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by each Cu within the [Cu302] core. Upon inspection of the crystal structure of the fully reduced form of ascorbate oxidase i l l ). the \ ,, three trigonally ligatedoCu(I) centers (average Cu...Cu distance, 4.5 A) appear geometrically predisposed toward accommodation of O2 and formation of a [Cu,02] cluster. However, no current spectroscopic studies of the metastable oxygen intermediates of multicopper oxidases and their derivatives support the existence of an intenselv absorbing 0x0-Cu(II1) chromophore, and no unusuaiy short CU-0 bond distances such as those observed in 2 are indicated (1 2, 13, 32). In accordance with these'htudies, however, the facile reaction of three Cu(1) monomers with 0, to form the mixed-valence bis(p3-oxo)[Cu(II)Cu(II) Cu(III)] species 2 does suggest that O2 bond cleavage at trinuclear Cu sites requires full 4 e reduction of 0 , . In the case of native laccase, the fourth electron is provided by the remote "blue" Cu center, whereas in 2, the extra electron must'be obtained at the cost of further oxidation of one of the Cu sites.

Accreted terranes, comprising a wide variety of Jurassic and Cretaceous igneous and sedimentary rocks, are an important and conspicuous feature of Cuban geology. Although the Mesozoic igneous rocks are generally poorly exposed and badly altered, we have collected and geochemically analyzed 25 samples that place new constraints on plate tectonic models of the Caribbean region. From our recognizance sampling, six main lava types have been identified within the Mesozoic igneous rocks of Cuba: rift basalts, oceanic tholeiites, backarc basin lavas, boninites, island arc tholeiites (IAT), and calc-alkaline lavas. We suggest that the rift-related basalts may have formed during the development of the proto-Caribbean, as the Yucatan block rifted away from northern South America in Jurassic-Early Cretaceous time. The Early Cretaceous oceanic tholeiites have flat rare earth element patterns, and are compositionally similar to Pacific mantle plume-derived oceanic plateaus of similar age. The Early Cretaceous arcrelated rocks are either backarc basalts, boninites, or relatively trace element-depleted IAT lavas. A limited amount of geochemical and field evidence hints that two parallel arc systems existed in the western proto-Caribbean area in Early Cretaceous time. This leads us to speculate that in the proto-Caribbean at this time there was a western arc with a northeast-dipping subduction zone erupting IAT lavas (with Farallon plate being consumed), and a more eastern boninitic arc with a southwest dipping subduction zone (with proto-Caribbean plate being consumed). This latter arc was relatively short lived and after being aborted was mostly eroded away. The Cretaceous primitive (IAT) arc survived and, later in Cretaceous time, as this arc system moved into the widening gap between North and South Americas, calc-alkaline lavas began to be erupted. The evidence suggests that the change from IAT to calc-alkaline lavas was gradual and not abrupt. These new data, although limited, provide geochemical constraints on the tectonic development of the northern part of the Caribbean plate. In consequence, we present a new plate tectonic model for this area of the Caribbean.

Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their ''last appearance'' datum at Ϸ11,000 radiocarbon years before present (yr BP) or slightly less in North America, Ϸ10,500 yr BP in South America, and Ϸ4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial-interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the slothbearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people.

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This report summarizes the results of paleontological and geological investigations carried out during the 1990s at Domo de Zaza, a late Early Miocene vertebrate locality in southcentral Cuba. Paleontologically, the most important result of fieldwork at Zaza was the first discovery of terrestrial mammals of Tertiary age in Cuba. Three terrestrial mammal taxa are now known from this locality-a megalonychid sloth (Imagocnus zazae), an isolobodontine capromyid rodent (Zazamys veronicae), and a platyrrhine primate (Paralouatta marianae, new species). In addition to these finds, a number of selachian, chelonian, crocodylian, cetacean, and sirenian remains have been recovered. Domo de Zaza is a low hill transected by a large artificial channel, the Canal de Zaza, whose walls provide an extensive exposure of Miocene sediments attributable to the Lagunitas Formation (Fm). This formation is laterally and vertically complex, showing evidence of at least four different depositional regimes. However, the sedimentary sequence indicates that all depositional phases took place within a broader episode of transgression. Estimated Burdigalian age (16.1-21.5 Ma) for Lagunitas Fm is based on the presence of marine invertebrate taxa corresponding to the late Early Miocene Miogypsina-Soritiidae zone. Most of the vertebrate fossils were recovered from lagoonal and alluvial beds; those from lagoonal beds are exceptionally well preserved. The terrestrial facies displays evidence of paleosol formation, subaerial erosion, and plant life in the form of grass and palm pollen. Other evidence indicates that most of the present-day highlands of Cuba, including the Cordillera del Escambray near Zaza, have been continuously subaerial since the latter part of the Late Eocene. Although no land vertebrate fossils of this age are known from Cuba, recent discoveries elsewhere in the Greater Antilles indicate that land vertebrates could have colonized landmasses in the Caribbean Basin as early as 33-36 Ma.Recently, marine geological data have been interpreted as showing that (1) the Mona Passage began to form in the Early Oligocene, and (2) the Puerto Rico/Virgin Island block was entirely transgressed by shallow marine environments during the period between the Late Oligocene and the Early Pliocene. However, the seismic reflection profile evidence for an Early Oligocene opening of the Passage is ambiguous. Even if the separation of Puerto Rico and eastern Hispaniola occurred relatively early, it remains more probable than not that this happened in the medial Oligocene or even somewhat later (i.e., Յ30 Ma). On the other hand, the evidence is not at all ambiguous concerning the hypothesized mid-Cenozoic inundation of Puerto Rico: it did not happen. When available land and marine indicators are adequately compared, apparent contradictions in datasets can be evaluated and resolved. When examined in this way, the preponderance of evidence supports the contention that Puerto Rico has been an emergent landmass and has supported terrestrial environme...

Cuba is considered here to consist of two separate geological units: afoldbelt and a neoautochthon. The foldbelt can be subdivided into: (i) continental units, comprising Mesozoic Bahamian Platform and slope deposits, which are overlain by a Paleocene‐ Late Eocene foreland basin; and the Cuban SW terranes (Guaniguanico, Pinos and Escambray), which were probably originally attached to the Yucatan Platform; (ii) oceanic units, namely: the northern ophiolite belt; the Cretaceous (?Aptian‐Campanian) volcanic arc, which is overlain by a series of Latest Cretaceous — Late Eocene “piggy‐back” basins; and the Paleocene‐Middle Eocene volcanic arc which is overlain by a late‐Middle — latest Eocene “piggy‐back” basin. The neo‐autochthon is composed of slightly‐deformed, latest Eocene to Recent sedimentary rocks, which unconformably overlie the folded belt. A large number of tectonic models for the Caribbean area have been published in recent years, but rarely include modern data on the geology of Cuba. The Author here presents a plate‐tectonic model for the western Caribbean which is based on the following premises: (i) opening of the Caribbean took place along several parallel rifts‐zones, and a main transform fault located between the entrance of the Gulf of Mexico and the Demarara Plateau; (ii) the Cretaceous Greater Antilles volcanic arc faced the ProtoCaribbean Sea, and essentially northward‐dipping subduction took place; and (Hi) the western Caribbean Paleocene‐Middle Eocene volcanic arc also faced the Caribbean Sea, with subduction dipping towards the NNW. Hydrocarbon production in Cuba comes from oilfields located in both continental and oceanic units. The Northern Oil Province coincides with the Bahamian platform and slope deposits and the Guaniguanico Terrain. The Southern Oil Province is represented by the latest Cretaceous — late Eocene sedimentary basins and the Cretaceous volcanic arc.

Petrological and geochronological data of six representative samples of exotic blocks of amphibolite and associated tonalite-trondhjemite from the serpentinitic me´lange of the Sierra del Convento (eastern Cuba) indicate counterclockwise P-T paths typical of material subducted in hot and young subduction zones. Peak conditions attained were 750°C and 15 kbar, consistent with the generation of tonalitic partial melts observed in amphibolite. A tonalite boulder provides a U-Pb zircon crystallization age of 112.8 ± 1.1 Ma, and Ar ⁄ Ar amphibole dating yielded two groups of cooling ages of 106-97 Ma (interpreted as cooling of metamorphic ⁄ magmatic pargasite) and 87-83 Ma (interpreted as growth ⁄ cooling of retrograde overprints). These geochronological data, in combination with other published data, allow the following history of subduction and exhumation to be established in the region: (i) a stage of hot subduction 120-115 Ma, developed upon onset of subduction; (ii) relatively fast near-isobaric cooling (25°C Myr )1 ) 115-107 Ma, after accretion of the blocks to the upper plate lithospheric mantle; (iii) slow syn-subduction cooling (4°C Myr )1 ) and exhumation (0.7 km Myr )1 ) in the subduction channel 107-70 Ma; and (iv) fast syn-collision cooling (74°C Myr )1 ) and exhumation (5 km Myr )1 ) 70-60 Ma.