Collection and Research (2012) 25: 9-16 9 Notes on Cone-In-Cone Structures from Kaohsiung, Southwestern Taiwan Shih-Wei Wang 1* and An-Sheng Lee 2 1 Department of Geology, National Museum of Natural Science, Taichung 404, Taiwan. 2 2nd Fl., 51-1, Lane 702, Anzhong Rd., Section 1, Tainan 709, Taiwan. (Received December 8, 2011; Accepted December 30, 2011; Published online Agust 23, 2012) Abstract. This study presents a rock sample composed of thin layers of calcite cone-in-cone structures and muddy silts. The sample was collected from debris-flow deposits covering the bed of the Chishan River at Hunghuatzu, Namasia District, Kaohsiung City, southwestern Taiwan. It is considered to possibly be a chaotic block which eroded from upstream Miocene formations. Diagnostic features of the cone-in-cone structures, such as stacks of concentric circular cones, clay film parting between the cones, fine to distinct radiating striations, and parallel annular corrugations on the cone surface, are all presented in the cone-in-cone layer of this specimen. This is the first report of cone-in-cone structures in Taiwan. Key words: cone-in-cone structures, calcite, diagenesis, Kaohsiung, southwestern Taiwan. *E-mail: [email protected]INTRODUCTION Cone-in-cone structures are a kind of secondary sedimentary structure that occur as thin, generally calcareous layers of some shales and/or as distinct envelopes surrounding some large calcareous concretions in dark shale. These structures are characterized by a set of concentric circular cones which fit into one another in inverted positions (cone base upward, cone apex downward), commonly separated by clay films. Heights of the cones range 1~200 mm, among which, those 10~100 mm are most common. Basal sizes depend on the heights and apical angles of the cones. The apical angles are usually 30°~60°, and the cone axes are perpendicular to the bedding or the outline of the concretion; the conic surfaces are usually striated, and marked with annular corrugations that are more pronounced near the bases and finer and more obscure near the apical parts (Tarr, 1961; Pettijohn, 1975; Neuendorf et al., 2005). The principle mineralogy of cone-in-cones is usually composed of fibrous calcite, and less commonly of gypsum (Tarr, 1961) or siderite (Hendricks, 1937). Exceptionally silicified and pyritic cone-in-cone structures were reported by Woodland in 1964 and 1975 respectively, and all were interpreted as results of mineralogical replacement of calcite. Cone-in-cone structures were reported from sedimentary rocks ranging from Precambrian to Tertiary on land (Pettijohn, 1975), and at least two are of Mesozoic age from deep-sea borehole cores (Tarney and Schreiber, 1977; Maillot and Bonte, 1983). Moreover, being characteristic of certain stratigraphic horizons of the Phanerozoic, some cone-in-cone structures can be used for correlating sedimentary sequences (Kolokol’tsev, 2002; Song et al., 2010). The first description and drawing of cone- in-cone structures were made by Ure (1793), on page 253 and fig. 8 of pl. XX, although it was recognized as a fossil. Since then, the high degree of order and reproducibility of cone-
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Collection and Research (2012) 25: 9-16 9
Notes on Cone-In-Cone Structures from Kaohsiung, Southwestern Taiwan
Shih-Wei Wang1* and An-Sheng Lee2
1Department of Geology, National Museum of Natural Science, Taichung 404, Taiwan.22nd Fl., 51-1, Lane 702, Anzhong Rd., Section 1, Tainan 709, Taiwan.
(Received December 8, 2011; Accepted December 30, 2011; Published online Agust 23, 2012)
Abstract. This study presents a rock sample composed of thin layers of calcite cone-in-cone structures and muddy silts. The sample was collected from debris-flow deposits covering the bed of the Chishan River at Hunghuatzu, Namasia District, Kaohsiung City, southwestern Taiwan. It is considered to possibly be a chaotic block which eroded from upstream Miocene formations. Diagnostic features of the cone-in-cone structures, such as stacks of concentric circular cones, clay film parting between the cones, fine to distinct radiating striations, and parallel annular corrugations on the cone surface, are all presented in the cone-in-cone layer of this specimen. This is the first report of cone-in-cone structures in Taiwan.
Cone-in-cone s t ructures are a kind of secondary sedimentary structure that occur as thin, generally calcareous layers of some shales and/or as distinct envelopes surrounding some large calcareous concretions in dark shale. These structures are characterized by a set of concentric circular cones which fit into one another in inverted positions (cone base upward, cone apex downward), commonly separated by clay films. Heights of the cones range 1~200 mm, among which, those 10~100 mm are most common. Basal sizes depend on the heights and apical angles of the cones. The apical angles are usually 30°~60°, and the cone axes are perpendicular to the bedding or the outline of the concretion; the conic surfaces are usually striated, and marked with annular corrugations that are more pronounced near the bases and finer and more obscure near the apical parts (Tarr, 1961;
Pettijohn, 1975; Neuendorf et al., 2005).The principle mineralogy of cone-in-cones
is usually composed of fibrous calcite, and less commonly of gypsum (Tarr, 1961) or siderite (Hendricks, 1937). Exceptionally silicified and pyritic cone-in-cone structures were reported by Woodland in 1964 and 1975 respectively, and all were interpreted as results of mineralogical replacement of calcite. Cone-in-cone structures were reported from sedimentary rocks ranging from Precambrian to Tertiary on land (Pettijohn, 1975), and at least two are of Mesozoic age from deep-sea borehole cores (Tarney and Schreiber, 1977; Maillot and Bonte, 1983). Moreover, being characteristic of certain stratigraphic horizons of the Phanerozoic, some cone-in-cone structures can be used for correlating sedimentary sequences (Kolokol’tsev, 2002; Song et al., 2010).
The first description and drawing of cone-in-cone structures were made by Ure (1793), on page 253 and fig. 8 of pl. XX, although it was recognized as a fossil. Since then, the high degree of order and reproducibility of cone-
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in-cone structures have engaged the attention and imagination of geologists for more than 2 centuries (Kolokol’tsez, 2002). In reviewing research of early times, some cone-in-cone structures were identified or described as fossils (Tarr, 1961). Before the 1960s, the origins of these structures were illustrated as a result of pressure induced by calcareous concretion growth, expansion pressure produced by aragonite inversion to calcite, lithostatic loading, deformation of calcite fibers by tension, calcite fiber growth pressure during early diagenesis in which the enclosing muddy sediment was plastic, and so on (Franks, 1969), and most researchers believed that cone-in-cone structures were primary sedimentary features. Among them, Tarr (1st ed. published in 1932; 2nd ed., completely revised in 1961) proposed a breakthrough idea that cone-in-cone structures are a secondary overgrowth to fibrous calcite crystals (i.e., epigenetic structures), which are produced by pressure that creates the conical shear surfaces. Although his proposition was later expanded and modified, and has become the most popular model (Kowal-Linka, 2010), relationships between the original occurrence and diagenetic environments are still insufficiently understood. Another problem concerns the creation mechanisms of the bedding-parallel space that is required for cone-in-cone structure formation which also attracted many investigations, including the force of crystallization, hydraulic fracturing as horizontal compression, and dilatant shear failure during upward fluid seeping (Kowal-Linka, 2010). To the present, there is still no definite conclusion for the development mechanism of cone-in-cone structures.
As men t ioned above , many cone - in -cone structures were reported. However, this kind of structure is rarely mentioned in recent sedimentological literature (Boggs, 2009). This article presents a Miocene rock sample with calcite cone-in-cone structures collected from Kaohsiung, southwestern Taiwan. To the best of our knowledge, this is the first record of cone-in-cone structures in Taiwan.
MATERIALS AND METHODS
A chaotic rock sample with cone-in-cone structures was collected by Mr. An-Sheng Lee (the second author) from the upstream riverbed
of the Chishan River on March 23, 2010. This collection was made during fieldwork to examine Miocene cold-seep carbonates, which outcrop on the riverbed about 200 m downstream from the collecting site. The sample site is located at Hunghuatzu, Namasia District, Kaohsiung City, southwestern Taiwan. The geographical coordinates of this site are 23°12'29.2"N, 120°40'56.6"E (in WGS84 datum), located ca. 9.5 km from the downstream Shiaolin Village that was destroyed and buried by catastrophic landslides during typhoon Morakot on August 9, 2009 (Lee et al., 2009; Tsou et al., 2011). This specimen is now stored at the National Museum of Natural Science (NMNS) and catalogued as NMNS006514-P016464.
The rock sample with cone-in-cone structures is approximately the size of one's hand, with dimensions of about 10 x 9 x 5 cm. A rock slice was cut vertically for a 5 x 7-cm standard petrographic thin section, and the cutting plane was polished and photographed. The rock section was polished and photographed using cross-polarized light in order to reveal the internal texture. Measurements of the apical angle and axis divergence of the cones were made from the photograph of the thin section using Adobe Photoshop CS2 software. Four powder samples for mineralogical analysis were secured from the polished cutting (XRD-1~4) using a hand-held drill. Bulk mineralogy was determined by X-ray diffraction (XRD) analysis on powdered samples using a Rigaku Diffractometer with Cu Kα radiation (1°/min) at the National Museum of Natural Science (NMNS, Taichung, Taiwan).
RESULTS AND DISCUSSION
Occurrence of cone-in-cone structures
The rock sample with cone-in-cone structures was collected as a chaotic boulder from debris flow deposits (Plate 1, Fig. 1) that covered the bed of the Chishan River after typhoon Morakot had devastated the area in 2009.
This rock sample was composed of thin layers of interbedded cone-in-cone structures and muddy silts, with thicknesses of 20~32 and 10~14 mm, respectively. The original top-to-bottom orientation of this specimen was determined by features of several small cones nested in a larger cone (Plate 1, Fig. 4). No overlying sediment was
Wang and Lee : Notes on Cone-In-Cone Structures from Taiwan 11
left on the cone-in-cone layer top. The boundary between the cone layer and muddy silt layer was discernable with the naked eye (Plate 1, Figs. 3, 6) and was more distinct in the rock thin section under cross-polarized light (Plate 1, Figs. 7, 8). Diagnostic features of cone-in-cone structures such as stacks of concentric circular cones, clay film partings between the cones, fine to distinct radiating striations, and parallel annular corrugations on the conic surface are all present in this specimen (Plate 1, Figs. 2, 3, 5). In addition, some irregular calcite veinlets within the cone layer were clearly revealed on the polished cutting (Plate 1, Fig. 6).
Apical angles and cone axis divergences were measured from a petrographic thin section that was cut across the center of a large cone set (Plate 1, Fig. 7). Results of measurements (Table 1) showed that these angles ranged 26.0°~51.3° and 0.5°~11.2°, respectively. All apical angles were 30°~60° except one which was as narrow as 26°. Most cone axes were nearly perpendicular to the bedding with divergences of < 9°. The largest axis divergence was measured from Cone 06 as shown in Fig. 7 of Plate 1, which was situated at the base of Cone 07~12 stacks. As shown on the thin section, all cones above Cone 06 possessed a flat base of various lengths. In addition, the entire cone set that includes Cone 06~12 shows a shifting cone axis as the cones are traced from the base upward.
The ca lca reous muddy s i l t l ayer was composed of angular silt-sized quartz grains and calcareous cement. The top of this silt layer was roughly parallel to the bottom, which was assumed to be the bedding plane. No graded or reverse-graded bedding was observed in this layer. Two dark ‘lines’ within the silt layer are discernable on both the polished cut and thin section (as clearly shown in Plate 1, Fig. 8). These lines are approximately parallel to the top of the silt layer and are probably solution seams, although a final determination of this requires additional studies.
Mineralogy of the cone-in-cone structures
Results of the XRD analyses showed that all samples (XRD-1~4) were mainly composed of quartz and calcite (TEXT-FIGURE 1). The muddy silt layer was mainly composed of quartz silts with calcite as cement, while the cone-in-cone layer consisted mainly of calcite with a minor
amount of quartz. The quartz within each sample can be used as an internal standard to obtain the precise reflection peak positions that represent the (112) plane of the calcite crystal lattice. 2θ angles of calcite in XRD-1~4 were 29.50°, 29.55°, 29.5°, and 29.50° respectively. By matching these data to the degree 2θ - Mg mole% graph of Scholle (1978: 228), all of the carbonates present in both layers were determined to be low-Mg calcite.
Possible origin of the exotic boulder with cone-in-cone structures
Typhoon Morakot brought extraordinarily heavy rains and caused serious f looding, landslides, and debris flows in southwestern Taiwan on August 2009 (EPA, 2009). After this,
TEXT-FIGURE 1. Compiled X-ray diffraction (XRD) spectra of powdered samples XRD-1~4. For sampling sites of the XRD analyses see Fig. 6 of Plate 1.
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the riverbed of the sample locality was filled with a thick layer of debris-flow deposits, and the nearby downstream cold-seep carbonate outcrop was buried beneath an even thicker layer of debris. Therefore, the exotic boulder with calcite cone-in-cone structures must have been carried downstream by this event.
The sample locality of this rock specimen was located at the lithostratigraphic boundary of the overlying Hunghuatzu Formation and the underlying Sanmin Shale (CPC, 1989). Upstream from this site, a continuous stretch of the Middle Miocene (Huang, 1984) Sanmin Shale is about 13 km in length (CPC, 1986, 1989). In the Chishan River area, the Sanmin Shale extends to a length of about 11 km in a N-S direction, reaching a maximum of 2.5 km in breadth (Chung, 1962). For these reasons, this exotic boulder with cone-in-cone structures most likely eroded from the Sanmin Shale, although it also could have eroded from other Miocene Formations (e.g., the Hunghuatzu Formation or Changchihkeng Formation) that outcrop further upstream along the Chihshan River. This can only be verified in future field surveys of Miocene outcrops.
CONCLUSIONS
This article presents the first discovery of calcite cone-in-cone structures in Taiwan. The rock sample composed of thin layers of cone-in-cone structures and calcareous muddy silts was assumed to be an exotic block that eroded from Miocene.
ACKNOWLEDGMENTS
We thank Kun-Ming Chuang for his assistance in the field, Kun-Wei Chung for making the petrographic thin section, and Li- Fang Wang for the XRD analyses of rock samples. Special thanks are given to Drs. Leh-Chyun Wu and Wen-Shan Chen for their valuable comments on a previous draft. This study was supported by the National Museum of Natural Science, and grants from the National Science Council, Taiwan (NSC 98-2119-M-178-002).
REFERENCES
Boggs Jr., S., 2009. Petrology of sedimentary rocks. 2nd ed. Cambridge University Press; New York. 610 pp.
Chung, C. T., 1962. Geology of the Hunghuatzu Anticline, Kaohsiung, Taiwan. Petrol. Geol. Taiwan 1: 31-50.
EPA (Environmental Protection Administration, Executive Yuan, R.O.C.), 2009. Extreme events and disasters are the biggest threat to Taiwan- Typhoon Morakot. Available at http://ivy1.epa.gov.tw/unfccc/english/_uploads/downloads/01_Extreme_Events_and_Disasters_from_Typhoon_Morakot-the_Biggest_Threat_ever_to_Taiwan.pdf. Accessed on 27 November, 2011.
Table 1. Measurements of apical angles and axis divergences of the cones
* The cone axis divergence is the included angle of the cone axis and the vertical line perpendicular to the bottom of the cone layer.
Wang and Lee : Notes on Cone-In-Cone Structures from Taiwan 13
Franks , P. C . , 1969. Nature , o r ig in , and significance of cone-in-cone structures in the Kiowa Formation (Early Cretaceous), north-central Kansas. J. Sediment. Petrol. 39(4): 1438-1454.
Hendricks, T. A., 1937. Some unusual specimens of cone-in-cone in manganiferous siderite. Am J. Sci. (Ser. 5) 33: 458-461.
Huang , T. , 1984 . P lankt ic fo ramin i fe ra l biostratigraphy and datum planes in the Neogene sedimentary sequence in Taiwan. Palaeogeogr. Palaeoclimatol. Palaeoecol. 46: 97-106.
Kolokol’tsez, V. G., 2002. The cone-in-cone structure and its origin. Lithol. Mineral Resources 37(6): 523-535.
Kowal-Linka, M., 2010. Origin of cone-in-cone calcite veins during calcitization of dolomites and their subsequent diagenesis--A case study from the Gogolin Formation (Middle Triassic), SW Poland. Sediment. Geol. 224: 54-64.
Lee, C.-T., Dong, J.-J., and Ling, M.-L., 2009. Geological investigation on the catastrophic landslide in Siaolin Village southern Taiwan. Sino-Geotechnics 122: 87-94. (in Chinese with English abstract).
Maillot, H., and Bonte, A., 1983. Cone-in-cone texture from Deep Sea Drilling Project Leg 71, Site 511, Falkland Plateau, South Atlantic Ocean. Initial Rep. Deep Sea Drilling Proj. 71: 345-349.
Neuendorf, K. K. E., Mehl Jr., J. P., and Jackson, J. A., 2005. Glossary of geology. 5th ed. American Geological Institute; Alexandria, VA, USA. 779 pp.
Pettijohn, F. J., 1975. Sedimentary rocks. 3rd ed. Harper & Row, New York. 628 pp.
Scholle, P. A., 1978. A color illustrated guide to carbonate rock constituents, textures, cements, and porosities. The American Association of Petroleum Geologists; Tulsa, OK, USA. The American Association of Petroleum Geologists Memoir 27. 241 pp.
Song, J., Jiao, Y-.Q., Wu, L.-Q., Rong, H., and Wang, R., 2010. Sedimentary feature and paleoenvironmental significance of cone-in-cones of Yan'an Formation in the northeast of Ordos Basin. Geol. Sci. Technol. Inform. 29(2): 31-37.
Tarney, J., and Schreiber, B. C., 1977. Cone-in-cone and beef-in-shale textures from DSDP site 330, Falkland Plateau, south Atlantic. Initial Rep. Deep Sea Drilling Proj. 36: 865-870.
Tarr, W. A., 1961. Cone-in-cone. In: Twenhofel, W. H. (Ed.). Treatise on sedimentation. 2nd ed., completely revised. pp. 716-733. Dover Publications, New York.
Tsou, C.-Y., Feng, Z.-Y., and Chigira, M., 2011. Catastrophic landslide induced by typhoon Morakot, Shiaolin, Taiwan. Geomorphology 127: 166-178.
Ure, D., 1793. The history of Rutherglen and East-Kilbride. David Niven; Glasgow, UK. 334 pp.
Woodland, B. G., 1964. The nature and origin of cone-in-cone structure. Fieldiana Geol. 13(4): 187-305.
Fig. 1. A chaotic block sample with cone-in-cone structures collected by Mr. An-Sheng Lee (the second author; as shown in the photo) from the upstream bed of the Chishan River on March 23, 2010. The photograph was taken facing the upstream direction.
Fig. 2. Top view of the rock sample showing the cone-in-cone structures (with the cone base toward the viewer). Close-up of the cone-in-cone as presented in Fig. 5 (the photo field is marked with dashed lines).
Fig. 3. Side view of the rock sample, showing stacks of concentric cones. CL, cone layer; MsL, muddy silt layer.
Fig. 4. Features of several small cones nesting in a larger cone (outlined in yellow) revealed in the photo. A red star marks the apex of each cone set. A thin slice was cut from the rock sample vertically along transect AA’ to obtain fresh samples for x-ray diffraction analyses (the cut surface was polished as shown in Fig. 6). The thin section was made by cutting across the center of a large cone set (along transect BB’) (Fig. 8).
Fig. 5. Close-up of the cone-in-cone structures. Features of radiating striations and parallel annular corrugations on the conic surface are shown in this photo.
Fig. 6. Photograph of the cut surface, showing the sample sites (circled in yellow) for the X-ray diffraction (XRD) analyses. Numbers 1~4 respectively indicate samples XRD-1~4. Sample XRD-3 was drilled on a whitish fracture filling. For results of the XRD analyses see TEXT-FIGURE 1 The slice was impregnated with epoxy to make a thin section. Calcite veinlets are marked with green arrows.
Fig. 7. Petrographic thin section photographed with cross-polarized light to reveal the internal texture of the rock sample. Apical angles and cone axis divergences were measured from Cone 01 to 12 (numbered 1~12). Cones 1, 3, and 5 were situated just above the base of the cone-in-cone layer.
Fig. 8. Photograph showing the sharp contact between the cone-in-cone layer and the underlying muddy silt layer. The dark lines in the muddy silt layer are most likely solution seams (marked with yellow arrows). Calcite veinlets are marked with green arrows.
Wang and Lee : Notes on Cone-In-Cone Structures from Taiwan 15
