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# Surface Geology

# of Dallas and

Ta 

# rra

# nt Cou

# nties, Texas

by Phil Scoggins TABLE OF CONTENTS 

## 1. INTRODUCTION 

## 2. TOPOGRAPHY AND FORMATION EXPOSURES 

## 3. FORMATION DESCRIPTIONS and INFORMATION 

## 4. REFERENCES INTRODUCTION Rocks, minerals, and fossils found on

### the surface 

### of Dallas and Tarrant Counties were deposited 

### in the Mesozoic 

### Era 

### and Cenozoic 

### Era. (See Time Chart) 

### The resulting 

### formations are 

### .either 

## of cretaceous 

### Age, 

### 66

## to 144 million years ago 

### (ma) or Quaternary 

### Age, present day

## to 10,000years ago (Dates 

### are approximations.) In Dallas County,

### the Cretaceous ranges 

### from about 75 ma

### to 90 ma. 

### In Tarrant County, 

### the Cretaceous ranges

### from 90 ma

### to 115 

### ma. 

### In other parts of Texas more 

### of the Cretaceous Era is represented. For instance, 

### the Cretaceous/Tertiary 

### (K/T) boundary. Cretaceous deposits 

### in North Texas are mostly marine 

### in origin. The Western 

### Interior Seaway

### at its greatest extent spanned 

### the 

### the North American 

### continent

### from the 

### Artic Circle 

## tothe present 

### day Gulf

### of Mexico. 

### Although 

### this was 

### the Age 

### of the Dinosaur, 

### their habitats were sparse 

### in Tarrant County 

### and non-existent 

### in Dallas County.The most abundant habitat was marine. The depth of 

### the ocean rose and fell 

### many 

### times. 

## In doing

### so, 

### the sediments deposited

### varied 

### from generally sandy shorelines and deltaic complexes 

### to low energy, deeper water.

Quaternary sediments 

### were deposited 

### in areas adjacent 

### to the 

### Trinity River 

### and its 

### tributaries. As 

### the 

### Trinity winnowed over 

### time, 

### it would leave terraces coveredwith 

### sand 

### and 

### gravel. These 

### river deposits 

### range 

## in age

### from 1.8 ma.

## to recent. Mammoth and bison bones are sometimes found along the 

### Trinity and itstributaries. 

### The 

### Sedimentary Record 

### To understand 

### the sedimentary 

### rock record 

### there arethree fundamental ideas to grasp: Time 

### units, Rock units, andTime-rock units. 

### Time 

### units are names given

### to intervals of

### time: The designation

### forTime units is in 

### years before

### the present. Designations 

### are abbreviated, 

### often as mya (millions of years ago) 

### or ma (mega-annum 

### or millions ago). 

### Time units define

### the chronological sequence of

### the events in rocks. Their ranking

### from longest

### to shortest is Eon, period,Epoch, then 

### Age. Age dating by radiometric and/or the fossil record are

### two methods 

### to define the 

### timing of events. 

### Rock 

### units are 

### the initial stratigraphic ranking 

### of rocks, Ranking 

### from largest to finest

### the order is Group, Formation, Member, bed.
The most common useof

### the rock unit classification is

### the 

### Formation. A formation is 

### a layer 

### of rock 

### that is uniform 

### in its makeup, corresponds 

### to other layers deposited 

### during 

### that period, and can 

### be defined 

### (by recognition, 

### fossil correlation 

### or other means) 

### over an area large enough 

### to be traced and mapped. Geologists

### call this 

### lithographic 

### and stratigraphic homogeneity. Members 

### subdivide

### a formatlon when there are distinctive changes 

### in some of

### the mlnor component. These changes can be 

### an increase 

### or decrease 

### in

### the number 

### of shale, llmestone 

### or sandstone beds 

### in a relatlvely short vertical section ofthe formation.
Formation nomenclature 

### is colloquial 

### in nature. Formation names commonly come 

### from 

### their general make-up, 

### the location where 

### it was 

### first described, 

### or the person 

### whom

### first discovered

### the layer. This can lead

### to some confusing names 

### until you learn 

### your way around 

## - for instance, 

### we have

### the "Austin Chalk" 

### in Dallas County! Recognizing formations 

### will assist 

### in finding fossils, identifying 

### them, and recording 

### them

### for study. Constructlon 

### of most geologic maps 

### is at the formation 

### level. In addition

### to maps, observations of 

### the rock types, 

### the fossils, and even 

### the vegetation can help identify 

### theformation. For example,

### the cedartrees around Cedar Hill prefer 

### limy 

### soil; Post Oak

### trees prefer sandy 

### soil. More detailed information

### on the formations comes later in this document, 

### Time-rock 

### units , System, Series and 

### stage, provide 

### the concept 

### of a sequence in time. Time-rock units do 

### not equate

### with a specific 

### time interval. Instead, 

### they define the duration of a geologic event in a geographic region.

Here is an example of Rock units, Time-rock units andTime units. Arlington, Texas was once 

### the setting 

### for a delta on

### the eastern shore 

### of 

### the Western 

### Interior seaway. Sands, 

### and clays are 

### the individual öeds 

### that comprise 

### the three Members 

## , Rush Creek, 

### Dexter, Lewisville and Arlington 

### of

### the Woodbine Formation



### .They 

### are in

### the Woodbine Group. These are 

### the rock units. Time-rock units andTime units can be confusing because the same name often applies

### to both. 

### The Time-rock 

### units

## of the Woodbine 

### Formation 

### place

## it in the Cenomanian Stage. The stage

### tells you

### the Woodbine is in

### the lower part 

### ofthe Gulf Series 

### in

### the Cretaceous System. These 

### are

### all relative times because 

### they differ according 

### to geographic 

### location. Deposition 

### of the Woodbine 

### did not occur 

### atthe same 

### time in all 

### the same places. 

### It took millions ofyears for the delta

### to advance 

### out into

### the sea way. 

### Time units 

### give us 

## a specific measurement

## in millions

## of years. The Cenomanian Age 

### (91

### to 97.5 ma) is 

### in

### the Late Epoch 

### (66.4

### to 97,5 ma) of

### the Cretaceous Period (66.4 

### to 144 ma).

TOPOGRAPHY AND FORMATION EXPOSURES 

### During 

### the Cretaceous Period, 

### the seas rose 

### and

### fell leaving multiple layers 

### of deposits

### with various çpmpositions. These formations represent 

### several deposltlon environments: shallow marine, deltaic, 

### and coastal. Ancient land deposits 

### to deeper-water sediments provlde 

### a rich varlety 

### of 

### fossils: vertebrate specimens 

### lnclude 

### marine reptiles, sharks, turtles, flshes and 

### rarely dinosaurs.There 

### are also 

### plenty of invertebrate fossils: 

### sea urchins, shells

## of clams, snails, 

### and ammonltes 

### (related

## to the Nautilus).

### After 

### the cretaceous Period

### the area

### tilted slightly resulting 

## in

## a L/2 degree dip due east. This slight dip across

### the

### thin deposits causes many formations 

### to outcrop on

### the surface 

## - much 

### like slicing

### an onion. The exposures 

### form bands

### that run generally 

### north-south. since 

### the various 

### rock units 

### are deposited 

### one

### on

### top

### of another, 

### the oldest 

### is on the 

### bottom and youngest 

### ontop. The

### tilting exposes 

### the oldest rocks 

### in the western part of

### the area and 

### theyoungest in

### the east. 

### During

### the Quaternary Period,

### theTrinity River carved

### out terraces 

### through

### the Cretaceous deposits. The 

### river 

### left behind clays, sands, and 

### gravel

### that are 

### of economic 

### value. Today, 

### theTrinity River headwaters 

### form 

### in western Tarrant 

### county, 

### fed by

### the many creeks 

### flowing from Parker, Jack 

### and Denton 

### counties. The 

### river causes 

### a dendritic drainage 

### pattern across most 

### of western Tarrant 

### country. Fossil 

### mammoth, bison and other mammal bones can befound along the

### Trinity River. Dallas 

### county has

### six formations represented 

### on

### the surface. Tarrant 

### county has 

### fifteen formations on

### the surface. The 

### list below is

### from most recent 

### to oldest. 

## PERIOD FORMATION Quaternary: Alluvium and terrace deposits 

### Cretaceous: Ozan (Lower Taylor Marl)

Austin Chalk 

### (often referred

### to as a Group) Eagle Ford (often referred 

### to as a Group) Woodbine 

### (often referred

### to as a Group) Grayson Marl Main Street Limestone Par¡¿-Paw Formation Weno Limestone Denton Clay Fort Worth Limestone Duck Creek Limestone Kiamichi Formation Goodland Limestone Walnut Clay Paluxy Formation 

### COUNTIES Dallas and Tarrant Dallas

Dallas
Dallas and Tarrant Dallas and Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant Tarrant

FORMATION DESCRIPTIONS and INFoRMATION 

### Quaternary 

### alluvium and 

### terrace deposits 

### - Dallas and Tarrant Counties

The Quaternary period has

### two subdivisions. The Holocene Epoch ranging 

### the present 

### to about 12,000 years ago and 

### the pleistocene 

### from 12,000 

### to about 1.8 ma. Although 

### the Pleistocene 

### is referred 

### to as

### the Ice Age,none of

### the ice sheets extended as

### far south as Fort Worth 

### or Dallas. The 

### maximum 

### extent, 18

## to 20 thousandyears ago, 

### of

### the Laurentide ice Sheet

### was barelytouching northeast Kansas, 

### The ecology 

### of DFW area 

### was somewhere 

### in the transition zone

### with respect

## tovegetation. A broadleaf 

### forest (included: chestnut, Paw Paw 

### or "Prairie Banana", Osage Orange) was present 

### in eastern North Texas 

### (Isthat why 

### they call 

### it the Eastern CrossTimbers?) 

### which gave 

### way

## to openwoodlands (include: 

### juniper and mesquite) 

### to the 

### west. The boundary is likely close

### to where 

### it istoday because, in part, 

### the soils becomes more rocky 

### to west and the climate is dryer. 

### Alluvial deposits 

### of clay, sand, and gravel 

### are found 

### in the flood-plain areas. 

### They are

### the youngest deposits 

### inthe area. Some deposits are 

### present 

### day as

### the result 

## of storms moving large volumes 

## of water requires high energy. Subsequently 

### there is enough energy

### to erode and move sediments as large as gravel and 

### boulders. Gravel bars are 

### a good place 

### to look 

### for fossils. 

### Terrace deposits 

### outcrop adjacent

## to and outside

## ofthe immediate channels 

### theTrinity River and 

### itstributaries. Their composition is

### that of 

### alluvium. Terraces

### were formedwhen

## the river changed course, abandoning 

### the previous 

### flood-plain, and

### the new channel 

### cuts deeper into the earth.



### anttguus), camel, horse 

### and 

### other mammal bones 

### are can be found in these Quaternary deposits. 

### Quaternary deposits unconformably 

### overlie 

## the Ozan 

### formation. The hiatus lasted about 70 million years. 

### Ozan 

### Formation 

### - Dallas County 

### The Ozan 

## is also referred

## to as

## the Lower 

### Taylor Marl. 

### The Ozan 

### unconformably 

### overlies

## the Austin Chalk. Descriptions

## of color and composition 

### vary widely because 

### often 

### the descriptions 

### are 

### either state 

### wide summaries 

### or of particular localities. The Geology 

### of Texas Volume 1, Stratigraphy by Sellards, Adkins, and Plummer describe 

### the Ozan as a dark 

### gray marl. The marl can be sandy, chalky 

### or glauconitic and can be 

### mostly sand. 

## Its generally 

## a calcareous micaceous 

### clay

### that coarsens upward 

### though

### the section 

### with increasing proportions 

### of calcareous silt 

### and sand. Occasionally 

### present 

### are glauconite, hematite 

### and 

### pyrite in 

### nolular

### form, and phosphate 

### pellets. When weathered, 

## it is 

### a brownish 

### gray color.

### The clay 

## in this formation contains 

## the clay mineral 

### montmorillonite

### that expands 

### when

### wet. Montmorillonite 

### is descused in more detail in

### the section on

### the Eagle Ford. The Ozan was deposited in a deep marine, low energy, environment. 

### The bivalve Inoceramus 

### is much smaller 

### than those 

### found 

### in the Austin 

### Chalk. Other fossils include shark's 

### teeth and microfossils. Trace fossils being burrows 

### of Ophiomorpha 

### (shrimp), Thalassinoides 

### (arthropod) and 

### Planolittes 

### (worm) can 

### be found while vertebrate fossils 

### are close to nonexistent. Although 

### not in Dallas orTarrant Counties, probably

### the best exposure and fossil collecting 

### is in

### the North Sulphur River. The Society's Occasional Papers Volume 

## 4, Fossil Collector's Guidebook

### tothe North Sulphur River, 

### by Mark McKinzie, Ron Morn and Ed 

### Swiatovy,2001 is an excellent resource. 

### Austin Chalk 

### - Dallas County

The Austin Chalk is considered 

### by many

### to be a group of formations. TheAustin 

### chalk has 

### five members. From bottom 

### totop is

### the Atco Member, 

### the Austin 

### chalk, Blossom 

### sand, Brownstown Marl 

### and Gober 

### chalk. In 

### Dallas 

### county,

## the Geologic

### Atlas

## of Texas, Dallas 

### sheet has not 

### differentiated mapped 

### area. specifically, 

### the condensed 

### section 

### at the base 

### oftheAtco Member 

### and known as

### the Fish Bed 

### conglomerate is present where 

### the Austin chalk-Eagle Ford Group contact 

### outcrops. The 

### Fish Bed conglomerate 

## is

## a light greenish 

### sandy calcareous clay. Phosphate nodules 

### are abundant. However,

### the reason 

### for the name is 

### the extreme abundance 

### of small 

### to microscopic

### fish teeth. The easiest 

### way 

## to collect 

### from

### the Fish Bed conglomerate 

### is

## to submerse large chunks 

### of material 

### in a weak acid 

### bath like vinegar 

### for afew days thèn wash 

### the material 

### through a

### fine sieve 

### to catch 

### the 

### teeth. The acid bath and wash may have 

### to be repeated several 

## time. the There used

### to be a 

### great exposure 

### along FM 1382 

### west 

### of 

### clark Road 

### in cedar Hill, Texas. 

### unfortunately, a retaining was was erected prevent erosion and rock falls along the sharp and

### tall roadcut, The western 

### extent 

### ofthe Austin 

### chalk is sometimes referred 

### to asthe 

### white Rock Escarpment. 

### The contrast between

## the chalk and the 

### underlying Eagle 

### Ford 

### is striking. Looking 

### east

### from locations 

### in Grand Prairie and 

### Irving, the Austin 

### chalk raises 

### out of

### the plains and appears 

### white overlying 

### the dark gray 

### or black Eagle 

### Ford. composition 

### of the 

### chalk 

## is primarily coccolithophores 

### from foraminifera. Coccoliths are calcareous plates found on

### the

### suface of some flagellate microorganisms. Austin 

### chalk covers 

### one-third to one-half of

### the surface 

### of Dallas county. Cedars prefer 

### limy soil and are prolific. The chalk dips 

### at a rate between 15 and 

### 40

### feet per mile

### tothe east or 

### southeast. 

### has many normal 

### faults and fractures, 

### all inactive 

### so don't 

### worry. This is 

### the same 

### formation

### that made horizontal 

### drilling famous. 

### oil companies use

### the faults and fractures 

### totheir advantage, especially 

### in Brazos 

### and Burleson

### counties, Texas,

### oil companies bore 

### verticallyto 

### thetarget depth 

### then bore horizontallythrough 

### the chalk. 

### A horizontal boring encounters more oil filled 

### faults and fractures avertical boring. So, 

### the horizontal 

### well produces 

### much more 

### oil or gas. several quarries 

### located 

### near Midlothian, Texas 

### mine 

### the chalk

### for use 

### in cement. The 

### quarries occasionally 

### grant permission 

### for members

### ofthis society to enter 

### the quarries 

### and collect 

### fossils. Fosslls 

### are generally sparce 

### in the Austin 

### chalk. A shark and afew mosasaur skeletons have been found. 

### Eagle 

### Ford Formation

## or Eagle 

### Ford Group

## - Dallas 

### and Tarrant Counties 

### The gently rolling 

### hiils are referred 

## to as

### the "Black 

### prairie" and the 

### residual 

### soil 

### as "black gumbo." 

### The Eagle Ford 

### contains bentonite, an 

### impure 

### clay

## that 

## is

## a product

## of weathered volcanic 

### ash. Bentonite 

### consists 

### mainly

## of the clay mineral montmorillonite. Differential swell/contraction 

### of montmorillonite as 

### it absorbs

### or looses 

### water can be 

### as much as seven inches causing problems 

### for foundations 

### and roads, Bentonite occurs 

### in

### the Eagle Ford 

### in layers 

### up

### toten inches

### thick. The 

### good news 

### is 

### that 

### the bentonite layers 

### are good sources 

### of samples

### for radiometric age dating. 

### The Eagle 

### Ford

### is 

## a bituminous shale

### with calcareous concretions and 

### large septaria; sandstone 

### and sandy limestone 

### inthe upper 

### parts; and 

### bentonitic 

### inthe lower 

### part. The laminated bedding 

### structure and dark color makes 

### the Eagle Ford easy

### to identify. 

### The Eagle Ford has

### four members: 

### the basal 

### unit is

### Tarrant Beds 

### or six Flags Limestone, 

### Britton shale,

### the Kamp Ranch Limestone 

### and the Arcadia Park shale, 

### top member, TheTarrant Beds isdark gray shale

### that

### weathers

## to brownish

## or bluish-gray. 

## It also includes 

### small lenses of either calcareous sandstone 

### or fossiliferous limestone covering 

### afew feet 

### laterally and approximately 

### two inches 

### thick. Overlying 

### the basal 

### unit is 

### the Britton Formation 

### consisting

### of dark gray, 

### silty shale

### that grades 

### laterally 

### into gray and

### tan shale. A

### thin limestone,

### flaggy,layer above 

## the Britton 

## is named

## the Kamp Ranch Limestone. Depositional environment 

### ofthe Kamp Ranch was 

### in shallow 

### water

### with moderate 

### to high energy. The abundance 

### of shell fragments 

### aid 

### inthe determination of

### the energy level. Overlying

### the Kamp Ranch is

### the Arcadia Park shale. The Arcadia Park and 

### the Britton are very similar in appearance and were deposited 

### in low energy 

### waters

### with depths between 

### 120 and 600 feet 

### which 

### is part 

### of the controversy 

### as whether

### the Eagle Ford 

### is 

### a single formation or a group. 

### The Eagle 

### Ford produces 

### quality specimens: ammonites 

### with shells composed of 

### the original mother 

### of pearl; shark 

### teeth of Leptostyrax and 

### Ptychodus, 

## fish and other marine vertebrate skeletons. Dallas Paleontological Society member 

### Arlene Pike

### was honored 

### for her fossil 

### crab 

### find which 

### was named Homolopsis 

### pikeae. Society members Van Turner was also honored 

### for his

### find Dallasaurus 

### turneri, and Mark Cohen for Russelosaurus Coheni, D.

### turneri and R. Coheni are the 

### twothe oldest known specimens 

## of mosasaur-like marine reptiles in North America. 

### Woodbine Formation or 

### group - Dallas and Tarrant Counties 

### As 

### a group, 

### the Woodbine consists 

### ofthe Rush Creek Member, Dexter member, Lewisville Member and the Arlington Member The Woodbine was 

## a fluvial deltaic system consisting 

## of both marine 

### and non-marine facies. The Woodbine Formation consists 

### of mostly fine grained sandstone 

### with clay and 

### shale. The basal 

### unit, Rush Creek Member, is composed of 

### marine prodelta clays, 

### silts and 

### sands. The 

### overlying Dexter Member is 

### predominately sandstone 

### with clay and sandy 

### or carbonaceous shales 

### interbedded. Features 

### include large scale cross-bedding, 

### ripple marks, 

### and large discoid concretions. 

### The Dexter Member 

### is interpreted

## to be deposited 

### from both marine and non-marine sediments. The Lewisville 

### Member 

## is

## a marine shale

### with various quantities

## of sand, 

## silt and carbonaceous

### clays. The 

### Arlington Member 

### is composed 

### of sandstone 

### and calcareous 

### sand lenses interbedded 

### with sandy

### shales, Beds of ironstone 

### and ironstone conglomerate 

### also occur

## inthe lower part. Sandstones 

### are occasionally 

### conglomeritic 

### and contain occasional 

### to 

### abundant 

### oyster shells.

### The Woodbine unconformably 

### overlies the Grayson Marl. The Woodbine provides soil 

### for awooded region called 

### the Eastern Cross Timbers where Post Oaks are common.The Woodbine is a sandy soil, rich 

### with iron. Iron nodules 

### litter 

## the ground. 

## Iron nodules 

### form when solutions deposit around 

### a "seed" 

### or nucleus of sand 

### or organic material, These concretion nodules look 

### like iron meteorites 

### but are distinguishable because 

### they do no have 

### the magnetic propefties. 

### Iron mineral mostly 

### limonite 

### and hematite 

### give

### the Woodbine 

## a characteristically reddishbrown any yellow hues. 

### The Woodbine Formation, 

## a secondary 

### aquifer 

## in Nofth Texas.

### To the 

### east, 

### the Woodbine produces 

### hard-water 

### as

### a result 

### ofthe iron. Many 

### water wells produce 

### from 

### the Woodbine 

### aquifer. Pesticides, herbicides and petrochemicals on 

### spilt onto surface exposures have 

### the potential 

### to seep down 

### intothis aquifer 

### and pollute 

### water wells down 

### dip (to the 

### east.) Tan colored clays 

### are interbedded 

### inthe Woodbine, 

### and used by companies 

### in Denton County 

### to make 

### brick. 

### In east Texas, 

### the Woodbine is

### the largest oil and gas producing reservoir rock in

### the state.Fossils from the woodbine include the ammonite Acanthoceras, 

### the oyster 

### Gryphea, dinosaurs 

### include

## an unnamed nodosaurid, 

## an unnamed nodosaurid 

### and 

### an unnamed hadrosaur and vadous mollusks. society 

### member 

### Bill Lowe

### was honored 

### by having 

### a trace fossil 

### footprint 

### of a 

### theropod 

### dinosaur named 

### after him, Magnoavipes 

### lowei. Also, member Gary Bird was honored 

### with his discovery, protohadros byrdii. 

### Grayson 

### Formation - Tarrant County The Grayson Formation 

### is 

### a chalky, yellow-white 

### to gray marl 

### with gray 

### shale beds.

## The transition

## from Grayson

## to overlying woodbine represents awithdrawal 

### or regression of Cretaceous seas. Fossils include ammonites 

## : scaphites subevolutus, Turrilites bosquensis, T. brazoensis, Adkinsia 

### sp.; pelecypods, Exogyra arientina (also known as "rams 

### horn") and E.plexa. Trace fossils include Thalassinoides (arthropod) and Serpula (worm tubes). 

### Main 

### Street Formation -Tarrant County 

### The Main 

### street formation overlaying

## the paw paw 

## is

## a resistant limestone 

### formed 

### from supersaturated 

### lime mud. The contact between 

### the two formations represents 

### atransgression 

### of the cretaceous oceans, The Main

### street weathers 

### to a

### white or grayish white color. was 

### a deeper water environment than 

### the Paw Paw. 

### Paw Paw Formation, Denton Clay, 

### Weno Limestone, 

### Fort Worth Limestone and

### the Duck Creek 

### Formation - Tarrant County 

## In Tarrant County, 

### these formations 

### are mapped 

### undivided 

### on the GeologicAtlas of Texas. 

### The Paw Paw's

### type locality 

### is Paw Paw 

### creek which begins 

### in Dennison and 

### flows generally northeast 

### tothe Red River.The 

### clay is dark gray or blackish 

### and somewhat lustrous 

### whenfresh and weathers red-brown to 

### yellowish. shales and clays 

### with some sandstone ledges comprise the 

### formation. Particularly 

### in northern Tarrant 

### county, concretions 

### and iron 

### nodules

### are abundant. 

### The Paw Paw 

### is 

## a ferruginous 

### clay 

## of shallow marine

### origin. Rocks here representthe transgression of cretaceous seas. Fossils include a unique miniature fauna such as ammonites lessthan one 

### inch 

### in diameter; frequently pyritized

### with intricate detail. 

### other genera 

### also 

### exhibit dwarlism 

### but 

### the reasons 

### for the dwarfism 

### are unknown. Shark's 

### teeth are common fossil in

### the paw paw.
The area north 

### of Loop 820 and North Beach 

### street and 

### the community 

### of Fossil 

### creek was productive 

### until development covered

### the site. Typical 

### fossils include 

### shark

### teeth and vertebrae and cartilage, crab claws and carapaces 

### fragments, and dwarf ammonites, 

### and

### the pelecypod, ostrea 

### quadriplicafa. 

### This 

### area has also produced 

### some unusual 

### finds 

### for a 

### marine depositional 

### environment.

### A nodosaur, Nodosauridae 

### indet, was 

### found 

### by

### then L2-year 

### old Johnny Maurice 

### the son

### of society member. 

### John Maurice. 

### unfortunately, 

## it was 

### not named 

## in his honor. Another 

### nodosaur, Pawpawsaurus 

### campbelli 

### wasfound 

## by then 19-year old 

### cameron campbell. 

### society afFiliation 

### unknown. Member Robert Reed found a (unnamed) 

### turtle associated 

### with nodosaur bones.



### weno Limestone has

### three units. The upper 

### unit is chiefly limestone, 

### It varies 

### from hard 

### and massive

### to soft and chalky.when fresh 

## it is light 

### gray

## to yellowish 

### gray and weathers 

### gray

## to yellowish 

### brown. Hardlimestone 

### will form topographic benches. 

### The middle 

### unit is generally a calcareous 

### clay 

### with occasional 

### lenses

## of sand-sized 

### shell fragments. 

### Color varies 

## from olive brown

## to olive gray.The lower 

## unit is predominantly limestone 

### with some sand. This fossiliferous 

### formation is 

### light gray, exceptwhere 

## it is sandy 

## it is medium gray. The lower unit 

### weathers

## to a yellowish 

## brown. Echinoids Macraster obesus, 

### Tetragramma; 

### worm tubes S_etWla; gastropods Gyrodes Conrad, Leptomarìa austinensis can be found. 

### Denton 

### Clay has alternating 

### layers

## of calcareous 

### clay 

### with marl and limestone weathers dusky brown. 

### Atthetime of

### the Denton Clay, deeper 

### water covered 

### the area. The calcium carbonate deposits hardened 

### into a 

### micritic limestone. Clay 

### units have abundant 

### shell debris 

### and some 

### burrowing 

## is evident. Marl beds

### varyfrom argillaceous limestone to calcareous 

### clay. Limestone 

### units are dark gray when 

### fresh and can have 

### thin (<0.6 

### ft.) Gryphea 

### beds. Fossils include pelecypods: Anomia, Pectin, 

### Gryphea 

## and Alectryonia; 

### echinoids: Heteraster 

## and Macraster;

am mon ite 

### : Pervi nquieria 

### The Fort Worth Limestone

### and

## the Duck Creek Limestone 

### are both 

### grayish

## to yellow-gray 

### or yellow-brown. Both formations 

### are limestone 

### and 

### difficult

### to differentiate. 

### FortWorth Limestone 

### is 

### a limestone with 

### alternating 

### thin layers

## of marly clay. 

### The upper 

### 40 feet are cream

### colored. The lower 10

### to 15

### feet has 

### alternating layers 

### of grayish-blue 

### clay/marl 

### with yellowish-white limestone. Pecten

### are more abundant in 

### the Fort Worth Limestone while Gryphea are more abundant 

### in

### the Duck 

### Creek 

### Fm.They 

### are generally 

### prairie 

### land. Fossils 

### include echinoids: 

### Holaster 

### simplex, Macraster; 

### ammonites: Pervinquieria, Mortoniceras; 

### pelecypods: Exogyra, 

### Gryphea and Alectryonia; brachiopod: Kingena wacoensis, and na utiloids 

### Goodland 

### Limestone Formation -Tarrant County 

### The Goodland 

## is a white, fossiliferous, 

### micritic, coarsely nodular, limestone. Bedding is massive 

### with some 

### thin clay beds, The upper 5feet 

## is a fossiliferous, massive, limestone 

## with oolites. Depositional 

### environment 

## is interpreted 

## as shallow,

### warmwater, marine (not necessarily 

### near shore), and 

### within

### the forces 

### and actions

## of waves. 

### Oolites

### are formed around

### a nucleus 

### where aragonite 

### crystals 

### grow in layered rings as 

### a result of

### the back and

### forth action 

### ofthe waves. Since aragonite is a polymorph of and is less stable than calcite, over, geologic, 

### time will convert 

### to calcite. The fragmentation 

### ofthe shells indicates an erosional 

### energy source (waves) and

### the intraclasts also indicate waves as 

### an erosional agent. The

### formation is medium

### to dark gray when fresh 

### and weathers

## to a yellowish brown. 

### This 

### unit has

## a low clay content making 

### it a good support

### for buildings. 

### Fossils 

## include

## the ammonite Oxytropidoceras acutocarinatum, pelecypods Protocardia, Pinna and Lima wacoensis, heaft-shaped urchins in abundance, and miscellaneous gastropods. 

### Kiamichi Formation 

### - Tarrant County 

### The Kiamichi 

### has alternating 

### layer

## of clay and limestone 

### with units 

### generally 

### not exceeding 

## 5 feet 

## in thickness. Sandstone 

## is

## a minor component. olive 

### brown flaky shale 

### that weathers

### totan. Unconformities bound 

### the Paluxy above and below. A transgressing sea deposited clays 

### to form

### the Walnut Clay

### formation. Oyster reefs

### of Gryphea mucronata create resistant, cliff forming benches over 

### the underlying Walnut Clay. 

### Walnut Clay Format¡on - Tarrant Countycalcareous clay and limestone interspersed 

### with Gryphea beds. 

### some of 

## the beds

## form topographic benches.

## clay units 

## are fossiliferous. Limestone 

### unitswhen 

### fresh,

### the color 

### is dark gray and weathers

### to a yellowish brown. 

### clay units are olive brown and weathers

### to a yellowish brown. 

### Paluxy Formation - Tarrant County characteristically, 

### the Paluxy Formation is 

### a reddish sandstone and shale 

### unit 

## that supports Post

### oaks. The environments 

## of deposition were coastal 

### streams 

### and beach environments. 

### Ancient beach 

### deposits form localized dunes of 

### white, well rounded,

### friable sand. 

### some iron stains are 

### present 

### in these dunes. These clean beachsands

### are unmistakable

- 

### miles away 

### from 

### the present

### day ocean. 

### Although 

### not from Tarrant 

### county, dinosaurs 

### like

### the Tenontosaur 

### at

### the Dallas Museum 

### of Natural History arefound in

### the Paluxy Formation 

### in parker and Jack counties.

REFERENCES 

### (not referenced by hyperlinks) Caldwell, 

### 8., and Brogdon, 

### L., 1995, Leaders, Field Trip, 

### Fotl Worth Geological Society Geology 

### of Tarrant County. (publisher 

### not listed.) Dawson, 

### W.C., McNulty, C. L., Reaser, D. F., Leaders, L979, Fieldtrip Guidebook for 

### stratigraphy and 

### structure of selected lJpper cretaceous Rocks 

### in No¡theast Texas. (Texas Academy of Science 82nd Annual Meeting, Arlington, Texas.) Fisher, W. L., Director, 

### t972, "Geologic Atlas ofTexas, Dallas Sheet": Bureau 

### of Economic Geology, (The 

### universiÇ of Texas at Austin, Austin, Texas.) Graham, 

### A. 1999, Late Cretaceous and Cenozoic history 

### of North American vegetation north of 

### Mexico. (Oxford Univ. press, New

### york.) Hagland, 

### J., McKinzie, M.G. and Wilson, M.,2OOL, Field Guide

### to the 

### stratigraphy of the Dallas Fort 

### wotth Area. 

### (self published by

### the Dallas Paleontological Society. ) Mason,

### 8., Berry, L. G., 

### 1968, Elements of Mineralogy (Freeman and Company, San Francisco, CA.) Matthews, R, 

### K., L974, Dynamic Stratigraphy. (prentice-Hall, Inc., Englewood Cliffs, New Jersy,) Mckinzie, M., Morin, R., 

### Swiatovy,8.,2001-, the North Sulphur River. (Dallas Paleontological Society.) Sellards, E. 

### H., Adkins, W. S., and F. B. plummer, The Geotogy

### of Texas (UniversiÇ ofTexas Bulletin 

### 3232,t932). Surles, M,A. 

### Jr., L984, "Nature and significance ofAustin-Taylor unconformity onwestern margin of east Texas basin.,' (American Association 

## of Petroleum Geologists, Bull. 

### ;Vol/Issue:68:4; AAPG annual convention; 2O May 1984; SanAntonio,

## il, USA.) þiþtþ.j sp?osti_!d=652290 S 

### "Texas 

### Dinosaurs, Systematics" 

# http tmWelton, B.

### J., PHD, Farish, R. F., 1993, The Collector's Guide 

### to Fossil Sharks 

### and Rays from the Cretaceous

### of Texas. (Before Time, Lewisville, TX.) Winkler, D.

### A., Murry, P.

### 4., Jacobs, L. L., Editors, 1989, Field Guide To TheVertebrate Paleontology Of The Trinity Group, Lower Cretaceous Of Central Texas. 

### (Institute for 

### the Study 

### of Earth and Man, Southern Methodist University, Dallas, Texas.) Winton, W. M.,Adkins, W. S. 1919, The Geology 

### of Tarrant County, (University of Texas Bulletin No. 1931.)

Link

### to Disclaimer. 

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