Carrara Formation Research Articles

Systematics, preservation and biogeography of radiodonts from the southern Great Basin, USA, during the upper Dyeran (Cambrian Series 2, Stage 4)

AbstractAnomalocaris, the most well‐known genus of the diverse stem euarthropod group Radiodonta, was first reported over 100 years ago from the Burgess Shale (Canada). This large Cambrian apex predator was later treated as occurring in the southern Great Basin (California and Nevada, USA). We re‐evaluate the systematic affinities of previously described material from the Pioche Formation, Nevada, and the Latham Shale, California, and describe the first radiodonts from the Pyramid Shale Member, Carrara Formation, California. Latham Shale (Cambrian Series 2, Stage 4, upper Dyeran) specimens previously assigned to Anomalocaris are reinterpreted as Ramskoeldia consimilis?, an amplectobeluid previously known only from the Chengjiang biota (Cambrian Series 2, Stage 3). Younger material from the Pioche and Carrara Formations (Series 2, Stage 4) is described as a new Anomalocaris species, A. magnabasis. This new species sheds light on the two‐part structure of Anomalocaris ventral endites, a potentially important character for distinguishing species, and reveals a sequence of five disarticulation stages for frontal appendages. The oldest Hurdia from Laurentia is also reported from the Pioche Formation (Cambrian Series 2, Stage 4). A changeover in taxonomic composition of the Radiodonta in the southern Great Basin is recognized: Anomalocaris replaces Ramskoeldia in the upper Dyeran, but it is not associated with a replacement of local olenelloid trilobites or seen in radiodonts elsewhere in Laurentia. These new data, combined with a summary of known radiodont occurrences, suggest that Anomalocaris species did not have large geographical distributions, when compared with other radiodonts such as Hurdia and Caryosyntrips.

Mercury chemostratigraphy across the Cambrian Series 2 – Series 3 boundary: evidence for increased volcanic activity coincident with extinction?

Flood basalt volcanism represented by the Kalkarindji Province (Australia) is temporally associated with a trilobite mass extinction at the Cambrian Series 2 – Series 3 boundary, providing one of the oldest potential links between volcanism and biotic crisis in the Phanerozoic. However, the relative timing of flood basalt volcanism (Kalkarindji Province, Australia) and the trilobite extinctions, first recorded in North America, is not known. Mercury (Hg) enrichment in the sedimentary record provides a potential proxy for volcanism which may facilitate improved chronologies of eruption and extinction. Here we report mercury records for three sections from mid-shelf strata of the Great Basin (western USA) that straddle the Series 2 – Series 3 boundary. One section (Oak Springs Summit, NV) features a Hg enrichment at the start of the extinction interval, but mercury anomalies are also present at lower levels. These older anomalies may record either earlier phases of Kalkarindji volcanism, eruptions in other locations, or may be the result of sedimentary and/or diagenetic processes affecting the Hg record. In the Carrara Formation at Emigrant Pass, CA, the precise extinction horizon is not well defined, but a carbon isotope anomaly (the Redlichiid-Olenellid Extinction Carbon isotope Event; ROECE) provides a stratigraphic tie point to the Oak Springs Summit section. At Emigrant Pass, Hg enrichments precede the ROECE interval and are absent in the inferred extinction zone. The Pioche Formation at Ruin Wash, NV, lacks Hg enrichment at the extinction horizon but contains older enrichments. The inconsistent Hg records between the three sections demonstrate that factors controlling Hg accumulation and preservation in marine sedimentary environments are not yet fully understood. The effects of redox fluctuations may complicate one-to-one association of sedimentary Hg enrichments and massive volcanism at the Cambrian Series 2 – Series 3 boundary and elsewhere in the geologic record.

Disc-shaped fossils resembling porpitids or eldonids from the early Cambrian (Series 2: Stage 4) of western USA.

The morphology and affinities of newly discovered disc-shaped, soft-bodied fossils from the early Cambrian (Series 2: Stage 4, Dyeran) Carrara Formation are discussed. These specimens show some similarity to the Ordovician Discophyllum Hall, 1847; traditionally this taxon had been treated as a fossil porpitid. However, recently it has instead been referred to as another clade, the eldonids, which includes the enigmatic Eldonia Walcott, 1911 that was originally described from the Cambrian Burgess Shale. The status of various Proterozoic and Phanerozoic taxa previously referred to porpitids and eldonids is also briefly considered. To help ascertain that the specimens were not dubio- or pseudofossils, elemental mapping using energy dispersive X-ray spectroscopy (EDS) was conducted. This, in conjunction with the morphology of the specimens, indicated that the fossils were not hematite, iron sulfide, pyrolusite, or other abiologic mineral precipitates. Instead, their status as biologic structures and thus actual fossils is supported. Enrichment in the element carbon, and also possibly to some extent the elements magnesium and iron, seems to be playing some role in the preservation process.

Trilobite extinctions, facies changes and the ROECE carbon isotope excursion at the Cambrian Series 2–3 boundary, Great Basin, western USA

The mass extinction of the olenellid trilobites occurred around the Cambrian Series 2–Series 3 boundary. Like many other crises, it coincided with a negative carbon isotope excursion but the associated palaeoenvironmental changes remain unclear. To investigate the causal mechanism for this event, we report facies changes, pyrite framboid petrography and carbon isotope values from Cambrian Series 2–Series 3 (traditionally Early–Middle Cambrian) boundary strata of the Carrara Formation (Death Valley region, California) and Pioche Formation (Nevada). These data reveal regionally changing water depths from high-energy, nearshore facies (oolitic grainstone) to more offshore silty marl and finer-grained carbonate mudstone. In the Carrara Formation, the series boundary occurs within a deepening succession, transitioning from high-energy, nearshore facies (oolitic grainstone and oncolitic packstone) to offshore marl, the latter of which contains pyrite framboid populations indicative of low-oxygen (dysoxic) depositional conditions. Intermittent dysoxia persisted below sub-wave base settings throughout the early and middle Cambrian, but did not intensify at the time of extinction, arguing against anoxia as a primary cause in the olenellid trilobite extinction. Within both field areas, the extinction interval coincided with a minimum in δ13Ccarb values, which we interpret as the regional manifestation of the Redlichiid-Olenellid Extinction Carbon isotope Excursion (ROECE). The Series 2–Series 3 boundary is reported to closely coincide with a large-amplitude sea-level fall that produced the Sauk I/II sequence boundary, but the placement of the Series 2–Series 3 boundary within a transgressive interval of the Carrara Formation shows that this is not the case.The main sequence boundary in the succession occurs much lower in the succession (at the top of the Zabriskie Quartzite) and therefore precedes the extinction of the olenellids and ROECE.

KochiellaPoulsen, 1927, andHadrocephalitesnew genus (Trilobita: Ptychopariida) from the early Middle Cambrian of western North America

Kochaspids are an informal group of ptychopariid trilobites that were both abundant and widespread in the early Middle Cambrian of North America. Based on the reassociation of pygidia and cranidia of some kochaspids,KochiellaPoulsen, 1927, is redefined andHadrocephalitesn. gen. is proposed.Hadrocephalitesincludes taxa previously assigned by Rasetti and Palmer toSchistometopusResser, 1938a.Schistometopusis considerednomen dubium.Representatives ofKochiellaandHadrocephalitesfrom the Pioche Shale and Carrara Formation of Nevada are described, including the new speciesKochiella rasettii, K. brevaspis, Hadrocephalites lyndonensis,andH. rhytidodes.Other kochaspids previously assigned toKochaspisResser, 1935;EiffelaspisChang, 1963;Schistometopus;andKochiellaare discussed and some are reassigned. The type specimens ofKochiella augusta(Walcott, 1886);K. crito(Walcott, 1917b);K. chares(Walcott, 1917a);K. mansfieldiResser, 1939;K. arenosaResser, 1939;Hadrocephalites carina(Walcott, 1917b), andH. cecinna(Walcott, 1917b) are re-illustrated.

KOCHIELLA POULSEN, 1927, AND HADROCEPHALITES NEW GENUS (TRILOBITA: PTYCHOPARIIDA) FROM THE EARLY MIDDLE CAMBRIAN OF WESTERN NORTH AMERICA

Kochaspids are an informal group of ptychopariid trilobites that were both abundant and widespread in the early Middle Cambrian of North America. Based on the reassociation of pygidia and cranidia of some kochaspids, Kochiella Poulsen, 1927, is redefined and Hadrocephalites n. gen. is proposed. Hadrocephalites includes taxa previously assigned by Rasetti and Palmer to Schistometopus Resser, 1938a. Schistometopus is considered nomen dubium. Representatives of Kochiella and Hadrocephalites from the Pioche Shale and Carrara Formation of Nevada are described, including the new species Kochiella rasettii, K. brevaspis, Hadrocephalites lyndonensis, and H. rhytidodes. Other kochaspids previously assigned to Kochaspis Resser, 1935; Eiffelaspis Chang, 1963; Schistometopus; and Kochiella are discussed and some are reassigned. The type specimens of Kochiella augusta (Walcott, 1886); K. crito (Walcott, 1917b); K. chares (Walcott, 1917a); K. mansfieldi Resser, 1939; K. arenosa Resser, 1939; Hadrocephalites carina (Walcott, 1917b), and H. cecinna (Walcott, 1917b) are re-illustrated.

Abstracts: Middle Cambrian Thrombolite Bioherms in the Jangle Limestone Member of the Carrara Formation, Southern Nopah and Resting Springs Ranges, Southeastern California 

Abstracts: Middle Cambrian Thrombolite Bioherms in the Jangle Limestone Member of the Carrara Formation, Southern Nopah and Resting Springs Ranges, Southeastern California 

Lateral Continuity of Facies and Parasequences in Middle Cambrian Platform Carbonates, Carrara Formation, Southeastern California, U.S.A.

ABSTRACT Lateral and vertical changes within a 40-m-thick interval of peritidal carbonates (Middle Cambrian Jangle Limestone Member, Carrara Formation, SE California) produce a mosaic pattern of laterally continuous and discontinuous facies, shallowing-upward cycles 2-20 m thick (parasequences), and surfaces bounding parasequences. This mosaic pattern was traced, bed by bed, across 1.8 km of continuously exposed outcrop, and then correlated to sections in nearby ranges. Within parasequences, contacts between successive subtidal facies tend to be sharp but may pass laterally into gradational contacts. Most subtidal facies extend laterally for less than 300 m, passing gradationally (over tens of centimeters to meters) into other, laterally adjacent subtidal facies. Lateral facies contacts between subtidal nodular ribbon rock and intertidal fenestral limestone are gradual over a few meters, whereas contacts between vertically juxtaposed facies generally are sharp. Parasequence boundaries generally are sharp and locally show several tens of centimeters of erosional relief over lateral distances of several meters. Most parasequences and their bounding surfaces extend for the 1.8 km of outcrop studied and correlate to nearby ranges with varying degrees of confidence. Several parasequences, however, do not extend laterally for more than a few hundred meters and are not distinguishable in a vertical profile from those that extend laterally for tens of kilometers. The stratigraphic relationships at Eagle Mountain (southeastern California) support a model in which the lateral continuity of parasequence surfaces is principally determined by accommodation variations, and the lateral continuity of facies is most strongly influenced by the intrinsic dynamics of spatially and temporally heterogeneous sediment production. The presence of parasequence boundaries of highly variable lateral extent suggests that the magnitude of accommodation variations was comparatively small, consistent with the independent evidence for passive-margin subsidence and transitional greenhouse conditions for the Middle Cambrian.

Stratigraphy and Paleogeographic Setting of Paleozoic Rocks in the San Bernardino Mountains, California

Extensive exposures of pre-Mesozoic metasedimentary rocks are present in the San Bernardino Mountains. Overlying Precambrian basement are quartzite-dominated sequences previously correlated with late Precambrian and Early Cambrian miogeoclinal strata of the Johnnie Formation, Stirling Quartzite, Wood Canyon Formation, Zabriskie Quartzite, and Carrara Formation. Overlying is a thick section of carbonate rocks previously lumped into the Furnace Limestone of Carboniferous age. During the last decade extensive detailed mapping and chemical and paleontological data have shown that the sequence can be subdivided and correlated with the Cambrian Bonanza King and Nopah formations, the unconformably overlying Sultan Limestone of Devonian Age, Mississippian Monte Cristo Limestone, and the unconformably overlying Bird Spring Formation of Pennsylvanian through Permian age. Ordovician and Silurian strata have not been recognized in the area. The carbonate strata are identical to cratonal and transitional miogeoclinal strata exposed in several ranges in the Mojave Desert region, and were deposited in a shallow-marine environment. Regional isopachous and facies trends originally extended southwest across the Mojave, and suggest a westward bulge in the continental margin prior to Mesozoic truncation and compressional tectonics.

Evidence of Uppermost Proterozoic to Lower Cambrian miogeoclinal rocks and the Mojave‐Snow Lake Fault: Snow Lake Pendant, central Sierra Nevada, California

Displaced uppermost Precambrian to Lower Cambrian miogeoclinal strata occur within Snow Lake pendant in the central Sierra Nevada. These rocks have been correlated with the Stirling Quartzite, the Wood Canyon Formation, the Zabriskie Quartzite, and the Carrara Formation in the western Mojave Desert and the San Bernardino Mountains (Lahren and Schweickert, 1989; Lahren, 1989). This correlation is based on new, updated, and previously reported data including (1) lithologic similarities, (2) overall stratigraphic sequence, (3) vertical sequence within individual formations, (4) approximate stratigraphic thicknesses, (5) Skolithos in the correct stratigraphie position, (6) depositional environments, and (7) petrographic character and provenance of quartz arenites. The correlation is strengthened by the fact that Snow Lake pendant and the western Mojave share many other close similarities including (1) initial 87Sr/86Sr ratios of associated granitic rocks >0.706, (2) passive margin tectonic setting of Precambrian to Cambrian miogeoclinal rocks, (3) dikes of the Independence dike swarm, (4) possible Lower Triassic overlap sequence, the Fairview Valley Formation, (5) petrographically similar gabbroic complexes of the same age, (6) associated eugeoclinal rocks, and (7) identical(?) pre‐Tertiary structural configuration. New U/Pb zircon geochronology unequivocally shows that dikes at Snow Lake pendant are coeval with the Independence dike swarm of the eastern Sierra and the western Mojave desert and that associated gabbroic complexes in both the Mojave and Snow Lake pendant are the same age. Correlation of Snow Lake pendant with the western Mojave requires about 400 km of dextral displacement of the rocks of Snow Lake pendant, together with associated rocks (Snow Lake block), from the western Mojave Desert along the Mojave‐Snow Lake fault. Displacement most likely occurred after 150 Ma, the age of the Independence dike swarm, and before about 110 Ma, the age of major plutons within the Sierra Nevada batholith. This interpretation, if correct, holds major implications for allochthonous terranes west of Snow Lake pendant, which were probably attached to the Snow Lake block before its northward transport. In addition, a number of Paleozoic and Mesozoic tectonic features in western Nevada and eastern California may have been offset dextrally along the proposed Mojave‐Snow Lake fault.

Proterozoic and Lower Cambrian miogeoclinal rocks of Snow Lake pendant, Yosemite-Emigrant Wilderness, Sierra Nevada, California: Evidence for major Early Cretaceous dextral translation

Detailed stratigraphic and structural studies at Snow Lake pendant have established new evidence for the presence of uppermost Precambrian and Lower Cambrian miogeoclinal strata within the axial region of the Sierra Nevada batholith. Lithologic and stratigraphic data along with trace fossils, a distinctive Triassic overlap sequence (Fairview Valley Formation?), dikes probably related to the Jurassic Independence dike swarm, and structural history suggest that the older rocks of Snow Lake pendant correlate with the Stirling Quartzite, Wood Canyon Formation, Zabriskie Quartzite, and Carrara Formation in the western Mojave Desert and San Bernardino Mountains. This correlation implies approximately 500 km of dextral transport of the rocks of Snow Lake pendant along the proposed Mojave-Snow Lake fault. Movement on the fault probably took place after 148 Ma, the age of the Independence dike swarm, and prior to 110 Ma, the age of plutons in the central part of the Sierra Nevada batholith.

A probable cave breccia in Middle Cambrian limestone, southern Nevada; petrography and paleomagnetic constraints on the time of formation

ABSTRACT A spectacular limestone breccia, which occurs at or near the contact between the Carrara Formation (Early-Middle Cambrian) and Bonanza King Formation (Middle Cambrian) in the Desert Range, southern Nevada, probably reflects a cave that has subsequently collapsed and healed. The breccia blocks are angular; represent a diverse suite of shallow-water limestones that can be recognized laterally in undisputed strata; and exhibit clean truncation of late diagenetic fabrics, such as stylolites and blocky spar cements, at clast edges. In the blocks, the in situ directions of a secondary magnetization have been scattered. The age of this magnetization probably lies in the range Late Cretaceous to mid-Cenozoic, which suggests that the time of brecciation is no older than Late Cretaceous. The reccia must be older than late Tertiary, however, because it is truncated by Basin-and-Range normal faulting.

Repetitive Carbonate-Bank Development and Subsequent Terrigenous Inundation; Cambrian Carrara Formation, Southern Great Basin: ABSTRACT

Three times during the deposition of the Lower and Middle Cambrian Carrara Formation, shallow-water carbonate banks developed in southern Nevada and southeastern California. Each bank attained a minimum width of 150 km normal to the depositional strike. Eastward the banks were bordered by terrigenous clays, silts, and sands from the stable craton, and westward they were bordered by siliceous lime muds lacking shallow-water depositional features. The position of rock units with respect to 5 trilobite faunules within the Carrara suggests that carbonate deposition waxed and waned subsequent to eastward and westward migrations of areas of detrital sedimentation. During each of the 3 episodes of carbonate deposition, a sequence of 4 lithologic changes is repeated as follows: (1) upward fining and thinning of terrigenous clastic deposits; (2) the beginning of carbonate deposition, first as scattered skeletal grainstones, later as oolitic grainstone, oncolite packstone, and lime mudstone accumulating as a shallow subtidal bank; (3) the deposition of loferites, bird's-eye and mudcracked limestones, cryptalgal laminites, and stromatolites as low carbonate islands on the western half of the banks; and (4) the relatively abrupt termination of carbonate deposition with renewed sedimentation of detrital clay and silt. Each sequence is repeated farther east during succeeding episodes of carbonate sedimentation. End_of_Article - Last_Page 782------------

Late Precambrian-Early Cambrian Stratigraphy of Kelso Mountains, Eastern Mojave Desert, California: ABSTRACT

A detailed study has been made of several outcrops of late Precambrian-Early Cambrian strata in the southern Kelso Mountains. These strata, which are part of the predominantly detrital basal sequence of the Cordilleran miogeocline, previously have been described only in reconnaissance. In the Kelso Mountains, these strata have been assigned to 5 regionally recognized formations. The late Precambrian Johnnie Formation, which lies unconformably on metamorphic basement, displays rapid lateral changes in lithology and thickness, perhaps due in part to infilling of uneven basement topography. Of 4 sections of Johnnie exposed, 3 are similar, consisting of 91-141 ft of quartzite and dolomite. Conformably overlying the Johnnie Formation are the late Precambrian Stirling Quartzite (186 ft thick, only the uppermost regional member is present), the late Precambrian-Early Cambrian Wood Canyon Formation (712 ft thick), the Early Cambrian Zabriskie Quartzite (75 ft thick), and the Early Cambrian lower part of the Carrara Formation (70 ft thick). Comparison of these strata with equivalent miogeoclinal strata in the Providence Mountains 8 mi southeast and with Early Cambrian cratonic strata in the Marble Mountains 30 mi south shows that the northeast-trending craton-miogeocline boundary was not an abrupt break (an interpretation based on comparison in Nevada and Utah of thick allochthonous miogeoclinal strata with autochthonous cratonic strata), but rather a relatively broad transition zone of gradual thickening of strata from southeast to northwest. End_of_Article - Last_Page 776------------

Precambrian and Paleozoic Stratigraphy of Specter Range Quadrangle, Nye County, Nevada

More than 22,000 feet of Precambrian to Upper Devonian rocks crop out in the Specter Range Quadrangle. These rocks have been divided into fourteen formations; from the oldest to the youngest they are the Johnnie Formation, Stirling Quartzite, Wood Canyon Formation, Carrara Formation, Bonanza King Formation, Dunderberg Shale, Nopah Formation (restricted), Lower Pogonip Group undifferentiated (which includes the Goodwin Limestone and Ninemile Formation), Antelope Valley Limestone, Eureka Quartzite, Ely Springs Dolomite, Undifferentiated Silurian rocks, Nevada Formation, and Devils Gate Limestone. The four oldest formations, Precambrian to lower Middle Cambrian, are composed of clastic rocks; quartzite, siltstone, and shale with thin beds of limestone and dolomite. From lowe Middle Cambrian through Upper Devonian, the rocks are mainly limestone and dolomite with thin beds of quartzite and quartz sandstone. The formational names recognized during this study are probably applicable over a wide area in south-central Nevada where in large part the stratigraphy is poorly known. Four formations are of particular interest. The Antelope Valley Limestone is mapped for the first time in this part of Nevada and its lithologic and time equivalence with the type section is demonstrated. The Goodwin Limestone and Ninemile Formation are also tentatively identified for the first time. The age of the Nevada Formation has been established as Lower Devonian (Spirifer kobehana Zone) and Middle Devonian (Stringocephalus Zone); equivalent to the rocks of the type section in the Eureka district.