Lime mudstone

Unit symbol: Ols
Age range Ordovician (485.4 to 443.4 Ma)
Lithology: Sedimentary
Group name: Farewell platform facies
Limestone and lime mudstone exposed in the northeast Taylor Mountains and southeast Sleetmute quadrangles. Unit consists of distinctive limestone lithologies, boundstone and packstone to wackestone, interspersed with the mudstone: the stratigraphically lowest part of the unit is thin- to medium-bedded, dark-gray, yellow-gray-weathering, burrow-mottled lime mudstone and lesser peloidal mudstone. Age control based on poorly preserved low-spired gastropods and conodonts including Drepanoistodus? sp., Fryxellodontis? n. sp. and other conodonts. This is apparently overlain by medium- to thick-bedded, dark-gray to brown algal-thrombolitic boundstone interbedded with light-gray-weathering, thin- to medium-bedded lime mudstone (Blodgett and Wilson, 2001). Trilobites and conodonts (identified by N.M. Savage, written commun., 1985), including fossils of the genus Hystricurus, indicate an Early Ordovician age for this boundstone Overlying this is an extremely poorly exposed brown and dark gray 'chippy' shale, silty shale and minor silicified limestone exposed in very small areas in the Taylor Mountains quadrangle, where exposures consist only of frost-boil chips of shale and rubbly outcrop; a better exposed area of rubble contains numerous diplograptid graptolites. The uppermost part of unit Ols consists of brown, medium- to thick-bedded skeletal lime packstone to wackestone (Blodgett and Wilson, 2001), which contains abundant pentameroid brachiopods (Tcherskidium, Proconchidium [or Eoconchidium] and a new smooth genus aff. Tcherskidium). Karl and others (2011) provides a comprehensive database of fossil data for the Taylor Mountains quadrangle and adjacent areas to the southwest

Source map information

Source map Blodgett, R.B., Wilson, F.H., and Shew, Nora, 2012, Unpublished data.
Symbol Ols
Unit name Ordovician burrowed mottled limestone unit, Nixon Fork Subterrane Facies Rocks
Description Thin- to medium bedded, medium gray to yellow-gray weathering, dark-gray fresh, burrow mottled lime mudstone. Unit originally defined in the Taylor Mountains D-1 quadrangle (Blodgett and Wilson, 2001), where it has yielded faunas indicative of Early Ordovician age. This unit is restricted to one exposure in the southeastern part of the Sleetmute A-2 quadrangle, where it is exposed at Hill 920, Section 28, T11N, R40W. Fossil locality 24, near the summit of the hill, yielded numerous horizontal burrows, a fine-ribbed orthid brachiopod and undetermined smooth brachiopod. The orthid brachiopod is of a morphology compatible with an Early Ordovician age
Lithology Sedimentary

Correlated geologic units

Label Ols
Description Lime mudstone
Geologic age Ordovician to Early-Ordovician
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Mudstone < Clastic < Sedimentary Calcareous Major