Geology of Isla Mona Puerto Rico, and notes on age of Mona Passage

Abstract

Isla Mona and the nearby rock of Monito are situated in Mona Passage, about midway between Puerto Rico and the Dominican Republic. Isla Mona has an area of about 21 square miles and Monito less than a quarter of a square mile. Isla Mona is a limestone tableland, bounded by steep to vertical cliffs and fringed about its southern perimeter by a narrow low-lying coastal terrace. The climate of the island is semiarid; its mean annual rainfall is 88.1 inches. The flora is zerophytic and consists mostly of cactus, leguminous plants, shrubs, and dwarfed trees. The density of the brush is surprising considering the sparse nature of the soil, and most of the larger plants seem to be rooted in narrow, soil-filled crevices in the limestone. The island was discovered by Columbus in 1494 during his second voyage. In early colonial times the island was a watering and provisioning station. At the present time its only inhabitants are the lighthouse crew. In the late 19th century the caverns with which the island abounds were extensively worked for their deposits of leached guano.Except for the thin soil of the tableland, Isla Mona consists entirely of limestone and dolomite. The Isla Mona limestone forms most of the mass of both islands and is probably early or middle Miocene in age. One sample of rock when tested in the laboratory proved to be dolomite. Unfortunately, it is not known how much of the rock exposed in the vertical sea cliffs of the north coast is dolomite nor whether the dolomite is confined to specific beds or represents irregular-shaped alterations of the limestone. The Isla Mona limestone is essentially flat lying, although apparent dips up to 3%° are visible in the cliffs. No faults were noted. In places a relatively thin cavernous limestone, the Lirio limestone, overlies the Isla Mona limestone. At Punta Este the two formations are separated by a slight angular unconformity. Only one fossil, a coral was found in the Lirio limestone, and from it the formation appears to be either Pliocene or Pleistocene in age. The low coastal terrace surrounding the south side of the island is mostly an elevated reef of Pleistocene age, thinly veneered with sand. Lineations on the plateau suface (best seen from the air) presumably reflect jointing. These have roughly a radial pattern, which suggests that the island has undergone a slight doming deformation since Lirio time.The scant reddish-brown residual soil of the tableland is a nonplastic, granular aggregate whose inorganic component consists mostly of a mixture of hematite, carbonaceous and amorphous substances (iron oxide?), boehmite, kaolinite, and mica. The isoil is rich in phosphorous and nitrogen. Veins and vermicular structures of reddish impure limestone are

Extension in Mona Passage, Northeast Caribbean

“…Using the North Coast basin of Puerto Rico (Briggs, 1961) (Kaye, 1959;Briggs and Seiders, 1972;Gonzalez et al, 1997). These limestones and dolomites do not correlate compositionally with the units of northern and southern Puerto Rico and are likely the result of localized reef build up (Ruiz, 1993).…”

Annual migrations and spawning of Coenobita clypeatus (Herbst) on Mona Island (Puerto Rico) and notes on inland crustaceans

“…A detailed description of the coastal geomorphology of Mona Island appears in Kaye (1959), Hernández-Ávila (1970), Briggs & Seiders (1972), Taggart (1992), and González et al (1997), the ora of the coastal plain was reported on by Woodbury et al (1977), and this vegetation was studied ecologically by Cintrón & Rogers (1991). The methodology used for this study follows Wiewandt (1975), and basically consisted in the observation and registration by means of photography and videos of the migration of C. clypeatus.…”

Preliminary geologic map of the Greater Antilles and the Virgin Islands

“…The geology of the island of Puerto Rico was based on the map compilation by Krushensky and Schellekens (1999), supplemented by mapping for Isla de Mona by Kaye (1959); the geology of Isla de Culebra was from mapping by Banks (1962); and the geology of Isla de Vieques was from mapping by Learned and others (1973).…”

“…In the U.S. Virgin Islands, Donnelly (1966) was the source of mapping for Saint John and Saint Croix, and Rankin (2002) was for Saint Thomas. Helsley (1960) was the primary source of mapping for the British Virgin Islands, with the exception of Anegada Island, whose geology was inferred from information in Kaye (1959).…”