Sedimentary Organic Matter Analysis and Paleoenvironmental Implications During the Late Jurassic–early Cretaceous in the Araripe Basin, Northeastern Brazil

Variations in sedimentary organic matter (SOM) along the stratigraphic succession provide valuable insights into facies distribution, detrital input, and depositional redox conditions. This study analyzes the composition and distribution of SOM based on 44 samples from Late Jurassic–Early Cretaceous succession of the Araripe Basin (Brejo Santo and Abaiara formations), northeastern Brazil. Phytoclasts dominate the assemblages, mainly opaques (60.26%), followed by non-opaques (13.41%), amorphous organic matter (7.0%), and scarce palynomorphs. Detrital proxies (Si/Al, Ti/Al, Zr/Al, and K/Al) indicate high-energy conditions associated with strong terrigenous influx, whereas redox-sensitive proxies (Fe/Al, Fe/Si, Fe/Zr, and Cr/S) reflect low-energy, reducing depositional conditions favored SOM preservation. The stratigraphic record documents a transition from lacustrine conditions (Interval I) to progressively shallower fluvio-lacustrine and deltaic environments (Intervals II and III), developed during the early rift evolution of the Araripe Basin. ✔ Transition from dysoxic lacustrine to oxidizing fluvio-lacustrine conditions. ✔ Interval I record deeper, restricted lacustrine settings. ✔ Intervals II- III mark a regressive, shallowing depositional trend with increasing fluvial influence. ✔ Maximum AOM peaks indicate enhanced preservation under low oxygen. ✔ Detrital proxies track increasing terrigenous influx upward.