitic pipes in ignimbrites (Mata de Limón Member) or possible brechoid peperites in lavas in the Crucitas mining prospect (Cureña Formation), or simple brechoid peperites in andesitic flow (Pacacua Formation, in Talamanca) or as hydroclastic breccias with fragments of dacitic composition in lava flow deposits of Carbonal Guanacaste, just between the beaches Cabuyal and Naranjo. All these rocks represented proximal equivalents of the explosive, effusive and subvolcanic volcanism (endogenous domes and criptodomes) and his concomitance with the fluvial sedimentation. In Quaternary period, we have a sample in the base of Tiribí Formation in contact with Palmares Lacustrine. Also this paper included possible and potential cases. It hopes that the description and interpretation of this type of rocks helps to its identification in other regions of Costa Rica and Central America in general, as well as a potential source for the exploration of valuable metals [ABSTRACT FROM AUTHOR]

The aim of this paper is to describe a fragment of left mandible of a juvenile specimen of Pliometanastes. That found brings some light about the phyletic relations among Pliometanastes protistus Hirschfeld & Webb, 1968 and ?Pliometanastes galushai Hirschfeld & Webb, 1968, and strongly suggests that Pliometanastes is a monospecific genus. [ABSTRACT FROM AUTHOR]

This paper summarizes available information on soil clay mineralogy in topsoils of Costa Rica, including clay minerals described in B horizons when significantly different from predominant mineralogy in the topsoil. The soil clay suites ("predominant clay groups") emphasized are grouped as: (1) smectites and interstratified clays (Vertisols and other soils with vertic properties), and (2) oxides-hidroxides-oxihidroxides-kaolinite-gibbsite (in Alfisols, Ultisols and Oxisols). The soil clay genesis of these dominant groups is discussed when enough information is available. [ABSTRACT FROM AUTHOR]

Findings in a total of 84 research papers identifying clay minerals on 520 soil samples of Costa Rica are summarized. This review emphasizes on the clay minerals described in the topsoil samples, although clay minerals in the B horizons are also discussed when they are different to predominant mineralogy in the topsoil. Sites where soil clays information is available were geo-referenced, to observe their geographical distribution. In general most of the country possesses soil clays identified, except for the Nicoya Peninsula, the Northern Zone, and the Eastern Talamanca Range. Clay mineralogy suites ("predominant clay groups") were grouped as: (1) vitrous-amorphous-halloysitic (Andisols and other soils with andic properties; (2) smectites and interstratified clays (Vertisols and other soils with vertic properties); (3) oxides-hidroxides-oxihidroxides-kaolinite-gibbsite (Alfisols, Ultisols and Oxisols); Plus a large area of soils with mixed clay mineralogy, found in places with little or no development (Entisols and Inceptisols). The soil clay genesis of the main clay types in the country is discussed when enough information was available. [ABSTRACT FROM AUTHOR]

During the night of December 8th, 1994, along an unstable area at the northern flank of Irazú volcano, Costa Rica, a small volcanic debris avalanche and subsequent debris flows took place, followed by an "ashfall" that reached 30 km southwest from the volcano. At that time, these processes were interpreted as the result of a phreatic explosion. However, a review of the descriptions given in the technical reports and other documents of the time, together with the analysis of the geomorphology obtained from aerial photographs taken on December 20, 1994, by the Costa Rica National Geographic Institute, lead to discuss the validity of this interpretation, which although not ruled out, it seems unlikely. This paper proposes, based on the facts and information available, a new hypothesis of the occurrence of a volcanic debris avalanche resulting from a major landslide near the northern summit area. Consequently, the following "ash" fall could be interpreted as generated by the dust produced by auto-fragmentation of the debris avalanche, so subsequently called co-debris avalanche dust-cloud deposit. [ABSTRACT FROM AUTHOR]