3TRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE UPPER &OX (ILLS AND LOWER (ELL #REEK &ORMATIONS AT THE #ONCORDIA (ADROSAUR 3ITE IN NORTHWESTERN 3OUTH $AKOTA -ARY # #OLSON 2USSELL / #OLSON AND 2ON .ELLERMOE -OORHEAD *UNIOR (IGH -OORHEAD -. 53! $EPARTMENT OF !NTHROPOLOGY AND %ARTH 3CIENCE -INNESOTA 3TATE 5NIVERSITY -OORHEAD -OORHEAD -. 53! $EPARTMENT OF "IOLOGY #ONCORDIA #OLLEGE -OORHEAD -. 53! !UTHOR TO WHOM CORRESPONDENCE SHOULD BE ADDRESSEDCOLSON MNSTATEEDU !"342!#4 -ANY OF THE DINOSAUR BEARING BONE BEDS IN THE (ELL #REEK &ORMATION OF THE $AKOTAS AND -ONTANA INVOLVE MULTIPLE SPECIES PRESERVED IN THE UPPER (ELL #REEK &ORMATION )N CONTRAST THE #ONCORDIA (ADROSAUR 3ITE IS MONO SPECIFIC WITH RESPECT TO DINOSAURIAN TAXA AND IS SITUATED IN THE LOWER (ELL #REEK &ORMATION IN A LITHOSTRATIGRAPHIC UNIT WE ASSOCIATE WITH THE ,ITTLE "EAVER #REEK -EMBER 4HIS MEMBER CONSISTS OF ORGANIC RICH SANDSTONES SILTSTONES AND CLAYSTONES THAT ARE DISTINCTIVE WITHIN THE (ELL #REEK &ORMATION BASED ON THEIR UNIFORMLY FINE GRAIN SIZE PUR PLISH COLOR AND PRESENCE OF HIGHLY LIGNITIC SHALE RATHER THAN COAL 3IMILAR LIGNITIC DEPOSITS OCCUR AT OTHER MARINEn TERRESTRIAL BOUNDARIES OF THE &OX (ILLSn(ELL #REEK &ORMATIONS IN THE ,ITTLE -ISSOURI AND -ISSOURI 2IVER VALLEYS 4HE BONE BED AT THE #ONCORDIA (ADROSAUR 3ITE #(3 IS ASSOCIATED WITH AN EXTENSIVE COASTAL SWAMP RATHER THAN A LOCALIZED FLUVIAL SUBENVIRONMENT SUCH AS RIVER CHANNEL FLOODPLAIN OR ABANDONED CHANNEL 4HE BONE BED ITSELF LIES AT THE TRANSITION FROM AN EXTENSIVE SWAMP REPRESENTED BY HIGHLY ORGANIC MUDSTONES TO A MORE FLUVIALLY DOMINATED DISTRIBUTARY ENVIRONMENT CHARACTERIZED BY VARIEGATED MUDSTONES SILTSTONES AND CHANNEL SANDSTONES 4HE THIRTY METERS OF EXPOSED SECTION AT THE #ONCORDIA SITE INCLUDE THE TOP OF THE &OX (ILLS &ORMATION AND LOWER PARTS OF THE (ELL #REEK &ORMATION 7E IDENTIFY MARINE SILTS MUDS AND SANDS COASTAL DUNE SANDS COASTAL SWAMP MUDS AND SILTS AND FLUVIAL SANDS AND SILTS 4HE SEDIMENTS ARE INDICATIVE OF THE MARINEnTERRESTRIAL TRANSITION FROM UPPER SHORE FACE AND FORESHORE ENVIRONMENTS TO A COMPLEX SYSTEM OF COASTAL DUNES SWAMPS AND DISTRIBUTARY CHANNELS THAT FORMED DURING THEPROGRADATION OF THE(ELL #REEK SEDIMENTS INTO THE#RETACEOUS &OX (ILLS SEAWAY ,OCALLY GRAIN SIZE ANDORGANIC FRACTION VARIED DUE TO DIFFERENCES IN THE PROXIMITY TO DISTRIBUTARY CHANNELS SUPPLY OF ORGANIC MATERIAL AND WATER DEPTH $ESPITE THE CONCENTRATION OF BONES DOMINATED BY A SINGLE SPECIES IN THE #(3 BONE BED THE HIGH CLAY FRACTION OF THE BONE BED MATRIX COMBINED WITH THE FACT THAT THE LOWEST PART OF THE BONE BED HAS THE GREATEST CLAY FRACTION INDI CATES THAT THE BONES WERE NOT INTRODUCED BY WAY OF A HIGH ENERGY CATASTROPHIC EVENT SUCH AS A FLOOD 2ATHER THE BONES ACCUMULATED IN AN AREA OF QUIET STANDING WATER !LTHOUGH PRELIMINARY EXAMINATION OF THE BONES IS CONSISTENT WITH THIS DEPOSITIONAL INTERPRETATION IT DOES NOT NECESSARILY PROVIDE DIRECT SUPPORT FOR IT +%9 7/2$3 COASTAL PROGRADATION #RETACEOUS %DMONTOSAURUS &OX (ILLS &ORMATION (ELL #REEK &ORMATION -AASTRICHTIAN .ORTH $AKOTA 3OUTH $AKOTA ).42/$5#4)/. INTERPRET NINE DEPOSITIONAL UNITS EXPOSED AT THE #(3 THAT 4HE PURPOSES OF THIS PAPER ARE TO DOCUMENT THE DEPO SPAN THE UPPER &OX (ILLS &ORMATION AND THE LOWER (ELL SITIONAL ENVIRONMENTS ACROSS THE &OX (ILLSn(ELL #REEK FOR #REEK &ORMATION /THER MARINEnTERRESTRIAL TRANSITIONS MATIONAL CONTACT AT THE #ONCORDIA (ADROSAUR 3ITE #(3 IN THE LOWER (ELL #REEK &ORMATION ARE ALSO EXAMINED ANDTODISCUSSTHERELATIONSHIPOFDEPOSITIONALENVIRONMENTS 4HE #(3 IS LOCATED IN A BLUFF ALONG THE 'RAND 2IVER TO THE PRESERVATION OF THIS RICH BONE BED 7E DESCRIBE AND IN #ORSON #OUNTY OF NORTHWESTERN 3OUTH $AKOTA 4HE 2OCKY -OUNTAIN 'EOLOGY V NO P n FIGS TABLES $ECEMBER - # #/,3/. 2 / #/,3/. !.$ 2 .%,,%2-/% BONE BED IS IN THE (ELL #REEK &ORMATION FIVEMETERS ABOVE REPORTED THAT FLOOD PLAIN AND CHANNEL DEPOSITS IN THE (ELL ITS CONTACT WITH THE &OX (ILLS &ORMATION 4HE BONE BED #REEK &ORMATION OF EASTERN -ONTANA AND WESTERN .ORTH IS CM THICK AND EXTENDS THE ENTIRE METER LENGTH $AKOTA PRESERVE THE LARGEST FRACTION OF THE TOTAL DINOSAU OF THE BLUFF !PPROXIMATELY SQUARE FEET OF THE BONE RIAN FAUNA WITH MEMBERS OF AT LEAST EIGHT FAMILIES REPRE BED HAVE BEEN EXCAVATED AT THE EAST END OF THE BLUFF PRI SENTED MARILY FROM TWO QUARRIES YIELDING NEARLY HADROSAUR BONES IDENTIFIED AS %DMONTOSAURUS #OLLECTED SPECIMENS ARE HOUSED AT #ONCORDIA #OLLEGE 342!4)'2!0()# 3%44).' $ISCOVERIES IN THE#(3 ADD SIGNIFICANTLY TO OUR UNDER STANDING OF ,ATE #RETACEOUS ENVIRONMENTS IN NORTHWEST )NTRODUCTION ERN 3OUTH $AKOTA 4HE #(3 IS LOCATED IN EASTERN PARTS OF 4HE &OX (ILLSn(ELL #REEK FORMATIONAL TRANSITION THE (ELL #REEK &ORMATIONS OUTCROP AREA OF 3OUTH $AKOTA RECORDS THE INTERMINGLING OF MARINE BRACKISH AND TER IN A LESS STUDIED AREA THAN OTHER EXPOSURES OF THE FORMA RESTRIAL PALEO ENVIRONMENTS AS THEIR REPRESENTATIVE SEDI TION *OHNSON ET AL )T IS SITUATED JUST ABOVE THE MENTS PROGRADED TOWARD THE #RETACEOUS 7ESTERN )NTERIOR MARINEnTERRESTRIAL TRANSITION FROM THE UPPER PART OF THE 3EAWAY 4HE CONTACT BETWEEN THE TWO FORMATIONS AND THE &OX (ILLS &ORMATION INTO THE LOWER PART OF THE (ELL #REEK STRATA ABOVE AND BELOW IT HAVE BEEN WELL STUDIED IN WEST &ORMATION 3EDIMENTOLOGICAL CHARACTERISTICS OF THE #(3 ERN AND SOUTH CENTRAL .ORTH $AKOTA &RYE +LETT SANDSTONES MUDSTONES AND BONE BED DIFFER SIGNIFICANTLY AND %RICKSON 7ROBLEWSKI -URPHY ET AL FROM OTHER (ELL #REEK DINOSAUR BEARING SITES WHICH ARE AND IN NORTH CENTRAL 3OUTH $AKOTA 7AAGE FOUND MOSTLY IN THE UPPER (ELL #REEK &ORMATION 4HE #HRISTIANS 0ALEOGEOGRAPHICALLY THE &OX (ILLS AND SEDIMENTOLOGY ALSO DIFFERS FROM OTHER BONE BEARING SITES IN (ELL #REEK &ORMATIONS OF NORTHWESTERN 3OUTH $AKOTA REP THE LOWER (ELL #REEK &ORMATION THAT ARE WITHIN A FEW MILES RESENTCOASTAL PLAINFACIES2OBERTSAND+IRSCHBAUM OF THE #(3 4HOSE SITES ARE UP SECTION NEAR THE &IRESTEEL 4HE DETAILED STRATIGRAPHY OF LOWER UNITS IN THE (ELL #OAL AND THEY CONTAIN A GREATER TAXONOMIC DIVERSITY OF #REEK &ORMATION THAT CONTAINS THE #(3 IS NOT WELL DOC DINOSAURS THAN DOES THE #(3 *ACOBSON AND 3ROKA UMENTED AND IT WAS SIMPLY MAPPED AS UNDIFFERENTIATED 4HE #(3 BONE BED DIFFERS FROM TYPICAL DINOSAUR LOWER (ELL #REEK BY #URTISS &URTHERMORE THE BEARING SITES OF THE (ELL #REEK &ORMATION IN THREE WAYS #(3 IS FIVE MILES WEST OF 7AAGES WESTERN MOST MAPPED )T IS IN LOWER RATHER THAN UPPER PARTS OF THE (ELL #REEK OCCURRENCE OF THE &OX (ILLS &ORMATION IN THE 'RAND 2IVER &ORMATION IT HAS A LOWER DIVERSITY OF DINOSAURS AND IT DOES VALLEY 7AAGE FIG "ASED ON OUR FORMATIONAL NOT OCCUR IN A PRIMARILY FLUVIAL DEPOSIT -ANY OF THE BEST COMPARISON AT THE #(3 WITH OTHER SITES IN SOUTHERN .ORTH DOCUMENTED VERTEBRATE SITES OF THE (ELL #REEK &ORMATION $AKOTA AND NORTHWESTERN 3OUTH $AKOTA WE PLACE STRATA OCCUR IN ITS UPPER PART )N EASTERN -ONTANA THIS IS DUE IN OF THE BLUFF IN THE UPPER &OX (ILLS AND LOWER (ELL #REEK PART TO STRATIGRAPHIC BIAS IN SAMPLING OF THE UPPER M OF &ORMATIONS 4HE STRATIGRAPHIC NOMENCLATURE OF &RYE THE (ELL #REEK &ORMATION WHERE OUTCROPS ARE LESS RUGGED IS APPLIED TO THE (ELL #REEK &ORMATION &IG AND MORE EASILY ACCESSIBLE THAN OUTCROPS IN THE LOWER PART AND WE USE THE NOMENCLATURE OF 7AAGE FOR THE &OX OF THE FORMATION #LEMENS !NOTHER BIAS MAY (ILLS &ORMATION ,ITHOSTRATIGRAPHICALLY THE #ONCORDIA BE DUE IN PART TO GREATER INTEREST IN EVENTS RELATED TO THE (ADROSAUR 3ITE IS IN THE 4IMBER ,AKE AND )RON ,IGHTNING #RETACEOUSn4ERTIARY BOUNDARY AS RECORDED AT THE TOP OF -EMBERS OF THE &OX (ILLS &ORMATION AND IN THE ,ITTLE THE FORMATION &ASTOVSKY AND $OTT &ASTOVSKY "EAVER #REEK -EMBER &RYES NOMENCLATURE OF THE LOWER .ICHOLS AND &LEMING *OHNSON AND (ICKEY (ELL #REEK &ORMATION &IORILLO *OHNSON ET AL )N SOUTHWEST ERN .ORTH $AKOTA -URPHY ET AL REPORTED THAT &OX (ILLS &ORMATION OF 3OUTH AND .ORTH $AKOTA DINOSAURIAN FOSSILS ARE FOUND PREDOMINANTLY IN THE MIDDLE 7AAGE STUDIED THE SEDIMENTOLOGY AND PALE TO UPPER PARTS OF THE (ELL #REEK &ORMATION 4HESE REMAINS ONTOLOGY OF THE &OX (ILLS &ORMATION OF THE 'RAND ARE FOUND IN FLUVIAL STRATA AND INCLUDE MANY SPECIES &RYE AND -OREAU 2IVER VALLEYS OF 3OUTH $AKOTA :IEBACH -OORE "UTLER &ASTOVSKY AND $OTT WESTERN $EWEY AND EASTERN #ORSON #OUNTIES (E &ASTOVSKY *OHNSON AND (ICKEY DIVIDED THE &OX (ILLS &ORMATION INTO THREE MEMBERS (OGANSON ET AL /AKLAND AND 0EARSON &IG AND DOCUMENTED A PROGRESSIVE hFRESHENINGv &IORILLO 7HITE ET AL 7HITE ET AL AS THE MARINE ENVIRONMENTS REPRESENTATIVE OF THE LOW 2OCKY -OUNTAIN 'EOLOGY V NO P n FIGS TABLES $ECEMBER 342!4)'2!0(9 !.$ $%0/3)4)/.!, %.6)2/.-%.43 /& 4(% #/.#/2$)! (!$2/3!52 3)4% ! ! "# $ % !& # !" # $% ' # " ( ( )$*+ !' # ! & ( " ! ! ", # $ ( ( ! %! -! . ! ! , ' #/ &IGURE 3TRATIGRAPHIC NOMENCLATURE AND BRIEF LITHOLOGIC DESCRIPTIONS FOR &OX (ILLS &ORMATION OF 3OUTH $AKOTA AND (ELL #REEK &ORMATION OF .ORTH $AKOTA !STERISKS INDICATE ROCK UNITS PRESENT AT #ONCORDIA (ADROSAUR 3ITE ERMOST 4RAIL #ITY -EMBER CHANGED UP SECTION TO THE &ORMATION (E INTERPRETED THE UPPER &OX (ILLS AND LOWER BRACKISH CONDITIONS OF THE )RON ,IGHTNING -EMBER (ELL #REEK &ORMATIONS TO BE DELTAIC FACIES ! VARIANT OF 7AAGE DIVIDED BOTH THE TOP AND BOTTOM MEMBERS THE #OLGATE LITHOFACIES FOUND IN %MMONS #OUNTY .ORTH INTO TWO LITHOFACIES TO ACCOMMODATE LATERAL VARIABILITY $AKOTA WAS DOCUMENTED BY +LETT AND %RICKSON WITHIN EACH MEMBER &IG 7AAGE P NOTED AND ASSIGNED THE NAME ,INTON