Mollusca, Archaeogastropoda
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Contr. Tert. Quateni. Geol 37(3-4) 57-65 4 figs. Leiden, December2000 The genus Solariella (Mollusca, Archaeogastropoda) from the Pliocene of Vale de Freixo, Portugal: palaeobiogeographic and palaeoclimatic implications Carlos Marques+da+Silva Universidade de Lisboa Lisboa. Portugal Bernard Landau InternationalHealth Centres Albufcira, Portugal and Jordi Martinell Universitat de Barcelona Barcelona. Spain & from the Plio- Silva, Carlos Marques da, Bernard Landau Jordi Martinell. The genus Solariella (Mollusca, Archaeogastropoda) — 57- cene ofVale de Freixo, Portugal: palaeobiogeographic and palaeoclimatic implications. Contr. Tert. Quatern. Geol., 37(3-4): 65, 4 figs. Leiden, December 2000. the first time from Pliocene In the present paper, trochid gastropod Solariellacincta (Philippi, 1836) is recorded for the (Piacenzian) strata exposed at Vale de Freixo (Pombal, central-west Portugal). This record of the species constitutes the first from the Atlantic Neogene; the taxon is here compared with other Miocene to Recent European species ofSolariella. At present, S. cincta is restricted in Mediterraneanand the to the coast ofWest Africa. During the Late Pliocene, it had a much wider distribution, occurring the along at least far north central-west Iberia. The of benthic such as S. European Atlantic coasts, as as presence thermophilic gastropods cincta, Tribia uniangulata (Deshayes, 1830), Solatiapiscatoria (Gmelin in Linné, 1790), Ancilla sp., Ficus sp., and Strioterebrum than still sp. in Pliocene strata at Vale de Freixo, clearly indicates that relatively high water temperatures (i.e. warmer today) pre- the Atlantic this between 3.2-3.1 and 2.7 Ma. vailed, at least sporadically, along European coast at latitude, c. Key words —Gastropoda, Trochidae, Pliocene, Portugal, palaeobiogeography, palaeoecology. de Universidade de da Escola P-1250 102 C M. da Silva, Departamento e Centro Geologia, Lisboa, Rua Politecnica, 58, Lisboa, Portugal [e-mail: [email protected]]; B.M. Landau, InternationalHealth Centres, Avenida Infante Dom Henrique 7, Areias de Sao Joao, P-8200 Albufeira, Portugal [e-mail: [email protected]]; J. Martinell, Departament d'Estratigrafia i Paleontolo- gia, Facultat de Geologia, Universitat de Barcelona, E-08028 Barcelona, Spain [e-mail: [email protected]]. Contents Introduction molluscs from central-west Introduction p. 57 Although Pliocene marine have been known for than hundred Systematic palaeontology p. 58 Portugal more one Discussion Choffat. of the classic p. 62 years now (see e.g. 1889), none Conclusion 63 localities has a fauna as diverse or well p. produced pre- served that at Vale de Freixo in the Pombal Acknowledgements p. 63 as region References p. 64 (Fig. 1). 58 the location of the Vale de Freixo in central-west Fig. 1. Map showing outcrop Portugal The Pliocene sequence in this region consists oftwo affinity, as defined by Raffi et al. (1989). The chrono- members, the Formagao Arenito de Carnide below, and logic overlap between biozone CN12a and molluscan time Formagao Arenito de Roussa-Paredes above. The for- unit MPMU2 provides a more precise assignment mer unit comprises barren, fine, silty, micaceous sand. ofBed 3 deposition at Vale de Freixo, viz. between 3.2- the last Locally, the lowermost portion of this formation con- 3.1 and 2.7 Ma, the latter documenting appear- tamalis tains a basal conglomerate and a sand rich in marine ance datum (LAD) of Discoaster (see Silva, molluscan shells. At Vale de Freixo, the maximum 1995). thickness of the basal fossiliferous beds of the Forma- gao Arenito de Carnide amounts to approximately 1 m (Fig. 2). These beds are remarkable for their relatively SYSTEMATICPALAEONTOLOGY abundant, well-preserved macrofossils, mostly bivalves and Gili for gastropods (see et al., 1995, more details). Superfamily Trochoidea Rafinesque, 1815 The material studied for the present paper was col- Family Trochidae Rafinesque. 1815 lected from Bed 3. Subfamily SolariellinaePowell. 1951 The molluscan assemblage from Vale de Freixo Genus and subgenus Solariella Wood. 1842 indicates a shallow marine, infralittoral environment with relatively high water temperatures (Silva, 1993a; Gili et al., 1995; Nolf& Silva. 1997). The fauna shows Solariella(Solariella) cincta (Philippi, 1836) an interesting combination of Mediterranean and Fig. 4 northern European Pliocene species (Gili et al., 1995), in addition to a number of probable endemics, most of which await description. 1836 Trochus cinctus Philippi, p. 185, pi. 10, fig. 20. 1898 Gibbula P. Fischer — According to Cachao (1990). the calcareous nan- inoptanda Locard, p. 51, 1, 24-27. nofossil assemblage of Bed 3 at Vale de Freixo indi- pi figs 1916 Solariella cincta (Philippi, 1836) — Cerulli- cates placement in the Discoaster tamalis Zone Irelli, p. 187, pi. 21, figs 23-25 (typical), fig. 26 (CN12a, see Okada & Bukry, 1980), i.e. Upper Plio- (var. depressa Seguenza), fig. 27 (var. conica Ce- cene. Piacenzian {sen.su Berggren et al., 1995). The rulli-Irelli). molluscan faunas from this bed allow assignment to the 1993 Solariella cincta (Philippi, 1836) — Waren, p Mediterranean Pliocene Molluscan Unit 2 of Raffi & 161, fig. lb, c. Monegatti i.e. the 3.2-3.1 Ma eco- (1993), postdating — 1993 Solariellainoptanda (Locard, 1897) Waren, p extinction event and lo- biostratigraphic (immigration 161, fig. 2e. cal of benthic molluscan taxa of — extinction) tropical 1993b Solariellasp. Silva, p. 116, pi. 2, figs 1-3 59 Fig. 2. Stratigraphy ofthe Vale deFreixo outcrop, representing the lowermost portion of the Pliocene (Piacenzian) sequence in the Pombal region (central-west Portugal). cords Diameterof 320-360 Material — Over 30 well-preserved specimens (Silva spiral (Fig. 4d-f). protoconch and Landau all from nucleus 180-200 Shell collns), representing growth stages, pm, of pm. small, trochiform, Bed 3 at Vale de Freixo (Pombal region, central-west maximum height 8.6 mm, maximum width 10.0 mm; Portugal); Pliocene, Piacenzian. teleoconch of 6 whorls with a prominent, subhorizontal, Diagnosis — A medium-sized Solariella with an angu- concave subsutural ramp, inward sloping in early lar periphery on the spire whorls, rounded body whorl, whorls, outward sloping in subsequent whorls. Whorl with ornament of three strong primary cords additional profile below subsutural ramp flat on early whorls, con- secondaries whorls and on later a wide, deep, ridged cave on body whorl. Teleoconch ornament of two umbilicus. granulose primary spiral cords on the first whorl, with a Description — Protoconch homeostrophic, paucispiral, third appearing towards the end of the second; adapical delineated from telcoconch, of about sharply consisting cord defines outer limit of subsutural ramp. Below, whorls with elevated nucleus. 1.25 a large, slightly whorl is flattened and slopes at an angle towards abapi- Whorl ornament consisting of several (3-4 ?) very fine cal cord, from which whorl profile drops vertically to- 60 wards suture, which is narrow, linear and shallow; ir- tions of spiral cords; parietal lip adherent to body whorl regularly spaced spiral secondaries and tertiaries appear with no callus formation. — similar the in interspaces between the three primaries on later Comparisons Solariella cincta is to Re- whorls. Axial ornament of numerous weak growth lines cent S. amabilis (Jeffreys, 1865), which ranges from overlying spiral ornament and forming granulose cords. southwest Iceland to the coast of western Morocco; it has wider and ornamented Growth lines most prominent over abapical cord, giving however, a more coarsely colour it a finely beaded appearance, strongest on the early umbilicus, more convex whorls, a prominent whorl well and smaller teleoconch whorls. Body developed, com- pattern a protoconch (Waren, 1993, p. 161). prising two-thirds of total shell height; whorl profile There is also a resemblance to Solariella maculata rounded rather than angular as in earlier teleoconch Wood, 1842 (p. 531, pi. 5, figs 7, 10), which is endemic whorls. Base flattened, concave with wide, deep umbili- to the Lower-Middle Pliocene of the North Sea Basin half of base. Ornament of This form has rounded, rather cus, occupying the diameter (Marquet, 1995, p. 64). 5-10 subequal spiral cords, wider than interspaces. Um- than angular whorls and evenly spaced spiral keel- bilicus delimited by a wider periumbilical cord crossed shaped cords, and also differs from S. cincta in other by numerous axial growth lines forming ridges on the details of ornament. Traces of coloration are also pres- cord. Inner face of umbilicus with 7-8 spiral cords, ent in many specimens of S. maculata (see Gevs & finely ridged by numerous, closely spaced axial growth Marquet. 1979. p. 68, pi. 27, fig. 5). but appear as radial lines. Aperture circular, with continuous peristome, lip spots rather than vertical flammules. thin and sharp with a sinuous edge, caused by elonga- Fig. 3. Stratigraphical and geographical distribution ofSolariella (S.) cincta (Philippi, 1836). 61 Fig. 4. Solariella (S.) cincta (Philippi, 1836), VFX.03.026 (Silva Colln), Upper Pliocene (Piacenzian), Vale de Freixo (Pombal A - 10.0 B - - region, central-west Portugal); dorsal view (height 8.6 mm, diameter mm); apertural view; C umbilical view; D-F - protoconch (scale bar 100 µm). 62 Two allied species occur in the Italian Pliocene. One Solariella sp.), the Mediterranean, southern Spain Solariella which of these, peregrina (Libassi. 1859), is (Estepona. Zanclean. pers. obs.), and ?Italy (Sicily and also known from