Abstract Paleoenvironmental conditions of the sediments of the Cretaceous Codo Formation in Brazil are still being debated. The main point of controversy is whether they were deposited in a strictly marine environment or under lacustrine conditions of varying salinity. In this study, organic facies and biomarker analyses were performed on samples from the Codo Formation in the Sao Luis Basin, northwest Brazil, to reconstruct the paleoenvironmental conditions, the origin, and the thermal maturity of the organic matter. Four types of palynofacies associations (PI – amorphous organic matter, PII – amorphous organic matter+sporomorphs, PIII – phytoclasts, and IV – marine palynomorphs) were identified. The total organic carbon (TOC) content exhibits a strong correlation (ρ = 0.75, p 80%). The thermal maturity indicators including vitrinite reflectance (%Ro), spore color index (SCI), Ts/(Ts + Tm) ratios, and C29 20S/(20S + 20R) and C29 ββ/(αα + ββ) indicate that the organic matter is immature to marginally mature.

中文翻译：

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有机相和生物标志物在巴西圣路易斯盆地中西部 Codó 组沉积物古环境条件和成熟度表征中的应用

摘要 巴西白垩纪科多组沉积物的古环境条件仍存在争议。主要争议点是它们是沉积在严格的海洋环境中还是在不同盐度的湖泊条件下沉积。在这项研究中，对巴西西北部圣路易斯盆地 Codo 组的样品进行了有机相和生物标志物分析，以重建有机质的古环境条件、起源和热成熟度。确定了四种类型的孢粉相组合（PI – 无定形有机质，PII – 无定形有机质+孢子形，PIII – 植物碎屑，和 IV – 海洋孢粉形）。总有机碳 (TOC) 含量表现出很强的相关性 (ρ = 0.75, p 80%)。