Herendeen Formation and similar units

Unit symbol: Khnl
Age range Lower Cretaceous (139.8 to 125 Ma)
Lithology: Sedimentary
Group name: Coquina and calcarenite
Thin calcarenite, limestone coquina, or similar rock units are widely present in Alaska. Units included are the Herendeen Formation on the Alaska Peninsula, the Nelchina Limestone in south-central Alaska, the Berg Creek Formation of eastern Alaska, and similar unnamed units in southwest and west-central Alaska in the Charley River quadrangle and the Brooks Range (“coquinoid limestone”). The Herendeen Formation was originally described as limestone (Atwood, 1911), but rocks are actually unusually uniform, thin-bedded, medium-grained, calcarenaceous sandstone (Detterman and others, 1996). Inoceramus fragments form major component of formation, although complete specimens have only been found in the Mount Katmai area. Presence of Buchia crassicollis indicates a Valanginian age for the Herendeen in its type area, and ammonite fossils and other collections indicate a Hauterivian and Barremian age at its northern extent (J.W. Miller, written commun., 1983–85; Detterman and others, 1996). The Nelchina Limestone (Martin, 1926) of south-central Alaska and the similar Berg Creek Formation (MacKevett and others, 1978) are lithologically similar to the Herendeen, which consists of “* * * massive dark-colored unaltered fine-grained limestone separated by thin laminae of gray shale. Some beds are highly siliceous and probably ought to be called calcareous sandstone (Martin, 1926).” Buchia crassicollis has also been reported from the Nelchina Limestone. The coquinoid limestone of the northern Alaska is a “[d]istinctive thin marker unit of gray to dark-gray limestone coquina composed of the pelecypod Buchia sublaevis, in beds up to 2 m thick, * * * interbedded with reddish-brown to black clay shale * * *” (Mull and others, 1994); its thickness is less than 10 m. Stratigraphically, unit has been associated with the Okpikruak Formation. Kelley (1990a) states that the unit occurs in both structural and stratigraphic settings; in depositional contact with the Otuk Formation and the undifferentiated Otuk and Shublik Formations; and as tectonic blocks in mélange in his Arctic Foothills assemblage (which is included here in unit JPzs). Tectonic blocks of coquinoid limestone in the Arctic Foothills assemblage, as well as those associated with Okpikruak Formation, may be olistostromal in nature. Other calcareous clastic units of similar age are known from southwestern Alaska (Hoare and Coonrad, 1978), western Alaska (Patton, 1966; Hoare and Condon, 1971; Patton and others, 2009) and in the Charley River area of eastern Alaska (Dover and Miyaoka, 1988). Also includes Kennicott and Kuskulana Pass Formations of eastern Alaska, composed dominantly of thin-bedded, fine-grained feldspathic graywacke and arkosic wacke and siltstone. Also includes shale and some conglomerate whose clasts are predominantly Nikolai Greenstone (unit ^n) at the base (MacKevett and others, 1978). Kennicott Formation is generally dark-greenish-gray, weathers brown, and has crude graded bedding, cross-bedding, sole markings, and spherical limy concretions; the older Kuskulana Pass Formation is generally similar. Both represent fairly rapid shallow marine deposition in a transgressive sea. An Albian age is assigned to the Kennicott on the basis of abundant molluscan fauna, particularly the occurrence of Inoceramus altifluminis McLearn (Patton, 1966) and pelecypods of genus Aucellina, whereas the age of the Kuskulana Pass Formation is defined as Hauterivian and Barremian based on a meager ammonite and pelecypod fauna (MacKevett and others, 1978)

Source map information

Source map Csejtey, Bela, Jr., Nelson, W.H., Jones, D.L., Silberling, N.J., Dean, R.M., Morris, M.S., Lanphere, M.A., Smith, J.G., and Silberman, M.L., 1978, Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner Healy quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-558-A, 60 p., 1 sheet, scale 1:250,000.
Symbol Ksu
Unit name Sedimentary rocks, Undivided
Description Shallow marine sequence of thinly bedded calcareous sandstone, siltstone, claystone, minor conglomerate, and thick-bedded to massive clastic limestone; over 100m thick
Lithology Sedimentary

Correlated geologic units

Label Knls
Description Early Cretaceous Nelchina Limestone
Geologic age Hauterivian to Barremian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Claystone < Mudstone < Clastic < Sedimentary Bed Indeterminate, major
Sandstone < Clastic < Sedimentary Calcareous Indeterminate, major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major
Conglomerate < Clastic < Sedimentary Bed Minor