SPRING 1963 Bulletin 4

The Bluehonnet Lake Waco Formation {Upper Central Lagoonal Deposit BURR A. SILVER thinking is more important than elaborate equipment-"

Frank Carney, Ph.D. Professor of Geology Baylor University 1929-1934

Objectives of Geological at Baylor

The of a geologist in a university covers but a few years; his education continues throughout his active life. The purposes of training geologists at Baylor University are to provide a sound basis of un­ derstanding and to foster a truly geological point of view, both of which are essential for continued professional growth. The staff considers geology to be unique among sciences since it is primarily a field science. All geologic research including that done in laboratories must be firmly supported by field observations. The student is encouraged to develop an inquiring objective attitude and to examine critically all geological concepts and principles. The development of a mature and professional attitude toward geology and geological research is a principal concern of the department.

PRESS WACO, TEXAS BAYLOR GEOLOGICAL STUDIES

BULLETIN NO. 4

The Member, Lake Waco Formation {Upper Central Texas - - A Lagoonal Deposit

BURR A. SILVER

BAYLOR UNIVERSITY Department of Geology Waco, Texas Spring, 1963 Baylor Geological Studies

EDITORIAL STAFF

F. Brown, Jr., Ph.D., Editor stratigraphy, paleontology O. T. Hayward, Ph.D., Adviser stratigraphy-sedimentation, structure, geophysics-petroleum, groundwater R. M. A., Business Manager archeology, geomorphology, vertebrate paleontology James W. Dixon, Jr., Ph.D. stratigraphy, paleontology, structure Walter T. Huang, Ph.D. mineralogy, petrology, metallic minerals

Jean M. Spencer, B.S., Associate Editor Bulletin No. 4

The Baylor Geological Studies Bulletin is published Spring and Fall, by the Department of Geology at Baylor University. The Bulletin is specifical­ ly dedicated to the dissemination of geologic knowledge for the benefit of the people of Central Texas. The pub­ lication is designed to present the results of both pure and applied research which will ultimately be important in the economic and cultural growth of the Central Texas region.

Additional copies of this bulletin can be obtained from the Department of Geology, Baylor University, Waco, Texas. $1.00 postpaid. CONTENTS

Page Abstract . . . .' . . Introduction Purpose Location ...... Procedures ...... 7 Previous work ...... 7 Acknowledgments ...... 7 Stratigraphy Regional geology ...... 8 General description ...... 8 Relationship to adjacent units ...... 8 Gross lithology ...... 8 Zonation Sedimentary petrology ...... 10 Limestone petrology ...... 10 Vertical variations ...... 10 Locality 154-B-41 10 Locality 154-B-43 10 Other localities ...... 11 Lateral variations ...... Shale petrology ...... 16 Vertical mineralogic variations 16 Calcium montmorillonite ...... 16 Sodium montmorillonite ...... 16 16 Kaolinite 16 Gypsum ...... 17 Quartz ... Calcite . . . . 17 Carbon 17 Lateral mineralogic variations ...... 17 Calcium montmorillonite ...... 17 Sodium montmorillonite ...... 17 Kaolinite ...... 17 Gypsum ...... 17 Quartz ...... - Calcite 17 Carbon Summary ...... 17 Paleontology ...... 22 Megafossils ...... 22 Microfossils ...... 22 Plants 23 Geologic history ...... 23 Bathymetry and distribution of 23 Depositional environment ...... 23 Geochemical environment ...... 29 Borderland features 29 ...... 36 Compaction ...... 36 Cementation ...... 36 Recrystallization ...... 36 Erosional history ...... 36 Conclusions ...... References ...... - 39 Appendix I Subsurface control ...... 40 Appendix II Measured sections ...... 41 Appendix III Mineralogic content determined by X-ray . 44 Appendix IV Microfaunal abundance ...... 45 Appendix V Methods and procedures ...... 46 ILLUSTRATIONS

FIGURES Page 1 Index map 6 2 Outcrop, isopach and locality map, Bluebonnet member, Lake Waco formation, central Texas . . . . . 9 3 Mineralogy and fauna, localities and 14-B-2, Bluebonnet member, Lake Waco formation 12 4 Mineralogy and fauna, locality 154-B-40, Bluebonnet Lake Waco formation 14 5 Mineralogy and fauna, locality 154-B-41, Bluebonnet member, Lake Waco formation 18 6 Mineralogy and fauna, locality 154-B-42, Bluebonnet member, Lake Waco formation 20 7 Mineralogy and fauna, locality 154-B-43, Bluebonnet member, Lake Waco formation 24 8 Mineralogy and fauna, locality 154-B-44, Bluebonnet member, Lake Waco formation . 26 9 Mineralogy and fauna, localities 154-B-45 and 109-B-15, Bluebonnet member, Lake Waco formation . 30 10 Mineralogy and fauna, locality 109-B-16, Bluebonnet member, Lake Waco formation 32 11 Mineralogy and fauna, locality 109-B-17, Bluebonnet member, Lake Waco formation 34 12 Summary of mineralogy and fauna, Bluebonnet Lake Waco formation, central Texas 37 13 Postulated evolution of Bluebonnet lagoon, central Texas 38

PLATES I Micro-features, limestone beds, localities 14-B-l and 14-B-2, Bluebonnet Lake Waco formation 13 II Micro-features, limestone beds, localities 154-B-40, Bluebonnet Lake Waco formation . . 15 III Outcrop and micro-features of limestone beds, locality 154-B-41, Bluebonnet member, Lake Waco formation .... 19 IV Outcrop and micro-features of limestone beds, locality 154-B-42, Bluebonnet Lake Waco formation 21 V Outcrop and micro-features of limestone beds, locality Bluebonnet member, Lake Waco formation 25 VI Micro-features, limestone beds, locality 154-B-44, Bluebonnet Lake Waco formation . . 27 VII Outcrop and micro-features of limestone beds, localities 154-B-45 and 109-B-15, Bluebonnet Lake Waco formation 31 VIII Micro-features, limestone beds, localities 109-B-16 and 109-B-17, Bluebonnet member, Lake Waco formation 33 IX Selected micro-features, limestone beds, Bluebonnet member, Lake Waco formation ...... 35 The Member, Lake Formation (Upper Central Texas A Lagoonal Deposit

BURR A. SILVER

ABSTRACT

The geologic history of the member, Lake Planktonic foraminifers, Waco formation, Eagle Ford group (Upper Cretaceous) la, as well as Gumbelina, increase in abundance upward in central Texas is interpreted along the following lines in the shale beds. Foraminifera exceed 40,000 in­ of distribution of clastic sediments, dividuals per cubic centimeter of residue locally in cen­ (2) depositional environments, (3) geochemical en­ tral McLennan and central Hill counties. Numerous vironments, (4) significance of microfaunal distribution, ammonites have been reported in the Bluebonnet mem­ and (5) diagenetic effects. ber, and normally ammonites are restricted to limestone The Bluebonnet depositional basin is confined to all beds in the lower part of the member. or portions of Bell, Falls, McLennan, Limestone, and Mineralogy of the Bluebonnet member includes cal­ Hill counties, central Texas. cium montomorillonite, sodium montmorillonite, kao­ The Bluebonnet member consists of 10 to 20 feet of linite, illite, gypsum, quartz, calcite, rhodochrosite, and limestone, shale and bentonite beds. Three zones are carbon. Only calcium montmorillonite, kaolinite, cal­ recognized within the member, each based on lithology cite, and carbon were used for geochemical interpreta­ and microfaunal abundance. A zone is not necessarily tions. Calcium montmorillonite reaches maximum time-equivalent throughout the area, but each represents abundance in Bell, southwestern McLennan and central a distinctive depositional environment. counties. The amount of kaolinite and carbon Limestone beds (1-12 inches thick) grade upward varies inversely with calcium montmorillonite content, from fine to medium-grained, well sorted, cross-bedded, whereas calcite varies directly with calcium montmoril­ ripple-marked biosparites to fine-grained, lonite content. Rhodochrosite is locally present in cen­ structureless Foraminifera biomicrites. Northward along tral McLennan and southern Hill counties. the outcrop the lower limestone beds (zone 1) are It is concluded that the Bluebonnet member is a Inoceramus biosparites in Bell and southern McLennan lagoonal deposit. Four stages of development are counties, Foraminifera biomicrites in central McLennan late youth, early mature, and mature. County, Inoceramus biosparites in northern McLennan The stage was characterized by bay-mouth bar County, biomicrites in southern Hill County and Ino­ and inlets as suggested by subsurface and surface data. ceramus biosparites in central Hill County. Limestone Field and petrographic data indicate cuspate and midbay beds in the middle and upper part of the member bars which are characterized by limestone beds ex­ (zones 2 and 3) are biomicrites except in Bell and hibiting high energy sedimentary structures, good sort­ southwestern McLennan counties where locally Ino­ ing and sparry calcite cement. Values of pH were ceramus biosparite beds occur in the middle part of the slightly alkaline and the Eh was probably positive or member. oxidizing. Shale beds are gray to black, thinly laminated, Late stage of the Bluebonnet lagoon was calcareous and contain abundant planktonic foraminifers. characterized by recession of the cuspate bar and mid- No benthonic megafossils were observed in the shales. bay bar forming a secondary cuspate bar. Shale deposi­ Shale beds are more thinly laminated in the middle tion was dominant in central and northern McLennan, part (zone 2) of the member than in the lower or upper and Hill counties. Marsh deposits occur in Hill County. parts (zones 1 and 3). Lamination is best developed in Values of pH in the southern half of the lagoon were central McLennan and southern Hill counties. Shale slightly alkaline, whereas in the northern part they were is the dominant lithology in the upper two-thirds slightly acidic. Values of Eh were positive (zones 2 and 3) of the member. near bar areas, but slightly negative (reducing) in the Bentonite beds inches thick) are more numer­ northern half of the lagoon. ous and thicker in central McLennan and southern Hill of the secondary cuspate bar and slight counties. Bentonite beds contain calcium montmoril- landward migration of the baymouth bar occurred lonite, kaolinite, sodium montomorillonite, and quartz, during early mature stage of lagoonal development. in relative order of abundance. Bentonite are Peripheral marsh deposits in the lagoon gradually con­ commonly reworked and laterally discontinuous. stricted the basin. Values of pH in the basin were 6 BAYLOR GEOLOGICAL STUDIES

ADAPTED FROM

MAP OF THE

UNITED STATES"

Fig. 1. Index map. CRETACEOUS BLUEBONNET LAGOON 7 acidic, and Eh values were negative. cent decrease in original sedimentary thickness. The lagoon was filled by marsh deposits Cementation of the bar-deposited limestone beds was during the mature stage of development. Water in the due to primary precipitation of sparry calcite and later lagoon was Eh was negative. Lagoonal sediments pressure solution. Recrystallization, a common dia- were covered and preserved by gray, thinly laminated genetic process in the member, nearly destroyed original shale deposits (Cloice member) of the transgressing sea. depositional fabrics in the upper limestone grain processes exhibited in the Blue- seeding and grain growth are two most prominent types bonnet member include compaction, cementation and re- of recrystallization. cry.stallization. Compaction resulted in about a per­

PURPOSE for many years. Ferdinand Roemer p. 68) called the black Eagle Ford shales the "fish beds." In The Bluebonnet member of the Lake Waco formation 1860, B. F. Schumard described rocks now assigned to (Upper Cretaceous) of central Texas has long been the Eagle Ford group, following earlier studies by his of interest to geologists because of complex lithologic brother, G. G. Schumard. B. F. Schumard applied relationships, sedimentary structures and the name "Marly Clay or Red River group" and placed variations which clearly distinguish it other Upper the unit above the Woodbine formation, but he incor­ Cretaceous rocks of the region. rectly considered it the base of the Cretaceous section. Earlier work by Chamness (1958) and Silver (1959) Marcou (1862) placed the "fish beds" of Roemer be­ considered the gross aspects of the member. Silver neath the Austin chalk. J. A. and S. Leverett {idem) suggested that Bluebonnet sediments were de­ (1893) first identified many of the Eagle Ford fossils. posited in a lagoonal environment, and further con­ In 1887 R. T. Hill applied the name "Eagle Ford cluded that much of the original sediment of the postu­ group" to this unit. In 1901 Hill more completely lated Bluebonnet lagoon is preserved along the present described the Eagle Ford group. Prather later (1902, outcrop or immediately eastward in the subsurface. p. 61) divided the Eagle Ford group into the South The purpose of the present study was to extend the Bosque and Eagle Ford formations, but included with­ scope of the earlier investigations {idem) and to under­ in the latter, rocks now assigned to the Pepper forma­ take other studies which might contribute to a more tion. complete and accurate interpretation of Bluebonnet dep­ Pace (1921) completed a reconnaissance geologic osition. study of McLennan County. She considered the This investigation considers the following major as­ shale between the Buda formation and lowermost lime­ pects in compiling and interpreting data pertaining to stone beds of the Eagle Ford (Pepper formation) a the geologic of the member : part of the Eagle Ford group {idem, p. 4). Adkins gross configuration and lithology; (2) distribution (1923) mapped the Eagle group in McLennan and significance of clastic sediments; (3) significance County, and later (1928; 1932, p. 434) identified fos­ of faunal variations; (4) postulated geochemical en­ sils of the Eagle Ford, but he contributed little strati- vironments ; (5) postulated sedimentary environments ; graphic data. and (6) diagenetic on the sediment. Adkins and Lozo (1951, p. 120) divided the Eagle Ford into the South Bosque and Lake Waco formations. LOCATION They further divided the Lake Waco formation into 3 The area of study includes portions of Bell, McLen­ Cloice and Bluebonnet in de­ nan, Hill, Falls, and Limestone counties in central scending order. The type locality of the Bluebonnet Texas (fig. 1). member is ". . . along the Bosque escarpment from the old south Bosque brickyard southwest into the Moody Hills, then PROCEDURES southward past Moody, McLennan County, Texas. The A field study of the Bluebonnet member was com­ type section is opposite Bagget's Station [154-B-402] east of State Highway 317, about miles south-south­ pleted including mapping, description, and collections west of McGregor" (Adkins and Lozo, p. 120). for laboratory analyses. A review of the literature re­ lating to the Bluebonnet member and lagoonal deposi­ ACKNOWLEDGMENTS tion was an early phase of the study. Laboratory pro­ cedures included peels and petrographic thin section Appreciation is extended to Professors O. T. Hay- studies of limestones, micropaleontological studies, min- ward, L. F. Brown, Jr., and Walter T. Huang, De­ eralogic analyses by X-ray diffraction, carbon analyses, partment of Geology, and Professor James T. McAfee, and carbonate analyses. Department of Chemistry, Baylor University, for guid­ ance and special help the project. Mr. Glenn PREVIOUS WORK McKinley, Skelly Oil Company, critically read the manuscript. The National Science Foundation spon­ The Eagle Ford group, which includes the Blue­ sored the research during the summer of 1961. My bonnet member, has been a formal stratigraphic unit wife, Linda, assisted in laboratory studies and prep­ aration of manuscript. thesis submitted in partial fulfillment of the requirements for the M.S. degree in Geology, Baylor University, 1963. 2Refer to locality on figure 2 and in Appendix 8 BAYLOR GEOLOGICAL STUDIES

STRATIGRAPHY

REGIONAL GEOLOGY

The area of study (fig. 1) is near the interior bound­ member at the surface in southern Bell, central Mc­ ary of the Gulf Coastal Plain of Texas. Quaternary Lennan, and central Hill counties (fig. 2). Cretaceous and Cretaceous rocks crop out in the Quaternary rocks strike northeastward, and dip southeastward; rocks are unconsolidated stream deposits and Creta­ west of the Balcones fault zone Cretaceous rocks dip ceous strata consist of limestone, calcareous shale and approximately 30 feet per mile, but east of the zone poorly cemented sand. the dip increases to about 90 feet per mile. Cretaceous The boundary between Lower and Upper Cretaceous rocks thicken eastward into the Tyler basin. rocks approximately coincides with the north-south Periodic transgression and regression of Cretaceous trending Bosque escarpment, which also marks the seas is indicated by several unconformities and sharp western edge of the Balcones fault zone (fig. 1). In lithologic and faunal changes in the Cretaceous section. this area the Balcones fault zone is composed of down- Lower Cretaceous rocks overlie Paleozoic strata in to-the-coast normal faults of large displacement the western part of the area and truncated Jurassic (?) feet) and numerous smaller compensating faults. The strata in the eastern part in McKee, et Balcones fault zone cuts the outcropping Bluebonnet

GENERAL DESCRIPTION

RELATIONSHIP TO ADJACENT UNITS Along the outcrop limestone beds compose approx­ imately 50 percent of the Bluebonnet member in central The Bluebonnet member unconformably overlies the Bell County, 15 percent in southwestern McLennan Pepper shale in the southern half of the map area (fig. County, 12 percent in central McLennan County, 17 2). The unconformity is indicated by (1) Bluebonnet percent in northern McLennan County, 35 percent in limestone fiUing cracks in the top of the Pepper shale southern County and 15 percent in central VII, fig. A), (2) a thin layer of phosphate nodules County (Appendix II). and sharks teeth along the contact V, fig. B), and (3) abrupt change in microfaunal aspect. Shale content in the Bluebonnet member increases In northern McLennan and Hill counties, the Blue­ northward. In central Bell County shale comprises bonnet member overlies sand of the Woodbine forma­ approximately 45 percent of the Bluebonnet member, tion. An unconformable contact is suggested by (1) in southwestern McLennan County 75 percent, in cen­ sharp change in lithology, (2) thin layer of phosphate tral McLennan County 78 percent, in northern Mc­ nodules and sharks teeth along the contact, and (3) Lennan County 80 in southern Hill County 85 distinctive faunal assemblages. percent, and in central Hill County 65 percent. The The Bluebonnet member appears to be gradational northward increase of shale occurs at the expense of with the overlying Cloice member since there is no limestone and bentonite. observable break in lithology or fauna. Lateral changes in the amount of shale within the member also coincide with color changes in the shales. GROSS LITHOLOGY In Bell and southern McLennan counties, the shale beds The Bluebonnet member averages 15 percent lime­ of the Bluebonnet display vertical changes upward from stone, 80 percent shale and percent bentonite. gray to black to light each color includes ap­ Limestone beds are lenticular, black to gray, fine to proximately one-third of the member. Lateral color medium-grained, cross-laminated, porous, fossiliferous, changes occur which are similar to the vertical color and weather gray to They are more abundant in variations; shale beds in southern Bell and McLennan the lower half of the member; the limestones commonly counties are gray, whereas those in central McLennan grade upward through the Bluebonnet from County are black, grading into light gray shale beds in gray, medium-grained, cross-bedded, clear crystalline southern Hill County. calcite-cemented, clastic limestone to dark gray, fine­ Bentonite beds of the Bluebonnet member are from grained, cross-laminated, chalky, foraminiferal lime­ of an inch to 10 inches thick, and are most commonly stone. composed of calcium montmorillonite. The thickest At numerous exposures limestone beds occur at sim­ bentonite beds occur in the upper part of the member ilar stratigraphic positions (fig. 12). However, except in southwestern and central McLennan County. In for the basal limestone bed, the of the other the map area bentonite beds increase in number and limestone beds is easily demonstrated since they can thickness northward to central McLennan County and rarely be traced for more than 200 yards. The basal then correspondingly decrease northward into Hill limestone bed is probably continuous in Bell and south­ County. In Bell County bentonite comprises approxi­ ern McLennan counties, but is absent in central Mc­ mately 1 percent of the Bluebonnet member, in south- Lennan County. A basal limestone bed of similar McLennan County 10 oercent. in northern lithology is present in parts of northern McLennan and McLennan County 3 percent, and in Hill County less southern Hill counties. than 3 percent. CRETACEOUS BLUEBONNET LAGOON 9

Fig. 2. Outcrop, and locality map, Bluebonnet member, Lake Waco formation, central Texas. 10 BAYLOR GEOLOGICAL STUDIES

ZONATION

Correlation of individual limestone and shale beds Zonation is not necessary to explain the environment is not possible by either field or laboratory means. Sim­ of deposition, but it facilitates the study of vertical and ilar lithologic sequences, however, occur throughout the lateral fades variations of the member. area. The Bluebonnet member can tentatively be di­ A zone is not necessarily time-ec|uivalent throughout vided into 3 zones (fig. 12). the region, but at any locality the 3 superimposed zones Zonation is on lithology and faunal represent deposition in succeeding environments. Sed­ abundance. The lithology, mineralogic composition, imentation was most rapid near-shore in that part of and microfaunal population of 9 exposures of the Blue- the Bluebonnet basin in Bell, Coryell, and Hill counties. bonnet member are illustrated in figure 12. Each zone At any given time the shoreward perimeter of the Blue­ is bounded by limestone beds are similar in thick­ bonnet basin was being filled by prograding land-de­ ness and almost identical in texture and mineralogy. rived sediments, while lagoonal sedimentation was still Shale beds in each zone are similar, including color in progress in the center of the basin. Therefore, the and degree of lamination. Furthermore, shale beds in zones may be more nearly time-equivalent in an east- each zone have similar m.crofaunal abundance (fig. 12). west direction than in a north-south direction.

SEDIMENTARY PETROLOGY

Mineralogic variations within the Bluebonnet member bed is an alternating micrite-sparite with were determined by petrographic and X-ray diffraction sparite predominant in the lower half and micrite in methods. the upper portion. This may indicate a change from relatively high energy deposition to low energy, since this is the last occurrence of a large amount of sparry LIMESTONE PETROLOGY calcite in this exposure. The upper 1 inch of the bed is cross-bedded micrite and sparite with foraminifers Polished and etched slabs, acetate peels and petro­ concentrated in the sparry cross-beds. Several burrows graphic thin sections of limestones were studied to de­ filled with crystalline calcite occur in this bed IX, termine internal sedimentary features after the field fig.E). relationships of the limestone beds had been determined. The third limestone bed from the base fig. Types and amounts of clay minerals in each limestone D) is the lowermost micrite. In the center of this 5- were determined by X-ray Petro­ inch bed are several laminae composed of Inoceramus graphic terminology and concepts proposed by Folk fragments cemented by sparry calcite. Thus, the bed 0959) and Bathurst (1958) are combined in a manner grades upward from micrite to alternating laminae of similar to that proposed by (1962) in de­ sparite and micrite and back to micrite. An uneven, al­ scribing and interpreting carbonate thin sections. most ripple-marked, micrite-sparite boundary occurs Limestones at 2 exposures, in southwestern Mc­ near the center of an acetate peel illustrated in PL Lennan County (154-B-41) and in central McLennan III, fig. D. This bed contains the first occurrence of County (154-B-43), are described to illustrate typical broken Inoceramus shells which do not show abrasion. vertical variations. Limestone beds at other exposures This suggests lower mechanical energy than in either are described in Appendix II, figures 3-11 and Plates of the underlying limestone beds. MX. The upper limestone beds at locality are VARIATIONS classified as Foraminifera biomicrites. Bed 14 is the only bed which contains substantial amounts of lam­ Locality lowermost Bluebonnet lime­ inated sparry calcite. Several laminae near the top of stone bed in southwestern McLennan County this bed are composed of Inoceramus cemented 41, fig. B) is a 4-inch biosparite. by sparry calcite. Each bed contains abundant discrete Patches of micrite occur throughout the bed. However, grains of hematite and magnetite. Many planktonic larger grains in the micrite areas are in optical conti­ foraminiferal tests contain hematite grains. nuity. This suggests that the rock has undergone grain growth in diagenesis. Planktonic foraminifers are Locality limestones in central present but not abundant in this limestone. Some for- McLennan County are normally biomicrites. The low­ tests are filled with radiating calcite crystals, ermost limestone bed (154-B-43, V, fig. B) is an whereas tests of others are recrystallized in optical argillaceous fragmental limestone containing phosphate continuity with large sparry grains. Grain size and nodules and pyritized plant fragments. The overlying ])resence of abundant fragments indicate limestone (idem, fig. C) is a Foraminifera biomicrite sustained, relatively high wave or current in which has undergone soft-sediment deformation (e.g., the depositional area. PL IX, fig. F). Such structures as load-casting, con­ The next overlying limestone bed fig. C) torted bedding, and flow structures are common. The is separated from the lower limestone by a 1-inch cal­ cium montmorillonitic bentonite. This limestone bed prisms are disaggregated, wedge-shaped or is classified as a Foraminifera biosparite. The 6-inch needle-like, calcite crystals (pseudomorph after aragonite) which originally composed the inner layer of Inoceramus shells. Original aragonite crystals were oriented at right angles to the 3Refers to mechanical energy, such as winnowing current, shell surface. The crystallographic C-axis is parallel to the and/or wave action. long dimension of the crystals. CRETACEOUS BLUEBONNET LAGOON 11 planktonic foraminifer is abundant in this This resembles the basal beds at two of the pre­ bed ; a few Giimbelina are present. ceding localities 2). Allochems The remaining limestone beds (PL V, figs. D, E) prisms) are more closely spaced, which may explain contain no benthonic fauna. The ripple-marked texture why pressure solution is common. Carbon content of and the presence of anhydrite are unique in limestone the limestone bed is lower than at the preceding local­ beds at this exposure. ities. Planktonic foraminifers are not abundant. Other limestone beds are lam­ Approximately 2 miles east of the preceding locality inated. Three possible origins of laminae are the basal limestone bed (154-B-41, PL III, (1) periodic variations in mechanical energy II, fig. B) is 4 inches thick. This bed has previously been fig. A), (2) chemical variations in the depositional area described (p. 10). A few foraminifers occur in the which resulted in alternating orthochemical constituents upper part of the bed. Hematite and magnetite occur VIII, fig. B), and (3) influx of different kinds of as discrete this is the southernmost occurrence clastic material fig. C). of heavy minerals in the basal limestone bed. Another prominent feature of many limestone beds About 4 miles south of McGregor, McLen­ is a layer of fossil detritus embedded in a micrite matrix nan County, and 4 miles northwest of the previous IV, fig. D; PL VIII, fig. B). In most beds that locality, the basal limestone bed (154-B-40, PL fig- this characteristic, the detrital fossil layer is A) is a gradational micrite-sparite sequence. At this approximately to of an inch thick and bordering exposure the basal limestone bed is 4 inches thick. The micro-crystalline calcite ranges from 2 to 4 inches bed is classified as a Foraminifera biomicrite-biosparite. thick. Fossil fragments appear to have been dumped Cross-laminae are well the laminae are com­ into a lime mud area during a short period of increased posed of Inoceramus fragments and foraminifers alter­ agitation. In this case a micrite matrix does not neces­ nating with micro-crystalline calcite. The alternation sarily indicate a low energy environment because of coarse and fine particles may represent an area be­ fragments display abrasion (PL VI, fig. C). tween high and low energy. Approximately 8 miles east-northeast of McGregor, McLennan County (154-B-42), the basal limestone is LATERAL VARIATIONS classified as a Foraminifera biomicrite. Very few al­ It was concluded (p. 10) that limestone beds lochems, with the exception of foraminifers, are em­ of the Bluebonnet member are not laterally continuous bedded in the predominantly micro-crystalline calcite. even though similar beds and similar sequences occur Loadcasting, contorted bedding, and other soft-sedi­ at several localities. However, it was noted (p. 8) ment deformation structures are common (PL IV, fig. that the basal limestone bed of the member is continuous B, and PL IX, fig. F). The bed was probably de­ over certain parts of the mapped area. posited in a sustained low energy environment as sug­ Southeast of Belton, Bell County the basal gested by the fine-grained texture and distinctive sedi­ limestone bed (PL I, fig. A) is a 7-inch thick Foram- mentary structures. inifera biosparite which has undergone grain growth About 5 miles west-southwest of Waco the during diagenesis. It exhibits, therefore, the coarsest basal limestone bed (154-B-43, PL V, fig. C) is 6 inches texture of any limestone of the Bluebonnet member. thick and classified as a Foraminifera biomicrite. The Recrystallization and grain growth occurred in 2 stages abundance of foraminifers and heavy minerals com­ to bedding and approximately to bedding. pares closely with those of the preceding locality. The Recrystallization is evidenced by (1) patches of orig­ brackish-water foraminifer, is abundant. Re­ inal micro-crystalline calcite, (2) optical continuity of crystallization of micro-crystalline calcite to microspar larger grains, (3) gradational contact between coarse is common near the top of the bed. fine grains, and (4) relic foraminifers composed Because of Balcones faulting the Bluebonnet mem­ of sparry calcite, which is in optical continuity with ber and most of the Eagle Ford group are absent at some of the surrounding grains. The relative sequence the surface for about 5 miles northeast of Waco, Mc­ of recrystallization can be determined, since the second Lennan County. In northern McLennan County the phase of grain growth to bedding) truncates the basal bed PL VI, fig. A) is a phase parallel to bedding. Inoceramus biosparite. The predominant allochems West of Temple, Bell County, approximately 4 miles are Inoceramus prisms and a few foraminifers. Hema­ north of the exposure described above, the basal lime­ tite and quartz are more common than at the preceding stone (14-B-2, PL I, fig. D) is composed predominantly locality. Higher energy (in comparison with the two of prisms cemented by sparry calcite. These previously described localities) is indicated by coarse prisms are widely dispersed, but where in contact, grains, cross-bedding and ripple-marked upper surfaces. pressure solution has occurred. This may be a source Patches of micrite matrix may have resulted from re­ of sparry cement ancl also suggests cementation after crystallization during diagenesis, but in this case it is deep burial. The paucity of planktonic foraminifers in probably due to incomplete winnowing of finer particles this limestone bed suggests that either depositional en­ by high energy currents. ergy removed the tests, or that they simply were not Approximately 17 miles north of Waco the basal bed is similar to that near Waco (154-B-43). The basal In northern Bell County (14-B-3, PL IX, fig. A) the bed (154-B-45, PL fig- B) is a structureless bio­ basal limestone bed is a 4-inch thick biopelmicrite. micrite. A few allochems such as frag­ In southwestern McLennan County (154-B-46) the ments and foraminiferal tests are embeckled in micro- basal limestone bed (PL IX, fig. B) is 14 inches thick, crystalline calcite. Fibrous calcite radiating small the thickest bed of limestone observed in this study. grains of hematite is common near the top of the 12 BAYLOR GEOLOGICAL STUDIES CRETACEOUS BLUEBONNET LAGOON 13

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. - 14 BAYLOR GEOLOGICAL STUDIES

CRETACEOUS BLUEBONNET LAGOON 15 16 BAYLOR GEOLOGICAL STUDIES

The hematite, which may have been con­ black shales of northern Bell and McLennan counties centrated in foraminiferal tests, may have seeded grain contain abundant disseminated carbon, whereas the growth. Thus, the appears to be recrystallizing to light gray shales, which weather tan in Hill County, microspar. have a ferrous iron pigment. In south-central Hill County the The northward increase in shale content in the Blue­ bonnet member is primarily caused by northward re­ limestone bed VII, fig. D) is a 7-inch placement of limestone by shale in the upper 2 Bedding planes are common but the lime­ stone is predominantly homogeneous Se­ zones of the member. Most of the Bluebonnet shale is well laminated. In­ lective recrystallization of fragments has dividual laminae decrease in thickness upward from occurred, normally the lied appears to possess its zone 1 to zone 2, and become thicker and less distinct original depositional fabric. in zone 3. North along the outcrop from Bell to cen­ Approximately 24 miles north of Waco the basal tral McLennan County, laminae become thinner and hmestone (109-B-16, VIII, fig. A) is a 4-inch more distinct. From central McLen County north­ biosparite. The bed contains a high con­ ward, laminae increase in thickness and become less centration of moderately rounded detrital quartz which distinct. decreases upward from the base. Hematite and magne­ The mineralogy of the shales was determined by X- tite are common throughout the bed. The dominant ray diffraction and chemical analyses. Variations in allochems are closely packed Inoceramus prisms. Cross- clay, quartz, calcite, and carbon content were particu­ bedding occurs near the top of the bed. Coarse grains larly useful in interpreting the depositional environment. and cross-bedding indicate high, sustained depositional Tabulated mineral data and procedures related to min­ energy. eral analyses are described in Appendix III and V, In central Hill County (109-B-17) the basal lime­ respectively. stone bed VIII, fig. D) is an Inoceramus biospar­ Calcium montmorillonite and kaolinite are the dom­ ite. The dominant allochems are Inoceramus prisms, inant clays of the Bluebonnet minor amounts whereas the dominant terrigenous constituent is quartz. sodium montmorillonite and illite are present. Other The quartz is poorly rounded and fine-grained, and is constituents are gypsum, quartz, calcite, and carbon. texturally similar to Woodbine sand. The quartz con­ tains overgrowths which appear to have been etched. This "etching" is probably due to incomplete overgrowth MINERALOGIC VARIATIONS resulting from a relatively low pH environment during Calcium Pepper shale at all most of Bluebonnet time. except southeast of Belton fig. 3), The northernmost exposure of the basal limestone contains a substantial amount of calcium montmorillon­ bed is approximately 5 miles west of Hillsboro, Hill ite, a greater percentage than normally occurs in the County. Here, the basal limestone bed (109-B-18, Bluebonnet member. At most localities calcium mont­ IX, fig. G) is an 8-inch thick biomicrite. Allochems morillonite in the Bluebonnet member (fig. 12) increases are very large, including whole specimens of Inocera­ upward, which may indicate a gradual change to normal mus. ammonites and fish vertebrae. Most Inoceramus marine conditions, or more likely, an increase in abund­ shells were macerated by shell-crushing ani­ ance of thin calcium montmorillonitic bentonite mals rather than mechanical energy, since the Inocera­ which raises the average percent in the upper shales. mus fragments contained in a micrite matrix show no Thicker beds in zone 1 were sampled indi­ abrasion. vidually. The calcium-sodium ratio of the calcium Lateral changes in the overlying limestones are more montmorillonite in the Bluebonnet member is approxi­ subtle than those of the basal bed. The upper lime­ mately 4:1. stones (zone 3) are absent in central Bell County (14- montmorillonite 2) and are best developed in McLennan County. is a minor constituent in the Pepper shale, as well as in The number of upper limestone beds decreases north­ the Bluebonnet member. Sodium montmorillonite is ward from Waco into Hill County. This variation is in the member at only 6 of the with a decrease in the amount of allochems localities studied. The calcium-sodium ratio of the and an increase in quartz and hematite content. dominant sodium montmorillonite in the Bluebonnet member is about 1 :4. The presence of sodium mont- may indicate near-shore deposition or a SHALE PETROLOGY area, which provided abundant calcium mont­ Shale beds were studied in terms of field relation­ morillonite. ships, mineralogic facies, and microfaunal population. formation contains Changes in color, shale-limestone ratios, and degree of illite in southern Hill County figs. 9-11). lamination were observed in the field. In Bell and Mc­ In this area the Bluebonnet member contains some il­ Lennan counties the color of shale beds changes upward lite in zone 1 (fig. 12), which may indicate that the from gray to black to light gray. Gray shale beds oc­ formation was the clay source for cur in zone 1 (fig. ; black shale beds occur in zone the Bluebonnet member. If so, the small amount of and a gradational color change from black to gray in the Bluebonnet member is since to light gray takes place in zone 3 of the Bluebonnet the Pepper and Woodbine formations each contain over member. Light gray shales characterize the overlying 40 percent Illite occurs in the Bluebonnet mem­ Cloice member. ber only where it occurs in the underlying Pepper- - Northward along strike the shale beds grade from Woodbine formation. gray shales of southern Bell County to gray to black most localities similar amounts of shales of northern Bell and McLennan counties, and occur in the Pepper formation and in the finally to the light gray shales in Hill County. The member. At 7 of 9 exposures illustrated CRETACEOUS BLUEBONNET LAGOON 17 in figure 12, kaolinite increases upward in the Bluebon- 3. If this occurrence in zone 3 is time-equivalent with net member, possibly reflecting a decrease in pH during sodium montmorillonite of southwestern McLennan deposition. Flocculation rates may determine the site County in zone 2, it can be assumed that the zone 3 of kaolinite, illite, and montmorillonite deposition. How­ facies is progressively younger southwestward. ever, flocculation is not considered a mechanism for In central County (109-B-17; fig. 11) sodium clay mineral segregation in the Bluebonnet basin montmorillonite occurs in zone 1. cause, as will be developed later, (1) circulation was varies from 0 to 20 percent in apparently poor, limiting means of transporting clastic the Pepper shale. Kaolinite increases northward along clays, (2) Bluebonnet basin was small, reducing the the outcrop to Waco, McLennan County, decreases effect of flocculation rates, and (3) the slightly in south-central Hill County (109-B-16; fig. 10) source of must have been immediately west of and then increases substantially in central Hill County. the basin in Bosque, Coryell, and western counties, Kaolinite is the second most abundant clay in the yet no east-west lateral gradation of illite-kaolinite- Bluebonnet member (fig. 12). Kaolinite content varies montmorillonite was observed in the Bluebonnet mem­ inversely with the calcium montmorillonite content along ber. the outcrop, which may reflect a pH control during general gypsum content increases deposition. This is further suggested by lateral varia­ slightly upward in the Bluebonnet member. Gypsum is tions in calcite in the Bluebonnet member. a weathering product. Crystals cutting shale laminae uniform lateral variation in gypsum and a rather heterogeneous vertical variation indicate content was noted in the Pepper formation. Likewise, secondary occurrence. no significant distribution pattern in gypsum content is a major constituent in the Pep­ occurs in the Bluebonnet member (fig. 12). Petro- per-Woodbine formation, but it occurs in minor amounts graphic relationships suggest a secondary origin. in the basal part of the Bluebonnet member (fig. 12). normally increases northward in Quartz normally increases upward in the Bluebonnet the Pepper formation. An abrupt increase occurs in member except in central Hill County (109-B-17; fig. northern McLennan and southern Hill counties where 11) where the quartz content is vertically uniform. sand of the Woodbine formation grades southward into This general upward increase may be due to more rapid shale of the Pepper formation. erosion of Woodbine sand or a prograding shoreline Quartz composes from 5 to 15 percent of the Blue­ during upper Bluebonnet time. bonnet member (fig. 12). The most abrupt increase in is absent in the Pepper shale, except quartz occurs in Hill County, where Pepper shale grades at 2 localities near Belton, County 2; fig. into Woodbine sand. This northward increase in 3). Calcite is the dominant carbonate in the Bluebon­ auartz in the Bluebonnet member is relatively uniform net member (fig. 12) ; it gradually decreases upward, throughout the section, indicating that Woodbine sand possibly reflecting decreasing pH during deposition was exposed in the source area of the Bluebonnet sedi­ which is also suggested by a corresponding increase in ments. kaolinite content. Pepper shale contains some calcite at content increases upward in the the two southernmost localities in Bell County (14-B-l, Bluebonnet member (fig. 12) at most localities in Bell fig. In northern Bell and southern McLennan and McLennan in Hill County carbon content counties the Pepper shale is however, decreases upward. Increasing carbon content may in­ it again becomes calcareous in northern McLennan and dicate decreasing Eh during deposition; this relation­ southern Hill counties as it grades into the ship suggests that the abundant hematite in the upper sand, which has calcite cement. part of the Bluebonnet member is secondary after The amount of calcite in the shale beds of the Blue­ pyrite, since primary hematite normally would not be bonnet member commonly decreases northward in all concentrated in a negative or reducing environment. 3 zones. In Bell County the Bluebonnet shales average 60 percent calcite, in McLennan County 55 percent, and in Hill County 50 percent. This northward decrease LATERAL MINERALOGIC VARIATIONS in calcite is indicative of a northward decrease in pH Calcium during deposition. This is further substantiated by a constitutes from 0 to 30 percent of the Pepper shale general northward decrease in calcium montmorillonite northward along the outcrop. and an increase in kaolinite. Laterally in zone 1 of the Bluebonnet member (fig. in zone 1 of the Bluebonnet mem­ 12) the calcium montmorillonite content varies ber normally increases northward across the area from with the limestone content. No significant change oc­ 1 to 20 percent (fig. 12). curs in zones 2, 3. In zone 2 carbon increases from 2 percent in Bell Sodium only 2 localities, south­ County to 10 percent in central McLennan County and west of Waco, McLennan County (154-B-42; fig. 6) decreases to 0 in southern Hill County (fig. 12). This and in southern Hill County fig. 9), sodium same pattern is repeated in zone 3. The abnormally montmorillonite is present in the Pepper shale. high carbon content in central Hill County (109-B-17; Sodium montmorillonite is a minor constituent in the fig. 11) is due to the presence of coal beds in the sec­ Bluebonnet member (fig. 12). Sodium montmorillonite tion (Appendix II). has been recognized at 5 localities in McLennan County figs. 4-8) and 1 locality in Hill County SUMMARY (109-B-17; fig. 11). At 3 of these localities in Mc­ Lennan County sodium montmorillonite Vertical and mineralogic variations in the occurs at successively higher stratigraphic positions Bluebonnet shale beds include (1) vertical variations northward in zone 2. West-southwest of Waco (154- in iron content as denoted by a vertical color change fig. 7), sodium montmorillonite occurs in zone from gray to black to light gray in zones 1, 2, and 3 BAYLOR GEOLOGICAL STUDIES

CRETACEOUS LAGOON 19 20 BAYLOR GEOLOGICAL STUDIES

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22 BAYLOR GEOLOGICAL STUDIES respectively; (2) vertical decrease in long-term depo- Lateral variations in and mineralogy include sitional energy as indicated by the upward decrease in a northward decrease in the prominence of laminae the amount, size, and abrasion of allochems in the lime­ in the shale beds suggesting a general northward in­ stones ; vertical variation in laminae in the shale crease in long-term depositional energy; (2) a north­ (4) the similar distribution of illite in the Pepper- ward increase in land-derived coarse suggesting Woodbine formation and the Bluebonnet member sug­ a dominant source to the north, probably of gesting a Pepper-Woodbine source for much of the origin; (3) a significant variation in carbon content in member : (5) upward increase in quartz in all 3 zones, suggesting changing sedimentary the Bluebonnet member indicating a prograding shore­ and (4) a northward decrease in calcite and calcium line ; and (6) gradual upward decrease in calcite and montmorillonite content and a northward increase in calcium montmorillonite and an upward increase in kaolinite suggesting a slight northward decrease in suggesting a gradual decrease in Eh and pH and Eh during deposition. Bluebonnet deposition.

PALEONTOLOGY

The flora and fauna aid in interpreting the deposi­ specimens of the fish Sepforia were found in northern tional environment of the Bluel)onnet member. In ad­ Hill County (109-B-18). Fish teeth and scales are dition, the distribution and abundance of the planktonic abundant throughout the member. Teeth are con­ microfauna may indicate current directions. centrated along the basal contact. Preservation of ver­ tebrates is probably due to absence of benthonic scav­ MEGAFOSSILS engers during shale deposition as indicated by the ab­ sence of benthonic fossils and the thinly laminated na­ The stratigraphic distribution of megafossils in the ture of the black shales. Bluebonnet member has been studied by Adkins (1928), Moreman (1942), Adkins and Lozo (1951), and MICROFOSSILS Stephenson (1955). Six genera and 13 species have been reported from the Bluebonnet member. A detailed study of Foraminifera was undertaken with Ammonites, which have received greatest attention the following objectives: (1) correlation of the upper of their importance in correlation, have been shale beds, (2) delineation of the relative energies and equated with Cenomanian ammonites of Europe. directions of local currents, and (3) determination of longsdalei, A. beilense, A. A. sedimentary environment through ecological relation­ stephensoni, A. leonense, Man- ships. telliceras tarrantense, Tur- The abundance of microfauna in a cubic centimeter rilites and have been reported of washed shale residue is illustrated in figures 4-11. from the member. Ammonites are most Techniques followed in the study are de­ abundant in the lower part of the Bluebonnet member, scribed in Appendix results of the analyses are re­ although the uppermost limestone bed contains Desmo­ corded in Appendix IV. Microfossil studies were lim­ ceras. Ammonite abundance is also related to the lime­ ited to shale beds, since it was not practical to extract stone-type ; they are most common in cross-bedded, rip­ microfossils from however, microfossils in ple-marked, fine to medium-grained limestone beds such the limestones were observed in thin sections I, fig. as units 4 and 2 at localities 154-B-40, 45 respectively A: HI, fig. B). (figs. 4, 9). Units 16 and 18 (154-B-40, 41 respec­ Three genera and 4 species of planktonic foraminifers tively; figs. 4, 5) contain abundant Desmoceras. were amabilis Loeblich and Pelecypods are represented by labiatus Tappan d'Orbignv), and arvanus. They occur in most limestone beds of brittonensis Loeblich and Tappan, the Bluebonnet member. Fragments and prisms Morrow and (Loeblich and Tappan, VL fig. B) are abundant in the lower limestone beds, 1961). whereas whole specimens occur in the upper beds In general, the planktonic microfaunal abundance in­ creases upward in the Bluebonnet member (fig. 12). Where whole specimens occur in lower limestone Lateral variations are not as uniform as vertical changes. beds, they form a coquinoid layer commonly to of The foraminifers are most abundant in all 3 zones in an inch thick at the top of the limestone bed. This may central McLennan (154-B-41, 43) and in north-central indicate (1) the gradual restriction of favorable Hill (109-B-17) counties. conditions resulting in local Shale beds of the Bluebonnet member contain no (2) gregarious nature of Inoccramus, or transport ])enthonic microfauna. It is that the absence of to the present location after death. The first of a benthonic fauna during Bluebonnet shale deposition 2 probably apply since specimens do not indicates unfavorable bottom conditions for benthonic show abrasion due to transportation. life. This may have resulted from toxic bottom Gastropods occur in the Bluebonnet member but absence of food source, unfavorable hydrogen preservation is poor and identification is difficult. The to oxygen ratio in water, or rapidly varying brackish gastropods occur mainly in the upper limestone beds in to marine conditions. The various geochemical indi­ Hill County. cators previously discussed suggest that the main de­ Vertebrates are by numerous genera. termining factor which prevented benthonic life was reptiles as plesiosaurs and mosasaurs have been toxic bottom waters and muds caused by cir­ reported in the Bluebonnet member. Several whole culation. CRETACEOUS BLUEBONNET LAGOON 23

The vertical variation in abundance of both species of The best preserved plants are cycad fragments. Hedbergella is similar (Appendix IV), which suggests Fragments vary from 1 to 10 inches wide and 3 to 21 that their ecology was similar. increases inches long, and are most commonly preserved by car­ upward in abundance more rapidly than Hedbergella bonization. The smaller and by far most common frag­ {idem), which indicates that the ecology of Gumbelina ments of fossil cycad wood were observed in the upper differed from that of Hedbergella. limestone bed at all exposures in McLennan and Hill counties. PLANTS Well preserved spores are common throughout the The member contains abundant plant member, but are most abundant in zone 3. The abun­ material as indicated by the high amount of carbon in dant and highly variable spore-pollen content and other both limestone and shale beds. The amount of carbon floral constituents in the Eagle Ford group have been in the limestone beds in zone 3 is 3 to 5 times greater recently described by Brown and Pierce (1962). Many than the amount of carbon in the limestones in zones 1 charophytes were observed in the shale beds of zone and 2. The amount of carbon in the Bluebonnet shale they are most common in McLennan (154-B-42, 43) beds in zone 3 is about twice that in shales of zones 1 and Hill counties (109-B-16, 17). and 2.

GEOLOGIC HISTORY

BATHYMETRY AND DISTRIBUTION OF CLASTICS

The isopach map 2) shows the extent and the outcropping Bluebonnet member. Poor ex­ topography of the floor of the Bluebonnet basin. Pre­ posures of the thin member prevented mapping the served depositional limits are indicated by the zero iso­ exact northern limit, but it disappears on the outcrop pach line. The exact southern limit of deposition was approximately 9 miles northwest of Hillsboro, Hill not determined, either because the member was faulted County. out by Balcones faulting or Leon River terraces con-

DEPOSITIONAL ENVIRONMENT

The Bluebonnet member is interpreted to be a sparite composed of approximately 80 percent allochems. lagoonal deposit. Lucke (1939) discussed the evolution Interpretation of the area immediately east of the cus­ of lagoons. Various stages in the development of the pate bar within the lagoon is based on exposures in Bluebonnet lagoon are illustrated by the 4 paleogeo- northern McLennan and southern Hill counties (154- graphic maps (fig. 13, A-D) which represent postulated B-45 and 109-B-15). In this area the basal limestone stages in the evolution of the Bluebonnet lagoon. The bed is a Foraminif era shales in zone 1 con­ landward part of the paleogeographic maps is hypo­ tain a large amount of clay and display poorly developed thetical, based on the presence of marginal lagoonal laminae, which suggest that deposition in this part of sediments in zone 3 in McLennan and Hill counties. the lagoon was probably more rapid than in adjacent The youthful stage of the lagoon is il­ areas to the south. Some of the bentonites indicate lustrated by the postulated paleogeography of zone 1 transportation by water because of the absence of glass the Bluebonnet member in Bell, southwestern McLen­ shards. nan, and central Hill evidence this stage Conditions which existed l)etween the cuspate bar is better than for later stages of basin history. The and mid-bay bar are indicated by exposures near Waco bar and inlet are suggested by the isopach (154-B-42, 43). The basal limestone in this area is a map (fig. 2). Since the postulated baymouth bar is not Foraminifera biomicrite, suggesting the absence of exposed at the surface, only limestone beds in the cus- higher energy characteristic of cuspate and/or mid-bay pate and midbay bars have been studied. Abundance bars. Sediments in zone 1 of this area are dominantly and distribution of planktonic microfossils suggest 2 gray to black, thinly laminated, calcareous, fossiliferous additional south-central Hill County near 109- (planktonic microfossils) shales. The relatively small and in southwestern McLennan County near amount of preserved plant material suggests that this Shales at each of these localities contain abnor­ area was near a plant source. Furthermore, the mal concentrations of planktonic microfossils relative amount of calcium montmorillonite is greater than in to adjacent localities, which suggests the presence of an adjacent areas, suggesting more normal marine condi­ inlet into the lagoon. Evidences for the cuspate bar at tions. Foraminiferal content is high in this area, which the north shore of the lagoon are features exhibited by further substantiates the occurrence of the ancient inlet limestone beds in north-central McLennan County as indicated by the isopach map (fig. 2). (1S4-B-44; fig. 8). At this locality large festoon The mid-bay bar is interpreted from exposures in cross-beds and ripple-marks are prominent in the basal southwestern McLennan and Bell counties (154-B-40, limestone bed. The limestone is an Inoceramus bio- 41, 46; 2) where basal limestone beds are cross- BAYLOR GEOLOGICAL STUDIES

26 GEOLOGICAL STUDIES

CRETACEOUS LAGOON 27

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Climatic changes, as well as suggested by the dominance of shale in zone 3, as well the width and of inlets, would have greatly as by Foraminifera biomicrites and micrites. Lime­ affected the turbulence of water in the lagoon. The stone beds of this zone contain a smaller amount of allo­ two bars were, therefore, continuously built and de­ chems and crystalline calcite compared to limestone beds stroyed as shown l)y the varying thickness of the basal in zone in addition, zone 3 limestones do not contain limestone bed. ripple marks or other high energy in­ Reworking of sediments in the Bluebonnet member dicators suggesting bar deposition. by benthonic organisms was limited to the bar-deposited Decreased circulation in the Bluebonnet lagoon, due limestone Boring organisms thoroughly reworked to gradual restriction of the main inlet, is suggested portions of the basal limestone IX, fig. E). The by texture and mineralogy of limestone and shale presence of undisturbed thin laminae and absence of in zone 3. Limestone beds in this zone are very fine­ filled borings in limestone beds deposited in postulated structureless Foraminifera biomicrites. Lime­ marsh environments may indicate toxic conditions stone beds contain a high carbon content, suggesting (and/or lower pH) in the mud areas. In addition heavy plant growth in surrounding marshes and sub­ l)oring organisms perhaps could not migrate from the sequent accumulation in the lagoon. The uppermost bars to the isolated areas of limestone deposition in the limestone bed contains well preserved cycad fragments marshes. and charophytes. The shale beds of zone 3 contain a The shale and limestone beds in zone 2 reflect high amount of kaolinite and carbon, but no benthonic sition during the stage (fig. of the foraminifers, suggesting a low pH environment. Lam­ Bluebonnet lagoon. The absence of a cuspate bar along inae are poorly developed indicating rapid deposition in the northern coast is suggested by the texture and com­ zone 3, relative to zones 1 and 2. Restricted circulation position of the limestone beds in zone 2. Zone 2 lime­ (low energy) is further indicated by a thick bentonite stone beds in northern McLennan and southern Hill bed containing glass shards in the upper part of zone 3 counties are biomicrites. Dominant in McLennan County (fig. 12). lochems are planktonic foraminifers with a few poorly Kaolinite and carbon content reached maximum abun­ rounded, poorly sorted fragments. The dance during this stage of sedimentation, whereas the and matrix suggest a long-term, low energy overall calcium montmorillonite and calcite contents environment. are at a minimum (fig. 12), which denotes a lower pH The recession of the mid-l)ay bar (which was a prom­ and Eh in the depositional environment of zone 3 than inent feature during youth) is evidenced by shale and in zones 1 and 2. This is expected since decaying plants limestone beds in zone 2 in southwestern McLennan should have resulted in sub-normal pH and Eh values. County (1S4-B-40, 41). Limestone beds in zone 2 in Deposition was more rapid along the perimeter of the this area are Foraminifera biomicrites, which are sim­ lagoon than in the open water near the center of the ilar to limestone beds of zone in southern Hill County. Shale beds of zone 2 in southwestern McLennan Coun­ Interpretation of the mature stage (fig. of the ty contain more kaolinite and less calcium montmoril- Bluebonnet lagoon is based on less evidence than the lonite and calcite than shale 1)eds of zone 1 in the same other stages. During this final stage, the lagoon was area. This suggests that the pH in this area during completely filled with marsh deposits and covered by deposition of zone 2 was slightly lower than for zone 1. the transgressing Cloice sea. The cuspate at the southern coast of the Blue­ The overlying Cloice member of the Lake Waco bonnet lagoon during late youth was the remnant of formation is a restricted shallow-water de­ 'the earlier mid-bay bar. This cuspate bar is indicated posit. A low energy, long-term depositional environ­ by limestone beds of zone 2 in central Bell County ment for the lower part of the Cloice is indi­ 2). These limestone beds are Inoceramus l)io- cated by wide-spread thinly laminated shale beds, uni­ sparites and biomicrosparites. Allochems, which con­ formly distributed microfauna, and relatively uniform stitute more than 80 percent of the limestone, are mod­ mineralogic composition in Bell, McLennan, and Hill erately rounded and well sorted. Cross-beds and ripple- counties. A low energy depositional environment per­ marked surfaces are common in these limestones. mitted the preservation of the soft unconsolidated marsh Sedimentation was slower in zone 2 than in zone 1 deposits of zone 3 of the underlying Bluebonnet mem­ as indicated by thinner laminae in shales and lime­ ber. CRETACEOUS BLUEBONNET LAGOON 29

GEOCHEMICAL ENVIRONMENT

It is difficult to determine a given suite of cessary mineral, a pH of 7.0-7.8 is indicated (Krum- minerals reflects sedimentary or diagenetic proc­ and Garrels, 1952). Calcite precipitation is not esses. Ranges of pH and Eh values of ancient affected oxidation-reduction potential, and is, there­ depositional environments, as inferred from con­ not an indicator of Eh in tained minerals, are of questionable value unless the Rhodochrosite, which occurs at localities 154-B-40, minerals can be verified to be primary in origin. In 43 (Appendix III), can be precipitated at a order to verify the origin of contained minerals it and at an (idem). is necessary to expand the number of lines of evi­ The pH and Eh values were high during the youthful dence to include physical and organic indicators, stage (fig. of the Bluebonnet lagoon. Water such as field relationships, sedimentary structures, surrounding the cuspate and mid-bay bars had a pH and fossils. 7.8 as indicated by the abundant calcite (zone 1). The Bluebonnet member was probably deposited in a The Eh have been positive since the water adjacent dominantly low energy, anaerobic environment as dem­ to the bars was oxygenated by agitation as evidenced by onstrated by (1) thinly laminated shale beds, (2) lack well sor'.ed, cross-bedded, ripple-marked, bar-deposited of benthonic fossils in shale beds, (3) abundance of limestone beds composed of shell fragments I, figs. well preserved scales, (4) carbonized plant frag­ A, D). ments, (5) thin lenticular coal seams, (6) predominance Values of pH and Eh were slightly lower between of structureless biomicrite limestone beds, and (7) low the cuspate and mouth bars (Hill County) than in energy soft sediment deformation structures. Low areas adjacent to the bars. This is suggested by a slight energy, anaerobic environments are associated with decrease in the amount of calcite and calcium montmoril­ negative Eh values. Values of Eh were negative both lonite and an increase in kaolinite in the interbar area above and below the depositional interface during de­ in zone 1. position of the Bluebonnet shales, but positive in the The late youthful stage (fig. of the Bluebonnet bar areas (fig. 13). It has been demonstrated (Krum- lagoon was characterized by lower pH and Eh values bein and Garrels, that diagenesis does not than was the youthful stage. The only area of rela­ normally alter primary minerals in a negative Eh en­ tively high pH and positive Eh was near the cuspate vironment. Garrels (1960) has demonstrated that pres­ bar along the southern coast of the lagoon. These high sure and temperature ranges in nature are not suf­ pH and positive Eh values are suggested by limestone ficient to cause a loss of pH-Eh control of mineral beds of zone 2 in central Bell County 2; stability. It is, therefore, concluded that the mineralogic I, figs. B, F), which are moderately sorted and slightly composition of the Bluebonnet member is primary and cross-bedded Inoceramus biosparites, indicating mod­ reflects pH and Eh values during deposition. erately agitated waters. Several geochemical indicators occur in the Blue­ bonnet these are kaolinite, calcium montmoril- The remaining sediments of the Bluebonnet lagoon lonite, calcite, rhodochrosite, and carbonaceous material. during the late youthful stage were deposited at a neu­ Kaolinite and calcium montmorillonite are not inde­ tral to slightly alkaline pH and negative to slightly posi­ pendently good geochemical indicators, but the ratio of tive Eh. These conditions are indicated by a decrease kaolinite to calcium montmorillonite may be important. in the amount of , calcium montmorillonite and calcite, Kaolinite-calcium montmorillonite ratio cannot be and an increase in the amount of kaolinite in zone 2 used as a pH indicator, unless it can be demonstrated shales, relative to zone 1. Eurthermore, in zone 2 the that the clay minerals reflect the environment of depo­ increase of well preserved fish scales and a slight trace sition and were not later altered. Clay minerals in the of rhodochrosite are indicative of an approximately neu­ Bluebonnet member are interpreted to reflect deposi­ tral (0.0) Eh environment. tional environments because little similarity occurs be­ During the early mature stage (fig. of the Blue­ tween the clay mineral suites of the Bluebonnet mem­ bonnet lagoon (zone 3) calcium montmorillonite and ber and underlying Pepper and Woodbine formations, calcite deposition was low, whereas kaolinite deposition probable source of the sediments. was at a maximum. This suggests that the pH was Normally an increase in precipitates calcite, also probably slightly acid during the mature stage. whereas saturation will not be reached in a low pH The Eh values were commonly negative as evidenced by environment. Therefore, abundant calcite suggests a abundant well plant fragments in shales and pH above 7.8 during when calcite is an ac­ rare benthonic fossils in the limestones in zone 3.

BORDERLAND FEATURES

The absence of coarse, land-derived sediments in the areas adjacent to the lagoon, as denoted by texturally limestone and shale beds suggests a land area of low similar quartz grains in the basal Bluebonnet limestone relief adjacent to the Bluebonnet lagoon. The Pepper bed VIII, fig. D) and in the Woodbine formation and Woodbine formations were apparently exposed in IX, fig. D) of Hill County. 30 BAYLOR GEOLOGICAL STUDIES

o o

32 BAYLOR GEOLOGICAL STUDIES

36 BAYLOR GEOLOGICAL STUDIES

HISTORY

COMPACTION area; the gradual lowering of pH within the water, in­ creasing the solubility of calcium It is estimated that a limestone specimen from locality rapid sedimentation during late youth and early matur­ displays 45 percent reduction due to vertical ity, which did not permit sufficient time for complete compaction. Pressures required to accomplish this re­ cementation. A of the above factors prob­ duction would 1,000 feet of overhurden ably occurred. 1959, p. 286). If this estimate is valid, nearly feet of overlying strata have been removed, which RECRYSTALLIZATION suggests that the Lake Waco, South and Austin formations, and part of the Taylor formation originally Recrystallization, which was an important factor overlay the Bluebonnet member in the map area. The during diagenesis of the Bluebonnet member, has been lithologic character of these formations in the area also observed throughout the limestone beds. Bar-deposited indicates a distant westward shoreline, and, therefore, limestone beds are composed of prisms, a greater extent than occurs today. which were cemented dominantly by sparry calcite. Two phases of recrystallization are evident in several of the bar-deposited limestones I, fig. A). The CEMENTATION first phase is grain growth parallel to the bedding. The second phase truncates the bedding and the first Cementation is a major process in phase at a angle. The first phase of recrystalliza­ the bar-deposited limestone beds, but the process is tion may have occurred contemporaneously with cemen­ much less important in shale. Cement in the bar-de­ tation as denoted by the large (l-2mm) crystals of posited limestone beds is sparry calcite, which may have sparry cement. The second phase at to the bedding formed as primary chemical cement by pressure solu­ may have resulted from forces associated with Balcones tion or by recrystallization of calcite faulting. to microspar and/or sparry cement. Sparry cement in Several of the Foraminifera deposited in the Bluebonnet is interpreted to be dominantly zones 2 and 3 of the Bluebonnet member, have been a cement precipitated from solution onto free surfaces recrystallized by the process of grain seeding (Bathurst, of prisms VIII, fig. D). Crvstals of 1958). Grain seeding is indicated by fibrous calcite calcite cement grew by precipitation of calcium car­ crystals radiating from a grain of hematite in a foram- bonate in lattice continuity with pre-existing free crys­ iniferal test fig. D). The hematite may be tals fig. A). Growth of some crystals ceased as altered deposited in the test. Alteration of they became enclosed by crystals with more favorable glauconite to hematite would have resulted in expansion, orientation. This process led to a reduction in the num­ which is suggested by microscopic fractures radiating ber, as well as an increase in the size of crystals. The from hematite in the center of the test. The micro- presence of sparry cement indicates original porosity, fractures would increase porosity which would which resulted from winnowing of fine particles during lead to recrystallization of micro-crystalline calcite to of the bar-deposited limestone beds. fibrous calcite. In the bar-deposited limestone beds the Inoceramits prisms (grains) were elastically strained at the inter- EROSIONAL HISTORY granular boundaries VI, fig. B) resulting in pres­ sure solution and reprecipitation. In general erosion was probablv not an important The occurrence of pressure solution in the limestones process in the Bluebonnet lagoon. The youth, late youth suggests that cementation by chemical precipitation was and early mature stages of the lagoon are well preserved not completed early in diagenesis. This may indicate in the outcrop belt. The mature is partially de- a depletion of calcium carbonate in the depositional in Hill County as a result of Recent erosion.

CONCLUSIONS

(1) The Bluebonnet of the Upper Cretaceous basal limestone bed at several localities is an Inocera­ Lake Waco formation occurs in parts of Bell, Falls, mus biosparite that contains abundant closely packed McLennan, Limestone, Hill, Robertson, and allochems. The allochems are well sorted Inoceramus Navarro counties, central Texas. The maximum thick­ prisms with long axes parallel. Shale beds are gray, ness of the member is 22 feet. The member strikes fissile, thinly laminated, calcareous, and weather buff. north-northeast and dips 40 to 80 feet per mile east- Bentonite beds are composed of calcium montmorillon- southeast. ite, which is free of glass shards, indicating the detrital (2) The Bluebonnet member is a secjuence of lime­ nature of the bentonites. stone, shale, and bentonite beds. Limestone beds are (3) The depositional environment was a shallow la­ dominantly Foraminifera however, the goon. Four general stages of lagoonal evolution can CRETACEOUS BLUEBONNET LAGOON 37 38 GEOLOGICAL

A B Youth. The baymouth bar Is Interpreted from subsurface Late Youth. The and cuspate bars of youth data. and cuspate bars are represented by ripple- stage receded. Clastic limestones are limited to the cuspate marked, cross-bedded, clastic limestone on the outcrop. bar. Thinly laminated, highly carbonaceous black shale Is shales black, and the dominant lithology. Shale beds contain no bcnthonic bonaceous. ic microfossils are concentrated fauna. beds are common and widely distributed. shale beds adjacent to the inlet. Values of pH and Eh microfossils are more abundant and evenly were probably between 7.8-8.6 and respectively distributed than In the youth Values of pH and lower values restricted to marsh areas. were probably those of youth, marsh areas.

c D Early The lagoon was characterized by marsh Mature. The lagoon was filled with marsh deposits and in deposition. Limestone beds low energy part covered by the transgressing Cloice Sea. deposits. Shale is the rock type. Carbon, energy during early Cloice time was low, as suggested by rhodochrosite, and planktonic microfossils reach widespread, thinly laminated shales of the lower Cloice maximum abundance. and calcium montmorillonite member (Lake Waco formation). Low energy Microfossils general resulted in preservation of unconsolidated marsh evenly distributed. Values of were probably between of the lagoon. Transgression is evidenced by the gradation 7.0-7.8; Eh was probably negative. from Bluebonnet to Cloice deposition.

Fig. 13. Postulated evolution of Bluebonnet lagoon, central Texas. CRETACEOUS BLUEBONNET LAGOON 39 l)e late youth, early mature, and pH was slightly alkaline and Eh values were positive mature. The youthful stage is characterized by cuspate for both limestone and shale areas. The bar-deposited and bars which are delineated by field rela­ limestone beds in the late youthful stage of the tionships, sedimentary structures, composition, and fab­ l)onnet lagoon were deposited in an environment similar ric of the limestone bed. The late youthful stage to that of the youthful the shale beds were de­ is marked by marsh sedimentation and recession of cus­ posited at a pH near neutrality and at a negative Eh. pate and mid-bay bars. Planktonic foraminifers are Most of the shale beds in the early mature and mature concentrated in the shale beds near the lagoonal inlet. stages of the Bluebonnet lagoon were deposited at a By early maturity the cuspate and mid-bay bars were slightly acidic pH and a negative Eh. covered marsh deposits as a result of reduced circu­ (6) history of the Bluebonnet mem­ lation due to nearly complete closure of the lagoonal ber is characterized by compaction, cementation, and inlet. Marsh deposits were the predominant sediments recrystallization. Compaction resulted in approximately during early maturity, while beds reached 45 percent decrease in original sedimentary thickness. maximum thickness and distribution. In the ma­ Cementation of the bar-deposited limestone l)eds was due ture stage of development, the lagoon was completely to contemporaneous precipitation of sparry calcite, and filled with marsh sediments and buried by deposits of the later pressure solution reprecipitation. This may overlying Cloice member of the Lake Waco indicate rapid sedimentation and/or depletion of cal­ energy during Cloice transgression was in­ cium carbonate from the depositional area due to a adequate to remove unconsolidated marsh deposits in lowering of pH. the upper Bluebonnet member. which was a common diagenetic (4) Bed by bed correlation is impossible, but the Bluebonnet member was divided into 3 distinct process in the Bluebonnet member, has commonly de­ stroyed original depositional fabric. Grain seeding and sequences or zones. Each zone is approximately grain growth, contemporaneous with cementation, are time-equivalent in an east-west direction, but not neces­ two of the most prominent types of recrystallization. sarily in a north-south direction. Each zone represents a distinctive depositional and geochemical environment (7) Bluebonnet rock types are not unique to the map throughout the with local variations such as bar, area (fig. 2). Similar rocks in the basal Eagle Ford lagoon, and marsh areas. group (often referred to as basal Eagle Ford flags) (5) The geochemical environment of the were observed as far south as the Del Rio area and as member is interpreted from the ratio of calcium mont- far north as Dallas (fig. 1). If these basal Eagle Ford morillonite to kaolinite, calcite, and rhodochrosite, as flags are environmentally similar to the rocks of the well as by fossil assemblage and sedimentary structures. Bluel)onnet lagoonal deposition was common During the youthful stage of the Bluebonnet lagoon the along the slowly transgressing Eagle Ford shoreline.

REFERENCES

W. S. (1923) Geology and mineral resources of Mc­ JULES (1862) Notes on the Cretaceous and Car­ Lennan Univ. Texas Bull. 2340, 202 pp. boniferous rocks 01 Texas : Proc. Boston Soc. Nat. Hist., W. S. (1928) Handbook of Texas Cretaceous fossils: vol. 8, pp. 86-97. Univ. Texas Bull. 2838, 385 pp. MASON, BRIAN (1960) Principles of geochemistry: McGraw- ADKINS W. S. (1932) The Mesozoic system in Texas in The Hill, New York, 385 pp. Geology of Univ. Texas Bull. 3232, pp. EDWIN D., at. (1956) Paleotectonic maps, Jurassic ADKINS, W. S. and Lozo, F. E. (1951) Stratigraphy of the U. S. Geol. Survey, Miscel. Geol. map Woodbine and Eagle Ford, Waco area in The Woodbine Paleogeography by Ralph W. and adjacent strata of the Waco area of central Texas: MoREMAN, W. H. (1942) Paleontology of the Eagle Ford of South. Meth. Univ., Fondren Sci. Ser. no. 4, pp. 105-164. north and central Jour. Paleontology, vol. 16, pp. R. G. C. (1958) Diagenetic fabrics in some British 192-220. Dinantian limestones: Liverpool and Manchester PACE, LULA (1921) Geology of McLennan County, Texas: The Jour., vol. 2, pp. 11-36. Baylor Bulletin, Baylor University, vol. 24, no. 1, 25 pp. BROWN, C. W. and PIERCE, R. L. (1962) Palynologic correla­ PRATHER, J. K. (1902) South Bosque marl: Trans. Texas tions in Cretaceous Eagle Ford group, northeast Acad. Sci., vol. 4, Pt. no. 8. Bull. Am. Assoc. Petrol. Geol., vol. 46, pp. 2133-2147. ROEMER, FERDINAND (1852) Die Kreidebildungen von Texas CHAMNESS, RALPH S. The Eagle Ford group in. Guide und ihre organischen Bonn (Germany), to the mid-Cretaceous geology of central Baylor Adolph Marcus, 100 pp. Geological Society guidebook, pp. 70-74. SHUMARD, B. F. Observations upon the Cretaceous FOLK, R. L. (1959) Practical petrographic classification of strata of Trans. St. Louis Acad. Sci., vol. 1, pp. limestones : Bull. Am. Assoc. Petrol. Geol., vol. 43, pp. 1-38. 582-590. GARRELLS, R. M. (1960) Mineral equilibria at low temperature SILVER, BURR A. (1959) The stratigraphy of the Bluebonnet and Harper and Brothers, New York, 254 pp. member, McLennan County, Baylor Univ. unpub­ HILL, R. T. (1887) The Texas section of the American Cre­ lished student geology paper no. 266. taceous : Am. Jour. Sci., ser. 3, vol. 34, pp. 287-309. KARL W. (1962) Quantitative petrographic study of Geography and geology of the Black and Paleozoic carbonate rocks, Caballo Mountains, New Mex­ Grand Prairies, Texas: U. S. Geol. Survey, 21st Ann. ico: Jour. Sed. Petrology, vol. 32, pp. 357-396. STEPHENSON, L. W. (1955) Basal Eagle Ford fauna in Johnson Kept., pp. 323-328. and Tarrant counties, U. S. Geol. Survey, Prof. KRUMBEIN, W. C. and GARRELS, R. (1952) Origin and classification of chemical sediments in terms of pH and Paper no. 274-C, pp. 53-67. oxidation-reduction Jour. Geol., vol. 60, pp. 1-33. J. A. and S. (1893) Report on the Cretaceous A. R. and TAPPAN, H. (1961) Cretaceous planktonic area north of the Colorado Texas Geol. Survey, Foraminifera, Part I, Micropaleontology, vol. 4th Ann. Rept., Pt. 1, pp. 239-354. 7, no. 3, pp. 256-305. WELLER M. Compaction of sediments: Bull. Am. LuCKE, J. B. (1939) A theory of evolution of lagoonal deposits Assoc. Petrol. Geol., vol. 43, pp. 273-310. on shorelines of emergence : Jour. Geol., vol. 42, pp. 561-584. 40 BAYLOR GEOLOGICAL STUDIES

APPENDIX I

SUBSURFACE

No 34. J. Caraway, Slaughter No. 1, McLennan 17 Thickness County. N ; 53' W ) (in feet) 35. J. L. Myers, City of Mart No. 1, McLennan 14 County. W) 1. A. R. P. Oil Company, John P. Mascheck No. 1. 13 36. Joe Thompson, Paul Shelby No. 1, McLennan 12 Bell County. 97 = 06' W) 2. W. P. Luse, Voltin No. 1, Falls County. 13 37. J L Myers, Midway School W) County. (31 29 97 W) 3. Humble Oil & Refining Company, Eleanor Carrol 11 Water Company No. 3, 8 No. 1, Falls County. N; W) AT 4. A. Delcambre, D. V. No. 1, Falls 14 39. J. Myers Waco Water District 4 No. 1, County. N; 97 W) McLennan County. (31 34 N; 97 05 5. Max Cohen, E. C. Stuart No. 1, Falls County. 9 40. Layne Company, Texas Power and 5 97 03' W) Company No. 1, McLennan County. (31 35 N; O/ W) 6. L. E. Lockhart, No. 2, Falls County. 8 41. J L Myers 1, McLennan County. 6 = (31 36 97 04 W) 7. J 3 42. Mt Carmel Center Mt Carmel 16 No. 1. Falls County. (31 = 10' N; 96 = 51' McLennan County. (31 35 N; 96 59 W) 8. Goodson, J. B. Barganier No. 1, Falls 6 43. Balcones 14 County. N; 96 = 50' W) (31 35 N; 96 49 W) 9. Maury Hughes, Trustee, A. PL Bell, C. L. Trice 4 44. M. M. Miller J. C. 12 No. 1, Falls County. (31 N ; 97-01' W) 10. W. P. Luse, Jones No. 4, Falls County. 16 4a. O. V,. Stone N o 1 Limestone 18 97 W) 37 N ; 96 42 W) 11. Jenkins Porter No. 1, Falls County. 1 46. Hunt Oil Company, Union Central , (31 = 14' 97 11' W) Company No. 1, Limestone County. (31 40' N; 96 45 W) 12. Ace Oil Cimpany & Ray Holbert, Harrison No. 1, 5 47. William H. Winn, James Morrow No. 1, 20 Falls County. (31-16' N ; 97-01' W) McLennan County. (31 39 N ; 96 57 13. P. W. Curry, Newman No. 1, Falls County. 22 J. H. et No. (31 17' 97-09' W) McLennan County. (31 N; 96 58 W) 14. Bailey and Obermeyer, Warren Allen No. 1, 4 49. Simon R. W. Ferguson 22 Falls County. (31-16' N; 96 53' W) McLennan County. (31 41 96 W) 15. L. E. Miers and Dr. C. A. Greenwalt, O. R. 3 50. Layne-Texas Company Gilliam No. 1, Falls County. N; 96 = 50' W) No 3 McLennan County. (31 39 N; 97 05 W) 16. H. C. Pockburn and Zephyr Oil Company, 3 51. Lake-View Water J. E Passmore No. 1, 10 N. D. Buie No. 1, Falls County. (31 = 16' N; 96 = W) Q 17. Paine, Eubank, No. 1, McLennan County. 10 52. Chalk Bluff Water Supply, Chalk Bluff No. 1, 9 97 = 13' W) McLennan County. (31 40 N; 97 08 W) 18. Jet Oil Company, Wills No. 1, McLennan 16 53. C. R. Porter No. McLennan 13 County N 97 = 15' W) County. N ; W) 19. Hamilton Guderian Est. No. 1, 11 54. Layne-Texas, 20 Falls County 97 06' W) McLennan County. (31 44 N; 97 01 W) 20. Midstates Oil Corporation, B. E. Mitchell 8 55. Baylor Geology Department, 6 No. 1, Falls County. N; 97 = 00' W) 21. Gray Oil Company, Warren No. 1, McLennan 12 (31 45 N; 97 08 County N W) 56. C. P. Prause No. 1, McLennan 8 22. Rosental Water Company, O'Dowd No. 1, 9 County. (31-47' N; 97 = 07' W) . , McLennan County. 97 = 06' W) 57. Camtex Od Corporation Cartwnght No. 1, 4 23. J. E. Banks, No. 1, Falls County. 4 County. (31 47 96 54 W) (31 = 96 = 58' W) 58. Joe Thompson, Easter Doherty No. 2, 7 24. A. Sheaf, Pavelka No. 1, Falls County. 12 County. N ; 53' 96 = 54' W) 59. Eureka Tool Company, Daugherty No. 1, 4 25. F. Jackson, Samuel B. No. 1, 7 County. (31 N ; Falls County (31=26' N; 97 = 50' W) Davidson and Grant No. 1, 26. Lone Star (ias Production Company, Criswell 10 County N ; 96 = 51' W) No. 1, Limestone County. (31=25' N; 96 = 42' W) U. J. Hester et Beard No. 1, County. 27. Beacon Oil Company, Trice No. 1, McLennan 12 (31 48 N; 96 50 W) . .,, County 97 = 14' W) St. Anthony Corporation, Allen No. 1, 8 28. Chapel 'Hill Water No. 1, 13 Limestone County. (31 N ; W) McLennan County. (31 W) 63. A. O. and American Liberty, Vosburg 7 J. L. Myers, Waco Memorial Park No. 1, 9 No. 1, County. (31 50 N ; 96 W) McLennan County. N; 97 = 09' W) 64. J. L. Myers, Penelope Water Well No. 1, 4 30. J. L. Myers, Youngblood No. 1, McLennan 12 (31 52 ; 96 55 W) County ; 97 = 06' W) 65. C. R. Porter, E. D. Mazanec No. 1, McLennan 12 31. Max Wardlaw No. 1, McLennan 19 County. (31 50' N ; W County (31=29' N; 97 00' W) R. J. McMurrey, Joe F. Janek No. 1, 6 32. Layne Texas Company, Texas Power and Light 20 Company No. 2, McLennan County. N; 96-59' W) C. A. Lee, County. 3 33. Riesel Ind. School Corporation, Ricsel Ind. 17 (31 53 N 96 48 School Water Well No. 1, McLennan County. 68. George Lewis No. 1, 6 (31=28' N; 96-56' W) County. (31 N ; 50' W) to 2 for location of CRETACEOUS BLUEBONNET LAGOON

APPENDIX II MEASURED Unit Thickness Pepper Formation (feet) 1 Shale, Hack, fissile, blocky, jarosite on weathered surface, non-

(Fig. 3) calcareous, weathers gray In south bank of Leon River approximately 800 yards of Farm Road 496, about miles southeast of intersection of State way 317 and U. S. 190, and approximately 7 miles southwest 41 of and Highway Bell County, (31 01 N; 97 2,S W). Limestone 56%, shale Highway 317, approximately 4 miles south-southeast of 1.,. McGregor, and 5 miles north-northwest of Moody, McLennan County, Texas 97 W). Limestone 31%; shale 68%; ben- 8c Limestone, tan, micro-crystalline calcite matrix, thinly bedded, moderate weathers buff formation) 8a tan, tan, fissile, very poorly laminated, calcareous, weathers moderate porosity, weathers buff 7 Shale, gray, fissile, thinly laminated, calcareous, severely (Lake Waco formation) weathered, 6 tan to 6 thinl7 15 Shale, tan weather, fissile, spoorl light-tay laminatedn , calcareous, severely stone, weathers huff 5 Limestone, tan to brown, medium-bedded, fine-grained, moder- tan thinly ate porosity, opposing ripple marks on upper surface, wavy- fera 0.2 bentomte seam from under- calcareous, severely lying limestone, weathers weathered weathers buff 4 tan to moderate Limestone, tan, thinly bedd7c7viry finely crystalline, excellent on upper surface, wavy-bedded, bentomte porosity, planktonic Foraminifera, weathers buff seam middle, weathers tan Mack, fissile, thinly laminated, calcareous, 3 Shale, gray to black, fissile, thinly laminated, calcareous, 0.7 weathers tan; intercalated limestone 0.5 Limestone, gray, thinly bedded, micro-crystalline calcite matrix, 2 Limestone Limestone, tan to brown, excellent porosity, lenticular, weathers tan well sorted and poorly rounded grains, thinly laminated, well calcareous, slight cemented, Inoceramus fragments, porosity, cross- content, weathers thin bentonite bed at 1.0 bedded, wavy-bedded, weathers brown; two intercalated shale 1.0 beds, gray, fissile, thinly laminated, calcareous, weather tan laminated, calcareous, slight­ ly limonitic, weathers buff, 4-inch bentonite bed in middle of Pepper Formation 1.0 1 gray, indurated, blocky, slightly calcareous, jarosite on b"ed7ed, micro-crystalline calcite weathered surface, weathers light matrix, porous, limonitic, weathers buff 7 Shale, gray, fissile, thinly laminated, calcareous, weathers thin bentonite bed in upper 0.7 6 Limestone, light-brown, thinly bedded, micro-crystalline LOCALITY 14-B-2 c matrix, porous, weathers buff In bank of Pepper Creek approximately 400 yards southeast ot U. and shale. Limestone, light-brown, thinly Highway 81, about 4 miles northwest of intersection of State Highway micro-crystalline calcite matrix, low porosity, weathers buff. 317 and U. S. Highway 190, and approximately 4 miles southwest of Shale, gray, fissile, thinly laminated, calcareous, weathers buff intersection of State Highway 36 U. S. Highway 81, County, Limestone, brown, thinly bedded, fine to medium-grained, Texas N; W). Limestone 31%; shale 57%; ben- crystalline, moderate porosity, wavy-bedded, cross-bedded, tonite weathers buff 3 Bentonite, yellow to tan, severely weathered Bluebonnet Member (Lake Waco formation) . , 2 Shale and limestone interbedded. Shale, gray fissile, laminated, 6 Shale, tan, slightly fissile, slightly laminated, calcareous, calcareous, phosphate nodules and sharks teeth near severely weathered, weathers 2.0 Limestone, gray, medium-grained, dominant 5 Limestone, tan, thinly bedded, calcite matrix, constituents are Inoceramus fragments, bonded by micro- excellent porosity, limonitic, weathers bentomte at crystalline matrix base of unit 0.3 4 Limestone, tan to brown, medium-bedded, Pepper Formation calcite matrix, moderate porosity, wavy-bedded, extremely to black, indurated, non-calcareous, jarosite fossilifcrous at top, weathers buff weathered surface, weathers 23.1 3 Bentonite, yellow to tan, severely weathered 2 Shale and limestone. Shale, gray, laminated, calcareous, weathers 35.8 tan; limestone, gray, fine-grained, well and poorly rounded grains, well cemented, medium-bedded, ripple-marked, LOCALITY 154-B-41 (Fig 5) wavy-bedded, low porosity, Inoceramus fragments, weathers downstream from tan to county road, about 9 miles southeast of McGregor and approximately 5 miles northeast of Moody, McLennan County, Texas indurated, blocky, non-calcareous, jarosite on W). Limestone 17% ; shale 75% ; bentonite 8%. weathered surface, weathers Member (Lake Waco formation) 21 Covered ± - . Shale, tan, fissile, poorly laminated, calcareous, several inter­ calated beds of bentonite, weathers tan LOCALITY 14-B-3 In road cut on Farm Road 2601, 0.5 mile west of intersection Bluebonnet Member (Lake Waco formation) State Highway 317, about 4.4 miles southwest of Moody, and 6.6 Bentonite-calcilutite. Bentonite, yellow, glass shards; of intersection of State Highways 36 and 317, Bell cilutite, yellowish-tan, finely crystalline, well sorted grains, ex- County, Texas N ; 97 W). cellent porosity 18 Limestone, brown, thinly laminated, micro-crystalline calcite Bluebonnet Member (Lake Waco formation) matrix, porous, lenticular, weathers yellowish-tan 10 Shale, severely weathered, 3 thm lenticular limestone 4.0 interbedded, severely weathered 9 Limestone, tan, very thinly bedded, very finely crystalline, Shale, gray, fissile, thinly laminated, calcareous, interbedded weathers tan with 2 and 3-inch thick bentonite seams ; 2 inches of limestone 8 Shale and limestone, severely weathered shale weathers 7 Shale, severely Shale, gray to black, fissile, thinly laminated, calcareous, inter- 6 Limestone, tan, thinly bedded, micro-crystalline matrix, vugular bedded with limestone and bentonite, weathers 2.3 porosity with clay and limonite filling many vugs, weathers Limestone, gray, thinly bedded, micro-crystalline calcite brown porous, high carV'onaceous content, 0.4 5 Shale, severely Shale, gray to black, fissile, laminated, high carbonaceous 4 Limestone, severely weathered, thin bentonite seam separating content, calcareous, concretions of bedded limestone, weathers limestone beds, highly limonite-stained Two thin bentonite beds, 1.0 foot and 2.5 feet from base 3 Shale, covered of unit respectively 2 Limestone, blue-gray, thinly bedded, coarse-grained, micro- Shale, gray to black, fissile, laminated, carbonaceous, crystalline calcite matrix, Inoceramus fragments, weathers tan calcareous, weathers light-gray; 3-inch limestone bed shale Limestone, gray, thinly bedded, micro-crystalline calcite matrix, to figure 2 for location. porous, Inoceramus fragments, weathers gray 42 BAYLOR GEOLOGICAL STUDIES

10 Bentonite and shale. Bentonite, yellowish-tan, lenticular, 9 Limestone, blue, thinly laminated, cross-laminated, finely severely weathered; shale, fissile, poorly laminated, crystalline, porous, weathers gray careous, weathers tan 0.4 8 Shale, gray to black, fissile, thinly laminated, calcareous, 9 Shale, gray to black, thinly laminated, fissile, calcareous, weathers two thin bentonite beds in upper half of 3 thin beds of bentonite, weathers 2.0 8 Limestone, gray to tan, medium-bedded, micro-crystalline 7 Limestone, dark-gray, thinly bedded, very finely crystalline, calcite matrix, Inoceramus fragments near top, porous, weathers Inoceramus fragments near top, moderate porosity, weathers light-brown to gray thin bentonite bed at 0.4 7 Shale, gray to black, fissile, thinly calcareous, silty, 6 Shale, gray, fissile, thinly laminated, calcareous, weathers gray weathers 5 Limestone, blue, thinly laminated, very finely crystalline, 6 Bentonite, yellow to tan, lenticular porous, contorted bedding, weathers gray 5 Shale, gray to black, fissile, thinly laminated, calcareous, 4 Shale, gray, fissile, thinly laminated, calcareous, weathers weathers buff 4 Limestone, fine-grained, moderately sorted, poorly rounded and 3 dark-gray, thinly laminated, micro-crystalline calcite cemented, Inoceramus fragments, moderate porosity, matrix, porous, some distorted laminae, weathers 0.5 cross-bedded, wavy-bedded, ripple-marked, weathers 0.4 Shale, dark gray, fissile, thinly laminated, calcareous, phosphate 3 Bentonite, yellow to tan, severely weathered nodules, sharks teeth, 2 thin limestone beds, weathers 2b Limestone, tan to brown, fine-grained, well sorted, moderately 0.7 rounded and well cemented grains, elongate phosphate modules at lower contact, Inoceramus fragments, cross-bedded, weathers Pepper Formation tan to brown 1 Shale, dark gray, fissile, blocky, fractured, non-calcareous, 2a Shale, gray, fissile, thinly laminated, calcareous, fecal pellets, weathers hght-gray weathers Hght-gray 23.4 Pepper Formation 1 Shale, gray to black, fissile, blocky, jarosite on weathered sur- LOCALITY (Fig 8) face, non-calcareous, weathers light-gray tributary of Aquilla Creek, about yards north of county road, about 21 miles south of Hillsboro, and about 11 miles north of 22.9 Waco, McLennan County, Texas N; W). Limestone 17%; shale 80% ; bentonite 3%. LOCALITY 154-B-42 (Fig. 6) In northwestern bluff of South Bosque brick yard, about 7 miles Cloice Member (Lake Waco formation) southwest of intersection of U. S. Highway 84 and State 6, Covered approximately 9 miles northeast of McGregor, McLennan County, 18 Limestone, gray, very thinly laminated, very finely crystalline, Texas W). Limestone 14% ; shale 78% ; ben- argillaceous, weathers tan tonite 8%. 17 Shale, gray to tan, fissile, laminated, calcareous, weathers buff to 3.0 Cloice Member (Lake Waco formation) 16 Limestone, gray, very thinly laminated, very finely crystalline. 18 Shale, gray to tan, fissile, laminated, calcareous, high iron argillaceous, some Inoceramus fragments, weathers 0.2 content, weathers tan 15 Shale, gray to tan, fissile, laminated, calcareous, weathers buff to light-gray Bluebonnet Member (Lake Waco formation) 17b Bentonite, severely weathered, grades into Bluebonnet Member (Lake Waco formation) argillaceous calcilutite, very fine-grained, well sorted grains, Calcilutite, yellow, argillaceous, weathers light-tan to reddish- high clay content, weathers light-brown brown Shale, gray, fissile, laminated, calcareous, weathers 0.4 Bentonite, yellow to white, fractured 16 light-gray, laminated, finely crystalline, porous, con- 12 Shale, gray to tan, fissile, laminated, calcareous, jointed near torted bedding, weathers 0.2 top, weathers tan to gray Shale, gray, fissile, thinly laminated, calcareous, contains 2 Limestone, tan, thinly laminated, finely crystalline, porous, beds near base, weathers light-gray Inoceramus at base, weathers 0.2 14 Shale, gray, fissile, poorly laminated, 10 Shale, light-gray, thinly laminated, calcareous, thin bed of careous. weathers bentonite. 0.5 pseudo-aragonite near middle, weathers light-gray Shale-bentonite. gray, fissile, laminated, calcareous, 9 Limestone, light-gray, thinly laminated, distorted laminae, weathers tan ; bentonite, severely 0.5 porous, weathers brownish-gray 12 Limestone, light-gray, laminated, finely crystalline, porous, 8 Shale, tan to gray, fissile, thinly laminated, calcareous, thin contorted bedding, weathers tan to buff 0.2 bentonite bed about 5 inches above base of unit, weathers Shale, gray to black, fissile, thinly laminated, calcareous, light-tan highly carbonaceous, weathers gray 7 Limestone, gray to tan, thinly laminated, finely crystalline, Limestone, blue, thinly laminated, finely crystalline, porous, porous, weathers light-gray lenticular, weathers gray 6 Shale, gray to black, fissile, laminated, calcareous, thin 9 Shale, gray, fissile, thinly laminated, calcareous, high car- tonite bed 18 inches from base of unit, weathers 2.0 bonaceous content, 3-inch bentonite at base of unit is severely 5 Limestone, blue to tan, Inoceramus fragments (some whole weathered, shale weathers gray specimens) in micro-crystalline calcite matrix, weathers 0.6 8 Limestone, gray to brown, laminated, micro-crystalline calcite 4 Bentonite, yellow to white, 0.2 matrix, Inoceramus fragments near base, moderate porosity, 3 Shale, gray to black, fissile, thinly laminated, calcareous. weathers 0.4 Limestone, tan, fine to very fine-grained, lenticular, near top 7 Shale, gray, fissile, thinly laminated, calcareous, limonitic at of unit, weathers hght-gray base, weathers buff to tan 0.7 2b Limestone, blue, fine-grained, moderately sorted to well sorted 6 Limestone, blue to gray, thinly laminated, distorted laminae, and cemented grains, cross-bedded, thinly bedded, low micro-crystalline matrix, dense, weathers thin bentonite porosity, gray at base of 0.5 2a Shale, gray to black, fissile, laminated, calcareous, phosphate Shale, gray to black, fissile, thinly laminated, calcareous, nodules, sharks teeth, intercalated thin beds, oysters and sharks teeth common, weathers weathers light-gray 4 Limestone, tan to white, very thinly bedded, micro-crystalline calcite matrix, porous, wavy-bedded, weathers gray to 0.6 Pepper Formation 3 Shale, gray to k, fissile, laminated, calcareous, limonitic, 1 Shale, gray to black, indurated, blocky, non-calcareous, weathers tan jarosite on weathered surface, weathers dark-gray 2 Shale, gray to black, fissile, laminated, calcareous, phosphate nodules and sharks teeth near base, contains 2 thin beds of moderately crystalline limestone, weathers light-gray LOCALITY 154-B-45 (Fig. 9) Pepper Formation In tributary of Aquilla Creek, al.out 200 yards west of county 1 Shale, gray, indurated, blocky, non-calcareous, jarosite on road, about miles south of Hillsboro, and about 4 miles west of weathered surface, weathers light gray West, McLennan County, Texas N; W). Limestone 14%; shale ; bentonite 6%. 44.9 Bluebonnet Member (Lake Waco formation) LOCALITY 154-B-43 (Fig. 7) 11 Limestone, buff, thinly bedded, abundant carbonized plant In ditch, 400 yards from county road, about miles west of material, weathers light-tan intersection of S. Highway 84 and State Highway 6, about miles 10 Shale, gray to black, fissile, slightly laminated, calcareous, northeast of McGregor, McLennan County, Texas weathers gray to 0.8 Limestone 12%; shale 78% 10%. 9 0.3 8 ? Cloice Member (Lake Waco formation) 7 Shale, severely 1.0 2.0 6 Shale, tan, slightly fissile, shghtly laminated, calcareous, Shale, gray to tan, slightly fissile, laminated, calcareous, weathers buff weathers tan 5 Limestone, tan, thinly laminated, very finely crystalline, abund­ ant carbonized plant material on upper surface, unevenly bed- Bluebonnet Member (Lake Waco formation) ded, weathers 0.2 13 Bentonite-calcilutite. Bentonite, yellow, grades into cal- 4 Calcilutite, yellow, weathers buff to light-tan calcilutite, to tan, well sorted grains, weathers 3c Shale, light-gray, fissile, laminated, calcareous, some carbonized 0.9 plant material, weathers buff 12 Shale, gray to black, fissile, thinly laminated, calcareous, 3b Limestone, tan, very finely crystalhne, thinly bedded, weathers weathers tan, contains 4 bentonite 3.0 buff 11 Bentonite, yellow to tan; extensive fractured shale seam in 3a Shale, tan, fissile, slightly laminated, calcareous, weathers 0.2 center of bentonite 2b Limestone, blue to gray, very thinly laminated, 10 Shale, gray to black, fissile, thinly laminated, calcareous, crystalline calcite matrix, porous, weathers yellow to tan 0.2-1.0 contains limestone concretions, lenticular coal seam, weathers 2a Shale, gray to black, fissile, laminated, calcareous, weathers light-gray light-gray to 0 1 CRETACEOUS BLUEBONNET LAGOON 43

Pepper Formation 5 yellow, fine-grained, friable, bentonite near top of 1 Shale, gray to black, blocky, jointed, non-cal­ unit careous, on weathered surface, weathers 8. 4 Limestone, gray, thinly laminated, micro-crystalline calcite matrix, slightly porous, weathers thin interbedded shale 3 Limestone, tan, medium to fine-grained, well-sorted, poorly LOCALITY rounded and well cemented grains, cross-bedded, Inoceramus In tributary of South Fork of Cow Bayou, about 400 yards west fragments, low porosity, weathers brown of Farm Road 2113, 8 miles south-southeast of McGregor and about 3 miles north-northeast of Moody, McLennan County, Texas Woodbine Formation 2 Sandstone, tan, medium to fine-grained, sub-angular to sub- N; W). rounded grains, calcite cemented, friable, limonite-stained, Cloice Member (Lake Waco formation) weathers brown 1 Sandstone, buff, medium to fine-grained, to sub- 4 Shale, covered ronnded grains, friable, limonite-stained, weathers 2.0 Bluebonnet Member (Lake Waco formation) 11.5 3 Shale and limestone, severely weathered. Al:out 6 limestone beds alternating with shale beds approximately 2 feet thick. LOCALITY 109-B-17 (Fig. 11) Several thin beds of petrified wood fragments com­ In small creek, 300 yards north of county road, 4.5 miles mon near 15.3 south-southwest of Hillsboro and about 4 miles south-southeast of 2 Limestone, blue-gray, medium-grained, well sorted, very poorly Peoria, Hill County, Texas W). Limestone 35%; rounded and well cemented grains, cross-bedded, ripple-marked, shale 63%; bentonite 2%. Inoceramus fragments, low porosity, weathers 1.2 Cloice Member (Lake Waco formation) Pepper Formation 13 Shale, gray to tan, poorly laminated, calcareous, weathers 2.0 1 Shale, black, fissile, blocky, non-calcareous, jarosite on weathered weathers gray Bluebonnet Member (Lake Waco formation) Bentonite, yellow, severely weathered 44.2 11 Shale, gray, fissile, thinly laminated, calcareous, weathers buff Limestone and shale. Limestone, tan, very finely crystalline, LOCALITY 109-B-15 (Fig. 9) very porous, high limonite content, weathers shale, gray, In tributary of Aquilla Creek, about 600 yards west of county poorly laminated, calcareous, carbonaceous, weathers 0.3 road, approximately 4 miles northwest of West, and about miles 9 Shale, gray, fissile, thinly laminated, calcareous, carbonaceous, south of Hillsboro, County, Texas W). Lime­ lenticular beds of coal, weathers buff. Thin limestone bed in stone 15% ; shale 85%. lower third of 0.7 Limestone, yellow to gray, laminated, very finely crystalline, Bluebonnet Member (Lake Waco formation) and porous, weathers 0.2 Shale, tan, fissile, very poorly laminated, calcareous, carbon­ 7 Shale, gray, fissile, laminated, calcareous, jointed, with clay ized plant material common, weathers 2.4 joints, weathers buff 10c Limestone, tan, thin-bedded, finely crystalline, limonitic, 6 Limestone, yellow to gray, laminated, very finely crystalline, carbonized organic material common, weathers 0.2 very porous, Inoceramus at top, weathers 0.4 10b Shale, tan, fissile, poorly laminated, calcareous, weathers 0.4 5 Shale, gray to fissile, thinly laminated, calcareous, 10a Limestone, tan, thin-bedded, finely crystalline, carbonized weathers buff; 1-inch bentonite bed in middle of 0.7 organic material common, weathers buff 4 Limestone and shale. Limestone, gray, finely crystalline, high 9 Shale, gray, fissile, laminated, calcareous, weathers 2.0 limonite content, porous, weathers light-brown 8 Limestone, tan, very finely crystalline, weathers 0.2 3 Shale, gray to tan, fissile, slightly laminated, calcareous, sandy, 7 Shale, gray, fissile, thinly laminated, calcareous, weathers 2.2 weathers buff 6 Limestone, blue, laminated, finely crystalline, laminae not con­ 2 Limestone, blue to gray, fine-grained, well-sorted, moderately tinuous, weathers 0.5 rounded grains, cross-bedded, Inoceramus fragments, porous, 5 Shale, gray, fissile, thinly laminated, calcareous, limonitic, weathers brown weathers tan 4 Limestone, blue to gray, very thinly laminated, micro-crystal­ Formation line calcite matrix, porous, weathers yellow to 0.6 1 Shale, gray to dark gray, indurated, blocky, calcareous, jarosite 3 Shale, tan, fissile, slightly laminated, calcareous, weathers 0.4 on weathered surface, weathers light-gray

Woodbine Formation 12.2 2b Shale, tan, indurated, blocky, sandy, calcareous, weathers 0.5 2a Sandstone, tan, medium to fine-grained, sub-angular to sub- LOCALITY 109-B-18 rounded, well sorted grains, triable, weathers tan In ditch along county road, about 5.5 miles west of Hillsboro and 1 Sandstone, tan, medium to fine-grained, sub-angular to sub- about 1.3 miles north of Peoria, Hill County N; W). rounded, well sorted grains, friable, weathers tan Member (Lake Waco formation) 28.2 ir 2 Limestone, blue-gray, medium-grained, poorly sorted, poorly rounded grains, micro-crystalline calcite matrix, Inoceramus LOCALITY (Fig. 10) and ammonite fragments, reptile vertebrae common, weathers tan In north of Cobb Creek, about 200 yards west of county road, about 7.8 miles northwest of West, and about 7.4 miles southwest Formation of Hillsboro, Hill County, Texas N; W). Limestone 30%; 1 Orthoquartzite, tan, fine-grained, moderately sorted and shale 66% ; bentonite 4%. medium-rounded grains, massive-bedded, calcite cement, low porosity, weathers buff Cloice Member (Lake Waco formation) 13 Shale, tan, fissile, very poorly laminated, carbonaceous, 3.4 severely weathered at top of unit, weathers dark-tan LOCALITY 109-B-19 Bluebonnet Member (Lake Waco formation) In small creek, yards south of county road, about 7 miles Bentonite, yellow northwest of Hillsboro and about 7 miles northeast of Peoria, 11 Shale, gray, fissile, poorly laminated, calcareous, carbonaceous, County, Texas (32 05' W). weathers thin limestone bed at top of 2.0 10 Limestone, tan, very finely crystalline, porous, high limonite Eagle Ford Group content, weathers buff; 1-inch shale near middle 0.4 3 Shale, severely weathered, several thin limestone beds (1-inch 9 Shale, gray, fissile, laminated, calcareous, bentonitic, weathers or less thick) near top of buff 2 Clay, tan, bentonitic, weathers buff 8 Limestone, buff, thin-bedded, finely crystalline, porous, alter­ light and dark bedding, near top, weathers Woodbine Formation dark-brown 1 Orthoquartzite, medium-grained, moderately sorted and 7 Shale, gray, fissile, thinly laminated, calcareous, moderately rounded grains, massive-bedded, calcite cement, low weathers buff porosity, weathers 3.1 6 Limestone, blue to gray, thinly laminated, finely crystalline, porous, Inoceramus and ammonites, weathers 0.3 8.3+ 44 BAYLOR GEOLOGICAL STUDIES APPENDIX III PERCENTAGES DETERMINED BY X-RAY DIFFRACTION 4 2 90 5 10 10 2 6 65 6 a 20 15 3 1 60 6b 1 1 90 1 7 10 5 2 8 60 13 8 88 2 9 10 10 10 50 io OJ 10 1 ,1 8 2 6 50 11 18 8 2

12 5 6 OTS 15 II '5 5 G 9 a '5 13b 8 15 5 5 5 60 9 LOCALITY 70 15 4 10 70 15 4 5 5 5 60 9 2 30 2 15 15 1 5 CO 16 1 2 85 4 50 2 2a ~5 20 3 18 10 10 5 9 8 55 10 2b 5 4 17b 80 5 5 1 2c ~5 20 ~4 16 50 2 18 10 5 1 8 70 5 2d 8 2 90 19 5 1 90 2 3 a 30 15 15 15 20 3 20a 12 5 1 9 70 4 3b 10 5 4 82 20b 60 5 2 25 3c 30 15 15 20 3 10 5 4 82 4 4 5 90 LOCALITY 1S4-B-43 5 5 1 6 2 8 90 1 10 12 65 8 8a 90 1 5 1 78 2 8b Covered 2 4 1 7 81 7 8c 8 90 1 3 3 92 4 4 ~5 3 76 4 5 12 7 4 75 3 LOCALITY 14-B-2 '__ 10 1 15 70 4 6 10 1 7a 25 10 -- 25 - - 45 12 1 1 7b 13 18 2 2 20 1 8 75 2 6 1 2b - - 6 - 4 90 1 2 90 7 9 1 4 -- - - II 7 10 70 12 10 7 5 10 - 2 - - 15 11a 30 12 2 20 8 50 11c 40 20 15 25 LOCALITY 14-B-3 3 12 70 4 12 10 3 13a 65 18 15 13b 50 4 40 14 11 4 1 70 4 LOCALITY 154-B-40 LOCALITY 154-B-44 1 20 15 60 3 2 5 12 72 4 20 65 8 36 1 10 3 44 2a 2 4 15 8 4 5 1 I 2 10 80 1 90 3 2b 1 5 5 12 4 8 1 95 3 ~8 6 4 45 5 10 40 7 10 "5 8 75 2 2 94 1 5 8 5 1 ~5 70 9 5 6 ~5 To 9a 7 8 90 3 9b ~C 5 ~5 10 60 8 10 50 3 8 10 9c 40 9 5 1 3 3 10 12 1 1 5 6 6 7 10 15 To 11 5 12 70 1 4 90 1 1 85 2 11 12 ~3 12 68 10 10 55 5 12a 20 15 5 15 10 ~2 1 85 4 14 5 90 2 4 5 25 8 5 4 75 4 85 1 14 20 16 5 5 1 ~5 2 10 8 6 15a 20 17a 70 24 20 2 10 10 18 14 4 60 7 1 85 2 16 10 ~

LOCALITY 154-B-41 LOCALITY 1S4-B-45

1 20 10 4 45 10 1 65 1 1 30 2a 15 1 5 10 1 19 60 1 1 94 2a 8 2b 2b 7 2 1 5 80 2 3 Severely weathered 8 12 2 1 94 1 3a 15 4 1 5 2 88 3 4 10 44 10 5 10 3c 10 8 3

6 15 8 4 5 ! 5 2 70 7 3d 6 7 5 5 15 2 50 5 92 1 4 25 3 5 1 1 8 12 52 5 5 15 Io 6 10 10 2 15 5 9 a 5 ~8 60 11 5 5 7 Severely weathered 10 15 5 5 8 65 1 2 85 1 8 Covered 11 10 9 19 15 2 20 34 10 1 10 60 6 12 15 10 10 9 2 4 70 ~4 5 1 45 9 13a 25 11 12 2 22 60 2 13b 10 8 15 55 8 14 5 2 2 89 2 2 10 70 7 10 LOCALITY 154-B-46 15b 15 2 10 60 9 16a 85 90 1 50 20 ~2 15 10 - - -- 17 20 10 60 5 2 18 10 1 86 LOCALITY 109-B-I5 19 90 10 20 10 75 3 82 10 2a 45 20 ~3 60 3 LOCALITY 154-B-42 25 50 4 10 2 8 4 1 20 15 15 2 40 5 15 15 65 5 2a 10 5 5 10 65 5 6a 5 15 2 15 50 10 2b 10 3 8 8 60 7 6b 10 1 5 80 1 3 5 10 10 10 55 10 Sample 2% Sample contams 4% phosphate contains 3% rhodochrosite CRETACEOUS LAGOON 45

2 8 70 10 1 10 70 8 2 15 5 4 85 6 3 15 8 2 4 50 8 5 4 75 2 10 2 4 10 5 3 9 35 5 5 2 5 80 5 a 60 35 10a 5 60 4 2 10 16 12 52 5 5b 75 5 c 2 25 40 10c 5 5 ~3 7 90 11 15 20 4 45 4 6 7a To ~4 15 50 11 7 b 20 7 3 18 50 2 LOCALITY 109-B-16 8 10 87 2 9a 15 "5 ~5 10 60 5 1 10 5 80 5 9b 8 2 5 80 3 15 CO 1 ~1 9c 5 5 10 60 5 3 10 ~5 10 75 2 10 2 75 4 8 87 2 11 10 10 ~4 15 60 3 5 25 25 45 5 12 20 3 30 10 6 5 4 85 1 20 17 3 10 45 6 7 25 15 10 45 8 5 90 3 9 10 10 15 55 5 LOCALITY 109-B-18 10 8 2 90 1 11 10 ~3 20 55 2 - 3 90 3 12 25 10 20 10 13 15 25 ~4 15 35 2 LOCALITY LOCALITY 109-B-17 20 80 3 20 40 40 1 5 20 3 60 10

APPENDIX IV

8 . 83,200 21,504 1,024 105,728 11,904 33,024 8,320 3,072 44,416 11,392 Unit Total3 12,160 3,584 0 15,644 128 14 28,800 2,944 92,544 10,240 LOCALITY 154-B-4D 2 26,444 1,928 1,560 29,932 493 LOCALITY 1S4-B-44 5 33,664 2,688 1,792 38,144 512 7 41,344 2,048 256 43,648 384 8,260 3,420 2,264 13,944 0 9a 55,680 2,944 4,224 62,848 1,280 22,328 14,848 4,608 41,784 2,944 9c 58,880 11,280 3,328 73,488 13,568 ,9,440 2,504 73,728 9,344 11 24,960 1,280 1,664 27,904 4,224 3,584 35,328 6,144 13 8,804 1,664 384 0 21,400 1,920 33,560 7,120 15 76,800 ~ 76,80" 0 8,832 3,304 87,936 33,792 16,304 15,152 1,152 32,608 1,664 17b 31,701 4,211 1,623 37,535 2,421 1,156 27,787 986 15a 35.584 33.2833,280 1,408 70,272 3,100 15b 20,480 18,204 512 39,196 3,100 LOCALITY 154-B-41 17 27,776 15,000 1,536 44,112 4,096

2a 3,200 1,728 20,928 0 3,840 5 1,280 14,400 128 LOCALITY 154-B-4S 7 5,312 9a 5,248 256 7,104 128 511 9b 1 804 1,664 28,300 64 5,462 07 5. 13a 28,248 2 304 832 31,384 2,496 64 7,962 25,342 624 27,979 92 15a 8,596 6,848 14,592 512 15b 21,224 28,632 1,088 8,640 38,400 3,456 1,024 42,880 7,552 17 3,712 26,624 3,840 21,248 7,872 59,840 2,496 20 LOCALITY

3 3,840 1,024 88,064 1,408 LOCALITY 154-B-42 2,176 1,152 21,376 6,400 0 23 296 320 7 57',600 4,992 896 63,488 1,920 2a 20,416 12,160 176 704 38 040 64 9 80,640 3,456 640 84,736 128 2b 960 10,240 11 39,740 5,748 1,119 46,607 4,001 3 20,608 5 1,024 25,856 3,712 7 13,013 8 940 41 21,994 3,201 9 8,192 8,'064 512 16,768 14,208 LOCALITY 11 8,462 4 261 641 13,364 11,420 7,680 39 936 2,816 50,432 3,328 5 37,488 2,432 640 40,560 640 15 9,282 4,096 55,874 6,656 7 41,600 3,328 768 45,696 512 16 17,152 4 352 62,976 5,376 9 49,896 6,912 896 57,704 17,664 18 46,592 109'066 4,096 159,754 99,940 50,026 8,042 962 59,030 8,561 13 5,641 2,712 1,620 9,973 2,113

LOCALITY 154-B-43 LOCALITY 109-B-17 2 48,256 4 736 256 53,248 1,280 4 33,920 13 056 512 47,488 492 3 63,104 19,072 768 82,944 768 6 46,720 2 68,836 4,484 4 18,688 7,808 384 26,880 1,920 5 30 592 6,400 384 37,376 128 280 22,400 512 120,192 30,976 values represent the number of specimens in a cubic centi- 14.592 1,024 56,192 20,352 meter of the 80-180 mesh separate or residue. Refer to Appendix V. 14,511 3,620 60,092 32,426 2predominantly Morrow. 11 15,232 83,072 2,688 3Total Foraminifera, 13 2,624 64 3,264 256 46 BAYLOR GEOLOGICAL STUDIES

APPENDIX V

METHODS AND PROCEDURES

representing a large ve section were MAPPING PROCEDURE thoroughly mixed. Samples were pulverized and sifted through a 1 The Waco sheet S. Army Map Service, Corps of Waco NH14-3; scale 1/250,000, contour interval 50 feet) was enlarged screen (200 mesh/in'; .074 and placed in a desiccator which to 1/125,000 for use as a base map. In the northern half of the maintained a relative humidity of 50 percent for 48 hours. mapping was undertaken on quadrangle maps a scale of X-ray samples (200 mesh and 50 percent humidity) 1/24,000 (contour interval 10 feet) and transferred to the base map. were x-rayed under conditions following : Aerial photographs (1/20,000) were used in southern McLennan County. 1. span- 2 theta Data for subsurface mapping were obtained from electric of 2. speed- 2 theta per min. approximately 150 wells; 68 key wells are m Appendix I. he isopach map (fig. 2) is based on surface and subsurface data. 3. scale- 80 4. time constant- 3 sec. CALCITE PERCENTAGE 5. scale factor- 30 methods are available to estimate the approxi­ A sample weighing 5 to 9 grams was pulverized (-80 mesh), mate mineralogic composition of bulk samples from X-ray diffraction and placed in a 250 ml flask. Dilute hydrochloric acid (10:1) was slowly patterns : prepare and run a suite of known compounds, comparing poured over the sample until vigorous reaction ceased. was added their patterns with unknown patterns, or (2) determine the percent of until the flask was the reaction was allowed to continue for 24 calcium carbonate of each sample by insoluble residue method, compare hours, until all calcium carbonate was dissolved. the known percent to the intensity of the calcite diffraction and Ashless filter paper was weighed, the sample was filtered and washed estimate the percentage of other constituents by relative comparison of in­ with 250 ml of distilled water, and dried at room temperature for 48 tensities with the calcite diffraction line. The latter method was adopted. hours before being placed in an oven for 4 hours. The sample and filter paper were weighed and the percentage of residue was determined. MICROFAUNAL ANALYSIS

CARBON PERCENTAGE One hundred grams of sample were boiled and washed through 80 and 180 mesh Tyler screens. Foraminifera were absent the 0-34 The residue from the calcium carbonate analyses on filter and 34-80 mesh separates. paper was placed in a weighed crucible and heated by a Fisher burner for 1 hour. The crucible and sample were cooled to temperature Foraminifera in a cubic centimeter of the 80-180 mesh separate were and weighed. The weight of carbon, driven off as was de­ population counts were made of each species in the sample. termined and converted to a percentage value. Cubic centimeter samples containing abundant Foraminifera were split microsplit technique into fractions, such as 1/2, 1/4, 1/16, and the microfossils in the fractional sample were counted and converted to a X-RAY PROCEDURES one cubic centimeter equivalent by multiplying x2, x4 or xl6.

type was sampled. Where microfaunal abundance data on figures 4-11 are individuals of the unit is greater than 1 foot, it was channeled and divided into 2 or the mesh residue. Precise population figures for each species are more overlapping units. Samples were selected to avoid intensely weathered included in Appendix IV. material. INDEX

7, 10. 13, 15, 19,

33 20, 24, 26, 30, 32, 34 36 10, 22 J. K., foraminifers, 10, 19, 21, 22, 25, 27, 28, sec Balcones fault zone, 8, 36 31, 33, 35, 36 Bar-deposited limestone, 36 11, 23 Recrystallization, evidences, 11, 36, 39 Bathurst, R. G. C, 10, 36 Hedbergella, 11, 13, 19, 22, 23 Reptiles, 22 Bathymetry, 23 F., 7 Bentonite beds, 8, 21, 23 Biomicrite, 10, 11, 13, 15, 16, 19, 21, 23, 25, Garrels, R. M., 29 c , 27 28, 31, 33, 36 Geological time units, 7, 8 . 35 Cretaceous, 7, 8, 36 Schumard, G. G., 7 13, 15, 16, 19, 35 Jurassic, petrology, 10-22 7, 8, 16, 22, 23, 29, 30, Paleozoic, 8 m Bluebonnet member, 16-22, 23, 31,32,33,34,35,38,39 Quaternary, 8 conclusions 36-39 General description, Bluebonnet member, 8-10 mmeralogy, 16-22 fauna, {see Fossils) 9, 14, 20, environment, 29 summary mmeralogy, 17, 22 . 22 23. 24. 26. 30. 32, 34, 37 Gross lithology, 8-10 ver, field relationship, 8 geologic history, 23-36 gross lithology 8 Hayward, O. T., 7 Stratigraphy, 8-23 12, 14, 16, 18, 20, 26, Hill, R. T., 7 units, W T 7 Austin formation, 7, 36 Huang, Bluebonnet member, {see Bluebonnet ou crop, and locality map, 9 member), 17, 28, 29, 36 paleontology 22-23 Fossils) map, Bluebonnet basin, 9, 23 Buda formation, 7 1 member, 7, 8, 28, 38, 39 plants, , Eagle Ford group, 7, 39 sedimentary petrology, Krumbein, W. C., 29 "Fish beds limestone petrology 10-16 Lake Waco formation, 7, 9, 12, 13, 14, shale petrology, 16-22 21, 24, 25, 26, 27, 28, 10, 37 Lagoon, 23, 28, 38, Borderland features, Lagoonal evolution, " Bosque escarpment, 8 Leverett, S, formation, 7, 8, 16, 17, 22, 29 Brown, C. W., 23 Limestone, Bluebonnet member, 7 L. F., 7 10-16, 22, 28 29, Sol 36 19, 21, 25, Woodbine formation, 7, 8, 16, 17, 22, 29 Cementation, 36, 39 31, 33, 35 R. S., 7 outcrop, 19, 21, 25, 31 Taff, J. A., 7 Chemical analysis, 12, 18, 20, 24, 26, 30. 32, 34 vertical variations, 10-11 9, 23 Lozo, F. E., 7, 22 bathymetry and distribution, 23 Lucke, J. B., 23 station, 10 Compaction, 36, 39 County, 7, 8, 10, 11, 16, 17, 23, 28, T 7 29, 36 7 Marcou, J., 11 17 7, 29, 36 McAtee, J. T., 7 7 Eh, 17, 22, 28, 29, 38, 39 10 Coryell County, 10, 17 ber Dallas, 39 Bluebonnet lagoon, 28, 29, 36, 38, 39 Bluebonnet Del Rio, 39 early mature stage, 28, 29, 38 12, 14, 17, 18, 20, 24, 36 late youthful 28, 29, 38 20, 24, 26, 28, 30, Gulf coastal mature stage, 28, 29, 38 County, 7, 8, 10, 16. 22, youthful stage. 29. 38 23.28,29,36 Environments, geochemical, 29 glaucomte, Hillsboro, 16, 23 evidence, anaerobic environment, 29 ' ' ' Limestone County, 7, 36 Eh value, 29 17 14 17 18 28 McLennan County, 7, 8, 10, 11, pH-Eh control, 29 17, 21, 22, 23, 25, 28, 36 pH-Eh values, 29 16, 17, 18, 20, 24, 26, pH indicator, 29 90 Moody, 7 Erosional history, 36 14 16 17 18 20 Moody hills, 7

6 32. 37 ' ' ' ' 17, 21, 23, 25, 31

Fossils, 22 Robertson County, 36 abundance, 12, 18, 20, 24, 26, 30, Moreman, H, 22 Mosasaurs, 22 22 Vertebrates, 22 ammonite, 22 Oxidation-reduction potential, 29 fish scales, 22 22 fish teeth, 22 gastropod, 22 reptiles, 22 10, 11, 13, 15, 16, 19, 22, Pace, L., 7 23,27,28,31,33,35,36 29 Weller, J. M., 36 22 Paleontology, 22-23 22 X-ray diffraction, 7, 10, 12, 14, 16, 18, 20, ' ' ' 24,26,30,32,34

BAYLOR GEOLOGICAL

Baylor Geological Society

1. Type electric log of McLennan Countv. 1"-100'; 1"-S0'- $2.00. 2. Reptile of flying and swimming rep­ tiles. each. Comparison of the dinosaurs. $0.10 each. .5. Guide to the mid-Cretaceous geology of central Texas, May, 1958. $4.50 per copy. 4. Location map of logged wells in McLennan County, 1959. 1"-1 mile, $7.50 per copy. 5. Layman's guide to the geology of central Texas, 1959. Out of 6. Collector's guide to the geology of central Texas, Out of print. 7. One hundred million years in County, 1960. Out of print. 8. Cretaceous stratigraphy of the Grand and Black Prairies, 1960. $5.00 per copy. 9. Popular geology of central Texas, west central McLennan County, 1960. Out of print. 10. Popular geology of central Texas, Bosque County, 1961. $1.00 per copy." 11. Popular geology of central Texas, northwestern McLennan County, 1961. $1.00 per copy. 12. Popular geology of central 'Texas, southwestern McLennan County and eastern Coryell 1962. $1.00 per copy. 13. Upper Cretaceous and Lower Tertiarv rocks in east central Texas, Fred E. Smith, Leader, 1962". $1.00 per copy. 14. Precambrian igneous rocks of the Wichita Mountains, Oklahoma, Walter T. Huang, Leader, 1962. $1.00 per copy. 15. Why teach geology? A discussion of the importance and cost of teaching geology in high schools, junior colleges and small 4-vear institutions. Free upon request. 27 pp. (1961) Baylor Geological Studies 16. Holloway, Harold D. (1961) The Lower Cretac Trinity McLennan County, Baylor Geological Studies Bull. No. 1 (Fall). $1.00 per copy. 17. William A. (1962) The Lower Cretaceous Paluxy sand in central Texas : Baylor Geological Studies Bull. No. 2 (Spring). $1.00 per copy. 18. E. Robert (1962) Water diagenesis in Lower Cretaceous Trinity aquifers of central Texas: Baylor Geological Studies Bull. No. 3 (Fall). $1.00 per copy.

available from Baylor Geological Society or Baylor Geological Studies, Baylor Waco, Texas