From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

Bureau Seminar, October 31, 2003

BEG Studies of the Orinoco Delta, Venezuela

Edgar Guevara

Abstract:

Bureau of Economic Geology researchers conducted studies of the Orinoco Delta, Venezuela, from late 1997 through 1999. The main objective was to characterize the physical setting of the ecosystems of this ~22,000-km2, poorly known, almost pristine delta. Another goal was to produce a GIS geoenvironmental baseline database for use in land-use planning by governmental and private organizations related to expected increased hydrocarbon exploration and production. UT’s Center for Space Research and Venezuelan universities participated in the project. The original 5-year research program, funded by Petróleos de Venezuela, S.A. (PDVSA), was revised at the beginning of 1999 to end in November of that year, as a result of funding priority changes by the new Venezuelan authorities. A Final Report was submitted to PDVSA, and project results have been presented at meetings of geoscience societies and published in refereed professional journals.

The investigations comprised field studies, remote-sensing data processing and interpretation, and published and proprietary data integration. Field studies included low-altitude, airplane and helicopter flyovers covering most of the delta, and on-site investigations in the northwest delta. Hand-auger cores as deep as 8 m were cut at 42 localities, and 31 organic-rich samples were radiocarbon dated. To characterize the channel networks, sediment samples were collected along 16 transects using a Ponar bottom-sampler, hand-held transducer, and GPS. DGPS data were collected to georeference the Radarsat image and to document flyover trajectories and observation and sample locations.

Two distinct sectors having contrasting geomorphic characteristics, sedimentary processes, and lithofacies were recognized. The southeastern delta plain is dominated by the straight to anastomosing Río Grande and characterized by overbank flooding and sedimentation. The coastline is dominated by estuaries, interchannel mangrove islands, and tidal sand ridges. In contrast, an intricate network of distributary channels and tidal creeks is present in the northwest delta plain. Distributary channels, which separate densely vegetated flood basins containing peat beds as thick as 10 m in areas as large as 200 km2, produce mud- and peat-encased sand bodies that are as wide as 1 km and as thick as 15 m. About 20- to 30-mile, late Holocene shoreline progradation in the northwest delta resulted mostly from construction of coast-parallel mudcapes. The mudcapes, typically 5 to 10 km wide and up to 30 km long, comprise wave-modified suspended sediment largely transported by northwest-directed longshore currents and are comparable to those of the Suriname coast. Shale mobilization is manifested by mud volcanoes along the northwest delta coast. Shale diapirs locally form hydrocarbon traps.