2019 AAPG Annual Convention and Exhibition:

Datapages, Inc.Print this page

Generating Well-Constrained Chronostratigraphic Age Models: Case Study From the Late Paleocene Through Middle Eocene When Major Carbon Cycle Changes Took Place


0 false 18 pt 18 pt 0 0 false false false /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0in; line-height:107%; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} The process of generating well-constrained chronostratigraphic age models is never straightforward, regardless of the stratigraphic interval or the time interval of interest. Integrating multiple age constraints (i.e. carbon cycling records, biostratigraphy, and magnetostratigraphy) enables well-constrained age models to be built, such as during well-documented intervals of earth history. A detailed characterization of the late Paleocene through middle Eocene, an interval when major environmental change and multiple climatic perturbations took place, provides the ideal backdrop to carry out such an assessment. Here we extend and increase the resolution of previous lithologic and carbon isotope records from the Mead Stream section, located in Marlborough, New Zealand to place all these events into an integrated chronostratigraphic age model. This was done to better understand late Paleocene through middle Eocene carbon cycle changes. New data presented at this time complements previous work at this locality and at the nearby Branch Stream and at other localities in the Pacific Ocean such as Site 1209 (Westerhold et al., 2018), such that detailed records now extend from 58 to 38 Ma. Once placed into a well-resolved chronostratigraphic age model, it becomes clear the long-term drop in δ13C from 58-52 Ma was followed by a long-term rise in δ13C and related lithological changes. Numerous geologically-brief (<0.2 Myr) but relatively minor (<1.0‰) carbon isotope excursions (CIEs) occur through this interval, although it is not clear if many of them are hyperthermals. Particularly low carbonate contents span late early Eocene strata, an indication that the flux of carbonate to the seafloor decreased, either because of lower surface water carbonate production or extreme shoaling of the lysocline. This record now provides a single-site carbon isotope template and related lithological changes from late Paleocene through middle to early late Eocene placed into a common timeframe.