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The Sedimentary Record Paleoclimate and the Origin of Paleozoic : Time to Re-Examine the Origins of Chert in the Rock Record

C. Blaine Cecil Scientist Emeritus, U.S. Geological Survey, MS 956, 12201 Sunrise Valley Drive, Reston, VA 20192-0002

INTRODUCTION: THE CHERT PROBLEM conditions associated with chert occurrence. Depositional Paradigms regarding the origin of sedimentary chert have interpretations for Paleozoic CPM examples include the remained largely unchanged for decades. Extant paradigms following: a) inferred deep marine along paleo-continental generally focus on some aspect of biogenic extraction and margins, b) shallow shelves and epicontinental seas, c) precipitation of silica from seawater without explicitly supratidal environments, and d) nonmarine chert associated addressing the primary source of silica (e.g., Gutschick and with aeolinites. Chert that may have formed on abyssal plains Sandberg, 1983; Maliva, et al., 1989; Beauchamp and Baud, has been lost to subduction. I compare chert examples for 2002; Pope and Steffen, 2003). The primary sources of each of these settings to paleoclimate interpretations of Boucot silica in modern oceans have been attributed predominantly et al., (2013). to river input with lesser amounts coming from submarine groundwater discharge, dust, seafloor weathering, and CHERT: TO PERMIAN hydrothermal vents respectively (Tréguer and De La Rocha, Cambrian and chert 2013). However, any changes in the order of predominance Examples of CPM in inferred deep water include the among these sources through time are unknown. In this paper Middle and Late Ordovician Bigfork*** and Maravillas I reintroduce a rarely discussed paradigm that attributes the in the Ouachita-Marathon structural trend (Goldstein, 1959), predominant source of silica for Paleozoic chert to aeolian and Ordovician chert in the Cordilleran basin margin in deposition of siliceous sediments (hereinafter, dust) (Haught, Nevada and Idaho (Ketner, 1969). Virtually all these cherts 1956; Banks, 1970; Cecil, 2004). The dust hypothesis contain dispersed detrital quartz sand and silt (Goldstein, also may help explain chert of nonmarine origin, as will be 1959; Ketner, 1969) suggesting aeolian deposition. An arid discussed subsequently. The dust hypothesis is based in part paleoclimate prevailed across the NAC during the Cambrian on an apparent empirical correlation between chert occurrence and Ordovician (Boucot et al., 2013; Maps 1-4) when CPM and paleoaridity (Cecil, 2004)*. The empirical correlation was deposited. The source of silica for much of the late between chert occurrence and paleoaridity is further developed Middle and Late Ordovician chert I refer to as deep water herein by comparing multiple depositional environments has been attributed to upwelling on subtidal ramps (Pope for Paleozoic chert parent material (CPM) across the and Steffen, 2003). However, chert is common throughout conterminous (North America craton; NAC) Cambrian and Ordovician strata across the NAC (Hein and to the paleoclimate maps of Boucot et al., (2013)**. Inferred Parrish, 1987) where upwelling does not appear to reasonably depositional environments for CPM are derived from the account for CPM deposition far removed from inferred zones literature (e.g., Hein and Parrish, 1987, Appendix 2-1; among of upwelling or for detrital quartz in chert. many others), or personal experience. Where applicable, I also Both bedded and nodular cherts also occur in Cambrian present ancillary observations on the relation between arid and Ordovician shallow water carbonates (Hein and Parrish, paleoclimates and the temporal and spatial distribution of 1987). In the Appalachian basin (AB), shallow water quartz arenites whose textural and mineralogical maturity may, carbonates contain silicified oolites (Upper Cambrian Mines in part, be attributed to ancient aeolian processes (e.g., Dott, Dolomite Member, Gatesburg Formation; Early Ordovician 2003), regardless of the final depositional environment; such Nittany Dolomite, Beekmantown Group; Centre Co. PA), processes could have been major producers of dust. and silicified intraclastic carbonate with pellet structure (Early Ordovician Axemann of Beekmantown CPM Depositional Settings Group, Centre Co., PA) (e.g., Folk and Pittman, 1971) and CPM depositional settings discussed herein partially the Middle Ordovician Lincolnshire Formation in illustrate the myriad of water depths and hydrologic (Figure 1A). In addition to shallow water chert, Montañez

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Figure 1: Photomicrographs of chert with quartz detritus floating in chert matrices. The primary source of silica for chert parent material, including detritus, is interprted to be the result of atmospheric deposition of siliceous dust. 1A. Chert in Middle Ordovician (Blackriveran) Lincolnshire Formation, Rich Patch, VA. Rounded quartz sand grain floating in the chert matrix (arrow). Scale bar is 100 μm. 1B. () Shriver Chert, Goshen, VA. Rounded quartz sand grains floating in a chert matrix. Scale bar is 200 μm. Blue color in upper right is light transmitted through mounting medium. 1C. (Visean; late Osagean to Meramecian) . Sample from road cut, Interstate 55, south of St Louis, MO. Rounded quartz sand grains (arrows) floating in a calcareous chert matrix. Scale bar is 1.0 mm. 1D. Photomicrograph, Permian (Wordian) Rex Chert Member, Phosphoria Formation. Rounded quartz sand grain (arrow) floating in a calcareous chert matrix. Numerous quartz silt grains are also present. Scale bar is 500 μm. and Read (1992) documented ANCILLARY OBSERVATIONS supermature sandstones in the Arbuckle chert replacement of gypsum ON ORDOVICIAN Mountains, Oklahoma (Dapples, 1955; (cauliflower chert) in supratidal sabkha SANDSTONES Ethington, et al., 2012) in settings that environments (Late Cambrian to The origin of Middle to Late were not far removed from the inferred Early Ordovician Upper Knox Group; Ordovician supermature quartz deep water Ordovician chert in the Maryland, Virginia, and ). arenites appears to be related to aeolian Ouachita-Marathon trend. The sand of They also noted the presence of quartz processes (e.g., Kelly et al., 2007; Dott, the Middle to Late Ordovician Eureka silt, and rounded sand grains in the 2003). Well-rounded quartz grains in Quartzite (i.e., quartz arenite) in the supratidal dolomites (Isabel Montañez, the St. Peter Sandstone are thought to western NAC is nearly identical to that personal communication) consistent be indicative of arid aeolian processes of the coeval St. Peter and Simpson with aeolian deposition. The supratidal (Kelly et al., 2007). Deposition of the (Ketner, 1966). These approximately chert occurrences indicate a probable St. Peter was approximately coeval coeval, and morphologically identical aeolian source of silica. with deposition of much of the supermature sands overlie the sub- Simpson Group to the south, including Tippecanoe I Sequence boundary of

September 2015 | 5 The Sedimentary Record Sloss (1988), an exposure surface where 1970). McBride and Thompson chert characterizes the middle division vast deserts likely existed from the Early (1970) suggest water depth in the when the climate was relatively humid. Ordovician through most of the Middle Marathon basin during Caballos CPM Relatively pure CPM deposition Ordovician, a time span of more than deposition “was probably greater than resumed for the upper novaculite 20 myr. Hypothetically, dust derived 300 feet (~90 meters [m]) and may division when the NAC became arid from Early to Middle Ordovician have been several thousand feet (meters) during the Viséan (Osagean). sand seas may have supplied the CPM deep”. Hass (1951) recognized three Deposition of CPM ceased in the in the deep-water settings, as well as divisions of the Arkansas novaculite; Ouachita-Marathon structural trend shallow water cratonic seas and adjacent an Early to Middle Devonian lower with the onset of a humid climate sabkhas. division, a middle division spanning over the central and eastern NAC in the Devonian- boundary, the (Mississippian, late chert and a Mississippian (late Kinderhookian Chesterian) (Edgar and Cecil, 2003). The Silurian paleoclimate was arid to Osagean) upper division. CPM CPM deposition in the Ouachita (Boucot et al., 2013; Map 5). Silurian deposition for the lower division (pure basin was replaced by an influx of age chert occurrences are relatively novaculite) was approximately coeval siliciclastics (Late Mississippian Stanley minor compared to other time periods with aridity (Boucot et al., 2013; Maps Group, the Early (Hein and Parrish, 1987), and will not 6 and 7) and the Early Devonian hiatus Jackfork Sandstone, and the early be discussed further here. that resulted in the sub-Kaskaskia 1 Middle Pennsylvanian Atoka groups sequence boundary of Sloss (1988). respectively). The Caballos Novaculite DEVONIAN-EARLY The impure middle division spans the stratigraphy (Folk and McBride, 1976) CARBONIFEROUS Devonian-Mississippian boundary, is consistent with a similar climatic (MISSISSIPPIAN) when deposition was coeval with change interpretation. Deep-water chert the late and Water depth is uncertain in the pluvial event in the eastern Laurentia Devonian Shallow Water Chert Ouachita/Marathon structural trend (Appalachian basin) (Cecil, 1990; Early and early Middle Devonian during CPM deposition for the Cecil, et al., 2004; Brezinski, et al., shallow water cherts are widespread Devonian-Mississippian Arkansas 2009). Unlike the pure novaculite across the NAC (Dennison, 1961) Novaculite (Hass, 1951) and Caballos comprising the lower division when when the climate was arid (Boucot Novaculite (McBride and Thompson, the climate was arid, shale and impure et al., 2013, Maps 6, 7, and 8). The examples discussed herein focus on the AB where chert is common from southwestern Virginia into New York. Chert commonly occurs in strata that underlie and overlie the sub-Kaskasia I sequence of Sloss (1988). These accumulations were coeval with the deep-water CPM deposition of the lower division of the Arkansas and Caballos Novaculite. Bedded chert below the sequence boundary in the AB includes the Shriver Chert (Oriskany Group) and the chert-bearing Corriganville Limestone (Helderberg Group) in Maryland and West Virginia, and time equivalent chert in adjacent states. The (Figure 2) overlying the sequence boundary consists of relatively pure chert in Figure 2: Devonian () Huntersville Chert, Frost, WV. Variations in bed thicknesses north central West Virginia (Sheppard are interpreted to be the result of fluctuations in dust storm duration and intensity. Person for and Heald, 1984), grading into chert scale in photo center. with minor argillaceous material in southeastern West Virginia. According 6 | September 2015 The Sedimentary Record

Figure 3: Pennsylvanian (Desmoinsian) Honaker Trail Formation; San Juan River Gorge, Raplee Anticline; Mexican Hat, Utah. A. Outcrop photo of cm-scale chert beds (arrows) in peritidal carbonate (walking sticks on right side of photo and hammer, bottom right, for scale). B. Round quartz sand grain floating in the chert. to Sheppard and Heald (1984), “even greatly diminished in cratonic seas of noted abundant aeolian sand (quartz) the cleanest chert in the Huntersville eastern Laurentia. With the return in the dolostone members. Banks has at least small amounts of dolomite of aridity in the Viséan (Osagean, suggested that the aeolian quartz sand and silt-size (quartz) detritus,” as does Meramecian, and early Chesterian) was the most likely, if not the only, the Shriver Chert (Figure 1B). The (Boucot et al., 2103, Map 10), major source of silica for the syngenetic chert. quartz detritus is consistent with dust as CPM deposition resumed across the Osagean evaporites in subtidal the source of silica. NAC. CPM deposition sites included to peritidal carbonates of the the Appalachian basin (Greenbrier Burlington and Keokuk were replaced ANCILLARY OBSERVATIONS Limestone and ), syngenetically by silica, now in the ON DEVONIAN mid-continent (Fort Payne, Boone form of geodes (e.g., Chowns and SANDSTONES Formation, Burlington, Keokuk, Elkins, 1974). Chowns and Elkins Devonian quartz arenites (Oriskany, and Warsaw ) and the (1974) noted detrital quartz silt Rocky Gap, and Healing Springs western U.S. (Redwall, Leadville, and and sand in Fort Payne and Warsaw Sandstones, AB; Sylvania Sandstone, Madison Limestones) (Gutschick and Formation supratidal dolomites, but Michigan Basin; Dutch Creek and Sandberg, 1983) among many other they suggested sponge spicules as the Hoing Sandstones, basin) occurrences. Early Viséan (Osagean) source of silica for chert replacement underlie and overlie the sub-Kaskaskia chert is common in environments of evaporate nodules. However, I sequence boundary of Sloss (1988). interpreted as carbonate shelf, shelf detrital quartz sand and silt (Figure These quartz arenites appear to have edge, and basin/trough (Gutschick 1C), suggests that syngenetic alteration been derived from reworking of sand and Sandberg, 1983). These authors of dust may have been the primary seas during sea level rise (Carman, attributed the primary source of source of silica for biogenic silica as 1936; Grabau, 1940; Cecil et al., 1991), CPM during the late Osagean to well as chert replacement of evaporites indicating these sand seas could have upwelling. However, their inferred in supratidal, peritidal, and subtidal supplied quartz-rich dust for chert. paleowind direction is not consistent environments. As with the deep-water with upwelling. Furthermore, detrital chert, CPM deposition ceased in Mississippian shallow water and quartz in chert as well as deposition of eastern NAC basins with the onset of a supratidal chert CPM in epicontinental seas that were humid climate in the late Mississippian The humid climate that developed far removed from possible upwelling (Serpukhovian) (Boucot et al., 2013; over the eastern NAC in the late zones also makes upwelling an unlikely Map 11). CPM deposition in cratonic Famennian continued through the source. environments (central and eastern Tournaisian (Cecil et al., 2004; Banks (1970) described syngenetic NAC) was replaced by accumulations Brezinski et al., 2009; Boucot et al., chert in Osagean dolostones within the of parent materials for shale, sandstone, 2013). Chert formation ceased or was Leadville Limestone in Colorado and and coal. September 2015 | 7 The Sedimentary Record

Figure 4: Early Permian, Cutler Group, Cedar Mesa Formation. A. Photo of Mokie Dugway road cut (UT RT 261), SE Utah. Dark red bands of chert (jasper) are along interpreted sand sheet facies bedding planes. Two of the chert bands are indicated with double arrow. Knife for scale (single arrow) is 8 cm. B. Two beds (double arrow) of red chert (jasper), Indian Creek drainage, SE Utah. Lower chert directly overlies dune facies; upper chert is at or near the top of inter-dune sabkha facies. Hammer, including handle, is 38 cm.

Late Carboniferous (Pennsylvanian) Lands National Park, Utah, to the sequence boundary is interpreted to chert aeolian deposition. I observed similar be the result of aeolian sediment delivery A general perhumid (“everwet”) sedimentary cycles in the upper part initiated by increasing atmospheric climate (Boucot et al., 2013, Map of the Hermosa Group (Honaker Trail high pressure, wind speeds, and climate 12) prevailed across the eastern and Fm) in exposures along the San Juan drying as sea level first began to rise. The central part of the NAC during most River trail near Mexican Hat, Utah, in loess was ultimately flooded as sea level of the and Moscovian the Paradox basin. These Missourian continued to rise, and is sequentially (Morrowan, Atokan, and Desmoinesian (?) age strata contain lowstand overlain by peritidal cherty limestone, Series). These humid conditions nonmarine sandstones (aeolianites) in impure chert, and a cherty open marine essentially eliminated low-stand deserts, marine/nonmarine cycles, whereas thin limestone capped by an unconformity, as evidenced by intense chemical (cm scale) rhythmically bedded red the upper 4th order sequence boundary. weathering and humid climate paleosols chert occurs in the marine carbonates. Paleowind directions interpreted across the NAC (Boucot et al., 2013, The aeolinites in the nonmarine parts from aeolian cross-stratification, p. 113-115). These paleosols delineate of the cycles suggest dust as a possible and paleoclimate modeling (Parrish the Sub-Absaroka sequence boundary of source of silica for these red chert beds and Peterson, 1988) indicate that Sloss (1988). as does detrital quartz in chert matrices Pennsylvanian strata in Arrow Canyon Pennsylvanian aridity and deserts (Figure 1D). were deposited down-wind of sand were restricted to far western Pangea Pennsylvanian 4th order sequences in seas in Wyoming, Colorado, and Utah. (e.g., Parrish and Peterson, 1988; Arrow Canyon, Nevada, are replete with These sand seas were probable dust Soreghan, 1992; Boucot et al., 2013, bedded chert, cherty limestones, and sources of proximal loessites (20-80 Map 12) where chert is common in decimeter scale fine-grained sandstones μm dust size fraction) overlying the Pennsylvanian marine carbonates. interpreted as aeolinites (Bishop et al., 4th order sequence boundaries, as well Two examples presented here include 2010; Cecil et al., 2003). Subaerial as chert derived from aeolian dust (< the Middle Pennsylvanian Honaker crusts and microkarst weathering on 20 μm fraction) deposition in ever Trail Formation, Paradox Basin, Utah the unconformity exposure surfaces of expanding distal marine environments as (Condon, 1997), and the Bird Spring marine carbonates suggest a relatively sea level rose. Formation, Arrow Canyon Nevada humid weathering during a hiatus (Cecil et al., 2003; Bishop et al., 2010). in deposition following exposure. ANCILLARY OBSERVATIONS Loope (1985) attributed nonmarine Following the weathering interval, ON PENNSYLVANIAN sandstones in marine/nonmarine cycles fine-grained sandstones and siltstones, SANDSTONES in the upper part of the Hermosa interpreted as loessites, were deposited The quartzose sandstones that overlie Formation (Honaker Trail?) in Canyon (Cecil et al, 2003). The loessite overlying the Sub-Absaroka sequence boundary 8 | September 2015 The Sedimentary Record in the Eastern Interior and Appalachian Utah (Loope, 1985; Mountney and under atmospheric high pressure, which basins are fluvial and relatively Jagger, 2004). Red chert commonly might have driven offshore winds and immature (Siever, 1957). This overlies facies interpreted as inner dune upwelling along continental margins. textural and mineralogical maturity sabkhas or ponds (Mountney and Conversely, it seems highly unlikely contrasts sharply with the supermature Jagger, 2004) and both underlie and that upwelling could have supplied sandstones associated with older Sloss overlie the red dune facies of the Cedar silica to the vast cratonic shelves and sequence boundaries that formed under Mesa Formation (sandstone), Utah basins far removed from continental arid paleoclimates. CPM deposition (Figure 3). Chert also occurs within margins. Provenance regions for was nearly nil in the humid regions of a facies I interpreted as a sand sheet quartz arenites that owe their textural central and eastern Pangea where there (Figure 4). The occurrence of chert and mineralogical maturity to aeolian is no evidence for aridity. Sand seas in this continental setting provides processes are interpreted as probable were restricted to western Pangea (e.g., compelling field evidence that dust sources of this quartz rich dust for Weber and Tensleep Sandstones) where was the source of silica for CPM rather CPM. Consequently, dust needs to be chert is common in marine carbonates. than upwelling, volcanics, or diagenesis further considered as a viable source of marine organisms. Dust apparently for CPM based on the empirical Permian chert collected through adhesion to moist correlation between paleoaridity and CPM for the widespread Permian silty mud surfaces or was deposited in chert occurrences as developed herein. (Wordian) Rex Chert Member of very shallow saline interdune ponds, the Phosphoria Formation (Idaho, as well as the sand sheet facies. It is * Discussion of the importance of Utah, Montana and Wyoming) noteworthy that the dust paradigm enhanced solubility of quartz dust, accumulated in western Pangea under is consistent with dust as the source and dust diagenesis could not be arid conditions when the NAC was of silica for silcretes (paleosol chert included in this paper because of space situated between 0° and 30 N (Boucot duricrust) that formed under arid to limitations (see Cecil, 2004, for a brief et al., 2013, Map 15). The phosphate, semiarid conditions (Summerfield, overview). chert, and other constituents in the 1983). ** Paleoclimate maps could not be Phosphoria Formation have been included in this paper because of space attributed to upwelling (c.f., McKelvey, CONCLUSIONS limitations. 1946; Hein et al., 2004). Ketner When compared to the paleoclimate *** In so far as possible, geologic names (2009) suggested that upwelling could scenarios included in Boucot et al. and ages used are in accordance with not have extended across the broad (2013), the Cambrian to Permian chert the US Geological Survey (URL:http:// cratonic expanse of the Rex Chert examples herein illustrate that CPM ngmdb.usgs.gov/Geolex/search) occurrence. Other workers attribute deposition was restricted to regions quartz siltstones in the Phosphoria of paleo-aridity, regardless of age or ACKNOWLEDGEMENTS to aeolian deposition (loess?) in the depositional environment. In contrast, Numerous colleagues made Phosphoria shelf environments (Carroll chert is rare or nonexistent when and valuable contributions to this et al., 1998). Whether or not there was where the paleoclimate was relatively paper, either through fieldwork, upwelling in the Phosphoria seaway humid. The empirical correlation discussions, manuscript reviews, or all remains equivocal. Deposition of < between chert occurrence and paleo- of the preceding. Principals among 63 μm aeolian dust (siltstones), and aridity is probably not coincidental. these include the following: Scott in particular the < 20 μm fraction The chert-aridity correlation supports Elrick, John Nelson, Joe Devera, (chert) may have been the primary the hypothesis that quartz-rich dust Illinois Geological Survey; William and predominant source of siliceous might be the primary and predominant DiMichele, Smithsonian Institution; sediments in the Phosphoria as well source of silica for chert. Furthermore, Frank Dulong, Bruce Wardlaw, John as for the nutrients delivered to the the enhanced solubility of quartz dust* Repetski, US Geological Survey; and Phosphoria shelf during Late Permian is a plausible source of silica for silica Peter Isaacson, University of Idaho. CPM accumulation. secreting organisms. Upwelling (e.g., I thank Earle McBride, University of Hein and Parrish, 1987; Maliva et al., Texas (Emeritus), and Michael Pope, Nonmarine chert 1989) and volcanic processes (e.g., Texas A & M University, for their Chert is not restricted to marine Goldstein 1959) are not as uniformly helpful reviews of the manuscript. environments. Red chert (jasper) applicable to the wide variety of occurs in the Early Permian Cedar CPM depositional models as is dust. Mesa Formation in the Paradox Basin, Conceivably, CPM dust was deposited September 2015 | 9 The Sedimentary Record REFERENCES DENNISON, J.M. 1961. Stratigraphy of the KETNER, K. B. 1966. Comparison of Ordovician BANKS, N.G. 1970. Nature and origin of early Onesquethaw stage of the Devonian in West eugeosynclinal and miogeosynclinal quartzites of and late cherts in the Leadville limestone Virginia and bordering states. West Virginia the Cordilleran geosyncline. U.S. Geological Colorado. 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