Geochemical Composition of Beach Tar From the Se Coast of the Paria Peninsula, Ne Venezuela: Derivation From Natural Seepages

Abstract

Tar residues (“tarballs”) occur frequently on the SE coast of the Paria Peninsula, NE Venezuela. This paper reports on tarballs recovered from approximately 14 km of shoreline during monthly sampling over a two‐year period ending in April, 2011. The tarballs were analysed geochemically and results show that more than 70% of them could be included within a single compositional group on the basis of their physical and organoleptic properties. The tarballs were fingerprinted using biomarkers (hopanes, steranes, alkanes, aromatic steroids, phenanthrenes and dibenzothiophenes) by gas chromatography and gas chromatography – mass spectrometry. Sulphur and trace element contents were also determined. These analyses indicate that the tarballs do not have an anthropogenic origin, but that they probably originated from petroleum generated by argillaceous limestones in the Turonian – Campanian Naparima Hill Formation. This formation includes marls and organic‐rich shales and limestones, and is an important source rock at oilfields in Trinidad and the southern Gulf of Paria. In the southern part of the Gulf, petroleum escapes from Neogene reservoirs to the seafloor via natural seepages associated with the Los Bajos and other fault systems. It is inferred that the petroleum is then transported by wind and tidal currents to the coast of the SE Paria Peninsula where it strands as tarballs. The geochemistry of the tarballs collected is discussed to investigate their source.

Rhizophora zonation, salinity, and nutrients in the western atlantic

“…This result suggests the preferential uptake of those elements by the vegetation and their recycling in litterfall. Additionally, Ca concentration is probably associated with the mountain range's lithology at the northern border of the Paria gulf (Colonnello et al, 2009; Marquez et al, 2013). The pattern of Na accumulation in higher tidal zones probably is a consequence of the decreasing frequency of tidal flushing with distance from the coastline.…”

Marine Tar Residues: a Review

“…Heyerdahl ( 1971 ) made qualitative observations of tar pollution that were observed during transatlantic voyages. Some studies of beached tar on the Atlantic coasts include physical descriptions and observations on few (<10) localized beaches (Okera 1974 ; Saner and Curtis 1974 ; Debrot et al 1995 ; Butler et al 1998 ; Gabche et al 1998 ; Debrot et al 1999 ; Marquez et al 2013 ), while other researchers conducted more extensive surveys that spanned large coastal areas (Georges and Oostdam 1983 ; Jones and Bacon 1990 ; Asuquo 1991 ; Corbin et al 1993 ; Debrot et al 2013 ).…”

“…They concluded that carbon isotope analysis was particularly useful in determining tar ball sources. Marquez et al ( 2013 ) analyzed tar balls from the Northeastern Venezuelan coast. GC/MS and biomarker analyses showed that the tar balls were likely derived from natural sources, specifically from oil seeps and petroleum originating from the source rocks in the region.…”

Geochemical investigation of tar balls collected on a beach on Žirje Island (Croatia) using petroleum biomarkers

“…Environmental forensic chemists use biomarkers to fingerprint tar balls 6,7 and correlate them to weathered crude oils. 8 The formation of crude oil 9 occurred many millions of years ago from decaying plants and animals.…”