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A Paleogene calcareous microfossil Konservat-Lagerstätte from the Kilwa Group of coastal Tanzania

P.R. Bown^,1, T. Dunkley Jones¹, J.A. Lees¹, R.D. Randell¹, J.A. Mizzi¹, P.N. Pearson², H.K. Coxall², J.R. Young³, C.J. Nicholas⁴, A. Karega⁵, J. Singano⁵ and B.S. Wade⁶

¹ Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, England, UK
² School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, Wales, UK
³ Department of Palaeontology, The Natural History Museum, London SW7 5BD, England, UK
⁴ Department of Geology, Trinity College, Dublin 2, Ireland
⁵ Tanzania Petroleum Development Corporation, PO Box 2774, Dar-es-Salaam, Tanzania
⁶ Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843-3115, USA

View larger version (24K): [in this window] [in a new window]   Figure 1. (A) Stratigraphic extent of the TDP boreholes. Nannofossil zonation (NP Nf. Zones) from Martini (1971) and planktonic foraminifer zonation (PF Zones) from Berggren and Pearson (2005). Correlation of the two plankton zonation schemes and time scale are from the latter. (B) Location of the Kilwa Group in coastal Tanzania. Detailed location is given in Nicholas et al. (2006).

View larger version (73K): [in this window] [in a new window]   Figure 2. Paleogene Kilwa Group foraminifera and nannofossils exhibiting aspects of the exceptional preservational quality. Scale bars for foraminifera are 100 µm (A, B, and E) and 10 µm (C and D) and for nannofossil images are 1 µm (F–K). (A–D) Specimens of Subbotina velascoensis from Site TDP 7A (early Eocene), (A) in reflected light, showing the glassy appearance and lack of any carbonate infilling or overgrowth. (C–D) High-resolution scanning electron micrographs, showing microgranular textures (early Eocene, Sample TDP7A/64-1, 50–65 cm). (E) Tubulogenerina sp., a previously undescribed benthic foraminifera species from Site TDP 12 (late Eocene, Sample TDP12/16-3, 43–51 cm) exhibiting exquisite preservation of the ornate test wall. (F) Chiasmolithus bidens (late Paleocene, Sample TDP16B/12-2, 9 cm) with a proximal perforate plate. A minute (1-µm), undescribed, Calciosolenia coccolith (diamond-shaped) lies on the upper-right shield surface. (G) Semihololithus biscayae (late Paleocene, Sample TDP14/9-1, 20 cm) with pristine holococcolith preservation and unfilled cavate structure. (H) Campylosphaera dela (late Paleocene, Sample TDP16B/12-2, 9 cm). (I) Coccosphere of an undescribed placolith coccolith species (late Paleocene, Sample TDP14/9-1, 20 cm) with fragile, central-area grills. (J) Ellipsolithus andoluensis (late Paleocene, Sample TDP16B/12-2, 9 cm), not previously seen in SEM and showing exquisite preservation of a perforate grill. (K) Braarudosphaera bigelowii (late Paleocene, Sample TDP14/9-1, 20 cm) coccosphere showing laminated ultrastructure.

View larger version (112K): [in this window] [in a new window]   Figure 3. Calcareous nannofossil images from the Paleogene Kilwa Group. Scale bars are 1 µm. (A–D) Gladiolithus flabellatus. These images (A, C, and D) are the first pre-Quaternary records of this extant, deep–photic-zone coccolithophore. A modern coccosphere (B) is provided for comparison. (A) Collapsed coccosphere comprising long tube-coccoliths and basal-disc lepidoliths (late Eocene, Sample TDP12/26-2, 62 cm). (B) Modern coccosphere from Hawaiian Ocean Time series (HOTS) station. (C and D) Collapsed Gladiolithus coccospheres (late Paleocene, Sample TDP16B/12-2, 9 cm). (E) Minuscule (<1 µm), undescribed, cup-like coccoliths with tall, hollow spines (late Eocene, Sample TDP12/23-2, 79 cm). (F) Syracosphaera sp. (late Eocene, Sample TDP12/26-2, 62 cm). (G) Clathrolithus ellipticus holococcolith (late Paleocene, Sample TDP16B/12-2, 9 cm). (H) Zygrhablithus bijugatus holococcolith (late Paleocene, Sample TDP16B/12-2, 9 cm). (I–L) Collapsed coccospheres. (I) Cruciplacolithus inseadus, a species only previously known from the Danian but found in all our SEM samples (late Paleocene, Sample TDP16B/12-2, 9 cm). (J) Neochiastozygus imbriei grouping, most likely a collapsed coccosphere, but displays significant morphological variation between coccoliths, with significant implications for species-level taxonomy (late Paleocene, Sample TDP14/9-1, 20 cm). (K) Calciosolenia brasiliensis displaying morphological variation between coccoliths identical to that seen in modern examples (e.g., Young et al., 2003) (middle Eocene, Sample TDP20/23-1, 40 cm). (L) Undescribed, very small (<2 µm) coccolith species (late Paleocene, Sample TDP16B/12-2, 9 cm). (M) Coccolithus pelagicus with previously undescribed, gracile central-area cross bars (late Paleocene, Sample TDP16B/12-2, 9 cm). (N) Blackites deflandrei (middle Eocene, Sample TDP13/20-1, 50 cm). (O) Blackites morionum showing an intricately constructed, hollow spine and dissolution-susceptible rim architecture (late Paleocene, Sample TDP16B/12-2, 9 cm). (P) Undescribed placolith coccolith with a fragile, central-area grill (late Paleocene, Sample TDP16B/12-2, 9 cm).

View larger version (19K): [in this window] [in a new window]   Figure 4. Comparative nannofossil diversity (species richness) data for the Paleogene interval. The values represent all nannofossil species, excluding holococcoliths, recorded within each nannofossil zone on the Gradstein et al. (2004) time scale. The aggregate global diversity data are from Bown et al. (2004), and deep-sea data are from Bralower (2005—Site 1209, Shatsky Rise, NW Pacific) and Bralower and Mutterlose (1995—Hole 865B, Allison Guyot, Central Pacific).

View larger version (24K): [in this window] [in a new window]   Figure 5. Size-frequency histograms for (A) Paleogene coccoliths from the Kilwa Group, and (B) modern coccolith species, as observed in the plankton and Holocene fossil record. The data are an estimate of maximum coccolith size and for the Paleogene were based on measurements chosen from many thousands of light micrographs. The modern data are from Young et al. (2005) and are based on measured light-micrograph and published images.