Origin of anhedral Sr‐rich calcite in deep‐water mixed sediment, north‐east Australia

Abstract

At burial depths of 800‐1000 m, within the epicontinental Queensland Trough of north‐east Australia (ODP Site 823), microcrystalline inter‐ and intraskeletal mosaics of anhedral (loaf‐shaped, rounded) calcite have Sr2+ values ranging from below microprobe detection limits (<150 ppm) to 8100 ppm. Host rocks are well lithified, fine‐grained mixed sediment to clayey wackestone and packstone of Middle and Late Miocene age. Petrography demonstrates that calcite precipitation has spanned shallow to deep burial, overlapping formation of framboidal pyrite in the upper 50 m; shallow‐burial dolomitization (<300 m); and dedolomitization during sediment consolidation and incipient chemical compaction at greater (>400–500 m) depths. Petrographic observations illustrate that the calcite microfabric formed through coalescing crystal growth resulting from one or a combination of displacive growth in clay, porphyroid neomorphism of aragonite/vaterite, and clay replacement by calcite. Sr2+ mean concentrations in calcite between depths of 800 and 1000 m are similar to an expected equilibrium pore‐water concentration, using a Dsr of 0.06, and may indicate active calcite precipitation. However, Sr2+ variation (2000–5000 ppm) within and among crystals, and concentrations that range well above predicted equilibrium values for a given depth, illustrate either variable Sr2+ retention during recrystallization of shelf‐derived aragonite (and authigenic local vaterite) or relative uptake of Sr2+ during calcite precipitation with burial. Within the context of calcite formation during burial to 1 km, diagenetic attributes that affect the latter process include increased concentrations of pore‐water Sr2+ with depth associated with aragonite recrystallization/dissolution; upward migration of Sr‐rich pore water; and increased DSr related to local variation in precipitation/recrystallization rates, differential crystal sector growth rates and/or microvariation in aragonite distribution.

The geochemistry of carbonate diagenesis: The past, present and future

“…tial aragonite in the section and the processes of carbonate dissolution and precipitation allow the concentration of Sr to reach up to 5 mmol. The predicted concentration of Sr in any diagenetic carbonate formed from these pore fluids would be 4% and these concentrations are reflected in diagenetic cements at ODP sites such as Site 823 (Dix, 1995).…”

“…The Sr content of the diagenetic carbonates would be expected to be high, reflecting the extent of sulphate reduction in the sediments. In some instances, calcites with Sr concentrations as high as 3000 ppm (Dix, 1995) and dolomites with values of 2000 ppm (Swart & Melim, 2000) have been reported. Such high Sr concentrations in ancient rocks might be misinterpreted as reflecting precipitation from hypersaline brines.…”

Ballıca (Elazığ Güneyi, Doğu Anadolu) Civarindaki Denizel Sedimanter Kayaçların Jeokimyasal Özellikleri

“…Toplam NTE CaO ve Sr dışındaki major ve iz elementlerle pozitif korelasyon göstermektedir (Şekil 5a-b). CaO ve Sr elementi karbonat minerallerine bağlı olup (Dix 2006), diğer major oksit ve iz elementlerin NTE 'ler ile pozitif korelasyonu bu elementlerin ve fillosilikatlara bağlı olduğunu yansıtır. Fillosilikatların NTE'leri içerdiği Coppin vd.…”

The mineralogical and geochemical composition of Holocene sediments from Lake Hazar, Elazığ, Eastern Turkey: implications for weathering, paleoclimate, redox conditions, provenance, and tectonic setting

“…Cr may be linked with clinopyroxenes and opaque minerals, while Y and Hf might be associated with heavy minerals (Craigie, 2018). Sr is significantly negatively correlated with Al 2 O 3 (r = -0.92) since Sr is generally bound to carbonate minerals (Dix, 2006).…”