The Earliest Cambrian Record of Animals and Ocean Geochemical Change

INNVITEDVITED REEVIEWVIEW ARRTICLETICLE

The earliest Cambrian record of animals and ocean geochemical change

Adam C. Maloof1,†, Susannah M. Porter2, John L. Moore2, Frank Ö. Dudás3, Samuel A. Bowring3, John A. Higgins1, David A. Fike4, and Michael P. Eddy1 1Department of Geosciences, Princeton University, Guyot Hall, Washington Road, Princeton, New Jersey 08544, USA 2Department of Earth Science, University of California, Santa Barbara, California 93106, USA 3Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 4Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri 63130, USA

ABSTRACT are associated with rapid reorganizations of of macroscopic Ediacara fossils (e.g., Tyler the carbon cycle, and are superimposed on and Barghoorn, 1954; Barghoorn and Tyler, The Cambrian diversifi cation of animals long-term increases in sea level and the hydro- 1965; Ford, 1958; Glaessner and Wade, 1966; was long thought to have begun with an explo- thermal fl ux of Sr. Schopf, 2000) helped solve this conundrum, sive phase at the start of the Tommotian Age. but the sudden diversity of the Cambrian fos- Recent stratigraphic discoveries, however, INTRODUCTION sil record remained a puzzle (cf. Cloud, 1948, suggest that many taxa appeared in the older 1965). Despite abundant evidence for a vari- Nemakit-Daldynian Age, and that the diver- In his book On the Origin of Species, Charles ety of life extending back to at least 3.5 Ga, sifi cation was more gradual. We map lowest Darwin suggested that one of the greatest chal- Precambrian fossils mostly record the evo- Cambrian (Nemakit-Daldynian through Tom- lenges to his ideas was the “sudden appearance lution of bacteria and microbial eukaryotes. δ13 motian) records of CCaCO3 variability from of groups of Allied Species in the lowest known The earliest evidence for animals predates Siberia, Mongolia, and China onto a Moroc- fossiliferous strata” (Darwin, 1859, p. 306). He the Precambrian-Cambrian boundary by δ13 can U/Pb– CCaCO3 age model constrained wrote (Darwin, 1859, p. 307): only ~100 m.y. (Xiao et al., 1998; Yin et al., by fi ve U/Pb ages from inter bedded volcanic 2007; Love et al., 2009, Maloof et al., 2010b), ashes. The δ13C correlations ignore fos- “… if my theory be true, it is indisputable that before and the few unquestioned examples of Pre- CaCO3 the lowest Silurian stratum was deposited, long peri- sil tie points, so we assume synchroneity in ods elapsed, as long as, or probably far longer than, cambrian Bilateria are <15 m.y. older than δ13C trends rather than synchroneity in fi rst the whole interval from the Silurian age to the pres- the beginning of the Cambrian (Fedonkin and appearances of animal taxa. We present new ent day; and that during these vast, yet quite unknown, Waggoner , 1997; Martin et al., 2000; Jensen , δ13C , 87Sr/86Sr, uranium, and vanadium data periods of time, the world swarmed with living crea- 2003; Droser et al., 2005). Signifi cant increases org tures. … To the question why we do not fi nd records from the same carbonate samples that defi ne of these vast primordial periods, I can give no satisfac- in trace fossil diversity and complexity across δ13 the Moroccan CCaCO3 curve. The result is tory answer.” the boundary and the absence of soft-bodied a new absolute time line for fi rst appear- animals in upper Precambrian Burgess Shale– ances of skeletal animals and for changes in The dilemma Darwin faced was that if all type biotas (Xiao et al., 2002) suggest that the the carbon, strontium, and redox chemistry life descended via gradual modifi cation from general absence of bilaterian animal fossils from of the ocean during the Nemakit-Daldynian a single common ancestor, then the complex- upper Precambrian rocks is not a preservational and Tommotian ages at the beginning of ity and diversity of fossils found in Cambrian artifact. Rather, it appears that animals origi- the Cambrian. The time line suggests that strata (at that time referred to the lower part nated and began to diversify relatively close to the diversifi cation of skeletal animals began of the Silurian) demand a long interval of evo- the base of the Cambrian. Although early stud- early in the Nemakit-Daldynian, with much lution prior to the beginning of the Cambrian. ies using a “molecular clock” suggested that of the diversity appearing by the middle of During Darwin’s time, there was no evidence the divergences between major animal groups the age. Fossil fi rst appearances occurred in of this life, and all that he could offer as expla- long predated the Cambrian (Wray et al., 1996; three pulses, with a small pulse in the earliest nation was the incompleteness of the geologi- Bromham et al., 1998), some of the more recent Nemakit-Daldynian (ca. 540–538 Ma), a larger cal record: The interval of time during which work has produced dates that are closer to (if pulse in the mid- to late Nemakit-Daldynian the ancestors to trilobites, brachiopods, mol- still older than) those supported by the fossil (ca. 534–530 Ma), and a moderate pulse in the luscs, and other Lower Cambrian taxa evolved record (Aris-Brosou and Yang, 2003; Peterson Tommotian (ca. 524–522 Ma). These pulses is not preserved in the rock record. et al., 2004, 2008). Furthermore, Konservat- Beginning in the 1950s, discoveries of Pre- Lagerstätten such as the Chengjiang biota and †E-mail: [email protected] cambrian microfossils in chert and shale and the Burgess Shale record a breathtaking array

GSA Bulletin; November/December 2010; v. 122; no. 11/12; p. 1731–1774; doi: 10.1130/B30346.1; 20 ﬁ gures; 4 tables; Data Repository item 2010293.

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

of soft-bodied animals by the late Early and Lower Cambrian fossils indicate that diver- et al., 1996). Although of signifi cant interest, Middle Cambrian (Briggs et al., 1994; Hou gences among the major groups of animals this high disparity soon after a group’s appear- et al., 2004), respectively, and, together with must have occurred by that time, the assembly ance is not unique to the Cambrian. more conventional skeletal assemblages, sug- of the major animal body plans—the suites The second puzzling aspect of the Cambrian gest a great radiation of animal life during the of characters that defi ne the living phyla—in explosion, the high rate of diversifi cation, ap- Early Cambrian. many cases took longer (Budd and Jensen, pears to be in part an artifact of a frequently These observations led scientists to focus in 2000). In other words, crown-group represen- incomplete Cambrian record with a dearth of re- particular on two puzzling aspects of the Cam- tatives of most phyla (i.e., those that possess liable radiometric age constraints. Using radio- brian radiation, both encompassed by the term all of the characters of the living groups) fi rst metric dates of volcanic ash units inter bedded in “Cambrian explosion” (cf. Marshall, 2006). appear later than the Early Cambrian, and in fossiliferous strata, workers discovered that the The fi rst is the dramatic increase in disparity some cases much later. Most Early Cambrian base of the Cambrian is ca. 542 Ma (Bowring (morphological distinctness) as represented by animals are, in fact, the intermediate taxa or et al., 1993; Grotzinger et al., 1995; Bowring the supposed appearance of nearly all major stem-groups that were thought to be miss- et al., 2007), rather than 570 Ma (Harland et al., animal body plans (equivalent to the animal ing from the early animal record (Budd and 1990) or ca. 600 Ma (Holmes, 1960; Harland phyla) within a geologically brief interval of Jensen , 2000; Conway Morris and Peel, 1995; et al., 1982). This newly compressed Cam- time near the beginning of the Cambrian (e.g., Shu et al., 2001; Budd, 2002; Caron et al., brian Period led numerous authors to conclude Gould, 1989; Valentine, 1994, 2002, 2004). 2006; Skovsted et al., 2008). that diversifi cation rates had to be twice as fast This problem was compounded by an apparent Nonetheless, it is true that many Early Cam- as they already were thought to be. Despite lack of evidence for “intermediate” taxa—taxa brian taxa are at least recognizably related to these new geochronological constraints on the that lie close to the last common ancestor of crown-group phyla, suggesting that many of the Ediacaran-Cambrian (E-C) boundary and the different phyla in the metazoan tree (Marshall, basic features that distinguish the major groups length of the Cambrian Period, the duration 2006). The second diffi culty is the high rate of of animals had evolved by this time (Budd, of individual Cambrian stages associated with diversifi cation (increase in number of species) 2008). In other words, the Early Cambrian diver- specifi c animal radiations remained poorly con- in the Early Cambrian, particularly the appar- sifi cation of animals is marked by high disparity. strained. Additional U/Pb dating of zircons in ent spike in diversifi cation during the Tommo- However, the observation that disparity reaches volcanic ash layers demonstrated that the Early tian and Atdabanian ages (Fig. 1), spanning an its peak early in a group’s history seems to re- Cambrian is in fact quite long, spanning 32 m.y. interval that seemed short relative to subsequent fl ect a general phenomenon, also observed in and nearly 60% of Cambrian time (Bowring radiations (e.g., Sepkoski, 1992; Zhuravlev, plants (Boyce, 2005), the Ediacara biota (Shen et al., 1993; Grotzinger et al., 1995; Landing 2001; Marshall, 2006). et al., 2008), Precambrian microfossils (Huntley et al., 1998). Recent work suggests that the Evidence accumulated over the past 20 yr, et al., 2006), and within many individual animal Nemakit-Daldynian Stage alone was 17 m.y. however, suggests that both of these problems clades, such as crinoids (Foote, 1997), gastro- long (Landing et al., 1998; Maloof et al., 2005, have been somewhat exaggerated. Although pods (Wagner, 1995), and ungulates (Jernvall 2010a). An equally important factor as the re- fi ned time scale is the recognition that the appearance of dozens of animal taxa at the base of the Tommotian Stage in the stratotype Nemakit- West Siberia Global South China Daldynian–Tommotian (ND–T) boundary sec- (used here) Avalonia tions at Dvortsy and Ulakhan Sulugur (Siberia), 520 Atdabanian Series 2 Qiongzhusian which contributed to the classic view of an ex- ? plosive early phase of diversifi cation, actually Tommotian refl ects the presence of a signifi cant uncon- Stage 2 525 formity just below that horizon (see following ? discussion). Other lowest Cambrian sections in 530 Meishucunian Placentian northwestern Siberia and in Mongolia suggest Age (Ma) Nemakit- instead that these “Tommotian” taxa appeared Daldynian in a more gradual sequence in older rocks (Knoll

535 Lower Cambrian Fortunian Lower Cambrian Lower Cambrian et al., 1995b; Kaufman et al., 1996; Brasier Terreneuvian et al., 1996). Thus, rather than being mostly devoid of fossils, the Nemakit-Daldynian Stage 540 records the earliest diversifi cation of Cambrian animals, spread out over 17 m.y. Figure 1. Lower Cambrian stratigraphic terminology from selected Here, we examine in detail the Nemakit- regions and the global standard. Global standard names are from Daldynian through Tommotian diversifi cation the International Stratigraphic Chart (2009). Boundary ages for of animals, and, in particular, the skeletal ani- Siberia are from Maloof et al. (2005, 2010a). Correlations with mals often referred to as “small shelly fossils.” South China and West Avalonia are from Steiner et al. (2007), al- We use carbon isotope chemostratigraphy of though boundary ages are tentative. The lower boundary of the δ13 carbonates ( CCaCO3), derived from the same Lower Cambrian in each region is not necessarily synchronous. rocks that host the small shelly fossils, and cali- Because most of the sections discussed in this paper are from brate the chemostratigraphy using U/Pb zircon Siberia , and because the boundaries for global stages 2–4 have not geochronology of interbedded volcanic ashes. yet been defi ned, we use the Siberian terminology. δ13 The result is a CCaCO3 age model indepen-

1732 Geological Society of America Bulletin, November/December 2010

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Earliest Cambrian diversiﬁ cation of animals and ocean geochemical change

dent of fossil fi rst appearances. This method BACKGROUND Ediacaran (Knoll et al., 1995a; Brasier et al., of correlation is preferred over biostratigraphy 1996). Anabaritids are conical tubes, probably for two reasons: (1) the abundant evidence that Paleontology of the Lowest Cambrian originally aragonitic, with prominent triradial Lower Cambrian fossil ranges are strongly symmetry; although their systematic position re- facies-controlled (e.g., Brasier et al., 1994b; Small Shelly Fossils mains controversial, they have often been allied Lindsay et al., 1996a; Kouchinsky et al., 2007); Among the most striking fossils of the low- with cnidarians (see Kouchinsky et al., 2009). and (2) the circularity associated with inferring est Cambrian are the so-called small shelly Later-appearing groups of tubular fossils in- paleobiological patterns from biostratigraphi- fossils (Matthews and Missarzhevsky, 1975). clude the phosphatic hyolithelminths (Fig. 2B) cally correlated rock sequences. We fi nd that These consist of a variety of shells, sclerites, and aragonitic coleolids, the latter of which bear there appear to be several pulses of fossil fi rst and other biomineralized structures produced helically coiled ornamentation; their simple appearances spanning the Nemakit-Daldynian– by many independent metazoan lineages, and morphology hampers phylogenetic placement,

Tommotian interval: a small pulse (pulseeND) they are widespread in phosphatic limestones although the former may be cnidarians (Vinn, occurring ca. 540–538 Ma and recorded only from this time. Although some of these skele- 2006). The phosphatic carinachitiids and hex-

in Mongolia; a large pulse (pulsemND) occur- tons were originally phosphatic, most were angula conulariids may share afﬁ nities with the ring between 534 and 530 Ma and observed in originally calcareous and later diagenetically conulariids, probable scyphozoans (Conway both China and Siberia; and a moderate pulse phosphatized (Bengtson and Conway Morris, Morris and Chen, 1992; Van Iten et al., 2010).

(pulse T), occurring between 524 and 522 Ma 1992; Porter, 2007, 2010), allowing for their Another characteristic group of earliest Cam- during the Tommotian Stage. easy study in samples prepared through acid brian small shelly fossils are phosphatic spines Carbon isotopes in carbonates have long macera tion. Small shelly fossils are common termed protoconodonts (Fig. 2C), which are been recognized as a useful tool for strati- from the lowest Cambrian through the Boto- very similar in overall form, microstructure, and graphic correlation (e.g., Scholle and Arthur, mian in the upper Lower Cambrian, but they apparatus architecture to the grasping spines of 1980; Knoll et al., 1986; Magaritz et al., 1991; are only rarely found through the Middle Cam- modern chaetognaths (Szaniawski, 1982, 2002; Kaufman et al., 1993; Narbonne et al., 1994; brian and above, refl ecting in part the decline of Vannier et al., 2007). Protoconodonts would Brasier et al., 1994b; Knoll et al., 1995b; their primary mode of preservation—secondary therefore demonstrate the emergence of macro- Jacob sen and Kaufman, 1999; Hayes et al., diagenetic phosphatization (Dzik, 1994; Porter, scopic predation among animals. 1999; Veizer et al., 1999; Saltzman et al., 2000; 2004a). Nemakit-Daldynian and Tommotian as- Hyoliths are one of the most diverse and Walter et al., 2000; Halverson et al., 2005; semblages of small shelly fossils are particu- abundant groups of small shelly fossils. They Maloof et al., 2005). However, carbon isotopes larly well described from the Siberian platform are generally divided into two groups: the of both carbonate and organic matter also may (reviewed in Sokolov and Zhuravleva, 1983; hyolithomorphs (Fig. 2D), which have a shell preserve information about the global carbon Missarzhevskiy, 1989; Rozanov and Zhuravlev, consisting of a conical conch, an operculum to cycle, and reorganization of the carbon cycle 1992), South China (reviewed in Qian, 1989, cover the aperture of the conch, and two curv- may be a cause or an effect (or both) of paleo- 1999; Qian and Bengtson, 1989), Mongolia ing supports termed helens (Martí Mus and biological change (e.g., Hayes and Waldbauer, (Voronin et al., 1982; Esakova and Zhegallo, Bergström, 2005); and the orthothecimorphs 2006). We compare the paleontological patterns 1996), and Avalonia (Brasier, 1984; Landing, (Fig. 2E), which lack helens and have less in the lowest Cambrian with the carbon isotope 1988, 1991; Landing et al., 1989). elaborate opercula and conchs than those of δ13 composition of carbonate ( CCaCO3) and or- Small shelly fossils are signifi cant because the hyolithomorphs (Malinky, 2009). Hyoliths δ13 ganic matter ( Corg), and the strontium isotope they record the beginnings of widespread have variously been considered to be a group of (87Sr/86Sr) and trace element (Mn, Rb, Sr, V, Th, biomineralization among animals. Probable molluscs (Marek and Yochelson, 1976; Malinky U) compositions of carbonate, and speculate biomineralized metazoans are known from the and Yochelson, 2007) or a separate clade, pos- about possible causal relationships between Ediacaran, but they are low in diversity: there sibly allied with the sipunculans (Runnegar biological and environmental change during are fl anged, nested tubes (Cloudina; Grant, et al., 1975; Kouchinsky, 2000). Although some the earliest Cambrian. We show that the long- 1990; Hua et al., 2005), simple nested tubes ortho thecimorphs are clearly related to hyolitho- term Nemakit-Daldynian decline in 87Sr/86Sr is (Sinotubulites; Chen et al., 2008), goblet-shaped morphs, many Early Cambrian forms have such consistent with an increase in the hydrothermal fossils (Namacalathus; Grotzinger et al., 2000), a simple morphology that they could well be- alteration of oceanic crust and a rise in global and modular encrusting organisms (Nama- long to separate groups (Malinky, 2009). There sea level that spans the ND–T. Stratigraphic poikia; Wood et al., 2002), all of which appar- also are a variety of other conical fossils, such variability of uranium and vanadium indicates ently disappear from the fossil record at the end as Cupitheca (Fig. 2F), Paragloborilus, and a nearly monotonic increase in the oxidation of the Ediacaran (Amthor et al., 2003). Bio- Neogloborilus, that are not generally accepted of the sediment-water interface on shallow- markers recovered from sedimentary rocks sug- as hyoliths and lack satisfactory placements water carbonate platforms, consistent with the gest that demosponges were present by the latest elsewhere (Qian, 1989; Bengtson et al., 1990; gradual increase in the depth of sediment bio- Cryogenian (Love et al., 2009), and they may Malinky and Skovsted, 2004; Li et al., 2007). turbation and in the diversity of animals. We have produced spicules (Sperling et al., 2010), Many small shelly fossils do not represent

ﬁ nd that pulsemND coincides with a twofold in- but there are very few specimens that have been the entire shell of an animal, but are instead iso- δ13 crease in the amplitude of CCaCO3 oscillations identiﬁ ed as possible Cryogenian (Maloof et al., lated elements (sclerites) from a complex exter- and a switch from a carbon cycle dominated by 2010b) or Ediacaran (Gehling and Rigby, 1996; nal skeleton (scleritome). Most of them remain changes in the isotopic fractionation between Brasier et al., 1997; Reitner and Wörheide, problematic, since they are only known from dis- inorganic and organic carbon (542–534 Ma and 2002) sponge body fossils. articulated sclerites, but studies of their structure 525–517 Ma), to a carbon cycle dominated by The anabaritids are among the earliest of the and microstructure have allowed several differ- changes in the relative rate of burial of carbon- small shelly fossils to appear (Fig. 2A), and ent groups of scleritome-bearing metazoans to ate and organic matter (534–525 Ma). already may have been present in the terminal be recognized. Prominent among these are the

Geological Society of America Bulletin, November/December 2010 1733

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

A B C D E F G

H I J

K L M N

Figure 2. Cambrian small shelly fossils representing a variety of groups that ﬁ rst appear in the earliest Cambrian: (A) the anabaritid Anabarites tripartitus; (B) the hyolithelminth Hyolithellus sp.; (C) the protoconodont Protohertzina unguliformis; (D) a hyolithomorph hyolith; (E) the orthothecimorph hyolith Conotheca brevica; (F) the problematic tubular fossil Cupitheca sp.; (G) the coeloscleritophoran Australohalkieria superstes, a halkieriid; (H) the coeloscleritophoran Archiasterella hirundo, a chancelloriid; (I) the tommotiid Micrina sp.; (J) the paracarinachitid Paracarinachites sinensis; (K) the cambroclave Cambroclavus fangxianensis; (L) the mollusc Anabarella simesi; (M) the mollusc Pelagiella deltoides; (N) the cap-shaped fossil Ocruranus ﬁ nial. All scale bars are 100 μm. (A) is from the Pestrotsvet Forma- tion along the Dzhanda River, Siberia; (B) and (C) are from the Kuanchuanpu Formation at Shatan, Nanjiang, Sichuan, China; (D), (L), and (M) are from the Gowers Formation, Georgina Basin, Queensland, Australia; (E) and (K) are from the Xihaoping Member of the Dengying Formation at Xiaowan, Xixiang, Shaanxi, China; (F) is from the Parara Limestone, Horse Gully, South Australia; (G) is from the Monastery Creek Formation, Georgina Basin, Queensland, Australia; (H) and (I) are from the Parara Limestone, Curramulka Quarry, South Australia; (J) and (N) are from the Zhongyicun Member of the Zhujiaqing Formation at Dailibaoqing, Xundian, Yunnan, China; (H) and (I) are from the Parara Limestone, Curramulka Quarry, South Australia. Image (A) is courtesy of Artem Kouchinsky and reprinted from Kouchinsky et al. (2009); (B) and (C) are courtesy of Michael Steiner and reprinted from Steiner et al. (2007) and Steiner et al. (2004a), respectively; (F) is courtesy of Chris Emerling; (G) is reprinted from Porter (2004b); (H) is reprinted from Porter (2008); (J) is courtesy of Marites Villarosa Garcia; (L), (M), and (N) are courtesy of Michael J. Vendrasco and are reprinted from Vendrasco et al. (2009, 2010).

coeloscleritophorans (Figs. 2G and 2H), which sessile, radially symmetric, and superﬁ cially pearances have led many workers to conclude have hollow aragonitic sclerites (Bengtson and sponge-like (Bengtson and Hou, 2001; Janus- that the Coeloscleritophora is polyphyletic, but Missarzhevsky, 1981). Complete specimens sen et al., 2002; Randell et al., 2005), while the the similarity of their sclerites has led others to representing different groups of coelosclerito- halkieriids were bilaterally symmetric, slug-like retain the group (Bengtson, 2005; Porter, 2008), phorans are known from Burgess Shale–type animals (Conway Morris and Peel, 1995; Vin- as we do here. Less well understood coelo- deposits, revealing that the chancelloriids were ther and Nielsen, 2005). Their very different ap- scleritophorans include the siphogonuchitids

1734 Geological Society of America Bulletin, November/December 2010

(Qian and Bengtson, 1989; Conway Morris asymmetry commonly seen in the more nearly ing radiocyaths (Zhuravlev, 1986b), which have and Chapman, 1996) and sachitids (Bengtson plani spirally coiled forms (Gubanov and Peel, variously been interpreted as sponges or calcar- et al., 1990). 2000); they have also been interpreted as coiled eous algae, and the corallomorph Cysticyathus, Another major group of scleritome-bearing “worm” tubes unrelated to molluscs (Bockelie interpreted as a cnidarian (Debrenne et al., 1990; metazoans is the phosphatic tommotiids and Yochelson, 1979). Kruse et al., 1995). (Fig. 2I). Recent discoveries have allowed the A wide variety of low, cap-shaped shells that Some of the animals recorded by small partial reconstruction of several different tom- superfi cially resemble limpet-like molluscs are shelly fossils are also known from larger speci- motiids, showing that they range from forms also present (referred to herein as “cap-shaped mens. For example, there are several known with a bivalved shell to others with a tube cov- fossils”; Qian and Bengtson, 1989; Peel and occurrences of centimeter-scale helcionelloid ered with numerous irregular sclerites; their Skovsted, 2005). Some of these may indeed molluscs (Dzik, 1991; Martí Mus et al., 2008), microstructure closely resembles that of lin- represent univalved molluscs (Ponder et al., hyoliths (Orłowski and Waksmundzki, 1986), guliform brachiopods, and the tommotiids are 2007), but others have been interpreted as iso- and larger calcareous tubular problematica and probably stem-group brachiopods (Skovsted lated valves from the scleritome of a halkieriid coleolids, some of which formed small bio- et al., 2008, 2009a, 2009b; Holmer et al., 2008; or other coeloscleritophoran (Bengtson, 1992b; stromes (Landing, 1993). Other larger shelly Balthasar et al., 2009; Kouchinsky et al., 2010). Conway Morris and Peel, 1995), isolated fossils include brachiopods. Early brachio- A wide variety of other earliest Cambrian valves from a superfi cially brachiopod-like pods include Khasagtina from the Nemakit- sclerites remain more enigmatic; these include animal (Bengtson et al., 1990; Parkhaev, 1998), Daldynian of Mongolia, interpreted as a the nail- or tack-shaped cambroclaves (Fig. 2K; and isolated plates from a polyplacophoran kutorginid (Ushatinskaya, 1987), and the Tom- Bengtson et al., 1990; Conway Morris and (Fig. 2N; Vendrasco et al., 2009). Another motian paterinids Aldanotreta and Cryptotreta Chen, 1991; Conway Morris et al., 1997), rows problematic group that may be allied with mol- from Siberia (Laurie, 2000); the supposed of spine-bearing plates called paracarinachitids luscs is the stenothecoids, which had a bivalved Tommotian obolellid Nochoroiella (Grigor’eva (Fig. 2J; Qian and Bengtson, 1989; Conway shell with bilaterally symmetric valves simi- et al., 1983) may not be a brachiopod (Popov Morris and Chen, 1991), the phosphatic plates lar to those of brachiopods (Yochelson, 1969; and Holmer, 2000). of Tumulduria (Bengtson et al., 1987), and a Kouchinsky, 2001). Soft-bodied animals have a poor fossil variety of spine- or tooth-shaped fossils such as Sponge spicules have occasionally been re- record during the earliest Cambrian. Most Cyrtochites, Fomitchella, Kaiyangites, Rhombo- ported from pre-trilobitic assemblages (Zhurav- Ediacara-type fossils disappear by the end of corniculum, and Yunnanodus (Bengtson, 1983; leva in Sokolov and Zhuravleva, 1983; Pel’man the Ediacaran, but a few are now known to have Qian and Bengtson, 1989; G. Li et al., 2003; et al., 1990), as have rare fragments that have survived into the basal Cambrian (e.g., Jensen Qian et al., 2004; Yao et al., 2005). Mober- been interpreted as the remains of bivalved ar- et al., 1998). Burgess Shale–type deposits do gellans are round phosphatic plates generally thropods (Skovsted et al., 2006). Occasional not become important until the Atdabanian, interpreted as opercula from a tube-like form phosphatized soft-bodied remains, most no- with the Sirius Passet (northern Greenland) of uncertain identity, although they have also tably eggs and embryos, are also associated and Chengjiang (South China) biotas. The old- been argued to be isolated sclerites or univalved with the biomineralized small shelly fossils. est known Burgess Shale–type deposits are limpet-like shells (Bengtson, 1968; Conway A variety of spectacularly preserved embryos from South China, in the Hetang Formation Morris and Chapman, 1997; Skovsted, 2003). have been reported from the lowest Cambrian, of Anhui Province (Xiao et al., 2005) and the The most diverse group of small shelly fossils including the probable cnidarian Olivooides lowermost Niutitang Formation of Guizhou and with clear affi nities to an extant taxon is the mol- (Yue and Bengtson, 1999), the ecdysozoan Hunan Provinces (Steiner et al., 1993, 2001; luscs (Figs. 2L and 2M). Most molluscs from worm Markuelia (Donoghue et al., 2006a), and Mehl and Erdtmann, 1994; Zhao et al., 1999), the earliest Cambrian have been classifi ed as several unnamed forms, some of which may be all of uncertain Tommotian or Atdabanian age. helcionelloids, a group that ranges to the Ordo- from a segmented animal (Steiner et al., 2004b; These faunas are dominated by sponges, includ- vician and is characterized by univalved shells Donoghue et al., 2006b). ing hexactinellids and demosponges; those of that range in shape from limpet-like caps to high the Niutitang Formation also include bivalved cones to helically coiled forms; they probably Other Metazoan Body Fossils arthropods similar to Perspicaris. Finally, small include both epifaunal and shallow infaunal Body fossils of animals larger than those that organic-walled tubes called sabellidtids are com- species (Gubanov and Peel, 2000). Long con- produced the small shelly fossils do not become mon in lowermost Cambrian rocks (Urbanek sidered to be monoplacophorans, the systematic widespread until the appearance of archaeo- and Mierzejewska, 1977; Ivantsov, 1990), and position of helcionelloids is unclear, and they cyaths in the Tommotian. Archaeocyaths were likely appear fi rst during the Ediacaran Period; may not be monophyletic; they have variously long considered problematic, but are now gener- they have often been compared with tubes con- been considered as a paraphyletic stem group ally regarded as being sponge-grade metazoans structed by modern pogonophoran worms, but from which all other conchiferan molluscs are (Rowland, 2001); they made calcitic cup-like this assignment is unlikely. derived (Runnegar and Pojeta, 1974), as ances- structures and were probably fi lter feeders. Along tral only to the cephalopods and rostroconchs with calcifi ed microbes, archaeocyaths were im- Trace Fossils (Peel, 1991), as early gastropods (Parkhaev, portant framework-builders of bioherms in the Lowest Cambrian trace fossils offer a record 2001, 2008), or as an entirely extinct group of Tommotian of Siberia (Riding and Zhuravlev, of the evolution of macroscopic, primarily soft- early molluscs (Yochelson, 1978; Geyer, 1994). 1995; Kruse et al., 1995). Archaeocyaths were bodied, animals. They are also among the few Asymmetrically coiled forms such as Aldanella restricted to the Siberian platform in the Tommo- fossils to be found in siliciclastic rocks from this and Pelagiella are superfi cially reminiscent tian, and did not spread elsewhere until the Atda- time, and consequently have been the focus of of gastropods and have long been interpreted banian (Zhuravlev, 1986a). Other large, sessile, study in the hope that they could offer a means as such (Runnegar, 1981), but they also may calcareous organisms appear in the Tommotian, of biostratigraphic correlation (e.g., Crimes, be helcionelloids that have exaggerated the often in association with archaeo cyaths, includ- 1987). Although a variety of metazoan traces

Geological Society of America Bulletin, November/December 2010 1735

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

are known from the Ediacaran, they mostly rep- Doushantuo-Pertatataka acritarchs during the that do not preserve Treptichnus pedum, such resent very simple, typically unbranched hori- Ediacaran. Acritarchs increase in both diver- as Oman (Amthor et al., 2003; Bowring et al., zontal traces formed at or very near the sediment sity (Knoll, 1994; Vidal and Moczydłowska- 2007) and Morocco (Maloof et al., 2005), the surface (Jensen et al., 2006). Deeper burrowing Vidal, 1997) and disparity (Huntley et al., E-C boundary has been identifi ed using this does not become widespread until the appear- 2006) through the Early Cambrian. It has been marker carbon-isotope excursion (Amthor et al., ance of treptichnids, which are now known suggested that this diversifi cation is a result of 2003; Maloof et al., 2005). In Oman, weighted from the upper most Ediacaran (Jensen et al., the appearance of metazoans capable of con- mean 206Pb/238U dates of 542.3 ± 0.2 Ma and δ13 2000; Gehling et al., 2001). The fi rst appearance suming plankton (Butterfi eld, 1997), refl ecting 541.0 ± 0.2 Ma, below and during the CCaCO3 of Treptichnus pedum (previously known as the ecological principle that the introduction of excursion, respectively, constrain the age of the Phycodes pedum and sometimes called Tricho- predators can drive diversifi cation of their prey carbon isotope excursion (Bowring et al., phycus pedum) in the Chapel Island Formation (Stanley, 1973). 2007). These ages are broadly consistent with at Fortune Head, Newfoundland, defi nes the Calcifi ed cyanobacteria (such as Renalcis, a recalculated weighted mean 206Pb/238U date of global stratotype for the Ediacaran-Cambrian Epiphyton, and Obruchuvella) diversify through 540.61 ± 0.88 (see Appendix section A5) on a tuff boundary (Brasier et al., 1994a; Landing, 1994) the earliest Cambrian (Riding, 2001), form unconformably below sediments containing the and broadly corresponds in age to the last ap- bioherms in the Nemakit-Daldynian of Siberia fi rst Treptichnus pedum in the Nama basin of pearance of the soft-bodied Ediacara biota (Luchinina, 1999) and Mongolia (Kruse et al., southern Namibia (Grotzinger et al., 1995). The δ13 (Seilacher, 1984; Brasier, 1996). Treptichnids 1996) and thrombolites in the Tommotian of negative CCaCO3 anomaly occurs just after the consist of a series of short segments alter nating Morocco (Latham and Riding, 1990), and con- last appearance of the calcifi ed metazoan Nama- in a zigzag-like pattern, probably represent- tinue to be important framework builders in calathus and Cloudina (Grotzinger et al., 2000; ing a series of feeding and dwelling traces of Tommotian archaeocyathan reefs (Riding and Amthor et al., 2003). δ13 a worm-like animal feeding on detritus on the Zhuravlev, 1995; Kruse et al., 1995). Helically The CCaCO3 records also help calibrate sediment surface (Jensen, 1997; Dzik, 2005). coiled probable cyanobacterial fi laments are Nemakit-Daldynian time and locate the These and other early deep burrows were not known from some small shelly fossil assem- Nemakit-Daldynian–Tommotian boundary in common enough to thoroughly mix the upper blages (Peel, 1988; Qian and Bengtson, 1989). sections that lack appropriate small shelly fossils sediment layers. Unlike those of the rest of the Coccoidal and fi lamentous microfossils some- or early archaeocyaths (Maloof et al., 2010a). Phanerozoic, earliest Cambrian silts at the sedi- times are preserved in chert together with acri- Although isotope records may be truncated ment surface remained relatively fi rm, and there tarchs; some resemble cyanobacteria, but some by stratigraphic hiatuses, the morphology of δ13 was a sharp sediment-water interface (Droser tubular forms likely are not cyanobacterial (Yao CCaCO3 curves between hiatuses remains intact et al., 2002). Widespread microbial mats simi- et al., 2005; Dong et al., 2009). and may be compared from section to section. lar to those characteristic of Ediacaran and A few compressions of possible macroscopic Furthermore, we document a monotonic decline older seafl oors persisted, and some trace fos- algae have been described from the Nemakit- in 87Sr/86Sr through the Nemakit-Daldynian and sils record animals grazing on these microbial Daldynian Yanjiahe Formation of the Yangtze Tommotian that provides a unique test of the δ13 mats (Dornbos et al., 2004; Weber et al., 2007). Gorges area, Hubei Province, South China CCaCO3 correlations. In the following section, Bioturbation became much more intense in the (Guo et al., 2008); they are accompanied by we describe the geological setting of the key Atdabanian (Droser and Bottjer, 1988); eventu- problematic conical and tubular fossils that lowest Cambrian sites, and discuss the construc- ally this increase in bioturbation would result in may be metazoans. Vendotaenids are problem- tion of an age model for the Nemakit-Daldynian the destruction of microbial mats and the pro- atic fossils of possible algal or bacterial origin through Atdabanian. The result is a U/Pb- δ13 duction of a much soupier, water-rich layer at (Cohen et al., 2009), and are represented in the calibrated age model that is based on CCaCO3 the sediment surface, in what has been termed Nemakit-Daldynian by Tyrasotaenia (Gnilov- and 87Sr/86Sr correlations, that is independent of the Cambrian substrate revolution (Bottjer et al., skaya, 1985). fossil fi rst appearances, and that we use to eluci- 2000). While the makers of most trace fossils date the evolution of small shelly fossils and the from the earliest Cambrian remain unclear (al- Chemostratigraphic Correlation geochemistry of Early Cambrian oceans. though some workers have interpreted treptichnids and other traces such as Didymaulichnus Carbon isotopes have proven useful for iden- Geological Setting and Correlations of Key as the products of priapulids or similar worms; tifying the E-C boundary where sedimentary Lowest Cambrian Sites Dzik, 2005; Vannier et al., 2010), a variety of environments or lithologies are not conducive arthropod scratch marks and resting traces are to the preservation of Treptichnus pedum. In Siberia, southwest Mongolia, and South known from strata preceding the fi rst trilo- numerous mixed carbonate-siliciclastic sys- China are the only locations with more or less bites in the upper part of the Lower Cambrian tems such as the Mackenzie Mountains, Canada continuous Nemakit-Daldynian to Atdabanian δ13 (Crimes, 1987; Weber and Zhu, 2003). (Narbonne et al., 1994); Death Valley, Califor- records of small shelly fossils and CCaCO3. nia (Corsetti and Hagadorn, 2000); the Olenek Morocco is the only location with an expanded Nonmetazoan Fossils Uplift, northeastern Siberia (Fedonkin, 1985; Nemakit-Daldynian to Atdabanian record of δ13 87 86 A variety of nonmetazoan fossils also are Knoll et al., 1995a); the Dzabkhan basin, south- U/Pb-calibrated CCaCO3 and Sr/ Sr. Strati- known from the lowest Cambrian. Among pro- western Mongolia (Brasier et al., 1996; but see graphic section locations are depicted in ap- tists, these include siliceous radiolarian-like fos- Ragozina et al., 2008); and South China (Zhu proximate Early Cambrian (Fig. 3) and modern sils (Braun et al., 2007) and agglutinated tubes et al., 2001b; Weber et al., 2007), the fi rst ap- (Fig. 4) geographic coordinates. However, the (Platysolenites and Spirosolenites) regarded pearance of Treptichnus pedum occurs just plate reconstruction in Figure 3 should be con- δ13 as foraminiferans (McIlroy et al., 2001). Acri- above a deep negative CCaCO3 excursion sidered tentative and almost certainly incorrect tarch diversity is low at the beginning of the (from 0‰ to 2‰ down to –4‰ to –7‰ and in detail (uncertainties and assumptions are de- Cambrian, following the disappearance of the back again). In carbonate-dominated successions scribed in Appendix section A8). In the following

1736 Geological Society of America Bulletin, November/December 2010

Se Al ? Le MONG Kh SIB Bo KT Ts,Sa Ba Ko Su

Uralian Margin SC Xi Me Ji BALT An

I a

p Tornquist Margin

LAUR e

u EK

s MR

O KS

a TT n IB OS a ZB A omi NT SM va ad TY lonia - C WG WA AM

Figure 3. Tentative paleogeographic reconstruction for ca. 525 Ma (following Hoffman, 1991; Cawood and Pisarevsky, 2006; McCausland et al., 2007). Cratons are labeled: LAUR—Laurentia, AM—Amazonia, WA—West Africa, BALT—Baltica, SIB—Siberia, MONG—Mongolia, and SC—South China. West Gondwana is positioned such that the paleomagnetic pole from the 525 ± 5 Ma Itabaiana dikes (IB) of Amazonia (Trindade et al., 2006) is near the South Pole. Laurentia is positioned so that the paleomagnetic pole from the Mont Rigaud and Chatham- Grenville (MR) syenitic intrusions (McCausland et al., 2007) is near the South Pole. Siberia is located so that the 533–523 Ma paleomagnetic poles from the Kessyusa sandstone (KS) and Erkeket limestone (EK) from the Khorbusuonka section (Ko; Fig. 4B) are near the South Pole. Baltica is positioned so that the paleomagnetic pole from the 540–520 Ma Torneträsk Formation siltstone is near the South Pole. Mongolia and South China have no Lower Cambrian paleomagnetic constraints. Paleomagnetic poles (Table A1) and rotations (Table A2) can be found in Appendix section A8. Lower Cambrian stratigraphic sections are labeled: Morocco: ZB—Zawyat n’ Bougzoul, OS—Oued Sdas, TY—Talat n’ Yissi, SM—Sidi M’Sal; Siberia: Se—Selinde, Al—Aldan (Dvortsy and Ulakhan Sulugur), Le—Lena (Isit’ and Zhurinsky Mys), Kh—Khorbusuonka, Bo—Bol’shaya Kuonamka, Ko—Kotuikan, Su—Sukharikha; Mongolia: Ts,Sa—Tsagaan Gol and Salaany Gol, Ba—Bayan Gol, KT—Kvete- Tsakhir-Nuruu; and South China: Me—Meishucun, Xi—Xiaotan, An—Anjiahe, Ji—Jijiapo. This plate reconstruction is fraught with uncertainties and assumptions and only should be considered as a very general guide to the relative location of continents during the Early Cambrian (see Appendix section A8 for details).

Geological Society of America Bulletin, November/December 2010 1737

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

A C

MOROCCO Middle Lower Cambrian (Tata Gp) A Khorbusuonka B ! Early Lower Cambrian (Taroudant Gp) Ediacaran (Ouarzazate Gp) Lemdad Ediacaran granite

Cryogenian Kotuikan ! Proterozoic Agadir 60°N Tiout-Aguerd)" Trough Taroudant Tiout Bougzoul Dudinka Road " Yakutsk Strat. Section SukharikhaSukharika " Sdas ! Tiout City Zhurinsky Mys Isit’ DvortskyDvortsy SelindeSelinde Mirny " Ula.Sulugur Lensk " " Aldan 30°N

Msal Tiznit Tafraoute

Bol’shayaBolshaya Kuonamka ! Ust-Kut " YissiYissi 50°N Kansk Akka Krasnoyars k " " Chita Keme rovo " SIBERIA " Middle Cambrian IrkutskIrkutsk Ulan-Ude Novokuznet sk " " Early Cambrian " Aguerd Late Ediacaran Kyzyl Early Ediacaran " 29°N Roads Rivers 0 40 km Strat. section 351°E 352°E 90°E 110°E City 96°E C D 32°N Zuune Arts Jijiapo ! ! )"Chengdu Anjiahe

Jargalan 47°N )"Chongqing

Xiaotan ! Salaany Gol Tsagaan Gol 28°N

Bayan Gol Tayshir )"Guiyang

Kvete Tsakir Nuruu SOUTH CHINA MONGOLIA Middle Cambrian Cambrian Early Cambrian Ediacaran Ediacaran ! Cryogenian Meischucun Cryogenian Road Road Altai River River Strat. section Strat. section 96° 01530km City 104°E 108°E City

1738 Geological Society of America Bulletin, November/December 2010

Figure 4. Geological maps for (A) Morocco (modifi ed from Saadi et al., 1985); (B) Siberia land (Brasier et al., 1994a; Landing, 1994), it (modifi ed from Nalivkin, 1965); (C) Mongolia (modifi ed from Terman, 1973), and (D) China generally has been accepted that the Nemakit- (modifi ed from Ma, 2004). Paleogeographic locations for these maps are depicted in Early Daldynian is earliest Cambrian in age, although Cambrian coordinates in Figure 3. some workers would prefer to continue regarding the base of the Tommotian as the base of the Cambrian (most recently, Rozanov et al., 2008; Khomentovsky, 2008). sections, we summarize the geological setting conditions than those found in the Taroudant Correlation of lowest Cambrian strata across and basic correlation of each of the key low- Group (Geyer, 1989). The upper Igoudine For- the Siberian Platform has been hampered by est Cambrian sites that we use to construct the mation (ca. 519 Ma in Fig. 5) contains the old- lateral facies variations and unconformities of global age model. est known skeletal fossils from Morocco and uncertain duration. Although a great deal of bio- includes trilobites, archaeocyaths, brachiopods, stratigraphic work has been done on the lowest Morocco and chancelloriids of Atdabanian age (Geyer Cambrian of Siberia, the precise correlations The western Anti-Atlas margin of Morocco and Landing, 1995). of sections in different areas remain conten- (Fig. 4A) preserves the most expanded Lower tious (compare, for example, Val’kov, 1987; Cambrian record of carbonates in the world. Siberia Missarzhevsky, 1989; Repina and Rozanov, Following rift volcanism (577–560 Ma) and Across the Siberian Platform (Fig. 4B), upper 1992; Khomentovsky and Karlova, 1992, 1993, succeeding deposition of mixed carbonates and Ediacaran and Cambrian sediments unconform- 2002, 2005; Vasil’eva, 1998). Most authors do siliciclastics in isolated grabens, as much as ably overlie a wide range of rocks of Protero- at least recognize a lower Nemakit-Daldynian 2.5 km of dominantly carbonate sediment accu- zoic age. The location of the E-C boundary was interval characterized by anabaritids, proto- mulated on the thermally subsiding continental interpreted to be constrained by a weighted mean conodonts, and coeloscleritophorans, followed shelf (Maloof et al., 2005). Volcanic ash beds 207Pb/206Pb ID-TIMS zircon date of 543.9 ± by an upper Nemakit-Daldynian interval with a punctuate this stratigraphy, and four of these 0.24 Ma for a reworked volcaniclastic brec- wider range of small shelly fossils, and then the tuffs have yielded weighted mean 206Pb/238U cia near the base of the Nemakit-Daldynian Tommotian with a great variety of small shelly isotope dilution–thermal ionization mass spec- at Khorbusuonka (Bowring et al., 1993). The fossils accompanying the fi rst appearance of trometry (ID-TIMS) ages with ±150 k.y. preci- zircons in this breccia have lost Pb, but for the archaeocyaths. sion or better (e.g., Maloof et al., 2005, 2010a). most concordant grains, the 206Pb/238U dates are The base of the Tommotian is defi ned by an With these four ashes (and a weighted mean 542.8 ± 1.3 Ma, herein interpreted as the maxi- unconformity at the type sections at Dvortsy 206Pb/238U age of 515.56 ± 1.16 Ma, recalculated mum age for the rock. This 542.8 ± 1.3 Ma date and Ulakhan Sulugur: the upper part of the [see Appendix section A5] from the published should be used when comparing this result to Yudoma Formation is karsted, and the Tom- 207Pb/206Pb age of 517.0 ± 1.5 Ma [Landing other 206Pb/238U dates in this paper. Excellent motian fossils reported from these layers et al., 1998] from an upper Tata Group ash in preservation of small shelly fossils in lowest are in cavity fi ll deposited with the overlying δ13 the Lemdad syncline; Fig. 4A) and CCaCO3, Cambrian strata allows for a direct link between Pestrotsvet Formation (see Khomentovsky and 87Sr/86Sr, and physical stratigraphy from the four biostratigraphy and chemostratigraphy. As a re- Karlova, 1993, 2002). The duration of the hia- most complete sections in the western Anti- sult, the stage system for the Lower Cambrian tus below the Pestrotsvet Formation has been Atlas (Fig. 4A), we built the age model depicted on the Siberian Platform, where it is divided controversial; the sudden appearance of many in Figure 5. The most uncertain calibration point into the Nemakit-Daldynian, Tommotian, Atda- taxa that appear more gradually in other sec- is the E-C boundary itself, which, in the absence banian, Botomian, and Toyonian (Repina and tions suggests that it was relatively long (e.g., of Treptichnus pedum, is identifi ed based on the Rozanov , 1992; Rozanov et al., 2008), has be- Knoll et al., 1995b; Kaufman et al., 1996). Ac- δ13 morphology of the CCaCO3 curve alone. The come widely used worldwide (Fig. 1). cording to an alternative view, this hiatus was δ13 labeled CCaCO3 peaks (1p–7p and II–IV) were The Tommotian was originally defi ned as relatively short and the sudden appearance of named in Siberia (e.g., Kouchinsky et al., 2007). encompassing all of the subtrilobitic Lower many taxa refl ects their migration from other We interpret the lack of sequence boundaries Cambrian (Rozanov and Missarzhevsky, 1966; parts of Siberia (Khomentovsky and Karlova, δ13 and smooth CCaCO3 record in Morocco to in- Rozanov et al., 1969); the stratotype is on the 2002, 2005). Carbon isotope chemostratigraphy dicate that there are no signifi cant intervals of Aldan River in the southeastern Siberian Plat- supports the presence of a long unconformity missing time in the stratigraphic succession. form, where its lower boundary is defi ned near beneath the stratotype of the Tommotian, re- Unfortunately, the Nemakit-Daldynian and the top of the Yudoma Formation at the level corded elsewhere by strata in the northwestern Tommotian Stages in Morocco, recorded in the where archaeocyaths fi rst appear together Siberian Platform (Kouchinsky et al., 2007), Taroudant Group, are diffi cult to distinguish with a great diversity of small shelly fossils the western and eastern Anabar Uplift (Knoll biostratigraphically. No small shelly fossils (Rozanov , 1984; Repina and Rozanov, 1992). et al., 1995b; Kaufman et al., 1996; Kouchin- have been reported from the dolomitic Adou- The discovery that small shelly fossils ap- sky et al., 2001), and the southeastern Siberian dounian Formation (Fig. 4A; 540–524 Ma in pear more gradually in sections elsewhere in Platform (Kouchinsky et al., 2005). Fig. 5). Thrombolites in the upper half of the Siberia led to proposals for a pre-Tommotian Maloof et al. (2005) mapped the carbon iso- predominantly limestone Lie de Vin Formation stage, with broadly correlative strata being re- tope records from Ulakhan Sulugur (Brasier (ca. 521 Ma in Fig. 5) contain calcifi ed remains ferred to as the Nemakit-Daldynian (see Kho- et al., 1993) and Dvortsy (Magaritz et al., 1991) δ13 of cyanobacteria such as Renalcis (Latham and mentovsky and Karlova, 1992) or Manykayan onto the CCaCO3 curve from Morocco and Riding, 1990), but no small shelly fossils or (Missarzhevsky, 1982, 1983) stages, based on located the Nemakit-Daldynian–Tommotian archaeocyaths have been found. The overlying type sections in the Anabar Uplift. Following boundary at the zero crossing in the record of δ13 limestone-dominated Tata Group (520–516 Ma) designation of the global stratotype for the base declining CCaCO3 after the last positive anom- records a transition to more energetic marine of the Cambrian at Fortune Head in Newfound- aly (6p; Fig. 5), where Maloof et al. (2010a)

Geological Society of America Bulletin, November/December 2010 1739

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Age (Ma) 540 535 530 525 520 Zawyat n’ Bougzoul EDIAC NEMAKIT - DALDYNIAN TOMMOTIAN ATDAB MR Oued Sdas 6 Talat n’ Yissi Sidi Msal Se Selinde 4 IV Ulakhan Sulugur 3p LA Dvortsy 4p Isit’ 2p 2 5p 6p II Zhurinsky Mys Kh Khorbusuonka 1p III 7p Bo Bol’shaya Kuonamka C (‰) 0 Ko Kotuikan 13 Su Sukharikha δ Tsagaan Gol Salaany Gol –2 MG Bayan Gol Kvete-Tsakhir-Nuruu ZuuneArts –4 Me Meishucun Xi Xiaotan Anjiahe –6 Ji Jijiapo

MR15 1 Anabaratids 8 16 6 7 2 Protoconodonts 1 512 15 16 Se 4 2 3 Cap-shaped fossils 3 1514 6 12 4 Hyoliths 5 8 LA 1 7 5 Hyolithelminthes 7 4 3 8 6 1 4 16 Kh 6 Coeloscleritophorans 3 5 7 Tommotiids 8 2 1 4 Bo 8 Molluscs 2 3 9 Conulariids 1 8 6 2 4 16 Ko 10 Cambroclaves 15 8 11 Paracarinachitids 1 7 616 Su 12 Coleolids 5 13 Calcareous brachiopods 6 4 ? 3 7 14 Phosphatic brachiopods 1 5 8 13 15 MG 2 4 6 15 Archaeocyaths 1 5 11 ? 16 Trilobites 4 9 8 16 Me 3 7 12 2 1–9 m/my 1 Dolostone 8 10–29 5 ? Limestone 4 6 10 7 16 Xi 30–59 2 3 Phosphorite First appearance 6 60–99 Siliciclastic # aragonite shell 5 ? 100–149 4 8 16 Ji seq. bound # phosphate shell 12 150– # calcite shell 1 fault

Figure 5. Carbon isotopes and fossil ranges plotted against age. The age model for the Moroccan data (gray shapes: Zawyat n’ Bougzoul, Oued Sdas, and Talat n’ Yissi [Maloof et al., 2005], and Sidi M’sal [Maloof et al., 2010a]) assumes constant sediment accumulation rates between U/Pb zircon tie points. U/Pb tie points are illustrated as gray (Morocco: Maloof et al., 2005, 2010a), red (China: Brooks et al., 2006), and yellow (Oman: Bowring et al., 2007) rectangles, the centers and widths of which represent the ages and 2σ error bars, respectively, of δ13 each analysis. Each group of colored shapes represents CCaCO3 data from a different stratigraphic section. Siberia (blue)—Selinde River (Kouchinsky et al., 2005), Ulakhan Sulugur (Aldan River; Brasier et al., 1993), Dvortsy (Aldan River; Magaritz et al., 1986; Brasier et al., 1993), Isit’ and Zhurinsky Mys (Lena River; Magaritz et al., 1991; Kirschvink et al., 1991), Khorbusuonka River (Olenek Uplift; Knoll et al., 1995a), Bol’shaya Kuonamka (Anabar Uplift; Kouchinsky et al., 2001), Kotuikan River (Anabar Uplift; Knoll et al., 1995b; Kaufman et al., 1996), Sukharikha River (Kouchinsky et al., 2007). Mongolia (green)—Tsagaan Gol, Salaany Gol, Bayan Gol, Kvete-Tsakhir-Nuruu, and Zuune Arts (Brasier et al., 1996). China (red)—Meishucun (Brasier et al., 1990), Xiaotan (Zhou et al., 1997), Anjiahe (Ishikawa et al., δ13 2008), and Jijiapo (M. Zhu, 2010, personal commun.). The labeled CCaCO3 peaks (1p–7p and II–IV) were named in Siberia (e.g., Kouchinsky δ13 et al., 2007). Sections for which both CCaCO3 and biostratigraphy are available are plotted below, with line-width representing sedimentation rates inferred from the age model in meters per million years (m/m.y.), and line color representing dominant lithology (dolostone, limestone, phosphorite, or mixed siliciclastics). The lines are ﬁ lled if they represent a fossiliferous interval, and they are hollow if they are unfossiliferous. Blue hexagons, green pentagons, and red squares depict the ﬁ rst appearance of organisms producing aragonite, apatite, and calcite skeletons, respectively.

1740 Geological Society of America Bulletin, November/December 2010

reported an ash with a weighted mean 206Pb/238U of fi ne siliciclastics and laminated limestones and small shelly fossils, but even this place- date of 524.837 ± 0.092 Ma. This placement is shoaling upward into platformal carbonates ment has been controversial (Luo et al., 1991; consistent with combined biostratigraphic and (Lindsay et al., 1996a). We correlate the E Brasier et al., 1990; Zhang et al., 1997; Shen and δ13 CCaCO3 data from the rest of Siberia (Brasier (Salaany Gol, Section 2, Unit 7; Bayan Gol, Schidlowski, 2000; Zhu et al., 2001a). Further et al., 1993; Khomentovsky and Karlova, 1993; Section 3B, Unit 21; and Kvete-Tsakhir- complicating basinwide and global correlations, Knoll et al., 1995a, 1995b; Rowland et al., 1998; Nuruu, Section 4, Unit 7) and F (Salaany Gol, the lower Nemakit-Daldynian (542–533 Ma) of δ13 Kouchinsky et al., 2001, 2007), where the fi rst Section 2, Unit 11/12) 4‰–5‰ CCaCO3 peaks South China is not dominated by the 1‰–3‰ δ13 appearance of archaeocyaths occurs stratigraph- of Brasier et al. (1996) in the upper Bayan Gol positive CCaCO3 excursions with frequencies of δ13 ically above the last large positive CCaCO3 Formation with the pair of terminal Nemakit- 0.5–1 m.y. that are so characteristic of Morocco, δ13 anomaly (6p; Fig. 5). (Selinde may be an excep- Daldynian positive CCaCO3 excursions, 5p Siberia, and Mongolia (Fig. 5). The most dis- δ13 tion to this pattern, where archaeocyath debris and 6p, respectively (Fig. 5). tinctive Nemakit-Daldynian CCaCO3 tie point appears to occur stratigraphically below the last in China is the fi rst shift toward ≥+4‰ values δ13 large positive CCaCO3 anomaly; Kouchinsky China (peak 5p; Fig. 5). This shift is well developed at et al., 2005.) In particular, the most complete The Yangtze Platform of South China Xiaotan (Zhou et al., 1997), Anjiahe (Ishikawa Siberian record, from the Sukharikha River (Fig. 4D) began as a rifted margin during the et al., 2008), and Jijiapo (M. Zhu, 2010, per- (Fig. 4B), matches the Nemakit-Daldynian to breakup of Rodinia, with ca. 820 to ca. 780 Ma sonal commun.), and the beginning of the shift δ13 Atdabanian CCaCO3 curve of Morocco peak- bimodal volcanic rocks fl ooring the basin (Li, is pinned at Meishucun (Brasier et al., 1990) for-peak (Maloof et al., 2005; Kouchinsky et al., 1998; Z. Li et al., 2003). The overlying Cryo- by a tuff from Bed 5 that has a weighted mean 2007; Fig. 5). This calibration places the ND-T genian succession includes two glacial deposits 206Pb/238U ID-TIMS zircon age of ca. 533 Ma boundary at a recognizable and radiometrically and is capped by the Doushantuo Formation, the (Brooks et al., 2006; see also Compston et al., δ13 206 238 dated CCaCO3 shift and constrains the duration base of which has a weighted mean Pb/ U 2008; Jenkins et al., 2002) (Fig. 5). This Bed 5 of the Nemakit-Daldynian Stage to 17 m.y. ID-TIMS zircon age of 635.2 ± 0.6 Ma (Con- tuff provides the best estimate for the durations don et al., 2005). The upper Doushantuo Forma- of the pair of upper Nemakit-Daldynian positive 206 238 δ13 Mongolia tion has a weighted mean Pb/ U ID-TIMS CCaCO3 excursions. The Dzabkhan basin of southwestern Mon- zircon age of 551.1 ± 0.7 Ma (Condon et al., golia (Fig. 4C) was formed on the margins of 2005), and is overlain by uppermost Ediacaran RESULTS a ribbon continent that experienced andesitic recrystallized dolostones of the Dengying For- Small Shelly Fossils volcanism at ca. 800 Ma (Badarch et al., 2002), mation. The cause of slow but long-lived sub- prior to rifting from southern Siberia in the sidence during Ediacaran–Cambrian time on the One surprising result from Figure 5 (also earliest Cryogenian (Kuzmichev et al., 2001). Yangtze Platform is poorly understood—the en- see Fig. 6) is evidence for early appearances of Platformal carbonates and siliciclastics of the tire Lower Cambrian succession is usually con- calcareous brachiopods, archaeocyaths, and tri- Tsagaan Oloom Formation (1500 m thick) ac- tained within 120 m of condensed, phosphatic lobites. Calcareous brachiopods are thought to cumulated during Cryogenian and Ediacaran dolomites and argillites. have appeared in the mid-Tommotian, after the rifting and subsequent thermal subsidence In South China, the lowest Cambrian is re- appearance of phosphatic brachiopods (Ushatin- (Macdonald et al., 2009). Diamictites in the suc- ferred to as the Meishucunian Stage (Qian, skaya, 2001, 2008), but our age model suggests cession have been interpreted as glacial in ori- 1977), with trilobites fi rst appearing in the over- that Khasagtina, accepted as an early calcare- gin (Lindsay et al., 1996b), and recent mapping lying Qiongzhusian Stage. The biostratigraphy ous brachiopod of possible kutorginid affi nity δ13 and CCaCO3 chemostratigraphy correlated the of the Meishucunian recently has been revised (Ushatinskaya, 1987; Bengtson, 1992a; Popov younger of two glacial deposits to the Marinoan (Qian et al., 2001; Steiner et al., 2007). The and Williams, 2000), comes from rocks that ice age (Macdonald et al., 2009), which ended lowermost part of the Meishucunian is domi- are late Nemakit-Daldynian in age, ca. 528 Ma ca. 635 Ma (Hoffmann et al., 2004; Condon nated by anabaritids and protoconodonts, and a (Ushatinskaya, 1987). (Note that there is con- et al., 2005). A signifi cant Ediacaran hiatus correlation with the lower Nemakit-Daldynian fl icting evidence regarding kutorginid brachio- preceded obduction of ca. 570 Ma ophiolites to has generally been accepted; higher zones in the pod mineralogy; some may have had a partially the south of the Dzabkhan basin (Khain et al., Meishucunian have been more diffi cult to corre- aragonitic shell [James and Klappa, 1983]. The 2003), which suggests there was south-dipping late (Qian and Bengtson, 1989). Recent work has mineralogy of Khasagtina is not known.) Evi- subduction (in present-day coordinates) that favored the view that the Meishucunian includes dence for Nemakit-Daldynian archaeocyaths is led to rapid accumulation of the upper Tsagaan equivalents to both the Nemakit-Daldynian and more questionable, and is based on fragments of Oloom Formation (Zuune Arts Member) in a Tommotian (Steiner et al., 2007). As trilobites archaeocyaths reported from Selinde in rocks infl exural basin (Macdonald et al., 2009). The fi rst appear at the base of the Atdabanian in Si- ferred by our age model to be ca. 530 Ma (2.7 m Ediacaran-Cambrian boundary has been placed beria and the base of the Qiongzhusian in South and 5 m above the base of the Pestrotsvet For- in the uppermost Tsagaan Oloom Formation China, these levels often have been regarded as mation; Korshunov et al., 1969; Khomentovsky δ13 where CCaCO3 descends from 1‰ (1p; Fig. 5) correlative, although the correctness of this in- and Karlova, 2002). However, specimens are to a nadir of –6‰ (W; Brasier et al., 1996), and terpretation remains undemonstrated; different not illustrated in those reports, making evalu- anabaritids and small burrows fi rst appear (Kho- correlations suggest that the base of the Qiong- ation diffi cult, and other detailed stratigraphic mentovsky and Gibsher, 1996) (Fig. 5). zhusian is above (Steiner et al., 2007) or below studies place the fi rst appearance of archaeo- The overlying Bayan Gol and Salaany Gol (Qian et al., 2001) the base of the Atdabanian. cyaths in much higher rocks (21 m above the Formations (1000–1500 m thick) contain a Some workers have attempted to defi ne the base of the Pestrotsvet Formation, inferred by diversity of Lower Cambrian small shelly fos- E-C boundary in South China by the strati- our age model to be ca. 525 Ma), suggesting the δ13 sils (Voronin et al., 1982; Esakova and Zhe- graphically highest negative CCaCO3 excursion earlier reports may have been in error (Voronova gallo, 1996) and consist of stacked sequences below the fi rst appearance of Treptichnus pedum et al., 1983; Repina et al., 1988; Kouchinsky

Geological Society of America Bulletin, November/December 2010 1741

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

544 542 540 538 536 534 532 530 528 526 524 522 Age (Ma) EDIAC NEMAKIT-DALDYNIAN TOMMOTIAN

50 genera

all SSFs

anabaritids protoconodonts cap-shaped fossils

hyoliths

hyolithelminths coeloscleritophorans tommotiids

molluscs

conulariids cambroclaves paracarinachitids coleolids calcareous brachiopods phosphatic brachiopods

? archaeocyaths ? trilobites

ARAG CALCITE ARAGONITE-CALCITE TRANSITION SEA SEA

Figure 6. The timing of animal appearances in the earliest Cambrian and temporal constraints on aragonite and calcite seas. Spindles show the total number of small shelly fossil (SSF) genera that have appeared by a particular time (i.e., the number of genera that appear in older time bins plus the number of new genera); they do not indicate standing diversity. Archaeocyaths and trilobites are not represented by spindle diagrams; only their presence or absence is shown. Colors indicate mineralogy of skeletons: blue—aragonitic; green—phosphatic; red—calcitic; purple (calcareous brachiopods)—either calcitic or aragonitic. (Note that although we depict them here as distinct, recent evidence suggests that the shells of calcareous and phosphatic brachiopods are homologous with those of tommotiids [Skovsted et al., 2008; Balthasar et al., 2009].) See Figures A2–A4 for more details of genus occurrence data. Constraints on aragonite and calcite seas are from Mg/Ca in ﬂ uid inclusions (see Porter, 2007, 2010, and references cited therein) and are consistent with the 87Sr/86Sr record (Fig. 9). The timing of the aragonite-calcite transition in the Nemakit-Daldynian is not well constrained and could have occurred at any time between 542 Ma and 525 Ma.

1742 Geological Society of America Bulletin, November/December 2010

et al., 2005). Although the mid-Tommotian age Another factor of note in Figure 6 is the pat- primarily in Mongolia and could reﬂ ect local for trilobites from the Meishucun and Xiaotan tern of ﬁ rst appearances of small shelly fossil preservational conditions within the Bayan Gol

sections refl ects the best fi t between the Chi- taxa. It is important to emphasize that the thick- section. In contrast, pulsemND and pulseT appear δ13 nese and Moroccan CCaCO3 curves, this fi t ness of each segment in the spindles shown in to be insensitive to the removal of any paris poorly constrained, and the fi rst appearance Figure 6 does not indicate standing diversity; ticular section and are recorded in both China

of trilobites in China could be much younger. rather, it records the total number of genera that and Siberia (although pulsemND is shifted later However, the age constraints on trilobites from had appeared by the indicated time bin, calcu- in Siberia). These pulses may refl ect a global Sukharikha are much better; the fi t between lated as the number of genera that appeared in preservational bias (e.g., the effects of eustasy δ13C curves from Sukharikha and Morocco has earlier time bins plus the number of new genera or ocean geochemistry), real pulses in diversifi - almost no mismatch (Fig. 5), and the rocks in that appear at that time. Thus, the spindles rep- cation, or perhaps both (cf. Peters, 2005). which the trilobites occur correlate with strata resent cumulative fi rst appearances; they do not from Morocco that are radiometrically con- take into account extinctions, which are diffi cult Isotopes and Trace Elements strained to be older than 520.93 ± 0.14 Ma and to infer from our database. Because a taxon’s δ13 younger than 522.85 ± 0.22 Ma (Maloof et al., time of origin always predates its appearance So far, we only have considered CCaCO3 as a 2010a). Interestingly, archaeocyaths typical of in the fossil record, the cumulative number of tool to generate a fossil-independent age model Atdabanian strata elsewhere also appear at this fi rst appearances shown in Figure 6 should be within which the paleontological data from horizon, suggesting a mismatch between bio- understood as a minimum estimate: we can state Siberia, Mongolia, and China can be interpreted stratigraphic and chemostratigraphic boundaries how many small shelly fossil genera must have (Fig. 5). This analysis contains the implicit as- δ13 (Kouchinsky et al., 2007). evolved by a certain time, but the real number sumption that CCaCO3 in platformal carbonates Figure 6 summarizes the fi rst appearance may be much higher. A number of notable pat- records a global signal. Workers frequently call δ13 data of the groups highlighted in Figure 5, terns emerge from these data. First, the major upon the observation that CCaCO3 time series color-coded according to skeletal mineralogy. groups of small shelly fossils (anabaritids, proto- may be matched peak-for-peak between separate A factor of particular note is the sequence of conodonts, etc.) appear early: fi ve are present continents as the strongest evidence for a global mineral acquisition. The fi rst taxa to appear are by 540 Ma, and all except the coleolids appear by signal (e.g., Halverson et al., 2005; Maloof either aragonitic or phosphatic; the fi rst calcitic 532 Ma. This proliferation of higher taxa seems et al., 2005; Macdonald et al., 2009). However, δ13 taxa do not appear until either the late Nemakit- to outpace proliferation of genera within each synchronous CCaCO3 signals in globally dis- Daldynian or the beginning of the Tommotian taxon, consistent with the observation (see sec- tributed platformal carbonates may not neces- (depending on the original mineralogy of the tion “Intro duction”) that disparity reaches its sarily refl ect a change in global ocean dissolved calcareous brachiopod Khasagtina and the fi rst peak early in a group’s history (although small inorganic carbon (DIC). For example, global appearance of archaeocyaths at Selinde). No shelly fossils are a polyphyletic assemblage). processes such as climate and sea-level change new acquisitions of aragonitic skeletons occur Second, although outpaced by the proliferation of may affect the distribution of mineralogies and after the Nemakit-Daldynian until the appear- higher taxa, small shelly fossil genera do appear the depositional and diagenetic environments δ13 ance of the kilbuchophyllid corals in the Ordo- quite early as well, with 46% of the small shelly that control CCaCO3 on shallow-water carbon- vician and scleractinian corals in the Triassic fossil taxa known from Nemakit-Daldynian ate platforms, so that some changes in platform δ13 δ13 (Porter, 2010). The sequence of fi rst appearances and Tommotian sections studied here appearing CCaCO3 do not mimic changes in the C of of aragonitic and calcitic taxa shown in Figure 6 by 534–532 Ma, and 72% appearing by 526– open-ocean DIC (Swart, 2008). Along similar also is observed within each section, suggesting 524 Ma. This result suggests a gradual unfold- lines, Hayes and Waldbauer (2006) proposed that it is a relatively robust pattern. As shown in ing of diversity through the Nemakit-Daldynian that temporal changes in the global importance Figure 5, all aragonitic taxa appear either before (Brasier et al., 1996; Knoll et al., 1995a), rather of diagenetic reactions (e.g., methanogenesis) or at the same time as calcitic taxa. In combi- than a burst at or just before the Tommotian in sediments could produce globally similar nation with evidence that seawater chemistry boundary. Finally, Figure 6 indicates that the patterns of local alteration. We consider this favored aragonite precipitation during the late dominant contributors to small shelly fossil diver- assumption extensively in Appendix section A9, δ13 Precambrian and favored calcite precipitation sity are molluscs and hyoliths, with more minor and conclude that the dominant CCaCO3 signal during the Tommotian (Porter, 2007; see section contributions from cap-shaped fossils and coelo- recorded in Lower Cambrian carbonate plat- “Strontium”; Fig. 6), the pattern shown in Fig- scleritophorans. If these four groups are closely form sediments primarily refl ects changes in the ures 5 and 6 supports the hypothesis that car- related (Marek and Yochelson, 1976; Bengtson, isotopic composition of global DIC. bonate skeletal mineralogy is determined by 1992b; Vinther and Nielsen, 2005), then the the chemistry of seawater at the time carbonate Nemakit-Daldynian and Tommotian diversifi ca- Carbonate Carbon δ13 skele tons fi rst evolve in a clade (Porter, 2007, tion of small shelly fossils predominantly refl ects The CCaCO3 chemostratigraphies of Mo- 2010; Zhuravlev and Wood, 2008). Although the radiation of a single clade. rocco, Siberia, Mongolia, and China depict a δ13 several phosphatic groups are known to appear Figure 7 shows the number of small shelly superposition of CCaCO3 oscillations with dif- later in the Early Cambrian (e.g., the prob- fossil genera that fi rst appear in each time bin, ferent characteristic periods and amplitudes. lematica Mober gella, Tumulduria, and Rhombo- for all sections combined (global data) and High-frequency signals with periods ≤105 yr corniculum in the Tommotian and bradoriids and for different subsets of sections (each region and amplitudes of 1‰–3‰ are present as re- Micro dictyon in the Atdabanian), the clustered by itself or all sections but one). The global gionally and often globally reproducible signals appearance of important Early Cambrian phos- data suggest several pulses of fossil fi rst ap- between 542 and 533 Ma, and as globally well-

phatic bio mineralizers may be meaningful, per- pearances: a pulse (pulseeND) between 540 deﬁ ned excursions at other times, such as the

haps reﬂ ecting seawater chemistry responsible and 538 Ma, a pulse (pulsemND) between 534 and negative spike at 529 Ma (Fig. 5). Even higher-

for widespread phospho genesis at this time (e.g., 530 Ma, and a pulse (pulseT) between 524 order variability of <1‰ amplitude may be

Cook and Shergold, 1984). and 522 Ma. PulseeND appears to be recorded present, but the sampling density is too coarse to

Geological Society of America Bulletin, November/December 2010 1743

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

60 A PulsemND 50 China Mongolia 40 Siberia Global data PulseT 30

20 PulseeND

Number of new genera 10

0 542 540 538 536 534 532 530 528 526 524 522 60 B PulsemND 50 Without China Without Lena-Aldan Without Selinde PulseT 40 Without Khorbusuonka Without Bol'shaya Kuonamka Without Kotuikan 30 Without Sukharikha Without Mongolia Global data 20 PulseeND

Number of new genera 10

0 542 540 538 536 534 532 530 528 526 524 522 Age (Ma)

Figure 7. Number of new genera appearing in each 2 m.y. time bin calculated for (A) all sections (global data) and for each region, and (B) all sections except one (as indicated).

determine whether or not this variability reﬂ ects (ca. 720–635 Ma; Swanson-Hysell et al., 2010) genesis and reﬂ ects young organic carbon in- δ13 temporally coherent oscillations. The CCaCO3 and Ediacaran (635–542 Ma; Calver, 2000; Fike corporated into the sediment at the time of variations of substantially longer period (4–7 et al., 2006; McFadden et al., 2008) carbonate depo si tion. Possible sources of uncertainty δ13 m.y.) and larger amplitude (8‰–11‰) domi- successions display relatively invariant Corg, include the effect of thermal maturation and δ13 nate the middle to upper Nemakit-Daldynian, despite large changes to CCaCO3. Rothman et oxidation on bulk total organic carbon (TOC) δ13 while moderate-frequency oscillations with al. (2003) originally observed this behavior in Corg values (Des Marais et al., 1992), contam- periods of ~106 yr and amplitudes of 2‰–4‰ the Hayes et al. (1999) compilation of globally ination by migrating hydrocarbons, and con- δ13 δ13 characterize the Tommotian–Atdabanian. averaged CCaCO3 and Corg data and proposed tamination by weathered detrital organic carbon. From a subset of the same carbonate samples a controversial model for the late Neoprotero- Although quantifying the effects of contami- δ13 that we used to generate the CCaCO3 chemo- zoic carbon cycle in which a very large, semi- nation and diagenetic alteration on bulk TOC δ13 87 86 13 δ13 stratigraphy, we develop Corg, Sr/ Sr, refractory, C-depleted dissolved or particulate Corg values is beyond the scope of this study, uranium, and vanadium time series. In the organic carbon (DOC or POC) reservoir main- there are several qualitative points that may be following paragraphs, we document these ad- tained nearly constant carbon isotope composi- important. First, a basinwide decrease in TOC ditional time series and interpret them in the tion and, through incorporation into sediments, due to thermal maturation or oxidation will tend δ13 δ13 context of the CCaCO3 and paleobiological overwhelmed the isotopic signal from contem- to shift TOC toward more enriched Corg val- records. poraneous primary-biomass-fractionating DIC. ues, changing the absolute value of the differ- ε δ13 δ13 In contrast, the carbon isotope composition of ence ( ) between CCaCO3 and Corg but not δ13 Organic Carbon the relatively small DIC pool would be suscep- Corg trends (Des Marais et al., 1992). Sec- Throughout most of the Phanerozoic Eon, tible to large negative swings associated with ond, contamination by migrating hydrocarbons δ13 paired records of carbonate carbon ( CCaCO3) DOC/POC remineralization. should be porosity and permeability dependent. δ13 and coeval bulk organic carbon ( Corg) suggest Past reconstructions of the global organic As a result, the effects of contamination on the δ13 δ13 a model in which the organic carbon in marine carbon cycle using C of bulk organic car- Corg value of bulk TOC are expected to de- sediments is derived and isotopically fraction- bon (e.g., Rothman et al., 2003) rely on the as- pend on lithofacies and the degree of early dia- ated from contemporaneous DIC. In contrast, sumption that the δ13C of the measured organic genetic cementation (see Fig. A1 in Appendix). δ13 δ13 δ13 CCaCO3 and Corg records from Cryogenian carbon ( Corg) is relatively unaltered by dia- Finally, contamination by detrital Corg may be a

1744 Geological Society of America Bulletin, November/December 2010

signiﬁ cantly underappreciated source of TOC in Ediacara fauna (Sperling et al., 2007). In Oman, the ND-T boundary (post-6p negative excur- Precambrian shallow-marine sediments. Recent the Ediacaran-Cambrian boundary δ13C excursion; Fig. 5; Maloof et al., 2010a). Larger [DIC]

work on the recycling of ancient TOC in modern sion appears to display excellent covariance in or smaller Fburial lead to more sluggish response δ13 δ13 tectonically active continental margins indicates CCaCO3 and Corg (Fike, 2007), but, to our times (Bartley and Kah, 2004). For example, a δ13 that at sites with high sedimentation rates, up to knowledge, no detailed paired CCaCO3 and steady-state model of the ND-T boundary nega- δ13 δ13 30% of the TOC in marine sediments is detrital Corg record has previously been generated tive CCaCO3 shift (post-6p; Fig. 5) constrained (Aller et al., 1996; Blair et al., 2003; Drenzek from Lower Cambrian carbonates. We describe to last 330–686 k.y. will only work for modern δ13 et al., 2009). Also, it is important to note that the Corg methods in Appendix section A2 and dis- values of [DIC] if Fburial is four times larger than

organic carbon contents of these sediments are play new data from Morocco in Figures 8 and today, or if the change in forg was much more not trivial (0.1–1 wt% TOC; Blair et al., 2003), A1 (see Appendix). extreme than the beginning and ending values δ13 suggesting that wt% TOC may not be a sufﬁ - Figure 8 depicts no Neoproterozoic-like for CCaCO3 suggest. Furthermore, most authors δ13 cient predictor of detrital contamination. Efﬁ - invariance in Corg, but instead shows that believe that the Cambrian Period had elevated δ13 δ13 cient reburial of TOC in these environments is CCaCO3 and Corg are uncorrelated from 542 [DIC], up to 9 mM (Berner et al., 1983), due

thought to be due to the short time that the fossil to 532.5 Ma and 524.85 to 520.5 Ma, and are to the higher pCO2 required to compensate for δ13 organic carbon is exposed to oxidizing condi- correlated from 532.5 to 524.85 Ma. The Corg a 5% weaker Sun (Bahcall et al., 2001) and to tions (Blair et al., 2003). Lower concentrations curve is reproduced from two stratigraphic sec- explain the lack of glaciation (Hambrey and Har- 2– of the major oxidants in seawater (O2, SO4 ) tions that are separated by over 100 km and con- land, 1981). High atmospheric pCO2 could have in the late Precambrian and early Phanerozoic tain signiﬁ cantly different facies associations been maintained with lower [DIC] if ocean pH should be asso ciated with less oxidative expo- representing outer-shelf (Oued Sdas, MS-7) and was very low and calcium concentrations were

sure and more efﬁ cient reburial of fossil organic inner-shelf (Sidi M’Sal, MS-16) environments high enough to maintain CaCO3 saturation (Hig- carbon globally (i.e., not just in active margin (Maloof et al., 2010a). Some workers have ex- gins et al., 2009), although we have no evidence sediments). A large contribution of fossil or- pressed concern that carbonates with low total for such a low-pH ocean. For [DIC] ~9 mM,

ganic carbon should be associated with damped organic carbon may be prone to contamination an Fburial 16 times larger than modern carbon δ13 (or invariant) bulk TOC Corg values. by external sources of organic carbon. The Mo- burial ﬂ ux is required to generate the observed δ13 Despite the potential complications associ- roccan samples have TOC ~0.05 wt%, typical CCaCO3 shift in ca. 500 k.y. δ13 ated with interpreting bulk TOC Corg values of many Neoproterozoic and Phanerozoic car- On time scales >100 k.y., Finput = Fburial should in ancient rocks, the Rothman et al. (2003) bonates, and we observe no correlation between reﬂ ect volcanic (e.g., Berner et al., 1983) and δ13 hypothesis of a large and dynamic DOC pool Corg and TOC (Fig. A1B [see Appendix]) or metamorphic (e.g., Evans et al., 2008) outgas-

is an intriguing one in light of the large vari- lithofacies (Fig. A1 [see Appendix]), suggest- sing rates of CO2. To explain the lowest Cam- δ13 ability in the isotopic composition of carbon- ing that porosity- and permeability-dependent brian CCaCO3 shifts, Cambrian volcanoes or δ13 ate carbon ( CCaCO3). The form and size of the contamination associated with migrating hydro- orogenies (e.g., Squire et al., 2006) must have

required organic carbon pool depends crucially carbons was not important. Furthermore, the been 4–16 times more potent CO2 producers δ13 δ13 on the time scale of the observed CCaCO3 ex- lack of correlation among Corg, TOC, and than those of today (see section “Strontium”). It cursions (Higgins and Schrag, 2006) and the lithofacies suggests that size and density sort- is important to note that on geologic time scales, oxidant budget of the ocean (Bristow and Ken- ing during sediment transport of fossil carbon the high rates of volcanic/metamorphic outgas- nedy, 2008). Rothman et al. (2003) proposed particles did not preferentially concentrate fos- sing required by our data must be balanced by

DOC pools 100–1000 times larger than those sil carbon into specifi c lithologies (and thus carbon sinks (CaCO3, Corg, or both). Although μ δ13 of today (DOC is ~45 M in the deep ocean fossil carbon may not impact Corg). absolute rates of carbonate burial are diffi cult to today; Hansell and Carlson, 2001) in order to extract from the geologic record, the observa- δ13 get the observed decoupling of CCaCO3 and Paired Carbonate and Organic Carbon tion that large carbonate depositional systems on δ13 δ13 Corg, but these values assume roughly modern Coherent excursions in the C record of the shallow continental shelves may have extended concentrations of DIC in the ancient ocean: the global DIC reservoir of the magnitude and du- poleward of the Antarctic Circle (Appendix sec- carbon cycle dynamics depend critically on the ration observed in the Cambrian are diffi cult to tion A8; Fig. 3) is consistent with higher overall relative sizes of DOC and DIC, not the absolute reconcile with our current understanding of the rates of carbonate burial during this time. size of DOC. Today, millimolar-level concentra- budgets and dynamics of the global carbon cycle If we consider the Phanerozoic system where tions of DOC are common in lake environments on geologic time scales. Carbon isotope excur- organic carbon is derived from contempora- (O’Loughlin and Chin, 2004; Smith et al., 1993; sions of 5‰–10‰ over 0.1–2.0 m.y. require neous DIC, the long-term steady-state (i.e., Takacs et al., 2001; Giri et al., 2004), in marine both extreme changes in the ratio of organic greater than the relaxation time of the ocean-

pore waters (Lahajnar et al., 2005), and in the carbon to total carbon outputs (forg = Corg/Ctotal) atmosphere carbon cycle, which presently is a euxinic waters of the Black Sea (Agatova et al., and extreme absolute rates of carbon throughput. few hundred thousand years; Holser et al., 1988) 1989, 2001; Torgunova, 1994), where even the Maloof et al. (2010a) calculated response times carbon-isotopic mass balance for the ocean can

oxic upper waters have DOC elevated up to 5× to a step change in forg from 0.4 to 0.14 (these forg be written: δ13 δ13 that of normal seawater (Cauwet et al., 2002). values were calculated from CCaCO and C 3 org 13 13 13 δ13 δ C =(1−f )δ C +(f )(δ C −ε) The apparent end of Corg invariance in values assuming steady-state carbon cycling in org CaCO3 org CaCO3 , (1) the latter stages of the Shuram-Wonoka iso- [Kump and Arthur, 1999] for various [DIC] and δ13 tope anomaly ca. 551 Ma (Condon et al., 2005) carbon burial (Fburial) and input ﬂ uxes (Finput = where Cin is the isotopic composition of DIC

has been interpreted as the demise of the large Fburial in steady state). For Fburial and [DIC] simi- entering the ocean (approximately mantle com- δ13 DOC source (Fike et al., 2006), perhaps associ- lar to those of modern oceans, this change in forg position), CCaCO3 is the isotopic composition δ13 ated with the radiation of benthic microsuspen- would require 3.5 m.y. to generate a CCaCO3 of the oceanic DIC pool derived from chemi- sion feeders such as sponges and some of the excursion similar in magnitude to that seen at cal weathering, ε is the difference between DIC

Geological Society of America Bulletin, November/December 2010 1745

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Age (Ma) 541 537 533 529 525 521 517 A Uncorrelated Correlated Uncorrelated

6 –18

4 –20

2 –22 δ 13 (‰) C 3 0 –24 org CaCO (‰) C 13 δ –2 –26

–4 –28

–6 –30

1 B δ13C CaCO3 13 0.8 δ Corg R2 0.6 R2 0.4

0.2

0 0 2 4 6 8 10 12 14 16 Interval length centered on 529 Ma

Figure 8. (A) Paired carbonate (gray) and organic carbon (green) δ13C data from Morocco with intervals of correlation and lack of correlation highlighted in yellow and blue, respectively. (B) The evolution of R2 (calculated from δ13 δ13 the correlation between CCaCO3 and Corg) as a function of the size of a symmetric analysis window centered at ca. 529 Ma. At a distance of ± 3.5 m.y. from 529 Ma (i.e., within the yellow window), R2 remains greater than 0.6, while analysis windows expanding beyond this region show declining R2.

and organic carbon (often dominated by the end members. Assuming that the global carbon fractionation, organic matter preservation, or kinetic isotope fractionation associated with cycle in the Cambrian can be approximated by contamination by ancient organic carbon weath- the uptake of carbon by photoautotrophs), and the steady state described in Equation 1, we ered from the continents. Unlike DIC, which is

forg = Corg/Ctotal is the fraction of carbon buried suggest that the lower Nemakit-Daldynian and generally thought to be globally homogeneous δ13 3 that is organic (Kump, 1991). Changes in forg Tommotian intervals of uncorrelated CCaCO3 on time scales longer than the 10 yr mixing δ13 δ13 correspond to changes in the burial fl uxes of and Corg and relatively low CCaCO3 volatil- time of the ocean, Corg can be dominated by oxidized and reduced carbon species. Changes ity (Fig. 8) were dominated by local variability local infl uences (associated with carbon fi xation in ε correspond to changes in the difference be- in the carbon isotopic composition of organic mechanisms and rates, degree of remineraliza- tween the isotopic compositions of those carbon matter associated with variability in biological tion, and trophic structure). These factors can

1746 Geological Society of America Bulletin, November/December 2010

δ13 lead to local changes in Corg, separate from both their magnitude and the short duration Modeled processes include carbonate and sili- δ13 and superimposed on any changes in Corg over which they occur. The covariance between cate weathering, high-temperature hydrothermal δ13 δ13 inherited from changing the isotopic composi- CCaCO3 and Corg during most of the large- alteration of oceanic crust, burial of carbonate tion of DIC, which is the source for the carbon. amplitude changes suggests that the carbon minerals, and dolomitization (see Appendix In contrast, we interpret the upper Nemakit- isotope excursions are related to changes in the section A11). Mechanisms for a decline in the δ13 δ13 Daldynian interval of correlated CCaCO3 and C of contemporaneous DIC and not to dia- Mg/Ca ratio of seawater on time scales of tens δ13 δ13 Corg, high CCaCO3 volatility, and virtually genesis (e.g., Derry, 2010) or the dynamics of a of millions of years include an increase in the no small shelly fossil ﬁ rst appearances (Fig. 5) large, homogeneous DOC pool (e.g., Rothman rate of high-temperature hydrothermal alteration

as dominated by changes in forg, perhaps associ- et al., 2003). Given the caveats involved in in- of the oceanic crust or an increase in the rate of δ13 ated with changes in oceanic redox conditions, terpretation of bulk TOC Corg data, the lack dolo mite formation (Holland and Zimmermann, carbon to phosphorus ratios of buried organic of correlation during periods of high-frequency, 2000; Hardie, 1996). δ13 matter, or phosphate versus nitrate limitation low-amplitude CCaCO3 excursions is likely due Rising global sea level in the Early Cambrian δ13 δ13 (Saltzman, 2005; Maloof et al., 2005). to local variability in Corg, unrelated to the C (e.g., Miller et al., 2005; Haq and Schutter, ≥ Over the 100 k.y. time scale required to of DIC or buffering by detrital Corg. However, in 2008) is consistent with increased submergence achieve carbon-isotopic steady state, phos- the context of our current understanding of the of shallow-water carbonate platforms, higher 3– phate (PO4 ) is likely to be the limiting nutrient global carbon cycle on geologic time scales, rates of dolomitization, and a consequent de- for primary productivity (Broecker and Peng, the magnitude and rapidity of the carbon iso- cline in the Mg/Ca ratio of seawater. The ef- 1982; Smith, 1984; Lenton and Watson, 2000; tope excursions require extreme changes in the fect of an increase in dolomitization on the Sr

Tyrrell, 1999; Schrag et al., 2002). It follows relative rates of Corg and CaCO3 burial and rates isotopic composition of seawater is diffi cult that the burial of organic carbon is controlled of volcanic outgassing that are up to an order of to constrain, although it is likely to be small. 3– by the river ine fl ux of PO4 to the ocean and its magnitude larger than modern fl uxes. Decar- Thus, an increase in dolomitization through the

removal in sediments and hydrothermal systems bonation of carbonaceous sediments (CaCO3 Cambrian may help to explain the observed de- (Kump, 1988; Schrag et al., 2002). As pointed and Corg), either in subduction zones or in meta- crease in the Mg/Ca ratio of seawater and shift out by Schrag et al. (2002) and Junge et al. morphic terranes, a likely source of some of the from aragonite to calcite seas, but it does not (1975), an increase in silicate weathering would additional carbon. Although it is uncertain to help to explain the decline in 87Sr/86Sr or the rise lead to an increase in the fl ux of both riverine what extent higher rates of continental meta- in sea level. 3– PO4 and alkalinity to the oceans, enhancing the morphism are expected during periods of super- An increase in the rate of hydrothermal al- burial of organic and carbonate carbon in ap- continent assembly, the earliest Cambrian is teration of oceanic crust is consistent with the 87 86 proximately equal proportions and keeping forg associated with the latter stages of the breakup observed decrease in the Sr/ Sr of seawater δ13 (and thus CCaCO3) about the same. This argu- of southern Rodinia and the assembly of Gond- between 543 and 521 Ma (e.g., Edmond, 1992; δ13 δ13 ment suggests that positive CCaCO3 and Corg wana (Figs. 3 and 10). Though it is tempting Richter et al., 1992). If caused only by changes swings in the Early Cambrian ocean must have to regard the volatility in forg and high rates of in the rate of hydrothermal alteration of oceanic 87 86 been driven by increasing burial of Corg rela- carbon throughput as having a common cause, crust, a 0.0006 decline in the Sr/ Sr of sea- 3– tive to PO4 . Unfortunately, the processes that exactly how tectonic processes infl uence or- water would require a 2.25× increase in the fl ux

control the relative rates of Corg and P burial are ganic carbon burial and atmospheric O2 remains of seawater through high-temperature hydro- not well understood. Because the vast majority a mystery (but see Campbell and Squire [2010] thermal systems at mid-ocean-ridge crests, from of P delivered to sediments is associated with for one hypothesis). 3.75 × 1013 kg seawater per year to 8.4 × 1013 kg

Corg, and most Corg that is delivered to sediments seawater per year (Fig. 9; Table 1). A smaller is respired, it is the processes that infl uence the Strontium increase in the hydrothermal fl ux of seawater leak of P back to the ocean that will ultimately During the earliest Cambrian, seawater would be required if the 87Sr/86Sr of the weath- 87 86 control the rate of P burial relative to Corg. There Sr/ Sr, as recorded in carbonate rocks from ering fl ux declined appreciably during this in- is some evidence from organic compounds that Morocco, Siberia, Mongolia, and China, de- terval. For example, model calculations indicate 3– local anoxia enhances the leak of PO4 back clined monotonically by ~0.0006 (Fig. 9A). that no change in hydrothermal fl ux of seawater 87 86 to seawater, allowing for higher rates of Corg Seawater chemistry is thought to have alternated would be required if the Sr/ Sr of the weather- 3– burial relative to PO4 . On short time scales, this throughout Earth history between states that ing fl ux declined from 0.7105 to 0.7096 from feedback has been argued to amplify anoxia, favor aragonite production (during intervals re- 543 to 521 Ma (Table 1). Such a decline in the although on million-year time scales, enhanced ferred to as aragonite seas) and those that favor 87Sr/86Sr of the weathering fl ux could be accom-

burial of Corg will lead to the accumulation of calcite production (during calcite seas). The modated by any combination of a reduction in

atmospheric O2 and a return to more oxic con- major control on mineralogy is thought to be the rate of silicate weathering, an increase in the ditions (Ingall and Van Cappellen, 1990; Ingall the Mg/Ca ratio of seawater, with ratios above rate of carbonate weathering or recrystal- et al., 1993; Van Cappellen and Ingall, 1996; ~2.0 favoring aragonite, and lower ratios favor- lization, or a reduction in the average 87Sr/86Sr Ingall and Jahnke, 1997). Exactly how this ing calcite (Stanley and Hardie, 1998; Lowen- of weathered carbonate and silicate rocks mechanism could produce the oscillations in stein et al., 2001). We explore the implications (Edmond, 1992). Observations of rising eustatic δ13 CCaCO3 observed in the Cambrian is not clear. of the observed shift from aragonite to calcite sea level through this interval (Miller et al., In addition, recent studies found the unexpected seas during the Early Cambrian (Fig. 5; Porter, 2005; Haq and Schutter, 2008) do not favor in- result that apatite precipitation and sequestra- 2007) and the associated decline in the 87Sr/86Sr creased rates of carbonate weathering. 3– tion of PO4 are favored in anoxic conditions of seawater (Figs. 9A and A9 [see Appendix]) for The recrystallization of metastable carbon- (Goldhammer et al., 2010). changes in the chemistry of seawater through the ates, speciﬁ cally the conversion of aragonite The large carbon isotope excursions that Cambrian using a numerical model of the global to low-Mg calcite, can have a signiﬁ cant effect characterize the Cambrian are remarkable for magnesium, calcium, and strontium cycles. on the Sr concentration and isotope budget of

Geological Society of America Bulletin, November/December 2010 1747

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

A Morocco tallization as the volume of sedimentary arago- Siberia nite was progressively depleted. Although not modeled here, the loss of this additional source Mongolia 0.7100 of carbonate Sr may help to explain the appar- China ent inﬂ ection in the 87Sr/86Sr of seawater toward Model 0.7095 higher values after 525 Ma.

output r Model calculations indicate that a 55% de- S 6

8 cline in the rate of silicate weathering would 0.7090 / r be required to explain the observed decline in

S 87 86 7 the Sr/ Sr of seawater (Table 1). However, 8 0.7085 there is no independent evidence for a cooling that could cause a change of this magnitude, and Early Cambrian plate reconstructions sug- 0.7080 gest that the climate may have warmed during this interval to allow for development of high- latitude shallow-water carbonate microbialites (see Appendix section A8; Fig. 3). It is well B 2.25× increase in seafloor spreading known that changes in the weathering of rocks 5 containing highly radiogenic Sr can have a large effect on the 87Sr/86Sr value of the weathering ﬂ ux (e.g., Edmond, 1992; Richter et al., 1992; 4 Derry and France-Lanord, 1996; Galy et al., 1999). Thus, for instance, chemical weathering of exhumed lower-crustal granulites in Pan- 3 African orogens (Squire et al., 2006; Campbell

Mg / Ca and Squire, 2010) may have supplied unradio- (mol/mol) aragonite seas 87 86 2 genic material to rivers and lowered the Sr/ Sr of seawater. While a change in the 87Sr/86Sr of calcite seas the weathering fl ux may be signifi cant, we be- 1 lieve that an increase in the rate of hydrothermal alteration of oceanic crust is likely the most important contributor to the observed decline 0 in 87Sr/86Sr, because a hydro thermal explana- 541 537 533 529 525 521 517 tion is consistent with independent observations Age (Ma) of a decrease in the Mg/Ca ratio of seawater and the switch from aragonite to calcite seas 87 86 Figure 9. (A) Time evolution of Sr/ Sr from Morocco (this paper), Siberia (Derry et al., across the ND-T boundary (Fig. 5; Porter, 2007). 1994; Knoll et al., 1995a; Nicholas, 1996; Kaufman et al., 1996), Mongolia (Brasier et al., The simplest way to increase the rate of 87 86 1996), and China (Ishikawa et al., 2008; Sawaki et al., 2008). The unfi ltered Sr/ Sr record hydrothermal alteration of oceanic crust is to and a description of fi lter design are reported in Appendix section A10. (B) Modeled impact increase the total length of mid-ocean ridges 87 86 on Mg/Ca for a 2.25× increase in the hydrothermal fl ux of Sr/ Sr over 20 m.y. around the world. If total hydrothermal alteration scales linearly with ridge length, then an seawater (Stoll and Schrag, 1998). Aragonite of aragonite buried in sediments represents a approximate doubling of ridge length over contains roughly 5–9 times more Sr than does potential source of relatively unradiogenic Sr 20 m.y. would be required. The late Neoprotero- low-Mg calcite precipitated from seawater. Be- that will be mobilized if rates of aragonite burial zoic to Early Cambrian is a time of continent dis- cause aragonite is metastable at Earth’s surface or recrystallization change. It is diffi cult to say persal during the breakup of Rodinia. Centered conditions, it tends to recrystallize to low-Mg how rates of recrystallization might be affected around Laurentia (North America) (Hoffman, calcite on a range of time scales (Swart et al., by rising sea level, but the reduction in aragonite 1991), the breakup of northern Rodinia spalled 2001; James et al., 2005). In the process, 80%– burial associated with the shift from aragonite future east Gondwanan continents (e.g., Aus- 90% of the Sr contained in the primary aragonite to calcite seas at ca. 525 Ma is expected to have tralia, Antarctica, India, South China) across the is released back to seawater. Thus, the volume diminished the fl ux of Sr associated with recrys- incipient Pan thalassa Ocean starting as early as

TABLE 1. PARAMETERS USED IN MODELING THE Sr CYCLE 87 86 87 86 87 86 Model run Sr/ SrSil Sr/ SrCaCO3 Silicate/carbonate High-T Sr/ Sr weathering (1) weathering (1) weathering (1) hydrothermal (2) hydrothermal (1) 10 13 ×10 mol/yr (% carbonate/% silicate) (×10 kg H2O/yr) Initialization 0.7150 0.7070 1.89, (43/57) 3.75 0.7030 (+) high-T hydrothermal 0.7150 0.7070 1.89, (43/57) 3.75 to 8.4 0.7030 (–) 87Sr/86Sr of weathering 0.7150 to 0.7141 0.7070 to 0.7061 1.89, (43/57) 3.7 5 0.7030 (–) silicate weathering 0.7150 0.7070 1.89, (43/57) to 1.48, (32/68) 3.75 0.7030 Note: (1) Allègre et al. (2010); (2) Elderﬁ eld and Schultz (1996).

1748 Geological Society of America Bulletin, November/December 2010

ca. 800 Ma (Wingate et al., 1998; Z. Li et al., in mantle viscosity, the effect of dynamic topog- tive sea-level rise was diachronous, depending 2003; Pisarevsky et al., 2003) and perhaps raphy on basin volume, and thus sea level, is on the initial elevation of the continent and dy- culminating with the fi nal rift-to-drift transi- nearly removed. In summary, changes in ridge namic topography. The increase in mid-ocean- tion from the modern western margin of North production (and thus plate velocities) likely will ridge production also should have led to an America in the Early Cambrian (Bond and lead to a net increase in eustatic sea level, but increase in the rate of volcanic outgassing and Kominz, 1984; Bond et al., 1988). In contrast, the amplitude, and even the sign, of the associ- climate warming, which may help to explain the southern Rodinia (or Pannotia) did not break ated dynamic topographic infl uence on eustasy existence of the Moroccan carbonate belt at re- apart into Laurentia, Baltica (northern Europe), is diffi cult to determine (Conrad and Husson, markably high latitude (e.g., McCausland et al., Siberia, and west Gondwana (now Africa and 2009). No glacial sediments of defi nitive Early 2007; Fig. 3). South America) until latest Ediacaran (Fig. 3), Cambrian age have been found (Hambrey The new Lower Cambrian 87Sr/86Sr record with a well developed rift-to-drift transition and and Harland, 1981), so glacioeustasy is not a nicely connects the composite Neoproterozoic opening of the Iapetus Ocean in the Early Cam- viable alternative for sea-level change (but see and Phanerozoic 87Sr/86Sr curves compiled by brian (Bond et al., 1984, 1988). The opening of Norin , 1937; Runkel et al., 2010; Landing and Halverson et al. (2007, 2010) and Veizer et al. Iapetus alone could have doubled mid-ocean- MacGabhann, 2010). (1999), respectively (Fig. 10). Halverson et al. ridge lengths. A sea-level rise of 10–70 m is consistent (2007) used this compilation to challenge the Parsons (1982) and Rowley (2002) used with the general observation that virtually every idea that orogenesis leads to a rise in marine the area/age versus age distribution of modern continent underwent progressive fl ooding start- 87Sr/86Sr (Raymo et al., 1988; Asmerom et al., oceanic lithosphere to suggest that there have ing sometime in the Early Cambrian (e.g., the 1991; Edmond, 1992; Kaufman et al., 1993) by been no signifi cant changes in global seafl oor “Cambrian transgression” of Matthews and pointing out that the culminations in both Ro- production rates over the past 180 m.y. Seafl oor Cowie, 1979; McKie, 1993) and culminating dinia and Pangea assembly correspond to nadirs production is a function of both ridge length and in the Middle–Late Ordovician “Sauk” high- in the 87Sr/86Sr curve. The isolation of supercon- seafl oor spreading rates. The primary source of stand (e.g., Sloss, 1963; Haq and Schutter, tinent interiors from moisture sources probably error in such ridge-production estimates is the 2008). However, the relative position of shore- plays the crucial role in reducing the continental inherent uncertainty in reconstructing the now- lines is not a direct measure of eustasy, because weathering fl ux of Sr to the oceans (Donnadieu subducted ridges in the Pacifi c and Tethyan changes in subsidence and sediment supply et al., 2004; Halverson et al., 2007). The rifting Ocean basins. In those studies that contradict also infl uence shoreline location. Numerous of northern Rodinia brought moisture to previ- Parsons (1982) and Rowley (2002) and sug- workers have attempted to use sequence strati- ously dry cratons, increasing the weathering fl ux gest a 5%–20% mid-Cenozoic (Conrad and graphic boundaries such as fl ooding surfaces of 87Sr/86Sr and swamping any increase in the Lithgow-Bertelloni, 2007) and 50%–100% and erosional unconformities preserved in the hydrothermal fl ux due to the generation of new long-term Cretaceous–Tertiary (Kominz, 1984; sedimentary records of cratonic basins as more mid-ocean ridges. The acceleration in the rate of Engebretson et al., 1992) decrease in crust pro- accurate indicators of relative sea-level change 87Sr/86Sr increase at the base of the Cryogenian duction, it is the seafl oor production along these (Vail et al., 1977; Haq et al., 1987; Miller may have been caused by the glacial removal of subducted ridges that is responsible for the dis- et al., 2005; Haq and Schutter, 2008). The a long-lived continental regolith that accumu- crepancy. Unfortunately, none of these studies sub-Tommotian unconformity and subsequent lated during the 1.5 b.y. gap between Proterozoic has enough seafl oor area to work with to deter- northwest-to-southeast transgression of the ice ages (Swanson-Hysell et al., 2010). mine how ridge length and production changed Siberian platform (see section “Siberia”) is an The rifting of southern Rodinia and the open- during the early stages of the breakup of Pangea example of a Lower Cambrian fl ooding event. ing of the Iapetus Ocean may have caused the (200–170 Ma), a time when plate reconfi gura- Correlations of sequence boundaries of similar Lower Cambrian dip in 87Sr/86Sr because, by tion and continent dispersal were most analo- ages from different continents are what have then, continents were suffi ciently dispersed gous to the Early Cambrian. Therefore, we led to interpretations of global eustatic change, to receive consistent moisture and maintain consider it possible that ridge length and ridge although such correlations are challenging be- chemical weathering of their interiors, while production could both increase during the cause interpolation between Lower Cambrian the increase in Iapetus mid-ocean-ridge length breakup of a supercontinent. sections without radiometrically dated ash contributed a new hydrothermal 87Sr/86Sr source A doubling of ridge length would lead to beds or suffi cient bio- and chemostratigraphy to the ocean. No single process can elegantly an increase in ridge volume of ~5 × 106–25 × can lead to age uncertainties as large as 10 m.y. explain the time-evolution of marine 87Sr/86Sr 106 km3 for average half-spreading rates of Furthermore, even sequence stratigraphic ob- over the past 1000 m.y.; however, the monotonic 1–5 cm yr –1. Assuming transgressing shorelines servations are notoriously poor indictors of ND-T decline in 87Sr/86Sr provides a useful com- δ13 on a planet with a similar distribution of con- eustasy, as coastlines around the world are in panion to CCaCO3 for interbasinal correlation, tinental elevations as today, this change in the constant motion relative to sea level due to the and may signal a change in hydrothermal fl ux mid-ocean-ridge system would cause a 10–70 m dynamics of mantle convection (e.g., Moucha and Mg/Ca in the ocean that had an important sea-level rise (e.g., Pitman, 1978). However, et al., 2008). impact on the skeletal mineralogy of animals Gurnis (1990) suggested that increased ridge Despite all of these caveats, we propose that that evolved during the Early Cambrian. production would be offset by faster subduction the Lower Cambrian 87Sr/86Sr record presented and lead to an increase in the negative dynamic here is consistent with an increase in the rate of Uranium and Vanadium topography near convergent margins, thus di- hydrothermal alteration of seafl oor basalt and The concentration of redox-sensitive trace minishing the sea-level rise associated with the consequent transition from an aragonite to ele ments in seawater, and their incorporation the ridge volume change. Husson and Conrad a calcite sea (Fig. 9). A feature associated with into marine carbonates, depends critically on (2006) disputed the idea that ridge-displaced the increase in mid-ocean-ridge production is the oxi dation state of the ambient water col- water could be stored in trenches by showing a global sea-level rise that fl ooded parts of all umn (e.g., Schröder and Grotzinger, 2007). In that, if plate acceleration is enabled by a change the continents (e.g., Worsley et al., 1984). Rela- particular, both V and U become enriched in

Geological Society of America Bulletin, November/December 2010 1749

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

‘South’ Rodinia breakup Continent dispersal ‘North’ Rodinia breakup Pangea breakup Rodinia Supercontinent assembly Gondwana Pangea Tonian Cryogenian Ediacaran CambOrdov Sil Dev Carbon Perm Tri Juras Cretac Tert Halverson et al. (2010) Maloof et al. (this paper) 0.7090 Derry et al. (1994), Montañez et al. (1996) Veizer et al. (1999)

r 0.7080 S 6 8 / r 0.7070 S 7 8

0.7060

Low-latitude continent(s) At least some high-latitude continents 0.7050 1000 900 800 700 600 500 400 300 200 100 0 Age (Ma)

Figure 10. Time evolution of 87Sr/86Sr during the Neoproterozoic and Phanerozoic, modiﬁ ed after Halverson et al. (2007). Snowball Earth intervals are highlighted in light blue (Hoffman et al., 1998), intervals dominated by low-latitude continents are highlighted in orange, and periods of supercontinent assembly (black) and dispersal (gray and red) are marked. The new Lower Cambrian data from Morocco nicely connect previously published Neoproterozoic (Halverson et al., 2007, 2010) and stratigraphically higher Cambrian (Derry et al., 1994; Montañez et al., 1996) 87Sr/86Sr curves. The Lower Cambrian decline in 87Sr/86Sr occurs during the ﬁ nal rifting of “south” Rodinia and the opening of the Iapetus Ocean.

sediments deposited under anoxic conditions larger oceanic reservoirs and generally more U increases in U and V. This hypothesis must be (Jones and Manning, 1994; Piper, 1994; Piper and V in sediments. tested with trace-element time series that span and Isaacs, 1995). V enrichment usually occurs Decreasing U and V suggest progressive oxi- the Lower Cambrian from other continents. at redox conditions typical of nitrate reduction, dation of the sediment-water interface, consis- while U enrichment generally corresponds to tent with the observation that both bioturbation DISCUSSION redox conditions typical of sulfate reduction in (e.g., Crimes, 1987) and benthic biodiversity the marine environment (Jones and Manning, (see section “Small Shelly Fossils”) increase In this paper, we map lowest Cambrian δ13 1994; Piper and Isaacs, 1995). Although the through the same interval (in Morocco and records of CCaCO3 variability from Siberia, trace-element proxy for seawater redox condi- globally ). Furthermore, the U and V signals are Mongolia, and China onto the Moroccan U/ δ13 tions originally was developed for the study of consistent in four stratigraphic sections (Fig. A9, Pb– CCaCO3 age model constrained by fi ve sin- siliciclastic sediments, the method recently has see Appendix), indicating that the oxygenation gle-zircon U/Pb ages from interbedded volca- δ13 been applied to carbonate strata (e.g., Schröder of shelfal waters occurred simultaneously across nic ashes (Fig. 5). We also present new Corg, and Grotzinger, 2007; Amthor et al., 2003). more than 300 km2 of the Anti-Atlas margin. 87Sr/86Sr, uranium, and vanadium data from the After applying a fi lter designed to exclude The only signifi cant short-term perturbations same carbonate samples that defi ne the Moroc- 87 86 δ13 diagenetically altered samples from the Sr/ Sr to this trend are positive U and V anomalies dur- can U/Pb- CCaCO3 age model. The result is a δ13 analysis and correcting for contamination by ing the negative CCaCO3 excursions between new absolute time line of fi rst appearances of terrestrial clays using Th content (see Appen- 5p–6p, 6p–7p, and III–IV. These positive U skeletal animals (Figs. A2–A4 [see Appendix]) dix section A10), we overlay normalized U and V anomalies are similar to those found in that avoids the circularity associated with using δ13 and V records from Morocco on the CCaCO3 carbonates and shales associated with the E-C biostratigraphic correlations and that is pre- δ13 curve (Fig. 11). The salient long-term trend is boundary negative CCaCO3 excursion in Iran, sented in the context of coincident changes a monotonic decline in the concentrations of Oman, and China (Kimura and Watanabe, 2001; in the cycling of carbon and trace elements in both elements over the duration of the Nemakit- Amthor et al., 2003; Schröder and Grotzinger, the ocean. Better than ever before, we are now Daldynian, Tommotian, and Atdabanian Stages. 2007; Wille et al., 2008). This association sug- capa ble of determining the absolute timing of δ13 This long-term decline is particularly impres- gests that these negative CCaCO3 anomalies biological and environmental change in the ear- sive because, if the rate of hydrothermal altera- may not be entirely controlled by global reduc- liest Cambrian. ε tion of oceanic crust increased over the same tions in forg or , but may have been driven partly The time line of small shelly fossil fi rst ap- interval, as postulated in section “Strontium,” by isotopic gradients caused by local upwelling pearances indicates the following (Figs. 6 and 7). then the hydrothermal input of U and V to the of basinal waters that provided isotopically light (1) All aragonitic taxa appeared in the ocean also should have increased, leading to carbon and enough reducing power to drive Nemakit-Daldynian, before the fi rst appearances

1750 Geological Society of America Bulletin, November/December 2010

6 1

IV 4 0 4p 3p 2 2p –1 Normalized U 5p 6p II

C (‰) III 0 1p 7p 13 δ

–2 1

–4 0

–6 –1 Normalized V

–8 541 537 533 529 525 521 517 Age (Ma)

δ13 Figure 11. Time evolution of uranium (red) and vanadium (blue) against CCaCO3 (gray) in Moroccan carbonates. Large and small squares depict samples that pass and fail, respectively, the combined [Sr] and Mn/Sr test for diagenetic alteration (see Appendix section A10). Regardless of whether we include all data or only the ﬁ ltered data, linear regressions (yellow lines) depict a statistically signiﬁ cant decline in U and V with time: all U data R2 = 0.25, p = 1.11 × 10–12; filtered U data R2 = 0.19, p = 2.71 × 10–7; all V data R2 = 0.30, p = 6.54 × 10–15; filtered V data R2 = 0.25, p = 9.22 × 10–10.

of calcitic taxa, conﬁ rming earlier studies small shelly fossil diversiﬁ cation, but could also by local changes in biology, preservation, or

(Porter, 2007; Zhuravlev and Wood, 2008), reﬂ ect the inﬂ uence of local (pulseeND) or global contamination.

and suggesting that the Mg/Ca ratio of sea- (pulsemND, pulseT) preservational biases. Superimposed on this 1–10 m.y. time scale water determines skeletal mineralogy at the Although we do not understand the causes variability in skeletal animal fi rst appearances time that carbonate skeletons fi rst evolve in of these pulses or of the large-scale changes and the carbon cycle, there is a 20 m.y. monotonic a clade. Phosphatic taxa appear through the in the Early Cambrian carbon cycle, it may be decline in uranium, vanadium, and 87Sr/86Sr. The Nemakit-Daldynian as well, although their signifi cant that just subsequent to the largest uranium and vanadium records suggest long-

fi rst appearances are not restricted to this time pulse (pulsemND), the first of the two large term oxidation of the sediment-water interface interval (unlike those of aragonitic taxa). reorganizations of the carbon cycle during in shallow continental shelf environments, and (2) The major groups of small shelly fossils the Early Cambrian occurred. At ca. 533 Ma, are consistent with the Lower Cambrian record δ13 appear early; fi ve appear by 540–538 Ma, and CCaCO3 begins to rise and eventually reaches of increasing depth and thorough ness of biotur- all but one appear by 534–532 Ma. ≥+4‰ for the fi rst time. From 533 to 525 Ma, bation. The 87Sr/86Sr record is consistent with a δ13 (3) By the middle of the Nemakit-Daldynian the CCaCO3 oscillations are twice as large relative increase in the hydrothermal fl ux of Sr (534–532 Ma), nearly half of the total number and ~4 times less frequent than in the previ- to the ocean that would have led to a gradual δ13 of small shelly fossil genera recorded in our data ous 9 m.y. Furthermore, by 532 Ma, Corg decrease in the Mg/Ca ratio of seawater (Fig. 9). set had appeared, and by the end of the Nemakit- behavior has changed from being uncorre- This change in Mg/Ca ratio predicts a switch δ13 Daldynian, nearly three-quarters had appeared, lated with CCaCO3 (variability in the carbon from aragonite to calcite seas at ca. 525 Ma, suggesting that diversifi cation of these animals isotopic composition of organic matter associ- which is refl ected in a change from aragonite occurred throughout the Nemakit-Daldynian, ated with differences in biology, preservation, to calcite in the mineralogies of animals that rather than being concentrated at the end of that or contamination by ancient organic carbon evolve carbonate biomineralization associated time. The dominant contributors to the pattern weathered from the continents) to being cor- with the youngest pulse of fi rst appearances near δ13 δ13 of fi rst appearances are the molluscs and hyo- related with CCaCO3 ( C changes dominated the Nemakit-Daldynian–Tommotian boundary liths, and to a lesser extent cap-shaped fossils by changes in global forg). Similarly, the third (Porter, 2007).

and coeloscleritophorans, all of which may be pulse (pulseT) occurs after the 8‰ negative The increase in the rate of hydrothermal al- δ13 closely related. CCaCO3 shift that accompanies the Nemakit- teration of basalt also is consistent with an in- (4) Three pulses in fossil ﬁ rst appearances, Daldynian–Tommotian boundary. This nega- crease in mid-ocean-ridge length associated with δ13 the smallest in the early Nemakit-Daldynian , tive CCaCO3 shift lasted just 506 ± 126 k.y. the initial opening of the Iapetus Ocean (Fig. 3) ca. 540–538 Ma (pulseeND), the largest in the (Maloof et al., 2010a) and corresponds to the and a rise in global sea level. The diachronous

middle Nemakit-Daldynian, ca. 534–530 Ma switch from forg-dominated carbon cycle vola- ﬂ ooding of at least part of all the continents dur- δ13 (pulsemND), and the third in the Tommotian, tility back to much smaller-amplitude CCaCO3 ing the Early Cambrian could be associated with δ13 ca. 524–522 Ma (pulseT), may reﬂ ect peaks in oscillations and Corg variability affected this predicted rise in global sea level, although

Geological Society of America Bulletin, November/December 2010 1751

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

δ13 dynamic topography associated with mantle con- APPENDIX a y-intercept equal to Cin: 0.2–0.3 and –6‰, re- vection must have had an equally large impact spectively, for the Cenozoic (Rothman et al., 2003). δ13 A1. CCaCO3 Methods However, Figure A1C has a slope of unity and an in- on the regional sea level observed in the stratig- tercept of –22.6‰, typical of Cryogenian and Edia- raphy of continental margins. Regardless of the δ13 δ13 δ13 No previously unpublished CCaCO3 data are re- caran carbonates, where CCaCO3 varies but Corg origin of the observed fl ooding of continental ported in this paper. For Morocco (Maloof et al., does not (Rothman et al., 2003). Because the δ13 margins (Matthews and Cowie, 1979; McKie, 2005, 2010a), clean dolostones and limestones with Corg signal is damped by a factor of 1.5–2 with re- δ13 minimal siliciclastic components and secondary vein- spect to CCaCO3, and because data in the cross plot 1993; Haq and Schutter, 2008), recent work by δ13 ε ing or cleavage were targeted. Samples were slabbed span a variety of events and >20 m.y., the CCaCO3- Peters (2005) supports the long-standing hypoth- and polished perpendicular to bedding and ~5 mg of cross plot is misleading and demonstrates that blind esis (Newell, 1952, 1962; Valentine and Moores, powder were microdrilled from individual lamina- use of cross plots without stratigraphic context and 1970; Schopf, 1974; Simberloff, 1974; Hallam tions for isotopic analysis. Aliquots of approximately event-by-event analysis can be dangerous. The damp- δ13 and Wignall, 1999) that the total global area of 1 mg of powder were heated to 200°C to remove ing of the Corg signal may refl ect the possibility that δ13 vola tile contaminants and water. Samples were then some part of the CCaCO3 signal recorded in restricted fl ooded continental shelves, and thus the total placed in individual borosilicate reaction vessels and platformal carbonates does not represent open-ocean area of shallow marine habitat, controls the rate reacted at 76°C with three drops of H3PO4 in a Finnigan DIC (Appendix section A9), or that some part of the δ13 of taxonomic origination and extinction. MAT Kiel I preparation device coupled directly to the Corg signal refl ects ancient organic matter (be it A wide variety of different causes for the inlet of a Finnigan MAT 251 triple collector–isotope DOC or recycled sedimentary carbon). δ13 δ18 Cambrian “explosion” have been presented ratio–mass spectrometer, and C and O data were acquired simultaneously. δ13C and δ18O are reported in A3. 87Sr/86Sr Methods over the years (reviewed by Marshall, 2006), the standard delta notation as the ‰ difference from including environmental triggers, increased the Vienna Peedee belemnite (VPDB) standard. Pre- Available 87Sr/86Sr data for Siberia, Mongolia, and genetic complexity, and feedbacks relating to cision and accuracy of data were monitored through China were gleaned from the literature with little increasing ecological complexity. The environ- daily analysis of at least six standards, which were run possibility for quality control. All 87Sr/86Sr data from to racket sample suites at the beginning, middle, and mental parameter most commonly invoked as a Morocco were acquired at the MIT Radiogenic Iso- end of the day’s runs. Measured precision was main- tope Laboratory. The 5–10 mg aliquots of carbonate trigger for animal radiation is atmospheric pO , σ δ13 δ18 δ13 2 tained at better than 0.1‰ (1 ) for both C and O. from the same powders prepared for Corg were fi rst which could have reached a threshold level in reacted sequentially in an ultrasonic bath 3–5 times δ13 the earliest Cambrian that allowed for larger or- A2.1. Corg Methods for 15–45 min in 1.0 mL of 0.2 M ammonium acetate ganisms with complex physiologies and abili- to exchange loosely bound Sr cations, which included Organic carbon isotopic values for Morocco were radiogenic 87Sr derived from 87Rb decay (Gao et al., ties to create collagen-containing tissues (Towe, obtained from the total organic carbon (TOC) of in- 1996; Montañez et al., 1996; Bailey et al., 2000). 1970). There is no independent evidence for a soluble residues. After removing the outside layer of Three 15–30 min sequential ultrasonic washes in rise in atmospheric oxygen at the Ediacaran- surface oxidation and large veins, whole-rock samples water removed residual ammonium and some of the Cambrian boundary, however. An explanation were crushed into powder. Insoluble residues for or- suspended clay fraction. The remaining carbonate was for the processes responsible for the radiation ganic carbon isotope analysis were obtained by acidi- reacted for 5 min with 1.0 mL 1.4 M acetic acid, and fying these whole-rock powders in 6 N HCl for 24 h insoluble residue was removed by centrifugation. Sr of animals, and of whether the radiation was a to dissolve all carbonate minerals. Care was taken to was isolated via standard chromatographic techniques consequence or a cause of associated geochem- ensure that acid was added and acidifi cation continued using EIChroM SR-spec resin and eluted with ultra-

ical changes, requires a thorough understand- until there was absolutely no visible carbonate disso- pure H2O. Samples were analyzed by thermal ion- ing of the pattern of that radiation, to which this lution, so that the analyses would not be affected by ization mass spectrometry (TIMS) on a Micromass contamination from residual inorganic carbon. The in- IsoProbe T in dynamic mode. All data were cor- paper contributes. soluble residues were then rinsed with deionized (DI) rected for internal mass bias using 86Sr/88Sr = 0.1194. water, dried, and loaded into tin capsules for isotopic Analyses were referenced against NBS SRM 987 CONCLUSIONS analysis. At the Massachusetts Institute of Technol- (0.710250), with a long-term average of 0.710240 and ogy (MIT) and Washington University, samples were 2σ external precision of 0.000014 (N > 100). In his chapter on the imperfection of the geo- fl ash combusted at 1030°C in a Costech ECS 4010 Elemental Analyzer. The resulting CO2 gas was ana- A4. Elemental Concentration Methods logical record, Darwin alludes in passing to a lyzed by continuous fl ow on a Delta V Plus continu- δ13 different explanation for the supposed sudden ous fl ow–isotope ratio–mass spectrometer. The Corg Elemental concentrations (e.g., Ca, Mg, Fe, Mn, appearance of animals in the lowest fossilifer- values were calibrated against the NBS 22 standard Rb, Sr, Th, U, V) for Morocco samples were deter- δ13 ous strata. He writes “[w]e should not forget using the accepted value of Corg = –30.03‰. Repro- mined by inductively coupled plasma–mass spec- ducibility (typically better than 0.5‰) was verifi ed by that only a small portion of the world is known trometry (ICP-MS). All samples were prepared by duplicate sample analyses and regularly interspersed digesting a 0.5 g aliquot from the same carbonate with accuracy” (Darwin, 1859, p. 307). It is this δ13 87 86 international standards (IAEA-CH-6, –10.45‰). The powder used for Corg and Sr/ Sr in aqua regia at δ13 explanation—the incompleteness of our knowl- Corg values are reported in standard delta notation 90°C in a microprocessor-controlled digestion block edge—that has turned out to be closer to the relative to VPDB. Organic C concentrations were for 2 h. This digestion was not total and would not truth. The problem of missing fossil ancestors measured using standards with known carbon con- dissolve silicates or oxides. The solution was diluted centration and the intensity of mass 44. TOC values and analyzed by ICP-MS using a Perkin Elmer SCIEX was solved by the discovery of the Precambrian for the bulk samples were calculated by combining ELAN 6100 at ActLabs. One blank was run for every fossil record, the problem that nearly all the ani- the carbon concentration data with measurements 68 samples, along with digested certifi ed reference mal phyla appear in the Lower Cambrian with no of the ratio of insoluble residue to original pre- materials USGS GXR-1, GXR-2, GXR-4, and GXR-6. decarbonated powder. The values of δ13C , δ13C , evidence of intermediate taxa was solved by the CaCO3 org An in-house control was run every 33 samples. Internal ε, and TOC are plotted together in Figure A1. recognition that most Lower Cambrian fossils control standards and a duplicate were analyzed after every 10 samples. External error (1σ), determined by represent stem-groups of living phyla, and the A2.2. Carbon Cycle Systematics repeat analyses, was 7% for all elements, with the best problem of the explosive diversifi cation of ani- precision achieved for Ca, Mg, and Sr.

mals at the start of the Tommotian was solved If forg (forg = Corg/Ctotal is the fraction of carbon buried that is organic) is constant, the δ13C versus A5. U/Pb Geochronology Methods by improved correlation and radiometric dating CaCO3 ε (ε is the difference between DIC and organic carbon, of Lower Cambrian sequences—to which we often dominated by the kinetic isotope effect associ- No new geochronological data are reported in contribute here—showing that this diversiﬁ ca- ated with the uptake of carbon by photoautotrophs) this paper. However, all of the ages from Morocco,

tion was drawn out over more than 20 m.y. plot (Fig. A1C) should have a slope equal to forg and Siberia, China, and Oman used to construct our age

1752 Geological Society of America Bulletin, November/December 2010

Age (Ma) 541 537 533 529 525 521 517 A Uncorrelated Correlated Uncorrelated 6 –18

4 –20

2 –22 δ 13 (‰) C 3 0 –24 org (‰) CaCO C 13 δ –2 –26

–4 –28

–6 –30

0.05 B C y = 0.92x – 22.6 0.04 R2 = 0.61 6 4 0.03 δ 2 13 C %TOC

0.02 CaCO δ13C CaCO3 0 All lithologies 3

0.01 (‰) 13 δ Corg , %TOC, ε –2 0 Pre / Post ND-T –29 –27 –25 –23 –21 / Microbialaminate –4 13 / Grainstone δ Corg (‰) / Stromatolite –6 / Thrombolite / Ribbonite 18 20 22 24 26 28 30 32 ε Figure A1. Paired carbonate and organic carbon δ13C from the same carbonate samples from Oued Sdas and Sidi M’Sal. Data are color δ13 δ13 coded for lithology. (A) CCaCO3- Corg variation through time, with intervals of correlated and uncorrelated behavior highlighted in δ13 δ13 ε yellow and blue, respectively. (B) Total organic carbon (TOC) versus Corg. (C) CCaCO3versus , with a linear ﬁ t computed using the reduced major axis method.

Geological Society of America Bulletin, November/December 2010 1753

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

model were obtained at the MIT geochronology the ca. 517 Ma 207Pb/206Pb age is recalculated using new For example, although the lower Nemakit-Daldynian labora tory over the past two decades. During that decay constants (see Appendix section A5), fi ve single (542–534 Ma) contains the right number of negative 206 238 δ13 δ13 time, techniques have evolved. Perhaps the most im- grains have a weighted mean Pb/ U date of 515.56 CCaCO3 excursions, CCaCO3 never reaches the +1‰ portant change in technique is the routine application ± 1.03 Ma. The oldest four of these dates are labeled to +2‰ peaks characteristic of Morocco, Siberia, and of Mattinson’s (2005) chemical abrasion technique. with gray bars along the bottom of Figure 5. Two other Mongolia. Also, although there is no better place in In the chemical abrasion method, high-temperature indirect radiometric ages are used as tie points for the the Lower Cambrian to place it, the nadir between 7p δ13 annealing repairs radiation damage in zircon and pre- Morocco CCaCO3 record. The onset (1p; Fig. 5) of and II is deeper in China than in Morocco, Siberia, δ13 vents preferential leaching of Pb relative to U during the Ediacaran-Cambrian boundary negative CCaCO3 or Mongolia (Fig. 5). The Shiyantou and Yu’anshan multistep digestions. Annealed zircons were dissolved excursion is pinned to a weighted mean 206Pb/238U zir- formations that contain this nadir are dominated by δ13 in two steps with the initial HF digestion step pref- con date of 542.3 ± 0.2 Ma from Oman (yellow bar silt and sand, and perhaps the CCaCO3 from these erentially dissolving the most damaged zircon, which in Fig. 5; Bowring et al., 2007). The beginning of the units is not reliable. Nevertheless, at the ±1 m.y. level, ≥ δ13 is most likely to be affected by postcrystallization Pb fi rst +4‰ positive CCaCO3 excursion (5p; Fig. 5) is the proposed age model for China is the best fi t to the 206 238 δ13 87 86 loss, isolating the highest quality low-U zircon for pinned to a weighted mean Pb/ U zircon date from CCaCO3 and Sr/ Sr records from Morocco, Siberia, fi nal analysis. Bed 5 Meishucun of ca. 533 Ma (Brooks et al., 2006; and Mongolia. Prior to routine use of chemical abrasion, many Jenkins et al., 2002; red bar in Fig. 5). Between each All of the stretches applied to generate the age analyses were affected by Pb loss, despite mechani- of these radiometric tie points, sediment accumulation model are collected in the GSA Data Repository.1 207 206 δ13 cal abrasion. In these situations, the Pb/ Pb date rates are assumed to be constant. We pay particular With the best-fi t U/Pb- CCaCO3 age model con- is older than the 207Pb/235U date, which is in turn older attention to each predicted change in sediment accu- structed independent of the fossil record, small shelly than the 206Pb/238U date. In many of these cases, the mulation rate to determine whether these changes are fossil fi rst appearances from different continents may most precise estimate for the age of an ash bed was consistent with visible sedimentary or stratigraphic be studied in the context of relative and absolute time derived by taking the weighted mean 207Pb/206Pb date evidence. For example, in Morocco, the transition (Fig. 5; see next section). of the most concordant analyses, with the 206Pb/238U between the Adoudounian and Lie de Vin Formations date often being much younger. In samples treated by heralds an increase in silici clastic input to the basin, A7. Small Shelly Fossil Methods chemical abrasion, it is common to calculate weighted and a simultaneous increase in relative sea level and mean 206Pb/238U, 207Pb/235U, and 207Pb/206Pb dates for sedimentation rate within the Tiout-Aguerd Trough Occurrence data for small shelly fossils were ob- each sample based on coherent clusters of data for (Maloof et al., 2005, 2010a). tained from the literature for sections from which δ13 which all scatter can be explained by analytical uncer- Next, individual CCaCO3 records from Siberia , carbon isotopic data are available, using the follow- tainty alone. Most high-precision zircon data exhibit Mongolia, and China are stretched to best fi t the ing sources: Sukharikha—Voronova and Rozanov 206 238 δ13 a slight but systematic discordance (with Pb/ U < Moroccan U/Pb- CCaCO3 age model. The least am- in Rozanov et al. (1969), Meshkova (1974), 207Pb/235U < 207Pb/206Pb dates) likely related to inaccu- biguous correlation is for Sukharikha (Kouchinsky Luchinina et al. (1997), and Kouchinsky et al. (2010); δ13 racy in one or both of the U decay constants (Mattin- et al., 2007), where the CCaCO3 curve matches Kotuikan—Missarzhevsky in Rozanov et al. (1969), son, 2000, 2010; Schoene et al., 2006). Thus, it has Morocco peak for peak in remarkable detail (Fig. 5). Val’kov (1975), and Savitsky et al. (1980); Bol’shaya become accepted to use the weighted mean 206Pb/238U Several workers have already generated a suite of Kuonamka—Val’kov (1975); Khorbusuonka—Kar- δ13 date as the most precise and accurate representation consistent correlations between CCaCO3 stratigra- lova and Vodanyuk (1985) and Karlova (1987); of the eruption/depositional age, and we follow this phies within Siberia (Magaritz et al., 1986, 1991; Zhurinsky Mys—Sysoev (1972) and Grigor’eva and practice here. Mattinson (2010) also proposed that Kirschvink et al., 1991; Brasier et al., 1993, 1994c; Varlamov in Rozanov and Sokolov (1984); Isit’— a new decay constant should be calculated for 235U, Knoll et al., 1995b; Kaufman et al., 1996; Brasier and Missar zhevsky and Rozanov in Rozanov et al. (1969), assuming that the decay constant for 238U is accurate, Sukhov, 1998; Kouchinsky et al., 2001, 2005, 2007). Sysoev (1972), Meshkova (1974), and Grigor’eva and such that the two U-Pb dates will be concordant. In We tune all of these individual records to Morocco, Repina in Rozanov and Sokolov (1984); Dvortsy— the soon-to-be-published version of the geological taking note of each change in sedimentation rate Krylov et al. in Rozanov et al. (1969), Sysoev (1972), time scale (GTS2010), an attempt has been made to required to fi t the age model. For example, the base Val’kov (1983), Grigor’eva in Rozanov and Sokolov propagate decay constant uncertainties and to correct of the Tommotian Stage is defi ned by an uncon- (1984), and Fedorov et al. in Repina and Rozanov the 235U decay constant for legacy data (M. Schmitz, formity at the type sections at Dvortsy and Ulakhan (1992); Ulakhan Sulugur—Krylov et al. in Rozanov 2010, oral communication). In general, the net effects Sulugur, leading to a controversy over the duration et al. (1969), Grigor’eva in Rozanov and Sokolov are to decrease the published 207Pb/206Pb dates and to of this sedimentary hiatus (e.g., Knoll et al., 1995b; (1984), and Fedorov et al. in Repina and Rozanov signifi cantly increase the age uncertainties. However, Kaufman et al., 1996; Khomentovsky and Karlova, (1992); Selinde—Korshunov et al. (1969), Val’kov δ13 if the analyses are rendered concordant after the cor- 2002, 2005). The U/Pb- CCaCO3 age model supports (1982), Voronova et al. (1983), Khomentovsky and rection, one can use the higher-precision weighted the hypothesis that a substantial unconformity breaks Karlova (1986), and Repina et al. (1988); Salaany mean 206Pb/238U date. Thus, for legacy data, Pb-Pb the stratotype section of the Tommotian, while a well- Gol—Korobov and Missarzhevsky (1977), Voronin δ13 and U-Pb dates should not be used interchangeably structured CCaCO3 curve exists elsewhere in Siberia et al. (1982), Endonzhamts and Lkhasuren (1988), when calculating durations or rates. A good example during this time interval. and Esakova and Zhegallo (1996); Bayan Go1— is sample 94-N-11 (Grotzinger et al., 1995), for which The Mongolian carbonates are mixed with silici- Khomentovsky and Gibsher (1996) and Esakova and 207 206 δ13 ten multigrain fractions resulted in a Pb/ Pb date clastics for which there are no CCaCO3 records. How- Zhegallo (1996); Kvete-Tsakhir-Nuruu—Esakova of 543.3 ± 1.0 Ma, and a weighted mean 206Pb/238U ever, despite these gaps, a strong correlation can be and Zhegallo (1996); Meishucun—Qian (1989) and δ13 date of 540.61 ± 0.88 Ma. Recalculating the data made to virtually every positive CCaCO3 excursion Qian and Bengtson (1989); Jijiapo—Chen (1984); and with a new decay constant yielded a weighted mean. observed in Morocco and Siberia (except perhaps Xiaotan—Li et al. (2001). The stratigraphic data in 206 238 δ13 The preferred weighted mean Pb/ U age is much 3p; Fig. 5). In particular, the +4‰ to +5‰ CCaCO3 these publications were compared with those associated closer to the estimate for the E-C boundary in Oman peaks E (Salaany Gol, Section 2, Unit 7; Bayan Gol, with the isotopic data to assign fossil occurrences with (Bowring et al., 2007) based in CATIMS 206Pb/238U Section 3B, Unit 21; and Kvete-Tsakhir-Nuruu, the closest available isotopic sample (see GSA Data data. Where relevant, we report both the originally Section 4, Unit 7) and F (Salaany Gol, Section 2, Repository [see footnote 1]). Where fossils were stated published and recalculated ages. Unit 11/12) of Brasier et al. (1996) in the upper Bayan to be present from an unspecifi ed level within a unit Gol Formation match well with the upper Nemakit- from which several isotopic measure ments are avail- δ13 δ13 A6. U/Pb- CCaCO3 Age Model Daldynian (533–525 Ma) positive CCaCO3 excur- able (e.g., Bed 3 in the Meishucun section, for which sions 5p and 6p, respectively (Fig. 5). The favored there are three samples with isotopic measurements), δ13 87 86 The CCaCO3 record from Morocco is directly age model also is consistent with the Sr/ Sr records the fossil occurrences were assigned to the stratigraph- constrained by four weighted mean 206Pb/238U zircon from Morocco, Siberia, and Mongolia (Fig. 9). ically highest sample. If no isotopic measurements δ13 dates from ash beds within the carbonate stratigraphy: China is pinned to the Moroccan U/Pb- CCaCO3 525.343 ± 0.088 Ma (Maloof et al., 2005, 2010a), age model by the fi rst appearance of Treptichnus δ13 1 524.837 ± 0.092 Ma (Maloof et al., 2010a), 523.17 ± pedum and the CCaCO3-defi ned Ediacaran-Cambrian GSA Data Repository item 2010293, Micro- 0.16 Ma (Maloof et al., 2010a), 520.93 ± 0.14 Ma boundary, as well as the ca. 533 Ma date from Bed 5 at soft Excel Workbook containing stratigraphic, geo- (Landing et al., 1998; Compston et al., 1992; Maloof Meishucun (Brooks et al., 2006; Jenkins et al., 2002). chemical and biostratigraphic data presented in this 207 206 δ13 et al., 2010a), and one weighted mean Pb/ Pb zir- However, several aspects of the Chinese CCaCO3 paper , is available at http://www.geosociety.org/pubs/ con date of 517 ± 1.5 Ma (Landing et al., 1998). When record do not match Morocco, Siberia, and Mongolia. ft2010.htm or by request to [email protected].

1754 Geological Society of America Bulletin, November/December 2010

were available from the bed in which fossils occurred, ent from the only other Lower Cambrian pole from latitude. (2) The Anti-Atlas margin may be alloch- the fossil occurrences were associated with the clos- Laurentia. The Mont Rigaud and Chatham-Grenville thonous to West Africa prior to the Early Ordovician est overlying isotopic measurement. These procedures pole comes from two shallowly emplaced syenite in- (Mitchell et al., 2010). However, the basement to the are conservative in that fi rst appearances are placed as trusions along the failed rift arm of the Iapetus ocean Anti-Atlas mountains consists of 2070 Ma metasedi- late as possible. In any case, the age of most such units (western Quebec) (Kumarapeli and Saull, 1966). ments (Walsh et al., 2002) intruded by 2050–2032 Ma falls within a single time bin, and thus the choice of The intrusions are dated using 40Ar/39Ar on horn- granitoids (Walsh et al., 2002; Thomas et al., 2002; the sample to which to assign fossil occurrences does blende and potassium feldspar, but neither passes Roger et al., 2001; Hassenforder et al., 2001; Mortaj not infl uence the overall patterns presented here (e.g., a conclusive fi eld test (McCausland et al., 2007). et al., 2000; Aït Malek et al., 1998), similar in age to all of Bed 3 in the Meishucun section is assigned an Paleomagnetic poles from Baltica (Torneträsk For- the Birimian crust that makes up most of the West age of 534–533 Ma). In the sections at Dvortsy and mation; Torsvik and Rehnström, 2001) and Siberia African craton (Boher et al., 1992). The Anti-Atlas Ulakhan Sulugur, the upper layers of the Yudoma For- (Kessyusa Formation and overlying Erkeket Forma- Mountains would have to represent a ribbon continent mation are karsted, and the fossils in these layers may tion, Khorbusuonka; Pisarevsky et al., 1997) come rifted from West Africa during the Paleo- or Meso- be younger material in cavern fi ll (e.g., Khomentovsky from sedimentary units with no radiometric ages, proterozoic, and amalgamated with a Neoproterozoic and Karlova, 1993; but see Khomentovsky , 1997); as yet they are well-constrained in age in the context of arc complex prior to Late Cambrian or Early Ordovi- δ13 a result, all material in the upper Yudoma Formation the new U/Pb- CCaCO3 age model presented in this cian collision with West Africa along a hidden suture at these localities was associated with the stratigraphi- paper. Unfortunately, none of these poles from Bal- beneath the Tindouf basin. Not only is this hypoth- cally lowest isotopic measure ment from the overlying tica or Siberia has undergone a rigorous fi eld test. The esis ad hoc, but in the paleogeographic framework of Pestrotsvet Formation. 40Ar/39Ar age of 525 ± 5 Ma and the positive baked Figure 3, it is not clear where the Anti-Atlas ribbon In many cases, the taxonomy of the fossils has been contact test make the Itabaiana mafi c dikes (northeast continent could have resided such that it enjoyed low revised since the publication of the references listed Brazil, Amazonia) a particularly relevant paleomag- latitudes during the Early Cambrian (i.e., far from here. Consequently, the lists of species from the vari- netic pole for Early Cambrian plate reconstructions northwestern Gondwana) but joined West Africa by ous sections were compared with the most recent and (Trindade et al., 2006). The Ntonya igneous ring Early Ordovician time. (3) The paleomagnetic data authoritative systematic literature in order to place complex (Malawi-Congo craton) has an 40Ar/39Ar age from Amazonia is younger than the 40Ar/39Ar age im- them in the most appropriate genera and higher groups of 522 ± 13 Ma, but no positive fi eld test (Briden, plies, or Gondwana was moving very rapidly during (see Data Repository [see footnote 1]). It should be 1968; Briden et al., 1993). the Early Cambrian (see following). noted that much of this material (notably the hyoliths) In the absence of paleomagnetic poles with posi- Even during the preceding Ediacaran Period, the is still in need of systematic revision, so the generic tive fi eld tests and statistically indistinguishable ages, APW-based approach to plate reconstructions has assignments used here should only be regarded as an alternative way to create plate reconstructions is been unsuccessful. While it is possible to choose or to tentative. The mineralogy of each higher group was to fi t small circle arcs representing the apparent polar reject subsets of any continent’s paleomagnetic data- assessed by reviewing the relevant literature (e.g., wander (APW) path of paleomagnetic poles for each base in order to create a time-progressive APW path Bengtson and Conway Morris, 1992; Porter, 2010). craton. Assuming constant long-term plate motion, that does not require unrealistic rates of plate motion, it As described in Appendix section A6, chrono- specifi c ages can be interpolated along the APW paths is impossible to do so entirely within the bounds of any metric dates were assigned to each carbon isotopic and used as reconstruction points. Additionally, if each objective quality fi lter (e.g., Kirschvink et al., 1997; measurement, allowing a date to be placed on each craton has two or more paleomagnetic poles that fall Torsvik et al., 1998; Evans et al., 1998; Pisarevsky fossil occurrence. Fossil occurrences for each genus on a small circle, then the APW path for each craton et al., 2000; Meert et al., 2001). This problem has led a were then placed in 2 m.y. time bins, and these were should overlap, and the need for individual poles of number of authors to propose that the Early Cambrian used to construct Figures 5 and 6. In Figures A2–A4, identical age diminishes. Unfortunately, few cratons was characterized by anomalously high plate motions all Chinese sections were lumped together, as were moved together during the continued continental dis- or true polar wander (TPW—the wholesale rota- all Mongolian sections, and all sections in the Lena- persal of the Early Cambrian (e.g., Hoffman, 1991), tion of the mantle and crust relative to the fl uid outer Aldan region (Dvortsy, Ulakhan Sulugur, Zhurinsky and even western Gondwana (shown nearly joined in core) (Kirschvink et al., 1997; Evans, 1998; Mitchell Mys, and Isit’). For Figure 6, the number of genera Fig. 3) may not have been sutured yet (Tohver et al., et al., 2010). True polar wander causes paleomagnetic that fi rst appear within each time bin was determined. 2006). In the absence of combined individual pole poles to carve out great circle arcs perpendicular to the To test the effects of individual sections on the pat- and APW path constraints, relative paleolongitudes, paleo-nonhydrostatic minimum moment of inertia, tern of fi rst occurrences, the data for a particular sec- and thus parameters such as the width of the Iapetus rather than the small circle arcs about Euler poles pre- tion were omitted and the number of fi rst occurrences Ocean, remain unknown. dicted for plate tectonic–driven motion. Additionally, recalculated. Similarly, to determine the contribution Not only are APW paths of marginal utility for if rapid TPW is oscillatory and fast (beyond the time from each region (Siberia, Mongolia, or China), the the 525 Ma reconstruction, but even the high-quality resolution of the paleomagnetic database), the great data for the other two regions were omitted and Itabaiana dykes pole for Amazonia may not strictly circle distribution of poles may look like a zigzagging the number of fi rst occurrences recalculated. constrain the latitude of West Africa if the continents smear, rather than an age-progressive path. In a world had yet to be sutured. This point is particularly im- where continental motion is dominated by rapid (e.g., A8. Paleogeography Methods portant because the fairly traditional (e.g., Hoffman, <10 m.y.) oscillatory TPW events, poles from differ- 1991; Cawood and Pisarevsky, 2006; McCausland ent cratons of suffi ciently similar age (e.g., ±1 m.y.) to Traditionally, plate reconstructions are made by et al., 2007) reconstruction in Figure 3 shows the warrant linear reconstruction may not exist at all, ren- rotating paleomagnetic poles of similar age from 2-km-thick stromatolite/thrombolite/microbialite– dering traditional plate reconstruction methods impos- different continents into collinearity. Then, one and later archaeocyath-dominated carbonate plat- sible. However, a paleogeography can be reconstructed continent is moved around the mutual pole (i.e., form of Morocco poleward of the Antarctic Circle. by rotating the great circle fi ts to paleomagnetic poles across lines of paleolongitude) until an acceptable There are three possible solutions to this problem. from individual cratons into coplanarity, thus bypass- paleogeographic fi t is achieved. Figure 3 is an ex- (1) Tommotian–Atdabanian climate was similar to ing the relative age of individual poles and capturing ample of such a plate reconstruction for ca. 525 Ma that of the middle Cretaceous (e.g., Huber et al., the effect of TPW on plate motions (Maloof, 2004; using the paleomagnetic poles collected in Table A1 1995; Herman and Spicer, 1996; Jenkyns et al., 2004) Raub et al., 2007). Maloof (2004) and Raub et al. and the rotations in Table A2. However, this paleo- or early Eocene (e.g., Shackleton and Boersma, (2007) performed this exercise using paleomagnetic geography is poorly constrained and almost certainly 1981; Greenwood and Wing, 1995; Sloan et al., poles spanning the 600–500 Ma time window and inaccurate in detail. 1995; Huber and Sloan, 2001), with generally warm found that a plate reconstruction remarkably similar to First, no two poles from different continents are temperatures and a very small equator- to-pole tem- that shown in Figure 3 could be generated, with Gond- of the same quality or age (Table A1). Two Lower perature gradient (e.g., Sloan and Pollard, 1998). wana together and geologically consistent positions for Cambrian poles exist for Laurentia. The Wichita However, this solution may be inconsistent with the Laurentia, Baltica, Siberia, and South China. Mountains granite (Oklahoma) is precisely dated observation that fi rst and last appearances of archaeo- Unfortunately, even the TPW great circle tech- with a U/Pb zircon age of 533 ± 3 Ma (Wright et al., cyath reefs seem to be latitude-dependent, since they nique does not bring us closer to defi ning the latitu- 1996). Although there is some suggestion of a posi- appear and disappear as continents such as Laurentia dinal distribution of the continents between 542 and tive baked contact test with the discordantly underly- move through the carbonate belt (e.g., Debrenne and 517 Ma. Whether we constrain the plate reconstruc- ing Glen Mountains Anorthosite (Roggenthen et al., Courjault-Radé, 1994). Also, even during the equable tion using geology, individual paleomagnetic poles, 1981), the Wichita granite paleomagnetic pole has no climates of the mid-Cretaceous and Eocene, frame- APW paths, or TPW great circles, we typically ar- rigorous positive fi eld test and is substantially differ- work carbonate reefs did not develop poleward of 45° rive at a geography similar to that shown in Figure 3.

Geological Society of America Bulletin, November/December 2010 1755

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

EDIAC NEMAKIT-DALDYNIAN TOMMOTIAN AT 544-542 542-540 540-538 538-536 536-534 534-532 532-530 530-528 528-526 526-524 524-522 522-520

Cambrotubulus Anabaritids Anabarites Aculeochrea Selindeochrea Mariochrea Protoconodonts Mongolodus Protohertzina Hertzina Oneotodus Prooneotodus Maikhanella Purella Cap-shaped fossils Postacanthella Rozanoviella Lathamella Aegitellus Ernogia Aegides Granoconus Ocruranus Ramenta Stictoconus Conotheca Spinulitheca Kunyangotheca Ladatheca Loculitheca Allatheca Crossbitheca Khetatheca Kotuitheca Turcutheca Uniformitheca Orthothecimorph hyoliths Doliutheca Exilitheca Laratheca Nikatheca Antiquatheca Dabanitheca Eonovitatus Gracilitheca Isititheca Majatheca = China = Mongolia Mooritheca = Lena-Aldan Region Obliquatheca = Kotuikan Ovalitheca = Khorbusuonka = Bol’shaya Kuonamka Paraeonovitatus = Selinde Tchuranitheca = Sukharikha Adyshevitheca open symbol denotes uncertainty Lenatheca Malykanotheca Novitatus Tetratheca

Figure A2. Occurrence data for 150 skeletal metazoan genera that are present in the earliest Cambrian (page 1 of 3). Genera are grouped according to higher taxa; orthothecimorph and hyolithomorph hyoliths are shown separately. Age boxes are defi ned δ13 by the U/Pb-calibrated CCaCO3 age model, independent of the fossil fi rst appearances themselves. See Appendix section A7 for detailed information regarding the construction of this fi gure.

1756 Geological Society of America Bulletin, November/December 2010

EDIAC NEMAKIT-DALDYNIAN TOMMOTIAN AT 544-542 542-540 540-538 538-536 536-534 534-532 532-530 530-528 528-526 526-524 524-522 522-520 Pseudorthotheca Hyolithelminths Torellella Hyolithellus “Coleolella” Leibotheca Rushtonia Torellelloides Halkieria Lopochites Coeloscleritophorans Siphogonuchites Dabashanites Chancelloria Drepanochites Lomasulcachites Sachites Allonnia Archiasterella Sinosachites Camenella Tommotiids Porcauricula Lapworthella Sunnaginia Micrina Tannuolina Aldanella Anabarella Archaeospira Barskovia Bemella Ceratoconus Crestoconus Igorella Ilsanella Latirostratus Maidipingoconus Obtusoconus

Pileconus Molluscs Protoconus Pelagiella Salanyella Watsonella Xianfengella Humilospira Mellopegma = China = Mongolia Nomgoliella = Lena-Aldan Region Oelandiella = Kotuikan Philoxenella = Khorbusuonka = Bol’shaya Kuonamka Stenothecoides = Selinde Tannuella = Sukharikha Merismoconcha open symbol denotes uncertainty Igorellina Mackinnonia Spatuloconus Yochelcionella

Figure A3. Occurrence data for 150 skeletal metazoan genera that are present in the earliest Cambrian (page 2 of 3). Genera are grouped according to higher taxa; orthothecimorph and hyolithomorph hyoliths are shown separately. Age boxes are defi ned δ13 by the U/Pb-calibrated CCaCO3 age model, independent of the fossil fi rst appearances themselves. See Appendix section A7 for detailed information regarding the construction of this fi gure.

Geological Society of America Bulletin, November/December 2010 1757

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

EDIAC NEMAKIT-DALDYNIAN TOMMOTIAN AT 544-542 542-540 540-538 538-536 536-534 534-532 532-530 530-528 528-526 526-524 524-522 522-520 Yacutolituus Korilithes Aimitus “Ambrolinevitus” Hyolithomorph hyoliths Burithes Crestjahitus Doliutus Dorsojugatus Jacuticornus “Linevitus” Notabilitus Oblisicornus Tuojdachites Microcornus Paracarinachitid

Oxytus Conulariid Rarissimetus Trapezovitus Arthrochites

Paracarinachites Cambroclave Zhijinites Coleolids Coleolus Coleoloides Salanacus Tianzhushanella Quadrochites Miscellaneous Problematica Cyrtochites Yunnanodus Cupitheca Paragloborilus = China Pseudovalitheca = Mongolia = Lena-Aldan Region Fomitchella = Kotuikan Tommotitubulus = Khorbusuonka Lophotheca = Bol’shaya Kuonamka = Selinde Tumulduria = Sukharikha Neogloborilus open symbol denotes uncertainty Rhombocorniculum Mobergella Embryos Archaeooides Olivooides Markuelia Calcareous brachiopods Phosphatic brachiopods Archaeocyaths Trilobites Bradoriids

Figure A4. Occurrence data for 150 skeletal metazoan genera that are present in the earliest Cambrian (page 3 of 3). Genera are grouped according to higher taxa; orthothecimorph and hyolithomorph hyoliths are shown separately. Age boxes are defi ned by the U/Pb-calibrated δ13 CCaCO3 age model, independent of the fossil fi rst appearances themselves. See Appendix section A7 for detailed information regarding the construction of this fi gure.

1758 Geological Society of America Bulletin, November/December 2010

TABLE A1. PALEOMAGNETIC POLES USED TO GENERATE THE PALEOGEOGRAPHY IN FIGURE 3

Craton Unit Code PLAT PLON A95 Q Unit age (Ma) Age method Laurentia Wichita Granite (1) WG –2.0 327.0 8.5 4 533 ± 3 (2) 206Pb/238U Laurentia Mt. Rigaud and Chatham-Grenville (3) MR 11.9 4.6 4.8 5 532 ± 2 (3) 40Ar/39Ar Baltica T orneträsk Formation (4) TT 56.0 116.0 12.0 4 533 ± 9 stratigraphic Siberia Kessyusa Formation (5) KE –37.6 165.0 9.3 4 533 ± 8 stratigraphic Siberia Erkeket Formation (5) EK –44.8 158.7 5.7 4 522 ± 3 stratigraphic Amazonia Itabaiana dikes (6) IB 31.4 331.0 10.0 6 525 ± 5 (6) 40Ar/39Ar Congo Ntonya Ring (7) NT 27.7 344.9 1.8 4 522 ± 13 (8) 40Ar/39Ar

Note: South China and Mongolia have no Lower Cambrian paleomagnetic constraints. PLAT, PLON, A95, and Q refer to the latitude, longitude, 95% conﬁ dence circle, and quality factor (van der Voo, 1990) for each paleomagnetic pole. (1) Spall (1968) and Vincenz et al. (1975); (2) Wright et al. (1996); (3) McCausland et al. (2007); (4) Torsvik and Rehnström (2001); (5) Pisarevsky et al. (1997); (6) Trindade et al. (2006); (7) Briden (1968); (8) Briden et al. (1993).

The reconstructions still lack rigorous constraints on TABLE A2. TOTAL ROTATION FOR EACH CRATON USED TO CONSTRUCT FIGURE 3 parameters such as the width of the Iapetus Ocean and Craton Code RLAT RLON Counterclockwise rotation the absolute rates of plate motion and true polar wan- Laurentia LAUR 37 208 –151 der, and the reconstruction places Morocco at a lati- Baltica BALT 24 210 –148 tude that appears too high for such thick shallow-water Siberia SIB 17 220 –139 microbial carbonate accumulation. Better-resolved Amazonia AM 9216 –14 1 paleogeographic solutions may lie in paleomagnetic West Africa WA–4 244 –13 6 South China SC –62 140 107 studies of the same sediments that contain the stratigraphic records of δ13C , 87Sr/86Sr, and fossils (e.g., Note: RLAT and RLON refer to the latitude and longitude, respectively, of the Euler pole for rotating the CaCO3 continent. The Mongolia ribbon continent is drawn without quantitative rotation. Pisarevsky et al., 1997; Maloof et al., 2006; Mitchell et al., 2010).

δ13 A9. Are CCaCO3 Data Records of the Global Ocean? behavior ) tend to elevate δ13C in any carbonate pre- do not record the Pliocene–Pleistocene positive δ13C cipitated on the Great Bahama Bank (Lowenstam and swing that is documented on the slope. Swart and δ13 δ13 We hypothesize that the CCaCO3 data from peri- Epstein, 1957; Andres et al., 2006). Additionally, at Eberli (2005) interpreted the Pleistocene C shift tidal Lower Cambrian carbonates record a global sig- low to moderate water temperatures, aragonite is natu- in Great Bahama Bank carbonates to values between δ13 13 nal linked to the open ocean. However, new CCaCO3 rally enriched in C by 1‰–2‰ compared to low-Mg –0.3‰ and –3.0‰ as a record of meteoric diagenesis data from upper Cenozoic carbonate platforms (Swart calcite precipitated from the same waters (Rubinson during subaerial exposure caused by repeated glacial- and Eberli, 2005; Swart, 2008) have called into ques- and Clayton, 1969; Emrich et al., 1970; Romanek interglacial sea-level changes of ~100 m. tion the assumption that ancient shelfal carbonates et al., 1992), further increasing δ13C in Great Bahama Fluids responsible for meteoric diagenesis of necessarily record the δ13C of open-ocean dissolved Bank aragonite. Thus, Swart and Eberli (2005) pro- carbonate rocks are rich in oxygen and poor in car- δ13 inorganic carbon. Furthermore, two recent papers posed that CCaCO3 preserved in Great Bahama Bank bon. Therefore, altered specimens that show severe (Knauth and Kennedy, 2009; Derry, 2010) suggest slope sediments does not record changes in the global oxygen-isotope depletion still may faithfully record δ13 δ13 δ13 that negative CCaCO3 with covarying CCaCO3 and carbon cycle, but instead refl ects the relative effi ciency the C of oceanic DIC (Banner and Hanson, 1990; δ18 OCaCO3 are necessarily diagenetic in origin. of mud export from platform to slope. This aragonite Jacobsen and Kaufman, 1999). However, work on Ocean Drilling Project Leg 166 retrieved fi ve cores mud transport effi ciency, in turn, depends on rela- the upper Cenozoic carbonates from the Great Ba- from 362–658 m water depth on the leeward (western) tive sea level and the geometry of the carbonate bank hama Bank (Swart and Eberli, 2005; Swart, 2008) δ13 slope of the Great Bahama Bank (Ginsburg, 2001). (e.g., open ramp or fl at-topped platform). Although suggests that even CCaCO3 can be shifted a few δ13 These aragonitic sediment cores depict a consistent the positive Pliocene–Pleistocene CCaCO3 trend is per mil toward more negative values through dia- δ13 Pliocene–Pleistocene rise in CCaCO3 from ambient damped, Swart (2008) demonstrated a similar anticor- genetic interactions with coastal pore fl uids charged δ13 Miocene and Pliocene values of 1.5‰ to 2.5‰ to relation between CCaCO3 from open-ocean plank- in iso topically depleted organic carbon. Covariant δ13 δ18 Pleistocene values of 3.0‰–4.5‰ (Swart and Eberli, tonic forami nif era and the slopes adjacent to platform CCaCO3 and OCaCO3 values have been proposed 2005). In contrast, open-ocean planktonic forami nif- carbonates in the Maldives and around Australia. Iron- as an index for differentiating between pristine and era (low-Mg calcite) during the same interval record ically, periplatform carbonates do not seem to be sim- adulterated δ13C values in diagenetically altered car- δ13 δ13 mean C values of 1‰ to 2‰ during the late Mio- ple recorders of changes in open-ocean CCaCO3, and bonates (Irwin et al., 1977; Kaufman et al., 1991). cene (7–8 Ma) (Billups et al., 2008), followed by yet they record a synchronous Pliocene–Pleistocene Knauth and Kennedy (2009) even suggested that δ13 δ13 δ13 fl uctuating mean values of –0.5‰ to 1.0‰ during the rise in CCaCO3 and suggest that a global forcing, such highly depleted CCaCO3 and covariation in CCaCO3 δ18 Pliocene (Billups et al., 2008), Pleistocene (Shackle- as sea-level change, is controlling the effi ciency of and OCaCO3 during the middle Ediacaran “Shuram” ton et al., 1983; Curry and Crowley, 1987), and Holo- aragonite export from platforms (Swart, 2008). anomaly (Burns and Matter, 1993; Fike et al., 2006; cene (Wefer and Berger, 1991), with an ~1‰ gradient In contrast to the western slope of the Great Bahama McFadden et al., 2008) are diagenetic in origin and between ocean basins. Therefore, the leeward slope of Bank, some carbonates on the bank itself do not re- indicative of terrestrial “greening.” However, in δ13 the Great Bahama Bank appears to be anticorrelated cord the Pliocene–Pleistocene positive CCaCO3 shift. another attempt to explain the very deep Shuram δ13 with planktonic foraminifera of the open ocean dur- For example, Holocene aragonite muds from inner CCaCO3 anomaly, Derry (2010) found that covary- δ13 δ18 ing the Pliocene–Pleistocene (Swart and Eberli, 2005; regions of the Great Bahama Bank (northwest Andros ing CCaCO3- OCaCO3 only resulted when two fl uids 13 Swart, 2008). Island; Maloof, 2008, personal obs.) and Florida Bay (a CO2-charged water depleted in C from inter- Swart and Eberli (2005) showed that the Bahamas (Patterson and Walter, 1994) have low δ13C ranging actions with organic matter and an 18O-enriched cores each recorded a positive correlation between from 1‰ to 2‰, consistent with similarly depleted brine) were allowed to alter the sediments at ~100°C δ13 Σ aragonite:calcite ratio and CCaCO3. They speculated CO2 in adjacent water. This signal is thought to be during burial diagenesis. that the source of the 13C-enriched aragonite found in caused by progressive enrichment of 12C from respired Despite the apparent decoupling of Pliocene– the slope cores is mud precipitated by the calcifying organic matter in aging water masses. Patterson and Pleistocene carbonate shelf and open-marine 12 δ13 green algae (e.g., Halimeda, Penicillus, and Udotea) Walter (1994) likened this mechanism of C enrich- CCaCO3 records and the new ideas for meteoric or inhabiting the shallows (1–10 m water depth) of the ment to the vertical evolution of open-ocean water basinal brine diagenesis, there are several reasons to Great Bahama Bank (Swart and Eberli, 2005). Prefer- under the infl uence of the biological pump, with in- think that the carbon isotope data in the Lower Cam- 12 Σ ential uptake of C by highly productive benthic sea creasing CO2 and oxygen utilization with age and brian record a global DIC signal, and not just internal grasses, algae, and microbial mats coupled to rela- depth of the water mass (Kroopnick, 1985). processes related to (1) meteoric diagenesis, (2) basin tively sluggish mixing of shallow Great Bahama Bank Even cores from the outer edge of the Great Ba- restriction, (3) riverine input, and (4) changes in waters with the open ocean (i.e., semi–closed-system hama Bank itself (Clino and Unda; Ginsburg, 2001) aragonite mud transport effi ciency:

Geological Society of America Bulletin, November/December 2010 1759

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Meteoric Diagenesis In Lower Cambrian limestones and dolostones, δ13 8 lower CCaCO3values are not necessarily associated δ18 with lower OCaCO3. In fact, there is no statistically signiﬁ cant covariation between δ13C and δ18O , CaCO3 CaCO3 whether carbon and oxygen are compared between continents (Fig. A5) or by mineralogy and lithofacies 4 (and thus initial porosity and permeability) in Morocco (Fig. A6F). For example, the ND-T transition is char-

δ13 C (‰) acterized by a 9‰ drop in CCaCO3 over 50–200 m δ18 0 (Fig. 5). No sympathetic negative OCaCO3 shift is ob- 13

δ18 δ served across the ND-T boundary. Instead, OCaCO3 varies chaotically between –5‰ and –8‰ throughout the entire interval, with no signifi cant correlation to −4 δ13 CCaCO3 or lithofacies (Maloof et al., 2005). Subaerial exposure surfaces are abundant in Mo- Morocco rocco, and yet brecciated and recrystallized dolo- Siberia stones immediately below exposure surfaces rarely −8 Mongolia 13 0 show C depletion of more than 1‰. It is impossible China to assess accurately the duration of subaerial exposure on these surfaces. However, we can infer a maximum −20 −15 −10 −5 0 average duration of 10–30 k.y. based on the ~26 expo- 18 sure surfaces recorded during the ND-T transition at δ O (‰) Zawyat n’ Bougzoul and Sidi M’Sal. We also suggest that base-level drops were minimal because, with very Figure A5. δ18O vs. δ13C cross plot. Data from Morocco few exceptions, karstic relief never exceeds 10 cm. CaCO3 CaCO3 Perhaps large base-level drops (50–120 m) of long du- (including all measured sections from Maloof et al., 2005), Siberia, ration (30–90 k.y.) typical of the Pleistocene (Siddall Mon golia, and China all depict a similar population with no et al., 2003; Bintanja et al., 2005) and a substantial δ18O-δ13C covariance. terrestrial biomass are required to impart a diagenetic δ13 CCaCO3 signal to subaerial exposure surfaces. Basin Restriction Africa and was not permanently isolated from riverine rocco can be matched peak for peak without violat- In Morocco, wavy laminated carbonate muds and input the way the Great Bahama Bank is today. The ing biostratigraphic or geochronological constraints silts from interior lagoonal environments (Fig. 4A, Lie de Vin Formation heralds a westward (modern (Maloof et al., 2005). Such consistent correlation 11—Zawyat n’ Bougzoul and 16—Sidi M’Sal) are day coordinates) progradation of fl uvial sands from between geographically distant sedimentary basins offset –1‰ to –3‰ from outer-shelf stromatolites the continent, which would have increased freshwater characterized by very different lithologies and sedi- and microbialites of the central Tiout-Aguerd trough discharge into the basin. However, 75% of the ND-T mentation rates suggests that global forcing played (Fig. 4A, 7—Oued Sdas) (Maloof et al., 2010a). δ13 CCaCO3 negative shift was accomplished within the a dominant role. We conclude that high-amplitude This isotopic offset is similar to that observed today Adoudounian Formation, prior to any indication of δ13C variability in Lower Cambrian shelfal car- in Florida Bay (Patterson and Walter, 1994) and may CaCO3 13 increased siliciclastic input to the system. bonates records an open-ocean signature of a chang- represent progressive depletion in C as aging water ing global carbon cycle. masses on the poorly mixed interior of the shelf ac- 12 Aragonite vs. Calcite cumulated C from respired marine organic matter. A transition from aragonite seas to calcite seas did A10. Diagenesis and 87Sr/86Sr, Uranium, We also think that geometry, restriction, and water occur sometime during the Nemakit-Daldynian Stage, and Vanadium depth associated with coalescence and isolation of perhaps near the ND-T boundary (Fig. 6; Porter , shelf areas, or changing sea level through time could 2007), which could be linked to a 1‰–2‰ negative While the isotopic composition of major con- δ13 lead to vertical CCaCO3 variability not asso ciated δ13 shift in CCaCO3 (4–8× smaller than the observed stituents like carbon may remain intact during neo- with changes in global ocean DIC. For example, δ13 ND-T boundary negative CCaCO3 shift; Maloof et al., morphism and recrystallization, trace elements such Immenhauser et al. (2003) explained a 1‰–2‰ posi- 2010a). However, the idea that stratigraphic δ13C as strontium may be ejected from the carbonate lattice tive shift in δ13C that is progressively damped CaCO3 CaCO3 variability is due to changes in the export effi ciency and replaced with better-fi tting magnesium, calcium, landward across the late Carboniferous platform of of carbon-isotopically distinct platform material to or manganese. Dolomite (CaMg[CO ] ) is a major northern Spain as the transition from shallow, old, 3 2 13 the slope is not tenable for at least two reasons. First, constituent of Lower Cambrian carbonate rocks, but C-depleted water and frequent meteoric diagenesis calcareous plankton had not yet evolved in the Early it is rare in Holocene sediments (Given and Wilkin- to deeper water better connected to the open ocean. Cambrian (Lipps, 1993; Hou et al., 1996; Katz et al., son, 1987; Sun, 1994). The origin of ancient dolo- Holmden et al. (1998) made a similar argument for a 2007), so platformal benthic skeletal debris and muds stones (Zenger et al., 1980; Purser et al., 1994) has δ13 0‰–3‰ positive CCaCO3 excursion damped across were likely the dominant source of carbonate both on been interpreted as replacement of CaCO3 at elevated the Mohawkian (Ordovician) epicontinental seaway the platform and on the slope. Second, in Morocco, burial temperatures (e.g., Mountjoy and Amthor, of North America, and demonstrated that different virtually the entire 2.5 km stack of sediment preserved 1994), replacement of CaCO below the sediment- δ13C values are associated with unique conodont 3 CaCO3 in the Anti-Atlas Mountains was deposited above water interface in suboxic environments where sulfate ε compositions, indicating that shelfal waters were Nd storm wave base, and most of the material was depos- (a possible kinetic inhibitor to dolomite formation) is mixing slower than the ~300 yr residence time of Nd ited in the photic zone on the continental shelf, where removed and alkalinity is added by bacterial sulfate in the ocean. Although epeiric seas are bound to de- slope processes are irrelevant. In fact, narrow peri- reduction (e.g., Baker and Burns, 1985; Vasconcelos velop geochemically distinct and time-varying water, platform slope environments tend to get severely de- and McKenzie, 1997; Warthmann et al., 2000), or as we have not found related mechanisms that could be formed during orogenesis and rarely are preserved in primary dolomite precipitated under changing global responsible for the large-amplitude 4‰–9‰ variabil- large, structurally simple mappable units. Therefore, ocean conditions (e.g., Arvidson and Mackenzie, ity observed in at least approximately contemporane- most Cambrian stratigraphic successions (including 1999; Burns et al., 2000). Limestones likely began as ous Lower Cambrian δ13C records in Morocco, CaCO3 the Siberian, Mongolian, and Chinese sections in aragonite or high-Mg calcite that later neomorphosed Siberia, Mongolia, and China (Fig. 5). Fig. 5) record almost exclusively platformal signals. to more stable calcite spar. Riverine Input One of the most striking arguments against an It is common to exclude altered samples based on Although the Cambrian shelf in Morocco is simi- internal-process origin for anything but small- cutoff values of isotopic and elemental characteris- δ13 lar in size to the Great Bahama Bank, the Anti-Atlas amplitude CCaCO3 variability in Morocco is that tics identifi ed in general studies of Neoproterozoic δ13 margin fringed the large emergent continent of West Lower Cambrian CCaCO3 from Siberia and Mo- carbonates (Derry et al., 1989; Kaufman et al., 1993;

1760 Geological Society of America Bulletin, November/December 2010

1600 1000 Pre / Post Nd-T 1400 A / Microbialaminate B / Grainstone 800 1200 / Stromatolite / 1000 Thrombolite / Ribbonite 600 800

[Sr] (ppm) 400 [Mn] (ppm) 600

400 200 200

0 0 −6 −4 −2 0 2 4 6 8 −6−4−202468 30 80 C 70 D 25 60 20 50 15 40 Sr/Ca Mn/Sr 10 30

5 20

0 10

0 −6−4−202468 −6 −4 −2 0 2 4 6 8 0 0.712 E F

0.711 −5 r (‰) 3 S 6 8 / r

0.710 CaCO S 7 O 8

18 −10 δ 0.709

0.708 −15 −6 −4 −2 0 2 4 6 8 −6 −4 −2 0 2 4 6 8 δ13C (‰) δ13C (‰) CaCO3 CaCO3

87 86 δ18 δ13 Figure A6. Cross plots depicting (A) [Mn], (B) [Sr], (C) Mn/Sr, (D) Sr/Ca, (E) Sr/ Sr, and (F) OCaCO3 versus CCaCO3 show no statistically signiﬁ cant covariation. Furthermore, no lithofacies-dependent trends emerge, such as would be expected if diagenetic alteration were controlled by primary porosity and permeability.

Geological Society of America Bulletin, November/December 2010 1761

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Pre / Post Nd-T 1400 A / Microbialaminate 900 B / Grainstone 800 1200 / Stromatolite 700 1000 / Thrombolite / Ribbonite 600 800 500

[Sr] (ppm) 400

[Mn] (ppm) 600 300 400 200 200 100

−12 −10 −8 −6 −4 −12 −10 −8 −6 −4 δ18O (% ) δ18O (% ) CaCO3 CaCO3

C 0.712 D 25

20 0.711

15 Sr 86 Mn/Sr 0.710

10 Sr / 87 0.709 5

0.708 −12 −10 −8 −6 −4 −11 −10 −9 −8 −7 −6 −5 −4 −3 δ18O (% ) δ18O (% ) CaCO3 CaCO3

0.712 E 0.712 F

0.711 0.711 Sr Sr 86 0.710 86 0.710 Sr / Sr / 87 87 0.709 0.709

0.708 0.708 200 400 600 800 1000 –10 10 30 50 70 Sr/Ca Mn/Sr

87 86 δ18 87 86 87 86 Figure A7. Cross plots depicting (A) [Mn], (B) [Sr], (C) Mn/Sr, and (D) Sr/ Sr versus OCaCO3; (E) Sr/ Sr versus Sr/Ca; and (F) Sr/ Sr versus Mn/Sr. No lithofacies-dependent trends emerge, such as would be expected if diagenetic alteration were controlled by primary porosity and permeability.

1762 Geological Society of America Bulletin, November/December 2010

Fölling and Frimmel, 2002). We prefer to establish Hanson, 1990). The result of diagenetic overprinting lattice-bound) 87Sr from the decay of rubidium-rich the geochemical criteria for excluding altered samples is a sharp increase in 87Sr/86Sr below a threshold [Sr] clays, was not applied to solutions used for U and V on a case-by-case basis because there is no reason to (Fig. A8), as predicted by water-rock geochemical analyses. Therefore, there is the potential that some assume that rocks with different geological histories models (e.g., Banner and Hanson, 1990; Jacobsen and of the U and V measured in carbonate powders is should have experienced the same alteration pathways Kaufman, 1999). Because the initial [Sr] of carbon- detrital in origin, preserved in clays mixed into the (Bartley et al., 2001; Halverson et al., 2007). We fi nd ates differs signifi cantly as a function of original min- rocks rather than U and V complexes in the carbon- that Sr concentration (Figs. A7 and A8) is the most eralogy (calcite vs. aragonite) and varying seawater ate lattice itself. To correct for terrestrial contamina- useful single parameter for assessing the potential [Sr] (e.g., Stoll et al., 1999), and due to variable [Sr] tion, we use Th, which is virtually absent in normal preservation of primary seawater 87Sr/86Sr (Halverson concentrations in diagenetic fl uids, this [Sr] threshold seawater, as a proxy for terrestrial contamination, and et al., 2007). Mn/Sr (Fig. A7F) also is a sensitive indi- is different for every rock. We establish the cutoff subtract U and V using the U/Th and V/Th ratios of cator of meteoric diagenesis (Brand and Veizer, 1980; [Sr] based on a cross plot of 87Sr/86Sr versus [Sr] for post-Archean average shale (PAAS) compositions Banner and Hanson, 1990; Jacobsen and Kaufman, each Lower Cambrian section (i.e., Morocco, Siberia, (Taylor and McLennan, 1985). The data set was nor- 1999), although high [Mn] may indicate primary car- Mongolia, and China; Fig. A8). A similar Mn/Sr malized to aid in visualization. bonate precipitation from dysoxic waters. Another versus 87Sr/86Sr cross plot (Fig. A7F) results in a δ18 potential metric for diagenetic alteration is OCaCO3. nearly identical fi lter. A11. Numerical Model of Mg, Ca, and Sr However, in Morocco, Siberia, Mongolia, and China, Redox-sensitive trace elements such as uranium in Seawater δ18 there is no consistent covariation between OCaCO3 and vanadium are sensitive to the same diagenetic and 87Sr/86Sr (Fig. A7D). processes that reduce [Sr] and increase Mn/Sr in The geochemical cycles of magnesium, calcium, We are justifi ed in basing our selection criterion carbonates, and we may apply the same fi lter that and strontium in seawater refl ect the balance between on [Sr] since most alteration pathways decrease [Sr] we derived for 87Sr/86Sr to exclude altered U and sources and sinks: (but see Derry, 2010), thus increasing the suscepti- V data. However, the ammonium acetate leaching bility of a given 87Sr/86Sr signature to overprinting method (see Appendix section A3), which effectively dMg = + − − WMg-carb WMg-sil H Mg-clays PMg-carb, (A1) (Brand and Veizer, 1980; Veizer, 1989; Banner and removes radiogenically ingrown (non–carbonate- dt

0.714 0.7092 A Morocco B Siberia 0.713 0.7090

0.712 r 0.7088 S 6 8 / 0.711 0.7086 r S 7 8 0.710 0.7084

0.709 0.7082

0.708 0.7080 0 200 400 600 800 1000 0 200 400 600 800 1000 1200

0.7090 0.718 C Mongolia 0.717 D China 0.7088 0.716

r 0.715 0.7086 S

6 0.714 8 / r 0.7084 0.713 S 7

8 0.712 0.7082 0.711 0.710 0.7080 0.709 0.7078 0.708 0 500 1000 1500 2000 2500 0 400 800 1200 1600 [Sr] (ppm) [Sr] (ppm)

Figure A8. Low concentrations of Sr suggest diagenetic removal of Sr from the carbonate lattice, and make bulk carbonate 87Sr/86Sr more susceptible to contamination by rubidium decay in clays and the ingrowth of non-lattice- bound 87Sr. For Morocco (A) and China (D), the [Sr] cutoff is obvious and marked with a thick gray vertical line, while for Siberia (B) and Mongolia (C), the relationship between [Sr] and 87Sr/86Sr is less clear, and the fi lter is less reliable. For Morocco, a Mn/Sr-based fi lter is slightly less stringent but yields a similar result. The open symbols in A are from strongly recrystallized archaeocyath reefs at Talat n’ Yissi and Sidi M’Sal (Fig. 4A), and it is not known why that unit has uniquely high 87Sr/86Sr and [Sr]. The effect of fi ltering the Morocco data is depicted in stratigraphic context in Figure A9. Filtered 87Sr/86Sr data for Morocco, Siberia, Mongolia, and China are plotted δ13 together in the CCaCO3 age model in Figure 9.

Geological Society of America Bulletin, November/December 2010 1763

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Age (Ma) δ13C 87Sr 87Sr 541 537 533 529 525 521 517 [Sr]>100 ppm [Sr]<100 ppm Sidi M’sal 6 Oued Sdas 0.7110 Talat n’ Yissi 4 Zawyat n’ Bougzoul 0.7105

0.7100

2 87 Sr / (% ) 3

0 0.7095 86 Sr CaCO C 13

δ –2 0.7090

–4 0.7085

–6 0.7080

Normalized U –1

Normalized V –1

541 537 533 529 525 521 517 Age (Ma)

δ13 87 86 Figure A9. Time evolution of CCaCO3, Sr/ Sr, uranium, and vanadium for Morocco. Colors depict different stratigraphic sections, and symbol size indicates whether a sample passes (large) or fails (small) the [Sr] and Mn/Sr tests for diagenetic alteration (see Fig. A8). The very high 87Sr/86Sr values that pass the [Sr] ﬁ lter between 522 and 519 Ma are from recrystallized archaeocyath reefs at Sidi M’Sal and Talat n’ Yissi.

dCa P is the magnesium, calcium, or strontium sink the 22 m.y. window (543–521 Ma) to ﬁ t the observed = W +W + H − P , (A2) X-carb dt Ca-carb Ca-sil Ca-basalt Ca-carb associated with the formation of carbonate minerals Mg/Ca and Sr isotope data. The quality of the ﬁ t is (aragonite, calcite, dolomite), and n refers to each iso- established by visual inspection. n tope of Sr: 86Sr, 87Sr, and 88Sr. The 87Sr/86Sr ratio of d Sr = + + − A12. Final Table Wn Wn H n Pn , (A3) dt Sr-carb Sr-sil Sr-basalt Sr-carb seawater is calculated by dividing the two appropriate equations. Equations A1–A3 are solved numeri- Please see the spreadsheet entitled “2010293.xls”

where WX-carb and WX-sil are the fl uxes of magnesium, cally in Matlab given estimates of global magnesium/ in the GSA Data Repository materials (see footnote 1). calcium, and strontium due to subaerial weathering of calcium/strontium fl uxes and the strontium isotopic The spreadsheet presents all of the data on fossil δ13 δ18 δ13 87 86 carbonate and silicate rocks (Meybeck, 2003), HMg-clays composition of the various sources (silicates, carbon- occurrences, CCaCO3, OCaCO3, Corg, Sr/ Sr, is the loss of magnesium in seawater due to the pre- ates, hydrothermal). Initial conditions for these fl uxes uranium, and vanadium for each of the sections used 13 n δ cipitation of clay minerals, and HCa-basalt and H Sr-basalt and other model variables are given in Tables 1 and in this paper. It also includes composite CCaCO3 δ18 87 86 δ18 are the sources of calcium and strontium asso ciated A3. The model is initially run to a steady state over (and Corg and Sr/ Sr where available), OCaCO3, with the weathering of ocean crust during hydro- ~100 m.y., which presumably refl ects seawater com- and biostratigraphic data, as well as a table of current thermal circulation on mid-ocean-ridge crests and position in the Ediacaran. Following spin-up, fl uxes generic assignments for all of the small shelly fossil fl anks (Edmond et al., 1979; Mottl and Wheat, 1994). or isotopic composition of the fl uxes are varied over taxa found in our literature sources.

1764 Geological Society of America Bulletin, November/December 2010

TABLE A3. VARIABLES USED IN THE NUMERICAL MODEL OF Mg, Ca, AND Sr Barghoorn, E.S., and Tyler, S.A., 1965, Microorganisms Weathering Hydrothermal from the Gunﬂ int Chert: Science, v. 147, p. 563–575, doi: 10.1126/science.147.3658.563. W 1.7 × 1012 mol/yr (1) k 3.75 × 1013 kg H O/yr (3) Mg-carb 2 Bartley, J.K., and Kah, L.C., 2004, Marine carbon reservoir, W 12.0 × 1012 mol/yr (1) H k · [Mg] Ca-carb Mg-clays C -C coupling, and the evolution of the Proterozoic W 1.1 × 1010 mol/yr (2) H α · H org carb Sr-carb Sr-basalt Sr/Ca Ca-basalt carbon cycle: Geology, v. 32, p. 129–132, doi: 10.1130/ W 3.1 × 1012 mol/yr (1) α 1 (4) Mg-sil Mg/Ca G19939.1. W 4.0 × 1012 mol/yr (1) α 0.0013 (5) Ca-sil Sr/Ca Bartley, J.K., Semikhatov, M.A., Kaufman, A.J., Knoll, A.H., W 0.8 × 1010 mol/yr (2) Sr-sil Pope, M.C., and Jacobsen, S.B., 2001, Global events across the Mesoproterozoic-Neoproterozoic bound- 87Sr/86Sr Precipitation ary: C and Sr isotopic evidence from Siberia: Pre- 12 W87/86Sr-sil 0.7150 (2) PCa-carb 18.75 × 10 mol/yr (6) cambrian Research, v. 111, p. 165–202, doi: 10.1016/ 12 W87/86Sr-carb 0.7070 (2) PMg-carb 1.8 × 10 mol/yr (7) S0301-9268(01)00160-7. H87/86Sr-basalt 0.7030 (2) PSr-carb (Sr/Ca)seawater · KSr · PCa-carb Bengtson, S., 1968, The problematic genus Mobergella from KSr 0.2 (8) the Lower Cambrian of the Baltic area: Lethaia, v. 1,

Note: (1) adapted from Meybeck (2003); (2) adapted from Allègre et al. (2010); (3) fl ux of H2O in hydrothermal p. 325–351, doi: 10.1111/j.1502-3931.1968.tb01625.x. systems assuming 100% of the heat fl ux at 350 °C (Elderfi eld and Schultz, 1996); (4) assumes 1:1 stoichiometry Bengtson, S., 1983, The early history of the Conodonta: Fos- between Mg uptake and Ca release during basalt alteration; (5) calculated assuming 200 ppm Sr and 10 wt% sils and Strata, v. 15, p. 5–19. CaO; (6) calculated assuming carbonate minerals are the only alkalinity sink; (7) estimated from the long-term rate Bengtson, S., 1992a, Proterozoic and earliest Cambrian of dolomitization (Wilkinson and Algeo, 1989); (8) homogeneous distribution coeffi cient for Sr in calcite (Mucci and skeletal metazoans, in Schopf, J.W., and Klein, C., Morse, 1983). eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge, UK, Cambridge University Press, p. 1017–1033. ACKNOWLEDGMENTS land arc weathering in the oceanic Sr isotope budget: Bengtson, S., 1992b, The cap-shaped Cambrian fossil Earth and Planetary Science Letters, v. 292, p. 51–56, Maikhanella and the relationship between coelo- Maloof and Bowring were supported by National doi: 10.1016/j.epsl.2010.01.019. scleritophorans and molluscs: Lethaia, v. 25, p. 401– Science Foundation (NSF) Sedimentary Geology Aller, R.C., Blair, N.E., Xia, Q., and Rude, P.D., 1996, Re- 420, doi: 10.1111/j.1502-3931.1992.tb01644.x. & Paleobiology grants EAR-0638660 and EAR- minerali zation rates, recycling, and storage of carbon Bengtson, S., 2005, Mineralized skeletons and early animal evolution, in Briggs, D.E.G., ed., Evolving Form and 0638634, respectively, and Higgins was supported in Amazon shelf sediments: Continental Shelf Re- search, v. 16, p. 753–786, doi: 10.1016/0278-4343(95) Function: Fossils and development: Proceedings of a by a Hess Postdoctoral Fellowship. Michael Bender, 00046-1. symposium honoring Adolf Seilacher for his contribu- David Evans, John Grotzinger, Paul Hoffman, Matt Amthor, J.E., Grotzinger, J.P., Schröder, S., Bowring, S.A., tions to paleontology, in celebration of his 80th birth- Hurtgen, Jon Husson, Jamie Kellogg, Andy Knoll, Ramezani, J., Martin, M.W., and Matter, A., 2003, day: New Haven, Connecticut, Peabody Museum of Francis Macdonald, Jon Payne, Denis Poussart, Extinction of Cloudina and Namacalathus at the Natural History, p. 101–124. Pascale Poussart, Sara Pruss, Jahandar Ramezani, Precambrian-Cambrian boundary in Oman: Geology, Bengtson, S., and Conway Morris, S., 1992, Early radiation Catherine Rose, Dan Rothman, Blair Schoene, v. 31, p. 431–434, doi: 10.1130/0091-7613(2003)031 of biomineralizing phyla, in Lipps, J.H., and Signor, Frederik Simons, Dan Schrag, and Danny Sigman <0431:EOCANA>2.0.CO;2. P.W., eds., Origin and Early Evolution of the Metazoa: New York, Plenum Press, p. 447–481. challenged us with stimulating discussions. Claire Andres, M.S., Sumner, D.Y., Reid, R.P., and Swart, P.K., 2006, Isotopic fi ngerprints of microbial respiration Bengtson, S., and Hou Xianguang, 2001, The integument of Calmet, Jessica Creveling, Doug Erwin, Galen Haver- in aragonite from Bahamian stromatolites: Geology, Cambrian chancelloriids: Acta Palaeontologica Polonica, son, Gawen Jenkin, Sören Jensen, David Jones, Artem v. 34, p. 973–976, doi: 10.1130/G22859A.1. v. 46, p. 1–22. Kouchinsky, Michael Melchin, Jon Payne, and Nick Aris-Brosou, S., and Yang, Z., 2003, Bayesian models of Bengtson, S., and Missarzhevsky, V.V., 1981, Coelo- Swanson-Hysell provided detailed reviews of the epi sodic evolution support a late Precambrian explo- scleritophora—A major group of enigmatic Cambrian manuscript. Brendan Murphy supported the project sive diversifi cation of the Metazoa: Molecular Biol- metazoans: U.S. Geological Survey Open-File Report and edited the paper. Lahssen Baidder and Univer- ogy and Evolution, v. 20, p. 1947–1954, doi: 10.1093/ 81–743, p. 19–21. sité Hassan II, Said Mazouad, Mhamed Mouaacha, molbev/msg226. Bengtson, S., Fedorov, A.B., Missarzhevsky, V.V., Rozanov, A.Yu., Zhegallo, E.A., and Zhuravlev, A.Yu., 1987, and Driss Najid provided generous logistical sup- Arvidson, R.S., and Mackenzie, F.T., 1999, The dolomite problem: Control of precipitation kinetics by tempera- Tumulduria incomperta and the case for Tommotian port. Mohamed Mazouad, Ryan Ewing, Jay Ewing, ture and saturation state: American Journal of Science, trilobites: Lethaia, v. 20, p. 361–370, doi: 10.1111/ Lida Teneva , and Guoxiang Li assisted us in the fi eld. v. 299, p. 257–288, doi: 10.2475/ajs.299.4.257. j.1502-3931.1987.tb00797.x. Claire Calmet, Christine Chen, Will Jacobsen, Becca Asmerom, Y., Jacobsen, S.B., Knoll, A.H., Butterfi eld, N.J., Bengtson, S., Conway Morris, S., Cooper, B.J., Jell, P.A., and Levin, Julie Michelman, Jacquie Nesbit, Catherine and Swett, K., 1991, Strontium isotopic variations Runnegar, B.N., 1990, Early Cambrian Fossils from Rose, Justin Strauss, Lija Treijbergs, and Nora Xu of Neoproterozoic seawater: Implications for crustal South Australia: Association of Australasian Palaeon- helped with sample preparation. Roger Summons evolution: Geochimica et Cosmochimica Acta, v. 55, tologists Memoir 9, 364 p. made his MIT laboratory available for sample prepara- p. 2883–2894, doi: 10.1016/0016-7037(91)90453-C. Berner, R.A., Lasaga, A.C., and Garrels, R.M., 1983, The carbonate-silicate geochemical cycle and its effects on tion and analysis. Jenn Kasbohm and Benita Sonntag Badarch, G., Cunningham, W.D., and Windley, B.F., 2002, A new terrane subdivision for Mongolia: Implications for atmospheric carbon dioxide over the past 100 million helped with Figure 4. Maoyan Zhu graciously allowed the Phanerozoic crustal growth of Central Asia: Journal years: American Journal of Science, v. 283, p. 641–683. δ13 us to use the C data from Jijiapo (South China). of Asian Earth Sciences, v. 21, p. 87–110, doi: 10.1016/ Billups, K., Kelly, C., and Pierce, E., 2008, The late Mio- Chris Emerling, Artem Kouchinsky, Michael Steiner, S1367-9120(02)00017-2. cene to early Pliocene climate transition in the Michael Vendrasco, and Marites Villarosa Garcia pro- Bahcall, J.N., Pinsonneault, M.H., and Basu, S., 2001, Solar Southern Ocean: Palaeogeography, Palaeoclimatol- vided fossil images for Figure 2. models: Current epoch and time dependences, neutrinos, ogy, Palaeoecology, v. 267, p. 31–40, doi: 10.1016/ and helioseismological properties: The Astrophysical j.palaeo.2008.05.013. REFERENCES CITED Journal, v. 555, p. 990–1012, doi: 10.1086/321493. Bintanja, R., van de Wal, R.S.W., and Oerlemans, J., 2005, Bailey, T.R., McArthur, J.M., Prince, H., and Thirlwall, Modelled atmospheric temperatures and global sea Agatova, A.I., Sapozhnikov, V.V., and Torgunova, N.I., M.F., 2000, Dissolution methods for strontium isotope levels over the past million years: Nature, v. 437, 1989, Novye dannye po biogidrokhimii organicheskogo stratigraphy: Whole rock analysis: Chemical Geol- p. 125–128, doi: 10.1038/nature03975. veshchestva v Chernom more: Doklady Akademii ogy, v. 167, p. 313–319, doi: 10.1016/S0009-2541 Blair, N.E., Leithold, E.L., Ford, S.T., Peeler, K.A., Holmes , Nauk SSSR, v. 309, p. 706–710. (99)00235-1. J.C., and Perkey, D.W., 2003, The persistence of Agatova, A.I., Lapina, N.M., Torgunova, N.I., and Kirpichev, Baker, P.A., and Burns, S.J., 1985, Occurrence and forma- memory: The fate of ancient sedimentary organic car- K.B., 2001, Biogeochemical study of brackish-water tion of dolomite in organic-rich continental margin bon in a modern sedimentary system: Geochimica et marine ecosystems: Water Resources, v. 28, p. 428– sediments: The American Association of Petroleum Cosmochimica Acta, v. 67, p. 63–73, doi: 10.1016/ 437, doi: 10.1023/A:1010401907179. Geologists Bulletin, v. 69, p. 1917–1930. S0016-7037(02)01043-8. Aït Malek, H., Gasquet, D., Bertrand, J.-M., and Leterrier, Balthasar, U., Skovsted, C.B., Holmer, L.E., and Brock, Bockelie, T.G., and Yochelson, E.L., 1979, Variation in a J., 1998, Géochronologie U-Pb sur zircon de grani- G.A., 2009, Homologous skeletal secretion in tom- species of “worm” from the Ordovician of Spitsbergen: toïdes éburnéens et panafricains dans les boutonnières motiids and brachiopods: Geology, v. 37, p. 1143–1146, Norsk Polarinstitutt: Skrifter, v. 167, p. 225–237. protérozoïques d’Igherm, du Kerdous et du Bas Drâa doi: 10.1130/G30323A.1. Boher, M., Abouchami, W., Michard, A., Albarède, F., and (Anti-Atlas occidental, Maroc): Comptes Rendus de Banner, J.L., and Hanson, G.N., 1990, Calculation of simul- Arndt, N.T., 1992, Crustal growth in West Africa at 2.1 l’Académie des Sciences, sér. 2, Sciences de la Terre taneous isotopic and trace element variations during Ga: Journal of Geophysical Research, v. 97, p. 345– et des Planètes, v. 327, p. 819–826. water-rock interaction with applications to carbonate 369, doi: 10.1029/91JB01640. Allègre, C.J., Louvat, P., Gaillardet, J., Meynadier, L., Rad, diagenesis: Geochimica et Cosmochimica Acta, v. 54, Bond, G.C., and Kominz, M.A., 1984, Construction of S., and Capmas, F., 2010, The fundamental role of is- p. 3123–3137, doi: 10.1016/0016-7037(90)90128-8. tectonic subsidence curves for the early Paleozoic mio-

Geological Society of America Bulletin, November/December 2010 1765

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

geocline, southern Canadian Rocky Mountains: Impli- v. 25, p. 303–306, doi: 10.1130/0091-7613(1997)025 signifi cance]: Professional Papers of Stratigraphy and cations for subsidence mechanisms, age of breakup, <0303:ESSCFS>2.3.CO;2. Palaeontology, v. 13, p. 49–66, 2 pl. (in Chinese with and crustal thinning: Geological Society of America Braun, A., Chen, J., Waloszek, D., and Maas, A., 2007, First English summary). Bulletin, v. 95, p. 155–173, doi: 10.1130/0016-7606 Early Cambrian Radiolaria, in Vickers-Rich, P., and Chen Zhe, Bengtson, S., Zhou Chuanming, and Yue Zhao, (1984)95<155:COTSCF>2.0.CO;2. Komarower, P., eds., The Rise and Fall of the Edia- 2008, Tube structure and original composition of Bond, G.C., Nickeson, P.A., and Kominz, M.A., 1984, caran Biota: Geological Society of London Special Sinotubulites: Shelly fossils from the late Neoprotero zoic Breakup of a supercontinent between 625 and 555 Ma: Publication 286, p. 143–149. in southern Shaanxi, China: Lethaia, v. 41, p. 37–45. New evidence and implications for continental histo- Briden, J.C., 1968, Paleomagnetism of the Ntonya ring Cloud, P.E., Jr., 1948, Some problems and patterns of ries: Earth and Planetary Science Letters, v. 70, p. 325– structure, Malawi: Journal of Geophysical Research, evolution exemplifi ed by fossil invertebrates: Evolu- 345, doi: 10.1016/0012-821X(84)90017-7. v. 73, p. 725–733, doi: 10.1029/JB073i002p00725. tion; International Journal of Organic Evolution, v. 2, Bond, G.C., Kominz, M.A., and Grotzinger, J.P., 1988, Briden, J.C., McClelland, E., and Rex, D.C., 1993, Proving p. 322–350. Cambro-Ordovician eustasy: Evidence from geo- the age of a paleomagnetic pole: The case of the Ntonya Cloud, P.E., Jr., 1965, Signifi cance of the Gunfl int (Pre- physical modeling of Cordilleran and Appalachian ring structure, Malawi: Journal of Geophysical Research, cambrian) microfl ora: Science, v. 148, p. 27–35, doi: miogeoclines, in Kleinspehn, K., and Paola, C., eds., v. 98, p. 1743–1749, doi: 10.1029/92JB01254. 10.1126/science.148.3666.27. New Perspectives in Basin Analysis: Berlin, Springer- Briggs, D.E.G., Erwin, D.H., and Collier, F.J., 1994, The Cohen, P.A., Bradley, A., Knoll, A.H., Grotzinger, J.P., Verlag, p. 129–160. Fossils of the Burgess Shale: Washington, D.C., Smith- Jensen, S., Abelson, J., Hand, K., Love, G., Metz, J., Bottjer, D.J., Hagadorn, J.W., and Dornbos, S.Q., 2000, sonian Institution Press, 238 p. McLoughlin, N., Meister, P., Shepard, R., Tice, M., and The Cambrian substrate revolution: GSA Today, v. 10, Bristow, T.F., and Kennedy, M.J., 2008, Carbon isotope Wilson, J.P., 2009, Tubular compression fossils from the no. 9, p. 1–7. excursions and the oxidant budget of the Ediacaran Ediacaran Nama Group, Namibia: Journal of Paleon- Bowring, S.A., Grotzinger, J.P., Isachsen, C.E., Knoll, A.H., atmosphere and ocean: Geology, v. 36, p. 863–866, tology, v. 83, p. 110–122, doi: 10.1666/09-040R.1. Pelechaty, S.M., and Kolosov, P., 1993, Calibrating doi: 10.1130/G24968A.1. Compston, W., Williams, I.S., Kirschvink, J.L., Zhang rates of Early Cambrian evolution: Science, v. 261, Broecker, W.S., and Peng, T.-H., 1982, Tracers in the Sea: Zichao, and Ma Guogan, 1992, Zircon U-Pb ages from p. 1293–1298, doi: 10.1126/science.11539488. Palisades, New York, Lamont-Doherty Geological Ob- the Early Cambrian time-scale: Journal of the Geo- Bowring, S.A., Grotzinger, J.P., Condon, D.J., Ramezani, J., servatory, 690 p. logical Society of London, v. 149, p. 171–184, doi: Newall, M.J., and Allen, P.A., 2007, Geochronologic Bromham, L., Rambaut, A., Fortey, R., Cooper, A., and 10.1144/gsjgs.149.2.0171. constraints on the chronostratigraphic framework of the Penny, D., 1998, Testing the Cambrian explosion Compston, W., Zhang Zichao, Cooper, J.A., Ma Guogan, Neoproterozoic Huqf Supergroup, Sultanate of Oman: hypothesis by using a molecular dating technique: Pro- and Jenkins, R.J.F., 2008, Further SHRIMP geo- American Journal of Science, v. 307, p. 1097–1145, ceedings of the National Academy of Sciences of the chronology on the Early Cambrian of South China: doi: 10.2475/10.2007.01. United States of America, v. 95, p. 12,386–12,389, doi: American Journal of Science, v. 308, p. 399–420, doi: Boyce, C.K., 2005, Patterns of segregation and convergence 10.1073/pnas.95.21.12386. 10.2475/04.2008.01. in the evolution of fern and seed plant leaf morpholo- Brooks, B.-G.J., Crowley, J.L., Bowring, S.A., Cervato, C., Condon, D., Zhu Maoyan, Bowring, S., Wang Wei, Yang gies: Paleobiology, v. 31, p. 117–140, doi: 10.1666/ and Jin Yugan, 2006, A new U/Pb date for the basal Aihua, and Jin Yugan, 2005, U-Pb ages from the Neo- 0094-8373(2005)031<0117:POSACI>2.0.CO;2. Meishucun section and implications for the timing of proterozoic Doushantuo Formation, China: Science, Brand, U., and Veizer, J., 1980, Chemical diagenesis of a the Cambrian explosion: University of Sheffi eld, The v. 308, p. 95–98. multicomponent carbonate system: 2. Stable isotopes: Palaeontological Association, 50th Annual Meeting Conrad, C.P., and Husson, L., 2009, Infl uence of dynamic Journal of Sedimentary Petrology, v. 51, p. 987–997. Abstracts, p. 18. topography on sea level and its rate of change: Litho- Brasier, M.D., 1984, Microfossils and small shelly fossils Budd, G.E., 2002, A palaeontological solution to the arthro- sphere, v. 1, p. 110–120, doi: 10.1130/L32.1. from the Lower Cambrian Hyolithes Limestone at pod head problem: Nature, v. 417, p. 271–275, doi: Conrad, C.P., and Lithgow-Bertelloni, C., 2007, Faster sea- Nuneaton, English Midlands: Geological Magazine, 10.1038/417271a. fl oor spreading and lithosphere production during the v. 121, p. 229–253, doi: 10.1017/S0016756800028296. Budd, G.E., 2008, The earliest fossil record of the animals mid-Cenozoic: Geology, v. 35, p. 29–32, doi: 10.1130/ Brasier, M.D., 1996, The basal Cambrian transition and and its signifi cance: Philosophical Transactions of the G22759A.1. Cambrian bio-events, in Walliser, O.H., ed., Global Royal Society, ser. B, v. 363, p. 1425–1434, doi: 10.1098/ Conway Morris, S., and Chapman, A.J., 1996, Lower Cam- Events and Event Stratigraphy in the Phanerozoic: rstb.2007.2232. brian coeloscleritophorans (Ninella, Siphogonuchites) Berlin, Springer-Verlag, p. 113–138. Budd, G.E., and Jensen, S., 2000, A critical reappraisal of from Xinjiang and Shaanxi, China: Geological Magazine, Brasier, M.D., and Sukhov, S.S., 1998, The falling ampli- the fossil record of the bilaterian phyla: Biological Re- v. 133, p. 33–51, doi: 10.1017/S0016756800007238. tude of carbon isotopic oscillations through the Lower views of the Cambridge Philosophical Society, v. 75, Conway Morris, S., and Chapman, A.J., 1997, Mobergel- to Middle Cambrian: Northern Siberia data: Canadian p. 253–295, doi: 10.1017/S000632310000548X. lans from the Lower Cambrian of Mongolia, Sweden, Journal of Earth Sciences, v. 35, p. 353–373, doi: Burns, S.J., and Matter, A., 1993, Carbon isotopic record of and the United States: Molluscs or opercula of incertae 10.1139/cjes-35-4-353. the latest Proterozoic from Oman: Eclogae Geologicae sedis ?: Journal of Paleontology, v. 71, p. 968–985. Brasier, M.D., Magaritz, M., Corfi eld, R., Luo Huilin, Wu Helvetiae, v. 86, p. 595–607. Conway Morris, S., and Chen Meng’e, 1991, Cambroclaves Xiche, Ouyang Lin, Jiang Zhiwen, Hamdi, B., He Burns, S.J., McKenzie, J.A., and Vasconcelos, C., 2000, and paracarinachitids, early skeletal problematica from Tinggui, and Fraser, A.G., 1990, The carbon- and Dolomite formation and biogeochemical cycles in the the Lower Cambrian of South China: Palaeontology, oxygen-isotope record of the Precambrian-Cambrian Phanerozoic: Sedimentology, v. 47, supp. 1, p. 49–61, v. 34, p. 357–397. boundary interval in China and Iran and their correla- doi: 10.1046/j.1365-3091.2000.00004.x. Conway Morris, S., and Chen Meng’e, 1992, Carinachitiids, tion: Geological Magazine, v. 127, p. 319–332. Butterfi eld, N.J., 1997, Plankton ecology and the Proterozoic- hexangulaconulariids, and Punctatus: Problematic Brasier, M.D., Khomentovsky, V.V., and Corfi eld, R.M., Phanerozoic transition: Paleobiology, v. 23, p. 247–262. metazoans from the Early Cambrian of South China: 1993, Stable isotopic calibration of the earliest skeletal Calver, C.R., 2000, Isotope stratigraphy of the Ediacarian Journal of Paleontology, v. 66, p. 384–406. fossil assemblages in eastern Siberia (Precambrian- (Neoproterozoic III) of the Adelaide Rift complex, Conway Morris, S., and Peel, J.S., 1995, Articulated Cambrian boundary): Terra Nova, v. 5, p. 225–232, Australia, and the overprint of water column stratifi ca- halkieriids from the Lower Cambrian of North Green- doi: 10.1111/j.1365-3121.1993.tb00253.x. tion: Precambrian Research, v. 100, p. 121–150, doi: land and their role in the early protostome evolution: Brasier, M., Cowie, J., and Taylor, M., 1994a, Decision on 10.1016/S0301-9268(99)00072-8. Philosophical Transactions of the Royal Society of the Precambrian-Cambrian boundary stratotype: Epi- Campbell, I.H., and Squire, R.J., 2010, The mountains that London, ser. B, Biological Sciences, v. 347, p. 305– sodes, v. 17, p. 3–8. triggered the Late Neoproterozoic increase in oxygen: 358, doi: 10.1098/rstb.1995.0029. Brasier, M.D., Rozanov, A.Yu., Zhuravlev, A.Yu., Corfi eld, The second great oxidation event: Geochimica et Cos- Conway Morris, S., Crampton, J.S., Xiao Bing, and Chap- R.M., and Derry, L.A., 1994b, A carbon isotope refer- mochimica Acta, v. 74, p. 4187–4206, doi: 10.1016/ man, A.J., 1997, Lower Cambrian cambroclaves (in- ence scale for the Lower Cambrian succession in Siberia: j.gca.2010.04.064. certae sedis) from Xinjiang, China, with comments on Report of IGCP Project 303: Geological Magazine, Caron, J.-B., Scheltema, A., Schander, C., and Rudkin, the morphological variability of sclerites: Palaeontol- v. 131, p. 767–783, doi: 10.1017/S0016756800012851. D., 2006, A soft-bodied mollusc with radula from ogy, v. 40, p. 167–189. Brasier, M.D., Corfi eld, R.M., Derry, L.A., Rozanov, A.Yu., the Middle Cambrian Burgess Shale: Nature, v. 442, Cook, P.J., and Shergold, J.H., 1984, Phosphorus, phos- and Zhuravlev, A.Yu., 1994c, Multiple δ13C excursions p. 159–163, doi: 10.1038/nature04894. phorites and skeletal evolution at the Precambrian- spanning the Cambrian explosion to the Botomian cri- Cauwet, G., Déliat, G., Krastev, A., Shtereva, G., Becque- Cambrian boundary: Nature, v. 308, p. 231–236, doi: sis in Siberia: Geology, v. 22, p. 455–458, doi: 10.1130/ vort, S., Lancelot, C., Momzikoff, A., Saliot, A., 10.1038/308231a0. 0091-7613(1994)022<0455:MCESTC>2.3.CO;2. Cociasu, A., and Popa, L., 2002, Seasonal DOC accu- Corsetti, F.A., and Hagadorn, J.W., 2000, Precambrian- Brasier, M.D., Shields, G., Kuleshov, V.N., and Zhegallo, mulation in the Black Sea: A regional explanation for a Cambrian transition: Death Valley, United States: Geol- E.A., 1996, Integrated chemo- and biostratigraphic general mechanism: Marine Chemistry, v. 79, p. 193– ogy, v. 28, p. 299–302, doi: 10.1130/0091-7613(2000)28 calibration of early animal evolution: Neoprotero- 205, doi: 10.1016/S0304-4203(02)00064-6. <299:PTDVUS>2.0.CO;2. zoic–Early Cambrian of southwest Mongolia: Geo- Cawood, P.A., and Pisarevsky, S.A., 2006, Was Baltica Crimes, T.P., 1987, Trace fossils and correlation of late logical Magazine, v. 133, p. 445–485, doi: 10.1017/ right-way-up or upside-down in the Neoproterozoic?: Precambrian and Early Cambrian strata: Geo- S0016756800007603. Journal of the Geological Society of London, v. 163, logical Magazine, v. 124, p. 97–119, doi: 10.1017/ Brasier, M., Green, O., and Shields, G., 1997, Ediacar- p. 753–759, doi: 10.1144/0016-76492005-126. S0016756800015922. ian sponge spicule clusters from southwestern Mon- Chen Ping, 1984, [Discovery of Lower Cambrian small Curry, W.B., and Crowley, T.J., 1987, The δ13C of equa- golia and the origins of the Cambrian fauna: Geology, shelly fossils from Jijiapo, Yichang, west Hubei and its torial Atlantic surface waters: Implications for ice-age

1766 Geological Society of America Bulletin, November/December 2010

pCO2 levels: Paleoceanography, v. 2, p. 489–517, doi: ed., Evolving Form and Function: Fossils and Devel- Foote, M., 1997, The evolution of morphological diversity: 10.1029/PA002i005p00489. opment: Proceedings of a symposium honoring Adolf Annual Review of Ecology and Systematics, v. 28, Darwin, C., 1859, On the Origin of Species by Means of Seilacher for his contributions to paleontology, in cele- p. 129–152, doi: 10.1146/annurev.ecolsys.28.1.129. Natural Selection, or the Preservation of Favoured Races bration of his 80th birthday: New Haven, Connecticut, Ford, T.D., 1958, Pre-Cambrian fossils from Charnwood in the Struggle for Life: London, John Murray, 479 p. Peabody Museum of Natural History, p. 125–138. Forest: Proceedings of the Yorkshire Geological So- Debrenne, F., and Courjault-Radé, P., 1994, Répartition Dzik, J., 1991, Is fossil evidence consistent with traditional ciety, v. 31, p. 211–217, doi: 10.1144/pygs.31.3.211. paléogéographique des archéocyathes et délimita- views of the early metazoan phylogeny?, in Simonetta, Galy, A., France-Lanord, C., and Derry, L.A., 1999, The tion des zones intertropicales au Cambrien inférieur: A.M., and Conway Morris, S., eds., The Early Evolu- strontium isotopic budget of Himalayan rivers in Bulletin de la Société Géologique de France, v. 165, tion of Metazoa and the Signifi cance of Problematic Nepal and Bangladesh: Geochimica et Cosmochimica p. 459–467. Taxa: Cambridge, UK, Cambridge University Press, Acta, v. 63, p. 1905–1925, doi: 10.1016/S0016-7037 Debrenne, F., Lafuste, J., and Zhuravlev, A., 1990, Coralo- p. 47–56. (99)00081-2. morphes et spongiomorphes à l’aube du Cambrien: Dzik, J., 1994, Evolution of ‘small shelly fossils’ assem- Gao, G., Dworkin, S.I., Land, L.S., and Elmore, R.D., 1996, Bulletin du Muséum d’Histoire Naturelle, Paris, sec- blages of the early Paleozoic: Acta Palaeontologica Geochemistry of Late Ordovician Viola Limestone, tion C, sér. 4, v. 12, p. 17–39. Polonica, v. 39, p. 247–313. Oklahoma: Implications for marine carbon mineralogy Derry, L.A., 2010, A burial diagenesis origin for the Edia- Dzik, J., 2005, Behavioral and anatomical unity of the earliest and isotopic compositions: The Journal of Geology, caran Shuram-Wonoka carbon isotope anomaly: Earth burrowing animals and the cause of the “Cambrian ex- v. 104, p. 359–367, doi: 10.1086/629831. and Planetary Science Letters, v. 294, p. 152–162, doi: plosion”: Paleobiology, v. 31, p. 503–521, doi: 10.1666/ Gehling, J.G., and Rigby, J.K., 1996, Long expected sponges 10.1016/j.epsl.2010.03.022. 0094-8373(2005)031[0503:BAAUOT]2.0.CO;2. from the Neoproterozoic Ediacara fauna of South Aus- Derry, L.A., and France-Lanord, C., 1996, Neogene Hima- Edmond, J.M., 1992, Himalayan tectonics, weathering tralia: Journal of Paleontology, v. 70, p. 185–195. layan weathering history and river 87Sr/86Sr: Impact processes, and strontium isotope record in marine lime- Gehling, J.G., Jensen, S., Droser, M.L., Myrow, P.M., and on the marine Sr record: Earth and Planetary Science stones: Science, v. 258, p. 1594–1597, doi: 10.1126/ Narbonne, G.M., 2001, Burrowing below the basal Letters, v. 142, p. 59–74, doi: 10.1016/0012-821X science.258.5088.1594. Cambrian GSSP, Fortune Head, Newfoundland: Geo- (96)00091-X. Edmond, J.M., Measures, C., McDuff, R.E., Chan, L.H., logical Magazine, v. 138, p. 213–218, doi: 10.1017/ Derry, L.A., Keto, L.S., Jacobsen, S.B., Knoll, A.H., and Collier, R., Grant, B., Gordon, L.I., and Corliss, J.B., S001675680100509X. Swett, K., 1989, Sr isotopic variations in Upper 1979, Ridge crest hydrothermal activity and the bal- Geyer, G., 1989, Late Precambrian to early Middle Cambrian Proterozoic carbonates from Svalbard and East ances of the major and minor elements in the ocean: The lithostratigraphy of southern Morocco: Beringeria , Greenland: Geochimica et Cosmochimica Acta, v. 53, Galapagos data: Earth and Planetary Science Letters, v. 1, p. 115–143. p. 2331–2339, doi: 10.1016/0016-7037(89)90355-4. v. 46, p. 1–18, doi: 10.1016/0012-821X(79)90061-X. Geyer, G., 1994, Middle Cambrian mollusks from Idaho and Derry, L.A., Brasier, M.D., Corfi eld, R.M., Rozanov, A.Yu., Elderfield, H., and Schultz, A., 1996, Mid-ocean ridge early conchiferan evolution: New York State Museum and Zhuravlev, A.Yu., 1994, Sr and C isotopes in hydrothermal fluxes and the chemical composition Bulletin, v. 481, p. 69–86. Lower Cambrian carbonates from the Siberian craton: of the ocean: Annual Review of Earth and Plan- Geyer, G., and Landing, E., 1995, The Cambrian of the A paleoenvironmental record during the ‘Cambrian ex- etary Sciences, v. 24, p. 191–224, doi: 10.1146/ Moroccan Atlas regions, in Geyer, G., and Landing, plosion’: Earth and Planetary Science Letters, v. 128, annurev.earth.24.1.191. E., eds., Morocco ’95: The Lower-Middle Cambrian p. 671–681, doi: 10.1016/0012-821X(94)90178-3. Emrich, K., Ehhalt, D.H., and Vogel, J.C., 1970, Carbon iso- Standard of Western Gondwana: Würzburg, Beringeria Des Marais, D.J., Strauss, H., Summons, R.E., and Hayes, tope fractionation during the precipitation of calcium Special Issue 2, p. 7–46. J.M., 1992, Carbon isotope evidence for the stepwise carbonate: Earth and Planetary Science Letters, v. 8, Ginsburg, R.N., 2001, The Bahamas drilling project: Back- oxidation of the Proterozoic environment: Nature, p. 363–371, doi: 10.1016/0012-821X(70)90109-3. ground and acquisition of cores and logs, in Ginsburg, v. 359, p. 605–609, doi: 10.1038/359605a0. Endonzhamts, Zh., and Lkhasuren, B., 1988, Stratigrafi ya R.N., ed., Subsurface Geology of a Prograding Car- Dong, L., Xiao, S., Shen, B., Zhou Chuanming, Li Guoxiang, pogranichnykh tolshch dokembriya i kembriya Dzab- bonate Platform Margin, Great Bahama Bank: Results and Yao Jinxian, 2009, Basal Cambrian microfossils from khanskoy zony, in Khomentovsky, V.V., and Shenfi l’, of the Bahamas Drilling Project: Society for Sedimen- the Yangtze Gorges area (South China) and the Aksu area V.Yu., eds., Pozdniy dokembriy i ranniy paleozoy tary Geology (SEPM) Special Publication 70, p. 3–16. (Tarim block, northwestern China): Journal of Paleontol- Sibiri , Rifey i vend: Novosibirsk, Institut Geologii Giri, B.J., Bano, N., and Hollibaugh, J.T., 2004, Distribu- ogy, v. 83, p. 30–44, doi: 10.1666/07-147R.1. i Geofi ziki, Sibirskoe Otdelenie, Akademiya Nauk tion of RuBisCO genotypes along a redox gradient Donnadieu, Y., Goddéris, Y., Ramstein, G., Nédélec, A., and SSSR, p. 150–162. in Mono Lake, California: Applied and Environmen- Meert, J., 2004, A ‘snowball Earth’ climate triggered Engebretson, D.C., Kelley, K.P., Cashman, H.J., and Richards, tal Microbiology, v. 70, p. 3443–3448, doi: 10.1128/ by continental break-up through changes in runoff: M.A., 1992, 180 million years of subduction: GSA AEM.70.6.3443-3448.2004. Nature, v. 428, p. 303–306, doi: 10.1038/nature02408. Today , v. 2, p. 93–95, 100. Given, R.K., and Wilkinson, B.H., 1987, Dolomite abun- Donoghue, P.C.J., Kouchinsky, A., Waloszek, D., Bengtson, Esakova, N.V., and Zhegallo, E.A., 1996, Biostratigrafi ya dance and stratigraphic age: Constraints on rates and S., Dong Xiping, Val’kov, A.K., Cunningham, J.A., i fauna nizhnego kembriya Mongolii: Sovmestnaya mechanisms of Phanerozoic dolostone formation: and Repetski, J.E., 2006a, Fossilized embryos are Rossiysko-Mongol’skaya Paleontologicheskaya Eks- Journal of Sedimentary Petrology, v. 57, p. 1068–1078. widespread but the record is temporally and taxonomi- peditsiya, Trudy, v. 46, 216 p., 24 pl. Glaessner, M.F., and Wade, M., 1966, The Late Precambrian cally biased: Evolution & Development, v. 8, p. 232– Evans, D.A., 1998, True polar wander, a supercontinental fossils from Ediacara, South Australia: Palaeontology, 238, doi: 10.1111/j.1525-142X.2006.00093.x. legacy: Earth and Planetary Science Letters, v. 157, v. 9, p. 599–628, pl. 97–103. Donoghue, P.C.J., Bengtson, S., Dong Xiping, Gostling, p. 1–8, doi: 10.1016/S0012-821X(98)00031-4. Gnilovskaya, M.B., 1985, Vendotaenids—Vendian meta- N.J., Huldtgren, T., Cunningham, J.A., Yin Chongyu, Evans, D.A., Ripperdan, R.L., and Kirschvink, J.L., 1998, phytes, in Sokolov, B.S., and Iwanoski, A.B., eds., The Yue Zhao, Peng Fan, and Stampanoni, M., 2006b, Polar wander and the Cambrian (response): Science, Vendian System, Volume 1: Berlin, Springer-Verlag, Synchrotron X-ray tomographic microscopy of fossil v. 279, p. 9 (correction p. 307). p. 138–147. embryos: Nature, v. 442, p. 680–683. Evans, M.J., Derry, L.A., and France-Lanord, C., 2008, De- Goldhammer, T., Brüchert, V., Ferdelman, T.G., and Zabel, Dornbos, S.Q., Bottjer, D.J., and Chen Junyuan, 2004, gassing of metamorphic carbon dioxide from the Nepal M., 2010, Microbial sequestration of phosphorus in Evidence for seafl oor microbial mats and associated Himalaya: Geochemistry, Geophysics, Geosystems, anoxic upwelling sediments: Nature Geoscience, v. 3, metazoan lifestyles in Lower Cambrian phosphorites v. 9, no. 4, art. 04021, 18 p. p. 557–561, doi: 10.1038/ngeo913. of southwest China: Lethaia, v. 37, p. 127–137, doi: Fedonkin, M.A., 1985, Paleoichnology of Vendian Meta- Gould, S.J., 1989, Wonderful Life: The Burgess Shale and 10.1080/00241160410004764. zoa, in Sokolov, B.S., and Iwanowski, A.B., eds., The the Nature of History: New York, W.W. Norton, 347 p. Drenzek, N.J., Hughen, K.A., Montluçon, D.B., Southon, Vendian System, Volume 1: Berlin, Springer-Verlag Grant, S.W.F., 1990, Shell structure and distribution of J.R., dos Santos, G.M., Druffel, E.R.M., Giosan, L., p. 132–137. Cloudina, a potential index fossil for the terminal and Eglinton, T.I., 2009, A new look at old carbon in Fedonkin, M.A., and Waggoner, B.M., 1997, The Late Pre- Protero zoic: American Journal of Science, v. 290-A, active margin sediments: Geology, v. 37, p. 239–242, cambrian fossil Kimberella is a mollusc-like bilaterian p. 261–294. doi: 10.1130/G25351A.1. organism: Nature, v. 388, p. 868–871, doi: 10.1038/ Greenwood, D.R., and Wing, S.L., 1995, Eocene conti- Droser, M.L., and Bottjer, D.J., 1988, Trends in depth 42242. nental climates and latitudinal temperature gradients: and extent of bioturbation in Cambrian carbonate Fike, D.A., 2007, Carbon and Sulfur Isotopic Constraints Geology, v. 23, p. 1044–1048, doi: 10.1130/0091-7613 marine environments, western United States: Geology, on Ediacaran Biogeochemical Processes, Huqf Super- (1995)023<1044:ECCALT>2.3.CO;2. v. 16, p. 233–236, doi: 10.1130/0091-7613(1988)016 group, Sultanate of Oman [Ph.D. thesis]: Cambridge, Grigor’eva, N.V., Mel’nikova, L.M., and Pel’man, Yu.L., <0233:TIDAEO>2.3.CO;2. Massachusetts, Massachusetts Institute of Technology, 1983, Brachiopods, ostracodes (bradoriids) and prob- Droser, M.L., Jensen, S., and Gehling, J.G., 2002, Trace 231 p. lematical fossils from the stratotype region of the fossils and substrates of the terminal Proterozoic- Fike, D.A., Grotzinger, J.P., Pratt, L.M., and Summons, Lower Cambrian stages: Paleontological Journal, v. 17, Cambrian transition: Implications for the record of R.E., 2006, Oxidation of the Ediacaran ocean: Nature, no. 3, p. 51–56. early bilaterians and sediment mixing: Proceedings of v. 444, p. 744–747, doi: 10.1038/nature05345. Grotzinger, J.P., Bowring, S.A., Saylor, B.Z., and Kaufman, the National Academy of Sciences of the United States Fölling, P.G., and Frimmel, H.E., 2002, Chemostrati- A.J., 1995, Biostratigraphic and geochronologic con- of America, v. 99, p. 12,572–12,576, doi: 10.1073/ graphic correlation of carbonate successions in the straints on early animal evolution: Science, v. 270, pnas.202322499. Gariep and Saldania belts, Namibia and South Af- p. 598–604, doi: 10.1126/science.270.5236.598. Droser, M.L., Gehling, J.G., and Jensen, S., 2005, Edia- rica: Basin Research, v. 14, p. 69–88, doi: 10.1046/ Grotzinger, J.P., Watters, W.A., and Knoll, A.H., 2000, Cal- caran trace fossils: True and false, in Briggs, D.E.G., j.1365-2117.2002.00167.x. cifi ed metazoans in thrombolite-stromatolite reefs of

Geological Society of America Bulletin, November/December 2010 1767

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

the terminal Proterozoic Nama Group, Namibia: Paleo- for the seafloor carbonate factory: Earth and Plan- Ingall, E.D., and Van Cappellen, P., 1990, Relation between biology, v. 26, p. 334–359, doi: 10.1666/0094-8373 etary Science Letters, v. 284, p. 25–33, doi: 10.1016/ sedimentation rate and burial of organic phosphorous (2000)026<0334:CMITSR>2.0.CO;2. j.epsl.2009.03.039. and organic carbon in marine sediments: Geochi- Gubanov, A.P., and Peel, J.S., 2000, Cambrian mono- Hoffman, P.F., 1991, Did the breakout of Laurentia turn mica et Cosmochimica Acta, v. 54, p. 373–386, doi: placophoran molluscs (class Helcionelloida): Ameri- Gondwanaland inside-out?: Science, v. 252, p. 1409– 10.1016/0016-7037(90)90326-G. can Malacological Bulletin, v. 15, p. 139–145. 1412, doi: 10.1126/science.252.5011.1409. Ingall, E.D., Bustin, R.M., and Van Cappellen, P., 1993, In- Guo Junfeng, Li Yong, Han Jian, Zhang Xingliang, Zhang Hoffman, P.F., Kaufman, A.J., Halverson, G.P., and fl uence of water column anoxia on the burial and pres- Zhifei, Ou Qiang, Liu Jianni, Shu Degan, Maruyama, Schrag, D.P., 1998, A Neoproterozoic snowball ervation of carbon and phosphorous in marine shales: S., and Komiya, T., 2008, Fossil association from the Earth: Science, v. 281, p. 1342–1346, doi: 10.1126/ Geochimica et Cosmochimica Acta, v. 57, p. 303–316, Lower Cambrian Yanjiahe Formation in the Yangtze science.281.5381.1342. doi: 10.1016/0016-7037(93)90433-W. Gorges area, Hubei, South China: Acta Geologica Hoffmann, K.-H., Condon, D.J., Bowring, S.A., and Crowley, Irwin, H., Curtis, C., and Coleman, M., 1977, Isotopic evi- Sinica (English edition), v. 82, p. 1124–1132. J.L., 2004, U-Pb zircon date from the Neoproterozoic dence for source of diagenetic carbonates formed dur- Gurnis, M., 1990, Ridge spreading, subduction, and sea Ghaub Formation, Namibia: Constraints on Marinoan ing burial of organic-rich sediments: Nature, v. 269, level fl uctuations: Science, v. 250, p. 970–972, doi: glaciation: Geology, v. 32, p. 817–820, doi: 10.1130/ p. 209–213, doi: 10.1038/269209a0. 10.1126/science.250.4983.970. G20519.1. Ishikawa, T., Ueno, Y., Komiya, T., Sawaki, Y., Han Jian, Shu Hallam, A., and Wignall, P.B., 1999, Mass extinctions and Holland, H.D., and Zimmermann, H., 2000, The dolomite Degan, Li Yong, Maruyama, S., and Yoshida, N., 2008, sea-level changes: Earth-Science Reviews, v. 48, problem revisited: International Geology Review, v. 42, Carbon isotope chemostratigraphy of a Precambrian/ p. 217–250, doi: 10.1016/S0012-8252(99)00055-0. p. 481–490, doi: 10.1080/00206810009465093. Cambrian boundary section in the Three Gorge area, Halverson, G.P., Hoffman, P.F., Schrag, D.P., Maloof, A.C., Holmden, C., Creaser, R.A., Muehlenbachs, K., Leslie, South China: Prominent global-scale isotope excur- and Rice, A.H.N., 2005, Toward a Neoproterozoic S.A., and Bergström, S.M., 1998, Isotopic evidence sions just before the Cambrian explosion: Gondwana composite carbon-isotope record: Geological Soci- for geochemical decoupling between ancient epeiric Research, v. 14, p. 193–208. ety of America Bulletin, v. 117, p. 1181–1207, doi: seas and bordering oceans: Implications for secular Ivantsov, A.Yu., 1990, New data on the ultrastructure of 10.1130/B25630.1. curves: Geology, v. 26, p. 567–570, doi: 10.1130/ sabelliditids (Pogonophora?): Paleontological Journal, Halverson, G.P., Dudás, F.Ö., Maloof, A.C., and Bowring, 0091-7613(1998)026<0567:IEFGDB>2.3.CO;2. v. 24, no. 4, p. 125–128. S.A., 2007, Evolution of the 87Sr/86Sr composition of Holmer, L.E., Skovsted, C.B., Brock, G.A., Valentine, J.L., Jacobsen, S.B., and Kaufman, A.J., 1999, The Sr, C and O Neoproterozoic seawater: Palaeogeography, Palaeo- and Paterson, J.R., 2008, The Early Cambrian tom- isotopic evolution of Neoproterozoic seawater: Chemi- climatology, Palaeoecology, v. 256, p. 103–129, doi: motiid Micrina, a sessile bivalved stem group brachio- cal Geology, v. 161, p. 37–57, doi: 10.1016/S0009-2541 10.1016/j.palaeo.2007.02.028. pod: Biology Letters, v. 4, p. 724–728, doi: 10.1098/ (99)00080-7. Halverson, G.P., Wade, B.P., Hurtgen, M.T. and Barovich , rsbl.2008.0277. James, N.P., and Klappa, C.F., 1983, Petrogenesis of Early K.M., 2010, Neoproterozoic chemostratig raphy: Holmes, A., 1960, A revised geological time-scale: Trans- Cambrian reef limestones, Labrador, Canada: Journal Precambrian Research (in press), doi:10.1016/ actions of the Edinburgh Geological Society, v. 17, of Sedimentary Petrology, v. 53, p. 1051–1096. j.precamres.2010.04.007. p. 183–216. James, N.P., Bone, Y., and Kyser, T.K., 2005, Where has all Hambrey, M.J., and Harland, W.B., eds., 1981, Earth’s Pre- Holser, W.T., Schidlowski, M., Mackenzie, F.T., and May- the aragonite gone? Mineralogy of Holocene neritic Pleistocene Glacial Record: Cambridge, UK, Cam- nard, J.B., 1988, Geochemical cycles of carbon and cool-water carbonates, southern Australia: Journal of bridge University Press, 1004 p. sulphur, in Gregory, C.B., Garrels, R.M., Mackenzie, Sedimentary Research, v. 75, p. 454–463, doi: 10.2110/ Hansell, D.A., and Carlson, C.A., 2001, Marine dissolved F.T., and Maynard, J.B., eds., Chemical Cycles in the jsr.2005.035. organic matter and the carbon cycle: Oceanography Evolution of the Earth: New York: John Wiley & Sons, Janussen, D., Steiner, M., and Zhu Maoyan, 2002, New (Washington, D.C.), v. 14, no. 4, p. 41–49. p. 105–173. well-preserved scleritomes of Chancelloridae from Haq, B.U., and Schutter, S.R., 2008, A chronology of Paleo- Hou Xianguang, Siveter, D.J., Williams, M., Walossek, D., the Early Cambrian Yuanshan Formation (Cheng- zoic sea-level changes: Science, v. 322, p. 64–68, doi: and Bergström, J., 1996, Appendages of the arthropod jiang, China) and the Middle Cambrian Wheeler Shale 10.1126/science.1161648. Kunmingella from the Early Cambrian of China: Its (Utah, USA) and paleobiological implications: Jour- Haq, B.U., Hardenbol, J., and Vail, P.R., 1987, Chronology of bearing on the systematic position of the Bradoriida nal of Paleontology, v. 76, p. 596–606, doi: 10.1666/ fl uctuating sea levels since the Triassic: Science, v. 235, and the fossil record of the Ostracoda: Philosophical 0022-3360(2002)076<0596:NWPSOC>2.0.CO;2. p. 1156–1167, doi: 10.1126/science.235.4793.1156. Transactions of the Royal Society of London, ser. B, Jenkins, R.J.F., Cooper, J.A., and Compston, W., 2002, Age Hardie, L.A., 1996, Secular variation in seawater chem- v. 351, p. 1131–1145. and biostratigraphy of Early Cambrian tuffs from SE istry: An explanation for the coupled secular varia- Hou Xianguang, Aldridge, R.J., Bergström, J., Siveter, D.J., Australia and southern China: Journal of the Geo- tion in the mineralogies of marine limestones and Siveter, D.J., and Feng Xianghong, 2004, The Cam- logical Society of London, v. 159, p. 645–658, doi: potash evaporites over the past 600 m.y: Geology, brian Fossils of Chengjiang, China: The Flowering of 10.1144/0016-764901-127. v. 24, p. 279–283, doi: 10.1130/0091-7613(1996)024 Early Animal Life: Oxford, Blackwell Science, 233 p. Jenkyns, H.C., Forster, A., Schouten, S., and Sinninghe <0279:SVISCA>2.3.CO;2. Hua Hong, Chen Zhe, Yuan Xunlai, Zhang Luyi, and Xiao, Damsté, J.S., 2004, High temperatures in the Late Cre- Harland, W.B., Cox, A.V., Llewellyn, P.G., Pickton, C.A.G., S., 2005, Skeletogenesis and asexual reproduction in taceous Arctic Ocean: Nature, v. 432, p. 888–892, doi: Smith, A., and Walters, R., 1982, A Geologic Time Scale: the earliest biomineralizing animal Cloudina: Geology, 10.1038/nature03143. Cambridge, UK, Cambridge University Press, 131 p. v. 33, p. 277–280, doi: 10.1130/G21198.1. Jensen, S., 1997, Trace Fossils from the Lower Cambrian Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Huber, B.T., Hodell, D.A., and Hamilton, C.P., 1995, Mickwitzia Sandstone, South-Central Sweden: Fos- Smith, A.G., and Smith, D.G., 1990, A Geologic Time Middle–Late Cretaceous climate of the southern high sils and Strata: Oslo, Scandinavian University Press, Scale 1989: Cambridge, UK, Cambridge University latitudes: Stable isotopic evidence for minimal equa- no. 42, 111 p. Press, 263 p. tor-to-pole thermal gradients: Geological Society of Jensen, S., 2003, The Proterozoic and earliest Cambrian Hassenforder, B., Roger, J., Baudin, T., Chalot-Prat, F., America Bulletin, v. 107, p. 1164–1191, doi: 10.1130/ trace fossil record; patterns, problems and perspec- Gasquet, D., Berrahma, A., Chèvremont, P., Marquer, 0016-7606(1995)107<1164:MLCCOT>2.3.CO;2. tives: Integrative and Comparative Biology, v. 43, D., Razin, P., and Benlakhdim, A., 2001, Feuille Huber, M., and Sloan, L.C., 2001, Heat transport, deep p. 219–228, doi: 10.1093/icb/43.1.219. NHI-29-X-1c, Sidi Bou’Addi: Carte Gologique du waters, and thermal gradients: Coupled simulation Jensen, S., Gehling, J.G., and Droser, M.L., 1998, Ediacara- Maroc à 1:50,000: Notes et Mémoires du Service of an Eocene greenhouse climate: Geophysical Re- type fossils in Cambrian sediments: Nature, v. 393, Géologique du Maroc 414, 1 sheet, scale 1:50,000. search Letters, v. 28, p. 3481–3484, doi: 10.1029/ p. 567–569, doi: 10.1038/31215. Hayes, J.M., and Waldbauer, J.R., 2006, The carbon cycle 2001GL012943. Jensen, S., Saylor, B.Z., Gehling, J.G., and Germs, G.J.B., and associated redox processes through time: Philo- Huntley, J.W., Xiao, S., and Kowalewski, M., 2006, On the 2000, Complex trace fossils from the terminal Protero- sophical Transactions of the Royal Society of London, morphological history of Proterozoic and Cambrian zoic of Namibia: Geology, v. 28, p. 143–146, doi: ser. B, Biological Sciences, v. 361, p. 931–950, doi: acritarchs, in Xiao, S., and Kaufman, A.J., eds., Neo- 10.1130/0091-7613(2000)28<143:CTFFTT>2.0.CO;2. 10.1098/rstb.2006.1840. proterozoic Geobiology and Paleobiology: Dordrecht, Jensen, S., Droser, M.L., and Gehling, J.G., 2006, A critical Hayes, J.M., Strauss, H., and Kaufman, A.J., 1999, The Springer, p. 23–56. look at the Ediacaran trace fossil record, in Xiao, S., abundance of 13C in marine organic matter and isotopic Husson, L., and Conrad, C.P., 2006, Tectonic velocities, dy- and Kaufman, A.J., eds., Neoproterozoic Geobiology fractionation in the global biogeochemical cycle of car- namic topography, and relative sea level: Geophysical and Paleobiology: Dordrecht, Springer, p. 115–157. bon during the past 800 Ma: Chemical Geology, v. 161, Research Letters, v. 33, art. L18303, 5 p. Jernvall, J., Hunter, J.P., and Fortelius, M., 1996, Molar p. 103–125, doi: 10.1016/S0009-2541(99)00083-2. Immenhauser, A., Della Porta, G., Kenter, J.A.M., and tooth diversity, disparity, and ecology in Cenozoic un- Herman, A.B., and Spicer, R.A., 1996, Palaeobotanical evi- Bahamonde, J.R., 2003, An alternative model for gulate radiations: Science, v. 274, p. 1489–1492, doi: dence for a warm Cretaceous Arctic Ocean: Nature, positive shifts in shallow-marine carbonate δ13C and 10.1126/science.274.5292.1489. v. 380, p. 330–333, doi: 10.1038/380330a0. δ18O: Sedimentology, v. 50, p. 953–959, doi: 10.1046/ Jones, B., and Manning, D.A.C., 1994, Comparison of geo- Higgins, J.A., and Schrag, D.P., 2006, Beyond methane: j.1365-3091.2003.00590.x. chemical indices used for the interpretation of palaeo- Towards a theory for the Paleocene–Eocene thermal Ingall, E., and Jahnke, R., 1997, Infl uence of water-column redox conditions in ancient mudstones: Chemical maximum: Earth and Planetary Science Letters, v. 245, anoxia on the elemental fractionation of carbon and Geology, v. 111, p. 111–129, doi: 10.1016/0009-2541 p. 523–537, doi: 10.1016/j.epsl.2006.03.009. phosphorous during sediment diagenesis: Marine (94)90085-X. Higgins, J.A., Fischer, W.W., and Schrag, D.P., 2009, Oxy- Geology, v. 139, p. 219–229, doi: 10.1016/S0025-3227 Junge, C.E., Schidlowski, M., Eichmann, R., and Pietrek , genation of the ocean and sediments: Consequences (96)00112-0. H., 1975, Model calculations for the terrestrial

1768 Geological Society of America Bulletin, November/December 2010

13 Σ carbon cycle: Carbon isotope geochemistry and evo- Kirschvink, J.L., Magaritz, M., Ripperdan, R.L., Zhuravlev, Kroopnick, P.M., 1985, The distribution of C of CO2 in lution of photosynthetic oxygen: Journal of Geo- A.Yu., and Rozanov, A.Yu., 1991, The Precambrian/ the world oceans: Deep-Sea Research, v. 32, p. 57–84, physical Research, v. 80, p. 4542–4552, doi: 10.1029/ Cambrian boundary: Magnetostratigraphy and carbon doi: 10.1016/0198-0149(85)90017-2. JC080i033p04542. isotopes resolve correlation problems between Siberia, Kruse, P.D., Zhuravlev, A.Yu., and James, N.P., 1995, Pri- Karlova, G.A., 1987, Pervye nakhodki skeletnoy fauny v Morocco, and South China: GSA Today, v. 1, p. 69–71, mordial metazoan-calcimicrobial reefs: Tommotian turkutskoy svite Olenekskogo podnyatiya: Doklady 87, 91. (Early Cambrian) of the Siberian Platform: Palaios, Akademii Nauk SSSR, v. 292, p. 204–205, 1 pl. Kirschvink, J.L., Ripperdan, R.L., and Evans, D.A., 1997, v. 10, p. 291–321, doi: 10.2307/3515157. Karlova, G.A., and Vodanyuk, S.A., 1985, Novye dannye o Evidence for a large-scale reorganization of Early Kruse, P.D., Gandin, A., Debrenne, F., and Wood, R., 1996, perekhodnykh k kembriyo otlozheniyakh basseyna r. Cambrian continental masses by inertial interchange Early Cambrian bioconstructions in the Zavkhan Basin Khorbusuonki (Olenekskoe podnyatie), in Khomen- true polar wander: Science, v. 277, p. 541–545, doi: of western Mongolia: Geological Magazine, v. 133, tovsky, V.V., ed., Stratigrafi ya pozdnego dokembriya 10.1126/science.277.5325.541. p. 429–444, doi: 10.1017/S0016756800007597. i rannego paleozoya Sibiri, Vend i rifey: Novosibirsk, Knauth, L.P., and Kennedy, M.J., 2009, The late Precam- Kumarapeli, P.S., and Saull, V.A., 1966, The St. Lawrence Institut Geologii i Geofi ziki, Sibirskoe Otdelenie, Aka- brian greening of the Earth: Nature, v. 460, p. 728–732. valley system: A North American equivalent to the East demiya Nauk SSSR, p. 3–13. Knoll, A.H., 1994, Proterozoic and Early Cambrian pro- African rift valley system: Canadian Journal of Earth Katz, M.E., Fennel, K., and Falkowski, P.G., 2007, Geo- tists: Evidence for accelerating evolutionary tempo: Sciences, v. 3, p. 639–658. chemical and biological consequences of phytoplank- Proceedings of the National Academy of Sciences of Kump, L.R., 1988, Terrestrial feedback in atmospheric oxy- ton evolution, in Falkowski, P.G., and Knoll, A.H., the United States of America, v. 91, p. 6743–6750, doi: gen regulation by fi re and phosphorus: Nature, v. 335, eds., Evolution of Primary Producers in the Sea: Am- 10.1073/pnas.91.15.6743. p. 152–154, doi: 10.1038/335152a0. sterdam, Elsevier, p. 405–430. Knoll, A.H., Hayes, J.M., Kaufman, A.J., Swett, K., and Kump, L.R., 1991, Interpreting carbon-isotopic excursions: Kaufman, A.J., Hayes, J.M., Knoll, A.H., and Germs, G.J.B., Lambert, I.B., 1986, Secular variation in carbon iso- Strangelove oceans: Geology, v. 19, p. 299–302, doi: 1991, Isotopic compositions of carbonates and organic tope ratios from Upper Proterozoic successions of 10.1130/0091-7613(1991)019<0299:ICIESO>2.3.CO;2. carbon from Upper Proterozoic successions in Namibia: Svalbard and East Greenland: Nature, v. 321, p. 832– Kump, L.R., and Arthur, M.A., 1999, Interpreting carbon- Stratigraphic variation and the effects of diagenesis and 838, doi: 10.1038/321832a0. isotope excursions: Carbonates and organic matter: metamorphism: Precambrian Research, v. 49, p. 301– Knoll, A.H., Grotzinger, J.P., Kaufman, A.J., and Kolosov, Chemical Geology, v. 161, p. 181–198 327, doi: 10.1016/0301-9268(91)90039-D. P., 1995a, Integrated approaches to terminal Protero- Kuzmichev, A.B., Bibikova, E.V., and Zhuravlev, D.Z., Kaufman, A.J., Jacobsen, S.B., and Knoll, A.H., 1993, The zoic stratigraphy: An example from the Olenek Uplift, 2001, Neoproterozoic (~800 Ma) orogeny in the Tuva- Vendian record of Sr and C isotopic variations in sea- northeastern Siberia: Precambrian Research, v. 73, Mongolia Massif (Siberia): Island arc–continent col- water: Implications for tectonics and paleoclimate: p. 251–270, doi: 10.1016/0301-9268(94)00081-2. lision at the northeast Rodinia margin: Precambrian Earth and Planetary Science Letters, v. 120, p. 409– Knoll, A.H., Kaufman, A.J., Semikhatov, M.A., Grotz- Research, v. 110, p. 109–126, doi: 10.1016/S0301-9268 430, doi: 10.1016/0012-821X(93)90254-7. inger, J.P., and Adams, W., 1995b, Sizing up the (01)00183-8. Kaufman, A.J., Knoll, A.H., Semikhatov, M.A., Grotzinger, sub-Tommotian unconformity in Siberia: Geology, Lahajnar, N., Rixen, T., Gaye-Haake, B., Schäfer, P., and J.P., Jacobsen, S.B., and Adams, W., 1996, Integrated v. 23, p. 1139–1143, doi: 10.1130/0091-7613(1995)023 Ittekkot, V., 2005, Dissolved organic carbon (DOC) chronostratigraphy of Proterozoic-Cambrian boundary <1139:SUTSTU>2.3.CO;2. fl uxes of deep-sea sediments from the Arabian Sea beds in the western Anabar region, northern Siberia: Kominz, M.A., 1984, Oceanic ridge volumes and sea-level and NE Atlantic: Deep-Sea Research, Part II. Topical Geological Magazine, v. 133, p. 509–533, doi: 10.1017/ change—An error analysis, in Schlee, J.S., ed., Inter- Studies in Oceanography, v. 52, p. 1947–1964, doi: S0016756800007810. regional Unconformities and Hydrocarbon Accumula- 10.1016/j.dsr2.2005.05.006. Khain, E.V., Bibikova, E.V., Salnikova, E.B., Kröner, A., tion: American Association of Petroleum Geologists Landing, E., 1988, Lower Cambrian of eastern Massachu- Gibsher, A.S., Didenko, A.N., Degtyarev, K.E., and Memoir 36, p. 109–127. setts: Stratigraphy and small shelly fossils: Journal of Fedotova, A.A., 2003, The palaeo-Asian ocean in the Korobov, M.N., and Missarzhevsky, V.V., 1977, O pogranich- Paleontology, v. 62, p. 661–695. Neoproterozoic and early Palaeozoic: New geochrono- nykh sloyakh kembriya i dokembriya Zapadnoy Mon- Landing, E., 1991, Upper Precambrian through Lower logic data and palaeotectonic reconstructions: Pre- golii (khrebet Khasagt-Khairkhan), in Tatarinov, L.P., Cambrian of Cape Breton Island: Faunas, paleoenvi- cambrian Research, v. 122, p. 329–358, doi: 10.1016/ ed., Bespozvonochnye paleozoya Mongolii: Sovmest- ronments, and stratigraphic revision: Journal of Paleon- S0301-9268(02)00218-8. naya Sovestsko-Mongol’skaya Paleontologicheskaya tology, v. 65, p. 570–595. Khomentovsky, V.V., 1997, Sizing up the sub-Tommotian un- Ekspeditsiya, Trudy, v. 5, p. 7–9. Landing, E., 1993, In situ earliest Cambrian tube worms and conformity in Siberia: Comment: Geology, v. 25, p. 286, Korshunov, V.I., Repina, L.N., and Sysoev, V.A., 1969, K the oldest metazoan-constructed biostrome (Placentian doi: 10.1130/0091-7613(1997)025<0286:SUTSTU> stroeniyu pestrotsvetnoy svity vostoka Aldanskoy Series, southeastern Newfoundland): Journal of Paleon- 2.3.CO;2. anteklizy: Geologiya i Geofizika, v. 1969, no. 10, tology, v. 67, p. 333–342. Khomentovsky, V.V., 2008, The Yudomian of Siberia, Ven- p. 18–21. Landing, E., 1994, Precambrian-Cambrian boundary global dian and Ediacaran systems of the international strati- Kouchinsky, A.V., 2000, Skeletal microstructures of hyoliths stratotype ratifi ed and a new perspective of Cam- graphic scale: Stratigraphy and Geological Correlation, from the Early Cambrian of Siberia: Alcheringa, v. 24, brian time: Geology, v. 22, p. 179–182, doi: 10.1130/ v. 16, p. 581–598, doi: 10.1134/S0869593808060014. p. 65–81, doi: 10.1080/03115510008619525. 0091-7613(1994)022<0179:PCBGSR>2.3.CO;2. Khomentovsky, V.V., and Gibsher, A.S., 1996, The Neo- Kouchinsky, A.V., 2001, Mollusks, hyoliths, stenothecoids, Landing, E., and MacGabhann, B.A., 2010, First evidence proterozoic–Lower Cambrian in northern Govi-Altay, and coeloscleritophorans, in Zhuravlev, A.Yu., and for Cambrian glaciation provided by sections in western Mongolia: Regional setting, lithostratigraphy Riding , R., eds., The Ecology of the Cambrian Radia- Avalonian New Brunswick and Ireland: Additional and biostratigraphy: Geological Magazine, v. 133, tion: New York, Columbia University Press, p. 326–349. data for Avalon-Gondwana separation by the earli- p. 371–390, doi: 10.1017/S001675680000755X. Kouchinsky, A., Bengtson, S., Missarzhevsky, V.V., est Palaeozoic: Palaeogeography, Palaeoclimatology, Khomentovsky, V.V., and Karlova, G.A., 1986, O nizhney Pelechaty, S., Torssander, P., and Val’kov, A.K., 2001, Palaeoecology, v. 285, p. 174–185, doi: 10.1016/ granitse pestrotsvetnoy svity v basseyne r. Aldan, in Carbon isotope stratigraphy and the problem of a pre- j.palaeo.2009.11.009. Khomentovsky, V.V., ed., Pozdniy dokembriy i ranniy Tommotian Stage in Siberia: Geological Magazine, Landing, E., Myrow, P., Benus, A.P., and Narbonne, G.M., paleozoy Sibiri, Sibirskaya platforma i vneshchyaya v. 138, p. 387–396, doi: 10.1017/S0016756801005684. 1989, The Placentian Series: Appearance of the old- zona Altae-Sayanskoy skladchtoy oblasti: Novosibirsk, Kouchinsky, A., Bengtson, S., Pavlov, V., Runnegar, B., est skeletalized faunas in southeastern Newfoundland: Institut Geologii i Geofi ziki, Sibirskoe Otdelenie, Aka- Val’kov, A., and Young, E., 2005, Pre-Tommotian Journal of Paleontology, v. 63, p. 739–769. demiya Nauk SSSR, p. 3–22. age of the lower Pestrotsvet Formation in the Selinde Landing, E., Bowring, S.A., Davidek, K.L., Westrop, S.R., Khomentovsky, V.V., and Karlova, G.A., 1992, The Pre- section on the Siberian platform: Carbon isotopic evi- Geyer, G., and Heldmaier, W., 1998, Duration of the cambrian-Cambrian boundary and principles of its jus- dence: Geological Magazine, v. 142, p. 319–325, doi: Early Cambrian: U-Pb ages of volcanic ashes from tifi cation in Siberia: Russian Geology and Geophysics, 10.1017/S0016756805000865. Avalon and Gondwana: Canadian Journal of Earth Sci- v. 33, no. 11, p. 1–18. Kouchinsky, A., Bengtson, S., Pavlov, V., Runnegar, B., ences, v. 35, p. 329–338, doi: 10.1139/cjes-35-4-329. Khomentovsky, V.V., and Karlova, G.A., 1993, Biostratig- Torssander, P., Young, E., and Ziegler, K., 2007, Car- Latham, A., and Riding, R., 1990, Fossil evidence for raphy of the Vendian–Cambrian beds and the Lower bon isotope stratigraphy of the Precambrian-Cambrian the location of the Precambrian/Cambrian bound- Cambrian boundary in Siberia: Geological Magazine, Sukharikha River section, northwestern Siberian plat- ary in Morocco: Nature, v. 344, p. 752–754, doi: v. 130, p. 29–45, doi: 10.1017/S0016756800023700. form: Geological Magazine, v. 144, p. 609–618, doi: 10.1038/344752a0. Khomentovsky, V.V., and Karlova, G.A., 2002, The bound- 10.1017/S0016756807003354. Laurie, J.R., 2000, Paterinata, in Williams, A., Brunton, ary between Nemakit-Daldynian and Tommotian Kouchinsky, A., Bengtson, S., Feng Weimin, Kutygin, R., C.H.C., and Carlson, S.J., eds., Treatise on Invertebrate Stages (Vendian–Cambrian systems) of Siberia: Stra- and Val’kov, A., 2009, The Lower Cambrian fossil ana- Paleontology, Part H, Brachiopoda (Revised), Volume tigraphy and Geological Correlation, v. 10, p. 217–238. baritids: Affi nities, occurrences and systematics: Jour- 2: Boulder, Colorado, Geological Society of America, Khomentovsky, V.V., and Karlova, G.A., 2005, The Tommotian nal of Systematic Palaeontology, v. 7, p. 241–298, doi: p. 147–157. Stage base as the Cambrian lower boundary in Siberia: 10.1017/S1477201909002715. Lenton, T.M., and Watson, A.J., 2000, Redfi eld revisited: Stratigraphy and Geological Correlation, v. 13, p. 21–34. Kouchinsky, A., Bengtson, S., and Murdock, D.J.E., 2010, 1. Regulation of nitrate, phosphate, and oxygen in the Kimura, H., and Watanabe, Y., 2001, Oceanic anoxia at A new tannuolinid problematic from the Lower Cam- ocean: Global Biogeochemical Cycles, v. 14, p. 225– the Precambrian-Cambrian boundary: Geology, brian of the Sukharikha River in northern Siberia: 248, doi: 10.1029/1999GB900065. v. 29, p. 995–998, doi: 10.1130/0091-7613(2001)029 Acta Palaeontologica Polonica, v. 55, p. 321–331, doi: Li Guoxiang, Zhang Junming, and Zhu Maoyan, 2001, <0995:OAATPC>2.0.CO;2. 10.4202/app.2009.1102. Litho- and biostratigraphy of the Lower Cambrian

Geological Society of America Bulletin, November/December 2010 1769

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Meishucunian Stage in the Xiaotan section, eastern Cambrian boundary problem: Carbon isotope correla- sion and accuracy of zircon ages: Chemical Geology, Yunnan: Acta Palaeontologica Sinica, v. 40, supple- tions for Vendian and Tommotian time between Siberia v. 220, p. 47–66, doi: 10.1016/j.chemgeo.2005.03.011. ment, p. 40–53. and Morocco: Geology, v. 19, p. 847–850, doi: 10.1130/ Mattinson, J.M., 2010, Analysis of the relative decay con- Li Guoxiang, Zhu Maoyan, and Steiner, M., 2003, Micro- 0091-7613(1991)019<0847:PCBPCI>2.3.CO;2. stants of 235U and 238U by multi-step CA-TIMS structure and functional morphology of the Early Malinky, J.M., 2009, First occurrence of Orthotheca Novák, measurements of closed-system natural zircon samples: Cambrian problematical fossil Rhombocorniculum: 1886 (Hyolitha, Early Devonian) in North Amer- Chemical Geology, v. 275, p. 186–198, doi: 10.1016/ Progress in Natural Science, v. 13, p. 831–835, doi: ica: Journal of Paleontology, v. 83, p. 588–596, doi: j.chemgeo.2010.05.007. 10.1080/10020070312331344510. 10.1666/08-164R.1. McCausland, P.J.A., Van der Voo, R., and Hall, C.M., 2007, Li Guoxiang, Steiner, M., Zhu Xuejian, Yang Aihua, Wang Malinky, J.M., and Skovsted, C.B., 2004, Hyoliths and small Circum-Iapetus paleogeography of the Precambrian- Haifeng, and Erdtmann, B.-D., 2007, Early Cambrian shelly fossils from the Lower Cambrian of North-East Cambrian transition with a new paleomagnetic con- metazoan fossil record of South China: Generic diver- Greenland: Acta Palaeontologica Polonica, v. 49, straint from Laurentia: Precambrian Research, v. 156, sity and radiation patterns: Palaeogeography, Palaeo- p. 551–578. p. 125–152, doi: 10.1016/j.precamres.2007.03.004. climatology, Palaeoecology, v. 254, p. 229–249. Malinky, J.M., and Yochelson, E.L., 2007, On the sys- McFadden, K.A., Huang Jing, Chu Xuelei, Jiang Ganqing, Li, Z.X., 1998, Tectonic history of the major East Asian tematic position of the Hyolitha (kingdom Animalia ), Kaufman, A.J., Zhou Chuanming, Yuan Xunali, and lithospheric blocks since the mid-Proterozoic—A in Laurie, J.R., and Paterson, J.R., eds., Papers in Xiao, S., 2008, Pulsed oxidation and biological evolu- synthesis, in Martin, F.J., Chung, S.-L., Lo, C.-H., Honour of John H. Shergold 1938–2006: Asso- tion in the Ediacaran Doushantuo Formation: Proceed- and Lee, T.-Y., eds., Mantle Dynamics and Plate Inter- ciation of Australasian Palaeontologists Memoir 34, ings of the National Academy of Sciences, U.S.A., actions in East Asia: American Geophysical Union p. 521–536. v. 105, p. 3197–3202. (AGU) Geodynamics Series 27, p. 221–243. Maloof, A.C., 2004, Thermal Contraction Cracks, Polar Wan- McIlroy, D., Green, O.R., and Brasier, M.D., 2001, Palaeo- Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., Zhang, S., and dering, and Global Carbon Cycling: Non-Uniformi- biology and evolution of the earliest agglutinated Zhou, H., 2003, Geochronology of Neoproterozoic tarian Changes that Shaped the Neoproterozoic and Foraminifera: Platysolenites, Spirosolenites and re- syn-rift magmatism in the Yangtze craton, South Early Cambrian Earth [Ph.D. thesis]: Cambridge, Mas- lated forms: Lethaia, v. 34, p. 13–29, doi: 10.1080/ China, and correlations with other continents: Evi- sachusetts, Harvard University, 193 p. 002411601300068170. dence for a mantle superplume that broke up Rodinia: Maloof, A.C., Schrag, D.P., Crowley, J.L., and Bowring, McKie, T., 1993, Relative sea-level changes and the de- Precambrian Research, v. 122, p. 85–109, doi: 10.1016/ S.A., 2005, An expanded record of Early Cambrian velopment of a Cambrian transgression: Geologi- S0301-9268(02)00208-5. carbon cycling from the Anti-Atlas margin, Morocco: cal Magazine, v. 130, p. 245–256, doi: 10.1017/ Lindsay, J.F., Brasier, M.D., Dorjnamjaa, D., Goldring, Canadian Journal of Earth Sciences, v. 42, p. 2195– S0016756800009894. R., Kruse, P.D., and Wood, R.A., 1996a, Facies and 2216, doi: 10.1139/e05-062. Meert, J.G., Van der Voo, R., Pisarevsky, S.A., Komissarova, sequence controls on the appearance of the Cam- Maloof, A.C., Halverson, G.P., Kirschvink, J.L., Schrag, R.A., and Khramov, A.N., 2001, New palaeomagnetic brian biota in southwestern Mongolia: Implications D.P., Weiss, B.P., and Hoffman, P.F., 2006, Combined result from Vendian red sediments in Cisbaikalia and for the Precambrian-Cambrian boundary: Geologi- paleomagnetic, isotopic, and stratigraphic evidence the problem of the relationship of Siberia and Lau- cal Magazine, v. 133, p. 417–428, doi: 10.1017/ for true polar wander from the Neoproterozoic Akade- rentia in the Vendian: Comment and reply: Geophysi- S0016756800007585. mikerbreen Group, Svalbard, Norway: Geological So- cal Journal International, v. 146, p. 867–870, doi: Lindsay, J.F., Brasier, M.D., Shields, G., Khomentovsky, ciety of America Bulletin, v. 118, p. 1099–1124, doi: 10.1046/j.0956-540x.2001.01474.x. V.V., and Bat-Ireedui, Y.A., 1996b, Glacial facies asso- 10.1130/B25892.1. Mehl, D., and Erdtmann, B.-D., 1994, Sanshapentella ciations in a Neoproterozoic back-arc setting, Zavkhan Maloof, A.C., Ramezani, J., Bowring, S.A., Fike, D.A., dapingi n. gen., n. sp.—A new hexactinellid sponge Basin, western Mongolia: Geological Magazine, Porter, S.M., and Mazouad, M., 2010a, Constraints from the Early Cambrian (Tommotian) of China: Ber- v. 133, p. 391–402, doi: 10.1017/S0016756800007561. on Early Cambrian carbon cycling from the dura- liner Geowissenschaftliche Abhandlungen E, v. 13, Lipps, J.H., ed., 1993, Fossil prokaryotes and protists: Bos- tion of the Nemakit-Daldynian–Tommotian boundary p. 315–319. ton, Blackwell Science, 342 p. δ13C shift, Morocco: Geology, v. 38, p. 623–626, doi: Meshkova, N.P., 1974, Khiolity nizhnego kembriya Si- Love, G.D., Grosjean, E., Stalvies, C., Fike, D.A., Grotz- 10.1130/G30726.1. birskoy platformy: Akademiya Nauk SSSR, Sibirskoe inger, J.P., Bradley, A.S., Kelly, A.E., Bhatia, M., Maloof, A.C., Rose, C.V., Beach, R., Samuels, B.M., Otdelenie, Trudy Instituta Geologii i Geofi ziki, v. 97, Mere dith, W., Snape, C.E., Bowring, S.A., Condon, Calmet, C.C., Erwin, D.H., Poirier, G.R., Yao, N. and 111 p. D.J., and Summons, R.E., 2009, Fossil steroids re- Simons, F.J., 2010b, Possible animal-body fossils in Meybeck, M., 2003, Global analysis of river systems: From cord the appearance of Demospongiae during the pre-Marinoan limestones from South Australia: Nature Earth system controls to Anthropocene syndromes: Cryogenian period: Nature, v. 457, p. 718–721, doi: Geoscience, v. 3, p. 653–659, doi:10.1038/ngeo934. Philosophical Transactions of the Royal Society of 10.1038/nature07673. Marek, L., and Yochelson, E.L., 1976, Aspects of the biol- London, ser. B, Biological Sciences, v. 358, p. 1935– Lowenstam, H.A., and Epstein, S., 1957, On the origin of ogy of Hyolitha (Mollusca): Lethaia, v. 9, p. 65–82, 1955, doi: 10.1098/rstb.2003.1379. sedimentary aragonite needles of the Great Bahama doi: 10.1111/j.1502-3931.1976.tb00952.x. Miller, K.G., Kominz, M.A., Browning, J.V., Wright, Bank: The Journal of Geology, v. 65, p. 364–375, doi: Marshall, C.R., 2006, Explaining the Cambrian “explosion” J.D., Mountain, G.S., Katz, M.E., Sugarman, P.J., 10.1086/626439. of animals: Annual Review of Earth and Planetary Cramer, B.S., Christie-Blick, N., and Pekar, S.F., Lowenstein, T.K., Timofeef, M.N., Brennan, S.T., Hardie, Sciences, v. 34, p. 355–384, doi: 10.1146/annurev. 2005, The Phanerozoic record of global sea-level L.A., and Demicco, R.V., 2001, Oscillations in earth.33.031504.103001. change: Science, v. 310, p. 1293–1298, doi: 10.1126/ Phanero zoic seawater chemistry: Evidence from Martí Mus, M., and Bergström, J., 2005, The morphol- science.1116412. fl uid inclusions: Science, v. 294, p. 1086–1088, doi: ogy of hyolithids and its functional implications: Missarzhevsky, V.V., 1982, Subdivision and correlation 10.1126/science.1064280. Palaeontology, v. 48, p. 1139–1167, doi: 10.1111/ of the Precambrian-Cambrian boundary sequences Luchinina, V.A., 1999, Reef frameworks on the Siberian j.1475-4983.2005.00511.x. based on certain ancient groups of skeletal organisms: Platform through the Vendian–Cambrian boundary: Martí Mus, M., Palacios, T., and Jensen, S., 2008, Size of International Geology Review, v. 25, p. 745–759, doi: Russian Geology and Geophysics, v. 40, p. 1753–1762. the earliest mollusks: Did small helcionellids grow to 10.1080/00206818309466763. Luchinina, V.A., Korovnikov, I.V., Sipin, D.P., and Fedoseev, become large adults?: Geology, v. 36, p. 175–178, doi: Missarzhevsky, V.V., 1983, The stratigraphy of the oldest A.V., 1997, Upper Vendian–Lower Cambrian biostratig- 10.1130/G24218A.1. Phanerozoic sequences of the Anabar Massif: Inter- raphy of the Sukharikha River section (Siberian Martin, M.W., Grazhdankin, D.V., Bowring, S.A., Evans, national Geology Review, v. 26, p. 394–406, doi: Platform): Russian Geology and Geophysics, v. 38, D.A.D., Fedonkin, M.A., and Kirschvink, J.L., 2000, 10.1080/00206818409466566. p. 1385–1397. Age of Neoproterozoic bilatarian body and trace fos- Missarzhevsky, V.V., 1989, Drevneyshie skeletnye okamenel- Luo Huilin, Wu Xiche, and Ouyang Lin, 1991, Facies and sils, White Sea, Russia: Implications for metazoan osti i stratigrafi ya pogranichnykh tolshch dokembriya i correlation of the Sinian-Cambrian boundary stratig- evolution: Science, v. 288, p. 841–845, doi: 10.1126/ kembriya: Akademiya Nauk SSSR, Ordena Trudovogo raphy: Sedimentary Facies and Palaeogeography, v. 4, science.288.5467.841. Krasnogo Znameni Geologicheskiy Institut, Trudy, p. 27–35 (in Chinese with English abstract). Matthews, S.C., and Cowie, J.W., 1979, Early Cam- v. 443, 238 p., 32 pl. Ma Lifong, chief compiler, 2004, Geological Map of brian transgression: Journal of the Geological So- Mitchell, R.N., Evans, D.A.D., and Kilian, T.M., 2010, China: Beijing, Geological Publishing House, scale ciety of London, v. 136, p. 133–135, doi: 10.1144/ Rapid Early Cambrian rotation of Gondwana: Geol- 1:2,500,000, 1 sheet. gsjgs.136.2.0133. ogy, v. 38, p. 755–758, doi: 10.1130/G30910.1. Macdonald, F.A., Jones, D.S., and Schrag, D.P., 2009, Matthews, S.C., and Missarzhevsky, V.V., 1975, Small shelly Montañez, I.P., Banner, J.L., Osleger, D.A., Borg, L.E., Stratigraphic and tectonic implications of a newly fossils of late Precambrian and Early Cambrian age: A and Bosserman, P.J., 1996, Integrated Sr isotope discovered glacial diamictite–cap carbonate couplet in review of recent work: Journal of the Geological Soci- variations and sea-level history of Middle to Upper southwestern Mongolia: Geology, v. 37, p. 123–126, ety of London, v. 131, p. 289–304, 4 pl. Cambrian platform carbonates: Implications for the doi: 10.1130/G24797A.1. Mattinson, J.M., 2000, Revisiting the “gold standard”—The evolution of Cambrian seawater 87Sr/86Sr: Geology, Magaritz, M., Holser, W.T., and Kirschvink, J.L., 1986, Car- uranium decay constants of Jaffey et al., 1971: Eos v. 24, p. 917–920, doi: 10.1130/0091-7613(1996)024 bon isotope events across the Precambrian/Cambrian (Transactions, American Geophysical Union), v. 81, <0917:ISIVAS>2.3.CO;2. boundary on the Siberian Platform: Nature, v. 320, Spring Meeting supplement, p. S444–S445. Mortaj, A., Ikenne, M., Gasquet, D., Barbey, P., and Stussi, p. 258–259, doi: 10.1038/320258a0. Mattinson, J.M., 2005, Zircon U-Pb chemical abrasion J.M., 2000, Les granitoïdes paléoprotérozoïques des Magaritz, M., Kirschvink, J.L., Latham, A.J., Zhuravlev, (“CA-TIMS”) method: Combined annealing and multi- boutonnières du Bas Drâa et de la Tagragra d’Akka A.Yu., and Rozanov, A.Yu., 1991, Precambrian/ step partial dissolution analysis for improved preci- (Anti-Atlas occidental, Maroc): Un élément du puzzle

1770 Geological Society of America Bulletin, November/December 2010

géodynamique du craton ouest-africain: Journal of Af- Problematic Taxa: Cambridge, UK, Cambridge Uni- on the pattern of small shelly fossil decline: Palaios, rican Earth Sciences, v. 31, p. 523–538, doi: 10.1016/ versity Press, p. 157–177. v. 19, p. 178–183, doi: 10.1669/0883-1351(2004)019 S0899-5362(00)80005-6. Peel, J.S., and Skovsted, C.B., 2005, Problematic cap-shaped <0178:CTPWTF>2.0.CO;2. Mottl, M.J., and Wheat, C.G., 1994, Hydrothermal circula- fossils from the Lower Cambrian of North-East Green- Porter, S.M., 2004b, Hakierids in Middle Cambrian phosphatic tion through mid-ocean ridge fl anks: Fluxes of heat and land: Paläontologische Zeitschrift, v. 79, p. 461–470. limestones from Australia: Journal of Paleontology, v. 78, magnesium: Geochimica et Cosmochimica Acta, v. 58, Pel’man, Yu.L., Ermak, V.V., Fedorov, A.B., Luchinina, V.A., p. 574–590. p. 2225–2237, doi: 10.1016/0016-7037(94)90007-8. Zhuravleva, I.T., Repina, L.N., Bondarev, V.I., and Porter, S.M., 2007, Seawater chemistry and early carbon- Moucha, R., Forte, A.M., Mitrovica, J.X., Rowley, D.B., Borodaevskaya, Z.V., 1990, Novye dannye po strati- ate biomineralization: Science, v. 316, p. 1302, doi: Quéré, S., Simmons, N.A., and Grand, S.P., 2008, Dy- grafi i i paleontologii verkhnego dokembriya i nizhnego 10.1126/science.1137284. namic topography and long-term sea-level variations: kembriya r. Dzhandy (pravyy pritok r. Aldan ), in Repina, Porter, S.M., 2008, Skeletal microstructure indicates chancel- There is no such thing as a stable continental platform: L.N., ed., Biostratigrafi ya i paleon tologiya kembriya loriids and halkieriids are closely related: Palaeontology, Earth and Planetary Science Letters, v. 271, p. 101– Severnoy Azii: Akademiya Nauk SSSR, Sibirskoe v. 51, p. 865–879, doi: 10.1111/j.1475-4983.2008.00792.x. 108, doi: 10.1016/j.epsl.2008.03.056. Otdelenie, Trudy Instituta Geologii i Geofi ziki, v. 765, Porter, S.M., 2010, Calcite and aragonite seas and the de novo Mountjoy, E.W., and Amthor, J.E., 1994, Has burial p. 3–32, 3 pl. acquisition of carbonate skeletons: Geobiology, v. 8, dolomiti zation come of age? Some answers from the Peters, S.E., 2005, Geologic constraints on the macroevo- p. 256–277, doi: 10.1111/j.1472-4669.2010.00246.x. Western Canada sedimentary basin, in Purser, B., lutionary history of marine animals: Proceedings of Purser, B., Tucker, M., and Zenger, D., eds., 1994, Dolo- Tucker, M., and Zenger, D., eds., Dolomites: A Volume the National Academy of Sciences of the United States mites: A Volume in Honour of Dolomieu: Oxford, in Honour of Dolomieu: Oxford, Blackwell Scientifi c, of America, v. 102, p. 12,326–12,331, doi: 10.1073/ Blackwell Scientifi c, 451 p. p. 203–229. pnas.0502616102. Qian Yi, 1977, [Hyolitha and some problematica from the Mucci, A., and Morse, J.W., 1983, The incorporation of Mg2+ Peterson, K.J., Lyons, J.B., Nowak, K.S., Takacs, C.M., Lower Cambrian Meishucun Stage in central and S.W. and Sr2+ into calcite overgrowths: Infl uences of growth Wargo, M.J., and McPeek, M.A., 2004, Estimating China]: Acta Palaeontologica Sinica, v. 16, p. 255–278, rate and solution composition: Geochimica et Cos- metazoan divergence times with a molecular clock: 3 pl. (in Chinese with English abstract). mochimica Acta, v. 47, p. 217–233, doi: 10.1016/ Proceedings of the National Academy of Sciences of Qian Yi, 1989, Early Cambrian small shelly fossils of China 0016-7037(83)90135-7. the United States of America, v. 101, p. 6536–6541, with special reference to the Precambrian-Cambrian Nalivkin, D.V., chief compiler, 1965, Geologicheskaya doi: 10.1073/pnas.0401670101. boundary: Stratigraphy and palaeontology of systemic Karta SSSR: Moscow, Ministerstvo Geologii, scale Peterson, K.J., Cotton, J.A., Gehling, J.G., and Pisani, D., boundaries in China, Precambrian-Cambrian bound- 1:2,500,000, 17 sheets. 2008, The Ediacaran emergence of bilaterians: Con- ary, Volume 2: Nanjing, Nanjing University Publishing Narbonne, G.M., Kaufman, A.J., and Knoll, A.H., 1994, gruence between the genetic and the geological fossil House, 342 p., 99 pl. Integrated chemostratigraphy and biostratigraphy of records: Philosophical Transactions of the Royal So- Qian Yi, ed., 1999, [Taxonomy and biostratigraphy of small the Windermere Supergroup, northwestern Canada: ciety of London, ser. B, Biological Sciences, v. 363, shelly fossils in China]: Beijing, Science Press, 247 p. Implications for Neoproterozoic correlations and the p. 1435–1443, doi: 10.1098/rstb.2007.2233. (in Chinese with English summary). early evolution of animals: Geological Society of Piper, D.Z., 1994, Seawater as the source of minor elements Qian Yi, and Bengtson, S., 1989, Palaeontology and biostra- America Bulletin, v. 106, p. 1281–1292, doi: 10.1130/ in black shales, phosphorites and other sedimentary tigraphy of the Early Cambrian Meishucunian Stage 0016-7606(1994)106<1281:ICABOT>2.3.CO;2. rocks: Chemical Geology, v. 114, p. 95–114, doi: in Yunnan Province, South China: Fossils and Strata, Newell, N.D., 1952, Periodicity in invertebrate evolution: 10.1016/0009-2541(94)90044-2. v. 24, 156 p. Journal of Paleontology, v. 26, p. 371–385. Piper, D.Z., and Isaacs, C.M., 1995, Minor elements in Qian Yi, Li Guoxiang, and Zhu Maoyan, 2001, The Mei- Newell, N.D., 1962, Paleontological gaps and geochronol- Quaternary sediment from the Sea of Japan: A record shucunian Stage and its small shelly fossil sequence in ogy: Journal of Paleontology, v. 36, p. 592–610. of surface-water productivity and intermediate-water China: Acta Palaeontologica Sinica, v. 40, supplement, Nicholas, C.J., 1996, The Sr isotopic evolution of the oceans redox conditions: Geological Society of America p. 54–62. during the ‘Cambrian explosion’: Journal of the Geo- Bulletin, v. 107, p. 54–67, doi: 10.1130/0016-7606 Qian Yi, Li Guoxiang, Zhu Maoyan, Steiner, M., and Erdt- logical Society of London, v. 153, p. 243–254, doi: (1995)107<0054:MEIQSF>2.3.CO;2. mann, B.-D., 2004, Early Cambrian protoconodonts 10.1144/gsjgs.153.2.0243. Pisarevsky, S.A., Gurevich, E.L., and Khramov, A.N., and conodont-like fossils from China: Taxonomic revi- Norin, E., 1937, Geology of western Quruq Tagh, eastern 1997, Palaeomagnetism of Lower Cambrian sedi- sions and stratigraphic implications: Progress in Natu- T’ien-Shan: Reports from the Scientifi c Expedition ments from the Olenek River section (northern Si- ral Science, v. 14, p. 173–180. to the North-Western Provinces of China under the beria): Palaeopoles and the problem of magnetic Ragozina, A., Dorjnamjaa, D., Krayushkin, A., and Serezh- Leadership of Dr. Sven Hedin, III: Stockholm, Bok- polarity in the Early Cambrian: Geophysical Jour- nikova, E., 2008, Treptichnus pedum and the Vendian- förlags Aktiebolaget Thule, Volume 1, 194 p. nal International, v. 130, p. 746–756, doi: 10.1111/ Cambrian boundary, in 33rd International Geological O’Loughlin, E.J., and Chin, Y.-P., 2004, Quantifi cation and j.1365-246X.1997.tb01869.x. Congress Abstracts: Oslo, abs. HPF-07. characterization of dissolved organic carbon and iron Pisarevsky, S.A., Komissarova, R.A., and Khramov, A.N., Randell, R.D., Lieberman, B.S., Hasiotis, S.T., and Pope, in sedimentary porewater from Green Bay, WI, USA: 2000, New palaeomagnetic results from Vendian red M.C., 2005, New chancelloriids from the Early Biogeochemistry, v. 71, p. 371–386, doi: 10.1007/ sediments in Cisbaikalia and the problem of the rela- Cambrian Sekwi Formation with a comment on s10533-004-0373-x. tionship of Siberia and Laurentia in the Vendian: Geo- chancelloriid affinities: Journal of Paleontology, Orłowski, S., and Waksmundzki, B., 1986, The oldest Hyo- physical Journal International, v. 140, p. 598–610, doi: v. 79, p. 987–996, doi: 10.1666/0022-3360(2005)079 litha in the Lower Cambrian of the Holy Cross Moun- 10.1046/j.1365-246X.2000.t01-1-00056.x. [0987:NCFTEC]2.0.CO;2. tains: Acta Geologica Polonica, v. 36, p. 225–231, 2 pl. Pisarevsky, S.A., Wingate, M.T.D., Powell, C.M., Johnson, Raub, T.D., Kirschvink, J.L., and Evans, D.A.D., 2007, True Parkhaev, P.Yu., 1998, Siphonoconcha—A new class of S., and Evans, D.A.D., 2003, Models of Rodinia assem- polar wander: Linking deep and shallow geodynamics Early Cambrian bivalved organisms: Paleontological bly and fragmentation, in Yoshida, M., Windley, B.E., to hydro- and biospheric hypotheses, in Kono, M., ed., Journal, v. 32, p. 1–15. and Dasgupta, S., eds., Proterozoic East Gondwana: Treatise on Geophysics: Volume 5. Geomagnetism: Parkhaev, P.Yu., 2001, The functional morphology of the Supercontinent Assembly and Breakup: Geological Amsterdam, Elsevier, p. 565–589. Cambrian univalved molluscs—Helcionellids: Paleon- Society of London Special Publication 206, p. 35–55. Raymo, M.E., Ruddiman, W.F., and Froelich, P.N., 1988, tological Journal, v. 35, p. 470–475. Pitman, W.C., III, 1978, Relationship between eustasy and Infl uence of late Cenozoic mountain building on ocean Parkhaev, P.Yu., 2008, The Early Cambrian radiation of stratigraphic sequences of passive margins: Geological geochemical cycles: Geology, v. 16, p. 649–653, doi: Mollusca, in Ponder, W.F., and Lindberg, D.R., eds., Society of America Bulletin, v. 89, p. 1389–1403, doi: 10.1130/0091-7613(1988)016<0649:IOLCMB> Phylogeny and Evolution of the Mollusca: Berkeley, 10.1130/0016-7606(1978)89<1389:RBEASS>2.0.CO;2. 2.3.CO;2. University of California Press, p. 33–69. Ponder, W.F., Parkhaev, P.Yu., and Beechey, D.L., 2007, Reitner, J., and Wörheide, G., 2002, Non-lithistid fossil Parsons, B., 1982, Causes and consequences of the relation A remarkable similarity in scaly shell structure in Demo spongiae—Origins of their palaeobiodiversity between area and age of the ocean fl oor: Journal of Early Cambrian univalved limpets (Monoplacophora; and highlights in history of preservation, in Hooper, Geophysical Research, v. 87, p. 289–302, doi: 10.1029/ Maikhanellidae) and a Recent fi ssurellid limpet (Gas- J.N.A., and Van Soest, R., eds., Systema Porifera: New JB087iB01p00289. tropoda: Vetigastropoda) with a review of Maikhanel- York, Kluwer/Plenum, p. 52–68. Patterson, W.P., and Walter, L.M., 1994, Depletion of 13C lidae: Molluscan Research, v. 27, p. 129–139. Repina, L.N., and Rozanov, A.Yu., eds., 1992, Kembriy Sibiri: Σ in seawater CO2 on modern carbonate platforms: Popov, L.E., and Holmer, L.E., 2000, Obolellata, in Rossiyskaya Akademiya Nauk, Sibirskoe Otdelenie, Signifi cance for the carbon isotopic record of car- Williams, A., Brunton, C.H.C., and Carlson, S.J., eds., Trudy Instituta Geologii i Geofi ziki, v. 788, 135 p. bonates: Geology, v. 22, p. 885–888, doi: 10.1130/ Treatise on Invertebrate Paleontology, Part H, Brachio- Repina, L.N., Borodaevskaya, Z.V., and Ermak, V.V., 1988, 0091-7613(1994)022<0885:DOCISC>2.3.CO;2. poda (Revised), Volume 2: Boulder, Colorado, Geo- Opornyy razrez po r. Selinde (yugo-vostochnaya Peel, J.S., 1988, Spirellus and related helically coiled micro- logical Society of America, p. 200–208. okraina Aldanskogo shchita), in Zhuravleva, I.T., and fossils (Cyanobacteria) from the Lower Cambrian of Popov, L.E., and Williams, A., 2000, Kutorginata, in Repina, L.N., eds., Kembriy Sibiri i Sredney Azii: Aka- North Greenland: Grønlands Geologiske Undersøgelse Williams, A., Brunton, C.H.C., and Carlson, S.J., eds., demiya Nauk SSSR, Sibirskoe Otdelenie, Trudy Insti- Rapport, v. 137, p. 5–32. Treatise on Invertebrate Paleontology, Part H, Brachio- tuta Geologii i Geofi ziki, v. 720, p. 3–31. Peel, J.S., 1991, Functional morphology of the class Helcio- poda (Revised), Volume 2: Boulder, Colorado, Geo- Richter, F.M., Rowley, D.B., and DePaolo, D.J., 1992, Sr nelloida nov., and the early evolution of the Mollusca, logical Society of America, p. 208–215. isotope evolution of seawater: The role of tectonics: in Simonetta, A.M., and Conway Morris, S., eds., The Porter, S.M., 2004a, Closing the phosphatization window: Earth and Planetary Science Letters, v. 109, p. 11–23, Early Evolution of Metazoa and the Signifi cance of Testing for the infl uence of taphonomic megabias doi: 10.1016/0012-821X(92)90070-C.

Geological Society of America Bulletin, November/December 2010 1771

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Riding, R., 2001, Calcifi ed algae and bacteria, in Zhurav- v. 14, p. 311–322, doi: 10.1111/j.1502-3931.1981. phospace: Science, v. 319, p. 81–84, doi: 10.1126/ lev, A.Yu., and Riding, R., eds., The Ecology of the tb01104.x. science.1150279. Cambrian Radiation: New York, Columbia University Runnegar, B., and Pojeta, J., Jr., 1974, Molluscan phylog- Shen Yanan, and Schidlowski, M., 2000, New C isotope Press, p. 445–473. eny: The paleontological viewpoint: Science, v. 186, stratigraphy from southwest China: Implications for Riding, R., and Zhuravlev, A.Yu., 1995, Structure and diver- p. 311–317, doi: 10.1126/science.186.4161.311. the placement of the Precambrian-Cambrian boundary sity of oldest sponge-microbe reefs: Lower Cambrian, Runnegar, B., Pojeta, J., Jr., Morris, N.J., Taylor, J.D., on the Yangtze Platform and global correlations: Geol- Aldan River, Siberia: Geology, v. 23, p. 649–652, Taylor, M.E., and McClung, G., 1975, Biology of ogy, v. 28, p. 623–626. doi: 10.1130/0091-7613(1995)023<0649:SADOOS> the Hyolitha: Lethaia, v. 8, p. 181–191, doi: 10.1111/ Shu, D.-G., Conway Morris, S., Han, J., Chen, L., Zhang, 2.3.CO;2. j.1502-3931.1975.tb01311.x. X.-L., Zhang, Z.-F., Liu, H.-Q., Li, Y., and Liu, J.-N., Roger, J., Gasquet, D., Baudin, T., Chalot-Prat, F., Hassen- Saadi, S., Hilali, E., Bensaïd, M., Boudda, A., and Dahmani, 2001, Primitive deuterostomes from the Chengjiang forder, B., Marquer, D., Chèvremont, P., Berrahma, A., M., 1985, Carte Géologique du Maroc: Rabat, Ministère Lagerstätte (Lower Cambrian, China): Nature, v. 414, Destombes, J., Razin, P., and Benlakhdim, A., 2001, de l’Énergie et des Mines, Service Géologique du Maroc, p. 419–424, doi: 10.1038/35106514. Feuille NHI-29-X-1d, Tamazrar: Carte Géologique scale 1:1,000,000. Siddall, M., Rohling, E.J., Almogi-Labin, A., Hemleben, C., du Maroc à 1:50,000: Notes et Mémoires du Service Saltzman, M.R., 2005, Phosphorus, nitrogen, and the redox Meischner, D., Schmelzer, I., and Smeed, D.A., 2003, Géologique du Maroc 415, 1 sheet, scale 1:50,000. evolution of the Paleozoic oceans: Geology, v. 33, Sea-level fl uctuations during the last glacial cycle: Na- Roggenthen, W.M., Fischer, J.F., Napoleone, G., and p. 573–576, doi: 10.1130/G21535.1. ture, v. 423, p. 853–858, doi: 10.1038/nature01690. Fischer, A.G., 1981, Paleomagnetism and age of mafi c Saltzman, M.R., Ripperdan, R.L., Brasier, M.D., Lohmann, Simberloff, D.S., 1974, Permo-Triassic extinctions: Effects plutons, Wichita Mountains, Oklahoma: Geophysi- K.C., Robison, R.A., Chang, W.T., Peng Shanchi, of area on biotic equilibrium: The Journal of Geology, cal Research Letters, v. 8, p. 133–136, doi: 10.1029/ Erga liev, E.K., and Runnegar, B., 2000, A global car- v. 82, p. 267–274, doi: 10.1086/627962. GL008i002p00133. bon isotope excursion (SPICE) during the Late Cam- Skovsted, C.B., 2003, Mobergellans (Problematica) from Romanek, C.S., Grossman, E.L., and Morse, J.W., 1992, brian: Relation to trilobite extinctions, organic-matter the Cambrian of Greenland, Siberia and Kazakhstan: Carbon isotopic fractionation in synthetic aragonite burial and sea level: Palaeogeography, Palaeoclimatol- Paläontologische Zeitschrift, v. 77, p. 429–443. and calcite: Effects of temperature and precipitation ogy, Palaeoecology, v. 162, p. 211–223. Skovsted, C.B., Brock, G.A., and Paterson, J.R., 2006, Bi- rate: Geochimica et Cosmochimica Acta, v. 56, p. 419– Savitsky, V.E., Zhuravleva, I.T., Kir’yanov, V.V., Luchinina, valved arthropods from the Lower Cambrian Mern- 430, doi: 10.1016/0016-7037(92)90142-6. V.A., Meshkova, N.P., and Shishkin, B.B., 1980, merna Formation, Arrowie Basin, South Australia, and Rothman, D.H., Hayes, J.M., and Summons, R.E., 2003, Nemakit-daldynskiy fatsiostratotip granitsy dokem- their implications for identifi cation of Cambrian ‘small Dynamics of the Neoproterozoic carbon cycle: Pro- briya i kembriya Sibiri, in Sidorenko, A.V., ed., Mezh- shelly fossils,’ in Paterson, J.R., and Laurie, J.R., eds., ceedings of the National Academy of Sciences of the dunarodnyy Geologicheskiy Kongress, XXVI sessiya, Cambro-Ordovician Studies II: Association of Austral- United States of America, v. 100, p. 8124–8129, doi: Doklady sovetskikh geologov, Dokembriy: Moscow, asian Palaeontologists Memoir 32, p. 7–41. 10.1073/pnas.0832439100. Nauka, p. 164–170. Skovsted, C.B., Brock, G.A., Paterson, J.R., Holmer, L.E., Rowland, S.M., 2001, Archaeocyaths—A history of Sawaki, Y., Ohno, T., Fukushi, Y., Komiya, T., Ishikawa, T., and Budd, G.E., 2008, The scleritome of Eccen- phylogenetic interpretation: Journal of Paleontol- Hirata, T., and Maruyama, S., 2008, Sr isotope excur- trotheca from the Lower Cambrian of South Australia: ogy, v. 75, p. 1065–1078, doi: 10.1666/0022-3360 sion across the Precambrian-Cambrian boundary in the Lophophorate affi nities and implications for tommotiid (2001)075<1065:AAHOPI>2.0.CO;2. Three Gorges area, South China: Gondwana Research, phylogeny: Geology, v. 36, p. 171–174, doi: 10.1130/ Rowland, S.M., Luchinina, V.A., Korovnikov, I.V., Sipin, v. 14, p. 134–147, doi: 10.1016/j.gr.2007.11.002. G24385A.1. D.P., Tarletskov, A.I., and Fedoseev, A.V., 1998, Bio- Schoene, B., Crowley, J.L., Condon, D.J., Schmitz, M.D., Skovsted, C.B., Balthasar, U., Brock, G.A., and Paterson, stratigraphy of the Vendian–Cambrian Sukharikha and Bowring, S.A., 2006, Reassessing the uranium J.R., 2009a, The tommotiid Camenella reticulosa River section, northwestern Siberian Platform: Cana- decay constants for geochronology using ID-TIMS from the Early Cambrian of South Australia: Mor- dian Journal of Earth Sciences, v. 35, p. 339–352, doi: U-Pb data: Geochimica et Cosmochimica Acta, v. 70, phology, scleritome reconstruction, and phylogeny: 10.1139/cjes-35-4-339. p. 426–445, doi: 10.1016/j.gca.2005.09.007. Acta Palaeon tologica Polonica, v. 54, p. 525–540, doi: Rowley, D.B., 2002, Rate of plate creation and destruc- Scholle, P.A., and Arthur, M.A., 1980, Carbon isotope 10.4202/app.2008.0082. tion: 180 Ma to present: Geological Society of fl uctuations in Cretaceous pelagic limestones: Poten- Skovsted, C.B., Holmer, L.E., Larsson, C.M., Högström, America Bulletin, v. 114, p. 927–933, doi: 10.1130/ tial stratigraphic and petroleum exploration tool: The A.E.S., Brock, G.A., Topper, T.P., Balthasar, U., Petter- 0016-7606(2002)114<0927:ROPCAD>2.0.CO;2. American Association of Petroleum Geologists Bulle- son Stolk, S., and Paterson, J.R., 2009b, The scleritome Rozanov, A.Yu., 1984, The Precambrian-Cambrian bound- tin, v. 64, p. 67–87. of Paterimitra: An Early Cambrian stem group ary in Siberia: Episodes, v. 7, p. 20–24. Schopf, J.W., 2000, Solution to Darwin’s dilemma: Dis- brachiopod from South Australia: Proceedings of the Rozanov, A.Yu., and Missarzhevsky, V.V., 1966, Biostrati- covery of the missing Precambrian record of life: Pro- Royal Society B, Biological Sciences, v. 276, p. 1651– grafi ya i fauna nizhnikh gorizontov kembriya: Aka- ceedings of the National Academy of Sciences of the 1656, doi: 10.1098/rspb.2008.1655. demiya Nauk SSSR, Geologicheskiy Institut, Trudy, United States of America, v. 97, p. 6947–6953, doi: Sloan, L.C., and Pollard, D., 1998, Polar stratospheric v. 148, 127 p., 13 pl. 10.1073/pnas.97.13.6947. clouds: A high latitude warming mechanism in an an- Rozanov, A.Yu., and Sokolov, B.S., eds., 1984, Yarusnoe Schopf, T.J.M., 1974, Permo-Triassic extinctions: Relation cient greenhouse world: Geophysical Research Letters, raschlenenie nizhnego kembriya, Stratigrafi ya: Mos- to sea-fl oor spreading: The Journal of Geology, v. 82, v. 25, p. 3517–3520, doi: 10.1029/98GL02492. cow, Nauka, 184 p. p. 129–143, doi: 10.1086/627955. Sloan, L.C., Walker, J.C.G., and Moore, T.C., Jr., 1995, Pos- Rozanov, A.Yu., and Zhuravlev, A.Yu., 1992, The Lower Schrag, D.P., Berner, R.A., Hoffman, P.F., and Halverson, sible role of oceanic heat transport in early Eocene cli- Cambrian fossil record of the Soviet Union, in Lipps, G.P., 2002, On the initiation of a snowball Earth: Geo- mate: Paleoceanography, v. 10, p. 347–356, doi: 10.1029/ J.H., and Signor, P.W., eds., Origin and Early Evo- chemistry, Geophysics, Geosystems, v. 3, no. 6, art. 94PA02928. lution of the Metazoa: New York, Plenum Press, 1036, 21 p. Sloss, L.L., 1963, Sequences in the cratonic interior of p. 205–282. Schröder, S., and Grotzinger, J.P., 2007, Evidence for anoxia North America: Geological Society of America Bulle- Rozanov, A.Yu., Missarzhevsky, V.V., Volkova, N.A., at the Ediacaran-Cambrian boundary: The record of tin, v. 74, p. 93–114, doi: 10.1130/0016-7606(1963)74 Voronova , L.C., Krylov, I.N., Keller, B.M., Korolyuk, redox-sensitive trace elements and rare earth elements [93:SITCIO]2.0.CO;2. I.K., Lendzion, K., Michniak, R., Pykhova, N.G., and in Oman: Journal of the Geological Society of London, Smith, R.L., Miller, L.G., and Howes, B.L., 1993, The Sidorov, A.D., 1969, The Tommotian Stage and the v. 164, p. 175–187, doi: 10.1144/0016-76492005-022. geochemistry of methane in Lake Fryxell, an amictic, Cambrian lower boundary problem: New Delhi, Am- Seilacher, A., 1984, Late Precambrian and Early Cambrian permanently ice-covered, Antarctic lake: Biogeochem- erind Publishing Co., 359 p., 55 pl. Metazoa: Preservational or real extinctions?, in Holland , istry, v. 21, p. 95–115, doi: 10.1007/BF00000873. Rozanov, A.Yu., Khomentovsky, V.V., Shabanov, Yu.Ya., H.D., and Trendall, A.F., eds., Patterns of Change in Smith, S.V., 1984, Phosphorus versus nitrogen limita- Karlova, G.A., Varlamov, A.I., Luchinina, V.A., Pegel’, Earth Evolution: Berlin, Springer-Verlag, p. 159–168. tion in the marine environment: Limnology and T.V., Demidenko, Yu.E., Parkhaev, P.Yu., Korovnikov, Sepkoski, J.J., Jr., 1992, Proterozoic–Early Cambrian di- Oceanography, v. 29, p. 1149–1160, doi: 10.4319/ I.V., and Skorlotova, N.A., 2008, To the problem of versifi cation of metazoans and metaphytes, in Schopf, lo.1984.29.6.1149. stage subdivision of the Lower Cambrian: Stratigraphy J.W., and Klein, C., eds., The Proterozoic Biosphere: Sokolov, B.S., and Zhuravleva, I.T., 1983, Yarunsoe rasch- and Geological Correlation, v. 16, p. 1–19. A Multidisciplinary Study: Cambridge, UK, Cam- lenenie nizhnego kembriya Sibiri, Atlas okamenelostey: Rubinson, M., and Clayton, R.N., 1969, Carbon-13 frac- bridge University Press, p. 553–561. Akademiya Nauk SSSR, Sibirskoe Otdelenie, Trudy In- tionation between aragonite and calcite: Geochi- Shackleton, N., and Boersma, A., 1981, The climate of stituta Geologii i Geofi ziki, v. 558, 216 p., 72 pl. mica et Cosmochimica Acta, v. 33, p. 997–1002, doi: the Eocene ocean: Journal of the Geological Soci- Spall, H., 1968, Paleomagnetism of basement granites of 10.1016/0016-7037(69)90109-4. ety of London, v. 138, p. 153–157, doi: 10.1144/ southern Oklahoma and its implications; progress re- Runkel, A.C., Mackey, T.J., Cowan, C.A., and Fox, D.L., gsjgs.138.2.0153. port: Oklahoma Geology Notes, v. 28, p. 65–80. 2010, Tropical shoreline ice in the late Cambrian: Im- Shackleton, N.J., Hall, M.A., Line, J., and Cang, S., Sperling, E.A., Pisani, D., and Peterson, K.J., 2007, Poriferan plications for Earth’s climate between the Cambrian 1983, Carbon isotope data in core V19–30 confi rm paraphyly and its implications for Precambrian palaeo- Explosion and the Great Ordo vi cian Biodiversifi cation reduced carbon dioxide concentrations in the ice biology, in Vickers-Rich, P., and Komarower, P., eds., Event: GSA Today, v. 20, no. 11, p. 4–10, doi: 10.1130/ age atmosphere: Nature, v. 306, p. 319–322, doi: The Rise and Fall of the Ediacaran Biota: Geological GSAT684A.1 10.1038/306319a0. Society of London Special Publication 286, p. 355–368. Runnegar, B., 1981, Muscle scars, shell form and torsion in Shen, B., Dong, L., Xiao, S., and Kowalewski, M., 2008, Sperling, E.A., Robinson, J.M., Pisani, D., and Peterson, Cambrian and Ordovician univalved molluscs: Lethaia, The Avalon explosion: Evolution of Ediacara mor- K.J., 2010, Where’s the glass? Biomarkers, molecu-

1772 Geological Society of America Bulletin, November/December 2010

lar clocks, and microRNAs suggest a 200-Myr miss- Szaniawski, H., 1982, Chaetognath grasping spines recog- Valentine, J.W., 2002, Prelude to the Cambrian explosion: An- ing Precambrian fossil record of siliceous sponge nized among Cambrian protoconodonts: Journal of nual Review of Earth and Planetary Sciences, v. 30, p. 285– spicules: Geobiology, v. 8, p. 24–36, doi: 10.1111/ Paleontology, v. 56, p. 806–810. 306, doi: 10.1146/annurev.earth.30.082901.092917. j.1472-4669.2009.00225.x. Szaniawski, H., 2002, New evidence for the protoconodont Valentine, J.W., 2004, On the Origin of Phyla: Chicago, Uni- Squire, R.J., Campbell, I.H., Allen, C.M., and Wilson, origin of chaetognaths: Acta Palaeontologica Polonica, versity of Chicago Press, 614 p. C.J.L., 2006, Did the Transgondwanan Supermountain v. 47, p. 405–419. Valentine, J.W., and Moores, E.M., 1970, Plate-tectonic trigger the explosive radiation of animals on Earth?: Takacs, C.D., Priscu, J.C., and McKnight, D.M., 2001, regulation of faunal diversity and sea level: A Earth and Planetary Science Letters, v. 250, p. 116– Bacterial dissolved organic carbon demand in model: Nature, v. 228, p. 657–659, doi: 10.1038/ 133, doi: 10.1016/j.epsl.2006.07.032. McMurdo Dry Valley lakes, Antarctica: Limnology 228657a0. Stanley, S.M., 1973, An ecological theory for the sudden and Oceanography, v. 46, p. 1189–1194, doi: 10.4319/ Val’kov, A.K., 1975, Biostratigrafi ya i khiolity kembriya origin of multicellular life in the late Precambrian: lo.2001.46.5.1189. severo-vostoka Sibirskoy platformy: Moscow, Nauka, Proceedings of the National Academy of Sciences of Taylor, S.R., and McLennan, S.M., 1985, The Continental 140 p. the United States of America, v. 70, p. 1486–1489, doi: Crust: Its Composition and Evolution: An Examination Val’kov, A.K., 1982, Biostratigrafi ya nizhnego kembriya 10.1073/pnas.70.5.1486. of the Geochemical Record Preserved in Sedimentary vostoka Sibirskoy platformy: Moscow, Nauka, 92 p., Stanley, S.M., and Hardie, L.A., 1998, Secular oscilla- Rocks: Oxford, Blackwell Science, 312 p. 16 pl. tions in the carbonate mineralogy of reef-building and Terman, M.J., chief compiler, 1973, Tectonic Map of China Val’kov, A.K., 1983, Raspostranenie drevneyshikh skelet- sediment-producing organisms driven by tectonically and Mongolia: Boulder, Colorado, Geological Society nykh organizmov i korrelyatsiya nizhney granitsy kem- forced shifts in seawater chemistry: Palaeogeography, of America, scale 1:5,000,000, 1 sheet. briya v yugo-vostochnoy chasti Sibirskoy platformy, in Palaeoclimatology, Palaeoecology, v. 144, p. 3–19, doi: Thomas, R.J., Chevallier, L.P., Gresse, P.G., Harmer, R.E., Khomentovsky, V.V., ed., Pozdniy dokembriy i ranniy 10.1016/S0031-0182(98)00109-6. Eglington, B.M., Armstrong, R.A., de Beer, C.H., paleozoy Sibiri, Vendskie otlozheniya: Novosibirsk, Steiner, M., Mehl, D., Reitner, J., and Erdtmann, B.-D., Martini, J.E.J., de Kock, G.S., Macey, P.H., and Institut Geologii i Geofi ziki, Sibirskoe Otdelenie, Aka- 1993, Oldest entirely preserved sponges and other fos- Ingram, B.A., 2002, Precambrian evolution of the demiya Nauk SSSR, p. 37–48. sils from the lowermost Cambrian and a new facies Sirwa Window, Anti-Atlas orogen, Morocco: Pre- Val’kov, A.K., 1987, Biostratigrafi ya nizhnego kembriya reconstruction of the Yangtze platform (China): Ber- cambrian Research, v. 118, p. 1–57, doi: 10.1016/ vostoka Sibirskoy platformy, Yudomo-Olenekskiy re- liner Geo wissenschaftliche Abhandlungen E, v. 9, S0301-9268(02)00075-X. gion: Moscow, Nauka, 137 p., 16 pl. p. 293–329. Tohver, E., D’Agrella-Filho, M.S., and Trindade, R.I.F., Van Cappellen, P., and Ingall, E.D., 1996, Redox stabilization Steiner, M., Wallis, E., Erdtmann, B.-D., Zhao Yuanlong, 2006, Paleomagnetic record of Africa and South of the atmosphere and oceans by phosphorous-limited and Yang Ruidong, 2001, Submarine-hydrothermal America for the 1200–500 Ma interval, and evalua- marine productivity: Science, v. 271, p. 493–496, doi: exhalative ore layers in black shales from South tion of Rodinia and Gondwana assemblies: Precam- 10.1126/science.271.5248.493. China and associated fossils—Insights into a Lower brian Research, v. 147, p. 193–222, doi: 10.1016/ van der Voo, R., 1990, The reliability of paleomagnetic Cambrian facies and bio-evolution: Palaeogeography, j.precamres.2006.01.015. data: Tectonophysics, v. 184, p. 1–9, doi: 10.1016/ Palaeo climatology, Palaeoecology, v. 169, p. 165–191. Torgunova, N.I., 1994, New ideas on dissolved matter distri- 0040-1951(90)90116-P. Steiner, M., Li Guoxiang, Qian Yi, and Zhu Maoyan, 2004a, bution in the Black Sea: Oceanology (Moscow), v. 34, Van Iten, H., Zhu Maoyan, and Li Guoxiang, 2010, Re- Lower Cambrian small shelly fossils of northern Sich- p. 50–54. description of Hexaconularia He and Yang, 1986 uan and southern Shaanxi (China), and their biostrati- Torsvik, T.H., and Rehnström, E.F., 2001, Cambrian palaeo- (Lower Cambrian, South China): Implications for the graphic importance: Geobios, v. 37, p. 259–273. magnetic data from Baltica: Implications for true polar affi nities of conulariid-like small shelly fossils: Palaeon- Steiner, M., Zhu Maoyan, Li Guoxiang, Qian Yi, and Erdt- wander and Cambrian palaeogeography: Journal of the tology, v. 53, p. 191–199. mann, B.-D., 2004b, New Early Cambrian bilaterian Geological Society of London, v. 158, p. 321–329, doi: Vannier, J., Steiner, M., Renvoisé, E., Hu, S.-X., and Casa- embryos and larvae from China: Geology, v. 32, 10.1144/jgs.158.2.321. nova, J.-P., 2007, Early Cambrian origin of modern p. 833–836. Torsvik, T.H., Meert, J.G., and Smethurst, M.A., 1998, Polar food webs: Evidence from predator arrow worms: Pro- Steiner, M., Li Guoxiang, Qian Yi, Zhu Maoyan, and Erdt- wander and the Cambrian: Technical Comment: Sci- ceedings of the Royal Society B, Biological Sciences, mann, B.-D., 2007, Neoproterozoic to Early Cambrian ence, v. 279, p. 9. v. 274, p. 627–633, doi: 10.1098/rspb.2006.3761. small shelly fossil assemblages and a revised biostrati- Towe, K.M., 1970, Oxygen-collagen priority and the early Vannier, J., Calandra, I., Gaillard, C., and Żylińska, A., graphic correlation of the Yangtze Platform (China): metazoan fossil record: Proceedings of the National 2010, Priapulid worms: Pioneer horizontal burrow- Palaeogeography, Palaeoclimatology, Palaeoecology, Academy of Sciences of the United States of America, ers at the Precambrian-Cambrian boundary: Geology, v. 254, p. 67–99. v. 65, p. 781–788, doi: 10.1073/pnas.65.4.781. v. 38, p. 711–714, doi: 10.1130/G30829.1. Stoll, H.M., and Schrag, D.P., 1998, Effects of Quaternary Trindade, R.I.F., D’Agrella-Filho, M.S., Epof, I., and Brito Vasconcelos, C., and McKenzie, J.A., 1997, Microbial sea level cycles on strontium in seawater: Geochim- Neves, B.J., 2006, Paleomagnetism of Early Cambrian mediation of modern dolomite precipitation and dia- ica et Cosmochimica Acta, v. 62, p. 1107–1118, doi: Itabaiana mafi c dikes (NE Brazil) and the fi nal assem- genesis under anoxic conditions (Lagoa Vermelha, Rio 10.1016/S0016-7037(98)00042-8. bly of Gondwana: Earth and Planetary Science Letters, de Janeiro, Brazil): Journal of Sedimentary Research, Stoll, H.M., Schrag, D.P., and Clemens, S.C., 1999, Are sea- v. 244, p. 361–377, doi: 10.1016/j.epsl.2005.12.039. v. 67, p. 378–390. water Sr/Ca variations preserved in Quaternary forami- Tyler, S.A., and Barghoorn, E.S., 1954, Occurrence of struc- Vasil’eva, N.I., 1998, Melkaya rakovinnaya fauna i bio- nifera?: Geochimica et Cosmochimica Acta, v. 63, turally preserved plants in Pre-Cambrian rocks of the stratigrafi ya nizhnego kembriya Sibirskoy platformy: p. 3535–3547, doi: 10.1016/S0016-7037(99)00129-5. Canadian Shield: Science, v. 119, p. 606–608, doi: Saint Petersburg, Vserossiyskiy Neftyanoy Nauchno- Sun, S.Q., 1994, A reappraisal of dolomite abundance and 10.1126/science.119.3096.606. Issledovatel’skiy Geologorazvedochnyy Institut, 139 p., occurrence in the Phanerozoic: Journal of Sedimentary Tyrrell, T., 1999, The relative infl uences of nitrogen and 50 pl. Research, v. A64, p. 396–404. phosphorous on oceanic primary production: Nature, Veizer, J., 1989, Strontium isotopes in seawater through time: Swanson-Hysell, N.L., Rose, C.V., Calmet, C.C., Halverson, v. 400, p. 525–531, doi: 10.1038/22941. Annual Review of Earth and Planetary Sciences, v. 17, G.P., Hurtgen, M.T., and Maloof, A.C., 2010, Cryo- Urbanek, A., and Mierzejewska, G., 1977, The fi ne struc- p. 141–167, doi: 10.1146/annurev.ea.17.050189.001041. genian glaciation and the onset of carbon-isotope de- ture of zooidal tubes in Sabelliditida and Pogonophora Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, coupling: Science, v. 328, p. 608–611, doi: 10.1126/ with reference to their affi nity: Acta Palaeontologica F., Carden, G.A.F., Diener, A., Ebneth, S., Godderis, Y., science.1184508. Polonica, v. 22, p. 223–240, 18 pl. Jasper, T., Korte, C., Pawellek, F., Podlaha , O.G., and Swart, P.K., 2008, Global synchronous changes in the carbon Ushatinskaya, G.T., 1987, Unusual inarticulate brachiopods Strauss, H., 1999, 87Sr/86Sr, δ13C and δ18O evolution of isotopic composition of carbonate sediments unrelated from the Lower Cambrian sequence of Mongolia: Phanerozoic seawater: Chemical Geology, v. 161, p. 59– to changes in the global carbon cycle: Proceedings of Paleon tological Journal, v. 21, no. 2, p. 59–66. 88, doi: 10.1016/S0009-2541(99)00081-9. the National Academy of Sciences of the United States Ushatinskaya, G.T., 2001, Brachiopods, in Zhuravlev, A.Yu., Vendrasco, M.J., Li Guoxiang, Porter, S.M., and Fernandez, of America, v. 105, p. 13,741–13,745, doi: 10.1073/ and Riding, R., eds., The Ecology of the Cambrian C.Z., 2009, New data on the enigmatic Ocruranus- pnas.0802841105. Radiation: New York, Columbia University Press, Eohalobia group of Early Cambrian small skeletal fos- Swart, P.K., and Eberli, G., 2005, The nature of the δ13C of p. 350–369. sils: Palaeontology, v. 52, p. 1373–1396. periplatform sediments: Implications for stratigraphy Ushatinskaya, G.T., 2008, Origin and dispersal of the earli- Vendrasco, M.J., Porter, S.M., Kouchinsky, A., Li Guoxiang, and and the global carbon cycle: Sedimentary Geology, est brachiopods: Paleontological Journal, v. 42, p. 776– Fernandez, C.Z., 2010, New data on molluscs and their v. 175, p. 115–129, doi: 10.1016/j.sedgeo.2004.12.029. 791, doi: 10.1134/S0031030108080029. shell microstructures from the Middle Cambrian Gowers Swart, P.K., Elderfi eld, H., and Ostlund, G., 2001, The geo- Vail, P.R., Mitchum, R.M., Jr., Todd, R.G., Widmier, J.M., Formation, Australia: Palaeontology, v. 53, p. 97–135. chemistry of pore fl uids from bore holes in the Great Thompson, S., III, Sangree, J.B., Bubb, J.N., and Hatlelid, Vidal, G., and Moczydłowska-Vidal, M., 1997, Biodiver- Bahama Bank, in Ginsburg, R.N., ed., Subsurface W.G., 1977, Seismic stratigraphy and global changes of sity, speciation, and extinction trends of Proterozoic Geology of a Prograding Carbonate Platform Margin, sea level, in C.E. Payton, ed., Seismic stratigraphy— and Cambrian phytoplankton: Paleobiology, v. 23, Great Bahama Bank: Results of the Bahamas Drilling Applications to hydrocarbon exploration: American Asso- p. 230–246. Project: Society for Sedimentary Geology (SEPM) ciation of Petroleum Geologists Memoir 26, p. 49–212. Vincenz, S.A., Yaskawa, K., and Ade-Hall, J.M., 1975, Special Publication 70, p. 163–174. Valentine, J.W., 1994, Late Precambrian bilaterians: Grades Origin of the magnetization of the Wichita Moun- Sysoev, V.A., 1972, Biostratigrafi ya i khiolity ortotetsimorfy and clades: Proceedings of the National Academy tains granites, Oklahoma: Geophysical Journal of nizhego kembriya Sibirskoy platformy: Moscow, of Sciences of the United States of America, v. 91, the Royal Astronomical Society, v. 42, p. 21–48, doi: Nauka, 152 p. p. 6751–6757, doi: 10.1073/pnas.91.15.6751. 10.1111/j.1365-246X.1975.tb05848.x.

Geological Society of America Bulletin, November/December 2010 1773

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019 Maloof et al.

Vinn, O., 2006, Possible cnidarian affi nities of Torellella Wille, M., Nägler, T., Lehmann, B., Schröder, S., and Yue Zhao and Bengtson, S., 1999, Embryonic and post- (Hyolithelminthes, Upper Cambrian, Estonia): Paläon- Kramers , J.D., 2008, Hydrogen sulphide release to embryonic development of the Early Cambrian cnidarian tologische Zeitschrift, v. 80, p. 384–389. surface waters at the Precambrian/Cambrian boundary: Olivooides: Lethaia, v. 32, p. 181–195. Vinther, J., and Nielsen, C., 2005, The Early Cambrian Halk- Nature, v. 453, p. 767–769, doi: 10.1038/nature07072. Zenger, D.H., Dunham, J.R., and Ethington, R.L., eds., ieria is a mollusc: Zoologica Scripta, v. 34, p. 81–89, Wingate, M.T.D., Cambell, I.H., Compston, W., and Gibson , 1980, Concepts and Models of Dolomitization: So- doi: 10.1111/j.1463-6409.2005.00177.x. G.M., 1998, Ion microprobe U-Pb ages for Neo- ciety of Economic Paleontologists and Mineralogists Voronin, Yu.I., Voronova, L.G., Grigor’eva, N.V., Drozdova, protero zoic basaltic magmatism in south-central Aus- Special Publication 28, 320 p. N.A., Zhegallo, E.A., Zhuravlev, A.Yu., Ragozina, tralia and implications for the breakup of Rodinia: Zhang Junming, Li Guoxiang, Zhou Chuanming, Zhu A.L., Rozanov, A.Yu., Sayutina, T.A., Sysoev, V.A., Precambrian Research, v. 87, p. 135–159, doi: 10.1016/ Maoyan, and Yu Ziye, 1997, Carbon isotope profi les and Fonin, V.D., 1982, Granitsa dokembriya i kem- S0301-9268(97)00072-7. and their correlation across the Neoproterozoic- briya v geosinklinal’nykh oblastyakh (opornyy Wood, R.A., Grotzinger, J.P., and Dickson, J.A.D., 2002, Cambrian boundary interval on the Yangtze Platform, razrez Salany-Gol, MNR): Sovmestnaya Sovetsko- Proterozoic modular biomineralized metazoan from China: Bulletin of the National Museum of Natural Mongol’skaya Paleontologicheskaya Ekspeditsiya, the Nama Group, Namibia: Science, v. 296, p. 2383– Science (Taiwan), v. 10, p. 107–116. Trudy, v. 18, 150 p., 40 pl. 2386, doi: 10.1126/science.1071599. Zhao Yuanlong, Steiner, M., Yang Ruidong, Erdtmann, Voronova, L.G., Grigor’eva, N.V., Zhegallo, E.A., Missar- Worsley, T.R., Nance, D., and Moody, J.B., 1984, Global B.-D., Guo Qingjun, Zhou Zhen, and Wallis, E., 1999, zhevsky, V.V., and Sysoev, V.A., 1983, Vozrast sloev tectonics and eustasy for the past 2 billion years: [Discovery and signifi cance of the early metazoan “Oelandiella” korobkovi–Anabarella plana na Si- Marine Geology, v. 58, p. 373–400, doi: 10.1016/ biotas from the Lower Cambrian Niutitang Formation birskoy platforme: Izvestiya Akademii Nauk SSSR, 0025-3227(84)90209-3. Zunyi, Guizhou, China]: Acta Palaeontologica Sinica, Seriya Geologicheskaya, v. 1983, no. 12, p. 80–84. Wray, G.A., Levinton, J.S., and Shapiro, L.H., 1996, v. 38, supplement, p. 132–144, 2 pl. (in Chinese with Wagner, P.J., 1995, Diversity patterns among early gastro- Molecular evidence for deep Precambrian divergences English abstract). pods: Contrasting taxonomic and phylogenetic de- among metazoan phyla: Science, v. 274, p. 568–573, Zhou Chuanming, Zhang Junming, Li Guoxiang, and Yu scriptions: Paleobiology, v. 21, p. 410–439. doi: 10.1126/science.274.5287.568. Ziye, 1997, Carbon and oxygen isotopic record of the Walsh, G.J., Aleinikoff, J.N., Benziane, F., Yazidi, A., and Wright, J.E., Hogan, J.P., and Gilbert, M.C., 1996, The Early Cambrian from the Xiaotan Section, Yunnan, Armstrong, T.R., 2002, U-Pb zircon geochronology southern Oklahoma aulocogen: Not just another South China: Scientia Geologica Sinica, v. 32, p. 201– of the Paleoproterozoic Tagrara de Tata inlier and its B.L.I.P.: Eos (Transactions, American Geophysical 211 (in Chinese with English abstract). Neoproterozoic cover, western Anti-Atlas, Morocco: Union), v. 77, Fall Meeting supplement, p. 845. Zhu Maoyan, Li Guoxiang, and Zhang Junming, 2001a, Precambrian Research, v. 117, p. 1–20, doi: 10.1016/ Xiao, S., Zhang Yun, and Knoll, A.H., 1998, Three-dimensional New C isotope stratigraphy from southwest China: S0301-9268(02)00044-X. preservation of algae and animal embryos in a Neo- Implications for the placement of the Precambrian- Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P., and proterozoic phosphorite: Nature, v. 391, p. 553–558. Cambrian boundary on the Yangtze Platform and global Hill, A.C., 2000, Dating the 840–544 Ma Neo protero- Xiao, S., Yuan Xunlai, Steiner, M., and Knoll, A.H., correlations: Comment: Geology, v. 29, p. 871–872, doi: zoic interval by isotopes of strontium, carbon, and 2002, Macroscopic carbonaceous compressions in 10.1130/0091-7613(2001)029<0871:NCISFS>2.0.CO;2. sulfur in seawater, and some interpretive models: Pre- a terminal Proterozoic shale: A systematic reassess- Zhu Maoyan, Li Guoxiang, Zhang Junming, Steiner, M., cambrian Research, v. 100, p. 371–433, doi: 10.1016/ ment of the Miaohe biota, South China: Journal Qian Yi, and Jiang Zhiwen, 2001b, Early Cambrian S0301-9268(99)00082-0. of Paleontology, v. 76, p. 347–376, doi: 10.1666/ stratigraphy of east Yunnan, southwestern China: A Warthmann, R., van Lith, Y., Vasconcelos, C., McKenzie, 0022-3360(2002)076<0347:MCCIAT>2.0.CO;2. synthesis: Acta Palaeontologica Sinica, v. 40, supple- J.A., and Karpoff, A.M., 2000, Bacterially induced Xiao, S., Hu Jie, Yuan Xunlai, Parsley, R.L., and Cao Ruiji, ment, p. 4–39. dolomite precipitation in anoxic culture experi- 2005, Articulated sponges from the Lower Cambrian Zhuravlev, A.Yu., 1986a, Evolution of archaeocyaths and ments: Geology, v. 28, p. 1091–1094, doi: 10.1130/ Hetang Formation in southern Anhui, South China: palaeobiogeography of the Early Cambrian: Geo- 0091-7613(2000)28<1091:BIDPIA>2.0.CO;2. Their age and implications for the early evolution of logical Magazine, v. 123, p. 377–385, doi: 10.1017/ Weber, B., and Zhu Maoyan, 2003, Arthropod trace fos- sponges: Palaeogeography, Palaeoclimatology, Palaeo- S0016756800033471. sils from the Zhujiaqing Formation (Meishucunian, ecology, v. 220, p. 89–117. Zhuravlev, A.Yu., 1986b, Radiocyathids, in Hoffman, A., Yunnan) and their palaeobiological implications: Yao Jinxian, Xiao, S., Yin Leiming, Li Guoxiang, and Yuan and Nitecki, M.H., eds., Problematic Fossil Taxa: Ox- Progress in Natural Science, v. 13, p. 795–800, doi: Xunlai, 2005, Basal Cambrian microfossils from the ford, Oxford University Press, p. 35–44. 10.1080/10020070312331344450. Yurtus and Xishanblaq Formations (Tarim, north-west Zhuravlev, A.Yu., 2001, Biotic diversity and structure dur- Weber, B., Steiner, M., and Zhu Maoyan, 2007, Pre- China): Systematic revision and biostratigraphic cor- ing the Neoproterozoic–Ordovician transition, in cambrian-Cambrian trace fossils from the Yangtze relation of Micrhystridium-like acritarchs: Palaeontol- Zhuravlev, A.Yu., and Riding, R., eds., The Ecology of Platform (South China) and the early evolution of ogy, v. 48, p. 687–708. the Cambrian Radiation: New York, Columbia Univer- bilaterian lifestyles: Palaeogeography, Palaeoclimatol- Yin Leiming, Zhu Maoyan, Knoll, A.H., Yuan Xunlai, sity Press, p. 173–199. ogy, Palaeoecology, v. 254, p. 328–349, doi: 10.1016/ Zhang Junming, and Hu Jie, 2007, Doushantuo em- Zhuravlev, A.Yu., and Wood, R.A., 2008, Eve of biominer- j.palaeo.2007.03.021. bryos preserved inside diapause egg cysts: Nature, alization: Controls on skeletal mineralogy: Geology, Wefer, G., and Berger, W.H., 1991, Isotope paleontol- v. 446, p. 661–663. v. 36, p. 923–926, doi: 10.1130/G25094A.1. ogy: Growth and composition of extant calcareous Yochelson, E.L., 1969, Stenothecoida, a proposed new class species: Marine Geology, v. 100, p. 207–248, doi: of Cambrian Mollusca: Lethaia, v. 2, p. 49–62, doi: 10.1016/0025-3227(91)90234-U. 10.1111/j.1502-3931.1969.tb01250.x. MANUSCRIPT RECEIVED 4 JUNE 2010 MANUSCRIPT ACCEPTED 3 AUGUST 2010 Wilkinson, B.H., and Algeo, T.J., 1989, Sedimentary car- Yochelson, E.L., 1978, An alternative approach to the in- bonate record of calcium-magnesium cycling: Ameri- terpretation of the phylogeny of ancient mollusks: can Journal of Science, v. 289, p. 1158–1194. Malaco logia, v. 17, p. 165–191. Printed in the USA

1774 Geological Society of America Bulletin, November/December 2010

Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/122/11-12/1731/3400785/1731.pdf by Princeton University user on 09 September 2019