2010 Overboard in the Mojave - Biological Science - California State ...

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to several cm in thickness. They are nearly always found at or just above the contact of alluvial fan gravels with overlying lacustrine deposits and are associated with lake transgression (Awramik et al., 2000). Our observations indicate that oncoid coats tend to be thin (or absent) in distal fan positions, where single layers of coated clasts may be found, and on active fan-lake margins, where multiple layers of clasts with thin coats may be deposited. Distal fans in the Manix basin are typified by oxidized muddy sand and fine gravel with little soil development. Fine gravel is easily wave-transported and this, combined with rapid lake transgression over low-gradient distal fans, may inhibit oncoid formation. Thick oncoid coats are most common along stable medial to proximal fan-lake margins, where they accreted on pebbles to boulders composing, or reworked from, a desert pavement overlying moderately to well-developed soils formed on fan m. c. reheis and d. m. miller gravel. These relations, together with the absence of tufa towers or mounds constructed by groundwater—lake interaction as is common today at Mono Lake and Pyramid Lake, suggest that the calcium required to construct the oncoids is derived from near-surface pedogenic carbonate of the subjacent alluvial fan during lake transgression. 1. Fluvial-deltaic deposits Fluvial-deltaic deposits at the junction of the perennial Mojave River and Lake Manix are widely exposed as the uppermost 8-10 m of outcrop along the northern bluffs of the modern Mojave River near and west of the USGS Manix core site (Fig. 2). They were described as “Member D” of the Manix Formation by Jefferson (2003) and accumulated between about 50 and 25 ka (Miller and Mc- Geehin, 2007; Reheis et al., 2007b). These deposits form nearly parallel-bedded exposures on faces parallel to the Figure 4. Fluvial-deltaic and nearshore sediments photographed in the USGS Manix core. Depths below surface shown in headers; scale in cm. A, core segment MX-3; note 10-15° dips in bottom half. B, core segment MX-7; note laminated sand in middle of core and brown laminated silty clay at base. Photographs by J. Honke (U.S. Geological Survey). 28 2010 Desert Symposium
environments of nearshore lacustrine deposition in the pleistocene lake manix basin modern Mojave River (Fig. 3A), that is, oriented parallel to past streamflow, and form notably lenticular-bedded deposits in faces perpendicular to stream flow. Lenses fill channels cut into adjacent deposits and into the top of older Lake Manix deposits, and generally channels are draped by mud and sand interpreted as overbank deposits. The overbank deposits fine upward from pebble gravel to mud beds with rip-up mud balls common near the base and mudcracks common at the top. The sand beds in places contain calcium-carbonate nodules and plates (Fig. 3B) that we interpret as forming from groundwater discharge; locally, shell beds were dissolved and re-precipitated as soft nodules (G. Jefferson, written commun., 2010). Most beds are composed of grussy sand and fine-grained gravel, with less common mud beds and laminae (Figs. 3C and D); the clast composition indicates deposition by the Mojave River. Sedimentary facies and structures are largely fluvial and include “cross-bedded channel-fill deposits, crevasse-splay deposits, marsh, and floodplain deposits” (D. Miller, p. 23-24 in Reheis et al., 2007b). The rare beds that least ambiguously indicate lacustrine deposition are planar-bedded, very thin, and composed of well-sorted fine-grained sand (Fig. 3B), some of which are diatomaceous. Intervals of poorly sorted sand and silt, including armored mud balls, are locally observed in the USGS Manix core (Fig. 4A). Poorly sorted sands and those with curving crossbeds are interpreted as fluvial, whereas wellsorted, oscillatory ripple-bedded sands are interpreted as lacustrine (Fig. 3B). Thin intervals (10-20 cm) of very well sorted, sometimes gently dipping, sand and silt are also interpreted as lacustrine (beach) deposits (Fig. 4B), and thin intervals of steeply dipping deltaic foreset beds are present (Reheis et al., 2007). Moderately sorted, planar-bedded sands (basal sand, Fig. 3D) may represent either lacustrine or fluvial deposition. The fluvial-deltaic sediments contain fossils of freshwater invertebrates and some vertebrates ( Jefferson, 1987, 2003). Beds with abundant Anodonta shells found in these deposits have provided radiocarbon ages. Some beds also contain freshwater snails and turtle remains (Clemmys marmorata; Jefferson, 2003). However, modern representatives of these fossils live in a variety of freshwater habitats including streams, rivers, ponds, lakes, and bogs. Jefferson (1987) interpreted the mixture of fossils from different habitats in two beds near the bottom and top of the fluvial-deltaic section to represent deposition by floods. Anodonta occupy both fluvial and lacustrine habitats, and were historically present in the Mojave River (reported in Meek, 1990); thus, their presence is not diagnostic of depositional setting. The Anodonta beds we sampled for dating were composed of clusters of whole and half shells with no other species present, and likely grew in-situ or 2010 Desert Symposium were little reworked. Fish fossils (Gila bicolor mojavensis; Jefferson, 2003) and lacustrine ostracodes (Steinmetz, 1987; Bright et al., 2006), have been identified in older, finer grained sediments of Lake Manix and also in younger lacustrine sands in the Afton subbasin (K. Gobalet, CSU Bakersfield, written commun., 2005), but have not been reported in the fluvial-deltaic deposits. Thin white beds of diatomaceous sand occur in the central part of “Member D” in some sections north of the core site. Diatoms identified by Scott Starratt (USGS, written commun., 2008), are mostly benthic forms that populate shallow (
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econnaissance geochronology of tuff
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Stratigraphy, age, and depositional
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stratigraphy, age, and depositional
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2010 Desert Symposium stratigraphy,
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2010 Desert Symposium stratigraphy,
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Correlation of the Miocene Peach Sp
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correlation of the miocene peach sp
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Table 1 continued 2010 Desert Sympo
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While in Barstow, Buwalda stayed in
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mammalian litho- and biochronology
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2010 Desert Symposium mammalian lit
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2010 Desert Symposium mammalian lit
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Figure 1a. Locality and outcrop ref
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strontium prospects (Durrell, 1953)
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Mountains site contains 28% CaCO by
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Toomey Hills-Yermo Hills (Emerald B
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14.0 Ma (Pagnac, 2009). The Miocene
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Dokka, R.K. and C.J. Travis. 1990.
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Lister, K. H., 1970, Paleoecology o
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miocene and late pleistocene stickl
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75 years of fieldwork in the Barsto
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75 years of fieldwork in the barsto
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Paleomagnetism of Miocene volcanic
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paleomagnetism of miocene volcanic
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nite and monzodiorite while the met
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geology and tectonic development of
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geology and tectonic development of
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Basalt is present east of the axis
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Schermer, E.R., Luyendyk, B.K., and
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2010 Desert Symposium camel tracks
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The Palm Borate Company operations,
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Claim Name Section 2010 Desert Symp
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Geology and ore genesis of epitherm
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geology and ore genesis of epitherm
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Figure 2. Cladoplebis sp. equal len
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Figure 8. c.f. Adocus sp. ogy to Gl
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Figure 13. Iguanodont tooth. Figure
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Hickey, L.J. and Doyle, J.A., 1977,
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3 are extremely rare. Member 4 is s
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new marine sites from member 4d of
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new marine sites from member 4d of
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Plantae Pieces of fossil wood (some
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A juvenile specimen of Archaeohippu
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2010 Desert Symposium a juvenile sp
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Table III: Lower tooth measurements
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Pagnac, D. C. 2009. Large mammal bi
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early pleistocene range extension f
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2010 Desert Symposium early pleisto
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The first tungsten-mining boom at A
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Atolia in 1909. USGS Hess. Their sh
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them a fine concentrating propositi
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St. Elmo Dist. etc. What I would li
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article which was published in the
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in sight and that after a little fu
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from this mine.—In drilling for w
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little over 150 feet and runs about
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here and now brand as a deliberate
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[Excerpts:] Thomas McCarthy, the Ra
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Thermal infrared airborne hyperspec
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Figure 3. The Calipatria fault (CP)
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detection of ammonia venting on the
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Kirkland, L. E., K. C. Herr,, and J
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serve the full array of sensitive n
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exposure. The LCROSS experiment was
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Paleomagnetic and radiocarbon recor
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contrast, very little information i
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the fine-grained fluvial sands on t
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lakes between 25 and ~9.9 cal ka, e
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