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Telychian (Llandovery, Silurian) conodonts from the LaPorte City Formation of eastern Iowa, USA (East-Central Iowa Basin) and their implications for global Telychian conodont biostratigraphic correlation

Christopher B.T. Waid and Bradley D. Cramer

Plain Language Abstract

The Silurian Period (approximately 444 to 419 million years ago) was a time of intense climate change. The beginning of the Silurian was an ice age, and the Earth transitioned into warm greenhouse conditions throughout the rest of the period. Much like modern, human-induced climate change, variation in the amount of carbon dioxide present in the atmosphere is thought to be linked with Silurian climate change, making it an important interval of Earth history to study perturbations to the climate system. The relative order that rock units were deposited must be precisely understood on a global scale in order to determine cause and effect relationships within various climate cycles, and to distinguish between local and global environmental changes. The rocks in Iowa record an interval of time that is rarely preserved in carbonate rocks in most basins and could be of great use to Silurian paleoclimate research. However, the relative age of the units in Iowa is fairly poorly understood, and the goal of this project is to use fossils called conodonts to more precisely determine the relative age of the Silurian rock of Iowa.

The order that new species of conodonts appear in the rock record can be used to determine their relative age, and rocks that contain the same fossil were likely deposited at similar times. The order that Silurian conodont species appear and disappear is well understood in the Baltic Basin, but there has been very little conodont data from North America that is directly comparable to the Baltic. The Telychian (Silurian) Age conodont data from this study is the first from North America that is directly comparable to data from the Baltic Basin and allows for the most precise relative age assignments to date for the Silurian strata of Iowa. They also indicate that origination and extinction of several species occurred at different times in North America than in the Baltic.

Resumen en Español

Los conodontos del Telychiense (Llandovery, Silúrico) de la Formación LaPorte City en el este de Iowa, Estados Unidos (Cuenca del Centro-Este de Iowa) y sus implicaciones para la correlación bioestratigráfica global del Telychiense realizada con conodontos

Los conodontos de la Formación LaPorte City del este de Iowa (Cuenca del Centro-Este de Iowa) indican una edad Telychiense temprano a medio para la formación. Fueron obtenidos conodontos diagnósticos para la Superzona Pterospathodus eopennatus, la Zona Pterospathodus eopennatus ssp. n. 2 y la Zona Pterospathodus amorphognathoides angulatus, permitiendo la primera comparación directa de los rangos estratigráficos de las especies de conodontos en las cuencas de Illinois y del Báltico. Una especie hasta ahora no descrita de Pseudolonchodina similar a Pseudolonchodina fluegeli se encuentra en la Formación LaPorte City. Se distingue de Pseudolonchodina fluegeli por la ausencia de dentículos fusionados en los elementos Pa y dentículos discretos a casi discretos en los otros elementos. Debido a la naturaleza fragmentaria de los especímenes, se hace uso de la nomenclatura abierta para esta especie. Wurmiella? polinclinata polinclinata se encuentra mucho más baja en la Cuenca del Centro-Este de Iowa (Zona Pt. eopennatus ssp. n. 2) que en la Cuenca del Báltico, y por lo tanto no puede ser utilizada como un fósil índice diagnóstico de la Zona Pt. am. amorphognathoides en las correlaciones globales. Este estudio documenta la utilidad de las pequeñas formaciones de caliza en el flanco noroeste de la Cuenca Centro-Este de Iowa para refinar la zonación bioestratigráfica global del Silúrico con el uso de conodontos.

Palabras clave: Conodontos; Bioestratigrafía; Silúrico; Llandovery; Continente medio norteamericano; Formación LaPorte City

Traducción: Enrique Peñalver (Sociedad Española de Paleontología)

Résumé en Français

text

Translator: Antoine Souron

Deutsche Zusammenfassung

Conodonten aus dem Telychuim (Llandovery, Silur) aus der LaPorte City Formation von Ost-Iowa, USA (östliches zentrales Iowa Becken) und ihre Bedeutung für die globale biostratigraphische Korrelation von Conodonten aus dem Telychium

Conodonten aus der LaPorte City Formation von Ost-Iowa, USA (östliches zentrales Iowa Becken) deuten altersmäßig für diese Formation auf das frühe bis mittlere Telychium hin. Es werden Conodonten geborgen, die diagnostisch für die Pterospathodus eopennatus Superzone, Pterospathodus eopennatus ssp. n. 2 Zone und die Pterospathodus amorphognathoides angulatus Zone sind. Diese ermöglichen den direkten Vergleich der stratigraphischen Reichweite von Conodonten-Arten im Illinois Becken und Baltischen Becken. In der LaPorte City Formation kommt eine bisher unbeschriebene Art von Pseudolonchodina vor, die Pseudolonchodina fluegeli ähnlich ist. Sie unterscheidet sich von Pseudolonchodina fluegeli durch das Fehlen von verwachsenen Dentikeln auf den Pa-Elementen und durch diskrete bis nahezu-diskrete Dentikel auf den anderen Elementen. Wegen der fragmentarischen Erhaltung der Stücke, wird die Art in der offenen Nomenklatur belassen. Wurmiella? polinclinata polinclinata kommt im östlichen zentralen Iowa Becken viel weiter unten vor (Pt. eopennatus ssp. n. 2 Zone) als im Baltischen Becken und kann daher bei globalen Korrelationen nicht als diagnostisches Indexfossil für die Pt. am. amorphognathoides Zone genutzt werden. Diese Studie dokumentiert den Nutzen kleiner Kalksteinformationen an der Nordwest-Flanke des Zentralen Iowa Beckens durch die die globale biostratigraphische Conodonten-Zonierung im Silur konkretisiert werden kann.

Schlüsselwörter: Conodonten; Biostratigraphie; Silur; Llandovery; North American Midcontinent; LaPorte City Formation

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

TABLE 1. Conodont specimens from the Garrison Core.

Sample (m) 111.38-111.63 114.75-114.94 115.51-115.76 118.20-118.41 120.88-121.13 121.62-121.88 124.66-124.93 128.85-129.11 130.20-130.48 130.79-131.09 131.95-132.23 134.06-134.31 135.65-136.10 137.12-137.40
Sample (ft) 365.42-366.25 376.50-377.10 379.10-379.80 387.80-388.50 396.58-397.41 399.00-399.86 409.00-409.86 422.75-423.58 427.17-428.09 429.10-430.10 432.92-433.84 439.83-440.66 445.66-446.53 449.87-450.79
Mass (kg) 0.52 0.523 0.526 0.522 0.544 0.555 0.562 0.554 0.52 0.521 0.551 0.561 0.56 0.561
Total Conodonts 4 17 31 15 26 33 33 54 74 63 77 42 80 32
Pterospathodus amorphognathoides angulatus Pb1     1                      
Pb2 1     1                    
Sb1     1 1                    
Pterospathodus eopennatus ssp. n. 2 Pa               1 1 1 1      
Pb1               3 2 1 1      
Pc                 1          
M                   2        
Sc1               2 1          
Sb2               1 1          
Aulacognathus sp. n. P1                   1     1  
Wurmiella? polinclinata polinclinata P1           1   2 3 1 4 3    
P2   1 1 1 1   3 3 2 3   2    
M                     1      
S3/4     1                 5    
S1/2     2   1     1 5   1 3    
S0   2         3   1 1        
Wurmiella? polinclinata estonica P1                         3  
P2                         3  
M                         3  
S3/4                         1  
S1/2                         2 1
S0                         1 2
Psuedolonchodina sp. n. Pa     1             1        
Pb     1   1     1   3   1 1 1
M   1 1   2     2 2   2 1    
Sc     4 1 1 2   4 4 4 5 2   1
Sb   1 1         1   3   1    
Sa     2   1 3   1            
Aulacognathus angulatus P1         1       1     1 1  
P2         1               1  
S1/2                         1  
Aulacognathus kuehni P1                     3      
Aulacognathus bullatus P1         1                  
Astrolecignathus cf. milleri Pa           1                
Distomodus staurognathoides Pa         1   1 1 1   2   4  
Sb   1           1       2 3  
Oulodus sp. Pa?                         1  
Pb       1 1                  
Sc                 1     2 2  
Sa         2         1       1
Oulodus cf. petilus pacificus Sc                       1    
Sb                 1          
Pb                   1        
Panderodus unicostatus aeq                 1   1      
tort   2 2 1 1   1   5 1 3 1 2 1
falc   1 2   1       2 4 4   3  
grac   1 2 1 3 3 2 4 18 13 14 1 10 4
trunc     1 1 1 1   1 4 1 3   3  
arc   1       1 1   2 2 4 1 1 1
Panderodus equicostatus aeq                         1  
tort       1   1 2       1   1  
falc         1 2 1 2 1         1
grac     2 2 3 6 11 4 3 4 5 1 12 6
trunc             1?       1? 1    
arc         1 1 2 1 1 1 2   2 1
Panderodus panderi falc                   1        
grac 1           3 2 1 6 4     3
trunc   1       1   1 1 2 2      
arc             1       1     1
Panderodus greenlandensis grac     1                      
arc       1 1             1    
Panderodus cf. P. unicostatus grac                           2
Panderodus sp. indet.   1         6 2 3 3   4 4 2 4
Walliserodus curvatus dysc               2   1   2    
curv               2 1 2   1    
unicost               1 1 2        
mlticost                 1       4  
Pseudooneotodus beckmanni                         1 1  
Unidentified ramiforms   1 5 5 3   3   7 2   9 4 10 2

 

 

TABLE 2. Conodont specimens from the DX5 outcrop.

Sample (m) 0.04-0.08 0.67-0.74 1.34-1.54 3.49-3.59 4.59-4.61
Mass (kg) 3.078 2.802 6.515 7.153 5.098
Total Conodonts 7 15 12 117 24
Pterospathodus sp. Indet.       1    
Pterospathodus amorphognathoides angulatus Pa       1 1
Pb1       3  
Pb2         1
Sc2       1?  
Ozarkodina polinclinata polinclinata P1       4 3
P2         1
M     1   1
S1/2     1?    
Psuedolonchodina sp. n. Pb         1
M       1  
Sc       1 1
Sb       5  
Sa       1  
Aulacognathus bullatus P1 1? 2      
P2     1?    
Apsidognathus tuberculatus Pa     1    
Distomodus staurognathoides Pa       1  
Sb?         1?
Oulodus sp. Sc       2  
Kockelella cf. K. abrupta P1   1      
Panderodus unicostatus aeq       2  
tort 1     4 1
falc       4  
grac 1 2   18 3
trunc       5  
arc       3 1
Panderodus equicostatus tort       5  
falc       3  
grac       15  
trunc       3  
arc       6  
Panderodus panderi grac       3  
trunc       4  
arc       2  
Panderodus greenlandensis grac   1     1
Panderodus sp. indet.         7 8
Pseudooneotodus beckmanni         1  
Unidentified ramiforms   4 9 7 16  
 

authorChristopher B.T. Waid. Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, IA 52242, USA; Present address: Ohio Geological Survey, 2045 Morse Rd. Building C, Columbus, OH 43229, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Chris Waid recently received a M.S. in Geoscience from the University of Iowa, and received his B.A. in Geological Sciences from SUNY Geneseo. He is interested in any aspect of geology related to Earth History, and has focused on conodont biostratigraphy and taxonomy, lithostratigraphy, and chemostratigraphy throughout his undergraduate and graduate education. He is currently a geologist at the Ohio Geological Survey, where he works on high-resolution subsurface stratigraphy in the Energy Resources Group.

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cramerBradley D. Cramer. Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, IA 52242, USA. This email address is being protected from spambots. You need JavaScript enabled to view it.

Brad Cramer is an Earth-systems scientist with a background in stratigraphy and isotope geochemistry. He investigates global change events in deep time with an emphasis on Pre-Mesozoic stratigraphy. His work integrates biostratigraphy, stable and radiogenic isotope chemostratigraphy, sequence stratigraphy, and high-precision geochronometry to develop high-resolution/high-precision time scales of Earth history and to evaluate the cause-and-effect relationships within the Earth system. He specializes in lower Paleozoic Earth history but has worked on topics ranging from the Proterozoic to the Permian in basins around the world. He is also the director of the University of Iowa MicroPaleontology Laboratory (http://bradley-cramer.weebly.com/micropaleo-lab.html). 

 

FIGURE 1. Telychian conodont zonation based on Baltic fauna with ranges of biostratigraphically important species. Red lines are used for ranges in Iowa when they differ from the Baltic. Wurmiella? polinclinata polinclinata and Aulacognathus bullatus extend lower in Iowa than in the Baltic. Wurmiella? polinclinata estonica does not range as high in Iowa. Dashed lines in Pteropathodus eopennatus ssp. n. 1 Zone indicate uncertainty in stratigraphic range in Iowa. Modified from Männik (2007a).

 figure1

FIGURE 2. 1, Paleogeographic map showing the locations of the continents during the lower to middle Silurian. Black box indicates approximate location of the Illinois Basin. From Torsvik et al. (1996, figure 13). 2, Map showing the deepest part of the Illinois and East-Central Iowa basins, and trans-Iowa sag in Iowa and nearby states during the Silurian. Shading indicates extent of basins. Modified from Cramer et al. (2006, figure 1).

figure2 

FIGURE 3. Cross section of Silurian strata in eastern Iowa. The lower two members of the Hopkinton Formation become indistinguishable in the western part of the cross section. The Sweeney and Marcus members are referred to as Hopkinton A, the Farmers Creek Quarry Member as Hopkinton B, and the Picture Rock Member as Hopkinton C in this manuscript. Note the change in datum at the CC core in Linn County. Modified from Witzke (1992, figure 6).

 figure3

FIGURE 4. Specimens reported from the DX5 outcrop section in Metzger (2005). All specimens in lateral view. 1-3, 5, Pterospathodus eopennatus ssp. n. 2 sensu Männik (1998), Pa element, DLH 4, SUI 132418 (1); Pa element, DLH 6, SUI 132420 (2); Pb element, DLH 6, SUI 132420 (3); and Pa element, DLH 9, SUI 132423 (5). 4, 6-9, Pterospathodus amorphognathoides angulatus, Pa element, DLH 6, SUI 132420 (4); Pb element, DLH 6, SUI 132420 (6); Pa element, DLH 6, SUI 132420 (7); Pb element, DLH 6, SUI 132420 (8); and Pa element, DLH 11, SUI 132425 (9). 10, Aulacognathus bullatus? Pb element, DLH 11, SUI 132425.

 figure4

FIGURE 5. Stratigraphic column and conodont range chart for the LPC in the Garrison Core. Dashed lines indicate uncertainty in range. M = mudstone, W = Wackestone, P = Packstone, F = Floatstone for carbonate lithologies. L.H. = Lower Hopkinton. Log colors represent the color of the rock. Correlation of conodont biozonation to chronostratigraphic units from Cramer et al. (2011).

figure5 

FIGURE 6. Stratigraphic column and conodont range chart for the LPC at the DX5 outcrop. Dashed lines indicate uncertainty in range. See Figure 5 for lithology and symbol legend. The samples included from Metzger (2005) included are DLH 4, DLH 6, DLH 11, and DLH 13, in ascending stratigraphic order.

figure6 

FIGURE 7. Simple cone elements from Garrison Core. All specimens in lateral view except for 6. 1-2, Panderodus equicostatus, graciliform, GC 124.66-124.93 m, SUI 142251 (1) and graciliform, GC 121.92-121.88 m, SUI 142253 (2). 3-5, Panderodus panderi, graciliform, GC 124.66-124.93 m, SUI 142252 (3); arcuatiform, GC 131.95-132.23 m, SUI 142254 (4); and graciliform, GC 111.38-111.63 m, SUI 142255 (5). 6, Psuedooneotodus beckmanni, oral view, GC 135.65-136.10 m, SUI 142256. 7, Panderodus cf. P. unicostatus, falciform, GC 135.65-136.10 m, SUI 142257. 8-11, Panderodus unicostatus, falciform, GC 131.95-132.23 m, SUI 142258 (8); fused cluster of 8 elements, GC 130.20-130.48 m, specimen destroyed processing for SEM (9); fused cluster of 6 elements, GC 131.95-132.23 m, SUI 142260 (10); and tortiform element, GC 131.95-132.23 m, SUI 142261 (11); 12-13, Walliserodus curvatus, dyscritiform, GC 134.06-134.31 m, SUI 142262 (12) and curvatiform, GC 128.85-129.11 m, SUI 142263 (13). 14-15, Panderodus greenlandensis, arcuatiform GC 118.20-118.41 m, SUI 142264 (14) and graciliform, GC 134.06-134.31 m, SUI 142265 (15). White scale bar represents 0.5 mm.

figure7 

FIGURE 8. Conodonts from the Garrison Core. 1-12, 19, Psuedolonchodina sp. n., Sa element, posterior view, GC 115.51-115.76 m, SUI 152266 (1); Sa element, posterior-aboral view, GC 121.62-121.88 m, SUI 142267 (2); Sb element, anterior view, GC 134.06-134.31 m, SUI 142268 (3); Sc element, lateral view, GC 130.20-130.48, SUI 142269 (4); Sc/M? element fragment, lateral view, GC 128.85-129.11 m, SUI 142270 (5); M element, lateral-posterior view, GC 131.95-132.23 m, SUI 142271 (6); M element, anterior-lateral view, GC 134.06-134.31 m, SUI 142272 (7); Pa element, oral view, GC 134.06-134.31 m, SUI 142273 (8); Pa element, oral view, GC 130.79-131.09m, SUI 142274 (9); Sc element, lateral view, GC 135.65-136.10 m, SUI 142259 (10); Pb element, lateral, and lateral-aboral views, GC 115.51-115.76 m, SUI 142275 (11 and 12); and Pb element, lateral view, GC 130.79-131.09 m, SUI 142276 (19). 13, 15, Oulodus sp. indet., Sa element, anterior-lateral view, GC 137.12-137.40 m, SUI 142277 (13) and Pa element, posterior view, GC 135.65-136.10 m, SUI 142278 (15). 14, 16-17, Oulodus cf. Ou. petilus pacificus, Sc element, lateral view, GC 134.06-134.31 m, SUI 142279 (14); Sb element, posterior-oral view, GC 130.20-130.48 m, SUI 142280 (16); and Pb element, anterior-lateral view, GC 130.79-131.09 m, SUI 142281 (17). 18, 21-22, Distomodus staurognathoides, Sb element, posterior view, GC 134.06-134.31 m, SUI 142282 (18); Pa element, oral view, GC 135.65-136.10 m, SUI 142283 (21); and Pa element, oral view, GC 135.65-136.10 m, SUI 142282 (22). 20, Aulacognathus angulatus, P2 element, lateral view, GC 135.65-136.10 m, SUI 142285.

figure8 

FIGURE 9. Conodonts from the Garrison Core and DX5 outcrop. 1-8, Wurmiella? polinclinata polinclinata, S0 element, anterior view, GC 130.79-131.09 m, SUI 142286 (1); S1/2 element, posterior view, GC 115.51-115.79 m, SUI 142287 (2); S3/4 element, lateral view, GC 115.51-115.76 m, SUI 142288 (3); M element, lateral view, GC 130.20-130.48 m, SUI 142289 (4); P2 element, lateral view, GC 130.20-130.48 m, SUI 142290 (5); P2 element, GC 130.79-131.09 m, SUI 142291 (6); P1 element, lateral view, DX5 4.59-4.61 m, SUI 142292 (7); and P1 element, lateral view, DX5 3.49-3.59 m, SUI 142293 (8). 9-10, Aulacognathus angulatus, P1 element, oral view, GC 135.65-136.10 m, SUI 142294 (9) and S1/2 ? element, posterior view, GC 135.65-136.10 m, SUI 142295 (10). 11-14, Aulacognathus bullatus, P2 element, lateral view, DX5 1.34-1.54 m, SUI 142296 (11); P1 element, oral view, DX5 4.59-4.61 m, SUI 142297 (12); P1 element, oral view, DX5 0.67-0.74 m, SUI 142298 (13); and P1 element, oral view, GC 120.88-121.13 m, SUI 142299 (14). 15-16, Aulacognathus kuehni, P1 element, oral view, GC 131.95-132.23 m, SUI 142300 (15) and juvenile P1 element, oral view, GC 131.95-132.23 m, SUI 142301 (16). 17, Astrolecignathus cf. milleri, Pa element, oral view, GC 121.92-121.88 m, SUI 142302. 18, Apsidognathus tuberculatus, Pa element, oral view, DX5 1.34-1.54 m, SUI 142303.

figure9 

FIGURE 10. Conodonts from the Garrison Core and DX5 outcrop. 1-7, Pterospathodus amorphognathoides angulatus, Sc1 element, posterior view, GC 115.51-115.76 m, SUI 142304 (1); Pb1 ? element, lateral view, GC 115.51-115.76 m, SUI 142305 (2); Pb2 element, GC 111.38-111.63 m, SUI 142306 (3); Pb1 element, inner lateral, and oral views, GC 115.51-115.76 m, SUI 132410 (4 and 5); Pa element, oral view, DX5 3.49-3.59 m, SUI 142307 (6); and Pa element, lateral view, DX5 4.59-4.61 m, SUI 142308 (7). 8-19, Pterospathodus eopennatus ssp. n. 2 sensu Männik (1998), Sb2 element, posterior, and lateral views, GC 130.79-131.09 m, SUI 142309 (8 and 9); Sc 1 element, lateral view, GC 130.79-131.09 m, SUI 142310 (10); M element, GC 130.79-131.09 m, SUI 142311 (11); Pb1 element, lateral view, GC 128.85-129.11 m, SUI 142312 (12); Pc element, lateral view, GC 130.20-130.48 m, SUI 142313 (13); Pb1 element, lateral view, GC 130.20-130.48 m, SUI 142314 (14); Pa element, lateral view, GC 128.85-129.11 m, SUI 142315 (15); Pb1 element, lateral view, GC 130.20-130.48 m, SUI 142316 (16); Pa element, lateral, and oral views, GC 130.79-131.09 m, SUI 142317 (17 and 18); and Pa element fragment, oral view, GC 130.20-130.48 m, SUI 142318 (19). 20-21, Aulacognathus sp., juvenile P1 element, oral, and lateral-anterior views, GC 135.65-136.10 m, SUI 142319. 22-23, Kockelella cf. K. abrupta, P1 element, oral, and lateral views, DX5 0.67-0.74 m, SUI 142320.

figure10 

FIGURE 11. P1 elements of Wurmiella? polinclinata estonica and Wurmiella? polinclinata polinclinata. 1-11 are classified as W.? polinclinata polinclinata. 12 and 14 show some characteristics of each subspecies, but compare most closely to W.? polinclinata polinclinata. 13, 15-17 are classified as W.? polinclinata estonica. All specimens in lateral view. 1, GC 121.92-121.88 m, SUI 142321; 2, GC 128.85-129.11 m, SUI 142322; 3-5, GC 130.20-130.48 m, SUI 142323 (3), 142324 (4), and 142325 (5); 6, GC 130.79-131.09 m, SUI 142326; 7-11, GC 131.95-132.23 m, SUI 142327 (7), 142328 (8), 142329 (9), 142330 (10), and 142331 (11); 12-14, GC 134.06-134.31 m, SUI 142332 (12), 142333 (13), and 142334 (14); and 15-17, GC 135.65-136.10 m, SUI 142335 (15), 142336 (16), and 142337 (17).

figure11

 

 

Specimen slide SUI numbers.

Slide SUI Numbers
Sample SUI Number
GC 365.42-366.25' 142338
GC 376.5-377.1' 142339
GC 379.0-379.8' 142340
GC 387.8-388.5' 142341
GC 396.58-397.41' 142342
GC 399.0-399.86' 142343
GC 409.0-409.86' 142344
GC 429.1-430.1' 142345
GC 422.75-423.58' 142346
GC 427.17-428.09' 142347
GC 432.92-433.84' 142348
GC 439.83-440.66' 142349
GC 445.66-446.53' 142350
GC 449.87-450.79' 142351
DX5 0.04-0.08 142352
DX5 0.67-0.74 142353
DX5 1.34-1.54 142354
DX5 3.49-3.59 142355
DX5 4.59-4.61 142356