Abstract:Structures active during the Pennsylvanian Period and paleoenvironments in whichPennsylvanian strata were formed strongly influenced the character and location of coal resources in the Illinois Basin. Sediment filling the basin probably originated in the Canadian Shield and perhaps the highlands of the northern Appalachians. Major river systems transported this sediment to the Illinois Basin, where it was deposited in fluvial and deltaic paleoenvironments on a broad coastal plain and adjacent shallow shelf. Lo… Show more
“…Erosion may also have been promoted by riftassociated uplift of the Appalachians or by a drop in eustatic sea level at this time. A maximum of about 1000 m of Pennsylvanian sediment is preserved in the Illinois Basin [Hopkins and Simon, 1975;Trask and Palmer, 1986], but coalification patterns suggest that a significant thickness of Pennsylvanian sediment has been eroded [Damberger, 1971]. Indeed, only small remnants of Permian strata are preserved in the central Appalachian Basin (Figure 8).…”
Apatite fission track ages and confined‐length distributions were collected from 38 basement outcrop and 5 basement drillcore samples in order to reconstruct the Phanerozoic thermal history of the Michigan Basin and southern Canadian Shield. The apatite data indicate two periods of thermal activity in the region: Triassic heating/cooling that affected the basin and adjacent shield and Cretaceous or post‐Cretaceous heating/cooling that primarily affected the basin. The magnitude, timing, and cause of Cretaceous thermal activity cannot be identified with the present data. Model calculations suggest that some of the shield samples and probably all of the basin samples were heated to temperatures of at least 90°C just prior to relatively rapid cooling in the Triassic. Available stratigraphic and geochemical constraints suggest that these elevated temperatures were the result of burial by an additional 2–5 km of late Paleozoic (probably Pennsylvanian and Permian) sediments. It is likely that the basin was buried during the Alleghenian Orogeny as observed for the adjacent Appalachian Basin.
“…Erosion may also have been promoted by riftassociated uplift of the Appalachians or by a drop in eustatic sea level at this time. A maximum of about 1000 m of Pennsylvanian sediment is preserved in the Illinois Basin [Hopkins and Simon, 1975;Trask and Palmer, 1986], but coalification patterns suggest that a significant thickness of Pennsylvanian sediment has been eroded [Damberger, 1971]. Indeed, only small remnants of Permian strata are preserved in the central Appalachian Basin (Figure 8).…”
Apatite fission track ages and confined‐length distributions were collected from 38 basement outcrop and 5 basement drillcore samples in order to reconstruct the Phanerozoic thermal history of the Michigan Basin and southern Canadian Shield. The apatite data indicate two periods of thermal activity in the region: Triassic heating/cooling that affected the basin and adjacent shield and Cretaceous or post‐Cretaceous heating/cooling that primarily affected the basin. The magnitude, timing, and cause of Cretaceous thermal activity cannot be identified with the present data. Model calculations suggest that some of the shield samples and probably all of the basin samples were heated to temperatures of at least 90°C just prior to relatively rapid cooling in the Triassic. Available stratigraphic and geochemical constraints suggest that these elevated temperatures were the result of burial by an additional 2–5 km of late Paleozoic (probably Pennsylvanian and Permian) sediments. It is likely that the basin was buried during the Alleghenian Orogeny as observed for the adjacent Appalachian Basin.
“…During this time, the basin was located along tropical latitudes and likely maintained a tropical to humid subtropical climate that was subject to wet and dry seasons (Cecil 1990). The lithologies for each examined member consist primarily of discontinuous limestone and interbedded shale (Shaver et al 1986), and the depositional setting is interpreted as a nearshore marine environment with deltaic influence (Ferm et al 1971; Trask and Palmer 1986; Rexroad et al 2001; Brown and Rexroad 2009; Brown et al 2016). A specific example of the independence between morphologic pattern and lithologies is evident between the Perth and Holland Limestone Members.…”
Section: Discussionmentioning
confidence: 99%
“…The Mecca Quarry Shale and Velpen Limestone Members were combined and sampled as one interval, because previous conodont sampling did not differentiate between the two members (Rexroad et al 2001). For all units, the depositional environment is interpreted as a nearshore, deltaically influenced marine setting (Ferm et al 1971; Trask and Palmer 1986; Rexroad et al 2001; Brown et al 2016). Thus, any Neognathodus sample variation was likely not affected by changing paleoenvironments.Figure 2Map showing sampling localities and stratigraphic units of the 390 photographed specimens used in geometric morphometric (GM) analysis.…”
Conodont fossils are highly valuable for Paleozoic biostratigraphy and for interpreting evolutionary change, but identifying and describing conodont morphologies, and characterizing gradual shape variation remain challenging. We used geometric morphometric (GM) analysis to conduct the first landmark-based morphometric analysis of the biostratigraphically useful conodont genus Neognathodus. Our objective is to assess whether previously defined morphotype groups are reliably distinct from one another. As such, we reevaluate patterns of morphologic change in Neognathodus P1elements, perform maximum-likelihood tests of evolutionary modes, and construct novel, GM-based biozonations through a Desmoinesian (Middle Pennsylvanian) section in the Illinois Basin. Our GM results record the entire spectrum of shape variability among Neognathodus morphotypes, thus alleviating the problem of documenting and classifying gradual morphologic transitions between morphotypes. Statistically distinct GM groups support previously established classifications of N. bassleri, N. bothrops, and N. roundyi. Statistically indistinct pairs of GM groups do not support literature designations of N. medadultimus and N. medexultimus, and N. dilatus and N. metanodosus, and we synonymize each pair. Maximum-likelihood tests of evolutionary modes provide the first statistical assessment of Neognathodus evolutionary models in the Desmoinesian. The most likely evolutionary models are an unbiased random walk or a general random walk. We name four distinct biozones through the Desmoinesian using GM results, and these align with previous biozonation structure based on the Neognathodus Index (NI), illustrating that Neognathodus-based biostratigraphic correlations would not change between GM or NI methods. The structural similarity between both biozonations showcases that determining GM-based biozones is not redundant, as this comparison validates using landmark-based GM work to construct viable biozonations for subsequent stratigraphic correlations. Although this study is limited to the Illinois Basin, our quantitative methodology can be applied broadly to test taxonomic designations of additional genera, interpret statistically robust evolutionary patterns, and construct valid biozones for this significant chordate group.
“…There is substantial evidence that the distribution of very thick sandstones in the lower part of the Mansfield Forma tion, such as those in the Evansville paleovalley fill, was in fact partially controlled by Early Pennsylvanian movement on some of these faults. Structural influence on the distribution of Pennsylvan ian rocks in Illinois was suggested by Trask and Palmer (1986).…”
Section: Implications For Hydrocarbon Explorationmentioning
A unifying working model for regional tectonics is proposed as an explanation for several anomalous geologic features that have been observed for many years in the Illinois basin.Proterozoic (1.3-1.0 Ga) tectonics related to plate-margin rifting produced a series of steeply dipping northeast-southwest-trending faults in the Precambrian (1.5 Ga) granite-rhyolite province of Indiana. These faults are projected to intersect a set of west-northwest-trending basement faults in northwestern Ohio and northern Indiana. Little is known about the interval 1.5-1.3 Ga. In western Indiana, the northeast-trending basement faults appear in part to be an extension of the Wabash Valley fault system. Recurrent movement on these faults has occurred during various episodes of Paleozoic compression and extension. This movement subtly influenced the thickness distribution of certain lower Paleozoic stratigraphic units such as the Mount Simon Sandstone, Eau Claire Formation, Knox Supergroup, and Maquoketa Group. These recurrent motions also affected the dis tribution of Late Silurian reefs, and channel-fill sequences in the Lower Pennsylvan ian Mansfield Formation.The general location of these faults in Indiana is based on several lines of evi dence including (1) oil field studies, (2) reinterpretation of published structure maps, (3) occurrence of anomalous structural attitudes in outcrops, (4) distribution of earthquake epicenters, (5) presence of anomalous thermal events, (6) unpublished gravity and magnetic studies, and (7) some seismic reflection data. A northwest trend of basement faults may also exist, but there is very little evidence that they affected the Paleozoic in southern Indiana.
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