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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

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

Holger Cremer1; Oscar A. Abbink1; Linda Garming1; Elisa Guasti1; Roel Verreussel1

(1) TNO Built Environment and Geosciences, Utrecht, Netherlands.

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

However, the total BSP abundance in the single samples considerably varies. A total of 22 BSPs with significant morphological differences could be hitherto identified. BSP assemblages in the Rotliegend are currently examined to determine how they can provide information on stratigraphy. The examined BSP-based biostratigraphic approaches include first and last occurrence dates and variability in the down-core abundance patterns. If the stratigraphic importance of BSPs could be confirmed in the ongoing studies, BSPs will provide a new tool for subdividing and correlating the mostly barren Rotliegend sequences.