Luís B. Piló

Lagoa Santa Karst: Cradle of Brazilian Cave Studies

The Lagoa Santa Karst is the best known karst area in Brazil and has been studied since the early 1800s. This area is developed over Precambrian limestone of the Sete Lagoas Formation, Bambui Group, and displays scenic surface karst landforms, especially limestone cliffs, karst lakes, and karst plains, in addition to numerous solution dolines. Thick soil sequences derived from overlying phyllites cover a significant portion of the karst, but exhumation is presently taking place, exposing karst outcrops with subsoil karren features. Karst hydrology is primarily autogenic, with short groundwater flow routes. Limestone outcrops are vertically dissected, exposing ancient paragenetic caves intersecting cliff faces. More than 700 caves are known in the area, the majority of which are short ( 350 kyr). Lund was also the first to describe ancient human remains frequently found in caves and rock shelters. Lagoa Santa is now known to contain hundreds of archaeological sites dating from the Early Holocene/Late Pleistocene and has been at the center of the debate on the origin and age of human colonization in the Americas. The Lagoa Santa Karst faces severe environmental threats due to limestone mining and the expansion of the metropolis of Belo Horizonte and its surrounding towns. A number of preservation areas have now been established, improving the conservation status of this landmark Brazilian karst area.

Carajás National Forest: Iron Ore Plateaus and Caves in Southeastern Amazon

The Carajas National Forest in the Amazon is an outstanding area of conservation. The occurrence of mafic and felsic volcanic (Neoarchean) rocks is associated with banded iron formation (BIF) lenses, including jaspilites. Particularly on the BIF, there is the occurrence of ferruginous breccia which supports the tops of several mountain plateaus , generally referred to as the Carajas Ridge. Hills, drainage channels, and a number of closed depressions are commonly found on the surface, in addition to savannah surrounded by a luxuriant tropical forest. Subsurface rainwater drainage (throughflow) occurs via a network of small conduits on the tops of the mountain ranges, in addition to rainwater draining superficially in channels that are directed to closed depressions or to drainage headwaters. Several rocky scarps exist on the edges of the mountain ranges, in addition to talus deposits. Over 1,000 caves have been recorded in the area, and shallow, short-length (about 30 m) caves are predominant in this region. Longer caves, which may reach over 300 m, are normally present as single semicircular, funnelled, or straight chambers and are comprised of very irregular interconnecting passages in various sizes. Within the caves, clastic deposits are predominantly autogenic and originate from collapsed parts of the ceilings and walls. Chemical deposits are generally made up of small-sized features with a diverse mineralogy. Crusts and coralloids predominate in addition to draperies and micro-rimstone dams, and irregular pendulous forms known as pingentes hang from the ceilings, and are similar to stalactites. Speleothems are composed mostly of iron oxide–hydroxide and phosphates. The Carajas National Forest is a protected federal area that is used for different purposes, including the operation of the world’s largest iron ore mines. The savannah environment which is embedded amidst the tropical forest must be protected as conservation areas to represent the most expressive remnants of the original context. In addition, environmental compensation areas contiguous to the National Forest are being purchased, and these will become part of the Carajas protected area.