Introduction

13.1.1. Location of Study Region

The Cuyaguateje River basin in western Cuba has an area of ca. 842 km2. The basin is located between the Sierra de Infierno to the northeast and the Sierra de In-

fierno to the southwest. The karstic massifs of Quemados, Cabezas, Sumidero, Resolladero, Pesquero, Mesa, and Guane are located in the area, including the main study site discussed in this chapter, Sierra de San Carlos (Fig. 1).

13.1.2. Geology

The region is characterized by a pronounced litho-logical and structural complexity, and several different models have been presented to explain its evolution (Piotrowska, 1978; Pszczolkowski, 1978; Iturralde-Vi-nent, 1977, 1988).

In general, the stratigraphic units dip gradually to

FIGURE 1 Location of Sierra de San Carlos (Cuyaguateje River basin, Sierra de los Órganos, western Cuba). 1, karst massifs; 2, permanent streams; 3, intermittent streams; 4, dry river beds; 5, water conduits in subterranean caves; 6, lagoons and lakes; 7, bank of a dam; 8, points of hydrological and hydrochemical measurements.

FIGURE 1 Location of Sierra de San Carlos (Cuyaguateje River basin, Sierra de los Órganos, western Cuba). 1, karst massifs; 2, permanent streams; 3, intermittent streams; 4, dry river beds; 5, water conduits in subterranean caves; 6, lagoons and lakes; 7, bank of a dam; 8, points of hydrological and hydrochemical measurements.

ward the southeast. The limestone portion is represented by the Jagua and Guasasa formations (Jurassic), as well as the Pons (Cretaceous) and Ancón (Paleogene) formations (Pszczolkowski, 1978). The terrigenous carbonate Pica-Pica formation is of Paleogene-Neogene age. The units of Alturas de Pizarras del Norte and Sur are composed mainly of terrigenous sequences of the San Cayetano formation of lower and middle Jurassic age.

13.1.3. Geomorphology

In the central portion of the basin, constituted by carbonate massifs, karstic and fluviokarstic processes have been the major geomorphologic agents. From the Pleistocene to the present, karst processes are associated mainly with climatic, physicochemical, biochemical, and hydrological factors, but are also controlled by tectonic and fracturing processes, which created conical and tower karst features (Kegel and Turmkarst).

The karstic phenomena are represented on the surface by the presence of exokarstic morphology, including poljes, mountain pits, crests, and boulder fields. Below the surface, caves have formed. In some cases, extensive cave systems exist, such as the Majaguas-Cantera, Santo Tomás, Palmarito, Fuentes, and Constantino caves, with more than 30 km of explored and mapped underground galleries.

In the lower portion of the basin, Quaternary fluvial plains, fluviomarine sediments, and deltas form the relief, with variable sediment thicknesses.

13.1.4. Hydrogeology

The northeast-to-southwest orientation of the network of surface drainage is related to structural and geomorphologic patterns and, locally, to tributary streams.

The upper and middle portions of the basin are characterized by surface drainage of rivers and streams flowing from the Alturas de Pizarras. After passing through contact valleys, they reach the karst massif through underground galleries. Underground, stream flow increases due to the autochthonous supply of water in the karst. There are also other surface streams originating from springs in the area of the carbonate massif, some with considerable annual flow, which contribute to the water balance of the area.

The hydrogeological system as a whole is formed by both surface and underground drainage and plays an important role in the hydrogeochemical, paleoclimatic, and paleoenvironmental processes. These processes, together with other geodynamic factors, have influenced the genesis and evolution of the karstic phenomena.

13.1.5. Modern Climate

Climate (Díaz, 1984) is characterized by mean annual temperatures between 21.8° and 24.9°C, rainfall of 1600-1800 mm/year (1720 mm average), and mean relative humidity of 77%. In the Sierra de los Órganos, a quantitative relation has been found between elevation and annual rainfall, increasing from ca. 1200 mm at 1020 m to 2200 mm at 500 m elevation (Gagua et al., 1976). In historical times between 1750 and 1871, rainfall at the Santiago de Cuba meteorological station was low and increased significantly between 1871 and 1984. Temperatures have increased by 0.5°C since the nineteenth century and by 0.2°-0.3°C in the last 40 years (Casablanca meteorological station in Havana City; Celeiro, 1999). Sea level has increased at the Siboney Station (eastern Cuba) by 2.9 mm/ year during the last 30 years (Hernández, personal communication).

13.1.6. Previous Work

Based on the presence of carbonates, silicates, and gypsum deposits, Ortega and Arcia (1982) reconstructed a paleorainfall map for Cuba for the last glacial period (Wisconsin) that suggested arid climates. On the basis of the coastal eolian formations of the Pleistocene in the western part of Cuba, Shanzer et al. (1975) suggested that arid climates were synchronous with glaciations at higher latitudes.

Based on the study of the continental Quaternary deposits in central and western Cuba, Kartashov and Mayo (1976) established the existence of oscillations between pluvial and arid phases. The authors correlated the pluvial periods with glacial advances in the Northern Hemisphere.

Based on weathering profiles of the Guane and Guevara Quaternary formations, Kartashov et al. (1981) divided the Cuban Pleistocene into two stages: a lower wet stage and an upper dry stage. Ortega (1983) presented a paleotemperature map for Cuba by estimating the elevation of the periglacial zone from sea surface temperature (SST) reconstructions in the Gates paleo-climate model (Gates, 1976).

From scallop analysis in a fossil fluvial gallery in the Perfecto cave in the Cuyaguateje region, Valdés (1974) calculated a paleorainfall value of 1400 mm. This suggests that the climate in the region at that time was more humid than it is today. Based on geomorpholog-ical correlation, an Illinoian age was assigned by Aceve-do (1971). Although the study of scalloping features in underground galleries, as well as the investigation of paleohydrological and paleoprecipitation processes, has been the focus of much research (White and White, 1970; Goodchild and Ford, 1971; Wigley, 1972; Curl,

1974; Valdés 1974; Lauritzen, 1981, 1982; Lauritzen et al., 1983; Molerio, 1997), the problems concerning the paleoclimate and paleoenvironment in the tropical karstic areas have received little attention. The most recent paleoclimate research in Cuba is related to the project Paleoclimate of the Cuban Quaternary: A Quantitative Characterization, by the Cuban National Program for Global Change and the Cuban Environment. In this chapter, we present data from a multidisciplinary study of the karst region in western Cuba.

13.1.7. Karst of Sierra de San Carlos

The geologic (Fig. 2), geomorphologic, hydrogeo-logic, and geodynamic characteristics of the Sierra de San Carlos karst and its surroundings are reviewed in detail in several papers (Acevedo, 1971; Acevedo and Valdés, 1974; Acevedo and Gutiérrez, 1976; Fagundo et al., 1978; Molerio, 1978).

The Sierra de San Carlos karst region is characterized by several cave levels related to past hydrological changes. Contemporary and past karstic processes are a result of changes in allochthonous and autochthonous drainage. Fluvial genesis also played an important role during karstification. These caves must have formed during major pluvial periods, probably during interglacial periods when sea level was high. Evidence shows the existence of alternating periods of erosion and infilling. For example, there are sediments of different particle sizes that are representative of complex matrix infilling in seasonally active, fossil, and subfossil galleries and a great number of scallops along gallery walls and ceilings, indicating recent and past erosional activities. In addition, large pebbles, composed mainly of sandstone, shale, and limestone, are deposited along several kilometers of active, seasonally active, and fossil underground galleries, originating from the Alturas de Pizarras del Sur. Several generations of speleothems of different mineralogical composition, including goethite, hematite, and ghassoulite, clearly indicate pa-leoclimatic and paleoenvironmental changes (Pajón et al., 1985; Pajón and Valdés, in press).

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