.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<KE ct al. (in press i. Riv er floodplain and delta plain compri se on e of the world's In t he present a rticle we describe the geo logic setting of the largest tropical -wetland com plexes (H AMILTON a n d LEWIS, del ta a nd t he principal ph ysi cal processes that influen ce del­ 199 0 ), ta evo lution , We t hen u se this infor m ation to develop a n ac ­ We con d uc ted a multidisciplinary st u dy to iden tify a nd cou nt of t he late Quaternary ev olut ion of the O rinoc o Delta . evaluate the ph ysi cal processes a nd process linkages t hat control sta bility a nd integr ity of t he Orinoco Delta ecosys ­ THE ORINOCO DELTA te ms ( WA I~NE 1'1 al. 1999), The aim of this prelimin a ry but com prehens ive st u dy was to ge ner ate, compi le, a nd in ter pret Like mo st major fiuvio-rnarino delta s , t he O ri noc o can be basel ine information need ed to anticipate, avoid, a nd mi t i­ subd ivide d into delta-plain, del ta -front a n d prodelta sect ors. gate impacts associa ted wit h human activity in the delta , Most of the Orin oco Delta is com posed of del ta-pla in wet­ la nds , a lt ho ugh delta- fr on t a nd prodel ta muds ex ten d off­ OU I50 r l'c('it'l'lI:1I Of'! ol", r 2000 ; ,,,'('('pl('d ill rcrision 12 J II IU' 200 1. shore a s much as 60 km fr om th e coast (N OTA, 1958: 1\:1 c - 226 Warne, Guevara a nd AsIan 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.