ARKANSAS POST QUADRANGLE, ARKANSAS Arkansas Geological Survey DGM-AR-00026 Bekki White, Director and State Geologist Correlation of Map Units

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DIGITAL GEOLOGIC MAP ARKANSAS POST QUADRANGLE, ARKANSAS Arkansas Geological Survey DGM-AR-00026 Bekki White, Director and State Geologist Correlation of Map Units

af a af e Unconformity Holocene Qalss Qcmpb Qcmac Qcm Qsonl Unconformity QUATERNARY GEOLOGIC MAP OF THE ARKANSAS POST QUADRANGLE, Qt Unconformity Pleistocene ARKANSAS AND DESHA COUNTIES, ARKANSAS Qbsl Unconformity Tj Eocene TERTIARY

! ! Description and Depositional Environments of Map Units About the Map

! !

! Introduction ! Qt ! !

! ! ! ! A ! afa The recognition and delineation of depositional Quaternary Age (Pleistocene) Terrace deposits are TH-30 ! Qt The Geologic Resource Inventory (GRI) Program !

!( ! ! 0 environments are the primary means of classifying and typically comprised of clays and silts, however, some sands of the National Park Service (NPS) provides each !

! ! subdividing the Holocene and Pleistocene deposits of the and occasional gravels have been observed. These

! ! of 270 identified natural area National Park

! ! alluvial valley. To geologists, depositional environments materials were deposited in a relatively level to slightly

! ! Service units across the nation with a geologic

! ! are geographically restricted complexes that are generally inclined surface that is bounded on one side by a steeply !

! ! scoping meeting, a digital geologic map, and a

! ! described in geomorphic terms. Classifying sedimentary ascending slope (e.g., a dissected upland) and on the other Q ! cmac ! ! ! sequences according to environments of deposition is by a steeply descending slope (a scarp) which drops to a geologic resource evaluation report. When ! ! afa ! afa

! particularly feasible when dealing with geologically young lower level (e.g., a stream floodplain). In this region of the possible, the GRI program provides large scale !

! 25

! ! ! ! sediments where the geomorphic processes responsible are Lower Mississippi Valley area, terraces are recognized as

! ! (1:24,000) digital geologic map coverage for each ! !

! ! currently operating in the area. Reconstruction of both narrow benches along modern stream valleys and as

! park’s area of interest, usually composed of the

! ! !

! depositional environments for alluvial sequences is a broad plains. These terrace deposits are considered older

! ! ! 7.5-minute quadrangles that contain park lands.

Qt ! Qt

! valuable tool in geologic and geomorphic interpretations. than the recent channel meander and overbank deposits, but

! ! !

! ! Maps of this scale (and larger) are useful to

! !

! The knowledge of these "environmental" conditions and younger than the underlying braided stream deposits.

! ! afa ! !

Qt ! resource management because they capture

! !

! the geomorphic processes at work thereby makes it possible Thickness is approximately 50 feet (15 meters) but is

! ! !

! to correlate and predict the range and distribution of soil locally variable. most geologic features of interest. This map was ! ! !

!( ! types and their physical properties. ! produced for the Department of the Interior

TH-48 !

! !

! Qalss ! Quaternary Age (Pleistocene) Braided stream lower ! Qbsl (DOI) – National Park Service and illustrates the

! ! ! Artificial fill agricultural are locally derived mixtures of deposits (shown in cross-section only) were deposited from

! ! geology of the Arkansas Post 7.5 minute

! af a

! !

! clays, silts, sands and occasional gravels piled above the glacial outwash. These deposits consist of a lower gravel-

! ! !

! quadrangle. This quadrangle was previously !

! !

! natural topographic surface (recognizable and mappable on bearing section overlain by deposits of “clean” sands. The ! !

! compiled at a 1:62,500 scale by Roger Saucier in !

! a a a 7.5-minute quadrangle) to serve as artificial levees in upward gradation from coarse- to fine-grained sediments f ! !

! 25! ! ! ! ! agricultural practices. These agricultural levees are reflects a progressive lowering of the stream and 1967 and Boyd Haley in 1969. Copies of this

! !

afa ! !

! 50 typically long linear features approximately 20 to 50 feet (6 sedimentation velocity as sea level gradually rose to nearly map are available from the Arkansas Geological

! !

! to 15 meters) in width and 5 to 10 feet (1.5 to 3 meters) in its present position. Thickness is locally variable but ! Survey, Little Rock, Arkansas.

! Qt !

! height. They tend to be temporary features that may be typically ranges from 40 to 130 feet (12 to 40 meters).

! ! !

! modified by enlargement or obliteration.

! !

! ! Tertiary Age (Eocene) Jackson Group (shown in cross-

! Tj

! ! !

! Qt

! Artificial fill engineered/ flood control/ navigation are section only) consists of mostly homogenous blue-gray to !

! !

! af e !

! ! locally derived mixtures of clays, silts, sands and dark-gray clays with widely scattered thin zones of silty ! ! occasional gravels piled above the natural topographic clay. Thickness ranges from approximately 270 to 420 feet afa ! ! surface (recognizable and mappable on a 7.5-minute (82 to 128 meters). ! a a ! f quadrangle) to serve as highway and railroad beds, and ! artificial levees for engineering, flood control and ! afa ! navigation purposes. This artificial fill may contain a core ! Natural Levee ! or be capped with rock rip-rap from distant sources. The Stream Overbank ! engineered levees for flood control and navigation are Undifferentiated (Qsonl) Qcmac ! Abandoned Channel ! typically long linear features approximately 50 to 500 feet (Qso) (Qcmac) ! ! (15 to 152 meters) in width and 5 to 30 feet (1.5 to 9 ! Small Streams ! meters) in height. They tend to be more permanent features ! (Qalss) Natural Levee uplands ! when compared to the agricultural levees but still may be ! (Qsonl) !( ! modified by enlargement or obliteration. TH-51 ! Terrace ! Backswamp Quaternary Age (Holocene) Small stream deposits are (Qsobs) (Qt) ! Qalss mixtures of clays, silts, sands and gravels deposited by afa ! present day smaller streams. Individual deposits are often Water

! Point Bar

lenticular and discontinuous. Thickness is locally variable. ! (Qcmpb) Q

t afa ! Qalss Quaternary Age (Holocene) Channel meander point bar

! Qcmpb Arkansas Post National Memorial deposits form crescent-shaped ridges that are deposited on Channel Meander ! Visitor's Center.

! the inside of meander loops as a stream migrates laterally Undifferentiated afa !

and downstream. As a result of this migration, a succession (Qcm) ! ! Stream Overbank

! ! of bars is formed that truncate each other in a complex Undifferentiated ! Jackson Group ! afa (Qso)

! manner. The height of these bars may be as much as 10 Point Bar

! Braided Stream (Tj) ! ! feet (3 meters). The shape tends to conform to the curvature

! afa Lower (Qcmpb)

! !

! of the channel in which they were laid down. Point bars (Qbsl)

! !

! consist mainly of silts and sands. The low areas between ! !

! the sandy ridges are called swales. Clays, silts and organic

! TH-54 ! An illustration of the principle depositional environments involved !( ! matter are laid down in these depressions. The ! afa in a typical meander belt (modified from Allen 1964).

! !

! combination of ridges and swale fillings creates what is

! afa !

! ! known as point bar accretionary topography. Thickness is

! ! !

! locally variable but typically ranges from 30 to 90 feet (9 to ! Q

afa t ! ! ! 27 meters).

! afa 25! ! ! ! !

! ! Quaternary Age (Holocene) Channel meander ! Acknowledgments ! Qcmac ! ! abandoned channel/course deposits are formed after a ! ! ! ! ! meander loop or segment of channel course is cut off from ! ! This map was produced for the DEPARTMENT ! 0 ! the main river. Over time many of the abandoned meander OF INTERIOR – NATIONAL PARK SERVICE, ! Typical flat topography of Backswamp ! loops and channel courses completely fill with sediment. ! ! under the Arkansas – National Park Service (Qsobs) deposits. ! ! This process forms the familiar ox-bow lakes that are ! (ANPS) Mapping Contract C2360086145. ! ! ! ! common features of the Lower Arkansas River Valley. The Special thanks to the National Park Service and ! ! ! ! upper arm of a cutoff meander loop fills with sandy and private landowners who graciously allowed ! !

! ! silty sediments. Deposits in the lower arm are usually finer ! access to their property during this geologic !

! ! grained than those in the upper, but may contain ! ! investigation. ! ! considerable amounts of silts and coarser materials. The ! ! !( afa ! TH-56 ! ! deposits of the central portion generally consist of uniform ! ! ! ! clays that constitute the so-called “clay plugs”. Thickness

2! 5

! is locally variable but typically ranges from 25 to 80 feet References ! !

! Qt (7.5 to 24 meters). 25! Allen, J. R. L., 1964, Studies in fluviatile sedimentation: ! Qcm Quaternary Age (Holocene) Channel meander Six cyclothems from the Lower Old Red Sandstone,

afe ! afa undifferentiated deposits are varying mixtures of Angle-Welsh basin, Sedimentology III, p.163-198.

afa ! Qsonl unconsolidated sands, silts, clays and occasional gravels Fisk, H. N., 1944, Geological investigation of the alluvial

! deposited by large streams and rivers that meander and

valley of the lower Mississippi River, U.S. Army ! shift laterally over time. The deposits that comprise this Corps of Engineers Mississippi River Commission,

! 680 unit lack the unique geomorphic features needed to further

!( Vicksburg, MS., 78p. ! differentiate them based on their specific depositional A' Artificial fill agricultural (afa) on

! 679 environments as observed in the point bar and abandoned Terrace (Qt) deposits. !( Haley, B. R., 1969, Geologic worksheet of the Gillett

! channel/course units. Large streams and rivers establish a Quadrangle, Arkansas Geological Commission:

! afe complex zone in which sedimentation rates are highest near ! afe Open-File Report, scale 1:62,500, 1 page. the active river channel resulting in an alluvial ridge

! Qsonl

! (meander belt) that is higher in elevation than the more

! Howard, J. M., 2008, Arkansas mineral commodity !

! distant floodplain. The division of this unit from Stream

! ! database; Arkansas Geological Survey, in house !

! overbank deposits is primarily based on geomorphic !

! Qcmpb data.

! considerations such as the presence of meander scars, point ! ! ! afe afe bars, and abandoned channels. Thickness is locally Krinitzsky, E. L., 1949, Geological investigation of gravel variable but typically ranges from 30 to 90 feet (9 to 27 deposits in the lower Mississippi Valley and Qcmac meters). adjacent uplands: Technical Report No. 3-273, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, 58p. Qsonl Quaternary Age (Holocene) Stream overbank natural Qcmpb levee are built up along the river banks by the deposition of afe McFarland, J. D., 2004, Stratigraphic summary of sands and silts during times of flood. They normally form afa Arkansas: Arkansas Geological Commission, Qt the highest portions of the land surface within the meander Qcmac Information Circular 36, 39p. belt. Typically, natural levees are incrementally deposited Qsonl Q l sedimentary laminates formed during “overbank” floods. !( a ss Saucier, R. T., 1967, Geological investigation of the Boeuf- This is especially observable in younger natural levees as 13-50 Qt Tensas Basin, lower Mississippi Valley: Technical Terrace (Qt) deposits along the flank Qcm thin, parallel layers of clays, silts and fine sands. However, Report No. 3-757, U.S. Army Engineer Waterways of Dismal Swamp. afa in older natural levees, biogenic reworking by plant roots Experiment Station, Vicksburg, MS, 1 page. Qcm Qcmpb and burrowing organisms has frequently removed most traces of bedding, leaving the clay and silt layers reworked Saucier, R. T., 1994, Geomorphology and Quaternary Qsonl Qalss afa into a homogeneous silty clay with irregular silt pockets. geologic history of the lower Mississippi Valley, Lithologically, natural levees are locally, regionally, and U.S. Army Corps of Engineers Waterways temporally the most variable of all fluvial environments. Experiment Station, v. I and II, 364 p. and 28 plates. Most natural levees overlie backswamp, undifferentiated Schultz, J. R., Mabrey, P. R., Schamberger, J. H., channel meander and undifferentiated stream overbank Krinitzsky, E. L., 1951, Geology of the lower Qcmpb deposits. They may be gradational with the underlying Arkansas River alluvial valley, Pine Bluff, deposits rather than separated by an unconformity. Qalss Arkansas to mouth: Technical Report No. 3-332, Thickness is locally variable but typically ranges from thin U.S. Army Engineer Waterways Experiment veneer to approximately 15 feet (4.5 meters). Station, Vicksburg, MS, 32p.

Symbols

Contacts (Dashed where approximate) A closer look at Terrace (Qt) deposits along Stratigraphic Column the flank of Dismal Swamp. ! 25! Stucture Contours (Contour Interval 25 feet) 250 Structure contours projected for the top of the 75 Tertiary Jackson Group in feet above mean sea Qalss Qsonl Qcmac H

level. o l TH-30 o c

(! e Surface well location Qcmpb n e

TH-30 Qcm A Subsurface well location A' TH-30 680

200 200 Qcmac TH-48 TH-56 200 afa TH-51 TH-54 afe Arkansas River Qt Qcmac afa afa afa afa Arkansas River Backwater 13-50 Backwater Qcmpb 175 679 Qt Qsonl 175 Qt Qalss Present day Point Bar (Qcmpb) deposits Qt along the Arkansas River. Qt Qcmac Qt Qcmac Qt Qalss 50

Qt Q Qt Qsonl Qsonl U Qt Qt A 150 150 T Qcmpb 150 E R

Qt N A R

Qt P Y l e i s t 125 o Disclaimer

125 c e n

e Although this map was compiled from digital data that was successfully processed on a computer system using ESRI ArcGIS 9.x software at the Arkansas Geological Survey 100 100 100 Qbsl (AGS), no warranty, expressed or implied, is made by the AGS regarding the unity of the data on any other system, nor shall the act of distribution constitute any such warranty. 25 The AGS does not guarantee this map or Qbsl Qbsl Qbsl digital data to be free of errors or liability for 75 Qbsl Qbsl Qbsl interpretations from this map or digital data, 75 or decisions based thereof.

The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily 50 50 representing the official policies, either 50 expressed or implied, of the Arkansas Geological Survey. T E E R o c T e I n 25 A e 25 Tj R Y

Tj Tj Tj Tj Tj Tj 0 0 0 m 0 ft. Scale: Scott M. Ausbrooks Horiziontal: 1 inch = 2000 feet Vertical: 1 inch = 25 feet (Exaggeration: 80x) William L. Prior 2009

Date: Scale: Digital Compilation: 1 : 24,000 Jerry W. Clark