Age and provenance of Late Miocene-Early Pliocene sedimentary rocks from the Patao high hydrocarbon reservoir offshore NE Venezuela – U-Pb detrital zircon age, Sm-Nd isotope, and biostratigraphic data

Abstract

Since discovery of hydrocarbon reservoirs in Late Miocene-Early Pliocene sedimentary rocks of the Patao High offshore northeastern Venezuela back in the 1980's the provenance of these rocks has been uncertain. In this contribution U-Pb LA-ICPMS detrital zircon ages of sandstone samples from offshore wells in the Patao High are presented together with Sm-Nd isotopes and biostratigraphy data. A total of 566 zircon grain analyses from six samples taken from six wells show a sediment mix with ages ranging from Archean to latest Miocene time. About half of the detrital zircon grains have Late Mesoproterozoic-Early Neoproterozoic (∼1.3–0.9 Ga), Paleozoic, and Jurassic ages, indicating Andean crystalline basement sources that travelled from west to east across the South American continent probably in the paleo-Orinoco River system. Cratonic sources like the Guayana Shield (>1.35 Ga) are relatively underrepresented (∼20%) compared to modern sediment from the Orinoco River and Miocene-Pliocene sedimentary rocks from Trinidad. The youngest zircon grains suggest syn-sedimentary Late Miocene (5.6 ± 0.3 Ma) volcanic activity. Such igneous activity has been reported from the eastern Paria Peninsula. Late Miocene-Early Pliocene sedimentation is further constrained by biostratigraphic data reported here. Mixing of continental South American sediment sources with juvenile sources of the Caribbean realm is indicated by Cretaceous and Cenozoic zircon (∼17%) and Sm-Nd isotope data (εNd = −10.6 to −8.0). Stratigraphic and sedimentological data together with a significant number of Late Neoproterozoic zircon, favor a model in which detritus from the paleo-Orinoco River was mixed with detritus from the paleo-Amazon River prodelta that traveled along the continental shelf northwestward by long-shore drift.