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David L. Jones

Publications and source records attributed to David L. Jones.

8 recordsLinked to original sources
USGS1992

Interoceanic variation in the rare earth, major, and trace element depositional chemistry of chert: Perspectives gained from the DSDP and ODP record

Rare earth element (REE), major, and trace element abundances and relative fractionations in forty nodular cherts sampled by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) indicate that the REE composition of chert records the interplay between terrigenous sources and scavenging from the local seawater. Major and (non-REE) trace element ratios indicate that the aluminosilicate fraction within the chert is similar to NASC (North American Shale Composite), with average Pacific chert including ~7% NASC-like particles, Indian chert ~ 11% NASC, Atlantic chert ~ 17% NASC, and southern high latitude (SHL) chert 53% NASC. Using La as a proxy for ∑REE, approximations of La ex (the amount of La in excess of that supplied by the detrital aluminosilicate fraction) indicate that Pacific chert contains the greatest La ex (85% of La total ) and SHL chert the least (38% of La total ). As shown by interelement associations, this La ex is most likely an adsorbed component onto aluminosilicate and phosphatic phases. Accordingly, chert from the large Pacific Ocean, where deposition occurs relatively removed from significant terrigenous input, records a depositional REE signal dominated by adsorption of dissolved REEs from seawater. Pacific chert CeCe * ⪡ 1 and La n Yb n ~ 0.8-1, resulting from adsorption of local Ce-depleted seawater and preferential adsorption of LREEs from seawater (e.g., La n Yb n ~ 0.4), which increases the La n Yb n ratio recorded in chert. Chert from the Atlantic basin, a moderately sized ocean basin lined by passive margins and with more terrigenous input than the Pacific, records a mix of adsorptive and terrigenous REE signals, with moderately negative Ce anomalies and La n Yb n "> La n Yb n ratios intermediate to those of the Pacific and those of terrigenous input. Chert from the SHL region is dominated by the large terrigenous input on the Antarctic passive margin, with inherited Ce Ce * ~1 "> CeCe * ~1 and inherited La n Yb n "> La n Yb n values of ~1.2–1.4. Ce Ce * "> ~1.2–1.4.CeCe * does not vary with age, either throughout the entire data base or within a particular basin. Overall, Ce Ce * "> CeCe * does not correlate with P 2 O 5 concentrations, even though phosphatic phases may be an important REE carrier. This and previous studies of the large-scale controlling parameters of sedimentary REEs across ocean basins collectively indicate that REE indices of depositional regime (e.g., Ce Ce * "> CeCe * , La n Yb n "> La n Yb n , La ex ) are reproducible in a variety of sediment and rock lithologies, ages, and ocean basins, and present a coherent tool for paleoceanographic and tectonic basin reconstructions.

Geochimica et Cosmochimica Acta↗
USGS1992

Rare earth, major, and trace element composition of Monterey and DSDP chert and associated host sediment: Assessing the influence of chemical fractionation during diagenesis

Chert and associated host sediments from Monterey Formation and Deep Sea Drilling Project (DSDP) sequences were analyzed in order to assess chemical behavior during diagenesis of biogenic sediments. The primary compositional contrast between chert and host sediment is a greater absolute SiO 2 concentration in chert, often with final SiO 2 ≥ 98 wt%. This contrast in SiO 2 (and Si Al "> SiAl ) potentially reflects precursor sediment heterogeneity, diagenetic chemical fractionation, or both. SiO 2 concentrations and Si Al "> SiAl ratios in chert are far greater than in modern siliceous oozes, however and often exceed values in acid-cleaned diatom tests. Compositional contrasts between chert and host sediment are also orders-of-magnitude greater than between multiple samples of the host sediment. Calculations based on the initial composition of adjacent host, observed porosity reductions from host to chert and a postulated influx of pure SiO 2 , construct a chert composition which is essentially identical to observed SiO 2 values in chert. Thus, precursor heterogeneity does not seem to be the dominant factor influencing the current chert composition for the key elements of interest. In order to assess the extent of chemical fractionation during diagenesis, we approximate the precursor composition by analyzing host sediments adjacent to the chert. The SiO 2 concentration contrast seems caused by biogenic SiO 2 dissolution and transport from the local adjacent host sediment and subsequent SiO 2 reprecipitation in the chert. Along with SiO 2 , other elements are often added (with respect to Al) to Monterey and DSDP chert during silicification, although absolute concentrations decrease. The two Monterey quartz chert nodules investigated, in contrast to the opal-CT and quartz chert lenses, formed primarily by extreme removal of carbonate and phosphate, thereby increasing relative SiO 2 concentrations. DSDP chert formed by both carbonate/phosphate dissolution and SiO 2 addition from the host. Manganese is fractionated during chert formation, resulting in MnO Al 2 O 3 "> MnOAl2O3 ratios that no longer record the depositional signal of the precursor sediment. REE data indicate only subtle diagenetic fractionation across the rare earth series. Ce Ce ∗ "> CeCe* values do not change significantly during diagenesis of either Monterey or DSDP chert. Eu Eu ∗ "> EuEu* decreases slightly during formation of DSDP chert. La n Yb n "> LanYbn is affected only minimally as well. During formation of one Monterey opal-CT chert lens, REE Al "> REEAl ratios show subtle distribution changes at Gd and to a lesser extent near Nd and Ho. REE compositional contrasts between diagenetic states of siliceous sediment and chert are of a vastly smaller scale than has been noted between different depositional environments of marine sediment, indicating that the paleoenvironmental REE signature is not obscured by diagenetic overprinting.

Geochimica et Cosmochimica Acta↗
USGS1992

Diagenetic formation of bedded chert: Evidence from chemistry of the chert-shale couplet

Theories concerning the formation of bedded chert traditionally have emphasized either depositional or diagenetic processes. Major and rare earth element data from Franciscan assemblage (Mesozoic) and Claremont Formation (Miocene) bedded chert sequences, along with physical observations such as the presence of rare and highly corroded radiolarians in shale interbeds, are most consistent with a dominantly diagenetic origin of chert-shale couplets and are incompatible with many depositional theories. Chemical distributions between Franciscan and Claremont bedded chert=shale closely match chemical fractionations recorded by Monterey Formation and Deep Sea Drilling Project-sampled cherts formed by diagenetic SiO 2 dissolution, transport, and reprecipitation, suggesting that diagenetic migration of SiO 2 from proto-shale to proto-chert is also largely responsible for chert-shale couplets. Identical Ce anomalies (Ce/Ce*) found in immediately adjacent chert-shale layers indicate that turbidites or other transport mechanisms are not responsible for the alternating beds. Neither the chemistry of the chert-shale couplet nor the overall stratigraphy of the sequences is consistent with couplet formation being caused by productivity fluctuations. Chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic SiO 2 to form entire stratigraphies of bedded chert.

Geology↗
USGS1980

Allochthonous Jurassic ophiolite in northwest Washington

Fragments of Jurassic ophiolite having U-Pb zircon ages narrowly grouped at 160 to 170 m.y. are widespread over parts of northwest Washington. The Haystack thrust fault is inferred to mark the base of the ophiolite in the San Juan Islands and adjacent Cascade foothills; other bodies of mafic and ultramafic rock in the western Cascades may be klippen of the Haystack thrust plate. The Haystack thrust fault is probably the structurally highest and possibly most extensive thrust yet recognized within a family of Late Cretaceous thrust faults in northwest Washington. The ophiolite and its time of emplacement (bracketed between about 100 and 88 m.y.) suggest a similarity with the Coast Range thrust of California which thrust Upper Jurassic ophiolite and the Great Valley sedimentary sequence over the Franciscan assemblage. However, relations in the Cascades are complicated by the extraordinarily diverse character of lower plate rocks, of which very few resemble the Franciscan. We conclude that an original subduction system was modified by later tectonic activity so that a variety of terranes was juxtaposed as a family of rootless thrusts, with the ophiolite forming, at least in some areas, the uppermost structural unit. Perhaps the emplacement of Wrangellia, an allochthonous microcontinent west of the San Juan Islands, caused the thrusting.

Washington↗
USGS1973

Upper Cretaceous (Maestrichtian) fossils from the Kenai-Chugach Mountains, Kodiak and Shumagin Islands, Southern Alaska

A thick sequence of highly deformed flyschlike metasandstone, slate, and argillite crops out in southern Alaska in the Kenai-Chugach Mountains and on Kodiak and the Shumagin Islands to the southwest. These poorly fossiliferous rocks have long been considered Cretaceous in age because of scattered occurrences of fragmentary shells of Inoceramus . Mainly on the basis of new fossil collections, the age of some of these rocks can now be firmly established as Late Cretaceous (Maestrichtian); the critical fossil is Inoceramus kusiroensis Nagao and Matsumoto. Inoceramus kusiroensis also occurs in the much more fossiliferous and only slightly deformed Matanuska Formation that forms a parallel belt north of the Chugach Mountains. On the basis of faunal, lithologic, and bedding characteristics, the Matanuska Formation is the shelf equivalent of the deepwater, trench, or continental-rise deposits of the Kenai-Chugach Mountains and islands to the southwest. " Inoceramya concentrica " Ulrich occurs with Inoceramus kusiroensis and is Maestrichtian in age, not Early Jurassic as E. 0. Ulrich suggested in 1910. The syntypes of I. concentrica are refigured and a lectotype is designated.

Alaska↗
USGS1973

Lower Jurassic ammonite from the south-central Sierra Nevada, California

A Lower Jurassic ammonite has been found in metasiltstone of the Boyden Cave roof pendant, south-central Sierra Nevada, Calif. Although too poorly preserved to permit positive generic and specific identification, its general shape, coiling, and ornamentation are characteristic of Early Jurassic forms. Strata associated with the fossiliferous rocks in the pendant include quartzite, andalusite hornfels, and marble. This assemblage differs strikingly from nearby volcanic rocks to the east, some of which in the Ritter Range pendant also contain Lower Jurassic fossils. The presence of nonvolcanic Lower Jurassic rocks of the Boyden Cave pendant lying west of coeval volcanic rocks of the Ritter Range pendant is anomalous and may be the result of large-scale tectonic dislocations.

California↗
USGS1973

Metamorphic facies indicated by vein minerals in basal beds of the Great Valley sequence, northern California

A reexamination of reported blueschist mineral localities in the basal strata of the Great Valley sequence revealed only prehnite-pumpellyite facies minerals. Franciscan graywacke thrust below the Great Valley rocks contains lawsonite-quartz blueschist assemblages. At a common pressure of about 4 kb, the Franciscan blueschists formed at lower temperatures than the overlying Great Valley prehnite-bearing rocks, lending support to tectonic models that involve rapid subduction of the Franciscan rocks.

California↗