Global change at the Paleocene-Eocene boundary: climatic and evolutionary consequences of tectonic events

Abstract

Rea, D. K., Zachos, J. C., Owen, R. M. and Gingerich, P. D., 1990. Global change at the Paleocene-Eocene boundary:climatic and evolutionary consequences of tectonic events. Palaeogeogr., Palaeoclimatol., Palaeoecol., 79: 117-128.Events of the Paleocene-Eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences. Recent advances permit well-constrained stratigraphic determination of several events that occurred at that boundary, in chron C24R: a many-fold increase in sea-floor hydrothermal activity, a global warming, a reduction in the intensity of atmospheric circulation, a conversion to salinity-driven deep ocean circulation, a marked lightening of oceanic 313C values, extinction and evolution of both benthic foraminifera and land mammals, and important plate-boundary reorganizations including the outpouring of the east Greenland volcanics and the initiation of the oceanic rift between Norway and Greenland.We hypothesize that enhanced sea-floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with COz, causing a reduced pole-to-equator temperature gradient and increased evaporation at low latitudes. Increased formation of warm, salty, probably low-nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity-driven, rather than temperature-driven, deep-water circulation. This newly-evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean, with concomitant changes in the circulation intensity of both. Reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents. A major extinction event among benthic foraminifera was probably a response to the new low-nutrient and chemically changed bottom waters, and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime.

Plant and mammal diversity in the Paleocene to early Eocene of the Bighorn Basin

“…The Paleocene/Eocene boundary interval increasingly is being recognized as an interval of rapid change in global ocean circulation and global climatic conditions (Rea et al, 1990;Kennett and Stott, 1991;Koch et al, 1992;Pak and Miller, 1992;Gibson et al, 1993). Oxygen isotope records from planktonic and benthic foraminifera at many DSDP sites indicate a strong warming trend beginning in the latest Paleocene and continuing into the latter part of the early Eocene (Shackleton et al, 1984;Miller et al, 1987).…”

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

“…The BajocianBathonian initiation of Atlantic seafloor spreading is coincident with the birth of the Pacific Plate. These plate tectonic reorganizations are often reflected in oceanic sedimentation; for example, the widespread Paleocene-Eocene plate reorganization at 57 Ma (chron C24R) coincides with a burst of metalliferous (hydrothermal) flux and decrease of eolian flux into Pacific sediments (Olivarez and Owen, 1989;Rea et al, 1990). In addition, major volcanic episodes, such as in the early Aptian, had global impacts through increased levels of atmospheric carbon dioxide, increased dissolution of carbonate in the oceans, climatic warming and slowing of atmosphericocean circulation, and increased organic-matter preservation Arthur et al, 1985).…”

“…data, 1992). Episodes of Pacific Plate reorganization during the Tertiary resulted in an increased hydrothermal activity and a corresponding pulse of higher mass accumulation rates of Fe and Mn into sediments at considerable distances from the active ridges (Leinen and Stakes, 1979;Owen and Rea, 1985;Olivarez and Owen, 1989;Rea et al, 1990). …”

“…The input of FeMn-oxides to oceanic sediments depends on distance from the ridge and spreading rates, but also displays pulses corresponding to episodes of plate reorganization (Leinen and Stakes, 1979;Owen and Rea, 1985;Olivarez and Owen, 1989;Rea et al, 1990). It would be expected that pelagic sediments deposited during such tectonic episodes may have elevated levels of FeMn-oxide and of Fe-smectite clays.…”

Introduction to Leg 145: North Pacific Transect

“…Prior work in the North Pacific has shown the presence of the Ir anomaly associated with the Cretaceous/Tertiary boundary (Kyte and Wasson, 1986) and the influx of hydrothermal components associated with the earliest Eocene plate-boundary rearrangements (Owen and Rea, 1985;Leinen, 1987Leinen, , 1989Rea et al, 1990). Drilling during Leg 145 was expected to recover all these signals, along with the geochemical signal associated with the plate boundary reorganization that occurred during the Late Cretaceous magnetic quiet zone.…”