What is diatomite?

Different types of biogenic remains, ranging from siliceous algae to carbonate precipitates, accumulate in the sediments of lakes and other aquatic ecosystems. Unicellular algae called diatoms, which form a siliceous test or frustule, are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments. When diatoms accumulate in large numbers in sediments, the fossilized remains can form diatomite. In sedimentological literature, “diatomite” is defined as a friable, light-coloured, sedimentary rock with a diatom content of at least 50%, however, in the Quaternary science literature diatomite is commonly used as a description of a sediment type that contains a “large” quantity of diatom frustules without a precise description of diatom abundance. Here we pose the question: What is diatomite? What quantity of diatoms define a sediment as diatomite? Is it an uncompacted sediment or a compacted sediment? We provide a short overview of prior practices and suggest that sediment with more than 50% of sediment weight comprised of diatom SiO2 and having high (>70%) porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated. Greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite, chert, and pure quartz.

Biogenic Opal Dissolution: SEM Observations of Gulf of Mexico Bottom Sediments

Siliceous biogenic remains from Gulf of Mexico bottom sediments illustrate numerous states of preservation when viewed with the scanning electron microscope (SEM). This report is a preliminary investigation of biogenic opal preservation from bottom sediment samples exclusive of the continental shelf regions from the Gulf basin. The open Gulf of Mexico is an area of low primary productivity with surface waters characterized by low silicate values generally less than 1 to 12 μg-at./l. These low values are reflected by the relatively low abundance of siliceous plankton living in the surface waters of the open Gulf. The low siliceous productivity along with the high terrigenous influx of sediment into the Gulf tends to favor dissolution of biogenic opal in the sediments.