Merrell A. Miller

Palynomorphs from the Silurian Medina Group (Lower Llandovery) of the Niagara Gorge, Lewiston, New York, U.S.A.

Abstract The Lower Silurian Medina Group from the Niagara Gorge at Lewiston, New York, contains one of the oldest known Llandovery palynomorph assemblages in North America. Age determinations using conodonts and brachiopods from the basal units of the overlying Clinton Group suggest that the Medina Group may be correlative with the Rhuddanian Stage of the Llandovery. A brief review of North American Lower Silurian series nomenclature is presented to place the Medina Group in a regional stratigraphic context. Previous recommendations that North American series nomenclature be replaced by the standard British Llandovery stages are followed. Well‐preserved acritarchs, chitinozoans, and spore‐like micro‐fossils have been recovered and described from the Whirlpool Sandstone, Power Glen Formation, and Grimsby Sandstone. Forty palynomorph species were recognized. Four new species and one new combination of acritarchs are proposed: Cymatiosphaera densisepta n. sp., Eupoikilofusa? rhomba n. sp., Micrhystridium? po...

Distinctive Silurian chitinozoans from the Itacurubi Group (Vargas Pena Shale), Chaco Basin, Paraguay

Abstract Three chitinozoan species are described from the rich assemblage present in the Lower Silurian Vargas Pena Shale, Paraguay. Plectochitina paraguayensis and Eisenackitina bejui are newly established. A new species of Pterochitina is described in open nomenclature. The Vargas Pena chitinozoans differ from those previously described from the Lower Silurian of South America and are the first to be illustrated from the Paraguayan Silurian. Acritarchs from the Vargas Pena Shale are interpreted to represent a middle Llandovery age, closely comparable to that determined using graptolites.

Velatasphaera hudsonii gen. et sp. nov., an Ordovician acritarch from Hudson Strait, North West territories, Canada

Abstract Bedrock samples from the floor of Hudson Strait, recovered during a CSS Hudson cruise in 1985, contain a diverse assemblage of acritarchs and chitinozoans. One of the acritarchs, Velatasphaera hudsonii gen. et sp. nov., is spherical and has a bilayered wall, with short tubiform processes separating the two layers. This acritarch is unique because the processes open distally and coincide with perforations in the outer wall. The excystment structure is a micropylome. V. hudsonii is a component of a largely undescribed acritarch and chitinozoan assemblage, which is interpreted to be late Ordovician in age.

A diagnostic excystment suture in the Silurian acritarch Circinatisphaera aenigma gen. et sp. nov.

Abstract The circinate suture is a preformed, levorotatory excystment suture present on specimens of the acanthomorphic acritarch Circinatisphaera aenigma gen. et sp. nov. The operculum is frequently adnate, but when detatched bears a distinctive notch on its margin. The offset of the excystment suture and corresponding opercular notch is new for acritarchs and can be used for orientation. The descending, levorotatory circinate suture resembles paracingula of many fossil dinoflagellate cysts in spiral direction, but Circinatisphaera aenigma lacks other characters typical of dinoflagellates. Specimens exhibiting this excystment structure have been isolated from Libyan and Saudi Arabian Lower Silurian strata.

Dr. Gordon D. Wood II, 1949–2015

Merrell A. Miller , Thomas Servais c,d and Reed Wicander the irf group, inc., 2753 East 23rd Street, Tulsa, Oklahoma, USA, 74114; The University of Tulsa, Department of Geosciences, 800 South Tucker Drive, Tulsa, Oklahoma, USA, 74104; Univ. Lille, CNRS, UMR 8198 Evo-Eco-Paleo, F-59000 Lille, France; Van Mildert College and Institute of Advanced Study, Durham University, Cosins Hall, Durham, DH1 3RL, United Kingdom; School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland, Australia 4072; Department of Earth and Atmospheric Sciences, Central Michigan University, Mount Pleasant, Michigan, USA 48859

A new Upper Jurassic species of Scenedesmus from the Bossier Formation, Texas, USA

ABSTRACT Scenedesmus Meyen 1829 is an extant freshwater representative of the Chlorophyta (Order Chlorococcales, Family Scenedesmaceae). Fossil representatives have been conclusively identified from Lower Cretaceous lacustrine sediments and some are possibly as old as the Middle Jurassic. Specimens clearly attributable to Scenedesmus were encountered in Upper Jurassic Bossier Formation palynology preparations from a proprietary hydrocarbon exploration well in Wood County, Texas, USA. This alga, named Scenedesmus texanus sp. nov., is described herein. Also occurring with Scenedesmus are other freshwater representatives of the Chlorococcales, including Tetrastrum multifilorum and Pediastrum sp. The Bossier Formation Scenedesmus specimens occur in a mixed palynological assemblage consisting of freshwater algae, pollen, spores and a few dinoflagellate cysts. The combined occurrence of these palynomorphs indicates a marginal marine depositional setting with a freshwater influence.

New palynomorphs from the Ordovician–Silurian boundary interval: Eastern North America and Saudi Arabia

ABSTRACT A distinctive coenobial palynomorph, Speculaforma gen. nov., and its two new species, S. delicata and S. elongata, are described from the Llandovery Grimsby Formation, Medina Group, from New York and are part of a more diverse palynomorph assemblage. Speculaforma delicata was also recovered from the Tuscarora Formation, West Virginia, and subsurface Hirnantian sediments in southern Saudi Arabia. Speculaforma is questionably assigned to the Hydrodictyaceae within the order Chlorococcales based on its geometrically regular coenobia. It is considered to be a freshwater or brackish-water alga. Occurring with this coenobium are two new acritarchs, Lunataforma parallela gen. et sp. nov. and Pertusidisca quadripora gen. et sp. nov. These acritarchs have been recovered from near-shore marine settings, in both North America and Saudi Arabia; but in North America Lunataforma was also recovered from sediments considered to represent an open marine environment.