Subaqueous plopstone deposits: a unique product of sinkhole development in eogenetic carbonates

• Published in: Carbonates and evaporites 2022-06, Vol.37 (2), Article 35
• Main Authors: Florea, Lee, Cymes, Brittany A.
• Format: Article
• Language: English
• Subjects: Aquaria; Aquariums; Aquifers; Calcite; Carbonates; Caves; Cementation; Clay; Deformation; Earth and Environmental Science; Earth Sciences; Electron microscopy; Fluid flow; Fluorescence; Fluvial deposits; Geology; Kaolinite; Metal oxides; Metals; Mineral Resources; Mineralogy; Miocene; Montmorillonite; Montmorillonites; Morphology; Original Article; Sand; Sandstone; Scanning electron microscopy; Sea level; Sediment; Sedimentary rocks; Sedimentary structures; Sediments; Sinkholes; Stokes law; Stokes law (fluid mechanics); Stratigraphy; Throughfall; X ray spectra; X rays; X-ray diffraction; X-ray fluorescence
• ISSN: 0891-2556; 1878-5212
• DOI: 10.1007/s13146-022-00773-6

Modern cover-collapse sinkhole development in the Brooksville Ridge of west-central Florida uncovered paleokarst solution features filled with Miocene Peace River Formation sediments. Sedimentary structures in this paleokarst fill included a 70 cm-thick package of sub-rounded and moderately well-sorted quartz sandstone, and indurated with poikilotopic calcite cement—confirmed using X-ray diffraction (XRD). The morphology of the sediment package includes mm-scale compositional banding inside cm-scale ‘plops’, akin to types of commercial aquarium stone. Scanning electron microscopy (SEM), energy-dispersive X-ray spectra (XEDS), and portable X-ray fluorescence (pXRF) measurements reveal that metal oxides create the compositional banding and that the grains are frosted with kaolinite–montmorillonite clay. The shape of this ‘plopstone’ deposit, the compositional banding, and structures associated with soft-sediment deformation indicate Stokes Law throughfall in a near-stagnant sub-aqueous setting, with ‘plops’ held together by the cohesion of clay—like kinetic sand. Following deposition, density separation occurred during extensional strain, and cementation progressed slowly in calcite-saturated waters. Collectively, this ‘plopstone’ represents a likely product of sand raveling common during the development of cover-subsidence sinkholes.