Surficial Geology of the Naples 7.5' Quadrangle, Maine
Total Page：16
File Type：pdf, Size：1020Kb
DE PART MENT OF CON SER VA TION Maine Geo logi cal Sur vey Rob ert G. Marv in ney, State Ge olo gist OPEN- FILE NO. 97-65 Ti tle: Sur fic ial Ge ol ogy of the Naples 7.5- minute Quad ran gle, Cum ber land County, Maine Author: Carol T. Hildreth Date: 1997 Fi nan cial Sup port: Funding for the prepara tion of this report was provided in part by the U.S. Geo logi cal Sur vey STATE MAP Pro gram, Co op era tive Agree ment No. 1434- 95- A- 01364. As so ci ated Maps: Sur fic ial ge ol ogy of the Naples quad ran gle, Open- File 97- 50 Surfic ial materials of the Naples quadran gle, Open- File 98-188 Con tents: 9 p. report Maine Geo logi cal Sur vey Open- File 97- 65 Surficial Geology of the Naples 7.5-minute Quadrangle, Cumberland County, Maine Carol T. Hil dreth CTH En ter prizes 135 Wash ing ton Street Hol lis ton, Mas sa chu setts 01746 IN TRO DUC TION The Naples 7.5' quadran gle has an area of about 133 km2 others (1985, p. 52) point out that de posit s of gla cial streams in (52 mi2). It is lo cated in south west ern Maine, within the Sea - Maine form a den dritic pat tern that may reflect pre gla cial drain - board Lowland physiographi c province , about 32 km (20 mi) age (Figure 2). Thus the pregla cia l Androscog gin River may northwest of Portland. Alti tudes range from 89 m (267 ft), which have flowed from Bethel southward down the Crooked River is the level of Sebago Lake, to more than 260 m (780 ft) on Bar- val ley into the Se bago Lake area; and the late- glacial An - ton Hill near the north eastern corner of the quadran gle. Most of droscoggin River, laden with melt water sedi ments, probably fol- the map area is under lai n by gran itic bed rock of the Se bago plu- lowed the Crooked River valley for some time during ton. The Se bago pluton is light-gray to pink, medium-grai ned, degla cia tion before being di verted to its mod ern course (Fig ures non- to slightly fo li ated, biotite-m uscovite granit e. The granit e 1 and 2). is in truded in places by Mesozoic pegm ati te dikes and basal t or It is also no table that deep val leys east and west of the dia base dikes. In a few places in the quad ran gle, there are ex po - Crooked River val ley contai n sparse gla cial out wash de posit s, sures of roof pendants of metas edim entar y rocks that the Se bago parti cular ly Pleasant Lake and Parker Pond on the east and Long plu ton in truded dur ing the Mis sis sip pian Pe ri od about 354 mil - Lake on the west (Figure 1). This sub ject invit es further inves ti - lion years ago (Hussey, 1985). gati on beyond the scope of this re port. Ridges in the Naples quadran gle com monly were shaped The present in vesti gati on was carrie d out as part of a coop - by glacia l ice flowing toward the south-southe ast and have been erati ve geologi c mapping project funded by the Maine Geologi - elongate d in that di recti on. The to pog raphy of the study area is cal Survey and the U.S. Geologi cal Survey . Two maps are also control led partly by joint ing in the Sebago pluton. For ex- as so ci ated with this re port. The geo logic map (Hildreth, 1997) am ple, the northwest ern part of Sebago Lake is up to 90 m (300 shows the dis tri bu tion of the sedi mentar y units and discusse s ft) deep. The great depth of this basin proba bly has re sulted from their age, com posi ti on, and ori gin. It also include s infor m ati on glacia l plucking of joint blocks in the Sebago granit e. relat ing to the geo logic his tory of the quadran gle, such as gla cial The major stream drain age in the Naples quadran gle is striati on azi muths and radio car bon dates on fossil or ganic re- southward via the Crooked and Songo Rivers into Se bago Lake. mains. The geo logic map provides the ba sis for the discus sion of These rivers merge at Songo Lock about 2.2 km (1.4 mi) north of glacia l and postgla cia l history present ed here. The ma te ri als the lake. The Songo River conti n ues from the lock to the lake, map (Hildreth, 1998) shows specif ic site data used to help com - into which it has built a sub stan tial Holo cene delta that is nor - pile the geologi c map. These data in clude ob serva ti ons from mally sub merged be cause a dam has raised the lake level. gravel pits, shovel and auger holes, con struc tion sites, and test The valley of the Songo River, which include s Long Lake borings. and Brandy Pond, is partly filled with sedim ents depos it ed by glacia l melt water , predom inantl y on the south and west sides. PREVIOUS WORK The val ley of the Crooked River is com pletely filled with gla cial meltwa ter de pos its. These sedim ents form a “valley train” out - Early work on the surfic ial geol ogy in this part of Maine wash system that extends from Sebago Lake up the Crooked was done gen er ally at a recon nais sance level and at a smaller River val ley as far as 32 km (20 mi) north, al most to the modern- scale (Bloom, 1960, 1963; Thomp son and Smith, 1977; Thomp - day An droscoggin River near Bethel (Figure 1). Caldwell and son and Borns, 1985a,b). Bloom (1959) produced a geologi c 1 C. T. Hildreth Figure 1. Map of west ern Maine show ing fea tures discussed in the text. Modi fied Figure 2. Map of a por tion of Maine show ing the con trast from the Surfic ial Geo logic Map of Maine (Thompson and Borns, 1985a). be tween the drain age pat tern of mod ern riv ers (solid lines) and the pa tern of glacial streams inferred from meltwa ter de posits (dashed lines). Modified from Caldwell and others (1985, Figure 8). map for his report on the geol ogy of Se bago Lake State Park, in all evidence of pre vious gla ciations in the Naples area was which he descri bed many of the feature s and landform s in de tail. obliter ate d during the last (late Wisconsi nan) epi sode, when the Signifi cant sand and gravel aqui fers were mapped by Wil liams Lau ren tide ice sheet ad vanced from the north west to a ter minal and Lanc tot (1987). Gla cial fea tures in the Naples area, such as po si tion on the con ti nen tal shelf. ma rine del tas and la cus trine rhyth mites were in ves ti gated and Evidence of gla cial ero sion within this area is no ticeable discusse d in re cent years by many workers (Thomp son and oth - mainly as glacia l stria tions on freshly exposed bed rock surface s. ers, 1989; Thomp son and oth ers, 1995a,b). The soil survey of Ramp- and- pluck to pog ra phy on bed rock knobs, in clud ing a few Cum ber land County greatly fa cili tated field work (Hed strom, roche mou tonnées as so ci ated with stria tions, defi nitely rec ords 1974). southeas tward movem ent of the ice. It should be noted that gla- cial stria tions weather rapidl y and survive only a very short time GLACIAL HIS TORY (gen er ally only a few dec ades) af ter ex po sure to sur face ele - ments in the Maine cli mate. Those seen along the shore of Se- South west ern Maine proba bly ex pe ri enced sev eral epi- bago Lake are on bedrock surface s recent ly stripped of overly ing sodes of glacia tion during the Pleis tocene Ice Age, but virtu all y sedi ments by wave ac tion (probably due to the lake level hav ing 2 Surficial Geology of the Naples Quadrangle been ar ti fi cially raised by the mod ern dam). Most other stria - in this part of the lake to ex clude the sea from the Crooked River tions were found on recent ly exca vate d bedrock surface s. val ley, be cause marine del tas and clay de pos its do oc cur along Gen er ally, the stria tions in di cate a south- southeast di rec - the east ern and southern mar gins of Sebago Lake” (Thomp son tion of ice flow; some variati ons can be at trib uted to local defle c- and Borns, 1985b). tion around ir regular iti es of the bedrock to pog raphy . At one The present author accept s the inter preta ti on of an ice local ity on Route 302 northwest of Thom as Pond, two sets of in - block in Sebago Lake and proposes that much of the gla cial melt - ter sect ing stria tions trend 158- 167o and 133-137 o, the lat ter be - water within the Naples quad rangle (possi bly even in the Ray- ing the ear lier set.