Shi et al.—Depauperate fusulinid faunas of the Tengchong block


(Lee, 1931). It ranges up to the Guadalupian Maokou Formation (Zhang et al., 1988). Schwagerina pseudocompacta occurs widely in theMaokou Formation in South China (Fan et al., 2013). These elements altogether suggest aWordian–Capitanian age. In 2008, we documented two other fusulinid faunas from the


northern Tengchong Block, the early Permian Eoparafusulina fauna fromthe Kongshuhe area and the middle Permian Caiyuanzi fauna from the Shanmutang area (Shi et al., 2008). The Eoparafusulina fauna includes four species belonging to Eoparafusulina, Parafusulina,and Monodiexodina,and the Chusenella-Monodiexodina (Caiyuanzi) fauna is composed of six species in five genera, including Pseudofusulina, Eoparafusulina, and Parafusulina besides the eponymous genera. The Caiyuanzi fauna is dominated by Chusenella mingguangensis and Monodiexodina gigas Shietal.,2008. The common dominant element in the three middle Permian


faunas of the Tengchong Block is Chusenella,and thespecies discovered, i.e., C. riagouensis, C. mingguangensis, C.cf. minuta, are all small ormedium in size. Chusenella is widely distributed in southern Europe, North America, Japan, South China, and Central and Southeast Asia, but more than two-thirds of the species are medium to large in size, which means over 6mm in test length. Most Chusenella species from the Tengchong Block are less than 5mm in length, and even the largest species, Chusenella mingguangensis, is only around 6mmlong. The small Chusenella species are also significant in the Lhasa Block, and those reported from the Xainza area are hardly over 4mmin length (Huang et al., 2007; Zhang et al., 2010; Zhang et al., 2013).


Discussion


Depauperate faunas and paleoenvironmental inference.—The common feature for all four faunas of the Tengchong Block is low generic and specific diversity with abundant specimens. Although fusulinid individuals discovered in all four locations were plentiful, no more than five genera and six species have been recovered in any given fauna, and nearly half the individuals of each fauna belong to the predominant species. Modern examples of depauperate foraminiferal assem-


blages are diagnostic of inhospitable environments. For example, Amphistegina lobifera Larsen, 1976 is a larger benthic foraminiferal species with a tolerance for low winter temperatures and mixotrophic feeding strategy. It is found in the Mediterranean and dominates the benthic foraminiferal assemblages there (Triantaphyllou et al., 2012). Androsina lucasi Lévy, 1977 thrives in open, dwarf-mangrove flats areas in exceptional abundance, owing to its euryhaline adaptation (Hallock and Peebles, 1993). The Frierfjord of Norway was heavily polluted by waste products for centuries and contains anoxic deep bottom water. An opportunistic species, Stain- forthia fusiformis (Williamson, 1858) thrives at > 50m water depth in this area with a large number of individuals (Alve,


1994). These species have developed the ability to survive and flourish in stressful environments. Similarly, the depauperate fusulinids of the Tengchong Block very likely suggest a somewhat inhospitable shallow sea for fusulinids during the early and middle Permian. Most fusulinids favored open shallow marine environ- ments with warm and clear water (Ross, 1995), probably or


19


Tengchong Block, it is difficult to discern the relationship between carbonate facies and fusulinids during that time. By contrast, middle Permian carbonates containing depauperate faunas include a variety of sedimentary facies (Fig. 5). One is skeletal grainstone in the Shuangheyan and Caiyuanzi areas, indicating high-energy open shallow marine environments (Fig. 5.5, 5.6). Within this facies, carbonate grains are usually moderately sorted and rounded. Skeletal grains are diverse with fusulinids, bryozoans, echinoderms, smaller foraminifera, green algae, etc., and fusulinid tests are more or less abraded. In the Shuangheyan area, the grainstone shows two distinct generations of spar cementation. It is also noteworthy that Monodiexodina in the Caiyuanzi area is particularly confined towell-sorted and rounded grainstone with mostly fine-grained bioclasts. This special facies type suggests a littoralmarine setting with high water energy. The second facies is poorly sorted and rounded skeletal packstone with fusulinids, smaller foraminifera, bryozoans, and intraclasts in the Shuanghe- yan and Caiyuanzi areas (Fig. 5.1, 5.2). The matrix was originally micritic, but it has undergone neomorphism to become pseudospar. These characteristics indicate open shallow platformwith moderate water agitation. It is interesting to note that fusulinids are broken and infilledwith blackmicrite in the packstone of the Shuangheyan area. This probably indicates that fusulinids experienced a certain degree of transportation or turbulence. Another facies type is partially dolomitized wackestone in the Shuangheyan and Xishancun areas (Fig. 5.3, 5.4). Chusenella and Nankinella/ Staffella are characteristically dominant, and algae are abundant in this facies, whereas other fusulinid taxa and other fossil groups are rather impoverished. In the Xishancun section, the micritic matrix of this facies shows a clotted structure. A more restricted platform with stagnant water could well generate such wackestones. These varied carbonate facies reflect various hydrodynamic


partly due to the likelihood that photosymbionts within them required sunlight (Vachard et al., 2004; Groves et al., 2012). Accordingly, the inhospitable environmental factors for fusulinids likely include low temperature and specific carbonate facies related with hydrodynamics, depth, and sunlight. Since there is only one early Permian fusulinid fauna from the


conditions inhabited by the depauperate faunas and suggest water turbulence is not responsible for the low diversities. The development of green algae in these faunas denotes adequate sunlight in these shallow marine environments. As a result, the probable controlling factor of these impoverished faunas could be unfavorable temperature. Therefore, we infer that Permian depauperate fusulinids in the Tengchong Block probably inhabited seas with relatively cool temperate temperatures.


The Gondwana-affinity feature and paleogeographic discussion.—We compiled all the fusulinid data hitherto documented from theTengchong Block in order to fully understand the fusulinid composition and their paleogeographic indications. There are several reports of Permian fusulinids from the Tengchong Block prior to 2008, although without illustrations or descriptions (Geological Survey of Yunnan, 1985, 1986; Fan, 1993; Nie et al., 1993). According to our recent study, specimens previously reported as Hemifusulina fromtheKongshuhe area (Fan, 1993; Nie et al., 1993) should be assigned to Eoparafusulina (Shi et al., 2008). All other reported fusulinid genera from the block are valid and considered in the following discussion.


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