Evidence of Internal-Wave and Internal-Tide Deposits in the Middle Ordovician Xujiajuan Formation of the Xiangshan Group, Ningxia, China
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中国科技论文在线 http://www.paper.edu.cn Geo-Mar Lett (2011) 31:509–523 DOI 10.1007/s00367-011-0253-z ORIGINAL Evidence of internal-wave and internal-tide deposits in the Middle Ordovician Xujiajuan Formation of the Xiangshan Group, Ningxia, China You-Bin He & Jin-Xiong Luo & Xiang-Dong Li & Zhen-Zhong Gao & Zhan Wen Received: 6 September 2010 /Accepted: 12 July 2011 /Published online: 19 August 2011 # Springer-Verlag 2011 Abstract The Xujiajuan Formation of the Lower Xiang- Introduction shan Group in Ningxia, China, is composed of grayish- green to yellowish-green, fine- to medium-grained sand- The study of internal waves in oceanography has a long stone, calcareous sandstone, siltstone, and shale. The upper history that can be traced back to the study of Stokes’ part is thin-bedded limestone. At the top of the second and interfacial wave theory of 1847 (Munk 1981). These are third members of the formation, a number of beds subaqueous waves that develop either between water layers intercalated between turbidites and deep-water shale show of different density or within layers with vertical density well-developed cross-bedding. These beds are composed gradients (LaFond 1966). They occur in all oceans and at mainly of thin- to medium-bedded calcareous siltstone, various depths (Munk 1981; Fang and Wang 1986; Du et al. fine-grained sandstone, fine-grained calcisiltitic limestone, 2001). Munk (1981) postulated that such internal gravity and silty shale. All bedding types reflect traction-current waves were as common as (or possibly even more prevalent action. The laminae of the bidirectional and unidirectional than) ocean surface waves. These gravity waves vary in cross-bedded units tend to dip either opposite to or at a amplitude, period, velocity, and depth (LaFond 1966; Munk large angle to the regional slope. The units vary in shape 1981; Gao et al. 1998). The longest periods correspond to and orientation in both upslope and downslope directions. those of semidiurnal or diurnal tides (Rattry 1960; LaFond A comprehensive evaluation of the sedimentary structures 1966; Munk 1981). Internal tides have frequently been and inferred paleocurrents suggests that the cross-bedded recorded in the oceans, and are more evident in deeper intervals were not formed by contour currents or turbidity water (depths exceeding 200–250 m; Shepard 1976). Both currents, but most probably represent internal-wave and internal tides and internal waves can generate large-scale internal-tide deposits. bidirectional flows at the seafloor, especially in submarine canyons and other types of submarine valleys (Shepard et al. 1979). Generally, the velocities of such currents range from 20 to 50 cm/s (Gao et al. 1998). Many aspects of internal waves are quite well understood because of Responsible guest editor: F.J. Hernández-Molina numerous observations and simulations. These include (1) Y.-B. He (*) : J.-X. Luo : X.-D. Li : Z.-Z. Gao : Z. Wen generation, superposition, propagation, and boundary-layer School of Geosciences, Yangtze University, phenomena (e.g., Nakamura and Awaji 2001; Tanaka et al. Nanhuan Road 1, 2003; Hibiya 2004; Lemckert et al. 2004; Nash and Moum Jingzhou 434023 Hubei, People’s Republic of China e-mail: [email protected] 2005; Rainville and Pinkel 2006), (2) breaking, reflection, diffraction, and attenuation when interacting with subma- Present Address: rine topography (e.g., Legg 2003; Small 2003; Troy and X.-D. Li Koseff 2005; Mercier et al. 2008), (3) swash–backwash Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, flows (e.g., Umeyama and Shintani 2004, 2006), (4) Beijing 100037, People’s Republic of China influence of various types of submarine topography (e.g., 转载 中国科技论文在线 http://www.paper.edu.cn 510 Geo-Mar Lett (2011) 31:509–523 Kunze et al. 2002; Pietrzak and Labeur 2004; Martin et al. al. 1997; He et al. 1998), Middle and Upper Ordovician 2006), (5) long and short periods (e.g., Marc et al. 1992; deposits of the central Tarim Basin (Gao et al. 1996, 2000; Anohin et al. 2006;D’Asaro et al. 2007), and (6) numerical He et al. 2003), Upper Paleozoic and Mesozoic deposits on simulations of sediment suspension (e.g., Bogucki et al. the western side of the Qinling Mountains (Jin et al. 2002; 1997; Venayagamoorthy and Fringer 2006). Wang et al. 2005), the Precambrian Anlelin and Xiushui Observations from underwater vehicles have revealed formations northwest of Jiangxi Province (Guo et al. 2003, that internal waves and internal tides can transport fine 2004), the Upper Ordovician at Linan, Zhejiang Province sand, and are able to generate ripples and dunes at water (Li et al. 2005a), the Precambrian Madiyi Formation at depths of several thousand meters (Mullins et al. 1982). Taojiang, Hunan Province (Li et al. 2005b), the Lower Lonsdale and Malfait (1974) suggested that the dune bed Cambrian Balang Formation at Shimen, Hunan Province forms observed in foraminiferal sands at a water depth of (He et al. 2005), the Middle Ordovician Pingliang Forma- 2,650 m on the northern flank of the Carnegie Ridge in the tion in the western Ordos Basin (He et al. 2007), and the eastern equatorial Pacific were generated by the spillover of Middle Ordovician Xiangshan Group (Li et al. 2009, 2010; dense, tide-driven water masses. Furthermore, using satel- He et al. 2010) in Ningxia Province. lite altimeter data from the Topex/Poseidon experiment, The investigation of internal-wave and internal-tide Egbert and Ray (2000) demonstrated that tidal dissipation deposits is still a young field in deep-water sedimentolog- in the open ocean also occurs at abyssal depths. Xu et al. ical research (He and Gao 1999;Shanmugam2008), (2002) reported the importance of tidal currents in the although some progress has been made these last years. Monterey Canyon, the largest submarine canyon along the One major obstacle is the lack of sufficient documentation. California coast. Shanmugam (2003) pointed out that tidal In the Xiangshan Group Xujiajuan Formation in the currents develop in deep-water canyons and channels. Xiangshan area, Ningxia, China, the recent discovery of Previous oceanographic investigations have shown that several depositional units considered to have been generat- internal waves and internal tides can also be important ed by internal tides and internal waves therefore offered a geological agents in deep waters, suggesting that such rare opportunity of studying such deposits in greater detail. sedimentary deposits should be preserved in the strati- The deposits comprise mostly mud and fine-grained sand graphic record. However, only a few sedimentologists have typically displaying sedimentary structures generated by considered the influence of internal tides in ancient deep- traction currents. Such structures, which include bidirec- water deposits. Thus, Laird (1972) reported tide-generated tional and unidirectional cross-bedding, flaser, wavy and bidirectional cross-laminations in pre-Devonian deep-water lenticular bedding, alternating parallel- and cross-bedded deposits of New Zealand. Klein (1975) identified flaser, laminae, double mud layers, climbing ripples, sigmoidal wavy and lenticular bedding in cores of Quaternary to cross-bedding, as well as reactivation surfaces, were used Cretaceous age recovered at water depths of 2,200–3,000 m here to reconstruct the mechanisms responsible for their on the Ontong-Java Plateau. McCave and Tucholke (1986) formation. proposed that mud waves could be produced by internal The main objective of this paper in this special issue is to waves. Karl et al. (1986) interpreted sand waves observed evaluate novel findings on sedimentary structures and at the Navarinsky Canyon head as internal-wave deposits, facies in terms of inferred internal-wave and internal-tide and Gao and Eriksson (1991) identified internal-tide action in the Middle Ordovician Xujiajuan Formation, deposits in the Ordovician of the central Appalachians, Xiangshan Group. Combined with existing regional knowl- USA. Gao et al. (1998) discussed the importance of internal edge, this should contribute to a better understanding of waves in the formation of large-scale sediment waves on these mechanisms in deep waters in general. modern seafloors, especially of sediment waves migrating upslope. Zhang et al. (1999) interpreted sediment waves in the northeastern Rockall Trough as internal-wave deposits. Regional and geological setting Finally, Shanmugam (2008) recently provided a compre- hensive overview of the general characteristics of deep- The study area is located in the Xiangshan and Miboshan water tidal deposits. mountains near Zhongwei, Zhongning, and Tongxin Since the work of Gao and Eriksson (1991) on the (central–south Ningxia Hui Autonomous Region, North- Ordovician of the central Appalachians, sedimentologists in west China; Fig. 1), within the adjoining portions of the China have pursued such investigations (see overviews by ancient lands of Ordos and Alashan, as well as the Gao et al. 2006, 2010) and, indeed, ancient internal-tide Qinling–Qilian orogenic system (Fig. 2). Early Paleozoic deposits are now known from several regions. These tectonic activity is closely related to the evolution of the include the uppermost units of the Upper Ordovician Qinling–Qilian–Kunlun Ocean and the formation of the Yankou Formation in Tonglu, Zhejiang Province (Gao et North Qilian island arc (Zhang et al. 2004;Xuetal.2006). 中国科技论文在线 http://www.paper.edu.cn Geo-Mar Lett (2011) 31:509–523 511 Fig. 1 Geological map of the study area showing outcrops of the Miboshan Formation, and the three formations of the Xiangshan Group. 1 Miboshan Formation, 2 Xujiajuan Forma- tion, 3 Langzuizi Formation, 4 Mopanjing Formation, 5 thrust fault, 6 transcurrent fault Zhang et al. (2004) suggested that, during the Middle overlying Devonian Zhongning Formation is marked by an Ordovician, there was a certain degree of back-arc angular unconformity. extension and subsidence, although no oceanic crust The lower part of the Miboshan Formation consists of formation. The study area is on the continental side of gray to dark-gray, thin-bedded calcirudite, siliceous shale, the retro-arc foreland basin oftheNorthQilianislandarc.