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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