Tectonostratigraphic development of the Miocene

Geological Society of America Special Paper 333 1999

Tectonostratigraphic development of the Miocene-Pliocene Furnace Creek Basin and related features, Death Valley region, California Lauren A. Wright* Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802

Robert C. Greene 31 Sea View Drive, Daly City, California 94015

Ibrahim -..-...."""'-.-""1

Rhyolite flows Sedimentary and volcanic units undivided Basaltic and andesitic flows

Tertiary plutons (late Miocene) Quartz monzonite Willow Spring diorite-gabbro Pre-cenozoic units

I: ::: ::: :::: :1

o

5

: ::: ::: : :::;

~ ~

Late Proterozoic, Paleozoic and earty

Miocene formations. undiVided Badwater Metamorphic Complex (Eartyand Late Proterozoic)

Figure 2. Generalized geologic map of the northwestern part of the Furnace Creek basin. Modified from McAllister (1970), Cemen (1983), and Greene (1997)

The distribution of the Artist Drive, Furnacc Crcck, and Funeral Fonnations in the area of the northern Black Mountains and the northeastern part of Furnace Creek Wash was later shown by Hunt and Mabey (1966) on a map, with a scale of 1:96,000, of much of the Death Valley region. On this map the fonnations are represented much like they are on the earlier map of Noble and Wright, although the name "Funeral fanglomerate" was abandoned and the name "Funeral Fonnation" was applied collectively to the Pliocene fanglomerate and the associated basaltic flows. A U.S. Geological Survey program aimed at exploration for borates led to the publication of two 1:24,OOO-scale geologic maps covering most of the basin, from the vicinity of Furnace

Creek Ranch to the Lila C mine in the Amargosa Valley (McAllister, 1970, 1973). McAllister (1971) also prepared an open-file map of the part of the Ryan 15' quadrangle that extends into the bordering Funeral Mountains. McAllister's mapping showed the borate deposits as confined to the Furnace Creek Formation, including a unit that he identified as the basal conglomerate of that fonnation. Cemen (1983) subsequently mapped the Billie mine area in upper Furnace Creek Wash and the Desolation Canyon area along the Black Mountains front in greater detail. Still later, Cemen et al. (1985) presented a summary ofthe general features of the Furnace Creek basin, and Cemen and Wright (1988) provided an updated account of the Artist Drive Fonnation. Limited

Tectonostratigraphic development of Miocene-Pliocene Furnace Creek Basin and related features

91

are broadly divisible into two categories: the large-scale dextral shear models, in which the extcnsion is controlled, in pull-apart fashion, by major displacement on both strike-slip and normal faults that deeply penetrate the crust (Wright, et aI., 1991; Serpa and Pavlis, 1996); and the rolling hinge model (Wernicke et aI., 1988), in which the Nopah Range, Resting Spring Range, and Black Mountains (Fig. 1) are required to have formed from east to west as "thin slivers of crust ... detached sequentially, such that rotation of each block occurrs at different times" (Wernicke, 1992). Present objectives and preview of the major conclusions

Drive block

Badwater turtleback surface

Figure 3. Simplified index map of the area of Figure 2, showing principal topographic features, fault zones, and location of Billie mine.

radiometric dating of tuff beds and basaltic and rhyolitic flows (McAllister, 1970; Fleck, 1970; Cemen et aI., 1985; Wright, et aI., 1991) indicated a 14- to 6-Ma age for the Artist Drive, a 6- to 5Ma age for the Furnace Creek, and a 5- to 3-Ma age for the Funeral Formation. In the1990s, Miller (1991, 1992a, b, this volume) has reported on an ongoing investigation of the the geology and kinematic development of metamorphic complex beneath the Badwater turtleback fault surface and of the structural development of the surface itself. In view of the location of these features along the margin of the Furnace Creek basin, many of Miller's observations bear directly on the development of the basin. The part of the Furnace Creek basinal succession that underlies the northern Black Mountains, between Gower Gulch and Dante's View, previously mapped only in reconnaissance (Streitz and Stinson, 1977), has been recently mapped on a 1:24,000 scale by Greene (1997). Because the Death Valley terrane is widely acknowledged to display the phenomenon of extreme crustal extension as completely and as as well constrained chronologically as at any other locality in the world, the tectonic setting of the Furnace Creek basin and the behavior of the bordering Furnace Creek fault are of greater than regional interest. The models that have been proposed for the kinematic development of the central Death Valley region

In previous investigations, the overall framework of the basin and the general nature of the basin fill became well established. The stratigraphy of the Artist Drive of the Black Mountains and its paleogeographic implications, however, were relatively unexplored, and much has remained to be learned of the detailed chronology, sedimentology, depositional environments, and provenances of the entire basin fill. Also, the tectonic environment, within which the basin has evolved, has been treated only in a general way (Cemen et aI., 1985; Wright et aI., 1991). In addressing the latter topic in the this chapter, we have been aided by the work of Mancktelow and Pavlis (1994), who included the central Death Valley region in an accounting of the close kinematic relationship between low-angle detachment faults and folds with axes parallel to the direction of extension. We have also benefited from Miller's investigation (this volume) of the timing of ductile deformation in the Badwater crystalline complex. In addition, we build on the observations and interpretations of the preceding chapter (Cemen et aI., this volume), which treats events in the area of the Furnace Creek basin 25-14 Ma ago, before the beginning of sedimentation in the basin. This chapter paper was assembled by Wright, who also prepared the line drawings for the illustrations. A large part of the database was obtained from the three maps of McAllister (1970, 1971,1973), the two maps ofCemen (1983), and the U.S. Geological Survey Open-File map and text by Greene (1997). Greene also contributed later observations and interpretations during the writing of the manuscript. Cemen provided an updated and expanded columnar section of the Artist Drive, unpublished petrographic descriptions of arkosic sandstones low in the Artist Drive, and informal observations based on his previous work in the Furnace Creek basin. The chapter has also drawn on unpublished data and interpretations in the doctoral dissertation of Cemen (1983). The underground mapping and interpretation of the basement rocks in the Billie mine were contributed by Johnson. Prave provided numerous stratigraphic observations and measurements, including pebble counts of conglomerates ranging from the upper part of the Artist Drive through most of the thickness of the Furnace Creek Formation. He also contributed the measurement of paleocurrent indicators in sandstones associated with the conglomerates. These activities have collectively led to four groups of observations, previously unreported in the refereed literature, that we

92

L. A. Wright et at.

SOUTHWESTERN FACIES

NORTHEASTERN FACIES

A

o

B

H

E

T

o 1

2

3km Conglomerate of

~~=y~l~and

f':':: '~:..: ;:"1 ::;: -:

'::

Feldspathlc-Ilthlc sandstone

r::::l L.::::::J

~

( yy ~ Basalt and basaltic andeSite Y.I, "

Non-volcanogenic siltstone

. '. [Z]

Feidspathio-lithic

• ~ ..'; 0; sandstone wfth : . :',' ~ •:.: subordinate

~ -< -< ...'" -
-:...;,;.;.

Air-fail Tuff

...

conglomerate

~

Rhyolitic lava flows

Ash-flow Tuff

Urnestone

Highly fractured late Proterozoic. Cambrian and Ordovician formations

Mlxed;eldsp~lItk>- ~ Metamorphic complex lithic sandstone'~ Iq composed mostly of Early and basalt flows . - ( Proterozoic gneiss with Infolded bodies of Late Proterozoic Noonday Dolomite

Figure 4. Oblique stratigraphic cross section of the Artist Drive Formation as exposed in the northern Black Mountains and mapped by R. C. Greene (1997). Capital letters indicate locations of sections scaled from Green's map: A = north from mouth of Buff Canyon; B = northeast from Fault Line Canyon; D south of Artist's Palette to Corkscrew Canyon; E Artist's Drive block, north-central part; H Natural Bridge block; T = Mount Perry. See text for further explanation. Note: Greene (1997) has informally introduced the name Buff Canyon for a large canyon draining westerly in its lower part and emptying into Death Valley directly north of the north end of Artist's Drive block and 1.6 km southwest of the mouth of Gower Gulch. The name is derived from the prominent buff or light yellowish brown color of the sedimentary rocks of unit Tal exposed in the canyon walls.

=

=

believe to be central to an understanding of the development of the basin. 1. We describe features in the rocks beneath the basin fill that record severe extension well before the initiation of sedimentation in the basin about 14 Ma ago. The event is evidenced both in the brittle deformation of the immediately underlying Paleozoic and late Proterozoic formations and in pre-14-Ma ductile deformation in a crystalline complex exposed immediately south of the basin (Miller, this volume), which we assume to underlie the basin at depth. 2. We summarize a newly recorded coherent stratigraphy of the Artist Drive Formation as revealed in continuous exposures

=

along the Black Mountains front. In this stratigraphy we observe the presence of a northwest-trending anticlinal warp that divides the formation into a dominantly volcanic facies on the southwest from a dominantly nonvolcanogenic sedimentary facies on the northeast. 3. We also observe that Mesozoic granitoid clasts, commonly interpreted as eroded from the Hunter Mountain batholith, now exposed in the southern Cottonwood Mountains about 50 km northwest of the northern Black Mountains, are present in heterogeneous conglomerates at various levels in the nonvolcanogenic facies of the Artist Drive. The conglomerates occur as lenses of various sizes in strongly cross-bedded sandstone. We

Tectonostratigraphic development oj Miocene-Pliocene Furnace Creek Basin and relatedJeatures

consider these observations as recording the recurrence, at intervals during nearly all of Artist Drive time, of a southeast-flowing braided stream system and also as evidence that the Hunter Mountain batholith lay to the northwest of the site of the present Black Mountains during that interval. 4. Finally, we observe that the conglomerates of the Furnace Creek and Funeral Formations record a major change in provenance, being fed as alluvial fans from the northeast and the south or southwest.

STRUCTURAL FRAMEWORK OF THE FURNACE CREEK BASIN

Northeastern margin of the basin and the role of the Furnace Creek fault zone

93

of a strike-slip fault (Fig. 1), it does not qualify as a typical pull-apart basin because, at least during its later history, it lacked the necessary right-lateral faulting on the southwest side, but is marked by an intertonguing of the basinal deposits with volcanic units of the igneous field to the south. It can, however, be viewed as occupying the northeastern part of a much larger crustal pull-apart bounded on the southwest by either the Sheephead fault or the Southern Death Valley fault zone (Fig.!) (Wright et aI, 1991). Evidence that much, perhaps most, of the strike-slip movement on the Furnace Creek fault zone occurred before the basal strata of the basin fill were deposited is contained in several observations. (1) Where the basal strata are exposed at the Billie mine in upper Furnace Creek Wash, they rest in depositional contact on formations that, unlike the occurrences of the same formations in the bordering Funeral Mountains, have been thoroughly brecciated and attenuated. (2) The fill itself appears to be nearly devoid of the low-angle normal faults that characterize highly extended terranes. (3) The nature and distribution of clasts in a pre-14-Ma fanglomerate exposed at Bat Mountain in the southern part of the Funeral Mountains apparently require an already attenuated source on the southwest side of the bounding fault (Cemen et aI., this volume). (4) The metamorphic complex now exposed in the Badwater turtleback surface and which we assume extends at depth beneath the Furnace Creek basin, has undergone strong, northwest-directed, ductile extension apparently well before 14 Ma ago (Miller, this volume). These features are treated in greater detail later in this chapter and in the cited references. The evidence for major pre-14-Ma movement on the Furnace Creek fault is of greater than local interest for several reasons. It would, for example, (1) link more closely the inception of the fault with the generally acknowledged inception, about 16 Ma ago, of volcanic activity in the nearby southwestern Nevada volcanic field; (2) shed new light on the chronology of the entire fault system of Fig. 1; (3) provide insights in the kinematics of basin development adjacent to strike-slip faults; and (4) provide an additional constraint on models designed to illustrate crustal extension in the Death Valley region. If we have correctly interpreted the evidence for early movement on the Furnace Creek fault, it indicates that early and major movement on the Furnace Creek fault occurred without detectable subsidence on the extending block; the subsidence began with a slackening of the strike-slip movement and the related crustal attenuation. Indeed, in the fossil alluvial fan at Bat Mountain, (Cemen et aI., this volume), we see evidence of strong uplift in the extending crust.

The basin-bounding Furnace Creek fault is well exposed in the area of Furnace Creek Wash (Figs. 1 and 2). Southeast of the drainage divide between the wash and the Amargosa Valley, it is hidden beneath Quaternary deposits, but obviously parallels the southwestern edge of the Funeral Mountains. Farther to the southeast the trace of the fault is obscured by the alluvial fill of Amargosa Valley. Because the main block of the Resting Spring Range is unbroken by northwest-striking faults, the Furnace Creek fault must end as a dominantly strike-slip feature west of the crest of the range. The main Furnace Creek fault has been commonly shown as ending beneath steeply tilted fault blocks on the west side of the Resting Spring Range (e.g., Wright et aI., 1991; Serpa and Pavlis, 1996). It was originally shown, however, as passing immediately west of Eagle Mountain (Fig.l) (Noble and Wright, 1954) where the terrane of Paleozoic and Proterozoic sedimentary rocks to the northeast is bordered on the southwest by the terrane of the Central Death Valley plutonic-volcanic field. That this, indeed, is the major break is supported by a strong dextral bending of the strata of the Bonanza King Formation at the south end of Eagle Mountain, as well as by the separation of the two terranes. Regardless of the location of the principal break in the Amargosa Valley area, strike-slip motion on the fault diminishes where joined to arcuate normal faults exposed in the volcanic terrane of Greenwater Range to the southwest (Fig. 1). Because these faults displace rock units in the 7- 8-Ma range, they are contemporaneous with the late Miocene stage of displacement on the Furnace Creek fault. Because the Furnace Creek basin has been long recognized as bounded by the Furnace Creek fault (Figs. 1 and 2), it has been classified as a strike-slip basin (Christie-Blick and Biddle, 1985). The Furnace Creek basin, however, differs from most other strike-slip basins in that it has formed in a region of Southwestern margin of the basin and role of the Badwater pervasive crustal extension. Consequently, the crust on both turtleback fault sides of the fault has been extended, the crust on the southThe southwestern margin of the basin is more difficult to west side much more so than the crust on the northeast side. Although the Furnace Creek basin lies along the terminal part define and delineate than the northeastern, fault-controlled mar-

94

L. A. Wright et al.

gin. This is largely because the middle and late Miocene rock units and/or structural features that record the nature of that margin in pre-Pliocene time are largely hidden beneath basaltic flows of the Funeral Formation and Quaternary alluvium. The features that identify the southwest margin of the Furnace Creek basin in Artist Drive time are exposed only on the western face of the Black Mountains in the vicinity of Natural Bridge Canyon and Badwater (Fig. 3). There, the upper part of the southwestern facies of the Artist Drive Formation terminates, with fault contact, against the metamorphic complex beneath the Badwater Turtleback surface (Fig. 4). On the southwestern side of the crest of the anticline that divides the two facies of the Artist Drive, most of the various extrusive volcanic units that compose the southwestern facies thicken southward toward the Badwater fault and the Central Death Valley plutonic-volcanic field. We view the thickening and the nearness of the igneous field as strong evidence that most or all of these volcanic bodies originated in the plutonic-volcanic field. Indeed, the extrusive volcanic rocks, as well as the intrusive bodies, of the igneous field were emplaced largely during the deposition of the Artist Drive time. Only one of volcanic units in the Artist Drive of the northern Black Mountains, however, is exposed on the immediately opposite side of the fault. This is a succession of rhyolitic flows high in the formation (Fig. 2) (Fig. 4, Ta13). It is about 400 m thick where adjacent to the fault and tapers to disappearance about 9 km northwest of the fault. South of the Badwater Turtleback, the Ta13 unit deposition ally overlies granitic plutons and ha.'l yielded KlAr ages averaging about 6.S Ma (Fleck, 1970). Both occurrences ofTa13 are depositionally overlain by the Greenwater volcanics that intertongue northward with units of the Furnace Creek Formation (Fig. 2). We interpret the two occurrences of Ta13 as once connected and later separated by erosion in the post-6.SMa-pre-S.S-Ma interval before deposition of the Greenwater volcanics. Between the two occurrences of Ta13, the Greenwater volcanics overlie the metamorphic complex with a gently dipping fault contact. Greene (1997) has traced this contact continuously northwestward, interpreting it there as the present southwestward extension of the Badwater Turtleback fault. Miller (1992a), however, has interpreted this contact as depositional. In the present exposures, the Badwater Turtleback fault steepens from essentially horizontal at the crest of the turtleback surface to about 2So on its northern slope (Fig. 4). The fault, however, is subparallel with planar features, in the complex, that define the northeastern limb of the antiform beneath the turtleback surface. We view the structural relief in this area, therefore, as produced by a combination of the folding and normal faulting. The most recent movement on the fault has occurred in post-S.5Ma time and is recorded in the blocks ofTa13 rhyolite and overlying units of the Greenwater volcanics that are strung out along the fault through most of the height of the Black Mountains escarpment (Fig. 4). This geometry indicates a dip-slip component of about 1.2 km. This dislocation, although severe, is confined to the Black Mountains block and related to its uplift during

the last 3 m.y. (Miller, 1991, 1992a; Knott, et aI., this volume) and cite as evidence the fact that, in the Greenwater Range to the southeast, the Greenwater volcanics are much less disrupted and essentially flat-lying, The earlier history of movement on the Badwater Turtleback fault and its relation to the development of the antiform of the Badwater Turtleback remain conjectural. We interpret the antiform as a contractional feature related to the early extensional event as proposed by Miller (1992 a, b) and in the sense implied by Mancktelow and Pavlis (1994). If so, the various southwardthickening volcanic units are earlier analogs of the Ta13 rhyolitic flows. If so, each of the extrusive felsic volcanics, originally extended to a source in the igneous field, was subsequently preserved on the down-dropped side of the fault and eroded from the immediately adjacent part of the uplifted side. If the Badwater fault formed on the southwest side of the Furnace Creek basin during the 14- to 6-Ma interval, the crust beneath the basin fill was then subsiding under extensional strain oriented orthogonally to the axis of the basin.

Basement rocks: Their deformational feature and evidence for pre-I4-Ma extension The Paleozoic basement rocks that depositionally underlie the Artist Drive Formation are exposed at three localities: at Eagle Mountain in the Amargosa Valley, at the Billie mine in upper Furnace Creek Wash, and in the vicinity of Desolation Canyon along the Black Mountains front. At each locality the Artist Drive Formation rests depositionally on Paleozoic rocks. At the Billie mine and Desolation Canyon localities, southwest of the Furnace Creek fault, the basement rocks are highly fractured; at Eagle Mountain, questionably on the northeast side of the fault, they are essentially intact. The ductilly deformed and metamorphosed Proterozoic rocks exposed beneath the Badwater Turtleback surface adjacent to the basin provide evidence of what underlies the Paleozoic rocks beneath the basin fill. Less direct evidence of the nature of the basement beneath the southeastern part of the basin in the early stages of its structural development is contained in exposures of the fanglomerate (ca. 17-16 Ma) at the southern end of the Funeral Mountains (Cemen et aI., this volume). Intact Cambrian basement at Eagle Mountain. We interpret the Cambrian formations at Ragle Mountain as ba.