7. LOWER CRETACEOUS AMMONOIDEA FROM THE NORTHERN ATLANTIC, LEG 47B, HOLE 398D, DSDP Otto Renz, Museum of Natural History, Basel, Switzerland l e n e e ) INTRODUCTION e Specimen Cor (cm Zon Stag Interva Sectio Subzon Hole 398D (40°57.6'N, 10°43.1'W) is under about 3900 72 meters of water, 90 kilometers from the western coast of the 1, 0-2 Beudanticeras sp., small fragment with segment of suture, probably still Albian Iberian Peninsula and south of Vigo Seamount. Drilling 73 penetrated the Paleocene-Cretàceous boundary at a sub- 74 bottom depth of 800 meters and terminated at 1740 meters in Hauterivian limestone. ) 75 tes i The Lower Cretaceous consists predominantly of a 720- N meter body of uniform, dark gray clay stones with thin tur- 76 ammon 1, 148-150 Small fragments of Inoceramus y b bidite interbeds. These clay stones yielded 21 ammonites, 2 ALBIA 77 } Lamellaptychi, 1 small gastropod, a fragment of In- LU > cc. 02 Phylloceras sp., test fragments 0- 0 78 oceramus, and some pieces of unidentified belemnites. CL z The ammonites are distinguishable into two assemblages: 79 Albian and Barremian. The younger Albian congregation of ammonites ranges from about 1110 to 1365 meters in Cores 80 72 to 99 (Figure 1). This assemblage includes the upper 81 Albian (although not proven on the basis of ammonite dis- —? — ? — tribution), a recognizable middle Albian, and the mammil- 82 latum Zone of the lower Albian. Ammonites are not present 83 that would indicate a tardefurcata Zone in the lowermost 1, 68-70 Beudanticeras sp., body chamber Albian. The older Barremian assemblage consists of only 84 2, 125-127 Lyelliceras sp., poorly preserved fragment three ammonites collected between 1636 and 1663 meters in Cores 127 to 130. 85 N A Lamellaptychus angulocostatus (Peters), recovered 86 BIA from 1720 meters in Core 136, indicates Hauterivian de- < LU 87 ntatui posits. a — I 88 . 5, 12-15 Lyelliceras lyelli (d'Orbigny) ALBIAN lyell - 6, 41-42 Parasilesites kilianiformis (Fallot) - 1,148-150 Phylloceras (Hypophylloceras)"! subalpinum (d'Orb.) The ammonite fauna of the Albian consists of 18 speci- 1, 70-73 Phylloceras {Hypophylloceras) cf. subalpinum (d'Orb.) mens that represent 11 identifiable species and subspecies of - 3, 13 Beudanticeras sp., strongly compressed 90 " 4, 65-67 Phylloceras (Hypophylloceras) cf. aphrodite the Families Phylloceratidae, Desmoceratidae, Douvil- Fallot and Termier, suture liceratidae and Lyelliceratidae. Among the Heteromorpha, 91 the Hamitidae and Ptychoceratidae are represented (Figure 92 1). The identified species and subspecies are: - 1 104 Ptychoceras cf. laeve Matheron, initial and second shaft 93 3 52 Phylloceras sp., test fragments Phylloceras (Hypophylloceras) cf. subalpinum (d'Or- " 3 146 Phylloceras sp., test fragments bigny) Plate 1, Figure 4; Phylloceras (Hypophylloceras) cf. 94 seresitense tanit Pervinquière (Plate 1, Figure 3); Phyl- < ε loceras (Hypophylloceras) cf. velledae velledae (Michelin) B 95 . 4 99-100 Hypacanthoplites milletianus (d'Orbigny) " 5 77-78 Hamites attenuatus J. Sowerby AL (Plate 1, Figure 2); Phylloceras (Hypophylloceras) cf. ap- R - 1 117-119 Phylloceras (Hypophylloceras) cf. velledae velledae 96 (Michelin), suture hrodite Fallot and Termier (Plate 1, Figure 1); Beudan- mammillati 1 123-128 Phylloceras (Hypophylloceras) cf. seresitense LOWE tanit Pervinquière ticeras sp. (Plate 2, Figure 3); Beudanticeras newtoni Casey 97 (Plate 2, Figure 2);Parasilesites kilianiformis (Fallot) (Plate j 2, Figure 1); Lyelliceras lyelli (d'Orbigny) (Plate 2, Figure 98 - 1 54-55 Beudanticeras newtoni Casey, with part of suture 5); Hypacanthoplites milletianus (d'Orbigny) (Plate 2, Fig- 99 ure 4); Hamites attenuatus J. Sowerby (Plate 2, Figure 6); and Ptychoceras cf. laeve Matheron (Plate 2, Figure 7). Figure 1. Distribution of ammonites in the Albian sedi- ments of Leg 47B, Hole 398D. With 8 specimens, the Phylloceratidae dominate the as- semblage and represent 44 per cent of the total Albian am- maining five specimens are distributed among the genera monites collected. The Desmoceratidae are second in abun- Hypacanthoplites, Lyelliceras, Hamites, and Ptychoceras dance, with 5 specimens representing 28 per cent. The re- (28 per cent of the total). 361 O. RENZ Upper Albian BARREMIAN Within the interval of Cores 72 to 82 (1120 to 1220 m), Three strongly compressed Barremian ammonites, also specifically unidentifiable fragments of tests of Phylloceras with their tests preserved, occurred between Cores 127 and sp. (Sample 77-CC, 0-2 cm) and fragments showing seg- 130 (1636 to 1663 m), 243 meters below the deepest Albian ments of the suture indicating a Beudanticeras (Sample ammonite. The genus Barremites is represented by two 73-1, 0-2 cm) are present. These remains do not permit specimens, which are accompanied by a juvenile Protet- reliable age determinations. The presence of Beudanticeras ragonites; all are specifically unidentifiable. Barremites is at the top of Core 73 suggests, however, an Albian age for widely distributed between southern England and northern the interval; according to its position in the section, these Africa, and several species from the Barremian of the sediments are considered upper Albian. Alicante region in southern Spain are described by Lillo Bevia (1975 a,b). Middle Albian HAUTERIVIAN The middle Albian ammonites are better preserved and The presence of Hauterivian deposits is suggested by a allow more accurate age determinations. This interval is single, favorably preserved Lamellaptychus angulocostatus represented by Cores 82 to 91 (1220 to 1310 m). Within the (Peters). This specimen (Plate 2, Figure 9) occurs in Core middle Albian, the following three ammonite zones are es- 136, 22.5 meters above the bottom of the hole. In the North tablished: the Euhoplites lautus, the Euhoplites loricatus Atlantic, L. angulocostatus has been recorded in several and the Hoplites dentatus zones (Owen, 1971). The ammo- DSDP holes: from Hole 105 (Core 18, pi. 4, fig. 1-5) in the nites in our samples are confined to the dentatus Zone, Hatteras Abyssal Plain, Leg 11 (Renz, 1972); Hole 367 which again is subdivided into three subzones. One of th- (Core 26, pi. 1, fig. 34, 35; Core 27, pi. 2, fig. 1-4) in the ese, the Lyelli Subzone (Figure 1), is ascertained in Core 88 Cape Verde Basin, Leg 41 (Renz, 1977); and from Hole (1270 m) by the presence of a relatively well preserved 391C (Cores 14 to 17, pi. 1, fig. 16, 17) in the Blake- specimen of Lyelliceras lyelli (d'Orbigny). This specimen is Bahama Basin, Leg 44 (Renz, in press). considered reliable evidence of middle Albian deposits. The middle Albian-lower Albian boundary seems fairly re- stricted between Cores 91 and 92 (1309 m). SYSTEMATIC DESCRIPTIONS The ammonites were received in June 1976 from Jacques Sigal who Lower Albian collected them on-board ship during Leg 47B. The material was still moist, and disintegrated rapidly when unpacked. Measures had to be taken im- The established ammonite zones of the lower Albian are mediately to avoid further disintegration of the clay stone, separation of the the Douvilleiceras mammillatum above, and the fossils from the matrix, and breakage of the ammonite tests. Leymeriella tardefurcata, below. Only the mammillatum Without exception, all ammonites had their tests well preserved and little diagenetical alteration occurred. The composition of test material from a Zone, which is subdivided into four subzones, is reliably Hamites attenuatus J. Sowerby (Sample 95-5, 77-78 cm) was analyzed by represented in Hole 398D. The age-indicating ammonite of X-ray diffraction by S. Graeser, mineralogist of the Museum. The Debye- importance is Hypacanthoplites milletianus (d'Orbigny) de- Scherrer diagram clearly shows that the test material is absolutely identical rived from Sample 95-4, 99-100 cm (about 1340 m). About with aragonite. The appearance of the test is mother of pearl-like, brilliant 25 meters deeper, Beudanticeras newtoni Casey occurs in light brown, and without visible traces of original color. This type of preservation is typical for shale-clay sequences, where Sample 99-1, 54-55 cm (1365 m). In southern England, this diagenetic exchange of shell material by solution is reduced to a minimum. species attains its greatest frequency within the ßoridum During sinking to the sea bottom, only the thin outer layer of the test, Subzone (the third of the four succeeding subzones) of the containing color pigment, was removed. The aragonite of the conch was mammillatum Zone. not affected by solution, nor was it transformed into calcite. We assume that the recovered ammonites did not live near the bottom of the sea, where Only a minute share of the Albian ammonite fauna in this they presently form part of a death community (thanatocoenosis). The area was recovered from Hole 398D. Abundant Phyl- conchs were probably rapidly buried by shale or turbidite flows. According loceratidae and Desmoceratidae, and the absence of to Friedman (1965), pteropod shells composed of aragonite apparently strongly ornamented Hoplitidae suggest an open basin Al- dissolve at a water depth of about 3500 meters. We might assume that the water depth during the Albian at Site 398D was considerably above this bian environment. Comparable depositional environments depth. are known from Mallorca (Fallot, 1910, 1920) and from The internal structure of the test is clearly observable on several speci- southern Spain in the Alicante region, where the faunal mens, especially Phylloceratidae. On lamellae forming the outer layer