Late Eocene to middle Miocene (33 to 13 million years ago) vegetation and climate development on the North American Atlantic Coastal Plain (IODP Expedition 313, Site M0027)

摘要

We investigated the palynology of sediment cores from Site M0027 ofIODP (Integrated Ocean Drilling Program)Expedition 313 on the New Jersey shallow shelf to examine vegetation andclimate dynamics on the east coast of North America between 33 and 13 millionyears ago and to assess the impact of over-regional climate events on theregion. Palynological results are complemented with pollen-based quantitativeclimate reconstructions. Our results indicate that the hinterland vegetationof the New Jersey shelf was characterized by oak–hickory forests in thelowlands and conifer-dominated vegetation in the highlands from the earlyOligocene to the middle Miocene. The Oligocene witnessed several expansionsof conifer forest, probably related to cooling events. The pollen-basedclimate data imply an increase in annual temperatures from∼11.5 °C to more than 16 °C during the Oligocene.The Mi-1 cooling event at the onset of the Miocene is reflected by anexpansion of conifers and mean annual temperature decrease of∼4 °C, from ∼16 °C to ∼12 °Caround 23 million years before present. Relatively low annual temperaturesare also recorded for several samples during an interval around ∼20million years before present, which may reflect the Mi-1a and the Mi-1aacooling events. Generally, the Miocene ecosystem and climate conditions werevery similar to those of the Oligocene. Miocene grasslands, as known fromother areas in the USA during that time period, are not evident for thehinterland of the New Jersey shelf, possibly reflecting moisture from theproto-Gulf Stream.The palaeovegetation data reveal stable conditions during the mid-Mioceneclimatic optimum at ∼15 million years before present, with only aminor increase in deciduous–evergreen mixed forest taxa and a decrease inswamp forest taxa. Pollen-based annual temperature reconstructions showaverage annual temperatures of ∼14 °C during the mid-Mioceneclimatic optimum, ∼2 °C higher than today, but∼1.5 °C lower than preceding and following phases of theMiocene. We conclude that vegetation and regional climate in the hinterlandof the New Jersey shelf did not react as sensitively to Oligocene and Mioceneclimate changes as other regions in North America or Europe due to themoderating effects of the North Atlantic. An additional explanation for therelatively low regional temperatures reconstructed for the mid-Mioceneclimatic optimum could be an uplift of the Appalachian Mountains during theMiocene, which would also have influenced the catchment area of our pollenrecord.