Transactions of the 16th Geological Conference, . Caribbean Journal of Earth Science, 39 (2005), 93-104. © Geological Society of Jamaica. Palaeoclimatology of the Pleistocene-Holocene using marine molluscs and hermatypic corals from northern

1 2 OLIVER MACSOTAY AND RAQUEL CACERES HERNANDEZ

1Apartado postal 62262, Chacao, , Venezuela. 2UniversidadPedagogica Experimental Libertador, Dept. de Biologia, Maracay, Venezuela.

ABSTRACT. Along the Venezuelan coastline and its islands, 47 outcrops of marine sediments were studied. Their ages, determined by radiometric and palaeontological means, ranged from Middle Pleistocene to Holocene. A total of 234 taxa was identified: Coelenterata 30; Gastropoda, 116 and Bivalvia 88. The Middle Pleistocene sediments are iron-rich sands and clays, only locally with bioclastic limestones. There is barely any coral and the molluscs are small-sized. The assemblages are bivalve-dominated with Atlantic affinities: Crassostrea patagonica, Ostrea puelchana, Anomalocardia spp., Gemma gemma and Macoma venezuelana. Gastropods include Cerithidea pliculosa and Melongena margaritana also suggesting temperate-affinity , strongly influenced by heavy rainfalls on coasts and islands. Late Pleistocene sediments are more calcareous allowing the development of reefal systems with medium biodiversity of corals: Pocillopora elegans, Acropora cervicornis and Milleaster sp. The molluscan assemblages are gastropod-dominated, with smaller sized shells than living Caribbean equivalents: Astraea, Cerithium, Conus, Murex, Chicoreus, Oliva, Ancilla, Persicula, Turritella and Vasum. The bivalves are Crassostrea patagonica, Chama ainuosa bermudensis, Scapharca couvana, and these also suggest Atlantic temperate-affinity faunas dominating the coastlines, but not the offshore islands. The rainfall influence is noted in coastal areas in western and eastern Venezuela, while inland and the Llanos became arid. The Holocene sediments are heterolithic and calcareous, with mangrove-forests on most of Venezuela’s coastline. Corals are mostly Porities and Millepora associations, with small sized Siderastrea colonies. Molluscs are very much like living assemblages, where invaders from West Africa appear briefly: Cerithium guinaicum, Cymatium spp. Climatic conditions are similar, but with higher coastal rainfall that contributed to the proliferation of mangroves. Early and Middle Pleistocene cooling of the surface waters in the southern Caribbean Sea preceded aridity of the Llanos and mountain glaciation of the Late Pleistocene (80 and 15 ka) of the Andean range.

1. INTRODUCTION assemblages by Bermudez and Fuenmayor (1962), Bermudez (1966) and Bermudez and There are very few studies concerning the Farias (1975) showed that many of the biostratigraphy of the marine Pleistocene- ‘Mio-Pliocene’ sediments of Venezuela really Holocene and the palaeoclimatic interpretation of belonged to the Late Pliocene-Pleistocene benthic faunas of tropical countries such as (Stainforth, 1969). The first shallow-marine Venezuela. Richards (1943) described Holocene was identified in northeastern fossiliferous terrace deposits with molluscs up to Venezuela by Van Andel (1967) by C-14 dating +5 m above sea level from Juan Griego of mollusc shells. (Margarita Island), which he referred to the Macsotay and Moore (1974) added more U-Th Pleistocene. Van Benthem Jutting (1944) ages from Late Pleistocene corals, and C-14 ages reported 20 fossiliferous marine deposits from from molluscs. Schubert and Szabo (1978) the northern Venezuelan coastline, including the reported Middle and Late Pleistocene U/Th ages offshore islands. According to the molluscan from offshore islands of Venezuela, and Rull faunas studied by P. Wagenaar Hummelinck, (2000) added more C-14 ages of Holocene these suggested a Pleistocene or even Holocene deposits along Venezuelan’s coastline. age, for some of the ‘terraces’. Weisbord (1962) Based on a study of more than 500 taxa of attributed the Abisinia Formation to the marine molluscs and about 30 coelenterates, a Pleistocene on the basis of its molluscan fauna, subdivision of Pleistocene-Holocene time is and a radiometric U-Th age of 300 ka. presented here, valid for the southern Caribbean The study of the planktic foraminiferal area. Recent reviews of the living molluscan

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fauna of Venezuela’s coasts and islands (Princz, patricia biozone, ubiquitous in the hypersaline 1982; Macsotay and Campos Villaroel, 2001) palaeoenvironments of the Late Pliocene, has its reveal that a high percentage of fossil species are extinction at this boundary. This time must have still living in this area. This fact increased the witnessed important climatic disturbances, as the percentage of recent species in the reef-forming corals disappear completely from ‘Mio-Pliocene’ fossiliferous units, which became the continental shelf area; they only survive on increasingly younger as was predicted by Gibson the offshore island shelves. The extinction of Smith and Gibson Smith (1979), some of them many calcitic bivalves, such as Lyropecten reaching Pleistocene horizons. This coincides arnoldi, Lopha spp. and Agerostrea spp. and the with ages derived from planktic foraminifers. decrease in gastropod biodiversity are associated This mollusc-coral subdivision scheme is with this horizon. proposed for shelf sediments of the circum- and The Middle/Late Pleistocene is marked by the infralittoral belts, including littoral and parallic increase of gastropods, mostly Atlantic-type palaeoenvironments. genera that replace the Caribbean forms; the coral reefs re-invade the continental shelves, with low 2. PLEISTOCENE SUBDIVISIONS diversity and small colony-sizes. Mangrove- related brackish molluscan assemblages become It is a generally accepted fact, that the replaced by fresh-water communities. Mollusc Globorotalia truncatulinoides total-range zone, shell-size has increased in relation to the Middle is the marine foraminiferal marker of the Pleistocene, but is still smaller than living Quaternary period (Bolli et al., 1985) for the representatives. tropical and temperate realms. The subdivision The Late Pleistocene/Holocene boundary is of the Pleistocene proposed on the basis of marked by the disappearance of Milleaster and planktic foraminifers in LEG 15, station 147 Pocillopora, and the temporary invasion of exotic (Rogl and Bolli, 1973) is useless in shallow- gastropods from West Africa and the withdrawal water facies, as is the case for most of the or disappearance of molluscs from the Atlantic Pleistocene and Holocene land-based outcrops. Ocean’s temperate fauna. Reef-corals re-invade Palaeontologically, the Pliocene/Pleistocene continental coastlines, and mangrove forests are boundary seems to be related to the biozone of common all along Venezuelan shores. Lyropecten arnoldi (Maloney and Macsotay, Palaeontological descriptions and biochrons will 1967) whose range seems to overlap with the be discussed elsewhere. Lopha messor zone of Hunter (1978), and is already within the Globorotalia truncatulinoides 3. STRATIGRAPHY biochronozone. The Turritella cartagenensis/T. maiquetiana 3.1. Early Pleistocene (1,750 - 700 ka) boundary (Macsotay, 1971) is very near the From the molluscan fauna, the following units 1.9 Ma time-line, or the Globorotalia tosaensis/ belong here: Amuay Member of the Paraguana G. truncatulinoides boundary, which is the Formation (Hunter and Bartok, 1976), Playa internationally accepted Late Pliocene/Early Grande Formation (Gibson Smith and Gibson Pleistocene boundary. Besides the extinction of Smith, 1979) and the Cumana Formation six species of the genus Turritella, it also marks (Macsotay, 1976). The last two units belong to the mass-extinction of over one hundred taxa of the Globorotalia truncatulinoides foraminiferal pacific affinity gastropods and bivalves biozone (Bermudez and Farias, 1975), but their (Woodring, 1974). molluscan fauna, suggests restriction to the Early A change in the composition of reef-crest and Pleistocene. In Trinidad, the Caparo Member of reef-buttress coral assemblages is marked by the the Talparo Formation and the Matura Formation, appearance of wave-resistant Acropora palmata contain the same fauna (Macsotay, 1976). The in latest Pliocene or earliest Pleistocene time in Cumana Formation has been identified in the the Caribbean Sea. Rapidly growing species of subsurface of the Carupano Basin, 300 km Acropora and Porites invade and dominate the northeast of the type locality (Castro and shallow-water, high-energy habitats of Mederos, 1985). Pleistocene and modern reefs. Sedimentary features. The early Pleistocene The Early/Middle Pleistocene boundary is marine sediments include a high percentage of based on molluscan extinction/appearance conglomeratic horizons, with psammitic matrix. horizons (Table 1) studied in Venezuelan and The Cumana and Playa Grande formations expose Trinidadian sedimentary rocks. The Anadara

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Table 1. Biostratigraphical ranges of taxa in the Middle Pleistocene to Recent of the southern Caribbean

thick conglomeratic units towards their tops. The represent flash flood deposits that otherwise Caigiiire and Chiguana formations develop them interrupt the dry climatic conditions on the towards their bases. Most of the conglomerates nearby mountains. Some of these alluvial fans form lenticular beds, with planar to festooned overrun the coastal plains, and entered coastal cross-bedding, and imbrication of clasts towards marine environments (Macsotay and Bladier, the base of the bed. Clast size varies from pebble 1987; Vivas and Macsotay, 1989; Rey, 1990). to cobble, and the conglomerates are usually Poorly-sorted terrigenous components (i.e., silts, poorly sorted. There are unfossiliferous sands and grits) dominate these infralittoral units; conglomeratic units of hundreds to thousands of carbonates are rare. Biodetrital carbonates are metres thickness, such as the Rio Seep, Coro, mostly restricted to shelves: Amuay Member, Las Pailas and Coche formations. All four Playa Grande and Cerro Gato formations. overlie well-dated Late Pliocene sediments, and Mineralogical features. A common feature in

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the Early Pleistocene marine sediments is the 1964) along the coast are in need of presence of evaporite minerals, such as gypsum, review. The famous Tortuga Formation (Patrick, anhydrite and copiapite. They are sulphates, 1959, emend. Maloney and Macsotay, 1967), products of evaporation of shallow marine found only on offshore islands, is the only embayments and shoals under a tropical semiarid coralgal limestone of this time-slice. Finally, La climatic regime. The Caigüire, Chiguana and Eminencia Formation (Macsotay and Peraza, in Paria formations are typical (Macsotay, 1976). press) is a sandy chalk with basal conglomerates, The continental beds, sandstones and cropping out in the Cumana and Paraguachoa conglomerates frequently develop duricrusts of areas, of eastern Venezuela. iron oxides and laterites; these are well exposed Sedimentary features. The mid-Pleistocene in the Coche, Las Pailas and Coro formations, sedimentary units are siliciclastics on the units otherwise with grey tones. They suggest a mainland outcrops and carbonates on the offshore subhumid tropical climate. Local peat lenses or islands. The siliciclastic units include fine- reworked lignites in the Caigüire, Paria and San grained conglomerates with a sandy matrix, grits, Gregorio formations suggest nearby coastal silts and some clays. The Goaiguaza clays and vegetation. silts were intensely bioturbated, suggesting Palaeontological features. Marine shales and organic-rich muds in the embayments. siltstones carry frequent pectinids: Nodipecten, The bioclastic and biolithic carbonates formed Argopecten, Leptopecten, Pecten (Oppenheimipecten), when La Tortuga and La Blanquilla were only Amusium besides Plicatula and Anomia, forming submarine banks or shoals. They must have oligomictic horizons, suggesting well circulated preserved the tropical island conditions, with marine conditions, with high planktic input. consistently warm temperatures and only Burrowing detritivore bivalves are common occasional rains, since Late Miocene times. (Table 1). Crassostrea-banks (not reefs) occur in Pleistocene times changed the previous most of the marine units. These ‘oyster’ beds are oceanographic conditions where hurricanes, found in the San Gregorio, Caigüire, Cumana originated in the , pushed their and Paria formations and suggest the presence of anticyclones southward. estuaries, dependant on rainy seasons. The shorelines on the mainland also suggest The scarcity of gastropods and corals, but moderate erosion nearby, and low rates of abundance of rodoliths and stromatolites (never sedimentation on the shores. The coastlines were in the same bed) suggest waters with fine dominated by waves, as is suggested by sediment in suspension, also related to heavy unidirectional cross-bedding. On Margarita rainfall along the emerged coasts. Island, a great fresh-water lake developed, behind Bivalves, stromatolites and echinoids attained Juan Griego village. It suggests humid tropical large sizes suggesting relatively low (21˚C ± weather over the central mountains (over 1000 m 3˚C) temperatures in the water-mass above the high) of the island. Paraguana also has this shelf. These low average temperatures are not phenomenon, but no lacustrine sediments have related to Caribbean upwelling, but to cold been found. water-masses entering from the Atlantic Ocean, Mineralogical features. The mid-Pleistocene as was suggested by Macsotay and Vivas (2000) age sediments only concentrated iron oxides in for Oligocene and Miocene times in eastern the nearshore sediments of the mainland Abisinia Venezuela. A good listing of the Early and El Alto formations. Their presence is related Pleistocene fauna was published by Macsotay to the weathering of mafic and ultramafic (1976). Some large-sized bones outcrops nearby. This chemical weathering was observed in the Caigüire Formation remain related to dry coastal conditions with tropical unstudied, but suggest a humid environment. rains on the mountains. The general absence of peat or lignite suggests dry weather. 3.2. Middle Pleistocene (700 ka - 125 ka) The unusual presence in Venezuela of chalky The units belonging here were identified through limestone suggests relatively low temperatures in radiometric dating and palaeontological the coastal marine waters in the Cumaná area. evidence. From west to east, we have studied: El The fine-grained quartz sand found in these Alto sandy conglomerates in Paraguana chalks, seems to be transported by aeolian Peninsula (Hunter and Bartok, 1975; Audemard, processes from nearby shorelines. 1996a) a beach deposit, very much alike the The advanced recrystallization/replacement Abisinia Formation of State (Weisbord, observable in all the outcrops of the Tortuga 1964). The Goaiguaza clays (Weisbord, 1962, Formation suggests the process had started

96 Macsotay and Caceres Hernandez – Pleistocene-Holocene palaeoclimatology of northern Venezuela

Figure 1. Surface and submarine distribution of Late Pleistocene marine sediments.

Figure 2. Surface outcrops of Late Miocene to Late Pleistocene marine and continental sediments on Margarita-Araya high.

97 Macsotay and Caceres Hernandez – Pleistocene-Holocene palaeoclimatology of northern Venezuela

Figure 3. Late Pleistocene to Holocene marine sediments in northern Venezuela and its islands. already during Middle Pleistocene times. As gastropods, genera (Tegula, Anachis, Nitidella, soon as the uplift of the carbonate banks, which Olivella, Bulla) that live on green algae and became atolls and later islands, exposed the eel-grass are frequent. Carnivorous genera coralgal reef and lagoon complexes, they must (Persicula, Conus and Cantharus) are also have been subjected to the present. Melongena margaritana Richards is recrystallization/replacement of aragonite. The more closely related to the floridian M. corona offshore islands of Venezuela must have been (Gmelin), than to the Caribbean M. melongena; subjected to heavy rains and tropical hurricanes Cerithidea pliculosa lives in the coastal lagoons in this epoch. of the Gulf of Mexico and Yucatan, but not in the Palaeontological features. The most southern Caribbean. outstanting feature in Middle Pleistocene marine On the offshore islands of Venezuela, this is sediments is the small size of the mollusc shells. the first horizon that contains extensive colonies The El Alto, Abisinia and La Eminencia of massive Acropora palmata (Lamarck) formations have a molluscan fauna dominated by suggesting high-energy wave activity, due to small bivalves, whereas the gastropods are frequent tropical storms. oligomictic. In these sediments, corals are represented by a few small colonies of Oculina, 3.3. Late Pleistocene (125 - 14 ka) which is an Atlantic genus that can withstand The Late Pleistocene units cited here belong to low temperatures (Table 1). three facies: two are marine and one is Bivalves with high diversity, including such continental. The first is an offshore island facies, forms as Crasspstrea, Ostrea (Ostrea), Gemma, consisting almost totally of white, beige and light Plicatula, Glycymeris and Anomia are temperate- grey carbonate and divisible into a biohermal affinity taxa which migrated from the Atlantic (coralgal) fore-reef complex and a back-reef Ocean and replaced the Pacific fauna of the lagoonal (mostly biodetrital material with some Miocene-Pliocene (Woodring, 1974). Among the siliciclastics) complex. This unit, called the Punt

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Figure 4. Mid-Late Pleistocene marine sediments near Juan Griego, Paraguaychoa, Venezuela. a de Piedraa Member, is found on the same start with a basal conglomerate followed by grits, offshore islands as the Tortuga Formation sensu and calcirudites with cross-bedded. Above this stricto (Maloney and Macsotay, 1967). The main horizon, calcarenites with intense bioturbation difference between them is that the Punt a de and tempestites are the most frequent structures. Piedraa Member shows only an initial Higher, some hardgrounds allowed the micritization, wheras the Tortuga Formation is establishment of hermatypic corals up to some completely recrystallized. tens of metres in size. Locally, stromatolites are A coastal, heterolithic, highly variable established at this horizon. Above, cross-bedded sediment consisting of a mixture of siliciclastics calcarenites and calcirudites, deposited under and biodetrital carbonates, called the El wave action, are thoroughly traversed by Manglillo Formation, occurs on the northern rhizoliths attributed to mangroves (Figs 4-5). coasts of Venezuela (Macsotay and Peraza, in In the calcretes formed at the top of the press) (Figs 1-4). succession, terrestrial gastropods are frequent, Overlying the last facies, are well-sorted and suggest permanently humid climates on the ferrugineous quartz sandstones, found on the Araya Peninsula, and Margarita and Cubagua Paraguaná Peninsula and Margarita Island (Fig. islands – these locations are xerophyic today 3). The term Faica Formation (Wehrmann and (Fig. 5). This unusual feature was also observed Macsotay, 1995) is available for both localities. also in the Paraguand Peninsula (Audemard, Their red, reddish brown and dark brown colours 1996b), and Castilletes in the Guajira Peninsula. are typical (Fig. 5). Macsotay (1965) published a faunal list of both Sedimentary features. The Late Pleistocene facies from Western Araya under the terms of marine heterolithic sediments are the coastal Castillo de Araya beds (infralittoral) and the expression of a maximum flooding surface. They ‘authentic Pleistocene’ (gravelly shorelines with

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Corallinemarineterraces Hanging alluvial and alluvial cones Mollusc-dominated marine terraces Fossil dune fields and aeolian deposits Vertebrate fossils, continental Palynological evidence of aridity Plant fossils, continental Anomalous drainages Sedimetary (moraines, etc.) Palaepedeologic evidence Present-day glaciers Relict savannas in present tropical forests Alluvial terraces Evidence of greater Pleistocene humidity Figure 5. Distribution of palaeoclimatic evidence mainly during the last glacial maximum (Late Pleistocene). Modified from Schubert (1988). mangroves). This relationship can be observed silt intensely bioturbated by Ophiomorpha, again in Macanao Peninsula and in the Chiguana Rhizocorallium and Thalassinoides. Some groups area (Macsotay and Caraballo, 1976). of hermatypic corals are found in growth At the top of the calcretes, there is a position, others displaced. At the top, mud-cracks development of ferrugineous quartz sandstones are preserved. Almost no calcrete has formed on with gravel lenses and small rhizoliths. top of these outcrops. According to Wehrmann and Macsotay (1995), Mineralogical features. No neoformed strong rains eroded the metamorphic rocks and minerals are present in the biohermal facies, the sands created filled the deep valleys formed suggesting a very dry climate during and after during the previous glacial stage. Subsequent dry emersion from the sea. This circumstance allowed climates resulted in the development of dune the preservation of the aragonite that has been fields that were cemented by iron oxides dated by the U/Th method. The heterolithic facies transported by ephimeral creeks and lagoons found onshore is marked by strong calcrete (Fig. 6). formation at the top and dolomitization in the The biohermal or fringing reef facies is the sink-holes, suggesting humid tropical conditions classical calcareous unit studied in detail in the (Fig. 5). Netherland (Herweijer and Focke, 1978) The red ferrolithic sands are a typical case of and Republica Pominicana (Schubert and lateritization of the massive, cross-bedded Cowart, 1980). The outstanding difference with sandstones. The duricrusts of goethite formed at the former is the fact that the reef structure and the base of channels, filled with quartz gravel and the lagoon behind it became preserved, with heavy minerals, by evaporation of the limited minimal changes, dues to emersion. These amount of water in the channels. calcirudites are composed of biohermal coral and Palaeontological features. The reestablishment algal assemblages in growth position. The open of the hermatypic reef corals along the space between the corals is filled with bioclasts continental shorelines of Venezuela and the of pebble to boulder size. The lagoonal facies is offshore islands is the most striking feature of the usually a heterolithic facies in which a basal Late Pleistocene. On the offshore islands, such as conglomerate is followed by calcareous sandy La Tortuga and La Blanquilla (Figs 1, 3), barrier

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Figure 6. Pleistocene sections. reefs and lagoonal facies developed in erosional same areas today. Exceptions include the frequent notches cut into sedimentary or igneous substrate presence of Pocillopora elegans (Dana) in the (Maloney and Macsotay, 1967). These southern and eastern Caribbean area during the bioconstructions are integrally preserved, Late Pleistocene (Geister, 1977). This species of containing most of the species that flourish in the hermatypic coral (abundant since Late Miocene

101 Macsotay and Caceres Hernandez – Pleistocene-Holocene palaeoclimatology of northern Venezuela

to Recent along the Pacific coasts of Central 3.4. Holocene (14 ka - Present) America) invaded the Caribbean reefs only to The only formally published Holocene unit is the briefly disappearing from the area later. Boca Chica Formation (Macsotay and Moore, Another common species is Dendrogyra 1974). It is a heterolithic unit which at first sight cylindrus Ehrenberg, which forms colonial masses is quite like the El Manglillo Formation of the up to 3 m high. It is not a living species of the Late Pleistocene. It is exposed in erosional or (Roos, benches, mostly in eastern Venezuela, due to 1964). The molluscan assemblages in the hermatypic neotectonic uplift. It consists of silty sand with facies are the same genera associated with these mollusc shells, and layers or fragments of peat. carbonates since Miocene times. The gastropods are Rhizoliths are commonly observed with the Diodora, Strombus, Cypraea, Cyphoma, Phalium original root turned peat. (Tyiocassis), Cymatium, Charonia, Coralliophila, Palaeontological features. The hermatypic Ancilla, Voluta and Knefastia; the bivalves, corals flourished, not only in offshore islands, but Barbatia, Pinna, Pteria, Spondylus. Lopha, Codakia, also along the continental shores. The average Chama, Lyrophora and Petricola. The high size of colonies is larger than those in the Late biodiversity and abundance of individuals is Pleistocene outcrops. In the extensive erosional noteworthy. Tropical genera are dominant, benches cut into the sedimentary rocks, dense suggesting a palaeotemperature similar to that of the populations of Porites spp., Siderastrea siderea Recent. Among the gastropods, an average smaller Ellis and Solander, Diploria strigosa (Dana) and size is observed. Manicina areolata (Linné) are present (Macsotay The bivalves (especially the calcitic shelled and Moore, 1974). ones) have a larger size than at present The molluscs have a high biodiversity, with (Macsotay and Campos, 2001). We conclude faunal compositions and average individual sizes tropical surface temperatures (26˚C), with similar to the living fauna in the same area of the periodical cooling of the bottom waters. Venezuelan shelf (Macsotay and Campos, 2001). No truly brackish water genera are found, Some extinctions are observed: Turritella suggesting relatively dry climates. The maiquetiana Weisbord is replaced by T. variegata heterolithic facies also has some unusual coral (Linné) and Crassostrea patagonica (d'Orbigny) species, such as Madracis decactis (Lyman), is replaced by C. rhizophorae. Cerithium Oculina diffusa Lamarck and O. valenciennesi guinaicum Philippi and Arca zebra abisiniana Milne-Edwards and Haime, which are branching Weisbord are immigrants from west African corals of boreal and austral distribution in the coasts that did not survive the Holocene. Atlantic Ocean. The hydrozoan Hilleaster sp., a The climatic inferences are warm tropical boreal taxon of the Mio-Pliocene that becomes weather, with more rain influence, not only on extinct during the Late Pleistocene, is also the mainland, but also on the nearby islands. frequent. Decimetric size stromatolites are Offshore islands remained arid. common in the outcrops of northeastern Paraguana (Audemard, 1996b). All the evidence suggests surface temperatures at least 4 or 5 ˚C 4. DISCUSSION below the Caribbean average. Early Pleistocene times brought climatic changes The molluscan assemblages in the in the southern Caribbean marine area. Mollusc heterolithic facies are dominated by the and coral species, whose larvae were transported following taxa – gastropods: Hemitoma, Tegula, to the area, rapidly took over the ecological Astraea, Modulus, Batillaria, Cerithium, Natica, niches of the Pacific-related taxa, which perished Purpura, Columbella, Strombina. Melongena, after the disappearance of the Panama-Costa Rica Nassanus, Vasum and Bulla; bivalves: Noetia seaway. These molluscs and corals came by the (Eontia), Glycymeris, Atrina, Isognomon, following paths: Crassostrea, Trachycardium, Macrocallista, 1. An Early Pleistocene invasion, mostly from Gemma, Anomarocardia and Protothaca. This Brazil, Uruguay and Argentina’s shelf areas. It is molluscan fauna contains many brackish-water explained by the activity of the Antarctic species suggesting a tropical humid climate. The Intermediate Current, which during Early Pleistocene dominant taxa are invaders from the Atlantic times occupied a shallower position, even upon the Ocean, such as Chama sinuosa barbadensis and shelves. This current introduced low temperature, Scapharca couvana, and survivors of invaders mineral-rich waters that helped the proliferation of that arrived during Early Pleistocene times temperate and austral faunas along the shorelines and [Crassostrea patagpnensis (d'Orbigny)]. islands of the southern Caribbean.

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2. A Middle Pleistocene invasion, this time Sea to the present confirms the existence of from the southeastern coast of North America, Quaternary biological ‘refuges’. Although denied bringing temperate-affinity corals and molluscs by Schubert (1988) from mainland evidence, into the already mixed faunas of the southern these refuges existed on the islands away from Caribbean. The temperature along the southern the routes of oceanic currents from the Atlantic shores of the Caribbean dropped drastically; Ocean that contoured the continental margins. plankton-poor surface waters developed together The molluscs attest to intense climatic changes in with a benthic population of small-sized the Quaternary, confirming drops in marine molluscs. Hermatypic corals virtually surface water temperatures of the southern disappeared. The whole northern coast of Caribbean. This event preceded climatic Venezuela represents a humid tropical anomalies including aridification on the Llanos environment, even on Paraguaná island, which and glaciation on the Venezuelan (VA on was still isolated on the shelf (Audemard, Fig. 5) by over a million years. 1996b). The cooling must have been of 4 to 5˚C The Late Pleistocene presents an increase in according to the molluscs and hermatypic corals, molluscan biodiversity and average size, and the not the 2˚C stated by CLIMAP Project Members re-establishment of some biohermal corals along (1981). During the Holocene, a general warming the coasts of the mainland (Macsotay and Moore, of surface waters is observed along the entire 1974). Humid weather affected an area in Venezuelan coast, except for the Cariaco trough northwestern Venezuela (Schubert, 1988) and and gulf, where relict species of temperate another in the northeast (Fig. 5) including the affinity still survive. nearshore islands. Contemporaneously, a wide area in the Venezuelan and Colombian Llanos, References became arid. The Margarita area also shows an Audemard, Fk.A. l996a. Late Quaternary Marine Deposits of alternation (Wehrmann and Macsotay, 1995) of the Paraguaná peninsula, State of Falcon, Northwestern humid and dry weather conditions (Fig. 6). In Venezuela: Preliminary Geological Observations and Cumaná and Juan Griego, extensive freshwater Neotectonic implica- tions. Quaternary International, 31, 5- lakes were formed at sea level as a result of the 11. humid weather conditions. Their periodic Audemard, Fk.A. 1996b. Field Trip Guidebook to the Late communication with the sea is attributed to Quaternary marine deposits of the Paraguana peninsula and th disruption of coastal sand-bars by storms. No Coro surroundings. 5 Annual CLIP Meeting, Punta Cardon, such lakes have been documented in eastern Venezuela. July, 1996, iii + 57 pp. Venezuela since Early Pleistocene times Bermudez, P.J. 1966. Consideraciones sobre los sedimentos del Mioceno medio al Reciente de las costas central y oriental de (Macsotay and Caraballo, 1976). Venezuela. Bol. Geol. (Caracas), 7(14), 333-411. During Holocene time, the warming of the Bermudez, P.J. and Farias, J. 1975. Contribucion al estudio surface waters offshore and nearshore is del Pleistocene marine de Venezuela. Mem. Soc. Venez. Cienc. registered by the molluscan and coral faunas. Nat. La Salle, 35(100), 69-118. More temperate affinity species disappear and Bermudez, P.J. and Fuenmayor, A.N. 1962. Notas sobre los the warm-water taxa re-occupy the ecological foramini- feros del Grupo Cabo Blanco, Venezuela. Asoc. niches from biological refuges. Venez. Geol. Min. Pertrol., Bol. Inform., 5(1), 3-16. The Margarita area and the Araya Peninsula Bolli, H., Saunders, J.B. and Perch-Nielsen, K. 1985. show a gradual drying of the climate, while Plankton Stratigraphy, Cambridge Univ. Press, 1032 pp. Castro, M. and Mederos, A. 1985. Litoestratigraffa de la humidity seems to displace to the delta Cuenca de Carupano. VI Congr. Geol. Venez., Caracas, 1985, and the Gulf of Paria (Macsotay and Moore, Mem. I, 202- 225. 1974). In western Venezuela, aridity extended to CLIMAP Project Members. 1981. The surface of the ice-age State, despite the tropical rains on the San Earth. Science, 191, 1131-1137. Luis Mountains, and a tombolo with dune Geister, J. 1977. Occurrence of Pocillopora in Late Pleistocene systems developed joining Paraguaná to the Caribbean Coral reefs. 2nd Symposium Internat. sur les coraux mainland (Audemard, 1996a). et recifs coralliens fossiles. Paris, Sept. 1975. Mem. Bur. Rech. The Llanos became a savanna-type plain, geol. min., 89, 378-388. dissected by many rivers, draining the mountain Gibson Smith, J. and Gibson Smith, W. 1979. The genus Arcinella (: Bivalvia) in Venezuela and some ranges. associated faunas. Geos, 24, 11-32. 5. CONCLUSIONS Herlfeijer, J.P. and Focke, J.W. 1978. 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Manuscript received: 12th May, 2005 Accepted: 14th May, 2005

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