Middle Miocene Global Change and Paleogeography of Panama

Abstract

Fossil leaves in the middle Miocene Cucaracha Formation along the Panama Canal are 10-15 cm long, thick, and entire-margined; fossil pollen is also dicot dominated, as expected for wet tropical forests. Fossil woods include palms and ring-porous dicots, with smooth bark as is found in weakly seasonal tropical climates. In contrast, late Hemingfordian to early Barstovian mammals of the Cucaracha Formation are the same as those found in Nebraska, Kansas, and Florida, where climate was drier and cooler and vegetation more open. Cucaracha paleosols reconcile these differences as evidence of a mosaic of swamps to mangal (mangrove forests) preserving plants and dry uplands preserving mammals. A dozen pedotypes represent as many vegetation types, including mangrove, fresh-water and marineinfluenced swamp, early successional riparian woodland, colonizing forest, dry tropical forest, and woodland. Many paleosols have calcareous nodules, and some have pedogenic barite nodules. Depth to carbonate and paleosol thickness with carbonate indicate mean annual precipitation of 573-916 ± 147 mm and mean annual range of precipitation of 27-65 ± 22 mm. Chemical analyses of paleosol Bt horizons confirm mean annual precipitation of 296-1142 mm and mean annual temperature of 15-16 ± 4.4°C. Low precipitation and temperature estimates imply a rain shadow from a high (1400-4000 m) volcanic mountain range to the west, with continuous land connection to allow immigration of mammals from North America. Partial enclosure of the Caribbean Sea by a mountainous Panama peninsula, as well as by Antillean arcs, initiated high Caribbean marine temperature and salinity well before Pliocene isthmian closure.

History of upwelling in the Tropical Eastern Pacific and the paleogeography of the Isthmus of Panama

“…As such, rather than an archipelago the proto-Isthmus must have been an entirely subaerial peninsula unconnected to south America until final closure, a conclusion supported by geological evidence (Montes et al, 2012). However, the mammal size-peninsula evidence is only pertinent to the middle Miocene, from when there exists questionable evidence of high mountainous regions in central Panama (Retallack and Kirby, 2007) and the paleogeography of the Isthmus in the critical times of the Late Miocene and Pliocene remains to be defined.…”

“…Although a Late Pliocene date for final closure is now well constrained and strongly supported by several lines of independent evidence, the form, elevation and degree of subaerial emergence of the southern tip of Central America after it collided with South America approximately 24 Ma (Farris et al, 2011) remains unresolved (Kirby and MacFadden, 2005;Retallack and Kirby, 2007;Schmidt, 2007;Molnar, 2008). Uplift rates based on paleobathymetries of marine sediments from across the Isthmus suggest that the majority of the volcanic arc was submerged up until very recently with bathyal sediments of latest Miocene age present in the Caribbean and Pacific of western Panama, the Caribbean of central Panama and eastern Panama (Coates et al, 1992;Collins, 1992Collins, , 1993Collins, , 1996Coates, 1999;Coates et al, 2000Coates et al, , 2003Coates et al, , 2004Coates et al, , 2005.…”

“…Strong similarities between Pacific and Caribbean Mio-Pliocene biota (Chaisson and Ravelo, 2000;O'Dea et al, 2007b) and near-identical environmental conditions on either side of the Isthmus (Keigwin, 1978(Keigwin, , 1982Keller et al, 1989;Haug and Tiedemann, 1998;Haug et al, 2001) in the Early Pliocene imply the CAS was maintained in some form until the mid-Pliocene. Nevertheless, well-studied and extensive lacustrine sediments, shallow water reefs and mangroves, plus a continental-like mammal fauna in the Canal Zone of Panama demonstrate the presence of substantial subaerial land(s) in the middle Miocene (Whitmore and Stewart, 1965;Kirby and MacFadden, 2005;Johnson and Kirby, 2006;Retallack and Kirby, 2007;Kirby et al, 2008). Accordingly, Coates and Obando (1996) proposed a semi-submerged archipelago of islands from the Miocene up to final closure.…”

Comparative Diagenesis and Rare Earth Element Variation in Miocene Invertebrate and Vertebrate Fossils from Panama

“…The Cucaracha Formation is primarily composed of clays but also includes lenticular sands and conglomeratic units. The finer-grained units within the Cucaracha Formation have considerable development of paleosols (Retallack and Kirby 2007). Taken together, a composite section of the Cucaracha Formation spans a thickness of about 140 m (Kirby et al 2008).…”

Paleosuelos del mioceno en el desierto de la tatacoa

“…Los paleosuelos panameños estaban en o cerca del nivel del mar. Estos ciclos de calor y humedecimiento también son evidentes en periodos similares en paleosuelos en Oregon, Montana, Nebraska, Alemania, Japón, Kenia, Pakistán y Australia (Retallack, 1991, 2004b, 2007y Schwarz, 1997.…”