Geology topics

S. Elrick

Publications and source records attributed to S. Elrick.

3 recordsLinked to original sources

USGS2011

No major stratigraphic gap exists near the Middle-Upper Pennsylvanian (Desmoinesian-Missourian) boundary in North America

Interregional correlation of the marine zones of major cyclothems between North America and eastern Europe does not support assertions that a major stratigraphic gap exists between the traditional regional Desmoinesian and Missourian stages in North America. Such a gap was previously proposed to explain an abrupt change in megafloral assemblages in the northern Appalachian Basin and by extension across all of North America. Conodont-based correlation from the essentially complete low-shelf Midcontinent succession (distal from the highstand shoreline), through the mid-shelf Illinois Basin, to the high shelf of the Appalachian Basin (proximal to highstand shoreline) demonstrates that all major ∼400 kyr cyclothem groupings in the Midcontinent are recognizable in the Illinois Basin. In the Appalachian Basin, however, the grouping at the base of the Missourian is represented only by paleosols and localized coal. The immediately preceding grouping was removed very locally by paleovalley incision, as is evident at the 7–11 Mine, Columbiana County, Ohio, from which the original megafloral data were derived. At the few localities where incised paleodrainage exists, there may be a gap of ∼1000 kyr, but a gap of no more than ∼600 kyr occurs elsewhere in the Appalachian Basin at that level and its magnitude progressively decreases westward into the Illinois (∼300 kyr) and Midcontinent (<200 kyr) Basins. Thus, while a gap is present near the Desmoinesian–Missourian boundary in North America, it is typically more than an order of magnitude smaller than that originally proposed and is similar to the gaps inferred at sequence boundaries between cyclothems at many horizons in the Pennsylvanian of North America.

Ohio↗

USGS2009

Incised channel fills containing conifers indicate that seasonally dry vegetation dominated Pennsylvanian tropical lowlands

The idea that the Pennsylvanian tropical lowlands were temporally dominated by rainforest (i.e., the Coal Forest) is deeply ingrained in the literature. Here we challenge two centuries of research by suggesting that this concept is based on a taphonomic artifact, and that seasonally dry vegetation dominated instead. This controversial finding arises from the discovery of a new middle Pennsylvanian (Moscovian) fossil plant assemblage in southeast Illinois, United States. The assemblage, which contains xerophytic walchian conifers, occurs in channels incised into a calcic Vertisol below the Baker Coal. These plants grew on seasonally dry tropical lowlands inferred to have developed during a glacial phase. This xerophytic flora differs markedly from that of the typical clubmoss-dominated Coal Forest developed during deglaciation events. Although preserved only very rarely, we argue that such xerophytic floras were temporally as dominant, and perhaps more dominant, than the iconic Coal Forests, which are overrepresented in the fossil record due to taphonomic megabias. These findings require the iconography of Pennsylvanian tropical lowlands to be redrawn. ?? 2009 Geological Society of America.

Geology↗

USGS2009

Catastrophically buried middle Pennsylvanian sigillaria and calamitean sphenopsids from Indiana, USA: What kind of vegetation was this?

A catastrophically buried stand of calamitean sphenopsids and sigillarian lycopsids is reported from the Middle Pennsylvanian of southwestern Indiana, in the Illinois Basin. The plants were exposed in the highwall of a small surface mine and were rooted in a thin bed of coal (peat), thus representing a flooded and buried swamp surface. Coarse, floodborne silts and sands buried the forest to a depth of <3 m or more, before further incursions of water and sediment truncated the deposit. The rocks are part of the Staunton Formation. Taking up >250 linear meters of exposed highwall surface, the vegetation appears to have been a patchwork of calamitean thickets, with stems perhaps as tall as 3-5 m, within which scattered, but much larger, emergent Sigillaria trees grew, possibly reaching heights of 10-15 m. No ground cover was observed, nor were foliage or reproductive organs attributable to the dominant plants found. The growth of this vegetation in a peat-forming swamp indicates conditions of high water availability, likely in a humid, high-rainfall climate. This kind of plant assemblage, however, cannot be characterized as a rain forest, given that it consisted of medium-height thickets of horsetails with scattered, emergent, and polelike, giant lycopsids, thus lacking a closed upper canopy and possibly only partially shading the ground. Copyright ?? 2009, SEPM (Society for Sedimentary Geology).

Palaios↗