Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California

Quaternary International xxx (2016) 1e21

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Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California Mary McGann U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 30 March 2016 Received in revised form 10 October 2016 Accepted 6 November 2016 Available online xxx

The pollen assemblage of a deep-sea core (15G) collected at lower bathyal depths (3491 m) on a levee of Monterey Canyon off central California was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record. Thirty-two samples were obtained down the length of the core, 19 from hemipelagic and mixed mud deposits considered to be the background record, and 13 others from displaced flow deposits. The pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19,000 cal yrs BP. A Q-mode cluster analysis defined three pollen zones: a Glacial Pollen Zone (ca. 20,000e17,000 cal yr BP), an overlying Transitional Pollen Zone (ca. 17,000e11,500 cal yr BP), and an Interglacial Pollen Zone (ca. 11,500 cal yr BP to present). Another Qmode cluster analysis, of both the background mud and flow deposits, also defined these three pollen zones, but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position. This was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched (~10e35% in some cases) in hydraulically-efficient Pinus pollen. A selective bias in the pollen assemblage, such as demonstrated here, may result in incorrect interpretations (e.g., climatic shifts or environmental perturbations) based on the floral record, indicating turbiditic deposits should be avoided in marine palynological studies. Particularly in the case of fine-grained flow deposits that may not be visually distinct, granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits. Determining the relative abundance and source of displaced shallow-water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so. Published by Elsevier Ltd.

Keywords: Marine pollen Climate Central California Late Quaternary Turbidites Selective bias Benthic foraminifera

1. Introduction Although palynological investigations typically utilize terrestrial records deposited in local lacustrine settings (e.g., Worona and Whitlock, 1995; West, 2003; Walsh et al., 2008), marine palynology can provide insight into geographically broader, and temporally longer and more continuous floral patterns and terrestrial climate of the adjacent continent from where the pollen and spores were derived (Groot and Groot, 1964, 1966; Cronin et al., 1981; Gardner et al., 1988; Mudie and McCarthy, 1994). As discussed in Mudie and McCarthy (1994), marine pollen records can also be compared directly to other proxies commonly used as a

E-mail address: [email protected].

basis for climate change studies (e.g., foraminifera, diatoms, % CaCO3, and alkenones) when the same samples are analyzed (e.g., Balsam and Heusser, 1976; Barron et al., 2003; McGann, 2015b), thereby reducing or eliminating uncertainties in marine and terrestrial correlations, especially in regard to the chronologic methods used in each. In the late 1970s, the U.S. Geological Survey conducted field investigations off central California to explore the biologic and geologic effects of climate change, as well as the sediment depositional processes associated with those changes. As part of this effort, nine piston and six gravity cores were obtained in May and June of 1978 on a geophysical and sediment sampling cruise by the R/V Sea Sounder (USGS cruise S3-78-SC) from depths of 1851 me3650 m. One of the longest cores, 15G, was a 4.72 m-long gravity core collected at a depth of 3491 m approximately 18 km

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Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

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M. McGann / Quaternary International xxx (2016) 1e21

from the crest of the western levee of the Monterey Fan Valley. The site was 200 m below the confluence of the Ascension Fan Valley and Monterey Fan Valley (Greene and Hicks, 1990), and 135 km southwest of Santa Cruz, CA (36
23.530 N, 123
20.520 W; Fig. 1). Because of its length, location, and depth of acquisition, this deep-sea core was eventually selected for detailed quantitative palynological and benthic foraminiferal analysis. Ultimately, it provided excellent paleoclimatologic and paleoceanographic records over the last ca. 19,000 cal yrs BP (McGann, 2015a, 2015b), as well as insights into submarine canyon depositional processes (McGann, 2014). What is presented here is a further investigation of those depositional processes and how they impact palynological records in a marine environment. The palynological assemblages from 19 mud samples are considered the background record to which those from 13 turbiditic samples are compared in order to understand the delivery processes of terrigenous material to submarine fans based on the biological component entrained in those sediments.

2. Regional setting 2.1. The Ascension-Monterey Canyon system The Ascension-Monterey Canyon system is one of the largest marine features located off central California (Fig. 1). To the north is

~ o Neuvo, the Ascension Canyon system, comprised of Ascension, An and Cabrillo Canyons; to the south is the Monterey Canyon system, made up of Soquel, Monterey, and Carmel Canyons (Greene and Hicks, 1990). Both canyon systems transport sediment to Monterey Fan. Because the Ascension Canyon system heads on the upper slope, it is most active during low stands (Normark and Hess, 1980; Normark et al., 1984; Greene and Hicks, 1990) although it still appears to be so today (Greene and Hicks, 1990), whereas the Monterey Canyon system transects the entire continental shelf, thereby being active during the low stand, the Holocene transgression, and the high stand that followed (Normark and Hess, 1980; Normark et al., 1980; Greene and Hicks, 1990; Paull et al., 2005; Fildani et al., 2006; Piper and Normark, 2009). Monterey Fan is the largest of several submarine fans off central California (Normark, 1970a, 1999; Hess and Normark, 1976; Normark et al., 1984; EEZ-SCAN 84 Scientific Staff, 1986) and one of the largest found off the contiguous United States (Greene and Hicks, 1990). Presently, it is characterized by an area of active fan growth that extends for more than 300 km from the base of the continental slope (Normark and Hess, 1980) resulting from the deposition of hemipelagic and turbidity current-derived sediments, similar to those of many other submarine canyons (Fildani et al., 1999; Normark, 1970a, 1999; Normark and Hess, 1980; Normark et al., 1984). The Monterey Fan Valley features an abrupt channel meander

~ o Neuvo, Fig. 1. Location map of the Ascension-Monterey Canyon system off central California and the site of core 15G. The Ascension Canyon system is comprised of Ascension, An and Cabrillo Canyons, whereas the Monterey Canyon system includes Soquel, Monterey, and Carmel Canyons (Greene and Hicks, 1990). The channel of Monterey Canyon is outlined in black.

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

M. McGann / Quaternary International xxx (2016) 1e21

(Shepard, 1966) that is the site of a probable Late Pleistocene channel diversion. That diversion resulted in the abandonment of the Monterey East Fan Valley, piracy of the lower end of the Ascension Fan Valley, followed by headward erosion of the Ascension Fan Valley into a hanging tributary of the Monterey Fan Valley (Normark, 1970a, 1970b). As a result, the primary source of sediments for Monterey Fan in the Quaternary is Monterey Canyon (Normark et al., 1984; Paull et al., 2005). The channel of Monterey Canyon transports sand that is believed to originate on the beach and shelf of Monterey Bay (Paull et al., 2005; McGann et al., unpublished data). Generally, these sands are confined to the channel except for rare occurrences when it flows over the bank. In contrast, muds representing lower-energy conditions are found on the canyon flanks (Paull et al., 2005). The Monterey Fan Valley is characterized by extensive levee development, as is the Ascension Fan Valley as well (Normark, 1970a, 1970b; Hess and Normark, 1976; Normark et al., 1984). The western levee of the Monterey Fan Valley is the largest and joins that of the Ascension Fan Valley at a depth of ca. 3290 m where the two valleys converge (Normark, 1970b; Greene and Hicks, 1990). Sediment waves trending subparallel to the levee crest occur on the backside of this levee away from the channel floor (Normark et al., 1980, 1984) and are considered depositional bedforms resulting from channel-overflow of fine-grained material of large turbidity currents (Normark et al., 1980). 2.2. The coastal central California flora A diverse flora characterizes the modern terrestrial vegetation of coastal central California. In the coastal zone, Pinus radiata (Monterey pine), P. muricata (Bishop pine), Cupressus goveniana (Gowen cypress), C. macrocarpa (Monterey cypress), and Quercus agrifolia (coast live oak) are sporadically distributed, whereas other nearshore regions are characterized by grassy meadows and low shrubs (Critchfield, 1971; Little, 1971; Munz and Keck, 1973; Griffin and Critchfield, 1976; Barbour and Major, 1977; Kuchler, 1977; Zinke, 1977). Baccharis pilularis (coyote brush), Artemisia californica (California sagebrush), Ceanothus thyriflorus (blue brush) and Rhamnus californius (coffeeberry) are locally common. Drought-deciduous shrubs thrive in the drier coastal regions, including Artemisia californica, Eriogonum fasciculatum (California buckwheat), Salvia apiana (white sage), S. mellifera (black sage), and Baccharis pilularis. Sequoia sempervirens (redwood), Notholithocarpus densiflora (tanoak), Umbellularia californica (California bay), Arbutus menziesii (madrone), and Quercus wislizenii (interior live oak) dominate the mesic sites further inland, Pseudotsuga menziesii (Douglas fir) and Quercus garryana (Oregon white oak) the drier locations, and Alnus rubra (red alder), Alnus rhombifolia (white alder), Acer macrophyllum (bigleaf maple), and Salix spp. (willow) the riparian woodlands bordering local rivers and creeks. Quercus agrifolia, Quercus chrysolepis (canyon oak), Arbutus menziesii, Aesculus californica (California buckeye), Notholithocarpus densiflora, Pinus coulteri (Coulter pine), P. lambertiana (sugar pine), Baccharis pilularis, and Abies bracteata (Santa Lucia fir) occupy the warmer and drier slopes of the eastern Coast Ranges. 3. Material and methods Mud dominates core 15G, although this fine sediment is occasionally interspersed with coarser-grained turbiditic flow deposits (Fig. 2). The hemipelagic muds (clay and silt, Tep; Bouma, 1962; Kuenen, 1964; Howell and Normark, 1982) are considered to be the background sedimentation that results from pelagic sediments that settle out of the water column or drop to the sediment surface due to pelletization, whereas the turbiditic deposits are

3

characterized by a higher silt or sand content and are the result of sediment flows of low-density turbidity currents (Bouma, 1962; Lowe, 1982) that overtop the channel levee. In this core, the latter range from turbiditic muds (Tet; Kuenen, 1964; Howell and Normark, 1982) to medium fine-grained sand. In 15G, a mixture of hemipelagic and turbiditic muds (“mixed muds”) occur as well. The turbiditic silts are most frequently deposited in laminated sequences referable to Bouma’s (1962) Td depositional division, although cross-bedded (Tc) turbiditic sand units occur at two horizons (248e250 cm and 294e298 cm). The basal members of the Bouma cycle, massive to graded fine- to coarse-grained sands with granules or pebbles at the base (Ta), and parallel laminae of fine- to medium-grained sand (Tb), are lacking so a complete Bouma sequence (Ta-e) is not represented in the core. Thirty-two sediment samples from fine- and coarse-grained deposits were processed for grain size and palynology. The grain size analysis utilized ~4e12 g of sediment that was treated by soaking in a 30% hydrogen peroxide solution to remove the organics, boiled, ultrasonificated, and centrifuged to remove the salts. The samples were then sieved into mud (silt and clay; <0.063 mm) and sand (0.063e2 mm) size fractions. This was followed by the clay fraction being soaked in a 10% sodium hexametaphosphate solution to disperse negatively charged clay particles. Each sample fraction was then dried, weighed, and analyzed using a Beckman Coulter LS 13 320 laser diffraction particle size analyzer measuring in quarter phi bins. These analyses were conducted at the USGS Pacific Coastal and Marine Science Center (PCMSC) Sedimentology Laboratory in Santa Cruz, California. The resulting quarter phi bin distribution data were quantitatively combined and plotted using EXCEL. Approximately 1 cm3 of sediment was used for the palynological analysis. Wet and dry weights were obtained for each, after which they were spiked with an exotic tracer (Lycopodium) in order to determine the absolute pollen concentration. The pollen samples were then prepared by successive immersion in 10% hydrochloric acid (overnight), warm sodium pyrophosphate (15 min), 52% hydrofluoric acid (overnight), 10% hydrochloric acid (2 min), 70% nitric acid (3 min), and a modified acetolysis solution of nine parts glacial acetic acid to one part concentrated sulfuric acid (5 min). Subsequently, the residues were stained with two drops of safranin and mounted in silicone oil. At least 300 pollen grains were identified for each sample based on reference material from western North America. Very poorly preserved grains were assigned to the indeterminate category, whereas representatives of the Polypodiaceae and Lycopodiaceae, as well as rare constituents of other related families, were placed in the general categories of monolete and trilete spores. Identification of the Cupressaceae is taxonomically difficult, but most of the grains recovered in this study are characterized by a relatively thick exine, locally dense verrucae, and a short papilla, and are considered to be Sequoia pollen. Therefore, the Cupressaceae curve is assumed to reflect changes in Sequoia abundance (Adam et al., 1981; Plater et al., 2006). Pollen percentages were calculated utilizing a sum of total pollen, whereas all palynomorphs were computed with the sum of total pollen, Pediastrum, dinoflagellates, and fungal spore type-A. Once the species counts were converted to frequency data, two Q-mode cluster analyses were used to describe the relationship between the pollen assemblages. The first used only the background (hemipelagic and mixed mud) samples, whereas the second used all of the samples (i.e., background and flow deposits). In both analyses, the samples were clustered by a square root transformation of the data, a Bray-Curtis similarity coefficient, and amalgamated by a group averaged linkage strategy. These methods were chosen because they treat all species equally while providing

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

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M. McGann / Quaternary International xxx (2016) 1e21

0

300

150

450 Td-ep

Td-ep

Depth in core 15G (cm)

820 cal yr BP

50

350

200

16,400 cal yr BP

100

250

12,200 cal yr BP Tc-ep

400

Td-ep Td-ep Td-ep

150

8000 cal yr BP

300

Hemipelagic and mixed muds

Tc-ep

450

Turbiditic muds

19,300 cal yr BP

Turbiditic silts and sands

Fig. 2. Lithology of core 15G. The core is comprised of hemipelagic muds (Tep), turbiditic muds (Tet), mixed hemipelagic and turbiditic muds (Tep and Tet), turbiditic silts (Td) and turbiditic sands (Tc). Bouma sequences Tc-ep and Td-ep are designated on the right side of the core. The lithology differs slightly from the original description presented in McGann and Brunner (1988) that was based on visual inspection (sediment color and estimated sediment granulometry). Bouma sequence abbreviations after Bouma (1962) and Howell and Normark (1982). The location of the five samples taken for radiocarbon dating are shown.

the most realistic grouping of the samples by depth (Clarke and Gorley, 2006). Principal Components Analysis (PCA) was performed on the palynomorph data in two ways as a means of comparison, one with all the palynomorphs (pollen, dinoflagellates, Pediastrum, and fungal spore A) and the second with those palynomorphs with a frequency abundance of >3%. The latter was used because retaining the rarer species in a PCA ordination has a strongly distorting effect (Clarke and Gorley, 2006). In both cases, the data were 4th roottransformed to yield a more symmetric distribution prior to analysis. Primer v. 6.1.6, a statistical software package created by Primer-E, Ltd., was used for both the cluster analysis and PCA (Clarke and Gorley, 2006). 4. Chronology Sediments of core 15G were dated using two methods. First, a biostratigraphic framework was established based on the abundance of two planktic foraminifera, left-coiling Neogloboquadrina pachyderma (Ehrenberg) and right-coiling Neogloboquadrina incompta (Cifelli) (previously referred to as right-coiling N. pachyderma; Darling et al., 2006). Increased abundance of Neogloboquadrina pachyderma is associated with colder water temperature and upwelling conditions (Naidu and Malmgren, 1996; Ivanova et al., 1999; Davis et al., 2014), whereas N. incompta prefers warmer surface waters and a relaxation in upwelling (Davis et al., 2014). Because the recovery of cores containing annually varved sediments off central California suggests that upwelling remained a continuous feature in the region from at least 15,000e4700 cal yr BP (Gardner and Hemphill-Haley, 1986), the variability in the ratio of N. pachyderma to N. incompta tests in core 15G is thought to reflect changes in surface and near-surface (<100 m; Reynolds and Thunell, 1986; Davis et al., 2014) sea

temperature instead of upwelling, with dominant N. pachyderma tests indicative of colder conditions (Mix et al., 1999; Fisler and Hendy, 2008). Thus, the ratio is valuable in identifying climatic changes in the overlying surface water over time. The radiocarbon measurement of five hemipelagic or mixed mud samples (Fig. 2) by accelerator mass spectrometry (AMS) was the second method used to determine the age of the deposits in core 15G. The Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratory measured three samples of mixed planktic foraminifera and Beta Analytic measured two additional samples, one of mixed planktic foraminifera and another of mixed benthic foraminifera. The radiocarbon ages were obtained by a 14C/12C ratio and then were converted to calibrated calendar ages (cal yr BP) using the CALIB 7.0.1 program (Stuiver and Reimer, 1993; Stuiver et al., 2005). The calibrated ages are reported as the peak probability ages rounded to the nearest decade for ages <1000 years and to the nearest century for ages >1000 years (Stuiver et al., 2005), although the 2-sigma ranges are also included on Table 1. A reservoir age of 800 years was used for the planktic foraminiferal sample with a radiocarbon age younger than 12,000 years (Kienast and McKay, 2001; Southon et al., 1990), and an 1100-year reservoir age for the two samples older than 12,100 years (Kovanen and Easterbrook, 2002). A 1750-year reservoir age was used for the benthic foraminiferal sample (Mix et al., 1999). 5. Results 5.1. Age models A faunal response to changing climatic conditions in the surface waters off central California is suggested by several distinct changes in the ratio of the planktic foraminifera N. pachyderma and N. incompta in core 15G (Fig. 3; after McGann and Brunner, 1988).

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

M. McGann / Quaternary International xxx (2016) 1e21

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Table 1 Radiocarbon ages, calibrated peak probability ages, and 2 sigma ranges for core 15G. Accession number

Depth in Core S3-15G (cm)

Benthic or planktic foraminifera

Radiocarbon age (14C yr BP)

Calibrated peak probability (Calendar Age) (cal yr BP)

2 sigma range (cal yr BP)

Beta-399329 Beta-399330 CAMS-21700 CAMS-21701 CAMS-21702

29e34 144e148 241.5e243.5 360e364 448e450

Benthic Planktic Planktic Planktic Planktic

2620 ± 30 7960 ± 30 11,180 ± 110 14,700 ± 180 17,130 ± 200

820 8000 12,200 16,400 19,300

732e898 7940e8113 11,856e12,574 15,894e16,969 18,872e19,840

Ratio of Neogloboquadrina pachyderma to Neogloboquadrina incompta (%)

Medieval Climate Anomaly (ca. 800-700 cal yr BP; 22-20 cm)

0

25

50

75

100 0

820 cal yr BP (732-898; 34-29 cm) 100

middle Holocene dry period (ca. 8000-6400 cal yr BP; 150-125 cm) 8000 cal yr BP (7940-8113; 148-144 cm) Pleistocene-Holocene boundary (11,500 yr BP; 226.5 cm) 12,200 cal yr BP (11,856-12,574; 243.5-241.5 cm)

200

Younger Dryas event (12,900-11,500 yr BP; 256-226.5 cm) Bolling-Allerod event (14,600-12,900 yr BP; 295-256 cm)

300

16,400 cal yr BP (15,894-16,969; 364-360 cm)

Depth in core 15G (cm)

Age, depth in core, and climatic events

400

19,300 cal yr BP (18,872-19,840; 450-448 cm) Neogloboquadrina pachyderma Neogloboquadrina incompta Barren of planktic foraminifera Fig. 3. Downcore ratio of Neogloboquadrina pachyderma (Ehrenberg) and Neogloboquadrina incompta (Cifelli) in core 15G, after McGann and Brunner (1988). Radiocarbon ages reported as calibrated years before 1950 (cal yr BP; in bold and italics) and include both the calibrated peak probability age and 2 sigma range. Ages of the Pleistocene-Holocene boundary and Younger Dryas and Bølling-Allerød events (in yr BP) based on Alley et al. (1993), Grootes and Stuiver (1997), Alley (2000), and Carlson (2013). Ages are estimated for the middle Holocene dry period (Thompson, 1992; Quade et al., 1998; Grayson, 2000; Benson et al., 2002; Mensing et al., 2013) and the Medieval Climate Anomaly (MassonDelmotte et al., 2013).

Cold-water (glacial) conditions are indicated in the lower part of the core (472e295 cm) as N. pachyderma far outnumbers N. incompta. The onset of climatic warming attributed to the Bølling-Allerød event (14,600e12,900 yr BP; Grootes and Stuiver, 1997) is apparent from 295 to 256 cm, as evident by a shift from predominantly N. pachyderma to N. incompta. A period of cooling occurs above this (256e243 cm) as N. pachyderma is dominant once more. This probably reflects the Younger Dryas event, a short glacial advance that is dated elsewhere at ca. 12,900 to 11,500 yr BP (Carlson, 2013). Warmer climate and accelerated deglaciation developed in the early Holocene immediately following the end of the Younger Dryas, as indicated by the predominance of N. incompta from 241 to 212 cm. The Pleistocene-Holocene boundary (ca. 11,500 yr BP; Carlson, 2013) occurs within this interval, and in this study it is assumed to be the mid-point (226.5 cm). The lack of precision of this boundary is due to the spacing of the planktic foraminiferal samples analyzed. An increase in abundance of N. pachyderma occurs from 200 to 150 cm. Extensive dissolution characterizes the planktic foraminiferal record (“barren zones” of Brunner and Ledbetter, 1989) for the remainder of the core (ca. 150e0 cm; Fig. 3) and the benthic foraminiferal record in the core-top sediments (0e4 cm) as well. This late Holocene dissolution event has been reported nearby off central California (Brunner and Normark, 1985; Gardner et al., 1988; Brunner and Ledbetter, 1989; McGann, 2011) and elsewhere in the Pacific Ocean (Keir and Berger, 1985, and references therein).

All five of the radiocarbon measurements obtained for core 15G were in stratigraphic order and corroborate the ages of the climatic events inferred by the variation in the N. pachyderma to N. incompta ratio. These dates suggest the core contains a sediment record of late Quaternary age, representing the last ca. 19,000 cal yr. BP (Table 1). The five measurements returned a peak probability calibrated age of ca. 19,300 (2 sigma range of 19,840e18,872) cal yr BP near the bottom of the core at 450e448 cm, ca. 16,400 (16,969e15,894) cal yr BP at 364e360 cm, ca. 12,200 (12,574e11,856) cal yr BP at 243.5e241.5 cm, ca. 8000 (8113e7940) cal yr BP at 148e144 cm, and ca. 820 (898e732) cal yr BP at a depth of 34e29 cm. 5.2. Granulometry and displaced benthic foraminifera Fine-grained sediment dominates core 15G, as the mean grain size values range from 5.17 to 7.71 phi with an average of 7.01 phi (fine silt; Table 2; McGann et al., 2016). Twenty-five of the 32 samples are characterized by a mud content >97% (range of 63.76e99.91%) and D90 (diameter for which 90 percent of the sediment, by weight, has a smaller diameter) <64 mm, with many of these in the 20e30 mm range. The percent sand ranges from 0.09 to 36.24%, >14% sand occurs in only six samples, and these same samples have D90 values of 90.0e204.5. No gravels were recovered. The grain size frequency distribution curves of 26 of the 32 samples (Fig. 4) exhibit a primary mode at ~8 phi (clay to fine silt),

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

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Depth in Core (cm)

Mean grain size all fractions (F)

Variance

Standard Deviation

Skewness

Kurtosis

Total Sediment Weight (g)

% Mud

% Sand

% Gravel

D90 (microns)

Displaced benthic foraminifera (%)

Prevalent benthic foraminiferal biofacies represented

Interpreted Sediment Deposit

0e4 20e22 40e42 46e48 60e62 80e82 97.5e99.5 120e122 130e132 133.5e136.5 140e142 152.5e154.5 168e170 171e173 180e182 190e192 210e212 230e232 248e250 270e272 290e292 310e312 330e332 336.5e338 347e349 370e372 390e392 410e412 412e414.5 430e432 445.5e447.5 467.5e469.5

7.52 7.56 7.41 5.78 7.69 7.69 7.69 7.71 7.38 5.67 7.34 7.32 7.20 5.86 6.89 7.39 7.08 7.34 5.17 7.11 7.06 7.17 7.26 6.23 7.48 6.96 7.30 6.97 5.28 7.22 7.32 7.12

2.95 2.91 3.20 5.43 2.79 2.82 2.78 2.80 3.09 4.24 3.38 3.41 3.48 4.92 4.59 3.28 3.76 3.45 5.26 3.60 3.67 3.50 3.30 5.11 3.09 3.72 3.35 3.86 6.43 3.29 3.26 3.94

1.72 1.70 1.79 2.33 1.67 1.68 1.67 1.67 1.76 2.06 1.84 1.85 1.87 2.22 2.14 1.81 1.94 1.86 2.29 1.90 1.92 1.87 1.82 2.26 1.76 1.93 1.83 1.97 2.54 1.81 1.81 1.98

0.07 0.02 0.15 0.52 0.05 0.04 0.00 0.03 0.13 0.81 0.02 0.02 0.08 0.54 0.01 0.00 0.06 0.07 0.78 0.04 0.08 0.03 0.05 0.22 0.04 0.14 0.00 0.04 0.37 0.04 0.05 0.11

2.26 2.33 3.14 2.09 2.34 2.36 2.28 2.28 2.17 2.75 2.15 2.14 2.14 2.24 2.00 2.20 2.14 2.32 2.57 2.21 2.19 2.28 2.30 2.06 2.40 2.16 2.32 2.31 2.28 2.40 2.21 2.49

4.10 4.66 5.01 6.26 4.70 6.31 6.70 6.75 7.00 11.04 6.62 5.82 6.10 7.28 7.48 7.17 8.14 8.99 9.79 8.53 7.89 9.91 6.02 7.57 7.70 8.23 7.83 8.76 11.75 10.24 9.43 11.53

99.73 99.68 99.68 75.78 99.70 99.68 99.91 99.87 99.83 85.51 99.52 99.49 99.07 83.01 93.47 99.61 98.81 98.30 63.76 98.35 98.05 98.25 98.72 85.71 99.25 98.25 98.84 97.44 67.57 99.07 99.54 97.53

0.27 0.32 0.32 24.22 0.30 0.32 0.09 0.13 0.17 14.49 0.48 0.51 0.93 16.99 6.53 0.39 1.19 1.70 36.24 1.65 1.95 1.75 1.28 14.29 0.75 1.75 1.16 2.56 32.43 0.93 0.46 2.47

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

26.6 25.8 29.3 105.9 23.7 23.5 23.1 23.3 29.9 85.3 35.0 35.9 38.3 93.7 63.1 32.7 43.6 35.2 151.2 40.3 41.9 38.1 33.4 90.0 28.2 45.1 33.7 46.1 204.5 34.3 33.2 43.3

n.a 1 15 79 8 1 3 4 44 50 6 5 9 61 41 8 13 54 77 10 9 17 35 81 19 25 12 35 70 41 11 3

LB LB IS-OS-LB UB-UMB-LB IS-OS-LB LB LB LB OS-UB-LB IS-OS-UB-UMB-LB OS-UB-LB LB UB-UMB-LB OS-UB-UMB-LB UB-UMB-LB OS-UB-LB OS-UB-UMB-LB UB-UMB-LB UB-UMB-LB OS-UB-UMB-LB OS-UB-UMB-LB OS-UB-LB UB-UMB-LB IS-OS-UB-UMB-LB UB-UMB-LB OS-UB-LB OS-UB-LB OS-UB-LB IS-OS-UB-UMB-LB OS-UB-LB OS-UB-LB LB

hemipelagic hemipelagic mixed mud turbiditic silt mixed mud hemipelagic hemipelagic hemipelagic turbiditic mud turbiditic silt mixed mud mixed mud mixed mud turbiditic silt turbiditic mud mixed mud mixed mud turbiditic mud turbiditic sand mixed mud mixed mud mixed mud turbiditic mud turbiditic silt mixed mud turbiditic mud mixed mud turbiditic mud turbiditic silt turbiditic mud mixed mud mixed mud

M. McGann / Quaternary International xxx (2016) 1e21

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

Table 2 Grain size, abundance of displaced benthic foraminifera, prevalent foraminiferal biofacies represented, and interpreted lithology of the core 15G samples. D90 ¼ diameter for which 90 percent of the sediment, by weight, has a smaller diameter. Values exceeding criteria for hemipelagic sediments are highlighted. Foraminiferal biofacies are: inner shelf (IS), outer shelf (OS), upper bathyal (UB), upper middle bathyal (UMB), and lower bathyal (LB).

M. McGann / Quaternary International xxx (2016) 1e21

7

Fig. 4. Grain size frequency distribution curves for the core 15G samples, plotted as percent sample per bin versus phi units. Hemipelagic deposits (A), mixed mud deposits (B), finegrained flow deposits (turbiditic muds, C), and coarse-grained flow deposits of turbiditic silt (D) and sand (E). Percentage of displaced benthic foraminifera listed for each sample in parentheses.

with 14 of these displaying a secondary, sometimes considerably less frequent mode at ~5e6 phi (medium silt). In contrast, the six samples with a mean grain size of 5.17e6.23 and sand content >14% have a single, primary mode at ~3e6 phi (coarse silt to very fine

sand). The frequency of displaced benthic foraminifera ranges from 1 to 81% in core 15G (Table 2). The mud samples fall into two categories, with 19 varying from 1 to 19% (averaging 8.6%), and seven

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

8

M. McGann / Quaternary International xxx (2016) 1e21

others from 25 to 54% (averaging 39.3%). The six silt and sand samples contain 50e81% displaced specimens, with an average of 69.8%. The displaced benthic foraminifera recovered in the samples represent from one to as many as five biofacies (i.e., inner shelf, outer shelf, upper bathyal, upper middle bathyal, and lower bathyal) commonly found on the continental shelf and slope off central California (McGann, 2014, Table 2). 5.3. Palynomorphs Absolute pollen abundance ranges from 5065 to 14473 grains/g (mean ¼ 8530 grains/g) in the hemipelagic and mixed mud samples of core 15G, 5522e11545 grains/g (mean ¼ 7764 grains/g) in the turbiditic muds, and 2044e10525 grains/g (mean ¼ 5484 grains/g) in the turbiditic silt and sand samples (Table 3). The ratio of broken Pinus grains relative to whole grains is 61.9e90.4% (mean ¼ 73.0%) for the hemipelagic and mixed mud samples, 64.8e78.5% (mean ¼ 71.9%) for the turbiditic muds, and 53.5e73.5% (mean ¼ 61.7%) for the coarse-grained (silt and sand) turbidites. Redeposited pollen grains are rare: only nine were encountered with no more than two occurring in any one sample (Table 4). The most abundant pollen types recovered in the mud samples of 15G were Pinus, Sequoia, Quercus and Asteraceae, whereas the minor constituents included Amaranthaceae, Rhamnaceae, Notholithocarpus densiflora, Alnus, Poaceae, Salix, low-spine Asteraceae and Eriogonum (Table 4). Pediastrum colonies occur most frequently in the Late Pleistocene and earliest Holocene deposits (349e180 cm), whereas, marine dinoflagellates increase dramatically beginning in the Late Pleistocene. Generally, the same pollen types were found in the coarse-grained turbiditic deposits. The Q-mode cluster analysis grouped the pollen assemblage of

the hemipelagic and mixed mud samples into three distinct clusters (Fig. 5A). Two of these are Pleistocene in age and one is Holocene. From oldest to youngest, they are referred to as the Glacial (472e381 cm, ca. 19,000e17,000 cal yr BP), Transitional (381e226.5 cm; ca. 17,000e11,500 cal yr BP), and Interglacial (226.5e0; ca. 11,500e0 cal yr BP) Pollen Zones. The Pleistocene pollen zones (Glacial and Transitional) are characterized by abundant Pinus, whereas the Holocene pollen zone (Interglacial) documents declining Pinus pollen and abundant Sequoia, Quercus, Asteraceae, Alnus, and Notholithocarpus densiflora (Fig. 6). The pollen assemblages of the mud samples (hemipelagic, mixed, and turbiditic) and turbiditic silt and sand samples also grouped into three clusters by Q-mode cluster analysis (Fig. 5B). Once again, Glacial, Transitional, and Interglacial Pollen Zones are recognized, although the pollen assemblages of four of the 13 turbiditic deposits are not aligned in stratigraphic superposition. In the PCA, five principal components (PC) explain 94.3% of the variance when the palynomorphs with a frequency abundance of >3% (i.e., Amaranthaceae, Artemesia, high-spine Asteraceae, Notholithocarpus, Pinus, Quercus, Rhamnaceae, Sequoia, Pediastrum, and dinoflagellates) were analyzed (Table 5A): PC1 (46.8%) is dominated by positive loadings of Sequoia, Notholithocarpus, and dinoflagellates, and negative loadings of Pinus; PC2 (20.8%) is positively loaded for Rhamnaceae and negatively loaded for Pediastrum; PC3 (13.6%) is negatively loaded for both Pediastrum and Rhamnaceae; PC4 (9.5%) is positively loaded for Notholithocarpus and Pinus and negatively loaded for Sequoia; and PC5 (3.5%) is positively loaded for Sequoia and negatively loaded for dinoflagellates. In contrast, the PCA utilizing all of the palynomorphs (Table 5B) was not nearly as successful, as five principal components (PC) explain only 60% of the variance. Several of the PCs are

Table 3 Dry sediment weight, number of palynomorphs counted, absolute pollen abundance, Pinus grains counted, ratio of broken to whole Pinus grains, and Q-mode cluster grouping (¼ pollen zone) of the core 15G samples. Broken Pinus grains counted as one-half. Depth in Core (cm)

Dry Sediment Weight (g)

Pollen Grains and Spores Counted

Lycopodium (Controls) Counted

Absolute Pollen Abundance (grains/g)

Pinus Grains Counted

Broken/Whole Pinus Grain Ratio (%)

Pollen Zone

0e4 20e22 40e42 46e48 60e62 80e82 97.5e99.5 120e122 130e132 133.5e136.5 140e142 152.5e154.5 168e170 171e173 180e182 190e192 210e212 230e232 248e250 270e272 290e292 310e312 330e332 336.5e338 347e349 370e372 390e392 410e412 412e414.5 430e432 445.5e447.5 467.5e469.5

0.48 0.52 0.59 0.90 0.52 0.54 0.62 0.56 0.83 1.23 0.68 0.72 0.85 1.07 0.71 0.72 0.86 0.76 1.52 0.75 0.83 0.78 0.87 1.19 0.83 0.94 0.89 0.90 1.07 0.81 0.77 1.01

377 414 416 396.5 380 371 398 393 371 386 381.5 383 362.5 375.5 361.5 365 372 383.5 381 375.5 367.5 369.5 381.5 368 383.5 365 360 386 360.5 371.5 367 380.5

1679 1872 1101 946 1794 1767 1805 2616 875 1147 1377 1918 989 1578 2084 1035 1153 1941 2771 1445 1119 1248 1453 1971 1358 1225 1771 1193 1365 1113 1465 1681

10572 9542 14473 10525 9206 8787 8038 6063 11545 6183 9208 6268 9745 5026 5522 11070 8479 5875 2044 7830 8942 8579 6821 3546 7689 7164 5162 8125 5578 9313 7353 5065

81 52.5 49 57.5 73 76 76 69 101 189 47.5 52 52.5 83.5 70.5 42 71 116.5 102 131.5 139.5 135.5 148.5 160 128.5 145 173 160.5 188 155.5 163 186

80.3 67.6 69.4 61.7 90.4 81.6 69.7 73.9 65.4 65.1 70.5 76.9 71.4 53.3 77.3 81.0 62.0 78.5 73.5 74.9 71.3 72.0 78.5 59.4 76.7 64.8 61.9 70.1 56.9 68.5 63.8 71.0

Interglacial Interglacial Interglacial Interglacial Interglacial Interglacial Interglacial Interglacial Transitional Transitional Interglacial Interglacial Interglacial Interglacial Interglacial Interglacial Interglacial Transitional Transitional/Glacial Transitional Transitional Transitional Transitional Glacial Transitional Transitional Glacial Glacial Glacial Glacial Glacial Glacial

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M. McGann / Quaternary International xxx (2016) 1e21

positively or negatively loaded for species that are rare (<3%). This reflects the fact that the PCA ordination may be strongly distorted if the rarer species are retained (Clarke and Gorley, 2006). 6. Discussion 6.1. Pollen transport to the core site The amount of pollen in marine sediments is controlled by the abundance of vegetation present as determined by regional and global climate patterns (Heusser and Balsam, 1977; Traverse, 1988), the distance from their source (Muller, 1959; Groot and Groot, 1966; Traverse and Ginsburg, 1966; Groot et al., 1967; Heusser and Balsam, 1977; Heusser, 1978b; Melia, 1984), the amount of river discharge (Heusser, 1978a, 1978b, 1988; Traverse, 1988; Chmura et al., 1999), and the transport processes responsible for delivering it to the deposition site. Terrestrially-derived pollen may be carried to a core site by coastal winds, water, and sediment flows. Studies have shown that flocculation, agglomeration, and grazing by zooplankton also contributes to pollen deposition (Mudie, 1982; Mudie and McCarthy, 1994; Chmura and Eisma, 1995; Robbins et al., 1996; Chmura et al., 1999), although this applies more to coastal and shallow shelfal regions than the deep sea. Wind has been shown to be the primary transport mechanism of palynomorphs in many regions (e.g., Mudie and McCarthy, 1994; Williams, 2010), and at a distance of 135 km from shore, the site of 15G is within the common limit of wind dispersion of pollen (10e150 km; Erdtman, 1943; Dyakowska, 1948; Heusser, 1978b). However, wind has probably been of minor significance in transporting pollen to the 15G core site because of the direction in which it most commonly blows. The prevailing winds in the Monterey Bay region today are onshore and south, perpendicular to the shelf (Halliwell and Allen, 1987; Winant et al., 1987; Dorman and Winant, 1995), the latter of which promotes coastal upwelling (Gaines and Airame, 2016). Due to the direction of these winds, aerial transport of palynomorphs from the adjacent mainland to the core site is probably negligible at this time and any windtransported pollen most likely is derived from vegetation directly along the coast. Furthermore, it is likely that this process has been in place for most of the 19,000 years recorded in core 15G, as the presence of annually varved sediments in other Monterey Bay area cores suggests upwelling (and the associated along shore wind) remained a continuous feature in the region from at least 15,000e4700 cal BP (Gardner and Hemphill-Haley, 1986). Similarly, Heusser and Balsam (1977) concluded the Pinus pollen in their northeast Pacific Ocean study was coastally-derived, leading Gardner et al. (1988) to suggest that the Pinus record in a core offshore of the Russian River off central California reflected the overall California Coast Ranges floral record and not that of a far larger geographic region. Most likely the same is true of the core 15G palynological record. Instead of wind, the influx of terrigenous palynomorphs via rivers probably plays the most significant role in transporting pollen to the marine realm off central California. Both Cross (1973) and Peck (1973) showed that terrigenous influx via rivers correlates positively with pollen concentration, and numerous studies have demonstrated that the highest pollen concentrations in surface sediments offshore occur opposite major rivers that reflect the vegetation in the drainage basin and along their course (Cross et al., 1966; Groot et al., 1967; Heusser and Balsam, 1977; Heusser, 1978a; Chmura and Liu, 1990; Heusser et al., 2015). It has been determined that coastal rivers are the major source of fine-grained Holocene sediments in the ocean off central California, and in Monterey Bay specifically, the rivers and creeks of its drainage basins contribute a combined total of suspended sediment in excess of 1.8 million tons

9

annually (Griggs and Hein, 1980). As a result, these rivers are thought to be the major transport mechanism of pollen and spores to core 15G. However, it is also likely that the pollen record includes some minor allochthonous components that have been subjected to long-distance water transport from the major streams to the north (Muller, 1959; Faegri and Iverson, 1964; Traverse and Ginsburg, 1966; Heusser and Balsam, 1977; Heusser, 1988) as they are transported southward by the wind- and wave-induced littoral current system (Storlazzi and Field, 2000; Barnard et al., 2013). Much of the sediment comprising core 15G reflects the settling of fine grained-sized (clay and silt) material out of suspension at the core site. The material is of both terrestrial and biogenic origin. The latter includes, among others, palynomorphs and the remains of planktic and endemic benthic microorganisms (McGann, 2015a, 2015b). Nearby, however, the axis of Monterey Canyon annually funnels more than 400,000 m3 of sand and organic-rich material from the littoral zone and continental shelf into the deep sea (Paull et al., 2003). This is evidenced by the trail of sand down the axis of the canyon (Paull et al., 2010), the presence of large crescentshaped bedforms (Paull et al., 2010), and the movement of bottom-deployed acoustic transponders and instrument frames (Garfield et al., 1994; Paull et al., 2003, 2010). With the channel serving as the major conduit for sediment transport to Monterey Fan (Greene and Hicks, 1990; Greene et al., 2002; Fildani and Normark, 2004; Paull et al., 2005), sediment flows occasionally overtop the channel levee, depositing additional palynomorphladen sediment at the core site. The downslope transport of sediment in the marine realm results from sediment failures (slides and slumps), debris flows, or turbidity currents that occur where gradients increase, often abruptly (Piper et al., 1999; Fildani et al., 2006, 2013; Piper and Normark, 2009; Maier et al., 2016). It is often assumed these originate in the upper canyons on the slope below the shelf break where enough relief exists to set the sediment in motion when the continental shelf can no longer accommodate the sediment supply and the sediment must move down canyon (Paull et al., 2005; Piper and Normark, 2009; Covault, 2011). However, the initiation sites can be highly variable. Sediment failures and debris flows may be localized and occur several times a year when triggered by small events such as storm waves, increased terrigenous input from local rivers during peak discharge, breaking of internal waves along the continental margin, bioerosion, anthropogenic dumping of dredge material near the head of the canyon, and canyon wall slumping (Southard and Cacchione, 1972; Normark et al., 1980; Piper and Normark, 1983; Greene and Hicks, 1990; Johnson et al., 2006; Xu et al., 2004; Wain et al., 2013). These failures may quickly transition into turbidity currents as the fine-grained sediment is mixed with the surrounding seawater (Hampton, 1972; Mohrig and Marr, 2003; Piper and Normark, 2009). In other instances, downslope transport is less confined locally and may be “staged”, where the sediment does not flow continuously downslope but accumulates behind slumps until released by an external force that breaks the dam (Greene and Hicks, 1990; Greene et al., 2002). Finally, in rare instances, exceptionally large triggers such as earthquakes, intense storm disturbances, and catastrophic failure of canyon walls may occur. These result in complete canyon and fan channel flushing events which pass out of the upper canyon and extend across the fan (Normark and Gutmacher, 1988; Garfield et al., 1994; Johnson et al., 2001; Greene et al., 2002; Paull et al., 2003; Piper and Normark, 2009). All of these processes have an impact on the abundance and character of the entrained palynomorph assemblage that will be deposited further down the canyon.

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10

M. McGann / Quaternary International xxx (2016) 1e21

Table 4 Census data (%) of the palynomorphs in the core 15G samples. Broken Pinus grains counted as one-half. Pollen percentages were calculated utilizing a sum of total pollen; all palynomorphs were computed with total pollen, Pediastrum, dinoflagellates, and fungal spore type-A. Pollen type

Abies Aesculus Alnus Amaranthaceae Artemisia Asteraceae, highspine Asteraceae, lowspine Caryophyllaceae Ericaceae Eriogonum Eucalyptus Galium Juglans Liguliflorae Malvaceae Monolete Spores Notholithocarpus Pinus Plantago Poaceae Polygonum Quercus Rhamnaceae Ribes Rumex Salix Salix-type Salvia Sambucus Sequoia Tilia Trilete Spore Typha-Sparganium Umbelliferae Urticaceae Indeterminate Unknown

Depth in Core (cm) 0-4

20-22 40-42 46-48 60-62 80-82 97.5-99.5 120-122 130-132 133.5-136.5 140-142 152.5-154.5 168-170 171-173 180-182 190-192

0.3

0.1

1.9 2.4 2.7 13

0.7 3.6 2.2 27.8

1.1

0.3

0.3

0.2 5.3 1.9 17.6

0.8 3.5 2.5 16.4

0.8 5 1.6 12.4

0.8 5.1 2.7 12.1

1.3 4 2 17.3

0.8 2 2 14.8

0.3 4.9 3.2 12.7

0.5

1

0.5

0.5

1

0.3

0.5

0.7

0.5

1.6

0.5

1

1.3

0.3

0.2

0.3 0.3

0.3

2.6 2.9 11.4

0.3

0.3 4.5 1.3 33.3

1.6 2.4 2.1 24.8

2.8 1.7 2.2 20.1

1.3 3.2 1.6 17.8

1.4 3 2.8 18.3

1.1 1.6 1.1 22.2

0.5

1.3

0.6

1.3

1.4

0.6

0.3

0.8

0.8

0.3

0.6

0.3

0.3

0.5 0.6

0.3 1.3 2.4 0.8 22.2 0.3

0.2 0.5

0.7 0.2

0.5

0.3 0.3

0.5

0.8 1.2 2.4 1.5 21.5 12.7

1.2 2.2 11.8

1.1

0.5

8 1.9

8.2 1.9

0.3 0.3

0.5 0.5

11.8 3.4

0.8 3.3 14.5 0.8

0.3

0.3

0.3

0.3

1.6 2.1 19.2

2.2 1.9 20.5

1 0.3 19.1 0.3 0.5

2.3 1.5 17.6 1.3

0.8 27.2 0.3 0.8

1.1 10.3 2.3

11.6 3.4

12.1 1.4

11.1 1.5

14.3 0.5

0.3

0.3

0.3 0.8

0.5 0.5

0.3 0.5 0.7

23.1 18.8

25.7

23

24.2

20.8

22.4

2.9

1.7

1.8

3.2

2.2

4.3

0.3 10.9 11.1 4.5 3.9

10.8 3.9

0.3 11.6 5.6

Total Pollen

376

416

Pediastrum Dinoflagellates Fungal Spore Type A

0.3 5.8

Total Palynomorphs

400

3.6

19.9 0.3 4.6

0.5

0.8 1 0.8 49 0.3 0.5

2.1 0.8 12.5 0.3

10.2 0.5

4.4

1.1 0.3

0.3

1.6 13.6

2.8 1.1 14.5

0.3

0.6

8.7 0.8

5 0.3

10.5

1.1

0.3 0.3

414

7.1 0.9 450

Lycopodium 1679 1872 (Controls) Redeposited Pollen

8.2 3.2

1.7 1.1 19.5

1.9 1.6 11.5 0.8

8.3

0.3

11.6

14.5 0.3

0.3 0.3 0.3

16.4

11.1

18.1

26.1

0.3 24

3.8

1

1.6

1.6

5

0.3

0.3 0.6

19.7

17.7

25.5

8 0.3 0.6

2.2

0.6

4 0.3 0.3

11.9 4.9

8.5 3.3

11.7 3.6

11.6 4

8.8 5.4

10.8 2.1

14.1 3.7

9.4 2.5

10.7 4

10 1.4

12.1 1.6

396.5 380

371

398

393

371

386

381.5

383

362.5

375.5

361.5

365

0.2 3.2

2.7

6.3 0.3

5.5 0.2

8.8 0.7

2.9 0.3

1.5

0.2 5.9 0.2

0.2 8.6 0.9

0.6 6.4 0.8

0.6 2.8 1.2

1.6 7.3 0.5

0.3 7.6

430

407.5 402

397

422

434

383

392

407.5

422

392.5

392.5

398.5

396

1101

946

1767

1805

2616

875

1147

1377

1918

989

1578

2084

1035

1

2

1

5.5

1794

6.2. Selective transport of palynomorphs Palynomorphs behave differently than terrigenous particles during transport. They are selectively entrained within turbidity flows and differentially deposited (e.g., Traverse and Ginsburg, 1966; Brush and Brush, 1972; Bradshaw and Webb, 1985; Holmes, 1990; Chmura et al., 1999) depending on their specific gravity and individual fall velocities that reflect their size (volume and surface area) and morphology (Brush and Brush, 1972; Holmes, 1990) as well any changes in size and shape or air loss within their structure (e.g., air bladder rupture in Pinus) that often occurs as they enter

1

1

water from the atmosphere (Brush and Brush, 1972). Differential pollen deposition takes place at the sediment-water interface at low velocities (~5 cm/s), whereas sorting no longer occurs when the flow velocity exceeds 30 cm/s and all grains remain in suspension and are transported (Holmes, 1990). Because coarsergrained, sand-dominated turbidity flows are estimated to travel at velocities several orders of magnitude faster (7e22 m/s in Komar, 1969, 1970, 1977 and Krause et al., 1970; 1.9 m/s measured by instruments attached to moorings along the axis of Monterey canyon as described in Xu et al., 2004), all of the pollen in its path will be swept up and incorporated in the flow. In contrast, fine-grained

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M. McGann / Quaternary International xxx (2016) 1e21

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Depth in Core (cm) 210-212 230-232 248-250 270-272 290-292 310-312 330-332 336.5-338 347-349 370-372 390-392 410-412 412-414.5 430-432 445.5-447.5 467.5-469.5 0.3

0.3

0.3

0.3

0.3

0.8

0.7

0.4

0.8

0.1 0.3

2.4 1.3 2.7 17.7

1.8 3.7 2.4 17.5

0.8 2.9 10.2 11.6

0.5 2.7 6.1 15.5

0.5 1.4 6.8 12.2

1.9 3.5 7.9 13.5

0.5 1.6 7.3 15.5

0.3 1.1 5.2 15.2

1.8 2.1 7 13.3

0.6 3.8 7.4 14.5

1.4 7.5 16.7

3.1 9.6 11.4

3.1 4.4 15

2.4 11.3 16.2

3.3 5.7 20.2

0.5 1.3 6.8 12.4

0.5

0.3

0.8

1.1

1.4

1.6

0.5

1

0.3

0.6

0.5

0.6

0.3

0.5

0.5

0.5

0.3 0.3 0.8

0.3

1

0.3

0.3

0.6

1.6

0.3

0.3

1.1

1.1

1

1.1

1.3

0.5

0.3 0.3 1.3 0.3 33.5 0.3 0.8

0.3

0.3

0.8 0.3 39.7 0.8 1.1

0.3

0.5 0.3

0.5

1.1 1.3 2.4 19.1 0.3

2.1 0.8 30.4 1 1.6

6.2 0.5

5.7 0.5

0.5

0.3 0.8 0.3 0.3

0.3 0.5

0.5 0.3 2.7

26.8

1.6 0.8 35

1.8

0.5

10

7.5

4.1 0.8

0.3 0.5

0.3 1.9

0.3 1.3

0.3

38 0.5 1.4

1.6 0.5 36.7 0.3 0.8 0.3 6.8 1.1

0.8 0.8 38.9 0.5 1.3

43.5

0.3 0.8

0.3

1.4

0.3

1.1

0.8 0.5 41.6 0.5 0.8

0.3 0.3 52.2

1.1

1.3 0.8 48.9 0.8

3.1 0.3 0.3

5.4

4.7

48.1

0.5

41.9 0.5 0.3

44.4 0.3 0.3

3.2 0.3

3.8

3.2 0.8

5.8 0.5

3.5 0.8

4.2 0.8

5.2 0.8

0.3

1.1

0.3 0.8

0.3 0.3 0.3

0.8

0.3 0.6

0.3 0.5

0.6

0.3 0.8

0.3

0.3

0.8

1

17.2

10.4

13.9

10.4

9.3

7.3

5.2

2.7

6.5

2.7

3.9

2.1

1.7

1.1

0.8

3.7

7.8

3.1

2.1

1.6

1.4

1.1

0.8

2.2

1.6

1.9

1.9

0.5

0.3

1.4

1.6

1.1

0.3

1

0.3

0.5

0.3

0.3

0.6

0.3 14.3 3.5

12 4.4

14.4 1.1

11.7 2.1

12.2 4.6

11.1 3

9.7 6

16.6 3.8

14.6 7.3

11.5 5.8

7.8 5.3

13 7.3

10.5 2.5

12.7 6.2

12.3 3.8

12.6 3.7

372

383.5

381

375.5

367.5

369.5

381.5

368

383.5

365

360

386

360.5

371.5

367

380.5

2.3 1.5 0.7

7.3 1.9 0.5

1.6 2.8

0.7 7.6 0.2

3.1 1.6

0.5 1.3 0.3

0.3 1.3

2.1 1.6

0.5 0.5 0.3

0.3

0.6 1.3

0.3 1.6

0.3 1.3 0.5

0.3 0.5

0.3 1.3 0.3

430

424.5

398

410.5

385.5

377.5

386.5

371

397.5

370

362

393

367.5

379.5

370

387.5

1153

1941

2771

1445

1119

1248

1453

1971

1358

1225

1771

1193

1365

1113

1465

1681

0.5 0.3

1

(silt-sized) turbidity flows are deposited at speeds of ~10 cm/s (Normark et al., 1980), as are flows resulting from small-scale mass wasting (Talling et al., 2013). Palynomorphs in these deposits will be selectively transported and deposited depending on their individual morphologic characteristics. Due to this differential deposition, pollen assemblages of hemipelagic and turbiditic deposits should be distinct.

6.3. Sedimentology of core 15G Hemipelagic and turbiditic flow deposits in marine settings may

0.3

1

1

be discerned, in part, based on sedimentological parameters. In a study of late Pleistocene levee deposits of Monterey Fan, Brunner and Ledbetter (1987) based their differentiation of the two deposits on mean grain size of the silt size fraction, grain size frequency distribution, and grading. Hemipelagic muds had means of the silt size fraction finer than 6.4 phi, grain size frequency distributions dominated by a single fine mode, and intervals with mean sizes that were not graded. Turbiditic muds had means in the silt size coarser than 6.4 phi, modes in grain size distribution of medium and coarse silt sizes, and graded muds. Turbiditic silts were dominated by a coarse mode and occurred in well-sorted silt and

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12

M. McGann / Quaternary International xxx (2016) 1e21

B

A Hemipelagic and mixed muds (this study)

Hemipelagic muds, mixed muds, and flow deposits (this study)

BRAY-CURTIS SIMILARITY 100

90

80

70

BRAY-CURTIS SIMILARITY

BRAY-CURTIS SIMILARITY 100

90

80

70

100

40-42

40-42

40-42

60-62

60-62

60-62

80-82

80-82

80-82

97.5-99.5

97.5-99.5

97.5-99.5

0-4 120-122 168-170

DEPTH IN CORE 15G (cm)

C Hemipelagic and mixed muds (McGann, 2015a)

Interglacial (Holocene)

0-4

0-4

120-122

120-122

Interglacial (Holocene)

46-48

130-132

190-192

171-173

20-22

180-182

140-142

168-170

210-212

210-212

190-192

152.5-154.5

152.5-154.5

20-22

168-170

270-272

140-142

190-192

210-212

270-272

152.5-154.5

310-312

130-132

370-372

230-232

330-332

270-272

390-392

310-312 347-349

Transitional (Pleistocene)

290-292 390-392 467.5-469.5 445.5-447.5

Glacial (Pleistocene)

90

80

70

Interglacial (Holocene)

20-22 140-142

410-412

290-292

Transitional (Pleistocene)

330-332 310-312

430-432

Transitional (Pleistocene)

Glacial (Pleistocene)

445.5-447.5

347-349 370-372 133.5-136.5 336.5-338 390-392 467.5-469.5

Glacial (Pleistocene)

412-414.5 410-412 430-432 445.5-447.5 248-250

Outlier

Fig. 5. A. Q-mode cluster diagram of the pollen assemblages of 19 hemipelagic and mixed mud samples from core 15G. B. Q-mode cluster diagram of the pollen assemblages of this study's 19 hemipelagic and mixed mud samples with the addition of 13 turbiditic (mud, silt, and sand) samples from core 15G. C. Q-mode cluster analysis of the pollen assemblages of 21 fine-grained samples from core 15G previously published (McGann, 2015a) based on visual interpretation of sediment type (i.e., sediment color and estimated sediment granulometry). The samples are listed by cm interval and each was grouped into three pollen zones (Glacial, Transitional, and Interglacial). Open stars ¼ displaced sediment samples aligned in stratigraphic superposition; filled stars ¼ displaced sediment samples not in expected stratigraphic superposition.

sand layers. It should be noted, however, that according to Brunner and Ledbetter (1987), investigating the grading of marine deposits requires sampling at 1-cm increments. This precise of a sampling protocol was not undertaken in this study and therefore, grading cannot be assessed in core 15G. Somewhat similar criteria for discerning hemipelagic and flow deposits were used by Maier et al. (2016) for marine deposits off southern California. Those considered hemipelagic were characterized by <25% sand content, a grain size distribution curve with a single skewed peak at ~20e30 mm (~6e5 phi), and D90 of <90 mm (~3.5 phi). Flow deposits had a higher content of sand or silt and a saddle-shaped dual grain size distribution curve. Hemipelagic and flow deposits also may be differentiated based

on their biological constituents. In their study of Monterey Fan deep-sea levee deposits, Brunner and Normark (1985) suggested that mud samples containing 0 to <1% shallow-water benthic foraminifera were mostly hemipelagic, those with >30% were turbiditic, and those from 1 to 19% were difficult to classify because some mixture of hemipelagic and turbiditic mud may occur due to bioturbation after deposition (Griggs et al., 1969) or because turbidity currents may incorporate different amounts of deep-sea sediment near the core site as they travel down the channel and over the levees (Phleger, 1951). In a later study, Brunner and Ledbetter (1987) again concluded that the presence of high frequencies of shallow-water benthic foraminifera flagged turbiditic muds in deep-sea deposits.

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

0

e an Ev d C en lim ts a tic

Ag

Pe ri o d

Po lle n

Lo

Zo ne

13

w Li -sp gu in e H liflo As ig ra te h- e r ac sp ea in e e As te ra Er ce io ae Po gon ac um Am ea e a Pe ran di th a a D stru cea in of m e la ge lla Ti te m s e

M. McGann / Quaternary International xxx (2016) 1e21

Medieval Climate Anomaly (ca. 800-700 cal yr BP)

Holocene

820 cal yr BP (732-898)

Interglacial

middle Holocene dry period (ca. 8000-6400 cal yr BP)

8000 cal yr BP (7940-8113) Pleistocene-Holocene boundary (11,500 yr BP)

200

12,200 cal yr BP (11,856-12,574) Younger Dryas (12,900-11,500 yr BP)

300

Pleistocene

Depth in core 15G (cm)

100

Transitional

Bolling-Allerod (14,600-12,900 yr BP)

16,400 cal yr BP (15,894-16,969)

400

Glacial 19,300 cal yr BP (18,872-19,840) 0

20

40

01 0

10

20

0

10

0

2

0 2

0 2

0

10 0 2 0

2 0

10

20

30

0

2 0

2 0 5

0

10 0

10

Abundance (%) Fig. 6. Pollen diagram of selected palynomorphs plotted with depth in core 15G. Pollen zones, calibrated peak probability ages and 2 sigma ranges (in bold and italics), position of the Bølling-Allerød and Younger Dryas events, the Pleistocene-Holocene boundary, the middle Holocene dry period, and the Medieval Climate Anomaly. Shaded intervals represent turbiditic deposits.

Based on the works of Brunner and Normark (1985), Brunner and Ledbetter (1987), and Maier et al. (2016), a sediment sample in this study is classified as hemipelagic based on the presence of all of these sedimentological factors: mean grain size >6.4 phi, percent sand content <5%, a single skewed grain size peak at <30 mm (<~5 phi), and a D90 value > 90 mm. In addition, it has a frequency of displaced shallow-water benthic foraminiferal species <5%. Using these criteria, five samples between 0 and 122 cm in core 15G are classified as hemipelagic sediments (Table 2; Fig. 4A) due to their fine-grained nature (averaging 7.64 phi, 0.29% sand, and D90 24.4 mm), single grain size frequency distribution peak at ~8 phi, and low frequency of displaced benthic foraminifera (<5%). Fourteen samples are interpreted as being primarily hemipelagic because they are fine-grained (means ¼ 7.25 phi, 1.08% sand, and D90 36.42 mm) and have a primary grain size frequency distribution peak at ~8 phi, but have some minor characteristics of flow deposits, such as a secondary, reduced grain size frequency distribution mode in the medium silt fraction (~5e6 phi) and slightly more displaced benthic foraminifera (5e19%). These are referred to as mixed mud deposits (Fig. 4B). There are two samples assigned to the mixed muds that differ slightly from these criteria: 1) 60e62 cm has a single grain size frequency distribution curve in fine silt/clay making it appear to be hemipelagic but has 8% displaced benthic foraminifera from the inner shelf and outer shelf biofacies (Table 2); and 2) 467.5e469.5 cm has only 3% displaced benthic foraminifera but is thought to be a mixed mud based on its dual-peaked grain size distribution curve. The remaining 13 samples of core 15G are interpreted as flow deposits, seven of which are fine-grained (i.e., turbiditic muds) and six others are coarse-grained (i.e., turbiditic silts and sand). Because the turbiditic muds are just slightly coarser (mean ¼ 7.15 phi, 2.13% sand, and D90 41.01 mm) than the hemipelagic and mixed muds, they are primarily distinguished from them by their high frequency of displaced benthic foraminifera (25e54%). They also have a nearly

equal (saddle-shaped; e.g., 370e372 cm) or unequal (e.g., 230e232 cm) bimodal grain size distribution in the fine (~8 phi) and medium silt (~5e6 phi) fractions (Fig. 4C), although the secondary peak may be coarser sediment as well (coarse silt range, ~4e5 phi; i.e., 180e182 cm). An exception to this is the single mode grain size distribution of fine silt seen at 130e132 cm, which except for the high frequency of displaced benthic foraminifera, would have been interpreted as a hemipelagic deposit. The six coarse-grained flow deposits are distinguished in this core by their extremely high frequency of displaced benthic foraminifera (50e81%), sand content >14%, and grain size of 5.17e6.23 phi (mean ¼ 5.7 phi). Two of the six (133.5e136.5 cm and 171e173 cm) have a skewed grain size frequency distribution curve with a single peak in medium silt (5e6 phi) and three others (46e48 cm, 336.5e338 cm, and 412e414.5 cm) in coarse silt (4e5 phi) (Fig. 4D). These five deposits are turbiditic silts. The last coarsegrained deposit (248e250 cm) has a skewed grain size frequency distribution curve in very fine sand (3e4 phi) (Fig. 4E) and is considered a turbiditic sand (confirmed by Brunner and Ledbetter, 1987).

6.4. Pollen record of core 15G 6.4.1. Absolute pollen abundance Similar to the trend found in the Gulf of California by Cross et al. (1966), absolute pollen abundance in core 15G correlates negatively with grain size (Table 3, Fig. 7A; p ¼ 0.0423, 95% confidence level). The coarsest deposit encountered in the core, the cross-bedded (Tc) sand unit occurring at 248e250 cm, is characterized by only 2044 grains/g, whereas the laminated silt units (Td) average 6172 grains/ g and the turbiditic muds (Tet) average 7764 grains/g. In contrast, the hemipelagic and mixed muds average 8530 grains/g, with a maximum of 14,473 grains/g in one horizon (40e42 cm). Results from flume experiments involving pollen and spores

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14

M. McGann / Quaternary International xxx (2016) 1e21

Table 5 Eigenvectors, principal components scores, eigenvalues, and percent variation for the first five variables of the principal components analysis of the (A) palynomorphs with frequency abundances >3% and (B) all palynomorphs in the samples of core 15G. A. Palynomorphs with frequency abundances >3% Eigenvectors Variable

PC1

PC2

PC3

PC4

PC5

Amaranthaceae Artemisia High-Spine Asteraceae Notholithocarpus Pinus Quercus Rhamnaceae TCT (Sequoia) Pediastrum Dinoflagellates

0.067 0.272 0.034 0.458 0.334 0.204 0.303 0.478 0.296 0.386

0.03 0.093 0.031 0.15 0.144 0.078 0.652 0.181 0.603 0.344

0.056 0.054 0.014 0.038 0.086 0.077 0.668 0.048 0.726 0.059

0.064 0.114 0.153 0.851 0.309 0.019 0.048 0.323 0.041 0.18

0.081 0.234 0.062 0.066 0.082 0.115 0.155 0.475 0.067 0.81

Principal Component Scores Sample

SCORE1

SCORE2

SCORE3

SCORE4

SCORE5

0e4 20e22 40e42 46e48 60e62 80e82 97.5e99.5 120e122 130e132 133.5e136.5 140e142 152.5e154.5 168e170 171e173 180e182 190e192 210e212 230e232 248e250 270e272 290e292 310e312 330e332 336.5e338 347e349 370e372 390e392 410e412 412e414.5 430e432 445.5e447.5 467.5e469.5

0.687 0.936 0.876 0.975 1.05 0.891 0.699 0.876 0.479 0.134 0.614 0.144 0.329 8.80E02 0.144 0.794 0.441 0.222 0.715 0.179 0.755 0.22 0.316 0.699 0.419 0.576 1.32 0.817 0.816 1.08 1.35 0.413

1.36E02 0.397 0.165 0.51 0.531 0.375 0.454 0.157 0.409 3.15E02 0.131 0.199 0.865 0.698 0.983 0.414 0.579 0.484 0.609 0.726 8.12E04 0.25 0.22 0.982 4.14E03 0.37 0.697 0.31 0.249 0.403 1.18E02 0.326

0.401 0.135 0.485 7.55E02 4.56E02 0.23 0.222 0.377 0.384 0.939 0.173 8.02E03 0.294 0.314 0.135 0.116 0.551 0.825 0.145 0.287 0.661 0.365 0.184 0.315 0.583 0.305 0.145 0.336 0.442 7.00E02 0.442 0.249

0.165 0.122 4.05E02 0.196 6.63E02 9.98E02 0.373 3.56E02 6.99E02 0.313 0.225 1.03 9.56E02 2.47E02 3.02E02 0.133 0.134 0.185 0.577 0.173 0.491 0.25 0.382 0.35 0.162 0.337 0.163 0.49 0.402 0.229 0.159 0.466

3.84E02 0.149 0.247 0.183 1.23E02 9.35E02 4.27E02 0.176 6.97E02 0.197 2.71E02 0.102 0.154 0.355 3.73E02 7.17E02 0.262 0.161 5.73E02 0.235 6.00E02 9.00E03 4.25E03 0.115 5.65E02 5.63E03 0.667 0.107 0.138 0.397 5.28E02 0.18

Eigenvalues Variance (%) Cumulative variance (%)

0.528 46.8 46.8

0.235 20.8 67.7

0.153 13.6 81.3

0.108 9.5 90.8

3.91E02 3.5 94.3

B. All palynomrprhs Eigenvectors Variable

PC1

PC2

PC3

PC4

PC5

Abies Aesculus Alnus Amaranthaceae Artemisia Caryophyllaceae Ericaceae Eriogonum Eucalyptus Galium High-Spine Asteraceae Juglans Liguliflorae Low-Spine Asteraceae Malvaceae Notholithocarpus

0.168 0.053 0.323 0.038 0.241 0.207 0.007 0.024 0.026 0.068 0.035 0.085 0.044 0.026 0.039 0.352

0.329 0.007 0.264 0.022 0.036 0.099 0.018 0.026 0.061 0.024 0.039 0.123 0.101 0.151 0.277 0.041

0.245 0.028 0.143 0.057 0.028 0.211 0.056 0.043 0.037 0.015 0.046 0.08 0.215 0.032 0.059 0.01

0.154 0.05 0.247 0.022 0.03 0.115 0.004 0.049 0.017 0.05 0.022 0.218 0.377 0.076 0.062 0.077

0.202 0.067 0.275 0.087 0.144 0.199 0.011 0.007 0.045 0.056 0.035 0.021 0.053 0.005 0.022 0.271

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M. McGann / Quaternary International xxx (2016) 1e21

15

Table 5 (continued ) B. All palynomrprhs Pinus Plantago Poaceae Polygonum Quercus Rhamnaceae Ribes Rumex Salix Salix type Salvia Sambucus TCT (Sequoia) Tilia Typha-Sparganium Umbelliferae Urticaceae Pediastrum Dinoflagellates Fungal Spore Type A

0.306 0.197 0.016 0.013 0.176 0.229 0.047 0.001 0.052 0.139 0.069 0.026 0.442 0.026 0.021 0.088 0.077 0.198 0.345 0.075

0.038 0.092 0.401 0.016 0.036 0.251 0.067 0.156 0.038 0.235 0.018 0.049 0.1 0.029 0.059 0.205 0.008 0.497 0.094 0.201

0.047 0.333 0.371 0.008 0.014 0.401 0.017 0.002 0.218 0.157 0.034 0.07 0.01 0.008 0.148 0.338 0.011 0.118 0.129 0.384

0.011 0.253 0.053 0.081 0.058 0.222 0.024 0.17 0.28 0.281 0.02 0.007 0.014 0.008 0.066 0.312 0.05 0.264 0.016 0.447

0.049 0.217 0.241 0.027 0.028 0.459 0.034 0.122 0.558 0.172 0.057 0.022 0.021 0.049 0.14 0.09 0.098 0.051 0.002 0.064

Principal Component Scores Sample

SCORE1

SCORE2

SCORE3

SCORE4

SCORE5

0e4 20e22 40e42 46e48 60e62 80e82 97.5e99.5 120e122 130e132 133.5e136.5 140e142 152.5e154.5 168e170 171e173 180e182 190e192 210e212 230e232 248e250 270e272 290e292 310e312 330e332 336.5e338 347e349 370e372 390e392 410e412 412e414.5 430e432 445.5e447.5 467.5e469.5

0.828 0.834 0.882 1 1.07 1.02 0.694 0.859 0.278 0.37 0.525 0.621 0.756 0.342 0.273 1.18 0.582 0.123 0.383 0.23 0.719 0.374 0.294 0.743 0.552 0.856 1.38 1.3 1.14 1.36 1.55 0.38

3.34E02 1.07 7.37E02 0.124 0.213 0.701 0.247 0.505 0.433 0.272 0.661 0.156 0.777 0.699 0.239 0.584 6.03E02 0.832 1.42 0.317 0.809 0.252 0.177 0.833 1.16 5.57E02 1.06 8.40E03 0.389 0.542 0.106 0.582

0.241 0.599 0.921 0.453 0.781 1.77E03 0.445 0.134 0.186 0.762 5.13E02 2.47E02 1.02 0.919 1.22 0.28 0.543 0.339 0.364 0.902 0.851 0.115 0.871 0.742 1.97E02 0.292 0.247 0.112 0.718 0.313 0.403 8.24E02

0.145 0.24 5.04E03 0.831 0.296 7.02E02 6.66E04 0.11 0.45 0.422 0.298 0.454 8.45E02 0.27 0.567 0.608 0.28 1.32 1.41 4.94E02 0.241 1.03 6.78E02 0.149 1.02E02 0.952 0.311 0.538 0.504 0.317 0.637 0.307

0.697 0.48 1.21E02 2.95E02 4.57E02 0.318 0.303 0.522 0.273 0.98 0.336 0.122 0.206 1.1 0.234 0.379 0.293 0.174 0.622 0.117 0.616 0.257 0.246 0.77 0.568 0.126 0.33 0.135 0.717 0.368 0.643 0.356

Eigenvalues Variance (%) Cumulative variance (%)

0.703 21.5 21.5

0.379 11.6 33.1

0.345 10.6 43.7

0.304 9.3 53.0

0.228 7.0 60.0

flowing over sand beds suggest these coarser deposits would have higher pollen abundances because they can trap large numbers of palynomorphs between the mineral grains (Holmes, 1990). However, this present study and others (e.g., Traverse and Ginsburg, 1966) have shown the opposite to be true. Holmes (1990) noted these contradictory field observations and hypothesized that several factors may counteract this filtering effect of sand beds given enough time: 1) winnowing of pollen and spores occurs due to resuspension; 2) palynomorphs may be removed by the movement of water through the interstices (throughflow) after sediment has been deposited; and 3) sands have greater permeability which

results in enhanced oxygenated water circulation resulting in biodegradation. The abundance of palynomorphs in samples of similar grain size from core 15G also varied through the last 19,000 years. Holocene mud samples contain more pollen grains, on average (9461 grains/ g), than do the Pleistocene muds (7543 grains/g; p ¼ 0.0456, 95% confidence level). This holds true for Holocene and Pleistocene laminated (Td) silt units as well (6814 grains/g and 6328 grains/g, respectively), although the trend is not statistically significant (p ¼ 0.1362), possibly because so few silt units were sampled in the Holocene to adequately test the hypothesis. The increased

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

M. McGann / Quaternary International xxx (2016) 1e21

16,000

100

12,000

Broken/whole Pinus grain ratio (%)

A 46-48 cm

8,000 4,000 Tc 8

7

6

Tc

60 40 20

5

60

Abundance of Pinus (%)

B

80

0

0

133.5136.5 cm

50 Glacial

40 30

Transitional

X

X

X

336.5338 cm

412414.5 cm 248250 cm X

Tc

20 Interglacial

10

7

6

12

C

171-173 cm

8

46-48 cm

0

Abundance of Dinoflagellates (%)

Absolute pollen abundance (grains/g)

16

5

D

10 8 6 4

Tc

2 0

8

7

6

5

8

7

6

5

Abundance of displaced benthic foraminifera (%)

Grain size (phi)

E

80

Tc

60 40 20 0 8

7

6

5

Grain size (phi) Fig. 7. Scatter diagrams of grain size (phi) versus (A) absolute pollen abundance (grains/g), (B) ratio of broken/whole Pinus grains (%), (C) abundance of Pinus pollen (%), (D) abundance of dinoflagellates (%), and (E) abundance of displaced benthic foraminifera (%). In (C), samples are grouped into three pollen zones (Glacial, Transitional, and Interglacial) and displaced sediment samples not in expected stratigraphic superposition are marked with an X. Open symbols ¼ hemipelagic and mixed mud samples, gray symbols ¼ turbiditic mud samples, and black symbols ¼ coarse-grained turbiditic deposits (silts and sands). Tc ¼ turbiditic sand sample at 248e250 cm.

abundance of pollen further up-core in both the muds and turbiditic deposits is thought to reflect warming conditions in the Holocene (e.g., Heusser et al., 2000) and explains why the sample at 46e48 cm is somewhat of an outlier compared to the other turbiditic silts and sands (Fig. 7A) with its higher pollen abundance (10,525 grains/g).

6.4.2. Pollen preservation Pollen preservation, as determined subjectively by visual inspection and by the ratio of broken to whole Pinus grains (Cushing, 1964, 1967; Adam, 1967), is enhanced in the coarse-grained deposits, as the silts and sands have fewer broken Pinus grains than do the muds (67.5% and 72.5% broken grains, respectively; Fig. 7B; Table 3; p ¼ 0.0423, 95% confidence level). This finding is in contrast to the results of field studies by Van Zinderen Bakker and Muller (1987) and Starling and Crowder (1980/1981) who noted that abrasion of palynomorphs by sediment movement in the bed load of coarse-grained sediment (sands) physically broke or degraded pollen and spores carried within it. Although it seems plausible that coarser sediment should be more abrasive to palynomorphs carried in the bed load, it is possible the enhanced preservation seen in the turbiditic deposits reflects the fact that those deposits may have moved rapidly downslope to their final deposition site, avoiding prolonged

exposure at the sediment-water interface and thereby reducing degradation due to oxidation, weathering, and grazing. In core 15G, those turbiditic deposits having the greatest abundance of wellpreserved palynomorphs contained benthic foraminiferal assemblages from as many as five biofacies (Table 2) representing the inner shelf to upper middle slope (i.e., upper middle bathyal), indicating they resulted from a swift, full canyon flushing event (McGann, 2014).

6.4.3. Differences between hemipelagic/mixed mud and turbiditic deposits The most abundant pollen types recovered in the hemipelagic and mixed mud samples of 15G (Pinus, Sequoia, Quercus and Asteraceae), as well as the minor constituents (Amaranthaceae, Rhamnaceae, Notholithocarpus densiflora, Alnus, Poaceae, Salix, lowspine Asteraceae and Eriogonum), are thought to reflect the local California Coast Ranges floral record over the last 19,000 years and not that of a broader geographic region (McGann, 2015a). These same pollen types were found in the turbiditic deposits as well, although Pinus pollen is enriched in these flow deposits (Fig. 7C; Table 4; p ¼ 0.0493, 95% confidence level). Pinus is known to be one of the most aero- and hydraulically-efficient pollen types (Bradshaw and Webb, 1985; Brush and Brush, 1972; Holmes, 1990; Mudie and McCarthy, 1994; Warny et al., 2003; Williams, 2010),

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

M. McGann / Quaternary International xxx (2016) 1e21

due to its large size (~65e88 mm), oval shape, winged morphology, and air bladder (Kapp, 1969). The pollen grain can float as high as 300 m in the atmosphere (Koski, 1970), be transported spatially from <1 km2 to >1000 km2 in distance (Williams, 2009), and once submerged, may change its fall velocity from a floating to falling state (Brush and Brush, 1972). The increased abundance of Pinus pollen in the turbiditic deposits clearly reflects its superior transport capabilities. In contrast to the Pinus pollen, dinoflagellates were significantly less common in the turbiditic silt and sand deposits (Fig. 7D; p ¼ 0.0069, 99% confidence level). These protists prefer heightened input of sediment and nutrient-rich organic matter (Faust et al., 2005) and are often abundant in marine sediments (see summary in Wall, 1971). For these reasons, they are typically indicators of coastal upwelling (Melia, 1984). The decline in dinoflagellates in the flow deposits is attributed to their small size (~15e40 mm) and selective winnowing. To summarize, the tubiditic deposits in core 15G typically have lower pollen abundance (Fig. 7A), an assemblage containing a higher proportion of well-preserved and morphologically-large Pinus pollen (Kapp, 1969, Fig. 7B and C), and a reduction in the frequency of small-sized dinoflagellates (Fig. 7D) compared to the mud samples. The flow deposits are characterized by a statistically very significant increase in displaced benthic foraminifera as well (Fig. 7E, Table 2; p ¼ 0.0001, 99% confidence level). For these reasons, it is suggested that these flow deposits contain a biased pollen assemblage (Hopkins, 1950; Traverse and Ginsburg, 1966; Brush and Brush, 1972; Davis and Brubaker, 1973). Many, if not all, of the factors mentioned above (i.e., hydraulic fractionation due to winnowing, throughflow, biodegradation, abrasion, and grazing) probably impacted the palynomorph assemblage at some point as the sediment initially accumulated, was transported, deposited, and potentially exposed on the sediment surface at the site of core 15G prior to burial by additional sediment. 6.5. Q-mode cluster analysis In this study, both hemipelagic and mixed mud samples typified by a dominant hemipelagic signature of a grain size frequency distribution peak in fine-grained (clay to fine silt) sediment and low frequency of displaced benthic foraminifera (<19%), are thought to adequately characterize the floral record in core 15G. As such, they may be used to reliably interpret floral changes brought on by climatic and environmental change. Based on this premise, a Q-mode cluster analysis of the palynomorph frequencies in the hemipelagic and mixed mud samples of core 15G was used to discern changes in the regional vegetation over the last 19,000 years (Fig. 5A). The analysis placed the samples into three clusters, with the samples in each cluster in agreement with stratigraphic superposition. These clusters are interpreted to represent three pollen zones, two of Pleistocene age (Glacial and Transitional Pollen Zones) and one in the Holocene (Interglacial Pollen Zone). The assemblage of the Glacial Pollen Zone (472e369.5 cm, ca. 19,000e16,100 cal yr BP) represents the last glacial maximum (Adam, 1967; Adam et al., 1981), with dominance by Pinus, and moderate amounts of Asteraceae and Artemisia, and less abundant Quercus, Sequoia and Abies. The Transitional Pollen Zone (369.5e241 cm; ca. 16,100e12,200 cal yr BP) is characterized by a pollen assemblage with slightly decreasing, but still very abundant Pinus, moderate Asteraceae, increasing Sequoia and Alnus pollen, and low abundance of Quercus and Artemisia. The Interglacial Pollen Zone (241e0 cm; ca. 12,200e0 cal yr BP) is evident by increasing abundances of Sequoia, Quercus, Notholithocarpus densiflora and Asteraceae, and a decline of Pinus and Artemisia, which reflects the onset of warmer and probably wetter conditions. A brief period of

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drier conditions followed (ca. 150e125 cm; ca. 8000e6400 cal yr BP) that correlates with the middle Holocene dry period (Thompson, 1992; Quade et al., 1998; Grayson, 2000; Benson et al., 2002; Mensing et al., 2013). Except for a sample near the core top (22e20 cm), the upper 125 cm of the core reflects the modern pattern of vegetation in coastal central California. The pollen record is characterized by abundant Sequoia, moderate amounts of Pinus, Quercus, and Asteraceae, and fairly rare Notholithocarpus densiflora, Artemisia and Amaranthaceae. Rhamnaceae increases slightly for the first time, while Eriogonum, Alnus, and grasses remain minor components. The pollen assemblage of the sample from 22 to 20 cm is characterized by a significant drop in Sequoia and rise in Asteraceae (Fig. 6), which marks the occurrence of another brief dry period that is coincident with the droughts associated with the Medieval Climate Anomaly (ca. 1000e700 cal yr BP; MassonDelmotte et al., 2013). The results of the Q-mode cluster analysis of the pollen assemblages of this study's hemipelagic and mixed mud samples (Fig. 5A) are surprisingly similar to that when both mud and turbiditic samples are used (Fig. 5B). However, four of the twelve turbiditic samples (130e132 cm, 133.5e136.5 cm, 248e250 cm, and 336.5e338 cm) do not group in the same pollen zone with the mud samples that would be dictated by stratigraphic superposition. For example, the samples from 130 to 132 cm and 133.5e136.5 cm should be Holocene in age and as such, included in the Interglacial Pollen Zone, however they cluster with the Transitional Pollen Zone samples instead. Similarly, the stratigraphic position of the sample from 336.5 to 338 cm should cluster with the mud samples of the Transitional Pollen Zone, but it clusters with the Glacial Pollen Zone. In all three of these cases, the alignment with noncontemporaneous mud samples is due to the enriched Pinus pollen in the assemblages. The sample with the coarsest grain size investigated in this study, the cross-bedded turbiditic sand (Tc) from 248 to 250 cm, is characterized by a unique assemblage that includes floral elements representative of pollen zones of both the Pleistocene (lower abundance of Sequoia and high-spine Asteraceae, and higher abundance of Artemisia), and Holocene (decreased Pinus and increased Quercus). As the only outlier, this sample first clustered with the Glacial and Transitional Pollen Zones, then with the Interglacial Pollen Zone. Because this sample had significantly less pollen than any other (2044 grains/g versus an average of 7977 grains/g), and an assemblage that is inconsistent with the others stratigraphically adjacent to it, it appears to be the result of hydraulic sorting. A comparison was also made between the results of the Q-mode cluster analysis based on this study’s identification of hemipelagic and mixed muds by mean grain size, % sand, D90, grain size frequency distribution mode, and frequency of displaced benthic foraminifera (Fig. 5A) with that of McGann (2015a) based on visual inspection (sediment color and estimated sediment granulometry; Fig. 5C) of core 15G. The McGann (2015a) study misassigned five of the six turbiditic mud samples of this study (130e132 cm, 230e232 cm, 330e332 cm, 370e372 cm, 410e412 cm, and 430e432 cm) as hemipelagic and mixed muds based on the fact that the grain size and distribution curves were compatible with the mixed mud samples. However, the percentage of displaced benthic foraminifera (25e54%) places them among the turbiditic muds instead. Three other samples not used by McGann (2015a) (i.e., 290e292 cm, 347e349 cm, and 467.5e469.5) were included in this study because they had grain size parameters and frequencies of displaced benthic foraminifera that were within the guidelines defined for the mixed mud deposits. The results are in good agreement between the two studies (Fig. 5A and C). The same three clusters (Glacial, Transitional, and Interglacial) were identified in

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

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A. Palynomorphs >3%

B. All palynomorphs

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Fig. 8. Plot of Principal Components Analysis PC1 versus PC2 using (A) palynomorphs with frequency abundances >3% and (B) all palynomorphs in the samples of core 15G. Open circles ¼ hemipelagic and mixed mud samples, gray circles ¼ turbiditic mud samples, and black circles ¼ coarse-grained turbiditic deposits (silts and sands). Samples assigned to the Glacial, Transitional, and Glacial pollen zones as well as the outlier (248e250 cm; Tc) are shown. X ¼ displaced sediment samples not in expected stratigraphic superposition.

each and the samples still align as expected by stratigraphic superposition. Only the boundaries between the three clusters are more precisely defined in the former study (McGann, 2015a) due to the increased size of the data set (i.e., Glacial Pollen Zone from 472 to 381 cm, ca. 19,000e17,000 cal yr BP; Transitional Pollen Zone from 381 to 221 cm, ca. 17,000e11,500 cal yr BP; and Interglacial Pollen Zone from 221 to 0 cm, ca. 11,500e0 cal yr BP). 6.6. Principal components analysis Using the palynomorphs accounting for >3% of the assemblage, the results of the PCA are very similar to those of the Q-mode cluster analysis. The first three components, which describe 81.3% of the variance (Table 5A), clearly separate those palynomorphs that are most prevalent in the Pleistocene (Pinus and Pediastrum) from those in the Holocene (Sequoia, Notholithocarpus, and dinoflagellates). A plot of these data (PC1 versus PC2) illustrates overlapping samples associated with the Pleistocene Glacial and Transitional pollen zones, separated from those of the Holocene Interglacial pollen zone, and the single turbiditic sand (248e250 cm) outlier (Fig. 8A). The results of the PCA using all of the palynomorphs shows a similar, but less constrained, pattern (Fig. 8B). In both of the PCAs, there is no separation of samples by lithology. Instead, the fine- and coarse-grained flow deposits are aligned just as they are in the Q-mode cluster analysis, with nine of the turbiditic samples grouping with the hemipelagic/mixed muds in expected stratigraphic superposition and four others not so. This pattern suggests that despite the fact that overall the flow deposits are characterized by a statistically significant biased palynological assemblage, in some cases they may not be altered enough to cause the sample to be assigned to a different pollen zone. In contrast, the Q-mode cluster analysis of the benthic foraminiferal samples clearly separated by lithology due to the presence of the allochthonous microfauna (McGann, 2014). 6.7. Use of sediment flow deposits in marine palynological studies Just as Brunner and Normark (1985) and McGann (2014) determined that the distribution of microorganisms in the marine realm is affected by hydraulic sorting during transport in turbidity currents, this study has shown the same to be true of its palynological component. Both have the potential to lead to mistaken interpretations of their records (e.g., climatic shifts or

environmental perturbations). This is particularly true of the finergrained turbiditic deposits (i.e., turbiditic muds and silts) that have a low percentage of sand and, therefore, are more difficult to discern from hemipelagic deposits. One sample (130e132 cm) from core 15G serves as a good example. The sediment was initially thought to be of hemipelagic origin based on visual inspection. Surprisingly, however, the pollen assemblage clustered with other samples in the Pleistocene-aged Transitional Pollen Zone instead of the Holocene-aged Interglacial Pollen Zone as expected based on its stratigraphic position in the core. Subsequently, microfaunal analysis determined the sample contained 44% shallow-water benthic foraminifera and clearly represented a displaced deposit originating on the shelf. Had it not been recognized as such, the floral constituents would have suggested the climate cooled at the time it was deposited, when in fact, the pollen assemblage was simply a consequence of hydraulic enrichment in Pinus pollen and winnowing of other smaller-sized pollen. This example serves as a reminder that although the presence of turbiditic sands in a core is visually obvious in most cases, that may not be the case for displaced turbiditic muds and silts. Determining the grain size of, and relative frequency of displaced shallow-water benthic foraminifera in, a marine sediment sample is essential in order identify, and ultimately, avoid using biased pollen assemblages of displaced deposits when constructing marine palynological records. 7. Conclusions A comparison of pollen assemblages of turbiditic deposits and background mud samples in a deep-sea core off central California suggests the sediment flow deposits contain a statistically significantly biased palynomorph assemblage due to hydraulic sorting and winnowing. Pollen abundance correlates negatively with grain size, such that the turbiditic deposits (muds, silts, and sands) have significantly fewer pollen and spores than the hemipelagic and mixed muds. They are also enriched in hydraulically-efficient Pinus pollen compared to coeval background mud deposits. This bias resulted in several turbiditic deposits being assigned to pollen zones that were unrealistic based on their stratigraphic position in the core. Unrecognized bias in floral records can, in turn, lead to misinterpretations of larger climatic or environmental trends. Turbiditic deposits, by their very nature of origin, are anomalies in marine sediment deposition and as such, should be avoided in marine palynological studies. The results of this study support that

Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003

M. McGann / Quaternary International xxx (2016) 1e21

fact. However, the usual characteristics commonly used to identify turbiditic deposits in marine palynological studies, such as visual inspection, sediment color, granulometry, and grain size frequency distribution curves do not always serve to properly identify finergrained flow deposits. This study has shown that in addition, determining the relative percentage of displaced shallow-water benthic foraminifera is critical in order to eliminate these anomalous samples when constructing marine palynological records. Acknowledgements Thanks to the captain and crew of the R/V Sea Sounder (USGS) for recovering core 15G and to the late William Normark (USGS) for kindly making it available for study. I would particularly like to thank Charlotte Brunner (University of Southern Mississippi) and Roger Byrne (University of California, Berkeley) for assisting in the design of this study. Christina Gutmacher (formerly USGS) and Charlotte also generously aided in the core description. Radiocarbon dates were provided by the Center for Accelerator Mass Spectrometry of Lawrence Livermore National Laboratory and the staff at Beta Analytic, and grain size data by Steve Low of the California Water Science Center, assisted by Angela Tan of the USGS, in the PCMSC sedimentology laboratory in Santa Cruz, California. Helpful discussions regarding the sedimentological analyses were also kindly provided by Michael Torresan, USGS PCMSC. This manuscript greatly benefited by suggestions provided by Charles Powell, II (USGS) and two anonymous reviewers. References Adam, D.P., 1967. Late-Pleistocene and recent palynology in the central Sierra Nevada, California. In: Cushing, E.J., Wright, H.E., Wright Jr., H.E. (Eds.), Quaternary Paleoecology. Yale University Press, New Haven, Connecticut, pp. 275e301. Adam, D.P., Byrne, R., Luther, E., 1981. A Late Pleistocene and Holocene pollen record from Laguna de Las Trancas, northern coastal Santa Cruz County, California. Madrono 28, 255e272. Alley, R.B., 2000. The Younger Dryas cold interval as viewed from central Greenland. Quat. Sci. Rev. 19, 213e226. Alley, R.B., Meese, D.A., Shuman, C.A., Gow, A.J., Taylor, K.C., Grootes, P.M., White, J.W.C., Ram, M., Waddington, E.D., Mayewski, P.A., Zielinski, G.A., 1993. Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event. Nature 362, 527e529. http://dx.doi.org/10.1038/362527a0. Balsam, W.L., Heusser, L.E., 1976. Direct correlation of sea surface paleotemperatures, deep circulation and terrestrial paleoclimates: foraminiferal and palynological evidence from two cores off Chesapeake Bay. Mar. Geol. 21, 121e147. Barbour, M.G., Major, J., 1977. Terrestrial Vegetation of California. John Wiley & Sons, New York, 1002 pp. Barnard, P.L., Foxgrover, A.C., Elias, E.P.L., Erikson, L.H., Hein, J.R., McGann, M., Mizell, K., Rosenbauer, R.J., Swarzenski, P.W., Takesue, R.K., Wong, F.L., Woodrow, D.L., 2013. Integration of bed characteristics, geochemical tracers, current measurements, and numerical modeling for assessing the provenance of beach sand in the San Francisco Bay coastal system. Mar. Geol. 345, 181e206. Barron, J.A., Heusser, L., Herbert, T., Lyle, M., 2003. High-resolution climatic evolution of coastal northern California during the past 16,000 years. Paleoceanography 18 (1), 1020, 20-1e20-14. http://dx.doi.org/10.1029/2002PA000768. Benson, L., Kashgarian, M., Rye, R., Lund, S., Paillet, F., Smoot, J., Kester, C., Mensing, S., Meko, D., Lindstrom, S., 2002. Holocene multidecadal and multicentennial droughts affecting northern California and Nevada. Quat. Sci. Rev. 21, 659e682. Bouma, A.H., 1962. Sedimentology of Some Flysch Deposits. Elsevier, New York, 168 pp. Bradshaw, R.H.W., Webb III, T., 1985. Relationships between contemporary pollen and vegetation data from Wisconsin and Michigan. USA. Ecol. 66 (3), 721e737. Brunner, C.A., Ledbetter, M.T., 1987. Sedimentological and micropaleontological detection of turbidite muds in hemipelagic sequences: an example from the late Pleistocene levee of Monterey Fan, central California continental margin. Mar. Micropaleontol. 12, 223e239. Brunner, C.A., Ledbetter, M.T., 1989. Latest Quaternary quantitative planktonic foraminiferal biostratigraphy in turbidite sequences of the central California continental margin. Micropaleontology 35, 321e336. Brunner, C.A., Normark, W.R., 1985. Biostratigraphic implications for turbidite depositional processes on the Monterey deep-sea fan, central California. J. Sediment. Petrol. 55, 495e505. Brush, G.S., Brush Jr., L.M., 1972. Transport of pollen in a sediment-laden channel, a

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Please cite this article in press as: McGann, M., Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California, Quaternary International (2016), http://dx.doi.org/10.1016/j.quaint.2016.11.003