GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Volume 8 2021 © 2021 Utah Geological Association. All rights reserved. For permission to copy and distribute, see the following page or visit the UGA website at www.utahgeology.org for information. Email inquiries to GIW@utahgeology.org. CARBONATE MOUND SPRINGS OF THE UPPER JURASSIC MORRISON FORMATION OF CENTRAL MONTANA AND THEIR PALEOCLIMATIC SIGNIFICANCE FOR THE NORTHERN FORELAND BASIN Dean R. Richmond, John Pigott, Richard Lupia, Michael Behm, and David Hein GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Production Cover Design and Desktop Publishing Douglas A. Sprinkel Cover Photomicrograph of carbonate spherulites formed by a Jurassic variant of the betaproteobacteria Ralstonia eutropha H16. The spherulites are commonly found in the upper surfaces of mound spring deposits of the Upper Jurassic Morrison Formation of central Montana. The black specks are interpreted to be fossil betaproteobacte- ria remnants preserved in the spherulite. Image shown in crossed nicols. i Become a member of the UGA to help support the work of the Association and receive notices for monthly meetings, annual field conferences, and new publi- cations. Annual membership is $20 and annual student membership is only $5. Visit the UGA website at www.utahgeology.org for information and membership application. The UGA board is elected annually by a voting process through UGA members. However, the UGA is a volunteer-driven organization, and we welcome your voluntary service. If you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. 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Foster Utah Field House of Natural History State Park Museum 435.789.3799 eutretauranosuchus@ gmail.com Editors GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 8 2021 1 ABSTRACT Recent investigations of the Upper Jurassic Morrison Formation in central Montana resulted in the dis- covery of 105 small (< 3 m diameter) carbonate buildups in close geographic and stratigraphic proximity. The buildups are divided into two groups by dominant mineralogic composition: siderite versus calcium carbonate. The buildups are found in five distinct spatial clusters and are distributed in association with, and in alignment to, regional Jurassic-aged structural lineaments. The buildups are distributed stratigraph- ically between 40 to 52 m above the base of the Morrison Formation. Interpretation of electrical resistiv- ity tomography surveys indicates that additional buildups are present in the subsurface. Carbonate-rich groundwater migrated up fractures to the capillary fringe or the surface. The siderite buildups formed in the near subsurface capillary fringe, whereas the carbonate mounds are subartesian mound spring tufa de- posits. The bulk rock negative δ18O and δ13C values demonstrate the buildups were produced by meteoric waters in a continental setting with the groundwater having a short residence time in the subsurface. The presence of the subsurface buildups and mound spring tufa deposits scattered throughout a 12-m portion of the Morrison section indicates that the region experienced extended periods of increased precipitation. Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Dean R. Richmond1, John Pigott1, Richard Lupia2, Michael Behm1, and David Hein3 1School of Geosciences, University of Oklahoma, Sarkeys Energy Center Suite 710, Norman, OK 73019, USA; drichmaond.ou.edu; jpigott@ou.edu; Michael.Behm@geodata.com 2Sam Noble Museum, University of Oklahoma, 2401 Chautauqua Avenue, Norman, OK 73072, USA; rlupia@ou.edu 31021 Toole Circle, Billings, MT 59105, USA Citation for this article. Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D., 2021, Carbonate mound springs of the Upper Jurassic Morrison Formation of central Montana and their paleoclimatic significance for the northern foreland basin: Geology of the Intermountain West, v. 8, p. 1–26, https://doi.org/10.31711/ giw.v8.pp1-26. © 2021 Utah Geological Association. All rights reserved. For permission to use, copy, or distribute see the preceeding page or the UGA website, www.utahgeology.org, for information. Email inquiries to GIW@utahgeology.org. INTRODUCTION The Upper Jurassic Morrison Formation, an expansive sequence of terrestrial sediments deposited in foreland basins formed by the North America Cordilleran orogenic system, covers approximately 1.5 million km2 of the Intermountain West (Dodson and others, 1980). The formation has been intensely studied for uranium (Turner-Peterson and Fishman, 1986), coal (Harris, 1966; Silverman and Harris, 1966), oil and gas (Johnson, 2005), and dinosaurs (Foster 2007). Jurassic dinosaurs have been discovered in every U.S. state where the Morrison Formation is exposed (Turner and Peterson, 1999). Age equivalent rocks are found in south-central Canada but have only yielded plant fossils; vertebrate fossils have yet to be discovered (Brown, 1946; Rouse, 1959; Jansa, 1972). The recent discovery of dinosaurs in the northernmost portion of the Morrison foreland basin prompted a geological investigation of the study area that led to the discovery of numerous strange hemisphere- shaped terrestrial carbonate mounds (Richmond and 2 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 others, 2020). These are the first terrestrial carbonate mounds for the Morrison Formation. The purpose of this paper is to document the surface and near- subsurface spatial configuration of the buildups, place them into a stratigraphic framework, compare them to other terrestrial carbonates and draw conclusions as to the environmental conditions that led to their development, and understand their paleoclimatic significance. GEOLOGIC SETTING The study area is in southeastern Fergus County, Montana, where the Morrison Formation is exposed along the flanks of the Spindletop Dome (figure 1). Based on field stratigraphic measurements and well log data, the Morrison Formation in the study area is 72 m in thickness. The formation is bounded by the underlying Upper Jurassic Swift Formation and the overlying Lower Cretaceous Kootenai Formation. In central Montana, the Morrison Formation is conformable with the underlying marine sandstone beds of the Swift Formation. The J-5 unconformity (Pipiringos and O’Sullivan, 1978), present at the base of the Morrison Formation in more southern states, is absent in central Montana (this study; Imlay, 1954; Uhlir and others, 1988; Khalid, 1990; Meyers and Schwartz, 1994; Fuentes and others, 2011). The Morrison Formation is undifferentiated in central Montana and consists of a mudstone-dominated section with fine-grained anastomosing fluvial channels and thin crevasse splay sandstone beds (Richmond and Murphy, 2020). The formation contains fossil invertebrates (Richmond and others, 2017), dinosaurs (Saitta, 2015; Richmond and Murphy, 2017), and fossil wood (Richmond and others, 2019a, 2019b, 2019c). The overlying Lower Cretaceous (Aptian) Kootenai Formation rests on the K-1 unconformity and is an alluvial and fluvial sequence comprised of deposits of coarse- to medium-grained fluvial sandstone beds, overbank deposits of mudstone, and calcrete paleosols, with the formation capped by interstratified lacustrine limestone and dolomite units (Dupree, 2009). There is a hypothetical relationship between the structural components of central Montana and the development of the Morrison carbonate buildups, therefore a summary of the structural features of the region is presented. The present-day structure of the Figure 1. Geographic distribution for carbonate (blue circles) and siderite (orange squares) buildups in southeastern Fergus County, Montana. The buildups are separated into five different clusters. Only a sample of the 105 buildups is represented in the stratigraphic section. Some of the carbonate mounds have associated fossil wood, as indicated. Height in the stratigraphic section is reported in meters above the conformable Swift/ Morrison formational contact. 3 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 central Montana region is complex (Porter and others, 2002) as verified by fracture swarms and compressional and extensional faulting. The structure of central Montana, and the majority of the state, is related to Precambrian laterally extensive basement faults that trend at approximately 50o azimuth from southwestern to northeastern Montana (Sims and others, 2004). Reactivation of these Precambrian zones of crustal weakness during the Laramide orogenic event of the Late Cretaceous and Early Paleogene likely formed many of the present-day structures of central Montana, including the anticlinal structures of the Big and Little Snowy Mountains, Spindletop Dome, Flat Willow, and the Cat Creek anticlines and many other local anticlinal features (Gardner, 1950). There are two major orthogonal lineaments present in the Montana Rocky Mountains and the adjacent plains (Maughan, 1993). The northeast-southwest lineaments (Great Falls, Greenhorn, Snake River-Yellowstone, and Greybull) strike between 45o to 50o azimuth and correlate to the Precambrian basement faults. The major northwest- southeast lineaments (Bridger, Chadron, and Cedar Creek) strike between 320o to 325o azimuth, (Maughan, 1993; figure 2). In central Montana, this broad zone of northeast-southwest-trending structures controlled depositional patterns for some Paleozoic and Mesozoic sedimentary rocks (O’Neill and Lopez, 1993). Steeply dipping basement faults that strike northeast-southwest and southeast-northwest in Fergus, Petroleum, and Garfield Counties have been mapped in central Montana and are thought to have been reactivated through geologic time (Nelson, 1995). During the Late Jurassic, Sevier orogenic thrusting formed large north-trending folds in southwestern Montana (Hutsinpiller and Parry, 1985). A paleogeographic/paleotectonic high called “Belt Island” in north-central Montana (Porter, 2011) was likely the result of Jurassic reactivation of Precambrian basement faults in the plate interior. However, there are no known plutonic emplacements in central Montana related to these Jurassic regional paleostresses. The earliest granitic plutonism occurred during the Late Cretaceous between 74 and 69 Ma in west-central Montana in the Big and Little Belt Mountains (Snee and others, 2002). METHODS Geological Data Collection Stratigraphic measurements were made using accepted geological methods and surveyed using a Nikon DTM-322 total station. Samples retrieved were thin sectioned by Wagner Petrographic (Lindon, Utah) and subsequently were examined under a Zeiss petrographic microscope. The spatial position of each buildup was determined by a handheld Garmin GPS. The buildups appear to have a linear component to Figure 2. Regional stress lineaments for the central Rocky Mountains have a prolonged geologic history. The latest reactivation occurred during the Laramide orogenic event. The major northwest-southeast lineaments (Bridger, Chadron, and Cedar Creek) strike between 320o to 325o azimuth, whereas the northeast-southwest lineaments (Great Falls, Greenhorn, Snake River-Yellowstone, and Greybull) strike between 45o to 50o azimuth. The lineaments are an important component of the development of the Morrison Formation carbonate mounds. The small black rectangle in southeastern Fergus County indicates the study area. Modified from Maughan (1993). 4 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 them, therefore best fit lines were drawn for the spatial latitude and longitude data. Geochemical Analysis Carbonate samples were prepared for X-ray diffraction (XRD) with accepted methods (Moore and Reynolds, 1997). Powder XRD analyses were performed at the University of Oklahoma School of Geosciences using a Rigaku Ultima IV diffractometer. Cu-K-alpha radiation (40 kV, 44 mA) was used with a scintillation detector. Data analysis was completed using Jade 2010 software with the International Centre for Diffraction Data PDF4+ database. A Thermo Scientific Niton XL3t Ultra Analyzer X-ray fluorescence (XRF) gun was used to measure the elemental abundance of the carbonates. The device measured each sample for 210 seconds. Forty-one elements were measured using the XRF tool; 28 of these elements provide useful insight into the rock’s mineralogic composition. Only the highest percentages of elements are shown for this study. Isotopic Data Collection Two siderite and fourteen carbonate mounds and the modern cascade tufa from Sitting Bull Falls, (Last Chance Canyon, New Mexico), were sampled for standard isotopic data. A single sample was analyzed from each mound and the Sitting Bull Falls tufa. The 17 samples were analyzed by Beta Lab Services in Houston Texas. Three duplicate samples (CM 13, CM 35, and CM 52) were also analyzed at the Stable Isotope Geoscience Facilities at Texas A&M University. All isotope values are reported in delta notation relative to the Vienna Pee Dee Belemnite (VPDB‰) isotopic standard. Geophysical Data Collection Electrical resistivity tomography (ERT) data were acquired using an ARES-II system with stainless steel electrodes at a 1-m and 2-m spacing. All four profiles were measured using a dipole electrode configuration, sensitive to both lateral and vertical changes in resistivity. The ERT data were processed and inverted using AGI EarthImagerTM 2D resistivity inversion and modeling software. Overall, a relatively moderate to low data misfit (< 6%) was achieved after removing data outliers with a small number of iterations. Challenges do arise in interpreting ERT measurements when pronounced heterogeneity resulting from varying fracture density, karstification, or thin layering occurs below the resolution threshold (e.g., Everett, 2013; Loke and others, 2013). Furthermore, electrical resistivity is largely governed by water content within the soil profile and greatly depends on the primary and secondary porosity of the rocks and soil. MORRISON FORMATION BUILDUPS The Morrison Formation buildups can be separated into five geographic distinct areas designated by local coulee dams or other surface features (figure 3). The names of the clusters moving west to east: Kootenai Ridge cluster (46°51'10.45"N., 108°48'33.03"W.), Homestead cluster (46°50'36.50"N., 108°48'21.86"W.), East Blue Dam cluster (46°50'37.61"N., 108°48'12.21"W.), West Ralph Dam cluster (46°50'31.10"N., 108°47'50.94"W.), and Prairie Dog Dam cluster (46°50'23.67"N., 108°46'46.52"W.). The Prairie Dog Dam cluster has the highest number of siderite and carbonate buildups (figure 3). The buildups are stratigraphically between 40 to 52 m above the base of the Morrison Formation. The majority of the buildups are small hemisphere-shaped features a meter in height above the ground surface elevation and up to 3 m in diameter. The buildups are divided into two classes: siderite (FeCO3) and carbonate (CaCO3) buildups. To distinguish between the two types of buildups, they will be referred to as siderite buildups (SB) and carbonate mounds (CM). At present, 34 siderite buildups and 71 carbonate mounds have been discovered. The buildups and mounds occur in 5 clusters and 10 carbonate mounds have fossil wood associated with them. All buildups and mounds are encased in variegated illitic or organic-rich mudstones with no associated fluvial or lacustrine facies. Some of the designated carbonate mounds have siderite present beneath and on the flanks of the mound. The contact between the siderite and carbonate is always sharp and distinct where these siderite-carbonate mounds occur. 5 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 Description of Siderite Buildups The Morrison Formation siderite buildups are typically found in clusters (e.g., Prairie Dog Dam cluster) but solitary siderite buildups are present (figure 3). The homogenous siderite buildups can be several meters in length but are less than half a meter in height (figure 4A). There are no sandstone beds, horizontal carbonate strata, or fossil fauna or flora associated with them. The buildups are more elongate than circular, and the uppermost surfaces are irregular from the protrusion of cone- in-cone apices (figures 4B and 4C). Cone-in-cone structures are common in the siderite buildups (figures 5A and 5B). In thin section, the siderite is homogenous displaying ghost traces of the cone-in-cone crystalline growth (figure 5C). Some carbonate mounds have siderite on the flanks and/or beneath an overlying mound (e.g., CM 40 and CM 52; figure 3). A large broad carbonate mound (CM 40) a meter in height with a 7-meter diameter overlays a siderite base (figure 6A). The carbonate-peripheral siderites also display small cone-in-cone structures (figure 5D). XRD results on three siderite samples (SB 20, CM 40, 52) indicate the buildups are composed of 48.7% calcium carbonate (CaCO3), 16.7% quartz (SiO2), 16.0% siderite/ ankerite (CaFe(CO3)/CaMgFe(CO3)2), 10.5% illite, 7.3% kaolinite, and 0.9% pyrite (FeS2). XRF was performed on five different siderite buildups (SB 12, 18, 19, 32, 33; appendix) and two carbonate-peripheral siderites (SB 40.1, 40.2; figures 6A and 7). The three major elements for each siderite buildup are calcium (Ca), iron (Fe), and silica (Si). The analysis demonstrates a percentage variation in these three main elements as well as the trace elements (potassium [K], magnesium [Mg], titanium [Ti], manganese [Mn], alluminum [Al], phosphorus [P], sulfur [S], chlorine [Cl], and strontium [Sr]) (figure 7). Standard isotope analysis was completed on two siderite buildups (SB 20, 40; table 1). The δ18O siderite Figure 3. Spatial map of the carbonate and siderite buildups. The buildups are divided into clusters that are named based on local surface features. The Prairie Dog Dam cluster is subdivided into arrays (insert). The dashed lines A‒A', B‒B', C‒C', and D‒D' represent the electrical resistivity tomography (ERT) profiles herein described. The four carbonate mounds highlighted by the red circles are specifically referred to herein. 6 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 data have close values of ‒5.08‰ and ‒5.49‰ with a mean of ‒5.29‰. The δ13C data ranges from ‒15.41‰ to ‒18.48‰ with a mean of ‒16.95‰. Description of Carbonate Mounds In contrast to the siderite buildups, the majority of the carbonate mounds are not found close to one another, but small clusters of carbonate mounds are present (figure 3). The homogenous carbonate mounds vary in length and height. The mounds are generally hemisphere-shaped, are typically a meter in diameter and less than a meter in height (figures 6B and 6C) although larger mounds are present. There are no sandstone beds or other terrestrial carbonate beds associated with the carbonate mounds. The mounds do not have macroscale cone-in-cone structures. The majority of the carbonate mounds are composed of orthochemical micrite. Clastic detrital grains common in many terrestrial carbonates (e.g., travertines, tufas, calcretes, etc.) are absent. In general, allochems are rare. Few macrofossils are present with the carbonate mounds. Ten carbonate mounds have fossil wood in proximity to the mound but only three have fossil logs incorporated into the mound (CM 13, 31, 52). Typical macrophyte debris (leaves or twigs), hydrophytes, or charophytes are generally absent. Only two microscopic woody macrophyte fossil fragments were discovered. The first is unidentifiable woody debris (figure 8A); the second is a partial tangential fragment Figure 4. Field images of the siderite buildups. (A) Siderite buildups can be a few meters long but are less than 50 cm high. They can be isolated or found in clusters. (B and C) Closeup views of the siderite buildup’s upper surfaces disrupted by cone-in-cone apices. Meter stick and hammer used for scale. Sample δ18O (0/00 VPDB) δ13C (0/00 VPDB) MT MRSN CM01 -12.03 -10.57 MT MRSN CM13 -16.72 -3.88 MT MRSN CM13* -15.49 -4.32 MT MRSN CM14 -9.27 -4.88 MT MRSN CM17 -16.05 -6.78 MT MRSN CM27 -10.83 -5.04 MT MRSN CM31 -16.96 -5.83 MT MRSN CM35 -16.11 -4.53 MT MRSN CM35* -16.00 -5.04 MT MRSN CM36 -12.85 -8.90 MT MRSN CM39 -15.48 -5.90 MT MRSN CM40 -15.48 -6.31 MT MRSN CM44 -11.83 -9.43 MT MRSN CM52 -15.59 -5.35 MT MRSN CM52* -16.88 -6.50 MT MRSN CM62 -15.39 -6.25 MT MRSN CM66 -14.30 -5.46 MT MRSN SB20 -18.48 -5.49 MT MRSN SB40 -15.41 -5.08 NM TUFA SB1 -8.13 -6.40 CM — carbonate mound; SB — siderite buildup *Different lab analyses Table 1. Oxygen and carbon isotope data from carbonate buildups. 7 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 of a homoxylous wood (figure 8B). In addition to the woody fragments, partial bryophyte leaves (liverworts; M. Philippe, University Lyon, written communication, 2020) are preserved in several mounds (CM 13, 17, 35; figure 8C). An organic fabric was discovered in mound CM 13 and might be tufa-associated green algae Oocardium stratum Nägeli (figure 8D). Fossil freshwater invertebrates such as ostracods or gastropods are not observed. Biogenic macrolaminae from cyanobacteria, typical of many terrestrial carbonates, are not observed. No trace fossils have been found. Petrographic features of the carbonates include long dogtooth calcite crystals. Some dogtooth crystals appear to be coated with microbial films (figure 9A). Spherulites are observed in some carbonate mounds and have a very distinctive texture (figures 9B and 9C). Spherulites have a radiating array of crystalline fibers that developed from a nucleus (Beck and Andreassen, Figure 5. Images of cone-in-cone features of the siderite buildups. (A) Siderite cone-in-cone feature in place. (B) The same cone-in-cone feature is shown in A. This has been removed from the buildup to display the large size of the cone-in-cone feature. The 9-cm-long acid bottle is for scale. (C) Photomicrograph of a cone-in-cone feature from a siderite buildup. The cone-in-cone feature (red lines) is difficult to differentiate in the micritic matrix. (D) Along the flanks or underlying some carbonate mounds (e.g., CM 52) are pale yellowish-orange to dark yellowish-orange siderites. These are referred to as peripheral siderites and exhibit small cone-in-cone ridges. The sample shown is from beneath carbonate mound CM 52. The mound in shown in figure 6C. Figure 6. Field images of carbonate mounds. (A) Carbonate mound CM 40. The hemispherical shape of the carbonate mound is visible. The carbonate mound (blue arrows) also displays peripheral and underlying siderites (orange line and arrows). Meter scale. (B) Carbonate mound CM 13. The buildup had a partially encased fossil log of Circoporoxylon Kräusel. Unfortunately, the log was stolen. The red arrow shows where the log was present. In the background is the encasing illitic mudstone. 50 cm scale. (C) Carbonate mound CM 52. A fossil log of Xenoxylon Gothan is encased atop the mound (not visible). Some displaced fossil wood fragments are visible (red arrow). Peripheral siderites are visible at the base and sides of the carbonate mound (orange arrows). Hammer for scale. 8 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 Figure 7. XRF comparison of several siderite buildups and two peripheral siderites (CM 40.1 and CM 40.2). The geochemical variability exhibited in the different buildups is thought to be the result of the interaction of the groundwater with different local soil chemistries during the development of the siderite buildup. Figure 8. Photomicrographic images of fossil organic material found in some carbonate mounds. (A) Unknown fossil woody debris in thin section. (B) The tangential view of a fossil homoxylous woody plant. (C) A partial fossil bryophyte (liverwort) leaf. The circular chambers (red-outlined arrows) are filled with fossil cyanobacteria and bounded by the spongy mesophyll (blue-outlined arrows). Collenchymatous cells (cluster of brown cells) present in the midline of the leaf (green-outlined arrows) are common in extant liverworts. (D) The fossil circular pores resemble the features of Oocardium stratum, a green alga that is commonly associated with modern tufa deposits. The mean pore diameter is ≈ 30 μm. The large pore (pink- outlined arrow) may represent the stem of a fossil hydrophyte. 9 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 2010). Interestingly, the spherical crystal growth appears to have pushed organic material to the rim. Organic material is concentrated in the interstitial space between adjacent spherules. Occasionally organic material is encompassed by the spherule’s mineral growth. The organic material is likely residual microphytes (algae) or bacteria (Chafetz and Folk, 1984). Many terrestrial carbonates have primary porosity. Primary porosity in the carbonate mounds is limited to intergranular spaces between the spherulites and the porous structures of macrophytes. In addition to the primary orthochemical micrite and radial-fibrous spherulites, many carbonate mounds have late diagenetic fractures annealed with sparry calcite. XRD analysis was run on several carbonate mounds (CM 13, 38, 52, and 64). The data indicate that the carbonate mounds are composed of 98% calcium carbonate and 2% carbon. XRF was executed on eight different carbonate mounds. The three major elements are Ca, Fe in minor amounts, and Si. Variation in the three main elements and the trace elements (K, Mg, Ti, Mn, Al, P, S, Cl, and Sr) (figure 10) indicates that the geochemistry was distinct for each buildup. Two carbonate mounds (CM 13 and 52) were analyzed with XRF on a cm-scale cross section from the bottom of a large cut slab of the buildup moving upward (figures 11 and 12). Carbonate mounds 13 and 52 are stratigraphically separated by 5 m (figure 1). Both mounds incorporate fossil wood, Circoporoxylon Kräusel and Xenoxylon Gothan, respectively. The most noticeable variation for carbonate mound 13 is the percentage of Mg (figure 11; letters C, G, S, T). Carbonate mound 52 data displays more consistent chemistry with only minor differences (figure 12). The fossil wood (Xenoxylon; letters L-WD and M-WD) has distinct chemistry from the mound and implies wood preservation may involve nonmetals (Si, P, S, and Cl; figure 12). Fourteen Morrison Formation carbonate mounds and a sample from the modern cascade tufa at Sitting Bull Falls, Sitting Bull Canyon, southwest of Carlsbad, New Mexico, were analyzed for standard isotope data (table 1). The δ18O Morrison data displays variability ranging from ‒3.88‰ to ‒10.57‰ with a mean of ‒6.37‰. The δ13C also shows variability ranging from ‒9.27‰ to ‒16.96‰ with a mean of ‒14.21‰. The mean δ13C values are slightly lower than the pre- industrial revolution atmospheric value of meteoric water precipitated calcite (‒6.5‰; NOAA data; Sharp, 2007). Electrical Resistivity Tomography Four localized electrical resistivity tomography (ERT) surveys were conducted to understand the Figure 9. (A) Photomicrograph of dogtooth calcite crystals with cyanobacterial rinds (blue arrows) suggesting that crystals grew uninterrupted into a subaerial, carbonate- rich pool and the cyano-bacteria had access to sunlight. (B and C) Photomicrographs of spherulites. The spherulites are interpreted to be bacteria-derived. Refer to text for information on the bacteria. Primary porosity is evident (red arrow; dark blue epoxy). The dark spots scattered throughout the spherulites are fossil remnants of the bacteria. Images B and C are crossed nicols. 10 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 Figure 10. XRF comparison of several Morrison Formation carbonate mounds. The changes in mineralogical composition are likely a result of groundwater interaction with local strata and soils. The carbonate mound data represent different stratigraphic positions in the formation. No XRF measurements were made on fractures. The bar at the far right is data from the modern cascade tufa from Sitting Bull Falls, Sitting Bull Canyon, southwest of Carlsbad, New Mexico. Figure 11. XRF data of CM 13 sampled at 1 cm increments. A large slab of the buildup was cut with measurement A at the bottom and moving upward. The most notable variation during the development of CM 13 is the increase in the percentage of magnesium (Mg). No XRF measurements were made on fractures. 11 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 structure and potential subsurface continuation of the surface mounds, as was previously applied to delineate the subsurface continuation of a fossil tufa outcrop in northeast Spain (Huerta and others, 2016). On average, the obtained resistivities range from 20 to 200 Ω-m. Based on the correlation with outcrops and surface geology, two lithologies are interpreted to be present in the subsurface. Lithology 1 (carbonate) resistivities range from 150 to 200 Ω-m with thicknesses that range from 0.5 to at least 1.5 m. Lithology 2 (mudstone) resistivities range 10 to 70 Ω-m. The lowest resistivities associated with lithology 2 are attributed to the increased moisture content of some surface areas (dark blue) (figure 13). ERT profile A‒A' (figure 13A) was run parallel to the Prairie Dog Dam (PDD) eastern array (figure 3). Although we attempted to pass over several carbonate mounds, the ERT profile only shows high resistivity (> 150 Ω-m) at the distal ends of the profile. The northeastern buildup is about 6 m across. The profile does not show any additional high-resistivity carbonates (CM) in the subsurface. ERT profile B‒B' (figure 13B) was oriented perpendicular to profile A‒A' trending northwest (figure 3) and crossing the western, central, and eastern PDD arrays. The surface high resistivity (> 150 Ω-m) at profile marker 58 m crosses over a small surface carbonate mound (figure 3). The ERT profile crosses many of the siderite buildups of the PDD central array between 86 to 100 m. This profile section displays low resistivities (< 25 Ω-m). Although the profile crosses over several surface siderite buildups, the buildups are not discernible in the profile. There are several potential reasons why the buildups are not seen in the profile. The topographic low where the siderite buildups reside may have had a higher water saturation (ephemeral creek bed). The buildups are highly fractured, and those fractures can hold conductive water. It is also possible that the siderite buildups are thin surface features that would make them indiscernible in the ERT since electrical current prefers conductive pathways. In Figure 12. XRF data of CM 52 sampled at 1 cm increments. A large slab of the buildup was cut with measurement A at the bottom and moving upward. Sample CM 52 shows less variability in mineral percentages. Measurements L and M include fossil wood encased at the top of the carbonate mound. The unique chemical signature of the fossil wood implies preservation may involve Si, P, S, and Cl. 12 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 contrast, the profile does discern a small carbonate mound from the PDD western array at 116 to 118 m. In the subsurface between 36 to 60 m is a high resistivity (110 to 200 Ω-m) zone interpreted to be a large mound or possibly two mounds separated stratigraphically. ERT profile C‒C' (figure 13C) was run parallel to the East Blue Dam cluster over the largest observed surface carbonate mound (CM 40; figure 3). The hemispherical mound (CM 40) is 7 m long and 1 m thick and is underlain by a thin siderite bed. Underlying the entire structure is a low resistivity zone (28 to 15 Ω-m) interpreted to be a ≈ 2-m-thick mudstone bed. Beneath this mudstone bed is a high resistivity zone (150 to 300 Ω-m) interpreted to be a significantly sized carbonate mound in the subsurface. The lateral extent of this mound may range from 15 to 41 m. The suggested minimum thickness is around 1.5 m Figure 13. Electrical Resistivity Tomography (ERT) profiles (A to D). Refer to figure 3 for profile lines. (A) ERT Profile A‒A' was run parallel to Prairie Dog Dam (PDD) eastern array. The ERT profile shows high resistivities (> 150 Ω-m) at the distal ends of the profile. The northeastern mound is about 6 m across. The profile does not show any additional high resistivity carbonates in the subsurface. (B) ERT profile B‒B' at Prairie Dog Dam was oriented perpendicular to profile A‒A' trending northwest across the western, central, and eastern arrays. The ERT profile crosses several siderite buildups of the PDD central array between 86 to 100 m. This profile section displays low resistivities (< 25 Ω-m) and the siderite buildups are not discernible in the profile. In contrast, the profile does differentiate a small carbonate mound from the PDD western array at 116 to 118 m. In the subsurface, between 36 to 60 m, is a high resistivity (110 to 200 Ω-m) zone, interpreted to be a large mound or possibly two mounds stratigraphically separated. (C) ERT profile C‒C' was run parallel to the East Blue Dam cluster over the largest observed surface carbonate mound (CM 40). This mound is underlain by a thin siderite bed. The hemispherical mound is 7 m long and 1 m thick. Underlying the mound is a low resistivity zone (28 to 15 Ω-m) interpreted to be a ≈ 2-m-thick mudstone bed. Beneath this mudstone bed is a high resistivity zone (150 to 300 Ω-m) interpreted to be a significantly sized carbonate mound in the subsurface. The lateral extent of this mound may be as long as 15 to 41 m. The estimated minimum thickness is 1.5 m. Near the end of the profile, the high resistivities appear disjointed and stratigraphically higher and may represent another mound. (D) ERT profile D‒D' was oriented perpendicular to profile C‒C'. High resistivities (150 to 200 Ω-m) at profile marker 18.2 m represent a small surface buildup. Underlying the high resistivity zone is a lower resistivity zone (30 to 20 Ω-m). Similar to profile C‒C', beneath the lower resistivity zone is a high resistivity zone (150 to 200 Ω-m). This zone is interpreted to represent a significantly sized buildup. The lateral extent of this mound is at least 24 m and may extend beyond the profile. The estimated thickness is 1 to 1.5 m. It should be noted that the large D‒D' profile subsurface mound(s) has a different subsurface elevation than the large C‒C' profile subsurface mound. Therefore, they are not stratigraphically equivalent. 13 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 because ERT images tend to blur vertically with depth. Near the end of the profile, the carbonate subsurface layers appear disjointed and stratigraphically higher. This may be interpreted as representing a different smaller carbonate mound. Given the inherent low resolution of ERT imaging, however, this interpretation is speculative. ERT profile D‒D' (figure 13D) was oriented perpendicular to profile C‒C' (figure 3). The high resistivities (150 to 200 Ω-m) at profile marker 18.2 m represent a small surface buildup. Underlying the high resistivity zone (CM) is a lower resistivity zone (30 to 20 Ω-m). Similar to profile C‒C', below the lower resistivity zone is a subsurface high resistivity zone (150 to 200 Ω-m). This zone is interpreted to represent a significantly sized mound, or possibly two coeval mounds. The lateral extent of this mound is at least 24 m and may extend beyond the profile. The estimated thickness is 1 to 1.5 m. It should be noted the large D‒D' profile subsurface mound(s) has a different subsurface elevation than the large C‒C' profile subsurface mound. They are therefore not stratigraphically equivalent. The four ERT surveys help to define the lateral extent of the surface mounds and the relative stratigraphy of several previously unknown carbonate mounds in the subsurface. The surface mounds and subsurface carbonates are decoupled by a thin low-resistivity zone that represents the encasing illitic mudstone. The ERT data indicate the presence of additional large stratigraphically isolated carbonate mounds in the subsurface. Groundwater-fed Carbonate Deposits Groundwater-fed carbonate deposits include travertine, tufas, sinters, and speleothems (Chafetz and Folk, 1984; Steinen, and others, 1987; Pedley, 1990; Golubic and others, 1993; Koban and Schweigert, 1993; Ford and Pedley, 1996; Pentecost and Coletta, 2007; Capezzuoli and others, 2014; Della Porta, 2015; Mohammadi and others, 2019). The classification of groundwater-fed carbonate deposits has a diverse history (see Jones and Renaut, 2010). Modern freshwater springs are categorized by the mean water temperature at the vent, where temperatures range from cold to boiling (Jones and Renaut, 2010). Pedley (1990) and Ford and Pedley (1996) use water temperature to delineate between travertine and tufa deposits. Herein we follow the general classification of Pedley (1990), but further define tufas as being precipitated under cooler water temperatures (< 20oC) whereas travertines as being precipitated under thermal conditions (> 20oC; Barilaro and others, 2012). Sinters can be siliceous or carbonaceous. They are commonly associated with hot springs or geysers in active volcanic terrains where mineral-charged geothermal fluids are discharged at the surface (Campbell and others, 2015; Munoz-Saez and others, 2016). At the other end of the temperature spectrum, speleothem deposits form in caves by evaporation of cool mineral-enriched waters. Travertines are usually considered abiotic due to the hydrothermal water conditions that prohibit the existence of higher organisms (Chafetz and Folk, 1984; Koban and Schweigert, 1993; Ford and Pedley, 1996; Evans, 1999). Different invertebrates, plants, mosses, protozoa, algae, fungi, and bacteria have different tolerances of high-water temperature (Renaut and Jones, 2000). As discharged thermal waters flow away from the vent and cool, biota with differing temperature tolerances begin to inhabit these varying temperature zones. Travertine is enriched in 13C and often contains high levels of sulfur (Pedley, 2009). Travertines tend to show less macrofacies diversity than tufa systems on account of their relatively limited lateral extent and biota (Ford and Pedley, 1996). Cool water tufa carbonate precipitation occurs at ambient temperatures (< 20oC) and is usually associated with proximal paludal or lacustrine depositional facies (Pedley, 1990; Ford and Pedley, 1996). These tufas are characterized by the presence of heterotrophic bacteria, cyanobacteria, microphytes (algae), hydrophytes, macrophytes, and freshwater invertebrates (Kerney, 1959; Pedley, 1990; Ford and Pedley, 1996, Koban and Schweigert, 1993; Evans, 1999; Capezzuoli and others, 2014). Vertebrate fossils can also be associated with tufa deposits (Kerney, 1959; Springer and others, 2017). Inorganic precipitation (e.g., degassing CO2) and organic microbial activity are important factors for carbonate precipitation in tufa environments. Tufa deposits have been further divided into allochthonous and autochthonous deposits (Pedley, 1990). Allochthonous tufas consist of either cemented 14 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 phytoclasts, intraclasts of silt- and sand-sized clasts sourced from tufas, micritic tufa material, or peloids and are usually associated with fluvial depositional systems (Pedley, 1990). Autochthonous tufas consist of stromatolitic horizontal laminations related to seasonal growth patterns of cyanobacteria (Janssen and others, 1999). MORRISON FORMATION SIDERITE BUILDUPS AND CARBONATE MOUND SPRINGS Interpretation of Near-surface Siderite Buildups The Morrison siderite buildups are interpreted to be near-surface buildups and not surface tufa deposits. Siderite is the product of the interaction of numerous dynamic inorganic and organic systems. Groundwater chemistry is the summation of meteoric and subsurface water interactions with the local geology, aquifer lithologies, and soils. The availability and solubility of iron in soils are partly a byproduct of the decomposition of organic matter. Ferrous carbonate (siderite/ankerite) and ferric hydroxide (goethite and polymorphs) precipitate at a circumneutral pH (Hedrich and others, 2011). Acidic groundwater (pH < 4) causes iron and carbonate (CaCO3) to remain in the solution. Alkaline groundwater (pH > 9) causes bicarbonate (HCO3) to precipitate and release CO2. To form siderite, the complexing agent CaCO3 binds with the ferrous/ferric iron at a circumneutral pH (Blöthe and Roden, 2009). Soils in wet climates are typically acidic, whereas in dry climates the soils are alkaline (Slessarev and others, 2016). The interaction of acidic surface soil waters with alkaline groundwater likely developed the circumneutral pH required for proteobacteria to precipitate siderite. In modern neutral pH freshwater environments iron-oxidizing phylum proteobacteria govern iron redox reactions (Blöthe and Roden, 2009; Hedrich, and others, 2011; Roden and others, 2012). Iron redox states are interconnected to inorganic compounds in soils and sediments. Micro-organisms play a fundamental function in iron redox reactions (Blöthe and Roden, 2009). Betaproteobacteria are the most common microbes in modern circumneutral pH freshwater environments including soil horizons (Roden and others, 2012). These lithotrophic iron-oxidizing bacteria often colonize in the soil transition zone between the anaerobic and aerobic subsurface environments (Roden and others, 2004). The position of the anaerobic/aerobic transition zone (i.e., the capillary fringe) can vary by precipitation, the upward migration of groundwater, or the deoxygenation of groundwater by microorganisms. The Morrison Formation siderite buildups formed from precipitation-fed groundwater at the capillary fringe or by moving up small fractures as subsurface seeps into the vadose zone. The groundwater then interacted with the organic- and iron-rich forest soils and aided by iron-oxidizing betaproteobacteria resulting in siderite precipitation. The chemical variabilities of the siderite buildups as shown by the XRF data (figure 7) likely resulted from homogenous groundwater interacting with localized variable soil chemistries. Cone-in-cone structures are common world-wide, known from every geologic age, and usually form in calcite, gypsum, or quartz (Cobbold and others, 2013). They commonly form in low-permeability saturated sediments such as shale or mudstone. Cobbold and others (2013) advocate that cone-in-cone structures develop from fractures that form coeval with mineral growth. The fractures are formed either by the force of crystallization, or fluid over-pressurization. Selles- Martinez (1994) agrees that crystalline fibers grow in saturated over-pressured regimes where fractures are induced by a decrease in pore pressure of the overlying sediments. In short, the difference between the saturated over-pressured zone (phreatic) and the hydrostatic zone (vadose) at the capillary fringe creates the boundary conditions that allow cone-in-cone structures to form. Although the paleoelevation of the capillary fringe is unknown, it is interpreted to have resided at a shallow burial depth based on the presence of peripheral-siderite buildups and owning to the similar elevation of proximal carbonate mounds. Terrestrial siderites form in humid continental environments where precipitation exceeds evaporation. Siderites typically accumulate in poorly drained/anoxic wetland soils (Sheldon and Tabor, 2009; Ludvigson and others, 2013; Fernandez and others, 2014). The presence of the Morrison siderite buildups indicates a humid climate 15 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 with a near-surface groundwater capillary fringe. The siderite buildup cluster in the Prairie Dog Dam central array (figure 3) may be related to an anoxic wetland. Interpretation of Carbonate Mound Springs The carbonate mounds lack the many characteristics that are recognized to define modern groundwater- fed terrestrial deposits such as travertine and tufas. The Morrison carbonate mounds are composed of orthochemical micrite, show low primary porosity, display no cyanobacterial laminae, and fossil allochems are scarce. The general characteristics suggest the carbonate mounds may represent travertine deposits. However, as stated previously, there are no known Jurassic-aged hydrothermal sources to have created groundwater-fed carbonate mounds with water temperatures above 20o C. Carbon dioxide degassing is an important component of travertine deposition with the bubbles being preserved in the carbonate. These primary porosity structures are not observed in the field, nor in the thin sections for any of the studied Morrison carbonate mounds. This suggests CO2 degassing was not violently occurring at the surface during precipitation and therefore the buildup was likely not hydrothermally sourced. Fossil evidence and standard isotopic data indicate the carbonate mounds are tufa deposits. The incorporation of the microscopic woody macrophyte fossil fragments, homoxylous wood, bryophyte leaves (liverworts; figure 8), and the proximity of logs of Cupressinoxylon, Circoporoxylon, and Xenoxylon indicate that plants were growing near the mounds. Although different plants can have varying water temperature tolerances, the proximity to such a small diameter mound suggests an ambient water temperature. The fossilized microphyte fabric that may be the eukaryotic microalgae (Zygnematophyceae) Oocardium stratum Nägeli (Pfiester, 1976) also indicates water temperature. The calcifying desmid O. stratum is a colonial freshwater green alga commonly associated with modern tufas (Pentecost, 1991, 2005; Linhart and Schagerl, 2011). The pore diameter of the Morrison fossil microphyte is ≈ 30μ, whereas the pore diameter of the calcite tubes of modern O. stratum is between 17 to 20μ (Ibarra and Sanon, 2019). The alga O. stratum is known from waters with a temperature range from 7o to 13o C but can exist in cooler (4o C; Tran and others, 2019) or warmer water temperatures with an optimum water temperature of 13oC (Pentecost, 1991; Sanders and Rott, 2009; Linhart and Schagerl, 2011; Rott and others, 2012; Ibarra and others, 2014). Additional observed niche conditions for modern O. stratum include carbonate supersaturation, gradual CO2 degassing, and circumneutral pH 7 to 8 in spring waters (Rott and others, 2012). Associated with the O. stratum are two 142μ diameter pores that may represent the stems of hydrophytes growing in association with the algae. If the fossil is O. stratum, its presence preserved in the carbonates indicates pH- neutral water with ambient temperatures (i.e., < 20o C). Radial-fibrous spherulites are found in outcrop at the upper surfaces of the carbonate mounds. Spherulites are a common feature of fossil and modern tufa deposits (Guo and Chafetz, 2012) and are present in the modern Sitting Bull Falls tufa. Bacterially precipitated vaterite and calcite in marine and terrestrial environments are well documented (Boquet and others, 1973; Chafetz and Folk, 1984; Merz, 1992; Castanier and others, 2000; Braissant and others, 2003; Párraga and others, 2004; Ronholm and others, 2014; Baumann and others, 2016). Chafetz and Folk (1984) suggest bacterial carbonate precipitation may account for 90% of a tufa’s framework grains. The spherulites are likely formed by the secretion of biofilms (i.e., glycocalyx) from betaproteobacteria such as Ralstonia eutropha H16 (Braissant and others, 2003), or a Jurassic variant. R. eutropha H16 is a chemolithoautotrophic bacterium able to grow within organic substrates under aerobic conditions (Müller and others, 2013). The modern bacterium R. eutropha H16 has an identical XRD diffractogram as calcium carbonate (Braissant and others, 2003). The bacterial formation of spherulites also indicates an ambient temperature. The standard isotopic data of the carbonate mounds indicate that they are tufas. The δ18O values are the product of meteoric water isotopic fractionation from latitude, elevation, precipitation and evaporation, seasonal temperature variation, and the precipitation of calcite (Dansgaard, 1964; Sharp, 2007). The mean δ18O value derived from marine shell carbonates during the Late Jurassic (150 Ma) is ‒1‰ VPDB (Veizer and others, 1999). 16 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 In general, freshwater carbonates have negative δ13C values, but these values can become even lighter if there are significant contributions of organic carbon (Sharp 2007). Paleo δ13C values require a correction due to secular variation of the δ13C throughout geologic time (Mackenzie and Pigott, 1981). The total dissolved carbon in the oceans has changed through geologic time. Variations in oceanic dissolved inorganic carbon are related to tectonism, erosion, productivity, and carbonate deposition (Sharp, 2007). During the Late Jurassic (150 Ma), the secular variation was near +2‰ VPDB (Veizer and others, 1999). For terrestrial environments, the δ13C of the freshwater carbonate is controlled by the dissolved inorganic carbon in the groundwater and its interaction with the soil. Carbonates precipitated at lower altitudes where vegetation productivity is generally higher (the Morrison planation surface of central Montana), should have lighter δ13C values due to a greater contribution of 12C from C3 plants. At higher elevations, where plant productivity is poor, δ13C will have isotopically heavier values. Isotopic data of the Morrison tufa deposits (table 1) shows the δ18O values are similar to the present weight annual δ18O global distribution for comparable latitudes, suggesting minimal diagenetic alteration (Darling and others, 2006). Based on isotopic analysis of pedogenic carbonates and fossils, δ18O values for paleometeoric waters of the Morrison Formation were highly depleted (Ekart and Cerling, 1996). The δ18O values derived from fossil crocodile teeth and turtle scutes from four locations in the Morrison Formation show comparable values. From south to north the fossil localities are Kenton, OK; Fruita, CO; Nine Mile Hill, WY; and Upton, WY with the respective δ18O values ‒16.14‰, ‒20.30‰, ‒16.31‰, and ‒16.94‰ (Brundridge, 2013). The central Montana δ18O values (table 1) are slightly heavier than the more southern Morrison Formation δ18O values signifying minor input from the retreating Sundance sea, perhaps due to changes in atmospheric circulation during the winter months. The central Montana Morrison δ13C data (table 1) indicate the dissolved inorganic carbon was derived from atmospheric CO2 and the groundwater had a short residence time with minor interactions with organic matter in the soil (Darling and others, 2006; Sharp, 2007). Woody plants (C3) are enriched in 12C with values of δ13C ≈ ‒25‰ (Park and Epstein, 1961; Sharp, 2007; Bacon and others, 2011) and the soils they produce have similar values (Diochon and Kellman, 2008). Pedogenic carbonates δ13C values are dominated by the isotopic signal of plant communities (Sharp, 2007). The δ13C values indicate these are not pedogenic carbonates. The Morrison siderite buildup, carbonate mound, and the Sitting Bull Falls tufa standard isotopic data were plotted on a cartesian graph with δ18O on the x-axis and δ13C on the y-axis (figure 14). Fluvial and lacustrine tufas have negative δ18O values. In contrast, lacustrine tufas have positive δ13C values, whereas fluvial tufas have negative δ13C values. In contrast, thermogenic waters exhibit low to very low negative δ18O values coupled with positive δ13C values. The negative δ18O values indicate a meteoric source (Gandin and Capezzuoli, 2008; Della Porta, 2015), whereas the positive δ13C values signify an increase in dissolved inorganic carbon as a result of deep subsurface circulation and longer residence times in limestone aquifers (Andrews, 2006). The Sitting Bull Falls tufa plots as expected in the region for fluvial tufas. The Morrison siderite buildup and carbonate mound data consist of both negative δ18O and δ13C values. The Morrison isotopic data plots in the range of the oldest North American tufas, those associated with the Lower Jurassic Navajo Sandstone (Parrish and others, 2019). The negative isotopic values for the Morrison Formation siderite buildup and carbonate mound reveal that they were produced by meteoric waters in a continental setting (Andrews, 2006; Sharp, 2007). The isotopic data also provides insights into the variation of water chemistry during the mound formation. The main cluster of δ18O values (mean ‒15.53‰) correspond to the expected values for the paleolatitude of ≈ 50o north (Terzer, and others, 2013; Richmond and others, 2019a). In drier climates, the groundwater’s residence time is increased owing to decreased recharge, resulting in isotopically heavier δ13C values (Tanner, 2010). The negative δ13C for the main cluster (mean ‒5.78‰) indicates the groundwater had a short residence time in the subsurface indicating regular and/or high precipitation. Several isotopic data points diverge from the main 17 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 data cluster, but these present insights into the climatic variance recorded by the tufas. The less negative δ18O values (figure 14, Group A; mean ‒10.05‰) implies a marine isotopic component. Changes in atmospheric circulation may have brought northern-sourced precipitation from the Sundance sea to central Montana. The more negative δ13C values (figure 14, Group B; mean ‒8.31‰) indicate short drier periods resulted in a longer subsurface residence time allowing groundwater to interact with plant carbon in the subsurface. The difference between the positive Late Jurassic oceanic δ13C values (+2‰) and the negative values (mean ‒6.13‰) of the Morrison Formation of central Montana suggest the region had a low elevation with high plant productivity and a wet climate. The observed and inferred characteristics of the Morrison carbonate tufa mounds are analogous with the artesian mound springs of the Great Artesian Basin (GAB) in the Lake Eyre South region of southern Australia (Keppel and others, 2011, 2012). The GAB mound springs acquired their name for their hemispherical shape that forms by the accretion of sediment around the spring Figure 14. A plot of published standard isotopic data of tufas and travertines and the isotopic data from the central Montana Morrison Formation siderite buildups and mound springs. Plotted data indicates that the mound springs are freshwater tufa deposits. The dark blue circles represent carbonate mounds (CM), the red squares are siderite mounds (SB), the light blue circles are carbonate mounds run at another lab for comparison. The green triangle represents the modern cascade tufa at Sitting Bull Falls, Sitting Bull Canyon, southwest of Carlsbad, New Mexico. The isotopic data shows that the buildups are ambient water-temperature tufa mounds. These are the first tufa mounds recorded for the Morrison Formation and are the second oldest tufa deposits in North America. The isotopic data also provides some insights into the variation in water chemistry. The δ18O matches the expected paleolatitude of the region. A few data points show variance in the geochemistry recorded by the tufas. The δ13C for the central cluster indicates the groundwater had a low residence time in the subsurface indicating regular and/or high precipitation. The more negative δ18O values in Group A suggest there may have been precipitation input from northern storms from the retreating Sundance sea. The more negative δ13C values of Group B suggest drier periods resulting in a longer subsurface residence time allowing groundwater to interact with plant carbon in the subsurface. 18 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 outlet. The outlet gradually rises in elevation forming a dome- or shield-shaped cone and are typically between 2 to 5 m in height (Williams and Holmes, 1978; Keppel and others, 2011). Many GAB mound springs do not consist of the characteristic calcareous mound but either emerges at ground level or consist of soft, silty mounds. The GAB mound springs form under a semiarid to arid climate (Harris, 1981). The GAB-associated paludal environments are limited in size due to the high rates of evaporation (> 10 mm/day; Holmes and others, 1981). GAB mound spring formation is related directly to a low flow rate (Ponder, 1986). Springs with higher flow rates have associated channels (i.e., spring tails) that distribute the discharged fluids away from the spring vent, whereas decreased flow rates allow for the precipitation at the vent, resulting in the building up of the mound. The GAB mound springs are composed of eolian sand, plant debris, and mud and sand carried up through fractures by the spring discharge (Ponder, 1986). According to Stokes law, a discharge rate of greater than 4 cm/s is required to lift fine sand within a fracture (Williams and Holmes, 1978). The Morrison carbonate mound springs are similar in shape to the GAB mound springs but have a subartesian component. No detrital sand or clay has been found in the Morrison mound springs suggesting discharge rates were < 4 cm/s. Low flow rates facilitated the building of the mound. The lack of associated fluvial, paludal, or lacustrine facies supports the interpreted low surface discharge rate. The spatial distribution of the siderite buildups and carbonate mounds in proximity to Late Jurassic faults or fractures corresponds to the azimuth orientation of the present-day major Montana lineaments (figure 15). The Morrison floral productivity in central Montana is a manifestation of low elevation and precipitation rates. The floral productivity resulted in abundant decomposing organic carbon on the forest floor and into the shallow subsurface. The precipitation and groundwater geochemically interacted with the organic carbon to produce more negative δ13C values. The high productivity of the region (Rees and others, 2000, 2004), and the low negative δ13C values suggest that the groundwater had a relatively short residence time in the subsurface otherwise the δ13C values would have been substantially isotopically lighter (≈ ‒25‰). In contrast, a relatively longer subsurface residence time is suggested by the isotopic values for Group B in figure 14. Paleoclimatic Significance Morrison Formation sediments are interpreted to have been deposited under a strongly seasonal arid to semi-arid climate (Dodson and others, 1980; Parrish and others, 1982, 2004; Hotton, 1986; Parrish and Peterson, 1988; Turner and Fishman, 1991; Valdes and Sellwood, 1992; Demko and Parrish, 1998; Demko and others, 2004). The aridity was likely generated by several factors including the latitudinal position in the subtropical dry belt, the Sevier orogenic belt acting as a rain shadow (Demko and Parrish, 1998), and oceanic upwelling driven by coastal wind patterns (Parrish and Peterson, 1988). Peterson and Turner-Peterson (1987) suggested the presence of narrow but extensive riparian environments that supported abundant plant life to sustain the large herbivorous dinosaurs that roamed the Morrison basin. Similar to modern continentality, the proximity of the northward-retreating Sundance sea during the Late Jurassic likely created cool and wet coastal climates in central Montana in contrast to the more southern inland continental regions. Palynological research over the Morrison basin shows the paleoclimate transitioned from arid in the southern latitudes to a more humid climate in the northern clines (Hotton and Baghai- Riding, 2010; Baghai-Riding and others, 2015). The discovery of the boreal wood Xenoxylon in the Morrison Formation of central Montana corroborates a wet climate in the northern basin latitudes (Richmond and others, 2019a). The newly discovered partial bryophyte leaves with their chambers occupied by cyanobacteria also provide some insights into the paleoclimate. Bryophytes live in a wide variety of habitats; however, they prefer moist environments (Schuster, 1966; Shaw and Renzaglia, 2004). Their preservation in mound springs indicates proximity to the outlet. If the microphyte fabric is O. stratum or a close relative, then its presence in association with the Morrison carbonate mound springs provides additional insights into the paleoclimate of the Morrison Formation of central Montana. Modern 19 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 O. stratum is present in warm- and cool-temperate climates (Pentecost, 1990, 2005) but is more prevalent in regions where summer temperatures exceed 25oC (Pentecost, 1991). Semi-arid conditions are incapable of sustaining the perennial highwater table necessary for continuous discharge to form tufa deposits (Pedley, 1990). Consequently, regions with higher rainfall and temperatures promote tufa formation (Ford and Pedley, 1996). An average annual temperature between 5o to 15o C is suggested to be the most favorable to tufa formation and growth (Pentecost, 1991; Ibarra and others, 2014). Stable isotope data from the mound springs have a negative δ18O. This verifies that during the Late Jurassic central Montana’s paleolatitude was between 40o to 50o (Richmond and others, 2019a) and that the area experienced increased rainfall. Tufas generally occur in regions characterized by an annual rainfall over 500 mm/year (Pentecost, 1991; Ibarra and others, 2014). Tufas with Oocardium commonly have rainfall that exceeds 1000 mm/year (Ibarra and others, 2014). Using the elemental analyses to calculate the calcium and magnesium weathering index (CALMAG) of paleosol B horizons in the Morrison Formation of south-central Montana, Myers and others (2014) estimated a mean annual rainfall for the region ≈ > 1200 mm/year. The occurrence of the tufas and a varied paleoflora and the CALMAG data of Myers and others (2014) indicate that during the Late Jurassic central Montana experienced a warm temperate (Rees and others, 2004) to cool temperate climate with dry warm summers and with increased precipitation during the cool winter months. The ERT data displays the presence of larger mounds in the subsurface, with mudstone strata between the Figure 15. Spatial map of the carbonate and siderite buildups. The buildups are divided into clusters. The insert shows the Prairie Dog Dam cluster arrays. Lines of best fit for the respective arrays and clusters are shown. The azimuth bearing of each line is similar to the strike of the regional lineaments of Montana, suggesting a correlation between the buildups and the structural lineaments. Refer to figure 2 for the locations of the structural lineaments. 20 Carbonate Mound Springs of the Upper Jurassic Morrison Formation of Central Montana and Their Paleoclimatic Significance for the Northern Foreland Basin Richmond, D.R., Pigott, J., Lupia, R., Behm, M., and Hein, D. Geology of the Intermountain West 2021 Volume 8 surface and the subsurface mounds. These subsurface data provide two inferences about the mounds. First, the larger mounds record a prolonged period of increased precipitation. Second, the environmental conditions required for the mounds were not continuous. The separation of the subsurface and surface by mudstone deposition suggests that there were dry periods with insufficient precipitation to create mounds. The numerous carbonate mound springs, and their variable stratigraphic positions within the formation (40 to 52 m), suggest wet cycles during the Late Jurassic of central Montana, interspersed with drier periods of undetermined duration. CONCLUSIONS The discovery of numerous mound springs represents the first observed occurrence of tufa deposits in the Morrison Formation and some of the oldest tufa deposits documented for North America (Dorney and others, 2017; Parrish and others, 2017, 2019). The spatial data demonstrate a linear relationship to the buildups and mounds that were likely sourced by carbonate-rich water from fractures along Jurassic-aged lineaments. The siderite buildups, with their cone-in-cone structures, formed in the subsurface near the capillary fringe. In the subsurface, the groundwater interacted with the iron-rich soils of the forest floor. XRF data of the various siderite buildups suggest a variable chemistry caused by the groundwater interacting with local soils. Betaproteobacteria advanced the precipitation of the iron carbonates in the subsurface. The carbonate mound springs formed from groundwater surface seeps leaking up fractures. Spring flow rates are interpreted to have been subartesian, as there are no connecting fluvial or lacustrine facies. The precipitation of the carbonate mounds was inorganic and organic. The presence of spherulites shows that betaproteobacteria played a part in the carbonate precipitation. The mound spring waters discharged at the surface are interpreted to have been cool (< 20oC) based on the isotopic data, the lack of evidence for CO2 degassing at the vent, low sulfur percentages, and the associated algal material (e.g., Oocardium). The presence of the algal material in the spherulites, algal films on the dogtooth calcite crystals, the incorporation of Oocardium, bryophyte leaves, and homoxylous wood of gymnosperm logs into the mounds also indicate the mounds formed at the surface with plants living near the springs. The isotopic δ13C data indicate that the groundwater was meteoric in origin, occurring in a low elevation continental setting that experienced high rainfall. The stratigraphic sections and the ERT subsurface data of the mound springs imply repeated periods of increased precipitation separated by drier periods. This wet climate for the Morrison Formation of central Montana is in contrast to the climate models and interpretations of the more southern regions. ACKNOWLEDGMENTS We especially thank the Hein family for access to their ranch and their wonderful support during this research project. The senior author is grateful to Nate Murphy of Judith River Dinosaur Institute, Billings Montana, for his continuous field support and use of field equipment. The senior author also wishes to express appreciation to Dr. Judith Totman Parrish (University of Idaho, emerita) and Dr. Giovanna Della Porta (University of Milan) for insights and discussions. REFERENCES Andrews, J.E., 2006, Palaeoclimatic records from stable isotopes in riverine tufas—synthesis and review: Earth- Science Reviews, v. 75, p. 85–104. 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XRF Data XFR SAMPLE K Ca Mg Sr Ti Mn Fe Al Si P S Cl Total ppm Ca% Fe% Si% K% Mg% Ti% Mn% Al% P% S% Cl% Sr% Total % 1 MT MRSN 5E SM 12 3131.18 132282.00 0.00 252.44 1745.10 1206.94 57066.34 2138.97 15601.95 1068.69 1046.38 715.58 216255.57 61.17 26.39 7.21 1.45 0.00 0.81 0.56 0.99 0.49 0.48 0.33 0.12 100.00 2 MT MRSN 5E SM 19 5972.02 36233.98 0.00 166.26 2841.83 1293.74 76482.52 2044.12 22295.95 2266.48 1776.42 846.10 152219.42 23.80 50.24 14.65 3.92 0.00 1.87 0.85 1.34 1.49 1.17 0.56 0.11 100.00 3 MT MRSN 5E SM 32 3569.41 42773.11 0.00 329.16 1097.50 1331.31 35802.16 1522.89 18405.64 2656.32 2068.02 1041.84 110597.36 38.67 32.37 16.64 3.23 0.00 0.99 1.20 1.38 2.40 1.87 0.94 0.30 100.00 4 MT MRSN 5E SM 33 3853.65 108347.52 11322.44 336.68 1323.54 823.06 41170.79 2628.18 14476.71 1889.63 2011.68 872.01 189055.89 57.31 21.78 7.66 2.04 5.99 0.70 0.44 1.39 1.00 1.06 0.46 0.18 100.00 5 MT MRSN 5E SM 40.1 (RTM) 6920.68 227556.95 9538.82 171.53 2240.90 1111.31 53465.97 47274.84 136991.89 0.00 889.17 0.00 486162.06 46.81 11.00 28.18 1.42 1.96 0.46 0.23 9.72 0.00 0.18 0.00 0.04 100.00 6 MT MRSN 5E SM 40.2 (RTM) 5245.61 307804.75 12134.64 222.29 1661.44 1585.15 51842.40 27104.46 88913.66 0.00 1129.22 151.20 497794.82 61.83 10.41 17.86 1.05 2.44 0.33 0.32 5.44 0.00 0.23 0.03 0.04 100.00 7 MT MRSN 5E CM 40 (RTM) 0.00 461396.53 0.00 531.89 0.00 2043.22 4191.58 0.00 8879.2 0.00 1430.72 0.00 478473.14 96.43 0.88 1.86 0.00 0.00 0.00 0.43 0.00 0.00 0.30 0.00 0.11 100.00 8 MT MRSN 5E CM 13 (TF1) 0.00 366751.13 4313.82 385.17 729.78 3371.20 932.58 0.00 4468.97 0.00 806.93 560.62 382320.21 95.93 0.24 1.17 0.00 1.13 0.19 0.88 0.00 0.00 0.21 0.15 0.10 100.00 9 MT MRSN 5E CM 14 (TF2) 855.99 442650.75 0.00 553.64 788.41 3335.80 2798.71 7202.68 20035.29 824.64 7478.83 69.49 486594.23 90.97 0.58 4.12 0.18 0.00 0.16 0.69 1.48 0.17 1.54 0.01 0.11 100.00 10 MT MRSN 5E CM 31 0.00 482371.59 0.00 512.65 312.63 1971.81 889.29 2791.17 5546.98 0.00 1190.16 141.59 495727.87 97.31 0.18 1.12 0.00 0.00 0.06 0.40 0.56 0.00 0.24 0.03 0.10 100.00 11 MT MRSN 5E CM 31 Fracture 0.00 438273.25 0.00 295.66 1022.15 2478.04 7409.45 9438.82 26429.73 0.00 1735.04 313.41 487395.55 89.92 1.52 5.42 0.00 0.00 0.21 0.51 1.94 0.00 0.36 0.06 0.06 100.00 12 MT MRSN 5E CM 35 0.00 473172.34 0.00 375.90 0.00 716.75 1539.01 0.00 3414.16 0.00 772.19 0.00 479990.35 98.58 0.32 0.71 0.00 0.00 0.00 0.15 0.00 0.00 0.16 0.00 0.08 100.00 13 MT MRSN 5E CM 52 (WTF) 0.00 373501.91 0.00 400.89 731.08 1852.91 1463.46 0.00 4361.09 0.00 1291.29 672.71 384275.34 97.20 0.38 1.13 0.00 0.00 0.19 0.48 0.00 0.00 0.34 0.18 0.10 100.00 14 MT MRSN 5E CM 52 PW1 0.00 25522.96 0.00 28.06 46.52 120.35 380.47 0.00 42517.47 1632.49 1276.36 617.77 72142.45 35.38 0.53 58.94 0.00 0.00 0.06 0.17 0.00 2.26 1.77 0.86 0.04 100.00 15 MT MRSN 5E CM 52 PW2 0.00 46060.44 0.00 46.48 55.81 248.88 306.75 0.00 41739.52 1505.88 1286.07 795.64 92045.47 50.04 0.33 45.35 0.00 0.00 0.06 0.27 0.00 1.64 1.40 0.86 0.05 100.00 16 MT MRSN 5E CM 62 0.00 472265.28 14118.54 450.99 258.67 4288.00 3661.13 3183.74 10151.90 0.00 1951.41 0.00 510329.66 92.54 0.72 1.99 0.00 2.77 0.05 0.84 0.62 0.00 0.38 0.00 0.09 100.00 17 MT MRSN 5E CM 64 0.00 464517.72 0.00 524.01 498.62 2183.68 3149.12 0.00 5178.43 0.00 366.01 176.92 476594.51 97.47 0.66 1.09 0.00 0.00 0.10 0.46 0.00 0.00 0.08 0.04 0.11 100.00 18 MT MRSN 5E Spring 1 0.00 450894.25 0.00 582.51 746.74 2431.35 2950.03 6019.50 16748.51 0.00 3103.56 63.74 483540.19 93.25 0.61 3.46 0.00 0.00 0.15 0.50 1.24 0.00 0.64 0.01 0.12 100.00 19 MT MRSN 5E Spring 2 0.00 1135.67 9515.13 115.71 2530.29 135.59 892.31 13490.54 464707.34 1253.83 1129.61 0.00 494906.02 0.23 0.18 93.90 0.00 1.92 0.51 0.03 2.73 0.25 0.23 0.00 0.02 100.00 20 MT MRSN 5E SM Lime 0.00 2256.36 7441.88 26.75 4731.57 0.00 2726.36 40057.17 395972.38 1503.80 805.60 0.00 455521.87 0.50 0.60 86.93 0.00 1.63 1.04 0.00 8.79 0.33 0.18 0.00 0.01 100.00 21 MT MRSN 5E Paleosol 1 0.00 69271.71 11306.36 114.51 3772.76 269.16 23357.60 8939.69 312282.59 931.69 1596.20 265.34 432107.61 16.03 5.41 72.27 0.00 2.62 0.87 0.06 2.07 0.22 0.37 0.06 0.03 100.00 22 MT MRSN 5E Paleosol2 0.00 4330.17 6967.00 66.35 5207.51 150.26 14377.39 6635.15 302754.63 1544.18 1367.18 78.98 343478.80 1.26 4.19 88.14 0.00 2.03 1.52 0.04 1.93 0.45 0.40 0.02 0.02 100.00 23 NM SIT BULL Tufa 0.00 441389.34 15766.72 250.37 941.36 77.18 847.50 4699.54 16960.11 0.00 1668.01 119.45 482719.58 91.44 0.18 3.51 0.00 3.27 0.20 0.02 0.97 0.00 0.35 0.02 0.05 100.00 CM 13 (Tufa 1) Index SAMPLE K Ca Mg Sr Ti Mn Fe Al Si P S Cl Total ppm Ca% Si% Mn% Fe% S% Ti% Cl% Sr% Mg% Al% P% 1.00 CM 13 T1 A 0.00 370368.28 0.00 396.79 224.56 3124.52 1224.04 1391.14 3980.99 0.00 2681.77 604.70 383996.79 96.45 1.04 0.81 0.32 0.70 0.06 0.16 0.10 0.00 0.36 0.00 100.00 2.00 CM 13 T1 B 0.00 364566.13 0.00 392.55 0.00 2789.28 3021.21 0.00 3934.17 0.00 2078.91 534.39 377316.64 96.62 1.04 0.74 0.80 0.55 0.00 0.14 0.10 0.00 0.00 0.00 100.00 3.00 CM 13 T1 C 0.00 374920.19 10370.35 383.74 257.94 1913.42 1459.74 0.00 3884.57 0.00 1342.35 550.14 395082.44 94.90 0.98 0.48 0.37 0.34 0.07 0.14 0.10 2.62 0.00 0.00 100.00 4.00 CM 13 T1 D 0.00 369914.47 0.00 391.53 333.31 1831.99 2401.01 0.00 3685.58 0.00 1256.41 627.81 380442.11 97.23 0.97 0.48 0.63 0.33 0.09 0.17 0.10 0.00 0.00 0.00 100.00 5.00 CM 13 T1 E 0.00 360265.50 0.00 386.59 428.45 1898.12 3502.09 0.00 3966.92 0.00 1188.92 693.95 372330.54 96.76 1.07 0.51 0.94 0.32 0.12 0.19 0.10 0.00 0.00 0.00 100.00 6.00 CM 13 T1 F 0.00 360922.09 0.00 350.31 490.64 1981.44 2075.44 0.00 4351.30 0.00 1229.82 614.35 372015.39 97.02 1.17 0.53 0.56 0.33 0.13 0.17 0.09 0.00 0.00 0.00 100.00 7.00 CM 13 T1 G 0.00 373122.53 23929.49 383.38 565.73 2180.98 715.37 0.00 4440.27 0.00 905.85 591.45 406835.05 91.71 1.09 0.54 0.18 0.22 0.14 0.15 0.09 5.88 0.00 0.00 100.00 8.00 CM 13 T1 H 0.00 377277.31 0.00 364.85 595.21 1902.61 1296.46 0.00 4707.07 0.00 1171.94 590.95 387906.40 97.26 1.21 0.49 0.33 0.30 0.15 0.15 0.09 0.00 0.00 0.00 100.00 9.00 CM 13 T1 I 0.00 378719.69 0.00 420.50 648.83 1894.45 1608.29 0.00 4631.01 0.00 951.76 664.55 389539.08 97.22 1.19 0.49 0.41 0.24 0.17 0.17 0.11 0.00 0.00 0.00 100.00 10.00 CM 13 T1 J 0.00 379652.97 0.00 433.80 664.51 1863.99 2619.07 0.00 4581.89 0.00 626.70 546.23 390989.16 97.10 1.17 0.48 0.67 0.16 0.17 0.14 0.11 0.00 0.00 0.00 100.00 11.00 CM 13 T1 K 0.00 387689.09 0.00 1060.70 713.29 2088.26 1540.34 0.00 4398.08 0.00 651.20 605.24 398746.20 97.23 1.10 0.52 0.39 0.16 0.18 0.15 0.27 0.00 0.00 0.00 100.00 12.00 CM 13 T1 L 0.00 377078.81 0.00 420.46 728.14 2047.69 1513.93 1333.34 4093.75 0.00 820.21 507.13 388543.46 97.05 1.05 0.53 0.39 0.21 0.19 0.13 0.11 0.00 0.34 0.00 100.00 13.00 CM 13 T1 M 0.00 383102.31 0.00 443.02 745.98 2145.64 818.92 0.00 5046.44 0.00 980.01 463.62 393745.94 97.30 1.28 0.54 0.21 0.25 0.19 0.12 0.11 0.00 0.00 0.00 100.00 14.00 CM 13 T1 N 0.00 386069.91 0.00 426.15 792.52 1933.16 1071.15 0.00 4169.70 0.00 694.96 547.56 395705.11 97.57 1.05 0.49 0.27 0.18 0.20 0.14 0.11 0.00 0.00 0.00 100.00 15.00 CM 13 T1 O 0.00 378143.66 0.00 438.33 807.13 1825.42 1104.27 0.00 4876.85 0.00 831.33 532.40 388559.39 97.32 1.26 0.47 0.28 0.21 0.21 0.14 0.11 0.00 0.00 0.00 100.00 16.00 CM 13 T1 P 0.00 361110.88 0.00 381.54 806.60 1515.15 2465.85 0.00 4667.98 0.00 1362.02 588.92 372898.94 96.84 1.25 0.41 0.66 0.37 0.22 0.16 0.10 0.00 0.00 0.00 100.00 17.00 CM 13 T1 Q 0.00 373837.81 0.00 418.60 853.52 1679.53 1586.49 0.00 5182.90 0.00 980.96 594.73 385134.54 97.07 1.35 0.44 0.41 0.25 0.22 0.15 0.11 0.00 0.00 0.00 100.00 18.00 CM 13 T1 R 0.00 368078.00 0.00 416.97 819.08 1579.81 1219.43 0.00 5054.91 0.00 909.77 592.73 378670.70 97.20 1.33 0.42 0.32 0.24 0.22 0.16 0.11 0.00 0.00 0.00 100.00 19.00 CM 13 T1 S 0.00 371777.38 17172.13 388.57 882.27 1755.04 1697.21 0.00 4977.64 0.00 1037.06 626.80 400314.10 92.87 1.24 0.44 0.42 0.26 0.22 0.16 0.10 4.29 0.00 0.00 100.00 20.00 CM 13 T1 T 0.00 377012.59 10889.51 420.83 848.94 1930.34 964.47 0.00 5076.95 0.00 1077.17 649.30 398870.10 94.52 1.27 0.48 0.24 0.27 0.21 0.16 0.11 2.73 0.00 0.00 100.00 21.00 CM 13 T1 U 0.00 364071.00 0.00 408.56 703.90 1782.86 1853.13 0.00 5154.03 252.09 1077.87 634.32 375937.76 96.84 1.37 0.47 0.49 0.29 0.19 0.17 0.11 0.00 0.00 0.07 100.00 CM 52 (WTufa) Index SAMPLE Ba Sn Ag Nb Zr Sr Bi Pb W Cu Co Fe Mn Cr Ti Ca Al P Si Cl S Mg Total Ca% Si% Mn% Fe% S% Ti% Cl% Sr% Ba% W% 1.00 CM 52A 207.58 0.00 0.00 4.50 34.07 385.41 13.05 0.00 134.47 91.53 63.59 1001.84 2982.96 0.00 501.71 366003.69 0.00 0.00 3904.69 529.01 820.15 0.00 376678.25 97.17 1.04 0.79 0.27 0.22 0.13 0.14 0.10 0.06 0.04 2.00 CM 52B 190.41 0.00 5.44 2.32 30.85 389.37 8.89 0.00 209.87 119.53 37.64 1114.55 2222.11 40.87 555.15 337175.22 0.00 0.00 4853.09 649.52 1005.34 0.00 348610.17 96.72 1.39 0.64 0.32 0.29 0.16 0.19 0.11 0.05 0.06 3.00 CM 52C 210.14 25.42 0.00 3.00 41.86 394.08 4.94 0.00 130.20 87.55 48.39 1293.03 2521.04 66.49 682.23 372918.78 0.00 0.00 4016.09 633.50 959.95 0.00 384036.69 97.10 1.05 0.66 0.34 0.25 0.18 0.16 0.10 0.05 0.03 4.00 CM 52D 236.10 17.90 0.00 3.36 44.69 381.85 7.03 0.00 117.28 83.65 61.10 1011.38 2604.37 0.00 646.74 365351.34 0.00 0.00 3838.44 441.74 914.95 0.00 375761.92 97.23 1.02 0.69 0.27 0.24 0.17 0.12 0.10 0.06 0.03 5.00 CM 52E 225.82 22.81 0.00 1.86 29.07 411.46 6.95 6.58 135.54 95.34 58.08 674.66 2624.24 0.00 676.07 376557.69 0.00 0.00 4591.11 397.09 699.27 0.00 387213.64 97.25 1.19 0.68 0.17 0.18 0.17 0.10 0.11 0.06 0.04 6.00 CM 52F 186.89 0.00 0.00 4.02 30.58 381.23 9.10 7.10 195.72 108.01 40.21 834.65 2828.43 0.00 762.17 343277.44 0.00 0.00 4990.37 619.81 827.78 0.00 355103.51 96.67 1.41 0.80 0.24 0.23 0.21 0.17 0.11 0.05 0.06 7.00 CM 52G 204.03 16.72 0.00 3.90 27.90 379.48 8.87 5.33 160.68 97.46 51.14 800.60 3108.79 0.00 730.61 363350.22 0.00 0.00 4629.61 600.32 800.30 13468.61 388444.57 93.54 1.19 0.80 0.21 0.21 0.19 0.15 0.10 0.05 0.04 8.00 CM 52H 231.37 21.25 5.05 2.96 25.35 384.57 5.58 5.84 134.70 98.99 39.77 1062.01 4619.75 0.00 874.71 376216.13 0.00 0.00 5133.17 658.38 787.57 12766.41 403073.56 93.34 1.27 1.15 0.26 0.20 0.22 0.16 0.10 0.06 0.03 9.00 CM 52I 252.42 23.56 6.03 3.26 25.41 388.77 5.16 0.00 145.02 94.40 55.26 777.10 4742.91 56.41 874.20 379984.66 0.00 0.00 4582.75 544.48 641.00 0.00 393202.80 96.64 1.17 1.21 0.20 0.16 0.22 0.14 0.10 0.06 0.04 10.00 CM 52J 223.93 16.07 0.00 2.34 33.74 371.51 5.58 4.93 140.56 93.28 50.70 720.99 3871.05 0.00 869.23 382692.31 0.00 0.00 4215.58 546.57 705.66 0.00 394564.03 96.99 1.07 0.98 0.18 0.18 0.22 0.14 0.09 0.06 0.04 11.00 CM 52K 216.89 15.01 4.58 3.82 25.30 369.12 10.32 5.28 144.93 94.78 59.29 967.58 4957.59 48.60 854.81 370734.97 1801.16 0.00 4403.77 546.42 714.21 21216.99 407195.42 91.05 1.08 1.22 0.24 0.18 0.21 0.13 0.09 0.05 0.04 12.00 TX Tufa 500.06 19.10 4.36 2.45 11.71 250.37 12.40 5.88 124.27 104.39 48.36 847.50 77.18 48.64 941.36 441389.00 4699.54 0.00 16960.10 11.45 1668.01 15766.70 483492.83 91.29 3.51 0.02 0.18 0.34 0.19 0.00 0.05 0.10 0.03