Diapiric Structures in Central Cuba1
Four évaporite diapirs have been reported in central Cuba. Their surroundings are stratigraphi-cally and structurally complex; therefore, an understanding of their structure and tectonic history requires a detailed knowledge of regional stratigraphy and tectonics.
There are at least five rock sequences in central Cuba—(1) an igneous-metamorphic basement of early Mesozoic or late Paleozoic age, (2) a Jurassic evaporite-redbed sequence, (3) a Portlandian-Turonian orthogeosynclinal suite, (4) a diversified Turonian-Eocene series, and (5) a postorogenic Eocene-Recent sedimentary cover.
The Portlandian-Turonian orthogeosynclinal suite includes, from south to north, four facies belts : eugeosynclinal suite, transitional suite associated with the median welt, miogeosynclinal carbonates, and platform carbonates. During middle Cretaceous and Eocene orogenies, the eugeosyncline was thrust northward, overriding the median welt and, locally, the miogeosyncline. The latter is deformed much more severely than the other belts.
The diapirs are north of the median welt in Matanzas and Camagiiey Provinces, and are localized by major faults. Two diapirs penetrate the eugeosynclinal rocks at or close to the surface. Exotic blocks in these two diapirs include fragments of eugeosynclinal, median welt, and miogeosynclinal facies.
The following tectonic history is proposed for the diapirs. During orogenesis, the miogeosynclinal carbonates were detached from the underlying evaporites, crushed between the median welt and platform, and overridden locally by the eugeosyncline. After middle Eocene time, the diapirs intruded along major faults and reached the surface bearing fragments from the overriding facies belts. The latest diapiric movements were post-Miocene. The small number of diapirs probably is related to the great competence of the thick, overlying, post-evaporite section.
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“Diapir” and “diapirism” come from the Greek diapeirein, which means “to pierce.” Diapirism sensu lato is a process by which earth materials from deeper levels have pierced, or appear to have pierced, shallower materials; it is divided into magmatic intrusion and diapirism sensu stricto on the basis of the temperature at which piercement occurs. Diapirs s.s. are composed of evaporites, argillaceous sediments, coal, peat, ice, serpentine, or other earth materials which have the critical characteristics of low equivalent viscosity and low density. These materials range in age from Precambrian to Recent. Diapirs are found in all parts of the world except the shield areas. They have many forms, ranging from smoothly rounded pillows to complexly injected laminae, are either connected with or disconnected from the “mother” bed, and are present either at the surface, where they form distinctive features, or at considerable depth. Diapirs have well-developed internal structures indicative of an origin by flow. Strata around a diapir may be strongly affected structurally and/or stratigraphically by the diapir, or they may be unaffected. Field and model studies indicate that diapirs have developed as a result of horizontal compression, gravitational instability, or both. Diapiric structures of various types contain large quantities of oil and gas, sulfur, salt, and potash and are important for underground storage and nuclear testing.