New Mexico

Spring, 2018 GEOLOGY Volume 40, Number 1

New Mexico Bureau of Geology and Mineral Resources/A Division of New Mexico Tech Spring, 2018 Volume 40, Number 1 New Mexico A publication of the New Mexico Bureau of Geology and Mineral Resources, GEOLOGY a division of the New Mexico Institute of Mining and Technology Science and Service Baculites (Ammonoidea) and the age of the Pierre Shale in the ISSN 0196-948X eastern Raton Basin, south-central Colorado New Mexico Bureau of Geology and Mineral Resources Director and State Geologist Keith Berry 1–5 Dr. Nelia W. Dunbar

Geologic Editor: Bruce Allen Revised basin geometry for the Bursum Formation (upper Layout and Production Editor: Richard Arthur Virgilian—lower Wolfcampian), central New Mexico Managing Editor: Gina D'Ambrosio

Steven M. Cather 6–16 Cartography & Graphics: Leo Gabaldon

Reassessment of features in the lava flows, Doña Ana EDITORIAL BOARD Dan Koning, NMBGMR County, New Mexico Barry S. Kues, UNM René A. De Hon and Richard A. Earl 17–26 Jennifer Lindline, NMHU Gary S. Morgan, NMMNHS New Mexico graduate student abstracts 27–33 New Mexico Institute of Mining and Technology President Dr. Stephen G. Wells BOARD OF REGENTS Ex-Officio Susana Martinez Governor of New Mexico Dr. Barbara Damron Secretary of Higher Education Appointed Deborah Peacock President, 2017–2022, Corrales Jerry A. Armijo Secretary/Treasurer, 2015–2020, Socorro

David Gonzales 2015–2020, Farmington Donald Monette 2015–2018, Socorro Emily Silva, student member 2017–2018, Farmington

New Mexico Geology is an online publication available as a free PDF download from the New Mexico Bureau of Geology and Mineral Resources website. Subscribe to receive e-mail notices when each issue is available at: geoinfo. nmt.edu/publications/subscribe. Editorial Matter: Articles submitted for publication should follow the guidelines at: . Address inquiries to Bruce Allen, Geologic Editor, New Mexico The Aden shield and crater rim, located 40 km southwest of Las Cruces, New Mexico, lies within Bureau of Geology and Mineral Resources, 801 the Organ Mountains-Desert Peaks National Monument administered by the Bureau of Land Leroy Place, Socorro, NM 87801. For telephone Management. Aden is situated along the northeastern side of the Potrillo , which inquiries call (575) 835-5177 or use the email covers 1,000 square kilometers and is represented by numerous eruptive centers and associated address given below. lava fields that were active during the Late Quaternary. The lava flows at Aden resulted from the extrusion of relatively low-viscosity basaltic magmas that spread passively across the landscape Email: [email protected] similar to present-day eruptions on Hawaii. Successive eruptions created a with a geoinfo.nmt.edu/publications/periodicals/nmg well-preserved, central crater. Aden Crater exhibits a rugged, circular rim consisting of solidified spatter, and contained a molten lake of lava when the volcano was last active. Volcanic features of the Potrillo Volcanic Field also include , including the extensively studied , which result when rising magma encounters groundwater, resulting in a violent eruption of steam, country rock, and magma into the atmosphere. Description and interpretation of features of the Aden field are discussed in the paper beginning on page 17 of this issue.Photograph and caption courtesy of René De Hon.