June R. P. Ross

Sea-level changes: An integrated approach

Sea-Level Changes: An Integrated Approach - In October 1985, SEPM sponsored a four-day conference entitled ?Sea-Level Changes ? An Integrated Approach.? The purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea-level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues. The conference was successful in bringing together scientists from industry, academia, and government, representing all of the major geosciences disciplines. Presentations of many new papers, plus significant releases of data that were previously held proprietary, provided fertile ground for discussion. This much-cited volume represents the best of the material presented at the conference. Includes the early ?Vail? chart.

Late Paleozoic depositional sequences are synchronous and worldwide

More than fifty transgressive-regressive depositional sequences are present in Carboniferous and Permian shallow marine successions on stable cratonic shelves worldwide. These were synchronous depositional events resulting from eustatic sea-level changes that generally ranged from 100 to 200 m. Each transgressive-regressive sequence is correlatable using current fossil knowledge. They average about 2 m.y. and range from 1.2 to 4 m.y. in length. The presence within these strata of numerous, synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate. These late Paleozoic transgressive-regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships.

Carboniferous and Early Permian biogeography

During the Carboniferous, changes in the biogeographical distribution of shelf-dwelling, benthic marine invertebrates were made in response to changes in physical paleogeography and climatic variations. Calcareous foraminifers and bryozoans are principal examples of the general trends during the Early Carboniferous, which show that Tournaisian and early and middle Visean faunas were broadly cosmopolitan in a circumequatorial belt and that latitudinal diversity gradients were relatively minor. During the later part of the Visean and early part of the Namurian, the Hercynian orogeny, caused by the collision of Euramerica with Gondwana, disrupted these cosmopolitan equatorial faunal patterns. This was also a time of progressively cooler temperatures throughout the world, of dramatic reduction in faunal diversity, and of high rates of extinction of both species and genera. During middle Carboniferous time, strongly provincial faunas were common. Spasmodic, but limited, dispersals gave a few widespread genera significantly different stratigraphic ranges in different provinces so that Tethyan and non-Tethyan distributions are recognizable. Faunal diversity gradually increased during the middle Carboniferous and then declined at the end of the epoch with additional high levels of extinction of species and genera. During late Carboniferous time, several new faunal lineages became well established. Some filled vacant ecological niches; however, others took advantage of the increase in the number of niches that became available because of gradually warming climates. Provinciality continued to be pronounced. Diversity gradually increased and continued to do so through the Early Permian.

Permian Sequence Stratigraphy

The Permian System contains a great number and diversity of depositional sequences (Fig. 1) which illustrate sedimentary responses to a series of sealevel fluctuations. These sea-level fluctuations had many different amplitudes and durations, and were accompanied by a wide spectrum of rates of deposition (Fig. 2). The mid-continent and southwestern North American stable cratonic successions serve as the basis for our Permian sea-level interpretations (Ross and Ross 1987a, b, 1988); however, equally useful sections appear to be present in China, particularly South China. In the southern hemisphere, Western Australia has marine and glacial-marine depositional sequences that may eventually help tie sea-level events in high and middle latitudes of Gondwana with those of low latitudes of cratonic North America and the Tethys.

Foraminiferal zonation of late Paleozoic depositional sequences

From the later part of the Devonian through the Permian, calcareous foraminifers became abundant and evolved rapidly. This rapid evolution of taxa forms the basis of a detailed zonation through the Carboniferous and Permian. Comparison of this evolutionary history of foraminifers, their biostratigraphic zonation, and the depositional sequences in which they occur suggests that sea-level events in late Paleozoic depositional history contributed significantly in subdividing a fairly continuous evolutionary record into a succession of about 75 identifiable foraminiferal zones during a 100–125 Myr time span. Although variable in terms of duration and vertical occurrences, the more completely recorded high-stand intervals give brief histories of the foraminiferal evolutionary record and are sandwiched between the poorly recorded or unrecorded low-stand intervals. Many of the individual foraminiferal zones are confined to a single depositional sequence. The late Paleozoic carbonate foraminiferal fossil record, as with the rest of the fossil record, is strongly affected by sediment deposition-nondeposition as a result of major changes in sea level. This incomplete fossil record is the result of repeated depositional breaks because of the way that depositional sequences form. It is not possible to ascribe macromutations, ‘punctuated’ evolution or ‘punctuated gradualism’ as the cause of this evolutionary pattern of the shelf-carbonate fossil record. This pattern is distinctive and we refer to it as ‘sequence evolution’ and ‘sequence extinction’. In the later part of the Middle Permian and in the Late Permian, the fossil record clearly illustrates that a series of faunal losses through ‘sequence extinctions’ progressively exceeded faunal replacements and new species through ‘sequence evolution’, but not a ‘mass extinction’ as is commonly ascribed to the end of the Permian Period. Most Permian faunas became extinct in the interval of 8 to 4 million years before the end of the Late Permian.

AGE AND GENERIC ASSIGNMENT OF YABEINA COLUMBIANA (GUADALUPIAN FUSULINACEA) IN SOUTHERN BRITISH COLUMBIA

Abstract The morphologic variation in Yabeina columbiana (Dawson) was carefully studied using probable topotype specimens from the Marble Canyon-Hat Creek area, southern British Columbia, and the material was compared with related species of neoschwagerinids from various parts of the circum-Pacific region. In the five Marble Canyon-Hat Creek samples examined, we found considerable individual variation in important characters, such as the size of the proloculi, and shape and development of primary and secondary transverse septula in relation to the growth stage of the test. These differences gradually changing from specimen to specimen within and among samples are thought to represent intraspecific variation within this species. Wide individual variations are also found in three different species of Yabeina from Japan, Yabeina sp., Y. kaizensis (Huzimoto), and Y. globosa (Yabe). Most North American species of Yabeina, such as Yabeina columbiana, have morphological features such as the occurrence of primary and secondary transverse and axial septula in later whorls and the average size of proloculi that reasonably place them as early species in the genus Yabeina. Yabeina columbiana is neither a Lepidolina nor a Colania as some authors had previously thought. Evolved forms of Neoschwagerinidae in the western Cordillera of North America consist of Yabeina cordillerensis Ross, Y. cascadensis (Anderson), Y. columbiana (Dawson), Y. packardi Thompson and Wheeler, and Lepidolina dunbari (Skinner and Wilde). The earliest North American Yabeina is thought to be Y. cordillerensis from northwestern British Columbia where it is associated with Afghanella sp., Pseudodoliolina sp., and the Wordian ammonoid Waagenoceras. This assemblage is closely comparable to that in the lowest zone of the Midian Stage in the Tethyan realm, the Afghanella robbinsae and Yabeina archaica Zone. The remainder of the known North American Cordilleran species of Yabeina are assignable to the second zone of the Midian Stage, the Yabeina globosa and Lepidolina multiseptata Zone and to the Japanese Yabeina globosa Zone. This zone is considered equivalent to the Capitanian Stage at the top of the Guadalupian Series in southwestern North America. Morphological and faunal analyses of these North American Cordilleran species of Yabeina and Lepidolina and most of the associated species of schwagerinids (for example, Chusenella andersoni, C. atlinensis, and Schwagerina pavilionensis) suggest ages that range through the late Guadalupian. The highest zone of the Tethyan Midian lacks Yabeina and other neoschwagerinids and is based on the ammonoids Eoaraxoceras and Anderssonoceras. This zone is found in sediments of post-Capitanian (post-Guadalupian) age in northern Mexico.

Thailandina and neothailandina, and Their Subfamily Thailandininae: An Example of an Invalid Taxonomic group of Permian Fusuline Foraminifera

Toriyama and Kanmera (1968), in one of their studies of fusulines from the Rat Buri Limestone, Thailand, proposed two Permian fusuline foraminifer genera, Thailandina and Neothailandina . Based on these two genera they established the subfamily Thailandininae and placed it in the family Neoschwagerinidae. The tests of these genera are invariably replaced by secondary mineralization to a fine-grained mosaic calcite such as seen in specimens of Staffellidae. The thailandinid wall was apparently originally composed of a tectum and keriotheca. Some Thailandina specimens illustrated by Toriyama and Kanmera (1968, pl. 6, fig. 8) are replaced individuals of Misellina , as Rauzer-Chernousova et al. (1996, p. 157) concluded. Rauzer-Chernousova et al. (1996) considered Thailandina a junior synonym of the genus Misellina . Some other specimens (e.g., Toriyama and Kanmera, 1968, pl. 6, figs. 1–3, 5–7) also are probably Misellina , in which the secondary replacement of …