International Journal of Coal Geology 190 (2018) 166–177

Contents lists available at ScienceDirect

International Journal of Coal Geology

journal homepage: www.elsevier.com/locate/coal

Climatic or tectonic control on organic matter deposition in the South China T Sea? A lesson learned from a comprehensive Neogene palynological study of IODP Site U1433 ⁎ ⁎⁎ Yunfa Miaoa,b, , Sophie Warnya,c, , Peter D. Clifta, Mitch Gregorya,c, Chang Liua a Department of Geology and Geophysics, Louisiana State University, E-235 Howe-Russell, Baton Rouge, LA 70803, USA b Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Institute, Chinese Academy of Sciences, Lanzhou 730000, China c Museum of Natural Science, Louisiana State University, 109 Foster Hall, Baton Rouge, LA 70803, USA

ARTICLE INFO ABSTRACT

Keywords: Palynomorphs and other organic particles are basic key components of palynofacies, yet quantitative analyses of Organic matters all types are rarely used together to investigate organic matter assemblage changes and evaluate the driving Tectonics forces behind the observed changes. In this paper, eight organic-walled microfossil and particle morphologies Monsoon (sporopollen, Pediastrum, Concentricystes, fungi, dinoflagellate cysts, structured/amorphous organic matters, Driving forces stomatal apparatus and scolecodonts) are tabulated and their concentrations and fluxes are evaluated over the Neogene past 17 million years (Ma) in sediments recovered from the South China Sea at International Ocean Discovery Program (IODP) Site U1433. Overall, these morphologies show roughly similar increasing trends but with dif- ferent levels of fluctuations. The uniform increase in all morphologies at ~8 Ma (named the ~8 Ma event) is the most notable feature of the past 17 Ma. To explain the trend, and because these various organic matters reflect various environmental conditions, we argue that the uniformity of the signal implies that tectonically-driven basin and drainage evolution played the key role, rather than paleoclimate (Asian summer monsoon). The ~8 Ma event was likely triggered by the onset of the Mekong River in its present location, although the role of monsoon evolution cannot be excluded completely.

1. Introduction paleoaltimeter (e.g., Axelrod, 1997; Miao et al., 2013a, 2016a; Sun et al., 2014). Quantitative data, such as percentages of different species, In palynological analysis, all of the acid-insoluble organic matters, are widely used and occasionally include the number of morphologies including palynomorphs (e.g., sporopollen (spores and pollen), fresh- (e.g., Jaramillo et al., 2006), the relative abundances, such as ratios of water algae, dinoflagellate cysts, fungal spores, and scolecodonts) and different ecological types (e.g., White et al., 1997; Warny et al., 2003), other organic particles (e.g., structured/amorphous organic matters, as well as the concentrations and fluxes (e.g., Luo and Sun, 2007; Miao resins (ambers), wood debris, stomatal apparati) collected from the et al., 2016b, 2017). Abundance, composition and preservation of the rock or unconsolidated sediments comprise a ‘palynofacies’ (Combaz, various components, together with the thermal alteration of the organic 1964). A variety of uses of these particles can be made depending on the matters can be used to investigate depositional palaeoenvironments specific aims of the researchers. The assemblages of different species in (e.g., Batten, 1982; Lorente, 1986; Batten and Lister, 1988; Tyson, the overall palynomorph assemblage can be used to estimate/in- 1984; Habib, 1979; Sweet and Cameron, 1991), petroleum or coal vestigate the ages of the sediments (e.g., Macphail, 1997; Shu et al., source potential (e.g., Batten, 1982; Ercegovac and Kostić, 2006), as 2008; Garzon et al., 2012; Akyuz et al., 2016; Miao et al., 2016a), re- well as biostratigraphic correlations on a regional, or local level (e.g., construct paleogeography, paleoecology and paleoclimate (e.g., Askin, Sturrock, 1996; Batten and Stead, 2005; Van der Zwan, 1990). In most 1989; Nichols, 1995; Jiang and Ding, 2008; Warny et al., 2009; Wu of these palynological studies, the non-palynomorph component et al., 2011; Anderson et al., 2011; Miao et al., 2012), gather data on (mostly the structured/amorphous organic matters (SOM/AOM) or re- plant evolution (e.g., Walker, 1974; Nichols, 1995; Retallack, 1995; sins) is not discussed or vice versa, the paper focuses on non-palyno- Miao et al., 2011; Griener and Warny, 2015) or be used as a proxy for morphs but not on the palynomorphs. Very few studies have used

⁎ Correspondence to: Y. Miao, Department of Geology and Geophysics, Louisiana State University, E-235 Howe-Russell, Baton Rouge, LA 70803, USA. ⁎⁎ Correspondence to: S. Warny, Department of Geology and Geophysics, Louisiana State University, E-235 Howe-Russell, Baton Rouge, LA 70803, USA. E-mail addresses: yunfi[email protected] (Y. Miao), [email protected] (S. Warny). https://doi.org/10.1016/j.coal.2017.10.003 Received 31 March 2017; Received in revised form 22 August 2017; Accepted 5 October 2017 Available online 03 November 2017 0166-5162/ © 2017 Elsevier B.V. All rights reserved. Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 1. a. Bathymetric map of the South China Sea showing the location of IODP Site U1433 and b. Lithological column against age-depth model (after Li et al., 2015) and locations of samples (shown by blue arrows). FAD = first appearance datum, LAD = last appearance datum stratigraphic depths and ages. Topography is from the Shuttle Radar Topography Mission (SRTM) plotted by GeoMapApp. Major fluvial systems which deliver sediments into the South China Sea are also shown, together with the Molengraaff River of glacial age crossing the Sunda Shelf (Molengraaff and Weber, 1919). Green arrows show surface currents active during the modern summer monsoon. Isobaths are shown in 1000 m intervals. VCH = Vietnamese Central Highlands = (Li et al., 2015). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) quantitative methods on the entire palynofacies (e.g., Cirilli et al., challenging as the record is complicated by factors such as provenance 2009). (Clift et al., 2008, 2014; Luo and Sun, 2007; Wan et al., 2007). In this study, we identified and quantified for the first time eight IODP Site U1433 is located in the southwestern part of the South different particle types in the palynological and structureless/amor- China Sea basin. The cored section overlies an oceanic basaltic base- phous class [sporopollen, algae (Concentricystes and Pediastrum), dino- ment dated at ~17 Ma, with age control provided through a combi- flagellate, fungi, SOM/AOM, remains (scolecodonts), and sto- nation of biostratigraphic and magnetostratigraphic data (Li et al., matal apparati]. Samples were collected from IODP Site 1433, a core of 2015). The sediments overlying the basement are approximately 800 m Neogene sediments from the South China Sea. The inferred relation- thick. Lithologically, the bottom of the core is dominated by massive ships between the observed yield and paleoenvironmental changes, reddish and yellowish brown claystone and claystone with silt, with such as paleoclimate, tectonics of the basin, and evolution of con- little coarser material present, although occasional thin silty turbidites tinental drainage systems around/in the South China Sea are discussed. occur, also do dark stains associated with bioturbation. The middle section primarily contains dark greenish gray clay and claystone with frequent medium to thick greenish gray nannofossil ooze and chalk 2. Geological setting and materials interbeds. This part is divided into upper and lower subunits based on the occurrence of thick to very thick (> 1 m) greenish gray nannofossil The South China Sea is one of largest marginal basins in Southeast chalk interbeds in lower subunits, compared to thinner beds in upper Asia. It receives most of its sediment from the modern Asian continent subunit. The upper portion of the core is composed of dark greenish through a number of smaller and well-known larger river systems, in- gray clay with very thin interbeds of clayey silt (Li et al., 2015). The cluding the Pearl, Red, and Mekong (Métivier and Gaudemer, 1999) calibrated biohorizons and paleomagnetic data indicate an extremely (Fig. 1a). These sediments are deposited as a result of the various low sedimentation rate (< 0.5 cm/ky) during the early to middle fl fl processes that re ect the competing in uences of tectonics, chemical , when the basal reddish-brown clay was deposited. In the late weathering, climatic and drainage basin evolution (Clift, 2006; Wei Miocene to early Pleistocene, sedimentation rates varied between ~5–6 et al., 2006; Luo and Sun, 2007; Wan et al., 2012). They served as a and ~9 cm/ky. The sedimentation rate during the Middle and Late fi robust proxy to investigate monsoon development. An intensi cation of Pleistocene increased sharply to around ~20 cm/ky (Li et al., 2015) summer monsoon would bring more precipitation, and therefore en- (Fig. 1b). hance the intensity of physical erosion as well as chemical alteration. However, building a climatic evolution within these specific areas is

167 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

3. Methods and results those of the SOM/AOM (Fig. 15). The stomatal apparatus were rare in most samples, the morphologies are easy to identify because the ob- 3.1. Methods vious stomatal pore, guard cell, the subsidiary and epidermal cell (Fig. 16); both concentration and fl ux were low during MMCO and One hundred and sixteen bulk sediment samples (Fig. 1b) were se- increased afterwards, the changes at ~8 are obvious (Fig. 17). Scole- lected. Samples were chemically processed following a palynological codonts, the portion of a jaw of a polychaete annelid (a common type of technique summarized by Brown (2008). For each sample, the available fossil-producing segmented worm useful in invertebrate paleontology) amount (ranging from 2.4 to 27.3 g) of dried sediment was weighed. (Fig. 18), is only found here in 6 samples before 8 Ma. The patterns of The sediment was spiked with a known quantity of Lycopodium spores concentration and flux were a little different from those of any other to allow assessment of the absolute abundance and the flux of organic- particles although the changes at ~8 Ma are evident (Fig. 19). walled microfossils to the sample. Acid-soluble minerals were digested In summary, the sporopollen, fungi, dinoflagellate cysts, SOM/AOM in hydrochloric acid (HCl) and hydrofluoric acid (HF) to remove car- and resins generally showed consistent patterns throughout the whole bonates and silicates, respectively. The organic-walled particles were core: specifically, both concentrations and fluxes were at their lowest then concentrated by filtration through a 10-μm mesh sieve. In total, during MMCO, after which the concentrations showed relatively com- eight basic types were identified and tabulated: sporopollen, fresh plicated trends but the fluxes all generally increased and become quite water algae (Pediastrum and Concentricystes), dinoflagellate cysts, fungi, steady after 8 Ma. Meanwhile, records of stomatal apparatus, amorphous resin, SOM/AOM, stomatal apparati, and scolecodonts. Concentricystes, Pediastrum and scolecodonts are relatively low and Concentration was calculated using the equation of Benninghoff discontinuous, mostly close to zero during MMCO but they too show a (1962): C = (Pc × Lt × T)/(Lc × W); and flux: I = more steady distribution after ~8 Ma. (Pc × Lt × T × R)/Lc × W × S, where C = concentration (number of particles per gram of dried sediment, grains/g), Pc = the number of 4. Discussion each morphological particle counted, Lt = the number of Lycopodium spores per tablet, T = the total number of Lycopodium tablets added per 4.1. Provenance sample, Lc = the number of Lycopodium spores counted, W = the weight of dried sediment (with dried weight in grams); I = flux (given Sediments deposited in the marine environment include organic particles/cm2/ka), R = sedimentation rates (cm/ka); S = dry density matters of a variety of origins. Individual analyses can provide details of sample (g/cm3). that elucidate the type of environment that existed during deposition. For instance, SOM/AOM are positively correlated with distance from 3.2. Results shore (Thomas et al., 2015) and their relative flux can guide sequence stratigraphic studies. Sporopollen are widely accepted as a product of The diversity of palynomorphs and organic particles tabulated for terrestrial plants with the exception of rare marine plants (Luo and Sun, this study is quite complex (Fig. 2). In order to provide an overview of 2007), Pediastrum and Concentricystes are mainly derived from terres- each category, a series of microphotographs of all key morphological trial fresh water realms (Dorning and Harding, 1998), such as lakes and types discussed are presented (Figs. 3, 5, 8, 10, 12, 14, 16, 18) before rivers. Dinoflagellate cysts are mainly marine phytoplankton although each type's concentrations and fluxes (Figs. 4, 6, 7, 9, 11, 13, 15, 17, 19, some forms also indicate freshwater environments. Fungi are regarded 20). as the most widespread living eukaryotic organisms, occurring on most In total, > 120 morphological types of plant pollen and spores environments (e.g., Cantrell et al., 2011); however the majority of the (sporopollen) were found (Fig. 3). Their concentration increased gra- fungal assemblage recovered from this study is of terrestrial origin dually from ~2 grains/g to over 10,000 grains/g, except for higher (Miao et al., 2017). The resins, stomatal apparatus and scolecodont are values during the period between 13 and 11 Ma; the lowest recovery complicated, and can all be produced from both terrestrial and oceanic was surprisingly during the Middle Miocene Climatic Optimum plants and/or . Therefore, the varying amounts of these parti- (MMCO, 18–15 Ma). Besides these times, the most outstanding change cles reflect broad environmental conditions over a large spatial scale was at ~8 Ma, where a sharp increase from ~200 to 5000 grains/g is from land to offshore. observed. We will refer to this sudden increase as the ~8 Ma event. Flux followed a roughly similar trend with relatively fewer fluctuations, 4.2. Driving forces except for the obvious change at ~8 Ma (Fig. 4). Regarding the fresh water algal Concentricystes, it is found in only two samples prior to 8 Ma It is quite noteworthy that a change of all eight types of palyno- and becomes steadily more abundant in samples of 8 Ma and younger morphs appeared at the same time interval, ca. 8 Ma. In order to discuss (Figs. 5, 6). The other major component of the fresh water algal group is the driving forces for the trends and changes, we combined all Pediastrum, slight differences can be identified in this genus (Fig. 5). morphologies together to show the changes in total organic particles They are absent from the assemblage before ~8 Ma and present is (Fig. 20a, b), the ratios of sporopollen and dinoflagellate to total or- consistently high abundance after ~8 Ma (Fig. 7). Dinoflagellate cysts ganic particles (Fig. 20c, d) and compared them to total organic carbon are common with rich types found only after 14 Ma (Fig. 8). Their content and sedimentary rates (Li et al., 2015)(Fig. 20e, f), respec- concentrations vary throughout the interval studied, but become more tively. The first two graphs ( Fig. 20a, b) show broadly increasing trends stable after ~8 Ma. The flux clearly shows more steady higher values showing some anti-correlation against the global δ18O record (Zachos after the ~8 Ma event (Fig. 9). Fungi are very abundant and di- et al., 2008)(Fig. 20g), i.e., which overall increase gradually as climate verse; > 30 morphologic types were found and grouped into three basic is cooling; and some weak correlation with the global δ13C record assemblages according to the cells numbers: single celled, double celled (Zachos et al., 2008)(Fig. 20h). and multicellular (Fig. 10)(Miao et al., 2017). The fungal concentra- tions and flux trends also show more steady high values after the 4.2.1. Paradoxical paleoclimate explanation ~8 Ma event (Fig. 11). The SOM/AOM are very common in most Comparison between trends in the total concentration of organic samples (Fig. 12), the concentrations are at their lowest during MMCO matters, flux rate and global δ18O are often widely used to propose that and higher at ~13 Ma; the ~8 Ma event is obvious, again marked by a the changes in total organic matter abundance through time are mainly change from high fluctuations to more steady values. The flux dis- driven by paleoclimate changes, such as changes in temperature and tribution follows a similar pattern but with a generally increasing trend moisture. Modern observations show that aboveground biomass across (Fig. 13). Patterns of distribution of resins (Fig. 14) were similar to the tundra biome in the Northern Hemisphere high latitudes

168 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 2. Representative palynofacies showing different morphologies of sporopollen and non-pollen grains and added Lycopodium clavatum from the IODP U1433 core (A: algae (dino- flagellate cysts); C: microcharcoal (not discussed in this study); F-fungi; L-Lycopodium clavatum; SOM/AOM: structured/amorphous organic matters; SP: sporopollen; R: resin; SA: stomatal apparatus).

Fig. 3. Light microscope photographs of selected morphologies of sporopollen. a: Polypodiaceae; b: Lycopodiaceae; c: Podocarpus, Podocarpaceae; d. Iridaceae?; e: Palmae; f: Casuarinaceae; g: Alnus, Betulaceae; h: Sonneratia, Sonneratiaceae (Lythraceae); i: Quercus, Fagaceae; j: Melastomataceae; k: Nyssa, Nyssaceae; l: Sapindaceae; m: Ilex, Aquifoliaceae.

169 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 4. Concentration and flux of total sporopollen with the blue bar marking the shift seen at ~8 Ma at IODP Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle marks the MMCO (Middle Miocene Climatic Optimum). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5. Light microscope photographs of selected morphology of algae. a, b: Concentricystes;c–f: Pediastrum.

Fig. 6. Concentration and flux of Concentricystes with the blue bar marking the changes at ~8 Ma at IODP Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) significantly increased as mean annual temperature increases (MAT) warmer Asia (Miao et al., 2016c). So, the biomass should have reached (Wang et al., 2016), which means that, theoretically, biomass produc- a maximum during the MMCO and then decreased afterwards, similarly tion increases as the climate becomes warmer. If such observations can to the content of total organic carbon collected from the same core (Li be used as references for the general relationships between the tem- et al., 2015)(Fig. 20 e); however, all the organic particles follow very perature and biomass, we can infer that the highest temperature period different patterns to those that are traditionally observed in response to of the late Cenozoic was the MMCO (Flower and Kennett, 1994) climate variation, and all were at their lowest during the MMCO and (Fig. 20g); and the sea-surface temperature in the tropics was ~4 °C to seem to increase since 8 Ma. Consequently, the trends in concentrations 6 °C higher during the MMCO and then subsequently decreased con- and fluxes seen in this study are likely not driven by climate (at least tinuously (Zhang et al., 2014; Herbert et al., 2016). The sporopollen temperature) but by other forcing mechanisms, especially around 8 Ma. assemblage in Inner Asia indicated a dense forest with a rather humid Precipitation should obviously be considered as the region is strongly climate during the MMCO (Miao et al., 2012, 2013b), with a large affected by monsoonal circulation. The geochemical and mineralogical number of warm- and wet-adapted , such as Platybelodon, records from the South China Sea have been interpreted to show that Pliopithecus, Anchitherium, Chalicotherium, Kubanochoerus and Palaeo- the East Asian summer monsoon has intensified since 8 Ma (Liu et al., tragus appearing (Deng, 2016). These observations support an East 2017). The sporopollen results from ODP Site 1143 would be consistent Asian summer monsoon (precipitation) intensification along with a with greater moisture and, potentially, with enhanced monsoonal

170 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 7. Diagrams showing concentration and flux of Pediastrum at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 8. Light microscope photographs of selected mor- phology of dinoflagellate cysts and other marine algae. a, c: Impagidinium spp.; b: Spiniferites sp., d: Lingulodinium ma- chaerophorum;e:Tuberculodinium vancampoae.

Fig. 9. Diagrams showing concentration and flux of total dinoflagellate cysts at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO and the blue bar marks the 8 Ma event. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) activity since ~8 Ma (Luo and Sun, 2007). However, the age of the the driving force for decreasing aridity in East and South Asia at inception of monsoonal conditions is debated. For instance, other 8–6 Ma, leading to widespread ecosystem changes in that region. chemical weathering constraints and erosion records from the South Overall, the monsoon evolution at ~8 Ma remains unclear, and should China Sea favor the onset of strengthening as early as the Early Miocene not be considered as the main driving force behind changes at ~8 Ma in (at ~23 Ma) with a decrease in strength after 8 Ma (Clift et al., 2008; the South China Sea. Clift et al., 2014; Wan et al., 2007). Steinke et al. (2010) even suggested that an abrupt weakening in the EASM around 7.5 Ma was most likely

171 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 10. Light microscope photographs of selected morphology of fungi (Miao et al., 2017). a: Exesisporites;b:Biporisporites;c:Alternia;d:Meliola;e:Diporisporites;f:Spegazzinia type; g: Striadiporites;h:Tetraploa aristata; i: unknown type.

Fig. 11. Diagrams showing concentration and flux of total fungi recovered at Site U1433 after Miao et al. (2017) (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO and the blue line the 8 Ma mark. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 12. Light microscope photographs of selected morphology of SOM/AOM. a, d, e, h, i: structured organic matters; b, c, f, g: amorphous organic matters.

172 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 13. Diagrams showing concentration and flux of SOM/AOM at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO while the blue marks the 8 Ma time. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 14. Light microscope photographs of selected resin morphologies. a: nearly rectangular resin; b–d, h: amorphous resins; e-g: suborbicular resins.

Fig. 15. Diagrams showing concentration and flux of total resins at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

4.2.2. Tectonic basin evolution and drainage changes the Middle Miocene, tectonic activity in the basin became relatively Besides paleoclimate, tectonically-driven basin evolution and drai- weaker until the uplift of the Vietnamese Central Highlands and the nage changes (river system or sea current) are also considered as co- extrusion of a thick basaltic sequence, mostly after ~8 Ma (Carter et al., existing factors which could be reflected in the deposition at IODP Site 2000; Cung et al., 1998). Such weakening in tectonic activity is re- U1433. flected by the decreasing volumes of lava emplacement (Hoang and Within the South China Sea, studies have suggested that seafloor Flower, 1998; Wang et al., 2001). A paleogeographic map of the South spreading ended at 20.5 Ma (Barckhausen et al., 2014), or that there China Sea at 17 Ma and 8 Ma shows that Luzon and the Philippine arc was a cessation at ~17 to 15 Ma according to earlier estimates based on have been moving from the Pacific towards the South China Sea pro- IODP drilling (Briais et al., 1993; Li et al., 2015; Li et al., 2014). After gressively over this interval, noting the emergence of Borneo prior to

173 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 16. Light microscope photographs of selected stomatal structure morphologies. a, b: large epidermal stomatas; c-d: small epidermal stomatas (possibly broken from the large ones).

Fig. 17. Diagrams showing concentration and flux of total stomatal apparatus at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 18. Light microscope photographs of selected morphology of animal remains. a-e: jaw apparatus of scolecodonts (jaws of marine worms).

8 Ma and the emplacement of the Central Highlands lavas at 8 Ma (Hall, contributor of sediment after 8 Ma (Liu et al., 2017), explaining the 2002). All these evidence suggest that the Mekong Basin and sur- synchronous signal seen in all organic matter types at 8 Ma, and the rounding lands, driven by tectonics during the last 17 Ma, were moving somewhat more stable signal seen in sediments younger than 8 Ma, towards a location which promoted the accumulation of all organic while the multiple sources prior to 8 Ma would explain the disparity particles. Furthermore, tectonics was also driving long-term uplift and and complexity of the signals. The drainage system changes associated widening of the Tibetan Plateau, where the headwaters of the Mekong with the tectonically-driven basin evolution best explain the ~8 Ma River lie. Accelerated clastic sedimentary rates from about < 0.5 cm/ event. Indeed, based on the clastic sedimentation as well as geochem- k.y. to ~20 cm/k.y. can be observed after 8 Ma (Li et al., 2015) ical and mineralogical provenance proxies, Liu et al. (2017) argued that (Fig. 20f). This indicate that Site U1433 start receiving increasing vo- most of the sediments deposited at Site U1433 since 8 Ma have been lumes of terrestrial sedimentary materials after that time, which is a derived from the Mekong River, with lesser inputs from other small trend opposite to that seen in the Pearl and Red River systems (Clift, rivers draining coastal Vietnam, including the Central Highlands. Re- 2006). Prior to 8 Ma, the possible sources are complex according to the gional sediment budgets for this area (Clift, 2006; Ding et al., 2016) geochemical and mineralogical provenance (Liu et al., 2017), probably show a sharp increase in sedimentation rates at around this time, representing a mix from Indochina, the Dangerous Grounds, and Pa- consistent with the Mekong either initiating or moving its mouth to the lawan, but it seems clear that the Mekong Basin became the main present location. Luo and Sun (2007) also ascribed this event to tectonic

174 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

Fig. 19. Diagrams showing concentration and flux of scolecodonts at Site U1433 (colors represent logarithmic values; grays represent linear values); the yellow rectangle represents the MMCO. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 20. Diagrams showing (a) total concentrations and (b) total fluxes of all types, ratios of (c) sporopollen and (d) dinoflagellate cysts to total organic particles, (e) organic carbon (wt%) and (f) linear sedimentation rate in the IODP Site U1433 (Li et al., 2015), (g) global ice volume/temperature and (h) carbon isotope records (Zachos et al., 2008) (shallow blue strip and yellow rectangle represent the change at ~8 Ma and MMCO (Middle Miocene Climatic Optimum)). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

175 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177 deformation occurring around the southern South China Sea. They constraints. Earth Planet. Sci. Lett. 286 (3), 514–525. imply that tectonic activity onshore resulted in the rapid uplift of sur- Clift, P.D., 2006. Controls on the erosion of Cenozoic Asia and the flux of clastic sediment – fi to the ocean. Earth Planet. Sci. Lett. 241, 571 580. rounding islands, most signi cantly Borneo, as well as the Central Clift, P.D., Hodges, K.V., Heslop, D., Hannigan, R., Van Long, H., Calves, G., 2008. Highlands of Vietnam, which would explain the higher fluxes in spor- Correlation of Himalayan exhumation rates and Asian monsoon intensity. Nat. opollen data collected from ODP 1143 (for location, see Fig. 1). Cer- Geosci. 1, 875–880. Clift, P.D., Wan, S., Blusztajn, J., 2014. Reconstructing chemical weathering, physical tainly, uplift of the Central Highlands would also have resulted in in- erosion and monsoon intensity since 25Ma in the northern South China Sea, a review tensified fluvial run-off and a possible increase in all particles. of competing proxies. Earth Sci. Rev. 130, 86–102. Combaz, A., 1964. Les palynofaciàs. Rev. Micropaleontol. 7, 205–218. 5. Conclusion Cung, T., Dorobek, S., Richter, C., Flower, M., Kikawa, E., Nguyen, Y., McCabe, R., 1998. Paleomagnetism of late Neogene basalts in Vietnam and Thailand, implications for the post-Miocene tectonic history of Indochina. In: Mantle Dynamics and Plate The study presents the evolution of eight types of palynological and Interactions in East Asia, pp. 289–299. structureless particles deposited during 17 Ma in the South China Sea Deng, T., 2016. Records and characteristics of the mammalian faunas of Northern China in the Middle Miocene climatic Optimum. Quat. Sci. 36 (4), 811–819 (in Chinese with and sampled at IODP Site U1433. The increasing trends in concentra- English abstract). tion and flux of organic matters are likely to reflect tectonic activity Ding, W., Li, J., Clift, P.D., Expedition, I., 2016. Spreading dynamics and sedimentary rather than paleoclimatic changes such as the Asian summer monsoon. process of the southwest sub-basin, South China Sea, constraints from multi-channel seismic data and IODP expedition 349. J. Asian Earth Sci. 115, 97–113. The distribution of organic matters of various source (terrestrial, Dorning, K.J., Harding, J.L., 1998. Environmental distribution of the -Recent marine and multiple-origin particles) all evidenced a major shift at terrestrial to freshwater acritarchs and algae, including Concentricystes, Moyeria and 8 Ma. This 8 Ma event likely reflects the onset of the sediment influx Pediastrum. In: CIMP Symposium and Workhops, Pisa, September 11–15, Abstracts, pp. 37. form the Mekong River as a result of drainage system evolution. Ercegovac, M., Kostić, A., 2006. Organic facies and palynofacies, nomenclature, classifi- cation and applicability for petroleum source rock evaluation. Int. J. Coal Geol. 68 Acknowledgments (1), 70–78. Flower, B.P., Kennett, J.P., 1994. The middle Miocene climatic transition, East Antarctic ice sheet development, deep ocean circulation and global carbon cycling. This research used samples and/or data provided by the Palaeogeogr. Palaeoclimatol. Palaeoecol. 108, 537–555. International Ocean Discovery Program (IODP). Funding for this re- Garzon, S., Warny, S., Bart, P.J., 2012. Sequence stratigraphic interpretation of search was provided by the U.S. Science Support Program to Louisiana Santonian-Maastrichtian strata from the Upper Magdalena oil-producing basin, cen- tral Colombia: a Palynological approach. Palynology 36 (Suppl. 1), 112–133. State University as well as by the NSFC Grants (41290252, 41772181). Griener, K.W., Warny, S., 2015. Nothofagus pollen grain size as a proxy for long-term The research was carried out at the Center for Excellence in Palynology climate change, an applied study on Eocene, Oligocene, and Miocene sediments from – (CENEX) in Baton Rouge, Louisiana. The visiting scholar fellowship to Antarcti. Rev. Palaeobot. Palynol. 221, 138 143. Habib, D., 1979. Sedimentary origin of North Atlantic palynofacies. Deep Yunfa Miao is funded by the Chinese Academy of Sciences through a Drilling Results in the Atlantic Ocean. In: Continental Margins and partnership with CENEX. PC thanks the Charles T. McCord Jr. Chair in Paleoenvironment, pp. 420–437. Petroleum Geology and USSAC for support during this study. Hall, R., 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SWPacific, computer-based reconstructions and animations. J. Asian Earth Sci. 20, 353–434. References Herbert, T.D., Lawrence, K.T., Tzanova, A., Peterson, L.C., Caballero-Gill, R., Kelly, C.S., 2016. Late Miocene global cooling and the rise of modern ecosystems. Nat. Geosci. Hoang, N., Flower, M., 1998. Petrogenesis of Cenozoic basalts from Vietnam, implication Akyuz, I., Warny, S., Oyebode, F., Bhattacharya, J., 2016. Palynology of the Turonian for origins of a ‘diffuse igneous province. J. Petrol. 39, 369–395. fi fl Ferron-Notom Sandstone, Utah: identi cation of marine ooding surfaces and Jaramillo, C., Rueda, M.J., Mora, G., 2006. Cenozoic plant diversity in the Neotropics. Milankovitch cycles in subtropical, ever-wet, paralic to non-marine paleoenviron- Science 311 (5769), 1893–1896. – ments. Palynology 40 (1), 122 136. Jiang, H.C., Ding, Z.L., 2008. A 20 Ma pollen record of East-Asian summer monsoon Anderson, J.B., Warny, S., Askin, R.A., Askin, R.A., Wellner, J.S., Bohaty, S.M., Kirshner, evolution from Guyuan, Ningxia, China. Palaeogeogr. Palaeoclim. Palaeoecol. 265 A.E., Livsey, D.N., Simms, A.R., Smith, T.R., Ehrmann, W., Lawyer, L.A., Barbeau, D., (1), 30–38. Wise, S.W., Kulhanek, D.K., Weaver, F.M., Majewski, W., 2011. Progressive Cenozoic Li, C., Xu, X., Lin, J., Sun, Z., Zhu, J., Yao, Y., Zhao, X., Liu, Q., Kulhanek, D.K., Wang, J., cooling and the demise of Antarctica's last refugium. Proc. Natl. Acad. Sci. 108 (28), 2014. Ages and magnetic structures of the South China Sea constrained by deep tow – 11356 11360. magnetic surveys and IODP Expedition 349. Geochem. Geophys. Geosyst. 15, Askin, R.A., 1989. Endemism and heterochroneity in the Late Cretaceous (Campanian) to 4958–4983. fl Paleocene palyno oras of Seymour Island, Antarctica, implications for origins, dis- Li, C., Lin, J., Kulhanek, D., 2015. The expedition 349 scientists, 2015. Site U1433. Proc. fl persal and palaeoclimates of southern oras. Geol. Soc. Lond. Spec. Publ. 47 (1), Int. Ocean Discov. Prog. 349. http://dx.doi.org/10.14379/iodp.proc.349.105.2015. – 107 119. Liu, C., Clift, P.D., Murray, R.W., Blusztajn, J., Ireland, T., Wan, S.M., Ding, W.W., 2017. fl Axelrod, D.I., 1997. Paleoelevation estimated from Tertiary oras. Int. Geol. Rev. 39 (12), Geochemical evidence for initiation of the modern Mekong delta in the southwestern – 1124 1133. South China Sea after 8 Ma. Chem. Geol. 451, 38–54. Barckhausen, U., Engels, M., Franke, D., Ladage, S., Pubellier, M., 2014. Evolution of the Lorente, M.A., 1986. Palynology and palynofacies of the Upper Tertiary in Venezuela. J. fl South China Sea, revised ages for breakup and sea oor spreading. Mar. Pet. Geol. 58, Cramer 217–222. – 599 611. Luo, Y.L., Sun, X.J., 2007. Deep sea pollen record during 12-1.6 Ma from the southern Batten, D.J., 1982. Palynofacies, palaeoenvironments and petroleum. J. Micropalaeontol. South China Sea and its response to environmental change. Chin. Sci. Bull. 52, – 1 (1), 107 114. 2115–2122. fl Batten, D.J., Lister, J.K., 1988. Early cretaceous dino agellate cysts and chlorococcalean Macphail, M.K., 1997. Late Neogene climates in Australia, fossil pollen-and spore-based algae from freshwater and low salinity palynofacies in the English Wealden. Cretac. estimates in retrospect and prospect. Aust. J. Bot. 45 (3), 425–464. – Res. 9 (4), 337 367. Métivier, F., Gaudemer, Y., 1999. Stability of output fluxes of large rivers in South and Batten, D.J., Stead, D.T., 2005. Palynofacies analysis and its stratigraphic application. In: East Asia during the last 2 million years: implications on floodplain processes. Basin – Applied Stratigraphy. Springer, Netherlands, pp. 203 226. Res. 11 (4), 293–303. ff Benningho , W.S., 1962. Calculation of Pollen and Spore Density in Sediments by Miao, Y.F., Fang, X.M., Herrmann, M., Wu, F.L., Zhang, Y., Liu, D.L., 2011. Miocene Addition of Exotic Pollen in Known Quantities. pollen record of KC-1 core in the Qaidam Basin, NE Tibetan Plateau and implications Briais, A., Patriat, P., Tapponnier, P., 1993. Updated interpretation of magnetic anomalies for evolution of the East Asian monsoon. Palaeogeogr. Palaeoclimatol. Palaeoecol. fl and sea oor spreading stages in the South China Sea, implications for the tertiary 299 (1), 30–38. tectonics of Southeast Asia. Journal of Geophysical Research, Solid Earth 98, Miao, Y.F., Herrmann, M., Wu, F.L., Yan, X.l., Yang, S.L., 2012. What controlled Mid-Late – 6299 6328. Miocene long-term aridification in Central Asia?—Global cooling or Tibetan Plateau Brown, C.A., 2008. Palynological techniques. In: Riding, J.B., Warny, S. (Eds.), Am. Assoc. uplift, A review. Earth Sci. Rev. 112 (3), 155–172. Strat. Palynologists, second edition. . Miao, Y.F., Wu, F.L., Herrmann, M., Yan, X.L., Meng, Q.Q., 2013a. Late early oligocene Cantrell, S.A., Dianese, J.C., Fell, J., Gunde-Cimerman, N., Zalar, P., 2011. Unusual fungal East Asian summer monsoon in the NE Tibetan Plateau, Evidence from a palynolo- – niches. Mycologia 103, 1161 1174. gical record from the Lanzhou Basin, China. J. Asian Earth Sci. 75, 46–57. Carter, A., Roques, D., Bristow, C., 2000. Denudation history of onshore central Vietnam, Miao, Y.F., Fang, X.M., Wu, F.L., Cai, M.T., Song, C.H., Meng, Q.Q., Xu, L., 2013b. Late constraints on the Cenozoic evolution of the western margin of the South China Sea. Cenozoic continuous aridification in the western Qaidam Basin, evidence from – Tectonophysics 322, 265 277. sporopollen records. Clim. Past 9, 1863–1877. Cirilli, S., Marzoli, A., Tanner, L., Bertrand, H., Buratti, N., Jourdan, F., Bellieni, G., Miao, Y.F., Wu, F.L., Chang, H., Fang, X.M., Deng, T., Sun, J.M., Jin, C.S., 2016a. A Late- Kontak, D., Renne, P.R., 2009. Latest onset of the central Atlantic magmatic Eocene palynological record from the Hoh Xil Basin, northern Tibetan Plateau, and its province (CAMP) volcanism in the fundy basin (Nova Scotia), new stratigraphic implications for stratigraphic age, paleoclimate and paleoelevation. Gondwana Res.

176 Y. Miao et al. International Journal of Coal Geology 190 (2018) 166–177

01, 0077. from DSDP site 534, Blake-Bahama Basin, western Central Atlantic. Mar. Pet. Geol. 1 Miao, Y.F., Fang, X.M., Liu, Y.-S.C., Yan, X., Li, S., Xia, W., 2016b. Late Cenozoic pollen (1), 3–13. concentration in the western Qaidam Basin, northern Tibetan Plateau, and its sig- Van der Zwan, C.J., 1990. Palynostratigraphy and palynofacies reconstruction of the nificance for paleoclimate and tectonics. Rev. Palaeobot. Palynol. 231, 14–22. upper to lowermost cretaceous of the Draugen field, offshore mid Norway. Miao, Y.F., Song, C.H., Fang, X.M., Meng, Q.Q., Zhang, P., Wu, F.L., Yan, X.L., 2016c. Late Rev. Palaeobot. Palynol. 62 (1–2), 157–186. Cenozoic genus Fupingopollenites development and its implications for the Asian Walker, J.W., 1974. Evolution of exine structure in the pollen of primitive angiosperms. summer monsoon evolution. Gondwana Res. 29, 320–333. Am. J. Bot. 61 (8), 891–902. Miao, Y.F., Warny, S., Liu, C., Clift, P.D., Gregory, M., 2017. Neogene fungal record from Wan, S.M., Li, A., Clift, P.D., Stuut, J.B.W., 2007. Development of the East Asian mon- IODP Site U1433, South China Sea, implications for paleoenvironmental change and soon, mineralogical and sedimentologic records in the northern South China Sea the onset of the Mekong River. Mar. Geol. 390 (1), 23–35. since 20 Ma. Palaeogeogr. Palaeoclimatol. Palaeoecol. 254, 561–582. Molengraaff, G.A.E., Weber, M., 1919. Het verband tusschen den plistoceenen ijstijd en Wan, S.M., Clift, P.D., Yu, Z., Li, A., Li, T., 2012. Tectonic and climatic controls on long- het ontstaan der Soenda-zee (Java-en Zuid-Chmeesche Zee) en de invloed daarvan op term silicate weathering in Asia since 5 Ma. Geophys. Res. Lett. 39, L15611. de verspreidmg der koraalriffen en op de land-en zoetwater-fauna. Verslag Van de Wang, J.H., Yin, A., Harrison, T.M., Grove, M., Zhang, Y.Q., Xie, G.H., 2001. A tectonic Gewone Vergaderingen der Wis-En Natuurkundige Afdeeling 28, 497–544. model for Cenozoic igneous activities in the eastern indo-Asian collision zone. Earth Nichols, D.J., 1995. The role of palynology in paleoecological analyses of Tertiary coals. Planet. Sci. Lett. 188, 123–133. Int. J. Coal Geol. 28 (2), 139–159. Wang, P., Heijmans, M.M., Mommer, L., van Ruijven, J., Maximov, T.C., Berendse, F., Retallack, G.J., 1995. -Triassic life crisis on land. Science 267 (5194), 77. 2016. Belowground plant biomass allocation in tundra ecosystems and its relation- Shu, J.W., Wang, W.M., Leopold, E.B., Wang, J.S., Yin, D.S., 2008. Pollen stratigraphy of ship with temperature. Environ. Res. Lett. 11 (5), 055003. coal-bearing deposits in the Neogene Jidong Basin, Heilongjiang Province, NE China, Warny, S., Bart, P.J., Suc, J.P., 2003. Timing and progression of climatic, tectonic and New insights on palaeoenvironment and age. Rev. Palaeobot. Palynol. 148 (2), glacioeustatic influences on the Messinian Salinity Crisis. Palaeogeogr. 163–183. Palaeoclimatol. Palaeoecol. 202 (1–2), 59–66. Steinke, S., Groeneveld, J., Johnstone, H., Rendle-Bühring, R., 2010. East Asian summer Warny, S., Askin, R.A., Hannah, M.J., Mohr, B.A., Raine, J.I., Harwood, D.M., Florindo, F., monsoon weakening after 7.5 Ma, Evidence from combined planktonic foraminifera 2009. Palynomorphs from a sediment core reveal a sudden remarkably warm Mg/Ca and δ18O (ODP Site 1146; northern South China Sea). Palaeogeogr. Antarctica during the middle Miocene. Geology 37 (10), 955–958. Palaeoclimatol. Palaeoecol. 289 (1–4), 33–43. Wei, G., Li, X.H., Liu, Y., Shao, L., Liang, X., 2006. Geochemical record of chemical Sturrock, S.J., 1996. Biostratigraphy. In: Emery, D., Myers, K. (Eds.), Sequence weathering and monsoon climate change since the early Miocene in the South China Stratigraphy. Blackwell Science, Oxford, pp. 89–107. Sea. Paleoceanography 21 (4), 1–11. Sun, J.M., Xu, Q., Liu, W., Zhang, Z.Q., Xue, L., Zhao, P., 2014. Palynological evidence for White, J.M., Ager, T.A., Adam, D.P., Leopold, E.B., Liu, G., Jette, H., Schweger, C.E., the latest Oligocene− early Miocene paleoelevation estimate in the Lunpola Basin, 1997. An 18 million year record of vegetation and climate change in northwestern central Tibet. Palaeogeogr. Palaeoclimatol. Palaeoecol. 399, 21–30. Canada and Alaska: Tectonic and global climatic correlates. Palaeogeogr. Sweet, A.R., Cameron, A.R., 1991. Palynofacies, coal petrographic facies and depositional Palaeoclimatol. Palaeoecol. 130 (1–4), 293–306. environments, amphitheatre formation (Eocene to Oligocene) and Ravenscrag for- Wu, F.L., Fang, X.M., Herrmann, M., Mosbrugger, V., Miao, Y.F., 2011. Extended drought mation (Maastrichtian to Paleocene), Canada. Int. J. Coal Geol. 19 (1–4), 121–144. in the interior of Central Asia since the Pliocene reconstructed from sporopollen re- Thomas, M.L., Pocknall, D.T., Warny, S., Bentley Sr, S.J., Droxler, A.W., Nittrouer, C.A., cords. Glob. Planet. Chang. 76 (1), 16–21. 2015. Assessing palaeobathymetry and sedimentation rates using palynomaceral Zachos, J.C., Dickens, G.R., Zeebe, R.E., 2008. An early Cenozoic perspective on green- analysis, a study of modern sediments from the Gulf of Papua, offshore Papua New house warming and carbon-cycle dynamics. Nature 451, 279–283. Guinea. Palynology 39, 410–433. Zhang, Y.G., Pagani, M., Liu, Z., 2014. A 12-million-year temperature history of the Tyson, R.V., 1984. Palynofacies investigation of Callovian (middle Jurassic) sediments tropical Pacific Ocean. Science 344, 84–87.

177