(E) Sediment geochemistry

Transcription

1 (E) Sediment geochemistry chemical composition of common arenites Pettijohn et al p.59 classification based on geochemistry Herron 1988 Pettijohn 1963,

2 Example: 1. 9% NCI glauconitic greensand oolithic ironstone reworked phosphorite gypsarenite 2. subarkose 5% Q quartzarenite sublitharenite Swiss Molasse Basin CE 1% calclithite 33% NCI-rich sandstone NCI-bearing sandstone sandstone s.str. NCI-rich hybrid arenite NCI-bearing hybrid arenite hybrid arenite NCE quartzarenite, arkose, litharenite CI calcarenite 25% lithic subarkose arkose lithic arkose F feldspathic litharenite litharenite L incl. CE log(fe O ) 2 3/K 2 O 1 Fe-shale shale litharenite wacke arkose Fe-sandstone sublitharenite subarkose -1 1 log(sio 2/Al2O 3) 2 quartz arenite classification based on geochemistry classification based on petrography Pettijohn et al p.59 2

3 Rollinson 1993 Tectonic Setting Discrimination diagrams (1) Major elements: Rollinson 1993 p.28 3

4 Rollinson 1993 p.27 discrimination of tectonic setting by major elements does it work properly? Armstron-Altrin & Verma 25, Sed Geol 177 4

5 success rate Armstron-Altrin & Verma 25 be very careful with such discrimination diagrams!!! the problem of grain-size D G-m O-m O-f O-g G-g G-f A C B A increasing grain size B C D Bhatia 1983, Bhatia & Crook 1986, Roser & Korsch 1988 greywackes from type-locality Oberharzer Grauwacke 5

6 Bivariate Ca / Mg / LOI-plots of Swiss Molasse sandstones (litharenites) CaO 3 CaO SiO LOI 2 16 MgO 12 8 MgO CaO LOI Ma G S 6 % WSW ENE

7 framework composition vs. wr-geochemistry von Eynatten 23 (2) Trace elements: Rollinson 1993 p.28 7

8 detection of various processes such as recycling, sorting, etc. Th/Sc monitors the compositional variation of the source area, and Zr/Sc monitors zircon enrichment due to sedimentary (sorting and) recycling 1 Th / Sc 1.1 Compositional variation Sediment Recycling Active Margin Turbidites.1.1 Trailing Edge Turbidites Andean Foreland Loess Zr / Sc McLennan 1993, GSA Spec Pap 284 Cr-spinel chemistry recycling TiO 2 [Gew.-%] IPB 1..5 MORB IAB Fe III /(Cr+Al+Fe) group I TiO 2 [Gew.-%] 2. group II group III MORB IPB IAB % L u (serpentinite clasts) Fe III /(Cr+Al+Fe) von Eynatten 23, Sedimentology 5 8

9 Ma WSW 8 SEDIMENTE > 75% 5-75% 25-5% 1-25% WSW Flysch Metasedimente (Ultra-)basite Granitoide 7 > > >? recycling? ~ 2 Ma Sedimente Sedimente 6 5 Metasedimente Granitoide ~ 25 Ma? recycling? SEDIMENTE 4? Sedimente Sedimente Granitoide (Ultra-)basite (Ultra-)basite ~ 21 Ma (Ultra-) basite SEDIMENTE ENE Granitoide ENE von Eynatten 23 Contribution of mafic to ultramafic (ophiolitic) source rocks ( Mixing! ) McLennan

10 Rare earth patterns of sediments from different sources McLennan 1993 Alteration (weathering, diagenesis,...) Chemical Index of Alteration: Al 2 O 3 CIA = 1 Al2 O 3 + CaO* + Na 2 O + K 2 O (with CaO* = CaO from silicate phases) increasing alteration Nesbitt & Young

11 Leeder 1999 Nesbitt & Young

12 chemical weathering of granitoid rocks Toorongo granodiorite (Nesbitt et al. 198, GCA 44) 1 A Ka C I A Chemical Index of Alteration: 1 Al 2 O 3 +CaO*+Na 2 O+K 2 O 5 Pl + Kf Al 2 O 3 CN K chemical weathering of granitoid rocks Toorongo granodiorite p(a) s k = (k p w1 ) g p w1 = (.49,.13,.38) 99.5% + g von Eynatten et al. 23 p(cn) p(k) 12

13 chemical weathering of granitoid rocks Toorongo granodiorite normalized to Al 2 O 3 = Al O CaO* Na O 2 KO k von Eynatten et al. 22, Math. Geol. 34 chemical weathering at global scales suspended sediment load of the world s major rivers (McLennan 1993, J. Geol. 11) s = cc (k p w2 ) p w2 = (.51,.13,.36) 97.1% p w1 = (.49,.13,.38) 99.5% p(a) Niger Congo Orinoco Indus Mekong river k St. Lawrence.13 Danube.25 Ganges.75 Indus.78 Orinoco 1.1 Mekong 1.87 Congo 2.15 Niger 3.49 Ganges p(cn) cc g Danube St. Lawrence Mackenzie p(k) von Eynatten et al. 23, Math. Geol

14 Observed trends often due not correlate with predicted trends She et al. 26, Chem Geol. X 1 superposition of processes 1 2? von Eynatten 24, Sed Geol a X 2 X 3 Trace elements such as Rb, Ba, Sr, U, Th, Zr, etc. may provide valuable additional information on weathering processes McLennan