Publicaciones Geolo_gicas Especiales Del lngeominas

ZONATION OF THE CRETACEOUS OF CEN TRAL COLOMBIA BY AMMONITES 13
tion a6 appeared on lJ. 720 (1963) and on
which the new term "Ubaque-Sandstein-Hypachanthoplites
Niveau" was Introduced. The
above discussed terminology is not followed in
the present study.
1--B-I_o ....
sT_R_A_T_W_ . _AP_H_Y R __ -[.
The following subdivision of the lithologic
sequences investigated in this report, based
on their faunal content (mainly ammonites),
that is their zonation, attempts to be in agree·
ment with the recommendations of the Intema·
ttonal Subcommission on Stratigraphic Classification:
"An International Guide to Stratigraphic
Classification, Tenninology, and Usage"
(1972). All the proposed zones in this scheme
are considered ••Assemblage-zones (Cenozones)".
The purpose-of estibliSJITng Oils zonation IS to--facilitate
the geological work currently being
done on the Cretaceous rocks of the Cordillera
Oriental Colombiana, and I am not attempting
to establish a rigid" Archetypical" scheme. I feel
it is important to have a reference element, an
objective starting point whose value it is hoped
will be challenged by others,
In other words, the subdivisions are
based on the succession of the paleontological
material collected in situ in the field and from
successive sequences of rocks as measured and
mapped at localities of easy access and unequi·
vocal identification. The lower boundary of the
units is established at the fll'S t known occurren·
ce of new taxa, especially genera; the upper
limits of the unit are consequently determined
by the occurrence of the next new groups at
the base of the overlying unit. Correlation or
time equivalence with the zonal scheme established
in Europe is not attempted in greater
detail other than the mere comparison of the
common occurrence of certain groups of
ammonites considered significant enough to
permit usage of the stage terminology for the
Cretaceous rocks as first proposed by_ d'Orbigny
and Coquand.
THE FOLLOWING ASSEMBLAGE ZO·
NES ARE HERE PROPOSED FOR USE IN CO·
LOMB lA.
As far as these studies demonstrate, the
zonal species have their rtrst appearance along
with the fU"S t record of Cheloniceras (EpichelonicerCI$),
Vectisites (Zambranoites), Riedelites,
Juandurhamiceras and GargasicerCI$, Cortezicenzs,
Pseudoptychoceras, Toxoceratoides (Colomboceratoides).
AS TYPE LOCALITY for the base of this
zo e the beds immediately above the white,
argillaceous (tuffaceous?) layer rich in compre·
sse specimens of ''Procheloniceras, cf. Proche­
lomceras albrectUJustriae Hoh." are selected.
These were previously recorded in Etayo-Sema
(1968), "Estacion 10e", columnar section Fig.3,
and "Est.lO", km. 28 on the road Sachica-Puen-
te Samac&, geological map. Lithologically this
zone is represented by La Paja Formation, sg
rE'lt
i!nt E as described by'"Etayo•Seiiia:,--1968. A
CE LOCALITY Cor the zone is the
previously described sections of the_ Socot8
Member on the road Anapoima-Apulo.
Species referred to the zone described in
this paper are:
Du{renoyia sanctorom Biirgl
Du{renoyia boteroi n. sp.
Du{renoyia codazziana (Karsten)
Stoyanowiceras treffryanus . (Karsten)
Stoyanowiceras cintatum n. ·sp.
Cheloniceras (Epicheloniceras) dognaeluirae
n. sp.
Cheloniceras (Epicheloniceras) camachoi
n. sp.
Cheloniceras (Epichelonicenzs) carlosacos-
tai n. sp.
Cheloniceras (Epicheloniceras) jimenoi n.
sp.
Cheloniceras (Epicheloniceras) barreroi
n. sp.
ChelonicerCI$ (Epicheloniceras) pardoi n.
sp.
ChelonicerCI$ (Epicheloniceras) leonhardtriedeli
n. sp.
Vectisites (Zamur-anoites) cadenai n. sp.
Vectisites (Zambranoites) crozi n. sp.
Vectisites (Za mbranoites) zambranoi n. sp .
Vectisites (Zambranoites) duquesi n. sp.
Vectisites (Zambranoites) mateusi n. sp.
Riedelites obliquum (Riedel).
Riedelites (?) quebradanegra n. sp.
Riede lites estheemae n. sp.
Juandurhamiceras juandurhami n. sp.
Juandurhamiceras giraldoi n. sp.
Gargasiceras interiectum (Riedel).
Gargasiceras pulcher (Riedel).
Corteziceras cortezi n. sp.
Pseudoptychoceras gilberti n. sp:
Toxoceratoides (Colo mboceratoides) renzoni
n. sp .
Aconeceras gutierrezpalmae n. sp.
Melchiorites palmeri n. sp.
Eogaudryceras helmsi n, sp.
Eogaudryceras (Eo te tragonites} cabaricoi
n. sp.
Pseudohaploceras le ivaense n. sp .
. Valdedoella (?) colombiana n. sp.
Colombiceras sarmientoi n. sp.
Eodouvilleiceras (?} tequendamai n. sp.
Colombiceras foreroi n. sp.
.P..lil. . aJ.Jw!HI.Gbi. · &gatfJahQuli&
.J!_ptocerati{orme Ass :_ ml Se - zone
As far as known to me these species have
their most occurrence in this part of the sequence;
the absence of Cheloniceras (Epicheloniceras},
Du{renoyia, Stoyanowiceras, Vectisites
(Zambranoites), Aconeceras, Eogaudryceras,
seems indicative also.
AS TYPE LOCALITY for the base of
this zone the clay-shale beds with abundant
argillaceous-calcareous concretions at point
C-127 on the road Anapoima-Apulo is design-
-