Geologic Origin of the Source of Bearhead Rhyolite (Paliza Canyon) Obsidian, Jemez Mountains, Northern New Mexico M

Geologic origin of the source of Bearhead Rhyolite (Paliza Canyon) obsidian, Jemez Mountains, Northern New Mexico M. Steven Shackley1,* Fraser Goff2, Sean G. Dolan3 1Geoarchaeological XRF Laboratory, Albuquerque, New Mexico, and Department of Anthropology, University of New Mexico, Albuquerque 87171, [email protected] 2Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque 87171 3Los Alamos National Laboratory, Los Alamos, NM 87545 *Corresponding author: [email protected] Abstract Nelson 1987). It is important to note that these samples Recent field and analytical studies of what has been were from late Quaternary, valley bottom alluvium and traditionally called “Paliza Canyon obsidian” in the thus geologically reworked. The goal of our study was to archaeological vernacular show it to be Bearhead locate the primary geologic source of these samples. Rhyolite that is part of the Late Tertiary (Neogene) The original “Paliza Canyon” source was characterized Keres Group of the Jemez Mountains, northern New as a small-nodule Neogene source, based on the age Mexico. The geological origin of all other archae- of adjacent volcanic rocks and small nodule sizes (as ological obsidian sources in the Jemez Mountains opposed to large nodule Quaternary sources, such as have been reported and are well documented in Valles Rhyolite obsidian). The small nodule sizes likely the literature. But the so-called “Paliza Canyon” reflect hydration and perlitization of volcanic glass over source, important as a toolstone to Pueblo Revolt relatively long periods of geologic time. Known Neogene Colonial period occupants of the Jemez Mountains area and present in regional archaeological contexts and Quaternary sources of archaeological obsidian in the throughout prehistory, had remained unlocated and Jemez Mountains have been well dated and chemically, undocumented. The Bearhead Rhyolite origin for the stratigraphically, and isotopically studied for a number “Paliza Canyon” obsidian (which we suggest should of years. The geologic context of the “Paliza Canyon” now be named “Bearhead Rhyolite”) solves this obsidian has been more difficult to decipher because of ambiguity and provides more precise geological and complexities in its geochemistry and geologic setting geographical data for archaeological obsidian source (compounded by its relatively old age), especially when provenance in the region. compared with most other Jemez Mountains sources (Gardner et al., 1986; Self et al., 1986; Spell and Harrison Introduction 1993; Ellisor et al., 1996; Goff et al., 1996; Kues et al., 2007; Kelley et al., 2013). An important type of obsidian used by Native Americans, Relatively recent geologic mapping and sampling traditionally called the “Paliza Canyon” obsidian efforts in the southern Jemez Mountains, combined (Nelson 1984; Baugh & Nelson 1987; Wolfman 1994; with XRF analyses of several samples, indicate that Glascock et al., 1999; Shackley 2005), is widespread in the primary source for the “Paliza Canyon obsidian” the archaeological record in New Mexico. Church (2000) is only a few kilometers north of the original proposed and Shackley (2012a) have both reported the presence source area. After providing a geologic background, we of Paliza Canyon obsidian in Rio Grande Quaternary use geochemical data to compare the “Paliza Canyon alluvium as far south as Las Cruces, New Mexico. It also obsidian” with possible primary geologic sources in the occurs commonly in Pueblo Revolt period archaeological area. We argue that the best candidate for a primary sites (late 17th century) in the southern Jemez Mountains source is a geologic unit called the Bearhead Rhyolite. To of northern New Mexico, including near Jemez Springs be consistent with our interpretations, in the rest of the (Fig. 1; Liebmann 2012; Shackley 2009a, 2012b). Using paper we refer to the archeological artifacts previously x-ray fluorescence spectrometric (XRF) analyses, these called “Paliza Canyon obsidian” as the Bearhead archaeological samples have been chemically correlated Rhyolite obsidian. to a “Paliza Canyon” geologic source defined in the Baugh and Nelson (1987) study. XRF is the preferred method for chemically characterizing archaeological obsidian because Geologic background of study area it is relatively inexpensive and can be accomplished non- Our study area (Figs. 1, 2) encompasses both our new destructively (Shackley 2005, 2011). Determining the sampling localities and the Paliza Canyon sampling area eruptive location of this unique archaeological obsidian of Nelson (1984) and Baugh and Nelson (1987). In this is crucial for understanding exchange, migration, and area, obsidian occurs in three types of geologic units (Fig. social networks during the Pueblo Revolt period (A.D. 2): 1) surficial, relatively weakly consolidated tephra, 2) 1680–1692), as well as all prehistoric through Colonial in valley-bottom alluvium, and 3) volcanic bedrock. In periods in New Mexico (Liebmann 2012; Shackley 2005). the study area, most surficial tephra is petrographically The original four samples of “Paliza Canyon” obsidian similar to what is now called the El Cajete Pyroclastic Beds were collected in a portion of Paliza Canyon, a drainage of the East Fork Member of Valles Rhyolite (Gardner et located in the southern Jemez Mountains (Figs. 1–2, near al., 2010; Goff et al., 2011), which we simply refer to as our sample locality 100915-2; Nelson 1984; Baugh and El Cajete pumice, whose age is interpreted as 74.7±1.3 ka 52 New Mexico Geology August 2016, Volume 38, Number 3 106°37.5' 106°30' LA 123 4 FR36 LA 541 4 SR 4 Unnamed Bearhead Rhyolite dome (F04-31) LA 481 Study Area (Fig. 2) Jemez Springs 4 100915-2 35° 45' Paliza LA 132/133 Canyon 091115-2 090413-2 Ruiz Peak 4 SR 290 090413-3/091115-1 0 1 2 3 4 5 mi 0 1 2 3 4 5 km Figure 1. Orthophoto over digital elevation model. Study area depicted by polygon. Labels show approximate location of collection localities (i.e. 090413–2, 100915-2, etc.), geographic features, USGS quadrangle borders (in light gray), and Pueblo Revolt archaeological sites (LA numbers) near our study area (Liebmann 2012; Shackley 2009a, 2012b). Our precise collection localities are shown in Figure 2. Abbreviations: SR = state highway; FR = Santa Fe National Forest route. (Zimmerer et al., 2016). However, in places the El (Lajčáková and Kraus 1993).” An 40Ar/39Ar age of 7.62 Cajete pumice is so thin that underlying tephras from ± 0.44 Ma was obtained from an obsidian marekanite older volcanic bedrock locally crop out at the surface, sample from this dome (Fig. 3; Goff et al., 2006; Kelley as discussed below. Geologically reworked obsidian et al., 2013). Other Bearhead Rhyolite domes and flows is abundant in late Quaternary alluvium filling Paliza in the vicinity yield ages ranging between 6.0 and 7.2 Ma Canyon proper, near the boundary of the Redondo Peak (Justet 1996; Kempter et al., 2004). and Bear Springs Peak Quadrangles (Fig. 2). The “Paliza In contrast to the felsic Bearhead Rhyolite, the Canyon” obsidian sampled by Baugh and Nelson in the volcanic domes and flows in the Paliza Canyon Formation 1980s very likely came from late Quaternary, valley- are all mafic to intermediate composition (Ellisor et bottom alluvium at this locality (Baugh and Nelson 1987; al., 1996; Goff et al., 2011; Kempter et al., 2004). Tim Baugh, personal communication, 2015). Beneath the aforementioned (often very thin) blanket Volcanic bedrock obsidian localities are in 6–8 Ma lavas of El Cajete pumice are irregular beds of volcaniclastic and volcaniclastic sediments. These volcanic units include conglomerates and associated pumiceous deposits (Tpv in the Bearhead Rhyolite and Paliza Canyon Formation. The Fig. 2) derived primarily from andesitic to dacitic rocks Bearhead Rhyolite consists of more than 50 felsic domes, of the Paliza Canyon Formation (Kempter et al., 2004; flows, dikes and sills emplaced throughout the Jemez Goff and Gardner 2004; Goff et al., 2006, 2011). These Mountains (Kelley et al., 2013). Exposures with obsidian conglomerates contain older tephras and obsidian. from the Bearhead Rhyolite are located just to the north of the aforementioned collection areas, one of which is the Sampling and field observations of F04–31 dome of Goff et al., (2006) (labeled in northeast obsidian sources corner of Fig. 2). The obsidian commonly comes in the form of marekanites (also referred to as “Apache tears”), Obsidian sampling efforts were undertaken in September which are aphyric vitreous remnants in a rhyolitic perlite of 2013 and September–October of 2015. The first trip that commonly erode into subrounded-rounded pebbles was mainly a reconnaissance. In the Fall of 2015, we 53 New Mexico Geology August 2016, Volume 38, Number 3 Tpb Qvec-- El Cajete Pyroclastic Beds F04-31 ewa T Group Qbt-- Bandelier Tuff, Tshirege Member Quaternary Tpa Tbh Tbh-- Bearhead Rhyolite Tpv-- Qvec Volcani- Tpa Tpd-- Dacite clastic Tpa-- mbr. of Tbh ertiary Andesite T Paliza Tpbhd-- Dacite of Cerro Pino Tpa Keres Group Formation Can. Fm. Qvec Paliza Canyon Tpb-- Basalt Tpa Qvec Tpv Tpbhd Tpbhd Paliza CanyonTpa Fault Sampling area Qvec Tpa Qbt Tpbhd Tpa Qvec Tpa Sample site Tpbhd 100915-2 Tpbhd 106° 35’ Redondo Qvec Qbt Tpbhd Peak Quad Tpv 35° 35’ Tpbhd Bear Springs Tpa Peak Quad Qvec Tpbhd Qvec Tpa Tpa Qbt Qbt Qbt Qal Tbh Qvec Qal Qvec Qvec Tpa Qvec Qal Paliza Canyon Qvec Qal Tpa Tpa Tpb Tpa Tpv Qvec Qbt Qal Qvec Tpv Tpv Tpv Tpd Qvec Tpa Tpa Qal Tpb Paliza Canyon Qvec Tpa Tpa 091115-2 Qal Qvec Qvec Ruiz Tpv Tpa Peak Qvec 090413-2 Tpv Tpv Tpa Qvec Tpv 090413-3 Qvec Tpb Tpv Tpa Tpa 091115-1 Tpa Tpb Tpv Tpv Qvec Qvec Tpb Tpa Tpb Tpb 1 km Figure 2. Simplified geologic map of the upper Paliza Canyon area, southern Jemez Mountains, New Mexico (modified from Kempter et al., 2004, and Goff et al., 2006; labels and terminology from Goff et al., 2011). Qal (dark yellow) = valley bottom alluvium.

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