NEOGENE DEEP SEA HIATUSES: 33+ YEARS OF OBSERVATION

In 1983 Gerta Keller and John Barron published a paper in the GSA Bulletin documenting and mapping the spatial extent seven widespread Neogene hiatuses in deep-sea sediments. Combined microfossil biostratigraphy (planktic foraminifers, calcareous nannofossils, diatoms, and radiolarians) allowed recognition of these hiatuses in deep-sea cores. Depending on their location on the sea floor, these hiatuses were attributed to erosion by bottom currents, drastically reduced biogenic sedimentation rates, and/or tectonic events. Larry Mayer and colleagues during DSDP Leg 85 recognized that in the central equatorial Pacific most of these Neogene hiatus (NH) intervals coincided with seismic reflectors located within biogenic sediments, presumably reflecting intervals of calcium carbonate dissolution and reduced biogenic sedimentation rates. Subsequent coring by ODP Legs 138 and 199 and IODP 320/321, utilizing advanced coring methods, high-resolution correlation of physical properties of multiple cores, and refined paleomagnetic stratigraphy, leading to a significant refinement of our knowledge of Neogene biogenic sedimentation in the central equatorial Pacific (CEP). A reevaluation of these NH events suggests that they likely represent periods when the geographic expression [spatial extent] of biogenic sedimentation in the CEP became more focused across the Equator resulting in a steeper cross-equatorial productivity gradient and restriction in the geographic extent of calcium carbonate deposition. In most cases, this focusing of productivity coincided with abrupt cooling events as recognized by the benthic foraminiferal oxygen isotopes curve. Updated age estimates of these NH events and their possible correlation to paleoceanographic events include: NH1 (17.2-16.7 Ma; carbonate dissolution at onset of Monterey Climate Optimum), NH2 (~16.2-15.6 Ma; slightly younger carbonate dissolution), NH3 (~13.2-12.8 Ma, abrupt cooling), NH4 (10.5-9.8 Ma; the Miocene carbonate crash), NH5 (~8.6-8.0 Ma; onset of the late Miocene biogenic bloom), NH 6 (7.1-6.6; late Miocene carbon shift), and NH 7 (5.2-4.7 Ma; end of the biogenic bloom). Many of these events correspond to lithologic transitions within the Monterey Formation of California, attesting to their broader paleoceanographic significance.