The Geology of Ukhaa Tolgod (Djadokhta Formation, Upper Cretaceous, Nemegt Basin, Mongolia)

Abstract

The lithostratigrahy and sedimentology of the fossiliferous Upper Cretaceous strata exposed in the Gobi Desert of Mongolia at Ukhaa Tolgod are described and mapped on aerial photos. Topographic features are also mapped by plane table and alidade.Five lithologic and sedimentologic facies are described: E-1, distinctly cross-stratified sandstone with fine structure, interpreted to represent eolian dune deposits; E-2, vaguely bedded sandstone with cross-stratified concretionary sheets, interpreted to represent eolian dune deposits modified by diagenetic formation of slope-parallel concretionary sheets of pedogenic calcite; S, structureless sandstone lacking concretions or cross-strata, interpreted to represent sandslide deposits generated by mass wasting along the lee slopes; C, conglomerate interpreted to represent basin-margin conglomerates washed into the dune field from adjacent topographic highs; and M, mudstone and siltstone interpreted to represent interdune deposition in ephemeral ponds and lakes. Facies E-2 and S have not been reported previously. Eleven stratigraphic sections at various localities within the Ukhaa Tolgod drainage basin are documented. The exposed composite section consists of about 75 m of pale orange sandstones, greenish-brown conglomerates, and brown siltstones that are products of an arid environment. Four schematic cross sections are documented to illustrate the lateral relationships among the five facies.

Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

“…The embryonic remains of P. andrewsi (1.8-m adult total length; Ceratopsia: Protoceratopsidae) derive from a nest composed of 12 eggs discovered in Campanian sediments of the Upper Cretaceous Djadochta Formation from the Gobi Desert of Mongolia by American Museum of Natural History-Mongolian Academy of Sciences expeditions (86) (Fig. 2A).…”

Dinosaur morphological diversity and the end-Cretaceous extinction

“…In the three-bin approach, if taxa were known from the first and third time bin, then they were also assumed to be present in the intervening time bin. The Djadokhta Formation is here considered to be late Campanian in age and the overlying Nemegt Maastrichtian, following the latest work on Asian Late Cretaceous stratigraphy 49,50 . There is some uncertainty regarding whether the Nemegt is entirely Maastrichtian or if its base may be late Campanian in age.…”

Craniodental anatomy of a new late cretaceous multituberculate mammal from Udan Sayr, Mongolia.

“…The recent American-Mongolian expeditions (1990 to the present) have followed that tradition and results have been plentiful, including the discovery of one of the richest Mesozoic localities in the world, Ukhaa Tolgod (Norell et al, , 2001(Norell et al, , 2006Novacek et al, 1994;Dashzeveg et al, 1995Dashzeveg et al, , 2005Rougier et al, 1996aRougier et al, , 1998Gao and Hou, 1996;Chiappe et al, 1998;Norell, 1998, 2000;Makovicky and Norell, 1998;Horovitz, 2000;Wible and Rougier, 2000;Clarke et al, 2001;Clarke and Norell, 2002;Makovicky et al, 2003;Ksepka and Norell, 2004;Norell and Hwang, 2004;Pol and Norell, 2004;Andres and Norell, 2005;Joyce and Norell, 2005;Dingus et al, 2008;Minjin, 2008). The Cretaceous localities of Mongolia, especially those of the Djadochta and similarly aged Barun Goyot Formations (Shuvalov, 2000;Jerzykiewicz, 2000), are exceptionally rich in well-preserved small vertebrates when compared to those in other parts of the world.…”

“…Tombaatar from Ukhaa Tolgod, a locality which is likely to be a Djadochta nearequivalent (Loope et al, 1998;Dingus et al, 2008). Obviously the faunas from (Webster, 1996).…”

“…Similarly, in Mangasbaatar the middle ear cavity is surrounded only partially by bone and most of its ventral surface must have been enclosed by membrane; therefore it is hard to accept the same degree of stiffness in multituberculates than, for example, in desert dwelling rodents with large middle ear spaces enclosed by a bulla (Webster, 1966;Fleischer, 1973;Mason 2006Mason , 2013. Nevertheless, many of these recent mammals with large middle ear spaces (Mason, 2004;Mason, 2013) spend a substantial portion of their lives underground; the environmental conditions in Ukhaa Tolgod and most of the Late Cretaceous Mongolian sites seem to indicate that the environment was dominated by sands and some degree of periodical or seasonal aridity (Loope, 1998;Dingus et al, 2008). In this context, an enlarged, more rigidly enclosed middle ear region would be consistent with an optimization for the perception of low frequency sound by increasing the non-pliable surfaces surrounding the middle ear.…”