Fig 1 - uploaded by David K. Brezinski
Content may be subject to copyright.
-Distribution of exposed Upper Mississippian strata of the central Appalachian Basin, with locations of outcrops examined. Dashed lines represent approximate limits of lithofacies groups discussed in text.
Source publication
The Loyalhanna Limestone is one of the most recognizable rock units in the Appalachian Basin. Differential weathering of its large-scale cross-bedding and massive character make this unit a widely used dimension and quarry stone. Diverging thoughts on the origin of the iconic cross-bedding have led to a long-standing debate over whether the genesis...
Contexts in source publication
Context 1
... County), the massive cross-beds are interbedded with intervals of red shale. Earlier workers termed this interval the Trough Creek Limestone Member of the Mauch Chunk Formation (White 1885). The Trough Creek Member consists of alternating units of pink, massive, cross-bedded, sandy limestone separated by rooted red siltstone and mudstone (Fig. 5, section 21). The massive, cross-bedded intervals in these areas commonly contain irregularly shaped carbonate clasts up to 5 cm in ...
Context 2
... as Salver (1962), Brez- inski (1984a), Gallagher (1984), and Edmunds (1997a) have noted abundant fragmented marine shells near the Loyalhanna's northeastern most occurrences. Brezin- ski and Kollar (2006) illustrated a number of locations in Maryland and adjacent Pennsylvania where macrofossils have been identified from Loyalhanna outcrops (Fig. 1). Although macrofossils have long been known from the overlying Deer Valley Limestone (Brezinski 1984a), the discovery of articulated brachiopods from the massive cross-bedded part of the Loyalhanna provided impetus for a more detailed study of the faunas from the unit. brachiopods and gastropod preserved as shell profiles but are also ...
Context 3
... evidence that argues against an eolian origin for the Loyalhanna comes in the form of paleocurrent directions. Adams (1970: fig. 13) demonstrated that the Loyalhanna's dominant cross-bedding azimuth is 72 degrees (i.e., to the east-northeast). Hoque's (1975) study of Loyalhanna paleocurrent directions agrees with that of Adams (1970). Based upon currently known paleogeographic reconstructions, the central Appalachian Basin was located at approximately 20 degrees ...
Context 4
... (1975) study of Loyalhanna paleocurrent directions agrees with that of Adams (1970). Based upon currently known paleogeographic reconstructions, the central Appalachian Basin was located at approximately 20 degrees south latitude during the Late Mississippian (Ahlbrandt 1995: fig 4; Blakey 2008). This would place the central Appalachian Basin within the southern tropics. ...
Context 5
... vertical and lateral distribution of lithologies and regional arrangement of lithofacies within the Loyalhanna basin are herein considered suggestive of an offshore to onshore transect within a shallow marine basin rather than a subaerial sand sea or erg. The interbedding of massive cross-bedded carbonate sand and marine limestone to the south is suggestive of intermittent marine incursions into the Loyalhanna basin (Brezinski 1989a, b). Moreover, the alternation of carbonate sand waves with ripple laminated and fossil-bearing limestones in two of the three identified lithofacies has been interpreted as representing shoaling episodes within a marine basin (Gallagher 1984;Brezinski ...
Citations
... This latter option is compatible with the magnetostratigraphy indicating that the NN1r-NN2n magnetozone interval could be coeval with an interval low in the early Brigantian with NN1n probably equivalent to the basal Brigantian as seen at Trowbarrow (Figure 12). These are the short (e.g., Brezinski & Kollar, 2021) and long (e.g., Ettensohn et al., 2022) duration options for the Mauch Chunk Fm of NE Pennsylvanian discussed by Hounslow (2022). Based on the arguments presented by Opdyke et al. (2014) and Hounslow (2022), the most likely position for the top of the magnetostratigraphy from the Mauch Chunk Fm (not shown in Figure 12) is near the base of the early Bashkirian. ...
Plain Language Summary
Nearly synchronous global changes in geomagnetic polarity give both a detailed irregular pacing to geological time and provide a glimpse into heat transfer processes across the core—mantle boundary which drives the Earth's geodynamo. Although the Late Carboniferous is characterized by some well‐studied reversals, details of the tempo of polarity changes in the Early Carboniferous are unknown. This work addresses this by providing a detailed record of polarity changes over a ∼2 million year interval at around 334.5–332.5 million years ago‐from the Trowbarrow Quarry section in NW England. We demonstrate that these limestones likely preserve magnetization from close to their time of formation and record at least 31 polarity reversals. These observations support the idea that the Earth's dynamo was in a hyperactive reversing state similar to those sustained for tens of Myr in the Late Jurassic, parts of the Cambrian and the Late Ediacaran. It further corroborates a ∼200 Myr cyclicity in paleomagnetic field behavior since the Precambrian, potentially linked to variable core heat flow forced by mantle convection.
This volume offers guides for GSA Connects 2023 in Pittsburgh, Pennsylvania, USA, that cover a diverse range of geologic time and processes from the Paleozoic to Recent. Chapters address Paleozoic and Pleistocene glaciation; the interplay of geology and climate in shaping the landscape; and aspects of cultural geology, including Frank Lloyd Wright’s Fallingwater and the setting of Youngstown, Ohio, USA.
