John B. Lyons

Deposition of channel deposits near the Cretaceous-Tertiary boundary in northeastern Mexico: Catastrophic or normal sedimentary deposits?

Investigation of Cretaceous-Tertiary (K-T) boundary channel deposits in three sections in northeastern Mexico reveal three lithologically and mineralogically distinct units separated by three or more disconformities. The units include a spherule-rich layer (unit 1), laminated sandstone (unit 2), and rippled sand and shale layers (unit 3). On the basis of paleontological, mineralogical, and geochemical evidence, the K-T boundary is just above the top of unit 3. Although the deposits have previously been interpreted as a tsunami deposit related to a presumed K-T impact at Chicxulub on Yucatan, we have found no evidence of a nearby impact. We suggest that deposition occurred in an incised valley setting and over an extended period of time.

Is there evidence for Cretaceous-Tertiary boundary-age deep-water deposits in the Caribbean and Gulf of Mexico?

Over most of the Gulf of Mexico and Caribbean a hiatus is present between the lower upper Maastrichtian and lowermost Tertiary deposits; sedimentation resumed ∼200 ka (upper zone Pla) after the K-T boundary. Current-bedded volcaniclastic sedimentary rocks at Deep Sea Drilling Project (DSDP) Sites 536 and 540, which were previously interpreted as impact-generated megawave deposits of K-T boundary age, are biostratigraphically of pre-K-T boundary age and probably represent turbidite or gravity-How deposits. The top 10 to 20 cm of this deposit at Site 536 contains very rare Micula prinsii, the uppermost Maastrichtian index taxon, as well as low values of Ir (0.6 pbb) and rare Ni-rich spinels. These indicate possible reworking of sediments of K-T boundary age at the hiatus. Absence of continuous sediment accumulation across the K-T boundary in the 16 Gulf of Mexico and Caribbean sections examined prevents their providing evidence of impact-generated megawave deposits in this region. Our study indicates that the most complete trans-K-T stratigraphic records may be found in onshore marine sections of Mexico, Cuba, and Haiti. The stratigraphic records of these areas should be investigated further for evidence of impact deposits.

Rb-Sr age of the New Hampshire Plutonic Series

Rb-Sr whole-rock isochrons for four main representatives of the syntectonic to post-tectonic New Hampshire Plutonic Series yield the following ages: Kinsman Quartz Monzonite, 411 ± 19 m.y.; Bethlehem Gneiss, 405 ± 78 m.y.; Spaulding Quartz Diorite, 402 ± 5 m.y.; and Concord Granite, 359 ± 11 m.y. (or 330 ± 3 m.y.?). The Kinsman and Spaulding ages are consistent with a growing number of Rb-Sr ages determined for northern Appalachian granites, which are of Early Devonian or younger geologic age, and represent a major magmatic pulse of the Acadian orogeny. Comparison of Rb-Sr ages and geology implies that the beginning of the Devonian Period can be no later than approximately 415 m.y. and that the entire Devonian time scale needs revision. The Concord Granite is at least 40 m.y. (possibly 70 m.y.?), younger than other members of the New Hampshire Plutonic Series, and its time of emplacement is therefore probably Late Devonian(?) or Mississippian(?). Isochron plots imply that, although the members of the New Hampshire Plutonic Series have been derived by anatexis of lower crustal rocks, there is admixture of and contamination by mantle-derived magmatic material.

Mesozoic erosion rates in northern New England

Ten stocks of the White Mountain Plutonic-Volcanic Series in New Hampshire have been sampled, and have yielded material for nine apatite and six zircon fission-track dates. The zircon ages (λ = 6.85 × 10 −17 y −1 ) are slightly younger than isotopic ages (chiefly K-Ar) which have been previously determined on these same intrusives, but the apatite ages are considerably younger, averaging about 55% of isotopic age for intrusives older than 130 m.y., and 85% of isotopic age for intrusives younger than 130 m.y. The differences between zircon and apatite ages have been used in conjunction with heat-conduction theory to show that 180 m.y. ago ambient wallrock temperatures of White Mountain intrusives (at the present erosion level) were ∼ 170 to 200°C. For intrusives 115 m.y. old, ambient wallrock temperatures were about 100°C. These numbers, assuming a 25 to 30 °C/km geothermal gradient, translate to depths of emplacement of ∼ 3 to 3.6 km (115 m.y.) and ∼ 5.3 to 7.6 km (180 m.y.), and indicate an average erosion rate, since Jurassic time, of 1 km per 32 m.y. (0.031 mm/yr). Jurassic isobaric surfaces are now tilted northeastward at an approximate gradient of 0.012 to 0.015 km per kilometre, Cretaceous isobaric surfaces at 0.007 to 0.008 km per kilometre and Devonian isobaric surfaces at an approximate gradient of 0.039 km per kilometre.

U-Th-Pb geochronology of the Massabesic Gneiss and the granite near Milford, South-Central New Hampshire: New evidence for avalonian basement and taconic and alleghenian disturbances in Eastern New England

U-Th-Pb systematics for zircon and monazite from Massabesic Gneiss (paragneiss and orthogneiss) and the granite near Milford, New Hampshire, were determined. Zircon morphology suggests that the paragneiss may be volcaniclastic (igneous) in origin, and thus the age data probably record the date (minimum of 646 m.y.) at which the rock was extruded. A two-stage lead-loss model is proposed to explain the present array of data points on a concordia diagram. Orthogneiss ages range only narrowly and are clustered around 475 m.y. Data for the granite of Milford, New Hampshire, are scattered, but may be interpreted in terms of inheritance and modern lead loss, yielding a crystallization age of 275 m.y. This is the only known occurrence of Avalonian-type basement in New Hampshire and as such provides evidence for the location of the paleo-Africa-paleo- North America suture. The geochronology also further documents the occurrence of disturbances during the Ordovician and Permian.

Planar lamellar substructures in quartz

Both single and multiple sets of lamellar features in quartz grains can be produced in shock experiments and are observed at known impact sites; they can also be produced in static, constant strain-rate experiments and are observed at known tectonic and explosive volcanic sites. The former are strictly planar and parallel and generally conform to rational crystallographic orientations in the quartz crystal structure. The latter can also be planar and parallel but sometimes show slight to moderate curvature with lamellar bifurcations and variable lamellar widths. Their orientations show a variety of forms with, in general, a broader angular distribution than that of the impact-generated lamellae. Deductions of physical conditions of deformation from optical morphology, spacing, multiplicity and orientation information alone remain somewhat conjectural; full characterization by transmission electron microscopy (TEM) appears to be necessary.

Mineralogy and petrology of the Haiti Cretaceous/Tertiary section

Abstract The Cretaceous/Tertiary sections in Haiti consist of a sequence of graded beds of turbidity current or gravity flow origin. Each section may consist variously of five major constituents: (1) black glass, (2) brown globules, veinlets and blobs, (3) argillaceous limestone clasts, (4) white clasts and shards, and (5) a fine-grained matrix rich in smectite, zeolites and calcite. In addition, there are trace amounts of a high-calcium yellow glass. The black glass particles are vesicular, apparently unaltered with an andesitic to dacitic composition, and in sharp contact with the secondary matrix and veinlet alteration products. The brown globules, veinlets and blobs consist of a palagonite-smectite mix of a distinctly different composition than the black glasses. White clasts and shards of a still different (more hydrated) composition are also present. All of these materials are sometimes associated with accretionary lapilli(?). The hydration or alteration products—brown globules, white clasts and shards, and matrix—amount to something in excess of 95% of the total deposits. The sedimentology, mineralogy and petrology of the Haiti sections has provided a record of a sequence of probable volcanic events.

KRb ratios in coexisting K-feldspars and biotites from some New England granites and metasediments

Abstract Coexisting K-feldspars and biotites of thirteen New Hampshire and three other New England rocks were analyzed quantitatively by X-ray fluorescence for potassium and rubidium. K Rb fractionation between the sixteen biotites and the sixteen K-feldspars is constant and not temperature dependent for the range of datum points observed. Other data in the literature suggest that there is very little K Rb fractionation between coexisting tecto- and phyllosilicates over the entire spectrum of geologic temperatures.

Carboniferous U-Pb age of the Sebago batholith, southwestern Maine: metamorphic and tectonic implications.

Two phases (pink and white granite) of the Sebago batholith of southwestern Maine have been dated by the U-Pb zircon method. Identical upper concordia intercepts of both rocks indicate an intrusive age of 325 ± 3 m.y. for the batholith. The lower intercept of the pink-phase sample, 114 ± 13 m.y., is inferred to represent episodic lead loss due to the intrusion of the nearby Cretaceous Pleasant Mountain stock. The lower intercept of the white-phase sample, 18 ± 21 m.y., suggests only modern dilatancy lead loss. Monazites have ages of 272 m.y. (pink) and 282 m.y. (white) which are thought to be cooling ages. Rb-Sr whole-rock data have low initial 87 Sr/ 86 Sr ratios of 0.7031 (pink) and 0.7053 (white). These data, in conjunction with published 40 Ar/ 39 Ar, Rb-Sr, K-Ar, and fission-track ages, suggest that little or no uplift occurred in this part of New England until the Permian and that the uplift rate from 275 m.y. to 225 m.y. was ∼3 times as rapid as was the rate for 225 m.y. to the present. The Carboniferous age of the Sebago batholith suggests that currently accepted metamorphic and tectonic interpretations for southwestern Maine and for east-central New Hampshire require revision.

Gravity signatures and geometric configurations of some Oliverian plutons: Their relation to Acadian structures

Oliverian plutons in west-central New Hampshire consist of Upper Ordovician mantled gneiss domes along the axis of the Bronson Hill anticlinorium, as well as other stocks farther west. All are intrusive into Middle Ordovician volcanic and metasedimentary rocks, but have been remobilized and have acquired their gneissic foliations during the late stages of the Early-Middle Devonian Acadian orogeny. Gravity studies are used to demonstrate that the Moody Ledge, Owls Head, and Baker Pond domes are irregularly shaped flat plutons with maximum thicknesses of 2.5 km. The Croydon dome, 4.2 km thick, is probably of laccolithic shape. The largest dome surveyed, the Mascoma, is mushroom shaped, with a stem extending to a depth of at least 4.5 km. The coeval Lebanon pluton west of the domes is a discordant north-northwest-plunging stock intrusive into a higher stratigraphic level (the Partridge volcanics), and extends to a depth of 8.5 km. It is bordered on the southeast, south, and west by the Cornish nappe, which is overfolded toward the west in the area south of the pluton, but is backfolded toward the east in a large region west and north of the stock. An oval outcrop area in the Mount Cube quadrangle resembles the surface outcrop of a subjacent Oliverian dome, but cannot be, because it lacks the appropriate gravity field. The Devonian Fairlee quartz monzonite is shown to be rootless, in accordance with the fact that Ammonoosuc normal fault passes beneath it, slightly below ground level. A subsurface (Devonian?) granitic stock occurs a short distance to the south. The Devonian Indian Pond pluton of Bethlehem gneiss in the Mount Cube quadrangle is also shown to be rootless, in agreement with its inferred structural position inside a nappe which has been overfolded from east to west, and just touches the present Earth9s surface. Recent pressure-temperature-time ( P-T-t ) metamorphic studies in western New Hampshire have led to proposals that there is a series of nested thrust plates involving the Bronson Hill and adjacent terranes. The possibility arises that the Oliverian domes may be allochthonous. However, nothing in the mapped geology, the geophysics, or the geochronology supports this hypothesis. We conclude that the basement below the Oliverian granites in western New Hampshire is likely to consist of metamorphic formations of Cambrian-Ordovician age.