Publicaciones Geolo_gicas Especiales Del lngeominas

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ZONATION OF THE CRETACEOUS OF CENTRAL COLOMBIA BY AMMONITES 21 area the ribs describe a wide adoral arc and on both sides of this arc two narrow adoral conca vities are formed; the ribs then trend obliquely and slightly arcuately across the flanks and fl. nallY they cross normal to th ventral medial axis where they become depressed and even very attenuated but not lnterrupted. The inter costal spaces are channel like with rounded bottom and usually subequal in width to the ribs but occasionally are a bit wider. The moilt adapical preserved segments of shaft have ribs of uniform strength that bear low, rounded to compressed bullae on either side of the vef\tral median depression;· now and then however a fmer, almost ventrally nontuberculated rib occurs, likewise stronger and ventrally noded ribs are intercalated. With maturity a clear differentiation of the ribs occurs: one non stressed rib alternates with one strong rib which bears one spinose tubercle on the periventral margin and a second mammiform tubercle at the boundlllY betwen the peridorsal and central thirds of the flank; the costal whorl section acquires a beveling of its profile on the adventral third of the flank. With further growth the primlllY ribs develop an additional, smaller, mammiform tubercle near the rim of the dorsal side but the ribs are nearly interrupted on venter, developping a weak channel along the ventral median line; two intercalary ribs may occur on mature stages. Later the section of the whorl becomes roun· ded subrectangular, the segment of the ribs between the ventral and lateral tubercles is flattened, with a tendency to split longitudinally. DIAGNOSIS. This species is characterized by A) the rapid increase in width of the shaft, B) the ontogenetic development of its ornament from undifferentiated barely tuberculate ·ribs, not interrupted on venter, to an alternation of trituberculate primary ribs and almost non tu· bereulate intercalatory ribs all of which become attenuated on venter, and C) the progressive development-of the lateral tubercles. COMMENTS. This species differs from .Toxoceratoides royerianus ("d'Orbigny) as emen· ded by Casey (1961, p. 77) because the ribs do not divide on the dorsum or if they do no more than two riblets appear; they differ also in the suture line which is less complicated in the Co· lombian species. However this difference may be due only to the diameter of the whorl at which the sutu:res were drawn. . This species is named in honor of the geo· logqt Giancario Renzoni. • OCCURRENCE. Paja Formation (Arci· llolitas ablgarradas. Segment E.). Upper Aptian. Toxcerutoides (Colomboceratoides} ren zom n. sp. . (Morph I). Text-Fig. 3P. Paratype. (U.N.C.M.H.N.C.P.Pt.N.2.) The shaft Is slightly arched. The early section of the whorl is vaulted; the dorsal area ia arched with the sides rounding outwardly up to the center of the whorl then evenly rounding toward venter which is flat. The ornament consists of prominent rounded ribs which cross the dorsal area linearly or with a slight adoral bow, they cross the flanks forming frst a weak adoral concavity on the dorsal rim and then trending prorsiradiate or describing a slight arc, or even forming an adoral concavity; on venter they become interrupted -on the internal mold- or very attenuated on exterior of the test around the ven· tral medial line; the end of the ribs converge toward the siphonal line forming a wide V with its apex pointing adorally. All ribs •develop rounded to spinose periventral tubercles. Though sporadically one rib may show greater strength, the ribs gain strength progressively and do not develop a regular alternation of strong and weak ribs. The intercostal spaces are deep and twice as wide as the ribs on the internal mold, but they appear shallow and narrower when the shell is preserved. · · . NOTE: This morph is notabl_e- for the steady growth of the section of the shaft, by the strong, uniform and unituberculate ribbing and the early stressing of the ventral tuberculation. OCCURRENCE. Socoti Member. Upper Aptian. Family P Y HOCERATIDAE. Genus 1 Pse udoptychoceras n. (} .=:: £o.plyrh11u -""A. TYPE SPECIES. Pse udoptychocerrzs gilberti n. sp. DIAGNOSIS. Straight or slightly undula· ted, slowly increasing initial shaft, ornamented with prominent, oblique annular rounded ribs, separated by conspicuous constriction-like intercostal spaces; the section of the whorl is elliptical to almost circular, the first shaft bends to a shorter (?) branch which leaves an opening ("needle hofe") before appressing against the :lorsum of the first shaft; this second branch is ornamented with annular acute ribs distant from each other. The suture line has short sub· rectangular elements, relatively undisected, L Is trifid. COMMENTS. This new genus differs from Ptychoceras because of its loop forming hook and its trifid L; from Euptychoceras (Breistroffer, 1947) because the fanner Is smaller and has strong ornamentation on both shaft and hook. Pseudoeachoceras gjlberti, n. sp. P[G, li'ig. 18; Text-Fig.3S, 3T. Holotype. C-223 (U.N.C.M.H.N.C.P. Ht. N. 6). Paratype. (U.N.C • .M.H.N.C.P.Pt. N.3) . There are three fragments of the shaft, two of them with part of the hook preserved. The shaft is straight, progreSBively tapering, It
22 has a subelliptical to subcircular section: the dol'Bal region is wide, flattened, abruptly changing into the feeble convex sides which evenly round toward the narrow arched venter. There are broadly rounded, low ribs, slightly thickened on venter. On the dorsal area the ribs are barely visible, they cross it as fm e lirae normal to the dorsal-central axis; at the margins of the dorsal region the ribs become well defmed and cross the flanks of the shaft in an arc convex toward the hook; they cross the venter normal to the ventral-central axis; the intercostal space, constriction-like in appearance, is prominent on flanks and venter and subequal to slightly narrower than the ribs. The beginning of the hook Is indicated by three narrower ribs which appear as a bundle at the dorsal margin; of the three ribs, that nearest to the hook is the most prominent and the one adjacent to it Is the weakest but this relationship may be inverted on other specimens; a second group of two ribs follows on the hook and thereafter only single ribs appear; on the hook the ribs tend to taper acutely toward the margin of the dorsal area and to broaden on venter; toward the beginning of the hook the ribs sometimes develop a weak tendency to depress along the ventral-central line. DIAGNOSIS. This species is characterized by: A) the change of tbe whorl section through development from circular to subovate, and B) its peculiar broad ribbing which gave it a wormlike aspect. COMMENTS. This species diffeD from the type species of the genera Ptychoceras and Euptychoceras as discussed under the genus. OCCURRENCE. Socota Member. Upper Aptian. Pseudoptychoceras gilberti n. sp., rMorph I] 1'1.6, Fig. 17. Paratype. (U.N.C.M.H.N.C.P.Pt. No.4). One complete hook (?) and a section of tbe shaft. The dorsum is flattened and rounds smoothly into the slightly bulging flanks which in tum grade into a narrowly arched venter. There are very broad rounded ribs separated by constriction-like interspace& which cross the flanks obliquely and project slightly on venter; both rib and constriction fade out at the margins of the donal area. The hook has only single ridge-like rib8'""whicb taper toward, the dorsal area and are rounded on venter, the adapical aide of these ridges is steep whereas the adoral side Is elongated giving that part of the shell the appearance of consisting of interlocking segments. NOTE: These fragments have the section of their shafts more inflated around the dorsal zone, the ribs are strong and rounded and cross the venter obliquely, and the ribs form interlocking rid- F. ETA YO · SERNA ges on the living chamber. OCCURRENCE. Socota Member. Upper Aptian. Rif.A::T:iliD A !i(j E m,-- ··---am=ilY:_A C O !I!iN EC E !ii uenus @co1eceros(Hyatt, 1M3. r;rcocros H'yaft, 19oa·;·p.loo. •.•• ,. •• ,.,... .,. ••• • •. . • -.. :.:-• - .. . · . .•. - 4'• .- -. . . . • ..- · .··-:- · .. TYPE SPECIES. Ammonites nisus d'Orbigny, mono typic. "ficw "ros tierrezealmf.- n.sp . . 6, Fig. 15;exi-Figs. 33Y, 3Z. Holotype.C-223 (U.N.C.M.H.N.C.P. Ht. N.7) Paratype. (U.N.C.M.H.N.C.P. Pt. N.5) A) Up to 10 mm diameter. The fil'Bt whorl of the phraginocone is inflated and has a whorl section only slightly higher than wide, evenly rounded and with a wide ventra] area. On the specimen studied the internal mold of the fiDt whorl shows a rounded rib parallelled on each side by a rather shallow constriction. On the se· cond whorl the section is ovoid and has a narrower ventral zone. On the third whorl the flanks become flattened and the ventral zone fastigate and slightly shouldered at its margins, the umbi· Iical wall is short but vertical with a blunt umbilical rim. The ornament consists of bundles of falcate pleats, they trend prorsiradiate to weakly concave from the umbical rim to the boundary between the adumbilical and middle thirds of the flank where they bend sharply, fonning cres· centic adoral concavity and fm ally projecting on venter. The pleats are stressed and slightly raised about the involution line where the sharp acute bend occurs. The space between the plea is narrower than the pleats themselves. B) Up to 20 mm diameter. The most im· portant aspect of the conch at this diameter is that the umbilicus has not increased its width at all, in spite of the great increase in the height of the whorl; the sides are noticeably flattened and the venter is planifastigate. The suture line has E/L divided by a lobe into two branches of which tbe external one is the widest and it is also bisected; the internal branch is subdivided into three ramose bran· ches. The L/U2 has the internal branch larger than the rest of the saddles; the external lobe is subsymmetrical. DIAGNOSIS. This species is characterized by: A) its ontogenetic development changing from inflated involute to septicarlnate oxycone; the internal mold is almost planlfastigate, and B) iUI strongly falcate Urae and the tendency of these to become stressed about the centrolateral ,cute bend. Meuuremental Holotype Para type D Euw 19 2 9 2 .. H. W D/Euw0h, D/HOfo 11 5 10 57 5 2 22 55 COl\!MENTS. This species can be differen-
Page 1 and 2: Publicaciones Geolo_gicas Especiale
Page 3 and 4: PUBLICACIONES GEOLOGICAS ESPECIALES
Page 5 and 6: CONTENTS ABSTRACT . . . . .. . . .
Page 7 and 8: Pl ate 4. Plate 6. Plate 6. Plate 7
Page 9 and 10: 2 F. ETA YO· SERNA The materials t
Page 11 and 12: 4 F. ETA YO· SERNA PHYSICAL STRATI
Page 13 and 14: FIGLH 1\ 2 2AJ Vl:LLA DE LEIVA CD -
Page 15 and 16: 8 Gloriaceras paulinae n. sp. Zumpa
Page 17 and 18: 10 F. ETA YO -SERNA coarse grained
Page 19 and 20: 12 F. ETA YO · SERNA trated in sev
Page 21 and 22: 14 F. ETA YO · SERNA ated. In the
Page 23 and 24: 16 F. ETA YO · SERNA TABLE I ASSEM
Page 25 and 26: 18 F. ETA YO ·SERNA tion consisfli
Page 27: 20 F. ETA YO ·SERNA increasing ove
Page 31 and 32: 24 F. ETAYO ·SERNA rounds abruptly
Page 33 and 34: 26 F. ETAYO · SERNA ffer, 1963, p.
Page 35 and 36: 28 F. ETA YO - SERNA this is partic
Page 37 and 38: 30 F. ETAYO ·SERNA and bifurcate;
Page 39 and 40: 32 F. ETA YO · SERNA thirds of the
Page 41 and 42: 34 F. ETA YO · SERNA Hypotype. (U.
Page 43 and 44: 36 F. ETA YO - SERN A tuberculation
Page 45 and 46: 38 F. ETAYO - SERNA they project sl
Page 47 and 48: 40 last whorl the ribs are inconspi
Page 49 and 50: 42 Hypacanthoplites dognaliciae n.
Page 51 and 52: 44 F. ETA YO · SERNA One large spe
Page 53 and 54: 46 F. ETAYO - SERNA "Acanthoplites
Page 55 and 56: 48 F. ETA YO · ERNA These tubercle
Page 57 and 58: 50 .,CQ.IQmQ.ik.er::fJ§. W forg.ro
Page 59 and 60: 52 Among the subsequent flared ribs
Page 61 and 62: ZONATION OF THE CRETACEOUS OF CENTR
Page 65 and 66: zoNATION OF THE CRETACEOUS OF CENTR
Page 71 and 72: ? ? ZONATION OF THE CRETACEOUS OF C
Page 79 and 80:
ZONATION OF THE CRETACEOUS OF CENTR
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
86 F. ETA YO - SERNA rent localitie
Page 93 and 94:
88 The adapical end of this conch h
Page 95 and 96:
90 F. ETAYO · SERNA dies out near
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92 OCCURRENCE. La Frontera Fonnatio
Page 99 and 100:
94 re is an asymmetrical sulcus bor
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96 (1898, p. 198, figs. 23a,b,c), w
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98 the flank and have a periventral
Page 105 and 106:
100 F. ETA YO - SERNA On the adapic
Page 107 and 108:
102 ventral third of the whorl side
Page 109 and 110:
104 but "Fundort: Von Stiibel im Be
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106 F. ETA YO · SERNA En dos regio
Page 113 and 114:
108 In due regioni della Cordiglier
Page 115 and 116:
110 REFERENCES ANDERSON, F. M. 1938
Page 117 and 118:
112 -- 1963.- Atlas des fossiles ca
Page 119 and 120:
114 KARSTEN, H. 1858.- Vber die geo
Page 121 and 122:
116 Colon. Geol. min. Resourc., uol
Page 123 and 124:
118 F. ETA YO • SERNA WIEDMANN, J
Page 125:
120 A) B) C) D) E) F) G) H) I) L) M
Page 129:
124 F. ETA YO • SERNA A) B) C) D)
Page 133 and 134:
FIGURA 7 A Q 8 ) / ! E I c K FIGUR
Page 136 and 137:
132. A) B) C) D) E) F) G) H) I) J)
Page 138 and 139:
134 Scatter diagram of the distribu
Page 140 and 141:
136 Scatter diagram of the relation
Page 142 and 143:
Page 144 and 145:
140 F. ETA YO · SERNA Scatter diag
Page 146 and 147:
Page 148 and 149:
144 F, ETAYO ·SERNA Scatter diagra
Page 150 and 151:
146 F. ETA YO · SERNA FIGURE 16 Sc
Page 152 and 153:
148 F. ETA YO · SERNA Scatter diag
Page 154 and 155:
PLATES 1-15
Page 157:
154 F. ETA YO · SERNA Fig. 1) Chel
Page 161:
158 F. ETA YO · SERN A PLATE 4 Fig
Page 165:
162 Fig. 1) Vectisites (Zambranoite
Page 169:
166 F. ETA YO · SERNA Fig. 1) Eodo
Page 173:
170 Fig. 1) Carloscaceresiceras cac
Page 179:
176 Fig. 1) Fig. 2) Fig. 3) Fig. 4)
Page 183:
180 Fig.1) Codaziceras scheibei (Ri
Page 186 and 187:
184 Engonoceras, 74. duartci, n. sp
Page 188:
186 Tegoceras, 82. benavidescaceres
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Publicaciones Geolo_gicas Especiales Del lngeominas

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