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Thrust-front evolution and implications for deep-water ... seismic-reflection data coverage Lakes...
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SPODDS Thrust-front evolution and implications for deep-water sedimentation, eastern Alps and Molasse foreland basin, Austria: Progress Report Jacob A. Covault , Hans-Gert Linzer , Ralph Hinsch , and Stephan A. Graham 1 2 1 2 1 2 Dept. of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, Rohöl-Aufsuchungs A.G., Schwarzenbergplatz 16, A1015 Vienna, Austria 1. Abstract 3D and 2D seismic-reflection data and extensive core and wireline-log data from Austria are provided by Rohöl-Aufsuchungs A.G. in order to interpret the structural evolution of the Eastern Alpine thrust front and controls on coarse-clastic sediment distribu- tion across the southern slope of the Molasse basin. The study area contains slope fans located directly forward of the eastern Alpine thrust front or in nappe-top minibasins located in synclines between adjacent nappes of the thrust front. Some slope fans are predominantly composed of relatively thick, amalgam- ated beds of coarse-grained sediment with few finer-grained interbeds, whereas others are predominantly composed of finer-grained sediment. Seismic-reflection data reveals the Oligocene to Miocene evolution of the eastern Alpine thrust front. Nappe-top minibasins and tear faults may have developed during thrust-front advancement. These structures may have served as sediment storage areas and conduits. The conduits may have been far-reaching channels that provided a pathway through which sediment from an Alpine hin- terland source area was transported to the southern slope of the Molasse foreland basin. Slope fans consisting of relatively coarse- grained sediment may have received detritus from these conduits. Alternatively, slope fans composed of relatively fine-grained sedi- ment may have been deposited as a result of slumping of the nearby, presumably finer-grained sediment that comprised the pa- leoshelf. Future work will support the seismic-reflection- and wireline-log-based interpretations presented in this progress report. 2. Eastern Alpine thrust front and Molasse foreland basin 48º15’ N 48º00’ N 47º45’ N 13º00’ E 13º30’ E 14º00’ E 14º30’ E 0 25 50 Kilometers A A’ Figure 3 F L Y S C H T H R U S T F R O N T F L Y S C H T H R U S T F R O N 10 20 30 Eocene Oligocene Miocene “Lithothamnium Limestone” Schöneck Formation Dynow Formation Eggerding Formation “Rupelian Sandstone” Innviertel Formation Upper freshwater molasse Basal sandstone Age (ma) Basin stratigraphy North South L. Puchkirchen Formation U. Puchkirchen Formation A1 A2 A3 A4 Hall Formation Cretaceous and Jurassic units Cenozoic Neogene Paleogene Priabonian Rupelian Chattian Aquitanian Burdigalian Langhian Serravallian Tortonian Eon Period Epoch Stage 1000 0 -1000 -2000 -3000 -4000 -5000 North South A A’ Flysch system nappes Calcareous Alps Innviertel Fm. Freshwater Molasse Hall Fm. Puchkirchen Fm. Lauterbach nappes Cretaceous Jurassic Crystalline basement Eocene METERS Kilometers 0 10 20 Molasse Flysch and Helvetic Northern Limestone Alps Bohemian Massif 3D seismic-reflection data coverage Lakes Germany-Austria international border Upper Austria- Salzburg border Study area The study area is located within the Austrian provinces of Salzburg and Upper Austria, and covers a surface area greater than 700 km of the East- ern Alpine thrust front and adjoining Molasse basin (Figure 1). The Eastern Alps and Molasse basin developed as a result of collision between the Adri- atic continental microplate and the European continental margin during counterclockwise convergence of the African plate with the European plate. The Austrian Molasse basin forms part of the North Alpine foreland basin, which extends to the west into Bavaria and Switzerland, and east into the Carpathian foredeep (de Ruig, 2003). The Bohemian Massif bounds the Molasse basin in the north (Figure 1). Clastic detritus from the advancing Alpine thrust front began to fill the Molasse basin during middle Oligocene time (Steininger et al., 1987; Wagner, 1996). The Molasse basin contains a thick succession of Upper Oligocene to Lower Miocene sediment gravity flow deposits, con- sisting of (from stratigraphically low to high) the informally named ‘Rupe- lian Sandstone,’ Lower Puchkirchen Formation, Upper Puchkirchen For- mation, and the basal Hall Formation (Figures 2 and 3) (Wagner, 1998; de Ruig, 2003). These deposits comprise the Puchkirchen turbidite system, and accumulated over a time interval of approxi- mately 10 My (from approx. 30 to 20 Ma), into a deep-water foreland basin with 1000 to 1500 m water depth (Rögl et al., 1979; Linzer, 2001; de Ruig, 2003; de Ruig and Hubbard, 2006; Hubbard, 2006). Examination of 3D seismic-reflection data surveys acquired during the 1990’s led to the interpretation of the Puchkirchen turbidite system as consisting of an exten- sive basin-axial channel belt and numerous slope fans along the southern margin of the basin (Linzer, 2001; de Ruig, 2003; de Ruig and Hubbard, 2006; Hubbard, 2006) (Figure 4). Figure 1 Figure 3 Figure 2 -860 1 km channel-belt deposits Haidach slope fan deposits -880 -900 -920 -940 -960 -980 -1000 -1020 -1040 -1060 -1080 -1100 -1120 -1140 -1160 -1180 Flysch thrust system boundary shale out reservoir erosional truncation Kilometers 0 4 2 Flysch thrust system boundary A B Figure 4 L A N D S H U T - N E U O E T T I N G H I G H Figure 4 2 3. Data 1 0 0 - F R O D 1 0 0 - S U A H 1 0 0 - P M A L 1 0 0 - G T S G 1 0 0 - W - S S U N 2 0 0 - W - S S U N 3 0 0 - W - S S U N 4 0 0 - W - S S U N 6 0 0 - W - S S U N 7 0 0 - W - S S U N 8 0 0 - W - S S U N 9 0 0 - W - S S U N 1 0 0 - T U A L 2 0 0 - T U A L 3 0 0 - T U A L 4 0 0 - T U A L 1 0 0 - R E P 1 0 0 - W S - T U A L 1 0 0 - T R 1 0 0 - M E H 1 0 0 - N R E B 1 0 0 - T L A P 1 0 0 - T S A 1 0 0 - H C O L 2 0 0 - H C O L 1 0 0 - L U T S 2 0 0 - T F H O 1 0 0 - D I A H 2 0 0 - D I A H 3 0 0 - D I A H 4 0 0 - D I A H 5 0 0 - D I A H 7 0 0 - D I A H 1 0 0 - O S - D I A H 1 0 0 - W N - D I A H 1 0 0 - W - N N U R B 1 0 0 - G A Z 1 0 0 - F H B O 2 0 0 - G A Z 1 0 0 - G E I Z 1 0 0 - I A R K 1 0 0 - G R U B 1 0 0 - G E R 1 0 0 - R U A 3 0 0 - I L 7 0 0 - I L 0 1 0 - I L 4 2 0 - I L 7 2 0 - I L 8 2 0 - I L 9 2 0 - I L 0 3 0 - I L 1 3 0 - I L 2 3 0 - I L EDT-001 Figure 8 Figure 14 B B’ G G’ H H’ D D’ E E’ Figure 7 Figure 10 Figure 11 0 5 10 Kilometers Figure 5 Figure 6 The primary tool employed in order to interpret the structural evolution of the Eastern Alpine thrust front and Molasse basin was 3D seismic-reflection data provided by Rohöl-Aufsuchungs A.G. (Figure 1). The entire seismic-reflection data survey covers an area greater than 2000 km . Rohöl-Aufsuchungs A.G. has drilled more than 700 wells through the Cretaceous and Pa- leogene strata in the Molasse basin and Eastern Alpine thrust front. This study only focuses on 55 wells that penetrate nappes of the Eastern Alps and the southern slope of the Molasse basin (Figure 5). Cores exist for 39 of the wells, and cuings exist from many of the wells. Wireline-log data are available for nearly all of the wells. Rohöl-Aufsuchungs A.G. paleontological in- terpretations superimposed on well completion logs provide depositional ages. Figure 6 shows seismic-reflection profile and amplitude map locations. F F’ Figure 12 2 Figure 9 4. Prominent Oligocene to Miocene structural features A1 basal Hall Fm. A2-A3 Rupelian-aged sediment 916-996 ms (TWTT) 1380-1716 ms (TWTT) 2 km 300 m B B’ Northwest Southeast 6 km Lauterbach imbricate thrust system basal Hall Fm. Haidach nappe Puchkirchen Fm. Lauterbach system Lauterbach fault basal Hall Fm. 2 km 300 m E E’ Northwest Southeast Haidach nappe Puchkirchen Fm. basal Hall Fm. Flysch system nappes 2 km 150 m G G’ Northwest Southeast Lindach imbricate thrust system Figure 7 Figure 11 Figure 10 Figure 9 Seismic-reflection profiles characterize the Lauterbach thrust system as a swarm of curved triangular nappes that are asymptotically shaped downward to a low-angle sole (or detachment) thrust fault, and spread upward into an imbri- cate fan (Figure 7). The Lauterbach thrust-system vergence ranges from north- west- to northeast-directed (Figure 9). Seismic-reflection profiles show that the system is comprised of a forward- propagating (“in-sequence”) series of thrust faults (Figure 7). Interpreted comple- tion logs from the PALT-001 and OBHF-001 wells (that penetrate the hindward- most nappe in the system) suggest that thrusting initiated in the west and oc- curred during or immediately following deposition of the Lower Puchkirchen Formation during Chaian time (based on the stratigraphically highest material in the hindward-most nappe) (Figure 2). Seismic-reflection profiles show that fold-and-thrust faulting may have deformed the basal Hall Formation sediment in the east (Figure 8). This suggests that thrust-front propagation ended in the east during Burdigalian deposition of the basal Hall Formation. The eastern seg- ment of the Lauterbach thrust system appears to have remained active aer the western and northern segments of the thrust system became inactive. The Late Oligocene through Early Miocene sequence of thrust faulting described above ap- pears to have developed in a forward-propagating fanning-out paern from north to east comparable to the way in which a Chinese folding fan opens (Figure 9). Seismic-reflection profiles show that the nearly 1 km- thick Haidach nappe rides on a high-angle (relative to the Lauterbach imbricate thrust system), emergent thrust fault that exhibits northeast-directed vergence (Figures 11 and 12). It structurally overlies the Lauterbach thrust system (Figures 11 and 12). Seismic-reflection profiles suggest that the Haidach nappe was emplaced over the Lauterbach thrust system as a result of a thrust fault that had propagated hindward (“out-of-sequence”). Interpreted completion logs from the OBHF-001 and LOCH-001 wells suggest that the onset of out-of-sequence thrusting occurred during or immediately following deposition of the Lower Puchkirchen Formation during Chaian time. Seismic-reflection data show that the nappe deformed the Burdigalian basal Hall Formation sedi- ment (Figure 11). This suggests that thrusting ended during deposition of the basal Hall Formation. The Haidach nappe was not part of the forward-propagating Lauterbach thrust system. Seismic-reflection profiles show that its emplace- ment may have truncated Lauterbach system structures (Figures 11 and 12). Seismic-reflection profiles also show that the nappe had been uplied later than would be pos- sible for it to be part of the forward-propagating Lauterbach thrust system (Figure 11). Seismic-reflection profiles characterize the Lindach thrust system as a swarm of curved triangular nappes that are asymptotically shaped downward to a low- angle sole thrust fault (cf. the Lauterbach imbricate thrust system), and spread upward into an imbricate fan (Figure 10). The Lindach thrust system exhibits northwest-directed vergence. Seismic-reflection profiles suggest that the Lindach thrust system is composed of a forward-propagating (“in-sequence”) series of thrust faults (Figure 10). Completion logs from the REG-001 well suggest that the onset of thrusting oc- curred during Aquitanian time. Seismic-reflection profiles show that thrusting deformed Burdigalian basal Hall Formation strata (Figure 10). This sug- gests that thrust-front propagation ended during deposition of the basal Hall Formation. basal Hall Fm. Puchkirchen Fm. Lauterbach system nappes Zagling conduit 1 km 100 m D D’ West East Flysch system nappes Figure 8 basal Hall Fm. Haidach nappe Flysch system nappes Puchkirchen Fm. Lauterbach lateral ramp 2 km 200 m F F’ Southwest Northeast Figure 12 minibasin minibasin minibasin minibasin Orange lines are interpreted thrust faults. Yellow lines are boundaries between formations and intrafor- mational units (e.g., A1 through A4 units of Upper Puchkirchen Formation). Green line is the ‘Oligo sur- face.’ Black line is an interpreted sediment conduit. Green line is the ‘Oligo-Miocene east surface.’ Seismic-reflection amplitude map (modified after Linzer, 2001) Dashed black lines are approximate boundaries of nappes. Green line is the ‘Oligo-Miocene west surface.’ Mounded seismic reflections on top of the Haidach nappe may be sediment gravity flow deposits shed directly from the nappe. 1 0 0 - F R O D 1 0 0 - S U A H 1 0 0 - P M A L 1 0 0 - G T S G 1 0 0 - W - S S U N 2 0 0 - W - S S U N 3 0 0 - W - S S U N 4 0 0 - W - S S U N 6 0 0 - W - S S U N 7 0 0 - W - S S U N 8 0 0 - W - S S U N 9 0 0 - W - S S U N 1 0 0 - T U A L 2 0 0 - T U A L 3 0 0 - T U A L 4 0 0 - T U A L 1 0 0 - R E P 1 0 0 - W S - T U A L 1 0 0 - T R 1 0 0 - M E H 1 0 0 - N R E B 1 0 0 - T L A P 1 0 0 - T S A 1 0 0 - H C O L 2 0 0 - H C O L 1 0 0 - L U T S 2 0 0 - T F H O 1 0 0 - D I A H 2 0 0 - D I A H 3 0 0 - D I A H 4 0 0 - D I A H 5 0 0 - D I A H 7 0 0 - D I A H 1 0 0 - O S - D I A H 1 0 0 - W N - D I A H 1 0 0 - W - N N U R B 1 0 0 - G A Z 1 0 0 - F H B O 2 0 0 - G A Z 1 0 0 - G E I Z 1 0 0 - I A R K 1 0 0 - G R U B 1 0 0 - G E R 1 0 0 - R U A 3 0 0 - I L 7 0 0 - I L 0 1 0 - I L 4 2 0 - I L 7 2 0 - I L 8 2 0 - I L 9 2 0 - I L 0 3 0 - I L 1 3 0 - I L 2 3 0 - I L EDT-001 1 2 3 4 II III IV V VI VII VIII 5 6 I Depth (ms) Depth (ms) Depth (ms) Depth (ms) Depth (ms) A B C D E F 85 507 340 900 340 1100 80 660 70 640 350 1250 Depth (ms) 0 5 10 Kilometers A B E F C D 1 - Dorfbeuern minibasin 2 - Heming minibasin 3 - Astaett minibasin 4 - Lauterbach minibasin I - Lauterbach fault II - Lochen fault III - Haidach fault IV - Brunn Fault V-VIII - faults near the Lindach system 5. Potential sediment storage areas and conduits Figure 13 (A) ‘Oligo-Miocene west surface’ map. (B) Haidach nappe sole thrust fault surface map. (C) ‘Oligo-Miocene east surface’ map. (D) Lindach thrust system sole thrust fault surface map. (E) ‘Oligo surface’ map. (F) Lauterbach thrust system sole thrust fault surface map. basal Hall Fm. Haidach nappe Puchkirchen Fm. 1 km 150 m H H’ Northwest Southeast Figure 14 Paleosurface and sole thrust fault surface maps were generated throughout the study area from seismic-reflection profiles (Figure 13; paleosurface interpretations are shown as green lines in Figures 7, 10, 12, and 14). The maps represent subsurface depth (in time units). A paleosurface is an approximately time-correlative surface interpreted over the seismic-reflection data. It approximates the seafloor paleogeomorphology in some locations. Paleosurfaces may have been modified by subsequent fold-and-thrust faulting, and may not be a perfect representation of seafloor paleogeomorphology. The ‘Oligo surface’ and ‘Oligo-Miocene east surface’ (Figures 13C and 13E, respectively) were interpreted over the tops of the Lauterbach and Lindach thrust systems, respectively (Figures 7 and 10). The nappes appear to have been buried by Upper Oligocene and Lower Mio- cene sediment following nappe emplacement. The ‘Oligo-Miocene west surface’ (Figure 13A) was interpreted over the Haid- ach nappe. This surface was extended into the Molasse basin over sediment that appears to have been eroded from the out-of- sequence nappe (Figure 12). Six potential nappe-top minibasins may serve as locations of significant sediment storage (Figures 13C and 13E). The nappe-top minibasins are structurally lo- cated in the syncline between adjacent nappes (i.e., “piggyback” orientation; cf. Ori & Friend, 1984; Ricci Lucchi, 1986) (Figures 7 and 10). These minibasins are iden- tified as 1 to 6 in Figures 13C and 13E and include the Doreuern minibasin (1), Heming minibasin (2), Astae minibasin (3), Lauterbach minibasin (4), and miniba- sins near the LI wells (5 and 6). Eight strike-slip faults abruptly truncate nappes (Figures 13A and 13C). They are oriented subparallel to the interpreted direction of thrust-front vergence. The vergence along the thrust front corresponds to the sense of motion along the strike-slip faults (e.g., northeast- and northwest-directed vergence corresponds to le- and right-lateral fault offset, respectively). The hindward extent of faults is difficult to determine because the seismic-reflection data do not extend far enough to the south. The forward extent of the faults is constrained by the position of the thrust front. None of the faults extend into the Molasse basin. Timing of deformation for each fault was resolved from superposition and differences in magnitude of offset over time. As a result of the observations presented above, we adopt the generic term “tear fault” for these types of faults that truncate contractional structures in the eastern Alpine thrust front. The tear faults are identified as I to VIII in Figures 13A and 13C and include the Lauterbach fault (I), Lochen fault (II), Haidach fault (III), Brunn fault (IV), and faults near the LI wells (V, VI, VII, and VIII). The Lauter- bach fault accommodates the movement of the Haidach nappe over the Lauterbach imbricate thrust system (Figure 11). Figure 14 shows a potential conduit formed along the Haidach fault. The tear faults (not including the Lauterbach fault) may have served as far-reaching conduits that delivered coarse clastic sediment to slope reservoirs of the Molasse basin, as occurs in the Apennine basin (cf. Pieri, 1983; DeCelles and Giles, 1996). Green line is the ‘Oligo-Miocene west surface.’ Con- tinuous seismic-reflections are above and below dis- rupted strata. 6. Summary The Lauterbach imbricate thrust system com- prises a forward-propagating sequence of thrust faults that verge towards the northwest and north- east in a fan-like paern. The Haidach nappe structurally overlies the Lauterbach thrust system and appears to have been uplied by an out-of- sequence thrust fault. The Lindach imbricate thrust system comprises a forward-propagating sequence of thrust faults that exhibit northwest- directed vergence. Numerous potential sediment storage areas and conduits are expressed in seismic-reflection data as nappe-top minibasins and tear faults. These linear features may have extended hindward into the Alps and provided far-reaching conduits through which coarse-clastic sediment was transported to the southern slope of the Molasse basin. Relatively coarse-grained slope fans may have received sedi- ment from these potentially far-reaching sediment conduits. Relatively fine-grained slope fans may have been deposited as a result of failure of the paleoshelf (cf. Pratson and Haxby, 1996; Figure 15). 0 25 50 Kliometers Monterey Canyon Big Sur Canyon slope gullies slope gullies Figure 15 Multibeam bathymetric map of the continental shelf and slope off the central California coast (modified after Pratson and Haxby, 1996). Vertical exaggeration is 4:1. Monterey Canyon and Big Sur Canyon are tectonically-influenced canyon-channel systems. They are conduits through which coarse-grained sediment is transported to deep water. Numerous slope gullies have formed as the result of failure of the relatively muddy shelf. 7. Future work Ninety-seven core samples and 29 samples of well cuings are available from wells that penetrate nappes and coarse-grained slope fans. Ar-Ar dating will be aempted on sandstone samples in order to infer the ages of nappes and potential source areas for slope fans. Conventional petrographical and rare earth element analyses will be per- formed on core samples for comparison between slope fans and potential sediment conduits, and in order to infer slope fan source areas. Paleontological data will be examined in order to refine the timing of thrust-front development and infer paleoenvironmental conditions. Core data will be interpreted in order to determine slope fan depositional processes and transport distance. Existing seismic-reflection interpretations will be enhanced and new interpretations will be extended to the east and west of the current study area. Balanced cross sections will be aempted across the study area in order to reinforce the structural interpretation. References de Ruig, M. J., 2003, Deep marine sedimentation and gas reservoir distribution in Upper Austria: new insights from 3D seismic data: Oil & Gas European Magazine, v. 29, p. 64-73. de Ruig, M.J., and Hubbard, S.M., 2006, Seismic facies and reservoir characteristics of a deep-marine channel belt in the Molasse foreland basin, Puchkirchen Formation, Austria: AAPG Bulletin, v. 90, p. 735-752. Hubbard, S.M., 2006, Deep-sea foreland basin axial channels and associated sediment gravity flow deposits, Oligocene Molasse basin, Austria, and Cretaceous Magallanes basin, Chile: Ph.D. thesis, Stanford University, 216 p. Linzer, H. G., 2001, Cyclic Channel systems in the Molasse Foreland Basin of the Eastern Alps – the Effects of Late Oligocene Foreland Thrusting and Early Miocene Lateral Escape (abs): AAPG Bulletin, v. 85, p. 118. Ori, G.G., and Friend, P.F., 1984, Sedimentary basins formed and carried piggyback on active thrust sheets: Geology, v. 12, p. 475-478. Pieri, M, 1983, Three seismic profiles through the Po Plain, in, Bally, W.A., ed., Seismic Expression of Structural Styles: AAPG studies in Geology 15, p. 3.4.1-3.4.9. Pratson, L.F., and Haxby, W.F., 1996, What is the slope of the U.S. continental slope?: Geology, v. 24, p. 3-6. Ricci Lucchi, F., 1986, The Oligocene to Recent foreland basins of Northern Apennines: International Association of Sedimentologists Special Publication 8, p. 105-139. Rögl, F., Hochuli, P., and Muller, C., 1979, Oligocene-Early Miocene stratigraphic correlations in the Molasse Basin of Austria: Annales Geologiques des Pays Helleniques, Tome hors series, v. 30, p.1045-1050. Steininger, F. F., Wessely, G., Rögl, F., and Wagner, L., 1987, Tertiary sedimentary history and tectonic evolution of the Eastern Alpine Foredeep: Giornale de Geologie, v. 48, p. 285-297. Wagner, L. R., 1996, Stratigraphy and hydrocarbons in the Upper Austrian Molasse Foredeep (active margin), in G. Wessely, and W. Liebl, eds., Oil and Gas in Alpidic Thrustbelts and Basins of Central and Eastern Europe: European Association of Geoscientists and Engineers Special Publication 5, p. 217-235. Wagner, L. R., 1998, Tectono-stratigraphy and hydrocarbons in the Molasse Foredeep of Salzburg, Upper and Lower Austria, in Mascle, A., Puigdefabregas, C., Luterbacher, H.P., and Fernandez, M., eds., Cenozoic Foreland Basins of Western Europe: Geological Society Special Publication 134, p. 339-369.
Transcript of Thrust-front evolution and implications for deep-water ... seismic-reflection data coverage Lakes...
SPODDS
Thrust-front evolution and implications for deep-water sedimentation, eastern Alps and Molasse foreland basin, Austria: Progress ReportJacob A. Covault , Hans-Gert Linzer , Ralph Hinsch , and Stephan A. Graham1 2 12 1 2Dept. of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, Rohöl-Aufsuchungs A.G., Schwarzenbergplatz 16, A1015 Vienna, Austria
1. Abstract 3D and 2D seismic-reflection data and extensive core and wireline-log data from Austria are provided by Rohöl-Aufsuchungs
A.G. in order to interpret the structural evolution of the Eastern Alpine thrust front and controls on coarse-clastic sediment distribu-
tion across the southern slope of the Molasse basin.
The study area contains slope fans located directly forward of the eastern Alpine thrust front or in nappe-top minibasins located
in synclines between adjacent nappes of the thrust front. Some slope fans are predominantly composed of relatively thick, amalgam-
ated beds of coarse-grained sediment with few finer-grained interbeds, whereas others are predominantly composed of finer-grained
sediment.
Seismic-reflection data reveals the Oligocene to Miocene evolution of the eastern Alpine thrust front. Nappe-top minibasins and
tear faults may have developed during thrust-front advancement. These structures may have served as sediment storage areas and
conduits. The conduits may have been far-reaching channels that provided a pathway through which sediment from an Alpine hin-
terland source area was transported to the southern slope of the Molasse foreland basin. Slope fans consisting of relatively coarse-
grained sediment may have received detritus from these conduits. Alternatively, slope fans composed of relatively fine-grained sedi-
ment may have been deposited as a result of slumping of the nearby, presumably finer-grained sediment that comprised the pa-
leoshelf. Future work will support the seismic-reflection- and wireline-log-based interpretations presented in this progress report.
2. Eastern Alpine thrust front and Molasse foreland basin
48º15’ N
48º00’ N
47º45’ N
13º00’ E 13º30’ E 14º00’ E 14º30’ E
0 25 50
Kilometers
A
A’
Fig
ure
3
F L Y S C H T H R U S T F R O N T
F L Y
S C H T H R U S T F R O N
10
20
30
Eoce
ne
Olig
oce
ne
Mio
ce
ne
“Lithothamnium
Limestone”
Schöneck Formation
Dynow Formation
Eggerding Formation
“Rupelian Sandstone”
Innviertel
Formation
Upper
freshwater
molasse
Basal sandstone
Age(ma)
Basinstratigraphy
North South
L. PuchkirchenFormation
U. PuchkirchenFormation
A1A2A3A4
HallFormation
Cretaceous and
Jurassic units
Ce
no
zo
ic
Ne
og
ene
Pale
oge
ne
Priabonian
Rupelian
Chattian
Aquitanian
Burdigalian
Langhian
Serravallian
Tortonian
Eon
Perio
d
Epoch
Stage1000
0
-1000
-2000
-3000
-4000
-5000
North South
A A’
Flysch system nappes
Calcareous AlpsInnviertel Fm.
Freshwater Molasse
Hall Fm.
Puchkirchen Fm.
Lauterbach nappes Cretaceous
Jurassic
Crystalline basement
Eocene
ME
TE
RS
Kilometers
0 10 20
Molasse
Flysch and Helvetic
Northern Limestone Alps
Bohemian Massif
3D seismic-reflection data coverage
Lakes
Germany-Austriainternational border
Upper Austria-Salzburg border
Study area
The study area is located within the
Austrian provinces of Salzburg and
Upper Austria, and covers a surface
area greater than 700 km of the East-
ern Alpine thrust front and adjoining
Molasse basin (Figure 1). The Eastern
Alps and Molasse basin developed as
a result of collision between the Adri-
atic continental microplate and the
European continental margin during
counterclockwise convergence of the
African plate with the European plate.
The Austrian Molasse basin forms
part of the North Alpine foreland
basin, which extends to the west into
Bavaria and Switzerland, and east
into the Carpathian foredeep (de
Ruig, 2003). The Bohemian Massif
bounds the Molasse basin in the north
(Figure 1). Clastic detritus from the
advancing Alpine thrust front began
to fill the Molasse basin during
middle Oligocene time (Steininger et
al., 1987; Wagner, 1996). The Molasse
basin contains a thick succession of
Upper Oligocene to Lower Miocene
sediment gravity flow deposits, con-
sisting of (from stratigraphically low
to high) the informally named ‘Rupe-
lian Sandstone,’ Lower Puchkirchen
Formation, Upper Puchkirchen For-
mation, and the basal Hall Formation
(Figures 2 and 3) (Wagner, 1998; de
Ruig, 2003). These deposits comprise the Puchkirchen turbidite system, and accumulated over a time interval of approxi-
mately 10 My (from approx. 30 to 20 Ma), into a deep-water foreland basin with 1000 to 1500 m water depth (Rögl et al.,
1979; Linzer, 2001; de Ruig, 2003; de Ruig and Hubbard, 2006; Hubbard, 2006). Examination of 3D seismic-reflection data
surveys acquired during the 1990’s led to the interpretation of the Puchkirchen turbidite system as consisting of an exten-
sive basin-axial channel belt and numerous slope fans along the southern margin of the basin (Linzer, 2001; de Ruig, 2003;
de Ruig and Hubbard, 2006; Hubbard, 2006) (Figure 4).
Figure 1
Figure 3
Figure 2
-860
1 km
channel-belt
deposits
Haidach
slope fan
deposits
-880
-900
-920
-940
-960
-980
-1000
-1020
-1040
-1060
-1080
-1100
-1120
-1140
-1160
-1180
Flysch thrust system boundary
shale o
ut
reservoir
ero
sio
nal tr
uncation
Kilometers
0 42
Flysch thrust system boundary
A B
Figure 4
L A N D S H U T - N E U O E T T I N G H I G H
Figure 4
2
3. Data
100-FROD
100-SUAH
100-PMAL
100-GTSG
100-W-SSUN
200-W-SSUN
300-W-SSUN
400-W-SSUN
600-W-SSUN
700-W-SSUN
800-W-SSUN
900-W-SSUN
100-TUAL
200-TUAL 300-TUAL
400-TUAL
100-REP
100-WS-TUAL
100-TR
100-MEH
100-NREB
100-TLAP100-TSA
100-HCOL 200-HCOL100-LUTS
200-TFHO
100-DIAH
200-DIAH300-DIAH
400-DIAH 500-DIAH
700-DIAH
100-OS-DIAH
100-WN-DIAH
100-W-NNURB
100-GAZ
100-FHBO
200-GAZ100-GEIZ
100-IARK
100-GRUB
100-GER
100-RUA
300-IL700-IL
010-IL420-IL
720-IL
820-IL920-IL
030-IL
130-IL
230-IL
EDT-001
Figure 8
Figure 14
B
B’
G
G’
HH’
D D’
E
E’
Figure 7
Figure 10
Figure 11
0 5 10
Kilometers
Figure 5
Figure 6
The primary tool employed in order to interpret the structural evolution of the Eastern Alpine thrust front and Molasse
basin was 3D seismic-reflection data provided by Rohöl-Aufsuchungs A.G. (Figure 1). The entire seismic-reflection data survey
covers an area greater than 2000 km . Rohöl-Aufsuchungs A.G. has drilled more than 700 wells through the Cretaceous and Pa-
leogene strata in the Molasse basin and Eastern Alpine thrust front. This study only focuses on 55 wells that penetrate nappes
of the Eastern Alps and the southern slope of the Molasse basin (Figure 5). Cores exist for 39 of the wells, and cu!ings exist
from many of the wells. Wireline-log data are available for nearly all of the wells. Rohöl-Aufsuchungs A.G. paleontological in-
terpretations superimposed on well completion logs provide depositional ages. Figure 6 shows seismic-reflection profile and
amplitude map locations.
F
F’
Figur
e 12
2
Figure 9
4. Prominent Oligocene to Miocene structural features
A1
basal Hall Fm.
A2-A3
Rupelian-aged sediment
916-996 ms (TWTT)
1380-1716 ms (TWTT)
2 km 30
0 m
B B’
Northwest Southeast
6 km
Lauterbach imbricate thrust system
basal Hall Fm.Haidach nappe
Puchkirchen Fm.
Lauterbachsystem
Lauterbachfault
basal Hall Fm.
2 km 30
0 m
E E’
Northwest Southeast Haidach nappe
Puchkirchen
Fm.
basal Hall Fm.Flysch system nappes
2 km 150
m
G G’
Northwest Southeast Lindach imbricate thrust system
Figure 7
Figure 11
Figure 10
Figure 9
Seismic-reflection profiles characterize the Lauterbach thrust system as a
swarm of curved triangular nappes that are asymptotically shaped downward to
a low-angle sole (or detachment) thrust fault, and spread upward into an imbri-
cate fan (Figure 7). The Lauterbach thrust-system vergence ranges from north-
west- to northeast-directed (Figure 9).
Seismic-reflection profiles show that the system is comprised of a forward-
propagating (“in-sequence”) series of thrust faults (Figure 7). Interpreted comple-
tion logs from the PALT-001 and OBHF-001 wells (that penetrate the hindward-
most nappe in the system) suggest that thrusting initiated in the west and oc-
curred during or immediately following deposition of the Lower Puchkirchen
Formation during Cha!ian time (based on the stratigraphically highest material
in the hindward-most nappe) (Figure 2). Seismic-reflection profiles show that
fold-and-thrust faulting may have deformed the basal Hall Formation sediment
in the east (Figure 8). This suggests that thrust-front propagation ended in the
east during Burdigalian deposition of the basal Hall Formation. The eastern seg-
ment of the Lauterbach thrust system appears to have remained active a"er the
western and northern segments of the thrust system became inactive. The Late
Oligocene through Early Miocene sequence of thrust faulting described above ap-
pears to have developed in a forward-propagating fanning-out pa!ern from
north to east comparable to the way in which a Chinese folding fan opens (Figure
9).
Seismic-reflection profiles show that the nearly 1 km-
thick Haidach nappe rides on a high-angle (relative to the
Lauterbach imbricate thrust system), emergent thrust fault
that exhibits northeast-directed vergence (Figures 11 and
12). It structurally overlies the Lauterbach thrust system
(Figures 11 and 12).
Seismic-reflection profiles suggest that the Haidach
nappe was emplaced over the Lauterbach thrust system as a
result of a thrust fault that had propagated hindward
(“out-of-sequence”). Interpreted completion logs from the
OBHF-001 and LOCH-001 wells suggest that the onset of
out-of-sequence thrusting occurred during or immediately
following deposition of the Lower Puchkirchen Formation
during Cha!ian time. Seismic-reflection data show that the
nappe deformed the Burdigalian basal Hall Formation sedi-
ment (Figure 11). This suggests that thrusting ended during
deposition of the basal Hall Formation. The Haidach nappe
was not part of the forward-propagating Lauterbach thrust
system. Seismic-reflection profiles show that its emplace-
ment may have truncated Lauterbach system structures
(Figures 11 and 12). Seismic-reflection profiles also show
that the nappe had been upli"ed later than would be pos-
sible for it to be part of the forward-propagating Lauterbach
thrust system (Figure 11).
Seismic-reflection profiles characterize the Lindach thrust system as a swarm of
curved triangular nappes that are asymptotically shaped downward to a low-
angle sole thrust fault (cf. the Lauterbach imbricate thrust system), and spread
upward into an imbricate fan (Figure 10). The Lindach thrust system exhibits
northwest-directed vergence.
Seismic-reflection profiles suggest that the Lindach thrust system is composed of
a forward-propagating (“in-sequence”) series of thrust faults (Figure 10).
Completion logs from the REG-001 well suggest that the onset of thrusting oc-
curred during Aquitanian time. Seismic-reflection profiles show that thrusting deformed Burdigalian basal Hall Formation strata (Figure 10). This sug-
gests that thrust-front propagation ended during deposition of the basal Hall Formation.
basal
Hall Fm.
Puchkirchen Fm.
Lauterbach system
nappes
Zagling conduit
1 km 10
0 m
D D’West East
Flysch system nappes
Figure 8basal Hall Fm.
Haidach nappe
Flysch system nappes
Puchkirchen
Fm.
Lauterbach
lateral ramp
2 km 200
m
F F’
Southwest Northeast
Figure 12
minibasin minibasin
minibasinFlysch s
minibasin
Orange lines are interpreted thrust faults. Yellow lines are boundaries between formations and intrafor-mational units (e.g., A1 through A4 units of Upper Puchkirchen Formation). Green line is the ‘Oligo sur-face.’
Black line is an interpreted sediment conduit.
Green line is the ‘Oligo-Miocene east surface.’
Seismic-reflection amplitude map (modified after Linzer, 2001)
Dashed black lines are approximate boundaries of nappes.
Green line is the ‘Oligo-Miocene west surface.’ Mounded seismic reflections on top of the Haidach nappe may be sediment gravity flow deposits shed directly from the nappe.
100-FROD
100-SUAH
100-PMAL
100-GTSG
100-W-SSUN
200-W-SSUN
300-W-SSUN
400-W-SSUN
600-W-SSUN
700-W-SSUN
800-W-SSUN
900-W-SSUN
100-TUAL
200-TUAL 300-TUAL
400-TUAL
100-REP
100-WS-TUAL
100-TR
100-MEH
100-NREB
100-TLAP100-TSA
100-HCOL 200-HCOL100-LUTS
200-TFHO
100-DIAH
200-DIAH300-DIAH
400-DIAH 500-DIAH
700-DIAH
100-OS-DIAH
100-WN-DIAH
100-W-NNURB
100-GAZ
100-FHBO
200-GAZ100-GEIZ
100-IARK
100-GRUB
100-GER
100-RUA
300-IL700-IL
010-IL420-IL
720-IL
820-IL920-IL
030-IL
130-IL
230-IL
EDT-001
1 2
3
4
II IIIIV
V
VI VII VIII
5 6
I
Depth (ms)
Depth (ms)
Depth (ms)
Depth (ms)
Depth (ms)
A
B
C
D
E
F
85 507
340 900
340 1100
80 660
70 640
350 1250Depth (ms)
0 5 10
Kilometers
A B
E F
CD
1 - Dorfbeuern minibasin
2 - Heming minibasin
3 - Astaett minibasin
4 - Lauterbach minibasin
I - Lauterbach fault
II - Lochen fault
III - Haidach fault
IV - Brunn Fault
V-VIII - faults near the Lindach system
5. Potential sediment storage areas and conduits
Figure 13(A) ‘Oligo-Miocene west surface’ map. (B) Haidach nappe sole thrust fault surface map. (C) ‘Oligo-Miocene east surface’ map. (D) Lindach thrust system sole thrust fault surface map. (E) ‘Oligo surface’ map. (F) Lauterbach thrust system sole thrust fault surface map.
basal Hall Fm.
Haidach
nappe
Puchkirchen
Fm.
1 km
150
m
H H’Northwest Southeast
Figure 14
Paleosurface and sole thrust fault surface maps were generated throughout the study area from seismic-reflection profiles
(Figure 13; paleosurface interpretations are shown as green lines in Figures 7, 10, 12, and 14). The maps represent subsurface
depth (in time units). A paleosurface is an approximately time-correlative surface interpreted over the seismic-reflection data.
It approximates the seafloor paleogeomorphology in some locations. Paleosurfaces may have been modified by subsequent
fold-and-thrust faulting, and may not be a perfect representation of seafloor paleogeomorphology. The ‘Oligo surface’ and
‘Oligo-Miocene east surface’ (Figures 13C and 13E, respectively) were interpreted over the tops of the Lauterbach and Lindach
thrust systems, respectively (Figures 7 and 10). The nappes appear to have been buried by Upper Oligocene and Lower Mio-
cene sediment following nappe emplacement. The ‘Oligo-Miocene west surface’ (Figure 13A) was interpreted over the Haid-
ach nappe. This surface was extended into the Molasse basin over sediment that appears to have been eroded from the out-of-
sequence nappe (Figure 12).
Six potential nappe-top minibasins may serve as locations of significant sediment storage (Figures 13C and 13E). The nappe-top minibasins are structurally lo-
cated in the syncline between adjacent nappes (i.e., “piggyback” orientation; cf. Ori & Friend, 1984; Ricci Lucchi, 1986) (Figures 7 and 10). These minibasins are iden-
tified as 1 to 6 in Figures 13C and 13E and include the Dor#euern minibasin (1), Heming minibasin (2), Astae! minibasin (3), Lauterbach minibasin (4), and miniba-
sins near the LI wells (5 and 6).
Eight strike-slip faults abruptly truncate nappes (Figures 13A and 13C). They are oriented subparallel to the interpreted direction of thrust-front vergence. The
vergence along the thrust front corresponds to the sense of motion along the strike-slip faults (e.g., northeast- and northwest-directed vergence corresponds to le"-
and right-lateral fault offset, respectively). The hindward extent of faults is difficult to determine because the seismic-reflection data do not extend far enough to the
south. The forward extent of the faults is constrained by the position of the thrust front. None of the faults extend into the Molasse basin. Timing of deformation for
each fault was resolved from superposition and differences in magnitude of offset over time. As a result of the observations presented above, we adopt the generic
term “tear fault” for these types of faults that truncate contractional structures in the eastern Alpine thrust front. The tear faults are identified as I to VIII in Figures
13A and 13C and include the Lauterbach fault (I), Lochen fault (II), Haidach fault (III), Brunn fault (IV), and faults near the LI wells (V, VI, VII, and VIII). The Lauter-
bach fault accommodates the movement of the Haidach nappe over the Lauterbach imbricate thrust system (Figure 11). Figure 14 shows a potential conduit formed
along the Haidach fault. The tear faults (not including the Lauterbach fault) may have served as far-reaching conduits that delivered coarse clastic sediment to slope
reservoirs of the Molasse basin, as occurs in the Apennine basin (cf. Pieri, 1983; DeCelles and Giles, 1996).
Green line is the ‘Oligo-Miocene west surface.’ Con-tinuous seismic-reflections are above and below dis-rupted strata.
6. Summary The Lauterbach imbricate thrust system com-
prises a forward-propagating sequence of thrust
faults that verge towards the northwest and north-
east in a fan-like pa!ern. The Haidach nappe
structurally overlies the Lauterbach thrust system
and appears to have been upli"ed by an out-of-
sequence thrust fault. The Lindach imbricate
thrust system comprises a forward-propagating
sequence of thrust faults that exhibit northwest-
directed vergence.
Numerous potential sediment storage areas and
conduits are expressed in seismic-reflection data as
nappe-top minibasins and tear faults. These linear
features may have extended hindward into the
Alps and provided far-reaching conduits through
which coarse-clastic sediment was transported to
the southern slope of the Molasse basin. Relatively
coarse-grained slope fans may have received sedi-
ment from these potentially far-reaching sediment
conduits. Relatively fine-grained slope fans may
have been deposited as a result of failure of the paleoshelf (cf. Pratson and Haxby, 1996; Figure 15).
0 25 50
Kliometers
Monterey Canyon
Big Sur
Canyon
slope gullies
slope gullies
Figure 15Multibeam bathymetric map of the continental shelf and slope off the central California coast (modified after Pratson and Haxby, 1996). Vertical exaggeration is 4:1. Monterey Canyon and Big Sur Canyon are tectonically-influenced canyon-channel systems. They are conduits through which coarse-grained sediment is transported to deep water. Numerous slope gullies have formed as the result of failure of the relatively muddy shelf.
7. Future work Ninety-seven core samples and 29 samples of well cu!ings are available from wells that penetrate nappes and
coarse-grained slope fans. Ar-Ar dating will be a!empted on sandstone samples in order to infer the ages of nappes
and potential source areas for slope fans. Conventional petrographical and rare earth element analyses will be per-
formed on core samples for comparison between slope fans and potential sediment conduits, and in order to infer
slope fan source areas. Paleontological data will be examined in order to refine the timing of thrust-front development
and infer paleoenvironmental conditions. Core data will be interpreted in order to determine slope fan depositional
processes and transport distance.
Existing seismic-reflection interpretations will be enhanced and new interpretations will be extended to the east and
west of the current study area. Balanced cross sections will be a!empted across the study area in order to reinforce the
structural interpretation.
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