Abstract: Palynoforaminifera (Foraminiferal Organic Linings and Allied Material): a New Tool for Petroleum Exploration

Arai, Mitsuru and Eduardo A. M. Koutsoukos - Petrobras/Cenpes

Palynoforaminifera have been reported for a long time from palynological preparations. The term is currently used to designate foraminiferal remains which commonly appear in palynological smear-slides. Besides the organic linings of foraminiferal tests, which are their main components, this group also includes foraminiferal internal molds and casts of solid bitumen. Palynoforaminifera are often abundant in palynological samples, but have been largely ignored or little-utilized, though some authors have emphasized their potential applications in biostratigraphy and paleoecology.

Recent palynological analyses of Brazilian marine strata reveal the importance of palynoforaminifera, as follows: (1) at certain strata, their occurrence is usually more regular and easier to be detected than that of calcareous foraminifera; (2) they are readily recoverable even from strongly indurated/cemented sedimentary rocks; (3) they contribute to improve the characterization of palynological assemblages; (4) they likely represent particular environmental settings within the marine realm; (5) they may be present even under incipient marine conditions; (6) in some marine sequences, they may outnumber dinoflagellates and terrestrial palynomorphs (pollen grains and spores).

In the Vraconian (Lower Cretaceous: uppermost Albian) of the Campos basin (offshore southeast Brazil), the frequency ratio between terrestrial palynomorphs (spores and pollen grains), palynoforaminifera and dinocysts has proven to be very useful in characterizing various petroleum reservoir units and associated rocks. The integrated approach provides detailed biostratigraphic data applied to high-resolution stratigraphic surveys. For example, the so-called Namorado Sandstone is related to only one formal biozone, but the frequency ratio fluctuations allow the identification of at least four reservoir unit groups (Fig. 1).

Because some palynoforaminiferal morphotypes closely resemble those of known calcareous foraminifera, the establishment of parental relationship between certain palynoforaminifera and actual foraminiferal genera and/or species is possible, resulting in further enhancement of their biostratigraphic and paleoecological applications. Furthermore some relationships established in this study confirm the long-suspected presence of organic linings in planktonic foraminiferal tests.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil