Faculty of Geosciences
Paleomagnetic laboratory 'Fort Hoofddijk'
Late Burdigalian sea retreat from the North Alpine
Foreland Basin: new magnetostratigraphic age constraints
Sant, K.
1, Kirscher, U.
1,2, Reichenbacher, B.
2, Pippèrr, M.
2, Jung, D.
3, Doppler, G.
3, Krijgsman, W.
11. 'Fort Hoofddijk', Utrecht University, The Netherlands 2. Ludwig-Maximilians-University, Munich, Germany
3. Bavarian Environmental Agency, Germany
Biostratigraphic framework
- Brackish (OBM): sandy Grimmelfin- gen Fm (GS) and fine-grained Kirch- berg Fm (KS) with endemic Rzhekia marker fauna
- Freshwater (OSM): silts/clays
- Detailed small mammal zonations Mixed demagnetization data
- 40-60% reliable samples
Clear composite polarity pattern - based on highest quality cores
Correlation to GPTS
- Option 1: KS to C5Cn.2r
best fit for constant sed. rates - Option 2: KS to C5Cr
with variable sed. rates and erosion
Magnetostratigraphic dating reveals an age of 16.6 ±0.1 Ma for sea re- treat from the central NAFB,
which:
• solves a long-standing age bias,
• backs up the age model of Reichen- bacher et al.3,
• updates the regional time scale, challenges paleogeographic recon- structions, e.g. it suggests a much later uplift of the Amstetten Swell.
Rhezakia fauna is now a tie point for correlation within the Paratethys Sea.
Magnetostratigraphy on scientific drill cores in the underlying OMM should improve NAFB chronostratigraphy.
Magnetostratigraphic dating reveals an age of 16.6 ±0.1 Ma for sea re- treat from the central NAFB,
which:
• solves a long-standing age bias,
• backs up the age model of Reichen- bacher et al.3,
• updates the regional time scale, challenges paleogeographic recon- structions, e.g. it suggests a much later uplift of the Amstetten Swell.
Rhezakia fauna is now a tie point for correlation within the Paratethys Sea.
Magnetostratigraphy on scientific drill cores in the underlying OMM should improve NAFB chronostratigraphy.
Burdigalian sea retreat
The transgressive-regressive infill of the North Alpine Foreland Basin (NAFB) reflects a major change in
Paratethys paleogeography during the Burdigalian. At this point the connection to western Mediterranean became limited, and the western NAFB (Switzerland and S-Germany) most likely became separated from the rest of the Central Paratethys Sea4. In the S-German Molasse Basin, the change is represented by a change from marine (OMM) via brackish (OBM) to freshwater (OSM) molasse.
Large age bias
An age bias of up to 0.7 Myr exists for the onset of freshwater deposition in S-German and Swiss Molasse regions, despite the use of very similar small mammal assemblages and independent dating techniques in both regions1,2. Recently, Reichenbacher et al.3 suggested an age of 16.5-16.7 Ma for the base of the OSM after a
low-resolution magnetostratigrphic study.
Magnetostratigraphy S-German Molasse Basin
Our objective is to refine the chronostratigraphy of the central NAFB by applying high-resolution magne- tostratigraphy on the OBM/OSM transition in eleven parallel drill cores from the S-German Molasse Basin.
The new age constraints will improve paleogeographic reconstructions of the NAFB.
References
Acknowledgements Updated chronostratigraphy
Updated paleogeography Introduction
Drill cores & Results
Conclusions & Follow-up
The mean age is 16.6 ± 0.1 Ma for sea re- treat from the S-German Molasse Basin. We exclude an age >17.5 Ma for the base of the OSM1. The age of base of the OSM is most likely similar in S-Germany and Switzerland.
1) Restricted Rhone connection and south NAFB: ++ clastic input Alpine front.
2) Deposition and erosion Graupensand gully 3) Transgression Kirchberg Fm.
4?) Disconnection NAFB and Central Parate- thys: uplift Amstetten Swell.
Burdigalian paleogeography NAFB
Updated time scale
1. Abdul-Aziz et al. (2010) 2. Kälin & Kempf (2009)
3. Reichenbacher et al. (2013) 4. Sissingh (2001)
5. Dan Palcu (marine map) 6. Jin et al. (1995)
7. Zijderveld (1967)
8. Hilgen et al. (2012) 9. Zachos et al. (2008) 10. Wal et al. (2011)
11. Kuhlemann and Kempf (2002)
A special thanks to employees of the Bavarian Envi- ronment Agency (LfU) from Hof for their help during the sampling.
This work was funded by the European Fund for Regio- nal Development (EFRE), ALW, and NWO through the VICI grant of WK.
Sant et al. (submitted to G&PC)
NAFB with studied area and photos of drill cores. After5,6
Magnetostratigraphic drill cores results with black/white/gray indicating normal/reversed/unclear polarities, and a
composite column based on highest quality cores. Demagn. plots7 of alt. field (AF) and thermally (TH) cleaned samples.
Sketches modified after 11
GS KS
OSM
0
80m 20
60 40
GS KS
OSM
0
m80 20
60 40
GPTS (2012)4
15
16
17
18Ma
C5Bn
C5Cn.1n C5Cn.2n 1r
C5Cn.3n
C5Dn
Option 1 Option 2
(according to Reichenbacher et al., 2013)
C5Dr.1r 1n C5Dr.2r
C5Cr
C5Cn.2r
C5Br
?
terrestrial lacustrine brackish
marine neritic open marine
?
paleogeography ~16.5A/17.0B Ma OBM (KS deposition)
Vosges
Black Forest
Franconian Platform
AS
AS Amstetten Swell CP Central Paratethys Geneva
Munich 0 km 100
c. grained delta fans limestone
Inntal Line
ancient Alpine front
Napf fan
Hörnli fan
Pfänder & Hochgrat fans
Nesselburg fans
Vosges
Black Forest
Franconian Platform
paleogeography ~18.0 Ma OMM
Geneva
Munich
Inntal Line
ancient Alpine front
Napf fan
Hörnli fan
Pfänder & Hochgrat fans
Nesselburg fans
Inn fan
0 km 100
terrestrial lacustrine brackish
marine neritic open marine c. grained
delta fans limestone
study area
Bohemian Massif
Bohemian Massif
study area
A age correlation 1 / B age correlation 2
(OMM in
W-Switzerland)
A
B
Graupensand channel
CP
46˚
47˚
48˚
49˚
50˚
5˚ 6˚ 7˚ 8˚ 9˚ 10˚ 11˚ 12˚ 13˚ 14˚ 15˚
Study Area
Danu eb
Inn hie
Rn
eLch
llerI
Bohemian Massif
Vosges Black F
orest
050
Munich Frankfurt
Geneva
Eastern Alps
B
DR HA LA GE
GU HO
DI BU
BUR
OF GL
3000 1000750 2000 3000 3500 4000
altitude (m)
Paleogeography of the Paratethyan Basins in Early Miocene.
Abbreviations for the Central Paratethys sub-basins: GB - Getic Basin, PCF - Polish Carpathian Foredeep, RCF - Romanian Carpatian Foredeep, STB - Styrian Basin, TB - Transylvanian Basin, UCF - Ukraininan Carpathian Foredeep, VB - Vienna Basin.
TB
E A S TE RN P ARA TE THYS
VB
M E D I T E R R A
N E A N
Rhone Strait
PCF
Basin
SLS?DLS
NAC
Switz.
Germany
France Austria
Central Paratethys
Early MioceneM. Miocene BadenianKarpatianOttnangianLang.Burdigalian BadenianKarpatianOttnangian
15.5
16
17
18
15.5
16
17
18 OSMOMM St. Gallen Fm
Ma Ma
GPTS 2012 Swiss Molasse Stratigraphy
Global time scale8 Med. stages Paratethys stages Par. stages (update)
C5Br
C5Cn.1n
C5Cn.2n C5Cn.2r
1r
C5Cn.3n
C5Cr
C5Dn C5Dr.1r C5Dr.2r
-1.8 -1.4 -1
d18O record 9,10
Miocene Climatic Optimum
500 pts mov. av.
Luzern Fm
S-German Molasse Stratigraphy
GS KS
GS
?
OSMOMMOBM
OBM/OSM:
16.6 ±0.1 Ma
? KS
option 1 option 2
GE
Grimmelf. FmOSM
90 80 70 50
60
u.KS?
l.KS KS/
GD?
HA-1
Grimmelfingen Fm
up.KS
l.KS
KS/
GD?
OSM
10
90 80 70 20
50 30
60 40
BU
Grimmelfingen FmOSM
80 70 20
50 30
60 40
up. KS l. KS
10
20
30
40
OSM
KS/GD GD
Grimmelfingen Fm
GU OSMGrimmelf. Fm
LA
30
40
50
OSM
10 HZ
20
50 30
60 40 up. KS
l. KS
GD
Grimmelfingen Fm
OF
up. KS
GD
Grimmelfingen FmOSM
10
70 20
50 30
60 40
BUR
As
OMM Baltringen FmSteinhöfe FmOSM
20
50 30
60 40
GL
As
up. KS
Baltringen F
mKh.OSM
90 80 70 50
60 OSM
DL
50 40 30 20
60 OBM
OMM
58.13
59.05 59.52
up. KS
GS OBM
up.
l.
Grimmelf. Fm (GS)
(GD)
Upper Freshwate Molasse (OSM) 10
0
80 70 20
50 30
60 40
KS
up.KS
l.KS
Legend
OSM Upper Freshwater Molasse KS (l./up.) Kirchberg Fm (lower/upper) GD Graupensand-Deckschichten GS Grimmelfingen Fm
OMM Upper Marine Molasse
As Albstein (regional limestone Fm)
DR
u.KS
lower Kirchberger Sch.GSOSM
10
116 110 80 70 20
50 30
60 40
reversal
@ base OSM
LA12A
N up/W
Inc -59.9 33.45 m
20
230
350 BUR12.B
N up/W
Inc 66.2
26.45 m 0
20 45
90
AF TH Composite polarity Age correlation
pattern
