Stromatolites in the Late Ordovician Eureka Quartzite: Implications for Microbial Growth and Preservation in Siliciclastic Settings
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Sedimentology (2009) 56, 1275–1291 doi: 10.1111/j.1365-3091.2008.01033.x Stromatolites in the Late Ordovician Eureka Quartzite: implications for microbial growth and preservation in siliciclastic settings PETER A. DRUSCHKE*, GANQING JIANG*, THOMAS B. ANDERSON and ANDREW D. HANSON* *Department of Geoscience, University of Nevada, Las Vegas, NV 89154-4010, USA (E-mail: [email protected]; [email protected]) Department of Geology, Sonoma State University, Rohnert Park, CA 94928, USA Associate Editor – Daniel Ariztegui ABSTRACT Well-preserved siliciclastic domal stromatolites, up to 2 m wide and 1Æ5m high, are found in a 10 to 15 m thick interval within the Late Ordovician Eureka Quartzite of Southern Nevada and Eastern California, USA. These stromatolites appear as either isolated features or patchy clusters that contain more than 70% by volume quartz grains; their association with planar, trough and herringbone cross-bedding suggests that they were formed in an upper shoreface environment with high hydraulic energy. In this environment, sand bars or dunes may have provided localized shelter for initial microbial mat colonization. Biostabilization and early lithification of microbial mats effectively prevented erosion during tidal flushing and storm surges, and the prevalence of translucent quartz sand grains permitted light penetration into the sediment, leading to thick microbial mat accretion and the formation of domal stromatolites. Decimetre-scale to metre-scale stromatolite domes may have served as localized shelter and nucleation sites for further microbial mat colonization, forming patchy stromatolite clusters. Enrichment of iron minerals, including pyrite and hematite, within dark internal laminae of the stromatolites indicates anaerobic mineralization of microbial mats. The occurrence of stromatolites in the Eureka Quartzite provides an example of microbial growth in highly stressed, siliciclastic sedimentary environments, in which microbial communities may have been able to create microenvironments promoting early cementation/lithification essential for the growth and preservation of siliciclastic stromatolites. Keywords Eureka Quartzite, Late Ordovician, microbial mats, siliciclastic stromatolite, Western Laurentia. INTRODUCTION depositional environment that inhibit stromato- lite growth and preservation. For example, due to In modern shallow marine environments, micro- the generally high sediment mobility in siliciclas- bial mats are common on both siliciclastic and tic environments, frequent disturbance by waves carbonate substrates (Gerdes et al., 2000; Riding, or tides may prevent the development of thick 2000; Porada & Bouougri, 2007) but siliciclastic microbial mats unless episodes of low or zero stromatolites are scarce compared to their carbon- sedimentation occur to allow microbial commu- ate counterparts in the rock record. The paucity of nities sufficient time to repeatedly re-establish stromatolites in siliciclastic strata may relate to and stabilize on sediment surfaces (Reineck & physical conditions and processes within the Gerdes, 1997; Lee et al., 2000; Draganits & Noffke, Ó 2008 The Authors. Journal compilation Ó 2008 International Association of Sedimentologists 1275 1276 P. A. Druschke et al. 2004). In siliciclastic environments with a turbid mats may be induced by cyanobacterial sheath water column, stromatolite growth may be inhib- calcification during photosynthesis (Riding, 2006; ited by reduced light penetration. Environments Arp et al., 2001; Kah & Riding, 2007). However, with mixed grain-sizes and composition may not microbial mat degradation and heterotrophic be as favourable for microbial mat growth as those bacterial metabolism may play a more critical with predominately clean, fine-grained to med- role (Pratt, 1984, 2001; Chafetz & Buczynski, ium-grained quartz sand (Gerdes & Krumbein, 1992; Knoll & Semikhatov, 1998; Bartley et al., 1987; Noffke et al., 2001, 2002). 2000). In the latter lithification process, carbonate These environmental limitations, however, are substrates are more favourable for catalyzing not unique to siliciclastic settings. Abundant, mineral overgrowth over pre-existing carbonate well-preserved stromatolites have been docu- crystals. In siliciclastic environments, stromato- mented in carbonate environments with compa- lites may experience early lithification only when rable sediment grain-size, water depth, wave localized environments induce high carbonate energy and nutrient supply. A more fundamental alkalinity through evaporation (Braga & Martı´n, control on the growth and preservation of silici- 2000) or by strong mineralization of microbial clastic stromatolites may be early cementation/ mats. lithification (Grotzinger & Knoll, 1999). Trapping This paper reports well-preserved stromatolites and binding of sediment particles by microbial from the Late Ordovician Eureka Quartzite in mats is a phenomenon common in both silici- Southern Nevada and South-eastern California of clastic and carbonate environments but these the Western USA (Fig. 1A). The Eureka Quartzite processes alone are insufficient to permanently in this region consists predominantly of fine- stabilize sediment in the absence of early cemen- grained to medium-grained quartz arenite depos- tation (Grotzinger & Knoll, 1999; Pratt, 1979). ited in tropical, high-energy shallow marine Under the appropriate conditions (e.g. a high environments. The presence of centimetre-scale 2þ 2À Ca =CO3 ratio), early lithification of microbial to metre-scale stromatolites in such a high-energy Fig. 1. (A) Location of measured sections in South-eastern California and Southern Nevada in the vicinity of Las Vegas: 1: Northern Nopah Range (NR); 2: Southern Sheep Range (SR); 3: North-western Arrow Canyon Range (ACR); 4: Silica Quarry within the South-eastern Arrow Canyon Range. (B) Generalized map showing the distribution of the Eureka Quartzite and its equivalent units along the western margin of Laurentia. Dashed boundaries indicate where original continuity is inferred (modified from Ketner, 1968). The ‘Las Vegas Arch’ (Cooper & Keller, 2001) refers to a potential Ordovician highland that may have influenced the distribution and thickness of the Eureka Quartzite. Additional ‘arch’ locations are from Burchfiel et al. (1992). (C) Generalized Ordovician stratigraphy of California and Nevada (modified from Cooper & Keller, 2001). Ó 2008 The Authors. Journal compilation Ó 2008 International Association of Sedimentologists, Sedimentology, 56, 1275–1291 Siliciclastic stromatolites in the Eureka Quartzite 1277 shallow marine setting provides insight into the thinning, fining and maturing trend of quartz ability of benthonic microbial mats to: (i) colonize arenite units along the Western Laurentian mar- highly stressed siliciclastic depositional environ- gin (Ketner, 1968) and the presence of 1Æ8to ments; and (ii) create localized chemical condi- 2Æ4 Ga detrital zircons within the Eureka Quartz- tions through mat mineralization that possibly ite, which is consistent with the age distribution facilitate early lithification and, ultimately, of Cambrian quartz arenites in the Peace River stromatolite preservation. Arch (Gehrels et al., 1995). The sections measured during this investigation are located in Southern Nevada and South-eastern GEOLOGICAL SETTING California (Fig. 1A). This region represents the southern limit of the Eureka Quartzite in the The Ordovician Eureka Quartzite represents the Western USA, as the early Palaeozoic platform only significant sandstone interval within the was truncated by late Palaeozoic sinistral strike- several kilometres thick Middle Cambrian to slip faulting that translated earlier platform depos- Devonian carbonate succession of the Western its south-eastward to Sonora, Mexico (Ketner, USA. The Eureka Quartzite is composed predom- 1986; Stone & Stevens, 1988). The original conti- inantly of fine-grained to medium-grained, silica- nuity of the lower Palaeozoic platform has been cemented quartz arenite (Ketner, 1968). The term disrupted further by the Cretaceous Sevier orog- ‘quartzite’ is a relic of antiquated sandstone eny and Cenozoic extensional faults along much classification terminology but, nevertheless, sur- of the North American Cordillera (Poole et al., vives as part of the formal stratigraphic nomen- 1992). Nonetheless, well-preserved Cambrian to clature of the Eureka Quartzite. Ordovician successions are exposed in this region and the Eureka Quartzite is a prominent marker for stratigraphic correlation in the field. Tectonic framework The Eureka Quartzite was deposited on a west- Stratigraphy and age dipping carbonate ramp along the Western Lau- In Southern Nevada and Eastern California, the rentian margin during Middle to Late Ordovician Eureka Quartzite rests on the Middle Ordovician times. The Western Laurentian margin has gen- Pogonip Group and is overlain by the Late erally been considered as a passive margin from Ordovician Ely Springs Dolomite (Fig. 1C). The the latest Neoproterozoic to Late Devonian (Bur- upper boundary of the Eureka Quartzite is con- chfiel et al., 1992; Poole et al., 1992). The Eureka formable but the lower boundary is marked by a Quartzite and correlative units crop out over a major karstic unconformity with considerable vast area of >450 000 km2 in Western North erosion (Cooper & Keller, 2001). America, including portions of Eastern California, The age of the Eureka Quartzite is roughly Nevada, Western Utah, Southern Idaho and constrained by the biostratigraphy