Timing and Correlation of Early Paleocene Asian Land Mammal Ages: New Results from the Nanxiong Basin, Gaungdong Province, China

Paleomagnetic and isotopic results from a ~1200 meter thick stratigraphic section in the Nanxiong Basin (Guangdong Province, China) provide temporal constraints on Asian vertebrate evolution from the late Cretaceous through the early Paleocene. The Nanxiong Basin is an extensional basin containing thick deposits of lacustrine and fluvial red beds. Four formations are recognized - the Upper Cretaceous Nanxiong Formation and the overlying Paleocene Shanghu, Nongshan, and Guchengcun Formations. Fossil mammals have been recovered from more than 50 localities throughout the Paleocene units in this basin preserving one of the best stratigraphic records of the Shanghuan and Nongshanian Asian land mammal ages. Fourteen fossil localities are directly correlated to our section, however the Shanghu-Nongshan Formation contact is obscured by a ~350 meter covered interval. Paleomagnetic analysis of 101 sites (287 samples) indicates several clearly defined polarity zones. Stable carbon isotope values of authigenic carbonates range from -3.69‰ to -13.47‰ and exhibit high frequency stratigraphic variations superimposed on a longer term minimum near the K/T boundary and a secular increase of >2‰ in the upper half of the section. Correlation of this magnetochemostratigraphic pattern to the global timescale suggests that the section ranges from Chron C30n to C26r. Placement of the K/T boundary has been controversial, however it is traditionally recognized by the last occurrence of dinosaur egg shell fragments and this falls within a reverse polarity zone we interpret as C29r, coincident with K/T boundary sites elsewhere. These new data are consistent with prior results from the Chijiang Basin (Jiangxi Province) that indicate the Shanghuan-Nongshanian ALMA boundary correlates closely with the Chron C27n-C26r transition and the Torrejonian-Tiffanian North American Land Mammal Age boundary. The uppermost Guchengcun Formation seems to fall entirely within Chron C26r suggesting that the latest Paleocene is not preserved in superposition in this section.