Cretaceous Ammonites from the Lower Part of the Matanuska Formation Southern Alaska
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Cretaceous Ammonites From the Lower Part of The Matanuska Formation Southern Alaska By DAVID L. JONES With a STRATIGRAPHIC SUMMARY By ARTHUR GRANT2 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 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-- _---------- 3 Unit C, strata of Cenomanian to Santonian(?) age--- Cenomanian - - - - - - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 Unit Gl, lutite of Cenomanian to Coniacian or Stratigraphic summary of the lower part of the Matanuska Santonian age-____----------------------- Formation, by Arthur Grants -------_______--------- Unit G2, composite sequence of Coniacian and Unit A, strata of Albian age ...................... Santonian(?) age .......................... Limestone Hills area- - ----____-------------- Regional correlation of the lower part of the Matanuska North front of the Chugach Mountains--- - - - - - Forrnation_____---------------------------------- Matanuska Valley---------_-____--------- Geographic distribution of ammonites- -----___--_----- Nelchina area and southwest Copper River lowland------------------------------ Correlation within the Matanuska Valley- Nelchina area.. ........................... ILLUSTRATIONS [Platas 1-9 follow index; plate 10 is in pocket1 Gaudryceras, Anagaudryceras, Lytoceras, and ParajauberteUa. Tetragonites and Sciponoceras. Calycoceras and Eogunnarites. Puzosia, Desrnoceras (Pseudouhligella), Scaphites, Otoscaphites, Hulenites, Moflites, Aucellina and Mesopuzosia. Grantziceras. Grantziceras, Brewericeras, and Subprionocyclus. Freboldiceras and Arcthoplites. Arcthoplites. Arcthoplites. Map of Matanuska Valley-Nelchina area, Alaska, showing fossil localities. Page Index map of Alaska____________--------------------..-----------------------------------------------2 Schematic diagram showing relationship of informal stratigraphic units- _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5 Generalized columnar section of the Matanuska Formation, Limestone Hills area- _ - - - - - - - - - - - - - - - - - - - - - - - - - 6 Generalized columnar section of the Matanuska Formation and correlation with rocks in the upper Chitina Valley area- - - - - -- - --- - _ - _ - - - - - _-_ - - - - - - -- - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - - - - - -- - - - - - -- -- - -- Cross section of Lytoceras sp- - - --------- -.-- ------ - --- ------- --- --- -------------- .................... Suture lines of Gabbioceras, Jauberticeras, Parajaubertella, and Anagaudryceras- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cross sections of Gabbioceras and Parajaubertella- - - - - - - _ _ - _ _ _ _ _ _ _ _ _ _ _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Suture line of Otoscaphites teshwensis- - - - - - - - .. - - - _ -.- - -- - - - - -- --- - - - - - - - - - - - - - - - - - - - - - - -- - - - - - -- - - - - - - - Cross section of Sciponoceras sp- - _ - - __ - _ _ _ _ _ _ _ _ _ __- - - - - - - - - - -- - - - - -- - - -- -- -- - - - - - - - - - - - - -- - - - - - - - -- - - - - Suture line of Sciponoceras sp------------------------------------------------------------------------ Suture line of Brewericeras hulenense- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Scatter diagram showing whorl relationship of Grantzieeras afine--- - - - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Scatter diagram showing relation of umbilical width to whorl shape in Grantziceras afine- - .. - - - - - - - - - - - - - - - - - Bar graph showing frequency distribution in Grantziceras afine.. _ - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Suture lines of Grantziceras afine- - - ---- - -- -- - -- - -------- ----------..................... -------------- Suture lines of Grantziceras glabrum- - - _ - _ _ _ _._ _ _ - _ _ _ _ __ _ _ - - _-- _ - _ - _ - _ -- - - - -- - - - - - - - - - - - - -- - - - - - - - - - - - - Derivation of Grantziceras, Freboldiceras, and Arcthoplites- - - _ - __ - - - - - - - - _--- -- - - - - - - - -- - - - - - - - .. - - - - - -- - - - Suture line of Freboldiceras singulare- - - - _ - _ - _ - _ _ _ _ _ .. _ _ _ _ _ - _ _ _ _ _ _ _ - _ -_- _ - - - - - - - - - - - - - - - - -- - - - -- - - - - - - - - Suture line of Arcthoplites talkeetnanus--- -- - -_- --_---_-- -----_-_..----------- ------------ ------------ --- Suture line of Mofitites robustus- - ----_-_-_-_-_____..-____-__-__-_-_-_--------------------------------- Reconstructed cross section of Calycoceras sp- _ _ _ _ _ _ _ _ - _ _ - _ _ _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Suture line of Subprionocyclus normalis- -_-_-_-_- _-_ -_-_-_- -.._-_-_------------------------- ------------ Suture line of Hulenitessp---------_____-_----_------------------------------------------------------- CONTENTS TABLES Page CRETACEOUS AMMONITES FROM THE LOWER PART OF THE MATANUSKA FORMATION SOUTHERN ALASKA 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 Szmtonian). 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 Rlountains. 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 Mqtanuska 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 (19M) 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 display different rock sequences, informally termed the northern, was considered by Imlay and Reeside (1954, p. 232) to 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 ,dimentation and defor- Znoceramus undu.htopZicatus, the supposed presence of mation of the Mahnuska Formation rests heavily on paleonto- Pmrapuaosia and Prohaue&eras, and the presence of logic correlations between these sequences. The oldest beds of the Matanuska Formation in the Matanuska Znoceramus close to I. uwajimemis. Imlay later Valley-Nelchina area, near Limestone Gap in the northern se- changed the identification of Prohazcericwus to Son- quence, consist of sandstone-bearing abundant specimens of n,inia of Bajocian age (written commun., 1954) and that AuceZZLa sp. and rare specimens of Moffitites robustus. These of Znocwm undubtopZka;tus to I. schidti 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 Brewericeras hulenemse occur in both the northern and southern Jones showed that the Pampzosia belongs to Cam- sequences but have not been positively identified in the central aduceras and that some of the specimens referred to as sequence. Middle Albian rocks are unknown throughout the I. uwajimsis belong to a new species of Cenomanian area, but upper Albian rocks may be present in the southern age. sequence. These changes, together with the identification by Cenomanian rocks, characterized by Desmoceras (Pseudoukli- gella) japonicum, rake specimens of Calycoceras sp., and a new Imlay (1959) of Albian ammonites