Caribbean datums and the integration of
geographical data
Keith M. Miller
ABSTRACT.
Modern electronic positioning systems are capable of locating a point in the
vicinity of the Earth’s surface to very high precision. Depending on the
sophistication of equipment in use, whether the requirement is relative or
absolute and the data processing time available, accuracy from 10 m down to a
few millimetres can be achieved in three dimensions. While it is not difficult
to measure the position of a point using today’s technology, it can be
problematic to relate measurements made today to those made in the past.
Advances in applications such as Geographical Information Systems (GIS) for
example, that integrate geographic data from a wide range of sources may give
misleading results if one position on the surface of the Earth can have a
number of different coordinate values. This paper is aimed at explaining the
reasons behind such dilemma while giving particular examples that relate to the
Caribbean region. It defines and explains the
different conventions that are adopted while providing local parameters that
enable conversion between modern and some of the traditional datums. The
reliability of this information is shown to be variable and there is a need for
improvement in the quality of parameters that are made publicly available.
Measurement-based
soil information systems for the Caribbean
Bheshem Ramlal
ABSTRACT.
Significant amounts of data are lost in the soil mapping process due to
classification and generalization. Although a soil map and a survey report are
prepared, the data presented in these documents are soil classes and
representative profiles for each soil class. The data collected in the field are
not made available to map users. Usually, in the digitization process, the same
data presented on soil maps and survey reports are stored in the database.
While these data are useful, the raw data are much more valuable for several
users. This paper describes a conceptual model for the storage of soil survey
observations and their data quality information. This schema is based on an
object-oriented data model. This approach allows greater flexibility in the
storage, access, modelling and analysis of the soil data that are stored in the
database. A more realistic representation of the soil landscape is therefore
achievable.
Enhanced earthquake
risk of Kingston due to wave field excitation in the Liguanea Basin, Jamaica
Margaret D. Wiggins-Grandison, Tarek R. M.
Kebeasy and Eystein S. Husebye
ABSTRACT.
Kingston, the capital of Jamaica, an island in the Northern
Caribbean, is situated on the Liguanea alluvial plain. Based on
intensity reports over several hundred years, the alluvial plain is generally
associated with an enhanced level of earthquake risk in Kingston. Two recently acquired 2 D depth
profiles across the plain have made it possible to model the 2-D wave-field
response of the Liguanea basin. Finite difference modeling was used to
investigate the effect of the basin and surrounding topography on local
shear-wave sources emanating from north, south and east of the basin. The
results show that energy partitioning across layer boundaries, location within
the basin, and source position in general, determined the level of wave-field
amplification within the sediments. In the extreme, amplitudes were highest by
one order of magnitude unit (a factor of 10) at the hill-basin margins and at
the margins nearest to the sources. Amplitudes were slightly lower at the
centre of the basin and away from the source, especially when the alluvium was
thick. When high inelastic attenuation of the sediments and the upper 3
kilometres of crust were introduced, the amplitude of ground motion was reduced
only marginally. The results predict variability on a scale of a few hundred
metres for ground motion over the Liguanea Plain that cannot be neglected in
future seismic risk studies. Additionally, it was determined that the
characteristic frequency for the Liguanea alluvium is about 6 Hz.
The trace fossil Schaubcylindrichnus coronus Frey and
Howard, 1981, from the White Limestone Group of northeast Jamaica
Donovan J. Blissett and Ron K. Pickerill
ABSTRACT.
The upper Lower-Middle Miocene Pelleu Island Formation of the Middle Eocene to
Middle Miocene White Limestone Group, northeast Jamaica, has yielded the trace
fossil Schaubcylindrichnus coronus
Frey and Howard, 1981. The documentation of this bundled trace fossil is
important because it is the first report of this ichnotaxon from Jamaica and indeed the Caribbean
region. As a corollary it therefore adds to the geographical distribution of
the trace fossil, and it is the first record that extends its
palaeoenvironmental range to a deep-water setting.
Field guide to the
geology and geomorphology of the Tertiary limestones of the Central Inlier and
Cockpit Country
Simon F. Mitchell, David J. Miller and
Ravidya Maharaj
ABSTRACT.
The geology and geomorphology of the rocks of the Yellow Limestone and White
Limestone Groups on the northern margin of the Central Inlier of central Jamaica are
described. The Yellow Limestone Group consists of limestones (Stettin
and Chapelton Formations) and clastic rocks (Guys Hill Formation). The
limestones of the Yellow Limestone Group give rise to doline karst, with low
residual hills, with the dolines locally amalgamated to form uvalas in the
Stettin Formation. The Guys Hill Formation forms to gently gullied topography
with shallowly incised stream systems of moderate drainage density. The overlying
White Limestone Group is represented by the Troy Formation and consists of
dolostones and crystalline limestones. The geomorphology is represented by
cockpit and tower karst, with intervening prominent enclosed depressions.
Detailed descriptions of eleven localities, representing a two-day field
excursion, are given to illustrate the important geological and
geomorphological aspects of this area.