Dolomite genesis in bioturbated marine zones of an early-middle Miocene coastal mud volcano outcrop (Kuwait)

Abstract

The origin of spheroidal dolomitized burrow from Al-Subiya sabkha in Kuwait was previously described as enigmatic as no evidence of precursor calcium carbonate was found in the siliciclastic sediment. An assumption for the genesis of spheroidal dolomite from the same area was attributed to hydrocarbon seepage but no evidence was provided. Here, we investigated a recently discovered early-middle Miocene coastal mud volcano outcrop in Al-Subiya sabkha where dolomitized burrows and spheroidal dolomite are found in bioturbated marine zones, and associated with traces of salt. Conversely, the continental zone lacks bioturbation features, dolomite and traces of salt, which together contrast with bioturbated rich marine zones. Geochemical signatures of Rare Earth Elements + Yttrium show a true positive Ce anomaly (Ce/Ce* > 1.2) and positive Eu/Eu* anomaly of spheroidal dolomite indicating strictly anoxic conditions, and sulphate reduction to sulphide, respectively. Our results are suggestive of a relationship between dolomite formation and interdependent events of hydrocarbon seepage, flux of hypersaline seawater, bioturbation, and fluid flow in the marine zones of the mud volcano. The bioturbation activity of crustaceans introduced channels/burrows in the sediment–water interface allowing for the mixing of seeped pressurized hydrocarbon-charged fluids, and evaporitic seawater. In the irrigated channels/burrows, the seeped pressurized hydrocarbon-charged fluids were oxidized via microbial consortia of methanotrophic archaea and sulphate-reducing bacteria resulting in elevated alkalinity and saturation index with respect to dolomite, thus providing the preferential geochemical microenvironment for dolomite precipitation in the bioturbated sediment.

High‐magnesium calcite skeletons provide magnesium for burrow‐selective dolomitization in Cretaceous carbonates

“…In reported cases of burrow‐selective dolomitization during periods with low seawater Mg/Ca ratios, depositional environments are the restricted lagoon or tidal flat settings with high seawater salinity and sufficient Mg supply. Additionally, host rocks in these environments are primarily composed of lime mudstone or wackestone causing the permeability superiority of burrows over surrounding matrices, which contributes to the preferential fluid flux and dolomitization within burrows (Morrow, 1978; Saller & Yaremko, 1994; Rameil, 2008; Baniak et al ., 2014; Newport et al ., 2020; Rahim et al ., 2020; Alibrahim et al ., 2021; Ye et al ., 2021; Yang et al ., 2022a). By contrast, the Rumaila Formation was deposited in an open marine with normal seawater salinity and the host rocks were dominantly packstone.…”

“…In addition to the Mg produced by burrow organisms and supplied by coeval seawater (Gingras et al ., 2004b; Rameil, 2008; Chatalov, 2018), several additional Mg sources and pump mechanisms have been proposed. The most prevalent source is dense saltwater with a high Mg concentration, pumped by shallow seepage reflux and/or evaporitic tidal pumping (Morrow, 1978; Saller & Yaremko, 1994; Zenger, 1996a; Baniak et al ., 2014; Baldermann et al ., 2015; Niu et al ., 2020; Rahim et al ., 2020; Alibrahim et al ., 2021; Ye et al ., 2021; Yang et al ., 2022a). Moreover, Callen & Herrmann (2019) found that the leaching of volcanic ash could provide Mg for burrow dolomitization.…”

Imaging of Ancient Microbial Biomarkers within Miocene Dolomite (Kuwait) Using Time-of-Flight Secondary Ion Mass Spectrometry

“…In a recent investigation, the geochemical signatures of dolomite were characterized, indicating strictly anoxic conditions that imply methane seepage during the Miocene period. Under such conditions, dolomite formation was suggested to be prompted by microbial consortia associated with the anaerobic oxidation of methane [47]. Despite the significance of these findings, the involvement of microbes in dolomite formation in Al-Subiya area was postulated but not verified.…”

“…The observed pockmarks indicate intense venting of hydrocarbon-charged fluids where the authigenic carbonates are consequences of the microbial anaerobic oxidation of seeped hydrocarbon. The geochemical signatures of positive cerium and europium anomalies of dolomite at the site provide strong evidence of strictly anoxic conditions and sulfate reduction events during the dolomite formation process [47]. Prior to rock sampling for our research, the site was divided into 3 zones based on apparent lithological and geomorphological characteristics (Figure 1).…”

Multielement Imaging Reveals the Diagenetic Features and Varied Water Redox Conditions of a Lacustrine Dolomite Nodule

“…So far, massive dolostones are attributed to slow burial or hydrothermal dolomitization of calcite or aragonite precursors by Mg-rich fluids at temperatures of >100 °C [3,5,6]. In contrast, other studies have asserted that dolomites can form at low temperatures in pore waters during early diagenesis [7,8]. According to the theory of penecontemporaneous replacement, early diagenetic dolomitization of calcite or aragonite precursors occurred at temperatures of <60 °C via Mg-rich reflux in pore water [9].…”