2. MIOCENE RADIOLARIAN BIOSTRATIGRAPHY OF THE DÉCOLLEMENT ZONE (NORTHERN BARBADOS RIDGE)1

Torsten Steiger 2

ABSTRACT

The décollement zone of the Lesser Antilles Volcanic Arc, drilled during Ocean Drilling Program Leg 156, contains soft radiolarian-bearing clayey lithologies. In the upper part of this zone, radiolarians are abundant; in the lower part, they are rare. Radiolarian preservation ranges from excellent (Hole 949B) to moderate and highly recrystallized (Hole 948C). The radiolarian faunas are of early Miocene age. The assemblages could be attributed to early early Miocene radiolarian zones (Lychnocanoma elongata Zone and Cyrtocapsella tetrapera Zone) and late early Miocene zones (Stichocorys delmontensis Zone, Stichocorys wolffii Zone, and Calocycletta costata Zone). In the lithologic column the radiolarian zones are separated by hiatuses associated with color changes, breccia horizons, and shear zones that are represented by intervals with rich scaly fabric. Occasional reworking of Miocene through late Eocene radiolarians can be observed. At the top and in the middle of the décollement, radiolarians are diagenetically recrystallized. In these zones, abundance and diversity is strongly reduced. Diagenetically stable forms are orosperids ("fat rad zone") and large nassellarians like Cyclampterium and Calocycletta.

1 Shipley, T.H., Ogawa, Y., Blum, P., and Bahr, J.M. (Eds.), 1997. Proc. ODP, Sci. Results,156: College Station, TX (Ocean Drilling Program).
2 Grafrather Straße 53a, 82288 Kottgeisering, Federal Republic of Germany. 100425.1104@compuserve. com