Manual de Plantas de Costa Rica | The physical environment| 69 
geological significance, all of these ultramafic serpentinized materials are of consider- 
able ecological and floristic import (see, e.g., Whittaker, 1954; Kruckeberg, 1984). 
Other plutonic rocks of Cretaceous to Paleogene age, mainly gabbro, diabase, and 
diorite, intrude the Nicoya Complex (including the Santa Elena Peninsula) and all of 
the more southerly formations of similar composition (see Castillo-Mufioz, 1983; 
Tournon & Alvarado, 1997). Paleogene intrusives occur sparingly in other localities as 
well (Tournon & Alvarado, 1997). 
The oldest exposed oceanic rocks in Costa Rica (and perhaps all of Central Amer- 
ica), which crop out on the south side of the Santa Elena Peninsula opposite Isla Pelada, 
are sedimentary. These comprise radiolarites, oceanic in origin, dating from the lower 
Jurassic (middle Lias to lower Dogger; see De Wever et al., 1985, and Tournon, 1994). 
Sedimentary rocks of middle Jurassic to upper Cretaceous age, mostly radiolaritic, 
occur elsewhere on the Santa Elena Peninsula, as well as on the Nicoya Peninsula. 
Limestones, conglomerates, and sandstones are also sparingly represented in the Cre- 
taceous Nicoya Complex. Sedimentary strata of upper Cretaceous age, overlying the 
Nicoya Complex, are exposed in the Rio Sapoa basin, on the Santa Elena Peninsula, 
and on the Nicoya Peninsula. Upper Cretaceous and Paleogene sedimentary rocks also 
occur southward, along with basaltic rock, in formations formerly attributed to the Ni- 
coya Complex (Quepos, Golfito, the Osa and Burica Peninsulas). These rocks also in- 
clude radiolarites, sandstone, conglomerates, and limestone. Limestone, of particular 
interest to floristics, crops out in upper Cretaceous to Paleogene formations along the 
entire Pacific coast: Punta Descartes, the southern tip of the Nicoya Peninsula (Punta 
Cueva), Tarcoles, Cerro Caraigres (south and west flanks), Punta Judas, near Parrita, in 
the Fila Costefia (Fila de Cal, etc.), near Golfito, and on the Burica Peninsula. The so- 
called Sapoa strata, at Pefias Blancas on the Nicaraguan border, comprise massive 
limestone blocks to 30 m in thickness (Weyl, 1980). On the Caribbean slope, lime- 
stones of similar age are exposed near Turrialba (Las Animas formation) and along the 
Rio Pacuare. Sandstones probably of Paleogene age crop out along the Rio San Juan, 
and on the Caribbean slope of the Cordillera de Talamanca. 
Irrespective of the absolute age of the rocks, apparently the longest continually ex- 
posed terrain in all of Central America is Costa Rica’s Santa Elena Peninsula, which 
has remained above sea level (initially as an oceanic island) for about 85 million years 
(Janzen, 1988, 1998). 
Neogene rocks 
Rocks of Neogene age, both sedimentary and volcanic, account for the majority of ex- 
posed formations in Costa Rica (and also presumably underlie regions of Quaternary 
vulcanism and alluvial deposits, discussed later). The Cordillera de Talamanca (in- 
cluding the Fila Costefia) is largely composed of sedimentary, volcanic, and plutonic 
rocks of Neogene age. The Cordillera de Tilaran, viewed by geologists as merely a 
