Characteristics and provenance implication of detrital minerals since ...

Acta Oceanol. Sin., 2013, Vol. 32, No. 4, P. 49-58 DOI: 10.1007/s13131-013-0281-9 http://www.hyxb.org.cn E-mail: [email protected]

Characteristics and provenance implication of detrital minerals since Marine Isotope Stage 3 in Core SYS-0701 in the western South Huanghai Sea ZHANG Junqiang1,2∗ , LIU Jian2,3 , WANG Hongxia3 , XU Gang3 , QIU Jiandong1 , YUE Baojing3 , ZHAO Guangtao1 1

Ocean University of China, Qingdao 266003, China Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao 266003, China 3 Qingdao Institute of Marine Geology, Qingdao 266071, China 2

Received 24 September 2011; accepted 15 August 2012 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2013

Abstract The previous studies of the sedimentology and chronology of sediment core SYS-0701, which was recovered from the western South Huanghai Sea (Yellow Sea), have revealed the changes in the sea-level and sedimentary evolution during the late Quaternary in the region. The present study used mineralogical data from the section of the core deposited since Marine Isotope Stage (MIS) 3, to decipher the provenance of sediments of the paleo-delta deposited during MIS 3 and MIS 1. Based on the lithologic features and the variations with depth of the concentrations of carbonates and both heavy and light minerals in bulk samples, the upper part of Core SYS-0701 can be divided into three units designated DU1, DU4, and DU5, in accord with previously used terminology. Sub-units of units DU1 (DU1-1 and DU1-2) and DU4 (DU4-1 and DU4-2) have also been identified. DU1 was deposited during MIS 1, and DU4 and DU 5 were formed during MIS 3. All data pertaining to dominant heavy mineral assemblages, diagnostic minerals, ratios of diagnostic minerals, light mineral associations, textural maturities, and carbonate contents, indicate that the sediments of Core SYS-0701 are comparable with Huanghe River (Yellow River) sediments. Moreover, the mineralogy of the sediment evidenced its dependence on supply rates and hydrodynamic conditions. Weak hydrodynamics (DU5 and DU4-2) and/or low sediment supply (DU1-2) led to sediment containing less hornblende and epidote, with a large specific gravity and high content of flaky minerals, and vice versa in cases of strong hydrodynamics (DU4-1) and very large sediment supply (DU1-1). Key words: heavy mineral, light mineral, carbonate, provenance, South Huanghai Sea (Yellow Sea) Citation: Zhang Junqiang, Liu Jian, Wang Hongxia, Xu Gang, Qiu Jiandong, Yue Baojing, Zhao Guangtao. 2013. Characteristics and provenance implication of detrital minerals since Marine Isotope Stage 3 in Core SYS-0701 in the western South Huanghai Sea. Acta Oceanologica Sinica, 32(4): 49–58, doi: 10.1007/s13131-013-0281-9

Qin et al., 1986; Yang, 1985). In the past two decades, studies have greatly extended knowledge of the stratigraphy, sedimentary environments, paleoclimatic changes, and sea-level fluctuations of the Huanghai Sea since the late Pleistocene (Alexander et al., 1991; Liu et al., 2010; Qin, 1989; Qin et al., 1986; Yang, 1985; Yang and Liu, 2007; Yang, 1994; Zhao et al., 2003; Zhao et al., 2001). However, the fact that little attention has been paid to the provenance of the sediments has, to some extent, prevented us from thoroughly understanding the sedimentation and environmental evolution that has taken place on eastern China continental shelf. Although natural processes such as weathering, physical abrasion, and hydrodynamic sorting during transport, deposition, and diagenesis may obscure or overprint the original provenance signals (Morton and Hallsworth, 1994; Morton and Hallsworth, 1999; Morton et al., 2005; Svendsen and Hartley, 2002), and heavy mineral assemblages have long been regarded as sensitive indicators of sediment sources (Garzanti and Andò, 2007; Garzanti et al., 2008; Garzanti et al., 2006; Garz-

1 Introduction The Huanghai Sea (Yellow Sea) is a shallow epicontinental sea with smooth topography that lies upon a stable flat shelf. The Shandong Peninsula divides it into two parts, the South and North Huanghai Sea. The Changjiang and Huanghe Rivers are the longest rivers in China, with mean annual sediment discharges of 0.5×109 t and 1.1×109 t, respectively (Cheng and Zhao, 1985; Milliman and Meade, 1983). Together they account for over 80% of the total sediment input from China’s major rivers and have a great influence on the sediment distribution pattern on the eastern China shelf. During the Quaternary drastic changes have taken place on the continental shelf of the Huanghai Sea. The changes in the sedimentary environment, sediment supply, and sedimentary systems have resulted from alternations of glacial and interglacial stages, the associated sea level fluctuations, and the shifting of river mouths. Most of the information on sea level changes and sea-land interactions has been preserved in the sediments (Liu et al., 1987; Qin, 1989;

Foundation item: The National Natural Science Foundation of China under contract No. 40876034; MLR Geologic Survey Project under contract Nos 1212010611401 and 1212010911072. ∗ Corresponding author, E-mail: zjq [email protected] −

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ZHANG Junqiang et al. Acta Oceanol. Sin., 2013, Vol. 32, No. 4, P. 49-58

anti et al., 2007; Garzanti et al., 2005; Heroy et al., 2003; Nechaev and Isphording, 1993; Pettijohn et al., 1987; Yang et al., 2009). Liu et al. (2010) found an incised river channel formed in the area during MIS 2 and, based on seismic and sedimentological data, and concluded that a large-scale paleo-delta had formed on the shelf of the western South Huanghai Sea during MIS 3. The clay mineralogy of Core SYS-0701, which was obtained from the shelf of the western South Huanghai Sea, demonstrates that the paleo-delta was built up mainly by the sediments from the Huanghe River (Liu et al., 2010). There seems to be no other evidence for the provenance, and further study is required to determine whether the paleo-delta contains sediments from the Changjiang River (Liu et al., 2010; Qin et al., 1986; Yang, 1994). To better understand the sources of the sediment and related environmental changes that have occurred since the late Pleistocene on the shelf of the western

South Huanghai Sea, we have combined in this paper information on the heavy minerals, light minerals, and carbonate minerals of the sediments deposited from MIS 3 to MIS 1 in Core SYS-0701, to reveal their provenance and influencing factors. 2 Materials and methods 2.1 Materials Core SYS-0701 (121◦ 27.0000 E, 34◦ 39.7535 N), which is 70.20 m in depth, was drilled at a water depth of 33 m (Fig. 1). In 2006, the Qingdao Institute of Marine Geology collected about 4 100 km of high-resolution shallow seismic profiles on the shelf of the western South Huanghai Sea, and Core SYS-0701 is located in the middle of line A22 (Fig. 1) [see Liu et al. (2010) for details]. We studied the upper 33.30 m of the core, the sediments of which were deposited since MIS 3 during the late Pleistocene.

Fig.1. Schematic map of the bathymetry and regional circulation pattern in the Huanghai Sea and adjacent areas during wintertime (a) [modified after Guan (1983) and Su (1986)] and geographic map of the study area, showing the track lines of the high-resolution shallow seismic profiles and locations of Core SYS-0701 (b). Water depth is in meters. BS represents Bohai Sea, SYS South Huanghai Sea (Yellow Sea), NYS North Huanghai Sea, KC Kuroshio Current, YSWC Huanghai Sea Warm Current, TC Tsushima Current, TWC Taiwan Warm Current, YSCC Huanghai Sea Coastal Current, SKCC South Korean Coastal Current, SSCC South Shandong Coastal Current, NJCC North Jiangsu Coastal Current, CDW Changjiang Diluted Water, and ECSCC East China Sea Coastal Current.

2.2 Methods After the core was opened, samples were taken at 0.5- to 2.0-m intervals. We analyzed a total of 57 samples from the uppermost 33.30 m of the core. The sediment was wet-sieved to obtain detrital grains within the size range 0.25–0.063 mm. We then used bromoform with a density of 2.88 g/cm3 to separate the detritus into light and heavy minerals. We determined the percentages of the mass contributed by the light and heavy minerals by weighing the fractions at a resolution of 0.000 1 g. We used a stereomicroscope (K-400D) and polarization microscope (OLYMPUS-PM20) to identify the minerals and determined the percentages of the minerals by counting 300–500 grains from each sample. To determine the mineralogy of the bulk samples, we first ground each sample into powder in a small agate bottle con-

taining acetone. Shell fragments were removed before the analysis. We then vibrated the small agate ball at a temperature of about 4◦ C to further grind the sample into grains smaller than 200 mesh. The powders were compacted into cylindrical tablets with a mass of 300 mg and diameter of 13 mm. The main mineral composition of the bulk samples was determined with a Rigaku D/max-rA X-ray diffractometer (XRD) with Cu Ka radiation. We performed all of the examinations and analyses at the Testing Center of the Qingdao Institute of Marine Geology, China Geological Survey. All of the 14 C dates of Core SYS-0701 were obtained from Liu et al. (2010). We converted dates more recent than the last glacial maximum (LGM) to calendar 14 C ages before AD 1950 (cal a BP). Ages older than the LGM were not calibrated and are given as 14 C years BP (14 C a BP).


3 Lithostratigraphy, sedimentation time and sedimentary environment Core SYS-0701 penetrated the paleo-delta sediment sequence on the shelf of the western South Huanghai Sea. Liu et al. (2010) divided the upper 33.30 m into three sedimentary units, i.e., DU 5, DU 4, and DU 1 from bottom to top. Units DU 3 and DU 2 are absent (Fig. 2). Units DU 5 and DU 4 are deltaic deposits that correspond to the early-middle episodes of MIS 3, about 60–40 cal ka BP. Unit DU 1 was deposited in the late Holocene and, with an age less than 1 000 a, is associated with the most recent period of MIS 1. Based on the correlation of its shallow seismic profile with the corresponding profiles of some boreholes in the shelf area (Liu et al., 2010), we concluded that Core SYS-0701 lacks sedimentary units DU3 (late MIS 3 to MIS 2, about 40–11.7 cal ka BP) and DU2 (early to middle MIS 1, Holocene). The lithology of the cores above a depth of 33.30 m is given in Fig. 2 (Liu et al., 2010). The sediment in the DU 5 unit (33.30–23.00 m) is associated with formation in a coastal-to-shallow marine environment representing a distal (muddy) delta front, whereas unit DU 4 (23.00–9.69 m) consists of a prodeltaic sediment. Units DU 5 and DU 4 came into being during early and middle episodes of MIS 3, respectively, roughly 60–40 cal ka BP. The DU1 unit (9.69–0 m) can be divided into two subunits: a bottom sub-unit (9.69–6.53 m) and middle-upper subunit (6.53–0 m). The former is a kind of tidal-channel infilling deposited within the last 1 000 a, and the latter has resulted from the distal sedimentation of the abandoned Huanghe River during 1128–1855, when the river mouth was located in northern Jiangsu. 4 Results and discussion 4.1 Assemblage characteristics and provenance implication of detrital minerals In the 0–33.30 m interval of Core SYS-0701, the detrital component content (the weight percentage of the 0.063–0.25 mm fraction of the dried bulk sample) varied from 0.9% to 73.6%, with an average of 14.2% (Table 1). The detrital component was dominated by light minerals (K-feldspar, plagioclase, and quartz), rock fragments, and bioclasts, which made up 97% of the clasts. Heavy mineral content, or the weight percentage of heavy minerals in the 0.063–0.25 mm fraction, was very low and made up only 0.07% to 8.82% (1.49% on average) of the detrital minerals. We identified 38 species of heavy minerals and 13 species of light minerals in Core SYS-0701 sediments. The heavy minerals in Core SYS-0701 could be classified into several groups. The widely distributed major heavy minerals (>5%) included hornblende, epidote, chlorite, weathered mica, and biotite. A second group of heavy minerals (1.5%–5%) included metallic minerals (ilmenite, magnetite, limonite, and hematite), muscovite, clinozoisite, and authigenic pyrite. Minor or locally distributed heavy minerals (0.4%–1.5%) consisted mainly of garnet, leucoxene, pyroxene, actinolite-tremolite, and apatite. The heavy minerals that were extremely rare or occurred in only a few samples were ilmenite, sphene, tourmaline, kyanite, authigenic pyrrhotite, phlogopite, allanite, and rutile. Authigenic mineral, such as pyrite, authigenic pyrrhotite, and glauconite, were almost never observed. The light components were dominated by feldspar (Kfeldspar and plagioclase), quartz, and rock fragments. In addtion, we discovered chlorite, weathered mica, carbonate,

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bioclasts, muscovite, organic matter, biotite, glauconite, and graphite made minor contributions. Vertical variations of the mineral assemblages depended on provenances and sedimentary environmental evolutions and therefore could be used as tools for stratigraphic division (Shi et al., 1994). Our results show that the sediments formed since MIS 3 could be divided into three segments according to the vertical distribution of detrital minerals (Fig. 3). The three segments correlate with the sedimentary units DU5, DU4, and DU1 (Table 1, Fig 3). Petrographic and mineralogical studies of the Changjiang River and Huanghe River sands provided key information for the provenance study and enhanced understanding of the complex depositional environment in the South Huanghai Sea. The heavy minerals in the Huanghe River sediments are dominated by flaky minerals, hornblende and epidote (Lin et al., 2003). Apatite is also very common, and the frequency of its appearance may be as high as 95% (Sun, 1990). In addition, garnet is generally high in the Huanghe River sediments (Wang et al., 2010). The main heavy mineral assemblage in the sediments of the Changjiang River, however, includes hornblende, epidote, and metalliferous minerals. Flaky minerals are less common (Yang et al., 2009). The widespread minerals in Changjiang River sediments, pyroxene, rutile, sphene, zircon, tourmaline, staurolite, and kyanite, are characteristic of a typical mineral assemblage of acid and intermediate-acid igneous and metamorphic rocks (Wang et al., 2007; Wang et al., 2006; Yang et al., 2009). Staurolite dominates the metamorphic rock minerals (Chen et al., 1982), and sphene is the characteristic mineral (Sun, 1990). The heavy mineral assemblage in Core SYS-0701 is evidently characterized by a high proportion of flaky minerals such as chlorite, muscovite, biotite, and weathered mica, followed by unstable minerals such as hornblende and epidote. The major mineral assemblages in units DU5–DU1 consist of flaky minerals and hornblende and epidote. With the exception of DU41, the flaky minerals in some samples accounted for over 35% of the mineral assemblage. The stable minerals sphene, zircon, tourmaline, and ilmenite are rare in all of the units, but garnet, a stable mineral, is relatively abundant. Though its concentration was low, apatite was present in more than 90% of the samples of all of the sedimentary units with the exception of DU5. Garnet and apatite were present in quite high concentrations in subunit DU4-1. Few samples contained rutile, tourmaline, and zircon. Pyroxenes were absent from many samples, the highest occurrence being in DU4-1. Sediment composition can be modified by numerous processes, including erosion, transport, pedogenesis, recycling, deposition, and diagenesis (Morton and Hallsworth, 1994; Morton and Hallsworth, 1999). These processes, either acting singly or in combination, may cause profound differences between the mineral composition of the present-day heavy mineral suite and that of the original source lithology (Morton et al., 2004). Hydrodynamic and diagenetic effects can be ignored if the ratios of stable minerals or so-called index values are used for provenance determinations. The indexes commonly used here is ATi (Apatite-tourmaline index) (Morton and Hallsworth, 1994; Morton and Hallsworth, 1999). The ATi is an important provenance-sensitive parameter affected by weathering in the sedimentation cycle. Because the ATi is affected by weathering on the floodplain, it may be possible to consider variations of this parameter as metrics of the extent of floodplain storage (Morton and Hallsworth, 1999). The zircon, tourmaline, rutile

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Fig.2. Lithologic column of Core SYS-0701 (Liu et al., 2010).

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Table 1. Heavy mineral assemblages in sediments of Core SYS-0701 and comparison with those from the Changjiang and Huanghe Rivers Unit

DU5 DU4-2

DU4-1

DU1-2

DU1-1

Depth Mineral assemblage

23.0–33.3 m Flaky mineral, hornblende, authigenic pyrite, epidote Flaky mineral

20.5–23.0 m Flaky mineral, hornblende, epidote, bioclast

9.69–20.5 m Hornblende, epidote, clinozoisite, flaky mineral

6.53–9.69 m Flaky mineral, hornblende, hematitelimonite, epidote

0–6.53 m Flaky mineral, hornblende, epidote, landwaste

Flaky mineral

4 5.16

Flaky mineral, hematitelimonite 6 12.38

Flaky mineral

16 1.35

Flaky mineral, apatite, garnet 18 36.65

1.00

1.46

2.11

0.94

1.38

0.0

0.1

0.8

4.0

0.3

2.5

1.6

2.3

13.4

1.5

0.0 0.1 0.0 0.1 7.6 0.2 27.8 0.4 0.1 8.2 16.2

0 0.2 0.1 0.2 7.4 0.3 15.3 0.1 0.3 7.7 31.9

0.5 0.6 0.2 0.4 18.7 1.5 51.5 2.3 0.9 0.2 0.9

1.6 0.2 0.1 0.3 7.8 2.1 20.1 0.7 0.5 11.5 18.8

0.1 0.3 0.0 0.3 13.1 0.6 32.9 0.2 0.4 9.3 19.6

0.3

0.2

1.0

0.3

0.8

4.8 0.43 17 21 40.9 7.5 3.5

2.8 0.43 65 20.8 35.2 3.4 2.1

0.3 0.75 67 28.3 49.4 6.5 2.3 this paper

0.7 0.35 53 24.6 55.6 7.2 1.4

4.7 0.15 56 22.9 41.6 6.5 4.3

Characteristic mineral Specimen number Detrital mineral content Heavy mineral content Magnetite Hematite Limonite Ilmenite Sphene Zircon Tourmaline Epidote Garnet Hornblende Pyroxene Apatite Biotite Chlorite Tremolite Actinolite Muscovite ZTR ATi Quartz Feldspar Calcite Dolomite Data source

DU4

DU1

Changjiang River

Huanghe River

12.5 — 3.2 3.2 1.4 0.5 0.7 14.9 3.0 55.2 2.3 0.5 0.2 1.6 0

0.4 0.1 1.4 0.4 0.5 0.1 0 2.2 1.6 9.0 0.1 0.3 64.7 0 0.8

0 0 1.2 42

2.1 4.8 0.07 100

Yang et al. (2009)

Lin et al. (2003)

13 5.86

Notes: Detrital mineral content is the weight percentage of the fraction of 0.063–0.25 mm from the dried bulk sample and heavy mineral content is the weight percentage of heavy minerals from the detrital mineral.

(ZTR) index indicates the maturity of the heavy mineral assemblage related to the distance of transportation (Haughton et al., 1991; Morton and Hallsworth, 1999; Wang et al., 2006). Weathering causes modification of source rock mineralogy, both at the source (prior to incorporation into the transport system) and on the floodplain during periods of exposure associated with transport (alluvial storage) (Morton et al., 2005). The Changjiang River sediments are derived from a complex association of parent rocks, including granitic and metamorphic rocks, in a wet and warm climate favorable to intensive chemical weathering (Chen et al., 1984; Li and Zhang, 2005) that will cause the decomposition of minerals such as apatite and garnet that are not ultrastable as the zircon, tourmaline and rutile. The sediments of the Huanghe River come from the loess plateau, where the dry and cold climate is associated with physical weathering (Chen et al.,

1984; Li and Zhang, 2005) that results in sediments that contain flaky and unstable minerals. The facts that the ATi (mostly>50) is high and the ZTR (