.Iournal of Coasta l l{('s('arch Spring :!OO:!
Late Quaternary Evolution of the Orinoco Delta, Venezuela
An drcw G. Warne ',Edgar H. G uevara, and An d res Aslan'"
The Univers ity of 'I'exus at 'Curr ent add ress: U.S. Current address: Austin Bureau of Economic Geologica l Survey GSA Departm ent of Ph ysical a nd Geology Unive rs ity Station Center, 651 Federal Drive En vironmen tal Scienc e Box X Austin, Texas 787]:3 Gu ayn abo , Pu erto Rico, Mesa State College 1'.0. 8924 00965-570 :3 Box 2647 Grand .l unction. agwa rn [email protected] Colora do 8 1502
ABSTRACT _ ••••••••••••••••••••••••••••_
WAHNE, A.G.: GU EVAHA, KH ., and ASLAN, A., 2002. Late quartern ary evolution of the Orinoco Delta. Vcru-zuol». ,tllllllll:. ,JIIIII'I/al II( Cllaslal Rcecarch , 1H121, 22ii-25:3. West Palm Beach (Florida ).ISSN 0 74 ~)" U 20 H . ~ The modem Ori noco Delta is till' latest of a series of sta cked delta s that have infilled the East c ru Venezueln» Basin susss~ ~ (E:V 13 1since th e Oligocene, Dur ing the late Pleistocene sea-level lowstand (20,000 to J(i,OOO yrs BPI, bedro ck cont rol -:::-z=::----- points at the posit ion of the presen t delta a pex prevented th e river channel from incising as deeply as man y o(her -+ w= major river syst ems. Sha llow seismic data indicate th at the lute Pleist ocene Or inoco incised into the pre-sen t conti nental shelf, where it form ed a bra ided-ri ver complex that trans porte d sediment to a series of s h e lf ~ e d g l' dl'ltas. As sea level rose from ](i,OOO to V,iiOO yrs 131', the Or inoco shoreline shifted ra pidly landward. causin g sha llow marine wav es a nd cu rre nts to form a wides pread t ra nsgress ive sa nd unit. Decele rating sea-level rise a nd a warmur, wette r climat e during th e earl y Holocene 1 ~) , ii OO to G.OOO yrs BP I induced delta developmen t within till' rclnt ivcly quiet-wat er environme nt of th e EVB embayment. Sea level a pproached its present stand in the middle Hu loceu r: IG.OOO to :3.000 yrs 131' ), an d the Orinoco coast prograd ed. broade ning th e delta pla in and infilling the EVB «mbavnu-nt. Significant q uaut.it.ies of Amazon sediment began to be transported to th e Ori noco coast by litt ora l curre nts . Cont inu cd progradation in the late Holocene caused the const riction at Boca de Scrpiontos to alter nearshore a nd shelf hydr o dynami cs and su bdivide th e submarine delta into two distin ct areas : th e Atla nt ic shelf and t ill' Gu lf of Pnriu. TIll' increased influence of littoral cur rents along th e coast promoted mudcape development. Becau se most of t h« wat r-r and sediment were tran sported across the delta plain throu gh the Rio Grande distr ibut ary in the southern dolta, much of the central and northwestern delt a plain becam e sediment sta rved. promoti ng wides pre ad accu mulation of peat de posits, Hum an impacts on t ill' delta are mostl y associated with till' Vole.in Dam on Cunu Man .uno. However. human activ ities have had relatively little effect on the delta processes and environments.
AD DITIONAL INDEX WORDS: Urt noco Delt a, Uri noco Hirer: late (llIal<,I'I/(//:I'. lat » I'l l'i" l oc('IIl' . Holoccn», Vc 'II('Z!ll'la. lut ma n i mpact". l~a " I <' 1'I 1 Vt'lIf 'zl/l'la B asi n, sea-lercl rhong ». «u bei dcur«. paleoclinrat«. Guavon« littoral current, Gniun« Coast ,
INT RO DUCTI O N Our evaluat ion of the Orinoco Delta is ba sed on geo mo r phic, sedim ento log ic, sha llow stratigra ph ic. pe do log ic, hydro Th e Ori noco Delta sustains a va st , largely undeveloped mo logi c, a nd botanic data gene rated duri ng a se r ies of de lta ex saic of tropica l wetlands a nd shallo w a quatic ecosystems peditions during 1998 a nd 1 ~) 9 9. Evaluation is a lso ba sed on within t he coa stal plain of eastern Ven ezuela . The t ria ngu la r satellite im age and hi storical aerial ph otogra ph a na lyses, a nd to trapezoi dal delta plai n enco mpasses ~ 2 2 , 0 0 0 km- of wet an exte ns ive literature revie w. This compre hens ive study is land forests a nd he rb aceous m arshes t hat a re subdivide d hy su m m a rize d in WAH " E et al. 11999), a nd t he !"egional sett ing networks of flu vial and tidal chan ne ls (Figure 1), The Orinoco of t he Orinoc o Delta is presented in WAI a b Punta Pescador es N ATLA NTI C OC EAN o 30 km Quaternary up land s Coa stal plain D Wat er D Orino co Delta t-_-_-_J Guayana Shiel d undifferentiated D undifferenti ated Figu re 1. (a) J EllS (Radar infero metri c) image of th e Orinoco Delt a. The composite image was acquired Sept ember through Decemb er 1995.(b) Geo graphic fea tures of the Orinoco Delta. Note that the sea wa rd limi t of major dist ribu taries are refer red to both as "Boca" (in refer ence to the mouth of the water body ) and "Barra" (in refer ence to the distribu tary mouth bar ). J ourn al of Coastal Research, Vol. 18, No.2, 2002 Late Quarternary Evolution of the Orinoco Delta, Ven ezuela 227 61 ' 60' 59 ' I I I I 100 km - 10' Predominant wind and wave dire ction -g' N + Approximate location of current and wave o Upl and and coas tal plain D Delta plain gaging stat ions @Q] Record ed littora l current velocitie s (em/sec) Q Mean tidal ~ ran ge (em) r.i -. Figure 2. Summar y of marine hydrodynamics along the Orinoco Delt a coast. Note the location of th e two tempora ry (December 1979 and May th rough August 1979 ) wave and current meter stations in centra l Gulf of Paria . Data gene ra ted from these sites are used to chara cte rize the marine hyd rodyn am ics of the Ori noco coast (GEOHIDRA CO/O; SULTO ltES, C. A., 1997a , b; ENSR VENEZUELA, 1998 ). Atlantic littora l cur rent and tide data are from KOLIlE"'J,J N (] 958), NOTA (] 958), VAN A/O;D EL (1967), HERREHAet al. (1981), and HERRERA and MASCIA:-IGIOLI (1984). CLELLAND ENGI NEERS, 1979). Th e Orinoco Delta is unusu al Grande and Canos Ara guao, Ma riusa , Macareo, and (former in that th e adjacent Gulf of Paria (Figure 2) is a major de ly) Manamo. Th e muddy cha nne ls are cha ra cterized by prox positional site for Orinoco depo sits, yet depo sitional processes ima l overbank sedimenta tion th at produces natural levees (and hence the st ratigraphy) in the Gulf of Paria are not th at rise 1 to :3 m abo ve and subdivide adjacent interdistri those typically associated with delta-front and prod elta de bu tary ba sin s. Blackwater channels mak e up most of the posits. cha nnel network in th e central and north western delta. The channel netw ork of th e Orinoco delta plain currently Th ese carry little sediment except perhap s during th e wet consi st s of six major distributaries radiating seawa rd from seas on, and tides and direct precipitation maintain bidirec the delta apex near Barrancas (Figure 1). Diurnal tides , tional flow. Th ese channels ha ve poorly developed na t ura l which ran ge from 2.0 ill at th e coas t to 0.6 m at th e delta levees. apex (Figure 2), maintain a network of channels throughout The hydrology of th e int erdi stributary islands an d basins the delta plain and reflect th e dynamic nature and intercon is controlled by a variable combination of direct precip itation, nectivity of th is deltaic system (VAN ANDEL, 1967). Near the river inflow , and tidal fluctuations. As a resul t of th e compl ex coast, many ofthe distributary channels (canes) deflect to th e a nd variable hydrologic regim e, t hese interdistributary is northwest under th e in fluenc e of the strong, northwest-di la nds and basins support a variety of grass , sedge, and forest rected Guayan a littoral current (Figure 2). Broad a rcua te ecosys tems (WARNE et al., 1999, th eir Plate 2). More than 80 promontories known as mudcapes form at th e mouths of in perc ent of th e interdistributary are as a re inundated for most termediate distributary channels, such as Ca nes Macareo of th e year, greatly limiting intentional bu rning and oth er and Mariusa , whereas es tua ries occupy th e mouths of major a nt hropogenic alte rations. distributari es such as Rio Gr ande (Boca Gr ande) and Ca no Across th e delta plain, two distinct, rou ghl y fan- shaped sec Manamo (Boca de Guan ipa) (Figure I ). tor s a re distinguished on th e basis of cha nne l abundance and With in t he delta plain, two distributary cha nnel types are geometry , sediment and soil types, shore line characte rist ics, distinguished; muddy and blackwater (Figure 3a, b). Muddy a nd dominant hydrologic processes (Figures 1,4). Th e south channels transport nearly all of th e sediment and includ e Rio ern sector cons ists primarily of an intri cate network of an as- Jo urnal of Coas tal Research, Vol. 18, No.2, 2002 228 Warne, Guevara and Aslan a b Figure 3. Ph otograph s of Orin oco Delt a environments.(a ) Floodplain lakes in the upper delta adjace nt to Rio Gra nde. Sus pended sediment concentrations are much higher in the se distri butaries than in those of th e northwe st ern delta (March 1998). (b) Middle reaches of Ca no Cocuinita, a typical blackwater cano in the nor thwest ern delt a. Note that the entire area is covered by low fores t, which is common in the middle delta (October 1998). (c) Central delta with an abandoned, partia lly infillcd cario. Note tra nsition from forest ed (palm) to her baceous interdist ributary basin in the dista nce. (d) Aggrad ing mud flats in the Boca de Guan ipa area . The mud flats are aggrading by lat eral accretion along the seaward edgc and colonization by ma ngroves along lan dwa rd porti ons. The de nsity of para llel tidal channels reflects the im portan ce of tid al processes in Orin oco coas ta l and delta-plain environments (March 1998). (e) Cano Tucupita (upper delt a near Tucupita ), whic h has been almost complete ly infilled wit h vegeta tion largely because of elimination of flood discharge since construction of Volcan Da m (March 1998!. (fJ Cleared and partially dr ained upper delta plai n near Tucupita. Desp ite the well-developed drainage system, there is abundant sta nding wat er , even during the dry season (March 1998). J ourn al of Coastal Research, Vol. 18, No.2, 2002 Late Quartern ary Evolution of the Orinoco Delta, Venezu ela 229 62' 6 1' Boca de Guanipa 10' ATLANTIC OCEAN N g' 1',:r:~\\ :::.: :;\: 1 ~~3~~~~mUd withminor sand. silt. lnterdistnbutary mud plain D (silt, clay, and muck) Chen ier ridge lnterdistributarypeat plain "<1f '"','.1 Distributary C? hannel and levee U e , ,' (fine sand, Silt , and clay) :;p.., (san d and she ll ) Figure 4. General distribution of environmen ts of deposition in th e Orinoco delta plai n. Th ese subdivisions were derive d from a geomorpbic map of the delt a plain ( WA I{ N E et 01., 1999, th eir Figure :J1 an d Table S) by grouping units that wer e form ed by similar geomorphic processes. Th e majori ty of terrigenous substra tes occur in th e south and southwes t, reflecting th e influence of RIO Gra nde , and formerly Cario Man amo , in the tra nspo rt a nd dist ribu tion of terrigenou s sediment. Vast peat plai ns of the central a nd northwest ern delt a show that these ar eas currently receive little or no terrigenous sediment and maintain high water levels. tomosing, muddy, fluvi a l/tidal cha nnels a nd channel islands. are observed updrift of river mouths dischargin g along the Wat er and sediment discharge through Rio Gr ande a nd ad coast. Along-sho re accretion of mudcapes diverts rivers north jacent distributaries is th e principal hydrologic process in th e and north westward. Accretion is mainatined primarily by southern sector. In contrast, th e central and northwestern longshore drift rather th an by th e river tha t th e mud cape is delta-plain sector consists of mor e widely spaced, blackw at er diverting. dist ribu tary cha nnels and vast herbaceous and forested wet Th e delta-front and prodelta deposits of the subaqueous lands that are underlain by organic-rich soils (Figure 4). In delta are as much as 70 m thick and form a rela tively na rrow, this delta-plain sector, tides and dire ct precipitation are th e steep, convex-up profile on the shelf (Figure 5). Th e Ori noco principal hydrologic pr ocesses controlling th e geomorphology shelf is a broad , low-gradient (0.02 to 0.5 perce nt ) fea tu re; and biologic composition and structure . such broad , low gradient shelves are cha racteristic of man y Th e centra l a nd northwest ern delta coast typi cally consists mode rn delta se ttings (WAHN E and STANLEY, 1995; PANIN of mudflats 2 to 5 km wide, which are bord ered on th eir land and ,J!PA, 1998; BERENDSEN, 1998; Coleman et al., 1998a ). ward side by mangrove forests (Figure 3d). The physiography Along the Atlantic ma rgin, the shelf extends offshore ~ 100 of th e Orinoco coast is much like th e Fren ch Gu ian a, Su ri km to th e shelf br ea k, which gene ra lly occurs at ~ 100- to nam e and Guy an a (Guia na) coas t to th e south, with alter 1I0-m water depth (KOLDEWl.JN, 1958; NOTA, 1958; VAN AN nating estua ries and mudcapes. Mud cap es are similar to DEL, 1967; BUTE1': KO and BARBOT, 1980). Like many modern sa nd spits in morphology, but they have a differen t origin deltas, the outer-she lf and slope surfaces are relict, sub (Figures 1, 4)(ALLISON et al., 1995, 2000; WAH NE et al., in merged coastal pla ins tha t developed during Pleistocen e sea press). Typically 5 to 10 km wide (per pendicular to th e coast) level lowstands an d subsequent transgression (e.g., ALLEN, and as mu ch as 100 km long (pa rallel to th e coast), mudcap es 1965; CHE:--I et al., 2000 ). Jo urnal of Coas tal Resear ch, Vol. IS. No. 2,2002 Warne , Guevara a nd Aslu n 63" 62" 61e 60" 59" 11" + Rad ioc arbo n dated samp les from shallow cores (WAR NE et al., 1999) A_A' Cross-section (Figure 13) Thickness of subrnerqed Holocene de lta deposits (m) (McC LELLAN D ENGINEERS , 1979) 10" 58, •Thickness of Holocene delta deposits (m) estimated from geotechnical borinq logs 9" t~ "... ~ '"-v ", /' .0 '. ~ " t. . ,! Information source of geotechnical bo ring logs @ FUNIND ES USB (1998) • FU GROGULFInc.(1979) o INTEV EP (1981) • GEOHIDRA CONS ULTORES , C.A . (1997a) E9 KIDWE LL and HUNT (1958) Figll l"l':>' :\lap ,;bowing t hv Ihick uess 01" l loloce no O rinoco Delt a ,;ed inH'nt,;. Dat a incl ud e geophy,;ica l survey s and " or in g (gpotech n ica li log,;. l nforrn uti on n 'gn rd in g i hr- location s . dept hs , a nd age s of rud iocu rbo n-da tc d samples is availu ble in \V AI: ~ E c! al . ( l H9B). Seaward of th e delta-front sedi ments a re relict sa ndy coast MAJOR PROCESSES CONTROLLING LATE a l-plain sedime nts (Figure 6) that were reworked and red e QUATERNARY DEVELOPMENT posited during th e late Pleisto cen e to Holocen e tran sgr ession . Partially ceme nte d, ca lcare ous, coralline mounds occur a long Th e geologic sett ing , clima te, river-water and -sediment dy na mics, distributary cha nnel-system dyn am ics, sea-level th e shelf edge (Figure (i ); these mounds a re interpret ed to be change , a nd coast and she lf hydrodyn ami cs are th e major fac late Pleisto cen e coral reefs (KOLIJI'; \Vl.JN, 1958; NOTA, 1958; tors controlling delta evolution (COLEMA N, 1981; STA NL~; Y MCCLI';L1 ,A"ll E!'\(;INI';J':I{S, 1979; B1 J'l'E !'\I(O and BAI WOT, a nd WAI{NE, 1998 ). Evaluation of major delta -forming pro 1984 l. Th ese features are similar to tho se found along th e cesses, a nd th eir cha nge through tim e, provides a basis for Mississippi Delta shelf (SllTI';J{ and BEJWYJl II.I., HJ86; ROII t.: gene rating a compreh en sive and viab le account of t he Ori I':I("I 'S ct al.. 1987l. "'. noco Delta evolution. u Th e Gulf of Pari a is a semionclosed, tectonic basin located seaward a nd adjacent to t he northwest Orinoco Delt a. Th e Geologic Se tting t wo rath er na rr ow inl et/outlet s, Boca de Serpicnte s in th e sout h a nd Boca del Dragon to th e north, cont rol water and Th e Orinoco Basin covers ~ 1.1 X 10'; km' oftropica l north sediment dyn amics in th e gulf. Boca de Serpientes is th e nar ern Sout h Ameri ca (Figure 7l. Th e Orinoco dra inage basin rower (as little as 15 km ) and sha llower (thalweg dep th as cons ists of - 50 percent Llanos, 35 per cent Guayana Shield, littl e as :l:3 m l of t he tw o inlet/outlets (VAN ANllI';La nd POST a nd 15 per cent And es and Coasta l mou ntain ran ges (Figure MA, 1954 l. Delta sediment is transported into th e Gulf of'Par 7 ). The vast grassy plains of the Llan os region are underlain ia by ( 11 discharge of rive r sediment from Ca no Ma nam o (pri by a foreland basin tha t is tilled with Ter ti ary and Quater or to const ruct ion ofVolcan Dam ) a nd (2) advection by wav es na ry sediments that were derived from th e risin g Andes a nd litt ora l cu rre nts via Boca de Se rpiente s (Figu re 2 l. Al Mountains to th e west. Th e sa ndy subst ra te of th e Llan os is t hough most sedime nt transpo rted to the gulf is deposited bro adl y inundated and exte nsively reworked by fluvial pro t here, a portion of th e Orinoco sedime nt is transp orted cesses during th e wet sea son. The Ouayana Shi eld is pri through Boca del Dra gon a nd into th e southern Ca ribbea n marily compose d of deeply weathered felsic to intermedi ate (MII.I.J!\I!lN e! al., EJ82; i\!IoNI';!'\'I'E, 1 9 8 ~J / HJ 9 0 a , b). plutonic rock s and gneisses (OIlIllS and BAJ{I{O N, 1983; Cvo- .lou rn a l of Coa s tu l \{e';l'a rch. Vol. 11'1 . No.2, 2002 Lat e Quarternary Evolution of the Orinoco Delta, Venezuela 231 Explanation Calcirud ite and calc areni te D San d D S,lty mud D Clay Distrib utary mouth .... bar san ds Bathymetric co ntour (m) VENEZUELA GUYANA , 100 km Figure 6. Sediment distribution and bat hymetry across the Orinoco shelf. Compiled from VAN ANm;L and POSTMA (1954 ), KOLUEW l,JN (19581, !'IoTA (1958), MORELOCK (1972), MCCLELLAND ENGINEERS (1979). The clay substrate sea ward of th e Orinoco coast re presents the sea wa rd limi t of the modern delta. The distribution of th e clay and silty mu d substrate indicat es th at th e Gu lf of Pari a and the sout h Ca ribbean Sea near Boca del Dragon are major depositional sites for Ori noco sediment. Th e clay and silt dist ribu tion reveals the impo rtance of littoral cnrr ents in distr ibu tin g of Ori noco and Amazon sediments. TECMIN, 1991a through O. Maximum relief on th e elevated pansion of the Llanos also inh ibits development of a mean shield is > 3,000 rn, but most of th e shield is low relief. Th e dering channel system, resulting in an a nas tomosing syste m dr ain age basin is bord ered on th e west and north by young, in the lower Orinoco River. Th e location a nd gradient of the high relief Andes and Coas tal Mountains, which supply ~ 9 0 lower Orinoco River are significantly influ enced by a series percen t of th e sediment to th e Orinoco River but compose of bedrock outcrop areas (cont rol poin ts) along its course only 15 percent of th e basin area. ( H A ~ I1LTO N a nd L E: WI S, 1990) (Figure 7). At a regional scale, th e Orinoco River cha nnel forms an arc Th e lower Orinoco River and Delta have developed in the along th e cont act betw een the foreland ba sin sediments of the Eastern Ven ezuel a Basin (EVS ) str uct ura l trough along the Llan os and th e crys talline ba sement of the Guayan a Shield sout h margin of th e South Caribbean plate boundary zone (Figure 7). Regional tilting to th e south-southeas t by uplift of (SCPBZ, ROBEtrr s ON and BUlU<.E, 1989)(Figure 8). Th e EVB th e Andes and northern coas tal ran ges a nd latera l expa nsion is a foredeep basin associated wit h tra nspressional tectonic of th e Llanos foreland basin sedime nts maintai n th e cours e activity between the Ca ribbea n an d Sout h Ameri can plates. of the Orinoco at 01' neal' th e boundary between th e bedrock Th e EVB is asymmetric, with distinct south an d north flan ks of the Guayana Shield and th e forela nd-b asin clastic wedge. (Figure 8). The south flank is moderately faul ted, with an Lateral expans ion of th e Llano s onto th e left-bank portion of overall slope to th e north of 25 to 80 m!km (FIORI LLO, 1984; th e floodplain maintains a rather narrow fringing floodplain, Pm ETo- CEDRARO, 1987). Th e Tertiary sediments within th e except at the intersections of major tributaries. Lateral ex- sou th flan k are gen tly folded but offset by a series of normal Journal of Coasta l Research , Vol. 18, No.2, 2002 232 Warne, Gueva ra a nd Asia n 75 ' 70 · 65 ' 60 ' CAR IBBEAN S EA 10' 5' \ Dr ainage-basin bo unda ry n COLOMBIA BRAZIL o 400 km ~ O·'-L-.------'------.J ij > Lla nos ; ~ , ">I! .. D O rogen ic te rra ins Ii, I Lla nos ; D Gua yan a Shield t D low-r eli e f a re a s ' " high- re lie f areas ~ St ream gaging s ta tio n \ Bed rock (Guayana S hie ld) con tro l o poi nts a lo ng lower Orino co River ..J .. Figure 7. Orinoco d ra inage basin show in g major physiogra phi c pro vin ces , princip a i tributaries, gaging site s, bedrock control poi nts , a nd Guri Dam . t Com piled from M EAD E et al . (983), NOllDII\" a nd P f':HEZ-lIE HNANJ) EZ (989), a nd H AM ILTON and L EW IS ( 1990). ( ..J fau lts th at strike N 60° E and dip north or south. Th e north 1980, 1984; PmETo- CEDRARO, 1987; DI CROCE et al., 1999) . flan k of the ba sin is characterized by complex folding a nd Many of these faults have sea floor expressions in the form of faulting tha t record inten se deformation associated with dif sca rps and linear seafloor trough s, a nd some of th ese appea r fer ential movement betw een the Caribbea n a nd South Amer to be active. Th ese faults are generally att ributed to over ican plates. Th e modern delta is located along th e transition steepening and rotational slumping of Quaternary delta de betw een the relatively deformed a nd und eformed portions of posits. Th e rotational listric normal fa ults and oth er soft-sed th e EVB (Figure 8). iment deform ation at th e shelf edge are characteri stic of The Offshore Orinoco Platform and Columbus Basin com man y Tertia ry a nd Quaternary delta seque nces (e. g., COLE pose the seaward, eas tern extens ion of th e EVB along th e MAN et al., 1974, 1988, 1998b; WINKLER and EDWARDS, 1988; pr esent continental she lf (LEONARD, 1988; DI CHO CE et al.. DOUST and OMATSOLA, 1990; KUEHL et al., 1997 ). 1999). LEONARD (1983 ) estimated that as much as 12,000 m Th e modern depocenter is located adjacent to but gene ra lly of upp er Mesozoic and Cenozoic sediments have accumulate d south of the inten sely deformed portion of th e SCPBZ (Figure in th e Columbus Basin (Figure 9). Sh allo w geophysical sur 8). However , a number of the fault systems within th e SCPB Z veys on the Orinoco Delta shelf indicate th at most of th e extend into th e Orinoco region (ROBERTSON and BURK F: , Pleistocen e st ra ta bene ath the shelf are uniformly dipping 1989 ) a nd have been a significant process in delta evolution - 8 to 28 m/km to the north or northwest or are generally by influencing the positions and orientation of man y of th e horizontal (MCCLELLANDENGINEERS, 1979). A number of re delta's cha nnels, differential subsiden ce across th e delta, and searchers ha ve reported exte ns ive fau lting of Tertiary a nd developm ent of local , near-surface fau lts and folds. Qu aterna ry strata along the outer shelf and slope (Figure 9a ) Currently the Orinoco Delta is seismically qui escent. The (MCCLELLANDENGINEERS, 1979; BUTENKO and BARBOT, only recorded seismic activity of consequen ce was in 1940, J ou rn al of Coasta l Resea rch, Vol. 18, No, 2, 2002 La te Qu a rt ernary Evo lution of the Or inoco Delta , Ven ezuela 233 SCPBZ Sou th Caribbean plate boundary zone I Ur Urica fault I I'Q Depth to crystalli ne SF San Francisco fau lt 0 , baseme nt (melers) S Sold ado fault LB Los Bajos fault Area of mud (~ :~ ~ ~ ~ : : ) vo lca nism/diapirism Anticline, syncline 0 Tu Tucupita /' /' Inferred faults o 100 200 km (::::~:: :::::~::::~) \ ) 65' 6 4' 63' 62' 6 1' 60' 59' .,.../ Normal faults Tertiar y ~~~~~~~3 Gu ayan a Sh ield 1>:'.:<.',:'1 Qu aternary D uplands ,:".:':,:-,' undifferentiated ,d Strike -s lip faults Cataclastic ~ Cen oz oic Hol ocene coastal zo ne ~ undiffer entiated • plain / Thr ust faults Me sozoic Q uaternary Holocene D.; ... . undifferen tiated D uplands D della plain Figure 8. Pri ncipal structura l fea tures a nd ge nera l geology of the Or inoco Delta region. Information deri ved from r EESe! al. (196 8), CASE a nd HOLCOMBE (]980). LEONARD (] 983) , PIMENT1': L·Dr:-BELLlZZIA (1984 ), ROBEH TSON a nd BURKE (1989 ), CVG-TECMIN (] 991a·O, BELTRAN (]993 ), a nd DI CHOCE et al. (1999 ). Th e term "baseme nt" in the figur e an d te xt refer to the crysta lline (igneous a nd met a morp hic) rock th a t is u ncon foma bly overla in by Ter tia ry and Quat ern ary sedime nts. when a ma gni tude-6.0 (Richter) ea rthquake occurr ed along (1999, th eir Figure 57) identified several lineaments that ap th e boundary of the Guayan a Shi eld . Faulting in the lower pear to influence th e position and orientation of distributar Orin oco River determines th e course of th e main channe l and ies, hydrology, and distribution of ecosyst ems in th e delta defines the boundary between the Guayana Shield and the pla in. However , the degree and exte nt of differen tial move EVB (FIORILLO, 1984; Pm ETo -CEDRARO, 1987). In th e Gulf men t a nd the nature and extent of hydrologic a nd ecologic of Paria region, on the oth er hand, reports of magni tude-6.0 chan ge across these lin ea ments remain und efined . (Richter) earthquakes are frequent and widespread (I:-lTEV E1', 1978; CASE and HOLCOM BE, 1980; GEOHlDHA COI'\SUL Subside nce TORES, C.A., 1997b ). Pri ncipal neotectonic features in the delta includ e th e di Subsidence-rate mea su rements are fund a mental for deter apiric Pedernale s anticline and associated mud volcanoes mining delta hi story and are essential for developing effective (KIDWELL and HUI'\T, 1958; WARNE et al., 1999; ASLAI'\et al., structura l and environmenta l engineering designs within the 2001) and th e Saban eta syncline and Macarco an ticline along delta. We defin e subsidence as the lowering of the land sur the centra l delta coast (Figure 8). On the ba sis of analys is of face or water -sedime nt interface rela tive to a topogr aphic da satellite ima gery and aeri al photography, PEES et al. (968 ), tum. Th is measu re is independent of sea-level changes but GEOI-IlDHA CONSULTORES, C.A. (1997a ), and WAHI'\ E et al. includ es lowering associate d wit h both sediment compaction -I ourn al or Coastal Research, Vol. 18, No.2, 2002 234 Warne, Guevara and Aslan a A Southwest Northeast A Holocene Orinoco Delta Growth faults Seismic travel time (sech Toe thrusts 1 / Barbados accretionary complex ...... /' 2 . Pleistocene Continental crust b B ,", ill r=~===::::i::=--'-I----'''':':''::=='----' en~~z 0..0 zill 1-----+--+--t--'===.::",...-3>--""::::---i ~ o I-- - -=J--.=::=t-- = ,j--..:::::..-__=-----:=i ~ ~O~ k m Figure 9. Cross sections showing development an d exte nt of Tertiary and Quatern ary Orin oco sedime nts . (a ) List ric growth faulti ng at present-day shelf edge is ass ociated with ra pid delta progradation an d overs tee pening du ri ng sea-leve l lowsta nds. Eastw ard movem ent of the Ca ribbea n Plat e deformation front induced thrust faulting along th e eas tern limit of th e delta deposits.Note th at this section is located in the outer halo of the deforma tion front, and the th rusts and anticlines trend southwest-northeas t, oblique to the section. Modified from DI CROCEet al. (1999). (b) Schema tic cross section showing progr adation of th e Tertiary and earl y Quaternary Orinoco Delta across the Columbus Basin. Th e bulk of th e Orinoco sediment was deposited in the Columbus Basin during the Pliocene and led to development of a broad shelf in the Pleist ocene, whi ch is a major influence on th e evolutio n of the modern delt a. Modified from LEONAI W 11983 1. Note that LEONAltD 11983, hi s Figu re 5) identified a la rge number of norma l faults in th e area , bu t this diagram re presents the stratigraphy prior to deformation. a nd tectonic activity . Data used to generate the subsidence 0.8 to 1.0 mm/yr for the upp er delta, rates are summarized in Table 1 an d Figures 5 and 10. For 0.8 to 2.0 mm/yr for th e middl e delta, subsidence-ra te calculations we used the following formula: 2.8 to > 6.0 mm/yr for the lower delta Punta Pescadores area, S = IS edTh - (SL + WD + 1<: l)J!A, o to 8.3 mm/yr for th e lower delta Boca de Guani pa area, in which S = subsidence rate,SedTh = sediment thickn ess and to dated horizon, SL = sea level (below pre sent mean sea 2.2 to 4.6 mm/yr for Gulf of Paria (T able n level) at time of deposition, WD = wat er depth at time of deposition, El = the delta-plai n eleva tion whe re the core was Subsidence ra tes show a clear increa se from the upp er to recovered, a nd A = age of date hori zon. the lower delt a, which is normal in delta-plain settings A discussion of th e assumptions and methodology used to (STAN LEY and CHEN, 1993; STANLEY and WARNE, 1993; calculate subsidence (and sediment accumulation) rates is STANLEY a nd HAlT, 2000). Th e vari able subsidence ra tes in presented in WARNE et al. ( 999 ). Sedime nt-accumula tion the Boca de Guanipa and Punta Pescadores areas may be an d subsidence-rate ca lculations deri ved from th e shallow rel ated to active folds (Figure 8) or may be caused by differ cores ta ken during the course of thi s study are based on ra entia l compaction, dewater ing, and deform ation of th e un dioca rbon dates from in situ peat 0 1' large wood frag ments; derl ying delta sedime nts . Subsidence rates in the Gulf of Par although these data provide accurate age/depth relation ia are similar to those of the lower delta plain. No su bsurface ships, they prov ide only short-term es timates for the lower da ta are currently available from th e southern delta sector delta plain subsidence. The deeper geotechnical boring logs (Figures 1, 4) where we sus pect tha t subsidence ra tes are (Figure 5 ) are poorly constra ined chronologica lly, but provide relatively high (on the basis of the position of Rio Grande and insight into longer -term subsidence rates. Calculated subsi Boca Gr an de and the generally estua rine cha ra cter of th e dence rates a re: sout hern delta ). J ourn al of Coas tal Research, Vol. 18, No.2, 2002 Late quarternary Evolution of the Orinoco Delta, Venezuela Although the subsidence-rate calculations shown earlier re +. quired a number of assumptions, and chronostratigraphic o 000 c-i C'i0 data available for the Orinoco Delta are limited, these cal culated rates are similar to those of the Mississippi, Ni Ie, Changjiang (Yangtze), Gangcs-Bramhaputra, and Ilhine Meuse Deltas, where more radiocarbon-dated subsurface o o o 00 data are available (COLEMAN and S1\;11TH, 1964; STANLEY and CHEN, 1993; STANLEY and WAI{NE, 1993; TORNqVIST and VAN DI.JK, 1993; ROBEl{TS et al., 1994; BEI{ENDSEN, 1998; STANLEY and I-IAIT, 2000). Q) Q) Q) Q) Q) 0., 0., 0., 0.,0., S S S S S Ci:l Ci:l Ci:l Ci:l Ci:l [fJ a: [fJ [fJ [fJ Late Pleistocene to Holocene Climate o o o o 0 Z Z Z zz Climate IS the driving force for a number of major delta processes, including sea-level change, river and delta-water and -sediment dynamics, coastal-water and -sedimcnt dy [fJ [fJ [fJ [fJ ...... I. >,>,>,>, namics, and biological composition and structure Currently 0000 o c.o L- 10 LO "'<:j< the climate of the Orinoco Basin and Delta is mostly tropical +I +1 +I +1 +I with pronounced wet and dry seasons. Orinoco Basin climate 0000 o Moo,...... ;"i" o "'<:j< C"l 10 00 LO is controlled primarily by the Intratropical Convergence Zone cD cD cD c-i c0 (ITCZ), which is the latitudinal belt along the equator where the easterly trade winds of both hemispheres converge, pro ducing warm, humid, unstable air masses that generate large volumes of rainfall. The ITCZ seasonally migrates across ~ 15° latitude, and because the Orinoco Basin lies along the northern boundary of this migration belt, marked wet (.Iune E through November) and dry seasons (Decemher through E April) characterize the region. This pattern of marked wet and dry seasons induces large oscillations in water discharge t 0000 o o Oo 010100 o 00 and stage levels In the river and delta (Figure l lal, which o o o C;o M so 10 10 S o o~ to ID0'l~' 1- OJ S c.oo promotes a pronounced seasonal inundation ofthe river flood c.o L- 0 C'1 cD ,...... ; C"l0C"l0 plain and delta plain that typically lasts for 4 to 6 months +~+~ (Figure l l a I. During the dry season, 30 to 40 percent of the ggg~ river channel bottom may be exposed, and strong easterly C; ~ II t- 10 c.o "'<:j< winds largely convert the channel system to an eolian regime (McKEE, 1989; NOIU)JN and P~~I{EZ-HEI{NANDEZ, 1989; CARB()N and SCI-IUBERT, 1994). A number of studies have demonstrated that the climate of northeastern South America was markedly different dur ~ --..; --:-.....; Cj Cj Cj Cj ing the late Pleistocene than it IS today. Analysis of ocean bottom cores from the Bermuda Rise (northern Sargasso Sea) by SACHS and LEHMAN (1999) indicates that the climate of northern South America was variable from 60,000 to :30,000 years before present (yrs BP):!. These authors identified 10 to 12 major oscillations In sea-surface temperatures (SST's) comparable in magnitude to the change from late Pleistocene glacial maximum to the early Holocene. On the basis of anal yses of pollen and sediment from the Eastern Cordillera re gion of Colombia, KUHHY et al. (1993) also recognized that the late Pleistocene was a time of alternating cool/dry and '~ .~ warm/wet periods and that the period of lowest temperatures c5 and least effective precipitation occurred between -. 21,000 I Biological composit.ion and structure refers to the variety and types of plant and animal taxa (composit.ion I. and the relative cov erage or density of the various taxa (structure). Of particular concern here is the type and density of woody stern plants, grasses, and sedg es, which are a major factor in controlling erosion rates. :.! All He ages are given as un calibrated values unless otherwise noted. -Iournal of Coastal Research, Vol. IH, No.2, 2002 War ne, Gueva ra a nd AsIan A No rth S ou th A' Gulf of Paria P edernale s Dep th (m) Al A2 A3 A4 A5 A6 Wat er 20 14C date of -9500 yrs BP 40 (KIDWELL and HUNT, 1958) 60 -- Cross-section Information source log 10 80 / / Al INTEVEP (1981 ) Late ... . A2 INTEVEP (1981 ) Pl ei stocene A3 INTEVEP (1981 ) A4 FUGRO GULF INC, (1979) 100 A5 KIDWELL a nd HUNT (195 8) A6 FUNINDES USB (1998) 0 30 km B2 to B6 GEOHIDRA CONS., C.A. (1997a) B B' We st East P ederna les Punta Pescador es Bo ca de Mariusa De pth (m) A5 B2 B3a B4 B5 B6 20 40 60 e '------_ Late Pl ei stoc ene 80 G Woo d fra gments ~ Sandy mud 100 ~ S ilty mud ~ Sh ell .~ Clay and mud (soft, plast ic) ~ Gypsum ~ Mud with shell fragm ent s [ii] Stiff mud Figure 10. Cross sections showing thickness an d general lithology of Holocene sedime nts in th e Gulf of Pari a a nd northwest ern Orinoco Delta. In most cases, the base of the Holocene is poorly defined and is assum ed to occur at the transiti on from sand and stiff, brown , a nd yellow silty, sandy mud to relat ively soft, da rk-gray to black, organic clay s (WARNE a nd STANLEY , 1995 ). In core A5, KJlJWELLa nd HUNT(1958 ) determin ed tha t the clay mineralogy of sediments in the lower Holocene section were indicative of deep-water environment, sugges ting that the delt a coas t was well land ward of th e Pcder nales area at that time. KIDWELL and HUNT (19581 desc ribed th e " C sa mple th ey da ted ( ~ 9 5 0 0 yrs BP) as shell material from th e upper tr an sgressive sand, just. below the lowerm ost. Holocene delta stra ta. The la rge volume of woody debris in wells B:l thro ugh B6 is similar to th at. of th e tropical Mahakam delt a front. and prodelt.a deposits (COWIAZ a nd l ll, MATIlAIlEL, 1978; GASTALDO, 1992). J ourn al of Coastal Research, Vol. 18, !\o . 2, 2002 Late Quarternary Evolution of the Orinoco Delta, Venezuela SCI-lUBEI~T, 1988). SCHUBEI{T (1988), Il{IONDO and LATIUJ BESSE (1994), and HOOGHIEMSTI{A and VAN DEl{ HAMMEN a 70 (1998), among others, provided evidence that the drier, late Pleistocene climate promoted widespread development of sa Guayaguayare vannas across northeastern South America such that the 60 tropical rain forests that characterize the modern uplands, were restricted to refugia. Evidence indicates that relatively modest changes in temperature and precipitation conditions u; 50 E Puerto can induce changes from forested to tropical conditions in (1) Ayacucho > northern South America (IIUONDO and LATI{U I~ESSE, 1994; 0 .0 HOOC;}--IIEMSTRA and VAN DER HAMMEN, 1998). DAMllTl1 and OJ 40 S FAIHBRIDGE (1970) and LATRUBESSE and RAMONELL (1994) Q) discussed the oceanic and barometric conditions that pro 0) OJ (;) 30 moted cool, semiarid to arid conditions during glacial periods Q) and warm, tropical conditions during interglacial periods. > ii Analysis of Cariaco Basin (Figures 7, 8) sediments dem 20 onstrates that the B0lling-Cller0d period ( 14,000 to 12,1)00 yrs BP) of generally warmer conditions was interrupted by a number of climatic oscillations (HUGIIEN et al., 1996). Anal 10 Ciudad yses of pollen and sediment in the Eastern Cordillera region Bolivar of Colombia indicate that a warming period between 14,000 and 13,000 yrs BP was followed by a cooler period between O----~---""T'""""----r----....,...... ---~ ~ 13,000 and 12,500 yrs BP (KUHI{Y et al., 199~31. Several re 1982 1983 1984 1985 Year searchers recognized a warm (Guantiva i period in northern South America from ~ 12,500 to 11,200 yrs BP. The Guantiva b 300....,..------.-- 18 interstadial was followed by the cool, dry EI Abra (or Younger ##.~_ Stage Dryas) period between '~11,200 and 9,500 yrs BP during U> were~4° "<: E which mean annual temperatures Celsius lower ~ (1) than those at present and Amazon River discharge was 60 ,, > , 12 0 ~ percent of present discharge (FAII{BANKS, 1989; KUIII{Ye! , .0 a!', , OJ , 1993; HUGHEN et al.. 1996; ROBEI{TS, 1998b; MASLIN and ,, -S ~', BURNS, 2000). .. (1) , 0) LEYDEN (1985) reported warm, wet conditions in the Lake ,, OJ .. , 6 U; - .... Valencia region (Figures 7, 8) for the period 9,800 to 8,300 (1) > yrs BP. Her data suggest that conditions were warmer and ii wetter during this interval than at any time later in the mid dle and late Holocene. Peats in the high plateaus of the Gua FMAM JJ A SON 0 yana Shield (SCHUBERT, 1988) and palynomorphs of forest Month vegetation in the highlands of the Eastern Cordillera region Figure 11. Water and sediment discharge characteristics of the Orinoco (KUHRY et al., 1993) also provide evidence that humid tropi River. (a) Stage at several stations along the Orinoco River. See Figurr: cal conditions were established in northern South America 7 for locations of gauging sites. The nenr-simultnucous peak discharge by ~8,900 to 8,000 yrs BP. Several authors recognized a pe along the river reflects the uniform chungt- in seasonal rainfall across the riod of enhanced wind activity in the Cariaco Basin region entire drainage basin. Modified from PI':ln:z-HEI{NANI)EZ and LOPEZ (Figures 7, 8) between~8,400 and 7,800 yrs BP, which was (1998l. (bl Monthly sediment and water discharge in the lower Orinoco River (Ciudad Bolivar) during 1982 and 198:3. Modified from M EADI<: et part of a briefbut apparently widespread transition to cooler, 01. (1990l. drier, windier conditions (HUGHEN et al.; 1996; ALLEY et al.. 1997; STAGER and MAYEWSKI, 1997). LEYDEN (1985, her Figure 9) provided evidence for a num ber of climatic oscillations during the middle and late Holo and 15,000 yrs BP. Mean annual temperatures at that time cene in the Lake Valencia region (Figures 7, 12). HOO(~I1II~:M were ~'5° Celsius cooler than those at present. STHA and VAN DEI{ HAMMI<:N (1998) presented evidence of a Analysis of ocean-bottom cores from the south Caribbean period of generally wet conditions r-fi.Otlt) yrs BP. ME(~(;I<:I{S Sea, mapping and analyses of extensive, relict dune fields in (1979) identified a generally cooler and drier period in north northeastern South America, identification of polygenetic eastern South America between ~4,000 and ~2,000 yrs BP, drainage networks, and analysis of lake sediments provide which was sufficient to induce widespread changes in forest evidence of a generally arid climate in northeastern South biota. EISMA et al. (1991) recognized dry periods in the Col America around the last glacial maximum (21,000 to 18,000 ombian Andes at ~ 1,300 yrs BP, from 900 to 600 yrs BP, and yrs BP) (CAILLEUX and TRICAI{'I', 1955; DAMUTH and FAIl{ from 400 to 200 yrs BP; the authors inferred that these dry BRIDCE, 1970; TI{lCAI{T, 1974a, b; ROA, 1979~ LEYDEN, 1985; periods reduced sediment discharge from the Amazon River. .Iou rnal of Coastal }{esearch, Vo!. 18, No.2, 2002 Warne, Guevara and Asian The BLACI\ et at. (1~)99) study of Cariaco Basin sediments identified enhanced trade-wind activity between 835 and 640, 590 and 410, and 310 and 120 yrs BP (Figure 12), which concurs with the findings ofE ISMA e! al. (1991). The Holocene Age, Cool, dry, Warm, wet, years Principal data enhanced diminished sources climate summary of BI{OECKEI{ (2001) shows the relatively B.P. Trade Winds Trade Winds warm period at about 8,500 to 9,000 yrs BP, the cool period BLACK et al. (1999) at about 7,400 to 8,200 yrs BP, and the relatively cool period 1,000 EISMA et al. (1991) from 2,000 to 4,000 yrs BP. 2,000 The EI Nino - Southern Oscillation phenomenon was an 3,000 MEGGERS (1979) important weather pattern in northern South America dur 4,000 ing the Holocene (DIAZ and MAI{KCI{AF, 1992; MEC(;EI{S, LEYDEN (1985) 5,000 1996; COLE, 2001; TIU}DHOPE ct al., 2001). The EI Nino HOOGHIEMSTRA and VAN DER HAMMEN (1998) Southern Oscillation events recur irregularly every 6 to 10 6,000 yrs; during El Nino years the ITCZ tends to remain in its 7,000 I southern position 2 to 4 months longer than normal, promot 8,000 - ALLEY et al. (1997) ing drought conditions in the Orinoco Basin (II{IONDO and 9,000 LEYDEN (1985) LATIUfBESSE, 1994). 10,000 Orinoco River Water and Sediment Dynamics 11,000 HUGHEN et al. (1996) 12.000 KUHRY et al. (1993) The Orinoco River is the third-largest river in the world in 13.000 terms of water discharge, eleventh-largest in terms of sedi 14,000 ment discharge, and is the principal supplier of water and sediment to the Orinoco Delta (MILLLMAN and MEADE, 198~3). 15,000 Because the Orinoco River basin lies within but near the 16,000 DAMUTH and northern limit of the ITCZ, there is pronounced annual var 17,000 FAIRBRIDGE (1970) iation in maximum and minimum discharge. Seasonal stage 18,000 TRICART (1985) fluctuations are typically 17 m in the lower river (Figure 19,000 I l a l. Mean monthly discharge at Musinacio (for the period 1970 through 1981) varied between 1,330 and 81,100 rn/sec. 20,000 The ratio of maximum to minimum flow during this period 21,000 was from 8:1 in 1972 to 54:1 in 1978, with an average of 26: 22.000 1 (NOI{DIN et al.. 1994). Such a large difference in seasonal 23,000 discharge for a major river system is unusual; for example, SCHUBERT (1988) 24.000 the wet season to dry season discharge ratio for the Amazon River is typically ~'3:1 (KINEKE and STEHNBER(;, 1995; WAI{ 25,000 NE ct al., in press). 26,000 Sediment discharge for the lower Orinoco River is estimat 27,000 ed to be 150 to 212 X 10(; tons/yr (MEADE et al., 1990; Fu 28,000 NINDES USB, 1999), and dissolved load, 28.6 X 10(j tons/yr (RAMII{EZ et al.. 1992). Sediment discharge in the lower ()ri 29,000 noco River typically has two distinct peaks during the flood 30,000 season (Figure I l bl, with a peak during rising flood (April 31,000 May), a minimum during peak water discharge (August-Bep 32,000 tember). and a secondary peak during the recession of flood 33,000 discharge (October-November) (NOI{DIN and PEI{EZ HI':I{NANDEZ, 1989; MEADE ct al., 1990; CAHB()N and SCHLJ 34,000 BEI{T, 1994), The two peaks in sediment discharge are attri 35,000 SACHS and LEHMAN (1988) buted to temporary ponding of left-bank tributary flood wa 36,000 ters during peak discharge at the intersection with the Ori 37,000 noco main channel, which results in short-term retention of 38.000 Andean-derived sediment: as stage in the Orinoco channel recedes, the ponded tributary water and sediment are re 39,000 mobilized, producing the second sediment discharge peak 40,000 (MEADE ct al., 1990). 41,000 Approximately half of the Orinoco sediment is deposited on 42,OOO-.L---~;;""----"""------"'" the delta plain (MEADE, 1994). In addition, sandy distribu Figure 12. Summary of late Pleistocene and Holocene climatic changes tary mouth bars occur at the seaward edge of many major in northeastern South America. distributary channels (Figure 6). Most terrigenous sediment .Iournnl of Coastal Hesearch, Vo!. IS, No.2, 2002 Lat e Quartern ary Evolution of th e Orinoco Delta, Venezuela 239 A' o A Southwest Northeast 2 i i 0 2 km :§: Cana 9 1>:>:-:';'::1 Brow n mott led Da rk-brown peat : .,'.':.'. :. sand and mud and clay ey peat ~=====3 Radiocarbon Dark -gray lam inated Gray to dark-gr ay Da rk-gray mud with • sampl e and I Core D mud and sand - - - - - bioturbated mud many gras s fibers ass ociated age Figure 13. Cross section showing natural-levee and flood-basin deposits of Canas Manamito and Cocuina nea r Tucupita. Not e th at ra diocarbon-dated peat buri ed by silty and sa ndy natura l levee and muddy flood-basin deposit.s provides a maximu m age of - 3,000 yrs BP for the se channel systems. A radiocarbon-dat ed orga nic flood-basin mud (buried A hori zon' ) passes beneath Carie Manamito natural-levee deposits, which suggests that this channel system may be younger th an - 1,500 yrs BP. The cross -section location is shown in Figure 5. deposited in the delta plai n accumulates as natural levees infilled (Figure 3a , c, e, 0 on a regul ar basis during the late along the flanks of major distributaries a nd as channel bars. Holocene (VAN ANDEL, 1967; WA]{I\'E et al., 1999). Ma ny of App roximately 85 percent of the sediment is transported t he blackwater distributari es, such as Ca nos Pedernales, Co th rou gh the Rio Grande distributary (MEAD E, 1994). As a cuina, Tu cup ita , and Gu ayaro appear to occup y channel sys result, mu ch of the delta plai n receives little or no mineral tem s formed by larger distributaries ii,e., they a re under fit sediment input. However, wid espread accumulation of organ channels). We infer that severa l of the sma ll nort heast-flow ic materi al mai ntai ns most of the delta-plain surface at or in g blackw ater rivers along the western delta , such as Rio near sea level , which pr ecludes development of in terdistri Morichal Largo and Rio Tigre, occupy channel syste ms of buta ry lak es (Figures 1, 3a, 4). Widespread development of coasta l-plain rivers that were active in the north western del peats provides evidence of long-term, perennial in undation ta prior to establis hme nt of Ca fio Manamo (VAl\' ANDEL, and/or sa turation of th ese interdistributary basins. However, 19(7). Areas of accret ed chenier ridges in th e cen tral delt a scattered charcoal wa s observ ed in shallow borings, suggest plain (Figure 4l, whi ch ty pica lly form on the down -drift side ing that water tables dropped below the peat surface and of majo r distribu tary channels, prov ide evide nce of t he loca fires parti ally consu med the peat during drier Holocene cli tion of form er major dist ributary channels. matic peri ods. Integrati on of the coastal and avu lsion hist ori es of Boca de Ma riu sita , Boca de Cocu ina, a nd Boca de Guanipa reveal s Distributary-Chann el System Dynamics tha t episodes of distribu tary-channel activity and shoreline evolution a rc closely linked . We infer that shallow bays at Sa tellite im agery, ae rial pbo tography, and field observa the mouths of large distribu taries such as Ca no Manama are tions reveal a large number of aba ndone d distributary cha n rapidly filled following distributary av ulsion and reduced flu nels acro ss the delta plain that are in various stages of in vial discharge (Figure 14 l. Bay filling probab ly occurs filling (e.g ., Figure 3c), Th ese aba ndone d and partiall y filled through a combination of littora l- and ti dal-current act ivity channels pr ovide evidence that cha nne l developm ent, av ul and mud ca pe development and expansion . sion, and aba ndonme nt are essentia l delta-plai n pr ocesses. Remote -sen sing images, field observ ations, and stratigra phic Sea-Level Change analysis of radioca rbon-dated shallow borings (Figure 13) provide evid ence that major distributaries (compa rable in Pleistocene an d Holocen e sea-level changes had a profound size to Canes Manamo and Macareo) evolved, avulse d, and influe nce on Orinoco Delta evoluti on, pa rticula rly with re- .Journ al of Coasta l Research, Vol. 18, No. 2, 2002 240 Warn e, Guevara and AsIa n ATLANTI C OCEAN o 5 mi I i ' l I o 5 km Figu re 14. Hist oric changes in Boca de Guan ipa area as shown by (a ) HJ51 aeria l photo gr aph mosa ic,(b) 1977 SLAH image, (c) 1990 LANDSAT TM image, a nd (d) 1996 RADARSAT image. Sha ded area of inset map shows approxi mate portion of delta covered by ima ges. Note ra pid shoreline progradation nea r mouth of Boca de Guanipa a nd form a tion of man grove islan ds southwest of Pedern ales. Construction of Vulcan Dam (Figure 1) in 1967 greatly red uced disch arge through Cano Man am o, which in turn accelerated infillin g of Boca de Gua nipa. spect to rive r ba se level, coastline position, a nd marine flow pr oximately 18,000 yrs BP, during the last glacial maximum, through the sha llow inlet at Boca de Serpientes. We define th e shore line was loca ted near the present shelf edge, about sea- level chan ge as the cha nge in th e ocean-water surface 120 m below pr esen t sea level. From - 18,000 to 10,500 yrs relati ve to a topogr aphic datum ra ther th a n relative sea-leve l HP, glaciers melted, ca us ing sea level to ris e rapidly. At about change, which typically includes the influ ence of both sea 10,500 yr s BP, glacial melti ng slowed, res ulting in a decel level cha nge a nd subsidence. era tion in the rate of sea-level rise. By - 6,000 yrs BP, sea Sea-level st udies along the coast of Surinam e (BI{I NKM AN level was near its presen t level (Figure 15). a nd PONS, 1968; ROELEV ELll and VAN LOON, 1978) and the Man y aspects of the sea-level hist ory in this rathe r struc Caribbean region (LICHTYet al., 1982; FAlJ{ BAl'.' KS, 1989 ; Pm turally complex region remain uncl ea r. VAN ANDEL and AZZOLI , 1991) pr ovide evidence of rapidly rising sea levels POSTMA (1954) and VAN ANDEL a nd SACHS (1964 ) deter during th e late Pleistocen e and early Holocene, decelerating mined th at ocean water entered th e Gulf of Paria through sea-level ri se in th e late ear ly Holocene, and slowly risin g sea Boca del Dragon ~ 13,000 yrs BP , bu t the marine cha nnel level from middl e Holocene to pr esent (Figure 15). through Boca de Serpi entes was not established until sea lev Su bsur face, remote sensing, a nd oceanographic data from el reached 45 m below present stand, approxima tely 9,500 the Orinoco Delta (VAl" Al"IlEL a nd POSTMA, 1954; KIDW ELL yrs BP . Th ey prop osed that, during th e Holocene, flow and HUNT, 1958; KOLllEWI.J N, 1958; J\iOTA, 1958; VA:-l AN through Boca de Serpi entes was interrupted for an und efined mcr., 1967 ; DANIELO, 1976; BlJTENKO a nd BAI UlOT, 1984)and period of time by a min or sea-level dr op until ~ 1,500 yrs BP, oth er major world deltas (STANLEY and WAl{NE, 1994; WAR whe n sea level rose and the hydraulic connection between the l"E an d STANLEY , 1995) indi ca te tha t th e late Pleistoc en e to Atlantic she lf and Gulfof Pari a was reestablish ed. GEOHIDRA recent sea-level history can be summarized as follows: at ap- COl"SULTORES, C.A. (1997a ), proposed that there was a rna- .Iourna l of Coast al Research, Vol. 18, No. 2, 2002 Lat e Quartern a ry Evolution of th e Or inoco Delta , Ven ezuela 24 1 Years before 10 000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,00 0 1,000 present ' ~ 10------~ '" ~ 0 Present sea leve l -. ... o .. ~ '" ~ ...... ~ ·1 0 ------: ..':' ...... -.. ..:, . ,: .. ------ ...... , ~ ..' ,~ -20------/ - - - ;''''':'------~ / iii Guiana Coa st dep ositi onal phases Subformation Mara Coroni e Formation Demerara European Pre Bo Atlantic Su bbo rea l Subat lantic clima te zo ne s Boreal real Deposition of ma rine mud s during constant or slowly ri sgin g D sea level, mostly by lateral accretion F==j Period s of nondep osition or erosion Depositio n of pyriti c mud s during rapidly rising sea level, • Radi ocarbon -dated coa stal-plain pea t D mostly by verti cal accretion ~ Sea-level curve of BRINKMAN and PONS (196 8) ... ·· ·· ~ e a-Ievel curve of FAIRBAN KS ( 1989) Figure 15. Holocen e sea- level curve and prin cipal deposi tional phases of th e Guia na coast region. Diagram modified from B I{lNKMAl': and PONS (1968 l. Phase, subformation, and form ation nomen clature from Bm :-lKMAN an d PO:-l S (1968 ) and R(m LEVELD and VAN Lo o rc (197 8 ). Th is is a relative sea -level curve because no estimates of subsidence wer e give n. However , thi s sea-level curve is genera lly concorda nt wit h regional an d globa l sea-level cha nge models (CLARK et al., 1978; LI GHTY et al., 1982; FAIrWA :-I KS, 1989; !'mAzzo Ll , 199 U. 1n addition, work by NOTA i 1958 ) indica tes that thi s portion of the coasta l plain experienced only minor subsidence during th e Holocene. jor change in th e coast al current regim e ~ 3 , 0 0 0 yrs BP, and to th e Orin oco Delta , whe re Tr inid ad disr upts th e marine lit th at circulation through Boca de Se rpient es was reestab toral-curren t sys te m (Figure 2l. On the Orinoco she lf, th e lish ed ~ 1,000 yrs BP , promoting littoral curren t processes Guayana Curren t splits, a nd one branch flows eastward and along th e Orinoco coast and development of mudcap es. northward, passes between Trinidad and Toba go, and is dis persed in the Caribbean Sea. Th e oth er br anch of the Gua Coast and She lf Water and Se diment Dynamics ya na Curren t flows into the Gul f of Paria through the Boca Th e broad shallow Orinoco she lf tend s to damp incoming de Serpientes (Figure 2). As the br an ch of th e Gu ayana Cur waves, resulting in a low- to moderate-energy wave regime. rent flows towa rd Boca de Serpientes, it is constricted , which Moreover, high-intensity storms , including hurri canes, are tend s to increase littoral-current velocity and hence inte nsify un common (FUNINDES USB, 1998; WARNE et al., 1999), and longshore erosiona l and deposition al processes along th e cen th erefore th e coas t lacks storm surge and oth er high-en ergy tral and northwest ern Orinoco coast a nd shelf. erosional and depositional features. Mean diurnal tides along Combined rem ote se ns ing and reconnaissance field a naly the coast range from ~ 1 .4 to 2.0 m (Figure 2). Th e coast is ses indi cate that the Orinoco shoreline, although genera lly strongly affected by the Guayan a Current (Figure 2), a pri pr ograding, ha s erosiona l and nondepositional coas ta l sectors marily northwest-directed littoral -current regim e with veloc as well (WAHNE et al., 1999, th eir Figure 39). Erosion al shore ities of 50 to 75 cm/s in th e spring and 25 to 40 ern in th e lines tend to be st ra ight to concav e (seawa rd) in ma p view; autumn (VAN ANDEL, 1967; COLIN and 13 o URLES, 1992). Th e they ty pically ha ve a small scar p at the shoreface; mat ur e Guaya na Current transports Ama zon sedime nt northwest mangr ove forests abut the shoreface; and th e mangro ves are ward - 1,600 km along th e shelf, prov iding ~ 5 0 percent of bein g actively und erm ined by t he enc roaching wa ves, ca using th e sedime nt deposited along th e Orinoco Delta shelf and th em to colla pse into th e surf. Histo rical aerial photogra ph s coast (EIS1\I Aet al., 1978, 1991 ; MEAD E, 1994). Th e Gua yana indicate th at th e coast ha s eroded landward as mu ch 2 km Current acts as a barrier to keep th e tu rbid water s of th e in some areas between Boca de Cocuina and Pedern ales Amazon a nd Orinoco Rivers on th e she lf, so th at sus pended (WAGNE R an d PFEFFERKORN, 1995). Nondepositional shore concentrations of surface waters on th e inner shelf are tens lin es a re typically st raight, and man grove forests abu t t he or hundreds of tim es grea ter th an tho se of th e outer shelf shoreface bu t are not colla psing into t he surf; in places, sma ll (EME I/YANOV and KHARIN, 1974). Th e Gua yana Current silty, sandy beaches develop. Accretiona ry shorelin es typical flows northwestward genera lly unimpeded from th e Amazon ly have mudfla ts th at are as much as 2 km wide during low J ournal of'Coastal Research, Vol. 18, No.2, 2002 242 Warne. Guevara and Asian tide. Accretional coastlines, which occupy approximately 50 gradation by tidal-flat and rnudcape accretion, particularly percent of the Orinoco coast (WAf{NE et al., 1~)99, their Figure along the central Orinoco coast. 39), occur along estuaries, as well as along the Atlantic coast. Mudflats are low gradient and tend to accrete laterally along LATE QUATERNARY EVOLUTION OF THE the break in slope at the seaward edge of the flats. The very ORINOCO DELTA shallow water conditions along the mudflats and the soft but The large climatic oscillations that characterized the late cohesive mudflat surface strongly attenuate incoming wave Pleistocene caused widespread and significant changes in energy, promoting vertical accretion along the landward por ecosystems (HOO(;}IIEMSTI{A and VAN I)E}{ HAMMEN, 1998; tions of the mudflats. Colonization by mangroves along the SACHS and LEHMAN, 1999). Biologic composition and struc landward portion of the intertidal zone further promotes ver ture were generally not as well established as at present tical accretion. Along and down drift from major distributar (HOOUHIEMSTI{A and VAN I)I;~I{ HAMMEN, 1998; IRIONl)O and ies, accretional sandy beaches develop. Sandy beaches are LATRUBESSE, 1994) so that vegetation was less effective at particularly well developed on the downdrift side of Boca de stabilizing soils than the present tropical system. Araguao area and most likely represent nascent chenier ridg es. Late Pleistocene (~20,000 to 16,000 yrs BP) Comparison of the physiography and coastal processes of the French Guiana, Surinatnc, and Guyana (Guiana) coast During the latter part of the late Pleistocene, climate was with those of the Orinoco Delta reveals several similarities generally arid, cooler, and more windy than at present (Fig (Figures 1, 16) (WAI{NE et al.; 1999, in press). Both consist of ure 12). The Orinoco Basin was largely covered by dryland alternating mudcapes and estuaries at the mouths of major savanna vegetation, and eolian dune formation was wide rivers. Both receive large volumes of sediment from the Am spread (TRICAI{'I', 1974a, b, 1985; ROA, 1979; IRIONDO and azon River by longshore transport, and both have been pro LATlUIBESSE, 1994). The Llanos region was particularly arid during this period (SCIIUBEI{T, 1988). grading seaward onto the shelfsince the early Holocene. Both We propose that river discharge was less, and more erratic are mesotidal systems in which large segments of the coast than at present, but snowmelt from the Andes provided a are composed of mudflats bordered by mangrove forest on perennial source of discharge through the semiarid to arid their landward side. The Guiana and Orinoco coasts are Orinoco Basin lowlands. Eolian activity produced a poorly de closely lin ked systems, largely related to the Guayana Cur fined drainage network across the Llanos region. We suggest rent and influx of sediment from the Amazon. Moreover, late that large volumes of sediments were delivered to the river, Quaternary sea-level and climatic oscillations were very sim which promoted development of a braided-river system in the ilar along these coastal systems. lower river. There are, however, marked differences between the Ori Sea level was as much as 120 m lower than the present noco and Guiana coasts: the Guiana coastal plain is largely stand (FAIRBANKS, 1989). As a result, the coastline was po composed of coalesced beach ridges and interridge marshes sitioned near the present shelf edge (Figure 18a). Along the (Figures 16, 17), whereas the Orinoco Delta is largely com present shelf, shallow seismic data (MCCLELLAND ENGI posed of distributary-channel, natural levees, and interdis NJ;:EI{S, 1979) indicate that the sea-level lowstand induced in tributary basin deposits, with only a few relict beach ridges cision of the coastal-plain river valleys. However, the resis apparent (Figure 4). The muddy Guiana coast is a strand tant Guayana Shield bedrock precluded deep incision of the plain depositional system between the two major depocenters river valley upstream of delta apex at Barrancas (Figure 7). of the Amazon and Orinoco Rivers. The muddy Guiana coast Remote sensing data and field observations suggest that the has high suspended-sediment concentrations that commonly smaller rivers that drain the less resistant Tertiary sedi exceed 1,000 mg/L (WELLS and COLEMAN, 1981a). The near ments to the north (Figures 7, 18a) of the Orinoco River de shore fluid muds, combined with the strong northwest-di veloped an incised drainage network that was distinct from rected Guayana Current, promote the widespread develop the Orinoco system icf. VAN ANDEL, 1967; DANIELO 1976). ment of mudbanks (WELLS and COLEMAN, 1981a, b; RINE Subsurface data indicate that the Gulf of Paria was a closed and GINSBERU, 1985; WAI{NE et a!', 1999, in press; ALLISON inland or restricted marine basin during this time, in which ct a!', 2(00). Mudbanks are dune-like features that extend evaporites (gypsum ) accumulated at its center (Figure lOa, obliquely from the nearshore, offshore to about the 20-m iso core A4). bath and have as much as 5-m relief (RINE and GINSBEI{(;, Available topographic and bathymetric data indicate that 1985). Observations along the Orinoco Delta coast indicate seaward (downstream) of the Barrancas knickpoint, the Ori that mudbanks are not a major feature (DANIELO, 1976; noco River was a relatively steep-gradient (~0.43 m/km) WAI{NE et a!', 1999). WAHNI;~ et al., (1999, in press) proposed braided river system that transported large volumes of rela that the general absence of mudbanks along the Orinoco tively coarse sediment across the coastal plain and to the coast was related to the large influx of fresh water that has coast ic]. FISK, 1944; STANLI1~Y and WA}{NE, 1993). We pro relatively low suspended-sediment concentrations at Boca pose that sediment was transported through a network of Grande. Nonetheless, preliminary observations indicate that moderately incised, bedload-dominated channels whose po nearshore waters along the Orinoco coast contain relatively sition and discharge capacity changed over time ic]. BERRY high concentrations of suspended sediment (MONENTE, 1989/ HILL and SUTEI{, 1986; SUTEI{ and BEIU{YHILL, 1986; SUTER, 1990a; WA}{NE et a!', 1999, their Table 10) that promote pro- 1986). .Iourna] of Coastal Research, Vol. IH, No.2, 2002 Late Qu arternary Evolution of the Orinoco Delta, Venezuela 243 58 ' 56' 54 ' 52' i i a o 100 km 8' ATLANTIC OCEAN 6' 4' b i MODERN o 5Clkm ~~ ;~~em~da~~~: ~~~~~~m ent HOLOCENE TEXTURE NAME ~ Ombrogenous peat Comowine phase Clay and silty clay, Comowine phase D. .'' river ine and estuar ine Coronie subfm . Comowine phase Clay and silty clay Coronie subfm . Moleson phase t=::::~ Clay and silty clay Coro nie subfm. Shells and calcareous Moleson pha se ..fine sand (ch eniers) Coro nie subfm. f:'·:/:'.i {1 Fine sand and loamy Wanica phase , .'.,,;.' fine sand (cheniers) Coro nie subfm. [:/ <:J Clay and silty clay Wanica pha se Coro nie subfm . ~iIII Pyritic clay, peaty Mara subformalion ,,;, ,,,, clay, and peat Demer ara Fm. PLEISTOCENE W···.·.:·:jFine sand , loamy fine Coropina/Lelyd orp Fm. ,..... , sand. and clay 6km TERTIARY UPLAND Poorly sorted sand Coes ewijne Fm. • and loam CRYSTALLINE BASEMENT (Guayana Shield) E=~=3:~~ Igneou s and metamorphic rock (undifferentiated) Figure 16, Geology of th e coasta l plain of the Surina me region. (a ) Major physiogr aphic featu res of the Fre nch Guia na , Sur iname, and Guya na coas t. Features include coast al-plain rivers, est uaries, an d mudcap es along the coast. (b) Geology of th e coastal plain of Sur ina me. Modified from R O ELEVEL D and VAN LOON (1978).(c) Geology of east ern Coronie district, Su rin ame. See Figure 15 for approxima te age ranges of phases, subforma tions (subfm.) and Formations (F m .), Cross sections are shown in Figure 17. Modified from I3IU NKMAK an d PONS (1968), .lourn al of Coasta l Research, Vol. 18, Ko. 2, 2002 244 Warn e, Gu evara and AsIan A1 A2 S outh North Lelydorp Fm. Mara sub fm. Coronia subfm. Moleson phase o 2 4+----r-'----,---.--,:--;-:..,:.:....-r-TL....-,-,..----r-.----.--.------r-,----,....:..:.,,.------.----r--,----r-r----r-,----,----,,.------.----r--,---, o 2 4 6 8 10 12 km 8 1 8 2 83 S outh No rt h Coronie subfm. I m Mara subfm. Wanica phase o V Comowin e phase, Coronie subfm ., Demera ra Fm ...... : ::.::: ', Moleson phase, Coronie subfm ., 4 ...... '. ' ,' IV Demerar a Fm. o 0.5 1.0 1.5 2.0 km III Wanica phase, Coronie subfm., Demerara Fm. ~ Ombrogenous peat II Mara subfm., Demerara Fm. Peaty clay, peaty fine sandy clay • and clayey peat Lelydorp Fm. C1 C2 ~ Clay, fine sandy clay, pyritic clay South North L23J Fine sandy clay m • Fine sandy loam 0 o Fine sand and loamy fin e sand (chen ier ridge) ~ Fine sand and loamy fi ne sand with varying quantities of she ll 2 !::::=J fragm ents , shell (ch enier ridge) !ml She ll and shell fragments with some sand 4 0 0.5 o Weathered (oxidized) , undiffer entiated sedim ent Figu re 17. Cross sections of th e eastern sector of the Coronie district, Suriname. Cross-section locations are shown in Figure 16c. See Figure 15 for approxima te age ra nges of phases, subformations (subfm.) and Formations (Fm.). Figure modified from BIUN Kl\IA N and P O N S (1968), Largely by comparison with other major delta sys tems , we with substa ntial short-te rm oscilla tions th at are typical of propose th at th e Orinoco coast compri sed a serie s of shelf glacia l-inte rglacia l tran sition periods (HEUSSER, 1993; edge deltas wit h associate d slope subma rine canyons and HUGHEN et al., 1996; ROBERTS, 1998b). The rapid ris e in sea base-of-slope deep-sea fans tha t were distribu ted across a level ca used the Orinoco shoreline to shift landward from th e broad region of the coast (ct BEJU1YHILL, 1986). Th e shelf wa s shelf edge. In the Orinoco dr ain age basin , un stable bu t gen narrow and steep during that period and, therefore , wa ves era lly wetter clima te promoted th e erosion and tran sport of and litt oral currents reached the coast un a ttenuated, rework large volumes of sediment to th e coastal plain , where most ing coarse material in the nea rshore and tra nsporting finer of the relatively coarse-grained material was deposited in t he materi al to th e slope a nd abyssal plain, resulting in th e de incised alluvial va lleys as sea level rose (cf FISK, 1944; FISK velopment of a series of coalesced, deep-sea fa ns. Betw een th e a nd McFA RLAN , 1955). shelf-edge deltas, a number of coral reefs form ed in th e near As the shoreline migr ated landward , th e near-surface por shore zone (NOTA, 1958). Reefs gen era lly develop in wate r tions of the preexisting coas tal-plain deposits were reworked th at has low concentrations of sus pended sediment, an d we by nearshore marine waves a nd currents to form a wide therefore suggest that fine-grained sedime nts transported to spread deposit of she lly sand and silty sa nd. Reworking of the coas t by the Orinoco River syste m and adj acen t rivers coasta l-plain sedime nts by coastal and shallow marine pro were directly transpor ted onto the slope and abyssal plain, so cess es promoted infilling of former riv er vall eys and resulted that the nearshore-zone waters of the int erdeltaic areas were in a br oad , ra ther featureless shelf. Intermitten t slowdowns low in sus pended sediment. or rev er sals in sea-level rise induced developm en t of marine terraces (KOLDEWIJN, 1958; NOTA, 1958). During the ea rly ph ases of rapid sea-level rise, the she lf-edge cora l reefs con Late Pl eist ocene ( 0 H ol ocene (16,000 to 9,500 yrs BP) tinued to develop (NOTA, 1958) but were eve nt ua lly drowned During this period climate in north eastern South Ameri ca and/or overwhelmed by sus pended sediment as waters deep became genera lly wa rmer a nd wetter but remai ned un st abl e, ened and the shore line migrated landward. J ourn al of Coastal Research, Vol. 18, No.2, 2002 Lat e Quarterna ry Evolutio n of the Orinoco Delta, Venezuela 245 a Early Holocene (-9,500 yrs BP) ~ Delta plain, interdi stributary ~ pe a t p l ai n t...... j Undifferentiated ...... coastal plain I·.. :: .. .. IDelt a front and prodelta b>ttd Alluvial fan Slope F==l Coalesced distal turbidit e r3=~=~=3 Guayana Shield ~ and pelag ic deep marine ~-- -=._ =o ~ Submarine canyon and • Evaporite basin .=-:: .=- proximal turbidite fan ~ Upland , dissected ~ Tertiary and Quaternary D Pelagi c deep marine Braided river and Nearshore marine alluvial plain (transgressive sand) Carbonate mound Delta plain, interdistributary Marine shelf and upper 100 km ", Submarine o mud plain and distal levee slope tidal ridge Estuary V:.,)./.o;-.':j Delta plain, distrubut ary 'l'i'l Beach ridge (chenier) '""-"",,, ... ,.", channel and levee Figure 18. Interpretive summary of Lat e Pleistocene to Holocene paleogeograp hy of the Orinoco Delta. By ~ 9 , 5 0 0 yr s BP, sea level was - 40 to 30 m below pr esent tw een the Atlantic shelf and the Gulf of Paria had a profound (Figure 15), an d th e hydraulic connection between the Atlan influe nce on sha llow marine circ ulation patterns a long the tic shelf an d th e Gu lf of Paria was established through Boca Orinoco coast by increasing th e influence of litt oral currents de Ser pientes. Establish ment of th e ma rin e conn ection be- in the coastal zone. By - 9,500 yrs BP, the pr esent-day Ori- J ourn al of Coastal Research, Vol. 18, No.2, 2002 24() Warne, Guevara and Aslan noco shelf and much of the delta plain were covered by shal Middle Holocene (~6,000 to 3,000 yrs BP) low sea (Figure 18b) ((f K(()vVELL and HUNT, 1958; DANIELO, The climate was generally warm and wet (LEYDEN, 1985; 1976; WAI{NE and STANLEY, 1995). SCHlTBEI{T, 1988; HOOCHIEMSTI{A and VAN DER HAMlVIEN, 1998), and we infer that the Orinoco Basin assumed the mod Early Holocene (~~9,500 to 6,000 yrs BP) ern character of large, seasonal, unimodal water discharge and relatively low sediment discharge of mostly silt and clay During the early Holocene the climate was warm and wet, (Figures 11, 12), perhaps more so than at any time later in the Holocene (LEY The delta plain continued to expand and the seaward gra DEN, 1985). Available data indicate, however, that there were dient declined so that riverine influence diminished relative mi ilcnnial-, centennial-, and decadal-scale climatic oscilla to the influence of tides and direct rainfall. As a result, prom tions (Figure 12), and we propose that these oscillations sig ontories at the mouths of major distributaries diminished and nificantly influenced Orinoco Basin water and sediment dy estuaries began to develop. In addition, interdistributary ba namics, as well as biologic composition and structure. Based sins expanded and peat began to accumulate in the basin on the findings of modern geomorphic studies (LANCBEIN and centers. SCHUMM, 1958; SCHlTMM, 1965; WILSON, 1973; JANSEN and Sea level approached its present level by 6,000 yrs BP (Fig PAINTEH, 1974) and regional paleobotanical studies (II{lON()O ure 15), The delta continued to prograde eastward as prodelta and LA'I'I{UBESSE, 1994; HO()(;IlIEMSTRA and VAN DEI{ HAM and delta-front deposits infilled the EVB embayment. We in MIj:N, 1998), we propose that vegetation had not fully stabi fer that progradation constricted the inlet at Boca de Ser lized sediments. so that sediment yield from the Orinoco Ba pientes, which subdivided the EVB embayment into two sec sin remained relatively high. Consequently, sediment:water tors (Atlantic and Gulf of Paria) and progressively increased discharge ratios in the lower river were substantially greater the influence of littoral currents on coastal evolution, such and sediment accumulation rates in the delta were higher that local chenier plains and mudcapes developed. However, than they are today. tides and river discharge continued to be the predominant The rate of sea-level rise decelerated and approached the coastal processes. present level (Figure 15), coastline positions stabilized, and To the south along the G-uiana coast, mud, shell, and sand the modern Orinoco Delta was well established by this time. accumulated by lateral (seaward) accretion of tidal mudflats Available data indicate that the delta plain was relatively and chenier ridges (BI{INKMAN and PONS, 1968; VANN, 1969; small and was located within the EVB embayment (KIDWELL ROELEVELD and VAN LOON, 1978; AUCUS'l'INUS et al., 1989; and HUNT, 1958) (Figure 18c). The delta-plain slope was rel ElsMA et al., 1991), Progradational phases were interrupted atively high because the slope on the small delta plain was by two intervals of erosion and nondeposition resulting in controlled by the difference in elevation between the bedrock development of continuous, prominent, sand-ridge complexes knickpoint at Barrancas (~~ 15 m above present mean sea lev (Figures 16, 17) (BIUNKMAN and PONS, 1968), EISMA et al. el) and sea level. High sediment discharge promoted devel (1991) and SOMMERFIELD et al. (1995) attributed these late oprnent of river-dominated delta-plain features, such as le Holocene changes in coastal-plain water and sediment dy vees along the distributary channels and promontories at namics to oscillations in wind and precipitation regimes in their mouths. Available subsurface data suggest that inter northeastern South America. Widespread lateral accretion distributary basins were relatively small and received large along the Guiana coast during this period (BI{INKlVIAN and volumes of clastic sediments (WAI{NE et al., 1999), PONS, 1968; ROELEVELD and VAN LOON, 1978), indicates Because the delta was positioned within an embayment at that Amazon sediment was available for transport and de that time, wave- and littoral-current processes were relative position along the Guiana and Orinoco coast. ly weak along the coast. We infer that tides were similar to those of today and, in the absence of strong littoral currents, Late Holocene (~3,000 to 1,500 yrs BP) tidal ebb and flow may have promoted development of shore After a relatively cool and dry period between 4,000 and perpendicular nearshore sand bodies (Figure 18c). The rapid 2,000 yrs BP, the climate became generally warm and wet. rise in sea level from 15,000 to 9,500 yrs BP created accom Documented millennial-, centennial-, and decadal-scale cli modation space seaward of the delta so that the high sedi matic (wet-dry) oscillations (Figure 12) most likely influenced ment discharge promoted development of thick prodelta and water and sediment dynamics within the Orinoco Basin, as delta-front facies, and, consequently, rapid infilling of the well as wind, wave, and littoral-current regimes along the deep-water portions of the quiet-water EVB embayment. Orinoco Delta coast and shelf ic]. ElsMA et al., 1991 L As the To the south along the Guiana coast, organic-rich, pyritic delta plain continued to expand, the influence of river stage Demerara clays were deposited in the late stages of the rapid and discharge on the lower delta diminished, and tides and rise in sea level, and sediment accumulation was primarily direct rainfall became more important processes in the de by vertical accretion of mangrove swamps (BRINKMAN and velopment of the central and northwestern delta. Because lit PONS, 1968; ROELEVELD and VAN LOON, 1978; AucusTINus tle accommodation space remained in the upper delta plain, ct 01., 1989;ElsMA et al., 1991). The contribution of Amazon lateral sedimentation/erosion processes were predominant, sediment to the Guiana and Orinoco coast at that time was whereas vertical accretion processes predominated in the in relatively small because much of the Amazon River sediment terdistributary basins in the middle and lower delta, where was deposited in the incised Amazon estuary and shelf. subsidence rates were more or less equivalent to sedimenta- .Iournal of Coastal Research, Vol. IH, No.2, 2002 Late Quarternary Evolution of the Orinoco Delta, Venezuela 247 tion rates. Local faults, diapiric structures, and low-ampli sediment dynamics within the delta plain, and (c) biologic tude synclines and anticlines (Figure 8) continued to influ composition, structure, and distribution. ence ecosystem development and distribution. The Orinoco River remains largely undeveloped, except for As the interdistributary basins expanded, the influence of hydropower development at Macagua and Guri Darns on the direct river discharge was limited to areas adjacent to dis Caroni River (Figure 7) and at small impoundments in the tributary channels so that river-borne sediments were no lon upper reaches of the Andean tributaries. Although the ()ri ger transported and deposited in the basin centers. Subsi noco Basin makes up 75 percent of Venezuela's land area, dence, coupled with tides and direct rainfall, maintained pe only 5 percent of the population resides there, and most are rennially inundated and saturated conditions across the ba indigenous. This region contains abundant natural resources, sins. The negligible input of clastic sediments into the middle including iron ore, bauxite, and petroleum (VAsqul':z, 1989; and lower delta-plain interdistributarv basins, in conjunction HACCEI{TY, 1993), and exploitation of these natural resourc with perennially wet substrates, induced development of es is a potential threat to ecosystems in the Orinoco River widespread peat deposits (Figures 4, 18e), El Nino years in Basin and Delta. At present, however, the cycle of river water duced pronounced dry seasons, which may have been con and sediment input to the delta remains much the same as ducive to burning of the upper portions of the peat plains. it has been during the late Holocene. Distributary-channel development, abandonment, and in Although the impact of human activity on the delta has filling were important processes throughout the low-gradient been modest, construction of the Volcan Darn across Cano delta plain. Development of major distributary channels ap Manarno has significantly influenced the hydrology and ecol pears to be linked to development of estuaries along the ogy of the northwestern Orinoco Delta. Clearing of forests for coast, and remote sensing analysis of a number of estuaries agriculture, livestock grazing, and human habitation in the along the coast indicates that partial or complete abandon upper delta have also impacted delta ecosystems (Figures 1, ment of distributaries promoted infilling of their estuaries by 3f), tidal and littoral-current processes (Figure 14), Chenier ridg es developed at the mouths of major distributaries; chenier Volcan Dam ridge development was likely enhanced during periods of cli This impoundment was constructed across Carro Manamo matically-induced, increased river sediment discharge. (Figure 1) in 1966 and 1967 to (1) protect Tucupita from During this period, delta progradation subdivided the EVB flooding, (2) expand agriculture in the delta by controlling embayment into two distinct submarine depocenters-the At flood regimes and providing the opportunity for drainage of lantic shelf and the Gulf of Paria, each having its own set of soils, and (3) raise water levels in the Rio Grande to enhance wave, current, and sediment regimes. As the channel through commercial navigation (COLONNI<:LLO and MEDINA, 1998J. Boca de Serpientes continued to narrow, littoral-current flow The dam has been effective in controlling flooding in Tucu was focused along the Orinoco coast, promoting mudcape de pita, the major city of the region. Expansion of agriculture in velopment. Narrowing of the Boca de Serpientes channel also the delta plain, however, was unsuccessful because of high intensified currents along the shelf, which inhibited deposi pyrite content in soils; draining induces oxidation of pyrite, tion of delta-front and prodelta deposits in the east-central which produces sulfuric acid, which in turn renders the soils delta and promoted sediment transport through Boca de Ser inhospitable for agriculture and even native plants. pientes and along southern Trinidad (Figure 2), Discharge through Cano Manamo prior to dam construc The Guiana coast continued to prograde seaward, although tion was generally between 3,500 and H,OOO mvscc, with a there was a depositional hiatus with associated development minimum discharge of 800 m/sec. Sediment discharge was of a large chenier ridge between -~-1,300 and 1,000 yrs BP estimated to be 25 X 10 l i tons/yr (Funindes USB, 1998 l. Since (Figures 15, 16, 17), By this time, large volumes of Amazon dam construction, Cano Manamo water discharge has been sediment were transported to the Orinoco coast by the Gua regulated at 150 to 250 mVsec, representing a reduction of yana Current, such that Amazon sediment composed .~. 50 from 10 to 0.5 percent of 1. he total Orinoco discharge (BI{AC)fO percent of the sediment deposited along the Orinoco shelfand et al., 1998; COLONNELLO, 1998). Sediment discharge coast (EISMA et al., 1991; MEADE, 1994), through upper Cano Manamo has been essentially reduced to zero, and the only sediment discharge 1'1'0111 the lower dis HlJMAN-INDUCED CHANGES IN THE tributary channel is supplied by streams, such as Rios Mor ORINOCO DELTA ichal Largo and Tigre, flowing from the west. There are many impacts associated with modification of Human activities tend to alter the timing, volume, and dis the natural water and sediment-discharge regirn« by the Vol tribution of water and sediment discharge within deltas can Darn, and these include (CHEN, 1998; ROBEI{TS, 1998a; STANLl':Y and WAl{Nl':, 1998), Humans have occupied and manipulated many major deltas •A marked increase in upstream tidal How of murine waters since the early to middle Holocene, but human modification that has induced upstream incursion of estuarine (brack of deltas has been particularly pronounced during the past ish) water. Cascading effects of the landward saltwater in century (STANLEY and WAl{NI':, 1997), We summarize the ef cursion include expansion of mangrove forests upstream fects of human activity on the Orinoco Basin and Delta to (1) and changes to a 1110re marine fish population (COLON describe the latest stage in delta evolution and (2) to help NELLO, 1998; COLONNELLO and MEDINA, 1998 J. Expan define relationships among (a) human activity, (b) water and sion of mangroves has significantly increased rates of sed- .lourunl of Coastal l{('~earch, Yo\. IH, No.2, 2002 \\'''1'11( '. ( ; l W \'ara an d Asbill int ent ent ra pmen t. whi ch in turn has acce lerated expan SUMMARY AN D CONCLU DING REMARKS sion ofcha n ne l islands in lower Ca no Mun umo a nd in fiIlin g of Boca de Gu anipa (Figu re 14 1(C() j,()NNI';I.I.(), I99HI, The Orinoco Del ta is a va st mosa ic oftropica lwetland a nd • Increa se in wa te r temperatures and dec re as e in di ssolved shallow aquatic ecosy stems th at s upport unique a nd div erse oxygen content in the cu nos . plant a nd a nim a l comm unities (Fi gures I, :l, 4 ) (WAI{:-J E c! • Reduct ion of se diment d isch arge t hro ug h Man nmo and al.. 1 ~) ~ l9 , the-ir Plate ~ l. T he wid e variety of ecosy ste ms that onto the su r rou nding delta p la in a nd coa st. occu r ac ross th o delta plai n is largely a fun ct ion of the com • Clogg ing of ca nos by floating vegetation (especia lly wal.er plex variation in hydrologic inputs from th e ri ver, raiufa ll. hya cint.h i. Water hya cinth in Ca nos Pod crna les and Ca and t.irlcs. pure ca n be so den se that navi gation is im peded . Cano 'l'uc T he mod ern Orinoco Delt a represen ts t he la test in a se ries up it a is a lmo st com plet e ly infi lled (Figure :3el. Moreover, of Terti ary and Qu a tc r narv delta s that hav e prograded into upon dying, the floa ting veg etat ion se t tl es to the hottom of a nd infil led t he EYB. Dev e lopment of t he bro ad she lf in t he cnnos , con suming a va ila ble oxygen (through mi crobia l con Plei stocen e ((·'igu re ~ ) b l ha s st rong ly influenced modern she lf s u m ption of the organic material I, a cce le ra t ing cha n ne l in and coa stal hydrody na mi cs a nd , thus, mod ern de lta ev olu filli ng, a nd ca using loss of sa ndy cha n ne l-bottom ha bita t tion. Th e modern depocentc r began to acc um u la te a s th e rate for fish a n d in verteb ra tes , of early Holocen e sea -level rise dece lerated (Figu re 15 1such t hat t he ra te of Orinoco Rive r sed iment input exceeded the The marked reduction in river-sedi ment di scharge to t he ca pacity of nearshore and coa stal processes to redistribute northwestern delta ha s converted large a reas a djacent to t he rive r se d iments. Ea r ly Holoce ne sedi ment di scharge wa s rel major distributaries r Mn nu m n, Ped crnnles. Cocu inu t from a tive ly high and t here wa s a quiet.water em ba y men t se a wa rd predominantly riv er-influ en ced to a lmost complete ly tide of the la rgely riv er-dominated de lta p la in. and, h ence, pro a nd pr ecipita t ion-i nfl uenced wetlands, which may induce delta a nd de lta-front a ccu mu lation rates were hi gh (Figures wetl a nd loss as the de lta plain su bsides a nd open -water con 10. I ~ . lSc ). Du ring the mid dl e Holocen e. t he delta plain rap d it ion s prev ai l, sim ila r to th e sit uation on t he Missi ss ippi id ly expanded a nd assu me d a ge ntl e r gra die nt so that the Del ta (D I·;LAIINI'; a nd 1'1':ZI·:SIII' 1. El94 : C() I.E ~ I A N ('I al.. delt a plai n became a more mi xed , rive r-a nd tide -domina te d 199Ha l. Reduction in min era l-sediment in flu x may be offset sy stem ( Figu re IHd I. Delt a prograd ation led to cons t rict ion of by bioac cumulation a ssociated with peat dev e lopment, which Boca de Scrpicntes, which subdivided t he I ~ Y B em bay ment occurs natura lly ac ross la rge portions of the del ta (Figu re 4 1. into t wo disti nct s ubma rine depoccntcrs. Sedi ment input However, th e hydrology, nutrient ba se, wa te r ch emistry, a n d Irum t he Am a zon River became a major part of th e se diment conseque n tl y t he ecosystems. of'the ri ver-in fluen ced wetlands bud get a long t he coa st a nd she lf during this period . During differ marked ly from t ide- and pr ecipitation-influenced wet t he lat e Holoce ne. t he Orinoco delta plain continu ed to ex lands . pa nd , ca us ing a decline in th e rate of terrigenous se diment Water a nd se diment di scharge th rou gh Ca iio Mucareo has in flu x to la rge area s of t he de lta plain t hat promot ed wid e doubled as the result of dam cons t r uct ion , increa sing fro m spread develop men t of peal. plains (Figu re 4 I.Exp ansion of --, () to I:l percent of tota l Orinoco River discha rge (FIlj\; INll!';S the delta pla in a lso pro moted div ersifi cation in eco syst em s. USI!, H) ~JH l. Th e doublin g of water a nd se d iment disc harge whi ch were control led by inte ra ct ion of a n in crea sing number has a cce le ra te d latera l cha nne l m igration and ha s in creased of processes. inc luding river inp ut, subsidence, direct precip overbank di scharge of fresh water a nd s us pended sedime n t ita t ion. tides. and littoral cu r re nts. Continued in filling of the into the a dja ce nt inte rdist ributa ry ba sin. Sate llite images EYB em ba y ment a nd constriction of Boca de Serpientes pro and historica l photographs show little crev a sse de velopment gTl'ssi ve ly increa sed t he in fluen ce of littoral currents a long across the delta pla in, and we t herefore s urm ise t hat t he the coast a nd she lf (Figure ~ I , wh ich in turn promoted de we ll-dev eloped cre vasse splays a long upper Ca no Macaroo velopme nt of' mudcapes but in h ibited a ccumulation of pro hav e dev e loped large ly in response to th e sudde n increa se in de lta a nd de lta fro nt deposits (Figures G. IRe l. di scha rge. Holo cen e clima te in northeastern So uth Am e rica wa s gen erally tropical wit h a pronounced dry season. Evidence sug G uri Dam ges ts th at th e re we re sig nificant oscillations in temperature. A major dam wa s const ru cted a cross !{io Ca ro ni a t t he site pre cipit ation and wind regimes during th e Holocen e (Figu res of the form er Necu irna wa terfa ll (Fig u re 7 1. Th e rese rvoir , I ~ . l fil a nd we propose t hat t hese clima t ic fluct ua tion s mark which ba s t he world's fourt.h-large:« ca pa city for hydroelec ed ly influenced ri ver and coa sta l processes , a nd conse quently t ricity, extends a long ~ 12 km of t he lower Rio Ca rom a nd biologic com pos ition, st r uct u re . a nd d istribution in the delta cove rs 4 , ~ (j 0 km -. Rio Ca roni accounts fur II pe rcen t of low er plain (Fig u res Hi. 17 1. Orinoco River disc harge (Lewis , 19HHI, a nd the dam ha s had T he coa stal wa ve and cu rre nt regimes a long t he Gu ia na a modest effect on di scharge to t he delta , reducing peak a nd and Orinoco coa sts, a s wel l a s the Ho locen e hi stories of these in crea sing low di scharge (WAIU, E ct al., H)9~) , th eir Figu re coa stal pla in s, are lin ked by th e in fluen ce of the Guaya na ()(jJ. Approxim ately 50 pe rcen t of th e sus pended se diment en littora l curre nt . sed ime nt supply from the Am azon River, a nd te ring t he Gu ri reservoir is retuincd (L I';WIS a nd SAlI j\; llEIlS, climati c oscillation s. As a re sult, th e Guiana a nd Orinoco con 1990I. J{jo Ca ro m hi storicall y con t rib uted < :l percent of sed tain a n u m ber ofs imila r Ho locene coa sta l-pla in features (Fig imen t input to t he de lta, a nd so t he im pa ct of G u ri Dam on ures I, ~ . 4, l G ), Howev er, DANII';U) ( 197(;1 a nd WAI{ NI-: ('I (I/. th e Orinoco De lta sedime nt budget is sma ll. (1999 1were una ble to re late t he Holocen e sedimenta ry ph as- -lou rnn l or (' o""t ,lI \{,·,;"", ·ch. Vol. IS. No. Z. zOOZ 1,,,1<' (/"""Il'''"'''',\' 1':"o l"lio" 01" th o Orinoco Ill·It". \I"'1('I.LI( 'I" es of the Guiana coa sta l plain to the O rinoco Delta . WAH'" I': gisticn l s u p port. We t hank Drs. ,lo se Mondex -Ba umondc a nd et al. ( 1999 ) a ttribute d the diffi culties in correla t ion to the Carlos Yanes of Univers idud Ce ntra l de Venezu e la for their relatively high se d iment input and s u bsi de nce ratl's in the' participution in the delta field excurs ions . Fie ldwork wou ld Orin oco Delta, as we ll a s poorly-defin ed ch ronost ra t ig ra ph ic not be poss ibl e without t ill.' logistical s u p po rt of Mr. Abelurdo framework in t he Holoce ne delt a depo si ts . Lara a nd hi s boat crew s a nd Dr. Freddy Hodulfo II' DVSA The middle a n d late Holocene e volution of th e O rinoco wa s Pa lm uv en r in Tucupita . sim ila r to that of the C ha ngj ia ng (Ya ngtz e ) De lta in that pro We a re g ratefu l to Dr. Rob ert Meade w ho cont ri bu te d com gradat ion occurred a lon g tidal m udflats downdrift of maj or pe lling idea s . provided essen t ia l data , a nd po inted ou t key di stributary channels (C III·;/\,. 1999 l. In a dd it ion, a sign ifica nt ref erences during com pila t ion a nd a na lys is of the regi on a l portion of the se dim e nt deposited a lon g t he Changjia ng coast dutu. We t hank Dr. Betty Meggers for her s ugges t ions a nd a nd s helf durin g the middle Ho locene wa s s u pplied by litto insights regarding pa leoc lim ate. The a rt icle wa s s uhs tant iu l ral-current t ra nsport of se d ime nt derived from the Huang h« ly improved a s a result of t horou gh a nd in s ightful revi e ws (Yellow: Riv e r (C III':/\', 199Hl. Ho locene Orinoco De,lt a e volu a nd comments of Drs . Daniel -Iea n Stan ley a nd Torbjiirn t ion resembles that ofthe N ile a nd Danube Delt a s in that I II 'I'ornqvist . these delt a s con sisted of se ve ra l major di stributa ry channe ls We thank Wil liam A. White , -In rn es C. G ihea ut, Rob ccc« C. wit h in a single, ge ne ra lly fa n-shaped depoconter: 121 the d is Smyth, Thoma s A. Trembla y , a nd -Jay Haney ofthe Un ive r charge and position of t he major di stributaries va r ied over sity of Texa s a t Au st in , Bureau of' Econ om ic Geology I BE G ) time, a lt houg h prograda t ion wa s ge ne rally uni form , without IiII' their contributions to t h is st u dy . We a re g ra te f'u l to Wi l significa nt rcgressionul cycles : 1:1) tho depocuntors dev eloped limn Bergquist,.Ioh n T. Am es, Patricia Alfa no..la na S . Rob within a tectonic reen t ra n t fcnture: (4) littoral cu rrents wen' in so n, -Ioel L. Lardnn . a nd Da vid M. Stephens (BEG) for ge n a m ajor dclta-furming process a long the s he lfn nd coast: and e ra t ing t he figu res. We t h ank Susan Doenges, Lana Dieterich 15 1they underwent a progressiv e a nd marked chnng e in ove r for ed it ing and Susan Llo yd a nd Scarlett Hurt IBE G I IiII' word a ll character during till' cou rse of the Ho locene as t ho ra tio processing . T he Director of' t he Burea u of' Economic Geo logy of ri ver se d iment disch urgo: de lta-pl a in a n 'n diminished and authorized pu blication of t h is paper. t he influence of marine processes in creased (S 'I'A:' .1"0 1'11 ,,1 " 1" ('",, ,,1,,1!i"';"" I'l·h. V"i. Iii. :'\o .~ . ~ () ()~ ~ ...... "'-...... :"-, .... ~ -- .... - -,-_ ...... --- ~------'"------ si ppi Iklta ('\'0111 1ion , ( ;/I!j'Coll sl A SS()(';III;oll oj' (; "o!og; m! S()(';"';('s C, '1.'' l\: ;-.J I·:I.I.' I. (i .. 1~)9 :-; . E I im puct o .unhientu l ea us ado pOI' 1'1 1'('1']'1' 'I'rll lI ,W/('/;OIl S :):-; , 44:1- 4:,2. sa m ic nto del Ca ii o Xlana mu: cam bios e ll In vegetuciun ripa rinn, u n BI{,\(' IIIl, 1-1 .: ( ;1':1(1 ':1':1 lAS, G.: Alm l·:AZ,\,1\I.: SMW III':Z, E.: DI': SM\'I'IS, casu de estud io. I II : L, >I' !':Z-SA;-J ' 'III': Z, .J.1..: S>\ AVI·:I>t {>\ -e liAI' H,\ , 1'.. a nd B,\I .I.,\I 'AI(I':S, C.. l!J9,q, Diug ruist ico a mliien tnl en De lt a 1.1., a nd I) l lllll ls -1\L\ln i;-.J Ez, 1\1. (eds .I, E! Rio 0 1';11 0" 0, 01'1'1I/ '1 " Am uru ru. I II : 1.1l1'I':Z-S,\ ;-J" III-: ;I.. ,J.I..: S,\,\\'I·:lll!.\ -C II,\ llI:,\ , 1.1. , a nd ch a m icn to sustrn tab lc: Pri nu -ra.... j O/'/I (ulas H 'Jll'zula /los cll' inrcsti DIII\(lls -1\L\l t riNI,:z,l\1. (eds. I, HI Rio 0 1'; 11 0('0 (I!'I'II/ 'I'('!UIIII;I 'lI/o SIlS' .~'III· ;' ; 11 solin- " I Hio 0 1';11 01'0. Ca racas, Von ozu olu: lnsti tu to de M,· tcnlubli': 1',.i JJ li'''OS jorncul a» Vr'l1l 'zolal1 os ell' iI11'('sl igal'i()11 sohr« 1,1 c.i ni cu de Fluidos, Fa cu lta d de Ingen il"·'a. Un ive rs ida d Ce ut ra l de Rio Uri noco. Caraca s, Ve nozu t-Ia : lnst it ut n de Mi-c.in ic» de Fhu Vc m-zu vln. pp. 24- :lfi. d o ~ . Fucu lt nd de Ingen il'l'ia , Un ivors idud Ce nt ra l do Venezue la , C()I.I' ;-J NI·:I.I.II, (; . and .\-11·:llINA, E.. Imm. Vegl'l a!ion cha nges ind uced pp. 2·\- :I:' . by dam con st.ruct iun in a t ropica l ustu nrv: tlu- ca SI' oft. ho Mrina mo BI:I :'.: I' \ I,\ :'.: . H. and I'Il Ns , 1".1.. 19G:-; . /\ !wdo·g" olllor"lw !og ;ml ('!IIS' rive r, Or ino co De lta (Ve IH'ZlIl'lal. I'!1I 11 1 /<;('o!ogy I:HJ. 14[,- 1[,4. s;/; ml;oll IIl1d 11I11" oj' 111I' Ho/o('('II" SI'd ;III1'lI/s ;11 III " coasl«] !'!O;II CIl ~ I B AZ , A. and DI': 1\L\TII ,\ I:J·:I., 1\1., IfJ7:-; . Organic sedimenta t ion oj' l h" 1111'I '" (;II;(///IIS. Wagen inge ll. Net Ill' 1'1 a nds: Th e Nctlu-rla ml« a nd ge lH'sis 01' pe troleum in Ma haka m I)l'lta , Burneo. American So;1 S/II'/" 'Y I lI s/;I /lI". So;1 S /II'/'I:\' Paper» No. ·1. 4 1 p. /\sso(';ol ;oll oj' I'l'/ro!1'1I111 (;m/og; "/ s HI/!!I'/;II (;2, ]( ' :-; 4 -]( ' ~) :' . BI:' II':' '1'1':1:, W.S.. :WOI . Was t.h« .\]edil'\'al Wa r m Period gloha l? S('; · CV, ,-T I·:n IIN, CA., I H ~ )l a .l lI / i Jl'l /I" tI ,, (/( ,(// /(, , ' NC · :! (J -Il y I:!. CIiIIlO , 1'11('(' 2 ~ )] , l ,t ~) 7 - 1 4 ~ 1 ~1 . p;('%gia. rwoJ) J( w!i}/og ia . rn"J1 0 I. Caracas. Venezuola : Ge renrin de 1\1''I'I':NI'll , .J. a nd B,\I WIl'l'. •J.I' .. 19 :-; 0. (~eo !o gi ca l ha za rds rolut.cd to Provoct.os Especia les. Proy octu ln vcnturio d,' 10;'; Recursos Na tu r offs hor« dril lillg a lld cnn st ru ct.i on in till' Or ino co Hivc r Delt a 0 1' a les de lu I{egi(>ll Gu a van n , pp . 1- 222. Vem -zur-l«. I II : O/I ~ ho r" 'n 'I'!l/w !ogy ('oll/i'I'I'III'''. Hou ston. May CV<:-T I':D IIN, C .A.. 1 ~l9 1 h . l niorn« dl' (//'a ll "" NC·2 /i - I I ." I:!. S uclo», I!J79. Pa pe-r :\:\9:', pp. :)2:\- :129. l'(',t.!:l'/(w itj/l , Tonto 11 . Caruca« , Vt'I1Pzup la: (~ prP IH ' i a de P roy ectos BII'I'I':N1" I,.J. a nd BAHI\' 1'1' , ,1.1'.. I ~ J:-;4 . Caractcristiro» g"o/l" 'II ;('os d" Especia les. Prov i-cto In venta rio de los Hecu rsos Na t ura les de la !os S('d ;IIII'lI /os IIlI/r;IIOS ('()slo/i"'rII Dclto d,,! Uri noco. Ca racas, Ven !h 'gi(1Il Gu a vnn a , pp. 22 :\-(i2 J. ('zu ela : Rr-port to lnst itutn T"CllOl(igico Voru-zola no (1t ,1 Pet.ro k-o. C V ,;- T I ': <: ~ II ;-J , C.A.. 1 ~ ) ~)J c. l njornu dl' 11I '1/111'" NC-2/i- lFi, CI;1II0, g"o I{e port No. INT -OI ](,. 7:-; , :ll p. l o,~fa . j..[('uI11 orji)/oMia. 'n Jl)lu I. Curacns , Venezu ela : ( ~ ( ~r ell c i a de C,\ II.I.I':II:\. A.'illd '1'1(1, ',\ Irr, .J., 19:':' . Cours de g,;oll w r" lI o!og;" , Pa ris, ['roye dos Especia les, Proy octo l nvi-utnri o de los Hecursos Na t u Fran ce: Ce-nt n - Docum outa t ion Unive rs iu ' 2;\(i p. ru !s de lu [{egi(1Il G uu yanu, PI'. 1- 474, C,\ ltIl" :'>! ,.1. a nd S" IIIIIII':H'I'. C.. 1 ~ ) ~ ) 4 . La te Ce nozo ic h istory 01'th« C V <: - T I ' : I ' ~ I I ;\i , C.A.. H I ~) l d . l uiorm, dl' 11I '111/1 '" NC·2 /i- I .1, S II"!O", 1',, east('1'Il Llan os of Vvnvzu oln: geolllOrpho!ogy an d st ra t igraphy of g l'! II(';'; II. Tont o 11. Ca ra cas , Vonr-zuolu: (; e rencia de Provectos Es t ill' 1\11',,1 Form a t ion. I II : II(I" :'>!I )(', M . le d .l. (I/lol " l'Ilw :1' oj' So/ll h pt-ciules . P roy ecto Invcntnrio de los Recu rsos Nat u rn les de la Re A III" r; m . (/ /1 1111'1'11(//:1' 1/l1" l'II ol ;I)//II ! 2 1. pp . ~) I - IOO . g.j( ')I1 Gu ny unu. pp . 47fl-l 0HH, C,\SI·:. .I.E . a nd 1I IlI.< ' Il ~ 1 1 1 1 ·: , '1'.1... I ~ ) :-; O . (;e o]ogic-tecl oni c ma p oftho C\'I:-T I·:<:\IIK. C.A., 1~l9I ,' . hr [ornu tk - 11 /'111 1" " N C·2/i-/(j, Clim«. gl'O' Ca ri hh,'a n n 'gio n. If. S. (; " o!og ;l'o! S(// '/" :\' ivl ;sl'" !!oll ,,o/l s 11I/'I's/; logia, gl'oI1 1urji)logia. Tor no I. Caracas, Von ezuela : Gel'l'llcia de gll l;oll S" r ;" s M al' I -I /()/I. scale I:1,000,000. :1 ~ h el'! s . Proyeclo s Es pec ia Ies, Prnyecto lnven tnrin de los Rec u rs o» Na tu r C III'::--: , X .. 199:-; . Cha ngj ia n (Ya ng tzl' l River Delta , Ch ina . .lou rn al oj' a les de la Regi(1Il Guavana . pp . I- :)I: \. ('oll sl o! NI's,'orl'h 141:),, :-;:):-;-:-;:,:-; . C VI :-'1'1':' ';\1101, C.A.. Hl9If', I ll /im il" d" 11I '1/11 1'1' NC·:!/i - f(; . SII"!OS, I"'· C III'::--: , Z.. I ~H I ~ I . ( i,'omll!'ph ology a nd c o a~ tl i n,' cha nge of t he lowe]' gt'/(wit)ll . T OIJ10 II. C a racas, Ve lleZlll'la: C l'l'el1cia de I' roypctos Es Yan g't z,' delta plain. Chi na . I II : M II.I.EH. A. •J. a nd (; III"I'A. A. leds. I, pecia les, I'royedo In\'I'nta rio de los Hecu rsos Nat ura les de la Re \ (II';I'I ;,'s oj' /ftl/ ';II! /imll , 1\I'W York: .Joh n Wil,'y & So ns, pp. '127 gi"' 11 (; ua ya lla , PI'. :1I4-:-; J7 . 4·t:\. Il M lI l'I'li. •J.E. a nd FAIIWI:tI)( :I':, ItW.. 1970. Equ atorial At la nti c CIII':N, Z,: SIl N(:, B.I'.: WAN(:, Z.I-I.. and CAl, '1'.1... 2000, La te qua de ep -sea a rkos ic sa nds a nd ice-age a ridity in t rop ica l South Am er (('r nary I'\'olut ion 0 1' t lH' ,~ u h - a q ll(' o u s Ya ngtzp Delt a , Ch ina : se di ica . (;('()!og ;m ! S()(';l'!." o{Awl'l';1'1I lill l !l'! ;11 :-; I. 1:-; 9- 20(;, IlH 'n ta t ion. st rat igraphy, pal .\'no logy a nd ,kfclI'Ill at ion . M o r ;II" (;" . D,\ NII':I.<', A.. 1 ~) 7 (; . I'h otoinll'rprd at ion , s'-'dillH'nta t ion I'l g'-'ochro n o!ogy ](,2, 42:1 -44 I. ologie d all ~ Ie de lt a de I'On 'n oqu,', Nt'I'III' d,' (~ I ; ogmp ll i l' . l 'h."s;'III" C I.,\ I{I', ,J.A,: F,\ I:I:I·:I.I.. W.F ., a lld 1'1':1.'1' 11':1:, W.IL 197:-; . G lohal 1'1 dl ' (; ,'o!og ;,, /)." " 1111I;'111 1'. 1:-;1:' I, 407-4 14 . change s in post-glacia l Sl'a 1('\'1'1 : a nu nwrica l ca lcu la t ion. (/I/ all'r · DI,:I.AIINI':, H,D , a nd PI':ZI':SIII, I, S.H.. W9·1. T Ill' in fluen ce 01' s u b~ i IIIII:\, f{ " sl'(/r..h ~ l , 2(i:' -2:-;7 . de llce a nd sa lt water intrusion on coa sta l lIla rs h s ta hility , Loui si CII I.I·:. ,J.. 200 1. A s lo\\' da nC( ' fl)l' EI Ni ll o. S(';" II(''' 2 ~ ) 1. 1 4 ~ )( i -1 4 H 7 . a na (; u ll' Coa s!. U.S.A. •l lIlI l'II a! oj' ('oa"l lI! U" " " a1'..11 , 12, 77-:-;fl. ( ', )1 .1':,\1,\ :'1 , .J.:\1.. I ~ JI\ I . /) I'II(/s: IJI'o(,('" s,'s o/ tl l'I}()S;I;OIl Olltl 1I/",II' !s /ill' DI,\ z, II .F . a nd 1\IAlo, <:H M', V. (eds.I, HHl2, I~! N;lill: II;s/ol';m l o lld I'.I'/,/oml ;oll . Boston , :\IA: 11l 1< 'l'Ila ti on a l lI u ma n ]{eSOU ITl'S 1)1'\'1,1 IJII!,'()('IiIll IlI ;1' " " 1)(','1" o{ III " SO/ll hl'1'II OS(';II III;III1 . !'i" \\' York: Cam 0PIlH'llt Co rpora t ion. 12·\ p. bridge Un i\'e rs ity Press, :)2 1p. C Il I.I · : ~ I , \ :'I . ,1.1\1.: 1'1 :J1l1 :. D.B.. a nd I.INIlS,\ Y. •J.F .. Ifl:-;:\. IJt·lt ai c ill DI C I{J)('«:. •J.: 1l,\I.I. Y, A.W.. a nd VAil.. 1'.. Hl99. Sequence stra t ig 11111' 11<'" on s lH'1 1' edgl' insta hility pr o c e s s e ~ . I II : S'I'ANI.I·:Y, IL J. a nd raphy 0 1' t he Ea stel'll Venezuel an Ba sin. I II : !\IANN, [' . led. I, CIl' .\-1, l( >In·:, ( i.T. 11" Is, J, 'I'll" ,,/i,,!/lll w ';..: a;l ;m ! ; 111 1'1'/(/('" 0/1('o/l lil,,"lo! I';hl>('(/II Ilas; lI s: Sl'd;lIlI' lI l ol'\' lill " ;II S o(tlll' Wllrld. Amsterdam: E! 1!1(I1:!...{in s. SOCii'I." oj' l~ l' O /l U l1 1 i l' 1'(lIt'oll lo!ogisls a/lel i.Hill( ,,. ol (},~· i8 Is sl'\'ie r. PI'. 4 17-474. SI"'..;a! I'l/hlil'lll;oll :1:1, pp. 121-1:)7. Dil l1ST, II . a nd O .\1J\'I'SIIIA E.. 1 ~J9 0 . N ige r Della . I II: E I)\\'AIWS,.J.D. ('11 1.1':\ 1,\ :--: . •1.1\1.: HIII:I';!:'I's . 11 .11 .. a lld S'I'll m: . C .W.. 19HR l. .\-li s s i ~ a lld SANT, II:]{ ' 'SSI, I'.i\. (l'ds . I, /) ;" " lg l'lI l l l )(IS" ;/'" IIIll1g;IIS. Tu! sa , s ippi Hi\'l'r d" lla : a n O\'('IYi,'\\', ./O(/I'II (/! oj' Co(/s/ll! H" " I'(/ I'< 'h , 14(:) 1, OK : A III"1';"1lII A "SIII';IlI;oll oj' I'elrol"1l11l ( ;" o!og ;" /s Akll w ;r -1 8, PI'. l i ~) :-; - 7 1( ' . 20 1-2:1K C, >1 .1 ':.\1>\ 1', .1..\1. a nd S ~ I I T II, W.( i.. 19(,4. I.atl' HeC('nt rise ol'sl'a I,,\'e!. E IS~ lA . D.: AI'<:IISTINIIS. 1',( i.E.F ., a nd AI.I·::\,\ 1': llI·:I{, C., I ~ J ~)1. Re (; " o!og ;l'II ! S(W;l'I y oj' /\/I/I'r ;1'II 111I!!I'/ ;11 7:' , I\I\: \ -:-;~) O. c,' nt a nd suhn 'cent cha ngl's in t ill' d i;.;persa l ol' Am a zon mud. Nl'! h · ('III.1·:I\I AN, .1.11 1.: S IIII>\Y ll>\ . N.0:.: WIII·:I.>\ ;-J , '1'., a nd WI:H:IIT. 1..1).. ,'r !wII/s ,/OIII'llIl I Ilj',""' 1I HI'''I 'an'h, 2HI:li, 1 :-;1 - 1 ~ ) 2 . 1974 . Ma ss InO\'('IlH'Il1 01'iVliss issippi Hi\'"r d" lta ;.; ed inw nts. (;/I!j' E IS ~ I , \ . D.: V,\!, I) ":I{ (; A,\ST, S.•J.: !\IAI{'I'I.\;. •J.!\I.. a nd T IIIl \ IAS. A.•J.. ( 'ousl A ssocia l ion o( ( ;i'o!u,!.!.'i('ul Sol'il'l ies T n ll l,w/d io/l s. 24 . 4D-liS. 197:-; . S us!ll·nded Ina ll ('/' a nd hottom dl'p lls its ol't lH' Or inoco Dl'lta : CIlI. I ' : ~I. \ N . .J.1\ 1.: W,\I .I' I':I:,II.,J.. an d C IL\Il >\ l i, W.E .. 1 ~) 9 I\ h . SedinH'llt t urhid ity , nlilll' ra ]ogy a nd e!e nH'n ta ry com pos it ion . N"l llI'l'lo llds in ~t abi li t ~ · in t ill' iV l i s si s ~ i ppi Hi\,(']' dl'lt a . ,]o/l m a! oj' ('oa" la l HI" ,/o/l n ll/! IIj' S('(/ H" S" OITh. 1212 1, 224 -2 4~1. " ('III'<-!I. 14(:11, :-; 72-:-;1\ 1. 1 ~ ~ lI · :I : Y A ;-.J Il V . E.l\1. a nd KII,\ ION, G.S, W 74. Sedi nH'ntation in t l1l' ('1l1.1:'I, (' . a nd BIlI I!:I.I·:s . B.. HHJ 2. \Veste l'll hounda ry CUITe nts in (i uia na a nd Nort h AnH'r ica n ha s ins in 1'(,la ti on to s,'di llH'nt dis I']'on t 0 1' Fn'n ch ( iu ia n,1. I II : I' I{" S'I'. .\-1.'1' (I'd . I, 1~' /,() ! 1I 1 ;0 1l ti l'S Iillo cha rge 01't lH' Am a zon and Ori noco [{in 'r s, Ulo!og ;a I I 'II!I'-'III' I s· 1'11I1 .1' tI" (;".1'111 11 ' 1'1 ti l' !a -'0111' ( 'am i'!> I' /lII'r;tl olIlI!1' 1'''" tillIII !" (1/1 0 ' IWI)(lI'wy,', 2, 22-2:' , 1" 1'1 11/;1'1'. I'a ris, Fr aIH',,: Edit ions dl' r O ]{STOl\1 Insti t ut Fra n\'ai s 1·: ;-.J s H VI·:NI·:ZIJi·:I.A, I ~m :-; . 1,'sl lId ;o dl' ;1IIf!(lI'/ o 1/1 11 h;1'1I 111 1, I'roY"l'I o I , d" Hl'rlH' rrl H' Scie nt ifiqu,' pour It' IJt'\'l'loppl'nH'nt en Coo pel':lt ion, 1'1'1'/;)/'(11';1;11 ".Ip !om/ol';o 1!I .'18. Hl OIIII" (; o!/i, dl' 1'01';11 I~ " I I' . Ca raca;.; . pp.7:)- 9 1. Ve lll'zu ela : Rq,ort fln' (\1<' .\-linist r.v 01' till' En\' ironnll' nt a nd He- .Iollr"a l 01' ('o asta l 1{" S! ,," ,c11. Vol. IH. No. :2 . :2 002 l.a u - Quu ru -rnurv !>: volutioo or t lu- Ori noco \)" ll a , Vl'Ill'z\H' la ne wa bh- N atural HeSOUIT('S olVonezur-ln hy till' (;ull'ol' l'aria Ea st K II)\\, I·:I.I.. A.L . and H II;\IT. •J.1\1.. 19 i"i ,';, :'-Jig ration o r oil in I{" (',, nl Opernt.i nj; Compa ny , 41i~p . s ed im e nt» or Pederna k-s . Veuezucln . 1//: Habitu! 01'0;1 . Tu ls a , OK : FA IIWA:-;"S . RG., Hl~!l. A 17.0 00 -ye a r glacio-e ust atic sea level 1',, Americ.m As socia tion or Petroleum G eologi st s . pp. 7 9 lJ -~ 17. co rd : inl luc nce or g lacial melt.ing rates on t.he Yo urun-r Dryas e ve n t K INI':I" ':, G.C. a nd STI·:II;\lIIEI!':. R W .. 199fi. Dixtri hut.iun o r flu id a nd doop -ocou n circ u la t io n . Nature. ;\42, (;;17-(;42. muds on the A mazon cun t ine ntal s h e lf: l nt ernutional -lournal or F ISI" I-I.N .. [!)44. (;('(Ilog;ml inrcstigation« ojllu: olllll';olmlll'y o/llw 11:/0 1';111' (;I'o/ogv, Gcoclu -r nistrv, ({IIII (;1'0/Jhys;('s. I ~ fi . I D : I - ~ : \ : 1. Louvr i'vl;" " ;,,,,;p p; H; I'I'I: Vicksburg, !VIs: U.S . Army Co rps of E n K( )I.I )E\V I.I I" . B.\V.. 19!)S. Guiana s !J('I( region: 1}1([1';//(, rwn/o{!,Y. s l, d i · g inee r s. M is s is si ppi River Commiss ion , 7X p. 1II1'/I/a/;o//, SOIl/h Amcric«: Sl'eI;III I'II /S or tlu: Poria-Trinidatt slul], F ls " . H .N . a nd i\kFAIl I..\ N, E .. Hlfifi. La te quatel'llary dcltuic do Amsterdam : The Hugu c. Nut hurlunds, Mouton & Co .. 1001 p . po si ts o r t he Missi s s ip pi Rive r. (;,'ol og;ml Societ » ol'Allwr;m Spl" K lI l·:IIL. S .A: LI·:\, Y. B.1\I.: !\I()()ln :, W .S .. and ALL IS() 0:. :\I. A.. 1 9 ~ ) 7 . 1';0 1 Pap er (;:!, pp. 279- :lO2. Subaq ueous de lta or th« G anges-Brahmaputra river sys t e-m. Ma F I()111 1.1,( I. G .. HlH4. Ex plo rat ion a nd evalu ation or t he O r inoco O il r; //1' (;""/ogy, 144 , X 1 - ~)(; . Be lt. I II : 1\"':YI':I1, H.F . 1('(1.1. Esplorutnn, [or h"IIl'y crui]« 0;1 II l1d KI IIIIIY, 1'.: H () () I : II I !': ~I S T I I . \ , II.: V.\ :--J G I·:I':I.. B.. a nd V,\ r-; [)r.:ll l l,\ \I natur al h; /III1Il'II . Tulsa, O K: Alller;('oll A ssol' ;O/;'JII or l 'l'/ m l" 11 111 ~ I !': ". '1' .. Hl~J : 1. T h e E I A hrn s tad ia l in Ea s t e r n Cord illera ol'f'nlmu (;eo /og;s/s St udic» ;11 ( ;eo/ogy No . :!r" pp. 10;1-1 14 . hia t South Americ.u . (i lla/l'l'IIa r v SI';I'//I'I' RI'I';I'lI' S, [ ~ . :1:\:1- :\4:1. F IIAZIt':I1 , D ,E " Hl(;7 . Recent de pos its or t he M ississi ppi Rive r, t hei r LA;\II:IIE I;\;. W .B. a nd S I' IIII.\ I\ I. S .A .. [ ~ J i"i ~ . Yield ol' s"dinH' n t in 1'(' developm ent a nd ch ro nology, ( ; 11 // (,'00"/ A " "oc;O/ ;'I// or (;eo/og;l'o l Jatio n to m en u a n n ua l prcci pit ution . A III1'1';('0 II (;" o/,hv s;n el llll ;oll So(';"';e" Transcu-tions . 17, 2~7-;n 1. '/'ra IlS(lI ·/;OIl S. :HJ. IlJ7(; -1O ~4 . F lII :II() GlIl.F, IN" .. nJ7!J. ( ;l'ol l'l'h ll ;m l ;III'I'S/;gO/;OIl , (;ol/i, ell' Poria, LATlllIBI·:SS I·:. K 1\!. a nd !{,\ \t< INI':I.I" C.G.. 1994. A climn t ir mork-l fur o!l ~hol'l ' Vi'II l'ZlIl'lo. Caracas. Venezue la : Hepurt to INTEV EP, He southwcstorn A m azon ia in la s t g lac ia l t inu-s . (i Il O/I'I'II III :v 111 11'1" port No. 79 -001i-fi, (;;\ p. national, ~ 1 . J(;;l - ](;9 . F U"INII!':S USII, I!J!)H. Est iu li« de ;III Pllc/O ambicntul pmwc/o ell' per LI·:():,\Alw . IL HJX;1. (;,'o logy and hydrocnrhon accumul ut ion s . ('0 [oracion exp /om/or;o Bloqu, Delta Ccntr». 1'0"1' I . C urucus, Vone lumbus Basi n . offshor« Trin ida d . AlIIl'r;('I/1I Associo/;Oll or l'otn» zu elu : De lta Cen t ro Operat ing Co mpany. fi4H p. 11'1/111 nl'lllog;s/ s !Jlllld;1I (;7( 71. !OXI-1 0!J:1. ~ J!J!J . F l lN1N11I':S USB. I C« I'lIc/l'r;20C;I)1I cli nuilica y eI,'1[uncioiuu nicut» LI·:WIS. W .M ..•l l!.. I ~ J XX . P r im ary pro duction in t he O r ino co Hivr-r. hidniuliro -fhu-iol d ol /) 1'1/0 d,'1 R i o 01';110 ('(1. " II I1II11 W:V or d"I·,'lop /<;('()/og v. (;9, (i 7 ~) -(i9~ . mcnt acti ritic« d uring tlu- fi r st vcar or st ud»: Caracas. Vcn ezu ola: LI':\\' ls . \V.M .. JI! . a nd S AL I;\;IlI':IIS. •1.10' .. Ill. ImJo . Clwmistry a nd ,,1 Progres s Report to PDVSNDAO, 70 p. em ent t ra nsport bv the Orinoco m a in stem a nd \0\\'('1' tri hut ari" s . I ~J ! ) 2 , GASTAI.IHI, [t A.. S " d in1l'n tar,v fa cies. deposit. ionul e n vi ro n I II : \V,·jlllh,·, ,,h,,. F .H .: Al.n n,·:z. H .. a nd LI·:\\,l s . \V.IVI.. .J I!. I E Il .~ .I . /.:/ m e nts , a nd d istri but.ion of phytocla st s in tho H" c"nt Maha k a m Nill (J r i l/f ll' lJ PI/I/II 1'1"11.";;''''/''/1/(/. ( ';\ 1";1<';1 ":, \ 'I' llI' /UI ,I ,, : J lllpn ' ,.:u :-- Rubel . pp. 21 1 - 2 : ~ ~ l. Ri ver delta , Ka lim a n ta n , lnd onesin. Palaio« (;. fi74 -i"i!JO. LI·:YllI·:r-; , B.W .. I !J ~ fi . La t<' Q uat l' l'Ila ry a r idity a nd H ulocc no mui s G Jo: () IIIIII1A C ()NSII I.T() llI':S, C .A .. nHJ7a. Estudi» d,' ;111/)1/1 '/0 «m bien Lure fluctu a t ion s in tl1l' Lnke Vak -nci u Ba s in . Ven ezucln. 1~ ('() / ogy. I~ s / I' tal proycct» d,' Il l'r/i".o(';, )1I rxplnratoria arm prioridcu! (i(i14I, 1279-1 2!Ji"i . 11/01/11" 1'11 11 /0 1'l'sm d'JI: Caracas , Ve- nezuela : AMOCO Venezu"Ja Lt<:IIT Y. RG.; M ,\I 'INTYI1 I·:. U ;.. a n d STIIl '''I·:NIIXrll. H.. 1!'H2 . , Ic'. E nergy Co mpany, P roj ect . ~J(; 0 1 7-E 4 . various ly pa gi n a tl' d . ropora 1'011110/ 0 re r-f fnuuowork: a n -Iiahl« ind icator or st'a 1<' \',,1 in GJo:() It IlIIIA C ()NSII I.'I'()llI·:S, C .A.. nJ!)7h. Es tndi« ell' impucto u mbicn t he wost.ern Atlunt.ic 1'01' till' pa st 10,000 ye a rs. ( 'om I HI" '/~ ' I , 12fi /0 1 de! provcct« Uno dl' pl'I'/i)/'(w;,)I/ cxploratori« drl Bloq u»: Guar iso. api ch». Cara ca s, V"I1l'zuala: Agl'nc ia Op" ntdont (;ua ra piclH' S . A. MASLIN, :vI.A. a nd BIIiI NS, S .•J.. ~OO O. Hl'co nstr uction ol'tlll' Amazon IAOGSA I, Proj "ct DA!)(;O;17. V"rsio n I. va rious ly pagi nat('d. Ba si n e fli:ctive m oi st u n ' a vai la bility over t he pa s t 14 .0 00 ,v"ars . GIBB S, A. and BAtl lll lN, C .N., 1 !J ~ : 1. TI H' Guiana S h i" ld )'('vil' \\'('d . SI' ;I'III'I'. 2!JO, 22~fi -22!J I . Ep ;sod l's, IHH;lI2 1. 7- 14. M, 'CU :I.I.ANII E :--JI: 11"1':I':I1 S, [9 7~) . 111 11'1'1'1'1'/0 / ;0 11 o llel O"SI'SS/lIl 'II/ or H N :I:!·:tlTY. It A. I"d. l. 1!J!J:1. \'<'lI l'zlIl'la : a I'OU /i/rv s/uely. Wa s h in g t on shalluw u('o!ngi{' and g(·()/C' ('!tnico! ('()/ ulitiol}s. Caracas. VPIH'zut' la: DC : F"d"ral Hesl'a r('h D ivision , Lihrary of Co ng r"s s. 2H7 p. Orinoco regio nal s u rv( ',\' a re as. ofl shorl' O r inoco [ll 'lt a . V"Ill'zu"la . H A\ III.T()N. S .K . and L I':\\'I s . W .1\l.. ,111 .. 1!J90 . P h ~' s i c a l character is \'. I , I ml p. tics of the fr in ging flood pl a in of till' O r inoco I{iv" r, Velll'zu" la . 111 MI 'KJo: I':, E .D .. I!J~ ~J . S (' d i m (' n tar~ ' s t ru ct u res and t, 'xtun's ol'Hio Ori /1'I'ciell l';a . lfi lG I, 4!Jl - fiOO . noco ('hannel sands. Ve lH'zu l' la a nd Co lom bia . lJ.S . (;l'o/og ;l'o l SlIr H EllIll':II,\ , L.K: F I':Btl l':S. C ., a nd AVilA H.. I ~) XI. La s m a)'( 'a s " n 1'(1' \\'a /er -S III ,p ly I 'aper \\' :!:i:!(j- II , p. B 1 ~ 1l 2 : 1 . aguas vl'nl'zolan a s y s u a m pl ifiw('itin ('n la )'('g itin d,,1 D" lt a d,, 1 ;v) j':AIll':. KH.. l !J!l4 . Sus pe nlkd se d inll'nts of t ill' mod,,1'll Am a zo n O r inol'O . Ada C ;I'II/i /;m Vi'III'Zolalla, :12, 2!JH- :lOH. HE IIIII': I1 A, L.E. n nd MAs , ·I,\ N(: I()I.I. P .. 1!)X4. Ca ract(')'isti('a s d" la s a nd O r inoco Hiv"rs . I II : 111 1()NIHI, iVI. l"d .l . (l ila/,'mlll:v or SOIl /h ~ 1. ~ !J - : \D . co r r ien!" s I'rent p a l d" lta d,,1Orin o('o, sector ol'('i(kntal (IPI Oc('a no Allw r ;m. q ll o/,'m lll:v I II /el'llo(ieJllo l . AtI ,intieo. Rel';s/a '/'1 ;I'II;m INTH V/~/ ' 4121, 1:1:1-1 44 . M I';AIIJo: , lU I.: N() llI lI r-; . C .F .. .11 1.: 1'I':I1 I,:z -l l l':I::-;.\ r-; IH:z . D.P.: _\ 1J.:.dA Im~: 1. H El ISSI':Il, C .•J.. I ~ J !J ; 1. Lal,,·g la cia l of' south prn S ou t h A nll'r ica . (ili a · B.A .. a nd G, IIHI)', .J..\'!.I' .. Sl'dinH'nt and wa t e r di sc harg(' ill /1'l'IIal'y 8 1';1'//1'1' RI'I';l'u'S, 12 , :l41i- :\liO. I{io O ri no ('o. Ve n"zuela and C olom hia . I II : I' ro l'l'" d ings ol' t l1l' S, ,(' H()()I : III E ~ I ST I I A . H . a nd Vi\ r-; D I':11 I IA\I MI':i'o: . '1'.. I!lH~ . N"og"fl(' a nd o nd In t e J'l1 a t ion al Sy nlposiu m o n I{ive r S"dinwntatio n, 11-](; 0 1' Quatl'ma ry (h'\'l' lop m pn t or t l1l' nl'otropiwl ra in lim'st: t h" li"',,st tollL'r . Nanjing, C h ina. Nanjing, C h in a: Wa tl'r Heso ur('('s and 1>: 1('(" rl' fugia hY]Jot lll' si s , a nd a Jit(,ntt u )'(' ]'('vi ,,\\' . /<;a l'/h SI' ;" III'" UI'I';I ·U'S. t r ic I' o wer Pn's s. pp . 11:\4-11 44 . 44 . 147 - 11':1. !VI ":AIlI':. K H .: W Jo:lI l1':ZAIt r-; , F .I I.: LI';\\' IS, \V.ll.. •JI1 .. a nd 1'I':llI':Z H I' I:III';;\;, I<.A.: On:llI' l':I 'K. •J.T .: 1'1':TI':IIS() i'o: . L.C .. and T ln l ~ IB() II I ' : . H ":ll r-; A:--JIl I':Z, D .. n' ~)o . S usp" n d('d-s" d inll' n t budgl'l iiII' till' O ri S .. I!l!J(;, Ha pi d climatic ('h ang"s in tIll' t ropical At lantic )'('gion noco Hiv"r. I //: \V 1':lm :z AIIN. F .H .: AI.V.\ llI':Z, H .. and LI':\\'IS, \\'.i\1.. duri ng th " la s t dl'glaciatio n . No/urI', ;m o. Ii l - fi,1. .JIL le ds . l. /<;1 Hio 0 1'; 110('(1 COII /lJ I'COS ; ,,/,'lIll1. Ca ra ca s . V" Ill'zu"la : I;\ITI':VI':I', 1!J7 ~ . 11l1'1',,/;g (Il' ;' ;1l " " hl'1' I';l'sgo " i"lII ;l'lI d l'l/a d l'l Ur;llo('o Im p n 'sos HullL'1. pp. :' i"i - 7 ~ J . 1'1'1'01'11' eI,' II/ W Il ·,'. Ca ra('as , V('Ill' zul'[a : I{" port (0 PDVSA. I{" port !VI Jo:':':I·:I1S. B.,l .. 1!J7!J, C lim a t ic os ('illa t ion as a I'a d o r in till' pn'his I l\ T - 0 0 7 : 1 . 7 ~ , variou sl y pa ginated. (o ry or Am a zo n ia . A III l'r;m ll AII/ie/II ;/Y. 4412 1. 2,, 2- 2(;(; . [,, '1'1':\ '1':1'. I!J~1. /);sl'l io "OIlI 'l'p/llal dl' p la/a/imuas pa l'll 1'1 N"I'/l' d, ' :\1Jo: ' it: 1·:IIS. IL l. . n)!)(; . 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