The Pitkin Formation, or Pitkin Limestone, is a fossiliferous geologic formation in northern Arkansas that dates to the Chesterian Series of the late Mississippian. This formation was first named the "Archimedes Limestone" by David Dale Owen in 1858, but was replaced in 1904. 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.
Paleofauna
Early work aimed at creating a comprehensive list for all fossils found in the Pitkin Formation was done by Easton in 1943. Unless otherwise stated, all species below can be found in his 'Fauna of the Pitkin Formation.'
A. stilus
A. rugosus
E. kleina
E. phrissa
E. explicata
E. rugosa
P. priscus
T. corona
Z. designata
Z. discoidea
- Conularia Originally considered to be a gastropod.
A. gracilis
C. variablilis
L. major
L. minor
M. macerimuris
P. eugenei
P. meekanum
P. elongatus
P. godoni
P. laminatus
P. obesus
P. platybasis
A. patulus
A. planus
B. figuratus
C. stevensi
C. eventus
L. floweri
O. pulaskiensis
P. aptus
P. durus
P. pitkini
P. stereostoma
P. modulus
P. cooksoni
P. irregularis
P. tridecibrachiatus
S. braggsi
S. dunlapi
S. garfieldi
T. whitfieldi
T. caespes
T. residuus
Z. foveatus
This group was originally place under Stelleroidia in early studies.
A. singulatus
Worms
Previous studies have grouped these diverse animals into a single, obsolete taxon: Vermes.
Bryozoa, "Moss-animals"
A. solida
- Archimedes (called Archimedipora in early studies)
A. communis
A. compactoides
A. compactus
A. distans
A. fosteri
A. fragilis
A. intermedia (A. intermedius)
A. invaginata (A. invaginatus)
A. lunatus
A. magnus
A. meekanus
A. moorei
A. pitkinensis
A. proutana (A. proutanus)
A. sublaxus
A. swallovana (A. swallovanus)
A. terebriformis
C. distans
C. regularis
D. levis
F. cumingsi
F. matheri
F. rectangularis
F. serratula
F. tenax
F. introspinosa
G. crassa
G. michilinia
L. solida
M. abrupta
M. tenuis
P. whitei
S. biserialis
S. cestriensis
S. subquadrans
T. cestriensis
T. microfistulata
T. poculoformis
T refiexa
T. subtilis
A. suspectum
A. cestriensis
B. arkansana
C. cestriensis
C explanata
C. oklahomensis
C. sericeus
C. tumescens
Cliothyridina
- C. sublamellosa
- Composita (See unidentified section)
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
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.
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
C. hesperium
C. richardsonianum
C. randolphensis
C. equoyahensis
D. eurekensis
E. globosus
E. bisulcatum
G. pustulosus
K. chesterensis
K. pitkinensis
P. mucronatus
G. optina
P. fayettevillensis
"Encrusting Algae" has been reported but not assigned to any genus.
A. cordillerensis
Unidentified
Following is a list of fossils also found in the Pitkin by Easton in 1943 that have gone unidentified.
- A "Cup Coral"
- A member of the genus Pentremites
- Three species within Agassizocrinus
- Two species within Scytalocrinus
- A totally unidentifiable Crinoid
- Two species of Bellerophon
- Two species of Gosseletina
- Two species of Leptoptygma
- Two Species of Strobeus
- One species each of Composita and Echinoconchus
- Two species of Cypricardella
- Two species of Coloceras, one of which may actually be Leuroceras
- One species of Dolorthoceras
- An unnamed shark spine
See also
References