Ham Rong Gr

Named after Ham Rong Bridge (Thanh Hoa Province). Lectostratotype: Nui Ban Hill (summit 80) Section near Ba Trieu Temple, Hoang Hoa District, Thanh Hoa Province (N= 19° 54'; E= 105°49'). Hypostratotype: along the Dai Lan Stream, from Lang Chieu Village to the Song Ma River side, Dien Lu Commune, Ba Thuoc District, Thanh Hoa Province (N= 20° 20'; E= 105° 10') (Pham Kim Ngan et al., 998). In the Viet Bo Basin, a lower Chang Pang Fm, and an upper Lutxia Fm have similar lithologic and paleontologic features as the Ham Rong "Fm" in West Bac Bo; therefore Tran Van Tri and Vu Khuc (2011; Geology and Earth Resources of Viet Nam) considered those to be formations within a generalized Ham Rong Gr (used here).

Synonym: Ham Rong Fm (West Bac Bo former usage). -Calcaires du Pont d'Ham-rong: Jacob C. 1921 (E-0); Saurin E. 1956 (£ -O). -H? tdng Ham Rdng: Pham Xu^n Anh ei ai 1989 (Di^p - £3); Vu IGiuc, Bui Phu My e( al. 1990 (Di?p - £3); Phgm Kim Ngdn 1991 (Di^p - £3); D§ VSn Chi el al 1992 (Di^p - £3); Nguy6n Dinh Hgp et al. 1993 (£3); Nguy6n VSn Hoanh e( al. 1994 (£3), 2001 (Ej-Oj); Luang H6ng Hur〇c et al. 1996 (83); Ph^im Kim Ngan et ai 1994, t995, 1996 (£₃-0〇; Tong Duy Thanh et ai 1995, Tong Duy Thanh in Vu Khuc et ai 2000 (£₃-0,); Tr^n Nuru D5n in Ph^m Kim Ng^n et ai 1998 (£₂-〇t)； Phgim Dinh Truong et al. 1999 (£₃); Nguyln VSn Trufit et al. 1999 (£3); Ph^m Kim Ngan et al. 2000 (£2~〇i)； Cong Hung et al. 2001 (8₂-〇i). -Tdng Bd Thuac: Nguy6n Tri Vdt et al. 1963 (£3); Ph^m Van Quang et ai 1973 (Di^p - 83). -Tang Ben Khi (part): Nguy6n Tri Vdt et al. 1963 (£r〇i)- -He tang Dong San (part.): Dovjikov A.E. et ai 1965 (£3 -O).-7V^叹 •认叩叩:Pkm Kim NgSn 1972, 1975, 1976, 1980,1982; Tiin VSn Trj 扨 a/. 1973, 1975, 1977, Tran Dang Tuylt et al. 1977; D$ag Trkn Qudn et al 1980; Tr4n NghTa ei al 1980. -Bi4p Bo Xinh (part.): Phaa San et al. 1974, 1978 (Sj-O)- -Di?p Dien Lu: Dinh Minh Mong et al. 1976 (£3). -Di4p Lang Vac: Dinh Minh Mong et at. 1976 (63). -Di^p Chang Pung: Pham Kim Ngan ei al. 1986 (£3); Lurong H6ng Huf(?c 1986,1987 (E₃); Phan C\rTien et ai 1989 (£_rOj).

[In Viet Bac - Upward succession of the Chong Pung Fm and the Lutxia Fm. See those for details.] Limestone: Characterized in West Bac Bo by carbonate beds, clearly distinguished from fine-grained terrigenous sediments of the underlying Song Ma Fm (Cm2 sm) and from the coarse-grained terrigenous sediments of the overlying Dong Son Fm (01 ds). Lectostratotype section is composed of two members, 320 m thick: (1). Greenish-grey thin-bedded dolomitic limestone, sandy limestone, about 150 m thick; containing trilobites Calvinella walcotti, Tsinania sp. and the brachiopod Billingsella tonkiniana in the lower part, and the trilobite Blountia sp. in the upper. (2). Dark grey, fine-grained, well bedded limestone interbedded with clay-chlorite shale, silty clay shale, 170 m thick; containing the brachiopod Billingsella sp. in the upper part. [For Viet Bac, see the individual entries for the lower Chang Pang Fm, and an upper Lutxia Fm.]

Trilobites and brachiopods. Late Cambrian - Early Ordovician age of the Ham Rong Gr (West Bac Bo) has been determined on the following bases: 1) in the lower part of the formation late Middle Cambrian trilobites and oncolites have been found, such as: Anomocarina sp., Conokephdliana sp., So- lenoparia sp.; 2) in its middle part there are Late Cambrian trilobites, such as: Paracoosia man- suyi_t Damesella brevicaudata, Cyclolorenzella tonkinensis, Blackwelderia sp., Drepanura premesnilU Chuangiella sp., Pagodia sp., Tsinania sp., Proceratopyge sp. and the brachiopod Billingsella sp.; in its upper part - Early Ordovician conodonts Drepanodus sp., Oneotodus sp. and crinoids Ramunicrinus sp,, Tetragonocylicus sp. [For Viet Bac, see the individual lower Chang Pang Fm, and an upper Lutxia Fm entries.]

Shallow marine, continental shelf facies