Biological matter enhanced iron release from shallow marine bioturbated sediments: a case study of Late Cretaceous sandstone, northern Saudi Arabia

• Published in: International journal of earth sciences : Geologische Rundschau 2023-11, Vol.112 (8), p.2313-2323
• Main Authors: Zhang, Yunlong, Li, Ziying, Qin, Mingkuan, Li, Zhixing, Yi, Longsheng, Jiang, Li
• Format: Article
• Language: English
• Subjects: Biological effects; Bioturbation; Cementation; Cretaceous; Earth and Environmental Science; Earth Sciences; Geochemistry; Geology; Geophysics/Geodesy; Iron; Iron content; Marine environment; Microenvironments; Mineral Resources; Nutrients; Nutrition; Original Paper; Oxygen; Pore water; Primary production; Productivity; Sandstone; Sediment; Sedimentary rocks; Sedimentology; Sediments; Structural Geology; Ventilation
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-023-02326-1

Shallow marine bioturbation plays a crucial role in enhancing pore-water ventilation, oxygen and nutrition cycling, and ecosystem productivity. In this study, it was found that a thin layer of sandstone in the uppermost part of the Late Cretaceous Zallum Formation from northern Saudi Arabia had been moderately bioturbated. The bioturbated sediments were consolidated through the cementation of remarkably preserved biological matter, resulting in the formation of a rod-shaped morphology. These rod-shaped bioturbated sediments were assembled, forming a distinctive network-like structure that enables them to be readily distinguished from the surrounding unconsolidated host sediments. Geochemical analysis revealed a notable pattern of iron enrichment in the biological matter, bioturbated sediments, and host sediments. The biological matter has a substantial total iron concentration, with a significant proportion of Fe(II). In contrast, the host sediments have a high iron enrichment factor, but a comparatively lower total iron content and proportion of Fe(II). Conventionally, bioturbation often leads to an increase in the iron content by promoting the fixation of iron in the form of Fe(III). Contrary to the conventional understanding, the results of this study suggest that the microenvironment established by the biological matter within the burrows actually accelerated the removal of iron from the burrowed sediments in the form of Fe(II) ions. The release of iron from the burrowed sediments could have implications for the supply of iron nutrients in the overlying water. As a result, this study provides further insights into the impact on primary productivity in a bioturbated shallow marine environment.