Cretaceous Ammonites From the Lower Part of The Matanuska Formation Southern Alaska GEOLOGICAL SURVEY PROFESSIONAL PAPER 547 Cretaceous Ammonites From the Lower Part of The Matanuska Formation Southern Alaska By DAVID L. JONES With a STRATIGRAPHIC SUMMARY By ARTHUR GRANTZ GEOLOGICAL SURVEY PROFESSIONAL PAPER 547 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. GS 66-286 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $1.25 (paper cover) CONTENTS Page Page Abstract_ ________________________________________ 1 Stratigraphic summary of the lower part of the Matanuska Introduction. ______________________________________ 1 Formation Continued Mid-Cretaceous faunal sequence in southern Alaska. 2 Unit B, sandstone of Cenomanian age_____________ 9 Albian _________________________________________ 3 Unit C, strata of Cenomanian to Santonian(?) age _ 10 Cenomanian_ __________________________________ 4 Unit C 1, lutite of Cenomanian to Coniacian or Stratigraphic summary of the lower part of the Matanuska Santonian age__-___________-__---_-_---__ 10 Formation, by Arthur Grantz______________________ 4 Unit C-2, composite sequence of Coniacian and Unit A, strata of Albian age____________________ 6 Santonian(?) age-_------_--_-_------------ 11 Limestone Hills area._______________________ 7 Regional correlation of the lower part of the Matanuska North front of the Chugach Mountains.------- 7 Formation _______________________________________ 12 Matanuska Valley______________________ 7 Geographic distribution of ammonites___-__--__----_-- 15 Nelchina area and southwest Copper River Systematic descriptions..---------------------------- 21 lowland__ __________________________ References--___--_--_-_-_--_-_---------_----------- 44 Correlation within the Matanuska Valley- Index. ____________________________-- 47 Nelchina area.___________________________ ILLUSTRATIONS [Plates 1-9 follow index; plate 10 is in pocketl PLATE 1. Gaudryceras, Anagaudryceras, Lytoceras, and Parajaubertella. 2. Tetragonites and Sciponoceras. 3. Calycoceras and Eogunnarites. 4. Puzosia, Desmoceras (Pseudouhligella), Scaphites, Otoscaphites, Hulenites, Moffitites, Aucellina and Mesopuzosia. 5. Grantziceras. 6. Grantziceras, Brewericeras, and Subprionocyclus. 7. Freboldiceras and Arcthoplites. 8. Arcthoplites. 9. Arcthoplites. 10. Map of Matanuska Valley-Nelchina area, Alaska, showing fossil localities. Page FIGUEE 1. Index map of Alaska._________________________________________________-__-__------------------------ 2 2. Schematic diagram showing relationship of informal Stratigraphic units._____-__-_------------------------- 5 3. Generalized columnar section of the Matanuska Formation, Limestone Hills area_______________--_-_------- 6 4. Generalized columnar section of the Matanuska Formation and correlation with rocks in the upper Chitina Valley area._______________________________-____________________-_-.,-_-_-_-_--------------------- 13 5. Cross section of Lytoceras sp_ _____________-____________-_____-___-_-__---_-_-_-_--------------------- 22 6. Suture lines of Gabbioceras, Jauberticeras, Parajaubertella, and Anagaudryceras------------------------------ 24 7. Cross sections of Gabbioceras and Parajaubertella.------------------------------------------------------- 27 8. Suture line of Otoscaphites teshioensis- ____________-_________________----------------------------------- 27 9. Cross section of Sciponoceras sp---------------------------------------------------------------------- 28 10. Suture line of Sciponoceras sp-._----_-_---------_--_----_------------_-------------------------------- 28 11. Suture line of Brewericeras hulenense------------------------------------------------------------------ 30 12. Scatter diagram showing whorl relationship of Grantziceras affine .--------------------------------------- 31 13. Scatter diagram showing relation of umbilical width to whorl shape in Grantziceras affine-------------------- 32 14. Bar graph showing frequency distribution in Grantziceras affine------------------------------------------- 32 15. Suture lines of Grantziceras affine--------------------------------------------------------------------- 34 16. Suture lines of Grantziceras glabrum------------------------------------------------------------------- 36 17. Derivation of Grantziceras, Freboldiceras, and Arcthoplites------------------------------------------------ 37 18. Suture line of Freboldiceras singular-e------------------------------------------------------------------ 38 19. Suture line of Arcthoplites talkeetnanus.---------------------------------------------------------------- 40 20. Suture line of Moffitites robustus---------------------------------------------------------------------- 42 21. Reconstructed cross section of Calycoceras sp---._---._----_-----_-__------_------------------------------ 42 22. Suture line of Subprionocyclus normalis---------------------------------------------------------------- 43 23. Suture line of Hulenites sp------------------------------...------------------------------------------ 44 IV CONTENTS TABLES Page TABLE 1. Checklist of fossils__________________________________________________________________________________ 16 2. Ammonite'and selected /nocerawus-bearing localities,___________________________________________________ 17 CRETACEOUS AMMONITES FROM THE LOWER PART OF THE MATANUSKA FORMATION SOUTHERN ALASKA By DAVID L. JONES ABSTRACT necessitates showing only the affinities of others. Although The lower part of the Matanuska Formation comprises a thick some of the forms discussed are apparently new, the scarce and and complexly intertongued assemblage of siltstone, shale, sand­ poorly preserved material now at hand does not warrant stone, and conglomerate that ranges in age from Early Creta­ assignment of new names at this time. ceous (Albian) to Late Cretaceous (Coniacian or Santonian). These rocks were deposited mainly on eroded Jurassic sedi­ INTRODUCTION mentary and volcanic rocks in a tectonically narrow trough lying between an emergent area to the north in the area The main purpose of this report is to provide of the Talkeetna Mountains and the northern Copper River paleontologic data to substantiate the correlation of Lowland and a sporadically emergent area to the south, complex sequences of upper Lower Cretaceous and which is now part of the northern Chugach Mountains. The rocks are overlain by claystone and siltstone of lower Upper Cretaceous rocks in the Matanuska For­ Santonian and Campanian age at the base of the upper mation of south-central Alaska (fig. 1). Ammonites part of the Ma,tanuska Formation. Deformation, uplift, from the upper part of the formation have been dis­ and erosion during deposition of the Matanuska Formation pro­ cussed by Jones (1964). duced intraformational unconformities which now bound many An account of the changing concepts concerning the of the cartographic units into which the formation has been divided. Statigraphic and structural studies by Arthur Grantz age of the Matanuska Formation and a brief description have shown that after (and perhaps also during) deposition of of the entire formation were given by Grantz (1964) the Matanuska Formation, the Nelchina area was broken into and Jones (1964) in earlier reports and will not be three major blocks by lateral movement on two splay faults of treated fully here. The lower part of the formation the Castle Mountain fault system, and that these major blocks was considered by Imlay and Reeside (1954, p. 232) to display different rock sequences, informally termed the northern, central, and southern sequences. The stratigraphic record be of Coniacian age on the basis of its stratigraphic of each sequence differs significantly from the others, and de­ position below beds bearing the Santonian species tailed reconstruction of the history of sedimentation and defor­ Inoceramus undulatoplicatws, the supposed presence of mation of the Matanuska Formation rests heavily on paleonto- Parapuzosia and Prohauericeras, and the presence of logic correlations between these sequences. Inoceramus close to 7. uwajimensis. Imlay later The oldest beds of the Matanuska Formation in the Matanuska Valley-Nelchina area, near Limestone Gap in the northern se­ changed the identification of Prohauericeras to Son- quence, consist of sandstone-bearing abundant specimens of ninia of Bajocian age (written commun., 1954) and that Aucellina sp. and rare specimens of Moffitites robustus. These of Inoceramus undulatoplicatus to /. scJvmidti of Cam­ rocks are assigned to the early early Albian zone of Moffitites panian age (written commun., 1955). Later studies by robustus. Upper lower Albian rocks assigned to the zone of Jones showed that the Parapuzosia belongs to Can- Brewericeras hulenense occur in both the northern and southern sequences but have not been positively identified in the central adoceras and that some of the specimens referred to as sequence. Middle Albian rocks are unknown throughout the 7. uwajimensis belong to a new species of Cenomanian area, but upper Albian rocks may be present in the southern sequence. These changes, together with the identification by Cenomanian rocks, characterized by Desmoceras (PseudouJili- gella) japonicum, rare specimens of Calycoceras sp., and a new Imlay (1959) of Albian ammonites obtained from