title: Sediment studies associated with drilling activity on a tropical shallow shelf.
abstract: Environmental monitoring studies were developed in an area located on the outer shelf in the Potiguar Basin, Brazilian equatorial margin. This tropical shelf represents a modern, highly dynamic mixed carbonate-siliciclastic system. Field sampling was carried out during 3 cruises surrounding a shallow-water exploratory well to compare sediment properties of the seafloor, including grain size, texture, mineral composition, carbonate content, and organic matter, prior to drilling with samples obtained 3 and 12 months after drilling. The sample grid used had 16 stations located along 4 radials from 50 m the well up to a distance of 500 m. Sediments were analyzed in the first 0-2 cm and 0-10 cm layers. The results show that sedimentary cover around the well is dominated by bioclastic sediments, poor to very poorly sorted. Only minor sedimentological variations occurred in the area affected by drilling operations. The most noticeable effects were observed during the second cruise, in terms of a change in grain size distribution associated to a slight increase in siliciclastic content. This impact occurred in the most surficial sediment (0-2 cm), in the radials closest to the well (50 m), and could suggest the effects of drilling. However, in the third cruise, 1 year after drilling, the sediments return to show the same characteristics as in the first cruise. These results show no significant sedimentological variations due to drilling activity and indicate that ocean dynamics in this area was high enough to recover the environment original characteristics.
authors.affiliation: Department of Geology, Geodynamic and Geophysics Programme, Federal University of Rio Grande do Norte, Campus UFRN, P.O. Box 1596, Natal, RN, 59072-970, Brazil, claudeteufrn@yahoo.com.br.
authors.forename: Claudete R
authors.initials: CR
authors.lastname: Souza
authors.forename: Helenice
authors.initials: H
authors.lastname: Vital
authors.forename: Germano
authors.initials: G
authors.lastname: Melo
authors.forename: Cleuneide R
authors.initials: CR
authors.lastname: Souza
authors.forename: Mary Lucia
authors.initials: ML
authors.lastname: da Silva Nogueira
authors.forename: Werner Farkatt
authors.initials: WF
authors.lastname: Tabosa
mesh_terms: D001938:Brazil; D004777:Environment; D004784:Environmental Monitoring / Q000379:methods*; D019652:Extraction and Processing Industry; D019015:Geologic Sediments / Q000737:chemistry*; D061329:Oil and Gas Fields; D014873:Water Pollutants / Q000032:analysis
chemical_list: D014873:Water Pollutants