Folds SW. Large. Folds NE. Amphitheater. S2. S3. S4. 34. 28. 31. 47. 25 30 ... Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, U.S.A.; ...
Submarine Mass Failure within the Shelfal-Deltaic Domengine Formation (Eocene), California (U.S.A.) Glenn R. Sharman1, Theresa M. Schwartz2, Lauren E. Shumaker3, Cody Trigg4, Nora M. Nieminski4, Zachary Sickmann4, Matthew A. Malkowski5, Sam Johnstone6, Jeremy K. Hourigan7, and Stephan A. Graham4 1 Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, U.S.A.; 2 Allegheny College, Department of Geology, Meadville, PA, U.S.A.; 3 Chevron Center of Research Excellence, Colorado School of Mines, Golden, CO, U.S.A.; 4 Stanford University, Department of Geological Sciences, Stanford, CA, U.S.A.; 5 U.S. Geological Survey, Santa Cruz, CA, U.S.A.; 6 U.S. Geological Survey, Lakewood, CO, U.S.A., 7 Department of Earth and Planetary Sciences, University of California-Santa Cruz, Santa Cruz, CA, U.S.A.
ABSTRACT
THE NEW IDRIA MASS-TRANSPORT DEPOSIT
Building the 3D model from aerial photographs: 1
Oblique, orthographic perspective of the 3D outcrop model, draped with a composite aerial photomontage. (Line drawing interpretation below.)
Outcrops within the Eocene Domengine Formation (central California) provide an exceptional opportunity to observe the relationship between depositional facies and submarine mass movement. The Domengine Formation is interpreted as an assemblage of heterolithic, shallow- to marginal-marine deposits that record progradation and aggradation of the coastline prior to regional flooding and local collapse of the shelf. Structural analysis of soft-sediment folds and reverse faults within the informally named New Idria Mass-Transport Deposit (MTD) suggest transport toward the west to southwest, which is consistent with paleoflow measurements from cross-bedding within the MTD. Depositional facies have a strong influence on the character of soft-sediment deformation (e.g., style and scale of folding and faulting), and major layer-parallel detachment surfaces within and below the New Idria MTD occur where mudstone-dominated or heterolithic units underlie sandstone-dominated units. Conditions favorable to gravitational instability and eventual collapse of the shelf include 1) high sedimentation rates within a rapidly aggrading system; 2) loading of under-compacted, mechanically weak, fine-grained layers by overlying, denser sand bodies; and 3) earthquake seismicity and/or over-steepening of slopes within a tectonically active, convergent margin setting. This study provides a rare detailed glimpse into the collapse of a shelfal-deltaic stratigraphic sequence, yielding insight into the linkage between marginal marine facies and depositional architecture and the propensity for submarine mass movement.
500 m
broad fold in DomengineLodo contact
Lodo Formation
Key
Tm (Kreyenhagen Fm & Temblor Fm)
Lodo Formation Tl (Arroyo Hondo Sh.) Tlc (Cantua Ss.) Tl (Cerros Sh.) Tlsc (San Carlos Ss.) Km (Moreno Fm.)
Td (Domengine Fm)
Kp (Panoche Group)
Qa (Quaternary) Ta (Tertiary non-marine)
Tdm (New Idria MTD)
N
Tdm New Id
Kf
Tlc
Tlc
Km
65
Tm
70
sp
San Benito Mt.
Cima Ss. Marca & Tierra Loma Sh.
h hit
Units 2-5 Unit 1
p m A 33
Tk
Tl (Lodo Fm.)
32
32
Large S2 Folds SW 35 34
33
Dominantly sandstone (shelfal to marginal-marine)
Kp
Kf
(Left) Geologic map of the Vallecitos Syncline (modified from Anderson et al., 1998, and Dibblee, 1974). (Right) Generalized stratigraphic column for strata in the Vallecitos Syncline (modified from Johnson and Graham, 2007). Depositional age constraints are from Schulein (1993), Anderson (1998), and Johnson and Graham (2007) using the time scale of McDougall (2007). Cret. = Cretaceous; Fm. = Formation; M. = Middle; Sh. = Shale; Ss. = Sandstone.
Unit 5
24
Tl
S3
31
Road Tectonic fault
Td
(dashed where covered or inferred)
Formational contact
(dashed where covered or inferred)
Measured section
?
43*
Tl
?
N 0m
709000
25
1000m 710000
atum mar dee per atum ine d mar
ine d
pervasive fracturing
not exposed
Fold vergence
not exposed
poorly exposed
262° (SAM) 258° (MAM) 256° (APM) Cross-bedding paleoflow (Unit 3) n = 67
(* indicates within MTD) (arrow points in direction of plunge) 711000
Geologic map of the study area. Basemap is a shaded digital elevation model generated from the 3D outcrop model (see above).
(Left) Orientations of fold axes and poles to axial planes. Black arrows indicate predicted transport direction from four methods of paleoslope analysis. Paleoflow measurements from Schulein (1993).
Domengine Fm outcrop
fan deltas
outcrop belt
Valle citos mini Synclin e -bas in
em (Right) A) Generalized e (Fr anc rge isc nt cross-section of central an J sub oaq du uin ctio California during Eocene n c Ridg om e ple time (modified from Inx) gersoll, 1979). B) Paleo0 km 5 km 10 km geographic reconstrucNon-marine Non-marine tion of the Vallecitos (highlands) (fluvial) Syncline region during Fluvial system (Francsican/forearc provenance) deposition of the Domengine Formation (modified from Schulein, 1993).
New Idria MTD (future)
Shallowmarine
Deepmarine
Fluvial system (Sierran provenance)
(Right) Scatterplot of fold axis vergence direction versus distance along the outcrop belt. Note gradual shift in fold vergence from toward the west-southwest to west, in the direction of MTD propagation.
N 315
Time 1: Deposition of Domengine Formation
(Northwest)
Unit 5 Unit 4
(West)
270
Unit 3 Unit 2
Fold vergence Mean + 1 s.d. 225
0
(Southwest)
1.0
Unit 1 Lodo Fm.
(Southwest) 2.0
3.0
4.0
(Northeast)
Distance along outcrop belt (km)
accommodation creation
Time 2: Regional transgression
D
Lodo Fm Section 1 San Carlos Creek
Lodo Fm 1.5 km
Section 2 Large Folds SW
Lodo Fm 0.75 km
Section 3 Amphitheater
Lodo Fm 0.5 km
Section 4 Large Folds NE
E
Strike & dip of bedding Fold axis
250 m 500 m
ine d
atum ine d mar dee per
Kreyenhagen Fm
Tl Key
30* 33 22* 35 33
Kreyenhagen Fm
A
S1
Dominantly sandstone (slope to basin-floor)
S4
Kreyenhagen Fm
268° (APIM)
34
San Carlos Creek
Dominantly mudstone
25 30
Fold axis (Z-fold) Fold axis (S-fold) Pole to axial plane (Z-fold) Pole to axial plane (S-fold) Mean axial plane (Z-folds) Mean axial plane (S-folds) Separation arc
northeast
emergent Griswold Hills
SUMMARY
STRUCTURAL ANALYSIS
43
29
Td
Tk
Dosados Ss
32
47 31 28
Slope to basin-floor turbidite fan systems and bathyal shale
Base-of-slope, slope, and outer-middle shelf (upwardshoaling)
25*
28*
30 3034 25
25*
26
Unit 4
r e t ea
45*
Qa
Kreyenhagen Fm
The sea level curve is interpreted based on our interpretations of depositional facies through time, and illustrates a phase of sea level regression followed by sea level transgression. Paleogeographic maps t1 through t6 correspond to points on the sea level curve, and are drawn based on the lateral distribution of facies within the outcrop belt. Paleocurrents in panel t3 are summarized from Schulein (1993).
Unit 3
Td (Domengine Fm.)
San Carlos Ss. Dos PalosTa Sh.
Large Folds NE
c
Unit 2
Cerros Sh.
southwest
Domengine Formation
Tk (Kreyenhagen Fm.)
Arroyo Hondo Sh.
Cantua Ss.
711000
Stratigraphic units
Slope and basin-floor bathyal shale (locally siliceous) Deltaic to marginalmarine
710000
4036000
Domengine Fm.
709000
4036000
Kreyenhagen Fm.
Eocene
Middle 60
Tlsc
Kf (Franciscan) sp (Serpentinite)
ria
Fig. 4 ? ?
Tumey Sh.
Depo. Setting
t1
Sierran coastal plain
~5 m
Lopez Canyon
5 km
Stratigraphy
s
B
1 km
Unit 1
Ta
San Carlos Ck.
atum
S3
m
t6: shelf failure (New Idria MTD)
Franciscan subduction complex
~50 m
250 m
t5: retrograding estuary complex (Unit 5)
Grain Size
STRATIGRAPHY
50
55
Unit 1
S4
4035000
Tm
Tm
Tl
ne
50 m
p
S2
0m
Unit 2
1 11
Unit 1
4035000
ncli
15
t2
n = 67
1 km
mar
8
slump-related thrust faults
4034000
s Sy
d 12,13 e r e 2-7 cov
Unit 2
Age (Ma)
Td
18
oceanic plate
sandstone-dominated (dashed where subaqueous)
Azimuth of fold vergence (degrees)
?
1 km
marine
mudstone-dominated
per
Unit 3
24
t4: retrograding estuary complex (Unit 4)
100 m
9 14
19 20,21 22,23
t3
per
Unit 4
10
Kreyenhagen Formation
Unit 3
forearc basin
brackish/restricted
tidal and/or estuarine bars
150 m
Units 4 & 5 absent
paleovalley margin
extinct Sierra Nevada magmatic arc
area shown in B
1 km
t4
dee
Unit 5
Paleocene Late Cret. M Early Late Early Moreno Fm. Lodo Fm.
Kp
Tm
t5
LITHOLOGY
LITHOLOGIC ACCESSORIES
sandstone
planar lamination
ripple lamination
oyster hash/reef
bioturbated sandstone
tangential cross-strat.
flaser bedding
gastropod casts
mudstone
trough cross-strat.
chert pebbles
Thalassinoides
peat paleosol
tabular cross-strat.
log casts
Macaronichnus
HCS and/or SCS
rooted horizons
Ophiomorpha
convolute lamination
upward-fining
Generalized measured sections illustrating the lateral variation in facies within the Domengine Formation.
Kreyenhag
en Fm.
B
Time 3: Collapse of shelf
C
~25 m
~80 m relief
1 km
A
terrestrial
c low
Domengine Formation
“SW Large Folds”
Northeast
“NE Large Folds”
“the Amphitheater”
Unit 4
t3: bayhead delta/estuary complex (Unit 3)
dee
undeformed Kreyenhagen
1 km
t2: back-beach lagoon/estuary (Unit 2)
metri
cito
Tlc
Unit 5
Thickness
Southwest
45
Silver Ck.
X
bathy
Vall e
0 m 50 m 100 m
200 m
Ta
Km
X
t1: prograding sandy shoreline (Unit 1)
t6
S4
S3
S2
40
Griswold Canyon
Kreyenhagen Fm
250 m
Qa
Kp
Interpreted Relative Sea Level
Stratigraphy (simplified)
STUDY AREA & GEOLOGIC BACKGROUND Orb Canyon
X
Z Y
PALEOGEOGRAPHY
We thank J. Jacobsen and K. Woods for permission to conduct field work on private property. The Stanford School of Earth, Energy, and Environmental Sciences and the Quantitative Clastics Laboratory provided funding and support for this project. We also thank Crystal Bennett, Nadja Drabon, and the students and graduate teaching assistants of the University of California Santa Cruz Field Methods class for assistance in the field.
Ta
3
Z Y
“the Amphitheater”
ACKNOWLEDGMENTS
Panoche
2
Z Y
A) Large folds within Units 4-5. B) Anticlinal folding within interbedded sandstone and mudstone (Unit 3). C) Asymmetrical folds within Unit 2 (syncline hinges marked with black arrows). D) Two low-angle reverse faults (black arrows) that displace a sandstone bed in Unit 2. E) Recumbent, isoclinal fold within a mudstone-dominated interval near the base of Unit 2.
detachment along mechanically weak zones
uninvolved in mass movement
