Late Cretaceous ostracod fauna from the Shenjiatun section (Songliao Basin, Northeast China): Biostratigraphic and palaeoecological implications

Ostracoda from the Santonian–Campanian (Upper Cretaceous) Nenjiang and Sifangtai formations, Songliao Basin, northeastern China

“…The lithologic record of the Songliao Basin mainly comprises fine clastic rocks intercalated with oil shales (Ye et al, 2002). In the Songliao Basin, the Upper Cretaceous strata have been subdivided into six formations, from older to younger: Quantou (K 2 q), Qingshankou (K 2 qn), Yaojia (K 2 y), Nenjiang (K 2 n), Sifangtai (K 2 s), and Mingshui (K 2 m) (e.g., Ye et al, 2002; Wan et al, 2013; C. Wang et al, 2013; Wang et al, 2017; Xi et al, 2019). The Cretaceous biota in the Songliao Basin includes ostracodes, spores and pollen, dinoflagellates, charophytes, spinicaudatans, gastropods, bivalves, fish, and dinosaurs (Gao et al, 1994; Huang et al, 1998; Ye et al, 2002; Xi et al, 2012, 2016; Wan et al, 2013).…”

“…Member 2 is composed of grayish to black mudstones interbedded with black shales near its top and oil shales at the bottom; these shales are an important element of stratigraphic correlation in the whole basin as they indicate maximum-flooding surfaces (Ye et al, 2002; Feng et al, 2012; Xi et al, 2012). Members 3–5 (not observable in the ZKY2-1 well) consist of grayish to black mudstones, gray argillaceous siltstones, and brownish-red mudstones and sandstones (Ye et al, 2002; Wang et al, 2011; Wang et al, 2017).…”

“…Ostracodes are small crustaceans with a calcified bivalved carapace that are easily preserved as fossils. The record of the group extends back to the Ordovician, which coupled with their abundant fossil record ecology and dispersal mechanisms makes them good index fossils for biostratigraphy (Meisch, 2000; Horne, 2002, 2009; Sames, 2011a, b, d; Sames and Horne, 2012; Xi et al, 2012; Wang et al, 2016, 2017; Do Carmo et al, 2018). Cretaceous limnic ostracodes have been widely studied worldwide (e.g., Anderson, 1941, 1985; Netchaeva et al, 1959; Horne, 1995, 2002, 2009; Hou et al, 2002; Ye et al, 2002; Hayashi, 2006; Whatley and Bajpai, 2006; Khand et al, 2007; Do Carmo et al, 2008, 2013; Sames, 2008, 2011a, b; Antonietto et al, 2012; Poropat and Colin, 2012a, b; Sames and Horne, 2012; Ayress and Whatley, 2014; Tomé et al, 2014; Choi et al, 2017).…”

“…Ostracode fossils are very abundant in Upper Cretaceous strata of the Songliao and provide unique materials to study Late Cretaceous limnic ostracode faunas (Ye et al, 2002; Xi et al, 2012; Qu et al, 2014). An extensive taxonomic analysis of the ostracodes from the Songliao Basin has been conducted in the past 60 years, with plenty of species described (Netchaeva et al, 1959; Hao et al, 1974; DOFEAD, 1976; Hou et al, 2002; Ye et al, 2002; Zhang et al, 2007; Qu et al, 2014; Wang et al, 2017). More recent works, however, suggest diversity and endemicity in the Songliao (and other Chinese basins) has been overestimated (Khand et al, 2007; Horne, 2009; Schudack and Schudack, 2009; Sames, 2011a, b; Y. Wang et al, 2013, 2016; Qin et al, 2018).…”

“…This can be attributed to a myriad of mishandlings by previous authors, including: (1) descriptions, diagnoses, and illustrations frequently ambiguous; (2) ontogeny and potential sexual dimorphism of species often ignored; and/or (3) information from previous literature wrongly reproduced on remarks about these taxa. Furthermore, most research efforts in the Songliao have focused on central and northern portions of the basin (e.g., Zhang et al, 2007; Xi et al, 2012; Qu et al, 2014; Qin et al, 2015; Wang et al, 2017).…”