THE ALASKAN CAVEHI Yo1 ur.~ 7 Number 3 May June 1982 Devonian Limestone Pi1 lars West of the Nabesna River
July 15 Glacier Grotto f:eeti ng. Ideeti rgs are held in roar.) 314 of Grant Hal 1, Alaska Pacific Uviversity at 7:20 pn. August 19 Glacier Grotto fleeti rg. rqeetings are held in roor,i 314 of Grant flrzll, Alaska Pacific Universjty at 7:30 pw. The program \,ill k an FISS slide show. Lator Day Possible caving trip to Chi tistoce Valley. Septer~ber 16 Glzcier Grotto fleeting. lleetings are held in room 214 of Grant Hall, Alaska Pacific University at 7:30 pn. Octoher 21 Glacier Grotto tleetirig. Meetings are held ir~ room 314 of Grant Hall, Alaska Pacific University at 7:30 pm. The progran will k an NSS slide show. The ALASKAN CAVER is a periodic publication of the Glacier Grotto of the National Spel col ogical Society. Sukscriptions sre free ta r.lenbers. Fle~~bership dues are $5 per annun. Dues can be sent to Elisabeth Hall at 4607 Klondike Crt., Acchorage, AK 99504. Copyright 1982 by Glacier Grotto. tlaterial pot copyrighted by individuals or other groups nay k copied by other IJSS pzlhlications provided credit is gfve~ to the ALASKAN CAVER snd a copy of such publication is sent to the editor. Editor: Richard Hal 1 Pub1 ishers: David Sloll Rusty Rubeck GROTTO OFFICERS President Julfus Rockwell V. President David Street Secret a ry Richard Hall Treasurer El i sahth Ha1 l At Large David flat I Pub1 icity Barbara Sansen LIrlESPOtJE IN THE EASTERN PART OF THE ALASKA RANGE The Alaska Rarge forms a large horseshoe in South Central Alaska with one end poirting southvlest don^ the Aleutian Rzmge and the other end pointing southeast at the St. El ias Flountains. Nowhere In the Alaska Range arc there expansive deposits of linestone due partly to extensive faulting ard partly to the luck of the draw. This discussion corers nost of thc IJabesva Quadrangle, the southern part of the tlount Hayes Quaclra~9le a~d ssiall portions of the Gul kana and Tanacross Quadrangles. Portions of the Alaskz! Range in this area are a1 so refered to as the Flentasta and Flutsoti n llour~tai ns. Tectonicly, the Alaska Range straddles the Defiafi fault in this area pith older Devonian base racks an the north side and rocks of various younger ages on the south side. There are also several other faults parallel to the Oenali fault and various age rocks can be seen juxtaposed to rmrg, different ages, The area of consideration is served by several hmIghvays. The Alaska Highway trends 30 to 40 ni'les mrth of the Denali Fault and the Richardson Highway is almost to the western border. The Glenn Hjghway (also called the Tok Cutoff in this area) cuts diagonally across the area and the Nabesrra Road runs parallel to the Alaska Range east of the Cutoff. Despite the extensive-sounding (for Alaska) road system, almost all of the liriestone is nore than a day's hike fron the roads.
fhrec ages of 1ir.lestnne have substantial outcrops in this area while several snalfe'r bands of 1 inestone occur in other places. Triassic rocks occur south of the Denali Fault. Pernian lincstone likewise appears south of the Denal i Faul t as we7 1 as i n the Healy Quadrangl e te the e~cst of the study area. North of the fault is some Devonian 1 ir,~estanu di ssinil ar to other nearby rocks. There are a1 so extensjve areas of g 1 aciers and Quaternary 1 ava which may a1 so contain caves. 1. The Triassi c I imestone referred to i n Mendenhaf 1 & Schrader, 1903, p34 as the Nabesna Linestone, is si~nilar to the Chitistone and Nizina Linestones which are prevaf ent in the Urangell Mountains of the lldarthy Quadrangle (Alaskan Caver V.6 No.1). They likewise unconfornab? y overly the Ni koF ai Greenstone. Richter, 1976 describes these f orrutations re1 ating that they: ""Pclude an upper unit of thin bedded linestone and a lower unit of massive 1 inestone separated by 1 ocal angular unconforni ties. Near intrusive racks the 1 imestone i s theraal ly metamorphosed to conspicuous white trenol i te-beari ng narbl e wi th garne tepi doteaagneti te tacti te. The upper unit consists of dark-gray fine-grained thin-bedded 1 inestone. The beds are a few centemeters to as nuch as 2 n thick with thin interbeds of black cherty siliceous argillite and dark gray carbonaceous shale. Minor beds of mediumto coursegrai ned calcareous sandstone and c a1 careous gri t as nuch as 1 meter thick, are scattered through unit. The linestone is chiefly micrite and bionicrite, locally racrystallized and do1 oai tized and weathers 1 i gh t gray (1.1icri te) and buff (spiculitic bionicrite) ." . "Thickness 0 to 120 n." "The lower unit i s gray to dark-gray and fine-grained nassivebedded 1 inestone with 1 enses and nodules of gray and bl ack chert and i rregul ar patchworks of di sreiai nated f ine-grai ned quartz. Beddi ng i s general ly not di scernabl e. Chiefly micrite, disnaicrite, or nicrosparite, comnon1,y recrystal 1 i zed or s trengly brecciated and vei ned by c oursely crystalline calcite; locally dolomitized. Ideathers light gray. Typically unfossiliferous." ...I1 mickness 20 to more than 250 n." Thi s description is for the Nabesna Quadrangle in general while the raakeup and thickness of the rocks differ from area to area. In the Mount Hayes Quadrangle it includes some fine-grained quartz and the upper thin-bedded rocks are missing. The overall thicknesses of the upper and lower Somations vary considerably and either one may be missing in a specific location either because of removal of the beds or faulting. Thi s 1 inestone i s known to contain caves in the McCarthy guadrangle and probably contains caves somewhere i n this area as 1 ong as a 1 arge enough thickness i s found and gradient and water requirements are met. 2. The Permian linestone is similar to the Skolai Limestone found in the llrangell Mountains [Alaskan Caver V.6 No.2) and is called the Eagle Creek Forr~ation in Nokleherg, 1982. Richter, 1976 describes it as:
cq I-&. Glaciers Roads -Faults all features are generalized
1IMESTOWE, GLACIERS, AND LAVA I9 TtlE SOUTHEAST ALASKA RANGE AND VICINITY (Portions of Gulkana, Mt. Hayes, Nabesna, and Tanacross Quadrangles) ALASKA
'Ti ght gra;f, thinto thick-bedded fossil iferaus 1 inestone; general 1y fi ne grained (biosparrudi te) but cornnon? y recrystallized. Contains ninor nodules of gray chert and base is locally marked by course-grained clastic limestone containing abundant volcanic cl asts. Linestone generally occurs at base of Eagle Creek Formation but is variable in thickness and locally absent." +..."Thickness 0 to 100 n.'" It appears at the base of a thick section of Permian argilf ite and above a thick section of Permian volcanic rocks. It i s seldom greater than a hundred feet thick but can go up to 100 meters and thins northward. The age and appearance correlate with the Golden Horn Lir,iestone Lentil in McCarthy Quadrangl e and its correlated band of 1 imestone elsewhere in the HcCarthy Quadrangle, The Golden Horn has a maxinun thickness of 250 neters but elsewhere (west and south) in the I4cCarthy quadrangle it is 1 inited to 100 neters. In Richter et al, 1977, which covers parts of the Mt. Hayes Quadrangle, the Eagle Creek Formation i s broken more finely than elsewhere in the area. Uhile most reports only break it into 1 inestone and argillite, Richter et a1 1977 breaks it into upper arcfill i te, upper 1 irnestone, lower argillite, and lower 1 inestone nenbers. 3. The Devonian 1 inestone appears north of the Denal i Faul t and though a ninor member in a wide area of Devonian rocks it is the most prominent nenber of the formation. Richter, 7976 briefly describes it as: "Gray to dark-gray recrystal i zed l inestone; weathers 1 i ght gray, and forms conspicuous cast1 es and pi nnacl es protruding above the general ly col luviun-covered phyll i te surf ace. Rugose and tabulate coral s from widely scattered local i ties indicate a Middle Devonian age." It is described in Moffit, 1941 p125-126 as follows: "The nost conspicuous nenbers of the Devonian group of sedimentary deposits are 1 inestone beds. They owe their prominence to the pecul i ari ty of thei r weathered outcrops, which, because of their fos1.1 and color are a notable feature of the landscape. The limestone is massive in structure, coursely crystalline and light bluish gray. Its resistance to weathering and its granul ar texture together with the acci dents of folding and faulting, have contributed to produce an a1 ignment of 1 i gh t-gray pi nnacl es and crags that contrasts strongly wi th the darker background, which stands high above the associated rocks and makes it easy for the eye to follow the course of the beds for many miles across the country. The 1 ifizestontr occurs .r'n several di stinc t beds separated by phyll jte or schist nenbers derived from original mud and sand deposits." 4. Richter et a1 1977 mentions some thinto mediun-bedded gray and 1 ight gray locally volcanic-rich l ir,~estone lenses up to 25 m thick within the Permi a ~Pennsyl vanian Age val cani c Sl ana Spur Formation in the Mt, Hayes 4-1 Quadrang? e,
Contents: Calendar of
Limestone in the Eastern Part of the Alaska Range --
Limestone, Glaciers, and Lave in the Southeast Alaska
Range and Vicinity / Rich Hall.