The Cretaceous System in central Sierra County, New Mexico Spencer G. Lucas, New Mexico Museum of Natural History, Albuquerque, NM 87104, [email protected] W. John Nelson, Illinois State Geological Survey, Champaign, IL 61820, [email protected] Karl Krainer, Institute of Geology, Innsbruck University, Innsbruck, A-6020 Austria, [email protected] Scott D. Elrick, Illinois State Geological Survey, Champaign, IL 61820, [email protected] Abstract (part of the Dakota Formation, Campana (Fig. 1). This is the most extensive outcrop Member of the Tres Hermanos Formation, area of Cretaceous rocks in southern New Upper Cretaceous sedimentary rocks are Flying Eagle Canyon Formation, Ash Canyon Mexico, and the exposed Cretaceous sec- Formation, and the entire McRae Group). A exposed in central Sierra County, southern tion is very thick, at about 2.5 km. First comprehensive understanding of the Cretaceous New Mexico, in the Fra Cristobal Mountains, recognized in 1860, these Cretaceous Caballo Mountains and in the topographically strata in Sierra County allows a more detailed inter- pretation of local geologic events in the context strata have been the subject of diverse, but low Cutter sag between the two ranges. The ~2.5 generally restricted, studies for more than km thick Cretaceous section is assigned to the of broad, transgressive-regressive (T-R) cycles of 150 years. (ascending order) Dakota Formation (locally deposition in the Western Interior Seaway, and includes the Oak Canyon [?] and Paguate also in terms of Laramide orogenic history: Our goal here is to present the [?] members), lower interval of the Mancos (1) T1 transgression of the seaway during first comprehensive study of the Cre- Formation (Graneros, Greenhorn, and Carlile middle-late Cenomanian time resulting taceous sedimentary rocks in central members), Tres Hermanos Formation (Atarque, in deposition of the Dakota Formation, Sierra County—their lithostratigraphy, Campana, and Fite Ranch members), D-Cross Graneros Member of the Mancos Formation and paleontology and age, sedimentary Greenhorn Member of the Mancos; (2) Turonian Member of the Mancos Formation, Gallup petrography and depositional history. Our R1 regression with deposition of the Carlile Formation, Flying Eagle Canyon Formation, study entails revisions to the Cretaceous Ash Canyon Formation, and the McRae Group, Member of the Mancos Formation and the Atarque and Campana members of the Tres lithostratigraphic nomenclature used in consisting of the José Creek, Hall Lake, and Double Sierra County and provides new precision Canyon formations. The name Tokay Tongue Hermanos Formation; (3) late Turonian T2 to correlation of parts of the section. Our of the Mancos Formation is abandoned as an transgression marked by deposition of the unnecessary term that reduces lithostratigraphic Fite Ranch Member of the Tres Hermanos analysis thus allows the Cretaceous strata precision. The new name Campana Member Formation and lower D-Cross Member of the of Sierra County to be integrated further of the Tres Hermanos Formation is proposed Mancos Formation; (4) R2 regression during late into a broader understanding of Cretaceous to replace the preoccupied (duplicate) name, Turonian-early Coniacian time, with deposition geological history in New Mexico. of the upper sandy part of the D-Cross Member, Carthage Member. The terms Mesaverde Some of the data collected in this study the Gallup Formation, and the lower part of the Formation (Group) and Crevasse Canyon are presented in appendices to this report, Flying Eagle Canyon Formation; (5) no clear Formation are no longer applied to part of the which are available as a separate, down- Cretaceous section in Sierra County. Instead, record of the T3, R3 or T4 events in Sierra County, but the Flying Eagle Canyon Formation loadable file. These data include graphic these strata are the Flying Eagle Canyon depictions of measured stratigraphic sec- Formation (new name) and redefined Ash likely encompasses the time from the last phase tions, representative photographs of thin Canyon Formation. The very thick McRae of R2 through T4 (Coniacian–Santonian); (6) Formation is raised in rank to the McRae R4 regression of early Campanian age and the sections used in petrographic analyses, Group, and its constituent members are raised onset of the Laramide orogeny, when deposition photographs of selected fossils, and a geo- to formations. The Double Canyon Formation of the Ash Canyon Formation took place; (7) logic map that shows the distribution of is a new lithostratigraphic unit comprising the the first significant influx of volcanic detritus at one of the new stratigraphic units discussed upper part of the McRae Group. Ammonite and the base of the McRae Group derived from the herein. Previous studies of the Cretaceous late Campanian-early Maastrichtian (~70–75 inoceramid bivalve biostratigraphy indicates strata in Sierra County are reviewed in the Ma) Copper Flat igneous complex; (8) onset of that the lower interval of the Mancos Formation appendices, which also include a summary is of middle Cenomanian-early Turonian age, Hall Lake Formation deposition during the late Maastrichtian (~66–68 Ma); (9) deposition of the of subsurface data in tabulated form and the Atarque Member of the Tres Hermanos a geologic cross section that incorporates Formation is early Turonian, the D-Cross bulk of the Hall Lake Formation and the Double those data. References in the main text to Member of the Mancos Formation is middle Canyon Formation, possibly extending into the Turonian, and the Gallup Formation is late Paleocene; and (10), the Love Ranch Formation items in the appendix are preceded with Turonian. Vertebrate biostratigraphy indicates of likely Eocene age representing the final pulse the letter “A” (e.g., Table A2.1). that the lower part of the Hall Lake Formation is of the Laramide orogeny in Sierra County. Lancian (late Maastrichtian) in age. Depositional Study area, methods, environments of the Cretaceous strata in Sierra Introduction abbreviations, and conventions County are both marine and nonmarine. They range from offshore marine (lower interval and Cretaceous sedimentary rocks are exposed The Cretaceous strata of central Sierra D-Cross Member of the Mancos Formation), County are exposed from the northern tip to shoreline deposition of various types (part in central Sierra County, southern New of the Dakota Formation, the Atarque and Mexico, in and around parts of the of the Fra Cristobal Mountains (just into Fite Ranch members of the Tres Hermanos Fra Cristobal and Caballo Mountains, as Socorro County) to the northern Caballo Formation, and the Gallup Formation), to non- well as in the lowlands between the two Mountains and its eastern periphery (Fig. marine fluvial channel and floodplain deposits mountain ranges, the structural Cutter sag 1). These strata extend eastward under Spring 2019, Volume 41, Number 1 3 New Mexico Geology the Jornada del Muerto basin and west- ward under the Rio Grande rift. Place Tv QTs names used in the text are those on the Tv K relevant United States Geological Sur- Qb vey topographic quadrangle maps. The 33°30´N Qs horizontal datum for coordinates reported Socorro Sierra X herein is NAD83 (UTM meters, zone 13). P The research reported here is based primarily on fieldwork undertaken during Tv 2013–2017, though some paleontological X data were collected as early as the 1980s. Tv This fieldwork was largely part of an effort SOC QTs to map the geology of the Fra Cristobal 33°24´N P QTs Mountains. Understanding the Creta- Qs ceous strata exposed in the Fra Cristobals Tv Fra Cristobal Mtns. QTs necessitated fieldwork to better under- Tv stand the Cretaceous strata exposed to the south, in the Cutter sag and in the northern Elephant Butte Tv Caballo Mountains. Data and interpreta- Reservoir P Qs Tv tions from oil-test boreholes—archived 33°18´N at the New Mexico Bureau of Geology and Mineral Resources (NMBGMR) 142 (Socorro)—were examined in order to QTs obtain additional estimates of thicknesses of some of the Cretaceous units in the Tv area, and are summarized herein. Data collection included: mapping 51 P Tim in the Fra Cristobal Mountains and the 33°12´N Pa area immediately to the south and south- SOC K Tv west of the range; measuring numerous D J o r n a d a d e l M u e r t o stratigraphic sections using a 1.5 m OC Tv X staff and Brunton pocket transit (Fig. T or C Tv 2); collecting numerous rock samples for petrographic analysis; and collecting QTs Tv Tv invertebrate and vertebrate fossils, primar- K Qs ily for biostratigraphic analysis. All fossils 33°06´N collected are part of the collection of the X New Mexico Museum of Natural History QTs and Science (NMMNH) in Albuquerque 25 Tim and bear NMMNH locality and catalog Pa numbers. Lithofacies codes assigned to QTs nonmarine sediments (e.g., Gt, St, etc.) are P Py K 10 km from Miall (1996, 2010). In petrographic 33°00´N Caballo analysis, sandstone composition was Qs Quaternary sediments Caballo Reservoir determined microscopically by identifying Qb Quaternary basalt Qs QTs Mtns. the different grain types at 250 equally X QTs Tertiary - Quaternary sediments spaced points across each thin section Tv TertiaryTv volcanics analyzed (Tucker, 1988), using thin section SOC K K Cretaceous P Pa QTs Py Permian (Yeso Group, San Andres Fm.) photographs and the program JMicro- Pa Permian (Abo Formation) Vision. In the petrographic analysis, Q D P Permian Tv PIP Permian and Pennsylvanian, undivided includes monocrystalline, polycrystalline, 32°54´N QTs and microcrystalline quartz, and chert. IP Pennslyvanian Qs X D Devonian Py Sandstones were classified using the scheme QTs SOC Cambrian - Ordovician - Silurian proposed by Pettijohn et al. (1987). Tv OC Cambrian - Ordovician N P X Proterozoic crystalline rocks As a convention in the lithostrati- PP Tv Tv graphic nomenclature used here, all units QTs P Tim Tertiary dikes Major faults are referred to as a group, formation, or 107°20´W 107°10´W 107°00´W member.