oa New Siliceous Microfossils in Permo-Carboniferous Rocks: Extraction, Origin, Application

Late Carboniferous to Middle Permian rocks resting on the Base Permian Unconformity in the<br>Netherlands are of great economic significance. The Rotliegend rock sequences contain the most<br>important gas reservoirs of the Netherlands, the Slochteren sanstones. However, the Rotliegend<br>reservoir rocks are typically barren of any fossils, including palynomophs, which hampers stratigraphic<br>control and correlation of these rocks. In a recent attempt of re-evaluation the barrenness of the<br>Rotliegend, siliceous microfossils, referred to as biogenic silica particles (BSPs), in considerable<br>morphological diversity could be extracted from these rocks. We applied a three-step approach to<br>prepare BSP-containing microscopic slides from Rotliegend samples: (1) pre-flotation treatments<br>aiming at the removal of large particles, organic matter, carbonate and clay, (2) repeated flotation<br>steps in order to extract and concentrate BSPs, and (3) slide preparation using Naphrax™ as mounting<br>medium. Many of the newly discovered siliceous microfossils resemble plant stones, so-called<br>phytoliths, tiny silica bodies of various shape and size that are incorporated as structural elements in<br>the roots, stems, and leafs of modern plants. Major plant groups like the gymnosperms, lycopods and<br>ferns existed already by the end of the Devonian which might imply that these early land plants have<br>also formed phytoliths in their tissues. The here reported BSPs constitute only the second evidence of<br>phytolith-like siliceous microfossils from the Paleozoic. The newly extracted microfossils may provide a<br>tool for subdividing and correlating Rotliegend rock successions. In order to test this hypothesis, Permo<br>-Carboniferous rocks from various wells in the Netherlands were studied. Biogenic silica particles<br>(BSPs) could be extracted from all studied wells and lithostratigraphic units.<br>However, the total BSP abundance in the single samples considerably varies. A total of 22 BSPs with<br>significant morphological differences could be hitherto identified. BSP assemblages in the Rotliegend<br>are currently examined to determine how they can provide information on stratigraphy. The examined<br>BSP-based biostratigraphic approaches include first and last occurrence dates and variability in the<br>down-core abundance patterns. If the stratigraphic importance of BSPs could be confirmed in the<br>ongoing studies, BSPs will provide a new tool for subdividing and correlating the mostly barren<br>Rotliegend sequences.