ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

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As Maxwell (1970) explained, there was a GENERAL GEOLOGY OF EAST TEXAS/INTRODUCTION 35 FIG.14/INLAND SALT MARSH NEAR GRAND SALINE,VAN ZANDT CO.WHITE CRUSTY SALT DEPOSITS CAN BE SEEN AT TIMES OF LOW WATER LEVEL (PHOTO BY GMD). FIG. 15/OIL DEPOSITS IN ASSOCIATION WITH SALT DOME (ADAPTED FROM ROADSIDE GEOLOGY OF TEXAS, DARWIN SPEARING, 1991, ©MOUNTAIN PRESS PUBLISHING COMPANY,MISSOULA,MT). and gravel from the west continued to pour in, forming a massive stack of sediments. These inclined sedimentary layers are thought to have added nearly 250 miles to the coastline of the North American continent and to total nearly 50,000 feet in thickness. During the Tertiary, sea levels rose and fell and shallow seas repeatedly covered and then retreated from much of the state. As a result, the conditions under which the sediments now underlying East Texas were deposited also showed a great deal of variation (Seldon 1979; Spearing 1991). As pointed out by Sellards et al. (1932), during the Tertiary there was ...a continuous and relentless struggle between the encroaching waters of the Gulf and heavily loaded, large streams. The sea endeavored to advance over the land, and the rivers constantly tried to build seaward a newly deposited land in the form of a deltaic plain. In some epochs the water forces prevailed, in others the land-building processes predominated. ...rhythmic alternating succession between marine and continental deposition. In most places massive sandstones are either delta deposits or were laid down by streams on a land surface. The fossiliferous clays are mostly shallow-water marine beds. The glauconitic clay and sandy clay beds were deposited during a change in the position of the shoreline, and the lignite beds were formed in swamps or lagoons on a low continental area above the shoreline.
36 INTRODUCTION/GENERAL GEOLOGY OF EAST TEXAS FIG. 16/FIGURE SHOWING AN EXAMPLE OF HOW TEXAS WAS COV- ERED BY AN INLAND SEA AT VARIOUS TIMES DURING THE CRETACEOUS (ADAPTED FROM ROADSIDE GEOLOGY OF TEXAS, DARWIN SPEARING, 1991, ©MOUNTAIN PRESS PUBLISHING COMPANY,MISSOULA,MT). The result is a complex intergrading and interbedding of Tertiary sediments, some representing off-shore marine layers (with fossil shells), some coastal mud flats, others sandy or gravelly coastal beach or delta deposits, and still others materials laid down in the swampy or marshy areas between the meanders of coastal plain rivers. Numerous layers were deposited over the area, the type of layer depending on water depth, distance from shore, and other factors. Often an alternation can be seen between material dominated by calcareous clay deposited under shallow water marine conditions and layers dominated by sand deposited on land. The following sequence, exposed in East Texas, is an example of such an alternation of geologic formations: Sparta (sand—S), Weches (calcareous clay—CC), Queen City (S), Reklaw (CC), Carrizo (S) (Sellards et al. 1932; Bridges & Orzell 1989a). These sedimentary processes continue today as modern rivers (e.g., Colorado, Brazos, Sabine) dump their clay, silt, sand, and gravel near, at, or off the Texas coast. (Sellards et al. 1932; Spearing 1991). However, a significant amount of the sediment moving down Texas rivers is today being trapped in man-made reservoirs. This results in the filling of the reservoirs and the eventual end of their usefulness, as well as the erosion of Gulf Coast beaches as lost sediments are not replaced. Eventually, pressure, heat, and time consolidated the sediments, in some cases producing rather hard sandstones. However, a variety of other materials also formed, including glauconite (a green-colored hydrous iron potassium silicate clay), iron ore (e.g., in the Weches formation), and lignite (a low grade coal). Later, changes in sea level and tectonic movements caused these sedimentary rocks, which now underlie East Texas, to be thrust above sea level. Erosion then removed material, in some places exposing older layers, and shaped the surface into its modern form—other than sedimentation, erosion is the most important geologic factor shaping the landscape of East Texas. In fact, all of East Texas is an erosional landscape, with sediments slightly more resistant to erosion occupying higher points in the landscape and more easily eroded layers occupying lower positions. As one drives from west to east across East Texas, progressively younger wedges of sediment are exposed at the surface, “arranged like a tipped stack of books” (Spearing 1991) or a stack of cards, with the youngest layers found near the present-day Gulf Coast (Figs. 19, 20). These sedimentary layers are more or less parallel to the coast (see Figs. 17, 18), giving stark visual evidence of their history—layer after layer laid down over tens of millions of years, little by little increasing the size of the North American continent. In fact, probably the best short-hand description of the geology of East Texas is given by Spearing (1991) who said the story “is one of tremendous sedimentation and progressive construction of the southern continental margin of North America....” The one significant exception to this pattern is the area associated with the Sabine Uplift in the northeastern part of East Texas in the vicinity of Harrison, Panola, Sabine, and Shelby counties (Collins et al. 1980) (Figs. 17, 21). This structural feature represents an area of regional uplift resulting in slightly older sediments being exposed at the surface. As a result, some geologic layers which are
Page 1 and 2: ILLUSTRATED FLORA OF EAST TEXAS
Page 3 and 4: ALLDREDGE, LINDA & JACK BATTERBAE,
Page 5 and 6: We would like to recognize and expr
Page 7 and 8: ISSN 0833-1475 ISBN 1-889878-12-X S
Page 9 and 10: “DEEP EAST TEXAS IS AN OLD, QUIET
Page 11 and 12: Elray S. Nixon E lray Nixon was bor
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Page 15 and 16: TABLE OFCONTENTS/ PAGE APPENDICES A
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Page 21 and 22: 4 INTRODUCTION/GEOGRAPHIC AREA OF E
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Page 37 and 38: 20 INTRODUCTION/GUIDE TO ENDANGERED
Page 39 and 40: 22 INTRODUCTION/GUIDE TO GLOSSARY,
Page 41 and 42: 24 INTRODUCTION/GUIDE TO ABBREVIATI
Page 43 and 44: 26 INTRODUCTION/SUMMARY DATA ON FLO
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Page 49 and 50: 32 INTRODUCTION/GENERAL GEOLOGY OF
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86 INTRODUCTION/PRESETTLEMENT, EARL
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88 INTRODUCTION/PRESETTLEMENT VEGET
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90 INTRODUCTION/CURRENT VEGETATION
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106 INTRODUCTION/POST OAK SAVANNAH
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110 INTRODUCTION/GEOLOGY AND SOILS
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112 INTRODUCTION/SOILS, FIRE, AND T
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114 INTRODUCTION/SOILS, FIRE, AND T
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116 INTRODUCTION/ PRESETTLEMENT, EA
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118 INTRODUCTION/VEGETATION OF POST
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124 INTRODUCTION/CONDITIONS TODAY O
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128 INTRODUCTION/RED RIVER AREA are
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130 INTRODUCTION/BLACKLAND PRAIRIE
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132 INTRODUCTION/GEOLOGY OF BLACKLA
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134 INTRODUCTION/PRESETTLEMENT AND
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144 INTRODUCTION/VEGETATION OF BLAC
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146 INTRODUCTION/FUTURE OF BLACKLAN
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148 INTRODUCTION/FUTURE OF BLACKLAN
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150 INTRODUCTION/CADDO LAKE LOCATIO
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152 INTRODUCTION/CADDO LAKE FIG.84/
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154 INTRODUCTION/PRESENT AND FUTURE
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156 INTRODUCTION/BIG THICKET THE BI
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158 INTRODUCTION/BIG THICKET GEOGRA
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160 INTRODUCTION/NATURAL HISTORY OF
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234 INTRODUCTION/HISTORY OF BOTANY
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248 INTRODUCTION/BOTANY AT UNIVERSI
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250 INTRODUCTION/BOTANY AT TEXAS A&
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252 INTRODUCTION/BOTANY AT TEXAS A&
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254 INTRODUCTION/OTHER CONTRIBUTION
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256 INTRODUCTION/CURRENT BOTANICAL
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