Ichnology of the Lower Cretaceous (Albian) Mesilla Valley Formation, Cerro de Cristo Rey, southeastern New Mexico, USA Kappus, Eric J., Southwest University at El Paso, El Paso, TX, 79925,
[email protected] Lucas, Spencer G., New Mexico Museum of Natural History, Albuquerque, NM, 87104 Abstract exposed by uplift and erosion (Lovejoy, 1976). These strata Invertebrate trace fossils from the Albian Mesilla Valley represent the top of the Fredricksburg Group, and the entire Formation (Washita Group) at Cerro de Cristo Rey, Sunland Washita Group, with the Cenomanian Mancos Formation Park, NM represent the following ichnotaxa: Ancorichnus at the top (Fig. 1D). This sedimentary section represents the isp., Arenicolites isp., Bergueria isp., Bichordites sp., overall complex history of transgression and regression of Cardioichnus foradadensis, C. biloba, Chondrites intricatus, the Cretaceous Interior Seaway during the late Albian and Cochlichnus anguineus, Coprulus oblongus, Gordia marina, early Cenomanian, across the Early-Late Cretaceous bound- Helicodromites isp., Lockeia isp., Ophiomorpha nodosa, ary (Lucas et al., 2010a). Palaeophycus tubularis, P. striatus, P. heberti, Planolites isp., Part of the upper Albian succession is the Mesilla Valley Protovirgularia dichotoma, Rhizocorallium commune var. Formation, a 65 m thick, dark gray to olive-colored, finely irregulare (with Coprulus oblongus), Skolithos isp., Sponge- laminated marine shale with intercalated thin, calcareous and liomorpha isp., S. sublumbricoides, S. oraviense, Taenidium fossiliferous siltstone lenses, each ranging from 5 to 60 cm isp., Thalassinoides isp., T. paradoxicus, Treptichnus isp., thick. In their revision of the stratigraphy of this unit, Lucas et a chimney structure (Chomatichnus?), and the biofilm al. (2010a) described the thinly-bedded siltstones as bioturbated Rugalichnus (“Kinneyia”).