![]() Bralower et al., 1999 Bottini et al., 2015) (yellow band in Fig. Although no biostratigraphic constraints are available stratigraphically above 2484 m, the trend of decreasing δ 13C values and positive excursion, as in the interval 2517–2450 m, are similar to the C8–C10/Ap8–Ap15 segments of the late Aptian (cf. Relatively high δ 13C values, as in the interval 2689–2517 m, characterize part of the so-called C7/Ap7 isotopic segment (latest early Aptian–earliest late Aptian interval), with the highest δ 13C values of the Aptian stage (e.g., Menegatti et al., 1998 Bottini et al., 2015) (purple band in Fig. 2): a stratigraphically lower section (2689–2517 m) showing relatively high δ 13C values (3.60‰–4.97‰) and a stratigraphically higher section (2517–2437 m) that shows a trend of decreasing δ 13C values from bottom (3.0‰–3.3‰) to top (1.2‰–1.6‰), interrupted by a positive excursion with values >4‰. The carbon isotope profile from Petrobras well CB-3 shows a defined pattern ( Fig. RESULTS AND STRATIGRAPHIC CORRELATION WITH REFERENCE SECTIONS 2), in which Aptian and younger calcareous nannofossils (e.g., Nannoconus truittii) and planktonic foraminifera are present (e.g., Globigerinelloides ferreolensis Ticinella raynaudi Azevedo et al., 1987 this study). Following platform drowning, deeper water sediments accumulated (Outeiro and Itanhaém Formations Fig. 2) containing planktonic foraminiferal species that are not age diagnostic (e.g., Favusella ex grege washitensis Azevedo et al., 1987). Above the evaporites, in distal settings, the early drift supersequence is represented by shallow-marine platform carbonates (Quissamã and Guarujá Formations Fig. The anhydrite probably formed from dewatering of gypsum during burial and shows textures typical of precipitation in subaqueous settings, such as thin laminations and twinned crystals, as well as nodules of probable sabkha facies ( Dias, 1998). 1), have Br contents and 87Sr/ 86Sr ratios that indicate derivation from marine waters ( Dias, 1998). Halite and anhydrite from the Espírito Santo Basin, north of the Campos Basin ( Fig. The evaporites terminate the postrift supersequence and comprise cycles of predominantly anhydrite and halite, locally with more soluble salts such as carnallite, sylvite, and tachyhydrite (Retiro and Ariri Formations Fig. 2) in distal settings, the overlying postrift supersequence comprises interbedded microbial carbonates and shales (Macabu and Barra Velha Formations Fig. Above the basement, the rift supersequence comprises volcanic rocks, continental siliciclastics, and interbedded lacustrine coquinas and organic-rich shales (Coqueiros and Itapema Formations Fig. The stratigraphic record, based on offshore wells, is divided into three main supersequences, rift, postrift, and drift, as described by Moreira et al. The Santos and Campos Basins formed during the opening of the central segment of the South Atlantic Ocean in the Early Cretaceous ( Davison, 2007 Chaboureau et al., 2013). GEOLOGICAL SETTING OF THE SANTOS AND CAMPOS BASINS All results, detailed methods, quality control, and compilation of data are provided in the GSA Data Repository 1. We also compiled δ 13C and total organic carbon (TOC) values from cuttings from supraevaporite Petrobras well X, Santos Basin ( Quintaes, 2006), and subevaporite Petrobras well CP-5, Campos Basin ( Dias, 1998), to generate composite carbonate carbon isotope and TOC curves (Santos-Campos composite), where original samples were not available for further analyses. The International Atomic Energy Agency CO-1 standard gave a standard deviation (σ) of <☐.07‰ for δ 13C and ☐.12‰ for δ 18O. Data are reported in parts per thousand (‰) relative to the Vienna Peedee belemnite standard. We analyzed 195 core samples (from depth interval 2437–2689 m) for carbon and oxygen isotopes (δ 13C and δ 18O) on bulk carbonate. We prepared and analyzed 171 core samples (from depth interval 2484–2689 m) for foraminiferal biostratigraphy in the Research Center of Petrobras (Rio de Janeiro, Brazil), using concepts from Premoli Silva and Verga (2004) and Huber and Leckie (2011). 1) and terminated an unknown distance above the evaporites ( Fig. Petrobras well CB-3 is located in the offshore Campos Basin (22☄4′S, 40☄0′E) ( Fig.
0 Comments
Leave a Reply. |