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Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea
Quaternary International xxx (2014) 1e12
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Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea Buyanbat Narantsetseg a, Gil Young Kim b, *, Jin-wook Kim a, Tae Soo Chang b, Gwang Soo Lee b, Hunsoo Choi b, Seong-Pil Kim b a b
Department of Earth System Sciences, Yonsei University, Seoul 120-749, South Korea Petroleum & Marine Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
Sixteen piston core samples collected from the Heuksan Mud Belt on the southeastern inner shelf of Korea were analyzed to characterize sediment property and distribution in relation to interpreted seismic units. The results from seven of 16 cores are presented in this study using core locations along a seismic track line. Variations in physical properties with depth gradually increased and/or decreased, depending on the characteristics of the specific property. Property patterns are primarily the result of dewatering caused by compaction and/or consolidation. Significant variations in depth are due to differences in sediment texture. In particular, core P03 is largely composed of sandy sediments below 170 cm. All core data come from three specific seismic Units: I, IIa and IIb, in descending order. The seismic patterns that define these units are interpreted as related to the rate of sea-level change during transgressions and depositional processes during the Holocene. Regionally, the variation of physical properties along the seismic profile is likely to reflect the relative characteristics of the seismic units. Unit I is characterized by low shear strength/wet bulk density and high porosity. Unit IIa appears to have higher shear strength than Units I and IIb. Unit IIb shows high wet bulk density and velocity. These observations suggest that the physical properties are mainly controlled by depositional processes related to sea-level change. Clay fabric analysis that uses a scanning electron microscope for two core samples shows the change of particle arrangement due to compaction caused by overburden loading with burial depth. In the upper part of the core, edge-to-edge and edge-to-face contacts dominate. In contrast, faceto-face contact characterized by the well-oriented arrangement of clay particles frequently occurs in the lower parts of the cores, indicating sediment compaction or initial consolidation caused by overburden pressure. Ó 2014 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Physical properties Seismic units Clay fabric SEM Heuksan Mud Belt
1. Introduction The physical and acoustic properties of marine sediments are important for understanding the geological history of marine environments (Hamilton, 1970; Hamilton and Bachman, 1982). Porosity in marine sediments is largely determined by composition, texture, and clay fabric (Stoll, 1977, 1989; Richardson et al., 1997). Bulk density, shear strength, and velocity increase as water content and porosity decrease as a result of overburden pressure after deposition. Sediment texture (mean grain size and clay content) is an important factor in the determination of the physical and
* Corresponding author. Korea Institute of Geoscience and Mineral Resources, Gas Hydrate Department, #124 Gwahang-no, Yuseong-gu, Daejeon 305-350, South Korea. E-mail address: [email protected] (G.Y. Kim).
acoustic properties of unconsolidated marine sediments (Kuster and Toksoz, 1974; Hamilton and Bachman, 1982; Kim et al., 2001a,b, 2007, 2011, 2012). Knowledge of clay fabric structure is important for understanding the physical and mechanical properties of marine sediments (Bennett et al., 1981; Bryant et al., 1990; Kim et al., 1998, 2007, 1999a,b). In particular, shear wave velocity and shear strength are largely controlled by the orientation of clay particles with burial depth (Kim et al., 2007). The physical nature and consolidation behavior of clay-rich sediments can be understood through knowledge of the microstructure (Bennett et al., 1977; Bryant et al., 1990; Kim et al., 1998). Kim et al. (1998, 1999a,b) studied the relationship between mineralogy and changes in clay fabric to examine how they affected the petrophysical properties of sediments. They showed that most clay domains develop face-toface contacts and become well-orientated with burial depth.
http://dx.doi.org/10.1016/j.quaint.2014.03.037 1040-6182/Ó 2014 Elsevier Ltd and INQUA. All rights reserved.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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The Yellow Sea including the Heuksan Mud Belt (Fig. 1) was completely exposed during the last glacial maximum (LGM), when the paleoshoreline was located about 120 m below the present sea level (Bloom and Park, 1985; Pirazzoli, 1991). Thus sea-level rise during the Holocene has significantly affected the formation of sedimentary units in the Yellow Sea (Jin and Chough, 1998; Jin et al., 2002; Shinn et al., 2007). The origin of sediments in the central Yellow Sea is well studied (Milliman et al., 1987; Alexander et al., 1991). This contrasts with the origin of sediments in the Heuksan Mud Belt, which is still poorly understood and the subject of debate (Park et al., 2000; Lee and Chu, 2001; Lim et al., 2013). Moreover, there is little information available on the physical properties and clay fabric of the Heuksan Mud Belt sediments (Kim et al., 2000). The purposes of this study are: (a) to quantify variations in the physical properties and seismic velocity of sediments in the Heuksan Mud Belt with increasing sediment depth, and (b) to evaluate the relationships between physical properties based on seismically defined units. In addition, we investigated changes in grain orientation with burial depth, which highlights the changes in clay fabric caused by compaction from overburden pressure.
2. Geological setting The Yellow Sea shelf, characterized by a low-gradient epicontinental sea, was completely exposed in a subaerial environment during the last glacial period. As the sea rapidly rose, late Pleistocene weathered deposits were unconformably overlain by transgressive deposits of variable thickness (Shinn et al., 2007). In the eastern part of the Yellow Sea, the transgressive deposits comprise retrograde tidal flat and channel facies, with overlying sand ridges and sheets above the ravinement surface (Lee and Yoon, 1997; Kim et al., 1999a,b; Shinn et al., 2007). The shelf ridges evolved from Pleistocene muddy tidal deposits to ridge surfaces covered by a Holocene sand veneer during the transgression (Jin et al., 2002; Shinn et al., 2007). Shinn et al. (2007) presented six transgressive depositional units in the southeastern Yellow Sea. The Heuksan Mud Belt, located at the southwestern tip of the Korean peninsula, consists mainly of fine-grained sediments. As to the origin of the sediments, there are two main hypotheses: one suggests that the sediments originate from the Geum River (Lee and Chu, 2001; Chough et al., 2004), whereas the other suggests that they were largely derived from the Changjiang or Huanghe rivers prior to about 7 ka, and have undergone significant erosion and reworking
Fig. 1. Map showing bathymetry and core locations for the Heuksan Mud Belt study area. The seismic track line is marked along with core location. Note the location of deep cores (YSDP 102, 103) drilled by the Korea Institute of Geoscience and Mineral Resources (KIGAM). Bathymetry contours are in meters.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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since (Park et al., 2000; Lim et al., 2013). Shinn et al. (2007) suggested that the depositional processes and variability of the transgressive deposits in the Heuksan Mud Belt were largely controlled by the rate of sea-level rise related to global flooding events triggered by melt water pulses. In addition, the oceanographic regime in the Yellow Sea has probably significantly influenced the distribution and morphology of the transgressive and Holocene deposits. 3. Materials and methods Sixteen piston core samples were obtained from the Heuksan Mud Belt on board R/V Tamhae II, Korea Institute of Geoscience and Mineral Resources (KIGAM). Fifteen cores (except one) are dominated by clay and silt sediments (6e7 Ø in mean grain size); muddy sand (2e4 Ø in mean grain size) is found in places within the southern part of the study area (KIGAM, 2012). Core descriptions (KIGAM, 2012) support the presence of various sedimentary facies including massive sand, shelly sand, shelly mud, laminated mud, homogeneous mud, and bioturbated mud. In this study, the results for seven cores (Table 1) along the seismic track line (Figs. 1 and 2) are presented. In the laboratory, the cores were split. One half of each core was used for visual descriptions and the other half was used for physical property, clay fabric, and X-Ray diffraction (XRD) analyses. Table 1 Summary of locations, water depths, core lengths and seismic units of the core samples used in this study. Sites
12HMB-P02 12HMB-P03 12HMB-P07 12HMB-P10 12HMB-P13 12HMB-P14 12HMB-P16
Location
Water Core Seismic depth (m) length (m) units
Latitude
Longitude
33 420 51.98500 33 460 08.28300 33 550 46.03600 34 020 41.95100 34 090 35.61000 34 160 43.61800 34 290 13.78800
125 480 26.29900 106.8 125 460 20.86900 82.8 125 420 31.60500 73.0 0 00 125 39 47.245 74.0 125 370 01.68600 63.2 125 340 12.00200 60.0 125 290 11.86100 54.4
5.07 5.0 7.43 6.6 0.69 7.38 7.44
Unit Unit Unit Unit Unit Unit Unit
IIa IIa IIa IIb I I I
3
3.1. Velocity, physical properties, and grain size The pulse transmission technique (Birch, 1960), using a set of piezoelectric transducers (PZTs), was employed to measure the velocity of samples taken from the cores. The resonance frequency was maintained at 1 MHz to assure that the wavelength of the transmitted pulse was greater than the largest grain size in the specimens (Kolsky, 1953). The velocity measurement system was designed by KIGAM. Physical properties (water content, porosity, density, etc.) were determined using the weight-volume method (Boyce, 1976). Sample weight was measured using an electronic balance. Each sample was cooled in desiccators after it was dried overnight in an oven at a temperature of approximately 105 C. The dry weight and volume of the sample were determined for dry samples by using a heliumdisplacement pycnometer (Model: Ultra PYC, Quantachrome Instruments). A salt correction was made assuming 35& salinity (Boyce, 1976). Shear strength was manually measured on each core sample with a hand-vane apparatus (Blum, 1997). Physical property analyses and velocity measurements were performed at 10 cm depth intervals under room temperature (23 C) conditions. Grain-size analyses for the mud fraction (>4 Ø) were performed using Sedigraph 5100 (Micromeritics); for the sand fraction (<4 Ø), a Ro-tap sieve shaker was used. Textural parameters and relative amounts of sand, silt, and clay were calculated using the classifications of Folk and Ward (1957) and Folk (1968). 3.2. Clay fabric and clay mineralogy A Scanning Electron Microscope (SEM) was used for particle fabric analysis. SEM observations were carried out with a JEOL JSM-5610LV (30 kV and a beam current of 80e90 nA) at Yonsei University, Seoul, Korea. The initial sample pretreatments were performed according to the L.R. White (LRW) resin impregnation method described by Kim and Peacor (1995). All interstitial water was removed from the samples by being replaced by 100% methyl alcohol for 24 h. Then the samples were further prepared with a mixture of methyl alcohol and LRW resin overnight. Finally, the samples were dried in a 60 C oven
Fig. 2. Seismic (air gun and Chirp) profiles showing the Heuksan Mud Belt along with piston core locations (KIGAM, 2013). Note Units I, IIa, IIb, IIIa and IIIb in descending order. YSDP-102 and 103 are marked.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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for about three days, after which pure LRW resin was added to all samples. The samples were polished using diamond paste and then coated with gold. The samples for clay fabric analysis were taken from depths of 120 and 392 cm at site 12HMB-P02. Six samples taken from various depths at three sites (12HMBP02, 12HMB-P03, and 12HMB-P07) were used for clay mineral analysis. X-Ray diffraction (XRD) analyses were performed on airdried and ethylene-glycolated clay samples at a scan speed of 1 / min with a Rigaku Miniflex II automated diffractometer utilizing CuKa radiation at the Department of Earth System Sciences of Yonsei University, Korea. 4. Results 4.1. Velocity and physical properties Site 12HMB-P02 (or P02, core sites are hereafter referred to in this simplified manner) is located in the most southern part of the study area (Fig. 1). This location, characterized by the deepest water depths, belongs to seismic Unit IIa (Fig. 2; Table 1). As shown in Fig. 3, the physical properties significantly change below a depth of 340 cm, corresponding to an increase in sand content (>60%). The porosity and water content abruptly decrease from 67 to 44% and from 45 to 24%, respectively. In contrast, the bulk density increases from 1.50 to 1.89 g/cm3. The velocity and shear strength also show abrupt increases from 1470 to 1561 m/s and from 5 to 37 kPa, respectively. Correspondingly, the values at depths shallower than 340 cm are almost constant. The mean grain size ranges from 6.1 to 7.46 Ø with an average of 6.86 Ø. The sediment texture is mostly composed of silt (87.5% on average). Sand content ranges from 2.2 to 12.3% with an average of 3.8%.
Site P03 is located in the southern part of the study area (Fig. 1) and is situated within Unit IIa on the seismic line (Fig. 2; Table 1). The physical properties are significantly different below a depth of 210 cm (Fig. 4), caused by the large increase in sand content. The porosity and water content range from 59 to 37% and from 37 to 18%, respectively, whereas the bulk density increases with sediment depth from 1.61 to 2.0 g/cm3. The velocity also increases from 1571 to 1708 m/s, and the mean grain size significantly increases from 6.99 to 2.41 Ø. Site P07 is located north of P03, and belongs to the margin of seismic Unit IIa (Figs. 1 and 2; Table 1). The porosity and water content in the lower part of the core from a burial depth of approximately 340 cm are slightly higher (>60% porosity, >40% water content) than in the upper part of the core (Fig. 5). Similarly, the wet bulk density below a depth of 340 cm is lower (<1.6 g/cm3) than in the upper part of the core (>1.6 g/cm3). The velocity gradually decreases from 1489 to 1423 m/s, exhibiting little fluctuation with depth (Fig. 5). As shown in Fig. 5, the shear strength from the seafloor to a depth of 160 cm gradually increases from 15 to 25 kPa, and is almost constant below that depth. Correspondingly, variations in the physical property data with sediment depth are characterized by the reverse trend, compared to their variations of normal sediments with depth. The silt content dominates (90.7% on average) throughout the core. The mean grain size ranges between 5.9 and 6.48 Ø. Site P10 is located in the central part of the study area (Fig. 1) and only within seismic Unit IIb (Fig. 2; Table 1). The porosity and water content are almost constant (56% and 36% on average, respectively) throughout the core (Fig. 6). The wet bulk density ranging between 1.60 and 1.78 g/cm3 (1.66 g/cm3 average) corresponds inversely to porosity. Both velocity and shear strength increase slightly with sediment depth (1480e1520 m/s, 10e17 kPa)
Fig. 3. Profiles of physical properties, velocity and sediment texture for core sample obtained from P02. Note the significant change of physical properties below 340 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 4. Profiles of physical properties, velocity and sediment texture for core sample obtained from P03. Note the significant change in values due to increasing sand content below 210 cm.
Fig. 5. Profiles of physical properties, velocity and sediment texture for core sample obtained from P07. Note reverse trend of physical property values below 200 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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above a depth of approximately 140 cm, and below exhibit little fluctuation to the bottom. Mean grain size ranges between 5.0 and 6.5 Ø (5.9 Ø on average). The sand content above a depth of 320 cm is higher than in the lower part of the core (Fig. 6). Site P13 is situated in the central part of the study area (Fig. 1) and within the southern tip of seismic Unit I (Fig. 2; Table 1). This core is the shortest (0.69 m) of all the cores (Table 1). As shown in Fig. 7, the porosity (70.5% on average) and water content (48% on average) do not show significant variation. The wet bulk density at a sediment depth of 45 cm has the lowest value (1.44 g/cm2) with an average of 1.48 g/cm2. The velocity ranges from 1478 to 1495 m/s. whereas the shear strength does not fluctuate throughout the core. Mean grain size ranges from 5.99 to 6.50 Ø. Sand is distributed throughout the core. Site P14 is located between P13 and P16. The location is in the central part of seismic Unit I (Fig. 2; Table 1). As shown in Fig. 8, the porosity and water content show a decreasing trend with sediment depth (from 68 to 60.83% in porosity, from 46.1 to 38.1% in water content). Correspondingly, the wet bulk density gradually increases from 1.49 to 1.64 g/cm3. Unusually, the velocity is characterized by low values (1340e1360 m/s) due to degassing cracks at depth intervals of 380e410 cm. The sediment shear strength at a depth of approximately 340 cm gradually increased from 2 to 9 kPa. The mean grain size ranges from 5.6 to 6.5 Ø. The average contents of sand, silt, and clay are 5.8%, 88.7%, and 5.46%, respectively. Site P16 is situated in the northern part of study area (Fig. 1) and is located within the northern tip of seismic Unit I (Fig. 2; Table 1). The porosity (60e69%) and water content (37e47%) seem likely to decrease with sediment depth (Fig. 9), but there are no significant differences throughout the core. Similarly, the variations of velocity and wet bulk density are not significant with sediment depth. In
contrast, the shear strength gradually increases with sediment depth (from 2 to 10 kPa) (Fig. 9). Mean grain size ranges from 5.3 to 6.6 Ø (6.13 Ø on average). 4.2. Clay fabric and clay mineralogy Clay fabric analysis was performed on the samples to investigate the rearrangement of grains caused by increased burial depth. Fig. 10a shows the clay fabric for a sample taken at a depth of 120 cm at P02. The sediment used for SEM analysis is characterized by high porosity (>70%) and water content (>49%) and low shear strength (<3 kPa) (refer to Fig. 3 for physical property data). The sediment textures are composed dominantly of silt (84%), with some sand (4%) and clay (11%). Illite and smectite are frequently identified in the SEM micrographs. The major clay particles are characterized by edge-to-edge (EE) and edge-to-face (EF) contacts. Fig. 10b shows the clay fabric from the sample taken from a depth of 392 cm at P02. The porosity and water content of the sediment have decreased to 45% and 24%, respectively, due to the effects of the overburden pressure. Furthermore, the shear strength also increases from 3 to 18 kPa. The dominant composition is silt (approximately 86%), with smaller amounts of sand (2.3%) and clay (10%). Similarly, the illite and smectite particles are readily observed in the SEM micrographs. Overall, face-to-face (FF) contacts are more dominant than edge-to-edge (EE) and edge-to-face (EF) contacts (Fig. 10b). Typical framboidal pyrites are easily identified in the SEM micrographs from a sediment depth of 120 cm (Fig. 10c). Calcite is also frequently observed in the sediment (Fig. 10d). Based on the XRD analysis performed on the samples taken from sites P02, P03 and P07, the major clay minerals are identified as
Fig. 6. Profiles of physical properties, velocity and sediment texture for core sample obtained from P10. Note decreasing velocity and shear strength below 100 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
Fig. 7. Profiles of physical properties, velocity and sediment texture for core sample obtained from P13. Note constant shear strength throughout the core.
Fig. 8. Profiles of physical properties, velocity and sediment texture for core sample obtained from P14. Note the low velocity and shear strength due to degassing cracks between 380 and 410 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 9. Profiles of physical properties, velocity and sediment texture for core sample obtained from P16. Note increasing shear strength throughout the core.
illite, chlorite, chlorite þ kaolinite, and kaolinite (Fig. 11). Illite is the most abundant of all clay minerals. 5. Discussion 5.1. Variation of velocity and physical properties within seismic units Based on high-resolution seismic profiles (frequency of 3e 10 kHz), the subsurface sedimentary strata of the Heuksan mud deposits can be classified into five seismic units: Unit I, Unit II (divided into two subunits IIa and IIb), and Unit III (IIIa and IIIb) (with the sequence in descending order) (Fig. 2)(KIGAM, 2013). Unit I is the uppermost depositional sequence; it is characterized by a semi-transparent character and weak reflectors, and divided by a strong erosional reflector from lower units, and restricted to the northern part of the study area (Figs. 1 and 2). Unit II is distributed within the southern part of the study area and is characterized by inclined reflections that indicate sediment progradation southward and eastward. Unit IIa and IIb are separated by erosional surface and dip direction of an internal reflector. Unit III is mostly covered by Unit I; it is restricted to the northern area with low-angle inclined reflections (KIGAM, 2013). Similar types of sequences occur throughout the stratigraphic sections in
the southeastern Yellow Sea (Jin and Chough, 1998; Jin et al., 2002; Shinn et al., 2007; KIGAM, 2013), although multiple suggestions for the classification of the sequence are still under debate (Jin and Chough, 1998; Park et al., 2000; Lee, 2012). Detailed interpretation of the seismic units is beyond the scope of this study. Three sites (P07, P10, and P16) which are representative of three main seismic units were selected to compare physical property data. Fig. 12 shows profiles of the physical properties for the three cores. As discussed earlier, P16 is located in seismic Unit I, P10 in seismic Unit IIb, and P07 in seismic Unit IIa. As shown in Fig. 12, grain size in P10 appears to be coarser than in P07 and P16 (Table 2). Correspondingly, the wet bulk density and velocity show high values in accordance with mean grain size (Fig. 12; Table 2). In the case of porosity, the values at P16 are higher than in the other two cores. Shear strength observed down-core at P07 shows the highest value of the three cores, especially in the upper part of the core (shallower than depths of 200 cm) (Fig. 12; Table 2). This suggests that sedimentary processes and the degree of compaction after deposition are different for each unit. Our results highlight how the physical properties of marine sediments are controlled by their sedimentary environments and processes, and in conjunction with their diagenesis after deposition (Hamilton, 1970; Hamilton and Bachman, 1982).
Table 2 Summary of the physical properties for the three cores corresponding to each seismic unit in descending order. Sites/Units
Mean grain size (Ø)
Porosity (%)
Wet bulk density (g/cm3)
Shear strength (kPa)
Velocity (m/s)
P16 (Unit I) P07 (Unit IIa) P10 (Unit IIb)
6.13 6.22 5.95
65.7 59.7 59.7
1.56 1.61 1.66
6.6 16.8 12.5
1470 1453 1489
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 10. Scanning electron micrographs showing clay fabric and clay orientation from the samples taken from (a) 120 cm and (b) 392 cm depths at P02. EE: Edge-to-Edge, EF: Edgeto-Face, FF: Face-to-Face. Note: (c) pyrite framboids at 120 cm depth and (d) calcite at 392 cm depth. EDS spectra show chemical compositions of pyrite and calcite.
The inter-relationships of physical properties analyzed for the three cores are grouped distinctly in accordance with each seismic unit (Figs. 13e15). As shown in Fig. 13, P16 (corresponding to seismic Unit I) is characterized by low shear strength and density, and high porosity (Table 2). The neighboring area, including Unit I, is largely covered by muddy sediments consisting of homogeneous or bioturbated mud (KIGAM, 2012). These sediments were mainly derived from neighboring rivers (e.g., the Huanghe and Seomjin rivers) during sea-level highstands (Lee and Chough, 1989; Alexander et al., 1991; Lee and Yoon, 1997; Park et al., 2000; Shinn et al., 2007; Lim et al., 2013). The wet bulk density and porosity of P10, located within seismic Unit IIa, are partly crossed
over with Unit IIb (Fig. 13). Similarly, the relationship between porosity and velocity is grouped well according to each unit (Fig. 14). Fig. 15 shows the relationships between mean grain size and wet bulk density/shear strength for the three sites. As shown in Fig. 15, P10 and P16 (corresponding to seismic Units IIb and I) are grouped distinctly. On the other hand, the wet bulk density of P07 (corresponding to Unit IIa) overlaps in both P10 and P16. Overall, P10 has a wide range of mean grain sizes, including the coarsest sediments, although the difference between the observed values is small (Table 2). In contrast, P07 shows a narrow range of mean grain sizes (Fig. 15). The relationships between physical properties at P10 occur as a scattering pattern with a wide distribution (5e
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 11. X-ray powder diffraction patterns of <2 mm fraction samples taken from P02, P03 and P07. Major clay mineralogy of these samples is chlorite (Ch), illite (I), and kaolinite (K). Note the minor smectites (16.7 A peak).
Fig. 12. Comparison of physical properties for three cores (P07, P10 and P16) obtained from seismic Unit I (P16), Unit IIa (P7) and Unit IIb (P10). Note gradual patterns of physical properties corresponding to each core.
6.5 Ø) of mean grain sizes. As discussed earlier, the seismic profiles of these units (Units IIa and IIb) show prograding reflection patterns toward the south and southeast in study area. Unit I at the location of P16 is characterized by an acoustically transparent layer with low shear strength and high porosity. Therefore, the sediments of seismic Unit I can be interpreted as a younger and softer formation corresponding to an initial step in the consolidation processes.
5.2. Characteristics of clay fabric associated with physical property variations Clay fabric is defined by the orientation and arrangement of particles and particle-to-particle relationships (Bennett et al., 1991). Various factors, such as consolidation, mineralogy, grain size, and diagenesis, affect clay fabric (O’Brien, 1970; Bennett et al., 1981; Bryant et al., 1991; Tribble et al., 1991). Therefore, clay fabric can
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 13. Relationships between shear strength (kPa) and porosity (%) / wet bulk density (g/cm3) for the three cores. Note the distinct differences between cores corresponding to each seismic unit.
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be used to improve our understanding of the mechanisms of consolidation and compaction that result from porosity reduction in sediments (Bennett et al., 1977; Kim et al., 2007). SEM micrographs (Fig. 10) recorded on core samples taken at sediment depths of 120 and 390 cm are characterized by different grain contacts, showing the expected consolidation effect with increasing burial depth. In particular, face-to-face contacts are more frequently identified in the SEM micrograph of the 390 cm depth sample compared to the one from 120 cm depth (Fig. 10b). In comparison, edge-to-edge contacts are randomly observed in the SEM micrographs (Fig. 10b). Generally, clay sediments with preferred orientations display high shear strength due to a greater surface area contact and higher bonding force, whereas clay sediments with random microstructure have lower shear strength (Kim et al., 2007). In other words, the microstructure of sediment is closely linked to its physical and mechanical properties. As discussed earlier in this study, the shear strength is significantly increased (from 3 to 18 kPa) with burial depth, compared to other physical properties. Therefore, sediment compaction by increasing overburden pressure seems likely to play an important role in the development of preferred orientations (face-to-face contacts) of clay particles. In the SEM micrographs (Fig. 10c), typical authigenic pyrites formed by ferrous ions and disulfide ions in anaerobic environments are frequently observed. Formation of authigenic pyrite is generated by sulfide-reducing bacteria under anaerobic conditions (Lynch, 1983; Kim et al., 1998, 2007). Occasionally, the formation of authigenic pyrite framboids in fine-grained sediment may influence clay fabric formation, and disturb the preferred orientation of clay particles (Kim et al., 1998, 2007). In addition, gas bubbles in gassy sediments may rearrange of clay particles in the sediment structure (Chiou et al., 1991). However, in this study, grain orientation caused by gas bubbles was not observed in the micrographs. SEM and XRD analysis show illite as the most abundant among all clay minerals and with the highest degree of preferred orientation with burial depth (Fig. 10).
6. Conclusions Fig. 14. Relationships between porosity (%) and velocity (m/s) for the three cores. Note the distinct differences between cores corresponding to each seismic unit.
Variations in physical properties with depth generally show gradual increases or decreases as a result of dewatering caused by compaction and/or consolidation. The one exception to this is significant variation in sediment texture. The physical properties of the core samples obtained from units I, IIa and IIb are readily classified, which shows that the observed patterns of sedimentation are consistent with interpreted seismic units. This indicates that the various depositional processes and system related to changes in the oceanographic regime in the study area have a strong influence on sediment properties. Clay fabric analyses of two samples taken from different sediment depths characterized different grain-contact structures (edge-to-edge, face-to-face, etc.), which correspond to the variations in physical properties such as porosity and shear strength. This close link between clay fabric and physical properties indicates that the process of sediment compaction with burial depth and/or initial consolidation after deposition is caused significantly by overburden pressure.
Acknowledgements Fig. 15. Relationships between mean grain size (phi) and wet bulk density (g/cm3) and shear strength (kPa) for the three cores. Note the distinct difference between cores corresponding to each seismic unit, although Unit IIa overlaps between Unit I and Unit IIb.
This work was supported by the Korea Institute of Geoscience and Mineral Resources (KIGAM) and the “International Ocean Discovery Program” project funded by the Ministry of Oceans and Fisheries, Korea.
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References Alexander, C.R., DeMaster, D.J., Nittrouer, C.A., 1991. Sediment accumulation in a modern epicontinental-shelf setting: the Yellow Sea. Marine Geology 98, 51e 72. Bennett, R.H., Bryant, W.R., Keller, G.H., 1977. Clay Fabric and Geotechnical Properties of Selected Submarine Sediment Cores From the Mississippi Delta. NOAA: Professional Paper 9. US Departments of Commerce, 86 pp. Bennett, R.H., Bryant, W.R., Keller, G.H., 1981. Clay fabric of selected submarine sediment: fundamental properties and models. Journal of Sedimentary Petrology 51, 127e152. Bennett, R.H., O’Brien, N.R., Hulbert, M.H., 1991. Determinants of clay and shale microfabric signatures: processes and mechanism. In: Bennett, R.H., Bryant, B.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 5e32. Birch, F., 1960. The velocity of compressional waves in rocks up to 10 kilobars. Journal of Geophysical Research 65, 1083e1102. Bloom, A.L., Park, Y.A., 1985. Holocene sea-level history and tectonic movements, Republic of Korea. Quaternary Research Japan 24, 293e315. Blum, P., 1997. Physical Properties Handbook: a Guide to the Shipboard Measurements of Physical Properties of Deep-sea Cores. ODP Tech. Note, 26. Boyce, R.E., 1976. Definition and Laboratory Techniques of Compressional Sound Velocity Parameter and Wet-water, Wet Bulk Density, and Porosity Parameter by Gravimetric and Gamma Ray Attenuation Zion Techniques. Initial Reports of the Deep Sea Drilling Project 33. Government Printing Office, Washington, DC, U.S., pp. 931e958 Bryant, W.R., Bennett, R.H., Burkett, P.J., Rack, F.R., 1991. Microfabric and physical properties characteristics of a consolidated clay section: ODP site 697, Weddell Sea. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of FineGrained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 73e92. Bryant, W.R., Bennett, R.H., Burkett, P.J., Rack, F.R., 1990. The fabric of a consolidating clayey sediment column, ODP site 697. In: Proceedings of the Ocean Drilling Program, Scientific Results, vol. 113. Chiou, W.A., Bryant, W.R., Bennett, R.H., 1991. Clay fabric of gassy submarine sediments. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 333e352. Chough, S.K., Lee, H.J., Chun, S.S., Shinn, Y.J., 2004. Depositional processes of late Quaternary sediments in the Yellow Sea: a review. Geosciences Journal 8, 211e 264. Folk, R.L., 1968. Petrology of Sedimentary Rocks. Hemphill’s, Austin, Texas, 170 pp. Folk, R.L., Ward, W.C., 1957. Brazos River. A study ion significance of grainesize parameters. Journal of Sedimentary Petrology 25, 3e27. Hamilton, E.L., 1970. Sound velocity and related properties of marine sediments, North Pacific. Journal of Geophysical Research 75, 4423e4446. Hamilton, E.L., Bachman, R.T., 1982. Sound velocity and related properties of marine sediments. Journal of Acoustical Society America 72, 1891e1904. Jin, J.H., Chough, S.K., 1998. Partitioning of transgressive deposits in the southeastern Yellow Sea: a sequence stratigraphic interpretation. Marine Geology 149, 79e82. Jin, J.H., Chough, S.K., Ryang, W.H., 2002. Sequence aggradation and systems tracts partitioning in the mid-eastern Yellow Sea: roles of glacio-eustasy, subsidence and tidal dynamics. Marine Geology 184, 249e271. KIGAM, 2012. Geological Characterization of Recent Muddy Sediment for Reservoir Potential, and in situ Analysis of Shallow Gas. KIGAM report (GP2012-0052012(1). 199 pp. KIGAM, 2013. Geological Characterization of Recent Muddy Sediment for Reservoir Potential, and in situ Analysis of Shallow gas. KIGAM report (GP2012-0052013(2). 169 pp. Kim, D.C., Kim, G.Y., Yi, H.I., Seo, Y.K., Lee, G.S., Jung, J.H., Kim, J.C., 2012. Geoacoustic provinces of the South Sea shelf off Korea. Quaternary International 263, 139e 147. Kim, G.Y., Kim, D.C., Kim, S.J., Seo, Y.K., Jung, J.H., Kim, Y.E., 2000. Physical properties of Southeastern Yellow Sea Mud (SEYSM): comparison with the East Sea and the South Sea mudbelts of Korea. Journal of the Korean Society of Oceanography 5, 335e345.
Kim, G.Y., Yoon, H.J., Kim, J.W., Kim, D.C., Khim, B.K., Kim, S.Y., 2007. The effects of microstructure on shear properties of shallow Marine sediments. Marine Georesources and Geotechnology 25, 37e51. Kim, G.Y., Kim, D.C., Yoo, D.G., Shin, B.K., 2011. Physical and geoacoustic properties of surface sediments off eastern Geoje Island, South Sea of Korea. Quaternary International 230, 21e33. Kim, J.W., Peacor, D.R., 1995. A technique for maintaining texture and permanent expansion of smectite interlayers for TEM observations. Clays and Clay Minerals 43, 51e57. Kim, J.W., Bryant, W.R., Watkins, J.S., Tieh, T.T., 1998. Mineralogical and fabric changes of changes of shale during burial diagenesis and their effects on petrophysical properties. Gulf Coast Association of Geological Societies Transactions 48, 139e150. Kim, J.W., Bryant, W.R., Watkins, J.S., Tieh, T.T., 1999a. Electron microscopic observations of shale diagenesis, offshore Louisiana, USA, Gulf of Mexico. Geo-Marine Letters 18, 234e240. Kim, Y.H., Lee, H.J., Chun, S.S., Han, S.J., Chough, S.K., 1999b. Holocene transgressive stratigraphy of a macrotidal flat in the southeastern Yellow Sea: Gomso Bay, Korea. Journal of Sedimentary Research 69, 328e337. Kim, D.C., Sung, J.Y., Park, S.C., Lee, G.H., Choi, J.H., Kim, G.Y., Seo, Y.K., Kim, J.C., 2001a. Physical and acoustic properties of shelf sediments, the South sea of Korea. Marine Geology 179, 39e50. Kim, J.W., Lee, Y.E., Tieh, T.T., Bryant, W.R., 2001b. Effects of laboratory consolidation on petrophysical properties of fine-grained marine sediments: electron microscopic observations. Marine Georesources and Geotechnology 18, 1e35. Kolsky, H., 1953. Stress Waves in Solids. Clarendon Press, Oxford. Kuster, G., Toksoz, M., 1974. Velocity and attenuation of seismic waves in two-phase media: part 1. Theoretical formulations. Geophysics 39, 587e606. Lee, H.J., Chough, S.K., 1989. Sediments distribution, dispersal and budget in the Yellow Sea. Marine Geology 87, 195e205. Lee, H.J., Chu, Y.S., 2001. Origin of inner-shelf mud deposit in the southeastern Yellow Sea: Huksan Mud Belt. Journal of Sedimentary Research 71, 144e154. Lee, H.J., Yoon, S.H., 1997. Development of stratigraphy and sediment distribution in the northeastern Yellow Sea during Holocene sea-level rise. Journal of Sedimentary Research 67, 341e349. Lee, G.S., 2012. Depositional History and Environment and Sequence Stratigraphy of the Late Quaternary Deposits in the Yellow Sea and East China Sea (Ph.D. Thesis). Pukyong National University, Busan, Korea, 166 pp. Lim, D.I., Choi, J.Y., Shin, H.H., Rho, K.C., Jung, H.S., 2013. Multielement geochemistry of offshore sediments in the southeastern Yellow Sea and implications for sediment origin and dispersal. Quaternary International 298, 196e206. Lynch, J.M., 1983. Soil Biotechnology. Blackwell Scientific Publications, Oxford, 191 pp. Milliman, J.D., Qin, Y.S., Ren, M.E., Saito, Y., 1987. Man’s influence on the erosion and transport of sediment by Asian rivers: the Yellow River (Huanghe) example. Journal of Geology 95, 751e762. O’Brien, N.R., 1970. The fabric of shale: an electron microscope study. Sedimentology 15, 229e246. Park, S.C., Lee, H.H., Han, H.S., Lee, G.H., Kim, D.C., Yoo, D.G., 2000. Evolution of late Quaternary mud deposits and recent sediment budget in the southeastern Yellow Sea. Marine Geology 170, 271e288. Pirazzoli, P.A., 1991. World Atlas of Holocene Sea-level Changes. Elsevier, Amsterdam, 300 pp. Richardson, M.D., Lavoie, K.B., Briggs, K.B., 1997. Geoacoustic and physical properties of carbonate sediments of the lower Florida keys. Geo-Marine Letters 17, 316e 324. Shinn, Y.J., Chough, S.K., Kim, J.W., Woo, J., 2007. Development of depositional system in the southeastern Yellow Sea during the postglacial transgression. Marine Geology 239, 59e82. Stoll, R.D., 1977. Acoustic waves in ocean sediments. Geophysics 42, 715e725. Stoll, R.D., 1989. Sediment Acoustics, Lecture Notes in Earth Sciences. SpringerVerlag, New York, 153 pp. Tribble, J.S., Mackenzie, E.T., Urmos, J., 1991. Physical property changes accompanying deep burial of clay-rich sediments. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 93e108.
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Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea Buyanbat Narantsetseg a, Gil Young Kim b, *, Jin-wook Kim a, Tae Soo Chang b, Gwang Soo Lee b, Hunsoo Choi b, Seong-Pil Kim b a b
Department of Earth System Sciences, Yonsei University, Seoul 120-749, South Korea Petroleum & Marine Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
Sixteen piston core samples collected from the Heuksan Mud Belt on the southeastern inner shelf of Korea were analyzed to characterize sediment property and distribution in relation to interpreted seismic units. The results from seven of 16 cores are presented in this study using core locations along a seismic track line. Variations in physical properties with depth gradually increased and/or decreased, depending on the characteristics of the specific property. Property patterns are primarily the result of dewatering caused by compaction and/or consolidation. Significant variations in depth are due to differences in sediment texture. In particular, core P03 is largely composed of sandy sediments below 170 cm. All core data come from three specific seismic Units: I, IIa and IIb, in descending order. The seismic patterns that define these units are interpreted as related to the rate of sea-level change during transgressions and depositional processes during the Holocene. Regionally, the variation of physical properties along the seismic profile is likely to reflect the relative characteristics of the seismic units. Unit I is characterized by low shear strength/wet bulk density and high porosity. Unit IIa appears to have higher shear strength than Units I and IIb. Unit IIb shows high wet bulk density and velocity. These observations suggest that the physical properties are mainly controlled by depositional processes related to sea-level change. Clay fabric analysis that uses a scanning electron microscope for two core samples shows the change of particle arrangement due to compaction caused by overburden loading with burial depth. In the upper part of the core, edge-to-edge and edge-to-face contacts dominate. In contrast, faceto-face contact characterized by the well-oriented arrangement of clay particles frequently occurs in the lower parts of the cores, indicating sediment compaction or initial consolidation caused by overburden pressure. Ó 2014 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Physical properties Seismic units Clay fabric SEM Heuksan Mud Belt
1. Introduction The physical and acoustic properties of marine sediments are important for understanding the geological history of marine environments (Hamilton, 1970; Hamilton and Bachman, 1982). Porosity in marine sediments is largely determined by composition, texture, and clay fabric (Stoll, 1977, 1989; Richardson et al., 1997). Bulk density, shear strength, and velocity increase as water content and porosity decrease as a result of overburden pressure after deposition. Sediment texture (mean grain size and clay content) is an important factor in the determination of the physical and
* Corresponding author. Korea Institute of Geoscience and Mineral Resources, Gas Hydrate Department, #124 Gwahang-no, Yuseong-gu, Daejeon 305-350, South Korea. E-mail address: [email protected] (G.Y. Kim).
acoustic properties of unconsolidated marine sediments (Kuster and Toksoz, 1974; Hamilton and Bachman, 1982; Kim et al., 2001a,b, 2007, 2011, 2012). Knowledge of clay fabric structure is important for understanding the physical and mechanical properties of marine sediments (Bennett et al., 1981; Bryant et al., 1990; Kim et al., 1998, 2007, 1999a,b). In particular, shear wave velocity and shear strength are largely controlled by the orientation of clay particles with burial depth (Kim et al., 2007). The physical nature and consolidation behavior of clay-rich sediments can be understood through knowledge of the microstructure (Bennett et al., 1977; Bryant et al., 1990; Kim et al., 1998). Kim et al. (1998, 1999a,b) studied the relationship between mineralogy and changes in clay fabric to examine how they affected the petrophysical properties of sediments. They showed that most clay domains develop face-toface contacts and become well-orientated with burial depth.
http://dx.doi.org/10.1016/j.quaint.2014.03.037 1040-6182/Ó 2014 Elsevier Ltd and INQUA. All rights reserved.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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The Yellow Sea including the Heuksan Mud Belt (Fig. 1) was completely exposed during the last glacial maximum (LGM), when the paleoshoreline was located about 120 m below the present sea level (Bloom and Park, 1985; Pirazzoli, 1991). Thus sea-level rise during the Holocene has significantly affected the formation of sedimentary units in the Yellow Sea (Jin and Chough, 1998; Jin et al., 2002; Shinn et al., 2007). The origin of sediments in the central Yellow Sea is well studied (Milliman et al., 1987; Alexander et al., 1991). This contrasts with the origin of sediments in the Heuksan Mud Belt, which is still poorly understood and the subject of debate (Park et al., 2000; Lee and Chu, 2001; Lim et al., 2013). Moreover, there is little information available on the physical properties and clay fabric of the Heuksan Mud Belt sediments (Kim et al., 2000). The purposes of this study are: (a) to quantify variations in the physical properties and seismic velocity of sediments in the Heuksan Mud Belt with increasing sediment depth, and (b) to evaluate the relationships between physical properties based on seismically defined units. In addition, we investigated changes in grain orientation with burial depth, which highlights the changes in clay fabric caused by compaction from overburden pressure.
2. Geological setting The Yellow Sea shelf, characterized by a low-gradient epicontinental sea, was completely exposed in a subaerial environment during the last glacial period. As the sea rapidly rose, late Pleistocene weathered deposits were unconformably overlain by transgressive deposits of variable thickness (Shinn et al., 2007). In the eastern part of the Yellow Sea, the transgressive deposits comprise retrograde tidal flat and channel facies, with overlying sand ridges and sheets above the ravinement surface (Lee and Yoon, 1997; Kim et al., 1999a,b; Shinn et al., 2007). The shelf ridges evolved from Pleistocene muddy tidal deposits to ridge surfaces covered by a Holocene sand veneer during the transgression (Jin et al., 2002; Shinn et al., 2007). Shinn et al. (2007) presented six transgressive depositional units in the southeastern Yellow Sea. The Heuksan Mud Belt, located at the southwestern tip of the Korean peninsula, consists mainly of fine-grained sediments. As to the origin of the sediments, there are two main hypotheses: one suggests that the sediments originate from the Geum River (Lee and Chu, 2001; Chough et al., 2004), whereas the other suggests that they were largely derived from the Changjiang or Huanghe rivers prior to about 7 ka, and have undergone significant erosion and reworking
Fig. 1. Map showing bathymetry and core locations for the Heuksan Mud Belt study area. The seismic track line is marked along with core location. Note the location of deep cores (YSDP 102, 103) drilled by the Korea Institute of Geoscience and Mineral Resources (KIGAM). Bathymetry contours are in meters.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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since (Park et al., 2000; Lim et al., 2013). Shinn et al. (2007) suggested that the depositional processes and variability of the transgressive deposits in the Heuksan Mud Belt were largely controlled by the rate of sea-level rise related to global flooding events triggered by melt water pulses. In addition, the oceanographic regime in the Yellow Sea has probably significantly influenced the distribution and morphology of the transgressive and Holocene deposits. 3. Materials and methods Sixteen piston core samples were obtained from the Heuksan Mud Belt on board R/V Tamhae II, Korea Institute of Geoscience and Mineral Resources (KIGAM). Fifteen cores (except one) are dominated by clay and silt sediments (6e7 Ø in mean grain size); muddy sand (2e4 Ø in mean grain size) is found in places within the southern part of the study area (KIGAM, 2012). Core descriptions (KIGAM, 2012) support the presence of various sedimentary facies including massive sand, shelly sand, shelly mud, laminated mud, homogeneous mud, and bioturbated mud. In this study, the results for seven cores (Table 1) along the seismic track line (Figs. 1 and 2) are presented. In the laboratory, the cores were split. One half of each core was used for visual descriptions and the other half was used for physical property, clay fabric, and X-Ray diffraction (XRD) analyses. Table 1 Summary of locations, water depths, core lengths and seismic units of the core samples used in this study. Sites
12HMB-P02 12HMB-P03 12HMB-P07 12HMB-P10 12HMB-P13 12HMB-P14 12HMB-P16
Location
Water Core Seismic depth (m) length (m) units
Latitude
Longitude
33 420 51.98500 33 460 08.28300 33 550 46.03600 34 020 41.95100 34 090 35.61000 34 160 43.61800 34 290 13.78800
125 480 26.29900 106.8 125 460 20.86900 82.8 125 420 31.60500 73.0 0 00 125 39 47.245 74.0 125 370 01.68600 63.2 125 340 12.00200 60.0 125 290 11.86100 54.4
5.07 5.0 7.43 6.6 0.69 7.38 7.44
Unit Unit Unit Unit Unit Unit Unit
IIa IIa IIa IIb I I I
3
3.1. Velocity, physical properties, and grain size The pulse transmission technique (Birch, 1960), using a set of piezoelectric transducers (PZTs), was employed to measure the velocity of samples taken from the cores. The resonance frequency was maintained at 1 MHz to assure that the wavelength of the transmitted pulse was greater than the largest grain size in the specimens (Kolsky, 1953). The velocity measurement system was designed by KIGAM. Physical properties (water content, porosity, density, etc.) were determined using the weight-volume method (Boyce, 1976). Sample weight was measured using an electronic balance. Each sample was cooled in desiccators after it was dried overnight in an oven at a temperature of approximately 105 C. The dry weight and volume of the sample were determined for dry samples by using a heliumdisplacement pycnometer (Model: Ultra PYC, Quantachrome Instruments). A salt correction was made assuming 35& salinity (Boyce, 1976). Shear strength was manually measured on each core sample with a hand-vane apparatus (Blum, 1997). Physical property analyses and velocity measurements were performed at 10 cm depth intervals under room temperature (23 C) conditions. Grain-size analyses for the mud fraction (>4 Ø) were performed using Sedigraph 5100 (Micromeritics); for the sand fraction (<4 Ø), a Ro-tap sieve shaker was used. Textural parameters and relative amounts of sand, silt, and clay were calculated using the classifications of Folk and Ward (1957) and Folk (1968). 3.2. Clay fabric and clay mineralogy A Scanning Electron Microscope (SEM) was used for particle fabric analysis. SEM observations were carried out with a JEOL JSM-5610LV (30 kV and a beam current of 80e90 nA) at Yonsei University, Seoul, Korea. The initial sample pretreatments were performed according to the L.R. White (LRW) resin impregnation method described by Kim and Peacor (1995). All interstitial water was removed from the samples by being replaced by 100% methyl alcohol for 24 h. Then the samples were further prepared with a mixture of methyl alcohol and LRW resin overnight. Finally, the samples were dried in a 60 C oven
Fig. 2. Seismic (air gun and Chirp) profiles showing the Heuksan Mud Belt along with piston core locations (KIGAM, 2013). Note Units I, IIa, IIb, IIIa and IIIb in descending order. YSDP-102 and 103 are marked.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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for about three days, after which pure LRW resin was added to all samples. The samples were polished using diamond paste and then coated with gold. The samples for clay fabric analysis were taken from depths of 120 and 392 cm at site 12HMB-P02. Six samples taken from various depths at three sites (12HMBP02, 12HMB-P03, and 12HMB-P07) were used for clay mineral analysis. X-Ray diffraction (XRD) analyses were performed on airdried and ethylene-glycolated clay samples at a scan speed of 1 / min with a Rigaku Miniflex II automated diffractometer utilizing CuKa radiation at the Department of Earth System Sciences of Yonsei University, Korea. 4. Results 4.1. Velocity and physical properties Site 12HMB-P02 (or P02, core sites are hereafter referred to in this simplified manner) is located in the most southern part of the study area (Fig. 1). This location, characterized by the deepest water depths, belongs to seismic Unit IIa (Fig. 2; Table 1). As shown in Fig. 3, the physical properties significantly change below a depth of 340 cm, corresponding to an increase in sand content (>60%). The porosity and water content abruptly decrease from 67 to 44% and from 45 to 24%, respectively. In contrast, the bulk density increases from 1.50 to 1.89 g/cm3. The velocity and shear strength also show abrupt increases from 1470 to 1561 m/s and from 5 to 37 kPa, respectively. Correspondingly, the values at depths shallower than 340 cm are almost constant. The mean grain size ranges from 6.1 to 7.46 Ø with an average of 6.86 Ø. The sediment texture is mostly composed of silt (87.5% on average). Sand content ranges from 2.2 to 12.3% with an average of 3.8%.
Site P03 is located in the southern part of the study area (Fig. 1) and is situated within Unit IIa on the seismic line (Fig. 2; Table 1). The physical properties are significantly different below a depth of 210 cm (Fig. 4), caused by the large increase in sand content. The porosity and water content range from 59 to 37% and from 37 to 18%, respectively, whereas the bulk density increases with sediment depth from 1.61 to 2.0 g/cm3. The velocity also increases from 1571 to 1708 m/s, and the mean grain size significantly increases from 6.99 to 2.41 Ø. Site P07 is located north of P03, and belongs to the margin of seismic Unit IIa (Figs. 1 and 2; Table 1). The porosity and water content in the lower part of the core from a burial depth of approximately 340 cm are slightly higher (>60% porosity, >40% water content) than in the upper part of the core (Fig. 5). Similarly, the wet bulk density below a depth of 340 cm is lower (<1.6 g/cm3) than in the upper part of the core (>1.6 g/cm3). The velocity gradually decreases from 1489 to 1423 m/s, exhibiting little fluctuation with depth (Fig. 5). As shown in Fig. 5, the shear strength from the seafloor to a depth of 160 cm gradually increases from 15 to 25 kPa, and is almost constant below that depth. Correspondingly, variations in the physical property data with sediment depth are characterized by the reverse trend, compared to their variations of normal sediments with depth. The silt content dominates (90.7% on average) throughout the core. The mean grain size ranges between 5.9 and 6.48 Ø. Site P10 is located in the central part of the study area (Fig. 1) and only within seismic Unit IIb (Fig. 2; Table 1). The porosity and water content are almost constant (56% and 36% on average, respectively) throughout the core (Fig. 6). The wet bulk density ranging between 1.60 and 1.78 g/cm3 (1.66 g/cm3 average) corresponds inversely to porosity. Both velocity and shear strength increase slightly with sediment depth (1480e1520 m/s, 10e17 kPa)
Fig. 3. Profiles of physical properties, velocity and sediment texture for core sample obtained from P02. Note the significant change of physical properties below 340 cm.
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Fig. 4. Profiles of physical properties, velocity and sediment texture for core sample obtained from P03. Note the significant change in values due to increasing sand content below 210 cm.
Fig. 5. Profiles of physical properties, velocity and sediment texture for core sample obtained from P07. Note reverse trend of physical property values below 200 cm.
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above a depth of approximately 140 cm, and below exhibit little fluctuation to the bottom. Mean grain size ranges between 5.0 and 6.5 Ø (5.9 Ø on average). The sand content above a depth of 320 cm is higher than in the lower part of the core (Fig. 6). Site P13 is situated in the central part of the study area (Fig. 1) and within the southern tip of seismic Unit I (Fig. 2; Table 1). This core is the shortest (0.69 m) of all the cores (Table 1). As shown in Fig. 7, the porosity (70.5% on average) and water content (48% on average) do not show significant variation. The wet bulk density at a sediment depth of 45 cm has the lowest value (1.44 g/cm2) with an average of 1.48 g/cm2. The velocity ranges from 1478 to 1495 m/s. whereas the shear strength does not fluctuate throughout the core. Mean grain size ranges from 5.99 to 6.50 Ø. Sand is distributed throughout the core. Site P14 is located between P13 and P16. The location is in the central part of seismic Unit I (Fig. 2; Table 1). As shown in Fig. 8, the porosity and water content show a decreasing trend with sediment depth (from 68 to 60.83% in porosity, from 46.1 to 38.1% in water content). Correspondingly, the wet bulk density gradually increases from 1.49 to 1.64 g/cm3. Unusually, the velocity is characterized by low values (1340e1360 m/s) due to degassing cracks at depth intervals of 380e410 cm. The sediment shear strength at a depth of approximately 340 cm gradually increased from 2 to 9 kPa. The mean grain size ranges from 5.6 to 6.5 Ø. The average contents of sand, silt, and clay are 5.8%, 88.7%, and 5.46%, respectively. Site P16 is situated in the northern part of study area (Fig. 1) and is located within the northern tip of seismic Unit I (Fig. 2; Table 1). The porosity (60e69%) and water content (37e47%) seem likely to decrease with sediment depth (Fig. 9), but there are no significant differences throughout the core. Similarly, the variations of velocity and wet bulk density are not significant with sediment depth. In
contrast, the shear strength gradually increases with sediment depth (from 2 to 10 kPa) (Fig. 9). Mean grain size ranges from 5.3 to 6.6 Ø (6.13 Ø on average). 4.2. Clay fabric and clay mineralogy Clay fabric analysis was performed on the samples to investigate the rearrangement of grains caused by increased burial depth. Fig. 10a shows the clay fabric for a sample taken at a depth of 120 cm at P02. The sediment used for SEM analysis is characterized by high porosity (>70%) and water content (>49%) and low shear strength (<3 kPa) (refer to Fig. 3 for physical property data). The sediment textures are composed dominantly of silt (84%), with some sand (4%) and clay (11%). Illite and smectite are frequently identified in the SEM micrographs. The major clay particles are characterized by edge-to-edge (EE) and edge-to-face (EF) contacts. Fig. 10b shows the clay fabric from the sample taken from a depth of 392 cm at P02. The porosity and water content of the sediment have decreased to 45% and 24%, respectively, due to the effects of the overburden pressure. Furthermore, the shear strength also increases from 3 to 18 kPa. The dominant composition is silt (approximately 86%), with smaller amounts of sand (2.3%) and clay (10%). Similarly, the illite and smectite particles are readily observed in the SEM micrographs. Overall, face-to-face (FF) contacts are more dominant than edge-to-edge (EE) and edge-to-face (EF) contacts (Fig. 10b). Typical framboidal pyrites are easily identified in the SEM micrographs from a sediment depth of 120 cm (Fig. 10c). Calcite is also frequently observed in the sediment (Fig. 10d). Based on the XRD analysis performed on the samples taken from sites P02, P03 and P07, the major clay minerals are identified as
Fig. 6. Profiles of physical properties, velocity and sediment texture for core sample obtained from P10. Note decreasing velocity and shear strength below 100 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
Fig. 7. Profiles of physical properties, velocity and sediment texture for core sample obtained from P13. Note constant shear strength throughout the core.
Fig. 8. Profiles of physical properties, velocity and sediment texture for core sample obtained from P14. Note the low velocity and shear strength due to degassing cracks between 380 and 410 cm.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 9. Profiles of physical properties, velocity and sediment texture for core sample obtained from P16. Note increasing shear strength throughout the core.
illite, chlorite, chlorite þ kaolinite, and kaolinite (Fig. 11). Illite is the most abundant of all clay minerals. 5. Discussion 5.1. Variation of velocity and physical properties within seismic units Based on high-resolution seismic profiles (frequency of 3e 10 kHz), the subsurface sedimentary strata of the Heuksan mud deposits can be classified into five seismic units: Unit I, Unit II (divided into two subunits IIa and IIb), and Unit III (IIIa and IIIb) (with the sequence in descending order) (Fig. 2)(KIGAM, 2013). Unit I is the uppermost depositional sequence; it is characterized by a semi-transparent character and weak reflectors, and divided by a strong erosional reflector from lower units, and restricted to the northern part of the study area (Figs. 1 and 2). Unit II is distributed within the southern part of the study area and is characterized by inclined reflections that indicate sediment progradation southward and eastward. Unit IIa and IIb are separated by erosional surface and dip direction of an internal reflector. Unit III is mostly covered by Unit I; it is restricted to the northern area with low-angle inclined reflections (KIGAM, 2013). Similar types of sequences occur throughout the stratigraphic sections in
the southeastern Yellow Sea (Jin and Chough, 1998; Jin et al., 2002; Shinn et al., 2007; KIGAM, 2013), although multiple suggestions for the classification of the sequence are still under debate (Jin and Chough, 1998; Park et al., 2000; Lee, 2012). Detailed interpretation of the seismic units is beyond the scope of this study. Three sites (P07, P10, and P16) which are representative of three main seismic units were selected to compare physical property data. Fig. 12 shows profiles of the physical properties for the three cores. As discussed earlier, P16 is located in seismic Unit I, P10 in seismic Unit IIb, and P07 in seismic Unit IIa. As shown in Fig. 12, grain size in P10 appears to be coarser than in P07 and P16 (Table 2). Correspondingly, the wet bulk density and velocity show high values in accordance with mean grain size (Fig. 12; Table 2). In the case of porosity, the values at P16 are higher than in the other two cores. Shear strength observed down-core at P07 shows the highest value of the three cores, especially in the upper part of the core (shallower than depths of 200 cm) (Fig. 12; Table 2). This suggests that sedimentary processes and the degree of compaction after deposition are different for each unit. Our results highlight how the physical properties of marine sediments are controlled by their sedimentary environments and processes, and in conjunction with their diagenesis after deposition (Hamilton, 1970; Hamilton and Bachman, 1982).
Table 2 Summary of the physical properties for the three cores corresponding to each seismic unit in descending order. Sites/Units
Mean grain size (Ø)
Porosity (%)
Wet bulk density (g/cm3)
Shear strength (kPa)
Velocity (m/s)
P16 (Unit I) P07 (Unit IIa) P10 (Unit IIb)
6.13 6.22 5.95
65.7 59.7 59.7
1.56 1.61 1.66
6.6 16.8 12.5
1470 1453 1489
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Fig. 10. Scanning electron micrographs showing clay fabric and clay orientation from the samples taken from (a) 120 cm and (b) 392 cm depths at P02. EE: Edge-to-Edge, EF: Edgeto-Face, FF: Face-to-Face. Note: (c) pyrite framboids at 120 cm depth and (d) calcite at 392 cm depth. EDS spectra show chemical compositions of pyrite and calcite.
The inter-relationships of physical properties analyzed for the three cores are grouped distinctly in accordance with each seismic unit (Figs. 13e15). As shown in Fig. 13, P16 (corresponding to seismic Unit I) is characterized by low shear strength and density, and high porosity (Table 2). The neighboring area, including Unit I, is largely covered by muddy sediments consisting of homogeneous or bioturbated mud (KIGAM, 2012). These sediments were mainly derived from neighboring rivers (e.g., the Huanghe and Seomjin rivers) during sea-level highstands (Lee and Chough, 1989; Alexander et al., 1991; Lee and Yoon, 1997; Park et al., 2000; Shinn et al., 2007; Lim et al., 2013). The wet bulk density and porosity of P10, located within seismic Unit IIa, are partly crossed
over with Unit IIb (Fig. 13). Similarly, the relationship between porosity and velocity is grouped well according to each unit (Fig. 14). Fig. 15 shows the relationships between mean grain size and wet bulk density/shear strength for the three sites. As shown in Fig. 15, P10 and P16 (corresponding to seismic Units IIb and I) are grouped distinctly. On the other hand, the wet bulk density of P07 (corresponding to Unit IIa) overlaps in both P10 and P16. Overall, P10 has a wide range of mean grain sizes, including the coarsest sediments, although the difference between the observed values is small (Table 2). In contrast, P07 shows a narrow range of mean grain sizes (Fig. 15). The relationships between physical properties at P10 occur as a scattering pattern with a wide distribution (5e
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 11. X-ray powder diffraction patterns of <2 mm fraction samples taken from P02, P03 and P07. Major clay mineralogy of these samples is chlorite (Ch), illite (I), and kaolinite (K). Note the minor smectites (16.7 A peak).
Fig. 12. Comparison of physical properties for three cores (P07, P10 and P16) obtained from seismic Unit I (P16), Unit IIa (P7) and Unit IIb (P10). Note gradual patterns of physical properties corresponding to each core.
6.5 Ø) of mean grain sizes. As discussed earlier, the seismic profiles of these units (Units IIa and IIb) show prograding reflection patterns toward the south and southeast in study area. Unit I at the location of P16 is characterized by an acoustically transparent layer with low shear strength and high porosity. Therefore, the sediments of seismic Unit I can be interpreted as a younger and softer formation corresponding to an initial step in the consolidation processes.
5.2. Characteristics of clay fabric associated with physical property variations Clay fabric is defined by the orientation and arrangement of particles and particle-to-particle relationships (Bennett et al., 1991). Various factors, such as consolidation, mineralogy, grain size, and diagenesis, affect clay fabric (O’Brien, 1970; Bennett et al., 1981; Bryant et al., 1991; Tribble et al., 1991). Therefore, clay fabric can
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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Fig. 13. Relationships between shear strength (kPa) and porosity (%) / wet bulk density (g/cm3) for the three cores. Note the distinct differences between cores corresponding to each seismic unit.
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be used to improve our understanding of the mechanisms of consolidation and compaction that result from porosity reduction in sediments (Bennett et al., 1977; Kim et al., 2007). SEM micrographs (Fig. 10) recorded on core samples taken at sediment depths of 120 and 390 cm are characterized by different grain contacts, showing the expected consolidation effect with increasing burial depth. In particular, face-to-face contacts are more frequently identified in the SEM micrograph of the 390 cm depth sample compared to the one from 120 cm depth (Fig. 10b). In comparison, edge-to-edge contacts are randomly observed in the SEM micrographs (Fig. 10b). Generally, clay sediments with preferred orientations display high shear strength due to a greater surface area contact and higher bonding force, whereas clay sediments with random microstructure have lower shear strength (Kim et al., 2007). In other words, the microstructure of sediment is closely linked to its physical and mechanical properties. As discussed earlier in this study, the shear strength is significantly increased (from 3 to 18 kPa) with burial depth, compared to other physical properties. Therefore, sediment compaction by increasing overburden pressure seems likely to play an important role in the development of preferred orientations (face-to-face contacts) of clay particles. In the SEM micrographs (Fig. 10c), typical authigenic pyrites formed by ferrous ions and disulfide ions in anaerobic environments are frequently observed. Formation of authigenic pyrite is generated by sulfide-reducing bacteria under anaerobic conditions (Lynch, 1983; Kim et al., 1998, 2007). Occasionally, the formation of authigenic pyrite framboids in fine-grained sediment may influence clay fabric formation, and disturb the preferred orientation of clay particles (Kim et al., 1998, 2007). In addition, gas bubbles in gassy sediments may rearrange of clay particles in the sediment structure (Chiou et al., 1991). However, in this study, grain orientation caused by gas bubbles was not observed in the micrographs. SEM and XRD analysis show illite as the most abundant among all clay minerals and with the highest degree of preferred orientation with burial depth (Fig. 10).
6. Conclusions Fig. 14. Relationships between porosity (%) and velocity (m/s) for the three cores. Note the distinct differences between cores corresponding to each seismic unit.
Variations in physical properties with depth generally show gradual increases or decreases as a result of dewatering caused by compaction and/or consolidation. The one exception to this is significant variation in sediment texture. The physical properties of the core samples obtained from units I, IIa and IIb are readily classified, which shows that the observed patterns of sedimentation are consistent with interpreted seismic units. This indicates that the various depositional processes and system related to changes in the oceanographic regime in the study area have a strong influence on sediment properties. Clay fabric analyses of two samples taken from different sediment depths characterized different grain-contact structures (edge-to-edge, face-to-face, etc.), which correspond to the variations in physical properties such as porosity and shear strength. This close link between clay fabric and physical properties indicates that the process of sediment compaction with burial depth and/or initial consolidation after deposition is caused significantly by overburden pressure.
Acknowledgements Fig. 15. Relationships between mean grain size (phi) and wet bulk density (g/cm3) and shear strength (kPa) for the three cores. Note the distinct difference between cores corresponding to each seismic unit, although Unit IIa overlaps between Unit I and Unit IIb.
This work was supported by the Korea Institute of Geoscience and Mineral Resources (KIGAM) and the “International Ocean Discovery Program” project funded by the Ministry of Oceans and Fisheries, Korea.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037
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References Alexander, C.R., DeMaster, D.J., Nittrouer, C.A., 1991. Sediment accumulation in a modern epicontinental-shelf setting: the Yellow Sea. Marine Geology 98, 51e 72. Bennett, R.H., Bryant, W.R., Keller, G.H., 1977. Clay Fabric and Geotechnical Properties of Selected Submarine Sediment Cores From the Mississippi Delta. NOAA: Professional Paper 9. US Departments of Commerce, 86 pp. Bennett, R.H., Bryant, W.R., Keller, G.H., 1981. Clay fabric of selected submarine sediment: fundamental properties and models. Journal of Sedimentary Petrology 51, 127e152. Bennett, R.H., O’Brien, N.R., Hulbert, M.H., 1991. Determinants of clay and shale microfabric signatures: processes and mechanism. In: Bennett, R.H., Bryant, B.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 5e32. Birch, F., 1960. The velocity of compressional waves in rocks up to 10 kilobars. Journal of Geophysical Research 65, 1083e1102. Bloom, A.L., Park, Y.A., 1985. Holocene sea-level history and tectonic movements, Republic of Korea. Quaternary Research Japan 24, 293e315. Blum, P., 1997. Physical Properties Handbook: a Guide to the Shipboard Measurements of Physical Properties of Deep-sea Cores. ODP Tech. Note, 26. Boyce, R.E., 1976. Definition and Laboratory Techniques of Compressional Sound Velocity Parameter and Wet-water, Wet Bulk Density, and Porosity Parameter by Gravimetric and Gamma Ray Attenuation Zion Techniques. Initial Reports of the Deep Sea Drilling Project 33. Government Printing Office, Washington, DC, U.S., pp. 931e958 Bryant, W.R., Bennett, R.H., Burkett, P.J., Rack, F.R., 1991. Microfabric and physical properties characteristics of a consolidated clay section: ODP site 697, Weddell Sea. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of FineGrained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 73e92. Bryant, W.R., Bennett, R.H., Burkett, P.J., Rack, F.R., 1990. The fabric of a consolidating clayey sediment column, ODP site 697. In: Proceedings of the Ocean Drilling Program, Scientific Results, vol. 113. Chiou, W.A., Bryant, W.R., Bennett, R.H., 1991. Clay fabric of gassy submarine sediments. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 333e352. Chough, S.K., Lee, H.J., Chun, S.S., Shinn, Y.J., 2004. Depositional processes of late Quaternary sediments in the Yellow Sea: a review. Geosciences Journal 8, 211e 264. Folk, R.L., 1968. Petrology of Sedimentary Rocks. Hemphill’s, Austin, Texas, 170 pp. Folk, R.L., Ward, W.C., 1957. Brazos River. A study ion significance of grainesize parameters. Journal of Sedimentary Petrology 25, 3e27. Hamilton, E.L., 1970. Sound velocity and related properties of marine sediments, North Pacific. Journal of Geophysical Research 75, 4423e4446. Hamilton, E.L., Bachman, R.T., 1982. Sound velocity and related properties of marine sediments. Journal of Acoustical Society America 72, 1891e1904. Jin, J.H., Chough, S.K., 1998. Partitioning of transgressive deposits in the southeastern Yellow Sea: a sequence stratigraphic interpretation. Marine Geology 149, 79e82. Jin, J.H., Chough, S.K., Ryang, W.H., 2002. Sequence aggradation and systems tracts partitioning in the mid-eastern Yellow Sea: roles of glacio-eustasy, subsidence and tidal dynamics. Marine Geology 184, 249e271. KIGAM, 2012. Geological Characterization of Recent Muddy Sediment for Reservoir Potential, and in situ Analysis of Shallow Gas. KIGAM report (GP2012-0052012(1). 199 pp. KIGAM, 2013. Geological Characterization of Recent Muddy Sediment for Reservoir Potential, and in situ Analysis of Shallow gas. KIGAM report (GP2012-0052013(2). 169 pp. Kim, D.C., Kim, G.Y., Yi, H.I., Seo, Y.K., Lee, G.S., Jung, J.H., Kim, J.C., 2012. Geoacoustic provinces of the South Sea shelf off Korea. Quaternary International 263, 139e 147. Kim, G.Y., Kim, D.C., Kim, S.J., Seo, Y.K., Jung, J.H., Kim, Y.E., 2000. Physical properties of Southeastern Yellow Sea Mud (SEYSM): comparison with the East Sea and the South Sea mudbelts of Korea. Journal of the Korean Society of Oceanography 5, 335e345.
Kim, G.Y., Yoon, H.J., Kim, J.W., Kim, D.C., Khim, B.K., Kim, S.Y., 2007. The effects of microstructure on shear properties of shallow Marine sediments. Marine Georesources and Geotechnology 25, 37e51. Kim, G.Y., Kim, D.C., Yoo, D.G., Shin, B.K., 2011. Physical and geoacoustic properties of surface sediments off eastern Geoje Island, South Sea of Korea. Quaternary International 230, 21e33. Kim, J.W., Peacor, D.R., 1995. A technique for maintaining texture and permanent expansion of smectite interlayers for TEM observations. Clays and Clay Minerals 43, 51e57. Kim, J.W., Bryant, W.R., Watkins, J.S., Tieh, T.T., 1998. Mineralogical and fabric changes of changes of shale during burial diagenesis and their effects on petrophysical properties. Gulf Coast Association of Geological Societies Transactions 48, 139e150. Kim, J.W., Bryant, W.R., Watkins, J.S., Tieh, T.T., 1999a. Electron microscopic observations of shale diagenesis, offshore Louisiana, USA, Gulf of Mexico. Geo-Marine Letters 18, 234e240. Kim, Y.H., Lee, H.J., Chun, S.S., Han, S.J., Chough, S.K., 1999b. Holocene transgressive stratigraphy of a macrotidal flat in the southeastern Yellow Sea: Gomso Bay, Korea. Journal of Sedimentary Research 69, 328e337. Kim, D.C., Sung, J.Y., Park, S.C., Lee, G.H., Choi, J.H., Kim, G.Y., Seo, Y.K., Kim, J.C., 2001a. Physical and acoustic properties of shelf sediments, the South sea of Korea. Marine Geology 179, 39e50. Kim, J.W., Lee, Y.E., Tieh, T.T., Bryant, W.R., 2001b. Effects of laboratory consolidation on petrophysical properties of fine-grained marine sediments: electron microscopic observations. Marine Georesources and Geotechnology 18, 1e35. Kolsky, H., 1953. Stress Waves in Solids. Clarendon Press, Oxford. Kuster, G., Toksoz, M., 1974. Velocity and attenuation of seismic waves in two-phase media: part 1. Theoretical formulations. Geophysics 39, 587e606. Lee, H.J., Chough, S.K., 1989. Sediments distribution, dispersal and budget in the Yellow Sea. Marine Geology 87, 195e205. Lee, H.J., Chu, Y.S., 2001. Origin of inner-shelf mud deposit in the southeastern Yellow Sea: Huksan Mud Belt. Journal of Sedimentary Research 71, 144e154. Lee, H.J., Yoon, S.H., 1997. Development of stratigraphy and sediment distribution in the northeastern Yellow Sea during Holocene sea-level rise. Journal of Sedimentary Research 67, 341e349. Lee, G.S., 2012. Depositional History and Environment and Sequence Stratigraphy of the Late Quaternary Deposits in the Yellow Sea and East China Sea (Ph.D. Thesis). Pukyong National University, Busan, Korea, 166 pp. Lim, D.I., Choi, J.Y., Shin, H.H., Rho, K.C., Jung, H.S., 2013. Multielement geochemistry of offshore sediments in the southeastern Yellow Sea and implications for sediment origin and dispersal. Quaternary International 298, 196e206. Lynch, J.M., 1983. Soil Biotechnology. Blackwell Scientific Publications, Oxford, 191 pp. Milliman, J.D., Qin, Y.S., Ren, M.E., Saito, Y., 1987. Man’s influence on the erosion and transport of sediment by Asian rivers: the Yellow River (Huanghe) example. Journal of Geology 95, 751e762. O’Brien, N.R., 1970. The fabric of shale: an electron microscope study. Sedimentology 15, 229e246. Park, S.C., Lee, H.H., Han, H.S., Lee, G.H., Kim, D.C., Yoo, D.G., 2000. Evolution of late Quaternary mud deposits and recent sediment budget in the southeastern Yellow Sea. Marine Geology 170, 271e288. Pirazzoli, P.A., 1991. World Atlas of Holocene Sea-level Changes. Elsevier, Amsterdam, 300 pp. Richardson, M.D., Lavoie, K.B., Briggs, K.B., 1997. Geoacoustic and physical properties of carbonate sediments of the lower Florida keys. Geo-Marine Letters 17, 316e 324. Shinn, Y.J., Chough, S.K., Kim, J.W., Woo, J., 2007. Development of depositional system in the southeastern Yellow Sea during the postglacial transgression. Marine Geology 239, 59e82. Stoll, R.D., 1977. Acoustic waves in ocean sediments. Geophysics 42, 715e725. Stoll, R.D., 1989. Sediment Acoustics, Lecture Notes in Earth Sciences. SpringerVerlag, New York, 153 pp. Tribble, J.S., Mackenzie, E.T., Urmos, J., 1991. Physical property changes accompanying deep burial of clay-rich sediments. In: Bennett, R.H., Bryant, W.R., Hulbert, M.H. (Eds.), Microstructure of Fine-grained Sediments from Mud to Shale. Springer-Verlag, New York, pp. 93e108.
Please cite this article in press as: Narantsetseg, B., et al., Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea, Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.03.037