Author of name: MACREADY (G. A.) (1921). Petroleum Industry of Trinidad. Trans. Amer. Inst. Min. Eng., vol. 65, p. 64.
Type locality: Forest oilfield, Fyzabad.
Thickness: About 2 900 feet.
MACREADY’S Forest clay of about 500 feet thickness is a blue and gray clay often very sticky and forms the imper¬vious cover over the Stollmeyer Oil Zone (now known as Forest sand). It is separated (torn the overlying Morne l’Enfer formation by a great unconformity but this is difficult to detect owing to the clayey non-resistant nature of the strata.
WARING (1926, p. 62) correlates the Forest or Lot One clay with his Red weathering Clay and together with the Forest Sands A-L) arrives at a thickness of about 1 100 feet for the Forest field.
LIDDLE (1928, p. 471) correlates his Forest formation with the Naparima formation, which in turn rests on Oligocene marls The Morne l’Enfer Sand, which he considers to form the basal member of the Moraga formation superimposes the Forest formation. He includes the Cruse oil zone (Sand G) in his Forest formation and places his Intermediate Clay between the Cruse sand and Forest Sand The Forest, or Cyclammina Clay forms the top of the Forest formation and carries 4 a great number of forarninifera, amongst which Cyclammina cancellata is most abundant. The thickness of the Forest clay is about 800 feet and for the total thickness of the Forest formation
2940 feet is given.
JEANNET (1928) reports two echinoids, Brissopsis jimenoi and Klelnia spec. from the Forest clay and BERRY (1925b) a number of plant leaves from Forest clay and Forest sand. Otherwise larger fossils are relatively rare but cyclic reoccurrences of foraminiferal assemblages are found to represent 1) marine turbid water environments (STAINFORTH, 1948, p. 1317), 2) silt environments and 3) end-of-cycle clear water environments
(SUTER, 1951, p. 209).
The Forest formation of the type area changes in easterly direction into a part of the silts and sands of the Moruga formation (s. str.).
At the type locality the total thickness of the Forest forma¬tion is not more than 2 000 feet (KUGLER, 1953, p. 54). This thick¬ness is subdivided from top to bottom into the following members: 1) Forest silt, 2) Upper Forest clay, 3) Forest sands and 4) Lower Forest clay (Intermediate clay of LIDDLE), (vide K. SCHMID in WILSON, 1940, p. 2103). The Forest formation gene¬rally rests unconformably on the Cruse formation and is followed conformably by the Morne l’Enfer formation.
(H. G KUGLER).
References: BERRY (E. W.) (1925b); WARING (G. A.) (1926); LIDDLE (R. A.) (1928); JEANNET (A.) (1928); WILSON (C. C.) (1940);
Sediments of the Forest Formation represent cyclical marine deposition under turbid water and clear water environments. Sandstones are strongly foreset bedded and lenticular. In grade they range from fine-medium grained to coarse grained, and are generally poorly sorted. Carbonaceous inclusions are common and residues from side wall cores have yielded glauconite. The sandstones alternate with grey and buff coloured silts and blue-grey and grey-green non-calcareous shales. The latter are frequently lignitic and usually unfossiliferous. Slump structures are common.
Maximum thickness is of the order of 2500 feet. The boundary with the Cruse formation is unconformable.