THE BIOSTRATIGRAPHY AND TAXONOMY OF MESOZOIC RADIOLARIA FROM THE SAMAIL OPHIOLITE AND HAWASINA COMPLEX, OMAN

This dissertation is based on the study of samples collected from radiolarian cherts and mudstones from the Hawasina Complex and Samail Ophiolite of Oman. Radiolarian biostratigraphic data confirms the hypothesis that rocks exposed in the Oman Mountains were deposited in a Mesozoic ocean basin and later tectonically emplaced in a vertical stratigraphic sequence. Radiolaria extracted from mudstones interbedded with the pillow lavas at the top of the Samail Ophiolite were Late Cretaceous (Cenomanian) in age, indicating a Cenomanian age of origin for the Ophiolite. Samples from the Haliw Formation of the Hawasina Complex were Triassic in age. No older pelagic sediments were found. These Haliw sediments, together with a Late Triassic horizon at the base of the Halfa Formation, overlie basalts and may represent deep-water sedimentation early in the basin's history. The longest sections of radiolarian chert and mudstone were deposited during another period of regional deepening and pelagic sedimentation during the Late Jurassic and Early Cretaceous. These cherts form most of the Halfa Formation. None of the siliceous samples collected were early to middle Jurassic in age, suggesting a hiatus in pelagic sedimentation during this time interval.; Detailed taxonomic studies were made at 2 localities. In the northern Oman Mountains 12 samples were collected from a measured section 55 m thick overlying pillow basalts of the Samail Ophiolite. The faunas extracted from these samples ranged in age from early Cenomanian to Coniacian. One hundred sixty-six species are figured, and 17 new genera and 56 new species are described. In the southern Oman Mountains, 114 samples were collected from a measured section 481 m thick near the type locality of the Halfa Formation. The faunas extracted from these samples ranged in age from Late Jurassic (Kimmeridgian/Tithonian) to Early Cretaceous (Hauterivian?Barremian). One hundred fourteen species are figured, and 3 new genera and 24 new species are described. The family Pseudodictyomitridae is well-represented in both parts of the Cretaceous section. It is reviewed and the genus Pseudodictyomitra is emended to include only those species like the type species. Twenty-eight species are figured, 3 new genera are created and 15 new species are described.