Syndepositional processes in the pigmentation of oceanic red beds: evidence from the Basque–Cantabrian Basin (northern Spain)

• Published in: Geological magazine 2021-09, Vol.158 (9), p.1683-1703
• Main Authors: Elorza, Javier, Gómez-Alday, Juan José, Jiménez Berrocoso, Álvaro
• Format: Article
• Language: English
• Subjects: aerobic environment; Atlantic Ocean; Bacteria; Basque Provinces Spain; Bay of Biscay; burial diagenesis; C-13/C-12; calcium carbonate; Cantabrian Basin; Carbon; carbonate rocks; Cenozoic; clastic rocks; Coccoliths; Cold water masses; Color; Colour; concentration; Cretaceous; Danian; deep-sea environment; deposition; Diagenesis; dissolved oxygen; early diagenesis; Electron microscopy; electron microscopy data; Europe; ferric iron; ferrous iron; Geochemistry; Geology; Haematite; Hematite; Iberian Peninsula; Iron; isotope ratios; isotopes; late diagenesis; Limestone; lower Maestrichtian; lower Paleocene; lower Turonian; Maestrichtian; marine environment; Marl; Mesozoic; metals; Micas; North Atlantic; O-18/O-16; Original Article; Oxidation; oxides; oxygen; Oxygen isotopes; Paleocene; paleoenvironment; Paleogene; Pigmentation; pigments; preservation; red beds; Scanning electron microscopy; Seawater; sed rocks, sediments; Sedimentary petrology; sedimentary rocks; Sedimentation & deposition; sedimentation rates; Sediments; SEM data; solutes; Southern Europe; Spain; stable isotopes; Staining; synsedimentary processes; Tertiary; Turonian; unconsolidated materials; Upper Cretaceous; upper Maestrichtian; Water masses; Water temperature; X-ray diffraction; X-ray diffraction data
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756821000248

Oceanic red beds (ORBs) are present in Upper Cretaceous and Danian deep-marine deposits in the Basque–Cantabrian Basin of northern Spain. The presence and regularity of the succession of marl–limestone couplets is exceptional based on the macroscopic, microscopic and geochemical evidence collected. Five types of marl–limestone couplets are identified based on the colour, and a high maximum sedimentation rate (3.6 cm ka–1 ) is noted. The oxidizing activity of deep, cold-water masses is indicated by the oxygen isotope signal in the lower–upper Maastrichtian and Danian sections and the presence of the boreal inoceramid Spyridoceramus tegulatus. In theory, the variation in colour from grey to greenish-yellow, purple and pink up to red tones correlates with the Fe2+/(Fe2++Fe3+) ratio. It is interpreted as the possible palaeoenvironmental transit of particles that sediment out slowly in oxic environments when they circulate through cooler, oxidizing water masses. The colour is considered to be a depositional feature, and hematite, detected by X-ray diffraction, is the main staining agent, without discarding the possible redistribution of previous oxyhydroxides passing to hematite as a final product. The cell filling of the foraminifer shells does not incorporate appreciable amounts of Fe and Mg during diagenesis. Bacterial activity is detected using scanning electron microscopy images, both in the coccolith debris and in the detrital micas, although there is uncertainty as to its importance in the staining process.