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. 99-110 Ti tle: Sur fic ial Ge ol ogy of the Bid de ford Pool 7.5- minute Quad ran gle, York County, Maine Author: Carol T. Hildreth Date: 1999 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 Co op era tive Geo logi cal Map ping (CO GEO- MAP) Pro gram, Co op era tive Agree ment No. 14-08-0001-A0432. As so ci ated Maps: Surfic ial geol ogy of the Biddeford Pool quad rangle, Open- File 99-79 Sur fic ial ma te ri als of the Biddeford Pool quad ran gle, Open- File 99-43 Con tents: 10 p. re port Maine Geo logi cal Sur vey Open- File 99-110 Surficial Geology of the Biddeford Pool 7.5-minute Quadrangle, York County, Maine Carol T. Hil dreth 135 Wash ing ton Street Hol lis ton, Mas sa chu setts 01746 IN TRO DUC TION The Bidde ford and Bidde ford Pool 7.5-minute quadran - gles com prise an area of about 55 square miles (142 km2) along the coast of southwest ern Maine, within the Seaboard Lowland physio graphic province , about 15 miles south of Portland. Alti - tudes range from sea level to about 200 feet (61 m) above sea level. The drain age patter n is dominate d by the Bid deford plu- ton (Fig ure 1), a large oval- shaped bioti te granit e mass that in - truded the sur rounding Precambrian- Silurian me tasedi men tary rocks of the Kitter y and Berwick Form ati ons about 354 mil lion years ago during the Missis sipian Peri od (Hussey, 1985). The Saco River skirts the north east edge of the pluton, and some of its minor tribu tar ies drain the northwest edge and northern part. The Ken nebunk River flanks the south ern edge, and some of its tribu tar ies, includ ing Goff Mill Brook, drain the south ern part. (NOTE: No major stream lies along the plutoni c contac t; per- haps there is a contact-m etamorphic horn fels border zone in the me tasedi men tary rocks that is equally re sis tant to weath er ing and erosion as the mar ginal phase of the pluton itsel f.) The cen- tral and east ern part of the pluton is drained by several small riv- ers and brooks, all of which enter the Atlan ti c Ocean via Goose fare Bay (Fig ure 1), where a bar rier is land of sandy beach and dune de posit s has formed across the mouths of their estu ar - ies. The stream pat tern over the plu ton it self is re marka bly rec ti- Fig ure 1. Bid de ford quad ran gle (out lined), show ing re la tion ship of lin ear, refle cting two major roughly right-angle joint drain age pat tern to bed rock struc ture (from Hussey, 1985). sets—north east and northwest trend ing. The joint patter n is very ob vious on air pho tos, espe cia lly in areas of abundant out crop, but the pat tern is not ob vious on the topographi c map becaus e the 20-foot con tour in ter val is too large to show the many disti nct, the northwest block and appar ent horizon tal southwest displac e- closely spaced, par allel bedrock ridges and poorly drained val - ment of the southeas t block, though the actual movem ent is un- leys throughout the areas of abundant out crop (by far the major known. Note also in Fig ure 1 that the fault trace is uncer tai n and char ac ter istic of the land sur face in this area). shown as a dashed line near the southern end of the pluton. Paral lel to the northeast-tre nding joint set, a 60-foot es- Drain age off this es carp ment fol lows the gen eral rec ti lin ear pat - carpm ent that roughly bisec ts the pluton re flects a mapped fault tern, ex cept near its south ern end where sev eral tribu tary streams (Hussey, l985) that has appar ent rela tive upward displac em ent of have a pronounced change in course to south-southwe st just be- 1 C. T. Hildreth low the scarp (in stead of a right-angle bend to a southwest direc - GLACIATION tion, which is what would be expect ed); this course change may re flect a change in the over all joint pat tern near the fault, or a South west ern Maine proba bly ex pe ri enced sev eral ad- change in the fault di recti on, or movem ent along the fault, or any vances of the Lauren ti de conti nental ice sheet during the Pleis to- com bi na tion thereof. cene Ice Age, but vir tu ally all evidence in this area for pre vious The landsca pe north of the Saco River in the Bidde ford gla cia tions was oblit er ated dur ing the last gla cia tion (late Wis - quadran gle is prim aril y a broad, sandy plain drained eastward to consi nan) when the conti nental glacie r advance d from the north- the At lan tic by Goose fare Brook; the shore there is char ac ter ized west across the area to a term inal posi ti on on the con ti nental by a clas sic Holo cene sandy beach complex that stretches for shelf. Gla cial ero sion within this area is mainly no tice able as miles north ward as “Old Or chard Beach.” glacia l stria tions on freshly exposed bedrock surface s; some The Bidde ford Pool quad rangle con tains many rock is - ramp and pluck topog raphy on bed rock knobs, in cluding a few lands, the larg est two of which are connect ed to the mainland by roche mou ton née and small- scale crag- and- tail features in con - two sandy tom bolos—Fletcher Neck and Hills Beach—which juncti on with the striati ons, defi nitely record southeas t move- enclos e a shallow tidal pool that is pres ently open to the sea only ment of the ice. It should be noted that gla cial stria tions weather through a deep narrow channel be tween the two rock islands rapidl y and survive for a very short time (gener all y only a few (Hul mes, 1981). years) af ter ex po sure to sur face ele ments in this cli mate; those There is some indi ca ti on that part of the glacia l and pregla - along the shore of the Saco River and At lanti c Ocean are on bed- cial Saco River may have fol lowed a more south erly course bef - rock expo sures recent ly stripped of overly ing surface sedi ments ore enter ing the sea, as inferred from the distri bu tion of by storm wave acti on. Most oth ers were found on re cently exca - melt water depos it s (Caldwell and others, 1985). One such vated bedrock surface s in borrow pits. Gener all y, the striati ons course could have been into the lower Kennebunk River, around indi cat e a south to southeas t di recti on of ice flow; some varia- the northwest nose of the Bid deford pluton (see Fig ure 1). This tions can be at trib uted to local defle cti on of the ice flow around thought invit es further inves ti gati on beyond the scope of this re - irregu lar iti es of the bedrock to pog raphy . At least four lo caliti es port. Also, during re-em ergence of the coastli ne in postgla cia l had two sets of in ter sect ing stria tions—(1) in the West Brook time, part of the Saco may have flowed briefly along an aban - valley , east of downtown Bidde ford (135° stria tions are older doned chan nel(?) that begins at its upstre am end along the cur- than 169- 183°); (2) in a borrow pit betwee n the Bidde ford City rent shore of the Saco betwee n Jordan Point and St. Fran cis Line and Beaver Pond (153-158° stria tions are older than 165- Col lege, thence southeas t landward of Hills Beach into Back 175°); (3) along the shore south of East Point in the Bid deford Bay and The Pool. The sur face of the Pre sumpscot marine clay Pool quad rangle (133-137° stria tions are older than 158- 152°); in The Pool is 15 to 20 feet be low sea level and deepens to the and (4) in a house founda ti on exca va ti on on South Road next to south of Fletcher Neck (Hul mes, 1979, 1981), where there ap- the Maine Turnpike where age rela ti ons of the striati ons were not pears to be an offshore sub marine channel. The present author clear. Where age re lations be tween two sets on the same outcrop proposes that, in downcut ti ng its chan nel through gla ciomarine are clear, the younger stria tions rep re sent a more south erly (in sedi ments, the an ces tral Saco en coun tered the bed rock at the places, even south west erly) ice flow direc tion.