Scale microfossils from the Early Cambrian of northwest Canada

Abstract

Scale microfossils are locally abundant in rocks of the uppermost Tindir Group and basal beds of the overlying Funnel Creek Limestone in northwest Canada. Co-occurring organic-walled fossils in this microbial mat biota resemble forms described from the Upper Proterozoic but mineralized spicules of Cambrian aspect are also present. The fossils occur in chert nodules or beds in flat laminated limestones interpreted to represent accumulation in a subtidal environment.The scale microfossils are of three basic shapes: Group 1, simple imperforate scales; Group 2, thin disk-like scales with prominent, regularly arranged pores; Group 3, ring-like scales with distinct three dimensional morphology. All taxa in Groups 1 and 2 have scales of a single morphology and narrow size range; Group 3 taxa may contain one, two, or (?)three morphotypes and sizes of scales. The scales of Group 1 taxa are not closely comparable to known Chromophyta but are similar to scales of several modern Rhizopoda. Some of the Group 2 taxa can be compared to members of the Chrysophyta, whereas others have general resemblance to centric diatom valves. Most Group 3 taxa are morphologically comparable to members of the Prymnesiophyta. All scales that could be analyzed petrographically are now siliceous and none could be confirmed as polycrystalline.The scale microfossils are referred to new taxa, including 17 genera, 26 species, and 6 varieties. Newly described taxa are: Group 1) Archeoxybaphon polykeramoides n. gen., n. sp., Archeoxybaphon diminutum n. sp., Archeoxybaphon amydrum n. sp., Hyaloxybaphon monokeramoides n. gen., n. sp.; Group 2) Paleohexadictyon litosum n. gen., n. sp., Paleohexadictyon myriotrematum n. sp., Paleohexadictyon coroniforme n. sp., Paleohexadictyon coroniforme var. tetragonum n. var., Paleohexadictyon coroniforme var. delicatum n. var., Chilodictyon caliporum n. gen., n. sp., Chilodictyon caliporum var. striatimarginatum n. var., Chilodictyon myriocanthum n. sp., Characodictyon skolopium n. gen., n. sp., Characodictyon skolopium var. tetragonum n. var., Characodictyon skolopium var. soleniscum n. var., Characodictyon diskolopium n. sp., Characodictyon diskolopium var. circulare n. var., Radiocerniculum inornatum n. gen., n. sp., Spinicerniculum tribulosum n. gen., n. sp.; Group 3) Petasisquama alta n. gen., n. sp., Petasisquama versicorona n. sp., Petasisquama laciniata n. sp., Bicorniculum brochum n. gen., n. sp., Confinisquama fimbriata n. gen., n. sp., Aqualisquama centritubula n. gen., n. sp., Invaginatibalteus dimorphus n. gen., n. sp., Invaginatibalteus depressus n. sp., Paterisquama crassa n. gen., n. sp., Altarmilla multistriata n. gen., n. sp., Patinisquama cirratomarginata n. gen., n. sp., Paleocrassalimbus spinosus n. gen., n. sp., and Paleomegasquama coccolithoides n. gen., n. sp.