PALYNOFACIES ANALYSIS OF SEDIMENTS FROM THE COTE-DIVOIRE GHANA TRANSFORM MARGIN - PRELIMINARY CORRELATION WITH SOME REGIONAL EVENTS IN THE EQUATORIAL ATLANTIC

Analyses of the palynofacies and sporomorph thermal alteration indices (TAI) of sediments from Ocean Drilling Program (ODP) Sites 959 to 962 in the Cote d'Ivoire-Ghana Transform Margin, West Africa were underta ken to (1) determine the source and depositional conditions of the org anic matter in the sediments, (2) refine a paleobathymetric curve deri ved from other data for Site 959, which drilled the most continuous se dimentary sequence from Pleistocene to Albian and (3) interpret the pa leothermal history of the area. Twelve types of dispersed organic matt er were identified: amorphous organic matter (AOM), marine palynomorph s, algae, resins; black debris, yellow-brown fragments, black-brown fr agments, cuticles, plant tissue, wood, sporomorphs and fungi. The rela tive abundances of these organic matter components at each site were a nalyzed using cluster analysis, resulting in the identification of sev en palynofacies assemblages at Sire 959, five each at sites 960 and 96 1, and four at Site 962. Amorphous organic matter (which is chiefly ma rine derived), black debris and wood have played the most significant role in defining palynofacies assemblages. The palynofacies assemblage s show some correlation with lithologic units, sediment sources and de positional environments. Previous palynofacies studies in passive marg ins have demonstrated that changes in the ratio of AOM to terrestrial organic matter are related primarily to proximal-distal positions of d epositional environments relative to the shoreline. However, this assu mption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution, at least in the early stages of evolution. Lithofacies, CCD paleodepths for the North Atlantic, trace fossil association, benthic foraminifera and palynofacies data were the criteria used for reconstructing a pal eobathymetric curve for Site 959. A cyclicity in the organic matter di stribution of the Upper Miocene to Lower Pliocene pelagic sediments co uld be related to fluctuations in productivity of biosiliceous and cal careous organisms, and sedimentation rates. A drastic increase in the amount of AOM and a decrease in black debris and wood in the carbonate and elastic rocks (Lithologic Unit IV) overlying the tectonized Albia n sediments (Lithologic Unit V) at Sites 959 and 960 coincide with the presence of an unconformity. Qualitative color analysis of palynomorp hs was undertaken for all sites: although the main focus was on Site 9 59 where detailed organic geochemical data were available. At Site 959 , TAI values indicate an immature stage of organic maturation (<2) dow n to the black claystones of Lithoiogic Unit III at about 918.47 mbsf. Below this, samples show an increase with depth to a moderately matur e stage (>2 except for the claystone samples between 1012.52 and 1036. 5 mbsf. and one limestone sample at 1043.4 mbsf), reaching peak levels of 2.58 to 3.0 in the tectonized Albian sediments below the unconform ity. These TAI values show a positive correlation with the T-max value s derived from Rock-Eval pyrolpsis data. The highest values recorded i n the basal tectonized units at all the sites (Sites 960-962 have mean values between 2.25 and 3.13) may be related to high heat flow during the intracontinental to syntransform basin stage in the region. (C) 1 997 Elsevier Science B.V.