Rhodoliths from deep fore-reef to shelf areas around Okinawa-jima, Ryukyu Islands, Japan

Marine Geology 282 (2011) 215–230

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Marine Geology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a r g e o

Rhodoliths from deep fore-reef to shelf areas around Okinawa-jima, Ryukyu Islands, Japan Shinya Matsuda a,⁎, Yasufumi Iryu b a b

Faculty of Education, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan

a r t i c l e

i n f o

Article history: Received 2 June 2010 Received in revised form 9 February 2011 Accepted 27 February 2011 Available online 11 March 2011 Communicated by J.T. Wells Keywords: rhodolith nongeniculate coralline alga encrusting foraminifer fore-reef Ryukyu Islands

a b s t r a c t The distribution, abundance, composition, and growth history of rhodoliths were investigated based on 222 grab samples and 202 submarine photographs taken from 223 sites arranged at regular intervals and on 13 additional samples (5 dredge and 8 grab samples). These samples were collected at water depths ranging from 15 to 970 m around Okinawa-jima, Ryukyu Islands, Japan. The rhodoliths grow in deep fore-reef to shelf areas at water depths of 50 to 135 m. Where rhodoliths occur, they cover 45% of the sea bottom. The rhodoliths are primarily spheroidal to ellipsoidal in shape (with mean diameters usually less than 8 cm); internally they are primarily composed of nongeniculate coralline algae and an encrusting foraminifer Acervulina inhaerens. The rhodoliths have envelopes of well-preserved, concentric to irregular laminations or, much more commonly, are bored and display various degrees of bioerosion. Constructional voids (primary spaces between encrusters) and borings range from empty to completely filled with unlithified and lithified mixtures of micrites and bioclasts. The bioerosion is more extensive with increasing water depth and is progressively much more pervasive at water depths greater than 90 m. The rhodoliths are covered with nongeniculate coralline algae and A. inhaerens associated with other epilithic skeletal and nonskeletal organisms. The living biotic cover on rhodoliths is relatively great down to water depths ~100 m; below this, the cover decreases rapidly with increasing water depth. Rhodoliths with similar size, shape, and composing organisms to those in the Ryukyu Islands are commonly found on deep fore-reef to shelf areas or on the banks and seamounts of tropical reef regions, likely as the combined result of ecological degradation (=decreased number and coverage) of hermatypic corals and the relative predominance of nongeniculate coralline algae and encrusting foraminifers in such areas. The slow accretion rates of rhodoliths (b 0.1 mm/year) indicate that their formation is commonly to frequently intermittent, probably because of their burial in the surrounding sediment. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Rhodoliths are algal nodules or unattached algal growths with a nodular form, consisting principally of nongeniculate coralline red algae. Rhodoliths are present in tropical to boreal regions and found from the intertidal zone to water depths exceeding 200 m in modern marine environments (Bosellini and Ginsburg, 1971; Bosence, 1983; Iryu, 1985; Foster, 2001); they are common constituents of fossil, especially Cenozoic, reefs and carbonate platforms. Many studies showed that rhodoliths are sensitive recorders of some environmental parameters (e.g., Bosellini and Ginsburg, 1971; Bosence, 1976; Foster, 2001; Bassi et al., 2009) and that their characteristics, such as shape, coralline algal growth form, coralline taxonomic assemblages, and diagenetic features, can be used as relatively significant paleoenvironmental indicators (e.g., Studencki, 1979; Bosence and Pedley, 1982; Braga and Martìn, 1988; Braga and Aguirre, 2001; Payri and Cabioch, 2004; Bassi, 2005; Checconi et al., 2010; Iryu et al., 2010). In ⁎ Corresponding author. Tel.: +81 98 895 8363; fax: +81 98 895 8316. E-mail addresses: [email protected] (S. Matsuda), [email protected] (Y. Iryu). 0025-3227/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2011.02.013

contrast, Reid and MacIntyre (1988) expressed doubt that those features have a predicable relationship with particular environmental conditions. Rhodoliths are abundant in the Ryukyu Group, Pleistocene reefcomplex limestones with associated siliciclastic marine and terrestrial deposits that crop out throughout the islands of the Central and South Ryukyus (=Ryukyu Islands) (Fig. 1). Rhodolith limestone is one of the major lithofacies of the group (MacNeil, 1960; Nakagawa, 1972; Nakamori et al., 1995a; Iryu et al., 1998; Iryu et al., 2006; Humblet et al., 2009). Minoura and Nakamori (1982) interpreted the depositional environment of the rhodolith limestone based on its stratigraphic position within the group and the rhodoliths' shape. They presumed that these rhodoliths originated in a shallow lagoon, grew while they rolled along the bottom of a sandy channel, and finally accumulated on a gentle fore-reef slope. An alternative interpretation was suggested by Iryu (1984, 1985), who concluded that the rhodoliths formed and accumulated in deep fore-reef to shelf areas at water depths exceeding 50 m. This interpretation was based on the stratigraphic position of rhodolith limestones that are widespread, encircling proximal coral limestones, and grade laterally into distal, poorly sorted detrital limestones, as well as the fact that the maximum elevation of rhodolith

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RHODOLITH COVER 60 % 40–60 %

<20 % Present (coverage not measured)

20–40 %

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Absent

Modified from Iryu et al. (2009b) Fig. 1. Distribution and coverage of fore-reef rhodoliths around Okinawa-jima and the neighboring islets based on sampling and submarine photographs. Ki = Kin Bay, N = Nakagusuku Bay, Se = Sesoko-jima, Tk = Tokashiki-jima, Z = Zamami-jima.

limestones is at least 50 m lower than that of the coral limestones (e.g., Okierabu-jima, Iryu et al., 1998; Toku-no-shima, Yamada et al., 2003). Additional supportive evidence was the discovery of modern analogs of the Pleistocene rhodoliths in fore-reef settings in the Ryukyus (Iryu, 1984, 1985). Subsequently, this interpretation was confirmed by intensive investigations of modern marine biota and sediments around Miyako-jima (Tsuji, 1993) and Okinawa-jima (Iryu et al., 1995), where rhodoliths are extensive and are the dominant component in deep forereef to shelf areas, in water depths ranging from 60 to 150 m and from 50 to 135 m, respectively. However, limited studies have been conducted on ecological aspects of the modern rhodoliths off the Ryukyus (Bassi et al., 2009, 2011). Modern rhodoliths that are common to abundant in deep fore-reef to shelf areas or on the banks and seamounts of tropical regions were termed fore-reef rhodoliths by Bosence (1983). Traditionally, such deep-water rhodoliths are studied based on grabbed and dredged samples (McMaster and Conover, 1966; Iryu, 1985; Reid and MacIntyre, 1988; Prager and Ginsburg, 1989; Tsuji, 1993; Foster et al., 1997; Marshall et al., 1998; Lund et al., 2000; Bassi et al., 2009). This method provides little ecologic information and is not suitable for verifying environmental conditions. High-resolution underwater camera/video images are more useful for ecological investigations on fore-reef rhodoliths (Littler et al., 1991; Iryu et al., 1995; Amado-Filho et al., 2007). Quantitative data on the distribution, standing stock, and primary productivity of deep-water rhodoliths were

first provided for the platform and slope of a seamount off San Salvador Island by Littler et al. (1991). However, only a few attempts have been made to quantify the two-dimensional spatial distribution, abundance, and biotic composition of rhodoliths at water depths greater than the capability of SCUBA surveys. This paper aims (1) to provide quantitative data on spatial and depth distributions and the abundance of modern rhodoliths in deep fore-reef to shelf areas around Okinawa-jima; (2) to describe their size, shape, internal structure, degree of bioerosion, and biotic composition; and (3) to demonstrate their significance as paleoenvironmental indicators. Because the rhodoliths examined in this study are composed of encrusting foraminifers, as well as nongeniculate coralline algae, the term foraminiferal–algal nodules (Reid and MacIntyre, 1988) or macroids (Hottinger, 1983; Bassi et al., 2011) might be more appropriate. However, the term rhodolith is used in this article because it has conventionally and traditionally been used in sedimentological, paleontological, and stratigraphical investigations on modern and Pleistocene deposits of coral reefs and associated shallow lagoons and fore-reefs in the Ryukyus and

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3. Materials and methods

because foraminifer-dominated and alga-dominated rhodoliths cannot be separated ecologically or morphologically.

Marine sediments around Okinawa-jima and the neighboring islets (Fig. 1) were investigated from aboard the R/V Tokai Daigaku Maru II (Nohara et al., 1980). Sediments were collected with a Smith–McIntyre grab and underwater photographs were taken by a camera mounted on the frame of the grab. Investigations were made at 223 sites, covering various topographic areas (bay, fore-reef slope, shelf, and shelf slope), at water depths ranging from 15 to 970 m (Appendix A). The sites were arranged at regular intervals of 5 km along lines from northeast to southwest and from northwest to southeast and roughly correspond the corners of squares with 5 km sides. Rhodolith coverage on the sea bottom was assessed using sketches of the underwater photographs. For this purpose, 57 well-defined photographs, taken perpendicular to the sea bottom, were selected from 202 shots. A limited amount of the sediment samples collected by the Tokai Daigaku Maru II were preserved except for several sites and almost all the rhodoliths had been decolorized. Therefore in order to study the size, shape, and composition of living organisms on rhodolith surfaces, we conducted to collect a large amount of “live” rhodoliths. For this purpose, rhodoliths were taken from four sites around the Kerama Bank (RN87D7, 79 m; RN88D5, 88 m; RN87D6, 98 m; and RN88D4, 102 m) by dredging and two sites off Ie-jima (RN88OK1, 82 m; RN88OK2, 124 m) with an Okean grab by the R/V Nagasaki Maru. These sites were selected to cover the whole water depth range of rhodoliths (50–135 m water depth). However, we could not collect samples from a shallower part of the range (50–79 m water depth). The sampled rhodoliths were dried onboard soon after collecting to preserve the colors of the living organisms. The upper living surface of the rhodoliths was photographed. Coverage of living organisms on the rhodolith surfaces (%) was calculated by using detailed sketches of enlarged (×5–8) photographs (i.e., coverage on the projective surface using a plan view of the rhodoliths). The internal structure, degree of bioerosion, and biotic composition were observed using thin sections and polished slabs of rhodoliths collected at nine sites at water depths ranging from 79 to 135 m to the

2. Study area The Ryukyus are located southwest of mainland Japan and consist of several tens of islands and islets, extending from Tanega-shima (30°44′N, 131°0′E) in the northeast to Yonaguni-jima (24°27′N, 123°0′E) in the southwest. These islands are arranged in a curve called the Ryukyu Arc, which is bounded by the East China Sea on the northwest and by the Pacific Ocean on the southeast. The climate in the Ryukyus is subtropical. Monthly mean seawater temperatures range from 21.5 °C to 29.0 °C at the surface and from 20.4 °C to 21.4 °C at a water depth of 150 m, where annual mean temperatures are 25.2 °C and 20.7 °C, respectively (Fig. 2). Annual mean salinity is 34.6 at the surface; it gradually increases with water depth and reaches a peak (34.8) at ~200 m. Most of the islands are rimmed by coral fringing reefs comprising two basic topographic zones: the reef flat and reef slope. The reef slope, a steep escarpment at the edge of the reef flat, occurs down to water depths of 50 m. The shelf around the Ryukyu Islands is mostly flat and slopes gently seaward. Its seaward margin (shelf edge) is at 90–170 m water depth. The width of the shelf ranges from 0 to 25 km (Hamamoto et al., 1979; Kato et al., 1982). Rhodoliths were found at 71 sites, ranging from 50 to 135 m water depth, on the fore-reef slope and shelf around Okinawa-jima (Fig. 1; Iryu et al., 1995). The number of sites was equivalent to 70% of all sampling sites (101 sites) in the deep fore-reef to shelf area (50 to 140 m deep). The spatial distribution of the rhodoliths was not uniform around the islands. The rhodoliths were found more frequently to the west of Okinawa-jima (around the Kerama Islets, Tonaki-jima, Aguni-jima, and Kume-jima and on the “Kerama Bank”) than around the island of Okinawa-jima. In the former area, shallow (mostly 50–100 m water depth) saddle-like ridges connect the islands and banks, and rhodoliths are very common in these areas. In contrast, they are not common in and offshore from Nakagusuku Bay and Kin Bay.

Water temperature (˚C) 16

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150

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August September October

250

November December 300 34.5

34.6

34.7

34.8

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34.9

35.0 Salinity Annual mean salinity

Fig. 2. Vertical profile of annual mean temperature, monthly mean temperature for coldest and warmest surface water throughout the year, and annual mean salinity of seawater off Okinawa-jima (127–128°E, 26–27°N) for 1906 to 2003. Data from JODC Data Online Service System provided by Japan Oceanographic Data Center (www.jodc.jhd.go.jp).

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west of Okinawa-jima (RN87D7, 79 m; OK-188, 80 m; RN88D5, 88 m; OK-128, 95 m; RN84D1, 96 m; RN87D6, 98 m; RN88D4, 102 m; OK-161, 118 m; and OK-190, 135 m). These sites were selected by the same reason mentioned above. A total of 332 thin sections and more than 300 slabs were examined. Rhodoliths collected from six sites with a Konishita grab during a GH08 cruise by the R/V Daini-Halurei Maru (Iryu et al., 2009b) were also cut for supplementary observations. Conventional 14C ages were obtained for 13 samples from 11 rhodoliths (Table 1) to calculate their accretion rates and to verify their autochthonous origin. The rhodoliths were cut into slices several millimeters thick. The outermost envelopes (~0.5 cm thick) and altered cores were removed, and the remaining parts were broken into very coarse sand-sized grains. After washing in an ultrasonic cleaner for 15 min, the grains of coralline algae and A. inhaerens were picked under a microscope. Unconsolidated sediments in the rhodoliths were completely removed during these procedures. Thin-section examination and X-ray diffraction analysis were performed to exclude samples containing significant amounts of marine cements. The samples (~20 g) were dated at Gakushuin University, using a Libby half-life of 5570 years. Terminology of coralline algal growth forms follows Woelkerling et al. (1993). Taxonomic concepts of coralline algae follow Harvey and Woelkerling (2007). 4. Results 4.1. Rhodolith coverage on the sea bottom Rhodoliths occur on the sea bottom composed of very coarse sand-sized to gravelly bioclasts of larger foraminifers (including Cycloclypeus carpenteri [Fig. 3A–D] and Operculina ammonoides), molluscs, bryozoans, solitary corals, echinoids, and brachiopods. Rhodolith coverage on the sea bottom varies greatly and ranges from 0.3% to 88%, averaging 45% (n = 57) where they occur. Coverage falls into two categories (Fig. 4): high coverage, exceeding 40% (Fig. 3A and B), and low coverage, less than 30% (Fig. 3C). High-coverage sites are confined to the saddle-like ridges to the west of Okinawa-jima, submerged banks to the west and southwest of Ie-jima, and around the shelf margins of Okinawa-jima and Aguni-jima (Fig. 1). Mud content in the sediments is significantly less at the high-coverage sites than at the low-coverage ones. No definite relationship was recognized between water depth and coverage; however, all of the deepest sites with rhodoliths (N110 m) have “high coverage” (Fig. 4). Rhodoliths cover 31% of the sea bottom of deep fore-reef to shelf areas at water depths of 50 to 140 m around Okinawa-jima: rhodoliths occur at Table 1 Radiocarbon dates for fore-reef rhodoliths and an altered rhodolith around Okinawajima. Nongeniculate coralline algae and encrusting foraminifers were still alive on four rhodoliths (Gak-13719, Gak-13722, Gak-13724, and Gak-14679/14680) at the time of collection by one of the authors (S.M.). The status was uncertain for the other rhodoliths because the materials had already faded by the time we retrieved them. However, the rhodoliths were in excellent states of preservation, implying that the encrusters might have been alive or died immediately after collection. 14

C Analysis #

Gak-13719 Gak-13722 Gak-13724 Gak-13725 Gak-13726 Gak-13727 Gak-13728 Gak-13729 Gak-13730 Gak-13731 Gak-13732 Gak-14679 Gak-14680

Site

Depth (m)

Diameter (mm)

Sample Type

Age (yr BP)

Bulk Bulk Bulk Bulk Bulk Inner Outer Bulk Bulk Bulk Bulk Outer Inner

660 ± 90 10 ± 100 40 ± 100 2750 ± 70 Modern 460 ± 70 60 ± 90 1810 ± 110 1910 ± 80 380 ± 90 620 ± 70 330 ± 90 1640 ± 90

RN87D6 RN87D7 RN84D1 OK-004 OK-083 OK-128

98 79 96 66 73 95

85 45 54 33 70 68

OK-176 OK-188 OK-190 OK-223 RN87D7

105 80 135 78 79

47 64 64 63 91

70% of the sampled sites, and the coverage averages 45% where they occur. Because the deep fore-reef to shelf, ranging in water depth from 50 to 140 m, is 2.4×103 km2 around Okinawa-jima, the area covered with rhodoliths is calculated to be 7.6×102 km2, which is ~40% of the area shallower than 50 m (1.9×103 km2), the primary water-depth range of coral reef growths. Although the area of coral reefs is unknown, it can be inferred that the rhodoliths are spread over less than half of the area shallower than 50 m, where mixed carbonate-terrigenous sediment dominates embayments, such as Nakagusuku and Kin Bays (Ujiié et al., 1983; Yamamoto and Ujiié, 1983). Consequently, it is assumed that the area covered with rhodoliths should be of the same order of magnitude as that occupied by the coral reefs. 4.2. Size and shape of rhodoliths Although the rhodoliths are generally pebble to cobble-sized with a mean diameter less than 8 cm (rarely up to 10 cm), the pebble-sized ones are much more dominant (Fig. 3B; Fig. 5). Locally, cobble-sized rhodoliths are abundant (e.g., Sites OK-162, OK-176, OK-191, and OK196; Fig. 3A). Such larger rhodolith-dominated sites are known from off Kikai-jima (Matsuda et al., 2010). Histograms of rhodolith size are unimodal at three sites (RN87D7, RN88D5, and RN88D4), bimodal at one site (RN88OK1), and do not have any significant peaks at two sites (RN87D6 and RN88OK2). There is no significant relationship between rhodolith size and living biotic cover. Rhodolith shapes are highly various from spheroidal, ellipsoidal, discoidal to irregular, with a bumpy, knobby, or rarely smooth surface. Unattached, sparsely fruticose forms of coralline algae (Lithothamnion australe and L. pulchrum) are also present. However, many plotted near the vertex corresponding to spheroidal shape in Sneed and Folk diagrams (Sneed and Folk, 1958) (Fig. 5). A similar feature is found in rhodoliths off Sesoko-jima (Bassi et al., 2009). 4.3. Living biotic composition on the rhodolith surfaces Nongeniculate coralline algae and an encrusting foraminifer (A. inhaerens) are the most dominant organisms on the outer surface of rhodoliths (Figs. 6 and 7A–E): their mean surface coverage is 34% and 10%, respectively. Serpulid worm tubes and sponges cover 5% of the surface. Subordinate to these are small filamentous and frondose algae (3%), peyssonneliacean algae (Cruoriella (?) sp. or Cruoriopsis (?) sp.) (2%), and bryozoans (1%). The mean surface coverage of Acervulina is less than one third of coralline algae coverage (10% versus 34%). In contrast, although the volume of Acervulina within rhodolith envelopes varies considerably, overall, it is greater than that of coralline algae. Acervulina generally forms thicker crusts than do the coralline algae, and it is a more significant framebuilder than coralline algae in many rhodoliths, despite its relatively low coverage. The living biotic cover on rhodoliths is ~50% or more down to water depths of 102 m. Below this, the coverage rapidly decreases and reaches a minimum of 31% at 124 m (Fig. 7F). This rapid decrease results mainly from a decrease in coralline algal coverage at water depths greater than 100 m. No significant relationship was found between the coverage of living organisms on rhodoliths and their size. Interspecific competition for space is clearly evident among between organisms on the surface of rhodoliths. Nongeniculate coralline algae and A. inhaerens dominate the surface, not necessarily outcompeting the other encrusters. 4.4. Nongeniculate coralline algal flora The nongeniculate coralline algae are mostly encrusting, warty, and lumpy; fruticose forms are rare. Twenty-eight species of nongeniculate coralline algae, belonging to the genera Spongites, Hydrolithon, Lithoporella, Lithophyllum, Mesophyllum, Lithothamnion, and Sporolithon (Fig. 8; Table 2), were identified. Of these, Lithothamnion is dominant and shows the greatest species diversity (11 species), which are identical to those

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Fig. 3. Photographs showing the occurrence of fore-reef rhodoliths on the sea bottom around Okinawa-jima. Underwater compass is 33 cm long. Arrows indicate a benthic foraminifer, Cycloclypeus carpenteri. (A) Concentration of up to cobble-sized rhodoliths (rhodolith coverage = 78%) ~ 16 km southwest of Tokashiki-jima, Kerama Islets, at a depth of 103 m (Site OK191). (B) Moderate to high concentration of rhodoliths (coverage = 64%) ~ 6 km west of Tonaki-jima, at a depth of 100 m (Site OK-150). Note that the sea bottom is paved with well-sorted pebble-sized rhodoliths in the right half of the photograph, which contrasts with the relatively sparse occurrence of cobble-sized ones in the left half of the photograph. (C) Sparse occurrences of rhodoliths (coverage = 4%) ~ 6.5 km southwest of Tokashiki-jima at a depth of 80 m (Site OK-203). Arrowheads point to rhodoliths. (D) Rhodoliths that are partially buried in ambient bioclastic sediment (compare with Fig. 4A), ~ 20 km southwest of Tokashiki-jima at a depth of 125 m (Site OK-186).

reported by Matsuda and Tomiyama (1988). Lithothamnion australe (Fig. 8D) and L. pulchrum occur as common rhodolith builders and are found as unattached thallial growths. However, comparisons of the other Lithothamnion species with hitherto-described Lithothamnion species have not been completed. We confirmed the occurrence of at least five Sporolithon species (Fig. 8E), including S. episoredion, S. molle, and undescribed species reported by Higa and Matsuda (2009). Spongites, which occurs in the whole range of the rhodoliths, is one of the major rhodolith-forming coralline algal genera, although it is not so common as Lithothamnion and Sporolithon. One encrusting species of

Lithophyllum, which may be conspecific with L. quadratum (Ishijima, 1954; Iryu et al., 2009a) (Fig. 8C), is common in shallower water (b~100 m water depth) off Okinawa-jima, whereas an undescribed Sporolithon species reported by Higa and Matsuda (2009) is dominant in deeper water (N~90 m) (Matsuda, 2004). Hydrolithon and Mesophyllum are comparatively minor components although they are local common. Only one Lithoporella species (L. melobesioides) has been found (Fig. 8B). This species occurs down to 135 m water depth, displaying no regular trend in abundance with depth. 4.5. Internal structure and components

100 HIGH COVERAGE

Coverage (%)

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60

40 LOW COVERAGE

20

0 0

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Depth (m) Fig. 4. Rhodolith coverage on sea bottom versus depth around Okinawa-jima.

Internally, rhodoliths have envelopes of concentric (Fig. 9A) to irregular (Fig. 9C, D, and E) skeletal encrustations, which are composed mainly of nongeniculate coralline algae and A. inhaerens (Fig. 8A) associated with subordinate peyssonneliacean algae. Other encrusting organisms, such as bryozoans and Homotrema rubrum (encrusting foraminifer), are present as minor constituents. Cyanobacterial filaments are rarely found among the skeletons of these encrusters. Some rhodoliths display distinct changes in the accretional direction of the envelopes (Fig. 9H). The nuclei of the rhodoliths are skeletal fragments of molluscs, larger foraminifers, and Halimeda; however, in many cases, they are not visible or identifiable because of extensive boring. Few rhodoliths have coral nuclei. In some rhodoliths, the shapes of the nuclei control the shapes of the rhodoliths. Rhodoliths display highly varying degrees of bioerosion (Fig. 9). Constructional voids and borings are commonly filled with bioclasts associated commonly with micrites. The bioclasts are coarsegrained sand-sized or finer and include larger foraminifers, molluscs,

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Frequency

RN87 D7 (79 m)

12 10 8 6 4 2 0

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Living Biotic Cover on Rhodoliths (%)

220

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Mean Diameter (mm)

Ellipsoidal

c:a

b:a

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120

Mean Diameter (mm) Living Biotic Cover on Rhodoliths (%)

Frequency

12

(a-b)/(a-c)

40

Mean Diameter (mm)

RN88 OK2 (124 m)

Discoidal

Mean Diameter (mm) Living Biotic Cover on Rhodoliths (%)

Frequency

12

120

60

Mean Diameter (mm)

RN88 D4 (102 m)

100

Mean Diameter (mm) Living Biotic Cover on Rhodoliths (%)

Frequency

12

80

80

Mean Diameter (mm)

RN87 D6 (98 m)

60

Mean Diameter (mm) Living Biotic Cover on Rhodoliths (%)

Frequency

12

40

100

Mean Diameter (mm)

RN88 D5 (88 m)

b:a

20

Mean Diameter (mm) Living Biotic Cover on Rhodoliths (%)

Frequency

12

c:a

40

Mean Diameter (mm)

RN88 OK1 (82 m)

Spheroidal

100

100

80

60

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b:a

40

20

0 20

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Mean Diameter (mm)

120

(a-b)/(a-c)

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

N = 37 N = 41 N = 30 N = 30 N = 30

N = Number of samples examined

N = 18

80 No living biotic cover (Including dead individuals/parts) Other sessile animals

60

Bryozoa

Alive

Surface cover on rhodoliths (%)

100

221

40

Frondose & filamentous algae Peyssonneliacean algae (dominated by Cruoriella (?) sp. or Cruoriopsis (?) sp.) Coralline algae

20

0 Site RN87 & D7 Depth 79 m

Acervulina inhaerens

RN88 OK1 82 m

RN88 D5 88 m

RN87 D6 98 m

RN88 D4 102 m

RN88 OK2 124 m

Fig. 6. Surface coverage of living organisms on in situ rhodoliths for different water depths. The rhodoliths were collected at four sites around the Kerama Bank (RN87D7, RN88D5, RN87D6, and RN88D4) and two sites off Ie-jima (RN88OK1 and RN88OK2).

coralline algae, echinoids, and less abundant bryozoans and Halimeda. Acicular sparry cements are common in conceptacle chambers and the constructional voids. The cement occurs as micro-botryoids, spheroids and isopachous blades. Using Feigl's stain and a titan yellow stain on thin sections, it was determined that the botryoidal cements in the conceptacle chambers are composed of aragonite and that the spheroidal and isopachous bladed cements in the constructional voids consist of aragonite or high Mg calcite. Coralline algal cell lumina are frequently filled with micrite. Within a single rhodolith, the inner part is more micritized and has more abundant micrite compared with the outer part. Even where micrite abounds in the cell lumina, the cell walls are not necessarily highly micritized. Filaments and their constituent cells are preserved and are clearly discernible with microscopy. “Boxwork rhodoliths,” which are characterized by a vacuolar, “boxwork” internal structure (Basso, 1998), were not recovered. 4.6. Bioerosion Rhodoliths have been commonly bored by bivalves, polychaetes, bacteria, algae, fungi and sponges. The degree of bioerosion and the state of preservation of the original rhodolith framework vary greatly with the water depth gradient. At water depths of 79 m (RN87D7) and 80 m (OK-188), relatively small to medium (b7 cm in diameter) rhodoliths show concentrically banded inner arrangement despite extensive inward bioerosion, and display a color gradation from the white surface to the dusty white center (Fig. 9A). Bioerosion is relatively pervasive in larger (N7 cm in diameter) rhodoliths (Fig. 9B). Large boring-bivalve traces of the ichnogenus Gastrochaenolites show a single chamber, straight and elliptical in shape, up to 1 cm long, and 0.4 cm width. The common ichnogenus for polychaetes with boring properties is Maeandropolydora which occurs as cylindrical bended or helicoidally arranged chambers with constant diameter (b0.3 cm). In many cases a void space, 1–2 cm width, formed by bioerosion occurs around the center in place of a nucleus and it is filled with unconsolidated mixtures of micrite and bioclasts originating from the sediment matrix. These bioclasts are coarse-grained sand-sized or finer and consist of benthic and planktonic foraminifers, bryozoans, molluscs, echinoids, and coralline algae. The superimposed laminae of coralline algae and/or A. inhaerens are bioeroded: borings, forming

interconnected boring void systems, are filled with unconsolidated sediments or, more commonly, empty. This laminar framework displays color gradations being more grayish inward. Bioerosion is progressively more pervasive at water depths greater than 90 m (OK-128, 95 m; RN84D1, 96 m; and RN87D6, 98 m; Fig. 9C, D and E). Large- to medium-sized rhodoliths (N5 cm in diameter) have been extensively bored. These rhodoliths consist of three parts grading one another: outer white part (b1 cm thick), middle pale gray part (b1 cm thick), and inner gray to brown part. This reflects that the bioerosion is more pervasive inward. The outer part is composed mainly of wellpreserved crusts of coralline algae and/or A. inhaerens. The inner framework has been largely destroyed by multi-cyclic borings (cylindrical, straight chambers and micro-galleries due to bacteria, fungi and algae). Maeandropolydora is frequent. The borings are empty or filled with lithified and/or unlithified micrite–bioclast mixtures. Remnants of encrusting organisms (coralline algae and/or A. inhaerens) appear to be floating in micrite–bioclast mixtures (Fig. 10). In contrast to large- to medium-sized rhodoliths, concentrically banded laminations are well preserved in smaller rhodoliths, especially those smaller than 3 cm in diameter. At water depths greater than 100 m (OK-161, 118 m and OK-190, 135 m), even relatively small rhodoliths show extensive bioerosion characterized by micro-galleries (Fig. 9F and G). The rhodoliths show an outer white part and an inner gray to dark gray part (bioeroded core) with or without a thin transitional zone between them, clearly emphasizing a more pervasive inward bioerosion (Fig. 5G). The inner core is commonly represented by framework-less mass. Many borings (Maeandropolydora) are found on the outer rhodolith surface not covered with living coralline algae or A. inhaerens. Comparison of similar-sized rhodoliths from different water depths revealed that (1) the inner gray bioeroded cores increase in volume with increasing water depth and (2) the borings on the rhodolith surface are more pervasive at greater water depths. 4.7. Radiocarbon ages Radiocarbon dating revealed that all analyzed rhodoliths are younger than 2750 years (Table 1), indicating that they formed after the sea level stabilized at the approximate present-day position

Fig. 5. Histograms showing rhodolith size (left), cross plots of coverage of living organisms on rhodoliths and their mean diameter (middle), and Sneed and Folk diagrams showing rhodolith shape (right). a, b, and c in the Sneed & Folk diagrams denote long, intermediate, and short axes, respectively.

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B

A

D

C

E F

Dead Individuals/Parts Alive Other Sessile Annimals Bivalvia Bryozoa Acervulina inhaerens

2 cm

Frondose & Filamentous Algae Peyssonneliacean Algae (Cruoriella (?) or Cruoriopsis (?) sp.) Coralline Algae Fig. 7. Sketch of living organisms on rhodoliths collected around the Kerama Bank and off Ie-jima. Biotic composition of the rhodolith surface is highly various from site to site and from sample to sample. The rhodoliths from sites RN87D7 (A), RN88D5 (C), and RN87D6 (D) are characterized by relatively high coverage of nongeniculate coralline algae. Noncoralline algal components are comparatively dominant at sites RN88OK1 (B) and RN88D4 (E). The coverage of living organisms is low at Site RN88OK2 where the water depth exceeds 120 m.

(Hongo and Kayanne, 2010). Two rhodoliths from OK128 and RN87D7 were less bioeroded than the others, which enabled sampling of the inner and outer envelopes; the accretion rates were calculated as 0.08 and 0.03 mm/year, respectively. 5. Discussion 5.1. Comparison with other fore-reef rhodoliths Fore-reef rhodoliths have been found in many tropical reefassociated shelves, banks, and seamounts (Bosence, 1983; Iryu, 1985; Foster, 2001). However, in many of the previous studies, their characteristic features were not described fully. Here, fore-reef rhodoliths from the Ryukyus are compared with those from the Mascarene Islands (Montaggioni, 1979), Gulf of Mexico (Rezak et al., 1985; Minnery, 1990), Florida (Prager and Ginsburg, 1989), San Salvador (Littler et al., 1991), eastern Caribbean Sea (Reid and MacIntyre, 1988), Bermuda (Focke and Gebelein, 1978), and Canary Islands (McMaster and Conover, 1966) based on the characteristics

listed in Table 3. The comparison shows that the following features are characteristic of fore-reef rhodoliths: (i) they are mostly pebble- to cobble-sized and spheroidal to ellipsoidal in shape; (ii) they are composed mainly of several individuals and species of nongeniculate coralline algae and several individuals of encrusting foraminifers (A. inhaerens in the Ryukyus, Miniacina miniacea and Carpenteria monticularis in the Mascarene Islands, and Gypsina plana or G. cf. vesicularis in the Atlantic Ocean), forming concentric to irregularly overlapping internal structures; and (iii) the rhodolith-forming algae are mainly thin, encrusting (and less commonly, warty to lumpy) forms. The biotic assemblage in deep fore-reef to shelf areas in the Ryukyus is comparable to an oligophotic (low light) assemblage (red algae and larger foraminifers) in somewhat deeper waters (~30– 150 m), as reported by Pomar (2001).

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

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Fig. 8. Thin section photomicrographs of rhodolith-building nongeniculate coralline algae and encrusting foraminifer. (A) Encrusting nongeniculate coralline algae (a), A. inhaerens (f), and bryozoa (br) (Site RN87D7, 79 m deep). (B) Superimposed thalli of Lithoporella melobesioides with a cavity of probable asexual (bi-/tetrasporangial) conceptacle (c) (Site RN87D7, 79 m deep). (C) Lithophyllum sp. with many conceptacle cavities (c) (Site RN87D7, 79 m deep). (D) Lithothamnion australe with asexual conceptacle cavities. Note mosaic cements within the conceptacle cavities (arrows) (Site OK-208, 80 m deep). (E) A. inhaerens (f) and Sporolithon sp. (s) with sporangial cavities (arrows) (Site RN87D6, 98 m deep).

Rhodolith coverage varies greatly in the Ryukyus. This contrasts well with that on the San Salvador Seamount (Littler et al., 1991), where the platform is quite uniformly covered (mean, 96%) with rhodoliths. This suggests that the oceanographic conditions and topography where rhodoliths are found vary greatly in the Ryukyus and include deep fore-reef and shelf areas, as well as isolated banks, compared with the San Salvador Seamount. Warm-temperate deep-water (N60 m water depth) rhodoliths off Fraser Island, Australia (Lund et al., 2000) are very similar in floral composition to those in the Ryukyus. In these areas, melobesioids (including Lithothamnion, Phymatolithon, and Mesophyllum) are common rhodolith formers and Sporolithon are abundant in deeper parts of the range of rhodolith formation (N90 m and N80 m water depth in the Ryukyus and off Fraser Islands, respectively). But encrusting foraminifers are not common in, and instead, peyssonnelicacean algae constitute a major component of the Fraser Island rhodoliths.

5.2. Rhodoliths as paleoenvironmental indicators Rhodoliths with the same features as those around Okinawajima have been known from deep fore-reefs and shelves around other islands of the Ryukyus since the mid-1980s: Amami-o-shima and around Kikai-jima (Matsuda et al., 2010), Tarama-jima (Iryu, 1984, 1985), Miyako-jima (Matsuda and Tomiyama, 1988; Tsuji, 1993), and Iriomote-jima and Ishigaki-jima (Matsuda and Tomiyama, 1988). It was noted in some articles published before the 1980s that algal nodules occur off Kume-jima, Miyako-jima, and Ishigaki-jima (Kamura et al., 1967; Yamazato et al., 1967). Thus, it is obvious that rhodoliths consisting mainly of coralline algae and an encrusting foraminifer (A. inhaerens) are abundant on deep fore-reefs and shelves throughout the Central and South Ryukyus and that their distribution is limited to water depths of 50 to 150 m. Iryu et al. (1995) noted that the upper bathymetric

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Table 2 Depth distribution of rhodolith-forming nongeniculate coralline algae. The relative abundance in the table refers to the percentage of thin sections in which each genus was present to the total number of sections examined. The majority of coralline algae from sites OK-161 and OK-190 could not be identified because they have been extensively bioeroded. Site Depth(m)

RN87D7 79

OK-188 80

RN88D5 88

OK-128 95

RN84D1 96

RN87D6 98

RN88D4 102

Spongites Hydrolithon Lithoporella Lithophyllum Mesophyllum Lithothamnion Sporolithon

C R C C + A C

C + + C + C C

A C R C + A C

C + + + + + +

R R A C + C A

R + R R + A A

C + + C + A A

OK-161 118

OK-190 135

+ + + +

+

A: Abundant (N20%), C: Common (10–20%), R: Rare (3–10%), +: Present (b3%).

limit for fore-reef rhodoliths (50 m) corresponds with the water depth below which hermatypic corals sharply decrease in number and coverage, although they thrive down to water depths ~ 100 m (Yamazato, 1972; Humblet et al., 2010). Our SCUBA survey down to water depths of 50 m reveals that algal-coated pebbles and cobbles are found on rather flat sea bottoms shallower than 50 m, as shown by Bassi et al. (2009); however, they have a thin coating

of coralline algae and differ from fore-reef rhodoliths by their lack of an envelope of concentric encrustations that consist of overgrowing coralline algae and/or encrusting foraminifers. The lowest limit (150 m) was thought to be indicative of the greatest water depth at which nongeniculate coralline algae and A. inhaerens can thrive, because living individuals have not been found in deeper water. Consequently, nongeniculate coralline

Fig. 9. Cross-sectional views and a thin section photo of fore-reef rhodoliths collected at water depths ranging from 79 to 135 m to the west of Okinawa-jima. Red arrows indicate unlithified bioclast–micrite mixtures. Note boring-bivalve traces of the ichnogenus Gastrochaenolites (G) and boring of the ichnogenus Maeandropolydora (polychaete) (M). (A) Rhodolith with wellpreserved encrustation of nongeniculate coralline algae and A. inhaerens (Site RN87D7, 79 m deep). (B) Rhodolith with irregular skeletal encrustations, which has been extensively bioeroded (Site OK-188, 80 m). (C) (D) and (E) Rhodolith composed of outer white (o), middle pale gray (m), and inner gray to brown (i) parts (C: Site OK-128, 95 m; D: Site RN84D1, 96 m; E: Site RN87D6, 98 m). (F) Extensively bioeroded rhodolith within very thin outer maninae (Site OK-161; 118 m). (G) Rhodolith consisting of this gray framework-less mass (bioeroded core) (i) and very thin white outer laminae (o) with a thin transitional zone between them (t) (Site OK 190; 135 m). (H) Rhodolith with an outer, whitish envelope that overlies an inner grayish part, which has been extensively bored and filled with a bioclast/micrite mixture (Site RN87D6, 98 m deep). Green arrows indicate growth directions of the rhodolith.

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225

depths greater than 60 m in Hawaii (Adey et al., 1982). Taking into account the flourish of Sporolithon at depths greater than ~ 90 m, the depth range of the rhodoliths is likely to be divided into upper Lithothamnion–Lithophyllum dominant zone (b~90 m) and lower Sporolithon zone (N~90 m). Mastophoroid species possessing large trichocytes, such as Hydrolithon onkodes, Neogoniolithon conicum, and N. variabile, which are characteristic of shallow coralline algal assemblages (Iryu and Matsuda, 1988, 1996; Matsuda, 1989; Iryu, 1992), do not occur in fore-reef rhodoliths. 5.3. Geological implications

Fig. 10. Thin section photo of an extensively bioeroded rhodolith (Site RN87D6; 98 m). Note that remnants of a skeletal encrustation (A. inhaerens; a) appear to be floating in multigenerational infilling sediments consisting of micrite–bioclast mixtures (1–3).

algae and A. inhaerens are overwhelmingly dominant compared with other benthos on deep fore-reef and shelf areas in the Ryukyus. The same is true for many other reef regions (Bosence, 1983; Iryu, 1985; Foster, 2001). The accretion rates estimated for rhodoliths from Okinawa-jima (0.03–0.08 mm/year) are very similar to those for rhodoliths from Miyako-jima (0.01–0.03 mm/year; Tsuji, 1993) and the Caribbean Sea (0.01–0.09 mm/year; Reid and MacIntyre, 1988). These values correspond to the total length/height of one to several cells/chambers of nongeniculate coralline algae or encrusting foraminifers that form forereef rhodoliths. This indicates that rhodolith accretion is not continuous; rather, it is commonly to frequently intermittent, probably as a result of repeated burial (Fig. 3D) and exposure. This interpretation is supported by disconformity in rhodoliths, such as distinct changes in the accretional direction of the envelopes (Fig. 9H) and the occurrence of altered cores, with extensive borings and infillings of micrite–bioclast mixtures in many rhodoliths examined (Fig. 9B, E, and G), as well as their occurrence as lag deposits between wave ripples (e.g., Site OK226). The slow accretion rates do not support the common view that a high-energy environment that causes frequent rotation is essential for their formation (Prager and Ginsburg, 1989). Instead, the strong current that was reported from the rhodolith-dominated deep-water shelves (e.g., Miyako-jima; Tsuji, 1993) may contribute to their formation, by sweeping bioclasts and exposing buried rhodoliths as well as by rarely rolling them. Abundant occurrence of borings on the rhodolith surface suggest a possible long residence time before the repeated burial. Rare occurrence of benthos such as echinoderms on the rhodolith-covered shelf in the Ryukyus (Iryu et al., 1995; Matsuda and Tomiyama, 1988; Bassi et al., 2011) does not indicate that the biotic seafloor activity plays an important role in rhodolith movement (Prager and Ginsburg, 1989). A possible link between the distribution of rhodolith and large foraminifer-dominated sediments on the outer shelf off Miyako-jima and nutrient-rich upwelling was reported (Tsuji, 1993). However, it is generally accepted that coralgal carbonate is specific to oligotrophic environments (Mutti and Hallock, 2003). The biotic assemblages of fore-reef rhodoliths from the Ryukyus are of environmental significance, because the rhodoliths contain encrusting frame builders typically found in deep water. A. inhaerens (identified as Gypsina plana) is found at water depths of 50 to 70 m off Sesoko-jima (Fig. 1) (Hohenegger, 1994). Despite the fact that many rhodolith-forming coralline algae have not been identified, their floral composition is peculiar to deep water. Some Lithothamnion species, including L. australe (Fig. 8D) and L. pulchrum, occur exclusively in fore-reef rhodoliths and have never been found growing in shallow reef environments. It is noteworthy that L. australe and L. pulchrum are characteristic of relatively deep environments; they are the two most abundant species at water

Rhodoliths that are abundant in the Pleistocene Ryukyu Group represent a good example of fore-reef rhodoliths in the fossil record (Iryu, 1997). As a result of field relationships and their similarity with regard to shape, coralline algal growth form, and biotic composition with present-day deep-water rhodoliths, rhodoliths of the Ryukyu Group are considered to have formed and accumulated in deep fore-reef to shelf areas, in water depths ranging from 50 to 150 m. Based on this fact and the distribution of marine biota and sediments around the Ryukyus, a single reef-complex deposit that is defined as the sequence which initiated during the lowstand, developed through the subsequent transgression and highstand, and terminated in the regression is discriminated within the Ryukyu Group, leading to a complete revision of its stratigraphy (Odawara and Iryu, 1999; Ehara et al., 2001; Sagawa et al., 2001; Oshimizu and Iryu, 2002; Yamada et al., 2003; Odawara et al., 2005; Yamamoto et al., 2006), although it was considered that the Ryukyu Group consists of terrace-forming deposits and that these terraces are an off lapping sequence of coral reefs (Inagaki et al., 2005). The restriction of two coralline algal species (Lithophyllum and undescribed Sporolithon species reported by Higa and Matsuda (2009)) to shallower and deeper water depth zones, respectively, within some of the rhodoliths off Okinawa-jima will enable more detailed reconstructions of their depositional environments. In their stratigraphic and paleontological studies, Matsuda (1995) and Nakamori et al. (1995b) noted that rhodoliths that are similar in size, shape, internal structure, and biotic composition to those examined in this study occur in fore-reef sediments on the Huon Peninsula, Papua New Guinea. Recently, similar rhodoliths were reported from the Pleistocene carbonate sequence in Tahiti (Iryu et al., 2010). The Tahitian rhodoliths were thought to represent a fore-reef environment, which was confirmed by paleobathymetric interpretations using assemblages of larger foraminifers (Fujita et al., 2010). Our study indicates that pebble (to cobble)-sized rhodoliths, composed mainly of nongeniculate coralline algae and an encrusting foraminifer (Acervulina and Gypsina), are common in deep fore-reef to shelf settings in tropical reef regions worldwide. Such rhodoliths are extensively exposed and easily observed in uplifted reef deposits at active margin settings. 6. Conclusions (1) Rhodoliths are found in deep fore-reef to shelf areas at water depths of 50 to 135 m around Okinawa-jima. These rhodoliths are found at 71 of 101 sampling sites on the fore-reef to shelf, where rhodolith coverage averages 45%. (2) Fore-reef rhodoliths are mostly spheroidal or ellipsoidal, usually smaller than 8 cm in mean diameter, and composed mainly of thin encrusting nongeniculate coralline algae and an encrusting foraminifer A. inhaerens. (3) Rhodoliths have envelopes of well preserved, concentric to irregular skeletal encrustations or, much more commonly, have been bored by bivalves, polychaetes, bacteria, algae, fungi and sponges. The borings are unfilled or have been filled with micrite– bioclast mixtures. Bioerosion seems to be more extensive with

Size

Main builders

Associated builders

Coralline–algal growth forma

Coralline–algal genera and speciesb

References

Mainly b 10 cm (rarely up to 15 cm)

Nongeniculate coralline algae, encrusting foraminifer (Acervulina inhaerens)

Annelids, molluscs, sponges, small filamentous and frondose algae, peyssonneliacean algae, bryozoans

Mostly encrusting to warty to lumpy

Tsuji (1993) This study

25–60 m

3–14 cm (mean size = 8.4 cm)

Nongeniculate coralline algae, encrusting foraminifers (Miniacina miniacea, Carpenteria monticularis)

Annelids (serpulids), bryozoans, molluscs

Mostly encrusting to warty to lumpy

Spongites, Hydrolithon, Lithoporella, Lithophyllum, Mesophyllum, Lithothamnion including L. australe and L. pulchrum, Lithoporella, Sporolithon Lithophyllum incrustans, Lithoporella melobesioides, associated with Porolithon, Lithothamnium, Dermatolithon, Hydrolithon

Atlantic Ocean Gulf of Mexico

45–80 m

1–20 cm

Not described

Not described

Florida

35–65 m

Coarse sand-sized to 9 cm

Nongeniculate coralline algae, Peyssonnelia sp., encrusting foraminifer (Gypsina sp.) Nongeniculate coralline algae, encrusting foraminifer (G. vesicularis), bryozoans.

Not described

Rezak et al. (1985) Minnery (1990) Prager & Ginsburg (1989)

San Salvador

67–91 m on platform, on slope to 290 m.

4–15 cm

Nongeniculate coralline algae, encrusting foraminifer (G. cf. vesicularis)

Encrusting foraminifers (Homotrema rubrum), sponges, serpulid and other polychaetes Encrusting corals (Madracis, Leptoseris, Porites)

Lithothamnium, Lithophyllum, Tenarea, Hydrolithon, Mesophyllum, Lithoporella, Archaelithothamnium, Melobesia Lithothamnium, Lithoporella, Tenarea, Mesophyllum, Lithophyllum, Archaelithothamnium Lithophyllum and other nongeniculate coralline algae

Eastern Caribbean

20–130 m (actively growing at 30 to 60 m)

2–15 cm

Nongeniculate coralline algae, encrusting foraminifer (G. plana)

Peyssonnelia sp., serpulid worm tubes, Homotrema rubrum, corals (encrusting forms of Porites astreoides, Madracis sp., and Stephanocoenia michelinii)

Reid & MacIntyre (1988)

Bermuda

50 m

3–12 cm

Nongeniculate coralline algae

Not described

Canary Islands

below 37 to 125 m

0.5–10 cm

Nongeniculate coralline algae

Foraminifers (mostly Homotrema rubrum), cheilostome bryozoans, small encrusting bivalves, serpulid worms, vermetid gastropods Benthic foraminifers, bivalves, worm tubes

Outer envelope: Mesophyllum syntrophicum, Neogoniolithon mammillare, Neogoniolithon sp., Hydrolithon børgesenii, Lithoporella? sp. Inner core: Mesophyllum syntrophicum?, Paragoniolithon sp., Archaelithothamnium cf. dimotum, Lithoporella? sp. Not described

Not described

Goniolithon accretum, Porolithon sp

McMaster & Conover (1966)

Up to cobble-sized

Nongeniculate coralline algae

Peyssonnelia sp., Polystrata sp., bryozoans, serpulid worms, encrusting foraminifers, vermetid gastropods

Encrusting, lumpy, and fruticose

Lithoporella, Lithophyllum, Mesophyllum including M. erubescens, Lithothamnion including L. australe, Phymatolithon, Sporolithon

Marshall et al. (1998), Lund et al. (2000)

Location

Depth

Pacific and Indian Oceans Ryukyu 50–150 m

Mascarene Archipelago

a b

Thallus morphology follows Woelkerling et al. (1993). Coralline–algal genera and species are cited as they are given in the papers listed.

Montaggioni (1979)

Littler et al. (1991)

Focke & Gebelein (1978)

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

Warm temperate region Off Fraser Island, 42–117 m eastern Australia

No significant cover of shallow water species, often with frutiose or lumpy forms Warty to encrusting

226

Table 3 Characteristic features of fore-reef rhodoliths over the glove. For comparison, characters of deep water rhodoliths in a warm temperate region from a depth range similar to those of fore-reef rhodoliths (east off Australia [Marshall et al., 1998; Lund et al. 2000]) are also shown.

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

increasing water depths and becomes pervasive at water depths greater than 90 m. (4) Nongeniculate coralline algae and A. inhaerens are major constituents on the surface of rhodoliths. The living biotic cover on the rhodoliths is relatively great down to water depths ~ 100 m. Below that, the coverage decreases rapidly with increasing water depth. (5) Rhodoliths with similar sizes, shapes, and composing organisms to those in the Ryukyus are commonly found on deep forereef to shelf areas or on the banks and seamounts of tropical reef regions. Thus, fore-reef rhodoliths are useful as paleoenvironmental indicators. (6) The predominance of rhodoliths in deep fore-reef to shelf areas in the Ryukyus may have resulted from ecological degradation (=decreased number and coverage) of hermatypic corals as well as the relative predominance of nongeniculate coralline algae and A. inhaerens at such a depth range. The slow accretion rates (b0.1 mm/year) indicate that rhodolith formation is commonly to frequently intermittent, probably as a result of their burial. Acknowledgements We are grateful to D. W. J. Bosence and K. Ishizaki for critical comments on the manuscript and improvement of the English text and to W. Ahr and L. Montaggioni for providing constructive suggestions for an earlier version of the manuscript. Thanks are also extended to M. Nohara for giving us the opportunity to examine samples and photographs around Okinawa-jima; the captain (S. Yata) and crew of the R/V Nagasaki Maru for onboard assistance; K. Arai and T. Itaki for providing rhodoliths collected during a GH08 Cruise; H. Oba and J. Hohenegger for identifying peyssonneliacean algae and A. inhaerens, respectively; K. Kigoshi for 14C dating; J. Nemoto for taking photographs; M. Shishido for making thin sections; and S. Iryu for preparing the manuscript. This work was funded, in part, by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan and from the Japan Society for the Promotion of Science (02640613, 11640465, and 20300261 to S.M. and 18340163 to Y.I.). We also thank Dr. J. T. Wells for the editorial handling and two anonymous reviewers for their constructive comments and suggestions. Appendix A. List of samples examined in this study

Site

Latitude (N)

Longitude (E)

Sites investigated by R/V Tokai Daigaku OK-001 26°14.1′ 127.38.1′ OK-002 26°11.7′ 127°35.9′ OK-003 26°07.7′ 127°35.9′ OK-004 26°04.0′ 127°36.2′ OK-005 26°02.0′ 127°38.0′ OK-006 26°02.1′ 127°42.0′ OK-007 26°03.9′ 127°44.1′ OK-008 26°06.0′ 127°47.9′ OK-009 26°04.0′ 127°49.3′ OK-010 26°06.0′ 127°49.9′ OK-011 26°04.0′ 128°51.2′ OK-012 26°06.1′ 127°53.1′ OK-013 26°04.1′ 127°54.2′ OK-014 26°06.0′ 127°55.0′ OK-015 26°08.0′ 128°53.1′ OK-016 26°07.8′ 128°56.7′ OK-017 26°07.9′ 128°00.0′ OK-018 26°10.9′ 128°00.2′ OK-019 26°14.0′ 128°00.1′ OK-020 26°13.05′ 128°59.3′ OK-021 26°13.0′ 127°57.1′

Depth Rhodolith Rhodolith Submarine (m) coverage photo (%) Maru II 54 P 50 P 56 66 P 106 P 330 84 P 59 P 255 71 P 270 130 430 220 48 120 360 180 120 120 60

10.1 30.0 75.0 55.0

78.6 70.7

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

227

Appendix A (continued) Site

Latitude (N)

Longitude (E)

Depth Rhodolith Rhodolith Submarine (m) coverage photo (%)

OK-022 OK-023 OK-024 OK-027 OK-028 OK-031 OK-034 OK-035 OK-036 OK-037 OK-038 OK-039 OK-040 OK-041 OK-042 OK-043 OK-044 OK-045 OK-046 OK-047 OK-048 OK-049 OK-050 OK-051 OK-052 OK-053 OK-054 OK-055 OK-056 OK-057 OK-058 OK-059 OK-060 OK-061 OK-062 OK-063 OK-064 OK-065 OK-066 OK-067 OK-068 OK-069 OK-070 OK-071 OK-072 OK-073 OK-074 OK-075 OK-076 OK-077 OK-078 OK-079 OK-080 OK-081 OK-082 OK-083 OK-084 OK-085 OK-086 OK-087 OK-088 OK-089 OK-090 OK-091 OK-092 OK-093 OK-094 OK-095 OK-096 OK-097 OK-098 OK-099 OK-100 OK-101

26°13.1′ 26°13.0′ 26°13.1′ 26°15.2′ 26°11.2′ 26°11.1′ 26°15.1′ 26°11.0′ 26°12.0′ 26°14.1′ 26°12.1′ 26°10.0′ 26°10.1′ 26°11.9′ 26°14.1′ 26°15.9′ 26°18.1′ 26°20.0′ 26°22.0′ 26°24.0′ 26°26.0′ 26°28.0′ 26°27.0′ 26°25.0′ 26°25.0′ 26°25.0′ 26°24.9′ 26°25.0′ 26°24.0′ 26°13.0′ 26°15.0′ 26°17.0′ 26°19.1′ 26°21.1′ 26°22.8′ 26°25.1′ 26°27.0′ 26°29.1′ 26°56.0′ 26°53.8′ 26°54.1′ 26°53.8′ 26°52.0′ 26°52.0′ 26°51.9′ 26°52.2′ 26°51.7′ 26°52.0′ 26°52.0′ 26°50.0′ 26°50.0′ 26°49.9′ 26°50.2′ 26°50.0′ 26°50.0′ 26°47.9′ 26°48.1′ 26°48.2′ 26°48.3′ 26°48.0′ 26°48.0′ 26°47.8′ 26°48.2′ 26°48.2′ 26°46.0′ 26°46.0′ 26°45.6′ 26°46.1′ 26°45.9′ 26°46.3′ 26°46.1′ 26°46.0′ 26°44.0′ 26°44.2′

127°55.0′ 127°52.9′ 127°51.0′ 127°51.0′ 127°51.1′ 127°53.0′ 127°55.1′ 127°55.0′ 127°55.9′ 128°58.1′ 128°58.1′ 128°58.1′ 128°01.9′ 128°02.1′ 128°01.9′ 128°01.8′ 128°02.0′ 128°02.0′ 128°02.0′ 128°02.1′ 128°01.9′ 128°02.1′ 128°00.0′ 128°00.0′ 127°57.9′ 127°56.0′ 127°53.9′ 127°52.0′ 127°52.0′ 128°04.0′ 128°03.7′ 128°03.9′ 128°04.0′ 128°03.9′ 128°04.1′ 128°04.0′ 128°03.9′ 128°04.0′ 127°50.0′ 127°52.0′ 128°00.8′ 128°03.9′ 128°13.8′ 128°10.0′ 128°06.4′ 128°02.0′ 127°58.0′ 127°54.0′ 127°49.7′ 127°52.0′ 127°56.0′ 128°00.0′ 128°01.0′ 128°08.0′ 128°12.0′ 128°10.0′ 128°05.8′ 128°02.4′ 127°58.0′ 127°54.0′ 127°50.0′ 127°46.2′ 127°42.1′ 127°38.0′ 127°39.8′ 127°42.2′ 127°47.9′ 127°52.0′ 127°55.6′ 128°00.0′ 128°04.2′ 128°07.8′ 128°05.9′ 128°02.2′

46 36 27 24 21 30 38 31 50 55 48 79 575 300 190 110 63 87 46 19 73 65 48 65 51 36 26 17 15 380 430 250 315 245 185 143 75 65 97 105 205 405 285 263 300 260 247 105 275 315 290 260 225 173 112 73 92 130 273 335 360 385 315 120 83 330 375 370 332 160 62 39 39 75

Yes

P

71.9

Yes Yes Yes Yes Yes Yes Yes

P Yes Yes Yes P P P Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

P

72.0

P

10.1

P P

19.8 50.6

P P

48.2 50.1

P

67.5

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

(continued on next page)

228

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230 Appendix A (continued)

Appendix A (continued) Site

Latitude (N)

Longitude (E)

Depth Rhodolith Rhodolith Submarine (m) coverage photo (%)

Site

Latitude (N)

Longitude (E)

Depth Rhodolith Rhodolith Submarine (m) coverage photo (%)

OK-102 OK-103 OK-104 OK-105 OK-106 OK-107 OK-108 OK-109 OK-110 OK-111 OK-112 OK-113 OK-114 OK-115 OK-116 OK-117 OK-118 OK-119 OK-120 OK-121 OK-122 OK-123 OK-124 OK-125 OK-126 OK-127 OK-128 OK-129 OK-130 OK-131 OK-132 OK-133 OK-134 OK-135 OK-136 OK-137 OK-138 OK-139 OK-140 OK-141 OK-142 OK-143 OK-144 OK-145 OK-146 OK-147 OK-148 OK-149 OK-150 OK-151 OK-152 OK-153 OK-154 OK-155 OK-156 OK-157 OK-158 OK-159 OK-160 OK-161 OK-162 OK-163 OK-164 OK-165 OK-166 OK-167 OK-168 OK-169 OK-170 OK-171 OK-172 OK-173 OK-174 OK-175 OK-176

26°44.1′ 26°44.0′ 26°44.0′ 26°44.1′ 26°43.9′ 26°42.0′ 26°41.5′ 26°40.0′ 26°39.7′ 26°40.0′ 26°38.0′ 26°36.0′ 26°37.0′ 26°36.0′ 26°34.9′ 26°34.0′ 26°34.1′ 26°34.0′ 26°33.9′ 26°33.0′ 26°31.8′ 26°31.2′ 26°32.0′ 26°31.0′ 26°34.1′ 26°32.8′ 26°32.9′ 26°30.0′ 26°28.0′ 26°26.1′ 26°24.2′ 26°22.1′ 26°24.0′ 26°22.2′ 26°19.9′ 26°20.4′ 26°20.2′ 26°20.3′ 26°19.9′ 26°20.1′ 26°20.0′ 26°20.0′ 26°20.0′ 26°12.0′ 26°22.0′ 26°24.5′ 26°23.7′ 26°22.1′ 26°20.2′ 26°20.1′ 26°20.0′ 26°22.2′ 26°20.2′ 26°16.3′ 26°18.0′ 26°18.2′ 26°18.1′ 26°18.1′ 26°18.2′ 26°18.0′ 26°18.0′ 26°18.2′ 26°18.0′ 26°17.9′ 26°18.2′ 26°18.0′ 26°18.1′ 26°18.1′ 26°16.1′ 26°16.1′ 26°17.2′ 26°16.0′ 26°16.0′ 26°16.0′ 26°16.0′

127°57.6′ 127°54.0′ 127°49.9′ 127°43.9′ 127°38.0′ 127°40.2′ 127°44.0′ 127°49.8′ 127°47.4′ 127°41.9′ 127°44.0′ 127°46.0′ 127°50.0′ 127°51.0′ 127°52.9′ 127°57.1′ 127°55.1′ 127°50.8′ 127°49.0′ 127°52.9′ 127°54.8′ 127°53.0′ 127°50.9′ 127°44.0′ 127°16.0′ 127°16.0′ 127°14.1′ 127°16.0′ 127°14.0′ 127°16.0′ 127°14.1′ 127°16.3′ 127°39.7′ 127°42.2′ 127°44.0′ 127°39.8′ 127°36.0′ 127°32.0′ 127°28.1′ 127°23.7′ 127°20.0′ 127°16.0′ 127°14.0′ 127°08.0′ 127°05.0′ 127°03.9′ 126°59.7′ 127°02.0′ 127°04.0′ 127°00.1′ 126°56.1′ 126°42.1′ 126°39.4′ 126°47.9′ 126°51.1′ 126°53.8′ 126°58.0′ 127°02.0′ 127°05.5′ 127°10.0′ 127°14.0′ 127°17.7′ 127°21.8′ 127°26.1′ 127°30.2′ 127°34.0′ 127°37.9′ 127°42.2′ 127°40.0′ 127°36.0′ 127°32.0′ 127°28.1′ 127°24.1′ 127°19.9′ 127°16.0′

195 325 290 350 100 345 55 91 170 65 280 300 180 180 220 53 105 290 320 280 82 100 340 355 95 100 95 565 580 690 600 660 205 44 47 190 405 690 690 718 620 520 285 90 59 725 970 32 100 78 65 84 460 88 66 88 160 210 235 118 125 410 440 400 425 108 80 71 54 78 104 89 90 120 105

OK-177 OK-178 OK-179 OK-180 OK-181 OK-182 OK-183 OK-184 OK-185 OK-186 OK-187 OK-188 OK-189 OK-190 OK-191 OK-192 OK-193 OK-194 OK-195 OK-196 OK-197 OK-198 OK-199 OK-200 OK-201 OK-202 OK-203 OK-204 OK-205 OK-206 OK-207 OK-208 OK-209 OK-210 OK-211 OK-212 OK-213 OK-214 OK-215** OK-216 OK-217 OK-218 OK-219 OK-220 OK-221 OK-222 OK-223 OK-224 OK-225 OK-226 OK-227 OK-228 OK-229

26°16.0′ 26°16.0′ 26°16.2′ 26°16.0′ 26°16.4′ 26°16.1′ 26°14.2′ 26°10.0′ 26°06.4′ 26°02.2′ 25°57.0′ 25°58.0′ 26°00.0′ 26°04.0′ 26°02.2′ 26°00.1′ 25°58.1′ 25°58.1′ 26°00.0′ 26°02.0′ 26°04.1′ 26°06.0′ 26°08.0′ 26°12.0′ 26°10.0′ 26°08.0′ 26°06.0′ 26°04.2′ 26°02.0′ 26°02.0′ 26°03.9′ 26°06.0′ 26°08.3′ 26°06.1′ 26°03.9′ 26°02.0′ 26°00.0′ 26°00.2′ 26°01.9′ 26°03.5′ 26°06.6′ 26°08.0′ 26°10.0′ 26°11.8′ 26°14.0′ 26°12.0′ 26°09.9′ 26°08.0′ 26°05.8′ 26°09.9′ 26°11.8′ 26°13.7′ 26°14.0′

127°12.2′ 127°07.9′ 127°04.0′ 127°00.2′ 126°55.6′ 126°51.8′ 127°10.0′ 127°10.0′ 127°10.0′ 127°10.3′ 127°12.0′ 127°14.0′ 127°12.0′ 127°12.1′ 127°14.1′ 127°16.2′ 127°17.8′ 127°22.0′ 127°20.0′ 127°18.0′ 127°16.0′ 127°14.1′ 127°12.0′ 127°11.9′ 127°13.7′ 127°16.0′ 127°18.0′ 127°20.0′ 127°22.0′ 127°25.9′ 127°23.9′ 127°21.0′ 127°23.8′ 127°26.0′ 127°27.9′ 127°30.0′ 127°32.0′ 127°35.7′ 127 34.0 ′ 127°32.0′ 127°29.6′ 127°28.0′ 127°25.9′ 127°24.0′ 127°26.0′ 127°27.9′ 127°29.9′ 127°31.9′ 127°34.2′ 127°33.9′ 127°31.9′ 127°30.0′ 127°34.3′

125 310 345 379 270 165 233 325 350 125 80 80 84 135 103 140 230 284 250 105 88 92 145 120 80 65 80 105 220 250 187 80 79 150 164 180 132 245 73 75 102 110 62 68 76 54 78 68 73 63 57 50 48

P

46.6

P

4.7

P

70.0

P P

P P P

P P

0.3

79.3 51.8 53.8

85.9

P P P P

63.8

P P P

76.9

P P

73.0 85.5

4.0

53.6

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

P P P P P

10.8 0.3 21.9 16.3

P

63.2

Yes Yes Yes Yes Yes Yes

P

66.4

P P P P P P

46.3 71.8 78.9 68.5 78.3

P P P

78.8 20.3 14.2

P P

8.3 3.6

P P

15.0 53.0

P

46.3

P P

69.2 40.7

P P P P P

85.6 44.6

P P P P

3.3 4.7 1.8 88.3

0.3 1.9

Rhodoliths collected by R/V Nagasaki Maru RN84D1 26°02.0′ 127°18.1′ 96 RN87D6 26°02.0′ 127°18.0′ 98 RN87D7 25°57.3′ 127°13.2′ 79 RN88OK1 26°46.4′ 127°37.0′ 82 RN88OK2 26°47.9′ 127°37.4′ 124 RN88D4 25°55.1′ 127°11.4′ 102 RN88D5 25°55.5′ 127°11.9′ 88 Rhodoliths collected during GH08 KG-24 25°54.1′ GH08 KG-110 26°00.9′ GH08 KG-111 26°02.1′ GH08 KG-114 26°06.9′ GH08 KG-128 26°08.5′ GH08 KG-300 26°30.0′

a GH08 cruise by R/V Daini-Hakurei 127°13.9′ 136 127°33.3′ 89 127°31.6′ 132 127°24.5′ 124 127°25.8′ 94 128°11.1′ 124

** No sample. P: Sites where rhodoliths are present. Yes: Sites where submarine photos were taken.

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

References Adey, W.H., Townsend, R.A., Boykins, W.T., 1982. The crustose coralline algae (Rhodophyta: Corallinaceae) of the Hawaiian Islands. Smithsonian Contributions in Marine Science 15, 1–74. Amado-Filho, G.M., Maneveldt, G., Manso, R.C.C., Marins-Rosa, B.V., Pacheco, M.R., Guimarães, S.M.P.B., 2007. Structure of rhodolith beds from 4 to 55 meters deep along the southern coast of Espírito Santo State, Brazil. Ciencias Marinas 33, 399–410. Bassi, D., 2005. Larger foraminiferal and coralline algal facies in an Upper Eocene storm influenced, shallow water carbonate platform (Colli Berici, north-eastern Italy). Palaeogeography, Palaeoclimatology, Palaeoecology 226, 17–35. Bassi, D., Nebelsick, J.H., Checconi, A., Hohenegger, J., Iryu, Y., 2009. Present-day and fossil rhodolith pavements compared: their potential for analysing shallow-water carbonate deposits. Sedimentary Geology 214, 74–84. Bassi, D., Humblet, M., Iryu, Y., (2011). Recent ichnocoenosis in deep water macroids, Ryukyu Islands. Palaios. doi:10.2110/palo.2010.p10-093r. Basso, D., 1998. Deep rhodolith distribution in the Pontian Islands, Italy: a model for the paleoecology of a temperate sea. Palaeogeography, Palaeoclimatology, Palaeoecology 137, 173–187. Bosellini, A., Ginsburg, R.N., 1971. Form and internal structure of Recent algal nodules (rhodolites) from Bermuda. Journal of Geology 79, 669–682. Bosence, D.W.J., 1976. Ecological studies on two unattached coralline algae from western Ireland. Palaeontology 19, 365–395. Bosence, D.W.J., 1983. The occurrence and ecology of Recent rhodoliths — a review. In: Peryt, T.M. (Ed.), Coated Grains. Springer-Verlag, Berlin, pp. 225–242. Bosence, D.W.J., Pedley, H.M., 1982. Sedimentology and palaeontology of a Miocene coralline algal biostrome from the Maltese Islands. Palaeogeography, Palaeoclimatology, Palaeoecology 38, 189–206. Braga, J.C., Aguirre, J., 2001. Coralline algal assemblages in upper Neogene reef and temperate carbonates in Southern Spain. Palaeogeography, Palaeoclimatology, Palaeoecology 175, 27–41. Braga, J.C., Martìn, J.M., 1988. Neogene coralline–algal growth-forms and their palaeoenvironments in the Almanzora River Valley (Almeria, S.E. Spain). Palaeogeography, Palaeoclimatology, Palaeoecology 67, 285–303. Checconi, A., Bassi, B., Carannante, G., Monaco, P., 2010. Re-deposited rhodoliths in the Middle Miocene hemipelagic deposits of Vitulano (Southern Apennines, Italy): coralline assemblage characterization and related trace fossils. Journal of Geology 225, 50–66. Ehara, Y., Iryu, Y., Nakamori, T., Odawara, K., 2001. Pleistocene coral reef deposits (the Ryukyu Group) on Kume-jima, Okinawa Prefecture, Japan. Galaxea 3, 13–24 (in Japanese with English abstract). Focke, J.W., Gebelein, C.D., 1978. Marine lithification of reef rock and rhodoliths at a fore-reef slope locality (− 50 m) off Bermuda. Geologie en Mijnbouw 57, 163–171. Foster, M.S., 2001. Rhodoliths: between rocks and soft places. Journal of Phycology 37, 659–667. Foster, M.S., Riosmena-Rodriguez, R., Steller, D.L., Woelkerling, W.J., 1997. Living rhodolith beds in the Gulf of California and their implications for paleoenvironmental interpretation. In: Johnson, M.E., Ledesma-Vázquez, J. (Eds.), Pliocene Carbonates and Related Facies Flanking the Gulf of California, Baja California, Mexico: Geological Society of America Special Paper, vol. 317, pp. 127–140. Fujita, K., Omori, A., Yokoyama, Y., Sakai, S., Iryu, Y., 2010. Sea-level rise during Termination II inferred from large benthic foraminifers: IODP Expedition 310, Tahiti Sea Level. Marine Geology 271, 149–155. Hamamoto, F., Sakurai, M., Nagano, M., 1979. Submarine geology off the Miyako and Yaeyama Islands. Report of Hydrographic Researches, Japan Coast Guard 14, 1–11 (in Japanese with English abstract). Harvey, A.S., Woelkerling, W.M., 2007. A guide to nongeniculate coralline red algal (Corallinales, Rhodophyta) rhodolith identification. Ciencias Marinas 33, 411–426. Higa, Y., Matsuda, S., 2009. An undescribed species of Sporolithon (Corallinales) from the deep insular shelf off Kerama Islands. Abstracts of the 158th Regular Meeting of the Palaeontological Society of Japan (Okinawa Prefectural Museum and Art Museum), p. 25. Hohenegger, J., 1994. Distribution of living larger foraminifera NW of Sesoko-jima, Okinawa, Japan. Marine Ecology 15, 291–334. Hongo, C., Kayanne, H., 2010. Holocene sea-level record from corals: reliability of paleodepth indicators at Ishigaki Island, Ryukyu Islands, Japan. Palaeogeography, Palaeoclimatology, Palaeoecology 287, 143–151. Hottinger, L., 1983. Neritic macroid genesis, an ecological approach. In: Peryt, T.M. (Ed.), Coated Grains. Springer-Verlag, Berlin, pp. 38–55. Humblet, M., Iryu, Y., Nakamori, T., 2009. Variations in Pleistocene coral assemblages in space and time in southern and northern Central Ryukyu Islands, Japan. Marine Geology 259, 1–20. Humblet, M., Furushima, Y., Iryu, Y., Tokuyama, H., 2010. Deep zooxanthellate corals in the Ryukyu Islands: insight from modern and fossil reefs. In: Amorosi, A. (Ed.), Proceedings of the 27th IAS meeting of Sedimentologists (September 20–23, 2009, Alghero, Italy), Medimond, Bologna, pp. 129–133. Inagaki, M., Omura, A., Yagi, H., Kato, M., 2005. U-series ages of carbonate sediments underlying the lowest marine terrace of the Upper Pleistocene in Kikai Island, central Ryukyu, Japan. Quaternary Reseach (Daiyonki Kenkyu) 44, 93–106 (in Japanese with English abstract). Iryu, Y., 1984. Discovery of recent deep water rhodoliths from the Ryukyu Islands, southwestern Japan, and its significance. Prompt Reports of the Comprehensive and Scientific Survey in the Ryukyu Archipelago, vol. 1. Kagoshima University, Kagoshima, pp. 47–55 (in Japanese with English abstract). Iryu, Y., 1985. Study on the Recent rhodoliths around the Ryukyu Islands. Prompt Reports of the Comprehensive and Scientific Survey in the Ryukyu Archipelago, vol.

229

2. Kagoshima University, Kagoshima, pp. 123–133 (in Japanese with English abstract). Iryu, Y., 1992. Fossil nonarticulated coralline algae as depth indicators for the Ryukyu Group. Transactions and Proceedings of the Paleontological Society of Japan, N.S. 167, 1165–1179. Iryu, Y., 1997. Pleistocene fore-reef rhodoliths from the Ryukyu Islands, southwestern Japan. Proceedings of the 8th International Coral Reef Symposium, Panama, vol. 1, pp. 749–754. Iryu, Y., Matsuda, S., 1988. Depth distribution, abundance and species assemblages of nonarticulated coralline algae in the Ryukyu Islands, southwestern Japan. Proceedings of the 6th International Coral Reef Symposium, Townsville, vol. 3, pp. 101–106. Iryu, Y., Matsuda, S., 1996. Hydrolithon murakoshii sp. nov. (Corallinaceae, Rhodophyta) from Ishigaki-jima, Ryukyu Islands, Japan. Phycologia 35, 528–536. Iryu, Y., Nakamori, T., Matsuda, S., Abe, O., 1995. Distribution of marine organisms and its geological significance in the modern reef complex of the Ryukyu Islands. Sedimentary Geology 99, 243–258. Iryu, Y., Nakamori, T., Yamada, T., 1998. Pleistocene reef complex deposits in the Central Ryukyus, southwestern Japan. In: Camoin, G., Davies, P.J. (Eds.), Reefs and Carbonate Platforms in the Pacific and Indian Oceans: Special Publication of the International Association of Sedimentologists, no. 25. Blackwell Science, 25. Blackwell Science, Oxford, pp. 197–213. Iryu, Y., Matsuda, H., Machiyama, H., Piller, W.E., Quinn, T.M., Mutti, M., 2006. Introductory perspective on the COREF Project. Island Arc 15, 393–406. Iryu, Y., Bassi, D., Woelkerling, W.J., 2009a. Re-assessment of the type collections of fourteen corallinalean species (Corallinales, Rhodophyta) described by W. Ishijima (1942–1960). Palaeontology 52, 401–427. Iryu, Y., Takayanagi, H., Kawamura, K., 2009b. Preliminary report on rhodoliths collected around Okinawa-jima. In: Arai, K. (Ed.), Marine Geological and Geophysical Studies around Okinawa Islands — Eastern off of Okinawa Island-, Preliminary Reports on Researches in the 2008 Fiscal Year. : GSJ Interim Report, vol. 46. Geological Survey of Japan, Tsukuba, pp. 158–163. Iryu, Y., Takahashi, Y., Fujita, K., Camoin, G., Cabioch, G., Westphal, H., Matsuda, H., Sugihara, K., Sato, T., Webster, J.M., 2010. Sealevel history recorded in the Pleistocene carbonate sequence in IODP Hole 310-M0005D, off Tahiti. Island Arc 19, 690–706. Ishijima, W., 1954. Cenozoic coralline algae from the western Pacific. Privately published, Yuhodo, Tokyo, 87 pp. Kamura, S., Nishijima, N., Yamazato, K., Eguchi, M., 1967. Submarine topography and sediments in the Ryukyu Islands. In: Operation Committee of the Submarine “Yomiuri-go”. (Ed.), Report of Fishery Resources in the Ryukyu Islands. Dobunsha, Tokyo, pp. 139–152 (in Japanese). Kato, S., Katsura, T., Hirano, K., 1982. Submarine geology off Okinawa Island. Report of Hydrographic Researches, Japan Coast Guard 17, 31–70 (in Japanese with English abstract). Littler, M.M., Littler, D.S., Hanisak, D., 1991. Deep-water rhodolith distribution, productivity and growth history at sites of formation and subsequent degradation. Journal of Experimental Marine Biology and Ecology 150, 163–182. Lund, M., Davies, P.J., Braga, J.C., 2000. Coralline algal nodules off Fraser Island, eastern Australia. Facies 42, 25–34. MacNeil, F.S., 1960. Tertiary and Quaternary gastropoda of Okinawa. United States Geological Survey Professional Paper 339, 1–33. Marshall, J.F., Tsuji, Y., Matsuda, H., Davies, P.J., Iryu, Y., Honda, N., Satoh, Y., 1998. Quaternary and Tertiary subtropical carbonate platform development on the continental margin of southern Queensland, Australia. In: Camoin, G., Davies, P.J. (Eds.), Reefs and Carbonate Platforms in the Pacific and Indian Oceans: Special Publication of the International Association of Sedimentologists, no. 25. Blackwell Science, Oxford, pp. 163–195. Matsuda, S., 1989. Succession and growth rates of encrusting crustose coralline algae (Rhodophyta, Cryptonemiales) in the upper fore-reef environment off Ishigaki Island, Ryukyu Islands. Coral Reefs 7, 186–195. Matsuda, S., 1995. Quaternary limestones on Huon Peninsula, Papua New Guinea with special reference to nonarticulated coralline algae (Rhodophyta, Corallinaceae). Journal of Geography 104, 706–718 (in Japanese with English abstract). Matsuda, S., 2004. Rhodolith-forming coralline algal assemblage on the deep fore-reef to insular shelf areas off Okinawa-jima and Kikai-jima, Ryukyu Islands, Japan. 10th International Coral Reef Symposium, Okinawa, Japan, Abstracts, 243. Matsuda, S., Tomiyama, T., 1988. An investigation of Recent deepwater rhodoliths from the Ryukyu Islands. Bulletin of the College of Education, University of the Ryukyus 33, 343–354 (in Japanese with English abstract). Matsuda, H., Arai, K., Inoue, T., Machiyama, H., Sasaki, K., Iryu, Y., Fujita, K., Humblet, M., Sugihara, K., Nara, M., 2010. Rhodolith-bearing gravelly carbonate sediments on the shelf off Kikai Island, Kagoshima Prefecture. Journal of the Sedimentological Society of Japan 69, 62. McMaster, R.L., Conover, J.T., 1966. Recent algal stromatolites from the Canary Islands. Journal of Geology 74, 647–652. Minnery, G.A., 1990. Crustose coralline algae from the Flower Garden Banks, northeastern Gulf of Mexico: controls on distribution and growth morphology. Journal of Sedimentary Petrology 60, 992–1007. Minoura, K., Nakamori, T., 1982. Depositional environment of algal balls in the Ryukyu Group, Ryukyu Islands, southwestern Japan. Journal of Geology 90, 602–609. Montaggioni, L.F., 1979. Environmental significance of rhodolites from the Mascarene reef province, western Indian Ocean. Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine 3, 713–723. Mutti, M., Hallock, P., 2003. Carbonate systems along nutrient and temperature gradients: a review of sedimentological and geochemical constraints. International Journal of Earth Sciences 92, 465–475.

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S. Matsuda, Y. Iryu / Marine Geology 282 (2011) 215–230

Nakagawa, H., 1972. Report on the Geology of Okierabujima. Kyushu Regional Agricultural Administration Office, Ministry of Agriculture and Forestry, Government of Japan, Kumamoto. (in Japanese). Nakamori, T., Iryu, Y., Yamada, T., 1995a. Development of coral reefs of the Ryukyu Islands (southwest Japan, East China Sea), during Pleistocene sea-level change. Sedimentary Geology 99, 215–231. Nakamori, T., Matsuda, S., Omura, A., Ota, Y., 1995b. Depositional environments of the Pleistocene reef limestones at Huon Peninsula, Papua New Guinea on the basis of hermatypic coral assemblages. Journal of Geography 104, 725–742 (in Japanese with English abstract). Nohara, M., Ohshima, K., Yokota, S., Murakami, F., Inouchi, Y., Ikeda, K., 1980. Marine sediments from the adjacent sea around the Okinawa Island. Environmental Agency, Japan (Ed.), Environmental Research in Japan. Volume II of 1979. Environmental Agency, Tokyo, pp. 3–28 (in Japanese with English abstract). Odawara, K., Iryu, Y., 1999. Pleistocene coral reef deposits (the Ryukyu Group) on Yoron-jima, Kagoshima Prefecture, Japan. Journal of the Geological Society of Japan 105, 273–288 (in Japanese with English abstract). Odawara, K., Kudo, S., Iryu, Y., Sato, T., 2005. Stratigraphy of the Zakimi Formation and the Ryukyu Group in Yomitan area, Okinawa-jima, Ryukyu Islands, Japan. Journal of the Geological Society of Japan 111, 313–331 (in Japanese with English abstract). Oshimizu, T., Iryu, Y., 2002. Stratigraphy of the Chinen Formation and the Ryukyu Group on islands off Katsuren Peninsula, Okinawa-jima, Ryukyu Islands, Japan. Journal of the Geological Society of Japan 108, 318–335 (in Japanese with English abstract). Payri, C.E., Cabioch, G., 2004. The systematic and significance of coralline red algae in the rhodolith sequence of the Amédée 4 drill core (Southwest New Caledonia). Palaeogeography, Palaeoclimatology, Palaeoecology 203, 187–208. Pomar, L., 2001. Types of carbonate platforms: a genetic approach. Basin Research 3, 313–334. Prager, E.J., Ginsburg, R.N., 1989. Carbonate nodule growth on Florida's outer shelf and its implications for fossil interpretations. Palaios 4, 310–317. Reid, R.P., MacIntyre, I.G., 1988. Foraminiferal–algal nodules from the eastern Caribbean: growth history and implications on the value of nodules as paleoenvironmental indicators. Palaios 3, 424–435.

Rezak, R., Bright, T.J., Mcgrail, W., 1985. Reefs and Banks of the Northern Gulf of Mexico. Wiley-Interscience, New York. Sagawa, N., Nakamori, T., Iryu, Y., 2001. Pleistocene reef development in the southwest Ryukyu Islands, Japan. Palaeogeography, Palaeoclimatology, Palaeoecology 175, 303–323. Sneed, E.D., Folk, R.L., 1958. Pebbles in the lower Colorado River, Texas, a study in particle morphogenesis. Journal of Geology 66, 114–150. Studencki, W., 1979. Sedimentation of algal limestones from Busko-Spa environs (Middle Miocene, Central Poland). Palaeogeography, Palaeoclimatology, Palaeoecology 27, 155–165. Tsuji, Y., 1993. Tide influenced high energy environments and rhodolith-associated carbonate deposition on the outer shelf and slope off Miyako Islands, southern Ryukyu Island Arc, Japan. Marine Geology 113, 255–271. Ujiié, H., Yamamoto, S., Okitsu, M., Nagano, K., 1983. Sedimentological aspects of Nakagusuku Bay, Okinawa, subtropical Japan. Galaxea 2, 95–117. Woelkerling, W.M.J., Irvine, L.M., Harvey, A.S., 1993. Growth-forms in non-geniculate coralline red algae (Corallinales, Rhodophyta). Australian Systematic Botany 6, 277–293. Yamada, T., Fujita, K., Iryu, Y., 2003. The Ryukyu Group (Pleistocene coral reef complex deposits) on Toku-no-shima, Kagoshima Prefecture, Japan. Journal of the Geological Society of Japan 109, 495–517 (in Japanese with English abstract). Yamamoto, S., Ujiié, H., 1983. Calcareous sediment around coast of the Okinawa-jima Island. News of Osaka Micropaleontologists 11, 48–62. Yamamoto, K., Iryu, Y., Sato, T., Chiyonobu, S., Sagae, K., Abe, E., 2006. Responses of coral reefs to increased amplitude of sea-level changes at the Mid-Pleistocene climate transition. Palaeogeography, Palaeoclimatology, Palaeoecology 241, 160–175. Yamazato, K., Kamura, S., Nishijima, N., 1967. Distribution of benthos in the Ryukyu Islands. In: Operation Committee of the Submarine “Yomiuri-go” (Ed.), Report of Fishery Resources in the Ryukyu Islands. Dobunsha, Tokyo, pp. 164–192 (in Japanese). Yamazato, K., 1972. Bathymetric distribution of corals in the Ryukyu Islands. Proceedings of the 1st International Coral Reef Symposium, India, pp. 121–133.