Organelle-sized fossils?

As we sipped bubble-tea the other night we were discussing how incredible it was to find a 550M years old single cell fossil. When we think about fossils we usually picture bones, which over time are permineralized, meaning the organic matter is replaced by minerals. Recently there has been accounts of soft body fossilization of the bone marrow. But that's still a long ways from intracellular fossilization. Even bacterial fossils are not single-cell fossils, they are usually remnant colony structures such as stomatolites of cyanobacteria or ferromagnetite deposits from magnetobacteria, or evidence of bacterial decomposition or "tunnels" (endoliths) left behind. So how can somthing like a flowing lipid-based membrane of a cell mineralize? Well it turns out the process is called diagenetic phophatization "Early diagenetic phosphatization of the remains probably occurs following shallow burial and in proximity to decomposing phosphate-rich macroaggregates. Depending on phosphate availability, the resulting phosphate layers are deposited on the outside, inside, or enveloping the acritarch organic walls from both sides...under local conditions where pH and activities of P and HCO₃- turn phosphatization on and off"