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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Earth and Atmospheric Sciences, Department Papers in the Earth and Atmospheric Sciences of 2005 New Stratigraphic Subdivision, Depositional Environment, and Age Estimate for the Upper Cretaceous Djadokhta Formation, Southern Ulan Nur Basin, Mongolia Demberelyin Dashzeveg Geological Institute of the Mongolian Academy of Sciences, [email protected] Lowell Dingus American Museum of Natural History, [email protected] David B. Loope University of Nebraska, Lincoln, [email protected] Carl C. Swisher III Rutgers University Togtokh Dulam Mongolian Geological Survey See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons Dashzeveg, Demberelyin; Dingus, Lowell; Loope, David B.; Swisher, Carl C. III; Dulam, Togtokh; and Sweeney, Mark R., "New Stratigraphic Subdivision, Depositional Environment, and Age Estimate for the Upper Cretaceous Djadokhta Formation, Southern Ulan Nur Basin, Mongolia" (2005). Papers in the Earth and Atmospheric Sciences. 209. https://digitalcommons.unl.edu/geosciencefacpub/209 This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Demberelyin Dashzeveg, Lowell Dingus, David B. Loope, Carl C. Swisher III, Togtokh Dulam, and Mark R. Sweeney This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/ geosciencefacpub/209 PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3498, 31 pp., 14 ®gures, 3 maps, 2 tables November 29, 2005 New Stratigraphic Subdivision, Depositional Environment, and Age Estimate for the Upper Cretaceous Djadokhta Formation, Southern Ulan Nur Basin, Mongolia DEMBERELYIN DASHZEVEG,1 LOWELL DINGUS,2 DAVID B. LOOPE,3 CARL C. SWISHER III,4 TOGTOKH DULAM,5 AND MARK R. SWEENEY6 ABSTRACT Studies of key and newly discovered sections of the Upper Cretaceous Djadokhta Formation along the southern margin of the Ulan Nur Basin allow a new subdivision based on lithology. The formation and its members were mapped at both Bayn Dzak, an area that includes the Flaming Cliffs, and Tugrugyin Shireh, an area about 50 km to the northwest of Bayn Dzak. Stratigraphic sections at both localities were remeasured. The considerably enlarged formation comprises a lower Bayn Dzak Member, dominated by moderate reddish orange sands with subordinate mudstone units, and an upper Tugrugyin Member, composed of pale orange to light gray sands. Investigations of key sections at Tsonzh and Alag Teer demonstrate the presence of transitional mudstone lenses between these members within the Djadokhta For- mation. Two distinct, sandy, sedimentologic facies are recognized in both members. Cross- bedded intervals, occasionally exhibiting wind-ripple cross lamination, document the presence 1 The Geological Institute of the Mongolian Academy of Sciences, Peace Street 63, Ulaanbaatar-51, Mongolia ([email protected]). 2 Division of Paleontology, American Museum of Natural History ([email protected]). 3 Department of Geosciences, University of Nebraska, Lincoln, Nebraska 68588-0340 ([email protected]). 4 Department of Geology, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854 ([email protected]). 5 Mineral Resources Authority of Mongolia, Mongolian Geological Survey, ``Gurvan Talst'' Company Ltd., Ulaan- baatar, Mongolia. 6 Desert Research Institute, University of Nevada, 2215 Raggio Parkway, Reno, NV 89512 ([email protected]). Copyright q American Museum of Natural History 2005 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3498 of a Cretaceous dune®eld in the Ulan Nur Basin. Structureless intervals are interpreted to represent wet sandy ¯uvial deposits and debris ¯ows that moved down the dune faces. In the Bayn Dzak Member, lenses of brownish mudstone are interpreted to represent interdune de- position in shallow ponds by ¯uvial action. Fluvial action is also represented in the Bayn Dzak Member by beds of caliche, which contain conglomerate at the base but ®ne upward into limestone. The vertebrate fauna from the Djadokhta Formation is summarized. Although the Bayn Dzak fauna lived somewhat earlier than that from Tugrugyin Shireh based on the superposition of the members, it is not clear how much earlier. The fauna from the Djadokhta Formation has previously been assigned ages from Cenomanian to earliest Maastrichtian. New magne- tostratigraphic data document a sequence of normal and reversed magnetozones through the Bayn Dzak Member up into the basal Tugrugyin Member. The presence of reversed magne- tozones establishes that the sediments containing the faunas were probably deposited after C34n. The quick stratigraphic succession of normal and reversed magnetozones suggests, but does not clearly establish, that the sediments may have been deposited during the rapid se- quence of polarity changes in the late part of the Campanian between about 75 to 71 Ma. INTRODUCTION imen were discussed by MaryanÂska (1971), in a paper not associated with the MPE. In 1922±1923 and 1925 the Central Asi- In 1963±1971 the Polish±Mongolian Pa- atic Expedition (CAE) of the American Mu- leontological Expedition (PMPE) searched seum of Natural History worked in the Ulan for Cretaceous mammals and dinosaurs at Nur (5 Ulaan Nuur of Benton, 2000) Basin Bayn Dzak. The main result was the discov- (Berkey and Morris, 1927; Andrews, 1932; ery of abundant fossils of multituberculates, Morris, 1936). Bayn Dzak (5 Bayan Zag of eutherian and deltatheroidan mammals in the Benton, 2000) was the main locality to be locality's concretionary sandstones (Kielan- studied by the CAE under the name of Sha- Jaworowska, 1969, 1970; Kielan-Jaworow- barakh Usu (5 Flaming Cliffs). There, ska and Dovchin, 1969; Kielan-Jaworowska Americans found dinosaur eggs and nests, and Barsbold, 1972), as well as numerous Cretaceous mammals, complete skeletons of lizards (see Alifanov, 2000, for review), and Protoceratops, and three forms of theropod a peculiar long-necked crocodile (OsmoÂlska, dinosaurs, including Velociraptor, Saurorni- 1972). thoides, and Oviraptor (Osborn, 1924). Ber- In 1971 a spectacular specimen termed the key and Morris ®rst referred the recognized ``®ghting dinosaurs'' was found by PMPE at Djadokhta Formation to the Lower Creta- Tugrugyin Shireh (5 ToÈgroÈgiin Shiree of ceous and then to the lower part of the Upper Benton, 2000). These articulated and asso- Cretaceous. GradzinÂski et al. (1977) provided ciated skeletons of Velociraptor and Proto- the lists of fossils known at that time from ceratops are discussed by Kielan-Jaworow- the Djadokhta, younger Barun Goyot (5 Ba- ska and Barsbold (1972) and OsmoÂlska ruungoyot of Benton, 2000), and Nemegt (1993). Another interesting ®nding of the Formations, and estimated the age of the PMPE at Tugrugyin Shireh was skeletons of Djadokhta Formation as ?upper Santonian Protoceratops andrewsi preserved in a ver- and/or ?lower Campanian. tical position (Jerzykiewicz et al., 1993). In 1946 the Bayn Dzak locality was rein- In 1969±1970 the joint Soviet±Mongolian vestigated by the Mongolian Paleontological Paleontological Expedition (SMPE) found Expedition (MPE) of the Academy of Scienc- skeletons of Protoceratops andrewsi and es of the USSR, which was headed by Efre- other fossils at Tugrugyin Shireh about 50 mov (1949, 1954). The investigations yielded km northwest of Bayn Dzak. Other results of less signi®cant results, including a complete both the SMPE and its successor, the Rus- postcranial skeleton of the armored dinosaur sian±Mongolian Expeditions are reviewed by Pinacosaurus grangeri Gilmore (5 Syr- Kurochkin and Barsbold (2000). mosaurus viminicaudus) (Maleev 1952, From 1992 to the present, the Japan±Mon- 1954). Additional results regarding this spec- golia Joint Paleontological Expedition 2005 DASHZEVEG ET AL.: STRATIGRAPHY OF DJADOKHTA FORMATION 3 (JMJPE) has conducted extensive ®eld sea- its in adjacent regions. The Djadokhta For- sons throughout the Gobi Desert. A recent mation was initially considered to consist account of their activities at both Bayn Dzak only of reddish orange sandstones at Bayn and Tugrugyin Shireh is presented by Ishii et Dzak. This understanding of its stratigraphic al. (2000, 2004). extent and lithologic composition held until In 1991 the Mongolian Academy of Sci- recently. Discussions of earlier geologic ence±American Museum of Natural History studies in the region include GradzinÂski et al. Expedition (MAE) began ®eld investigations (1969, 1977); Kielan-Jaworowska and Dov- based on the Agreement on Scienti®c Co- chin (1969); GradzinÂski (1970); GradzinÂski operation between those two institutions. In and Jerzykiewicz (1972); Kielan-Jaworows- 1991±1992, 1994±1996, and 1998 the MAE ka and Barsbold (1972); GradzinÂski and Jer- visited Bayn Dzak and Tugrugyin Shireh. zykiewicz (1974); OsmoÂlska (1980); Jerzyk- Signi®cant remains of multituberculates and iewicz and Russell (1991); Jerzykiewicz et placental mammals were collected. Many al. (1993); Kielan-Jaworowska et al. (2003); specimens in these collections are now being Benton et al. (2000) and chapters therein, in- studied. The MAE investigated