RI6 Some Observations on the Sediments of the Delaware River

Public Access Copy DO NOT REMOVE fro m room 208 . STATE OF DELAWARE DELAWARE GEOLOGICAL SURVEY REPORT OF INVESTIGATIONS NO.6 SOME OBSERVATIONS ON THE SEDIMENTS OF THE DELAWAR E RIVER SOUTH OF WILMINGTON By Robert R. Jordon and Johon J. Groot Newark, De laware February, 196 2 SOME OBSERVATIONS ON THE SEDIMENTS OF THE DELAWARE .RIVER SOUTH OF WILMINGTON By Robert R. lordan Geologist, Delaware Geological Survey and lohan I. Groot State Geologist February, 1962 CONTENTS P... Abstract ••• ••••••••••••••••••••••••••••••••••••••••• '.e •••••••• • .1 Introduction. •••••• •• ................................ .1 Description of samples .........•..•.................... • •••••••••• 1 Megascopic descriptions •. .....•................................... 1 Microscopic descriptions ...........................................•1 Mechanical analyses •• ......................... , .. 4 Heavy mineral analyses . .................... • 4 Clay mineralogy. ................................. 6 Plant microfossils • ...................................... .6 Discussion ' 6 References. ......................... 12 ILLUSTRATIONS Figure 1. Location of boring studied in this report ••••••••••••••••••••••••• •• 2 2. Log of boring showing location of samples •••••••••••••••••••••••••• 3 3. Cumulative curves of samples 20908· 20916 • • • • • • • • • • • • • • • • • • • • • • •• 5 4. Median grain size, heavy minerals and arborial pollen •••••••••••••••• •• 7 TABLES Table 1. Mechanical composition: statistical parameters. ••9 2. Percentages of heavy minerals 10 3. Percentages of arborial pollen ............................•......11 Abstract A series of cores was obtained from a boring in Dr. John K. Adams, Lniversiry of Delaware, inter the sediments of the Delaware River near the Dela preted the X-ray diffraction data, and Mr. Thomas C. ware Memorial Bridge. The mineralogy, texture and Gray prepared and made a preliminary study of the palynology of these samples have been studied. The pollen contained in the sediments. sedimentary and palynological records suggest that the Delaware River, while swollen with Wisconsin Description of Samples meltwarers, deepened its channel and that subse quent flooding of the mouth of the stream by rising Each sample has been examined megascopically sea waters initiated the deposition of estuarine silts and under the srereographic microscope, analyzed in post-Wisconsin time. to determine mechanical composition and heavy mineral content and studied by X-ray diffraction to Introduction identify the clay minerals. A set of cores taken from a test boring for a pro MEGASCOPIC DESCRIP TIONS posed bridge adjacent to the present Delaware Me morial Bridge between New Castle County, Dela Samples 20908 through 20914 (fig. 2) are identical ware and Salem County, New Jersey, provided an in megascopic appearance. They are dark gray, opportunity to study the sediments accumulating in slightly micaceous and organic, relatively uncom that portion of the Delaware River estuary. The pacted silts. Thin lamellar concentrations of very nature of these sediments is significant as a study fine sand are irregularly distributed through the finer of a depositional environment, as an inq uiry into material. The water content of the undisturbed cores the geologically recent history of the Delaware River was high, particularly in the upper samples. The and also because of the economic effects which driller. recorded little resistance to his tools which these sediments may have on the maintenance of generally sank through these sediments under their navigation channels, the shell fisheries, and the own weight. These are the sediments of primary quality of ground water drawn from wells along the interest to this study for they are the most recent shores of the Delaware. The present study must be sediments transported and deposited by the Dela considered as a preliminary investigation for it deals ware. only with a single point. Areal studies of much greater magnitude will be necessary to achieve a Below the gray silt is a thin brown silt from which more complete understanding of these sediments. no cores are available. Below this is a yellow, fine, quartz sand 8 feet thick. It is represented The boring from which the cores were taken is by sample 20915. Some small pebbles were reported located 200 feet north of the centerline of the exist from this sand by the driller. ing bridge and adjacent to its west tower (fig. 1). This point is approximately 2340 feet from the Dela Sample 20916 is a dense and compact light gray ware shore and 1050 feet west of the center of the clay with some streaks of red. It is the uppermost navigation channel. The total depth of this boring part of a thick seq uence of variegated and gray was 222 feet (sea level datum). Only the upper 85 clays and fine-grained sands. feet are considered here for this interval includes the relatively uncompacted river silts and the im mediately subjacent materials. An abbreviated log MICROSCOPIC DESCRIPTIONS of the boring, showing the positions of the 9 cores studied, is shown in figure 2. Apart from the clay minerals quartz is the domi nant component of the sediments. In the gray silt At present the Delaware River is brackish and the quartz is mainly subangular but ranges from tidal at the Delaware Memorial Bridge. The chloride angular to rounded. These samples, 20908 through ion concentration of the water at this point ranges through 20914, also contain organic debris and small from less than 50 ppm to more than 2000 ppm with amounts of mica, chert and glauconite. Very few fluctuations in runoff, tide and wind (City of Phila lithic fragments were found. delphia and U, S. Geological Survey, 1958). Surface currents average 2.4 knots during the ebb tide and Sample 20915 is a "clean"sand containing quartz 1.9 knots during the flood tide (V. S. Coast and and a little chert. The quartz is angular. Geodetic Survey, 1961). The sand size fraction of sample 20916 consists The writers gratefully acknowledge the help of almost entirely of very angular quartz. The only Mr. John R. Lewis, Resident Engineer of the Dela other mine rals noted were heavy minerals which are ware Memorial Bridge, in procuring the samples; comparatively rare. 1. DELAWARE ,,-- ........ /,,, ----- ,, / -r', I I .!. - ...... ....- ...__- JIlL._"'_- rLOCATION OF BORING CENTERLINE PROPOSED BRIDGE DELAWARE RIVER NEW JERSEY Figure I. Location of boring studied in this report ------..,...-~------ sea level SAMPLE NUMBER DEPTH DESCRIPTION 20908 36·38 Water 41-43 20909 __-_-:.== 36 feet 20910 46·48 ---------- 20911 51-53 20912 56-58----__~ _ Silt, dark gray 20913 61 -63---J:: _ 20914 66-68 ----It.~~~::71 20915 Silt, brown 20916 ~~::~ 88~r Sand, medium, brown 20922 97·99 Clay, variegated _.=:_ 96 :._---.......... Silt and clay, gray with ......... -- - --- some layers of fine sand '::'F.rn 132 /ii!;::r:.;:/ Sand, fine, gray :;'·:::':~166 Clay, variegated ~:.: 190 ., "..:.... ..'. Sand, fine, gray with ~~::~.;.":. lenses of silt and clay .:;.:.... ~ 222 total depth Figure 2. Log of boring showing locations of samples MECHANICAL ANAL YSES the grains. The he avy fraction was s eparated by centrifuging the samples in terrabromoethane (S.G . Mechanical an al yses of all samples were made 2.92) then freezing the lower portion of th e cent rif u sing V. s. s ta nd ard s ie ve s for the sand s i ze s and uge tubes and decanting th e li ght fraction. The hy drometer met hods for the finer sizes. The re sults method of separation is es s entially th at described by were plotted as cumulative grain size distribution Fes senden (1959). Between 100 and 150 non-opaq ue curves which are shown in figure 3. The grain s ize gra ins were identified for each sample using t he is meas ured in phi (q,) units (Knimbein, 193 4). Val line count method (Doeglas, 1940). ue s are recorded from the curves at the 50th pe rcen tile for the media n grain size (Mdq,) and at the 84 th The hea vy mine ra l suites from the deep clay, the (q,84) and 16th (q,16) percent il e s one s tanda rd devi sand and the upper silts a re somewhat different. ation ei ther s id e of the mean. Measures o f the sort The heavy mineral co ntent of each sample is gi ven io g (a¢) and skewness (aep) were calcul at ed using in ta bl e 2. T he ' clay has a restricted suite with a the formulae of Inman (1952): ve ry high staurolite COnte nt and rel ativel y large amounts o f tourmaline and z ircon. The sand has a muc h more varied s uite incl udin g hornblende, garnet, aq, 1/2 (q,84 - q,16) kyanire , fi brol ire, hyp ersthen e, tourm aline, stauro li te, s ill ima nite and zircon in order o f de c reasing abun aq, Mq, - Mdq, dan ce. The heavy minera l suites from each o f t he aq, samples of s ilt (20908 throu gh 20914) a re very simi l ar. All are domin ated by ho rnb lend e, which e xceeds where 1/2 (q, 16 + q,84) 50 ·percent of the non- opaque minera ls in each cas e. L e s ser amounts of to urmali ne, zi rcon, garn et, s ill i The s tatistical parameters for e ach s ample are manite and fibrol it e as we ll as other relatively given in table 1. Because of the very fine texture scarce minerals are p resent. of the sediments ¢ 84 did not fall within the limits of the cumul ative freq uency curves in all case s, Some of the features of tourmaline, zirc on, horn Values li sted as estimated are based on extended blende and garnet have been not ed. About one curves. Calculati ons of a¢ and a¢ based on these fourth of the tourmaline gra ins in th e s il t a nd clay estimates are, of cours e, also approximate. The are rounded. Tourmaline found in th e sand was al e rrors introduced in this mariner are thought to be most entirely an gular.

Load more