Chemostratigraphic-Based Age Model for the Black Peaks Formation: Implications for Early Paleogene Paleoclimate in Sub-Tropical North America

Abstract

While many 100 thousand year time scale climate events (e.g., hyperthermals) have been thoroughly studied for the early Paleogene (66 to 48 Ma), million year time scale terrestrial paleoclimate records are lacking for this period. Such records are required to better constrain the climate dynamic of this greenhouse interval. Here, we present a new regional terrestrial paleoclimate record from sub-tropical North America which spans most of the early Paleogene. We revisit the age model for the Black Peaks Formation (Tornillo Basin, Texas), by combining new chemostratigraphic data from pedogenic carbonate nodules with existing magnetostratigraphic and biostratigraphic data. Our new age model indicates that the Black Peaks Formation spans most of the Paleocene, from ~63 to ~54 Ma without significant (superior to 1 million years) unconformities. The secular variations of the carbon isotope ratio (δ13C) from carbonate nodules correlate well with million year trends observed in the δ13C from benthic foraminifera. At million year time scale, the δ13C record displays a slow rise, culminating around 58 Ma with the Paleocene Carbon Isotope Maximum, followed by a rapid decrease towards the Early Eocene Climatic Optimum. At 100 thousand year timescale, a δ13C excursion around 61 Ma is interpreted as reflecting the late Danian event, while several δ13C excursions between 57 and 54Ma could reflect early Eocene hyperthermals. We observe a strong correlation between the carbon and oxygen isotope ratios from carbonate nodules throughout the middle Paleogene which suggests a strong coupling between regional hydrological cycle and global carbon cycle. We tentatively interpret this coupling as the expression of a correlation between the North American monsoon strength and CO₂- driven temperature fluctuations. We suggest that enhanced moisture transport during the middle Paleocene may have contributed to wet climate and elevated organic carbon burial in mid-continental environments, potentially providing a source of carbon to the high CO₂ levels of the early Eocene.

AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015