The Northern Area of the Brazilian Equatorial Margin, including the Foz do Amazonas, Pará-Maranhão and Barreirinhas covers an area of approximately 560,000 km² until the 3,000 m isobath. The basins are directly related to the breakup of the African and American plates during Aptian-Albian times.

This multiclient study is based on a compilation of more than 35 oils and 35 wells with hundreds of rock samples studied. It is a unique integration of organic geochemistry that includes source rocks assessment by TOC and pyrolysis, bulk oil properties, carbon isotopes, gas chromatography and molecular and mass spectrometry analyses GCMS and oil cracking using diamondoids to assess the presence of three petroleum systems. The petroleum system identified in the Northern part of the Brazilian Equatorial Basins are undercharged but may be reinforced in importance with higher potential of hydrocarbons as condensates and oils generated from deeper source rocks offshore in deeper horizons in deeper water provinces.

Full references of all images are listed in the reports

1. Executive summary
2. Exploration significance
3. Introduction
4. Exploratory history
5. Regional geology
   1. Foz do amazonas (amazonas delta) basin
   2. Pará-maranhão basin
   3. Barreirinhas basin
6. Elements of the petroleum systems
   1. Source rocks and hydrocarbons
      1. Source rocks characterization
      2. Hydrocarbons characterization
7. Petroleum systems
   1. Lower and Aptian Codó – Barro Duro / Tutóia (?) petroleum system
   2. Upper Aptian / Lower Albian Codó – Barro Duro / Tutóia (?) petroleum system
   3. Upper Albian / Cenomanian Preguiças / Limoeiro-Barro Duro (!) petroleum system
   4. Travosas-Ilha de Santana (!) petroleum system
8. Conclusions and exploratory implications
9. References

1. Location map of the Northern Brazilian Equatorial Margin, including Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins.
2. Schematic stratigraphic charts of the Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins.
3. Seismic section of the Foz do Amazonas Basin and its depth-converted geologic section, illustrating the carbonate platform, growth faults along the shelf, and thrust faults with areas of extension and compression (modified from Silva et al., 1999 and Mello et al., 2001).
4. Miocene growth faults near the shelf edge and northeast-verging thrust faults (see figure 3 for section A-A’) modified from Miranda et al., 1999; Silva et al., 1999 and Mello et al., 2001).
5. Schematic regional geologic section of the Pará-Maranhão Basin (modified from Abrahão, 2002)
6. Generalized tectonic framework of Barreirinhas Basin (modified from Guardado et al., 1990).
7. Schematic geologic cross section of the Barreirinhas Basin showing the main semi-grabens synthetic systems.
8. Location map of the wells in which selected oils and rock samples were used in this study.
9. Total organic carbon content of the Codó Formation in the 1-CI-1-MA well, drilled in the Parnaíba Basin (after Rodrigues & Takaki, 1994).
10. Total organic carbon vs. Hydrogen Index cross plot from samples of the Codó Formation in the 1-CI-1-MA well, drilled in the Parnaíba Basin (after Rodrigues & Takaki, 1994).
11. Geochemical log of the 1-APS-18 well, located on the offshore Amapá Platform, showing the organic-rich sedimentary sequence of the Aptian Caciporé Formation. Note that although organic-rich the sequence is immature.
12. Geochemical log of a well located on the onshore Barreirinhas Basin showing typical sedimentary sequences of well 1-SJ-1-MA, Barreirinhas Basin. Note that the sediments of the Codó Formations have not been reached. Also, observe the presence of organic-poor sediments from Preguiças, Barro Duro, Bom Gosto, and Arpoador formations.
13. Plot of natural series versus depth based on Total Organic Carbon and Pyrolysis Rock Eval data from the onshore wells of the Barreirinhas Basin.
14. Gas data from wells drilled in the onshore Barreirinhas Basin (after Rodrigues & Takaki, 1994).
15. Geochemical log of well 1-MAS-12, Pará-Maranhão Basin. Note the presence of organic-rich sediments from Preguiças Formation.
16. Geochemical log of well 1-MAS-26, Pará-Maranhão Basin. Note the presence of organic-rich sediments from Preguiças Formation.
17. Geochemical log of well 1-MAS-32A, Barreirinhas Basin. Note the presence of organic-rich sediments from Preguiças Formation. By contrast, see the lean sediments of the Travosas and the Bom Gosto/ Arpoador sequences.
18. Geochemical log of well 1-APS-29, Foz do Amazonas Basin. Note the presence of organic-rich sediments from Upper Albian-Cenomanian Limoeiro Formation. By contrast, see the lean sediments of the Travosas sequences.
19. Geochemical log of well 1-APS-31, Foz do Amazonas Basin. Note the presence of organic-rich sediments from Upper Albian-Cenomanian Limoeiro Formation. By contrast, see the lean sediments of the Travosas sequences.
20. Plot of natural series versus depth based on Total Organic Carbon and Pyrolysis Rock Eval data from the offshore wells of the Foz do Amazonas Basin.
21. Plot of natural series versus depth based on Total Organic Carbon and Pyrolysis Rock Eval data from the offshore wells of the Pará-Maranhão and Barreirinhas Basins.
22. Geochemical log of a well 1-PAS-21 located on the offshore Northern part of the Pará-Maranhão Basin showing the presence of organic-poor sediments of the Travosas Formation.
23. Geochemical log of the 1-APS-36 well located on the offshore northern part of the Pará-Maranhão Basin showing the presence of organic-rich marine marls Eocene sediments of the Travosas Formation (from Mello et al., 1995).
24. Oil-source rock correlation using gas chromatograms of total n-alkanes, bulk and elemental parameters, and mass chromatograms of terpanes (m/z 191) and steranes (m/z 217), and absolute concentrations of C27  20S + 20R steranes and C30 Hopane of the 1-PAS-9 (C) and 1-PAS-11 (A) oils and the organic extract of a Eocene dark gray marls of the 1-APS 36 (B) well ( modified from Mello, 1988).
25. Plot of natural series versus depth based on Total Organic Carbon and Pyrolysis Rock Eval data from the offshore 1-PAS-21 well, close to the area of the 1-PAS-9 and 1-PAS-11 oils.
26. Map showing the geographic distribution of the oil types present in the Foz do Amazonas, Para-Maranhão and Barreirinhas basins.
27. API gravity versus Depth (m) of the oils from the Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. Note that, as a general trend, the API gravity data of the oils do suggest, with the exception of the biodegraded oils from Foz do Amazonas, a depth control for oil quality. The oils considered outsider from this trend are mixed oils composed of contribution from the marine hypersaline and siliciclastic petroleum systems.
28. API versus Sulfur content of the Foz do Amazonas,Pará-Maranhão and Barreirinhas oils. Note that oil mixtures and biodegradation do affect the sulfur data and does not allow good differentiation among the oil types from the Basins. In general, higher the sulfur content lower is the API gravity of the oils. Exceptions do occur with the mixed oils.
29. API versus Saturates content of the Foz do Amazonas , Pará-Maranhão and Barreirinhas oils. Note that oil mixing and biodegradation do affect the bulk data and does not allow good differentiation among the oil types. Except the mixed oils, higher the saturate content higher the API gravity of the oils.
30. Gas chromatograms of the oil types from Foz do Amazonas, Pará-Maranhão and Barreirinhas basins. Note that biodegradation did not affect the GC profile.
31. Pr/ Phy ratio versus whole oil carbon isotope data of the Foz do Amazonas, Pará-Maranhão and Barreirinhas oils. Note that oil mixtures, thermal evolution and biodegradation do affect the carbon isotope data and does not allow good differentiation among the oil types. Except for the mixed oils, the higher the Pr/ Phy ratio, the lighter are the carbon isotope values of the oils.
32. M/Z 191 Fragmentograms of oils from Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. Note the high abundance of gammacerane in the hypersaline oils compared with the marine anoxic, marine deltaic carbonate and the siliciclastic oils.
33. M/Z 217 Fragmentograms of oils from Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. Note the high abundance of C28 steranes in the Late Albian to Cenomanian anoxic oils when compared with all the others marine oils from the Equatorial Basins.
34. M/Z 231 Fragmentograms of oils from Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. Note the differences in the abundance of 3methyl/ 4methyl triaromatic steranes between the marine anoxic and siliciclastic versus hypersaline oils. The marine hypersaline oils present higher concentrations of 4methyl triaromatic steranes.
35. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from Pará-Maranhão and Barreirinhas Basins. A) Marine siliciclastic oil, from the 1-MAS-20 well, in the offshore area of the Barreirinhas Basin, showing a more carbonatic facies from the Lower Aptian Codó Fm. B) Marine anoxic oil from the 1-MAS-12 well, sourced from the Preguiças Formation showing its biomarker signature. C) Marine siliciclastic oil, from the 1-EO-1 well, in the onshore area of the Barreirinhas Basin, showing a similar biomarker signature when compared with the 1-MAS-20 oil.
36. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from onshore Barreirinhas Basins. Note the marine hypersaline character of the oils, in the onshore 1-SJ-1-Well at 1449m and 1963m. Observe a similar biomarker signature, with the steranes showing low thermal evolution. Such data contrast the very high saturates content of these oils, suggesting oil mixing.
37. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from onshore Barreirinhas Basins. Note the marine hypersaline and low maturity character of the oil from the 3-SJ-6-Well at 1686 m. By contrast, the oil at 2759 m shows a marine siliciclastic with much higher thermal evolution. Observe that the n-alkane trace of the samples at 1686 m is a mixture of both oils. The high saturate content of the 1686 oil contrast its low thermal evolution. Such data suggested migration upwards, in the same area of very high maturity condensates, from the Lower Codó mixing with less mature marine hypersaline oil from the Upper Codó.
38. Gammacerane index versus C35/ C34 hopanes content of the Foz do Amazonas,Pará-Maranhão and Barreirinhas oils. Note that oil mixtures do affect the biomarker data and does not allow good differentiation among the oil types from the Codó Source Rock. In general, the hypersaline oils from the Codó Formation are contains very high amounts of gammacerane index . By contrast the marine anoxic and carbonatic have higher C35/ C34 hopanes ratios.
39. Gammacerane index versus hopane/ sterane index content of the Foz do Amazonas ,Pará-Maranhão and Barreirinhas oils. Note that oil mixtures do affect the biomarkers’ data and does not allow good differentiation among the oil types from the Codó Source Rock (e.g. 1-SJ-1 and 1-RC-1). In general, the hypersaline oils from the Codó Formation are contains very high amounts of gammacerane index. By contrast the marine anoxic and carbonatic from the Pará-Maranhão and Foz do Amazonas Basins lower hopane/ steranes ratios. On the other hand, the siliciclastic oils from the Lower Codó oils have low gammacerane index and higher Hopane/ sterane ratios (e.g. Mello, 1988).
40. C27 C28  20S + 20R steranes content of the Foz do Amazonas,Pará-Maranhão and Barreirinhas oils. Note that oil biodegradation do affect the biomarker data and does not allow differentiation of the 1-APS-1 oil (e.g. see Appendix 1). In general, the Upper Cretaceous oils from Foz do Amazonas and Pará-Maranhão Basins presents, as expected high amounts of C28 steranes. By contrast the marine Aptian and Tertiary oils from the Pará-Maranhão and Barreirinhas Basins show higher C27 steranes (e.g. Mello, 1988; Peters and Moldowan, 1993).
41. C27 C28 Triaromatic-steranes versus gammacerane index of the Foz do Amazonas,Pará-Maranhão and Barreirinhas oils. Note that oil biodegradation do affect the biomarker data and does not allow differentiation of the 1-APS-1 oil (e.g. see Appendix 1). As can be observed the Triaromatic steranes do differentiate the marine hypersaline from the marine siliciclastic oils from Foz do Amazonas, Barreirinhas and Pará-Maranhão basins (e.g. Mello, 1988; Peters and Moldowan, 1993).
42. Plot of C29 αββ/(αββ + ααα) versus C29 20S/ (20S + 20R) steranes of the Foz do Amazonas, Pará-Maranhão and Barreirinhas oils. Note that the marine siliciclastic oils from the Lower Codó, Barreirinhas and marine anoxic oils from Pará-Maranhão Basins present the highest thermal evolution. By contrast, the marine anoxic oils from Foz do Amazonas and the marine hypersaline from Barreirinhas Basins show lower thermal evolution.
43. Plot of Ts/ Tm versus diasterane index of the Foz do Amazonas, Pará-Maranhão and Barreirinhas oils. Note that, as observed in the plot of figure 43, the marine siliciclastic oils from the Lower Codó, in the Barreirinhas and marine anoxic oils from Pará-Maranhão Basins present the highest thermal evolution. By contrast, the marine anoxic oils from Foz do Amazonas and the marine hypersaline from Barreirinhas Basins show lower thermal evolution.
44. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from Foz do Amazonas and Pará-Maranhão Basins. Note the Upper Cretaceous marine anoxic character of the oils based on a similar sterane biomarker signature, with high abundances of C28 steranes. Such data contrast the very low contents of this biomarker, in the Aptian and Tertiary oils (see Appendix II).
45. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from the 1-MAS-5 well. Note the thermal evolution difference of both sterane distribution biomarker signature. The deeper oil show a much higher sterane isomerization ratio, suggesting a post-peak generation stage, and consequently more than one migration pulse in the area.
46. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from the Foz do Amazonas Basin. Note the low thermal evolution and high biodegradation stage of these oils when compared with the oils from Pará-Maranhão Basin. The deeper oil (1-APS-31) shows a presence of biodegradation, suggesting percolation of meteoric water deeper in the stratigraphic section.
47. Plot of oil reservoir depth versus 25-Norhopano index of the Foz do Amazonas, Pará-Maranhão and Barreirinhas oils. Note that oil Paleo-Biodegradation do affect the biomarker data of the Foz do Amazonas oils (e.g. see Appendix II). As can be observed biodegradation is not an important process controlling oil quality in the Barreirinhas and Pará-Maranhão basins (e.g. Mello, 1988; Peters and Moldowan, 1993).
48. Show the oil-source rock correlation among the 1-APS-27 (A; Foz do Amazonas Basin) and 1-MAS-5A (C; Pará-Maranhão Basin) oils and the organic extract of an Upper Upper Albian/ Cenomanian organic-rich sediment of the Limoeiro Formation from the 1-APS-31A well (B) (from Mello et al., 1995).
49. Oil cracking evaluation of 1-APS-21(1875m), 1-APS-31A (4802m) in the Foz do Amazonas Basin and 1-PAS-11(4303m), 1-PAS-9 (4391m), 1-MAS-5A (3424m) and 1-MAS-12 (2430m) in the Pará-Maranhão Basin compared with other oils from the Greater Campos Basin. As can be noted, the oils from the Foz do Amazonas Basin were not cracked (red points). By contrast, the oils from the Pará-Maranhão Basin analyzed by diamondoids presented a mixture of non-cracked with cracked oils (light green).
50. Gas chromatogram, M/Z 191 and M/Z 217 Fragmentograms of oils from the 1-PAS-9 and 1-PAS-11 wells. Note the presence of Oleanane, diagnostic of Tertiary higher plant input. Also, observe the very high thermal evolution showed by the sterane biomarker signature. The 1-PAS-9 oil show a extended hopane distribution typical of marine carbonate derived oil (e.g. Mello, 1988; Mello et al., 1995 and Mello et al., 2001).
51. Simplified tectonic framework and main hydrocarbon occurrences (gases and oils) of the Lower Aptian Codó – Barro Duro/Tutóia (?) Petroleum System (modified from Azevedo, 1986)
52. Geologic cross section showing the main migration and accumulation pathways from the Codó Formation to the reservoirs of the Barro Duro and Tutóia formations reservoirs of the Codó – Barro Duro/Tutóia (?) petroleum system.
53. Event chart of the Lower Aptian Codó – Barro Duro/Tutóia (?) Petroleum System showing the specific times of source rock, reservoirs and seals deposition, trap formation, generation, oil and gas expulsion, preservation and trap
54. Simplified tectonic framework and main hydrocarbon occurrences (São João gas and oil accumulations) of the Upper Aptian Lower Albian Codó – Barro Duro/Tutóia (?) Petroleum System (modified from Azevedo, 1986).
55. Geologic cross section showing the main migration and accumulation pathways from the Upper Codó Formation to the reservoirs of the Barro Duro and Tutóia formations reservoirs of the Upper Codó – Barro Duro/Tutóia (?) hypersaline petroleum system. Modified from Gonçalves et al. (1992).
56. Event chart of the Upper Aptian-Lower Albian Codó – Barro Duro/Tutóia (?) Petroleum System showing the specific times of source rock, reservoirs and seals deposition, trap formation, generation, oil and gas expulsion, preservation and trap modification parameters.
57. Geologic cross section showing the main migration and accumulation pathways from the Upper Albian/ Cenomanian Preguiças/ -Barro Duro/Tutóia (?) Petroleum System (modified from Brandão et al., 1990).
58. Geologic cross section showing the main migration and accumulation pathways from the Upper Albian/ Cenomanian Limoeiro-Barro Duro/Tutóia (?) Petroleum System (Brandão et al., 1991).
59. Event chart of the Upper Albian/ Cenomanian Preguiças/Limoeiro-Barro Duro/Tutóia (?) Petroleum System showing the specific times of source rock, reservoirs and seals deposition, trap formation, generation, oil and gas expulsion, preservation and trap modification parameters.
60. Geologic cross section showing the main migration and accumulation pathways from the Upper Albian/ Cenomanian Limoeiro-Barro Duro/Tutóia (?) Petroleum System (modified from Brandão et al., 1989).
61. Event chart of the Lower Tertiary TRAVOSAS-ILHA DE SANTANA (!) Petroleum System showing the specific times of source rock, reservoirs and seals deposition, trap formation, generation, oil and gas expulsion, preservation and trap modification parameters.