Aptian to Turonian radiolaria from the Darvel Bay Ophiolite Complex, Kunak, Sabah

The Darvel Bay Ophiolite Complex is located in Kunak District, southeast Sabah. The predominant rocks in the study area are peridotite, serpentinite, gabbro, basalt, pillow basalt and reddish-brown chert. The aim of the research is to establish the age and environment of deposition of radiolarian chert. Eighteen chert samples were collected from two new outcrops along the Kunak-Semporna road. Fifty six species of radiolarians were indentified and 40 species are used for age determinations. The radiolarians are divided into three assemblages. Assemblage I (Aptian to Albian) is characterized by the occurrence of Sticomitra simplex, Crucella bossoensis, Xitus clava, Dictyomitra communis, Hiscocapsa asseni, Obeliscoites vinassai, Rhopalosyringium fossile, Paronaella grapevinensis, Stichomitra communis, Xitus spicularius, Phangalites perpicuus, Triactoma cellulosa and Becus horridus. Assemblage II (Albian to Cenomanian) consists of Xitus mclaughlini, Pseudoaulophacus sculptus, Dictyomitra gracilis, Torculum coronatum, Dictyomitra montisserei, Pogonias prodomus, Pessagnobrachia fabianii, Sciadiocapsa speciosa, Crucella messinae, Dictyomitra obesa, Pseudodictyomitra languida, Tuguriella pagoda, Dictyomitra formosa, Acaeniotyle rebellis, Pseudoaulophacus putahensis, Quadrigastrum oculus, Pseudodictyomitra tiara, Diacanthocapsa euganea, Patellula helios and Stichomitra stocki which represents Albian to Cenomanian. Assemblage III (Turonian) is composed of Pseudotheocampe tina, Ultranapora cretacea, Alievium superbum, Dictyomitra multicostata and Patellula ecliptica. The index fossil of Assemblage III is Crucella cachensis. The fossil assemblages show the age of radiolarian chert ranges from Aptian to Turonian, Cretaceous. The bedded chert which associates with mafic and ultramafic rocks represents a part of an ophiolite sequence. The bedded chert contains abundance of radiolarians, which reflects a high planktonic productivity probably related to upwelling of nutrient rich waters caused by the submarine volcanism activity. The absence limestone in the bedded chert, indicates that the radiolarians were deposited below the Calcite Compensation Depth level