Middle Ordovician Conodont Faunas Research Articles

Conodonts from the ‘Lower Limestone’ and Haengmae Formation in western Jeongseon, Korea and their implication for lithostratigraphic correlation

The Middle Ordovician conodont fauna consisting of six species was recovered from the upper part of the Lower Limestone and the middle part of the overlying Haengmae Formation in the western Jeongseon area, Korea. Two conodont biozones are established for this interval, the Erraticodon tangshanensis Interval Zone for the upper part of the Lower Limestone and the Eoplacognathus suecicus Range Zone for the uppermost part of the Lower Limestone to the middle part of the Haengmae Formation. The first biozone is comparable to the Darriwilian (early Dw2) Tangshanodus tangshanensis-Histiodella holodentata Zone in North China and the Tangshanodus tangshanensis Zone in South Korea. The second biozone corresponds to the eponymous Dar-riwilian (late Dw2) zones recognized in North China and Korea. The biostratigraphy indicates that the Lower Limestone and Haengmae Formation in the western Jeongseon area is correlated only with lower and middle parts of the Jeongseon Limestone in the central and eastern Jeongseon area, and thus the Jeongseon Limestone is not a valid lithostratigraphic unit for the western Jeongseon area.

A New Middle Ordovician Conodont Fauna from the Thong Pha Phum Area of Western Thailand

Abstract. Little is known about Ordovician litho- and biostratigraphy in northern and western Thailand because outcrops are scarce in these mountainous areas. Biostratigraphic and biogeographic studies of conodonts are limited to the uppermost Floian to lower Darriwilian strata in western Thailand. This paper describes and discusses a new Middle Ordovician conodont fauna that includes nine species from the Thong Pha Phum area of western Thailand. This is the first report of Eoplacognathus suecicus, Pygodus lunnensis, Protopanderodus calceatus, Protopanderodus cooperi, and Protopanderodus graeai in Thailand and indicates that a cool-water fauna existed in western Thailand and in southern peninsular Thailand during the Middle to Late Ordovician. The Dapingian to early Darriwilian sea-level rise likely resulted in an immigration of this “cooler or deeper water” fauna to the Thong Pha Phum area.

Conodonts from the Davidsville Group, north-eastern Newfoundland: Discussion

Stouge (1980) has reported a new record of a Middle Ordovician conodont fauna from the basal part of the Davidsville Group at Weir's Pond, north of Gander. This occurs on the east side of the Reach Fault, which has been considered (McKerrow and Cocks 1977) to represent the suture along which the Iapetus Ocean finally closed. To the west of the Reach Fault, on New World Island, the Cobbs Arm Limestone has yielded similar conodonts (Bergstrom et al. 1974), though some additional taxa are present in this limestone. Stouge (1980, p. 270) has concluded that the similar conodont faunas on either side of the suture implies that that boundary was insignificant. However, it has long been known that the North Atlantic conodont province was present on both sides of the Iapetus Ocean (Bergstrom 1971, Fig. 12): similar faunas are present in the Appalachians and Scotland (both northwest of the suture) and Scandinavia (east of the suture). Indeed, many of the Davidsville species recorded by Stouge were originally described from Scandinavia. During the Middle and Late Ordovician Epochs, only benthic faunas (like trilobites and brachiopods) were clearly distinct on either side of the Iapetus Ocean (McKerrow and Cocks 1976). As Bergstrom and Cooper (1973) have shown, many pelagic conodonts and graptolites were able to cross the Iapetus Ocean from Llanvirn and Llandeilo times onwards. As Middle Ordovician conodont distributions do not distinguish either side of the Iapetus Ocean, Stouge's criticisms of our conclusions are unfounded. The benthic faunas still indicate that the Reach Fault marks the site of the Iapetus suture.

Early Paleozoic Conodont Biostratigraphy and Paleogeography of Northwestern Canada: ABSTRACT

Early Paleozoic rocks in northwestern Canada were deposited on a broad Atlantic type shelf and include platform carbonate rocks and transitional and basinal facies that range in composition from calcilutites to cherts. The Paleozoic history of northwestern Canada began with widespread deposition of Lower Cambrian quartzite and carbonate. In the Middle and early Late Cambrian, shales were deposited in deep troughs and continental areas separated by tectonic arches. During the latest Cambrian and Early Ordovician, platform carbonates were deposited on a broad shelf adjacent to a belt of deep water limestone. Middle Ordovician time was characterized by uplift to the north; carbonate deposition changed abruptly basinward into graptolite shales to the south. Late Ordovician-Ea ly Silurian carbonate deposition on the platform graded basinward into shales and limestones. The phosphatic microfossil Mellopegma occurs in Lower to Middle Cambrian basinal strata while conodonts of the Late Cambrian Proconodontus Zone are common to both the platform and the basinal strata. A nearly continuous sequence of Early to Middle Ordovician conodont faunas is found in the platform carbonate rocks. These Mid-Continent type faunas include the Early Ordovician faunas A to E of Ethington and Clark and the Middle Ordovician faunas 1 to 9 of Sweet, Ethington, and Barnes. Coeval basinal and transitional facies of Early and Middle Ordovician age are characterized by North Atlantic type conodonts and a few Mid-Continent forms that sharply decline numerically toward the basin. Late Ordovician conodonts are poorly represented in the platform facies; spot samples from transition l and basinal facies yield predominantly North Atlantic taxa. Lateral and temporal distribution of conodont faunas from northwestern Canada closely resemble those of coeval faunas reported from the Ibex area of western Utah. End_of_Article - Last_Page 793------------

Conodont-Based Correlations of Lower and Middle Ordovician Strata in Western Newfoundland

Lower and Middle Ordovician conodont faunas from the Table Head Formation and the Cow Head Group in western Newfoundland to a large extent, or in some cases exclusively, contain forms that occur in the Balto-Scandian sequence, thus facilitating a correlation between the northern Applachians and Balto-Scandia. The lower boundary of the Table Head Formation probably lies within strata corresponding to the British Didymograptus bifidus Zone and corresponds to a level tentatively regarded as at the base of the Aluoja Substage. The upper boundary of the middle Table Head corresponds to a rather high level in the Lasnamagi Stage (in the upper part of the Didymograptus murchisoni Zone). The upper Table Head consists of black graptolitiferous shales, which have not been searched for conodont elements. Studies of conodonts from the Table Head, the Cow Head Group, and the uppermost part of the St. George Formation, and comparisons with published and nonpublished accounts of conodonts from the Fort Pena, the Joins and the Levis Formations, indicate that the North American bifidus Zone is at least partly equivalent to the British bifidus Zone, hence supporting the correlation suggested by Berry (1960).