Formic Acid Insoluble Residue Study of the Ordovician–Devonian–Mississippian Section in the City of Troy Well 2014-12, Lincoln County, Missouri

by

David L. Bridges

MISSOURI DEPARTMENT OF NATURAL RESOURCES MISSOURI GEOLOGICAL SURVEY

Joe Gillman, Director and State Geologist P.O. Box 250, Rolla, MO 65402-0250

(573) 368-2100 www.dnr.mo.gov/geology

2015

OFR-2015-106-GS

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TABLE OF CONTENTS Introduction .......................................................................................................................................... 3

Stratigraphy .......................................................................................................................................... 4 Mississippian Subsystem of Carboniferous System ...................................................... 6 Middle Mississippian Series .................................................................................................... 6 Osagean Stage ........................................................................................................... 6

Warsaw Formation (45'–100' depth) .................................................................... 6 Burlington-Keokuk Limestone undifferentiated (100'–350' depth) ....................... 6 Lower Mississippian Series ..................................................................................................... 6 Kinderhookian Stage .................................................................................................. 6 Chouteau Group undifferentiated (350'–400' depth) ............................................ 6 Hannibal Shale (400'–415' depth) ........................................................................ 7 Devonian System ...................................................................................................................... 8 Upper Devonian Series ........................................................................................................... 8 Grassy Creek-Saverton Shale undifferentiated (415'–425' depth) ....................... 8 Middle–Upper? Devonian Series ........................................................................................... 11 Cedar Valley Limestone (425'–450' depth) ........................................................ 11 Ordovician System ................................................................................................................. 12 Cincinnatian Series ............................................................................................................... 12 Maquoketa Shale (450'–475' depth) ......................................................................... 12 Mohawkian Series ................................................................................................................. 12 Kimmswick Limestone (475'–565' depth) ................................................................. 12 Decorah Group ............................................................................................................... 13 Guttenberg Limestone (565'–575' depth) ................................................................. 13 Spechts Ferry F.–Kings Lake Ls. undifferentiated (575'–600' depth) ....................... 14 Plattin Group undifferentiated (600'–695' depth) ............................................................ 14 Joachim Dolomite (695'–745' depth) ............................................................................... 14 St. Peter Sandstone (745'–1,005' depth) ........................................................................ 14

Structural Geology .......................................................................................................................... 15 Major Structures ..................................................................................................................... 15 Cap au Gres Structure .......................................................................................................... 15 Lincoln Fold ........................................................................................................................... 15 Troy Fault .............................................................................................................................. 16 Minor structures ..................................................................................................................... 16 Cuivre Anticline ...................................................................................................................... 16

Southern Lincoln County Structure ....................................................................................... 16 Cheltenham Syncline ............................................................................................................ 16 Troy-Brussels Syncline .......................................................................................................... 17

Depauperate Zone of Maquoketa Shale .................................................................................. 17 Previous Studies ....................................................................................................................... 17 Distribution ................................................................................................................................. 17 Fauna .......................................................................................................................................... 18

References .......................................................................................................................................... 19

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INTRODUCTION The City of Troy public water supply Well 2014-12 in Lincoln County, Missouri, was drilled to 1,005 feet total depth in May, 2014 (Fig. 1). The drilling contractor “grabbed” and bagged drill cuttings at 5-foot intervals and submitted them to the Missouri Geological Survey (MGS), where the cuttings underwent stratigraphic study. According to a time-honored procedure at MGS, “standard” volumes of cuttings were removed from the sample bags and systematically digested in 15% hydrochloric acid (HCl) to generate insoluble residues (McQueen, 1931; Grohskopf and McCracken, 1949; McCracken, 1963). The raw cuttings and the insoluble residues were studied to make a lithologic strip log of the well. It soon became apparent that the Devonian-Mississippian contact, which resides somewhere in a 25-foot-thick interval of shale, could not be determined conclusively based solely on the study of raw cuttings and HCl-generated insoluble residues. In this particular case—as is commonly the case in northeast Missouri and elsewhere in the Mississippi Valley—the raw cuttings from above the contact appear much the same as those from below the contact. The HCl-generated insoluble residues also appear much the same above and below the contact. Furthermore, it is generally known that 15% HCl tends to destroy any and all microfossils that are not silicified, particularly conodonts and other organophosphatic elements of the microfauna. The question arose as to whether the 15% HCl destroyed biostratigraphically diagnostic microfossils.

Figure 1. Maps showing location of City of Troy Well 2014-12, Lincoln County, east-central Missouri. Red star indicates well

location in SE¼ SE¼ NW¼ sec. 1, T. 48 N., R. 1 W., Troy 7.5' quadrangle. A special project was initiated to investigate the use of 10% formic acid (HCO2H) to generate insoluble residues. Digestion in formic acid tends to not destroy conodonts and other organophosphatic microfossils that are potentially useful in determining geologic age and “picking” formational boundaries. Indeed, the formic acid method succeeded in yielding diagnostic microfossils and other residues that allowed the Devonian-Mississippian contact to be picked with minimal error at 415 feet drill depth in Well 2014-12. During the course of this project, the author developed an interest in the structural geology of Lincoln County as well as an interest in the Depauperate Zone of the Maquoketa Shale as recognized by (Ladd, 1929). The purpose of this report is threefold: (1) demonstrate that the study of formic acid-generated insoluble residues facilitates greater accuracy in determining formational contacts when used in conjunction with the HCl method that has been standard practice at the Missouri Geological Survey since

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the early 1900s; (2) characterize the complex structural elements in Lincoln County and show how the stratigraphy in Well 2014-12 may contribute to a better understanding of those elements; and (3) document the presence of the diminutive fauna of the Depauperate Zone in the basal portion of Maquoketa Shale in Well 2014-12.

STRATIGRAPHY Well 2014-12 penetrates 45 feet of residuum and 960 feet of underlying Paleozoic sedimentary bedrock strata, ranging from the Middle Mississippian Osagean Warsaw Formation at 45 feet depth down into the Ordovician Mohawkian St. Peter Sandstone at 1,005 feet total drill depth (Fig. 2). The drilled interval of bedrock represents a significant portion of the column of sedimentary bedrock that crops out in Lincoln County (Fig. 3).

Figure 2. Geologic column of bedrock lithostratigraphic units ranging from the Warsaw Formation at 45 feet depth down into the St.

Peter Sandstone at 1,005 feet total drill depth in the City of Troy Well 2014-12. Forty-five feet of residuum overlies the Warsaw. Ordovician = Ordovician System; Devonian = Devonian System; Carboniferous = Carboniferous System; Mississippian = Mississippian Subsystem; Mohawkian = Mohawkian Series; C.= Cincinnatian Series; Kinder.= Kinderhookian Stage of Lower Mississippian Series; Osagean = Osagean Stage of Middle Mississippian Series; D.G.= Decorah Group.

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Mississippian Subsystem of Carboniferous System Middle Mississippian Series Osagean Stage Warsaw Formation (45'–100' depth) (55' thick) The Warsaw Formation is the youngest bedrock unit encountered in the well. Grohskopf et al. (1939) reported a thickness of 75 feet for the Warsaw in northeast Missouri. The Warsaw comprises white, gray-to-buff limestone with abundant chert in places. The limestone varies from fine grained to coarsely granular (Grohskopf et al., 1939). A minor amount of shale is present as thin beds between the strata. Cuttings yield a small amount (less than 15%) of dark gray to black shale throughout the unit. A white translucent chert and rough gray chert occurs. The abundance of gray chert increases downward to the base of the formation. Sponge spicules, bryozoans and silicified crinoid fragments are present. The shaly nature of the Warsaw helps to differentiate it from the underlying Burlington-Keokuk. Iron staining is present throughout the unit. Burlington-Keokuk Limestone undifferentiated (100'–350' depth) (250' thick) The Burlington Limestone and Keokuk Limestone are grouped together following Grohskopf et al. (1939). Drill thickness is 250 feet. This is thicker than the 130- to 200-foot thickness reported further to the north by Koenig (1961), Grohskopf et al. (1939) and McQueen et al. (1941). The lower portion of this section may actually be the Fern Glen Formation. Describing the Fern Glen in northeast Missouri, Grohskopf (1944b, p. 6) stated,

“In St. Charles, Lincoln, Pike and Ralls counties, there is a zone of limestone beneath the Burlington dolomite which occupies the position of the Fern Glen in St. Louis County. Its lithology does not possess the red and green of the St. Louis County Fern Glen, but the residues are somewhat different from those in the overlaying Burlington. Usually there is a decrease in the amount of chert and the chert is white, mealy, ‘popcorn’ type and frequently quartz and quartz crystals are found in the residue. This zone tentatively has been called Fern Glen in many wells in northeast Missouri.”

McQueen et al. (1941) reported 50 to 75 feet of Fern Glen in Lincoln County. Below the Fern Glen, the Kinderhookian Sedalia Formation is present. Grohskopf (1944b) described the Sedalia in northeast Missouri as “dark gray limestone and the residue is principally quartz.” McQueen et al. (1941) reported a thickness of 50 feet for the Sedalia along the Cuivre River just east of Troy, Missouri. The Fern Glen and Sedalia Formations were not differentiated in the present study, thus the Kinderhookian–Osagean boundary was not resolved. Chert can exceed 70% by volume of the insoluble residue. The residue consists primarily of white chert. A mottled gray chert occurs frequently in the top half of the unit, portions of which are quite fossiliferous with crinoid fragments, bryozoans and brachiopods. Pyrite is present, some exhibiting a framboidal character. Secondary overgrowths of silica sand form doubly terminated quartz crystals that are especially abundant from 165–195 feet depth and the basal 25 feet of the unit. Lower Mississippian Series Kinderhookian Stage Chouteau Group undifferentiated (350'–400' depth) (50' thick) The Kinderhookian Chouteau Group undifferentiated, represents part of the Chouteau Group (Thompson, 1986). Moore (1928) reported a thickness of 50 feet for outcrops along the Cuivre River just east of Troy. The Chouteau has a thickness of 50 feet in well 2014-12. The Chouteau Group of northeast Missouri consists primarily of argillaceous limestone. The unit contains more shale than the Chouteau Compton Limestone of central Missouri. The residue consists of a small amount of light brown shale and pyrite (Fig. 4). White porous chert is present; however, it likely caved from the overlying Burlington-Keokuk beds. Siliceous crinoid fragments are present in a few intervals of the unit. Insoluble residues produced by formic acid yielded several conodonts and other microfauna (Fig. 5). Siphonodella sp. is the most abundant genus—clearly indicating Kinderhookian age for Chouteau Group undifferentiated.

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Figure 4. Insoluble residue of Chouteau Group undifferentiated.

Figure 5. Fossil and lithologic materials in residue of Chouteau Group undifferentiated. (A) Typical silicified (left) and pyritized

(right) faunal elements. (B) Hexactinellid sponge spicule. (C) Doubly terminated quartz crystal comprising detrital quartz grain with euhedral syntaxial quartz overgrowth. (D) Siphonodella sp. conodont fragment. (E) Siphonodella sp. (F) Glauconitic foraminifer. (G) areneacous foraminifer. Siphonodella is an index fossil for the Kinderhookian Stage.

Hannibal Shale (400'–415' depth) (15' thick) The Hannibal Shale in its type area in Marion County consists primarily of gray to black shale that may be sandy in part, particularly towards the top of the unit. The unit thins quickly southward from the type area. Only the basal 15 feet is present in Well 2012-14. McQueen et al. (1941) reported 10–30 feet of Hannibal Shale in eastern Lincoln County. It is next to impossible to visually distinguish Hannibal Shale from underlying Grassy Creek-Saverton Shale undifferentiated. Residue of Hannibal Shale comprises mostly gray shale along with abundant pyrite (Fig. 6), and it is somewhat similar to residue of Grassy Creek-Saverton Shale undifferentiated. Little to none of the sand that has been often described in the Hannibal was observed.

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The advantage of the formic acid technique becomes apparent in situations where two or more shale formations of different age lie unconformably on top of one another. Using conodonts as biostratigraphic markers, it was possible to separate the Kinderhookian Hannibal Shale from the Upper Devonian Grassy Creek-Saverton Shale undifferentiated. The Hannibal Shale conodont fauna consists primarily of Siphonodella sp., namely, the earlier forms such as S. quadruplicata (Fig. 6D). Siphonodella sp. is found only in Kinderhookian strata.

Figure 6. (LEFT) Insoluble residue of Hannibal Shale. (RIGHT) Fauna recovered from the residue. (A) Arenaceous foraminifer.

(B) Siphonodella sp. fragment. (C) Sponge spicule. (D) Siphonodella quadruplicata fragment. (E) Glauconitic foraminifer. (F) Problematic specimen replaced by glauconite.

Devonian System Upper Devonian Series Grassy Creek-Saverton Shale undifferentiated (415'–425' depth) (10' thick) It is difficult to distinguish the Grassy Creek and Saverton Shales in drill cuttings (Koenig, 1961). The shales are described as dark gray to black and fissile or finely laminated (McQueen et al., 1941). According to Thompson (1993), the underlying Grassy Creek is darker gray and platy compared to the more bluish and clay-rich Saverton, possibly allowing them to be distinguished in outcrop. The Saverton Shale averages 10 feet thick north of Troy in Pike County, while the Grassy Creek averages 20 feet thick (Moore, 1928). Thus a combined thickness of 30 feet is implied north of Well 2014-12. Moore (1928) reported that both formations thin to the south. This thinning trend is confirmed in well 2014-12. As is much the case with the overlying Hannibal Shale, the Grassy Creek-Saverton residue is primarily gray to dark gray shale with abundant pyrite (Fig. 7). The Grassy Creek-Saverton is slightly more fissile than the overlying Hannibal Shale. Both contain doubly terminated quartz crystals that comprise rounded detrital quartz grains with syntaxial euhedral quartz overgrowths. The Grassy Creek-Saverton Shale microfauna contains forms that are restricted to the Devonian. Icriodus alternatus (Fig. 8C) is present in the Devonian only, and it serves as an excellent biostratigraphic indicator for the Devonian. Other diagnostic faunal forms are the scolecodonts, or annelid jaws (Fig. 8F). Scolecodonts appear to be prevalent from the Devonian Cedar Valley Limestone “Callaway facies” to the base of the Mississippian Subsystem.

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Figure 7. Insoluble residue of Grassy Creek-Saverton Shale undifferentiated.

Figure 8. Fauna of Grassy Creek-Saverton Shale undifferentiated. (A) Scolecodonts with matrix attached. (B) Polygnathus sp. conodont. (C) Icriodus alternatus Branson and Mehl. (D) Silicified bryozoan or coral. (E) Conodont fragment. (F) Scolecodonts. (G) Conodont fragment. (H) Polygnathus sp. with small amount of matrix.

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Figure 9. Two insoluble residues of Cedar Valley Limestone. Gray shale may be from caving of overlying shale formations.

Figure 10. Fauna of Cedar Valley Limestone. (A) Polygnathus sp. hindeodellan element fragment. (B) Polygnathus dubius Hinde

hindeodellan element: (top) oral view), (bottom) lateral view. (C) Problematical. (D) Spathognatus sp. (E) Silicified coral??? (F) Silicified bryozoan or coral. (G) Conodont fragment. (H) Broken brachiopod spine? (I) Scolecodont. (J) Polygnathus sp. (lateral view). (K) Polygnathus sp. (aboral view).

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Middle–Upper? Devonian Series Cedar Valley Limestone (425'–450' depth) (25' thick) The Cedar Valley Limestone comprises mostly limestone with subordinate amounts of shale and sandstone. This differs significantly from the sandy limestone that is commonly found in this formation in central Missouri. The Cedar Valley overlies the Ordovician Cincinnatian Maquoketa Shale in Well 2014-12. The residues are less than 25% and consist of brown porous shale and sand (Fig. 9). Chert increases in abundance in the lower 10 feet of the formation. Pyrite is present. The upper 15 feet contains doubly terminated quartz crystals that comprise rounded detrital quartz grains with syntaxial euhedral quartz overgrowths Conodonts are present in this formation along with limited other fauna (Fig. 10). Ordovician System Cincinnatian Series Maquoketa Shale (450'–475' depth) (25' thick) The Maquoketa Shale is composed of tan, bluish and gray shales (McQueen et al., 1941). The thickness of the formation varies greatly in the vicinity of Troy. McQueen et al. (1941, p. 106) stated, “It thins to the southwest in Lincoln County, as only 5 feet of Maquoketa is present in a well at Troy, Mo., whereas 60 feet was encountered 5 miles northwest of Troy.” This would suggest that the upper Maquoketa surface was extensively peneplaned (weathered) before deposition of overlying strata. The primary residue of the Maquoketa consists of light brown porous shale (Fig. 11) and gray shale. Some pyrite and quartz grains are present throughout the section. In the lower portion, phosphate buttons along with a diminutive fauna are present (Fig. 12). This fauna is discussed in detail in the section dedicated to the Depauperate Zone.

Figure 11. Insoluble residue of Maquoketa Shale.

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Figure 12. Fauna of Maquoketa Shale. (A) Bivalve shell. (B) Orthostrophic coiled gastropod. (C) Michelinoceras sp. Forste

nautiloid segment. (D) Gastropods. (E) Typical Ordovician coniform conodont fragments. (F) Michelinoceras sp. Forste nautiloid segment. (G) Trilobite cephalon.

Mohawkian Series Kimmswick Limestone (475'–565' depth) (90' thick) The Kimmswick Limestone is a coarsely crystalline, light gray, pure limestone. Some cuttings consist of single cleavage fragments of calcite. McQueen et al. (1941) reported 95–145 feet thickness in northeastern Missouri. The greater thicknesses occur in eastern Pike and northern Ralls Counties. The Kimmswick has a thickness of 90 feet in the Well 2014-12. The amount of residue from the Kimmswick cuttings is low; however, cavings from the shales and cherts above are present (Fig. 13). Silicified echinoderm fragments are abundant. Quartz is also present. The conodont fauna more diverse than any other formation studied in the well. It is dominated by Phagmodus sp., a characteristic Mohawkian to Cincinnatian Ordovician conodont (Fig. 14).

Figure 13. Insoluble residue of Kimmswick Limestone.

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Figure 14. Fauna of Kimmswick Limestone. (A–E, G–O) Various typical Mohawkian conodonts. (F) Nature of abundant organic

phosphatic fauna of the Kimmswick Limestone. (P) “THING 3” of Clark et al. (1999). (Q) Gastropods. Decorah Group Guttenberg Limestone (565'–575' depth) (10' thick) The Guttenberg Limestone is a slabby fossiliferous limestone separated by thin reddish brown (cinnamon) shale layers (Thompson, 1991). Grohskopf (1944b) described the shales of the Decorah Group as “green to cinnamon in color” and used this trait to differentiate the Decorah from other rock units based on drill cuttings. A section of the Guttenberg exposed in a quarry on the west bluffs of the Mississippi River in Lincoln County contains an 11-foot-thick section of Guttenberg overlain by Kimmswick and underlain by Kings Lake Limestone. Drill cuttings from well 2014-12 consist of brown shale and subordinate silt and green shale. Chert is abundant (Fig. 15), which clear distinguishes it from the overlying and generally chert-free Kimmswick and from the underlying green shale of the Decorah Group. The Guttenberg fauna consists mainly of conodont and shell fragments (Fig. 15).

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Figure 15. (LEFT) Insoluble residue of Guttenberg Limestone. (RIGHT) Fragments of conodonts and brachiopods from Guttenberg

Limestone. Spechts Ferry Formation–Kings Lake Limestone undifferentiated (575'–600' depth) (25' thick) The Spechts Ferry Formation and overlying Kings Lake Limestone are not differentiated for purpose of this report. This unit, when combined with the Guttenberg Limestone described above, provides a total thickness of 35 feet for the Decorah Group. In the quarry mentioned previously, Thompson (1991) described 30 feet of Decorah Group. According to Grohskopf (1944b), “The Decorah averages from 25 to 35 feet in thickness in most of the subsurface of Missouri.” The drill cuttings contain green shale and lesser amounts of brown shale. Quartz sand abundance decreases upwards from the base of the unit. Plattin Group undifferentiated (600'–695' depth) (95' thick) The Plattin consists of gray to bluish-gray, dense limestone that is as much as 100 feet thickness in northeastern Lincoln County (McQueen et al., 1941). Thompson (1991) reported a thickness of 90 feet or less in northeastern Missouri. Residues from drill cuttings are generally low. Near the Joachim–Plattin transition, abundant green shale is present marking the Establishment Shale Member of Bloomsdale Limestone located near the bottom of the Plattin Group. An oolitic limestone is also present at the base of the Plattin. Joachim Dolomite (695'–745' depth) (50' thick) The Joachim Dolomite is gray to tan, granular to finely crystalline dolomite with shale partings and thin shale beds (McQueen et al., 1941). Joachim strata typically lie above the St. Peter sandstone in Lincoln County. Thompson (1991) reported the Joachim pinching out northwest of Lincoln and Ralls Counties, where the unit is less than 50 feet. Drill cuttings yield brown or gray shale along with silt. Residue amount is generally less than 10%; however, the amount of sand increases to nearly 30% at the contact with St. Peter Sandstone. St. Peter Sandstone (745'–1005' depth) (260' thick) The St. Peter consists of medium to coarse grained quartz sand that is rounded and frosted and often pitted. In places it may be angular to subangular due to syntaxial enlargement. This is the bottom formation in Well 2014-12. Over short distances in Lincoln County, the thickness of the St. Peter can vary greatly from zero to over 100 feet.

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Figure 16. Structural features of Lincoln County. CA = Cuivre anticline. WD = Waterloo-Dupo anticline. Light blue circles, from

west to east, are locations of the towns of Winfield, Brussels and Grafton, respectively.

STRUCTURAL GEOLOGY Major Structures Cap au Gres Structure The Cap au Gres structure is a major basement structure that separates the Illinois basin from the Ozark uplift. The Cap au Gres forms an en echelon complex structure with the Lincoln fold (Fig. 16). It is principally a faulted monocline or draped fold that extends more than 200 miles (including the Lincoln fold) (Harrison and Schultz, 2002). The complexity of the Lincoln fold was succinctly addressed by Krey (1924, p. 46), who stated, “The Lincoln fold is not a simple symmetrical fold, but is rather an area of uplift on which are many minor structural features such as anticlines, domes, synclines and faults.” This complexity is shared by the Cap au Gres structure. The structure is recognized as the Waterloo-Dupo anticline in Illinois and metro St. Louis area. Further north it is recognized as the Florissant Dome before crossing the Mississippi valley and again into Illinois, where it becomes the Cap au Gres faulted monocline. After turning sharply west upon entering Illinois, the structure enters Missouri again just to the north of Winfield, Lincoln County. The faulted monocline continues west for a short distance before turning abruptly more northward. The Cap au Gres faulted monocline terminates in a horsetail-like structure in northwestern Pike County (Harrison, 1995) (Fig 16). The oldest strata exposed in this structure occurs one mile north of Winfield, where Ibexian Cotter Dolomite is exposed in a local anticline that intersects with the Cap au Gres structure (McQueen et al., 1941). Lincoln Fold The Lincoln fold continues as a northwest extension of the Cap au Gres fault structure into northwestern Lincoln County, where the Cap au Gres forms a horsetail structure and terminates in adjoining Pike County (Fig. 16). McQueen et al. (1941) named the major anticline the Lincoln fold because it is best developed in Lincoln County, Missouri. Previously, Krey (1924) used the terms “Lincoln fold” and “Lincoln anticline” interchangeably. The fold extends 165 miles northwesterly to the Iowa border (Gross, 1949). Width is up to 15 miles and structural relief is up to 1,000 feet (McCracken, 1971). The fold

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varies from a symmetrical anticline to an asymmetrical anticline with a steeply dipping southwest limb (Harrison and Schultz, 2002). The Ordovician Mohawkian St. Peter Sandstone the oldest formation exposed in the Lincoln fold, and that is where the fold is best developed in northeast Lincoln County. Troy Fault The Troy fault was addressed by McCracken (1971). In the vicinity of the City of Troy, She placed a dash line on her structure compilation map that extended northeast to the Cap au Gres structure (Fig. 16); however, she did not discuss the fault in her text or elucidate the meaning of the dashed line on her compilation map. Little (2004) did not indicate the structure when he mapped the Troy 7.5' quadrangle. Starbuck (2014) proposed that the structure may be a monoclinal fold. Downthrown Mississippian Meramecian strata crop out to the south of the structure and Mississippian Osagean strata crop out to the north of the structure. Faulted beds have not been directly observed or documented. Seeger and Starbuck (2012) reported an apparent displacement of 12 to 18 meters in a narrow zone associated with the structure. Middendorf (2006) reported an apparent 40 to 60 feet of displacement associated with the structure in the Warrenton Northeast 7.5' quadrangle, where the structure dies out. Minor Structures Cuivre Anticline Gross (1949) mapped, described and named the Cuivre anticline that trends N 80o W for approximately 7 miles from the vicinity where the Troy fault and Troy-Brussels syncline meet (Figs. 3 and 16). The south flank of this anticline forms the north flank of the Troy syncline. Gross (1949) reported a plunge of about 40 feet per mile to the southeast. How the Cuivre anticline interacts with the Troy fault is not clearly understood. Southern Lincoln County Structure This structure extends from near the town of Brussels in Calhoun County, Illinois, to a location southwest of Troy in Lincoln County, Missouri. Krey (1924) published the first description of the structure. The nature of this structure is not clear. The western portion was described and named Troy syncline by Little (2004), who reported that the structure trends and plunges east-northeast, which—according to Starbuck (2014)—was based on Little’s contouring of the contact between the Burlington-Keokuk and Warsaw rock units. Little (2004) reported that Meramecian strata, including the Warsaw, Salem and St. Louis formations, are preserved in the structure. The Warsaw Formation is encountered in Well 2012-14, which is located very near the axis of the fold. Specifically, Well 2014-12 is located near the axis of the Troy syncline (Fig. 2). The east segment of this structure was mapped and described as the Cuivre River monocline by Starbuck (2011, 2014). Similar to the Cheltenham and Troy-Brussels synclines, Early Pennsylvanian strata crop out in the central portion of the structure. Harrison (1995) depicted the structure as extending from just south of Winfield and terminating at the end of the Cuivre River monocline segment of Starbuck (2011). Cheltenham Syncline Fenneman (1911) published the first description of the Cheltenham syncline. The Cheltenham syncline is associated with the Waterloo-Dupo anticline that is located parallel to and immediate east of the Cheltenham syncline (Fig. 16). Subsurface data suggest the structure continues north-northwesterly into St. Charles County and crosses into Illinois near Grafton (Rubey, 1952; Harrison, 1997). Both structures trend north-northwesterly and south-southeasterly before crossing into Illinois. The north part of the structure curves sharply west in Illinois and enters Missouri at the town of Winfield, Lincoln County. Treworgy (1981) shows the Cheltenham syncline as the Troy-Brussels syncline, parallel to and just to the south of the east–west segment of the Cap au Gres fault structure in Illinois. These structures continue to parallel each other upon crossing the Mississippi River back into Missouri. Younger Pennsylvania strata crop out in the center of the structure in Lincoln County, as they do in the fire clay district of St. Louis City and County (Figs. 2 and 16).

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Troy-Brussels Syncline The Troy-Brussels syncline is the extension of the Cheltenham syncline that parallels the Water-Dupo anticline and Cap au Gres fault system in Illinois and Lincoln County, Missouri (Fig. 16) (McCracken, 1971; Treworgy, 1981). This structure was studied by Rubey (1952) who believed it was created by drag along the downthrown side of the Cap au Gres fault. Krey (1924) wrote the first description of the structure. McCracken (1971) shows the syncline very close to the southwest margin of the Cap au Gres fault system. McCracken believed that the “southern Lincoln County syncline” described by Krey (1924) is the same as Troy-Brussels syncline. The Troy-Brussels structure follows the Cap au Gres structure more closely and does not trend to the west of Troy as does the structure described by Krey (1924). Lack of detailed mapping at the time McCracken completed her structure compilation would enable this misidentification to be easily made. Starbuck (2011, 2014) mapped the structure as trending northwest through the town of Winfield.

DEPAUPERATE ZONE OF MAQUOKETA SHALE Previous Studies Ladd (1929) proposed that a distinctive faunal zone that includes the dark basal shale layer of the Maquoketa Shale should be called the “Depauperate zone.” He studied the Maquoketa Shale of Iowa and believed that it could be extended through all time-equivalent strata in the Mississippi Valley. This fauna has been referred to as a “dwarf fauna” by Grohskopf, (1944a,b) and other workers. Drawing a clear distinction between “depauperate” and “dwarf” faunas, Ladd (1929, p. 372) stated, “a depauperate fauna is one in which the great bulk of the species is composed of individuals which are distinctly (but not abnormally) small, yet abundant and diversified,” whereas a “dwarf fauna…is composed entirely of dwarfs of normally larger individuals.” The fauna of the Depauperate Zone was described initially by Daniels (1854) as the “nucula shale” in the state of Wisconsin. Daniels (1854, p. 14) further stated that “This deposit extends across the Mississippi into Iowa, and south into Illinois.” The basal Maquoketa Shale is equivalent to the “nucula shale” of Daniels. Distribution The first published description of the Depauperate Zone in Missouri is in Ladd (1929, p. 381). He described outcrops where the Depauperate Zone is exposed along a stream in Pike County.

“Pike County, Missouri.—In the center of section 15, township 54 north, range 3 west, the north-south road crosses a small creek. By walking downstream 330 paces from this point outcrops of the contact zone may be seen in the floor of the creek and in the left bank. The following section is exposed:

FEET INCHES 6. Paper-thin shales with interbedded hard layers up to 4 inches in thickness. Barren as far as observed ……........................................................3+ 5. Limestones, slightly phosphatic, with large pyrite crystals. Shows ‘cone-in-cone’ structure in section. Bedding planes show botryoidal structure with swellings downward ……............................................................................... 1 4. Paper-thin shale parting. Barren …….................................................................................. 1– 3. Conglomeratic limestone with some pyrite. Seven typical fossils of the Depauperate fauna ……....................................................................................................... 1± 2. McCune [Kimmswick] limestone. Contains much pyrite in irregular veins and clusters of crystals, also much crystalline calcite and sphalerite. Hundreds of large cephalopods pave the creek floor. Mostly straight forms ………................................................................................................. 3 1. McCune [Kimmswick] limestone. Shows cavernous weathering.

A similar section is exposed 105 paces upstream in the right bank of the creek. Here the Depauperate zone, containing 12 typical species, is overlain by several feet of clay shales, yellow at the base and blue-green above.”

McQueen and Hinchey (1941) mentioned the depauperate fauna, stop no. 26 of their road log, located in Lincoln County just to the east of Cuivre River Recreation Area. Grohskopf (1944a) reported

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that “Many wells have a phosphatic-pyritic dwarfed fauna at the base.” Grohskopf and McCracken (1949) state that this basal Maquoketa fauna has not been found in any other formation in Missouri. The zone is also present in Illinois according to Willman et al. (1975, p. 85), who described it as follows:

“The Maquoketa Shale contains two zones with distinctive pyritic and phosphatic beds, called depauperate zones because they contain only small fossils, largely a coquina of mollusks. The Lower Depauperate Zone, at the base of the Scales Shale [basal Maquoketa], is widely present throughout the state [Illinois], but the Upper Depauperate Zone, near the top of the Scales, has been found only locally in central and northeastern Illinois.”

Figure 17. (A–B) Residue of Depauperate Zone of Maquoketa Shale. (C) Thick yellow precipitate from ammonium molybdate wet

chemical test indicates strong presence of phosphate in residue. (d) Apatite grain. (e) Silicified crinoid columnal. (f) Rounded, discoidal, phosphatic sediment grain. (g) Unaltered pyrite.

Fauna The zone is characterized by a coquina-like collection of dominantly less than 0.25-inch-size mollusks, bivalves and a few trilobites. The fauna has been extensively replaced by phosphate and pyrite. The phosphate occurs as button-shape discs and other forms and it rarely present as cement. The discs were confirmed to be phosphatic by way of the venerable ammonium molybdate wet chemical test (P.S. Mulvany, personal communication) (Fig. 17C). The most characteristic fossil according to Ladd (1929) is Orthoceras sociale, a straight-shelled nautiloid. The binomial name has since been changed to Michelinoceras sp. Foerste (Fig. 12C,F). Ladd (1929) recognized 44 species in the Depauperate Zone in Iowa. He recognized 12 typical species of the Depauperate Zone in a section located in Pike County,

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Missouri. The fauna recovered from the Troy well is diverse (Fig. 12). McQueen et al., (1941, p. 106) reported that the Maquoketa Shale in northwest Pike County, west of Frankford “includes a coarsely granular, impure reddish-brown limestone which contains the depauperate fauna that is locally characteristic of the formation.”

REFERENCES (Cited—Selected) Clark, D.L., Sorenson, J.K., Ladd, A.N., and Freiheit, J.R., 1999, Probable microinvertebrates,

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Cole, V.B., 1961, The Cap au Gres fault, in Koenig, J.W., Martin, J.A., and Collinson, C.W, Guide book, Twenty-sixth Annual Field Conference, The Kansas Geological Society, northeastern Missouri and west-central Illinois. Missouri Geological Survey and Water Resources, Report of Investigations 27, p. 86-88.

Daniels, E., 1854, First annual report on the geological survey of the State of Wisconsin. David Atwood, Printer, 84 p.

Fenneman, N.M., 1911, Geology and mineral resources of the St. Louis quadrangle, Missouri–Illinois. U.S. Geological Survey, Professional Paper 438, 73 p.

Grohskopf, J.G., 1944a, Criteria for microscopic identification of various formations. Missouri Geological Survey, manuscript MSC-60505, 44 p.

Grohskopf, J.G., 1944b, Criteria for differentiating formations in well cuttings from original samples and insoluble residues. Missouri Geological Survey, manuscript MSC-63024, 20 p.

Grohskopf, J.G., and McCracken, E., 1949, Insoluble residues of some Paleozoic formations of Missouri, their preparation, characteristics and application. Missouri Geological Survey and Water Resources, Report of Investigations 10, 39p.

Grohskopf, J.G., Hinchey, N.S., and Greene, F.C., 1939, Subsurface geology of northwestern Missouri, a preliminary report. Missouri Geological Survey and Water Resources, Biennial report of the State Geologist transmitted to the Sixtieth General Assembly, Appendix I, 160 p.

Gross, R.E., 1949, The geology of the southwestern quarter of the Elsberry quadrangle, Missouri. University of Iowa, Master’s Thesis, 100p.

Harrison, R.W., 1995, Geologic map of the Eolia 7.5-minute quadrangle Lincoln and Pike Counties, Missouri. U.S. Geological Survey, Miscellaneous Field Studies Map MF-2277.

Harrison, R.W., 1997, Bedrock geologic map of the St. Louis 30' x 60' quadrangle, Missouri and Illinois. U.S. Geological Survey, Miscellaneous Investigations Series Map I-2533.

Harrison, R.W., and Schultz, A., 2002, Tectonic framework of the southwestern margin of the Illinois basin and its influence on neotectonism and seismicity. Seismological Research Letters, v. 73, p. 698–730.

Koenig, J.W., 1961, The Lincoln fold of northeastern Missouri, in Koenig, J.W., Martin, J.A., and Collinson, C.W, Guide book, Twenty-sixth Annual Field Conference, The Kansas Geological Society, northeastern Missouri and west-central Illinois. Missouri Geological Survey and Water Resources, Report of Investigations 27, p. 75–80.

Krey, F., 1924, Structural reconnaissance of the Mississippi valley area from Old Monroe, Missouri, to Nauvoo, Illinois. Illinois State Geological Survey, Bulletin 45, 86 p., also Missouri Bureau of Geology and Mines, Volume 18 (2nd Series), 86 p.

Ladd, H.S., 1929, The stratigraphy and paleontology of the Maquoketa Shale of Iowa, Part 1. Iowa Geological Survey, Volume 34, p.305–448.

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Little, W.W., 2004, Bedrock geologic map of the Troy 7.5' quadrangle, Lincoln and St. Charles Counties, Missouri. Missouri Geological Survey and Resource Assessment Division, Open File Map OFM-04-479-GS.

McCracken, M.H., 1963, Insoluble residues. Shale Shaker, v. 13, no. 10, p. 6–19.

McCracken, M.H., 1971, Structural features of Missouri. Missouri Geological Survey and Water Resources, Report of Investigations 49, 99 p.

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McQueen, H.S., and Hinchey, N.S., 1941, Fourth day of field conference, Saturday, August 30, 1941, St. Louis to Hannibal, Missouri, in Guide book, central and northeastern Missouri and adjoining area in Illinois. Kansas Geological Society, Fifteenth Annual Field Conference, p. 49–69.

McQueen, H.S., Hinchey, N.S., and Aid, K., 1941, The Lincoln fold in Lincoln, Pike, and Ralls Counties, northeastern Missouri, in Guide book, central and northeastern Missouri and adjoining area in Illinois. Kansas Geological Society, Fifteenth Annual Field Conference, p. 99–110; Reprinted, 1961, in Koenig, J.W., Martin, J.A., and Collinson, C.W, Guide book, Twenty-sixth Annual Field Conference, The Kansas Geological Society, northeastern Missouri and west-central Illinois. Missouri Geological Survey and Water Resources, Report of Investigations 27, p. 81–85.

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