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Microalgae are one of the important sources of organic matter which, if preserved well in sediments, can generate hydrocarbons during burial diagenesis. However, the preservation mode of microalgal organic matter within product aggregates induced by marine microalgae has rarely been examined. Herein, a strain of eukaryotic marine microalgae, Chlorella sp. MASCC-0008, was used to conduct biomineralization experiments in an f/2 medium with a 0.02 mol/L Ca2+ ion concentration and various Mg2+ ion concentrations of 0.05, 0.06, 0.07 and 0.10 mol/L. It was found that the soluble organic matter of the microalgae contains amino acids and fulvic acids which can attract and absorb cations. With an increase in Mg2+ ion concentration in the experimental group with Chlorella sp., the aragonite content of the mineral precipitates increased whereas the calcite content decreased. In contrast, calcite was the sole mineral precipitated in the control experiments with no Chlorella sp.. Due to the porous structure of minerals, their organic matters were preferred to be preserved in aragonite aggregates compared to calcite aggregates. The TOC content of the minerals aggregates is the highest (0.45%) and the hydrocarbon generation potential (S 1 + S 2) of organic matter is the greatest (3.66 mg/g) in those precipitated in the medium with a Mg2+ ion concentration of 0.10 mol/L. Microalgal organic matter has significant hydrocarbon generation potential due to its effective preservation in the product aggregates formed by the microalgal biomineralization. Squalene is the most abundant alkene detected in the pyrolytic products. These results suggest that microalgae can induce precipitation of carbonate minerals, a process that facilitates the sequestration of organic matter within the product aggregates precipitated, thus potentially preserving this microalgal organic matter into the burial diagenetic realm where, if conditions are appropriate, hydrocarbons may be developed. [ABSTRACT FROM AUTHOR]

Manganese (Mn) is a common trace element in dolomite, yet its precise role in dolomite precipitation, if any, has not been explored. This study aims to investigate carbonate mineral formation in the presence of extracellular polymeric substances produced by Bacillus licheniformis Y 1 in 14 cross-over experiments within the MgCl 2 -CaCl 2 -MnCl 2 system. The study involved the analysis and comparison of water chemistry, mineralogy and bacterial metabolites. The findings indicate that B. licheniformis Y 1 induces the formation of Mg-free calcite and low-Mg calcite in Mn-free solutions (Mg/Ca < 2). The addition of 0.001 mol/L Mn2+ results in the precipitation of Mg-rich calcite. In the presence of a relatively high Mg2+ content in the solution (Mg/Ca > 6), B. licheniformis Y 1 in a Mn-free solution induces the formation of aragonite and dypingite, whereas the addition of 0.001 mol/L Mn2+ leads to the formation of Mn-bearing dolomite in the precipitate. Notably, at Mg/Ca = 6, an increase in Mn2+ content of the fluid to 0.002 and 0.003 mol/L yields Mn-rich dolomite. The Mn-bearing dolomite exhibits a regular spherical aggregate morphology with diameters ranging from 15 to 60 μm. The 2θ position of the (104) crystal face is close to that of dolomite, and the thermal decomposition temperature is lower than that of calcite. XPS results show that Mn O bonds exist on the mineral surface. Acidic amino acids such as glutamic acid as well as humic acid in EPS, especially fulvic acid analogues, actually rise with increasing Mn2+ concentration and contain a large number of functional groups including carboxyl groups. Molecular dynamics simulations show that fulvic acid can effectively promote the dehydration of Mg-water complexes, thus promoting the formation of dolomite. These experiments indicate that the presence of Mn ions in the solution, along with bacteria and EPS, promote the precipitation of protodolomite. [Display omitted] [ABSTRACT FROM AUTHOR]