Introduction
The mid-late Paleogene and early Neogene rocks of Jamaica are represented by the Yellow Limestone and White Limestone groups. Although often considered to represent a layer-cake straigraphy, this is not so and the transition from from the Yellow Limestone to the White Limestone occurs at different times across the island. In addition the Richmond Formation interfingers with the rocks of the Yellow Limestone Group. So in reality the terms "Yellow Limestone" and "White Limestone" are uesful general terms, but it is their constituent formations that are more important in understanding the geology of Jamaica. Yet, the constituent formations still prove difficult to deal with. I am currently looking at approved terminology to detail the stratigraphic units that we see in Jamaica.
The Yellow Limestone
The rocks attributed to the Yellow Limestone Group (the term Yellow Limestone first being introduced by James Sawkins in 1869) represent the first to be deposited across the eroded mountains produced by the collision of the Jamaica arc with the Yucatan Block. In fact these deposits show the progressive development of the block and trough structure that characterised White Limestone depoistional patterns across the island. Yet the age of Yellow Limestone-type lithologies varies significantly across the island of Jamaica, with Yellow Limestone lithologies appearing in the mid Paleocene in eastern Jamaica (Portland) and extending into the Oligocene in far western Jamaica (western Westmoreland). The stratigraphy of the Yellow Limestone is best understood (or has been more fully investigated) in areas around the Central Inlier, which has become the 'type' succession for Jamaica, although no succession in Jamaica is at all representative. Yet the succession exposed around the Central Inlier is instructive, and demonstartes the progressive north to south transgression of the Yellow Limestone across this part of the Clarendon Block, with older rocks in the north being over-stepped by younger rocks to the south. Across the Central Inlier, the Yellow Limestone can be divided into two major cycles: the Freemans Hall - Stettin Cycle, and the Litchfield - Chapelton Cycle.
The Freemans Hall - Stettin Cycle
These rocks show a progressive onlap from north to south across Jamaica and eventually the establishment of open marine, platform carbonate deposits.
---- Freemans Hall Formation. This formation, named after Freemans Hall in southern Trelawny, is represented by conglomerates and minor sandstones. The conglomerates consists of rounded pebbles and cobbles, and locally contain an interesting suite of semiprecious rocks. Vein quartz, with clasts up to cobble size, is a nonable commpoent; whereas agates and silicified wood are also frequent. The formation has its greatest development at Stettin and along Hectrs River (forming the parish boundary between Trelawny and Manchester), but is absent elsewhere. It seems likely that the Freemans Hall Formation represents an incised valley fill, and is only found along the course of this very ancient river.
---- Stettin Formation. The Stettin Formation is named after the community of Stettin in southern Trelawny. It consists of pale lime mudstones and wackestones, and locally packstones and grainstones. Bioclasts are dominated by molluscs (gastropods and bivalves) and foraminifera, although corals and algae are aslo present. The formation is more than 100 m thick at Stttein, but thins progressively southwards and pinches out to the south of Chapelton.
The Litchfield - Chapelton Cycle
The Litchfield - Chapelton Cycle is considerably thicker than the underlying Freemans Hall - Stettin cycle.
---- Litchfeild Formation. This consists of a series of fluvial to deltaic sandstones and siltsones. Sandstones either show fuvial characteristics or tidal estuary characteritics. Interbedded with the sandstones are thin units of lignitic shales with mangrove leaves and low-diversity small molluscs (bivalves and gastropods). Thin limestones are also present, most tonably the Dump Limestone, which occurs in northeastern Manchester between the communities of Christiana and Coleyville.
---- Chapelton Formation. This fomration consists of impure limestones and has a gradational contact with the underlying Litchfield Formation. The limestones show a distinctive yellow-brown colour, dur to the weathering of the iron minerals they contain, and many are blue-hearted. The term blue-hearted refers to limestones that are yellow-bron on the surface, but when unoxidixed interiors are exposed are blue-grey. The Chapelton Formation contains abundant molluscs (bvavles and the gastropod Campanile) and foraminifers. Amongst the foraminifers, is Yaberinella, a particularly significant genus that abounds on the Nicaragua Rise, but is also present in Panama and Costa Rica.
The White Limestone
Rocks belonging to the White Limestone Group cover about two thirds of the surface area of Jamaica and were deposited from the late Eocene to the early or middle Miocene (some 12 to 45 million years ago). The White Limestone accumulated in two different dpositional settings: shallow-water environments and deep-water environments.
In the shallow-water environments, carbonate was produced as the skeletons of plants and animals. The most important being the foraminifers (Order: Foraminifera) and the algae. Other producers of carbonate include: molluscs, corals and echinoderms. In the deep-water areas, the carbonate was produced by pelagic algae (coccolithophores) and planktic (drifting or swimming in shallow waters) foraminifers, with some detritus shed from the carbonate platforms (blocks).
Despite extensive research since the White Limestone was named by Sir Henry Thomas De La Beche in 1825, we still do not understand the full sequence. Below I describe what we do know so far.
Blocks and Troughs
By the time that the White Limestone was being deposited, Jamaica was represented by a series of shallowly submerged platforms that were separated by deep-water troughs. These have been uplifted and are now represented by blocks (former platforms) and belts (former troughs) separated by faults. The Clarendon Block is the largest block and now occupies portions of the parishes of St. Elizabeth, St. James, St. Ann, St. Mary, St. Andrew, St. Elizabeth, Clarendon and Manchester. The geological succession is most completely understood on this block.
The Clarendon Block is bounded to the west by the Monteplier-Newmarket Belt, to the north by the North Coast Belt and to the east by the Wagwater Belt. These belts are composed of deep-water chalk successions that would have formed in deep-water areas with estimated depths of at least 700-1000 m. The belts are separated from the Clarendon Block by faults, some of which are active (Wagwater Fault and those in the Newmarket-Montpelier Belt) and some which are not (Northern Platform Boundary Fault). The block and trough structure has been created during faulting associated with the uplift of Jamaica.
Other shallow water blocks may have existed (e.g., Blue Mountains Block, Hanover Block), but much of the White Limestone succession has been stripped off of these areas during the uplift of Jamaica.
Simplified map showing the geology of Jamaica and the blocks and belts
Carbonate Petrography
The sedimentary rocks that are present in the White Limestone are represented by limestones (formed of CaCO3) and dolostones (formed of the mineral dolomite [MgCaCO3]). Originally the shells of the marine animals (foraminifers, molluscs, corals) and plants (algae) were formed of aragonite and/or calcite (both different forms of the calcium-carbonate - CaCO3). The calcite can also be differentiated as low-Mg calcite (when it has very little magnesium) or high-Mg-calcite (when it has up to 20% magnesium). Low-Mg-calcite is the most stable form, high-Mg-calcite intermediate, and aragonite the least (metastable) stable form of CaCO3. After death, the unstable minerals may be disolved or replaced by stable minerals (neomorphism - one mineral being replaced by another). Skeletons of organisms found in limestones may therefore be made of the original skeletal material, may be represented by holes (vugs), or may be replaced by other forms of calcite (or even other minerals such as silica).
Limestone can be classified using a scheme established by Durham in 1962. Durham introduced a series of terms (mudstone, wackestone, packstone, grainstone, boundstone and crystalline) that can be used to name carboante rocks in the field.
| Lime mudstone | Composed of fine grained carbonate (microcrystalline calcite or micrite) that cannot be seen with the hand-lens.
Up to 10% of grains may be present. |
| Wackestone | Composed of grains floating (that is, not touching) in a micrite matrix. The term packed wackestone can be used when there are a lot of grains. |
| Packstone | Formed of grains that are touching (grain-supported) with a micrite matrix. |
| Grainstone | Formed of grains that are touching (grain-supported) with a cement. The cement may completely or partially fill
the spaces between grains |
| Boundstone | Formed of a growth fabric (e.g., corals or algae). |
| Crystalline | Where the rock has been recrystallized or neomorphosed and the original texture cannot be seen. |
Dolomite usually forms through the replacement of aragonite and/or calcite in an original limestone. Some grains may be dolomitized, or the whole rock may be dolomitized. The Troy Formation is largely formed of dolostone, although some parts only show a fabric of crystalline calcite (this may have been a dolostone that has been de-dolomitized).
Historical Review of Lithostratigraphic Names
De la Beche (1825, 1827) introduced the name White Limestone Formation and it was subsequently used by the geologists undertaken the First Geological Survey of Jamaica from 1859 to 1967 (Sawkins, 1869). Hill (1899, p. 65) divided the White Limestone in Jamaica into two series: the Oceanic Series, or 'Upland White Limestone', and the Coastal Series. In his table (Hill, 1899, p. 42), he shows the Oceanic Series as containing three units, the Montpelier, the Moneague and the Cobre. Hill (1899, p. 142) appearsto use the name Brownstown for the Moneague and the Cobre.
Trechmann (1922, table facing p. 423) suggested that the White Limestone was divided into the Moneague Beds and the Montpelier Beds.
The subdivision of the White Limestone into members was carried out by Howard Versey (in his M.Sc. thesis dated 1956), and published in a series of papers over the following seven years (Hose and Versey, 1957; Versey, 1957; Vresey in Zans et al., 1963). In these papers various names were introduced: Troy Member, Swanswick Member, Claremont Member, Gibraltar Member, Brown's Town Member, Ipswich Limestone, Montpelier Member, Walderston Member and Newport Member. These 'members' were characterised partly by lithology and partly on the larger foraminiferal assemblages they contained.
Robinson (in Zans et al., 1963, p. 45) introduced the term Pelleu Island Formation for the chert-free chalky limestones at San San Bay between the Montpelier cherty limestones and San San Clay. Robinson (1967a, p. 569) introduced the term Bonny Gate Formation for the older cherty limestones, which he believed were separated from the Montpelier by a significant hiatus. He also introduced the term Lloyds Member (Robinson, 1967a, p. 570) for the lower part of the Bonny Gate Formation in the Yallahs area that contained non-carbonate conglomerate beds. Robinson (1967b, p. 35) introduced the name Spring Garden Member for chalks similar to the Monpelier Formation, but lacking cherts, that were exposed along the main road between Buff Bay and Spring Garden in Portland. Robinson (1969a) considered that the Pelleu Island Formation was equivalent to the Spring Garden Member and dropped the former name.
The first 1:50,000 scale geological maps with the Hose and Versey (1957) names appeared in April, 1974. These included the sheets for Balaclava, Alligator Pond, Mandeville, Discovery Bay, Spaldings and Falmouth (Bateson, 1974-f). The White Limestone Group was split up into the following formations: Troy-Claremont Limestone Formation (Etc) (although only Troy Limestone Formation [Etc] is shown on maps for Spaldings and Mandeville: Bateson, 1974e-f), Somerset Limestone Formation (Est), Swanswick Limestone Formation (Es), Gibraltar-Bonny Gate Limestone Formation (Egb), Walderston-Browns Town Limestone Formation (Owb), Montpelier Limestone Formation (Mm), and Newport Limestone Formation (Mn). Wright and Robinson (in Wright, 1974, p. 47-51) treated the following as formations: Troy/Claremont Formation; Bonny Gate Formation; Somerset Formation; Swanswick Formation; Walderston/Browns Town Formation; Montpelier Formation and Newport Formation.
Steineck (1974, 1985) studied the foraminiferal and ostracod assemblages of the Montpelier and Lower Coastal Groups. He suggested the introduction of the term Clarendon Group for the shallow water limestones of the Clarendon Block, and included within them platform interior formations (Troy, Claremont, Walderston and Newport) and platform edge formations (Swanswick, Gibraltar and Brown's Town). The deep water, Montpelier Group was divided up into Lloyds Member, Bonny Gate Formation, Sign Beds and Spring Garden Formation. The name Sign Beds being introduced informally (Steineck, 1974, p. 224) for the lower chert-yielding part of the Montpelier Formation (sensu Robinson, 1969a, c).
The lack of lithological definitions of units and the unfortunate habit of combining different 'member' names to make formations was recognized by Robinson and Mitchell (1999). They reverted to the use of a Moneague Formation separated up into members. Mitchell (2004) in the "White Limestone volume" (Donovan ed., 2004) provisionally retained the name Moneague Formation for the upper units of the shallow-water White Limestone above the Somerset Formation, with separate Troy, Swanswick and Somerset formations below the Moneague Formation. The Ipswich Limestone was also placed in the Yellow Limestone Group.
Following the publication of the White Limestone Volume, I have been systematically mapping the Yellow Limestone and White Limestone of Jamaica. My provisional scheme was published (Mitchell, 2013) after presentation at the Caribbean Geological Conference in Guadaloupe. The name Moneague Formation has been abandoned, and other formations are defined at lithological boundaries based on changes in texture and/or colour. These units are mappable across the shallow water platform and deserve the name 'formation,' but revisions need to be made to the published names. The deep-water successions are still under investigation, and a new scheme will be presented in due course.
Lithostratigraphy
The lithostratigraphic units in the White Limestone Group are described here starting with the oldest. These descriptions are taken from my 2013 paper, but have been updated to take into account new observations.
Simplified stratigraphy of the White Limestone Group from the North Coast Belt (Area 1) across the Clarendon Block (Areas 2 [north] to 5 [south])
Troy Formation
The Troy Member was named by Hose and Versey (1957) for a series of recrystallized limestones some of which were dolomitic with a type section (Hose and Versey 1957, p. 33) in "the higher part of [the] Cockpit Country of Trelawny, north of the District of Troy". Here the Troy Formation overlies the Chapelton Formation of the Yellow Limestone Group.
The Troy Formation consists of massive to medium-bedded limestones and dolostones; the unit is often pink or brown, but may also be white or grey, with all variations between. In general, dolostones and recrystallized limestones dominate. The dolostones consist of either brown sucrosic (sugar-like) dolomite, or pink dolomicrites (fine-grained dolostones). A large portion of the formation however is represented by crystalline calcium carbonate and is interpreted as dedolomitized dolostones because thin sections show replaced dolomite textures. Some levels in the formation do preserve original limestone depositional fabrics; they are represented by micritic limestones (mudstones or wackestones) with scattered low-diversity foraminiferal assemblages. A distinctive feature of the Troy Formation is the presence of micritic limestones with abundant irregular and locally laminoid fenestrae (Mitchell, 1996). Although not ubiquitous, such levels are frequent in the Troy Formation. The base of the Troy Formation is an unconformity (Mitchell, 2016) the unconformity cutting down from the Healthy Hill Formation through the Chapelton Formation and in some places resting on Cretaceous (Mitchell, 2016).
The age of the Troy Formation is difficult to determine because of the lack of foraminifers due to dolomitization. It is most likely of early Late Eocene age (although it could pass down into the latest Middle Eocene).
Sawnswick Formation
The name Swanswick Limestone was introduced by Hose and Versey (1957) for a succession of foraminiferal packstones and grainstones in the hills south of Swanswick in the parish of Trelawny. Versey (in Zans et al., 1963, p. 33) defined the type section as "in the hill on which Swanswick House stands, one mile east of Clark's Town, Trelawny".
The Swanswick Formation consists of pale (usually white) grainstones with subsidiary packstones, locally coloured (pink or brown). Bedding ranges from decimetre scale to metre scale and is not recognizable in many outcrops. In general, thin bedded units are common on the platform margin, whereas thickly bedded to unbedded units dominate in the platform interior. Bioclasts include abundant foraminifers as well as peloids, molluscan fragments and echinoderm fragments. The bioclasts are well sorted suggesting high-energy deposits. Most samples taken from the Sawnswick Formation have a calcite spar cement, but some levels have a micrite matrix; wackestones and packstones are very unusual. The base of the formation is defined as the lowest occurrence of extensive grainstones; in general the Swanswick Formation seems to resist dolomitization, and can be mapped across much of the Clarendon Block. The thickness may be up to 300 m at the platform edge; by it thins into the platform centre to about 20 m. Hose and Versey (1957, p. 35) quoted a thickness of about 100 m.
An abundant and diverse assemblage of foraminifers is present in the Swanswick Formation. On the shelf edge these include Lepidocyclina macdonaldi Cushman, L. pustulosa H. Douvillé, Eulepidina chaperi (Lemoine and R. Douvillé), Heterostegina ocalana Cushman, Fabiania cassis (Oppenheim) and Eofabiania grahami (Kupper), together with Cushmania americana and various miliolids. The platform interior facies contains abundant miliolids, but lacks many of the other forms; such samples can be confused with the grainstones of the Walderston Formation, although the latter are usually coloured whereas the former are generally white. Molluscs may occur in abundance at some levels. The shelf edge Lepidocyclina-Eulinderina-Heterostegina fauna is typically Upper Eocene (Robinson and Wright, 1993; Robinson and Mitchell, 1999; Robinson, 2004).
Claremont Formation
The Claremont Member was introduced by Versey (in Zans et al., 1963) for the mollusc-bearing limestones found at Claremont School in the parish of St. Ann. The name was extended by Mitchell (2013) to include the thick unit of micritic limestones (carbonate mudstones and wackestones) that occurs between the Swanswick and the Somerset formations. The type locality is at Claremont School, parish of St. Ann (Versey in Zans et al., 1963).
The formation consits of dominantly pale pink to white carbonate mudstones and wackestones. Bedding ranges from medium to very thick or unbedded. The lithology consists of carbonate mudstones, wackestones and a few thin packstones. Many of the mudstones and wackestones are very hard and brittle, whereas many of the packstone levels may be softer. For much of the formation, dolomitization is limited, but becomes more significant in the platform interior. Exposures with extensive dolomitization cannot be distinguished from the Troy Formation, other than for their stratigraphic position. The thickness ranges from 150 m to absent (it is cut out locally by the sub-Somerset unconformity). The dolomitized inner platform facies of the Claremont Formation will be mapped separately in future work.
The formation yields scattered miliolids together with common Cushmania americana. Fabularia hanzawai Robinson occurs in the lower part and Fabularia verseyi Cole and Cyclorbiculinoides jamaicensis Robinson occur rarely in the upper part of the formation. Molluscs are locally common and include the large bivalve Superlucina megameris (Dall) and even a species of the gastropod Campanile. The formation must be assigned to the Upper Eocene based on the ages of the underlying (Swanswick) and overlying (Somerset) formations.
Somerset Formation
The Somerset Member was introduced by Hose and Versey (1957), although no type locality was mentioned. The name was retained by Mitchell (2004, 2013) for the thin unit of grainstones and packstones with common F. verseyi that can be easily mapped across Jamaica. Hose and Versey (1957, p. 35) did not mention a type locality for their Somerset Member, but stated that "the member shows its greatest development between Somerset and Marshall's Pen, west of Mandeville and south of Spaldings, both areas being in Manchester". Versey (in Zans et al., 1963) stated "The type section is in the district of Somerset to the west of Mandeville in the parish of Manchester".
The formation consists predominantly of pink to grey to cream foraminiferal grainstones and packstones which locally contain a rich mollusc and coral fauna. Thin units of wackestones and carbonate mudstones may also be present and these are similar to the underlying Claremont Formation, although are very thin compared to the thick units that predominate in the Claremont Formation. Fabularia verseyi is particularly distinctive and occurs as speckled white ovals which can be seen without the need for a hand lens. The wackestones are characterised by low-diversity, low abundance assemblages of foraminifers and gastropods, while the carbonate mudstones yield the same species, and occasionally also contain irregular fenestrae. Bedding ranges from 30 cm up to 2 to 5 m. The base of the formation is defined by the change from predominately carbonate mudstones and wackestones to packstones and grainstones. In many sections, particular in the platform interior, this boundary is very abrupt and erosional, and undoubtedly represents an unconformity. Towards the shelf edge, the boundary is more gradational (e.g., Stoney Hill: Mitchell, 2004), with thin packstones occurring interbedded with wackestones in the passage beds. In such areas, the boundary is taken where packstones become dominant. The Somerset Formation is a relatively thin marker horizon, and is generally from 10 to 40 m thick.
Fabularia verseyi is ubiquitous; L. macdonaldi, Eulepidina chaperi and C. jamaicensis are common in shelf-margin facies; Fallotella spp. and miliolids are common in platform interior facies. A rich assemblages of corals and molluscs (gastropods and bivalves) is also locally common. Sr-isotope values from Kuphus tubes indicate a latest Late Eocene age (Robinson, 2004).
Walderston Formation
The Walderston Member was introduced by Hose and Versey (1957). Here, the name is used for a series of predominately cream grainstones with abundant miliolids. The type locality is along road cuts to the north of Walderston, in the parish of Manchester (Hose and Versey, 1957), although this is atypical and is dominated by packstones rather than grainstones.
The Walderston Formation consists of coloured grainstones and subsidiary packstones. It is generally medium to thickly bedded, but in many outcrops bedding is lacking. The unit is 'strongly coloured;' typically it is cream, but it may be pink or grey; white units may also be present, but are generally thin. The formation is typically 200 to 300 m thick.
Miliolids are abundant and scattered specimens of, or layers rich in, Eulepidina occur particularly close to the platform edge. Dictyoconids (Fallotella) occur commonly at some levels in the lower part, Praerhapydionina delicata Henson is common in the middle, and Heterostegina (Vlerkina) antillea Cushman occurs in a thin interval near the top of the formation. Molluscs are locally common. Several Sr-isotope values indicate an early Oligocene age (Robinson, 1994).
Hose and Versey (1957) and Versey (in Zans et al., 1963) regarded the Waldeston Formation as a lateral equivalent of the Browns Town Formation, the former being a platform interior facies, and the later a platform edge facies.
My mapping indicates the situation is more complex: the miliolid facies is progressively replaced by cream Eulepidina-rich grainstones towards the platform edge. Upwards on the platform edge, there is a change from cream Eulepidina-rich grainstones to white Eulepidina-rich wackestones and packstones, a change that may correlate with a similar change in colour at the boundary between the Walderston and Newport formations on the Manchester Plateau. A complete solution to the nomenclature is yet to be arrived at.
Browns Town Formation
The name Browns Town Formation was introduced by Hose and Versey (1957), but the name had also been used by Hill (1899). The name is retained here for the Eulepidina-rich limestones in the platform margin facies. The type locality is within quarries in the vicinity of Brown's Town, St. Ann, where black weathering bedded limestones are exposed.
The Browns Town Formation is characterized by white, and occasional pale pink, packstones, wackestones and carbonate mudstones with common to abundant large lenticular foraminfers or abundant corals. The estimated thickness is about 300 m.
Eulepidina undosa (Cushmann) and Lepidocyclina cancelli Lemoine and R. Douvillé are common to abundant; whereas Nummulites also occurs commonly. Corals are abundant at some levels and coral-rich intervals can be mapped locally as members. Molluscs are also locally common. Ages derived from Sr-isotope values (Land, 1989) indicate an early Miocene age. Stratigraphic considerations suggest: late Oligocene to early Miocene.
Newport Formation
The Newport Formation was named by Hose and Versey (1957) with a type locality at a quarry at Newport, parish of Manchester.
The Newport Formation is characterised by white or pale-coloured wackestones and carbonate mudstones; a few subsidiary packstones may be present. Exposures are thickly bedded or unbedded. The estimated thickness is 300 m.
Scattered miliolids and peneroplids are present together with Miosorites (=Amphisorus of previous authors) sp. Molluscs are also locally common. The age of the formation ranges from Late Oligocene to Early Miocene.
Montpelier Formation
The Montpelier Formation represents the deep-water facies (chalks and carbonate turbidites) of the White Limestone Group. Although various beds/members/formations have been erected (e.g., Spring Garden Member, Pelleu Island Member; Sign beds; Bonny Gate Formation) the mapping of these units is difficult.
Part of my current work is to try and understand the stratigraphy of the Montpelier Formation and relate it to the shallow-water White Limestone succession.
References
Here I list some of the papers where you can find information on the White Limestone and those that I have referred to on this webpage. Some are available for free on the internet, some are available from the authors, and some we have scanned to make available (we can remove any of these if they infringe anyone's copyright). Please inform me of any broken links!
de la Beche, H., 1825. Notice on the diluvium of Jamaica. Annals of Philosophy, new series no. 10, 54-58. - [This paper was the first to mention the 'Great White Limestone Formation of Jamaica' (in a footnote on p. 56) and you can download the whole volume from Google.]