Bernard L. Mamet

Carboniferous Biostratigraphy, Prudhoe Bay State 1 to Northeastern Brooks Range, Arctic Alaska

The 3,000-ft-thick Carboniferous section in Atlantic Richfield/Humble Prudhoe Bay State 1 is divided into two groups. The older rocks in the section, Endicott Group, are 1,200 ft thick and unconformably overlie argillites of the pre-Mississippian Neruokpuk Formation. Within the Endicott Group, the Kekiktuk Conglomerate is 600 ft of gray to dark-gray sandstone, shale, and thin-bedded coal, deposited in a paralic environment. The overlying Kayak(?) Shale is 620 ft of quartzitic and calcareous red sandstone, siltstone, shale, and arenaceous to ooid limestone; it represents transition to marine sedimentation and contains microfossils of Zone 16s (Chesterian). Overlying the Endicott Group, the Lisburne Group is 1,770 ft thick. Within the Lisburne Group, the Alapah L mestone, 1,050 ft thick, includes arenaceous bryozoan-echinoderm wackestone and packstone to lime mudstone and microdolomite with gypsum. The age of the Alapah Limestone ranges from Zones 16s through 18 (Chesterian). The overlying Wahoo Limestone, 720 ft thick, is a series of cyclic glauconitic-bryozoan-echinoderm-ooid packstone and grainstone capped by lime mudstone and arenaceous microdolomite. These are interpreted to represent cyclic deposition of tidal-flat lime mud developed directly over ooid tidal bars. The age of the Wahoo Limestone ranges from Zone 20 to Zone 21 (Pennsylvanian). In comparison with the section penetrated by this well the outcrop data 75-112 mi southeast show that the Endicott Group is diachronous because, in the Franklin Mountains, it has a lithology similar to that found in the Prudhoe well but contains (Meramecian) Zone 11 marine microfossils. During the Meramecian the Sadlerochit Mountains were high; the Endicott Group is either absent or less than 50 ft thick here. The Alapah Limestone of Prudhoe Bay State 1 is more dolomitic and arenaceous than its equivalent in the Franklin or Sadlerochit Mountains. The Wahoo Limestone of the Prudhoe Bay subsurface is similar in lithology and in environments of deposition to the outcrop sections in the Sadlerochit Mountains.

Foraminiferal Zonation and Carbonate Facies of Carboniferous (Mississippian and Pennsylvanian) Lisburne Group, Central and Eastern Brooks Range, Arctic Alaska

The Lisburne Group carbonate rocks of the central and eastern Brooks Range contain foraminiferal assemblages assigned to zones of late Tournaisian (Osage) to early Moscovian (Atoka) age. Representatives of both Eurasiatic and American cratonic microfaunas permit correlation with the original Carboniferous type sections in western Europe as well as with the standard Mississippian and Pennsylvanian sequences in the Mid-Continent region of North America. Correlation anomalies in the lower part of the sequence are discussed.

Role of Algal Assemblages in Middle Ordovician Deposits in St. Lawrence Lowlands: ABSTRACT

End_Page 628------------------------------The calcareous Algae of the Middle Ordovician sequence of the St. Lawrence lowlands show a lateral and regional constancy which reflects the stability of the shelf at that time. In addition, the algal groups, when considered separately, suggest aptitudes to adapt themselves to various habitats and conditions. Chazy rocks in the Lake Champlain area, New York, Trenton deposits outcropping in the Trenton region, New York, Black River section in its type section at Black River, New York, and the Simcoe Group in Lake Simcoe, Ontario, are studied and sampled for the examination of their algal contents. Thirty-four taxa are identified in these various deposits. Petrographic evidences and the interpretation of the algal microfacies in the four regions studied reveal the presence of as many as 22 types of lithological units distinguishable on their algal content and their relation to specific paleoecological environments. The abundance of Algae and algal components in the Middle Ordovician sequence, underlines the importance of their role in relation to sedimentation on the shelf in the regions studied. The diversity and the specificity of the Algae in the units and in the environments reflect a pattern of distribution which follows certain environmental controls similar to those prevailing in the modern seas. The algal assemblages show responses to physical, biological, and chemical variations of the environments. These assemblages play in the sedimentation the same role assumed by recent Algae, production of carbonates, trapping and stabilization of the sediments, algal mats, formation of oncolites and algal encrustations, and edification of bindstones-framestones. Although the Algae are not always useful as chronostratigraphic indices, they remain in the Ordovician successful paleoenvironmental indicators. End_of_Article - Last_Page 629------------

The Mississippian System of New Mexico and Southern Arizona: ABSTRACT

Lower Mississippian rocks of New Mexico and southern Arizona (pre-zone 7 Tournaisian age) are unconformable on rocks of Late Devonian to Precambrian age. Mississippian rocks were deposited during transgression on a surface of low relief. Tournaisian transgression began in southern Arizona, depositing the Escabrosa Limestone and, in southwestern New Mexico, the Keating (207 m), Caballero (18 m), and Lake Valley (180 m) Formations. At the end of Tournaisian time, epicontinental seas flooded southern and central Arizona, depositing the younger parts of the Escabrosa and Redwall Limestones. Osagean seaways extended to central and northern New Mexico depositing Kelly (35 m) and Espiritu Santo (35 m) Formations. The Espiritu Santo consists of subtidal to supratidal quartz sands one and carbonate rocks. Zuni Highlands and Pedernal Highlands formed two low islands. The end of the Tournaisian is marked by marine regression, regional uplift, and erosion. Major regional marine transgression in early Visean is represented by parts of Escabrosa Limestone of southern Arizona, massive encrinites of the Hachita Formation (107 m) in southwestern New Mexico, basin carbonate rocks of the lower part of the Rancheria Formation (46 m) in south-central New Mexico, and the subtidal Tererro Formation (18 m) in north-central New Mexico. The Cowles Member (10 m) of the Tererro Formation indicates that sedimentation ceased in northern and central New Mexico in late Visean time. In southwestern New Mexico, the Paradise Formation (134 m) represents shallow-marine sediments and ranges rom zone 15 into zone 19 (late Visean and Namurian). The Rancheria Formation (69 m) and the Helms Formation (50 m) of south-central New Mexico are deep-water facies of the Paradise Formation. Pennsylvanian sedimentary rocks in southern Arizona and in New Mexico truncate Mississippian sedimentary rocks of Namurian, Visean, and Tournaisian age. End_of_Article - Last_Page 671------------