Paul E. Damon

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP.

A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP

New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue). ABSTRACT. New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally rati- fied to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-res- olution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).

Calibration of Radiocarbon Dates: Tables Based On the Consensus Data of the Workshop On Calibrating the Radiocarbon Time Scale

A calibration is presented for conventional radiocarbon ages ranging from 10 to 7240 years BP and thus covering a calendric range of 8000 years from 6050 BC to AD 1950. Distinctive features of this calibration include: (1) an improved data set consisting of 1154 radiocarbon measurements on samples of known age, (2) an extended range over which radiocarbon ages may be calibrated (an additional 530 years), (3) separate 95% confidence intervals (in tubular form) for six different radiocarbon uncertainties (20, 50, 100, 150, 200, 300 years), and (4) an estimate of the non-Poisson errors related to radiocarbon determinations, including an estimate of the systematic errors between laboratories.

Cenozoic mineral deposits and subduction-related magmatic arcs in Mexico

Spatial distribution of isotopic ages of igneous rocks in northern Mexico shows that a magmatic arc commenced at 140 m.y. B.P. near a paleotrench, progressed 1,000 km eastward by 40 m.y. B.P., and then regressed to within 200 km of the continental margin by 18 m.y. B.P. During progression, a calcic and calc-alkaline continental-margin volcano-plutonic regime developed, but farther east, high-K calc-alkaline and alkaline facies formed in northeastern Mexico and west Texas. Following regression, calc-alkaline volcanism was renewed on the Pacific margin at ∼18 m.y. B.P. and continued until cessation of subduction by initiation of transform movements between Pacific and American plates. Benioff zone depth estimates from K 57.5 relationships suggest decreasing dip during progression and a variable-dip, variable-depth regime from 140 to 16 m.y. B.P. Both the dip-angle-convergence-rate relationship and independent convergence rates require increasing convergence but decreasing sinking rates of subducted oceanic slab from 80 to 42 m.y. B.P., followed by decreasing convergence and sinking rates from 42 to 16 m.y. B.P. Changes in subduction dynamics are attributed to plate reorganization at 44 m.y. B.P. and the approach of the East Pacific Rise. Differing hydrothermal ore assemblages in zones subparallel to the paleotrench are constrained by magma distribution in space and time Cu-(Mo-W) ores (106 to 40 m.y. old) in calc-alkaline magmas formed during progression, whereas Mo and CaF 2 deposits coincide with the alkaline belt during arc stillstand above the deepest subduction depths, and Pb-Zn-Ag deposits (49-26 m.y. B.P.) were formed during late arc progression and early regression. These geodynamic variations, plus Sr, Rb, and S isotopic characteristics of the arc terrane, suggest that processes associated with subduction and some crustal contamination, rather than local compositional anomalies in crust or mantle, account for different magma and mineral-deposit suites. Southern Mexico exhibits Fe and Cu zones, whereas the overlapping calc-alkaline trans-Mexican-Chiapanecan arc of late Miocene to Holocene age contains several base- and precious-metal deposits.

An oligocene (?) colorado plateau edge in arizona☆

Abstract Our emphasis is on the development history of the southern and southwestern physiographic edge of the Colorado Plateau Province in Arizona. This edge, which marks the southern termination of Permian cliff-making strata, diagonally bisects Arizona over a distance of about 500 km. This escarpment zone, frequently called the Mogollon Rim in central Arizona, long has been of geologic and popular interest. Its origin has often been linked with a major, late Cenozoic “plateau uplift” and faulting associated with the late Cenozoic Basin and Range disturbance. Our studies indicate that a pre-mid-Miocene rim history should be recognized, in general (Peirce et al., 1978), and an Oligocene (?) erosional event, in particular. Basically, a plateau edge escarpment had evolved by mid-Miocene time, prior to the onset of Basin and Range faulting and the development of the modern Grand Canyon. The location and trend of the physiographic edge of the plateau is influenced by a combination of a sequence of incompetent—competent late Paleozoic strata, and slight northeast tilting caused by at least two recognized tectonic events. These are: (1) pre-Turonian Mesozoic regional tilting, and (2) late Cretaceous—early Tertiary Laramide orogeny. The Eocene—Oligocene rim gravel was deposited by northerly-directed drainage above an early Tertiary erosion surface of regional extent. Later, in Oligocene (?) time, a generally unrecognized tectonic event induced erosion and down-cutting that outlined an ancestral Colorado Plateau physiographic margin with relief of up to 600 m. This escarpment zone formed a barrier to the regional, northerly trending drainage of Rim gravel time. Sediments of late (?) Oligocene—early Miocene age were deposited in the valleys at the base of the plateau edge. Subsequently, about 13 m.y. ago, relatively minor, discontinuous faulting, associated with the Basin and Range disturbance, was superimposed on or near the topographically low zone adjacent to the escarpment. One, the Oak Creek fault, extended into the preexistent plateau adge and influenced erosional modification. The preservation of Cretaceous marine strata along portions of the present plateau physiographic edge at elevations above 2 km is indicative of uplift relative to sea level. However, it is not yet possible to decipher the respective influences that the Laramide, mid-Tertiary, and late Cenozoic tectonic events might have had on elevations. Geographically, tectonic influence boundaries cannot yet be accurately assigned. The Colorado Plateau southern physiographic border in Arizona is primarily an Oligocene (?) erosional feature and is not a major tectonic boundary along which late Cenozoic differential “plateau uplift” is manifested.

High-precision radiocarbon dating of bristlecone pine from 6554 to 5350 BC.

ABSTRACT. New results of radiocarbon dating of ca 100 decadal bristlecone pine samples from 6554 Bc to 6084 BC and from 5820 to 5350 Bc are presented. Using 3 new 2.5L counters filled to ca 3atm with carbon dioxide, high-Precision dating has been performed by this laboratory for more than two years. Demonstration of the precision and accuracy of these counters is presented using ±20 o measurements from the SPorer minimum period. For the older samples, +3°oo measurements were made using ca 12-daY counting times. Results are presented both as 4C age BP vs dendro-Year BC, particularly for calibration PurPoses and as a14C vs time.

Enhanced cosmic‐ray production of 10Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions

The cosmogenic isotope 10 Be , total Be, and Al were measured in partly varved sediments from the upper 50 m of core 480, leg 64 (DSDP), Gulf of California. The concentration of 10 Be from 1 to 50 kyr is in general agreement with estimates of the geomagnetic dipole moment obtained from archaeomagnetic and marine core research. 10 Be anomalies were also found at 32 kyr and 43 kyr, contemporaneous with the Mono Lake and Laschamp excursions, respectively. The production of 10 Be required to explain these anomalies is too high, particularly for the Mono Lake excursion, to be produced by a combination of decreased geomagnetic field and unprecedented long-term solar activity. We conclude that the cause is a change in the galactic cosmic-ray flux consistent with a supernova event. The coincidence with the two excursions remains a paradox.

Fine and hyperfine structure in the spectrum of secular variations of atmospheric (super 14) C.

The coarse structure of the 14C spectrum consists of a secular trend curve that may be closely fit by a sinusoidal curve with period ca 11,000 yr and half amplitude ±51%0. This long-term trend is the result of changes in the earths geomagnetic dipole moment. Consequently, it modulates solar components of the 14C spectrum but does not appear to modulate a component of the spectrum of ca 2300-yr period. The ca 2300-yr period is of uncertain origin but may be due to changes in climate because it also appears in the 8180 spectrum of ice cores. This component strongly modulates the well-known ca 200-yr period of the spectrums fine structure. The hyperfine structure consists of two components that fluctuate with the 11-yr solar cycle. One component results from solar-wind modulation of the galactic cosmic rays and has a half-amplitude of ca ±1.5%. The other component is the result of 14C production by solar cosmic rays that arrive more randomly but rise and fall with the 11-yr cycle and appear to dominate the fluctuation of the galactic cosmic-ray-produced component by a factor of two.

Evolution of the central Rio Grande rift, New Mexico: New potassium-argon ages

Abstract New K Ar age determinations on mid-Oligocene to Pleistocene volcanic and shallow intrusive rocks from the central Rio Grande rift permit a more detailed understanding of the tectonic and magmatic history of the rift. Initial extension in the region of the central rift may have begun prior to 27 m.y. ago. By 25 m.y. ago broad basins existed and were filling with volcaniclastic sediments derived mainly from volcanic centers in the San Juan and Questa areas. Continued tectonic activity narrowed these basins by 21-19 m.y. ago, indicated in the Santa Fe area by tilting and faulting that immediately postdate 20-m.y.-old latite. Uplift of the Sangre de Cristo, Sandia, and Nacimiento Mountains shed clastic debris of the Santa Fe Group into these basins. Early rift magmatism is characterized by an overlap of mid-Tertiary intermediate intrusive and extrusive activity, extending to 20 m.y. ago, with mafic and ultramafic volcanism, ranging from 25 to 19 m.y. Both volcanism and tectonic activity were minimal during the middle Miocene. About 13 m.y. ago renewed volcanic activity began. Tectonism commenced in the late Miocene, resulting in the present, narrow grabens. The term “Rio Grande rift” should be restricted to these grabens formed during post-mid-Miocene deformation. Widespread eruption of tholeiitic and alkali olivine basalts occurred 3-2 m.y. ago. The Rio Grande drainage system was integrated 4.5-3 m.y. ago, leading to the present erosional regime. These intervals of deformation and magmatism correspond generally with a similar sequence of events in the Basin and Range province south of the Colorado Plateau. This similarity indicates that the Rio Grande rift is not a unique structure in the southwestern U.S., and must be related to the larger context of the entire Basin and Range province.

Dendrochronologic Calibration of the Radiocarbon Time Scale

Extensive radiocarbon analyses have been made of dendrochronologically dated wood. The resultant radiocarbon data are not in total agreement with the conventional solar calendar as exemplified by the tree-ring chronology. The discrepancy reaches a maximum between 4060 B.C. to 7350 B.C. when radiocarbon dates are too young by 800 to 870 yr. Using a compatible set of 549 dated samples as a working base, a calibration table has been derived for conversion of conventional radiocarbon dates to calendar dates. This conversion table covers the period of time from A.D. 1600 to 5400 B.C. Data are also given to facilitate the calculation of the accuracy of the corrected date by a simple, illustrated method.