Age: Early Cretaceous – Barremian through Aptian
The Cuche Formation consists of dark grey to black silty shales with occasional intercalations of arkosic quartz arenites, and in its upper part marly shales separated by some workers into the Maridale Member. The bulk of the formation has been deemed Barremian in age based on micro fauna (Bartenstein et al 1957), though some reworking of Neocomian and Hauterivian occurs and towards the top of the formation Aptian belemnites and foraminifera of Aptian/Albian aspect predominate (Kugler 1953). Total thickness is unknown because of the complexity of structure and the failure to identify either the base or the boundary with the overlying Gautier Formation.
The monotony of the shales implies a relatively low energy for the depositional area. Little free oxygen appears to have been available because disseminated organic material is preserved. The sandstones and limestone blocks suggest that relative peace was periodically disrupted by high-energy turbiditic flows. The sandstones appear to be more common in the east implying that the locus of clastic input was to the east. The proximity of land in the basal part of the formation is suggested by fossil plants (Kugler & Boli 1967) but the shallow water fauna.
The shales that are so characteristic of this formation are composed of clay and silt, with varying amounts of organic matter and disseminated calcium carbonate; the latter often forming veins. Bedding is generally poorly defined . Sandstones are generally medium to coarse grained and contained rip-up clasts of the underlying silty shale. This was also seen in Mt. Harris # 1. Thin sections of the core sandstones found then to be subarkoses, with a small (1-7%) proportion of albitic feldspar, in addition to the dominant quartz. Detrital white micas were common and were often found in the shale along bedding partings. Hand specimens of the same sandstones revealed load balls and graded beds.
The Cuche Formation consists of dark grey to black silty shales with occasional intercalations of arkosic quartz arenites, and in its upper part marly shales separated by some workers into the Maridale Member. Boli (1959) divided the Cuche Formation into two zones:
Lenticulina ouachensis zone – the older of the two where benthic taxa strongly dominate over planktic formanifera.
Lepoldina protuberans zone- the younger zone which contains a rich and diversified planktic fauna probably representing a deepening of the basin due to a continued normal fault activity. Outcrops of the Cuche Formation occur in the core of the central range mainly on the eastern section of the island.
Renz (1942) introduced the term ‘Cuche Formation’ and divided it into the La Carriere shale member below and the Marridale member above. The formation consists of a thick series of dark shales of 200 feet minimum and perhaps ammounting to as much as 5000 feet in thickness, with subordinate quartzose sands and conglomeratic limestones.
Three lithotypes are recognised:
*Black, silty, micaceous with lignitic or carbonaceous laminae which appear to be slightly metamorphosed or have undergone considerable diagenisis.
*Moderately well sorted, very fine grained to coarse grained sublithic arenites to quartz arenites. Contain mudstone ripup clasts.
*Reddish-brown clay ironstone conglomerate with intercalatations of grits (cherry cake conglomerate)
Maridale Marl: Hutchison observed a belemite bearing, foraminiferal marl. Renz (1942) described Neohibolites aptiensis and Neohibolites semicanaliculatus.
Encountered in the following wells Laventille #1 (shale/limestone), Northern Basin #1, Guaico #1, Mt. Harris #1, Esmeralda #1, Montserrat #1, Iguana River 1 and Ste. Croix 1.
Sandstone from Iguana River #1
- Bridge B-2, Cunapo Southern Road
- 13.5 km mark Cunapo Southern Road
- Light Pole 139 Plum Road