| Pitkin Formation | |
| Type: | Formation |
| Age: | Upper Visean-Serpukhovian[1] |
| Period: | Mississippian |
| Prilithology: | Limestone |
| Otherlithology: | Shale |
| Namedfor: | Pitkin post office, Washington County, Arkansas[2] |
| Namedby: | George Irving Adams and Edward Oscar Ulrich |
| Region: | Arkansas |
| Country: | United States |
| Subunits: | Imo Shale |
| Underlies: | Hale Formation |
| Overlies: | Fayetteville Formation |
| Thickness: | up to and over 400 feet[3] |
The Pitkin Formation, or Pitkin Limestone, is a fossiliferous geologic formation in northern Arkansas that dates to the Chesterian Series of the late Mississippian.[4] This formation was first named the "Archimedes Limestone" by David Dale Owen in 1858, but was replaced in 1904.[2] The Pitkin conformably overlies the Fayetteville Shale and unconformably underlies the Pennsylvanian-age Hale Formation. Some workers have considered the shales at the top of the Pitkin Formation to be a separate formation called the Imo Formation. More recently, others have considered the Imo to be informal member of the Pitkin Formation.
Early work aimed at creating a comprehensive list for all fossils found in the Pitkin Formation was done by Easton in 1943.[1] Unless otherwise stated, all species below can be found in his 'Fauna of the Pitkin Formation.'
A. stilus[5]
A. rugosus[5]
E. kleina[6]
E. phrissa[5]
E. explicata[5]
E. rugosa[5]
P. priscus[5]
T. corona[6]
Z. designata[5]
Z. discoidea[5]
A. gracilis
C. variablilis
L. major
L. minor
M. macerimuris[8]
P. eugenei
P. meekanum
P. elongatus[9]
P. godoni[9]
P. laminatus[9]
P. obesus[9]
P. platybasis[1]
A. patulus [10]
A. planus[10]
B. figuratus[10]
C. stevensi[10]
C. eventus[10]
L. floweri[10]
O. pulaskiensis[10]
P. aptus[10]
P. durus[10]
P. pitkini[10]
P. stereostoma[10]
P. modulus[10]
P. cooksoni[10]
P. irregularis[10]
P. tridecibrachiatus[10]
S. braggsi[10]
S. dunlapi[10]
S. garfieldi[10]
T. whitfieldi[10]
T. caespes
T. residuus
Z. foveatus
This group was originally place under Stelleroidia in early studies.[1]
A. singulatus
Previous studies have grouped these diverse animals into a single, obsolete taxon: Vermes.[1]
A. solida [1]
A. compactoides [11]
A. compactus [11]
A. fosteri [11]
A. fragilis [11]
A. intermedia (A. intermedius) [1] [11]
A. invaginata (A. invaginatus) [1] [11]
A. lunatus [11]
A. magnus [11]
A. meekanus [11]
A. moorei [11]
A. pitkinensis [11]
A. proutana (A. proutanus) [1] [11]
A. sublaxus [11]
A. swallovana (A. swallovanus) [1] [11]
A. terebriformis [11]
C. distans [11]
C. regularis [1]
F. cumingsi [11]
F. matheri [11]
F. rectangularis [11]
F. serratula [11]
F. tenax [11]
P. whitei [1]
S. biserialis [1]
S. cestriensis [1]
S. subquadrans [1]
A. suspectum
A. cestriensis
B. arkansana
C. cestriensis
C explanata
C. oklahomensis
C. sericeus
C. tumescens
Cliothyridina
C. subquadrata
C. trinuclea
C. infimbriata
D. arkansanum
D. formosum
D. illinoisensis
D. shumardanum
D. whitfieldi
E. alternatus
E. costata
E. pitkinensis
E. vera
G. indianensis
H. multicostata
K. lucerna
L. newberryi var. moorefieldana and ovata
L. pileiformis
O. kaskaskiensis
O. stenopsis[12]
O. subglobosus (var. protensa)
O. uspectum
P. cestriensis
P. fasciculatus
R. setigera
S. leidyi
S. pellaensis
S. spinosa
S. aequalis
T. neogenes
This group was also referred to by another name in earlier studies: Pelecypoda.[1]
A. walkeri
A. batesvillensis
A. eurekensis
A. keoughensis
A. morrowensis
A. multilineatus
A. pitkinensis
C. peculiare
E. crassa (Along with E. crassa var. suborbiculoidea)
E. pitkinensis
L. vaseyana
M. compressa
M. longicardinalis
N. illinoisensis
S. arkansanus
S. chesterensis
S. depressus
S. insignis
S. cherokeense
S. gibsonense
S. quadriplicatum
E. incarinatus
H. reticulatus
H. newtonensis
M. angulata
P. subrotundum
S. subcorpulenta
S. planidorsatus
S. triliris
A. furnishi[13]
C. hesperium
C. richardsonianum[13]
C. randolphensis
C. equoyahensis
D. eurekensis
E. globosus
E. bisulcatum[13]
G. pustulosus
K. chesterensis
K. pitkinensis[14]
P. mucronatus
G. optina
P. fayettevillensis
"Encrusting Algae" has been reported but not assigned to any genus.[1]
A. cordillerensis[5]
Following is a list of fossils also found in the Pitkin by Easton in 1943 that have gone unidentified.[1]