NEW BIO- AND MAGNETOSTRATIGRAPHIC DATA AT THE JURASSIC-CRETACEOUS BOUNDARY OF THE CHIGAN СAPE (VLADIVOSTOK REGION, RUSSIA)код для вставки
NEW BIO- AND MAGNETOSTRATIGRAPHIC DATA AT THE JURASSIC-CRETACEOUS BOUNDARY OF THE CHIGAN ?APE (VLADIVOSTOK REGION, RUSSIA) Guzhikov A.Yu.1, Arkadiev V.V.2, Baraboshkin, E.Yu.3, Feodorova A.A.4, Shurekova O.V.4, Baraboshkin E.E.3, Manikin A.G.1, Surinsky A.M.1, Golozubov V.V.5, Kasatkin S.A.5, Nechaev V.P.5 1Chernyshevsky Saratov State University, Saratov, Russia, 2Saint Petersburg State University, St. Petersburg, Russia, 3Lomonosov Moscow State University, Moscow, Russia, 4Research and Production Enterprise Geologorazvedka, St. Petersburg, Russia, 5Far East Geological Institute FEB RAS, Vladivostok, Russia, 42�'37.8''N 123�'47.0''E In September 2014 we have studied the well-known Chigan section (Chigan Cape, Podiapolsky Town region). Some geologists (Konovalov, Konovalova, 1997) supposed that the section contains Jurassic?Cretaceous (J/K) boundary interval. This section previously referred to Berriasella jacobi ammonite zone (Konovalova, Konovalov, 1997; Sey, Kalacheva, 1999) because of ammonite findings: Pseudosubplanites cf. grandis, P. aff. combesi, Berriasella ex gr. jacobi, Dalmasiceras, and others. (Konovalova, Konovalov, 1997) in calcite cement (Sey, Kalacheva, 1999) Outcrops 3046 and 3047 consist of gray sandstones, poorly sorted and muddy. These layers crop out in steep cliffs at a distance of 500 meters to the north from the section 3046. Its bedding is nearly subhorizontal and they are crossed by a number of Late Cretaceous gabbro dikes. The ichnogenus and lithology are typical for the lower shoreface zone (Members 1-3 and 5). A specific 1.5-m level of middle-upper shoreface massive sandstones (Member 4) was recognized in the middle part of the section. It is limited by the erosional surfaces at the base and at the top. The upper surface is a transgressive surface, which is overlaid by 10cm cross-bedded sandstone, replaced laterally by bioclastic rudstones. The visible thickness of the section is 33 m. 5 4 3 2 1 Recrystallised rudstones with quartz grains and bioclasts of bivalves (Bi) and crinoids (Cr) in calcite cement. Member 5. Thin-section 1314-3, nicols +. Polymictic sandstones of lower shoreface with Schaubcylindrichnus coronus. Member 2. Thin-section 1314-1-11, nicols +. For the comparison we have studied section 3050 to the south (~1.1 km), which continues the Chigan Formation (Sey, Kalacheva, 1999) and has the same stratigraphic age (Konovalov, Konovalova, 1997). Berriasella cf. jacobi Mazenot, cast. Pseudosubplanites cf. combesi Le H間arat. Collection of V.P. Nechaev, 2014. Collection OAO ?Primorgeologiya?, sample 15-1547. Collection of I.V. Konovalova, 1993. Scale bar = 10 mm. In the rockfall at the base of the section we found the remains of ammonites: an imprint of Pseudosubplanites cf. combesi Le H間arat and living chamber fragment of Pseudosubplanites sp. In addition, in the collection of I.V. Konovalov? (1993), courtesy of the "Primorgeologiya" Company, we have determined Berriasella cf. jacobi Mazenot and Pseudosubplanites sp., also found in the debris at the base of the same sections. All these findings characterize the Lower Berriasian Jacobi Zone. It should be noted that P. cf. combesi differs from other Pseudosubplanites by evolute shell and prevalence of bifurcate ribs. It is also very similar to some Upper Tithonian forms (Oloriziceras type). Palynology. The plant detritus, poor preserved gymnosperms pollen and spores, rare indeterminate proximochorate ? proximate cysts and dinocysts Sirmiodinium grossii Alberti, Systematophora areolata Klement ? Tubotuberella rhombiformis Vozzhen. were found in only one sample (3046/3) of 14. This assemblage ranges from Oxfordian to Early Valanginian. Dark brown organic residues indicates the mesocatagenetic stage with paleotemperature about 200�. 3050 uppermost 3046 3047 3050 lowermost Generic rate of foraminifers from Chigan formaition The differential thermomagnetic analysis and magnetic saturation demonstrate that magnetite or related titanomagnetite are principal magnetic minerals in the sandstones. The hematite was fixed at one level only (sample 3046/21 near the base of member 4). Results of thermomagnetic and alternating field cleanings. Statistic paleomagnetic characteristics of the Chigan cape section n D?? (o) I?? (o) ? ?95 (o) (R-) ??? ????????? ??? ?????????? 43 262.6 -79.4 8.23 8.1 (R-) ?????????, ????????? ??? ? ????????? ???????? ???????????? 40 259.3 -81.9 11.75 6.9 (N+) ??? ????????? 12 311.6 64.9 24.68 8.9 (N+) ?????? (?????? ?????) ? ???? ???????? 17 279.2 84.5 45.05 5.4 Results of contact test Thank you for attantion!