LakadongLmsMbr Fm
Type Locality and Naming
Lakadong Limestone Member of the Sylhet Fm type section is in the Lakadong Plateau, and at Therriaghat. Thickness is of 144 m. [Original Publication: Wilson, G.F., and Metre W.B. 1953: Assam and Arakan, In: Science of Petroleum, vol. 6(1), pp. 119-123.]
Lithology and Thickness
Limestone. Lakadong Limestone Member of the Sylhet Fm is pinkish grey, massive, hard, crystalline. The lower part is concretionary in Um Sohryngkew river section. Calcite veins and secondary fillings in the solution holes are a common feature.
[Figure 1: Paleocene-Lower Eocene sequence of Upper Assam with its subdivisions (after Bharali and Gogoi, 2012)]
[Figure 2: The Lakadong Limestone in MQS, position of the samples and simplified stratigraphic column of the quarry. The position of the boundary between SBZ 3 and 4 is tentative. The position of the lower samples (C1–5) from the first bench (B1), are not seen here. B: benches in the limestone. (after ErkanOzcan et al., 2018)]
Relationships and Distribution
Lower contact
It has a conformable lower contact with the Therria Fm in the type area, but to the north of Cherrapunji and in the Langrin Plateau it unconformably overlies the Mahadeo Fm.
Upper contact
Overlain by Sylhet LakadongSstMbr Fm
Regional extent
It is mappable and extends from the Langrin Plateau in the Garo hills in the West upto the eastern margin of the Shillong Plateau. In the north it continues beyond Cherrapunji.
GeoJSON
Fossils
This member is richly fossiliferrous and the common forms recorded are Miscelanea miscella, Lockhartia haimei, Discocylcina ranikotensis, Fasciolites primaevis, Nummulites thalicus, and various smaller calcareous benthic foraminifera, Globorotalia pseudomenardi etc.
[Figure 3: No-2 Glomalveolina-dasycladalean algae-miliolidwackestone-packstone with Glomalveolina cf. Sireli (gs) (after Erkran Ozcan et al., 2018)]
[Figure 4: No-10 Glomalveolinalevis (gl) (after Erkran Ozcan et al., 2018)]
[Figure 5: No-3 Orbitoclypeus schopeniramaraoi-neumannae; equitorial sections (after Erkran Ozcan et al., 2018)]
[Figure 6: No-10 Orbitoclypeus multiplicatus hauymanaensis-multiplicatus; equitorial sections (after Erkran Ozcan et al., 2018)]
[Figure 7: Lithostratigraphic column of the Lakadong Limestone in MQS, facies, and distribution of LBF and other fossil groups with inferred SBZ zones by Serra-Kiel et al. (1998). Facies explanation: 1: Miscellaneids-red algal wackestone–packstone, 2: Glomalveolina dasycladalean algae-miliolid wackestone–packstone, 3: Aberisphaera-red algal wackestone–packstone, 4: Miscellaneids-Glomalveolina wackestone–packstone, 5: Lakadongia-Glomalveolina wackestone–packstone, 6: Dasycladalean algal wackestone, 7; Orthophragminid-red algal- Distichoplax packstone–grainstone. (after Erkan Ozcan et al., 2018)]
Age
Depositional setting
Shallow open marine conditions.
Additional Information