Caribbean Journal of Earth Science, 37 (2003), 1-10.

 

 

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.

 

© Geological Society of Jamaica.