PRELIMINARY INVESTIGATION OF A DIVERSE LOWER CRETACEOUS INSECT FAUNA FROM ABDRANT NURU, ULAN NUUR BASIN, GOBI DESERT, MONGOLIA

Abundant arthropod and plant impressions were discovered in unnamed Lower Cretaceous rocks found at Abdrant Nuru, in the Uvor Khangai Aimag of Mongolia. Here, a fossiliferous Lower Cretaceous lacustrine and paper shale sequence is unconformably overlain by dinosaur-bearing fluvial red beds of Upper Cretaceous age. Many intracratonic lakes are known to have been present in Asia during the late Jurassic and early Cretaceous. Two distinct fossil bearing horizons were collected from the lacustrine sequence at Abdrant Nuru. Six quarries were sampled from the marly, paper shale lithology and two localities were collected from a concretion horizon in a shale.

Preliminary paleomagnetic results from the 160m section indicate that the sequence is normal, most probably deposited in C34n (Cretaceous Long Normal). Sixteen pollen samples were analyzed and productive samples include pollen of gymnosperms and spores of ferns. Although angiosperm megafossils were found, no angiosperm pollen was present, which indicates that the sediments are older than late Albian. If the Lower Cretaceous sediments from Abdrant Nuru are pre-Albian in age and lie within C34n, then they were deposited at some time between 112 and 118 Ma.

A diverse insect fauna of both terrestrial and aquatic species is preserved as partial and entire compressions and impressions. We have currently identified 19 morphotypes. Although diversity and abundance vary significantly in each quarry, Coleopterans are most abundant overall. Preliminary identifications include: 2 morphotypes of vermiform Diptera larvae, one with vertically articulated mouthparts assigned to Tabanus in the Tabinidae; vermiform-type larvae with three pair of legs, Notonectidae (backswimmer); 11 morphotypes of Coleoptera, 2 assigned to the basal Archostemmata; Blattodea (roach), 1 body impression, 2 wing impressions; Hemiptera; one unassigned female body impression with ovipostior; and one wing of unknown affinity. The two most abundant morphotypes in each quarry are the Tabanus and a type related to Ditisids or Hydrophyllids in the order Coleoptera. Cuticle is commonly preserved in these specimens and it may be possible to analyze the gut contents of these beetles, greatly contributing to the study of plant-insect interaction and the evolution of insects in the early Cretaceous of Asia.