Ceratolithaceae biostratigraphy of ODP Hole 999A, Caribbean Sea

Abstract

Ocean Drilling Program (ODP) Hole 999A was drilling during Leg 165 and is located on a promontory nearly 1000 m above the relatively flat Colombian Plain (Caribbean Sea) at 2828 m water depth. A total of 102 smear slides were studied from this hole between 224.58 meters composite depth below seafloor (mcd) and 180.59 mcd. To determine the fine details of the nannofossil structures, 46 samples were prepared for scanning electron microscopy (SEM) using a technique of centrifugation/filtration. The focus of our work is from the lowest occurrence of Amaurolithus primus at 211.12 mcd in sample 999B-24X-1, 90 cm, to the highest occurrence of Ceratolithus atlanticus at 158.22 mcd in sample 999B-17H-6, 90 cm. Amaurolithus delicatus, which evolved from A. primus, first appears at 209.06 mcd, followed by Nicklithus amplificus, which evolved from Orthorhabdus rugosus and appears at about 204.02 mcd. At 189.41 mcd, A. primus is no longer present, and at 181.93 mcd, N. amplificus is also absent. In the latest Messinian, a new ceratolith branch evolved from O. rugosus. The first species present is Ceratolithus finifer at 165.99 mcd. This sample also contains A. delicatus, the only species left from the previous ceratolith branch. Above the first appearance of C. finifer, the following species rapidly appear: C. acutus (165.56 mcd), C.? atlanticus (161.76 mcd), C. larrymayeri and C.? tricorniculatus (both at 160.91 mcd), C. armatus (160.50 mcd), and C. cristatus (159.65 mcd). The highest occurrences of C. finifer and C.? atlanticus are at 158.22 mcd. Ceratolithus? atlanticus is abundant, and it has a short range between 5.322 and 5.173 Ma (Lancis et al., 2024). Ceratolithus? tricorniculatus is scarce in the studied samples.