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Canadian Journal of Earth Sciences

First high-precision U-Pb CA-ID-TIMS age for the Battle Formation (Upper Cretaceous), Red Deer River valley, Alberta, Canada: implications for ages, correlations, and dinosaur biostratigraphy of the Scollard, Frenchman, and Hell Creek formations

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2018-0098.R2

Manuscript Type: Article

Date Submitted by the 05-Dec-2018 Author: Complete List of Authors: Eberth, David;Draft Royal Tyrrell Museum of Palaeontology, Kamo, Sandra; University of Toronto, Earth Sciences

Battle Formation, U-Pb dating, Dinosaurs, Cretaceous, Hell Creek Keyword: Formation

Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? :

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1 First high-precision U-Pb CA-ID-TIMS age for the Battle Formation (Upper 2 Cretaceous), Red Deer River valley, Alberta, Canada: implications for ages, 3 correlations, and dinosaur biostratigraphy of the Scollard, Frenchman, and 4 Hell Creek formations 5 6 7 8 David A. Eberth* and Sandra L. Kamo** 9 10 11 12 13 *Royal Tyrrell Museum of Palaeontology 14 Box 7500 15 Drumheller, Alberta T0J0Y0 16 [email protected] 17 18 **Jack Satterly Geochronology Laboratory 19 Department of Earth Sciences 20 UniversityDraft of Toronto 21 22 Russell St. 22 Toronto, ON, M5S 3B1 23 [email protected] 24

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26 Abstract

27 The Battle Formation (BFm) is a widespread Upper Cretaceous marker horizon in

28 western Canada that records a time of low sediment-input and marks the boundary between the

29 Edmontonian and Lancian land-vertebrate ages. Here, we present the first high-precision U-Pb

30 CA-ID-TIMS age of 66.936 ± 0.047/0.060/0.140 Ma for the Battle bentonite, an altered vitric

31 ash in the upper portion of the BFm at Knudsen’s Farm in the Red Deer River valley of Alberta.

32 This age supersedes those previously reported, confirms that rates of sediment accumulation for

33 the formation were very low (~1.40 cm/ka), and allows us to interpolate an age range of ~66.88–

34 67.20 Ma for the BFm. Our data also provide a maximum age of ~66.88 Ma for the base of the

35 overlying Scollard Formation, a dinosaur-rich unit. We combine our age data with calibrated

36 magneto- and palynostratigraphic data toDraft assess chronostratigraphic correlations among the

37 Scollard Formation (K-ScF) of Alberta, the Frenchman Formation (FFm) of Saskatchewan, and

38 the Hell Creek Formation (HCF) in eastern Montana. Whereas the combined data support

39 previous interpretations that equate the age ranges of the K-ScF, FFm, and the upper one-third of

40 the HCF in eastern Montana, they also indicate that all of the lower one-third (L3) and part of the

41 middle one-third (M3) of the HCF in Montana are chronostratigraphically equivalent to all or

42 part of the sub-BFm unconformity and the BFm in Alberta. Accordingly, a minimum age of

43 ~67.20 Ma is assessed for the base of the Hell Creek Formation in its type area.

45 Keywords: Battle Formation, Hell Creek Formation, U-Pb dating, dinosaurs, Cretaceous, 46 Maastrichtian

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47 Introduction

48 The Upper Cretaceous Battle Formation (BFm) in western Canada is a distinctive and

49 widespread kaolinitic to bentonitic marker horizon, typically less than 10 m thick, that has been

50 employed widely since the 1930s in stratigraphic and paleoenvironmental studies of the Western

51 Canada Sedimentary Basin (Sanderson 1931; Furnival 1942; Elliott 1960; Irish and Havard

52 1968; Irish 1970; Lerbekmo 1985; Binda 1992; Lerbekmo and Braman 2002; Hathway et al.

53 2011; Eberth and Braman 2012). It records a time of unusually cool temperatures, intense

54 volcanism, and low sediment-input in the basin (Eberth and Braman 2012), and its top marks the

55 conventional boundary between the Edmontonian (below) and Lancian (above) land-vertebrate

56 ages (Fowler 2017). Because of its broad stratigraphic utility, easy identification in both outcrop

57 and geophysical logs, and its rich volcanicDraft content, the BFm was one of the first Cretaceous

58 deposits in western Canada to be dated radioisotopically (Folinsbee et al. 1961; Baadsgaard

59 [unpublished age and data reported in Obradovich 1993]; Baadsgaard [unpublished age and data

60 reported in Lerbekmo 2009]). Published dates for the unit were originally limited to K-Ar

61 analyses with large calculated errors (± 1.6–5.0%, 2σ). For example, Folinsbee et al. (1961)

62 reported K-Ar dates of 65, 66, 66, 66, and 68 Ma for five samples collected near Strawberry

63 Creek and stated: “Assumed deviation in dates is 5%.”

64 More refined ages for the BFm were calculated by Baadsgaard (reported in Obradovich

65 1993 and Lerbekmo 2009), but analytical data were not included, thus compromising the utility

66 of the results (although see Fowler’s 2017 recalibration of Obradovich 1993). For example,

67 Baadsgaard obtained an 40Ar/39Ar age of 66.8 ± 1.1 Ma (95% confidence interval) for sample

68 AK-476 from Strawberry Creek (presented in Obradovich 1993, table 1) and later calculated a

69 U-Pb age of 66.5 ± 0.2 Ma for the same sample (presented by Lerbekmo 2009).

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70 To our knowledge no subsequent ages have been reported from the BFm. Accordingly,

71 these low-precision and undocumented results continue to be cited (e.g., Glass 1990; Hamblin

72 2004; Eberth and Braman 2012; Eberth et al. 2013; Fowler 2017), thus limiting our

73 understanding of (1) an accurate age for the BFm, (2) rates of sediment accumulation for this and

74 other stratigraphically associated units, (3) the chronostratigraphy of a variety of climatic and

75 biostratigraphic events in this portion of the western Canadian stratigraphic section (cf. Wu et al.

76 2007; Eberth and Braman 2012; Eberth et al. 2013), and (4) how the BFm correlates with non-

77 marine units within and beyond the basin (cf. Fowler 2017).

78 To improve our understanding of the depositional timing and duration of the BFm, we

79 dated a bentonite (here referred to as the Battle bentonite) from the upper portion of the unit

80 using U-Pb isotope dilution thermal ionizationDraft mass spectrometry on chemically abraded zircon

81 crystals (U-Pb CA-ID-TIMS; Mattinson 2005). Currently, the U-Pb CA-ID-TIMS technique is

82 the most accurate and precise means of dating geologic events in this and other parts of the

83 geologic column. The age of 66.936 ± 0.047/0.060/0.140 Ma for the Battle bentonite that we

84 present here is of high-precision and is well documented, and thus supersedes all previous age

85 interpretations for the formation. In turn, this high-precision age allows us to assess some

86 chrono- and biostratigraphic interpretations for the Maastrichtian portion of the Cretaceous

87 section in western Canada and Montana.

89 Location

90 We collected Battle bentonite samples from the Knudsen’s Farm locality (N51.90110

91 W113.01262), 7 km north of Tolman Bridge (Highway 585) along the west side of the Red Deer

92 River valley (Fig. 1). Our attempts to collect samples from the original Strawberry Creek locality

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93 of Folinsbee (1961) and Baadsgaard (in Obradovich 1993 and Lerbekmo 2009) were

94 unsuccessful due to a variety of factors, including extensive modern plant cover along the creek

95 bottom and margins, limitations imposed by widespread property development in the area, and

96 inconsistently and imprecisely reported legal land descriptions of the site in published reports.

97 Regardless of those limitations, we regard the Knudsen’s Farm locality as superior to the

98 original Strawberry Creek locality because the BFm at Knudsen’s Farm is much better exposed,

99 and is associated with a more completely exposed stratigraphic section that extends throughout

100 the Red Deer River valley. For example, the Knudsen’s Farm stratigraphic section extends from

101 the Drumheller Marine Tongue of the Horseshoe Canyon Formation at its base, to a few meters

102 above the Cretaceous-Paleogene (K-Pg) boundary at its top, and includes a complete section and

103 laterally extensive outcrops of the 4.5 mDraft thick BFm (Fig. 2; Eberth and Braman 2012, appendix

104 1). Southeast toward Drumheller, bedrock exposures extend down-section into the Campanian-

105 age, marine Bearpaw Formation, and to the north and west, exposures extend up-section into the

106 Paleocene-age, non-marine Scollard and Paskapoo formations (Gibson 1977; Hamblin 2004;

107 Eberth and Braman 2012; Eberth et al. 2013; Prior et al. 2013).

108

109 Stratigraphic and geological background

110 The BFm succession has been recognized as an important Upper Cretaceous

111 lithostratigraphic datum in south-central Alberta and south-western Saskatchewan since the

112 1930s (Sanderson, 1931). It was elevated to formational status by Irish and Havard (1968) and

113 included as part of Edmonton Group by Irish (1970). The formation lies unconformably on the

114 Whitemud Member of the Horseshoe Canyon Formation (Catuneanu et al. 1997; Catuneanu and

115 Sweet 1999; Hamblin 2004; Hathway 2011; Eberth and Braman 2012; and Eberth et al. 2013),

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116 and is overlain conformably by the alluvial Scollard Formation (Fig. 2; Catuneanu and Sweet

117 1999; Eberth and Braman 2012).

118 Paleoenvironmental studies of the BFm indicate that it consists mostly of altered volcanic

119 ash that has been modified syndepositionally by Cretaceous-age pedogenic and diagenetic

120 processes (Lerbekmo 1985; Binda 1992; Hamblin 2004; Eberth and Braman 2012). In outcrop

121 and core, the deposit is a dark olive-green-to-black color (5Y 3/2, 5Y 4/1, 5Y 2/1; GSA Rock

122 Color Chart 1991) and consists mostly of massive kaolinitic to bentonitic mudstone that includes

123 one or more light-grey (N7) siliceous concretionary horizons (the Kneehills Tuff) in the upper

124 one-third of the deposit.

125 Sediments of the BFm were originally deposited in wetland/lacustrine settings that were

126 widespread across southern Alberta andDraft southwestern Saskatchewan during and subsequent to a

127 Late Cretaceous drop in sea level (Lerbekmo 1985; Binda 1992; Lerbekmo 2009; Eberth and

128 Braman 2012). With very little terrigenous input other than multiple volcanic ashfalls, BFm

129 deposits became extensively modified during lengthy episodes of exposure, turbation, and

130 pedogenesis (Lerbekmo 1985; Binda 1992; Eberth and Braman 2012). The deposit is sparsely

131 fossiliferous, but locally yields rare pollen and spores, as well as highly degraded fragments of

132 bone and teeth, algal remains, and coalified wood (Binda and Srivastava 1968; Srivastava 1970;

133 Srivastava and Binda 1984; Koppelhus and Braman 2010).

134 Throughout southern Alberta, the BFm has been assigned to portions of magnetochron

135 30n, the Wodehouseia spinata miospore zone (Lerbekmo and Braman 2002; Wu et al. 2007;

136 Eberth and Braman 2012), and more recently, to the Striaticorpus pyriformis-Striatellipollis

137 radiatus biozone (Braman 2018). Based on inferred ages for litho-, magneto-, and

138 biostratigraphic units of the upper Horseshoe Canyon and Battle formations (Lerbekmo and

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139 Braman 2002; Hamblin 2004; Wu et al. 2007; Eberth and Braman 2012; Ogg et al. 2004; Ogg

140 and Hinnov 2012), the unconformity at the base of the BFm has been estimated as representing

141 ~750 ka (Eberth and Braman 2012; Eberth et al. 2013).

142 Assignment of the BFm to magnetochron 30n by Lerbekmo and Braman (2002) has

143 allowed low-resolution age assessments of the formation to be made by reference to calibrations

144 of magnetochron 30n presented by Ogg et al. (2004), Ogg and Hinnov (2012), Ogg et al. (2016),

145 and Sprain et al. (2014). Although the BFm appears superficially assignable to the lower one-half

146 of the 30n magnetochron (Lerbekmo and Braman 2002; Eberth and Braman 2012), the presence

147 of an ~750 ka unconformity at the base of the formation and the fact that 30n extends upward

148 into the lowest 15 m of the overlying Scollard Formation (Lerbekmo and Braman 2002, fig. 14)

149 suggest that the BFm occurs at neither theDraft base nor the top of the 30n magnetochron.

150 Accordingly, previous stratigraphic assessments have reasonably inferred that the BFm

151 correlates best with some portion of the middle one-third of magnetochron 30n. The most

152 recently calibrated age for magnetochron 30n presented by Ogg and Hinnov (2012) and

153 corrected by Sprain et al. (2014) suggests an age range of ~66.2–68.2 Ma for the chron, and an

154 age range of ~66.9–67.5 Ma for the middle one-third of the chron, during which time the BFm

155 likely accumulated.

156

157 Methods

158 Sampling

159 In general, BFm mudstones are heavily weathered and diagenetically modified making it

160 difficult to find datable phenocrysts and mineral grains (biotites, sanidines, plagioclases,

161 zircons). Thus, in order to obtain the best potentially datable zircon grains at Knudsen’s Farm we

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162 trenched the entire 4.5 m thick BFm to a depth of at least 50 cm, and inspected the fresh

163 exposures with a hand lens in 10 cm stratigraphic increments. We found a 1–2 cm-thick

164 bentonite (here named the Battle bentonite) in the upper one-quarter of the formation, 3.75 m

165 above the top of Whitemud Member of the Horseshoe Canyon Formation, 75 cm below the

166 contact with the Scollard Formation, and ~5 cm above local occurrences of Kneehills Tuff

167 siliceous concretions (Fig. 2). The Battle bentonite is an altered vitric volcanic ash that contains

168 vague laminae and unaltered (dark and compact) biotite phenocrysts visible in hand samples.

169 Well preserved biotite phenocrysts that are visible to the unaided eye are often an excellent

170 indicator for the presence of smaller, hard-to-see volcanic grains (including zircon grains) in

171 southern Alberta’s bentonites. Laboratory study of the bulk sample confirmed the presence of

172 zircons in our samples (Fig. 3C), whichDraft allowed us to undertake U-Pb CA-ID-TIMS dating.

173 The weathered Battle bentonite is similar in both overall color and texture to other BFm

174 exposures at Knudsen’s Farm, and elsewhere in western Canada (see above). It consists mostly

175 of massive silty claystone with dark, olive-green colors (5Y 3/2, 5Y 4/1, 5Y 2/1), and a vaguely

176 laminated fabric. The presence of a vaguely laminated fabric in this upper portion of the

177 formation suggests that the Battle bentonite may be slightly less pedogenicized and altered

178 compared to the bentonitic mudstones that make up lower portions of the formation.

179 Confirmation of this interpretation requires detailed pedogenic and petrographic analyses that are

180 beyond the scope of this study.

181 Samples were assigned the field number DAE 09-01-2017 and additional samples for

182 comparison and future analyses were accessioned into the Royal Tyrrell Museum’s geological

183 collections as TMP 2017.033.0001.

184

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185 U-Pb geochronologic methods

186 A 2.7 kg sample of the Battle bentonite was disaggregated in a blender and a heavy

187 mineral concentrate was produced by re-processing the heavy mineral splits on the Wilfley table

188 until a significantly reduced sample size of ~3–4 g was achieved. This was followed by standard

189 mineral separation procedures using magnetic (Isodynamic Frantz) and heavy liquid (methylene

190 iodide) methods.

191 U-Pb analysis was by isotope dilution-thermal ionization mass spectrometry methods on

192 chemically abraded zircon grains (CA-ID-TIMS) at the University of Toronto. Prior to

193 dissolution and analysis, zircon crystals were thermally annealed at 900º C for 48 hours to repair

194 radiation damage in the crystal lattice. The grains were then partially dissolved, or etched, in

195 ~0.1 ml ~50% hydrofluoric acid and ~0.020Draft ml of HNO3 at 200º C for 12 hours (Mattinson

196 2005). This procedure has the advantage of penetrative removal of alteration zones where Pb loss

197 has occurred, which generally improves results by producing more concordant systems in

198 individual analyses. Zircon grains were rinsed with 6N HCl followed by 8N HNO3 at room

199 temperature prior to dissolution. A 205Pb-233-235U spike from the EARTHTIME Project was

200 added to the Teflon dissolution capsules during sample loading. Zircon was dissolved using

201 ~0.10 ml of concentrated HF acid and ~0.020 ml of 7N HNO3 at 200° C for 5 days, then dried to

202 a precipitate and re-dissolved in ~0.15 ml of 3N HCl overnight (Krogh 1973). U and Pb were

203 isolated from the zircon using 50 μl anion exchange columns using HCl, deposited onto

204 outgassed rhenium filaments with silica gel (Gerstenberger and Haase 1997), and analyzed with

205 a VG354 mass spectrometer using a single Daly detector in pulse counting mode for Pb, and 3

206 Faraday cups in static analysis mode for U. Corrections to the 206Pb-238U ages for initial 230Th

207 disequilibrium in the zircon have been made assuming a Th/U ratio in the magma of 4.2. All

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208 common Pb in each analysis was assigned the isotopic composition of procedural Pb blank. Dead

209 time of the measuring system for Pb was 16 nanoseconds. The mass discrimination correction for

210 the Daly detector is constant at 0.05% per atomic mass unit. The thermal mass fractionation

211 correction for Pb was 0.10% per atomic mass unit (± 0.076%, 2); and the U thermal mass

212 fractionation correction was measured and corrected within each measurement cycle. Amplifier

213 gains and Daly characteristics were monitored using the SRM 982 Pb standard. Decay constants

214 are those of Jaffey et al. (1971). Age errors quoted in the text and table, and error ellipses in the

215 concordia diagram and weighted mean age plot (Fig. 3A–B) are given at the 95% confidence

216 interval. Plotting of U-Pb data employed Isoplot 3.00 (Ludwig 2003).

217

218 U-Pb results Draft

219 U-Pb dates reported below for single zircon grains are from the 238U – 206Pb decay

220 scheme. This is the most robust system for geologically young rocks due to (1) the much greater

221 abundance of 206Pb, which makes it less sensitive to common Pb corrections (a minor correction

222 in any case given the total amounts of common Pb are <1 picogram in most analyses), (2)

223 possible minor effects from initial deficiencies of 230Th that lead to deficits in 206Pb, or (3)

224 measurement bias issues, compared to the 235U – 207Pb decay scheme. Correction for initial

225 230Th disequilibrium has been made using an assumed Th/U of the magma of 4.2. However, for

226 zircon grains with low Th/U, a lower value of 2.5 may be more appropriate (Wotzlaw et al.,

227 2014). In our study, zircon grains have Th/U ranging from 0.4–0.6 and an assumed Th/U of 2.5

228 will have the effect of reducing the final age by ~10 ka. A summary of the U-Pb zircon isotopic

229 data is presented in Table 1. A concordia diagram and plot showing the weighted mean

230 206Pb/238U age are presented in Figure 3A–B.

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231 Abundant zircon grains were recovered and are generally fresh, euhedral, elongate-to-

232 short prismatic crystals approximately 100–200 microns in length (Fig. 3C). Results from 10 of

233 11 long prismatic, chemically abraded, single zircon grains gave a range of 206Pb/238U dates from

234 67.161 ± 0.080 Ma to 66.919 ± 0.095 Ma (2 errors reported here and throughout). One grain is

235 distinctly older at 67.441 ± 0.091 Ma and is significantly larger than the others (16 micrograms

236 versus 4–10 micrograms). It is therefore interpreted as a xenocryst, which suggests some

237 reworking of the volcanic layer, possible inheritance acquired from the magma source, or

238 assimilation during emplacement. A weighted average of the remaining 10 dates is 67.061 ±

239 0.068 Ma, but scatter of the dates varies beyond the associated individual analytical

240 uncertainties, with MSWD of 5.2. A younger and less precise age of 66.980 ± 0.150 Ma is

241 obtained if data for the 5 youngest grainsDraft are used in the mean. Altered volcanic ash beds

242 (bentonites) are well known to occasionally contain zircon grains that formed in the magma

243 source chamber over a duration of perhaps tens to hundreds of thousands of years prior to

244 eruption (‘antecrysts’). In such cases, inclusion of these pre-eruptive dates in a weighted mean

245 age calculation would, of course, bias the time of deposition towards too old an age. Therefore,

246 the youngest coherent population of grains should give the closest estimate for the time of

247 eruption and deposition of the volcanic unit. In the present case, the youngest 3 grains with a

248 weighted mean 206Pb/238U age of 66.936 ± 0.047/0.060/0.140 Ma (MSWD=0.42) provide the

249 best eruptive age estimate. Errors reported here are in X/Y/Z format (Schoene et al., 2006),

250 where X represents the internal analytical uncertainty, Y includes external uncertainty of the

251 Pb/U calibration of the isotopic tracer solution (i.e., for comparison to other U-Pb isotopic ages),

252 and Z includes X and Y, in addition to the 238U decay constant uncertainty (i.e., for comparison

253 to ages determined by other radio-isotopic dating methods). In this interpretation, it is assumed

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254 that there has been no Pb loss in the 3 grains. Given the severe 12-hour etch to the annealed

255 grains, the pristine condition of the analyzed zircons, and the strong overlap of the dates

256 (MSWD=0.42), it is assumed herein that the youngest cluster of dates at 66.936 ±

257 0.047/0.060/0.140 Ma represents the most robust estimate of the time of eruption and deposition

258 of the bentonite unit.

259

260 Discussion

261 The U-Pb age of 66.936 ± 0.047/0.060/0.140 Ma for the Battle bentonite is older and

262 more precise than all previously reported radiometric ages from the formation. Given that the

263 Battle bentonite was collected from the upper one-quarter of the BFm, its age should be

264 considered as approximating a minimumDraft age for the formation in the Red Deer River valley

265 region of southern Alberta.

266 Our age is compatible with previous age-range estimates for the BFm that are based on

267 its assignment to the middle of magnetochron 30n and, specifically, the middle one-third of the

268 30n age range (~66.9–67.5 Ma; Fig. 4; see above). Accordingly, we propose that our data, when

269 combined with calibrated magnetostratigraphies for this part of the Cretaceous—as presented by

270 Ogg and Hinnov (2012) and modified by Sprain et al. (2014)—can be used to refine (1) rates of

271 sediment accumulation for the BFm, (2) boundary ages for the BFm and other associated

272 Maastrichtian units, and (3) chronostratigraphic correlations among the BFm, other

273 Maastrichtian units, and significant geologic/biostratigraphic patterns and events recorded within

274 the units (cf. Wu et al. 2007; Lerbekmo 2009; LeCain et al. 2014; Scannella et al. 2014; Sprain et

275 al. 2014; Cande and Patriat 2015).

276

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277 Estimated rate of sediment accumulation for the Battle Formation

278 In order to estimate the rate of sediment accumulation in the BFm, we combined the

279 stratigraphic thicknesses of the BFm and the underlying Whitemud Member of the Horseshoe

280 Canyon Formation, the base of which coincides with the calibrated 30n-30r magnetochron

281 boundary (Fig. 4; Lerbekmo and Braman 2002; Ogg and Hinnov 2012). This enabled us to

282 chronostratigraphically bracket most of the Battle Formation over a relatively limited

283 stratigraphic interval by using our age and the calibrated 30n-30r boundary of Ogg and Hinnov

284 (2012). We interpolate a rate of sediment accumulation of ~1.4 cm/ka for the combined interval

285 using the formula, t/(b-a-750), where:

286 t = the thickness of the section between the base of the Whitemud and the Battle 287 bentonite (~700 cms). See Eberth and Braman (2012; appendix AS1-14) for the 288 Knudsen’s Farm section;Draft 289 b = the calibrated age for the base of 30n (~68,200 kya) as reported by Ogg and Hinnov 290 (2012); 291 a = the age of the Battle bentonite reported here by us (66,936 kya); 292 750 = the estimated timespan (in ka) of the unconformity between the Whitemud 293 Member and Battle Formation (Eberth and Braman 2012). 294

295 A rate of sediment accumulation of ~1.4 cm/ka for the BFm should be regarded as a

296 maximum because of the inclusion of the Whitemud Member in our calculation. Cross-bedded

297 fluvial sandstones are common in the Whitemud Member and can reasonably be assumed to have

298 had higher rates of sediment accumulation than the episodic volcanic ashfall events that

299 characterized sedimentation during BFm aggradation.

300 In combination with our knowledge of the thickness of the BFm and the stratigraphic

301 position of the Battle bentonite, a maximum rate of ~1.40 cm/ka allows us to estimate an age

302 range of ~66.88–67.20 Ma for the BFm, with a minimum timespan of ~320,000 years. However,

303 we anticipate that additional age data from the BFm will allow future workers to forego inclusion

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304 of the Whitemud Member in these calculations. In turn, that is likely to result in a lower

305 estimated rate of sediment accumulation and slightly expanded boundary ages for the BFm.

306 Although ~1.40 cm/ka overestimates the rate of sediment accumulation in the BFm, it is

307 still notably low, representing one-half or less of rates that are routinely calculated for typical

308 Upper Cretaceous non-marine stratigraphic units in the Western Canada Sedimentary Basin (3–

309 10 cm/ka; Eberth 2005; Lerbekmo 2005; Eberth and Braman 2012). A low rate of sediment

310 accumulation for the BFm is compatible with interpretations (of the combined Whitemud/Battle

311 interval) that posit (1) long-term sediment starvation in this portion of distal foredeep section, (2)

312 sediment accumulation primarily by volcanic ashfall, and (3) lengthy intervals of landscape

313 exposure (hiatuses) and modification, including widespread and thorough organic degradation

314 (Binda and Srivastava 1968; Lerbekmo Draft1985; Binda 1992; Catuneanu and Sweet 1999; Hamblin

315 2004; Eberth and Braman 2012). In turn, such conditions are compatible with observations that

316 vertebrate fossils are poorly preserved in both the Whitemud Member and the BFm, resulting in

317 a gap in our understanding of vertebrate assemblages from the middle and lower portions of

318 magnetochron 30n across western Canada, and obscuring the biostratigraphic nature of the

319 Edmontonian-Lancian land vertebrate age-transition in the region.

320

321 Correlating the Battle, Scollard, Frenchman, and Hell Creek formations

322 The data and patterns presented here provide important opportunities to assess

323 chronostratigraphic correlations of the upper Maastrichtian Battle, Scollard, Frenchman and Hell

324 Creek formations of Alberta, Saskatchewan, and Montana, and to assess latest Cretaceous

325 dinosaur biostratigraphic patterns across the northern portion of the Western Interior (Fig. 4).

326

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327 Scollard Formation

328 Because the contact of the Scollard Formation on the BFm is conformable in the

329 Drumheller region (Catuneanu and Sweet 1999 [interpreted by them as a conformable fourth

330 order sequence boundary]; Eberth and Braman 2012; Eberth et al. 2013) and lies only 75 cm

331 above the Battle bentonite, our estimated age of ~66.88 Ma for the top of the BFm in the

332 Drumheller region also serves as a reasonable age estimate for the base of the Scollard

333 Formation.

334 The K-Pg boundary is present in the Scollard Formation exposures at Knudsen Farm ~40

335 meters above the base of the formation (Eberth and O’Connell 1995; Sweet et al. 1999;

336 Lerbekmo and Braman 2002; Eberth and Braman 2012) and, thus, delimits a ~40 m thick

337 Cretaceous-age portion of the Scollard FormationDraft that we refer to as K-ScF. The age of the K-Pg

338 boundary accepted by us is 66.043 ± 0.043 Ma (Renne et al. 2013 modified by Sprain et al. 2014;

339 error includes decay constant uncertainty). Thus, the K-ScF has an estimated age-range of

340 ~66.88–66.04 Ma, a duration of ~840,000 yrs, and an average rate of sediment accumulation of

341 ~4.77 cm/ka. However, when the age of the 30n-29r magnetochron boundary (~66.20 Ma; 15 m

342 above the base of the ScF and 25 m below the K-Pg boundary) is also included in these

343 calculations, a significant difference in rates of sediment accumulation in the lower versus the

344 upper portions of the K-ScF is apparent. Using the age data presented above, the lower 15 m of

345 the K-ScF represents ~0.68 Ma and shows a low rate of ~2.20 cm/ka, whereas the upper 25 of

346 the K-ScF represents only ~0.16 Ma and exhibits a higher rate of ~15.63 cm/ka. These

347 differences are not unexpected given that the lower portions of the K-ScF are dominated by

348 deeply incised and stacked paleochannel deposits, which is compatible with an interpretation of

349 low sediment-accommodation and bypassing (Eberth and O’Connell 1995; Catuneanu and Sweet

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350 1999). In contrast, the upper portion of the K-ScF is dominated by rhythmically deposited

351 paleosols, paludal sediments, and well-spaced paleochannel sandstones (Eberth and O’Connell

352 1995), more typical of higher accommodation settings and histories.

353 Braman (2018) recognized two palynostratigraphic biozones in the K-ScF in the Red

354 Deer River valley. At Knudsen’s Farm, the lower one-half of the K-ScF falls within the

355 Reticorpus collaris-Parviprojectus reductus palynostratigraphic biozone (personal

356 communication, D.R. Braman, September, 2018). Accordingly, this biozone mostly encompasses

357 the uppermost 15 m of magnetozone 30n and possibly the lowermost 5 m of magnetozone 29r

358 (Lerbekmo and Braman 2002), and represents at least ~0.68 Ma of geologic time. Braman (2018)

359 also recognized a Triprojectus quadricretaeus-Wodehouseia amurensis palynostratigraphic

360 biozone above the R. collaris-P. reductusDraft biozone that encompasses the remaining upper 20 m of

361 the K-ScF at Knudsen’s Farm. It lies entirely within magnetochron 29r and likely represents

362 ~0.16 Ma of geologic time.

363 Eberth et al. (2013) documented the biostratigraphic distribution of K-ScF dinosaurs and

364 noted that 22 of 23 known macrofossil skeletons occur in the lowest one-half (20 m) of the K-

365 ScFm, thus coincident with the R. collaris-P. reductus palynostratigraphic biozone. The fossil

366 assemblage collected from this interval includes all known mega-herbivore skeletons from the

367 formation (the ceratopsian Triceratops, the ankylosaur Ankylosaurus, the leptoceratopsian

368 Leptoceratops, and a thescelosaurid) and the well-known KUA-1 vertebrate microfossil site. In

369 contrast, a well-preserved skeleton of Tyrannosaurus rex (TMP 1981.012.0001) and vertebrates

370 from the KUA-2 microfossil site were collected from the upper one-half of the K-ScF. These

371 specimens are assignable to the T. quadricretaeus-W. amurensis palynostratigraphic biozone of

372 Braman (2018) and lie within magnetochron 29r (Lerbekmo and Braman 2002). Because the

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373 occurrence of vertebrate fossils in the K-ScF is clearly biased toward the lowest and oldest

374 portions of the unit, its fossil assemblages provide poor opportunities to examine the composition

375 of vertebrate communities that existed during the last 0.1–0.2 Ma before the K-Pg boundary

376 event.

377

378 Frenchman Formation

379 Based on abundant magnetostratigraphic, palynostratigraphic, and sequence stratigraphic

380 data, the Frenchman Formation (FFm) of southeastern Alberta and southern Saskatchewan

381 appears to correlate entirely with the K-ScF of Alberta (Fig. 4; Catuneanu and Sweet 1999;

382 Lerbekmo 1999; Sweet et al. 1999; McIver 2002; Lerbekmo 2009; Braman 2018). Thus, we

383 propose that our estimated age range of Draft~66.88–66.04 Ma for the K-ScF at Knudsen’s Farm is

384 also a reasonable maximum age-range estimate for the FFm across southern Saskatchewan.

385 Because the FFm in Saskatchewan yields Triceratops material that has been assigned to the

386 geologically younger species, T. prorsus (Tokaryk 1986; Scannella et al. 2014), it is likely that

387 when species-specific remains of ceratopsians are found at time-equivalent horizons in the K-

388 ScF of Alberta, they too will be assignable to that taxon.

389

390 Hell Creek Formation (type area)

391 The Hell Creek Formation (HCF) of eastern Montana and the Dakotas has been well

392 studied largely because of its rich and stratigraphically diversified dinosaur and other vertebrate

393 assemblages, and its significance in studies of the K-Pg boundary (Hartman et al. 2002; Wilson

394 et al. 2014). The formation is ~85 m thick in the Hell Creek type area of Montana, and has been

395 divided into three, sub-equally thick lithostratigraphic units that were designated informally as

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396 the lower third (L3), middle third (M3), and upper third (U3)(Hartman et al. 2014; Scannella et

397 al. 2014; Fowler 2017). The top of the HCF has a broadly diachronous (younging) contact with

398 the overlying Fort Union Formation eastward into North Dakota, but in the Hell Creek type area,

399 it is essentially coincident with the K-Pg boundary (Renne et al. 2013; LeCain et al. 2014; Sprain

400 et al. 2014; Fowler 2017) and yields an age of 66.043 ± 0.043 Ma (Renne et al. 2013; Sprain et

401 al. 2014). In that same area, the 30n-29r magnetochron boundary is placed ~24 m below the top

402 of the formation, in the middle of a fluvial sandstone whose base marks the boundary between

403 M3 and L3 (LeCain et al. 2014). The lower 2/3 of the formation is assigned to magnetochron

404 30n, and the formation lies disconformably to unconformably on the kaolinitic Colgate Member

405 of the Fox Hills Formation (Hicks et al. 2002). The Colgate Member is regarded as the temporal

406 equivalent of the Whitemud in Alberta andDraft Saskatchewan, with its base marking the 30r-30n

407 magnetochron boundary and its top marking a regional drop in sea-level that resulted in

408 widespread kaolinization of paralic-to-nonmarine sediments (Lerbekmo 2009). Although the age

409 of the base of the Hell Creek Formation remains uncertain, we suggest that it is significantly

410 older than the base of the combined K-ScF/FFm interval in Canada (Fig. 4) for the following

411 reasons.

412 LeCain et al. (2014) place the 30n-29r magnetochron boundary in the middle of the Apex

413 Sandstone, ~24 m below the K-Pg boundary in the Hell Creek type area. Lerbekmo and Braman

414 (2002) place the 30n-29r magnetochron boundary ~25 m below the K-Pg boundary in the K-ScF

415 at Knudsen’s Farm. Lastly, Lerbekmo (1999) places the 30n-29r magnetochron boundary ~25 m

416 below the K-Pg boundary in the FFm at Wood Mountain, Saskatchewan (a relatively thick

417 expression of the formation in core). Given the similar thicknesses of the isochronous K-Pg–30n-

418 29r boundary interval in all three formations, the interval exhibits nearly identical rates of

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419 sediment accumulation in each region (~10.0 cm/ka). However, considering the much greater

420 down-section thickness of the Hell Creek Formation (at least twice that of the K-ScF and FFm)

421 in its type area (Hartman et al. 2014), it is highly likely that the basal strata of the Hell Creek

422 Formation are significantly older than the basal strata of the K-ScF and FFm, and therefore, that

423 the lowest strata in the HCF are equivalent in age (in whole or part) to the Battle Formation in

424 Alberta.

425 This simple chronostratigraphic hypothesis can be tested by examining two different sets

426 of biostratigraphic data that are shared by the three formations. First, Scannella et al. (2014)

427 proposed non-overlapping stratigraphic distributions for the two species of Triceratops in the

428 Hell Creek Formation type area. In their interpretation, T. horridus is restricted to L3 of the HCF

429 while T. prorsus is restricted to U3 of theDraft HCF, with “transitional” specimens of Triceratops

430 (specimens that exhibit combinations of morphological features of both T. horridus and T.

431 prorsus) occurring in the middle (M3) of the HCF (Fig. 4). The documented presence of T.

432 prorsus and apparent absence of T. horridus in the FFm (Tokaryk 1986; Scannella 2014), and the

433 coeval relationship of the FFm and K-ScF suggest that the latter two formations correlate

434 chronostratigraphically with all or part of U3 in the HCF, and that part of M3 and all of L3 are

435 likely older than either the K-ScF or FFm.

436 A second, more powerful biostratigraphic test of the hypothesis employs the

437 palynostratigraphic data of Braman (2018). Braman (2018) states that the Pseudoaquilapollenites

438 bertillonites palynomorph biozone is well represented in the lower Hell Creek Formation in the

439 type area, and that the overlying Striaticorpus pyriformis-Striatellipollis radiatus biozone is well

440 represented in the HCF below U3 (Fig. 4). In the Red Deer River valley section, Braman (2018,

441 fig. 3) assigns the P. bertillonites biozone to the Whitemud Member and the unconformity at the

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442 base of the Battle Formation, but also recognizes sporadic evidence for the biozone in locally

443 developed scour-fills at the base of the formation (Fig. 1C; personal communication, D.R.

444 Braman, September, 2018). He also assigns the overlying S. pyriformis-S. radiatus biozone to the

445 BFm, infers that the boundary between the S. pyriformis-S. radiates and R. collaris-P. reductus

446 biozones is coincident with the BFm-ScF contact (Fig. 4; Braman 2018, fig. 3), but also notes

447 that preservation of palynomorphs is extremely poor in the BFm. Finally, Braman (2018;

448 personal communication, September, 2018) recognizes that the R. collaris-P. reductus and T.

449 quadricretaeus-B. amurensis biozones (characterizing K-ScF and FFm) characterize U3 in the

450 Hell Creek Formation, but that the R. collaris-P. reductus zone may extend down into some

451 portion of M3.

452 Braman’s biozone distributions suggestDraft that (1) the base of the Hell Creek Formation is at

453 least as old as the base of the Battle Formation in southern Alberta (~67.20 Ma) and (2) all or

454 some of M3 in the HCF is older than the contact between the BFm and K-Scf (~66.88 Ma). The

455 estimated minimum age of ~67.20 Ma for the base of the Hell Creek Formation in Montana

456 suggests that the formation spans at least ~1.16 Ma, a slightly smaller time span than the ~1.36

457 Ma estimated by Hicks et al. (2002).

458

459 Summary and conclusions

460 Our high-precision U-Pb CA-ID-TIMS age of 66.936 ± 0.047/0.060/0.140 Ma for the

461 Battle bentonite is older and far more precise than any dates, ages, or estimates that have been

462 previously proposed for the Battle Formation. Given that the bentonite was collected from the

463 upper one-quarter of the formation, the U-Pb age presented here should be considered as an

464 approximate minimum for the BFm in the Red Deer River valley region. Applying a maximum

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465 estimated rate of sediment accumulation of ~1.40 cm/ka to the 4.5 m thick BFm in our field area,

466 we estimate that the formation spans a minimum of ~0.32 Ma, and accumulated from ~67.20–

467 66.88 Mya.

468 Combined with age data for the K-Pg boundary and a calibrated age-range for

469 magnetochron 30n, our age for the Battle bentonite allows us to assess a maximum age of ~66.88

470 Ma for the base of the overlying Scollard Formation, and an age range of ~66.88–66.04 Ma for

471 the K-ScF (the Cretaceous portion of the Scollard Formation).

472 Our age can also be combined with calibrated magneto- and palynostratigraphic data to

473 assess chronostratigraphic correlations among the Scollard, Frenchman (FFm) and Hell Creek

474 (HCF) formations. While these combined data support previous interpretations that equated the

475 age ranges of the K-ScF, the FFm, and theDraft upper one-third (U3) of the HCF with one another,

476 they indicate that the lower and middle portions of the Hell Creek Formation in Montana (L3 and

477 M3) are equivalent in age with all or part of the sub-Battle unconformity and the Battle

478 Formation of Alberta. In turn, this indicates that the base of the Hell Creek Formation in

479 Montana has a minimum age of ~67.20 Ma.

480 Increased precision in all of the chronostratigraphic relationships proposed here can be

481 achieved with additional U-Pb CA-ID-TIMS dating in all of these geographic areas, but

482 especially in the Hell Creek Formation of eastern Montana where ages for the L3-M3 and M3-

483 U3 boundaries are currently unknown. Significant improvements in correlation can also be

484 realized by clarifying and calibrating the lithostratigraphic expression of Braman’s (2018)

485 palynostratigraphic biozones in the Hell Creek Formation of Montana, as well as North and

486 South Dakota.

487

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488 Acknowledgements

489 SLK thanks the staff of the Jack Satterly Geochronology Laboratory for technical

490 support. DAE thanks David Evans, Dennis Braman, Caleb Brown, and James Gardner for

491 insightful discussions and comments on the manuscript. Allison Vitkus of the Royal Tyrrell

492 Museum of Palaeontology kindly provided assistance with Figure 1. We thank the reviewers and

493 editors of the Canadian Journal of Earth Sciences for their helpful criticisms of a previous draft

494 of this manuscript. The Government of Alberta provided significant financial support for this

495 component of the End-of-Dinosaurs Geochronology Project. The Tyrrell Museum Cooperating

496 Society provided financial support for travel, logistics, and publication, and we thank Patty

497 Ralrick of that organization. Any and all errors remain the responsibility of the authors.

498 Draft

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657 Figure Captions

658

659 Figure 1. Battle Formation at Knudsen’s Farm. (A) Distribution of the Battle Formation (BFm)

660 in Alberta. Field area location indicated by star. Other abbreviations: C, Calgary; D,

661 Drumheller; E, Edmonton; GP, Grande Prairie; RDR, Red Deer River; SCrk, Strawberry

662 Creek locality. (B) Google Earth satellite image (2010) of field area at Knudsen’s Farm,

663 west of Red Deer River. Red dot indicates sampling location. Red line indicates semi-

664 continuous exposure of BFm at this locality. White dotted line indicates the path of the

665 measured section illustrated in Figure 2. Measured section extends from the maximum

666 flooding surface (mfs) of the Drumheller Marine Tongue (DMT) up-section to just above

667 the Cretaceous-Paleogene (K-Pg)Draft boundary. Other abbreviations: m, meters; N, north. (C)

668 Battle Formation and Whitemud Member exposures at Griffith’s Farm, directly across the

669 Red Deer River from Knudsen’s Farm. Note scour-fill (sf) at the base of the Battle

670 Formation. Photo taken in 2003. (D) Close-up of weathered Battle bentonite horizon

671 (dashed line marks top) above the Kneehills “tuff”, a siliceous concretion horizon

672 throughout the region. Lens cap (6 cm). Photo taken in 2006.

673 Figure 2. Stratigraphic context for the Battle Formation (BFm) at Knudsen’s Farm in the Red

674 Deer River valley. Left column depicts the thickness and formal subdivisions of the

675 Horseshoe Canyon, Battle, and lower Scollard formations (data from Eberth and Braman

676 2012). Right hand column depicts a composite of two measured sections at and adjacent

677 to the Knudsen’s Farm locality. Outcrop at Knudsen’s Farm extends stratigraphically

678 from the base of the Tolman Member of the Horseshoe Canyon Formation upward to just

679 above the Cretaceous-Paleogene (K-Pg) boundary. The stratigraphic position of the

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680 Battle bentonite is indicated near the top of the formation. Abbreviations: B, bentonite; C,

681 Carbon Member; cl, claystone; cong, conglomerate; css, coarse sandstone; D, Drumheller

682 Member; DAE, measured-section field number; fss, fine sandstone; H, Horsethief

683 Member; M, Morrin Member; Ma, megaanum; mss, medium sandstone; sltst, siltstone;

684 SS, sandstone; T, Tolman Member; W and Wmd Mbr., Whitemud Member.

685 Figure 3. Graphic radioisotopic data. (A) Concordia diagram showing results of 11 single zircon

686 U-Pb CA-ID-TIMS analyses from the Battle bentonite at Knudsen’s Farm. (B) Plot of the

687 corresponding 206Pb/238U dates with the youngest three grains giving a calculated

688 weighted mean 206Pb/238U age of 66.936 ± 0.047/0.060/0.140 Ma (2σ; MSWD=0.42),

689 which is interpreted as the best approximation for the time of deposition of the Battle

690 bentonite. The dark horizontal lineDraft and associated grey band represent the weighted mean

691 age and 2σ error, respectively. (C) Photomicrograph of zircons from the Battle bentonite.

692 Figure 4. Chronostratigraphic correlation (65.5–69.0 Ma) of Maastrichtian–Paleocene formations

693 in Alberta, southern Saskatchewan, and eastern Montana. Superscripts indicate data

694 sources as follows: a, Sprain et al. (2014); b, Renne et al. (2013); c, this study; d, Ogg and

695 Hinnov (2012); e, Lerbekmo and Braman (2002); f, LeCain et. al (2014); g, Braman

696 (2018); h, Eberth and O’Connell (1995); i, Eberth and Braman (2012); j, Catuneanu and

697 Sweet (1999); k, Lerbekmo (1999); l, McIver (2002); m, Hartman et al. (2014); n,

698 Lerbekmo (2009); o, Scannella et al. (2014). Dashed lines and question marks indicate

699 age uncertainty. Arrows at top and bottom of columns indicate that a unit is incompletely

700 represented. Note the uncertain age ranges for (1) the sandy and muddy portions of the

701 Scollard Formation and (2) the three informal divisions of the Hell Creek Formation.

702 Abbreviations: AB, Alberta; BFm, Battle Formation; Fm, Formation; HCF, Hell Creek

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703 Formation; K-Pg, Cretaceous-Paleogene boundary; L3, lower third; Ma, megaanum; M3,

704 middle third; MT, Montana; n, normal; r, reversed; SK, Sakatchewan; T., Triceratops;

705 U3, upper third.

706 Table 1. U-Pb CA-ID-TIMS data for single zircon crystals from the Battle bentonite, upper one-

707 quarter of the Battle Formation, Knudsen’s Farm, southern Alberta, Canada (N51.90110

708 W113.01262).

Draft

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Draft

180x200mm (300 x 300 DPI)

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Table 1. U-Pb CA-ID-TIMS data for single zircon crystals from the "Battle bentonite," upper one-quarter of the Battle Formation, Knudsen's Farm, southern Alberta, Canada (N51.90110 W113.01262)

a) b) c) d) e) e) f) Age (Ma)

206 207 206 207 207 206 207 No. Weight PbC PbT/ U Th/U Pb/ Pb/ 2s Pb/* 2s Err Pb/* 2s Pb/ 2s Pb/* 2s Pb/* 2s 204 235 238 206 235 238 206 (mg) (pg) PbC (ppm) Pb U U Corr Pb U U Pb

Z1 16 0.8 10.6 50 0.49 679 0.06886 0.00090 0.010517 0.000014 0.714 0.04749 0.00057 67.62 0.85 67.441 0.091 74 29 Z2 10.1 1.9 7.4 133 0.42 486 0.06868 0.00044 0.010473 0.000013 0.763 0.04756 0.00026 67.45 0.41 67.161 0.080 78 13 Z3 4.3 1.0 12.3 259 0.56 770 0.06901 0.00041 0.010473 0.000012 0.712 0.04779 0.00025 67.76 0.39 67.160 0.079 89 12 Z4 3.8 1.2 32.4 934 0.41 2074 0.06869 0.00020 0.010468 0.000014 0.856 0.04759 0.00009 67.45 0.19 67.131 0.088 79 5 Z5 5.3 0.6 20.0 199 0.49 1261 0.06835 0.00063 0.010468 0.000012 0.656 0.04736 0.00040 67.13 0.60 67.129 0.079 67 20 Z6 4.7 0.5 20.6 194 0.49 1297 0.06863 0.00033 0.010463 0.000014 0.679 0.04757 0.00019 67.40 0.32 67.098 0.091 78 10 Z7 8.2 0.4 26.5 135 0.40 1705 0.06845 0.00120 0.010459 0.000016 0.667 0.04747 0.00079 67.23 1.14 67.071 0.102 73 39 Z8 9.4 0.5 34.3 177 0.44 2182 0.06822 0.00029 0.010456 0.000012 0.685 0.04732 0.00017 67.01 0.27 67.051 0.074 65 8 Z9 6.3 0.4 25.6 149 0.56 1582 0.06811 0.00042 0.010442 0.000012 0.560 0.04730 0.00026 66.90 0.40 66.965 0.079 65 13 Z10 4.3 0.9 17.2 313 0.64 1045 0.06831 0.00033 0.010435 0.000012 0.730 0.04748 0.00019 67.09 0.31 66.921 0.076 73 10 Z11 6.8 0.7 28.5 279 0.48 1794 0.06810 0.00028 Draft0.010435 0.000015 0.667 0.04733 0.00016 66.90 0.27 66.919 0.095 66 8 Notes: Zircon grains were chemically abraded ('CA', Mattinson, 2005). Errors are 2s absolute. a) total common Pb (in picograms); assumed isotopic composition of laboratory blank (206Pb/204Pb=18.49±0.4%; 207Pb/204Pb=15.59±0.4%;208Pb/204Pb=39.36±0.4%). b) ratio of total Pb in the analysis (radiogenic and common) to total common Pb c) Th/U calculated from radiogenic 208Pb/206Pb ratio and 207Pb/206Pb age assuming concordance. d) 206Pb/204Pb corrected for fractionation and common Pb in the spike. e) Pb/U ratios corrected for fractionation, common Pb in the spike, and blank. f) Error Corr is correlation coefficients of X-Y errors on the concordia plot. *Correction for 230Th disequilibrium in 206Pb/238U and 207Pb/206Pb assuming Th/U of 4.2 in the magma. Decay constants are those of Jaffey et al. (1971): 238U and 235U are 1.55125 x 10-10/yr and 9.8484 x 10-10/yr 238U/235U ratio of 137.88 used for 207Pb/206Pb model age calculation

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