Morne L’Enfer Formation
MORNE L’ENFER Formation Pliocene (Trinidad, B. W. I.).
Author of name: MACREADY (G. A.) (1921). Petroleum Indus tries of Trinidad. Trans. Amer. Inst. Min. Eng., vol. 65, p. 64.
Type locality: Morne I’Enfer Hill, 2 3/4 miles SE of the Pitch Lake.
Thickness: Up to 2 500 feet.
MACREADY’S Morne 1’Enfer formation is described as an alternating series of sandstones of uniform small quartz grains separated by bands of clay shale and rarely by lignite. No conglomerates known. The lowest 300 feet represent the tar sand of Morne L’Enfer. A maximum thickness of 2 500 feet is given for Erin Bay and 800 feet for the Morne 1’Enfer area. The Morne l’Enfer formation rests unconformably on the Forest Clay and is covered by the Upper Tertiary formation. It is characterised by porcellanites, lignites, fossilised wood, shales and clays but lacks conglomerates. MACREADY considers these beds to be of fresh water origin and tentatively gives them a Pliocene age (vide La Brea or Talpaor formations).
According to LIDDLE (1928, p. 476) the Morne l’Enfer sand stone and the younger Morne l’Enfer clay form the top of his Moruga formation. For the sand a thickness of about 350 feet and for the clay 400 feet is given.
SCHMID (K.) (in WILSON (C. C.), 1940, p. 2103) divides the Morne l’Enfer formation into a lower and an upper part with the Lot 7 Silts between the two. The base of the Morne l’Enfer formation in time Coora area is formed by a sheet—like sand. Within the Morne l’Enfer formation two persistent silt layers are recognised, namely the Coora silt which occurs 200—250 feet above the base of this sheet sand, and the Lot 7 silt which occurs 1000 – 1100 feet above the base of this sand.
According to the meeting of Pointe-a-Pierre (1955), the La Brea formation overlies the Morne l’Enfer formation and the contact of these two formations is placed at the base of the main mass of porcellanites outcropping at the coast south of Buenos
Ayres. (H. G. KUGLER).
References: LIDDLE (R. A.) (1928); WII.SON (C. C.) (1940).
The Morne l’Enfer is comprised predominantly of massive sandstones interbedded with siltstones and clay-shales which are commonly lignitic and pyritic. The sandstones are generally fine grained to very fine grained, subangular ard well sorted with carbonaceous material and glauconite as accessory minerals.
The sandstones frequently grade into siltstones. Two persistent silt layers are present within the formation, the Coora Silt and the Lot 7 Silt, occurring at approximately 200-250 ft. and 1,000 ft. respectively above the base of the formation. Both serve as reliable structural markers, particularly the Lot Silt which has proved to be an excellent seismic reflector.’
At its maximum development in the Erin Syncline the Formation is about 4000 feet thick. Its contact with the underlying Forest Formation is unconformable.
On the Kugler (1959) it occupies the 6a, 6b, 6c and 6d interval. The Lot 7 Silt subdivides the Formation into an Upper (tidal – fluvial)and Lower ( inner neritic – brackish water) member.