The Early Paleogene Rift Systems in Jamaica @ sfmgeology.com

Introduction

Two major rift systems of early Paleogene age are located in eastern Jamaica: the John Crow Mountains Rift and the Wag Water Rift. Although now in relatively close proximity, the two rift systems developed on different Cretaceous crustal types and are not genetically related. The John Crow Mountain Rift formed on crust associated with the Caribbean Large Igneous Province (CLIP), whereas the Wag Water Rift developed on island arc crust. Both rifts are now represented by tectonic belts have been inverted and deformed in the uplift of Jamaica over the last 12 to 14 million years.

The John Crow Mountain Rift

The John Crow Mountain Belt is situated in eastern Jamaica and comprises the rocks of the John Crow Mountains and Rio Grande valley. These rocks have a different stratigraphy to other parts of Jamaica. Inparticular, they have Paleocene deep-water conglomerates, sandstones and shales (possibly a K-Pe boundary succession), deep-water Paleocene bedded Marlstones-limestones (similar to the Font Hill Formation), and a massage into pure limestones (similar to the White Limestone) within the Paleocene.

The following units are present:-
White Limestone Group. Late Paleocene-Miocene. Shallow-water and deep-water limestones.
Nonsuch Formation. Mid Paleocene. Deep-water Paleocene impure bedded Marlstones-limestones (similar to the Font Hill Formation).
Mooretown Formation. Early Paleocene (?Latest Maastrcihtian). Turbiditic sandstone-shale sequence.
Bowden Pen Formation. Late Maastrichtian? Pebble conglomerates (syn rift sequence).

The Wag Water Rift

The Wagwater Belt is a tectonic Belt running across eatern Jamaica between the Blue Mountains Inlier and the Clarendon Block. The Belt is a tectonic feature defined by active faults and represented by an inverted rift sequence called the Wagwater Rift.

The fill of the Wagwater Rift is complex including coarse- and fine-grained clastics, basic and acidic volcanics and minor limestones.

The following formations are present:

Wagwater Formation (Paleocene to ?earliest Eocene). Predominately conglomerates divided into a variety of members:

- Ginger River Member. Red-bed conglomerates.
- Pencar River Member. Sandstones and shales associated with limestones (Woodford Limestone, Good Hope Limestone) and evaporites (Brooks Gypsum).
- Dry River Member. Red-bed conglomerates.
- Halberstadt Volcanics. Basic volcanics.
- Newcastle Volcanics. Acidic sills (dacites) associated with the Dry River Member.

Richmond Formation (early Eocene). Predominantly shales and sandstones with a basal conglomerate unit. Divided into:

- Port Maria Member. Conglomerates with a noticably content of limestone clasts.
- Roadside Member. Sanstones and shales.
- Langley Member. Mudstones and shales.
- Nutfield Volcanics. Basic and acidic volcanics associated with the Roadside Member.