span a timespan encompassing the Eocene (56 – 33.9 million years ago) to the Quaternary (last 2.58 million years) with gaps in the sediment sequence between the Cretaceous and the Eocene and between the Eocene and the Oligocene (33.9 – 23.03 million years ago). During the Eocene and Oligocene, older foraminifera were redeposited; there is evidence that sediments were actively eroded. During Tertiary phases of low sea level, sea currents swept sediments off the surface of Horizon Guyot, with fine sediments being particularly affected. Present state The top and almost all the upper slopes of Horizon Guyot are covered by sediments. Chert and chalk are found within the sediments; chert forms seismically reflective layers within the sediment cap. These layers crop out at the margin of the sediment platform. The seamount lies in a region of the Pacific with nutrient poor surface waters. Sea currents are unusually strong on the top of Horizon Guyot, probably due to the interaction of the slopes of Horizon Guyot with tidal currents. The seamount induces its own semidiurnal tide and the sea currents reach their maximum at the margin of the summit platform where have been measured. Scour marks have been observed. The currents sweep down the seamount slopes and may act to remove sediment from the seamount surface; this also results in sediments accumulating to form steep slopes that undergo landsliding. Most of the sediments however are transported upslope; those which do end up at the bottom of the seamount form talus deposits around Horizon Guyot. Ecology The surfaces of Horizon Guyot are inhabited by many organisms. Fish found on Horizon Guyot include batfish, bathypteroids, chimeras, morids, sharks and synaphobranchid eels. Brittle stars, chaetognatha (arrow worms), copepods, corals, crustaceans, hydroids, loricifera, molluscs, nematodes, nemertinea, ophiuroids, ostracods, polychaetes, sipuncula, squat lobsters, vermes and xenophyophorans make up the bulk of the fauna on Horizon Guyot today. At least 29 macrofaunal species have been found. Other lifeforms presently active on the seamount are barnacles, crinoids, echiurids, enteropneusts (acorn worms), gorgonians, holothuroids (sea cucumbers), pennatulids (sea pens), sponges and starfish. Unidentified stalk or twig-like creatures have also been observed on the platform, which are among the most common lifeforms there. Bacteria are also found in the sediment. Biological activity has left traces in the sediments such as mounds, pits, and trails on the surface. There is a certain zonation in the ecology of Horizon Guyot; for example