Paleokarst facies in la manga formation (Middle oxfordian), Southern Mendoza province
Studies carried out in different outcrops of La Manga Formation (middle Callovian-middle Oxfordian) in southern Mendoza province, have allowed the recognition of an internal discontinuity characterized by the presence of a paleokarst. This surface was mentioned by Groeber as alveolar limestones. He...
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| Autores principales: | , , , , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00044822_v74_n1_p40_Palma |
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| Sumario: | Studies carried out in different outcrops of La Manga Formation (middle Callovian-middle Oxfordian) in southern Mendoza province, have allowed the recognition of an internal discontinuity characterized by the presence of a paleokarst. This surface was mentioned by Groeber as alveolar limestones. He also recognized surfaces displaying shades of yellow, brown alteration colors and honeycomb erosion (alveolation processes) in the “blue limestones wih Gryphaea”. These surfaces appear on the top of reefal and oolitic barrier facies which define a shallowing-upward succession, or in intertidal-supratidal facies. Paleokarst deposits are represented by mantling breccias, collapse breccias and sinkhole breccias. Breccias are chaotic, with grain-supported to matrix supported fabrics. Some breccias can appear stratified. They are composed by clasts that vary between few millimeters to boulders, with irregular limits produced by dissolution. Sedimentology, morphology and diagenesis let recognize the epikarst in peritidal facies showing shorten shallowing-upward cycles in an internal ramp with low gradient. Fluctuations of the phreatic level during periods of subaerial exposure controlled the development of pendant cementation and drusy calcite cement with negative values of δ18O (-5.08 to-6.21‰) evidencing the action of meteoric waters. The epikarst shows dissolution cavities that reach 3 to 5 cm below surface, usually indicated by the presence of iron oxides and pisolites with an irregular distribution. The discontinuity is indicated by the paleokarst and by epikarst features, which are produced by subareal exposure and intense dissolution processes as a consequence of sea level fall. © 2017, Asociacion Geologica Argentina. All rights reserved. |
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