Reef margin collapse, gully formation and filling within the Permian Capitan Reef: Carlsbad Caverns, New Mexico, USA

An area of reef margin collapse, gully formation and gully fill sedimentation has been identified and mapped within Left Hand Tunnel, Carlsbad Caverns. It demonstrates that the Capitan Reef did not, at all times, form an unbroken border to the Delaware Basin. Geopetally arranged sediments within cavities from sponge–algal framestones of the reef show that the in situ reef today has a 10° basinwards structural dip. Similar dips in adjacent back-reef sediments, previously considered depositional, probably also have a structural origin. Reoriented geopetal structures have also allowed the identification of a 200-m-wide, 25-m-deep gully within the reef, which has been filled by large (some  >15 m), randomly orientated and, in places, overturned blocks and boulders, surrounded by finer reef rubble, breccias and grainstones. Block supply continued throughout gully filling, implying that spalling of reef blocks was a longer term process and was not a by-product of the formation of the gully. Gully initiation was probably the result of a reef front collapse, with a continued instability of the gully bordering reef facies demonstrated by their incipient brecciation and by faults containing synsedimentary fills. Gully filling probably occurred during reef growth, and younger reef has prograded over the gully fill. Blocks contain truncated former aragonite botryoidal cements, indicating early aragonite growth within the in situ reef. In contrast, former high-magnesian calcite rind cements post-date sedimentation within the gully. The morphology of cavern passages is controlled by reef facies variation, with narrower passages cut into the in situ reef and wider passages within the gully fill. Gully fills may also constitute more permeable zones in the subsurface.     

Non-adiabatic motion of charged particles traversing a weak magnetic field: Pitch angle scattering

Summary A charged particle moves with velocityv in a constant non-uniform magnetic fieldH, spiralling with Larmor radiusR. IfR is small compared with the scale lengthL of the field, the magnetic moment associated with the Larmor motion of the particle is nearly constant. Consequently , the (pitch) angle betweenv andH, varies as arcsinH ^1/2. Hence in such adiabatic motion is approximately the same at points on the path whereH has the same value. But the magnetic moment and the pitch angle may differ materially at two such points, each in the region whereR/L is small, if between them the particle traverses a region whereR/L is not small. This region of non-adiabatic motion scatters the pitch angles.Such scattering is investigated for regions of weak field (R large), with and without the presence of a neutral line along whichH=0. Either type of region, it is found, can scatter the pitch angles. This gives support to the theory proposed byAkasofu andChapman to explain why auroral arcs and bands are very thin.The scattering here examined is of interest also in connection with magnetic mirror devices for nuclear energy transformation. It may also have applications to phenomena of solar and stellar atmospheres.     

The Klippfisk Formation—a new lithostratigraphic unit of Lower Cretaceous platform carbonates on the Western Barents Shelf

A new Lower Cretceous lithostratigraphic unit of the Western Barents Shelf, named the Klippfisk Formation, is formally introduced. The formation represents a condensed carbonate succession deposited on platform areas and structural highs, where it consists of limestones and marls, often glauconitic. The limestones may have a nodular appearance, and fossil debris, which are dominated by Inoceramus prisms, may be abundant. The Klippfisk Formation is composed of two members: the Kutling Member defined herein from cores drilled on the Bjarmeland Platform, and the coeval Tordenskjoldberget Member described on Kong Karls Land. The base of the formation is defined by the abrupt decrease in gamma-ray intensity, where the dark shales of the underlying Hekkingen or Agardhfjellet formations are replaced by marls. It is often unconformable. The Klippfisk Formation is of Berriasian to Early Barremian age and appears to be time-transgressive over parts of the Western Barents Shelf (including Kong Karls Land). It passes laterally into the basinal Knurr Formation. On Kongsøya (Kong Karls Land) a thin shale unit, bounded by unconformities, earlier included in the Tordenskjoldberget Member, represents the northernmost extension of the overlying Kolje Formation in the Barents Shelf.     

Water Level Declines in the High Plains Aquifer: Predevelopment to Resource Senescence

A large imbalance between recharge and water withdrawal has caused vital regions of the High Plains Aquifer (HPA) to experience significant declines in storage. A new predevelopment map coupled with a synthesis of annual water levels demonstrates that aquifer storage has declined by approximately 410 km³ since the 1930s, a 15% larger decline than previous estimates. If current rates of decline continue, much of the Southern High Plains and parts of the Central High Plains will have insufficient water for irrigation within the next 20 to 30 years, whereas most of the Northern High Plains will experience little change in storage. In the western parts of the Central and northern part of the Southern High Plains, saturated thickness has locally declined by more than 50%, and is currently declining at rates of 10% to 20% of initial thickness per decade. The most agriculturally productive portions of the High Plains will not support irrigated production within a matter of decades without significant changes in management.