Middle Cambrian siliceous sponge-calcimicrobe buildups (Daegi Formation, Korea): Metazoan buildup constituents in the aftermath of the Early Cambrian extinction event

Sedimentary Geology 253-254 (2012) 47–57

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Middle Cambrian siliceous sponge-calcimicrobe buildups (Daegi Formation, Korea): Metazoan buildup constituents in the aftermath of the Early Cambrian extinction event Jongsun Hong a, 1, Seong-Hyeon Cho a, 1, Suk-Joo Choh a,⁎, Jusun Woo b, 2, Dong-Jin Lee c, 3 a b c

Department of Earth and Environmental Sciences, Korea University, Seoul 136–713, Republic of Korea Division of Polar Earth-System Sciences, Korea Polar Research Institute, Incheon 406–840, Republic of Korea Department of Earth and Environmental Sciences, Andong National University, Andong 760–749, Republic of Korea

a r t i c l e

i n f o

Article history: Received 26 November 2011 Received in revised form 21 January 2012 Accepted 23 January 2012 Available online 31 January 2012 Editor: B. Jones Keywords: Middle Cambrian (Series 3) Metazoan-microbial buildup Siliceous sponge Epiphyton

a b s t r a c t Numerous decimetre- to metre-scale carbonate buildups dominated by siliceous sponges and the calcimicrobe Epiphyton are reported from the Middle Cambrian (Series 3) Daegi Formation of Korea. These siliceous sponge-Epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and/or white clumps. The boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges. The white clumps and dark clots in the boundstones represent variously preserved Epiphyton. Siliceous sponges form constructional pore space and are commonly encrusted by Epiphyton. The sponges were probably the primary frame-builders, providing substrates for the attachment and subsequent growth of Epiphyton. Epiphyton is considered to be a binder when covering the surface of siliceous sponges, and a subordinate frame-builder when filling depositional voids created by siliceous sponges or growing on top of other Epiphyton growth bundles. The siliceous sponge-Epiphyton buildups of the Daegi Formation show similarities to previously described Late Cambrian (Furongian) anthaspidellid-calcimicrobe buildups from Iran and the USA. Together with recently reported examples from the Zhangxia Formation of eastern China, the sponge–Epiphyton buildups from Korea represent some of the oldest metazoan-calcimicrobe buildups, after the extinction of most archaeocyaths at the end of the Early Cambrian (Series 2). This implies that the incorporation of metazoans in Middle Cambrian (Series 3) carbonate buildups occurred much earlier than previously known. The buildup-forming siliceous sponges described in this study demonstrate that their role in Early Phanerozoic carbonate buildups has been grossly underestimated. © 2012 Elsevier B.V. All rights reserved.

1. Introduction The first metazoan-bearing carbonate buildups appeared in the early Neoproterozoic (Neuweiler et al., 2009), followed by those built by archaeocyath-calcimicrobe associations in the Early Cambrian (Terreneuvian and Series 2) (Rowland and Gangloff, 1988; Rowland and Shapiro, 2002). Renalcis-dominated archaeocyath-calcimicrobe buildups initially appeared on the Siberian Platform in the middle Early Cambrian (late Terreneuvian; Tommotian) and became widespread during the late Early Cambrian (early to middle Series 2; Atdabanian and Botomian), occurring throughout both Gondwana and Laurentia (Kruse et al., 1995; Riding and Zhuravlev, 1995). These buildups

⁎ Corresponding author. Tel.: + 82 2 3290 3180. E-mail addresses: [email protected] (J. Hong), [email protected] (S.-H. Cho), [email protected] (S.-J. Choh), [email protected] (J. Woo), [email protected] (D.-J. Lee). 1 Fax: + 82 2 3290 3189. 2 Fax: + 82 3 2260 6243. 3 Fax: + 82 5 4822 5467. 0037-0738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2012.01.011

consisted of metazoans such as archaeocyaths, radiocyaths, coralomorphs, cribricyaths, and siliceous sponges, together with various calcimicrobes, including Epiphyton, Renalcis, Girvanella and Botomaela (James and Gravestock, 1990; Wood et al., 1993; Wood, 1999; Rowland and Shapiro, 2002). Toward the end of the Early Cambrian (Series 2), metazoan-calcimicrobe buildups were composed of archaeocyaths of reduced diversity, as well as the calcimicrobes Renalcis, Epiphyton, Girvanella, and Serligia (Kobluk and James, 1979; James and Klappa, 1983; Rowland and Shapiro, 2002). The end-Early Cambrian (Series 2) extinction of archaeocyaths dramatically changed the characteristics of carbonate buildups (Zhuravlev, 1996) (Fig. 1); after the extinction, Middle Cambrian (Series 3) to earliest Ordovician carbonate buildups are typically dominated by the calcimicrobes Renalcis, Girvanella, and Epiphyton (Heckel, 1974; Wood, 1999; Rowland and Shapiro, 2002; Webby, 2002). Metazoans such as anthaspidellid sponges are sparse in Late Cambrian (Furongian) buildups (Table 1). In this study we document and assess buildups from the Middle Cambrian (Series 3) Daegi Formation of Korea, which represent some of the first metazoan-calcimicrobe buildups to occur after the end-Early Cambrian (Series 2) archaeocyath extinction. The buildups

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J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

Lower

Ordovician

(Ma) 480

Furongian

490

1st microbial-lithistid sponge-Calathium buildups15 Tremadocian

Stage 10 Stage 9 Paibian

Series 3

500

Guzhangian Drumian

Predominant microbial buildups with limited lithistid sponge and Lichenaria14 Girvanella-Tarthinia-anthaspidellid sponge buildups, Dotsero Fm.13 Microbial-anthaspidellid sponge buildups, Desert Valley Fm.12 Girvanella-anthaspidellid sponge buildups, Wilberns Fm.11 Anthaspidellid sponge-dendrolites buildups, Bonanza King Fm.10 Anthaspidellid sponge-Girvanella buildups, Mila Fm.9

Siliceous sponge-Epiphyton buildups, Daegi Fm.8 Epiphyton-thrombolite-anthaspidellid sponge buildups, Zhangxia Fm.7

Stage 5

Series 2

Cambrian

510 Stage 4

End-Early Cambrian (Series 2) extinction6 Decline of archaeocyath-calcimicrobe buildups5 Acme of archaeocyath-calcimicrobe mounds4

Stage 3

520

Terreneuvian

Stage 2

530

1st occurrence of archaeocyath-calcimicrobe buildups3

Fortunian Predominant stromatolitic buildups2

540 Cryogenian

-

-

Ediacaren

-

-

Tonian

-

-

Stenian

-

-

850

? 1st occurrence of sponge-like texture in mounds1

1000

Period of metazoan-microbial consortia in buildups

Period of predominant microbial components in buildups

Fig. 1. Evolutionary history of metazoan–microbial buildups from Late Proterozoic to Early Palaeozoic. 1: Neuweiler et al. (2009); 2: Rowland and Shapiro (2002); 3: Kruse et al. (1995), Riding and Zhuravlev (1995); 4: Rowland (1984), Debrenne et al. (1989, 2002), Álvaro and Clausen (2007), Hicks and Rowland (2009); 5: Kobluk and James (1979), James and Klappa (1983), Gandin and Luchinina (1993); 6: Rowland and Shapiro (2002); 7: Woo (2009), Park et al. (2011); 8: current study; 9: Hamdi et al. (1995), Kruse and Zhuravlev (2008); 10: Shapiro and Rigby (2004); 11: Johns et al. (2007); 12: Dattilo et al. (2004), Johns et al. (2007); 13: Johns et al. (2007); 14: Webby (2002); 15: Church (1974), Cañas and Carrera (1993), Pratt and James (1989).

documented in this study are compared with other Late Cambrian (Furongian) metazoan-calcimicrobe buildups from Iran and the USA, and their implications for the evolutionary pathway of Early Palaeozoic buildups are discussed. 2. Geological setting and study methods The Taebaeksan Basin is located in the east-central part of the Korean Peninsula where the Cambro-Ordovician mixed carbonate–

siliciclastic Joseon Supergroup overlies Precambrian metamorphic basement unconformably, and is overlain unconformably by the Carboniferous–Triassic Pyeongan Supergroup (Fig. 2A) (Choi, 1998). Based on palaeogeographical reconstructions, the basin is regarded as part of the North China Platform (Chough et al., 2000). In the northeastern Taebaeksan Basin, the Joseon Supergroup is represented by the Taebaek Group, which is subdivided into 11 lithostratigraphic units: Jangsan/Myeonsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol, Makgol, Jigunsan, and Duwibong formations, in ascending

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

49

Table 1 Reported occurrences of Middle (Series 3) to Late Cambrian (Furongian) metazoan-calcimicrobe buildups. Note the common occurrence of lithistid anthaspidellid sponges as metazoan component of buildups (except in the current study). Formation & Location

Age

Occurrence

Reference

Desert Valley Fm. Central USA Desert Valley Western USA Wilburns Fm. South-central USA

late Late Cambrian (Furongian; Stage 9–10) late Late Cambrian (Furongian; Stage 9–10) mid-Late Cambrian (Furongian; Stage 9)

Johns et al. (2007)

Bonanza King Fm. Western USA Mila Fm. Northern Iran Daegi Fm. Eastern Korea Zhangxia Fm. Eastern China

early Late Cambrian (Furongian; Paibian) early Late Cambrian (Furongian; Paibian) mid-Middle Cambrian (Series 3; Drumian) early Middle Cambrian (Series 3; Stage 5)

Girvanella-Tarthinia and anthaspidellid sponge boundstone; Buildup overlies a flat-pebble conglomerate bed; Up to 1.5 m thick Microbial reef with local patch of anthaspidellid sponge; Buildup surrounded with oolite; Up to 13 m thick Calcimicrobial (Girvanella and minor Tarthinia, Epiphyton and Renalcis) thrombolite with anthaspidellid sponge; Interreef sediments of eocrinoid grainstone to feldspathic siltstone; 0.5–10 m wide and up to 1 m thick Anthaspidellid sponge-dendrolite patch reefs with Renalcis-like microbes; Buildups surrounded by bioturbated dolowackestone and dolomudstone; 1–10 m thick Anthaspidellid sponge encrusted by Girvanella-like calcimicrobe filaments; Buildups enclosed within calcareous grainstone to rudstone; Metre-scale bodies Siliceous spiculate sponge-Epiphyton buildups; Very rare octagonal cone-shaped fossil; Interbedded with wackestone to bioclastic packstone; Decimetre- and metre-scale bodies Epiphyton-thrombolite bioherm with local anthaspidellid sponge and octagonal cone-shaped organisms; Bioherm surrounded by skeletal, oolitic, and oncolitic packstone to grainstone; Up to 30 m wide and 7 m thick

order (Choi, 1998; Choi and Chough, 2005). The study area is located about 20 km southeast of Taebaek City, where the 1100-m-thick Taebaek Group is well exposed along a forest service road (Choi et al., 2004) (Fig. 2B). The Daegi Formation, the lowest limestone-bearing unit in the Taebaek Group, is about 170 m thick in study area (Fig. 2C). The formation is interpreted to have been deposited in a shallow-marine setting, in lagoons, ooid shoals, mounds, and on the shallow shelf (Yun, 1978; Kim and Park, 1981; Park and Han, 1986, 1987; Park et al., 1987; Choi et al., 2004; Kwon et al., 2006; Sim and Lee, 2006). The Daegi Formation contains diverse invertebrate fossils, and a recent estimate of the geological range of the formation is from the late Stage 5 (early Middle Cambrian) to the middle Guzhangian (late Middle Cambrian). This estimate is based on the first appearance datum (FAD) of the Crepicephalina Biozone being lower than the lower boundary of Drumian, and the last appearance datum (LAD) of the Cyclolorenzela Biozone being considered to be in the middle of the Guzhangian (Geyer and Shergold, 2000; Kang and Choi, 2007; Peng et al., 2009) (Table 2). A 14-m-thick part of the outcrop with the best examples of the buildups, 48 m above the base of the formation, was selected for a detailed description of stacked siliceous sponge- and calcimicrobedominated buildups (Figs. 2C and 3). Microbial mounds consisting of Epiphyton and Renalcis have been previously recognized in the Daegi Formation (fig. 6A of Sim and Lee, 2006; Fig. 3I). The siliceous sponge-calcimicrobe buildup interval investigated in this study (Fig. 3) is located stratigraphically between the Crepicephalina and Amphoton trilobite biozones of Kang and Choi (2007), and is estimated to be early to middle Drumian. Seventy-nine samples were collected from the outcrop window, from which 101 large-format (5.2 × 7.6 cm) thin sections and 25 standard (2.7 × 4.9 cm) thin sections were cut vertically and horizontally with respect to bedding. Large-format thin sections and slabs were digitized by photographing them using a DSLR camera with a close-up lens (15.1 million total pixels), and the images used as a base map and digital archive for further petrographic analysis (e.g., De Keyser, 1999; Choh and Milliken, 2004). 3. Results 3.1. Field analysis Numerous siliceous sponge-calcimicrobe and calcimicrobedominated buildups were identified from the 45 to 140 m stratigraphic interval of the formation (Fig. 2C). The buildups were recognized in outcrop based on their lenticular to convex-upward, probable bulbous

Dattilo et al. (2004) Johns et al. (2007) Johns et al. (2007)

Shapiro and Rigby (2004) Hamdi et al. (1995) Kruse and Zhuravlev (2008) This study Woo (2009) Park et al. (2011)

and tabular geometries, and their clotted and/or millimetre-sized white clumpy texture at both outcrop- and slab-scale observation (Fig. 3). We divided the buildups into two groups based on size: smaller, decimetre-scale bodies in the range of ~0.2–0.6 m, and larger, metrescale bodies with a maximum thickness of 2.3 m. Because of the dip angle of the strata, the true lateral dimensions of most metre-scale bodies could not be accurately determined at outcrop. These buildups are enclosed by well-bedded grey wackestone to skeletal packstone with siliceous sponge spicules, peloids, trilobites, and eocrinoid fragments (Figs. 2C and 3). The buildup boundstones were subdivided into two textural types: (1) pale grey micritic boundstones with dark clots and/or white clumps (Fig. 4A and B), and (2) pale grey boundstones with thin, arcuate and elongate components and white clumps (Fig. 4C and D). The pale grey micritic boundstone with dark clots and/or white clumps is volumetrically the most prevalent rock type and is generally associated with both the decimetre- and metre-scale, lenticular to convex-upward and tabular buildups (Fig. 3). These white clumps and dark clots are composed mainly of poorly to well-preserved Epiphyton bundles. Most Epiphyton bundles are preserved as dark clots in the Daegi Formation, and white clumps are relatively rare. The remainder of pale grey micritic boundstone consists mostly of variously preserved siliceous sponges. It should be noted, however, that the remains of siliceous sponges are hardly recognizable at the field and slab scale, and microscopic examination is required for effective detection of the sponges. The pale grey boundstone with white clumps, along with thin, arcuate and elongate components occurs locally in metre-scale lenticular to convex-upward buildups (Fig. 3III, V, VII and VIII). The buildups have crusts of Epiphyton and Girvanella. 3.2. Thin section analysis 3.2.1. Siliceous sponge-Epiphyton boundstone facies Siliceous sponge and Epiphyton are the dominant constituents of boundstones in buildups of the Daegi Formation. The key criteria for recognition of the buildups are the presence of sponges and Epiphyton, and constructional pore spaces filled with sediment and cement (Fig. 5A–D). Siliceous sponges in the boundstones commonly show irregular morphology (Figs. 5A, B, and 6A) with variously preserved spicule networks. Lithistid sponges with a typical tube shape are very rare (Fig. 5G). These siliceous spiculate sponges show a wide range of preservational states, from well-preserved spicule networks (Figs. 5C and 6A), to peloidal fabrics with faint sponge spicules (Fig. 6B and C) to masses of randomly scattered sponge spicules (Fig. 6D). Wellpreserved spicule networks consist of aligned, slightly curved to

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

China 40°N

Korea

Daegi Formation Post-Ordovician sedimentary rocks

35°

125°E

130°

Taebaek

major fault

A

10 km PS

N

Dw Jg

Precambrian basement

Mg

Dm

Fa

ult

Dj

lri

Hj

Gw

an

gh

wa

Ss

Dg

0

1 km

Sesong Fm.

Joseon Supergroup Precambrian basement

Mb Ms

B

Shale

Oolitic grainstone

Nodule-bearing shale

Dolostone

Wackestone to packstone

Skeletal packstone to grainstone

Siliceous spongecalcimicrobe buildup

Covered

160 m

Middle Cambrian (late Stage 5 to middle Guzhangian)

50

Intrusion 140 m

120 m

100 m Daegi Fm. 80 m

60 m Fig. 3 40 m

20 m

0m Myobong Fm.

Sh/MW P G

C

Fig. 2. (A) Simplified geological map of the north-eastern Taebaeksan Basin (modified from Sim and Lee, 2006). (B) Geological map of the study area (modified from Choi et al., 2004). Ms = Myeonsan Formation, Mb = Myobong Formation, Dg = Daegi Formation, Ss = Sesong Formation, Hj = Hwajeol Formation, Dj = Dongjeom Formation, Dm = Dumugol Formation, Mg = Makgol Formation, Jg = Jigunsan Formation, Dw = Duwibong Formation, PS = Pyeongan Supergroup. (C) Simplified measured section of the Daegi Formation in the study area. Black and white arrows indicate the stratigraphic position and location of the outcrop described in Fig. 3, respectively. Shale or mudstone (Sh/M), wackestone (W), packstone (P), and grainstone (G).

irregularly or rectangularly arranged spicules, with diameters ranging from 60 to 70 μm. These networks commonly grade laterally into pockets of subangular, ovoid to globular, peloidal (diameters from 10 to 500 μm) fabric with fuzzy outlines and spicules. These spicule networks are interpreted to be the calcified remains of siliceous sponges. Peloidal fabrics with spicules appear to represent the remains of poorly calcified siliceous sponges (e.g., Warnke, 1995; Warnke and Meischner, 1995; Adachi et al., 2009), whilst random masses represent spicules that became scattered after the decay of soft sponge bodies (Beauchamp, 1989; Warnke and Meischner, 1995). In the boundstones, Epiphyton commonly consists of branching, circular to slightly curved, micritic filaments with diameters of 20 to 55 μm that form bushshaped growth bundles. Dark clots of the pale grey micritic boundstone observed in outcrop and in polished slabs commonly contain faint Epiphyton thalli or upward-widening micritic masses with a height of

less than 2 mm. These features are interpreted to be poorly preserved Epiphyton growth bundles (e.g., Pratt, 1984). Siliceous sponge-Epiphyton boundstones in the Daegi Formation typically contain preserved spicule networks and co-occurring bushshaped Epiphyton. Co-growth of siliceous sponges and Epiphyton created constructional pore spaces, which were later filled with internal sediments, drusy calcite cements, and rare late-stage quartz cements (Fig. 5A and C). The size of these constructional pore spaces varies widely, with larger pore spaces created by siliceous sponges being up to 8 mm in length, and smaller pore spaces associated with Epiphyton growth bundles being up to 1.5 mm in length. These siliceous sponges and Epiphyton boundstones can be further divided into three subtypes based on the relative proportions of sponges and Epiphyton: Sponge-Epiphyton boundstones, Epiphyton-dominated boundstones, and sponge-dominated boundstones. Siliceous sponge-

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

51

Table 2 Daegi formation trilobite biozones and their correlative biozones in North China (modified from Kang and Choi, 2007, Zhang, 2003, Kobayashi, 1966).

Taebaek, Korea Series

Stage

North China

Lithostratigraphy

Kobayashi (1966)

Kang and Choi (2007)

Lithostratigraphy

Zhang (2003)

Sesong Fm.

Drepanura Stephanocare

Drepanura Stephanocare

Gushan Fm.

Drepanura Blackwelderia

Olenoides

Cyclolorenzella

Guzhangian

DamesellaYabeia

Middle

Leiopaishania

Cambrian (Series 3)

Daegi Fm.

Zhangxia Fm.

Solenoparia

TaitzuiaPoshania

Drumian

Stage 5

Megagraulos

Amphoton Crepicephalina

Bailiella

Bailiella

Myobong Fm.

3m

B

3m

VII

II

#

?

BailiellaLioparia

I

Covered

V

VIII

Mantou Fm.

Epiphyton-dominated boundstones contain less than 10% siliceous sponges by volume and are characterized by dense, vertically to subvertically widening Epiphyton bundles (Fig. 5F). This subtype occurs scattered within small lenticular to convex-upward buildups surrounded by boundstones of the first subtype (Fig. 3II and III) or constitutes the entire body of a metre-scale buildup (Fig. 3VI). Sponge-dominated boundstones (Fig. 5G) occur as local pockets within metre-scale lenticular to convex-upward buildups (Fig. 3III, IV and VII) as well as decimetre-scale tabular (Fig. 3II) and lenticular bodies. The third subtype of boundstone consists commonly of well-preserved spicule networks, subordinate peloidal fabrics with spicules and

Epiphyton boundstones are composed of a subequal distribution of siliceous sponges and Epiphyton growth bundles, and are characterized by the co-growth of intermingled siliceous sponges and Epiphyton growth bundles (Fig. 5A). In this subtype, dense Epiphyton growth bundles are commonly attached to the top or side of siliceous sponges or other Epiphyton thalli showing upward to sideways branching. In some cases, Epiphyton growth bundles are attached to and hang upside-down from the roof of a constructional pore space (Fig. 5D and E). It is interpreted that the siliceous sponges provided suitable substrates for upward, sideward, and downward growth of Epiphyton bundles.

A

Amphoton Crepicephalina

VI ?

?

* x

?

x * # = sample locations

IV III

Covered

Legend Sponge-dominated boundstone

Sponge-Epiphyton boundstone

Epiphyton-Girvanella crust boundstone

Wackestone to packstone

Bedding plane

: Fig. 4A-B, 5A-E;

: Fig. 4C-D;

x : Fig. 5F;

: Fig. 5G, 6A;

Epiphyton-dominated boundstone Grainstone : Fig. 5H;

: Fig. 6B-C;

: Fig. 6D

Fig. 3. Panoramic view of an outcrop section showing multiple, stacked siliceous sponge-calcimicrobe buildups. (A) Each buildup body is recognized at outcrop by laterally thickening or thinning massive units and characteristic boundstone textures, such as clotted texture and/or the presence of white clumps. (B) Sketch of (A) with sample locations, outlines of each buildup body, and the distribution pattern of each boundstone type as determined from outcrop, slab, and microscope observations. Roman numerals in boxes indicate individual buildup bodies discussed in the text. Black arrow (I) denotes two decimetre-scale calcimicrobe buildups reported previously by Sim and Lee (2006).

52

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

A

B

1 mm

1 cm

D

C

2 mm

1 cm

Fig. 4. Two textural types of Daegi Formation buildups. (A) Photograph of a slab of pale grey micritic boundstone with dark clots and white clumps. Dark clots (white arrow) are commonly composed of poorly-preserved Epiphyton; white clumps (black arrow) consist of well-preserved Epiphyton. (B) Photomicrograph (plane-polarized light) of white clumps of pale grey micritic boundstone. Note that branching Epiphyton thallus appears as a series of peloids (e.g., Coniglio and James, 1985). (C) Slab of pale grey boundstone with white clumps and thin, arcuate to elongate, micritic components. Boundstone composed of Epiphyton (black arrow) and subvertically aligned Girvanella crust (white arrows). (D) Photomicrograph (plane-polarized light) of pale grey boundstone of Epiphyton and Girvanella crust. Epiphyton thalli (black arrow) and subvertically aligned arcuate Girvanella crusts (white arrows) associated with void-filling cements. Refer to Fig. 3 for the sample locations.

scattered spicules, and stromatactis-like pore spaces filled with sediment. Epiphyton is only rarely present (less than 10% by volume) in this type of boundstone. The matrix of the siliceous sponge-Epiphyton boundstone is composed mainly of micrite. The boundstone also contains a small quantity of trilobite and eocrinoid fragments, worm tubes, Renalcis, burrows, rare borings of well-preserved siliceous spicule networks, and very rare octagonal, cone-shaped organism (Fig. 5H) (Park et al., 2009, 2011). 3.2.2. Epiphyton–Girvanella crust boundstone facies The Epiphyton–Girvanella crust boundstone facies corresponds to the pale grey boundstone with arcuate-shaped components and white clumps. It is characterized by sparsely distributed, chamber- to bush-shaped Epiphyton thalli (up to 2 mm in length) growing attached to horizontally and vertically aligned arcuate Girvanella crusts (0.1– 1.0 mm in thickness and 2–13 mm in length). Individual Girvanella tubules are often poorly preserved in these Girvanella crusts, possibly due to neomorphism (e.g., James, 1981). Primary pore space is filled

with internal sediments consisting of peloids, micrites, as well as cement. This facies occurs locally as pockets surrounded by the siliceous sponge-Epiphyton boundstone facies (Fig. 3III), as a metre-scale lenticular body (Fig. 3VIII), or as the base of a metre-scale buildup (Fig. 3V) apparently grading upward into the sponge-Epiphyton boundstone facies. A well-preserved siliceous sponge spicule network is not associated with this boundstone facies, and only randomly scattered sponge spicules are present, with minor amounts of trilobite and eocrinoid fragments. This facies is interpreted to be the product of co-growth of Epiphyton bundles and Girvanella crusts where participation or preservation of siliceous sponges was minimal. 4. Discussion 4.1. Sedimentological role of siliceous sponges and Epiphyton Siliceous sponges were important reef constituents throughout the Phanerozoic and known to have assumed various sedimentological

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

A

53

B

1 cm

1 cm

C

D

Ep Sn

Ep

Cp I

Ep

downward growth of Epiphyton Ep Cp I Sn downward growth Cp of Epiphyton Ep Cp

F 2 mm

2 mm

E

Ep Cp

F

Ep

Sn

1 mm

1 mm

G

H Cp

I

Cp

Sn

I Sn 2 mm

I

1 mm

Fig. 5. (A) Photograph of a large-format thin section of siliceous sponge-Epiphyton boundstone. Darker grey area is siliceous sponge with preserved spicular network, and lighter grey area represents Epiphyton colonies growing on the surface of siliceous sponge. The remainder of constructional pore space is filled with internal sediments and cements. (B) Interpretive sketch of (A), highlighting the distribution and morphology of siliceous sponges (grey areas with black outlines) in siliceous sponge-Epiphyton boundstone. Note the irregular morphology of sponges. (C) Enlargement of dotted rectangle in (A) showing well-preserved spicular networks of siliceous sponges and Epiphyton growing attached to the surface of siliceous sponges. (D) Interpretative sketch of (C) showing the distribution of a well-preserved spicular network (Sn) of siliceous sponges, Epiphyton (Ep) growing from the surface of siliceous sponges, remaining constructional pore space (Cp) now filled with cements, and internal sediments (I) at the base of constructional pore space. (E) Enlargement of dotted rectangle in (D), showing Epiphyton (Ep) filaments apparently attached to the base of sponge and growing downward (white arrow), filling the bulk of primary pore space beneath siliceous sponge. (F) Photomicrograph of Epiphyton-dominated boundstone. Epiphyton grew vertically to subvertically on top of other Epiphyton growths. (G) Photomicrograph of siliceous sponge-dominated boundstone. Note the larger constructional pore space (Cp) than that of Epiphyton-dominated boundstone, and internal sediment (I) containing peloids and sponge spicules. (H) Rare example of toppled octagonal cone-shaped organism partially filled with internal sediment occurring within a sponge-dominated tabular buildup (Fig. 3-II). All photomicrographs in plane-polarized light. Refer to Fig. 3 for sample locations.

54

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57

A

B

Sn Pf Sn

1 mm

2 mm

D

C

1 mm

1 mm

Fig. 6. Range of preservation states of siliceous sponges in Daegi buildups. (A) Photomicrograph of well-preserved spicule network (Sn) with aligned, slightly curved to irregular pattern of spicules. (B) Networks (Sn) show a gradual transition to peloidal fabric (Pf) with spicules. (C) Enlargement of dotted rectangle in (B) showing various sizes of peloids (black arrows) and relicts of sponge spicules (white arrows). (D) Photomicrograph of a mass of randomly scattered sponge spicules. Some spicules show a rectangular pattern (arrows). All photomicrographs in plane-polarized light. Refer to Fig. 3 for the sample locations.

roles in diverse Phanerozoic buildups and reefs (Brunton and Dixon, 1994). Examples of this include: (1) siliceous sponges, represented by lithistid sponges, often being the main frame-builders in reefs, with characteristics such as in situ preservation of growth form and providing substrates for encrustation (Toomey, 1970; Narbonne and Dixon, 1984; Ellis et al., 1985; Wendt et al., 1989); (2) some lithistid sponges with dish-shaped or tabular forms are reported to have bound sediment (Narbonne and Dixon, 1984; Webb, 1987); and (3) cylindrical to conical lithistid sponges are also reported to have been possible sediment bafflers (Narbonne and Dixon, 1984). In siliceous sponge-Epiphyton buildups of the Daegi Formation, sponges, as the largest component of the buildup association, commonly formed primary constructional pore spaces that were subsequently filled with Epiphyton bundles, sediments and cements (Fig. 5A and B). In addition, the sponges provided the site of dense encrustation and upward, sideward and even downward growth of Epiphyton bundles (Fig. 5C–E). Consequently, the siliceous sponges of the Daegi buildups are considered to be probable primary frame-builders, based on their size and their ability to create cavities and substrates for Epiphyton to grow on and attach to. The calcimicrobe Epiphyton is one of the major constituents of buildups of the Cambrian to Early Ordovician (e.g., Riding and Toomey, 1972; James, 1981; Debrenne et al., 1989; James and Gravestock, 1990; Gandin and Luchinina, 1993; Álvaro et al., 2000;

Debrenne et al., 2002; Álvaro and Clausen, 2007; Woo et al., 2008; Adachi et al., 2009; Woo and Chough, 2010) and Late Devonian (Shen et al., 1997, 2005), and is also capable of assuming various sedimentological roles. These include: (1) acting as binders of larger framebuilding organisms by luxuriant encrustation on larger archaeocyaths, lithistid sponges, or Girvanella crusts (e.g., Riding and Toomey, 1972; Debrenne et al., 1989; Gandin and Luchinina, 1993; Álvaro et al., 2000; Álvaro and Clausen, 2007; Adachi et al., 2009); (2) acting as smallscale frame-builders which, except for the dimensions of the growth colonies, show similar characteristics to those of frame-building siliceous sponges (Debrenne et al., 1989; James and Gravestock, 1990; Shen et al., 1997, 2005); and (3) acting as bafflers of fine-grained sediments by the bush-like shape of their thalli (Riding and Toomey, 1972; Woo, 2009). In case of the Daegi buildups, in areas where it is dominant in the absence of larger taxa such as siliceous sponges or Girvanella crusts, Epiphyton grew on top of other Epiphyton growth bundles. In other situations, Epiphyton is intergrown with the larger components, forming dense encrustions with upward, sideward, and even downward growth habits. Therefore, Epiphyton is regarded as a subordinate frame-builder when filling depositional voids created by growth network of siliceous sponges or growing on top of other Epiphyton growth bundles. It is considered a sediment binder when densely colonizing the surfaces of sponges.

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Mixture of microbial colonies and sediments Disturbed finegrained sediments

Cone-shaped octagonal shells Geopetal sediment fill

Stromatolitic laminae

Cements

Sponge

Downward growth of

layered Epiphyton Angusticellularia Gradual increase in density of microbial colony Dense microbial colonies at the outermost part

Fig. 7. Microbial-metazoan carbonate buildup of the Zhangxia Formation (Middle Cambrian; Series 3), eastern China composed of thrombolites, Epiphyton masses, octagonal coneshaped organisms, and sponges. Octagonal cone-shaped organisms are marked by a dashed outline; sponges are marked by a white outline.

4.2. Comparison with other Middle to Late Cambrian metazoan-calcimicrobe buildups, and geological implication Early Cambrian (Terreneuvian and Series 2) carbonate buildups are characterized by calcimicrobes with metazoans such as archaeocyaths, radiocyaths, coralomorphs, cribricyaths and siliceous sponges (James and Gravestock, 1990; Wood, 1999; Rowland and Shapiro, 2002; Wood et al., 1993). Even though siliceous sponges are reported from these metazoan-microbial buildups, records of well-calcified and well-preserved siliceous spiculate sponges from Early Cambrian (Terreneuvian and Series 2) carbonate buildups are still scarce. Reported examples of siliceous sponges in Early Cambrian (Terreneuvian and

Series 2) carbonate buildups include scattered spicules in the matrix of the Tommotian archaeocyath-calcimicrobe buildups from Siberia (Kruse et al., 1995; Riding and Zhuravlev, 1995), siliceous sponge spicules occurring as one of the major components within the Atdabanian archaeocyath-siliceous sponge mud mounds from southern Australia (James and Gravestock, 1990; Brunton and Dixon, 1994), and scattered spicules in internal sediments of growth cavities of the Toyonian archaeocyath-calcimicrobe buildups from Canada (Kobluk and James, 1979). Although reefal sponges, such as anthaspidellids, survived the endEarly Cambrian (Series 2) archaeocyath extinction (e.g., Kruse, 1983), metazoan carbonate buildups were devastated by the extinction

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event. Carbonate buildups of the Middle Cambrian (Series 3) to earliest Ordovician are generally regarded as being dominated by calcimicrobes and being devoid of metazoans, with the exception of a few lithistid sponge-microbial buildups (Heckel, 1974; Zhuravlev, 1996; Wood, 1999; Rowland and Shapiro, 2002). These buildups commonly consist of tube- or cone-shaped lithistid anthaspidellid sponges with a regular, ladder-like skeleton (e.g., Finks, 1967) and one or more types of calcimicrobe such as Girvanella (Hamdi et al., 1995; Johns et al., 2007; Kruse and Zhuravlev, 2008), Renalcis and the related form Tarthinia (Mrozek et al., 2003; Shapiro and Rigby, 2004; Johns et al., 2007), and Epiphyton (Mrozek et al., 2003; Woo, 2009) (Table 1). The common traits of these buildups are decimetre- to metre-scale bodies encased in packstone to grainstone facies, indicating deposition in shallow subtidal environments, and the occurrence of anthaspidellid sponges surrounded by calcimicrobes. The proportion of anthaspidellid sponges in each example is highly variable, from a few anthaspidellid sponges scattered in thrombolite-Epiphyton buildups (Woo, 2009) to anthaspidellid sponges constituting up to ~30%–50% of the buildup volume (Hamdi et al., 1995; Shapiro and Rigby, 2004; Johns et al., 2007; Kruse and Zhuravlev, 2008). It has been suggested that these Late Cambrian (Furongian) anthaspidellid-calcimicrobe buildups were possibly formed by framework-building anthaspidellid sponges, which were subsequently encrusted by calcimicrobes (Hamdi et al., 1995; Kruse and Zhuravlev, 2008; Woo, 2009). Compared with these Upper Cambrian (Furongian) carbonate buildups, the Daegi Formation buildups are peculiar in that, rather than containing individual bodies of well-defined anthaspidellid sponges, they include siliceous sponges occurring widely as well-preserved siliceous spicule networks. These mid-Middle Cambrian (Series 3; early to middle Drumian) sponge-Epiphyton buildups reported in this paper represent one of the first metazoan-microbial buildup associations post-dating the endEarly Cambrian (Series 2) extinction (Fig. 1). The early Late Cambrian (Furongian; Paibian) anthaspidellid sponge-calcimicrobe buildups from Iran and the western USA (Hamdi et al., 1995; Shapiro and Rigby, 2004; Kruse and Zhuravlev, 2008) are generally considered to be the early forerunners of the Early Ordovician radiation of metazoan reefs (Dattilo et al., 2004; Kruse and Zhuravlev, 2008). However, in light of the current findings, we suggest that sponge-calcimicrobe buildups re-appeared significantly earlier than previously thought, less than 5 million years after the end-Early Cambrian (Series 2) extinction. We speculate that siliceous sponges possibly re-occupied the ecological niche of the archaeocyaths in carbonate buildups during the aftermath of the extinction. Other age-equivalent thrombolite-metazoan buildups in the North China Platform have been reported from the Zhangxia Formation in the eastern China (Woo et al., 2008). These buildups are characterized by Epiphyton, Angusticellularia, and a sessile metazoan association of cone- or tube-shaped anthaspidellid sponges and an octagonal, coneshaped organism (Park et al., 2009; Woo, 2009; Park et al., 2011) (Fig. 7). The sponge fauna, microbial community, and constructional mode of the buildups are similar to those of previously reported Upper Cambrian (Furongian) buildups. These parallel occurrences of different types of carbonate buildups are suggestive of rather diverse metazoan-related reef ecology in the Middle Cambrian (Series 3). In addition, as suggested by Johns et al. (2007), sponge-calcimicrobe buildup associations are believed to be much more extensive in the Middle Cambrian (Series 3) than previously identified. Given the variable preservation of siliceous spiculate sponges in the buildups and the difficulty in recognizing well-preserved spicule networks at outcrop, as affirmed in this study, it is likely that the role and contribution of siliceous spiculate sponges in the Middle (Series 3) to Late Cambrian (Furongian) carbonate buildups has been underestimated. This study also demonstrates the critical need for detailed petrographic studies of calcimicrobe-associated buildups, especially in the lower Palaeozoic, if we are to understand the early evolutionary history of Phanerozoic carbonate buildups.

5. Conclusion Numerous decimetre- to metre-scale carbonate buildups are reported from the Middle Cambrian (Series 3) Daegi Formation of Korea. The buildups are constructed of a co-growth of siliceous sponges and the calcimicrobe Epiphyton, and are surrounded by wackestones and skeletal packstones. Irregularly shaped siliceous sponges are often encrusted by smaller Epiphyton. Epiphyton attached to the top, side, or base of siliceous sponges or to other Epiphyton thalli showing upward to downward branching. Siliceous sponges are considered to be the probable primary frame-builder, providing substrate for the attachment and subsequent growth of Epiphyton. Epiphyton is considered to be a binder when covering the surface of a siliceous sponge, and a subordinate frame-builder when filling depositional voids created by siliceous sponges or growing on top of other Epiphyton growth bundles. The siliceous sponge-Epiphyton buildups of the Daegi Formation show similarities to anthaspidellid-calcimicrobe buildups of the Late Cambrian (Furongian) in terms of the sedimentological roles of the sponges, their association with calcimicrobes, their decimetre- to metre-scale dimensions, and their shallow subtidal origin. The Daegi buildups are, however, unique because of the presence of siliceous sponges. The siliceous sponge-Epiphyton buildups of the Daegi Formation are one of the earliest metazoan-calcimicrobe buildups known from after the endEarly Cambrian (Series 2) extinction, and indicate much earlier involvement of metazoans in Middle Cambrian (Series 3) carbonate buildups than previously regarded. This discovery demonstrates the critical need for re-evaluation of early Palaeozoic calcimicrobe-dominated mounds to better understand the Phanerozoic evolution of carbonate buildups. Acknowledgements This study was supported by a grant from the Korea Research Foundation (KRF-2007-331-C00247) to S.-J. Choh. We are grateful to E. Turner and S. Rowland for constructive comments on the manuscript. We appreciate S.-W. Kwon for his assistance in the field and for thin section preparation. We also thank T.-Y. Park for helpful discussions regarding Cambrian trilobite biozones. Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at doi:10.1016/j.sedgeo.2012.01.011. These data include Google maps of the most important areas described in this article. References Adachi, N., Ezaki, Y., Liu, J., Cao, J., 2009. Early Ordovician reef construction in Anhui Province, South China: a geological transition from microbial- to metazoandominant reefs. Sedimentary Geology 220, 1–11. Álvaro, J.J., Clausen, S., 2007. Botomian (Lower Cambrian) turbid- clear-water reefs and associated environments from the High Atlas, Morocco. In: Álvaro, J.J., Aretz, M., Boulvain, F., Munnecke, A., Vachard, D., Vennin, E. (Eds.), Palaeozoic reefs and bioaccumulations: climatic and evolutionary controls. Geological Society, London, pp. 51–70. Álvaro, J.J., Vennin, E., Moreno-Eiris, E., Perejón, A., Bechstädt, T., 2000. Sedimentary patterns across the Lower-Middle Cambrian transition in the Esla nappe (Cantabrian Mountains, northern Spain). Sedimentary Geology 137, 43–61. Beauchamp, B., 1989. Lower Permian (Artinskian) sponge-bryozoan buildups, southwestern Ellesmere Island, Canadian Arctic Archipelago. In: Geldsetzer, H.H.J., James, N.P., Tebbutt, G.E. (Eds.), Reefs, Canada and Adjacent Area, Memoir, vol. 13. Canadian Society of Petroleum Geologists, Calgary, Alberta, pp. 575–584. Brunton, F.R., Dixon, O.A., 1994. Siliceous sponge-microbe biotic associations and their recurrence through the Phanerozoic as reef mound constructors. Palaios 9, 370–387. Cañas, F., Carrera, M., 1993. Early Ordovician microbial-sponge-receptaculitid bioherms of the Precordillera, Western Argentina. Facies 29, 169–178. Choh, S.J., Milliken, K.L., 2004. Virtual carbonate thin section using PDF: new method for interactive visualization and archiving. Carbonates and Evaporites 19, 87–92.

J. Hong et al. / Sedimentary Geology 253-254 (2012) 47–57 Choi, D.K., 1998. The Yeongwol Group (Cambrian–Ordovician) redefined: a proposal for the stratigraphic nomenclature of the Joseon Supergroup. Geosciences Journal 2, 220–234. Choi, D.K., Chough, S.K., 2005. The Cambrian–Ordovician stratigraphy of the Taebaeksan Basin, Korea: a review. Geosciences Journal 9, 187–214. Choi, D.K., Chough, S.K., Kwon, Y.K., Lee, S.B., Woo, J., Kang, I., Lee, H.S., Lee, S.M., Sohn, Y.J., Lee, D.J., 2004. Taebaek Group (Cambrian-Ordovician) in the Seokgaejae section, Taebaeksan Basin: a refined lower Paleozoic stratigraphy in Korea. Geosciences Journal 8, 125–151. Chough, S.K., Kwon, S.-T., Ree, J.-H., Choi, D.K., 2000. Tectonic and sedimentary evolution of the Korean peninsula: a review and new view. Earth-Science Reviews 52, 175–235. Church, S.B., 1974. Lower Ordovician patch reefs in western Utah. Brigham Young University Geology Studies 21, 41–62. Coniglio, M., James, N.P., 1985. Calcified algae as sediment contributors to Early Paleozoic limestones: evidence from deep-water sediments of the Cow Head Group, western Newfoundland. Journal of Sedimentary Research 55, 746–754. Dattilo, B.F., Hlohowskyj, S., Ripperdan, R.L., Miller, J.F., Shapiro, R., 2004. Stratigraphic setting of an Upper Cambrian metazoan reef between the Nopah Formation to Goodwin Formation transition in southern Nevada. Geological Society of America Abstracts with Programs 36, 368. De Keyser, T.L., 1999. Digital scanning of thin sections and peels. Journal of Sedimentary Research 69, 962–964. Debrenne, F., Gandin, A., Rowland, S.M., 1989. Lower Cambrian bioconstructions in Northwestern Mexico (Sonora). Depositional setting, paleoecology and systematics of archaeocyaths. Geobios 22, 137–195. Debrenne, F., Gandin, A., Courjault-Radé, P., 2002. Facies and depositional setting of the Lower Cambrian archeocyath–bearing limestones of southern Montagne Noire (Massif Central, France). Bulletin de la Societe Geologique de France 173, 533–546. Ellis, P.M., Crevello, P.D., Eliuk, L.S., 1985. Upper Jurassic and Lower Cretaceous deepwater buildups, Abenaki Formation, Nova Scotia shelf. Society of Economic and Paleontologists and Mineralogists Core Workshop 6, 212–248. Finks, R.M., 1967. The structure of Saccospongia laxata Bassler (Ordovician) and the phylogeny of the Demospongea. Journal of Paleontology 41, 1137–1149. Gandin, A., Luchinina, V., 1993. Occurrence and environmental meaning of the Early Cambrian calcareous algae of the Tianheban Formation of China (Yangtse Area). In: Barattolo, F., De Castro, P., Parente, M. (Eds.), Studies on Fossil Benthic Algae. Societa Paleontologica Italiana Special volume 1, Mucchi, Modena, pp. 211–217. Geyer, G., Shergold, J.H., 2000. The quest for internationally recognized divisions of Cambrian time. Episodes 23, 188–195. Hamdi, B., Rozanov, A.Y., Zhuravlev, A.Y., 1995. Latest Middle Cambrian metazoan reef from northern Iran. Geological Magazine 132, 367–373. Heckel, P.H., 1974. Carbonate buildups in the geologic record: a review. In: Laporte, L.F. (Ed.), Reefs in time and space: SEPM Special Publication 18, Tulsa, Oklahoma, pp. 90–154. Hicks, M., Rowland, S.M., 2009. Early Cambrian microbial reefs, archaeocyathan interreef communities, and associated facies of the Yangtze Platform. Palaeogeography, Palaeoclimatology, Palaeoecology 281, 137–153. James, N.P., 1981. Megablocks of calcified algae in the Cow Head Breccia, western Newfoundland: Vestiges of a Cambro-Ordovician platform margin. Geological Society of America Bulletin 92, 799–811. James, N.P., Gravestock, D.I., 1990. Lower Cambrian shelf and shelf margin buildups, Flinders Ranges, South Australia. Sedimentology 37, 455–480. James, N.P., Klappa, C.F., 1983. Petrogenesis of Early Cambrian reef limestones, Labrador, Canada. Journal of Sedimentary Research 53, 1051–1096. Johns, R.A., Dattilo, B.F., Spincer, B., 2007. Neotype and redescription of the Upper Cambrian anthaspidellid sponge, Wilbernicyathus donigani Wilson, 1950. Journal of Paleontology 81, 435–444. Kang, I., Choi, D.K., 2007. Middle Cambrian trilobites and biostratigraphy of the Daegi Formation (Taebaek Group) in the Seokgaejae section, Taebaeksan Basin, Korea. Geosciences Journal 11, 279–296. Kim, J.Y., Park, Y.A., 1981. Sedimentological study on the Pungchon and the Hwajeol Formations, Gangweon–do, Korea. Journal of the Geological Society of Korea 17, 225–240. Kobayashi, T., 1966. The Cambro–Ordovician formations and faunas of South Korea, Part X, Stratigraphy of the Chosen Group in Korea and South Manchuria and its relation to the Cambro-Ordovician formations of other areas, Section A, The Chosen Group of South Korea. Journal of the Faculty of Science, University of Tokyo, Section II, 16, pp. 1–84. Kobluk, D.R., James, N.P., 1979. Cavity-dwelling organisms in Lower Cambrian patch reefs from southern Labrador. Lethaia 12, 193–218. Kruse, P.D., 1983. Middle Cambrian ‘Archaeocyathus’ from the Georgina Basin is an anthaspidellid sponge. Alcheringa 7, 49–58. Kruse, P.D., Zhuravlev, A.Y., 2008. Middle-Late Cambrian Rankenella-Girvanella reefs of the Mila Formation, northern Iran. Canadian Journal of Earth Sciences 45, 619–639. Kruse, P.D., Zhuravlev, A.Y., James, N.P., 1995. Primordial metazoan-calcimicrobial reefs: Tommotian (Early Cambrian) of the Siberian Platform. Palaios 10, 291–321. Kwon, Y.K., Chough, S.K., Choi, D.K., Lee, D.J., 2006. Sequence stratigraphy of the Taebaek Group (Cambrian-Ordovician), Mideast Korea. Sedimentary Geology 192, 19–55. Mrozek, S., Dattilo, B.F., Hicks, M., Miller, J.F., 2003. Metazoan reefs from the Upper Cambrian of the Arrow Canyon Range, Clark County, Nevada. Geological Society of America Abstracts with Programs 35, 500. Narbonne, G.M., Dixon, O.A., 1984. Upper Silurian lithistid sponge reefs on Somerset Island, Arctic Canada. Sedimentology 31, 25–50. Neuweiler, F., Turner, E.C., Burdige, D.J., 2009. Early Neoproterozoic origin of the metazoan clade recorded in carbonate texture. Geology 37, 475–478.

57

Park, B.K., Han, S.J., 1986. Middle Cambrian ooid shoal deposits: The oolitic carbonate rocks of lower Pungchon Limestone Formation, Korea. Journal of the Geological Society of Korea 22, 183–199 (in Korean with English abstract). Park, B.K., Han, S.J., 1987. Middle Cambrian back-reef deposits: carbonates interbedded in the lower part of Pungchon Limestone Formation, Korea. Journal of the Geological Society of Korea 23, 287–305 (in Korean with English abstract). Park, B.K., Han, J.H., Han, S.J., 1987. Cambrian peritidal mudstone deposits interbedded in the Pungchon Limestone Formation, Korea. Journal of the Geological Society of Korea 23, 60–66 (in Korean with English abstract). Park, T.-Y., Woo, J., Lee, S.-B., Choi, D.K., 2009. Middle Cambrian octagonal cup-shaped fossils from Shandong Province, China. 9th North American Paleontological Convention Abstracts, p. 69. Park, T.-Y., Woo, J., Lee, D.-J., Lee, D.-C., Lee, S.-B., Han, Z., Chough, S.K., Choi, D.K., 2011. A stem-group cnidarian described from the mid-Cambrian of China and its significance for cnidarian evolution. Nature Communications 2, 442. doi:10.1038/ncomms 1457. Peng, S., Babcock, L.E., Zuo, J., Lin, H., Zhu, X., Yang, X., Robison, R.A., Qi, Y., Bagnoli, G., Chen, Y., 2009. The Global boundary stratotype section and point (GSSP) of the Guzhangian Stage (Cambrian) in the Wuling Mountains, Northwestern Hunan, China. Episodes 32, 41–54. Pratt, B.R., 1984. Epiphyton and Renalcis - Diagenetic microfossils from calcification of coccoid blue-green algae. Journal of Sedimentary Research 54, 948–971. Pratt, B.R., James, N.P., 1989. Early Ordovician thrombolites, St. George Group, western Newfoundland. In: Geldsetzer, H.H.J., James, N.P., Tebbutt, G.E. (Eds.), Reefs, Canada and Adjacent Area, Memoir, vol. 13. Canadian Society of Petroleum Geologists, Calgary, Alberta, pp. 231–240. Riding, R., Toomey, D.F., 1972. The sedimentological role Epiphyton and Renalcis in Lower Ordovician mounds, Southern Oklahoma. Journal of Paleontology 46, 509–519. Riding, R., Zhuravlev, A.Y., 1995. Structure and diversity of oldest sponge-microbe reefs: Lower Cambrian, Aldan River, Siberia. Geology 23, 649–652. Rowland, S.M., 1984. Were there framework reefs in the Cambrian? Geology 12, 181–183. Rowland, S.M., Gangloff, R.A., 1988. Structure and paleoecology of Lower Cambrian Reefs. Palaios 3, 111–135. Rowland, S.M., Shapiro, R.S., 2002. Reef patterns and environmental influences in the Cambrian and Earliest Ordovician. In: Kiessling, W., Flügel, E., Golonka, J. (Eds.), Phanerozoic reef patterns: SEPM Special Publication Series No. 72, Tulsa, Oklahoma, pp. 95–128. Shapiro, R.S., Rigby, J.K., 2004. First occurrence of an in situ anthaspidellid sponge in a dendrolite mound (Upper Cambrian; Great Basin, USA). Journal of Paleontology 78, 645–650. Shen, J.W., Yu, C.M., Bao, H.M., 1997. A Famennian Renalcis-Epiphyton reef at Zhaijiang, Guilin, South China. Facies 37, 195–210. Shen, J., Teng, J., Pedoja, K., 2005. Middle and Late Devonian microbial carbonates, reefs and mounds in Guilin, South China and their sequence stratigraphic, paleoenvironmental and paleoclimatic significance. Science in China, Series D: Earth Sciences 48, 1900–1912. Sim, M.S., Lee, Y.I., 2006. Sequence stratigraphy of the Middle Cambrian Daegi Formation (Korea), and its bearing on the regional stratigraphic correlation. Sedimentary Geology 191, 151–169. Toomey, D.F., 1970. An unhurried look at a Lower Ordovician mound horizon, Southern Franklin Mountains, West Texas. Journal of Sedimentary Petrology 40, 1318–1334. Warnke, K., 1995. Calcification processes of siliceous sponges in Viséan Limestones (counties Sligo and Leitrim, Northwestern Ireland). Facies 33, 215–228. Warnke, K., Meischner, D., 1995. Origin and depositional environment of Lower Carboniferous mud mounds of northwestern Ireland. In: Reitner, J., Neuweiler, F., Flaijs, G., Vigener, M., Keupp, H., Meischner, D., Paul, J., Warnke, K., Dingle, P., Hensen, C., Schäfer, P., Gautret, P., Leinfelder, R., Hüssner, H., Kaufmann, B. (Eds.), Mud mounds: A polygenetic spectrum of fine-grained carbonate buildups, 32. Facies, pp. 32–42. Webb, G.E., 1987. Late Mississippian thrombolite bioherms from the Pitkin Formation of northern Arkansas. Geological Society of American Bulletin 99, 686–698. Webby, B.D., 2002. Patterns of Ordovician reef development. In: Kiessling, W., Flügel, E., Golonka, J. (Eds.), Phanerozoic reef patterns: SEPM Special Publication Series No. 72, Tulsa, Oklahoma, pp. 129–180. Wendt, J., Wu, X., Reihardt, J.W., 1989. Deep-water hexactinellid sponge mounds from the Upper Triassic of northern Sichuan (China). Palaeogeography, Palaeoclimatology, Palaeoecology 76, 17–29. Woo, J., 2009. Depositional environments and microbial sedimentation of the Zhangxia Formation (Middle Cambrian). Ph.D. dissertation, Seoul National University, Seoul, Korea. Woo, J., Chough, S.K., 2010. Growth patterns of the Cambrian microbialite: Phototropism and speciation of Epiphyton. Sedimentary Geology 229, 1–8. Woo, J., Chough, S.K., Han, Z., 2008. Chambers of Epiphyton thalli in microbial buildups, Zhangxia Formation (Middle Cambrian), Shandong Province, China. Palaios 23, 55–64. Wood, R., 1999. Reef evolution. Oxford University Press, Oxford. 414 pp. Wood, R., Zhuravlev, A.Y., Anaaz, C.T., 1993. The ecology of Lower Cambrian buildups form Zuune Arts, Mongolia: implications for early metazoan reef evolution. Sedimentology 40, 829–858. Yun, S.K., 1978. Petrography, Chemical composition and depositional environments of the Cambro–Ordovician sedimentary sequence in the Yeonhwa I Mine Area, Southeastern Taebaegsan Region, Korea. Journal of the Geological Society of Korea 14, 145–174. Zhang, W.T., 2003. Cambrian biostratigraphy of China. In: Zhang, W., Chen, P., Palmer, A.R. (Eds.), Biostratigraphy of China. Science Press, Beijing, pp. 55–119. Zhuravlev, A.Y., 1996. Reef ecosystem recovery after the Early Cambrian extinction. In: Hart, M.B. (Ed.), Biotic recovery from mass extinction events. Geological Society, London Special Publication 102, London, pp. 79–96.