summary in 700 words

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please give me summary of the paper in 700 words what it discusses, focusing on what the depositional environment of Central Texas was during the Cretaceous.

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A Publication of the Gulf Coast Association of Geological Societies www.gcags.org L C C T T B H , Peter R. Rose 718 Yaupon Valley Rd., Austin, Texas 78746, U.S.A. ABSTRACT In Central Texas, the Balcones Fault Zone separates the Gulf Coastal Plain from the elevated Central Texas Platform, comprising the Hill Country, Llano Uplift, and Edwards Plateau provinces to the west and north. The youngest geologic formations common to both regions are of Albian and Cenomanian age, the thick, widespread Edwards Limestone, and the thin overlying Georgetown, Del Rio, Buda, and Eagle Ford–Boquillas formations. Younger Cretaceous and Tertiary formations that overlie the Edwards and associated formations on and beneath the Gulf Coastal Plain have no known counterparts to the west and north of the Balcones Fault Zone, owing mostly to subaerial erosion following Oligocene and Miocene uplift during Balcones faulting, and secondarily to updip stratigraphic thinning and pinchouts during the Late Cretaceous and Tertiary. This study attempts to reconstruct the burial history of the Central Texas Platform (once entirely covered by carbonates of the thick Edwards Group and thin Buda Limestone), based mostly on indirect geological evidence: (1) Regional geologic maps showing structure, isopachs and lithofacies; (2) Regional stratigraphic analysis of the Edwards Limestone and associated formations demonstrating that the Central Texas Platform was a topographic high surrounded by gentle clinoform slopes into peripheral depositional areas; (3) Analysis and projection of regional updip thinning patterns of Upper Cretaceous and Tertiary formations from the Gulf Coast Basin northwestward along the San Marcos Arch, across the Balcones/Ouachita Downwarp, into the heart of the Central Texas Platform; (4) Derived published stratigraphic analyses of the Cretaceous Western Interior Seaway; (5) Estimation of burial depth from thermal maturity of Eagle Ford organic shales (overlying the Edwards by approximately 150 feet) in the outcrop area around Austin and Comstock, and in the subsurface of Wilson, Karnes, and DeWitt counties; and (6) Implications as to burial depth of Edwards and associated formations based upon the presence or absence of stylolites, which form in carbonate rocks under known subsurface conditions, including depth related to pressure. The Late Cretaceous through Tertiary geologic history of the Central Texas Platform may be summarized as follows: (a) Over the ~10 million years following the end of the Albian, the vast Edwards carbonate bank was mantled beneath a covering veneer of thin (<100 feet) early Cenomanian formations (Del Rio, Buda, and Eagle Ford–Boquillas) that did not eliminate the gentle depositional topography around the bank margins, and also did not cover some local highs along the bank margins. (b) The western interior of the Central Texas Platform was covered by 700 to 1100 feet of open marine Austin Chalk (Santonian), Taylor Clay, and Navarro Marl (Campanian and Maastrichtian), and Midway Clay (lower Paleocene), which muted but did not obliterate depositional topography of the covered bank margins. The low-lying muddy bank was periodically exposed during this ~28 million year period, and meandering streams developed along its margins with surrounding very shallow pelagic seas. (c) Upper Paleocene, Eocene, and Oligocene formations pinched out preferentially westward and northward onto the Balcones/Ouachita Downwarp, which coincided with the underlying Ouachita Thrust Belt and the future Balcones Fault Zone. Throughout this period (~37 million years), the exposed, low-lying bank (adjacent to coastal plain and fluvialdeltaic depositional tracts) began to be gently uplifted. This allowed subaerial erosion to begin, of surficial Eocene sediments as well as the mantle of lower Paleocene and Copyright © 2016. Gulf Coast Association of Geological Societies. All rights reserved. Upper Cretaceous soft mudrocks and marls. Gradual entrenchment of incised streams around the bank Manuscript received October 19, 2015; revised manuscript received April 28, 2016; margins also occurred. manuscript accepted May 13, 2016. (d) Beginning in late Oligocene time, the combination of accelerating gulfward downwarping and uplift of the GCAGS Journal, v. 5 (2016), p. 141–179. 141 142 Peter R. Rose interior resulted in increased exposure and erosion of the buried Central Texas Platform, until Georgetown and Edwards rocks began to be exposed and eroded, their detritus deposited in alluvial aprons on the adjacent coastal plain. Balcones faulting during the late Oligocene and Miocene (~23 million years) marked the culmination of uplift along the west and north side of the Balcones Fault Zone, and accelerated incision of existing streams, especially around the margins. (e) Continued regional uplift of the Colorado Plateau during late Miocene and Pliocene (~8 million years) elevated the western margins of the exposed Edwards carbonate bank, tilting the Plateau surface gently toward the southeast. Headward erosion from east and south began to cut into the high-standing carbonate mass. Streams feeding outward from the Plateau constructed sloping gravel aprons composed of carbonate and chert debris onto the coastal plain. So far, approximately 9300 cubic miles of rock has been eroded from the Edwards Plateau, Llano Uplift, Hill Country, and upper Gulf Coastal Plain as the result of Tertiary uplift and Balcones faulting, with such erosion continuing today. PREFACE I began my investigations of the Edwards Group of Texas in 1962, when I was a young geologist working for the Shell Oil Company in South Texas, sitting wells on the so-called Edwards Reef Trend (= Stuart City Reef), and the backreef Person-Fashing Fault Trend a dozen miles updip to the northwest. In 1966, I returned to the University of Texas (Austin), where my Ph.D. dissertation was a regional monograph integrating what I had learned about the Edwards in the subsurface (released courtesy of Shell), with results of my 1967 surface mapping of Edwards rocks in the eastern Edwards Plateau (Rose, 1972). During the same period Shell geologists C. I. Smith, Jr. and Johnnie B. Brown, under the leadership of the late Frank Lozo, were carrying out extensive stratigraphic investigations of outcropping Edwards and equivalent formations farther west and north, but this superb work, which facilitated the stratigraphic integration of Edwards and equivalent formations of the entire region, remained mostly proprietary until publication by the Texas Bureau of Economic Geology (Smith et al., 2000). As the dissertation approached completion, I was fascinated by new questions about the Edwards Plateau, especially the geologic events that occurred after deposition of the widespread, pelagic Buda Limestone, at the end of the Comanche Epoch. What was the Late Cretaceous and Tertiary history of the Plateau area? How deeply had the Edwards been buried by younger formations in the Plateau area? Was it subaerially exposed during the Late Cretaceous? The Early Tertiary? Or was it finally exposed and eroded only during and after uplift by Balcones faulting during the late Oligocene and early Miocene? Other questions concerned the entire immense carbonate bank complex that formed in West, Central, and South Texas, in the lee of the Stuart City Reef—how did it relate to extensive Lower Cretaceous terrigenous clastics of the Rocky Mountain Province? How did the Comanche carbonate shelf relate to the Cretaceous Western Interior Seaway? Addressing these geological questions was hampered by three basic problems: (a) most of the pertinent research was proprietary or still to be carried out; (b) Post-Edwards rocks were mostly absent in the region, either by non-deposition or later ____________________ erosion, so there was very little direct evidence bearing on the problem1; and (c) I was deeply involved in a professional career, with little time to spend on personal investigations. So I put further research on the Edwards Plateau on the shelf for nearly 40 years. I finally returned to these long-deferred questions in 2012, 50 years since I first began to study the Edwards, and 40 years after publication of Rose (1972). There is still much that remains unknown about these topics, but we do have more relevant data now, and they allow us to make reasonable inferences about what may have happened in Central and West Texas during the ~90 my from the Late Cretaceous through the Pliocene, after Balcones faulting elevated the southeastern margins of the Edwards Plateau during the late Oligocene and early Miocene. The present report thus addresses research questions that I have puzzled over for many years. INTRODUCTION The Edwards Plateau is an immense tableland that dominates the geography of West-Central Texas, covering more than 45,000 square miles, in parts or all of 29 counties (Fig. 1). Along its northern margin, the Plateau rises 100 to 300 feet above the adjacent rolling prairies; along its southern margin, it stands 500 to 1500 feet higher than the adjacent coastal plains of the Rio Grande Embayment. To the east, where the Plateau is dissected by east-flowing rivers, high-standing divides rise 100 to 400 feet above valleys cut in older formations. Erosional remnants of thin, deeply weathered Buda Limestone overlie the Edwards in flat, high divides in the heart of the Plateau. The Edwards Plateau extends westward across the Pecos River, where it is sometimes called the Stockton Plateau, and to the southwest, across the Rio Grande, where it is known as the Serrania del Burro, which owes its much higher elevation to Laramide uplift. To the northwest, the upper surface of the Edwards Plateau merges almost imperceptibly with the younger High Plains (or Llano Estacado) of West Texas and the Texas Panhandle (Rose, 2012). The Plateau is the topographic and geomorphic expression of a thick, widespread, flat-lying sequence of Lower Cretaceous (mostly middle and upper Albian) limestones and dolostones assigned to the Edwards Group, which thickens southwestward, from about 400 feet on the north to more than 800 feet along the southern edge of the Plateau. Edwards carbonate strata are generally harder and more resistant to weathering and erosion than the underlying softer, Trinity-age sandstones and marls, which is why the Edwards Plateau is a high-standing topographic feature, dissected and rough-edged around its margins (Rose, 2004). Neogene erosion of the eastern Edwards Plateau region, related to Balcones faulting and uplift, has stripped away much of the Edwards Group from alluvial valleys cutting eastward and southward across Trinity-age Glen Rose and Hensel formations, leaving only Edwards remnants in high-standing interfluvial divides. This distinctive landscape is known as the Texas Hill Country. In the valleys of the Colorado River and its eastflowing tributaries, the Pedernales, Llano, and San Saba rivers, erosion has cut down into Paleozoic and Precambrian rocks of the Llano Uplift. But prior to Balcones faulting, a continuous blanket of Edwards (and Buda) strata covered the entire Central Texas Province, including that part which is now in the subsurface (Woodruff, 2002). Edwards carbonate rocks record deposition on a vast offshore bank, far south and west of any substantial input of terrigenous sands, muds and clays. The climate was subtropical, temperate to arid. Depositional environments ranged from re- 1 Actually, only a very thin (<40 ft) veneer of Buda strata overlies the Edwards over much of the Edwards Plateau, with even thinner remnants of underlying Del Rio pinching out on the southern flank, and overlying Boquillas (= Eagle Ford) present in the central and southwestern sectors. Southward-thickening erosional wedges of Austin Chalk are present on the far southern flank of the Edwards Plateau, where it impinges on the Chihuahua Trough. Otherwise, there are no Upper Cretaceous or Tertiary formations present in the region, except for scattered Pliocene/Pleistocene high gravels around the Plateau margins, and Quaternary alluvial deposits in some river valleys. Late Cretaceous and Tertiary Burial History, Central Texas 143 Figure 1. Edwards Plateau, Llano Uplift, Hill Country, Balcones Fault Zone, and Coastal Plain, Central Texas. stricted shelf interior, to low-energy shallow open shelf, to highenergy bioclastic shelf-margin. Where such environments of deposition survived into latest Albian time (typically high on the Central Texas Platform), the sedimentary rocks that formed there are also called “Edwards,” even though they are coeval with uppermost Georgetown strata to the south and northeast (Rose, 1972; Young, 1974, 1986). A large body of well-documented geologic research has been carried out on the Edwards Group in the Edwards Plateau region over the past 50 years. But little has been written about the subsequent geologic history of the region after Edwards deposition ended—i.e., what younger formations may have covered the Edwards, their thickness and areal extent. We understand that the eastern and southern margins of the Edwards Plateau were elevated above the Gulf Coastal Plain beginning about 25 million years ago, during late Oligocene and early Miocene time, by Balcones faulting (Weeks, 1945a, 1945b). This event left unmistakable sedimentary evidence—a widespread carbonate and chert gravel-and-sand outwash plain—in Oligocene Catahoula and Miocene Oakville outcrops on the Gulf Coastal Plain to the east and southeast, representing alluvial and coastal plain deposits derived from recently uplifted, rapidly eroding carbonate uplands to the west and northwest. It is generally accepted that the gentle gulfward tilt of the Plateau is post-Miocene, related to the regional rise of the Colorado Plateau to the northwest (Galloway et al., 2011). Otherwise, the geologic timing of Edwards Plateau uplift remained unknown—was the Plateau subaerially exposed, weathered, and eroded beginning sometime in the late Cretaceous, or during the Eocene, or only incidental to Balcones faulting and uplift in the Oligocene and Miocene? Purpose The purpose of this paper is to summarize the geologic events that may have transpired between the emergence of the immense Edwards carbonate bank in the late Albian/early Cenomanian (100–98 million years ago), and the Pleistocene, especially how those events influenced the burial history of Edwards and associated formations. Because of the general absence of conventional geologic evidence in the subject area, such an undertaking has required consideration and synthesis of many geologic subspecialties—stratigraphy, tectonics, burial history, paleogeography, organic geochemistry, petrology, and porosity/ permeability analysis—to piece together various lines and items of evidence to construct a credible, though admittedly speculative, geologic history of this large region over the last ~100 million years (since the end of Edwards deposition). 144 Peter R. Rose Pertinent Previous Work Cretaceous rocks of the Edwards Plateau region are now well understood, thanks to careful, well-documented geologic mapping and stratigraphic syntheses, mostly by geologists involved with sustained efforts by the late Frank Lozo of Shell Development Co.: Lozo and Smith (1964), Moore (1967), Smith (1970), Rose (1972, 1986a), Halley and Rose (1977), Smith and Brown (1983), Miller (1984), and Smith et al. (2000). Such work provided the necessary stratigraphic framework for many subsequent diverse and detailed research projects. Research projects on equivalent formations in the subsurface of central and south Texas generated counterpart mapping, stratigraphic correlation and geologic synthesis: Winter (1961), Tucker (1962), Bebout and Loucks (1974), and Rose (1986b). Beginning in 1961, Lozo and Smith (1964) and Smith et al. (2000) mapped, correlated and synthesized the Fredericksburg and Washita stratigraphic succession from the central Edwards Plateau westward across Trans-Pecos Texas, and southward, into the Maverick Basin. Smith (1970) carried this sequence across the Big Bend region and into the Serrania del Burro of northern Coahuila, Mexico. Rose (1972) mapped and correlated Edwards and associated formations of the subsurface with their outcrop counterparts of the Balcones Fault Zone and eastern Edwards Plateau, connecting with the findings of Lozo and Smith, thus completing a complete stratigraphic synthesis of these formations across Central and Southwest Texas. Young (1974, 1986) reported on ammonite zonations that confirmed the physical stratigraphic correlations of Tucker (1962) and Rose (1972). Surface mapping of the entire Edwards Plateau region was provided by the Texas Bureau of Economic Geology’s mammoth 1:250,000 Geologic Atlas of Texas, including the Austin (1974), Del Rio (1977), Fort Stockton (1982), Llano (1981), Pecos (1975), San Angelo (1976), San Antonio (1983), Seguin (1974), Sonora (1981), and Waco (1970) sheets. Analogous regional mapping and stratigraphic research were also being carried out at about the same time to the north, in the broad area of the middle Cretaceous North American Interior Seaway, by many different geologists. Two especially pertinent papers were a regional synthesis by Kauffmann (1977), and a synthesis of middle Cretaceous stratigraphy in southeastern Colorado, southwestern Kansas, northeastern New Mexico, and the Oklahoma Panhandle by Scott (1977). In 2003, Scott et al. published an integrated Albian-lower Cenomanian stratigraphic synthesis of sedimentary formations of the North Texas–Tyler Basin, the basinal area northeast of the Edwards Plateau. Phelps et al. (2014) published a comprehensive paper synthesizing the Cretaceous stratigraphy of the Texas Gulf Coast, focusing on sequence stratigraphy. In 1975, Princeton University press published the Stratigraphic Atlas of North America, an extraordinarily comprehensive series of isopach, subcrop, and lithofacies maps, with accompanying cross-sections, prepared by the Exploration Department of Shell Oil Company, and edited by T. D. Cook and A. W. Bally. I have used this as a source for most of the isopach mapping of Upper Cretaceous and Tertiary formations included herein. Papers addressing the structural geology of Central Texas, including the Edwards Plateau, the subsurface Ouachita Fold Belt, the Balcones Fault Zone, and the subsurface of the inner Gulf Coastal Plain, include: Weeks (1945a, 1945b), Flawn et al. (1961, 1967), Murray (1961), Grimshaw and Woodruff (1986), and Ewing (1991, 2003, 2005). The Cenozoic history of the Gulf of Mexico Basin was published by Galloway et al. (2000), and a comprehensive synthesis of Cenozoic stream drainage systems feeding into the Gulf basin was published by Galloway et al. (2011). A recent series of publications by Jackson et al. (2011), Hudec et al. (2013), and Dooley et al. (2013) related offshore salt movements in the deep Gulf of Mexico to Tertiary tectonics in the northern margins of the onshore Gulf. REGIONAL STRUCTURAL ELEMENTS AND HISTORY The structural-geologic history of Central Texas is long and complex. Fig. 2 shows structural features that are important to the geologic history of Central Texas in general, and the deposition of Cretaceous and Tertiary formations, in particular. Ouachita Structural Belt In North and Central Texas the Ouachita Structural Belt, comprehensively described by Flawn et al. (1961), lies entirely in the subsurface. It passes from near Dallas southwesterly to the Austin area, then begins its westward swing, under San Antonio and Uvalde. It is interrupted by the late Paleozoic Devils River Uplift near Del Rio, then bears northwesterly and finally westerly into the area of the Marathon Dome (Laramide), West Texas, where it comes to the surface. The Ouachita Structural Belt is generally thought to ...
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Running Head: THE CRETACEOUS AND TERTIARY FORMATION

The Cretaceous and Tertiary Formation
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THE CRETACEOUS AND TERTIARY FORMATION

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Introduction
The primary objective of this paper is to give the chronology of events that marked
the formation of one of the most adorable physical features on the planet; the Edwards
Plateau which located in Central Texas in the United States of America (Ewing, 2005) The
central theme of this paper focuses on the Cretaceous period which refers to the millions of
years ago when the various structures of the planet earth were being formed. According to
geography, there usually are quite some events that transpired the formation of the various
physical features that we see in the world today and Edwards plateau is not an exception.
This plateau is such a humongous feature covering close to 29 countries although a better part
of it located in West-Central Texas in the United ...

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