JOHN RODGERS Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520

The Taconic Orogeny

Address as Retiring President of The Geological Society of America, Milwaukee, Wiscon- sin, 11 November 1970

ABSTRACT difficulty with this definition, for like a once The Taconic orogeny of eastern North popular definition of graywacke—the sedimen- America was not, as traditionally defined, a sin- tary analogue of gabbro as arkose is of granite gle erogenic event that occurred at the end of —it practically defines the thing out of exist- the Ordovician period, but rather a complex ence. Just as resedimented gabbro is rare and series of erogenic episodes or climaxes spread the original Saxon graywacke is nothing of the over the larger part of that period. In most sort, so the orogenic episode in the Appalachi- sectors of the northern Appalachians it in- ans exactly at the end of the Ordovician, if any, cluded at least three of the following: discon- was quite minor, and the early Paleozoic oro- formity in an external belt where carbonate was genic activity in the area of the Taconic Moun- accumulating; severe early deformation in an tains was all over by that time. Thus, the internal volcanic belt; gravity slides from inter- textbook definition I have cited reduces one to nal uplifts into the external belt; and wide- the state of the schoolboy who, having some spread deformation, especially in the more vague idea of the Baconian controversy, wrote external belts. In general, these events did not on an examination that the plays of William occur at the same time in the various sectors; Shakespeare were not written by William each took a considerable time, and they over- Shakespeare but by another man of the same lapped to some extent. The Taconic orogeny name. also affected the southern Appalachians and Now it happens that we have recently ac- may have been the most important one there, quired a great deal of reasonably accurate infor- but evidence for this assertion is meager and mation about the extent and timing of orogeny inconclusive. Detailed analysis of the "fine in the Taconic region (for example, Zen, 1968; structure" of the Taconic orogeny combats the Bird and Dewey, 1970; Berry, 1970) and of dogma that orogenies are sharp, discrete events roughly contemporaneous orogeny in other punctuating the geologic record (separating parts of the northern Appalachians (Poole, periods and abruptly terminating geosynclinal 1967; Pavlides, and others, 1968; Williams, sedimentation) and suggests instead that they 1969; Hall, 1969). The Taconic orogeny has reflect "random-walk" processes within the always fascinated me, for the Appalachians and Earth, in all likelihood the same as those re- specifically the Taconic region are home base sponsible for sea-floor spreading and the pre- for me. I was born and brought up in Albany, sent tectonic state of the Earth. New York, within sight of the western Taconic foothills, and my first independent field work brought me face to face with their geological INTRODUCTION problems. Hence, at the risk of being provin- The Taconic orogeny (for some the cial, I would like in this address to analyze the Taconian) is normally defined, in textbooks or information we now have to see if, in addition the AGI glossary, as the orogenic disturbance to telling us what and when the Taconic that occurred in eastern North America at the orogeny was, it can point us to any more gen- end of the Ordovician period. Indeed, Stille eral conclusions about orogeny and its time re- (1924) included it in his original list of world- lations. wide orogenic episodes at that point in the geo- The Taconic orogeny is of further interest as logic column. To be sure, there is a certain a mildly uncomfortable exception to the corn-

Geological Society of America Bulletin, v. 82, p. 1141-1178, 13 figs., May 1971 1141

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mon doctrine that orogeny closes geosynclinal HUDSON VALLEY AND TACONIC history. According to this doctrine, the history MOUNTAINS of the Appalachian geosyncline (the type geo- As the orogeny was first recognized because syncline, be it remembered) ought properly to of the unconformity in the Hudson Valley, we consist (and does in some accounts) of a long, may start there. The unconformity is well dis- uninterrupted period of sedimentation con- played in a number of places, from Becraft cluded by a single climactic Appalachian revo- Mountain and Mount Ida, which lie near the lution marking the end of the Paleozoic era, city of Hudson on the east side of the Hudson during which all or most of the Appalachian River, south past the Kingston area (Rondout structures were produced. Preliminary skir- and Rosendale) on the west side, and along the mishes, like the Taconic orogeny (or for that southeast front of the Shawangunk Mountain. matter the Acadian), disturb this straightfor- In some places the discordance is nearly a right ward picture, so easy to incorporate into ele- angle, and in all it is appreciable (Fig. 2, A and mentary lectures. Perhaps this is why there B). At Becraft Mountain, the older rocks show have been persistent efforts to derogate the im- not only intense folding but also cleavage; the portance of the Taconic orogeny and to rele- younger rocks there and throughout much of gate it to the status of a minor and quite local the region are also severely deformed but not episode or "disturbance." Yet the existence of enough to obliterate the unconformity. North a period of deformation older than the classical of Kingston, the oldest strata above the uncon- Appalachian folding of Pennsylvania and the formity belong to the topmost Silurian, if not Virginias was recognized as early as that folding the basal Devonian, and are dominantly car- itself, and by the same people, specifically bonate. To the southwest, older detrital strata Henry D. Rogers (no relation to the present come in, especially a unit of quartz-pebble con- speaker—note the spelling), who saw and un- glomerate and quartzite (Shawangunk con- derstood the resulting unconformity in the glomerate). Fossils are too few, however, to Hudson Valley in 1837,* and not much later indicate exactly how low in the Silurian these by Sir William Logan in the Gaspe Peninsula strata descend. Among the folded rocks and farther southwest in Quebec (Fig. 1). As beneath (which include beds as old as Early soon as correlations with Europe were estab- Cambrian), the youngest dated by fossils are lished, the unconformity was assigned a posi- Middle Ordovician,2 of Trenton age (medial tion between the Lower and Upper Silurian of Trenton of Kay, 1937; Barneveld of Fisher, Murchison (what we now call the Ordovician 1962; upper subzone of Zone 13 of Berry, and Silurian), and James D. Dana incorporated 1970. Thus, the span of time within which the the idea of such an epoch of deformation mark- deformation recorded by the unconformity ing the end of a period into the account of might have taken place is considerable. geological history in his Manual of Geology Farther south westward, however, the uncon- (1863, p. 226-229). In the second edition formity acquires narrower limits (Fig. 3). It can (1875, p. 212) he named it the Green Moun- be followed at least to the Lehigh River in east- tain Revolution, but in the fourth (1895, p. ern Pennsylvania and, in my opinion, consider- 386, 532) he renamed it Taconic, for the Ta- ably farther, probably to the Swatara River conic Mountains along the border between (Fig. 4A). Fossils reported to be lower Upper New York and Massachusetts, and that name Ordovician (assigned to the Eden—although has become the accepted one. still within Zone 13 of Berry—near the Dela-

1 In his 1838 report, Rogers mentioned only a locality "on the Delaware and Hudson canal....near Rondout" (p. 37), 2 Throughout this paper, I have followed the classical but in his final report (1858, v. 2, p. 785—actually written North American usage for the terms Lower, Middle, and about a decade earlier) he stated that the unconformity "was Upper Ordovician, which is based on the generally accepted discovered by me near the city of Hudson" at "Becraft's interpretation of the shelly faunas in the carbonate sequence Mount." W.W. Mather, within whose field area both these of the western Appalachians and the central platform; that is, localities lay, also saw it at "Becraft Mountain and Mount Lower Ordovician includes the Beekmantown; Middle Or- Bob" (now Mt. Ida; Mather, 1838, p. 165-166), presumably dovician the Chazy, Black River, and Trenton; and Upper at the same time but, if one may judge by the discussion in Ordovician the Eden, Maysville, and Richmond. As the Cara- his final report (1843, p. 368), his understanding of the doc of Great Britain is roughly equivalent to the Trenton, the unconformity and its implications was considerably less clear term Upper Ordovician here refers mainly to Ashgill equiva- than Rogers'. Perhaps Mather showed Rogers the localities, lents. If the classical North American subdivision is upset, the but Rogers first grasped the significance of what they saw. assignments in this paper will need revision.

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ware River, to the Maysville farther southwest) though mostly unfossiliferous, are now uni- are present in beds below the unconformity, formly classed as Upper Ordovician and the quartzite unit (Tuscarora quartzite) (Richmond and probably upper Maysville). above it clearly becomes lower and lower in the Apparently a disconformity is still present Silurian, for quite low Silurian faunas are found beneath these strata at Harrisburg (Stose, in overlying beds. Beginning at the Spitzen- 1930, p. 641; Willard and Cleaves, 1939, p. berg near Lenhartsville, Pennsylvania, and in- 1178-1179), although not farther northwest, termittently farther west, a formation or series bracketed within the Upper Ordovician (appar- of lenses of coarse gritty sandstone appears be- ently within the Maysville equivalents). The tween, more nearly parallel to the beds above coarsest clastic material lies immediately above than to those below (Willard and Cleaves, this disconformity where it is present, then fol- 1939, p. 1181-1183; Platt, and others, 1969). low probably uppermost Ordovician non- Near Harrisburg and farther north and west in marine red beds; apparently the sea did not Pennsylvania such strata belong to formations return to the region until Early Silurian time. (Juniata and Bald Eagle formations) that, al- Thus the sediments, like the disconformity, in-

Figure 2. "Classical" Taconic unconformity in the Hudson Valley, New York. A. Along Route 23 north- west of Catskill. Uppermost Silurian (Rondout forma- tion) on Middle Ordovician (Austin Glen graywacke). Dip of unconformity was imposed by later (Devonian or post-Devonian) deformation. Courtesy of John M. Bird. B. Along Route 32 north of Kingston (just west of King- ston-Rhinebeck Bridge). Upper Silurian (Wilbur mem- ber of Roundout formation) on Middle Ordovician (Austin Glen graywacke). Courtesy of Donald W. Fisher.

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dicate a climax of uplift during the Late Ordovi- ern ones vast blocks that slid, presumably by cian, but before the end of the period. gravity, into the Middle Ordovician sea, the Now Stille (1924) has laid it down as a basic higher and more eastern ones probably em- principle that if an unconformity can be traced placed along more conventional subterranean laterally into an area where it is only a discon- thrust faults, but all derived from an area tens formity but its age is closely delimited, then that of kilometers farther east, probably from above age limitation applies to the unconformity or just beyond the Precambrian basement that throughout its extent. Obviously this principle is now folded and telescoped into the present goes with the belief that erogenic episodes are Green Mountains and Berkshire anticlinoria. spasmodic and short-lived but of very great, if These allochthonous masses are composed of not worldwide, lateral extent and of precisely an alien, largely shaly, probably deep-water the same age throughout. For myself, I cannot stratigraphic sequence (Lower Cambrian to accept this view and would argue that an oro- Middle Ordovician), the Taconic sequence, genic episode might be expected to begin ear- contemporaneous with but quite different from lier and last longer in the area of maximum the autochthonous, largely carbonate sequence disturbance and to spread most widely at some that lies beneath them in the Hudson Valley intermediate time—in the case in point, from and vicinity. The latter sequence records a the Taconic area into eastern Pennsylvania dur- great shallow carbonate bank that persisted in ing the Late Ordovician. Yet neither view gives that region for tens of millions of years (Rodg- much comfort to the traditional dating of the ers, 1968) but finally foundered in Middle Or- "classical" Taconic orogeny of the Hudson dovician time. The final arrival above the Valley region as marking the end of the Or- autochtone of the more western Taconic masses dovician period. is fairly well dated by graptolites from the ma- But there is more to the Taconic orogeny in trix of a "blocks-in-shale" or "Wildflysch-type the Hudson Valley region than the disturbance conglomerate" unit (Fig. 3B) in the underlying and uplift recorded by this unconformity. The or adjacent autochthonous strata—a unit that long-debated Taconic klippe in the area east of contains blocks of all sizes of exotic Taconic the Hudson River and into the Taconic Moun- rocks (and also in places blocks of the carbonate tains has now been fairly conclusively shown sequence, as at Bald Mountain, Washington (see espeaallyZ-en, 1967) to be a whole series of County, New York). The date is Middle Or- great exotic masses, the lower and more west- dovician, of the same (Trenton) age as or even

Harrisburg Lehigh Gap Kingston

USil

I3a; T 12 9

Figure 3. Schematic stratigraphic diagram of Middle sandstone; lines: shale (where irregular: deformed or Ordovician to Upper Silurian strata along the outcrop metamorphosed); wall pattern: limestone (with slanting belt from the Hudson to the Susquehanna River. Ordi- lines: dolostone, in part); open irregular areas: blocks in nate is time, not thickness. Circles: conglomerate; dots: melange or slide breccia.

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older than the highest dated beds below the But there is still another unconformity (un- "classical" unconformity (lower subzone of conformity C) in the region, recording still Zone 13 o/Berry, 1970). Indeed, at Becraft another episode of disturbance. Within the au- Mountain that unconformity overlaps the edge tochthonous sequence exposed north and west of one of the exotic masses, which after their of the exotic Taconic masses, a disconformity emplacement were folded together with the un- separates Middle Ordovician from Lower Or- derlying autochthone into a vast synclinorium dovician carbonate strata in many if not most and were cut by slaty cleavage and perhaps places. In the Champlain Valley (except along mildly metamorphosed before the erosion that the west side at the south end), the beds above produced the unconformity. This folding, and it are the type Chazy group, that is quite low in not the arrival of the exotic masses, is therefore the Middle Ordovincian (additional disconfor- the deformation recorded by the "classical" un- mities may appear above the Chazy). Else- conformity. where, they are assigned to the higher Black How long the emplacement of the allochtho- River group but are nevertheless older than the nous masses took is not certain, but even to the youngest rocks beneath either of the unconfor- east near the source area they overlie autoch- mities discussed above. On the east side of the thonous Middle Ordovician limestone and slate Taconic region, moreover, from near Brandon, probably only a little older than that below Vermont, south along the Vermont marble belt their western edge—perhaps as much as one into western Massachusetts, northwestern Con- graptolite zone (fossils in the slate are assigned necticut, and southeastern New York as far as to Zone 12 of Berry). Moreover, within the New York City, the contact in many places is an northern part of the allochthonous Taconic ter- angular unconformity. The Middle Ordovician rain there is another unconformity (let us call it strata above (shale of the Walloomsac and cor- unconformity B), along which the main body of relative formations, commonly with a basal the Taconic sequence is beveled by Middle Or- limestone or limestone-conglomerate-Whipple dovician strata somewhat older than the'' blocks- or Balmville limestone) bevel down, although in-shale" unit that records the arrival of the irregularly, across the whole Cambrian succes- exotic masses in their final position (again Zone sion, locally reaching the Precambrian base- 12 of Berry). It is tempting, therefore, to fol- ment. The beds beneath the unconformity had low Bird (1969, p. 680-681) and assign this certainly been faulted already (near Danby, older unconformity to the time of uplift in the Vermont, the Middle Ordovician overlaps a source area of the allochthon, the uplift that fault separating Lower Ordovician from Pre- triggered the gravity sliding, or else to some cambrian; Thompson, 1967, p. 81, 87-89), and intermediate time during the sliding (Bird calls in many places they may well have been the beds above epikinallochthonous; that is severely folded. Near State Line, Massachu- deposited upon the slide mass during its motion setts-New York, according to Ratcliffe (1965; —an explanation comparable to that given by 1969, p. 12-13, 19-20), they were actually in- Merla, 1951, p. 212-221, for the Loiano forma- verted before the Middle Ordovician was laid tion of the northern Apennines). The uplift in down. Zen (1967, p. 40-44, 64-66; 1968, p.' what had been a deep depositional basin along 133-134) and Bird and Dewey (1970, p. 1038) with the foundering of the carbonate bank, have characterized this episode as mainly one of both during the later part of the Middle Or- irregular high-angle block faulting, and Zen dovician, resulted in an "inversion of relief suggests that on the downthrown blocks sedi- that entirely changed the paleogeography. mentation may never have been interrupted. In view of Ratcliffe's data, however, I am more 4 inclined to consider that, at least in the eastern Figure 4. A. "Classical" Taconic unconformity in part of the region, it was a period of folding and eastern Pennsylvania. Route 1-81 in Swatara Gap of Blue perhaps thrust faulting, accompanying the ini- Mountain. Lower Silurian (Tuscarora quartzite, on tial uplift and western thrust of the Green right) on lower Upper Ordovician (Martinsburg shale, Mountains and Berkshire anticlinoria, later on left). Courtesy of Pennsylvania Geological Survey, Arthur A. Socolow, State Geologist. B. "Wildflysch-type uplifts and thrusts of which presumably trig- conglomerate" east of Rensselaer, New York, along gered the gravity sliding and westward thrust- Route 151 just south of Rysedorph Hill; in autochtho- ing of the Taconic masses and then the nous Middle Ordovician shale. Blocks are mainly gray- synclinorial folding of allochthon and autoch- wacke (autochthonous?) but include blocks of other autochthonous and of allochthonous strata. Courtesy of thon together. Detailed mapping now in pro- John M. Bird. gress in Berkshire County, Massachusetts, and

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elsewhere should settle the matter. graywacke), about at the time of the uncon- Further information on the course of these formity (unconformity B) in the northern part disturbances can be obtained from the west- of the Taconic terrain or slightly later (Berry, ward encroachment of clastic materials that is so 1962b, p. 712-713; Zone 12), perhaps as the evident in the Middle and Upper Ordovician result of the uplift that that unconformity re- stratigraphy of the Hudson Valley-Taconic re- cords. In the belt next to the west, on the other gion and indeed of the whole of New York hand, in what is now the relative autochthon of State and beyond (Fig. 5), producing facies the Taconic-Hudson Valley region (beneath changes the main outlines of which were the allochthonous masses), carbonate deposi- worked out by Ruedemann (1908, p. 44-45; tion had been virtually continuous from some 1912) at an astonishingly early date. This en- time in the Cambrian into the Middle Ordovi- croachment seems to have taken place in ir- cian, the largest interruption being the discon- regular steps, which may reflect distinct formity between Lower and Middle Ordovician episodes in the uplift of the source area, the strata of the carbonate sequence (unconformity foundering of the former carbonate bank, or C). In the eastern part of this belt, mud from the both. In the deeper water east of the carbonate east (Walloomsac formation) appeared at about bank, where the Taconic sequence, now mostly the same time (Zone 12) that poorly sorted preserved in the allochthonous masses, was sand appeared in the source area of the Taconic originally laid down, mud had been the main sequence to the east,3 and it was soon followed deposit since early in the Cambrian, although by dirty sand (Austin Glen graywacke). Farther apparently it accumulated very slowly. In the west, however, mud did not appear until about Early Ordovician and into the Middle Ordovi- one graptolite zone later (lower subzone of cian (Poultney formation, including Mount Zone 13), when it spread quite suddenly across Merino shale), it was accompanied by siliceous the whole eastern half of New York State material, perhaps of volcanic origin, now im- 3 Argillaceous material of eastern provenance appeared pure chert. Poorly sorted sand, carried in by even earlier, however, in the probably Chazyan Middlebury turbidity currents, began to appear there rather and Youngman formations of the eastern Champlain Valley, abruptly in the Middle Ordovician (Pawlet which are cut out by disconformity farther south.

Lake Ontario Utica Albany Pittsfield

Carbonate sequence Ch Disconformity \ LOrd

U€

Figure 5. Schematic stratigraphic diagram of Upper England to Lake Ontario. Ordinate is time, not thick- Cambrian to Upper Silurian strata from western New ness. Symbols as on Figure 3.

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(Canajoharie shale), at least as far as Little Falls cian, it began with the uplift recorded by the at the southwest corner of the Adirondacks. unconformity (unconformity B) within the Again, dirty sand (Schenectady formation) fol- northern part of the Taconic terrain and the lowed not long after, and south of Kingston, accompanying flood of graywacke and ended from Hussey Hill to Illinois Mountain (Fisher, with the emplacement of the western Taconic 1969), overlying quartzite and conglomerate, masses and the rapid spread of mud and sand largely red, record the final filling of this part across eastern New York State. The third de- of the basin with clastic materials. It seems rea- formed allochthon and autochthon alike, fold- sonable to suppose that the sudden spread of ing the rocks to a point a short distance west of mud coincided approximately with the arrival Albany and into eastern Pennsylvania (uncon- of the exotic Taconic masses in the Hudson formity A) and sending detritus a third of the Valley region. Later on, mud spread even far- way across the continent (in this context it has ther west, first a short step to the Black River been called the Oswegan disturbance; Kay, Valley in late Middle Ordovician time (Utica 1942, p. 1631-1632). It may have begun al- shale—upper subzone of Zone 13), then very ready in the later part of the Middle Ordovician widely indeed in the Late Ordovician (Zones (perhaps overlapping the second and emplac- 14 and 15), finally reaching the upper Missis- ing the eastern Taconic masses as more conven- sippi Valley (Maquoketa shale). Sand followed tional thrust sheets), but it probably reached in the early Late Ordovician (Pulaski sand- climax in the early part of the Late Ordovician. stone), reaching at least to the present Lake Ontario, where it is overlain by red shale and CHAMPLAIN AND ST. LAWRENCE sandstone, evidently non-marine, the sea only VALLEYS, GREEN MOUNTAINS, returning to the region after the beginning of EASTERN TOWNSHIPS, AND Silurian time. It is natural to see this later spread NORTHERN GASPE of elastics as the effect of the "classical" phase Between Albany and the island of Anticosti, of the orogeny, recorded in the Hudson Valley no Silurian or Devonian strata are preserved in by the original unconformity (unconformity A) place along the west margin of the Appalachi- that there bevels autochthon and allochthon ans, and hence the "classical" unconformity alike. Obviously, the stratigraphy in Pennsyl- cannot be observed and none of the structural vania, already described in the discussion of the features in the Champlain and St. Lawrence age of that unconformity (see Fig. 3), is part of Valleys—thrust sheets, synclinoria, cleavage— the same picture. can be unequivocally assigned to the "classical" In the Taconic region, then, we have evi- phase of the orogeny. Indeed, because both dence of not less than three climaxes of oro- deformation and metamorphism in this region genic activity during the Ordovician. For increase eastward in intensity across the Green convenience, and in deference to the inveterate Mountains-Sutton and Notre Dame anticlinoria human habit of naming things in order to fit into the Gaspe-Connecticut Valley syn- them into neat pigeonholes, they could be la- clinorium beyond, where they affect Silurian beled the Tinmouth (Thompson, 1967, p. 88) and Lower Devonian rocks, they have gener- phase, the Taconic or Vermontian (Kay, 1937, ally been assigned not to the Taconic orogeny p. 290, 293) phase, and the "classical" or Hud- but to the Acadian (see, for example, Cady, son Valley (please! not Hudsonvalleyan) phase I960), although the Acadian age assignment of the Taconic orogeny. The first climax dates itself rests mainly on extrapolation to eastern from the early part of the Middle Ordovician Massachusetts and Rhode Island or to eastern and produced the disconformity or unconform- Maine, the nearest places that post-Acadian ity (unconformity C) beneath the Middle Or- sediments (Middle Devonian to Carbonifer- dovician strata of the carbonate sequence. ous) are known. In the St. Lawrence Valley east Conglomerate made of carbonate pebbles lies and northeast of Montreal, Ordovician clastic above it in places, but in general it did not deposition continued uninterrupted from mid- produce any great quantity of detritus (unless dle Middle Ordovician (mid-Trenton) time, the mud in the Chazy group of the Champlain when it first replaced carbonate deposition in Valley reflects it). The second, on the other that region, into late Late Ordovician (Rich- hand, produced the "inversion of relief al- mond) time, but the deposits are mostly rather ready mentioned, set off vast floods of debris, fine-grained; subordinate sandstone appears in and sent the Taconic exotic masses on their the lower part of the Upper Ordovician and red way. Entirely included in the Middle Ordovi- shale and sandstone in the upper part. At the

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east, along the western margin of the Appala- do not entirely agree on the details of the chian folded belt, all these strata are deformed successive stages. In general, early isoclinal and together so that, if the deformation was Ta- commonly more or less recumbent folds accom- conic, it was later than at least the time of widest panied by strong axial-plane cleavage have spread of the Hudson Valley phase into Penn- been refolded by later more nearly upright sylvania. folds generally accompanied by slip or fracture Evidence of earlier phases is also debatable, cleavage, although in places by a second schis- although in my opinion the Taconic-type rocks tosity. The age of these features also has been (Sillery group) of the Granby area, Quebec, in debate; at least the later folds and the accom- and northeastward are parts of an exotic mass or panying cleavage have seemed much the same masses that slid in from the east and now rest on as those in the Silurian and Devonian rocks in or adjacent to "Wildfiysch-type conglomerate" the Gaspe-Connecticut Valley synclinorium to like that in the Taconic region (Hathaway for- the east (Dennis, 1960, and Osberg, 1969, p. mation 0/Hawley, 1957, p. 68-76; parts of St. 697-698, would include the earlier schistosity Germain complex o/Clark, 1947, p. 15; "arg- as well), but radiometric evidence from south- iles-a-blocs" 0/St-Julien, 1968; Citadel forma- eastern Quebec (Rickard, 1965) suggests that tion of Osborne, 1956, p. 189-191). If so, the even the later cleavage in the anticlinorium is sliding here would be late Trenton ("Utica"), Ordovician. Down strike to the south, in the probably a little later than the Taconic phase in Green Mountains of Vermont, Albee (1968, p. the Taconic region (and also later than the ap- 329-331) has adduced evidence for an older pearance of mud on the carbonate platform pre-Acadian metamorphism, distinct from and around Montreal). A persistent disconformity overprinted by the Acadian one. Still farther beneath the Middle Ordovician (Chazy) lime- south, in Westchester County, New York, not stone in the same area reminds one of the Tin- far from New York City, radiometric evidence mouth phase, but again the timing may be a indicates sillimanite-grade metamorphism little off.4 before the end of the Ordovician (Long and The best evidence for Taconic orogeny in Kulp, 1962, p. 982; Ratcliffe, 1968; see also this region comes indeed not from the sedimen- Harper, 1968). Finally, Rosenfeld (1968, p. tary rocks along the west margin of the Appala- 196), during his studies of the rotated garnets chian folded belt but from the metamorphic in the Siluro-Devonian rocks of east-central rocks within it, along and east of the axis of the Vermont, found garnets in nearby Cambrian Green Mountains and related anticlinoria. Sev- rocks in which later and earlier deformations eral recent studies (for example Osberg, 1965; are both recorded, with a distinct break in crys- St-Julien, 1967; see summary /« Ueland, 1967) tal growth between (Fig. 6A). It is not often in the anticlinorium in southernmost Quebec that one can observe an angular unconformity and adjacent Vermont show that the history of entirely inside one mineral grain in a thin sec- deformation there was complex, although they tion! In view of all these data, I conclude that 4 Schuchert, in successive editions of his textbook and in much of the deformation and metamorphism in other publications, cited an angular unconformity in north- the Green Mountains anticlinorium, and also western Vermont as evidence for an orogenic episode at or the main folding and thrust faulting in the Cam- near the end of the Cambrian (based partly on work by brian and Ordovician rocks of the Champlain Keith). He called it variously the Green Mountains, Ver- and St. Lawrence Valleys to the west, were pro- mont, and Quebec disturbance (see also Kay, 1937, p. 290) and the Quebec phase of the Taconian disturbance, and he duced not in the Acadian but in the Taconic placed it first at the end of the Early Cambrian, then at the orogeny. Evidence on the exact date or dates of end of the Cambrian, and finally within the early Early Or- this orogenic and metamorphic activity must be dovician. The supposed unconformity is, however, only one of many such contacts in that area within Cambrian and Figure 6. Taconic unconformities. A. Probable Ta- Lower Ordovician limy shale, many of them overlain by beds conic unconformity within 2-cm garnet grain in Pinney of lime-breccia (Shaw, 1958, see especially p. 551, Fig. 10). Hollow formation (Lower Cambrian?), 5 mi north of Shaw ascribes these "unconformities" and the associated village of Townshend, Vermont. Courtesy of John lime-breccia beds to wave erosion around low islands or Rosenfeld; republished by permission from Rosenfeld reefs; I prefer to consider them scoured surfaces at the base (1968) in Zen and others, eds., Studies of Appalachian of submarine slumps down a slope into deep water at the foot geology: northern and maritime (Billings Vol.), Wiley- Interscience, Fig. 14-7. B. Anse du Cap-des-Rosiers, of the carbonate bank (Rodgers, 1968). In any case, they do northeast coast of Gaspe Peninsula, Quebec. Lowest not seem to record any significant regional uplift or erosion, Devonian? (Sayabec formation) on Lower (?) Ordovi- let alone orogeny. cian. Courtesy of C. F. Burk, Jr.

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sought on the east flank of the anticlinorium. Vermont at least, seem to be especially concen- Although fossils are sparse in the metamor- trated at the unconformable contact itself phosed rocks there, the contact of the Ordovi- (Stowe-Missisquoi contact on State Geologic cian strata in the anticlinorium with the Silurian Map of Vermont). Perhaps, indeed, the masses strata in the Gaspe-Connecticut Valley syn- on the contact are actually resedimented ser- clinorium to the east can be followed with pentine along the unconformity (compare with precision for the full length of the state of Ver- Lockwood, 1969; Cowan and Mansfield, 1970) mont and far northeast across the Eastern that have since been remetamorphosed, and the Townships of Quebec. In Vermont, this contact higher masses may be secondarily reintruded. is generally overlain by the Shaw Mountain for- If so, the original intrusion of the ultramafics mation, characterized by quartzite and quartz- could have preceded or accompanied the ear- pebble conglomerate but including also lier erogenic climax. In Quebec, albite por- metavolcanic rocks, probably of Early (but not phyry or granite cuts the rocks below this earliest) Silurian age, whereas in Quebec the unconformity but is found as pebbles above it. strata immediately above are as young as The fossils above this unconformity show that Devonian in some places. In Vermont, the con- the disturbance it records was over before the tact does not appear to cut out any formational end of the Taconic phase in the Taconic region units, so that there it cannot be shown to be an (final emplacement of the Taconic masses) but unconformity, although a disconformity is could be contemporaneous with the beginning clearly present; in Quebec, however, it does of that phase (unconformity B and appearance bevel units and seems to be an angular uncon- of graywacke within the Taconic terrain); Ste- formity. The age of the rocks below is well vens and others (1969) believe, however, that fixed only in southeastern Quebec, at Castle the original ultramafic intrusion was Early Or- Brook near Magog (Berry, 1962a), where mid- dovician. dle to upper Middle Ordovician graptolites All along the southern shore of the St. Law- have been found (both Zone 12 and Zone 13), rence estuary on the north coast of the Gaspe and nearby, where lower Upper Ordovician Peninsula and southwestward into the Eastern fossils are reported (St-Julien, 1967). Thus, the Townships, deformed Cambrian and Ordovi- unconformity could represent the Hudson Val- cian rocks, looking for the most part remarka- ley phase of the Taconic region or the corre- bly like those in the Taconic allochthonous sponding phase (if any) in the St. Lawrence masses, underlie a belt 10 to 30 km wide; on Valley. Moreover, the Middle Ordovician the Gaspe Peninsula they are bounded on the strata contain bodies of "Wildflysch-type con- south by a belt of more regularly folded glomerate," indicating a phase like the Taconic Silurian and Devonian strata. In the middle part phase on this side of the anticlinorium as well of the peninsula, the contact is mainly a high- as on the other. angle fault of uncertain character, but at the two Beneath the graptolite-bearing strata in ends it is clearly an angular unconformity (Fig. southern Quebec, however, is another uncon- 6B); the Cambrian and Ordovician rocks had formity (St-Julien, 1967), if anything stronger been severely deformed, intruded by ul- than the one above. It can be traced some dis- tramafics (now in good part serpentine), and in tance south into Vermont (beneath the Um- places metamorphosed to the greenschist facies brella Hill conglomerate o/Albee, 1957) and before the later strata were deposited (frag- northeastward almost to the Maine border and ments of the ultramafics are found in the basal perhaps even farther (Dresser, 1912, p. 25-26). beds of the Silurian). In an area southwest of The rocks beneath it are unfossiliferous elastics the peninsula (around Lake Temiscouata; Lesp- with some volcanics but can reasonably be cor- erance and Greiner, 1969), beds as old as early related with Cambrian and perhaps Lower Or- Early Silurian (early Llandovery) overlie the dovician strata on the west flank of the unconformity (apparently separated from anticlinorium (Cady, 1960). Furthermore, they younger strata by one or more additional dis- are intruded in both Quebec and Vermont by conformities), but over most of the region large bodies of ultramafic rock, including much (Lesperance and Bourque, 1970) the beds serpentine and containing the well-known asbe- above are younger (late Llandovery, Wenlock, stos deposits of Thetford Mines and vicinity. or even Ludlow), and at the east end of the Smaller serpentine bodies are present in the peninsula they are latest Silurian (PFidoli) or rocks above this lower unconformity (but no- even earliest Devonian (Gedinnian). Fossils are where above the upper one) and, in northern scarce in the beds below the unconformity; they

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range from Middle Cambrian to Middle Or- occur at Anticosti only in the upper Middle dovician, but close to the Silurian the youngest Ordovician Makasty shale (not exposed on the are Middle Ordovician graptolites of the same island but recognized in boulders along its age as the older fauna at Castle Brook in south- north shore also in drill holes beneath; Roliff, ern Quebec (Zone 12). At one such locality in 1968; Riva, 1969, p. 533-540), but the lime- the middle part of the peninsula, probably in a stone above includes some shaly beds well into fault sliver along the boundary fault there, the the Lower Silurian. Considering how far west fossils occur in black slate more deformed than mud and even sand were carried from the Ta- the adjacent Silurian but apparently considera- conic uplifts along the New York-New Eng- bly less deformed than the probably Cambrian land border and in southern Quebec, it is rocks immediately adjacent to the north (Mat- extraordinary that so little detritus reached An- tinson, 1964, p. 69-70), suggesting the exist- ticosti, now only 80 km north-northeast of the ence here too of an older unconformity like sharply unconformable base of the Silurian at that in southern Quebec. The older unconform- the east end of the Gaspe Peninsula, or of the ity has not been otherwise reported, however Middle Ordovician graywacke and "blocks-in- (but compare with Sikander and Fyson, 1969, p. shale" units on the north shore. It must be 1118); the younger one obviously spans the recognized, however, that the Silurian along same time as the "classical" Hudson Valley the unconformity in Gaspe also include rela- phase or its equivalent in the St. Lawrence Val- tively little coarse detrital material, especially ley and also the later part of the Taconic phase. where it was late in overlapping the older beds As the Silurian and Devonian strata in the (compare the relations above the main uncon- northern part of their outcrop belt just to the formity in the Hudson Valley). south—the central Gaspe folded belt—are There seems no particular reason to doubt folded rather openly, virtually all the deforma- that, whatever the timing, the result of all the tion of the Cambro-Ordovician rocks to the activity so far described was to created by Late north belongs to the Taconic orogeny in one or Ordovician time as orogenic uplift, a linear another of its "phases." Farther south across landmass or even a chain of mountains, extend- strike, however, post-Early Devonian deforma- ing from northeastern Gaspe through the East- tion becomes more severe. ern Townships and the Taconic region at least Somewhat higher Middle Ordovician fossils to southeastern Pennsylvania (Fig. 7). Berry (Zone 13) have been found along the north and Boucot (1971) have carefully documented 5 shore of the Gaspe Peninsula east of its center, this landmass—Taconica —and its gradual re- in graywacke beds (Cloridorme formation of submergence during the course of the Silurian Enos, 1969) and in a "blocks-in-shale" unit period. (Riva, 1968, p. 1381; Stevens, 1969, unpub. BRONSON HILL ANTICLINORIUM data) like that of the Taconic region, over AND NORTHERN MAINE which older Ordovician and Cambrian rocks VOLCANIC BELT have slid or been thrust. Once again, therefore, When Marland Billings (1937) established these fossils can be used to date the arrival of the stratigraphic section for central New Eng- slide or thrust masses of Taconic type; the tim- land in the Littleton area of northwestern New ing seems to be about the same as in the Ta-

conic region or a bit later, perhaps more nearly 5 the same as in the St. Lawrence Valley east of This landmass has sometimes been called Appalachia, but I believe this is a serious misnomer. It is clear from Schu- Montreal. chert's writings, beginning with his classical paper on North In the middle of the St. Lawrence estuary, American paleogeography in 1909 (p. 468-469) and con- northeast of the locality just discussed in eastern tinuing in his presidential address to this Society in 1922 Gaspe, lies the island of Anticosti, known for a (1923, p. 160-162) and his textbooks, that what he and his century to expose a conformable limestone se- contemporaries meant by Appalachia was a broad subconti- quence crossing the Ordovician-Silurian nent that lay entirely southeast of the "Appalachian geosyn- boundary. Indeed, the only clear disconformity cline" along the whole southeastern margin of North in this sequence lies between lower Middle and America, extended out into the present Atlantic Ocean, and Lower Ordovician strata exposed in the Mingan lasted throughout the Paleozoic, not an ephemeral if rather large island within the geosyncline that lasted barely a Islands on the north shore of the estuary; it period. Kay's name, Taconica (1937, p. 291), seems to me resembles the disconformity (unconformity C) the proper one for the landmass in question, and Kay's views associated with the Tinmouth phase of the Ta- on the paleogeography (Kay, 1951, see especially p. 31-33, conic region. Furthermore, truly detrital beds 72-77) the more nearly correct.

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Hampshire, he recognized that an angular un- across the unconformity (Boucot indeed called conformity beneath the Clough quartzite bev- the rocks below Precambrian, but others have els across several metasedimentary and considered tham Cambro-Ordovician, and geo- metavolcanic units and also across plutonic in- chronometry gives an Ordovician date for the trusions of granodiorite (Highlandcroft magma granodiorite). Furthermore, the unconformity series). As Silurian fossils were found in and (although generally without a pronounced above the Clough quartzite, he naturally metamorphic jump) has been found at every equated this unconformity with the "classical" locality where the appropriate beds are exposed unconformity in the Hudson Valley and called throughout the northern Maine volcanic belt the unfossiliferous beds beneath it "Ordovician (Pavlides and others, 1968) as far east and (?)." All work since has confirmed his insight, southeast as a north-south line west of Presque and the Middle Ordovician age of the underly- Isle and a northeast-southwest line through ing Partridge formation is now established Mount Katahdin and the Rangeley Lakes; pre- (Harwood and Berry, 1967). Moreover, the unconformity granodiorite is known here and Clough quartzite is now correlated with the there through the same region. In general, the Shaw Mountain formation on the other flank of beds below the unconformity through this the Gaspe-Connecticut Valley synclinorium, so whole belt are no younger than Middle Ordovi- that the unconformity may be correlated with cian, those above no older than late Early the upper unconformity in southern Quebec. Silurian.6 The unconformity spans the time of No metamorphic discontinuity is evident across the Hudson Valley phase and perhaps at least the unconformity one the Bronson Hill anti- part of that of the Taconic phase in the Taconic clinorium in western New Hampshire, for later region. Acadian metamorphism reached the upper In the northern Maine volcanic belt, how- greenshist or the amphibolite facies there. ever, as in southern Quebec, there is another Moreover, in much of the region the uncon- angular unconformity beneath the "classical" formity itself was deformed during the Acadian one, and here it is clearly the stronger one orogeny into great recumbent folds (Thomp- (Neuman, 1967, p. 31-33; Ekren and Frisch- son and others, 1968, p. 210-214), and the knecht, 1967, p. 4-5; Hall, 1969). In several of pre-Silurian intrusives were metamorphosed the anticlinoria that make up the belt, fossilifer- (and possibly locally remelted) to form the mas- ous Middle Ordovician strata rest unconforma- sive "plutonic" part of the Oliverian "magma" bly on older clastic sediments (for example, the series (Naylor, 1968, p. 238-239). Unconfor- Grand Pitch formation) that had already been mities have also been reported lower in the severely deformed and cleaved. The area section to the south along the anticlinorium where the older rocks are known spans at least (above the Middletown formation=Am- 150 km, not including "Somerset Island" monoosuc volcanics in Connecticut [Eaton and whose metamorphic rocks may well antedate Rosenfeld, I960] but below it in Massachusetts this older unconformity, as suggested by Bou- [Robinson, 1963,1967, p. 21]),, but they have dette (1970, p. 4-7; Boudette, like Boucot, pre- not been confirmed or traced regionally. fers to assign them to the Precambrian). No Northeastward into Maine, where the grade fossils are known in the rocks below, except the of Acadian metamorphism falls off, evidence track Oldbamia, which simply suggests a Paleo- for Billings' unconformity has multiplied; the zoic age, perhaps Cambrian; the rocks above most spectacular localities perhaps are those are mostly middle Middle Ordovician, again as around "Somerset Island" recorded by Boucot in Quebec. In one and perhaps two areas, how- (1961,1969b), where the rocks above are sedi- ever, lower Middle (if not Lower) Ordovician mentary (or volcanic) with Silurian and Lower fossils have been found above the unconform- Devonian fossils, those below schist, amphibo- ity (Neuman, 1968, p. 36-37); so far, they are lite, gneiss, and granodiorite. Thus here there is a pronounced metamorphic discontinuity * In northeastern Maine, Upper Ordovician fossils occur in several places (Neuman, 1968, p. 44), but generally only Figure 7. Paleogeographic sketch maps of Northern a disconformity is present at these localities. At the south wes- Appalachians and Newfoundland for (A) Late Cambrian ternmost locality (locality 3-a in Neuman, 1968; 57b in Pav- and Early Ordovician time; (B) late Middle Ordovician lides and others, 1968), the fossils occur in conglomerate time (Zone 13a); (C) Late Ordovician or earliest Silurian time. North-south lines: area of uplift; broken east-west exactly like that in the overlying Silurian (Neuman, 1967, p. lines: gravity slides; line of ellipses: line of volcanic is- 13-14) and, if an angular unconformity is present here, it lies lands. Base does not take into account shortening by later more probably below than above the Upper Ordovician deformation. strata.

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not known in sequence with the middle Middle trast to the northern Maine volcanic belt there Ordovician strata, so that there could be two is no evidence of any unconformity within the lower unconformities. Neuman (Neuman and stratigraphic section. In northeasternmost Rankin, 1966, p. 9; Neuman, 1967, p. 32) has Maine, indeed, fossils show clearly that deposi- proposed to call the erogenic disturbance re- tion was continuous from Middle Ordovician corded by the lower unconformity the Penob- into Late Silurian time, and the same seems to scot disturbance and to separate it from the have been true elsewhere in the belt. In several Tatonic orogeny. Questions of nomenclature areas close to the volcanic belt on the north- will occupy us later; now I simply wish to point west, to be sure, thick units of conglomerate are out that the age of the Penobscot disturbance intercalated in the section between Middle or could correspond to that of the earlier disturb- lower Upper Ordovician strata below and up- ance recorded in southern Quebec, less easily per Lower Silurian strata above; clearly, they to parts of the earlier phases in the Taconic record the same uplift of the volcanic belt as the region or the St. Lawrence Valley. upper or "classical" unconformity there. Far- The erosional unconformities on the Bron- ther southeast and east, not even this evidence son Hill anticlinorium and in the northern of orogeny persists and only quite fine-grained Maine volcanic belt evidently record the materials were deposited. In far northeastern growth of a landmass there. Perhaps it was sim- Maine (Aroostook County) and adjacent New ply the southeastern extension of Taconica, al- Brunswick, mud and lime-mud alternated rap- though more quickly submerged, as Berry and idly and repeatedly to produce a thick and char- Boucot show (1971), by the advancing Silurian acteristic "ribbon limestone" unit (Carys Mills sea, for an unconformity or disconformity is formation of Meduxnekeag group; Pavlides, recorded along both margins of the intervening 1968), which spans the whole period of the Gaspe-Connecticut Valley synclinorium from Taconic orogeny. Apparently this sediment was northeastern Maine at least to southern Ver- deposited in deep water, or at least far from mont (farther south the evidence is equivocal) shore or any source of detrital material. (Rend- beneath the very thick Silurian and Lower zina soils that have developed on this argilla- Devonian sediments (mainly deep water?) that ceous limestone account for the agricultural fill the synclinorium. If the present average richness of the Aroostook region, the chief width of the synclinorium in this region (60 potato belt of the East.) km) is not greatly less than the original width, Farther northeast, the belt in which the Or- this interpretation is reasonable, but if, as I be- dovician-Silurian boundary is hidden in a con- lieve, the intense polyphase folding in the Silu- formable sequence of argillaceous carbonate ro-Devonian strata records many-fold can be followed along the Aroostook- shortening, then more probably there was a Matapedia anticlinorium into and across the 7 separate linear island or landmass, of which southern part of the Gaspe Peninsula. Indeed, "Somerset Island" was a particularly rugged it also includes the Saint-Jean anticline in the part. southern part of the Gaspe folded belt, north of the northeast end of the deepest syncline of the AROOSTOOK REGION, SOUTHERN Gaspe-Connecticut Valley synclinorium and GASPE, AND NORTHERN only 30 km south of the exposures of the "clas- NEW BRUNSWICK sical" unconformity at the north edge of the folded belt. Attempts have been made, to be East and southeast of the Presque Isle-Mount sure, to find a "Taconic unconformity" at the Katahdin-Rangeley Lakes line already men- system boundary here, but the latest investiga- tioned lie the Aroostook anticlinorium and the tions (Skidmore, 1967) show that, as in the central Maine slate belt, in which in strong con- northeastern Maine "potato belt," muddy lime- stone was deposited from late Middle Ordovi- 7 If such a separate landmass requires a separate name, cian into Early Silurian time; coarse detritus was then from among the several rather barbarous possibilities— absent and carbonate sedimentation was not in- Bronsonhillia, Piscataquisia, Northernmainea—I would opt terrupted until about the end of Early Silurian for Highlandcroftia, from the Highlandcroft plutonic series, to emphasize that this belt contains most of the known grani- time, when volcanic debris arrived from a belt toid intrusions of Taconic age in the northern Appalachians of volcanoes to the south. South of the and may thus have been the core belt of the Taconic orogeny, northeast end of the deepest syncline (here the belt where Ordovician diastrophism began first and was filled with similar or less limy strata of Early most severe. Devonian age), the same situation prevails, ex-

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cept that here one finds lava flows interstratified early part of the Taconic phase (unconformity at the top of the Lower Silurian. B) in the Taconic region. The base of this conformable sequence is In southernmost Gaspe, south of the Aroos- known only in one small area, in easternmost took-Matapedia belt, Taconic unconformities Gaspe about 10 km west of Perce (Fig. 8). reappear. In the Port Daniel area (Ayrton, Here the muddy limestone (White Head for- 1967; jwFig. 8), the well-known shallow-water mation) seems to rest unconformably on car- Silurian sequence of Chaleur Bay rests on two bonate rocks of quite different aspect and of quite different sequences of clastic rocks; for Late and Middle Cambrian age (Fritz and oth- the most part its base is upper Lower Silurian, ers, 1970), in a facies totally different from the but in places lower Lower Silurian strata are (to be sure, rather poorly dated) Cambrian present. The younger of the underlying se- rocks of Taconic type in northern Gaspe. The quences (Mictaw formation) consists of some- first fossils above the unconformity are of late what more deformed shale and graywacke Middle Ordovician age (Zone 13?), younger containing middle or upper Middle Ordovician than those in the Ordovician rocks immediately graptolites, once again of the same age range as adjacent to the unconformity in northern those in northern Gaspe, at Castle Brook in Gaspe, but not younger, apparently, than those southern Quebec, and around the Taconic in the graywacke and "blocks-in-shale" units on klippe—those that date the Taconic phase the north shore. Thus, the only evidence in this there. Thus, the presumed unconformity be- whole belt for orogenic movement that could tween has roughly the span of the "classical" be classed as Taconic is certainly older than the phase of the Hudson Valley. The older se- "classical" phase of the orogeny in any of the quence (Maquereau group) in contrast consists areas so far discussed or even than the arrival of of unfossiliferous clastic rocks with subordinate slide or thrust masses in those areas, but it could volcanics and is far more severely deformed be coeval with the Penobscot phase or disturb- and mildly metamorphosed; Ayrton recognized ance in the northern Maine volcanic belt, with not only recumbent folds but also a possible the activity recorded by the lower unconform- unconformity within this sequence. Curiously, ity in southern Quebec, or, at a pinch, with the no unconformity can be observed between

(Midd/e Prn

.Cambrian •"C x>carbonate i u m P-»*V!.-

group

Figure 8. Sketch map of Gasp£ Peninsula to show ner of map. Dotted line indicates unconformity at base present relative position of various facies of Paleozoic of Silurian or Lower Devonian strata; it is absent on strata. Anticosti Island (autochthonous Ordovician and north flank of Matap^dia anticlinorium and on Anticosti. Silurian carbonate strata) lies just beyond northeast cor-

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these two pre-Silurian sequences; instead, they water) muddy limestone on Upper Cambrian are separated by a fault that, to judge by the (shallow-water) limestone behind them and coarse conglomerate in the younger sequence also the lack of any large clastic influx as close adjacent to it, was active during at least part of as Anticosti. The flimsiness of this speculation is the Middle Ordovician deposition. Neverthe- obvious; to test it by working out the timing of less, the presence of deformed and metamor- the movements will require closer stratigraphic phosed rocks (plus granitoid rock) among the discrimination among Middle Ordovician fos- cobbles in the conglomerate proves the exist- sils, especially graptolites, than we have had in ence of a major orogenic episode older than the the past. middle Middle Ordovician. In any case, the two areas in question, now Like several other investigators, Ayrton barely 50 km apart in southeastern Gaspe (Fig. (1967, p. 11-12) prefers a Precambrian age for 8), record totally different geologic histories. the rocks of the older sequence and for the In the area west of Perce, Cambrian shallow- pre-Middle Ordovician orogenic episode, water carbonates were apparently exposed and which he has called the Gaspesian orogeny eroded, then submerged again in the Middle (1967, p. 57-58). On the other hand, the rock Ordovician, after which the area received only types are much like those in the Cambrian part limy mud in deep water, or at least far from of the "Taconic-type" section in northern shore, during the rest of the Ordovician and Gaspe, southern Quebec, and the Taconic re- (save for volcanic debris) most or all of the gion, and also like those beneath the older un- Silurian, perhaps indeed into the Early conformity in the northern Maine volcanic belt, Devonian. In the area around Port Daniel, on so that for my part I am strongly inclined to the other hand, clastic and volcanic rocks of consider these rocks Cambrian and the orogeny undetermined age were very severely de- that deformed them roughly equivalent to the formed before the Middle Ordovician, briefly Penobscot phase in northern Maine or the submerged and covered with mud, sand, and older phase in southern Quebec. gravel, and finally overlapped by a thick shal- Now, although, as just noted, these rocks low-water Silurian platform sequence. resemble the Cambrian "Taconic-type" rocks The unconformity beneath the Silurian (and in several other parts of the northern Appala- Lower Devonian) Chaleur Bay sequence can be chians, they stand in the strongest contrast to recognized all along the south coast of Gaspe the nearest exposed Cambrian rocks, the car- and also in part of northern New Brunswick bonate strata that underlie Middle Ordovician (but not to the northwest in the Aroostook anti- muddy limestone west of Perce—strata that clinorium), especially around the north end of have a "carbonate-shelf look (as Professor F. the Miramichi anticlinorium, where Middle F. Osborne first pointed out to me), as if they Ordovician shale, graywacke, chert, and vol- belonged in the Champlain Valley or the car- canic rocks (Tetagouche group) were severely bonate autochthon of the Taconic region. If deformed, mildly metamorphosed, and appar- these parallels are justified, then one is led to ently intruded by granodiorite (Poole, 1967, p. speculate that the different rock types record 25) before being covered by Silurian strata. In the same contrast of carbonate bank and deeper one area in central New Brunswick, indeed, basin here as in the Taconic region and, further- Poole found in the pre-Silurian rocks a se- more, that the Taconic rocks of northern Gaspe quence of rock types and faunas so extraor- were originally deposited south of the carbonate dinarily like that in the northern Maine strata west of Perce but then moved some 50 volcanic belt that he was led to postulate a pre- km northward during the Middle Ordovician, Middle Ordovician—Penobscot—disturbance so that the carbonate strata are exposed in a there as well. Yet the conformable Ordovician- remnant of a tectonic window, since almost bu- Sjlurian sequence of the "potato belt" (Aroos- ried beneath later Middle Ordovician and took anticlinorium) entirely separates this younger deposits. To speculate still further, region from the northern Maine volcanic belt, perhaps the departure of the Taconic-type rocks and indeed the Ordovician and Silurian appear from their original home was considerably ear- to be conformable (although mainly as non- lier—a couple of graptolite zones?—than their calcareous slate or "argillite"—Charlotte arrival in northern Gaspe, and perhaps they group) around the southwest end of the never projected much above sea level but slid Miramichi anticlinorium near the New Bruns- on the sea bottom, explaining the overlap of wick-Maine border and into the east-west Fred- upper Middle Ordovician (probably deep- ericton synclinorium between it and the

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Kennebecasis anticlinorium of southern New conglomerate, conventionally assigned to the Brunswick. Apparently, therefore, the Chaleur Upper Ordovician but without fossil evidence). Bay-Miramichi area, although affected by oro- Nearby are considerably more deformed and genic disturbances comparable to and perhaps mildly metamorphosed phyllites, from which a contemporaneous with the Taconic phases that possibly Lower Ordovician fossil has been re- created Taconica, became a quite separate land- ported and into which granitoid rocks are in- mass (let us call it Miramichia) separated from truded. Elsewhere in the region, the Silurian Taconica (and Highlandcroftia) by a broad strata appear to rest at least disconformably on deep seaway. Even the present distance be- various older undated units, some of them tween them is 20 to 40 km in eastern Maine and mildly metamorphosed and perhaps intruded western New Brunswick, and I believe the by pre-Silurian granitoid rocks. original distance may have been several times On southeastern Cape Breton Island, scat- greater. tered remnants of coarse pre-Carboniferous clastic rocks rest unconformably on older more COASTAL MAINE, SOUTHERN NEW deformed rocks, which include Cambrian and BRUNSWICK, AND NOVA SCOTIA Lower Ordovician strata. Only one of these remnants has yielded fossils—land plants of Beyond the area of continuous deposition probably Early Devonian age; others are in- that surrounds Miramichia on the south and truded by pre-Carboniferous granite. Thus, the west, we find again a belt with a "Taconic" unconformity beneath them probably records unconformity. The unconformity is spectacu- the same general period of deformation as that larly displayed on Ames Knob at North Haven, more clearly recorded in coastal Maine and Maine, in Penobscot Bay (Smith and others, New Brunswick. 1907), and on Cookson Island in Oak Bay, In the southwestern peninsula of Nova New Brunswick (Fig. 9A), at the head of Pass- Scotia, Silurian and Lower Devonian rocks ap- amaquoddy Bay (Gumming, 1967, p. 16, PI. pear again, in sequence above the monotonous 4A). Elsewhere in the region it is mostly cut out slate of the upper Meguma group (Halifax for- by large Devonian intrusives, but it has been mation), which is dated only by a few Lower recognized elsewhere in coastal Maine (Gil- Ordovician (Tremadoc) graptolites (Crosby, man, 1966). Conglomerate above the uncon- 1962, p. 19-21). The lowest Silurian fossils formity forms the base of a thick largely here are Upper Silurian (Ludlow) and are also volcanic Silurian and Lower Devonian se- in slate; between the two fossiliferous slaty for- quence (Mascarene group and correlatives); at mations is the more varied White Rock forma- Oak Bay the conglomerate contains pebbles of tion, including quartzite and volcanics. At one quartzite with lower Lower Silurian fossils and place, at least, this formation rests unconforma- also of granitoid rocks that suggest the exist- bly on the (there unfossiliferous) Meguma ence here too of Ordovician intrusives. The group (Taylor, 1965, p. 17-22); according to rocks below the unconformity are unfossilifer- those who have mapped in this region, the un- ous slate, "argillite," or greenstone, except that conformity, although angular, is only local, but slate at Oak Bay contains Lower Ordovician I find it difficult to believe that deposition could (Arenig) graptolites close to the unconformity. have been continuous in this region from earli- These rocks are more severely deformed than est Ordovician to Late Silurian time without the Silurian, and in Maine some are mildly leaving a greater thickness of strata and more metamorphosed. fossil evidence, and I would interpret the unit The classical Cambrian to Lower Ordovician of quartzite and volcanics here as comparable to slate sequence around Saint John, New Bruns- the Shaw Mountain formation along the "classi- wick, is overlapped not by Silurian but by Car- cal" disconformity on the east side of the Green boniferous rocks, so that the existence of Mountains in Vermont and the unconformity Taconic deformation there cannot be demon- beneath it as reflecting the Taconic orogeny. strated. The next occurrence of Silurian rocks Upper Silurian and Lower Devonian volcan- to the east is in Nova Scotia, in the Cobequid ics are present also in northeastern Massa- and Antigonish Highlands and especially in the chusetts (Newbury volcanics), resting famous Arisaig section northwest of Antigon- unconformably on plutonic rocks that seem to ish. At Arisaig, lower Lower Silurian strata rest be mainly of very late Precambrian age. Fos- (perhaps disconformably) on volcanics and siliferous Cambrian strata are known not far these in turn on conglomerate (Malignant Cove away, but their relations with the Siluro-

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Devonian rocks are indeterminate, whereas in extraordinarily like the Taconic region (Fig. one place at least they too rest unconformably 10). From early in the Cambrian until early in on probably late Precambrian plutonics. the Middle Ordovician, it was part of the vast Hence, the unconformity beneath the Siluro- carbonate bank that formed the eastern border Devonian rocks may result from the very late of the North American continent (Rodgers, Precambrian Avalonian orogeny, which is also 1968). As in New York State, and elsewhere known to have affected parts of southern New on the bank as far as Alabama, a disconformity Brunswick, Cape Breton Island, and southeast- (unconformity C) generally separates Lower ern Newfoundland, especially the Avalon and Middle Ordovician carbonate strata. In the Peninsula (Hughes, 1970, 1971; Rodgers, Middle Ordovician, there was an "inversion of 1971). One cannot determine, therefore, relief; the bank foundered and began to re- whether eastern Massachusetts was affected by ceive mud and dirty sand from new uplifts to the Taconic orogeny, although it is on strike the east (Stevens, 1970), and soon afterward with the area in coastal Maine that was certainly large exotic masses of a contemporaneous but affected. quite different sequence of strata, remarkably The Taconic orogeny in these areas is dated similar to the Taconic sequence, slid by gravity only within rather broad limits, between quite into the deepening sea, probably coming from early in the Ordovician and some part of the the same uplifts (Rodgers and Neale, 1963). In Silurian (very early in the Silurian in the Arisaig contrast to the exotic masses in the Taconic region, or even late in the Ordovician if the region, however, these included large bodies of volcanics and conglomerate beneath the fos- basaltic volcanics and even larger ones of mafic siliferous Arisaig rocks are indeed pre- and ultramafic intrusives. There may be an un- Silurian), and hence spanning the time of all the conformity beneath the graywacke at the sum- phases recognized in the more northwestern mit of this sequence (Hugh D. Lilly, 1964, belts. Whether a single phase or several, the personal commun.), again as in the Taconics orogeny evidently produced a landmass or se- (unconformity B), but disharmony in the struc- ries of masses or islands, which we may call tural response of the different parts of the se- Kennebecasia, for the Kennebecasis anti- quence has been so extreme (Bruckner, 1966, clinorium in southern New Brunswick. Ken- p. 147-149) as to prevent certainty in the mat- nebecasia occupied roughly the same linear belt ter. Moreover, the uppermost beds in the au- as the older islands or landmasses produced by tochthon beneath include units of the Avalonian orogeny, although these had "blocks-in-shale" and "Wildflysch-type con- been largely destroyed in the meantime. In the glomerate." The exotic masses and the underly- Silurian, on the other hand, it or its northwest ing autochthon were then folded together into flank became the locus of intense volcanism, synclinoria; as in the Champlain and St. Law- perhaps in the form of a volcanic island arc. In rence Valleys, the age of this later deformation any case it was separated by open and probably is uncertain and could be either Ordovician deep water from /Miramichia and Taconica, (Taconic) or Devonian (Acadian). Silurian possibly indeed by a proto-Atlantic ocean (Wil- strata are present only in a very narrow strip son, 1966). along part of the west shore of the island, where they are apparently conformable (though per- NEWFOUNDLAND haps disconformable) with beds as old as late Recently it has become apparent that, at least Middle Ordovician that in turn rest with angu- during the Cambrian and the first half of the lar unconformity across the west margin of one Ordovician, northwestern Newfoundland was of the exotic masses (Rodgers, 1965; Stevens, 4 1970, Fig. 4, p. 171). This angular unconform- Figure 9. Taconic unconformities. A. Oak Bay, New ity would thus correspond to the "classical" un- Brunswick. Upper (zl) Silurian (Oak Bay conglomerate, conformity (unconformity A) in the Hudson on right) on Lower Ordovician (Charlotte group, dark Valley; as there, the rocks above are also de- argillite division, on left). Courtesy of L. M. Cumming formed but probably less than even the autoch- and Geological Survey of Canada; republished by per- mission from Cumming (1967), Geological Survey of thonous rocks below. Canada, Paper 65-29 (Plate IV A.) B. Old Gould Quarry, If, however, the sequence of events in west- east side of Kanouse Mountain north of Echo Lake, New ern Newfoundland is thus almost exactly paral- Jersey. Silurian (Green Pond conglomerate) on Lower Cambrian (part of Kittatinny dolostone, bedding paral- lel to that in the Taconic region, the timing is lel to hammer handle). Ancient karst surface. Photo- not. The equivalent of the "classical" uncon- graph by Ira B, Lamster; courtesy of Robert M. Finks. formity in Newfoundland is older than the ar-

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rival of the exotic masses in the Hudson Valley Humberian (Bird and Dewey, 1970), for the and even than the appearance of mud and sand Humber Arm of the Bay of Islands. there; in Newfoundland, on the other hand, Evidence of Taconic orogeny is also present that appearance and the arrival of the exotic farther east in Newfoundland, particularly in masses, called the Bonnian disturbance or and around the Burlington Peninsula and west- phase of the Taconian orogeny by Kay (1969c, ern Notre Dame Bay, but it has proved difficult p. 667-668), is still older,8 older than the un- to decipher fully, and numerous points in the conformity (unconformity B) within the upper geology are still in debate (compare with Phillips part of the Taconic sequence in the Taconics. and others, 1969; and with Church, 1969). The Finally, the appearance of graywacke (and the probably Silurian strata in that area, largely red- possible unconformity) within the "Taconic" beds and rhyolitic volcanics, are much less de- sequence in Newfoundland is Early Ordovi- formed and metamorphosed than the older cian, even older than the disconformity within strata, and in different places they lie with spec- the carbonate sequence (unconformity C), the tacular unconformity on and contain fragments only event that may have been contemporane- of granodioritic or ultramafic intrusives. It is ous in the two regions. The conformable or further possible that underlying Lower and paraconformable sequence of beds above the lower Middle Ordovician rocks, now largely "classical" unconformity in Newfoundland in- greenstone volcanics, are themselves uncon- dicates that no deformation affected the west- formable on a still older more metamorphosed ern edge of the island between middle Middle complex (containing small bodies of eclogite; Ordovician and Early Devonian time, but the Church, 1969, p- 224). The similarity of this presence of coarse, largely red elastics both be- history with that of the northern Maine vol- low and above a probably latest Silurian canic belt is evident, and it is enhanced by the (Pridoli) fossil zone (Boucot, 1969a, p. 477) presence in belts to the southeast (Botwood suggests uplift to the east in the Silurian and and New World Island belts 0/Williams, 1967; later Ordovician as well as in the Early Dildo sequence o/Kay, 1969a) of an apparently Devonian. No other post-tectonic, pre-Car- continuous succession of marine clastic strata boniferous strata are preserved to help us date from the Middle (perhaps Lower) Ordovician these uplifts. As already mentioned, Anticosti well into the Silurian. Within this succession are to the west across the Gulf of St. Lawrence intercalated first vast gravity slides or "me- records only a mild invasion of mud in the later langes" full of volcanic blocks (Dunnage com- Middle Ordovician. Probably these later uplifts plex and others; Home, 1969; Home and were successors to the main early Middle Or- Helwig, 1969; Helwig, 1970; Kay, 1970) and dovician uplift, which shed into the autochtho- then great thicknesses of coarse but fairly well nous basin first mud and sand and then the rounded conglomerate (Goldson conglomer- great exotic masses. It seems largely semantic ate, Upper Ordovician and Lower Silurian; whether we consider these Ordovician events Kay, 1969a; Helwig and Sarpi, 1969) contain- in Newfoundland phases of the Taconic ing volcanic and plutonic clasts obviously orogeny or coin a new name for them, such as derived from the belt to the northwest where the Taconic unconformity or unconformities 8The arrival of the exotic masses—the Bonnian phase—in are displayed. western Newfoundland is quite well dated. Graptolites in the Except for the absence of anything resem- underlying autochthonous shale (containing thin beds of graywacke) belong very low in the Middle Ordovician bling the Gaspe-Connecticut Valley syn- (Zone 6 of the British succession, according to Kay, 1969b, clinorium (which is narrowing where last seen p. 564; Zone 9 0/Berry, according to Whittington, 1968, p. in eastern Gaspe), the facies relationships in 53—in either case Llanvirn—but Zone 10, according to Erdt- northern and western Newfoundland are there- mann and Riva, as quoted by Stevens, 1970, p. 173—if so, fore exactly like those across Taconica (s.l.) in Llandeilo). The rich shelly fauna in the unconformably over- northern New England and adjacent Quebec, lying "neautochthonous" limestone (Long Point formation) and there seems no reason to doubt that the is classed as Wilderness (or partly higher) by most workers uplifted landmass in Newfoundland recorded (for example, Whittington and Kindle, 1969, p. 655) but as by these unconformities and gravity slides was Porterfield or even upper Chazy by Kay (1969c, p. 667- 668). The emplacement of the masses is thus fixed within two simply the northeastern equivalent of Taconica, or three graptolite zones, whereas the arrival of the Taconic if not its northeastern extension (see Fig. 7). masses in the Hudson Valley was a zone or more later than When, or indeed if, this landmass was again the beginning of "neautochthonous" deposition in New- submerged beneath the sea is hard to judge, foundland. however; marine Silurian strata are present on

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both its flanks, containing volcanic rocks that the New York-New Jersey border 30 to 35 km apparently thin out away from it, but on its crest southeast of the main outcrop of the uncon- the presumed Silurian rocks are mostly or en- formity. At the two ends of this syncline, tirely non-marine—red beds and rhyolitic vol- Silurian conglomerate (its position within the canics. Silurian is vague, for the first diagnostic fossils If anything like miramichia or Kennebecasia lie considerably above it and are already Upper was present farther southeast in Newfound- Silurian) rests on Cambrian and Lower Ordovi- land, the evidence for it is not yet clear. Around cian carbonate rocks (locally on overlying Mid- the head of Fortune Bay, red beds with rhyo- dle Ordovician shale), but at localities in litic volcanics assigned to the Silurian (Rencon- between it bevels down across the carbonates tre formation) have been reported to lie (Fig. 9B) to rest directly on the underlying Pre- unconformably above older sediments and vol- cambrian basement. On the other hand, the canics assigned to the Ordovician (Bradley, Middle Ordovician shale is present in full force 1962, p. 27), but the dating of both is totally all along the main outcrop belt northwest of the indirect and has recently been challenged (Wil- Highlands, and it also appears in a couple of liams, 1970) because similar rocks almost ex- outliers on the south side of the Highlands actly on strike (although separated by a southwest of and partly in line with the Green Devonian granite batholith) have always been Pond syncline (no Silurian rocks are preserved called Precambrian, although there again the there, however; instead, the Ordovician rocks dating is indirect, by correlation across strike to are overlapped by Triassic strata of the Newark the Bonavista and Avalon Peninsulas. Hence, basin). In most of these areas, as in the Hudson the relative importance of the various Paleozoic Valley, the shale is underlain by a thin unit or orogenies in southeastern Newfoundland is units of Middle Ordovician limestone that is still conjectural. itself disconformable on Lower Ordovician car- bonate. Fossils show that the base of the shale NORTHERN NEW JERSEY, EASTERN here is of approximately the same age as in the PENNSYLVANIA, AND VICINITY Hudson Valley—middle Trenton or Barneveld The course of the "classical" unconformity —and the top may extend up to the Eden or from the Hudson Valley southwest to Harris- even the Maysville, at least in the main belt in burg has already been mentioned in the discus- Pennsylvania. sion of the accurate dating of that Nevertheless, mixed in with this Middle Or- unconformity. It can also be recognized in the dovician shale, both at Jutland, New Jersey, outlying Green Pond syncline, which lies in the south of the Highlands (Harry Dodge, 1964, heart of the Precambrian Highlands athwart oral commun., and field trip), and in Pennsyl-

DEPOSITION EROSION DEPOSITION Bay of Islands ld Island

V V . V V V V V V V V V . . VVVVVVVvvvr* V VVVVVVVVVVVvvvi v v v v v V Precamb. v V v v V VVVVVVVVVU v v v vvvvvvVVVVVVVVVVv vv V V VVVVVVVV V CONTINENT OCEAN Figure 10. Schematic cross section across northern ment; crosses: felsic intrusives; pillow-like forms: mafic Newfoundland as of Early Silurian time. Symbols as on volcanics; heavy hatching: ultramafic rocks. Figure 3, plus—checks: Precambrian continental base-

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vania from near the Lehigh (Paul Myers, 1963, vania that the Hudson Valley phase can be oral commun., and field trip) to the Sus- closely delimited, and it is here also that recum- quehanna (Platt in Carswell and others, 1968, bent folding of that age is best demonstrated. p. 9-16), and perhaps a little beyond, are masses Clearly, the landmass Taconica extended south- of Taconic-sequence rocks containing Lower west from western New England along the pre- Ordovician graptolites and hence contempo- sent Highlands at least into southeastern raneous with part of the underlying carbonate Pennsylvania. sequence. As in the Hudson Valley, these masses are best explained as having slid by CENTRAL AND SOUTHERN gravity into the late Middle Ordovician sea APPALACHIANS: VALLEY AND from a source area to the east or south (Kay, RIDGE PROVINCE 1941), although in the absence of Cambrian The "classical" unconformity cannot be fol- faunas the problem has not been as obvious lowed beyond the Susquehanna River; indeed, until recently. According to Platt (in Carswell there is no reason to doubt that sedimentation and others, 1968), none of the masses near was continuous from some time in the Middle Harrisburg much exceeds 8 km in length, in Ordovician until some time in the Silurian contrast to the much more continuous masses of through most of the Appalachian Valley and Taconic-sequence strata in the Taconic region. Ridge province from central Pennsylvania to Furthermore, the Middle Ordovician (and Alabama.9 The great spread of Upper Ordovi- presumed lower Upper Ordovician )shale in cian elastics across New York and Pennsylvania these regions, especially eastern Pennsylvania, and into the Middle West has already been is cut by a strong slaty cleavage (eastern Penn- mentioned; clastic materials (for example, Mar- sylvania has been an important commercial tinsburg shale and Juniata formation) also slate district) and involved, along with all the spread southwest along what is now the Valley older rocks down to and including the Precam- and Ridge province, advancing in steps the last brian basement, in great recumbent folds or of which, in the later Late Ordovician, reached nappes with wave lengths measured in kilome- Alabama, although continental red beds did not ters and amplitudes probably in tens of kilome- extend past East Tennessee. Everything sug- ters (Ryan and others, 1961; Sherwood, 1964; gests, moreover, that these clastic materials Drake, 1970). Since the slaty cleavage is itself came from the same source as those in New cut and folded by a later slip or fracture cleav- York State and westward, the uplift Taconia age that seems to be roughly parallel to the only produced by the Taconic and Hudson Valley cleavage in the overlying Siluro-Devonian phases of the Taconic orogeny in western New strata, Maxwell (1962) concluded that the slaty England and easternmost New York and prob- cleavage was formed in Late Ordovician time, ably southwestward into southeastern Pennsyl- in the Taconic orogeny, and on similar vania. grounds, Drake (1970, p. 289), and others, In Tennessee and adjacent states, however, have concluded the same about the recumbent there is an earlier pile of clastic sediments (Fig. folds. Epstein and Epstein (1969, p. 165-170) 11), not as extensive as that just mentioned but combat this conclusion, but what I have seen of about equally thick in places and composed of the evidence seems to me to sustain it. almost exactly the same kinds of materials in the Thus, throughout this region the same series same order, so similar in fact that for many of orogenic events is recorded as in the Hudson decades the earlier deposits were correlated Valley—mild uplift and erosion between the with the later ones, until Ulrich and Butts (see Early and Middle Ordovician on the carbonate Wilmarth, 1938, p. 130) found the fossils that bank ("Tinmouth phase"), sudden appearance disproved the correlation. Mud, followed by of mud during the Middle Ordovician followed poorly sorted sand (now graywacke), appeared by gravity-slid masses of exotic rocks of the very early in the Middle Ordovician in what are Taconic sequence ('Taconic phase"), and now the southeastern belts of the Valley and finally, strong folding and formation of slaty cleavage followed by uplift and erosion before the deposition of Silurian and latest Ordovician * Only along the southeast side of the province in Ala- bama, Georgia, and southeastern Tennessee does a discon- conglomerate and sandstone ("Hudson Valley formity appear at this level; here Devonian (mainly Middle phase"). Moreover, the timing seems to be Devonian) strata, which elsewhere overlie the Silurian, di- compatible with that in the Hudson Valley; in- rectly overlie Middle or Lower Ordovician, possibly as the deed, as already discussed, it is only in Pennsyl- result of post-Silurian rather than post-Ordovician erosion.

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Ridge province in East Tennessee and nearby, tic pile, as the Silurian sea did over the later pile and as time went on they extended irregularly farther north, but fossils show that this trans- westward (Sevier shale, Tellico sandstone, and gression occurred in later Middle Ordovician related formations). Spectacular polymict con- (Barneveld) time when the northern invasion glomerates (Kellberg and Grant, 1956) are of elastics was only just beginning to spread known in the lower part of the clastic sequence over eastern New York State. in several localities in the southeasternmost belt This earlier pile of sediments in East Tennes- (see Fig. 1), and they contain fragments of older see and vicinity must therefore recorded an ear- strata down to the Lower Cambrian (already lier uplift and erogenic phase (called the lithifield quartzite and arkose), testifying to Blountain distrubance by Kay, 1942, p. 1632; substantial uplift at that time not far away to the and the Blountain phase of the Taconic southeast. Red beds, partly marine and partly orogeny by Rodgers, 1953, p. 94, for the continental (Moccasin and Bays formations), Blount group, a stratigraphic unit created by followed the marine mud and sand in the south- Ulrich in 1911, to include the bulk of the lower eastern part of the region, and at the same time Middle Ordovician clastic rocks in East Tennes- mud reached its maximum extension north- see), although to date no angular unconformity westward; even so, it barely reached the north- of this age has been recorded in the region. On west margin of the Valley and Ridge province. the other hand, its climax seems to have been Finally, the sea transgressed back over the clas- punctuated by a series of colossal volcanic ex-

Figure 11. Schematic stratigraphic diagram of Mid- coarseness of wall pattern roughly indicates grain size of dle and Upper Ordovician strata in East Tennessee. Or- limestone. Reproduced from Geological Society of dinate is thickness, not time. Symbols as on Figure 3, America Bulletin, Vol. 65, p. 258, Fig. 1. except—dashed lines: shale; continuous lines: red beds;

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plosions, the ash10 from which is now spread as son Valley-Taconic region (except that no Ta- thin layers over most of the eastern United conic slide masses are known south of States and into Ontario. The location of the Pennsylvania), but the climax was much earlier. volcanoes, like that of the orogenic uplift, is not precisely known, but the localization of the clas- CENTRAL AND SOUTHERN tic pile and the general increase in number and APPALACHIANS: PIEDMONT thickness of volcanic ash beds toward East PROVINCE Tennessee suggest a source somewhere in the Except for Lower Devonian rocks in the up- Carolinas. per part of the Talladega group at the extreme The unconformity between Middle and west edge of the province in Alabama, no Lower Ordovician carbonate strata (uncon- proved Silurian or higher Paleozoic strata are formity C), recognized from New York to known in the entire Piedmont, the crystalline Newfoundland, can be found also through core of the southern segment of the Appalachi- much of the southern segment of the Appala- ans. This is in strong contrast to the crystalline chians, as far as Alabama. The erosional surface, core of the northern segment—the Maritime probably an old karst (Fig. 12A), is particularly Provinces and New England—where Silurian well displayed in places in East Tennessee strata are important as far south as Massa- (Bridge, 1955), and paleohydrologic flow chusetts in several belts and probably extend related to it is currently held responsible for the into Connecticut, and where Carboniferous concentration of the East Tennessee and related strata are also widespread, reaching to Rhode zinc ores, some of the most important on the Island; the Silurian (and Lower Devonian) continent (Laurence, 1971). On the other rocks were involved in the major deformation hand, in some areas, notably Maryland (Neu- and metamorphism of the northern segment man, 1951, p. 282-284; Sando, 1957, p. 28-31) (the Acadian orogeny), but the Carboniferous and southwestern Virginia (Cooper, 1961, p. rocks are later, although they are themselves 28-34; 1964, p. 90-92), the disconformity deformed and even metamorphosed in places. seems to be absent locally and carbonate depo- In the southern segment, on the other hand, the sition to have been continuous. Cooper's data, youngest (and indeed almost the only) fossilif- and others (compare with those cited ^Rodgers, erous rocks in the main Piedmont are the Quan- 1953, p. 123-124), suggest indeed a period of tico and Arvonia slates, which form tight mild folding at this time. Shaw and Rodgers synclines within the Piedmont gneisses of (1963) suggested that the disconformity may northern and central Virginia; both are as- reappear at the base of the Talladega group in signed to the lower Upper Ordovician (roughly the westernmost Piedmont of Alabama, where Maysville) on the basis of adequate but rather locally a coarse conglomerate contains pebbles unusual faunas. The Arvonia slate can be ob- of gneiss and "granite." Mapping by Shaw served to rest unconformably and with a basal (1970) in that region further suggests severe sandstone on granodiorite near Carysbrook, folding of the Lower Ordovician and underly- Va. (Fig. 12B).11 As long as the Taconic ing carbonate rocks before the deposition of orogeny was assigned to the end of the Ordovi- the supposedly Middle Ordovician elastics of cian and was considered the only such event in the lower Talladega group, comparable to the the early Paleozoic of eastern North America, folding postulated by Ratcliffe in Berkshire this unconformity was held to prove the Pre- County, Massachusetts. In any case, there seems cambrian age of the underlying Piedmont rocks to be good evidence in the southern Appalachi- (except when the fossils were ignored and the ans for a phase like the Tinmouth phase (if a rocks containing them assigned to the Silurian), local name is needed, Douglas Lake phase will 1' Although this unconformity has been denied by Brown do, after the type locality of the karst-filling and Sunderman (1954), and by Smith and others (1964, p. deposits described ^Bridge, 1955). Thus, as in 14, but see their Fig. 3, which is Fig 12B of this article), Newfoundland, the sequence of events re- restudy in the field convinces me of its reality, and Brown corded in the southern Appalachian Valley and (1969, p. 31-32; 1970, p. 345) now agrees; the underlying Ridge province was much like that in the Hud- granodiorite was weathered but then remetamorphosed along with the overlying slate. The basal relations of the "•Commonly called bentonite or metabentonite, but the Quantico slate have not been observed, and those of the rock does not possess and probably never possessed the similar and possibly correlative but unfossiliferous Peach peculiar swelling properties that characterize the type bento- Bottom slate on the Maryland-Pennsylvania border are de- nite, derived from Cretaceous volcanic ash in the western scribed as gradational (Knopf and Jonas, 1929, p. 39; Agron, United States. 1950, p. 1268).

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but now that intra-Ordovician erogenic move- quence, somewhat above the marble unit. Hop- ments have been demonstrated up and down son has also supported the Precambrian age the Appalachians, it could well record some assignment of the sequence by the argument such movements which, although perhaps a lit- that it is cut by other metaigneous units, zircon tle early to correspond to the climax of the ages from which are approximately Early Cam- Hudson Valley phase farther north, might be brian. contemporaneous with its earlier stages, and in An alternative hypothesis seems possible, any case could certainly reflect the Blountian however. First virtually identical zircon ages phase. have been obtained from an obviously metavol- In order to date the remaining rocks of the canic unit in the same region (James Run northern Piedmont we must turn to geo- gneiss), suggesting a metavolcanic origin for chronometry, and fortunately many excellent the other dated metaigneous units as well; thus, data have been obtained on rocks from the Bal- the surrounding sediments would be coeval timore region in Maryland (see summaries by with instead of older than these metaigneous Hopson, 1964, p. 193-207; Tilton and others, rocks. Second, the stratigraphy and structure of 1970; also references there cited). In the Bal- the Baltimore region and of the area west of timore region, and in an area west of Phila- Philadelphia are extraordinarily like these of delphia, a series of gneiss domes expose a base- New York City and Westchester County, New ment core (Baltimore gneiss) mantled by a York, directly up strike (although the connec- thick metasedimentary sequence (Glenarm tions are buried beneath overlapping Creta- group) now mainly schist but including a basal ceous sediments), and in New York, as recently quartzite and schist unit overlain by a marble worked out by Leo Hall (1968), the quartzite unit and also containing many bodies of me- and marble units are clearly Cambro-Ordovi- taigneous rock, both metaplutonic and meta- cian, overlain by autochthonous elastics (above volcanic. (Probably the basement and mantle unconformity C), and these by probably alloch- had already been recumbently folded before thonous Taconic rocks (whose age is unknown the doming; for this argument, see Bailey and but could be Cambrian or late Precambrian). Mackin, 1937; McKinstry, 1961; Mackin, The presence of a widespread unit of slide 1962.) Zircon studies have confirmed the Pre- breccia not far above the marble unit in the cambrian age (approximately 1,100 m. y.) of Baltimore area invites the speculation that here the basement; on the other hand, the principal again a "blocks-in-shale" or "Wildflysch-type metamorphism of the mantle, as judged mainly conglomerate" unit lies at the top of the local by the Rb/Sr method, was not late Paleozoic as autochthon and that the overlying part of the originally surmised but earlier, probably Or- mantling sequence is allochthonous (and could dovician. This Ordovician metamorphism well be late Precambrian, as required by the probably extended westward, although de- rest of Hopson's evidence). Further implica- creasing in grade, as far as the Blue Ridge or tions of this speculation, requiring either tens of South Mountain anticlinorium, the formation kilometers of thrusting or tens of kilometers of of which described in a classic paper by Ernst strike-slip movement, are beyond the scope of Cloos (1947), was probably also Ordovician this discussion. In any case, the Baltimore re- (Cloos, 1964, p. 831-832). gion underwent a major period of metamor- The age of the mantling sequence, limited phism, probably recumbent folding, and gneiss between these two dates, has been variously doming during the Ordovician, comparable to given as Cambro-Ordovician and late Precam- and roughly contemporaneous with or a bit ear- brian. The arguments of Hopson (1964) and lier than the Hudson Valley phase as expressed others (see summary in Rodgers, 1970, p. 188, in eastern Pennsylvania, but earlier there had 190) strongly indicate that the top of the se- been a period of gravity-sliding comparable to quence, well to the west of Baltimore, conform- the Taconic phase, somewhat earlier in the Or- ably underlies Lower Cambrian strata; if, dovician if the speculation has merit, late in the therefore, the sequence is uninterrupted, it Precambrian if it does not. should be Precambrian. Cloos and Hopson The rocks of the mantling sequence of the have further demonstrated that one of the sup- Baltimore region extend south into Virginia posed metaplutonic units (Sykesville "granite" where they adjoin the Quantico and Arvonia and Laurel gneiss) is in fact metamorphosed slate synclines and are apparently intruded by sedimentary slide breccia, intercalated in the the granodiorite gneiss overlain unconforma- lower part of the main schist mass of the se- bly by the Arvonia slate. The slate itself is meta-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/5/1141/3432678/i0016-7606-82-5-1141.pdf by guest on 02 October 2021 Figure 12. Taconic unconformities in southern seg- granodiorite of uncertain age. Top of granodiorite was ment of Appalachians. A. Excavation for Douglas Dam, weathered before deposition of overlying beds, then Tennessee. Sinkhole within Lower Ordovician (Mascot metamorphosed with them; unconformity was later cut formation) filled with Middle Ordovician dolostone and by small faults. Courtesy of Virginia Division of Mineral volcanic ash (Douglas Lake member of Lenoir lime- Resources, James L. Calver, State Geologist; republished stone). Photograph by Granville Hunt, Tennessee Val- by permission from Smith, Milici, and Greenberg ley Authority; courtesy of Robert A. Laurence. B. (1964), Virginia Division of Mineral Resources Bulletin Railroad cut south of Carysbrook, Virginia. Upper or- 79, Fig. 3. dovician (basal Quartz ice of Arvonia formation) on

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morphosed, however, and evidence that the period, suggesting that the climax here was ear- unconformity is also a metamorphic discon- lier than in the New York-New England re- tinuity is not very convincing. Thus, at least one gion, although perhaps no earlier than in metamorphism in the region was later than Newfoundland. Likewise, the extent of the early Late Ordovician; if it was only a little landmass or landmasses produced in this later, it might still be the one recorded by geo- orogeny in the southern Appalachians is quite chronometry around Baltimore, but if it was unknown, as only the Blountian sedimentary much later, they must be separate events. pile appears to record it,12 and that pile was Evidence for the age of deformation and already overlapped by the sea during late Mid- metamorphism through the rest of the Pied- dle Ordovician time. mont is even more equivocal. The obvious im- portance of the late Paleozoic "Appalachian" GENERAL CONCLUSIONS —better, Alleghany—orogeny throughout the Now that we have summarized the data on Valley and Ridge and Appalachian Plateau Taconic and related erogenic movements in the provinces of the Central and Southern Appala- Appalachians, perhaps we can review them to chians has led to the general view that the main see what general principles, if any, can be in- period of orogeny and granite intrusion in the duced from them. We could, for example, Piedmont was also late Paleozoic, in contrast to make a correlation table (compare with Fig. 2, the Northern Appalachians and Newfoundland in Pavlides and others, 1968) of the various where clearly the mid-Devonian Acadian unconformities—that is, of the time spans that orogeny was the most important and the Al- can be deduced from each area where erogenic leghany was restricted in area and of lesser in- movements are recorded—and then see how tensity. Many Europeans, indeed, have few spasms of deformation or uplift could ac- expressed this contrast by dividing the Appala- count for the data, thus hopefully also deter- chians into two separate chains—a northern, mining more precisely the age of each spasm. Caledonian, and a southern, Hercynian. The This has been the usual approach to the analysis geochronometry so far done in the Piedmont, of erogenic movements everywhere. In the however, presents us with a wide scatter of case in point, it seemed at first as if the data dates, especially K/Ar dates, ranging from Or- required only one such spasm, the one re- dovician to Carboniferous or Permian. At first corded by the angular unconformity between these dates were considered to record several Silurian and Ordovician strata in the Hudson separate metamorphic "events," or perhaps a Valley and elsewhere and therefore assumed to long-continued migrating metamorphism, but mark the end of the Ordovician period, for it soon impossible contradictions appeared, and it was believed that "diastrophism is the ultimate is now evident that many, perhaps most, record basis of correlation," and that the standard geo- only the uplift of the particular area and its logical periods are delimited by diastrophic cooling below about 200° C (Hadley, 1964; events. Thus arose the classical definition of the Armstrong, 1966). That some of the post-tec- Taconic orogeny, to which I alluded at the out- tonic intrusions in the Piedmont are as young set. As evidence accumulated that some oro- as Carboniferous seems very probable, espe- genic movements took place during and not at cially a group of late gabbros in the Carolinas the end of Ordovician time (evidence in the locally associated with mildly alkalic syenites. form of unconformities and the like, within Or- My own prejudice is to put the most emphasis dovician or presumed Ordovician strata), these on the older dates and to consider that the main movements were assigned to other erogenic period of deformation, metamorphism, and episodes and given separate names, although syntectonic intrusion throughout the Piedmont sometimes considered as precursor phases of was not late Paleozoic but Ordovician, that is, the main Taconic orogeny at the end of the Taconic, older and not younger than in the period. (At least once, on the other hand, the northern Appalachians. (Years ago, indeed, Hess [1939, p. 279] asserted that the Taconic 12 Perhaps one should consider also the poorly dated orogeny was the major event in the develop- coarse elastics in the lower and middle parts of the Talladega ment of the whole Appalachian chain.) Only group, including the Cheaha-Butting Ram quartzite. The dis- conformity beneath the Devonian in the southeastern part of the sedimentary evidence of the Blountian the Valley and Ridge province in Alabama and vicinity (foot- phase, already discussed and the unconformity note 9) also suggests a low landmass there, possibly the edge beneath the Arvonia slate give us any clues to of a larger landmass in the nearby Piedmont inherited from a more exact timing within the general Taconic the Ordovician orogeny.

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name Taconic was denied to the "classical" un- ably a bit later still in southern Quebec. To conformity in the Hudson Valley, for which it achieve contemporaneity of individual oro- was first proposed by Dana, and applied instead genic phases one must equate the final, external to what I have been calling the "Taconic deformation (4) in one area with the gravity phase," on the grounds that that phase is the sliding (3) in another and with the early, inter- one best displayed in the Taconic Mountains nal deformation (2) in still another. from which the name is derived.) Entirely apart But why must we assume such contem- from the nomenclatorial problem, it has poraneity? Is it not at least equally probable a seemed a valid use of Occam's razor to reduce priori (and considerably more probable if we the number of such phases as far as the data accept the data) that these "events" migrated would permit, affirming that a single phase (for along and across the belt, that, for example, the example, the Penobscot phase) can be recog- gravity sliding of Taconic-type exotic masses nized from northern New England and south- took place at quite different times in different ern Quebec to Newfoundland, if not to Ireland sectors and indeed took a considerable length and Scotland, if the rather vague dating of the of time in any one sector? That orogenies can movements in the individual areas could be migrate along erogenic belts is not of course a forced so as to permit them to be considered new idea; Hess suggested it explicitly years ago contemporaneous. Even so, the present data (1955, Fig. 4), and the recent Soviet compila- can hardly be found into as few as four phases tion of data on the tectonics of Eurasia (Yan- (none of them exactly at the end of the Ordovi- shin, 1966, especially p. 445) demonstrates it cian), and each increase in precision in dating for the "Hercynian erogenic cycle" in Asia and the movements in individual areas seems to in- suggests it for other "cycles" as well. But these crease the number of phases required. This in- ideas do not seem to have penetrated far crease is well illustrated by the proliferation of enough to influence our actual thinking about names proposed for phases; I have already cited the data. As I once remarked about sedimen- a dozen above and may well have missed some. tary facies (inLongwell, 1949, p. 130), we may I believe the time has come to analyze the be all for such ideas in principle, just as when tacit assumptions behind this line of argument, we are in church we are against sin, but I won- to make them explicit and then ask if they are der how far this allegiance carries when we are justified. First is the assumption that a given faced in the field with the tectonic equivalent of phase should be contemporaneous in different carnal temptation. regions. The data I have summarized show The second assumption is related; it is that clearly that the course of events during the Or- orogeny normally occurs in sharply delimited dovician was astonishingly similar in several pulses: events, spasms, phases, episodes—I different sectors of the Appalachians. New- have been using these words myself throughout foundland, Gaspe and vicinity, southern Que- this discussion. Each event, and the like is then bec and northern Maine, the Taconic-Hudson assigned a name and considered a discrete en- Valley region with the Connecticut Valley, tity (whether it is assigned the rank of a phase, eastern Pennsylvania—in each of these regions a disturbance, or a "true" orogeny); as I have at least three of the following four "events" can already mentioned, the number of such names be recognized: (1) disconformity on the car- is already large and is growing, suggesting per- bonate bank (perhaps angular unconformity at haps a reductio ad absurdum. It seems to me its eastern or "internal" margin); (2) severe that our methods for studying the evidence we early deformination in a more easterly or "in- are dealing with are themselves seriously biased ternal" volcanic zone; (3) gravity slides from by this assumption. By their very nature, dis- near the latter into the former area, following conformities and unconformities seem to re- an "inversion of relief; and finally (4) wide- cord sharp, discrete, interrupting events, spread deformation (generally with some whereas more gradual erogenic processes pro- metamorphism), especially strong in the more duce much less spectacular regressions and westerly or "external" zones—in the phase ter- transgressions of clastic facies lacking precise, minology: (1) Tinmouth, (2) Penobscot, (3) easily intuited limits. Similarly, we commonly Taconic, and (4) Hudson Valley. Yet the data analyze radiometric dates for a given region (or also show clearly that at least the two latter worldwide) by plotting them as histograms and "phases" were considerably later in the Ta- then argue that the peaks on the histograms conic region than in Newfoundland, and prob- record special events, or at least "cycles," of

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limited time duration (although in the earlier straight lines or sine curves but would resemble Precambrian, some of the "cycles" are assigned the third graph in Figure 13. If several people durations exceeding that of post-Paleozoic were asked how many orogenies or orogenic time!). Are we now thus introducing our as- events, episodes, or phases should be recog- sumption into the data by our very methods nized and named in the region represented by (even leaving out of account the "monograph this third graph, they would almost certainly effect" and other results of our inevitably er- differ greatly, even more so if they had access ratic sampling)? In most scientific fields, one to different parts of the data or to graphs result- plots the data as a graph, carefully selecting ing from different degrees of smoothing (the those coordinates that best bring out the graph in question is already smoothed from the regularities in the data, and then determines the raw data), yet no one could be said to be right best fitting line or curve; this method minimizes or wrong—the question becomes mostly ver- rather than maximizes any real irregularities bal. Well, that graph is the course of the weekly there may be in the data. A pertinent example close of the New York Times average for 50 is the determination of rates of sea-floor spread- combined stocks on the New York Stock Ex- ing by plotting the distance of given magnetic change from the recession in late 1966 to the anomalies from a mid-ocean ridge against the present depression (early 1970), and it reflects age of the oldest fossils in the overlying sedi- the quasi-random input of a wide variety of ments, or against the magnetic anomaly dis- economic processes into market prices. Com- tances for another part of the ocean. If there paring the orogenic histories in differenent sec- were minor fluctuations in the rates, this tors of the Appalachians with each other or with method would damp or eliminate them along those of the Caledonides and Hercynides of with the errors of measurement, and so on, Europe and Asia would be like comparing whereas the methods we use to study orogeny graphs for the Toronto, New York, London, exaggerate such fluctuations, when they do not Leningrad, and Shanghai stock markets; there actually create them as a result of our hopelessly would certainly be common features but also imperfect sampling. I have deliberately men- time lags and individual local fluctuations not tioned sea-floor spreading in this connection, reflected in all or any other markets. because I convinced by the recent accumulation If this analogy has any value, how then can of data and the resulting conceptual break- we define the Taconic orogeny? As I have al- throughs in geological and geophysical think- ready mentioned, throughout this discussion I ing, that spreading and orogeny are opposite have been forced by the nature of the English sides of the same coin (and have been since language, nay of Indo-European languages gen- early Precambrian time), and it disturbs me erally, to describe what I consider to be climac- greatly that one is supposed to be essentially tic peaks of orogenic activity (highs in the stock continuous and the other essentially spasmodic. market) within an irregular continuum of such Fundamentally, I agree with Gignoux, who activity (agenerally bullish period between two wrote (1950, p. 178, footnote 2, in the English recessions) by using such words as event, translation; 1955, p. 248, footnote 17): "Envis- spasm, phase, episode, as though I believed ages dans I'ensemble du globe, les phenomenes they were discrete entities. Such is the tyranny geologiques n'ont obei, ni au baton d'un chef of the pigeon-hole concept, the idea that d'orchestre, ni a la regie d'un geometre." phenomena can and should be described in ("Considered on a global scale, geologic terms of discrete, separate things to which dis- phenomena have obeyed neither the baton of tinctive names can be attached and then water- an orchestra conductor nor the straight-edge of tight definitions of the names framed. This a geometrician.") I would like to suggest an tyranny seems particularly to enslave geolo- intermediate view that orogeny (and by im- gists; I once paid my respects to the pigeon-hole plication sea-floor spreading, or perhaps more as applied to rock nomenclature (Rodgers, likely its first time derivative) is neither sharply 1950), and now I welcome the opportunity to spasmodic, the spasms being separated by combat it again in tectonics and to urge that longer periods of calm, nor smoothly continu- orogeny be conceived instead as a continuing ous, but is a sort of random walk produced by on-going process, although irregularly uneven forces deeper in the Earth. Thus, its graph in its effects, and that somehow we adapt our against time would show neither isolated peaks tectonic nomenclature to this concept. Thus, I rising above a flat background nor smooth shall refuse to define the Taconic orogeny but

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cian activity was in fact considerably greater than either Cambrian or Silurian. So consid- ered, the Taconic orogeny was a major oro- genic climax, or rather a complex series of interrelated climaxes, in history of eastern North America. ACKNOWLEDGMENTS I am very grateful to John M. Bird, William H. Poole, and Richard L. Armstrong for read- ing and criticizing various drafts of this address, and also to those colleagues, students, and other friends who criticized for me the oral presentations in New Haven and Milwaukee in November 1970.1 also wish to thank all those who provided illustrative material. Rosanne Rowen drew the figures and with A. H. Cole- man prepared slides for the oral presentations, and the friends named below supplied an em- barrassment of photographic riches: John M. Bird, C. F. Burk, James L. Calver, L. M. Gum- ming, Donald W. Fisher, Robert M. Finks, Robert A. Laurence, John L. Rosenfeld, Samuel Figure 13. Graphs illustrating three possible inter- pretations of the course of orogeny through time: A, Root, Arthur A. Socolow, Robert K. Stevens. sharp spasms separated by periods of calm; B, smoothly continuous deformation; C, random-walk processes (C is actually the course of the New York Times index of the REFERENCES CITED weekly close of 50 combined stocks on the New York Stock Exchange from November 1966 to February Agron, S. L. Structure and petrology of the Peach 1970). Bottom slate, Pennsylvania and Maryland, and its environment: Geol. Soc. Amer., Bull., Vol. instead shall follow Poole (1967, p. 20) by us- 61, p. 1265-1306, 1950. ing the term "to describe the orogenic events Albee, A. L. Bedrock geology of the Hyde Park which affected the Appalachian Geosyncline quadrangle, Vermont: U.S. Geol. Surv., Geol. and bordering St. Lawrence Platform during Quad. Map, GQ 102, 1957. Ordovician time" (note that Poole too was Metamorphic zones in northern Vermont: in forced to use the word "events"), and suggest Studies of Appalachian geology, northern and that what I have been referring to in this ad- maritime (E-an Zen; W. S. White; J. B. Hadley; and J. B. Thompson, Jr., eds.), p. 329-341, dress as "phases" be relabeled as "climaxes" 1968. and be used, essentially locally, to describe a Armstrong, R. L. K-Ar dating of plutonic and vol- particular stage in the orogenic activity that canic rocks in orgenic belts: in Potassium argon affected a given area. Above all, let us be wary dating (O. A. Schaeffer; and J. Zahringer, eds.), of extending the climax names beyond the areas Springer, p. 117-133, Berlin, 1966. where continuity if not contemporaneity can be Ayrton, W. G. Chandler-Port Daniel area, Bona- established, and of extending the term Taconic venture and Gaspe-South Counties: Quebec orogeny13 beyond the region where Ordovi- Dep. Nat. Resour., Geol. Rep. 120, 91 p., 1967. Bailey, E. B.; and Mackin, J. H. Recumbent folding 13 Or even "Appalachian orogenic cycle," a term that in the Pennsylvania Piedmont — preliminary for me embraces the whole orogenic and hence geo- statement: Arner. J. Sci., 5th Ser., Vol. 33, p. synclinal history of the Appalachian chain during the 187-190, 1937. period when it acted independently from its surround- Boland, Jacques. Contributions from systematic stu- ings, from the Avalonian to the Alleghany orogeny dies of minor structures in the southern Quebec and the Palisades disturbance (Rodgers, 1967). Simi- larly, I am opposed to importing the terms Caledonian Appalachians: Roy. Soc. Can., Spec. Publ. 10, p. and Hercynian (orogenic cycles) from Europe, they 48-56, 1967. can be adequately described (if not defined) in Berry, W. B. N. On the Magog, Quebec, grapto- western Europe where they were first created, but lites: Amer. J. Sci., Vol. 260, p. 142-148, they are only Procrustean beds when applied in 1962a. North America or Central Asia. Stratigraphy, zonation, and age of Schaghticoke,

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