Comparison of Miocene fossil floras in lacustrine deposits: Implications for palaeoclimatic interpretations at the middle latitudes of the Pacific rim

Abstract

The Early Neogene Shanwang lacustrine deposit in eastern China is similar to the Clarkia deposit of northern Idaho, U.S.A., in age, sedimentary environment, and fossil preservation. Both lake deposits contain well-preserved non-marine fossil biotas, and both are especially rich in plant remains. The two floras shared a high percentage of common genera, and both showed similar taxonomic diversity and habit. The two Miocene floras are comparable to the present-day mixed mesophytic forests of the Yangtze River (Changjiang) Valley of China. Paleoclimatic comparisons are based on plant fossils for the most part, supplemented by information from other fossil groups and from sedimentological data. Evidence from (i) taxonomic associations (both plant and animal), (ii) foliar physiognomy, (iii) taphonomic characteristics, and (iv) sedimentologic data indicate that in the Early Neogene, the two areas experienced similar climatic conditions. The Clarkia area was slightly warmer and more humid compared to a more seasonal climatic regime in the Shanwang area- even though Clarkia was at about 10 degree higher latitude. Our results support the previous hypothesis that paleoclimate in Early to Middle Miocene time was more equable compared to the present day. Our data further suggest that at similar latitudes floras in western North America represent warmer climatic conditions than their Asian counterparts. The comparative study further suggests that the accuracy of paleoclimatic interpretations can be improved by utilizing large fossil floras of taxonomic diversity from similar environments, and by integrating evidence from other fossil groups and sedimentological records.