Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

More documents

Recommendations

Info

142 ADVANCES IN PALAEOICHTHYOLOGY Fig. 9. Stratigraphic ranges of acanthodian taxa and designated biostratigraphic intervals through the late Ludlow and Přidoli of the Lūžņi-4 borehole. Ludlow/Pridoli boundary, and perhaps this level corresponds to its entrance point into the sequence earlier referred to in publications. The Rohonilepis breviornatus interval (306.2-280.3 m) embraces the main part of the Varniai Beds (Minija Fm.) and except for the nominative species (Valiukevicius 2004), includes one more characteristic acanthodian of short range in the Baltic, Nostolepis sp. cf. N. linleyensis (Miles and Märss 1999). N. linleyensis is certainly obtained at the Minija/Jura boundary in Lithuania, and at a nearly coeval horizon in the Lužni core (see Fig. 9). The stratigraphical potential of this taxon is high for the assignment
J. Valiukevičius. Silurian acanthodians from Lūžņi-4 143 of the biozonal unit and wider correlations, as in the type locality (Linley Brook near Much Wenlock, UK) it is only known from the Downton Castle Sandstone Fm., the lower part of Pridoli (Miles and Märss 1999). Poracanthodes punctatus accompanied by Gomphonchus sp. cf. G. hoppei first appear at the same point, and distinguish the next interval (280.3-260 m). P. punctatus is the second acanthodian species of the Silurian Vertebrate Standard Scheme (SVSS), having its interval zone attached to the upper part of the Pridoli (Märss 1986, 1992, 1997, 2000; Märss et al. 1995, 1996). In the Lužni-4 core, the interval correlates to the Minija/Targale Fm. boundary beds, perhaps supporting the prior opinion on its first occurrence in Estonian localities. However, in Lithuania, particularly in the west area, which is characterized by the deepest marine sediments and most complete geological profile, it ranges for the entire Pridoli, in the Minija and Jura formations. The Arenaceacanthus arcuatacanalis interval (260-223 m) comprises almost full ranges of the index species (Valiukevicius 2004) and “Pruemolepis wellsi” Vieth (1983) (the last being only a specialized morphological variety of nostolepids), and Nostolepis musca Valiukevicius (2003 b) appearing high at the top of the interval. Both most valuable taxa demonstrate distinctly later stratigraphical entry as compared to Lithuania, where A. arcuatacanalis appears in Wenlock? (with some doubt according to conodont dating of rocks) and N. musca in the Ludlow. The next, Fecundosquama basiglobosa interval (223-210.8 m) is attached to the upper part of the Venzava Beds (Targale Fm.) and probably the previous showing a shorter range in comparison with Lithuania, where the nominative species makes the first occurrence in the Minija Fm. (Valiukevicius 2004). This species is of great interest in acanthodian biozonality as it is easy identifiable, with a restricted stratigraphic range and wide regional distribution. It is recognized in all Baltic republics and the Kaliningrad district of Russia. Of note, in this interval nostolepid squamae margaritatae (Gross 1971) first appear, possibly identifying a stratigraphic level useful for correlation over a wide area. The Garzde and Lužni Beds of the Targale Fm. are connected with the flourishing time for acanthodians in the late Pridoli. The acanthodian associations (likely as in the whole Baltic region) have shorter ranges, and the new indices and characteristic taxa reach maximum numbers here and appear with the highest frequency. The short-ranging Poracanthodes sulcatus sp. nov. interval (210.8-202 m) is distinguished at the base of Garzde Beds and marks a sequential dominance of ischnacanthid acanthodians in the taxa-rich associations. Alongside the index species, it is marked by the entry of two more Poracanthodes, P. cf. stonehousensis (sensu Vergoossen 2000) and P. marssae sp. nov., and also two representatives of Gomphonchus, G. cf. mediocostatus Vergoossen (1999 c) and G. hoppei (Gross 1947). Poracanthodids are not yet defined in Lithuania, but the stratigraphical level may be approximated by the representatives of Gomphonchus occurring in the Kelme Beds of the Jura Fm. The Monospina erecta interval (202-196.5 m) marks an essential renewal of acanthodian associations with the entering of most valuable Monospina erecta Valiukevicius (2003 d), Nostolepis elegans (Brotzen 1934), N. alifera sp. nov., N. amplifica Valiukevicius (2003 b) and ?Diplacanthus sp., whereas the overlying Nostolepis alta interval (196.5-186 m) yields only the index species of significance
Page 1 and 2:
LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 3 and 4:
LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 5 and 6:
Contents Ervīns Lukševičs and Ģ
Page 7 and 8:
ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 9 and 10:
Ervīns Lukševičs, Ģirts Stinkul
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Olga Afanassieva. Microrelief on th
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
D.K. Elliott, E. Mark-Kurik, E.B. D
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
C.G.Miller, T. Marss, H. Blom. New
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
H.-P. Schultze, T. Marss. Revisitin
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
O.A. Lebedev. A new tetrapod from R
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92: O.A. Lebedev. A new tetrapod from R
Page 99 and 100: ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 101 and 102: E. Lukševičs, I. Zupiņš. Sedime
Page 121 and 122: J. Valiukevičius. Silurian acantho
Page 141: J. Valiukevičius. Silurian acantho
Page 149 and 150: V. Pernegre, V. Dupret. Biostratigr
Page 159 and 160: Ž. Žigaite. New telodont from Tuv
show all

Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?