Asian Land Mammal Ages

The Asian Land-Mammal Ages (ALMAs) are the most recently named and the most tentative. Several schemes have been proposed over the past two decades or so. The sequence used here follows that of McKenna and Bell (1997), which stems principally from Li and Ting (1983) and Russell and Zhai (1987), although a few of the ages were initially named by Romer (1966). Important modifications were made by Tong et al. (1995) and Ting (1998). A comparison of these reports reveals that there is still no consensus regarding the appropriate name for some of the ALMAs. With a few exceptions, the Asian land-mammal sequence is poorly constrained geochronologically, and the sequence has been based largely on stage of evolution. Therefore further revisions and refinements are to be expected.

There is general agreement that the Shanghuan ALMA is early Paleocene and the Nongshanian ALMA is late Paleo-cene. Wang et al. (1998), however, suggested that the Nong-shanian may overlap with the late early Paleocene, partly based on the first K-Ar date (61.63 ± 0.92 Ma) from the Paleocene of China. Ting (1998) resurrected the Gashatan ALMA, named by Romer (1966), for latest Paleocene faunas that appear to be correlative with the Clarkforkian NALMA. Several names have been used for the first Eocene land-mammal age in Asia, including Ulanbulakian (Romer, 1966) and Lingchan (Li and Ting, 1983; Tong et al., 1995), but Bumbanian, proposed by Russell and Zhai (1987), is now generally accepted. The position of the Paleocene/Eocene boundary relative to the Gashatan and Bumbanian ALMAs has been controversial. However, the discovery that the CIE (and thus the Paleocene/Eocene boundary) is situated between Gashatan and Bumbanian faunas in the Lingcha Formation of China indicates that, at least in that section, Gashatan is entirely late Paleocene and Bumbanian is early Eocene (Bowen et al., 2002). The issue is not fully resolved, however, because it has been suggested that certain other Bumbanian faunas could be older than that of the Lingcha Formation.

Eocene ALMAs following the Bumbanian are very poorly constrained. There is general agreement that three ages can be recognized during the middle Eocene—Arshantan, Irdin-manhan, and Sharamurunian—but their boundaries are very uncertain. The Ergilian ALMA was proposed by Russell and Zhai (1987) as the earliest Oligocene ALMA, but it is now correlated with the late Eocene Priabonian and Chadronian. Consequently, the Shandgolian (Russell and Zhai's middle Oligocene ALMA, equivalent to Ulangochuian of Li and Ting, 1983) is early Oligocene and corresponds to the Rupelian and Orellan Land-Mammal Ages.

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