Matanuska Formation and correlative rocks

Unit symbol: Km
Age range Upper Cretaceous to upper Lower Cretaceous (113 to 66 Ma)
Lithology: Sedimentary
Group name: Shallow to moderate depth sedimentary rocks
Matanuska Formation is well-indurated, thinly bedded, dark-gray, fossiliferous marine shale deposited at shallow to moderate depths thatcontains conspicuous calcareous concretions, volcanic-lithic siltstone, sandstone, graywacke, and subordinate conglomerate (Winkler, 1992). According to Martin (1926), unit is at least 1,250 m thick. Grantz (1964) reported results of a stratigraphic reconnaissance of the Matanuska Formation and found it to include several mappable lithologic units and suggested that when these units are defined as formations, the Matanuska Formation merits elevation to group rank. Winkler (1992) described unit as diverse shallow to deep marine (in part, turbiditic) deposits derived from a northern source, either from an unidentified mid-Cretaceous magmatic arc or from the Jurassic arc represented in part by the Talkeetna Formation. Upper part of unit is coeval with the flysch of the Valdez Group to the south. Unit overlies and is separated from Early Cretaceous and older strata by a pronounced angular unconformity (Csejtey and others, 1978) and contains locally abundant marine fossils. In Wrangell Mountains, unit consists of Upper Cretaceous sedimentary rocks as defined by MacKevett (1978), which are locally subdivided into 1) Moonshine Creek Formation, siltstone and sandstone, with minor conglomerate; 2) Schulze Formation, porcellanite, with minor sandstone and conglomerate; 3) Chititu Formation, mudstone and shale, subordinate porcellanite, sandstone, and impure limestone; and 4) MacColl Ridge Formation, coarse sandstone and minor granule and pebble conglomerate. These correlate to part of the Matanuska Formation in the Talkeetna Mountains and Matanuska Valley

Source map information

Source map Richter, D.H., Preller, C.C., Labay, K.A., and Shew, N.B., 2006, Geology of Wrangell-Saint Elias National Park and Preserve, southcentral Alaska: U.S. Geological Survey Scientific Investigations Series Map SIM-2877, 15 p., 1 sheet, scale 1:350,000.
Symbol Ku
Unit name Marine sedimentary rocks -- Wrangellia terrane
Description Sandstone and siltstone deposited at shallow to moderate depths; locally abundant marine fossils. Includes the MacColl Ridge, Chititu, Schulze, and Moonshine Creek Formations
Lithology Sedimentary

Correlated geologic units

Label Ku
Description Late Cretaceous undifferentiated clastic rocks
Geologic age Albian to Maastrichtian
Geologic setting Sedimentary, shallow-marine-siliciclastic
Lithology Form Importance
Sandstone < Clastic < Sedimentary Bed Major
Shale < Mudstone < Clastic < Sedimentary Bed Minor
Siltstone < Clastic < Sedimentary Bed Minor