The Ecology of the Barí: Rainforest Horticulturalists of Latin America

2. Physical Environment

CHAPTER 2 Physical Environment Many of the particulars of the Barí natural environment derive from two general characteristics of its location: a northern tropical latitude and a landscape marked by mountain ranges on the south and west. From these features descends a string of consequences displaying two patterns, one temporal and one spatial. Temporally, this environment is marked by bimodal oscillations: two rainfall peaks per year, two river rises per year, and so forth. Spatially, it is arranged as a series of concentric rings (ring segments, strictly speaking) whose geometric center is near the mouth of the río Catatumbo. The annular order is manifested in landforms, soil types, vegetation zones, and other geographic features. The interplay of the two patterns is the basis for the organization of this chapter. Landscape and Climate The Maracaibo Basin is a structural depression, approximately bisected by the line of 10° N latitude, bounded by the arms of an enormous, tilted Y formed by the Eastern Cordillera of the Andes. The north-south arm of the Y, the Sierra de Perijá, forms the western border of the basin. On the south and east the basin is enclosed by the northeast-southwest arm of the cordillera, known as the Venezuelan Cordillera of the Andes or the Mérida Cordillera. The center of the basin holds Lake Maracaibo, a large body of slightly saline water (equivalent to about 3% seawater [Redfield et al. 1955: iii] since the dredging of its mouth in the early 1950s) open on the north to the Caribbean Sea, with which it communicates through a strait (el Estrecho de Maracaibo), a bay (el Tablazo), and a shallow gulf (el Golfo de Venezuela) (Map 2.1). Map 2.1. The Maracaibo Basin and the location of the Barí within it. Physical Environment 29 The area of the whole Maracaibo system, including the continental shelf in the Gulf of Venezuela and the Coro and Guajiro Peninsulas that enclose this shallow marine area on the east and west, respectively, is close to 125,000 km2 in extent. The hydrographic basin defined by the mildly brackish lake properly speaking and the rivers draining directly into it have an area of about 78,000 km2, with roughly 62,000 km2 in Venezuela and 16,000 km2 in Colombia (MARNR 1979: 170–171; Parra Pardi et al. 1979: 4; Acevedo Latorre 1969: ix). Lake Maracaibo itself has an area of 13,000 km2 and a maximum depth of only 34 m; it is about 150 km long from north to south and 120 km wide at its maximum east-west dimension (Ginés 1982: 25; Rodrígues 1973: 21). A geologically well-studied section (Servicio Geológico Nacional e Inventario Minero Nacional 1967) of one Colombian section of Motilonia, around the oil town of Tibú, can serve as a snapshot of the underlying geology of the region—at least on its western edge. The basement formation is made up of igneous and metamorphic rocks—schists, gneisses, and intrusive granites, largely Devonian and all pre-Mesozoic. Overlaying the basement rocks are middle and upper Cretaceous sediments up to 2 km thick, laid down in six formations of sandstones, limestones, and shales. Many of the limestones are fossiliferous, and five of the six formations have yielded oil. Of special interest here is the fact that a 45 to 86 m thick limestone formation named La Luna, from the early upper Cretaceous, is capped by phosphate deposits of sufficient richness to be commercially exploitable. One outcropping of this stratum occurs about 20 km west of Tibú, along the banks of the río Orú, a tributary of the Catatumbo; another is found about 15 km south of the town of Petrólea, not far from the río Sardinata, another tributary of the Catabumbo; a third one occurs along the course of the Catatumbo itself, near the town of La Gabarra. The significance of the phosphate stratum and its restricted outcroppings is discussed below. It is also of consequence that the topmost upper Cretaceous formation, the Catatumbo, contains coal. Overlying the Cretaceous sediments are seven Tertiary formations, primarily of sandstones and shales from the Paleocene, Eocene, and Oligocene and of sands and clays from the Miocene and Pliocene. These strata are up to 4 km thick in some places. The Barco formation, from the Lower Paleocene, is the major oil producer for the whole section. It is overlain by...