The Biotic‐Abiotic Control of Si Burial in Marine Carbonate Systems of the Pre‐Eocene Si Cycle

Abstract

The silicon (Si) cycle in the modern ocean might still be representative of some of the processes that occurred in the Si‐depleted post‐Eocene oceans resulting after the expansion of diatoms. However, silicon‐rich pre‐Eocene seas, where sponges and radiolarians were major Si users before the emergence of diatoms, were radically different from modern ocean scenarios. The spatial and temporal evolution of Si cycling in Earth history is recorded in geological deposits and could be reconstructed by petrographic and mineralogical analyses. The thick successions of carbonate siliceous rocks deposited in marine environments during the Paleozoic and Mesozoic indicate the significant role of Si outflow from the Si cycle via burial in sediments. The aim of this study is to fill an important gap in knowledge concerning the functioning of the main silicon sink in the oceans: burial in sediments. Si outflow from the marine biogeochemical Si cycle occurs via early diagenetic silica crystallization within seabed mud. The mechanisms leading to Si binding in silica minerals are a complex process controlled by abiotic global events, biological activity of silicifiers and geochemical conditions mediated by microbes. This study concentrates on reconstructions of the mechanisms of Si outflow from the Si cycle by silica polymorph crystallization below the seabed surface and was realized through mineralogical and microtextural analyses of the main components of Upper Cretaceous carbonate–siliceous rocks.

Campanian (Late Cretaceous) Theonellidae and Phymaraphiniidae (lithistid Demospongiae) from the Miechów and Mogilno‐Łódź synclinoria (southern and central Poland): new data and taxonomic revision

“…1989; Jurkowska et al . 2019 a ), indicates that this depositional environment differs from that of opoka in a higher rate of sedimentation as a result of a significant influx of detrital clays (Jurkowska 2022). This distinctive distribution of theonellid sponges is indicative of its association with facies characterized by a high rate of sedimentation (marly deposits) in offshore and onshore zones of the European epicontinental sea.…”

Opoka – a mysterious carbonate-siliceous rock: an overview of general concepts

“…In Poland, where the name opoka originates and was first described, it crops out in the Miechów Synclinorium and Middle Vistula River sections (e.g. Rutkowski 1965, Błaszkiewicz 1980, Walaszczyk 2004, Jurkowska & Świerczewska 2020a, Jurkowska 2022, which were determined as areas of typical opoka occurrence (Sujkowski 1926(Sujkowski , 1931) (Fig. 1A).…”

“…In recent studies, a compilation of a large dataset of opoka samples (Jurkowska et al 2019a, 2019b, Jurkowska & Świerczewska-Gładysz 2020a, 2020b, Jurkowska 2022, derived mainly from Poland and western parts of Europe, have indicated that opoka is a carbonate rock composed of calcite (38-90%) and an insoluble residue (10-62%), whose main component is authigenic opal-CT (4-46%) (Fig. 3) forming a distinctive siliceous rock framework (Fig.…”

“…3) forming a distinctive siliceous rock framework (Fig. 4B) (Jurkowska 2022). The subordinate components of the insoluble residue are: clays (<10%), detrital quartz (<10%) and rarely zeolites (clinoptilolite <5%) (Jurkowska 2022) (Fig.…”

“…The distinctive mineralogical composition expressed as opal-CT and insoluble residue content distinguishes opoka from chalk, which is almost pure calcium carbonate (Saïag et al 2019). The difference between opoka and gaize (another carbonate siliceous rock which also contain opal-CT) is the higher (>10%) content of detrital quartz in gaize (Cayeux 1929, Sujkowski 1931, Jurkowska 2022. Marls differ from opoka in the higher content of clays (>10%), while cherts (which occur in opoka succession in form of horizons of siliceous nodules) can be distinguished by different microtexture and higher content (>50%) of opal-CT (Jurkowska & Świerczewska-Gładysz, 2020b).…”