Stratigraphic Position of a Late Cretaceous (Cenomanian) Bonebed, East-Central Saskatchewan I

Stratigraphic Position of a Late Cretaceous (Cenomanian) Bonebed, East-central Saskatchewan I

Stephen L. Cumbaa 2 and Harold N. Bryant 3

Cumbaa, S.L. and Bryant, H.N. (2001): Stratigraphic position ofa Late Cretaceous (~ enomanian) bonebed, east-central . Saskatchewan: in Summary of Investigations 200 I, Volume I, Saskatchewan Geolog1cal Survey, Sask. Energy Mmes, M 1sc. Rep. 2001-4.1.

1. Introduction Determining the source and position of the bonebed fragments was important to our biostratigraphic Rocks exposed along river banks in the Pasquia Hills studies. From their distribution along the river bank, a of east-central Saskatchewan record a nearly complete source at or near McNeil and Caldwell's (1981) sequence of Middle to Late Cretaceous (Albian to "Outcrop Section 21 ", a 5 m outcrop of Ashville Campanian) marine sedimentation (McNeil and Formation, Belle Fourche Member, was indicated, but Caldwell, 1981 ). These hills are the northernmost could not be confirmed. extension of the Manitoba Escarpment, which forms the eastern erosional edge of the Western Interior Basin Subsequent fieldwork in 1995 and 1997 (Cumbaa and in mid-continental North America, a relic of the Tokaryk, 1999; Schroder-Adams et al., 1999; Collom, Cretaceous Western Interior Seaway (WIS). The WIS 2000) pinpointed the only possible location for the was a rich and productive marine environment bonebed "float", a 20 to 25 m exposure slightly (Russell, 1989), and its fossil vertebrate biota has been upstream from Outcrop Section 21. This exposure of the subject of a joint Royal Saskatchewan Museum the Ashville (Belle Fourche Member) and overlying (RSM}--Canadian Museum of Nature (CMN) study Favel Formation and Morden Shale is partly slumped, since 1991 (Cumbaa and Tokaryk, 1999). but preserves a Cenomanian to Coniacian record.

A thin, but very concentrated vertebrate bonebed, in The exposure was given our field number BR-3 (RSM the form of a bioclastic conglomerate of Cenomanian locality number 63E09-0003). In measured sections age, was di scovered by Mr. Dickson Hardie along the (Schroder-Adams et al. , 1999; Collom, 2000), the Carrot River near Arborfield, Saskatchewan some bonebed was tentatively placed within the Belle years ago, and was the subject of our initial Fourche Member of the Ashville Formation, near the investigations. The age, the unique bird fauna base of the exposure on the basis of similarities in the (Tokaryk et al., 1997), and the diversity of this section to the lithology of non-calcareous shales bonebed were the impetus for our team to look farther adhering to chunks of recently-detached bonebed afield to see whether or not the formation of that "float", and micropaleontological evidence from the bonebed had been more than a local phenomenon. adhering shales.

Cumbaa et al. ( 1997) and Cumbaa and Tokaryk () 999) 2. A Problematical Bonebed also suggested placement of the bonebed within the Belle Fourche Member. Their rationale was based on a) Discovery and Context fauna! content (primarily shark teeth of species known only from Albian and/or Cenomanian contexts), Jack of In 1994, Tim Tokaryk (RSM), Richard Day (CMN), any fragments of the distinctive bonebed above the and Cumbaa discovered a rich bioclastic conglomerate Ashville-Favel contact, and the lithology of adhering as "float" in the bed of the Bainbridge River, 100 km shales as described above. A general description of the northeast of the Carrot River locality, on the stratigraphy of the locality follows. northeastern slope of the Pasquia Hills. The individual pieces of"float", some exceeding 100 kg in mass, contained bones and teeth of birds, vertebrae and limb b) Stratigraphy of the Locality elements ofplesiosaurs, fragments of turtle, and Below a 2 to 3 m cap of churned and/or recently hundreds of sharks' teeth, as well as teeth, vertebrae deposited sediment, the exposure at BR-3 is and other elements of bony fishes. These pieces of approximately 23 m thick, the uppermost 5 m conglomeratic-looking bonebed were unlike any rock (approximate) of which are the slightly to non type seen in place within the stratified exposures along calcareous shales of the Morden Shale above the the river. Marco Calcarenite, a regional marker bed (McNeil and Caldwell, 1981 )(Figure I).

I Research supported by a Canadian Museum of Nature Research Advisol)' Committee grant to Cumbaa and by Royal Saskatchewan Museum support to Bryant. 2 Canadian Museum of Nature, Paleobiology, P.O. Box 3443, Station D, Ottawa, ON KIP 6P4. ' Royal Saskatchewan Museum, Earth Sciences, 2340 Albert Street, Reg ina, SK S4P 3V7.

Saskatchewan Geological Survey 121 Fourche Member of the Ashville ":'. -··.:.. .-:.. - 22 --· ·· --- fz,:c:,:,~ cJ shale Fonnation. Thus, the base of the Q) -~

18 m Macco •-~~- ~::: 3. 2000 Field Season ;~~!: bioetastic 17 ~~~~r;;;;;,i;;;;i;;;;g Calcarenite - - - conglomerate In July 2000, Bryant and Cumbaa 1111')( (bonebed) visited several of the Pasquia Q) 16 .0 ~ ' ~ bi oturbation Hills localities. The Bainbridge E Q) 15 River locality was our principal c:: ~ objective, in hopes that spring Cl) Q) 14 ·2: ·ac flooding had eroded the slumped ....0 .0 base of the exposure enough to c ·c 13 ~ .Q 'iii clear it off and reveal the rJ) bonebed layer. Fortunately, that ni ~ 12 E proved to be the case and we u..0 11 were able to locate the bonebed ai in situ and re-measure the lower > - 10 Laurier u.."' J:;l~~~:c:J:::::z::i Limestone part of the section (Figure I). ... 9 Q) A puzzling question for the .0 E 8 research teams over the years had - Q) ~ been the inability to find the c:: ')('JI')( Cl) 'O 7 bonebed in situ on the cliff face, ·c in that the specimens detached as Cl) ~ 6 E "float" are common, sizeable, and 0 c:: 5 ·x· Bentonite among the hardest rocks in the (I) Q) () c .0 sequence. This elusiveness, and 0 (I) E 4 the shape of some of the " float" ~ Q) iii ~ pieces eventually convinced us _J E Q) 3 .9 u..0 .c that the " bonebed" had fonned as (I) e 2 isolated lenses. This appears to ~ :::, 'o 5 0 have been a reasonable inference, -0 .c u.. rJ) ~ as can be seen in Figure 2. There ::E ~ ai al were two "chunks'' ofbonebed in 0 place in the lower Ashville; both were thin and lenticular and in vft mc,,_0 s andstone r1;'li the same stratigraphic position, ~ but separated horizontally by ~<:J &<::' several barren metres. The top of the bonebed was 2.02 m below Figure 1 -Simplified stratigraphic diagram oft he section at field locality BR-3 the base of the "X" bentonite, and Bainbridge River, Pasquia Hills, Saskatchewan. Modified from Schroder-Ada/tis et al. its base was only 5 cm above the (19?9). Collom (2000) notes the position ofinoceramid marker species in his Figure 3, which corresponds in general terms to the stratigraphic relationships presented here. 5 cm thick Ostrea heloiti lag deposit. A thin (I cm) but Below the Morden Shale, most of the upper three persistent bentonite is exposed quarters of the exposure are relatively resistant, approximately 30 cm below the Ostrea beloiri lag. calcareous shales of the Favel Fonnation, and represent deposition during the peak of the Greenhorn Cyclothem. The Laurier Limestone, another regional 4. Discussion marker (McNeil and Caldwell, 1981 ), separates the two members of the Favel Formation (Figure I). a) Deposition of the Bonebed

A 3 1 to 33 cm thick bentonite is clearly visible about Similarities between the Ostrea beloiti layer and the 5 m above the base of the exposure, and is thought to bonebed strongly suggest their development as lag represent the "X" bentonite which is widespread across deposits in shallow water, under tidal influence. Both the Western Interior Basin. The "X'' bentonite has a layers have relatively smooth, fl at to undulating upper 40Ar/ 39Ar age of93.3 Ma (Cadrin, 1992; Obradovich, surfaces, which suggest broad wave or ripple marks. 1993). The ''X" bentonite and the Ostrea be/oiti bed The oysters in the lower layer are closely packed, below it are markers for the upper part of the Belle disarticulated and randomly oriented; the bonebed is more than 60% coprolites, bones, and teeth, all

122 Summary of Investigations 200 I, Volume I b) Vertebrate Fauna and Paleoenvironment An overview of the faunal assemblage and aspects of the paleoenvironment have been presented in several preliminary papers (Cumbaa et al., 1997; Cumbaa, 1999; and Cumbaa and Tokaryk, 1999).

Vertebrate Update

J.O. Stewart (Natural History Museum, Los Angeles County) and Cumbaa are preparing a paper comparing the fauna of the Bainbridge and Carrot River bonebeds with that of two Graneros Shale localities in Kansas collected by Stewart. These localities are Cenomanian and stratigraphically below the ''X" bentonite. The Figure 2 - lens of bioc/astic conglomerate (bonebed) in Belle Fourche Member of the Ashville Formation situ. Note speckles ofbentonite dropped down from eroding " ... correlates biostratigraphically with the Graneros "X" bentonite 2 m above top of bonebed. The Ostrea beloili Shale of the standard section, although the part above layer is prominent underneath the ho11ebed at left ce11ter of the 0. beloiti beds may equate to the lowest part of the photograph. Scale for reference is 5 cm. Part ofthe Lincoln Limestone Member of the Greenhorn bonehed lens 011 the right ofthe photo has broken offand has been lost to erosio11, as has any portio11 which may Fonnation" (McNeil and Caldwell, 1981 , p5 I). have exte11ded outfrom the face ofthe exposure. The lens extended an unknown distance back into the exposure; the The Graneros Shale in Kansas also includes bonebeds, portion retrieved was approximately 60 cm in length. in both the middle and at the base of the section (Hattin, 1965). Hattin notes well-preserved ripple disarticulated and randomly oriented. Both indicate marks in the middle part of the fonnation, and suggests tossing, winnowing, and re-mixing under sediment that bonebeds were produced by brief periods of starved conditions, in the absence of strong currents. turbulence from storms scouring the sea floor, resulting Several large pieces of the Ostrea be/oiti layer exhibit in concentration into lenses and layers of coarse scour-filling on the bottom. Similarly, the in situ organic debris that had originally been more widely bonebed lenses (see Figure 2) reveal what appears to scattered. be trough filling with vertebrate debris which became the bioclastic conglomerate. Ripple-marked troughs Like the Bainbridge River bonebed, the Kansas separated by a few metres are suggestive of nearshore examples contain abundant coprolites as well as a rich shallow coastal areas, which can have two or three fauna ofhybodont, ptychodont, and other sharks, in lines of sandbars close to shore, with deeper troughs addit ion to several rays. There is a good match between. between many of the chondrichthyan taxa in the bonebeds from Kansas and Saskatchewan, save for the Additional evidence of wave involvement in the paucity of rays in the Pasquia Hills bonebeds. fonnation of the bonebed deposit is the very common occurrence of calcite crystal-lined vugs filled with Newly identified material from the Bainbridge River bentonite. These are interpreted as "rip-up" clasts of bonebed includes a number of neopterygian fishes, bentonite; chunks of compacted and degraded volcanic again exhibiting similarities to the Graneros fauna. At ash were incorporated in the bioclastic material, least two genera of pycnodonts, shallow water mollusc apparently before consolidation of the sediment, grazers, occur in the Bainbridge deposits, as well as an because the enclosing matrix is frequently defonned amioid, probably a caturid. A new "prim itive" teleost, around the clast. One large, ovate vug in a piece of common to both the Graneros and Ashville bonebeds, bonebed "float" measured approximately 30 cm by is a Belonostomus-like aspidorhynchid. A full 12 cm. The source of the bentonite in these clasts is description of these taxa will be presented elsewhere. unknown, as the bonebed horizon is well below the "X" bentonite, and the closest stratigraphically is the 1 cm bentonite 30 cm below the Ostrea layer. Collom Paleoenvironmental Studies (2000) discusses possible origins of these bentonites. Oxygen isotope analysis on teeth from various WIS No more than 5 cm of soft, black shale separate the localities was used to attempt an indirect measurement Ostrea layer and the bonebed, but there is some of ocean paleotemperatures (M unroe, 2000). The evidence that deeper water conditions were briefly re enamel from Squalicorax and Enchodus teeth, established in the interval between the shallowing including samples from th e Carrot River and cycles. A very thin, but complete inoceramid valve, Bainbridge River bonebeds, were processed at the approximately 15 cm in diameter, was discovered in Stable Isotope Mass Spectrometry Laboratory at Yale this shale unit, near the contact with the Ostrea beloiti University. layer. It is in the process of being identified. The temperature values from the Pasquia Hills samples, at 3 1° to 42°C, are higher than would be expected of water temperatures at an approximate

Saskatchewan Geological Survey 123 paleolatitude of 45°. Present-day summer surface Hattin, D.E. ( 1965): Stratigraphy of the Graneros Shale temperatures range from 37° to 40°C and to more than (Upper Cretaceous) in central Kansas; State Geo!. 30°C in the restricted basins of the Dead Sea and Red Surv. Kansas, Bull. 178, 83p plus accomp. map. Sea, respectively. In the much less restricted basin of the Gulf of Mexico, summer surface temperatures Kauffman, E.G. ( 1977): Geological and biological along the coasts approach 32°C. Using the same overview: Western Interior Cretaceous Basin; Mtn. methodology, samples from the Niobrara Chalk of Geo!., vl4, no3-4, p75-99. Kansas produced temperature proxies of about 22°C, which are comparable with previous estimates (McNeil McNeil, D.H. and Caldwell, W.G.E. ( 1981 ): and Caldwell, 1981 ). However, it is important to note Cretaceous rocks and their Foram inifera in the that the Kansas fossils are IO million years younger Manitoba Escarpment; Geo!. Assoc. Can., Spec. than the Saskatchewan samples, and represent an open Pap. 21 , 439p. ocean paleoenvironment. Munro, L.E. (2000): 180 / 160 isotopes as temperature Munroe (2000) provides an interesting hypothesis for indicators in Late Cretaceous fossil shark and bony the high Pasquia Hills paleotemperature estimates. She fish teeth; unpubl. B.Sc. thesis, Carleton Univ., postulates a mechanism invo lving the gyre concept as 38p. elaborated by Kauffman ( 1977), whereby influx of warm water from the south, acting in concert with a Obradovich, J.D. ( 1993 ): A Cretaceous time scale; in highly stratified water column in the northeastern basin Caldwell, W.G.E. and Kauffman, E.G. (eds.), of the WIS (Schroder-Adams et al. , in press), kept the Evolution of the Western Interior Basin; Geo!. water temperature elevated. These conditions were Assoc. Can., Spec. Pap. 39, p379-396. amplified by high salinity, shallow water, relatively low annual rainfall, little fresh water input, and high Russell, D.A. (1989): An Odyssey in Time: The evapotranspiration rates in an overall wanner climate Dinosaurs of North America; Univ. Toronto Press than the present (Munro, 2000). More isotope work is (in assoc. with Nat. Mus. Natur. Sci.), 239p. planned to further investigate these preliminary results. Schroder-Adams, C.J., Leckie, D.A., Craig, J., and Bloch, J. (1999): Upper Cretaceous Colorado 5. References Group in the Pasquia Hills, northeastern Saskatchewan: A multidisciplinary study in Cadrin, A.A.J. ( 1992): Geochemistry and progress; in Summary of Investigations 1999, paleoenvironmental reconstruction of the Volume I, Saskatchewan Geological Survey, Cretaceous Greenhorn marine cyclothem in the Sask. Energy Mines, Misc. Rep. 99-4. l, p52-56. Western Interior Basin of Canada; unpubl. Ph.D. thesis, Univ. Saskatchewan, 19lp. Schroder-Adams, C.J., Cumbaa, S.L., Bloch, J., Leckie, D.A., Craig, J., Seif El-Dein, S.A., Collom, C.J. (2000): High-resolution stratigraphy, Simons, D-J.H.A.E., and Kenig, F. (in press): Late regional correlation, and report of molluscan Cretaceous (Cenomanian to Campanian) faunas: Colorado Group (Cenomanian-Coniacian paleoenvironmental history of the eastern interval, Late Cretaceous), east-central Canadian margin of the Western Interior Seaway: Saskatchewan; in Summary of Investigations Bonebeds and anoxic events; Palaeogeog., 2000, Volume I, Saskatchewan Geological Palaeoclim., Palaeoecol. Survey, Sask. Energy Mines, Misc. Rep. 2000-4.1, p82-97. Tokaryk, T.T., Cumbaa, S.L., and Storer, J.E. ( 1997): Early Late Cretaceous birds from Saskatchewan, Cumbaa, S.L. (1999): Paleoecological implications ofa Canada: The oldest diverse avifauna known from marine bonebed fauna from the Late Cretaceous North America. J. Vert. Paleo., vl7, pl72-176. (Cenomanian) of Saskatchewan, Canada; J. Vert. Paleo., v 19 (supp. to No. 3), p40A.

Cumbaa, S.L. and Tokaryk, T.T. (1999): Recent discoveries of Cretaceous marine vertebrates on the eastern margins of the Western Interior Seaway; in Summary of Investigations l 999, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 99-4.1, p57-63.

Cumbaa, S.L. , Tokaryk, T.T., Collom, C., Stewart, J.D., Ercit, T.S., and Day, R.G. (1997): A Cenomanian bone bed of marine origin, Saskatchewan, Canada; J. Vert. Paleo., v17 (supp. to No. 3), p40A.

124 Summary of Investigations 2001 , Volume 1