Estilolitos horizontales en sedimentitas del cretácico de la cordillera oriental, y su significado tectónico

Stylolites are secondary, conical or needle-like structures common in sedimentary rocks, and are originated at different moments of the deformative history of strata by dissolutionary effects due to directed pressures. Two main types may be distinguished: the vertical (Y-S) and the horizontal stylol...

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Autores:: Mojica, Jairo

Tipo de recurso:: Article of journal

Fecha de publicación:: 1985

Institución:: Universidad Nacional de Colombia

Repositorio:: Universidad Nacional de Colombia

Idioma:: spa

Description
Summary:	Stylolites are secondary, conical or needle-like structures common in sedimentary rocks, and are originated at different moments of the deformative history of strata by dissolutionary effects due to directed pressures. Two main types may be distinguished: the vertical (Y-S) and the horizontal stylolites (H-S). The presence of H-S is of great significance as they are supposed to be the result of tectonic pressures that align the needles (stylolites s. str.) in the direction of maximal compression (axis (f,). The Y-S appear to have relationship with tectonic processes and are considered to be a consequence of vertical pressures resulting from normal faulting, forming before the H-S, at early deformation stages.Although some authors consider that the Y-S derive from solution of rock material due to pressure of the overburden. Field studies show that the cherts present mainly in the upper Cretaceous sequence of the Colombian Eastern Cordillera contain numerous H-S, usually well developed, and lesser, smaller V-S. The H-S occur mainly in the central part of the Guadalupe Group (Coniacian/Santonian - Maestrichtian), the Olini Group (Coniacian-Campanian) and the top of the Chipaque Formation (Cenomanian-Coniacian); they are also found in the dark cherts of the Hiló (Albian), La Luna (Turonian-Coniacian) and San Rafael (Turonian in part) Formations. H-S were also found out at one place in quatzitic sandstones of the "Une Formation", between Duitama and Santa Rosa de Viterbo. The results of measures carried out until now show that along the Eastern Cordillera there are two different assemblages of the H-S. The first one comprises the sector between SW Neiva and the southern termination of the Bucaramanga Fault, an important oblique slip of left lateral sense. The H-S orientations in this region are very regular, from NW to SE; subordinated NW-SW and E-W directions are also present at few outcrops. The second region corresponds with the northern part of the Santander Massif, (Pamplona area) where the H-S display three directions: a very conspicuous E-W, a less frequent NE-SW, and a scarce one N-S. The relation between the stylolitic surfaces and the bedding planes indicates that the H-S are pre-cinematic to sin-cinematic (no post-cinematic ones have been found), the direction of the needles being normal to the b axis of folds. These facts suggest that the H-S represent compressive processes ocurred in the early stages (Proto-Andine Phase) of the Andean Orogeny, during the Middle-Upper Eocene. Comparison of the compression directions deduced from H-S with those derived from study of recent joints shows a re-orientation of stress (to NW-SE) in the Pamplona area during the Quaternary.

Estilolitos horizontales en sedimentitas del cretácico de la cordillera oriental, y su significado tectónico

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