Microbially mediated dolomite in Cambrian stromatolites from the Tarim Basin, north‐west China: implications for the role of organic substrate on dolomite precipitation

Abstract

Dolomite [CaMg(CO 3 ) 2 ] is abundant in sedimentary rocks throughout the geological record, but it is rarely found in modern sediments. Also, it cannot be precipitated under lowtemperature conditions in the laboratory without microbial mediation and, as a result, its origin remains a long-standing enigma. This study reports biologically mediated dolomite precipitation in ancient microbial mats and biofilms from the Cambrian Tarim Basin. The ambient temperature at the time of dolomite precipitation was estimated from d 18 O values from early diagenetic dolomite, and the presence of structures asso-ciated with extracellular polymeric substances (EPS), is composed of fibres arranged in a reticular pattern, would favour epitaxial crystallization of dolomite on an organic substrate. In addition, poorly crystallized dolomite formed nanocrystal aggregates that strongly resemble the morphology and size distribution observed in microbial culture experiments. These lines of evidence confirm that microbial structures can be preserved in ancient dolomite and validate their use as biosignatures.

Multiphase dolomitization of deeply buried Cambrian petroleum reservoirs, Tarim Basin, north‐west China

“…There are abundant dolomitized burrows (size from 0·5 to 2·0 cm) (Baniak et al ., ) presented in restricted lagoon facies from the top of the Lower (Є 1w ) to the uppermost of the Middle (Є 2a ) Cambrian strata. Moreover, microbial rock (Zhang et al ., ) and probably extracellular polymeric substances (EPS) are also present in the Upper Cambrian stromatolites (You et al ., ). The above findings suggest that this dolomite type had a microbial origin.…”

“…Thin‐section and CL photomicrographs show different kinds of dolomites in Cambrian strata in the Tarim Basin. (A) Stromatolitic laminae of alternating dark dolomudstone (red arrow) and light microsparite layers (yellow arrow), pyrite and EPS fossils (You et al ., ) are presented in the dark dolomudstone, outcrop Xiaoerbulake, ∈ 3q . (B) Very finely crystalline dolomicrite (D2) (in dark colour; red arrows), and the associated anhydrite nodule (‘A’, white colour) from restricted lagoon facies, well ZS5, 6435·2 m, ∈ 1w .…”

“…Available well data are consistent with large areas of restricted lagoon facies being present in the upper part of the Lower (Є 1w ) and Middle (Є 2a ) Cambrian strata in the Tarim Basin (Zheng et al ., ). Extracellular polymeric substances (EPS) and dolomitized burrows have been found in these microbial dolomudstones (D1) (You et al ., ). The dolomite in D1 rocks is characterized by depleted δ 13 C values (Fig.…”

“…This paragenetically late quartz commonly occurs in the Upper Cambrian Qiulitage Formation (Є 3q ) and Middle Cambrian Sayilike Formation (Є 2s ). (You et al, 2013) are presented in the dark dolomudstone, outcrop Xiaoerbulake, 2 3q . (B) Very finely crystalline dolomicrite (D2) (in dark colour; red arrows), and the associated anhydrite nodule ('A', white colour) from restricted lagoon facies, well ZS5, 6435Á2 m, 2 1w .…”

Precipitates in landfill leachate mediated by dissolved organic matters

“…In fact, mineral precipitation is not only a chemical process, it also involves with biochemical reactions, such as the methanogenic decomposition of organics into CO 2 and CH 4 , which gives rise to partial pressure of CO 2 and concentration of CO 3 2− in aqueous solution. Latest evidence shows that metals tend to adsorb onto carboxyl surface and then crystallize with much faster reaction rate and much less energy required to overcome obstacles in chemical potentials that may be encountered in a reaction [14][15][16][17][18][19].…”