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Home My WebLink AboutGMC Data Report No. 250 Chronostratigraphic summaries based on palynological content of cuttings from the following Copper River Basin oil and gas exploratory wells: Aledo Oil Company Eureka No.2 (2,000' - 7,900'), Amoco Production Co. Ahtna Inc. No.1 (2,000' - 7,000'), Mobil Oil Corp. Salmonberry Lake Unit No.1 (1,500' - 7,800'), Pan American Moose Creek Unit No.1 (1,980' - 7,860'), and Union Oil Company of Cali fomi a Tazlina No.1 (2,670' - 8,837'). r~ GE~O'¿Q (~~ ~ ~ ( (;:I:) 0 Received 17 July 1995 Total of 6 pages in report Alaska Geologic Materials Center Data Report No. 250 CHRONOSTRA TIGRAPffiC SUMl'dARIES The chronostratigraphic interpretation of these wells based on palynological content is rather broad, and should be considered subject to revision as further infonnation becomes available. Overall, the wells contain few taxa having stratigraphic ranges adequately constrained by previous documentation; no published information on biostratigraphy from this basin is known to me. Certain anomalies and observed ranges appearing to conflict with published data from elsewhere, coupled with the presence of apparently undescribed taxa complicate the interpretation further. Individual instances of these problems will be discussed as appropriate in the well summaries that follow. These chronostratigraphic summaries are to be considered current best estimates of ages based on observen distributions of particular t~a. . , fan flMt-r/ca n fi;1 tJt>?e. (3r-ee/:. W n/r ;Vt), I MOOSE CREEK #1 ' , The examined section of the Moose Creek #1 well covers an interval from 1980- 7860' measured depth, with ·i~aividual samples ~omI'os'ited ovét intervals generally of 100-150'. A few,gaps occur ~J1th~ sample .c()yer,+ge,)ndic~ted by blank intervals pn the distri~ution chart. ' T~e interP~eted '~hr~riostr~tigraphy i~:, ' ',' , ' . 1980~3180' , proQabl,e çé,borriàn,iciri . 3180~5050'? A' tianJAlbi,', ," ' , "p"., "~ ' : 5170-6280' Hauten VHuiJ?Bårremian 6329~-7860" age :~n.ç~rtå,iIL' ,,' , ' , . .1 . -I ¡', ,',' , The probabie C~nomani~!int~ryâ1,(1980~3l80') is do~n(ited bY:,nÖnmarine taxa, es'pecially indeterq¡inate 'bisac'(:at,é 'gymnospèrmous 'pollen~' and including the spore sp'ecies Plicatella potomacèn'sis,P.' cristata,Costatoperforosporites foveolatus, Foveosporites cf. cenomanžcus and, near the base of the interval, Cicatricosisporites crassiterminatus. The latter speci7s is widely recorded in Cenomanian strata in central c..O~~t.<"~"L\I\:.~ . ßÞr~tN ·A \..,1; $~~ F -«.0 ~WS~~ ·t.U' T 1-.Nc;~ GMC Data Report No. 250 1/6 North America, and the others cited also are characteristic of mid-Cretaceous assemblages. Taxa known to be limited to Albian and older strata were not seen in this interval. Marine dinoflagellate cysts are present, but are confined to fonns of the genera Spiniferites, Impletosphaeridium and Circulodinium, and do not contain species of usefully limited stratigraphic occurrence. The placement of the Albian-Cenomanian boundary at 3180' is based on a conspicuous event revealed by the correlation coefficient matrix for this well , . It could comfortably be placed as low as 3400' based on the distribution of individual taxa, in particular the uppermost occurrence of Impardecispora apiverrucata. In this interval, other observed forms characteristic of Aptian/Albian strata include Foveosporites pantostiktos, Omamentifera baculata, O. echinata, Concavissimisporites variverrucatus, Callialasporites dampieri and Couperisporites complexus. Dinoflagellate cysts are somewhat more abundant in this interval than they are above, and include various forms assignable to Cribroperidinium, Odontochitina operculata, Oligosphaeridium sp. - indet., Dinopterygium? sp. - indet., and the uppennost occurrence of a peculiar dinoflagellate designated here as cf. Balcattia sp. 1. :' :" Tþe interval from 517o.~6~80t,; ,is cons~dered Hauterivian!?;Sarrerni~.in ,~ge. The pl~qemeri t' of the boundary, ag¡;µn coincides ,with an 'event delin~ated b'y 'ithe '':QITeJation êoeffici'etlt matrix.: '" Dinoflagellate' cysts bécôm~'consþic~öÜ~ly~or.e" å1?un~ant ~nd diverse: in this inte,rval théiI1, in, ,the, intervals, ab,ove,¡ and' iQc1ude . fprtns '~uch as Hy'$trichosphderinq ~¢.hindew(}lfii"Floreniinia cooksoniae,' Nelchinoþsis ¡¿ostromiensis (a 'Ùseful H,auterivÜÙi' "indicator on' the Alaska North Slope), Prolixosphaeridium parvispinum, 'U}d ap p:qundaI}pe q~ cf. ~alcattia sp. ~: ! ',' ','. . , '. . '" . I , , .' i Below'6320t~.'theobs~rved p~y~ológiè~asseIhblage consls.ts o,f a nch anddiv;erse poptilatibÌlof'~aleocene pölleÍt' arid spores con~id~red.·tò b~ contaminants from Ft.;Union lignites,whìch are commonly. used as mud. additives~ I No 'qlearly. in. situ ta~a, were óbserved, and below tlûs horiz():~ t~e,age ,of the stra~a must.. be considered ùncert,aiÍl~ . /) n ,'~ ,,0 i Ie ("'1 Ii vii of Ltd/f 01' '" /¿è T" ~ /, >,;, C4 /r/ p, / TAZLINA#l ' . " '. , ,',," " "'0,'. ¡. ", ,r. : I', f', ' ,'..,' . " The examined. section of. tbe Tazlina #1 well covers ari'interval from 2670-8837 measured depth, with individual samples composited over intervals generally of 150'. Again there are a few gaps occur in, the sample.coverage, indicated by blank intervals on thèdistributiOn chart.; The interpreted:chronQstr~tigraphy is: . .,. , , 2670;-5520' ?Cenomanian-SantQni~, 5820-6570' probableNeocÒrniari 6570~8837 . ?middle Jurassic . The interval from 2670~5520' contains a mixture of late Cretaceous marine and nonmarine taxa, within which, chronostratigraph~c' boundaries are difficult to ,place with confidence. The presence of Odontochitina porif~ras~ggests. an age, of Santonian for at least ,the. upper. part of the interval, as does· ,the 'extremely "r~repres'ence of Aquilapollenites spp., so long as these taxa are ~ò~ cay~d :.from overlYIng s.trata. ,.Most constituents of the overall assemblage observed In thIS Interval are stratIgraphIcally nondis tinctì ve. . At,5820' arid continuing downward is an assemblage containiI),g the spore species Cdntignisporites glebulentus, a form most commonly, recorded from Neo~omia? strata worldwide. Deltoidospora spp. become conspicuously more abundant than In the Interval GMC Data Report No. 250 2/6 above, although this characteristic of the assemblage is not strongly age-diagnostic. As above, most components of the population are long-ranging forms having little individual stratigraphic value. Below 6570' the palynomorph population is rich and diverse, and consists dominantly of nonmarine forms (the few marine forms seen may be caved from above). Deltoidospora spp. dominate throughout the interval, along with consistent occurrences of Eucommiidites troedssOllii and a form closely resembling (probably conspecific to) Micro reticula tisporites fuscus, a form not known with certainty to range above middle Jurassic strata. The absence of well-known late Jurassic taxa suggests that this interval should be regarded as middle or possibly early Jurassic. The 6570' depth horizon coincides with a conspicuous boundary-signature event on the correlation coefficient matrix 11 !'10CfH:::1t t,'ð"" eM/"! 1110 1v>C<.. I ý/C. AJo. I Samples from the Ahtna #1 well were consistently the richest and most diverse of ~qy ~eH, ~xarrµ.ned in :this project. ,Sam;ples wcre compo,sited unifqrrp.ly to 100' ,intervals over a,' 'totaldeptl1" 'Ü1t,e'r,va1.'bf 2000'.. 7,obo'~ , witti" no" gaps.'. Tqè: "irittÚ'p"reted êhonosttatigraphy is: : I , i,'" ":', ',I "', ",:" ", : " , ': : " '~ I ' 2000, :,~2900' Cenpmanian.. ?Santonian , : ,," , "I " I. , I :' . I, .. 2900..5600", 7A.piian-Albian .," .,' 56{)O-6900" Neo.cdlniari.- ?Barren1Ían' , , 69bO~7000'?,Jurasslc,(probáble Iiµddle Qr 'early) : , '.'. ,'" ..,' '" : ~ " i , " " . . ~ '. ' , " ' , " ' ,'. , " .' :.' , '.,' "',: , ~.' ", :', ',:, 'As inthe MÒose C~èek w~ll, th~, uppermost interval (2000-2900') ìnAhtna:'#l cqntains a mix of fotms,:with somewhat ,colitradictory knöwn, ranges of stratigraphj;c ocçurrerice, inclqdirig: ',singlespecimells q'f Contignisporites . glebuléntus' and TaurocÙsporites segmeiztCztus (usually regard:ed· as Early'· Cietaceou's indicàtors) and A..qíÛlapollenites trialatus (Santonian..Campanian). The fonner species may be reworked, or the latter may be caved. The consistent presence in abundance of p,istaltriangulisporites perplexus, an indicator of Cenomanian and older strata on the AlàskaNorth Slope, suggests a Cenomanian interpretation for the entire interval, if the occurrence of A. trialatus is frQm caved m~terial. The þoundary,at 2900' is: ,a conspicuous horizon.: on the correlaÙon coefficient matrix ' , " , , .., '. ',' . , ! . i; , . ' " ... Strata, frO:m2900-5600' are considered, ?Aptian..Albian , in 'age, and the palynomorph popÚ18.iion from this interval includes such conspicuous Albian and older forms as Rogalskaisporites cicatricosus, Callialasporites turbatus, Impardecispora marylandensis, 1., :exca.va,ta; : Forarninisporis 'wonthaggiensis, Stoverisporites lunaris and Ornamentifera . ,ec,hiriata., Among thedìnoflagellate cysts is Senoniasphaera cf. microreticulata; S.'microreticulata' sensu strièto is characteristic of Aptian and slightly . older strata on the Alaska North Slope. The uppermost occurrence of Hystrichosphaerina schindewolfii at 5100' may signify Barrenùanstrata, but there issome uncertainty about ,the range of this dinoflagellate cyst in Alaska. . ' A conspic-qou~ correlation coefficientbourtdary at 5600' is used for placement' of the Neocomian- ?Barremianl? Aptian-Albian boundary in this well. Below 5600' a very rich, di,verse "assernblage òf mixed dinoflagellate cysts and. pollen/spores is present, incJuding abundant occurrences of cf. Balcattia sp. 1 (note -- designated as "Bal,cattia? sp:. - reduced ornament" on Enclosure 3) and an apparent elongated vanant, of Prolixosphaeridium parvispinum, the latter not observed in any othèr well. Age GMC Data Report No, 250 3/6 detennination of this interval is somewhat conjectural, as it is lacking in well-understood stratigraphic indicators. . The lowermost sample in the well (6900-7000') contains a single occurrence of Microreticulatisporites fuscus, and is regarded as questionably Jurassic on this basis. f! ¡eel?> ()/I f~ VY1t~'77 Et<..f'efcz A..}V('< EUREKA~ ~~ Samples from Eureka #1 were composited at 100' intervals over a total depth interval of 2000-7900', with several gaps in the lower portion of the well as indicated on Enclosure 4. The interpreted chronostratigraphy is: 2000-4600' ?Turonian- ?Santonian 4600-6700' Albian- ?Cenomanian 6800- 7900' age uncertain The uppermost interval (2000-4600') contains a mixed marine-nonmarine ~ss~wblage inclupiIlg~ ,t~e ,dippf1~gellat~ cyst,~ . ChatClngielIa cf., ditissimcz, Odontochitina QP~tè~larq':ari?Xen(¡~cus cf.1 cërátiàid(d~' 'C.' ditisslm'å sensu stficto' ¡is present consistently Íil IJÛ'd-Campàhian: ~o Santonian strata in the North Slope. As a group, Chatangiella spp. range downward i,:t;1.to str~ta~s ,91d: a~. ~µrq~i~µ ini,~Qme, plac,es.. Certain of the spore ~p~~iesptesent iri 'this ,iritebal'(~~g., 1)i$t(lltriang~li~pq~it~s 'perplexu$, D. mutabilis, F'orami'nispàris 'w'ôiithag g'te'nsis,CallialasporiÚ!s dampieri, .: I Sestrosporites pseudoalveolatus) are usually suggestive of slightly older strata, but their uppermost l'ange.:of occurrence may differ here, or there may be some reworking. The lower bburicl.aiycorresponds to a conspicuous event signature on the correlation coefficient matrix .' ". . . ' ~.: ,¡ I ' :' _ '. " . . , .' , !,.., f " ,From 460.o-6700"'¡ ¡ the .palynologica~ assemblage more clearly consists Qf characteristic mid~Cretace6Ús' (A1biân~Cenöm.attian) taxa, such as Canningia colliveri, Cicatricosisporites crassitennir¡.atusand Plicat~llafucosa . I. I ',\,' " ','¡ '.' r . The 10werrpos~,'ÌnterVärin the .well (6800-6900') was only sparsely fossiliferous, and it is possible thateven these s'parsel fossils represent material caved from strata above. Two samples. were~ntirely barren, andtl1e others nearly so. The age i~ regarded therefore 'as uncertain. . ,. .", .. .. ':, '.. ",', M /) /; J¡Pi/r.:(}r-~ ,$Ú,,,,,, '" 6 Ii r7.· ... . Ú/; e. ,'¿¡VI d, "vt' r} SAtMONBÉRRY LAKE #1,. ' . : . ',' . ( J', . . Overall~ assemblages from the Salmonb:errÿLake #1 weÙwere the least diverse of any of the wells. ~amples cOnsiste,d uniforriùy of 100' composites over a tot'al interVal.of 1500~ 7800', with no sample gaps. 'Th~ ,interpretedcw()nostratigraphy is: . 1500~1900' Tertiary, u'ndifferentiated 1900.;.3100' Cenomaniàn- ?younger 31 00-7800' ?~ddle Jurassic . T~e ,uppennbst, i~tervaJ ~~nt,ains an, exclusivel'y,nonmari~e assem?l~ge, ín~l~d~ng charactenstlc long-rangln'g TertIary pollen such as Tzlzaepollenztes vesczpztes, Erzczpztes sp.,,13etulaceoipo?lenites group and Alnipollenites verus. This assemblage was not oþ~erved· in any other well. . GMC Data Report No. 250 4/6 A Cretaceous interval interpreted as Cenomanian- ?younger, characterized by a relative abundance of Džstaltriangulisporites perplexus is present from 1900-3100', This interval contains little else in the way of stratigraphically distinctive forms, and is dominated by material of nonmarine origin. Rare occurrences of Tertiary pollen, such as Alnipollenites verus, are probably caved. The longest interval in the well (3100-7800') consists of a relatively sparse and dominantly nonmarine ?middle Jurassic assemblage, of which Microreticulatisporites fuscus is the key element. GMC Data Report No. 250 ,', I 5/6 CORRELATIONS Figure 1 below shows diagramatically the inferred stratigraphic relationships among wells examined for this project, along with depths of interpreted boundaries. xxx TERllARY Cenomanian- ?Santonian ? Aptian- Albian Neocomian- Barremian ?Middle JURASSIC i I- I : uncertain --- GMC Data Report No. 250 MOOSE CREEK # 1 TAZLlNA #1 AHTNA#1 Figure 1 .J.l 2 SALMONBERRY EUREKA #i LAKE #1 ~!t~~fI\~;, .. ... . \~ , ~ 1 i' I' r~ ,,, 11 ~~~tl ~ 6/6