30963 1st pages / 1 of 22

Quasi-fl exural folding of pseudo-bedding

George H. Davis† Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

ABSTRACT These factors, plus the apparent ease with uncommon fold geometries and structural rela- which the limestone pseudo-beds deform by tionships in a limestone formation in the Pindos The disharmonic outcrop-scale folds and tectonically induced mass-transfer dissolu- fold-and-thrust belt in the Peloponnese, Greece. associated structures in a 300-m-thick Creta- tion creep, were responsible for the distinc- Particularly important is the infl uence on fold- ceous limestone formation in the Pindos Group tive structures observed in outcrop. These in- ing exerted by “pseudo-bedding” (Fig. 1), exposed on Mount Lykaion (Arcadia, Greece) clude indentation structures, where a part of which is created by pressure dissolution during can be understood only in the context of super- one fold limb indents into the other, or where diagenetic gravitational loading accompanying posed pre-tectonic and tectonic mass-transfer the hanging wall of a small thrust indents burial and primary compaction. This work calls dissolution creep. Though the structures de- into its footwall, or where the limbs of a com- particular attention to the kinematic limitations scribed may seem unusual, they are undoubt- mon anticline or syncline migrate toward one of pseudo-bedding stylolite surfaces in accom- edly abundant in strongly deformed pseudo- another by pressure dissolution removal of modating requisite fl exural slip on the limb of bedded limestone formations. In this example the axial-trace region. In terms of the overall a major anticline, and how fl exural-slip budget the Thick White Limestone Beds (TWLB) progressive deformation, tectonically driven defi cits are managed by tectonic pressure disso- formation displays pervasive “fl aggy” pseudo- layer-parallel shortening of pseudo-beds lution and certain uncommon mesoscopic-scale bedding, which is a diagenetic stylolitic layer- fi rst resulted in tectonic stylolites perpen- fold/fault mechanisms. Structural products that ing resulting from pressure dissolution. The dicular to pseudo-bedding, with teeth paral- result from this dissolution creep–dominated mass-transfer dissolution creep that produced lel to pseudo-bedding. This was superseded progressive deformation include quasi-fl exural the diagenetic stylolitic surfaces was achieved at the mesoscopic scale by a layer-parallel folding (Donath and Parker, 1964), an over- during gravitational loading accompanying shortening achieved by buckling of pseudo- looked category of folding which is likely com- burial, compaction, and lithifi cation, and was beds, with loci of buckling and incipient monplace in highly deformed pseudo-bedded driven by high stress concentrations at grain buckling geometries infl uenced primarily limestone formations in mountain belts of the contacts. The diagenetic stylolitic surfaces are by pseudo-bed thickness (and variations in world, such as within fold-and-thrust belts of the lined with insoluble residue and commonly same), wedge-outs of pseudo-beds, and the Appalachians, Arbuckles, Alps, Apennines, and are marked by interlocking stylolite teeth ori- mechanical properties of the pseudo-beds. the western Cordillera of North America. ented perpendicular to the pseudo-bedding. In some cases shortening and tightening of At the outcrop scale, individual pseudo-beds buckle folds involved fl exural-slip kinemat- MASS-TRANSFER DISSOLUTION display signifi cant thickness variability. More- ics, accommodated in part by slip or shear CREEP: AN OVERVIEW over, the individual pseudo-beds not uncom- along clayey insoluble residue at pseudo-bed monly wedge out and disappear laterally over contacts. Where diagenetic stylolite surfaces Stylolites very short distances. abruptly tipped out, or where friction along Along with all the Pindos Group strata, the them was excessively high, the slip defi cit Stylolites are surfaces of localized dissolution, TWLB formation was profoundly shortened (and thus shortening defi cit) was replaced by commonly displaying in cross-section a rough in the Late Cretaceous and early Tertiary as mass interpenetration of pseudo-beds, stylo- suture geometry lined with insoluble residue a result of inversion tectonics. The Pindos faulting, stylo-duplexing, and other forms of of clay, oxides, and/or organic matter (Fig. 2) Group limestone-dominated formations mass-transfer dissolution creep. Slip toward (Stockdale, 1922; Heald, 1955; Bayly, 1986; underlying and overlying TWLB readily ac- the tip lines of wedge-outs even may have Groshong, 1988; Aharonov and Katsman, 2009, commodated fl exural-slip folding, for these produced end loading that, in turn, generated p. 607). They occur at mesoscopic and micro- formations are marked by optimum mechan- adjacent localized buckle folds. The proper- scopic scales. Lengths of stylolite surfaces typi- ical stratigraphy, ubiquitous thin bedding, ties of the folds and associated structures in cally range from centimeters to many meters, and pervasive bedding-plane slip surfaces. the TWLB formation are introduced here as though trace lengths of individual stylolite sur- For the TWLB formation, however, strain a new category of quasi-fl exural folds in the faces of 1 km and more have been observed and accommodation by fl exural-slip kinematics Donath and Parker (1964) classifi cation. measured by Ben-Itzhak et al. (2012). Lengths was spotty and ineffi cient, primarily because of stylolite surfaces generally increase according individual diagenetic stylolite surfaces are by INTRODUCTION to the amount of contractional strain accommo- no means planar or smoothly curviplanar; dated by the stylolite (Benedicto and Schultz, they tip out over short distances; and their The purpose of this paper is to describe and 2010; Ben-Itzhak et al., 2012). interlocking stylolite teeth create elevated interpret the infl uence of mass-transfer dis- Stylolites that are sutured resemble brain frictional resistance to layer-parallel slip. solution creep, i.e., both pre-tectonic and tec- sutures and are distinguished by serrated sur- tonic, as a dominant deformation mechanism faces marked by abundant teeth (Geiser, 1974; †E-mail: [email protected]. that contributed to generating some apparently Geiser and Sansone, 1981; Ben-Itzhak et al.,

GSA Bulletin; Month/Month 2014; v. 1xx; no. X/X; p. 1–22; doi:10.1130/B30963.1; 30 fi gures.

For permission to copy, contact [email protected] 1 © 2014 Geological Society of America 30963 1st pages / 2 of 22 Davis

Diagenetic Stylolites

Diagenetic stylolites tend to be parallel or subparallel to bedding. They form in the late stages of diagenesis (Groshong, 1988; Smith, 2000; Larbi, 2003) within rock, not unconsoli- dated sediments (Merino et al., 1983; Merino, 1992). Sutured diagenetic stylolites display teeth oriented perpendicular to layering (see Fig. 1), consistent with the horizontality of original bed- ding and the verticality of gravitational loading at the time of their genesis (Larbi, 2003). During sediment burial, compaction, and diagenesis, the ever-increasing gravitational loading raises the magnitudes of compres- sive tractions at grain contacts, which bear the load. Under these conditions of contractional strain calcite grains may rotate, break, and/or twin, and additionally they may dissolve and go into solution as a response to pressure dis- solution (Groshong, 1988; Aharonov and Kats- man, 2009). Merino et al. (1983) and Aharonov Figure 1. Pseudo-bedding in building blocks, Temple of Apollo Epicurius in Bassai, Greece. and Katsman (2009) have elaborated on the Note thickness variations of individual pseudo-beds. Middle block is ~80 cm long. Diagenetic kinematics and mechanics of such dissolu- stylolites are lined with insoluble clayey residue (black), now etched by weathering. Light tion in calcite limestones. This deformational gray steeply dipping fabric elements are calcite veins, products of pressure dissolution. mechanism is a mass-transfer creep involving material dissolution, diffusion, and reprecipita- tion (Guzzetta, 1984; Bayly, 1986; Karcz and 2012). Stylo lite teeth are commonly quite Scholz, 2003). Grains are brought into grain- evident in outcrop and thin section because to-grain contact, thus producing elevated stress they are lined with dark insoluble residue (see concentrations (Railsback, 1993; Aharonov and Fig. 2). Amplitudes of teeth vary in size, but Katsman, 2009). Dissolution creep takes place generally range from 1 µm to 1 cm (Sheppard, at the locations of high stress concentration, 2002; Aharo nov and Katsman, 2009), though high surface energy, and high chemical potential Merino et al. (1983) have reported stylolite teeth (Koehn, 2011). Calcium carbonate is removed amplitudes in the range of tens of centimeters. by diffusion to sites of lower stress concentra- Groshong (1975, p. 1367) defi ned “stylolite” in tion and chemical potential. Dissolution at grain a way that eliminated any requirement for the contacts eases strain energy (Aharonov and presence of suture geometry. He considered a Katsman, 2009). Insoluble residue accumulates stylolite to be “any zone of relatively insoluble at faceted contacts. Where such pressure dis- residue against which the original fabric ele- solution operates, there is a slow interpenetra- ments of the rock are truncated by removal tion of grains and rock elements (Merino et al., rather than offset.” This broader defi nition of 1983; Aharonov and Katsman, 2009), and thus stylolite is well suited to the observations con- the limestone accommodates “compaction” as a tained in this research, for both sutured and non- result of gravitational loading. sutured stylolites are abundant in the study area. The orientations of the teeth that mark the The literature distinguishes two main catego- surface morphology of diagenetic stylolite sur- ries of stylolites: diagenetic and tectonic. Both faces are aligned parallel to the local direction of of these are expressions of contractional strain compaction (i.e., vertical gravitational loading). and attendant volume loss. Diagenetic stylolites Insoluble residue (clayey and carbonaceous are primary structures produced by gravitational material) accumulates at the contacts between loading during burial and lithifi cation (Wong and opposing teeth, with stripes of the insoluble res- Figure 2. Face of a newly cut limestone Oldershaw, 1981; Alvarez et al., 1985; Simpson, idue coating both sides. Not unexpectedly, the block at the Temple of Apollo Epicurius in 1985; Groshong, 1988; Bathurst, 1995; Smith, stylolites that develop during the earliest stages Bassai, Greece. Stylolite surfaces (black) are 2000; Sheppard, 2002; Brown, 2007). Tectonic of dissolution are tiny (millimeter scale), but lined with insoluble residue. Stylolite teeth stylolites are secondary structures produced progressively the teeth may achieve centimeter- are roughly perpendicular to pseudo-bed- during tectonic loading (Jaroszweski, 1969; scale amplitudes. Final average amplitude of ding. Pressure-dissolution loss of material is Nickelsen, 1972, 1986; Groshong, 1975; Alva- stylolite teeth can be used as a guide only to expressed by sharp truncations and offsets rez et al., 1976; Helmstaedt and Greegs, 1980; the minimum magnitude of material loss (Ben- of calcite veins. Green, 1984; Dean et al., 1988). Itzhak et al., 2012).

2 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 3 of 22 Quasi-fl exural folding of pseudo-bedding

Diagenetic Stylolites and Pseudo-Bedding

Simpson (1985) and Alvarez et al. (1985) demonstrated that pressure dissolution pro- duced by gravitational loading during burial and diagenesis commonly generates parallel, evenly spaced stylolite surfaces that resemble fl aggy bedding. They warned that such layering in limestone is not an expression of true bedding, and that the surfaces between layers are not true depositional surfaces, i.e., bedding planes. In fact, Alvarez et al. (1985) emphasized that the concept of bedding thickness is meaningless in such rocks! Simpson (1985) and Alvarez et al. (1985) used the expression “pseudo-bedding” in reference to such apparent bedding in limestone where tops and bottoms of a given “bed” are actually diagenetic stylolite surfaces. Pseudo- bedding is made especially prominent because weathering attacks the laminae of insoluble resi- due along the stylolite surfaces (Simpson, 1985). An individual pseudo-bed may be thought of as a primary stylolite-bounded limestone unit that Figure 3. Weathered face of a worked limestone block in the Sanctuary of Zeus, Mount survived complete pressure-dissolution elimina- Lykaion, Greece, showing bedding (fi ne-scale subhorizontal laminae) and primary dia- tion during burial and diagenesis. genetic stylolite surfaces (dark, spaced subhorizontal surfaces, with stylolite teeth). Diagenetic Primary stylolite surfaces locally cross-cut stylolites enclosing pseudo-beds 1 and 2 are locally discordant to bedding lamination in bedding laminations at slight angles, in ways ways that resemble mini–angular unconformities. that resemble miniature angular unconformi- ties (Fig. 3). Based on their work on diagenetic stylolites in pelagic carbonates in the Apennines wedging out altogether over distances of meters and Schultz, 2010; Ben-Itzhak et al., 2012). Yet, of northern Italy, Alvarez et al. (1985) concluded or tens of meters (Fig. 4B). where pressure dissolution has brought about that the average discordance between true bed- Guzzetta (1984) presented models showing major volume loss of host rock, sutured stylo- ding and pseudo-bedding was 5° to 10°. Pseudo- the incremental evolution of stylolites. The mod- lites may gradually “morph” to spaced cleavage bedding acquires its orientation and geometry in els can equally be used to illustrate the evolution (Alvarez et al., 1976; Geiser, 1974; Geiser and a way that is controlled by the direction of max- of pseudo-bedding. The model begins with a Sansone, 1981; Dean et al., 1988). imum gravitational loading during burial and sequence representing true bedding lamination, For host rocks of suitable composition and compaction. True bedding does not guide the as well as the location (heavy black line) where mineralogy, tectonic stylolites will form con- spacing of diagenetic stylolites. Instead, accord- a primary, diagenetic stylolite surface will form tinuously during progressive deformation, ing to Merino et al. (1983) and Simpson (1985), (Fig. 5). As pressure dissolution proceeds, some and thus the orientations of tectonic stylolites, the spacing of diagenetic stylolites (and thus the limestone laminae are completely removed. In including the orientations of teeth, will present thickness of the “fl aggy” pseudo-beds) is due to the fi nal state, stylolite surfaces separate lami- geometric and kinematic complexity in out- a self-organizing feedback that relates, at least nae that originally were never in direct contact, crop. Tectonic stylolites (i.e., the surfaces them- in part, to distributions of porosity. Spacing is but instead were separated by laminae now lost selves) are almost always transverse to bedding a function of travel distance of pore fl uid from to dissolution (Fig. 5). (Andrews and Railsback, 1997). The specifi c sites of pressure dissolution to sites of precipita- orientations of tectonic stylolites produced tion (Merino, 1992). Tectonic Stylolites in direct relation to folding will have orienta- An extraordinary display of pseudo-bedding tions that record partitioning of stress and strain produced by diagenetic pressure dissolution is The dissolution-creep mechanics that produce during progressive folding, which in turn is “Pancake Rocks,” located on the west shore of diagenetic stylolites also apply to the formation driven by the activity (or lack thereof) of differ- the South Island of New Zealand at Punakaiki of tectonic stylolites. The difference is the load- ent mechanisms, such as inner-arc shortening, (Fig. 4), which I visited in 2010. The stylolite ing mechanism, i.e., tectonic, not gravitational. tangential longitudinal strain, bulk fl attening, surfaces separating pseudo-beds are anastomos- Tectonic stylolites, including teeth, form in ori- and overall fl exural slip and/or fl exural fl ow ing and discontinuous, and are not uncommonly entations that are rational with respect to the (Ormand and Hudleston, 2003). Orientations of marked by stylolite teeth and lined with insolu- direction of tectonic loading (Nickelsen, 1972; teeth of tectonic stylolites not uncommonly are ble residue (see also Alvarez et al., 1985). Indi- Geiser, 1974; Groshong, 1975; Fletcher and oblique to the orientation of the stylolite surface vidual pseudo-beds appear from a distance to Pollard, 1981). Especially in the early stages with which they are associated, for the stylolite be of uniform thickness and marked by roughly of development of an individual tectonic stylo- teeth, at the time of their development, reli- planar “bedding” surfaces (Fig. 4A). However, lite, the amount of contractional strain accom- ably were oriented parallel to the direction of σ on closer inspection the individual pseudo-beds modated increases according to the length and greatest principal stress ( 1), regardless of the are seen to be variable in thickness, commonly amplitudes of stylolite topography (Benedicto orientation of the stylolite surface itself (Koehn

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A

B

Figure 4. (A) Pseudo-bedding in limestone (Miocene) exposed at Dolomite Point just south of the village of Punakaiki on the west coast of the South Island of New Zealand. Height of the limestone exposure is ~10 m. Known as the “Pancake Rocks,” the limestone layering is pseudo-bedding, and the upper and lower boundary surfaces of pseudo-beds are primary (diagenetic) stylolites. Individ- ual pseudo-beds display signifi cant thickness variability. (B) Macro-photograph showing tipping-out of diagenetic stylolites and wedg- ing-out of pseudo-beds.

et al., 2007). Moreover, the orientations of Tectonic stylolites that perhaps are easiest to folding and pseudo-bed rotation. Spacing of stylo lites will likely change as a result of rigid- interpret are the ones formed in horizontal bed- LPS stylolites in pseudo-beds appears to bear a body rotation experienced during progressive ding (or in pseudo-bedding) in the very earliest systematic relationship to pseudo-bed thickness, deformation (Andrews and Railsback, 1997). stages of horizontal contractional tectonic load- with spacing and thickness directly proportional As a result, the original “rational” relationship ing (Nickelsen, 1986; Dean et al., 1988). They are (see Fig. 6). This general proportionality is analo- between the orientation of early-formed tec- oriented perpendicular to layering, and they dis- gous to the systematics of joint spacing in stiff tonic stylolites and the loading direction that play teeth oriented parallel or subparallel to layer- layers (Hobbs, 1967; Narr and Suppe, 1991; produced them will be altered. ing, thus accommodating layer-parallel shorten- Gross, 1993; Pollard and Segall, 1987), though Koehn et al. (2007) and Ebner et al. (2010) ing (LPS). Figure 6 presents an example of such in this case the structures are “anti-cracks,” as have emphasized that the abundance and dis- “LPS stylolites” in an outcrop from the Mount explained below (Durney, 1974; Fletcher and tribution of insoluble clay particles, quartz Lykaion study area. The layering is pseudo- Pollard, 1981). grains, and lithic fragments in limestone have bedding, which for purposes of this illustration an important control on the roughness of stylo- is rotated vertically in the image, even though in Diagenetic and Tectonic Stylolites lite surfaces, irrespective of whether they are of outcrop it was moderately steeply dipping. As is as Anti-Cracks diagenetic or tectonic origin. These insoluble apparent, individual stylolite surfaces are perpen- elements are like tiny “pinning points” of armor dicular to the pseudo-bedding and tip out at the Fletcher and Pollard (1981) studied the prop- that infl uence the advance and retreat of the dis- upper and lower stylolite surfaces demarcating agation of the stylolite surfaces themselves, as solution fronts, which ultimately are expressed individual pseudo-beds. Thus, sets of LPS stylo- contrasted with the growth and development in the sutured stylolite surfaces. Koehn et al. lites are wholly contained within single individ- of stylolite teeth. They focused on mechani- (2007) have shown that the distribution of pin- ual pseudo-beds. The stylolite teeth are oriented cal loading and the migration of the tip line of ning points, in combination with loading direc- essentially parallel to the trace of pseudo-bedding tectonic stylolite surfaces. Fletcher and Pollard tion, controls interpenetration and thus the fi nite (see Fig. 6). Undoubtedly these LPS stylolites (1981) emphasized that as dissolution progres- sutured stylolite geometry. developed in horizontal pseudo-bedding before sively removes rock along a given stylolite

4 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 5 of 22 Quasi-fl exural folding of pseudo-bedding

Figure 5. Progressive development of diagenetic stylolites and pseudo-bedding. At the very top we see a sequence of limestone layers a–h (total thickness less than 1 meter).Vertical loading occurs during continued sedimentation and burial. The vertical loading causes pressure dissolution, which initiates (top diagram) at the interface (black) of layers d and e. This interface evolves into a stylolite surface. Dissolution takes place during time frames I, II, and III (right margin of fi gure). Numbers 1–9 denote the boundaries (edges) of dissolution domains. Bold verti- cal arrows within each domain denote whether layers above or below the stylolite surface undergo pressure dis- solution. Final product (base of fi gure) reveals that dissolution related to vertical loading causes stylolite teeth to form at expense of parts or all of individual layers. Note missing layers at stylolite surface. Figure modifi ed from Guzzetta (1984, his fi g. 2, p. 386).

surface, strain energy builds up in rock beyond stylolites “anti-cracks,” the antithesis of mode 1 Because pseudo-beds are bounded, top and the tip line. The strain energy is relieved by fur- (opening) cracks. Just like true mode 1 cracks bottom, by pressure-dissolution surfaces, and ther tip-line propagation through the loci of high and mode 2 and 3 faults, stylolite surfaces tip because stylolites are anti-cracks that tip out strain energy. Progressive lengthening of a stylo- out in all directions, with shapes that in all likeli- over relatively short distances (centimeter and lite surface thus results in a progressive loading hood are irregularly elliptical. meter scale), individual pseudo-beds themselves of its tips by compression. Durney (1974) and This work by Fletcher and Pollard (1981) wedge out over relatively short distances. This is Fletcher and Pollard (1981) considered such bears on the character of pseudo-bedding. in sharp contrast to the robust lateral continuity

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est Cretaceous the Pindos Basin was tectonically tion of bedding of the upper plate rocks (based inverted by profound shortening accommodated on stereographic projection of 183 poles to bed- by thrust faulting and folding (Skourlis and ding) is N31°E, 21°SE (Fig. 11A), which is sub- Doutsos, 2003). During basin inversion a fi fth parallel to the three-point-determined attitudes (synkinematic) stratigraphic unit was depos- of the Lykaion thrust itself (N33°E, 10°SE) ited: the Flysch Transition Beds (see Fig. 8). and the planar contact between Chert Series Strata within the Flysch Transition Beds were Beds and overlying First Flysch Beds (N35°E, deformed synkinematically by thrust faulting 08°SE) (Davis, 2009). and folding as inversion tectonics progressed. Beneath the klippe there are two distinct lower-plate domains (see Fig. 10): a western Lykaion Thrust Fault and Geologic Map domain that is overall homoclinal in nature, Relationships and an eastern domain marked by a system of large anticlines and synclines (Davis, 2009). The geology of the study area is quite con- The western domain, composed dominantly sistent with the regional tectonic character of of Flysch Transition Beds, Thick White Lime- the Pindos fold-and-thrust belt. My geological stone Beds, and Thin Platy Limestone Beds, is a mapping confi rmed the presence of a major homocline striking ~N37°E and dipping ~05°SE thrust fault, which I call the Lykaion thrust fault (based upon three-point methodology). Strati- (Fig. 9). The Lykaion thrust fault developed graphic formations in the homoclines (klippe, during the latest Cretaceous and early Tertiary. and western domain of the lower plate) display As documented originally through the geologic abundant outcrop-scale folds (Fig. 12). The char- mapping (1:50,000 scale) by Lalechos (1973) acter of folding differs from formation to forma- and Papadopoulos (1997), this thrust fault is tion because of differences in the mechanical one of dozens within the central Arcadian part stratigraphy of each formation, and thus overall Figure 6. Layer-parallel shortening (LPS) of the Pindos fold-and-thrust belt (Degnan and the folding is intraformational and disharmonic. tectonic stylolites (ts) in pseudo-beds. Tec- Robertson, 1998, 2006; Pe-Piper and Piper, However, from a geometric standpoint the fold- tonic stylolites are dark because they are 1984; Skourlis and Doutsos, 2003). The upper ing is quite systematic, as revealed in stereo- lined with insoluble residue. Teeth of the plate of the Lykaion thrust fault is a tectonic graphic projections of poles to bedding (Fig. tectonic stylolites are oriented parallel to the klippe (see Fig. 9). 11B) (Davis, 2009). Fold axes plunge ~10° due trace of pseudo-bedding. Crack-seal calcite The overall geology of the study area is south, with axial surfaces striking north-south veins (v) are evident in the very lower part shown in Figure 10, which is my geologic map and dipping steeply. The folds tend to be asym- of the middle pseudo-bed and oriented par- of the structural-geologic relationships. The metric with vergence toward the west, consistent allel to the trace of pseudo-bedding. elliptical trace of the Lykaion thrust fault at the with tectonic transport accommodated by the base of the klippe is disrupted in several places Lykaion thrust fault. Long limbs of these folds by active normal faults. The thrust klippe con- in the western domain of the lower plate strike of most true beds and bedding planes. Branch- tains an essentially homoclinal succession of N20°E and dip 35°SE, whereas the short limbs ing and tipping patterns of stylolite surfaces are the Chert Series Beds, First Flysch Beds, Thin strike N10°W and dip 04°SW (see Fig. 11B). common, as described by Railsback (1993). Platy Limestone Beds, and Thick White Lime- The outcrop-scale folds in Thin Platy Lime- stone Beds (see Fig. 8). This is what remains stone Beds and Flysch Transition Beds are fl ex- GEOLOGY OF THE STUDY AREA of an allocthonous sheet whose total transport ural-slip folds (Donath and Parker, 1964), and distance (from east to west) is probably on the the bedding that is folded is true bedding. The Location and Stratigraphy order of tens of kilometers. The average orienta- folds in these formations typically are marked

The study area (~25 km2 in area) is centered on the Sanctuary of Zeus, Mount Lykaion, in Arcadia, located ~15 km west-northwest of Megalopolis in the Peloponnese, Greece (Romano and Voyatzis, 2010) (Fig. 7). The Pindos Group stratigraphy in the region was framed by the work of Lalechos (1973) and Papadopoulos (1997), and for purposes of map- ping and structural analysis I identifi ed forma- Figure 7. Location of the Mount tions (Davis, 2009) in ways consistent with Lykaion study area, Greece. their work (Fig. 8). The four oldest stratigraphic units (Chert Series Beds, First Flysch Beds, Thin Platy Limestone Beds, and Thick White Limestone Beds) range in age from Jurassic to Paleocene and were formed in the Pindos Basin (Degnan and Robertson, 1998, 2006; Lalechos, 1973; Papadopoulos, 1997; Piper, 2006). In lat-

6 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 7 of 22 Quasi-fl exural folding of pseudo-bedding

Major Folds within which it is best exposed. The location of the Three Gorges anticline along Tria Remmata The eastern domain of lower-plate deforma- is shown by the white rectangle (labeled TGA) tion contains a system of six major folds that in Figure 10. The profi le of Three Gorges anti- trend north-south and dip at very low angles. cline is very well exposed over a vertical height Moreover, outcrop-scale folds are abundant in of ~800 m on the north face of Three Gorges Thin Platy Limestone Beds, Thick White Lime- ravine (Fig. 14; location is lat. 37.439°N, long. stone Beds, and Flysch Transition Beds on the 22.011°E). The deeper parts of this anticline limbs of these major folds. express the geometry of a perfectly upright Figure 13 presents several geologic cross fold, whereas the uppermost exposed reaches sections capturing the geometry and form of of the fold are strongly overturned to the west. folding of strata within the eastern domain, in Thus Three Gorges anticline is disharmonic. relationship to the tectonic klippe and to a sec- To the east and immediately adjacent to the ond exposure of the Lykaion thrust fault in the Three Gorges anticline is a near-isoclinal syn- easternmost part of the study area. These cross cline (see Fig. 13). Out-of-the-syncline west- sections are the result of iterative structural- ward “fl ow” produced the disharmony in the geological modeling through application of Three Gorges anticline. Figure 8. Stratigraphic column for the Mount MOVE technologies (Midland Valley Explora- Lykaion study area, Greece. tion, Ltd.) (Davis et al., 2009; Similox-Tohon BRIEF HISTORICAL NOTE ON THE et al., 2009). The structure section represents THREE GORGES ANTICLINE a best fi t to all geological contacts, bed-orien- by concentric (parallel) profi le geometries and tation data, thicknesses of stratigraphic units, The Three Gorges anticline is special from absences of hinge-zone thickening and limb panoramic photographs of outcrop expressions both an historical and Greek-mythological per- attenuation. Uncommonly there is incipient of the folds, and the mapped axial traces of spective. In the hinge of this fold, at the strati- development of axial-planar spaced cleavage in folds. Analysis of isogons resulted in establish- graphic level of the Thick White Limestone Beds tight folds in Flysch Transition Beds. Consistent ing likely variations in formation thicknesses formation, there is a saddle-reef opening that with the properties of concentric folds produced across the fold system. today is expressed as a rock shelter. In the mouth via fl exural slip, upright anticlines are seen to Six major fold structures populate the east- of the shelter, and fi lling most of the saddle reef systematically tighten downward, terminating ern domain. Stereographic projection of 95 space, is a three-story stockade built during the as near-isoclines at bedding-plane décollement. poles to bedding orientations in the eastern Greek War of Independence in the early 19th Both in the klippe and western domain of the domain demonstrates that the system of fold- century (Fig. 15). The stockade is locally known lower plate, outcrop-scale folds are abundant in ing is cylindrical, with fold hinges trending as “the Cave of Kolokotronis,” named after the Thick White Limestone Beds as well (see Fig. N08°W and essentially non-plunging (Fig. formidable leader of the Greek forces. The walls 12). As will be emphasized, the fold mechanism 11C) (Davis, 2009). The fold that is central and thus the shape of the stockade conform per- that produced these folds was not a straightfor- to this research is the Three Gorges anticline, fectly to the bedrock form of the hinge of the ward fl exural slip. named after the deep ravine (Tria Remmata) anticline (see Fig. 15). The walls are composed

Figure 9. South-directed photograph of the Sanctuary of Zeus, Mount Lykaion, Greece. Mountain skyline is Agios Elias (St. Elijah), the second-highest summit of Mount Lykaion. The dominant geologic structure is the Lykaion thrust fault, which dips easterly at 10°. Fore- ground of this photograph, beneath the thrust, is the “Lower Sanctuary”. Archaeological elements include the hippodrome (“a”) and stoa (“b”). Springs fl ow from the thrust trace proper, including the Agnos Fountain (“c”). Agios Elias is a tectonic klippe resting on the Lykaion thrust. At the summit of this klippe is the “Upper Sanctuary,” including an ash altar (“d”) dating back to the Bronze Age. Repetition of stra- tigraphy by thrusting is evident: outcrops of Thick White Limestone Beds (Cretaceous) can be seen both in lower-plate (right foreground, “e”) and upper-plate (upper left near skyline, “f”) positions.

Geological Society of America Bulletin, Month/Month 2012 7 30963 1st pages / 8 of 22 Davis

Figure 10. Geologic map of the study area, based on the work of the author. of unhewn limestone blocks, placed in such a 2002). Both the Dikteon Cave in south-central that here Cronus was deceived, and here took way as to butt tightly against the folded Thick Crete and the Ideon Cave on Mount Ida in Crete place the substitution of a stone for the child White Limestone Beds. The hinge area of the are considered possibilities for the Zeus birth- that is spoken of in the Greek legend” (Book fold conforms to the bulbous hinge-zone form cave references. The mythical Arcadian locale XXXVI). that Ramsay (1974) emphasized as a common for the Zeus birth cave is “Cretea” Ridge on the product of chevron folding (see also Price and fl ank of Mount Lykaion in Arcadia. Pausanias EXAMINATION OF OUTCROP-SCALE Cosgrove, 1990, p. 320). in 2nd century A.D. referenced this Arcadian “HYBRID” GEOLOGIC STRUCTURES Added to this rich history is an even more “Cretea” locale: “There is a place on Mount provocative dimension, namely that the rock Lycaetis called Cretea… The Arcadians claim Introduction shelter associated with the Cave of Kolokotro- that the Crete, where the Cretan story has it nis is a prime candidate for the mythical birth that Zeus was reared, was this place and not Of the fi ve stratigraphic formations that cave of Zeus. Indeed, classicists and archae- the island” (Pausanias, Book XXXVIII). “They occupy the Mount Lykaion area, the Thick ologists have emphasized that the birth cave allow that [Rhea] gave birth to her zone [Zeus] White Limestone Beds formation contains of Zeus is either in Crete or Arcadia (Olalla, on some part of Mount Lycaetis, but they claim the structures that are the basis for the discus-

8 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 9 of 22 Quasi-fl exural folding of pseudo-bedding

ABC

Figure 11. Stereographic projections of (A) poles to bedding in upper plate of Lykaion thrust, (B) poles to bedding in the western domain of lower plate of Lykaion thrust, and (C) poles to bedding in the eastern domain of lower plate of Lykaion thrust. See text for explanation. sion and conclusions of this paper. The Thick White Limestone Beds formation ranges up to ~300 m thick in the study area (Lalechos, 1973; Papadopoulos, 1997; Davis, 2009). The formation uniformly is composed of bright white limestone beds that tend to range from 1 to 4 m in thickness. The physical expression of Thick White Limestone Beds is conspicuous and easily recognized in the landscape, partic- ularly given its white hue, thick bedding, and sharp resistant protruding outcrops. The Three Gorges ravine, the head of which emerges at the village of Ano Karyes, offers especially well exposed structures and fabrics, in turn disclosing a variety of interconnected struc- tures and structural geometries. Except where noted in text or captions, the photographs that follow were taken of outcrop relations within the white-boxed area shown in Figure 10 and labeled TGA. Splendid outcrops can be found along the ravine itself and throughout the steep south-dipping wall of the ravine. The key ravine location is centered on lat. 37.438°N, Figure 12. Outcrop showing characteristic folding of the Thick White Limestone Beds for- long. 22.010°E. mation. Geologist is Tom Fenn. Location is lat. 37.451°N, long. 21.998°E.

W

E

TGA

Figure 13. East-west geologic cross sections of the Mount Lykaion study area, Greece. TGA—location of Three Gorges anti- cline. Formations are color coded: red—Chert Series Beds; orange—First Flysch Beds; blue—Thin Platy Limestone Beds; green—Thick White Limestone Beds; yellow—First Flysch Beds. Prepared by Midland Valley Exploration, Ltd.

Geological Society of America Bulletin, Month/Month 2012 9 30963 1st pages / 10 of 22 Davis

Figure 14. North-directed photograph of part of the Three Gorges anticline. Ridge in the immediate foreground obstructs the view of the deeper reaches of the Three Gorges anticline. Bedrock is the Thick White Limestone Beds formation. Exposure spans ~800 m of topographic relief. Sense for scale can be achieved by noting the three-story stockade immediately beneath location “a”. Deeper part of the fold is a perfectly upright anticline. Upper part of the fold (e.g., see “b”) is strongly overturned westward. South-dipping limb (left) of the anticline reveals a separate distinct panel of drag folding (“c”) and duplex structure (“d” and “e”). Location “f” marks a point along the trace of a goat path, which was helpful in gaining access. Location is centered on lat. 37.439°N, long. 22.011°E.

Pseudo-Bedding

What appears to be bedding in Thick White Limestone Beds is actually pseudo-bedding. Stylolite surfaces are quite evident in outcrop, made more noticeable by weathering and ero- sion of the insoluble residue that lines the stylo- lites (see Fig. 12). This same weathering expres- sion is a notable characteristic of the limestone blocks and column drums (fashioned from Thick Figure 15. Photograph of the Cave of Kolo- White Limestone Beds) composing the Temple kotronis, featuring a three-story stockade of Apollo Epicurius in Bassai (see Fig. 1). This built in the early 19th century during the temple is located just 5 km west of the Sanc- Greek War of Independence. tuary of Zeus, Mount Lykaion. The Temple of Apollo Epicurius in Bassai was designed by Iktinos, architect of the Parthenon, and built nearly 2500 years ago, sometime between ca. 450 and ca. 400 BCE. (Olalla, 2002). Current restoration and conservation efforts by the Committee of the Epicurean Apollo (Athens) include replacement of the most highly weath- ered and/or failed blocks and drums. As a result we can examine today the faces of freshly cut

10 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 11 of 22 Quasi-fl exural folding of pseudo-bedding limestone blocks and thus closely observe The worked blocks in the lower archaeologi- expressions described by Alvarez et al. (1985): the properties of diagenetic stylolites within the cal site clearly display profound and nonsys- lenticular and discontinuous. Thick White Limestone Beds formation (see tematic changes in pseudo-bed thicknesses over Pseudo-bedding is abundantly exposed in Fig. 2). The spacing of stylolites in the Thick very short distances (see Fig. 16). The stylolite bedrock exposures of Thick White Limestone White Limestone Beds typically ranges from 5 surfaces are typically deeply weathered, thus Beds in the Mount Lykaion area. But the rough- to 10 cm. As a result, the limestone appears to causing individual pseudo-beds, and changes in weathering appearance of typical outcrops in the possess fl aggy “bedding” (see Fig. 12), but it is thickness of same, to stand out in bold relief (see landscape tends to camoufl age the wedge-outs pseudo-bedding with thicknesses corresponding Fig. 16). Simpson (1985) repeatedly empha- of pseudo-beds (see Fig. 12). More smoothly to stylolite spacing. Degradation of the integrity sized that the similarity of pseudo-bedding to weathered limestone faces, such as the one fea- of the column drums at Bassai partly relates to true bedding derives from the fact that pseudo- tured in Figure 17, tend to reveal the presence the vulnerability of the stylolite surfaces to deep bedding is marked by “parallel, more or less of wedge-out geometries of pseudo-beds. At the weathering (Larbi, 2003). evenly-spaced stylolite surfaces” (Simpson, left base of the folded mass of limestone shown Clear expressions of (1) stylolite surfaces, 1985, p. 495 and p. 504). However, pseudo-bed- in Figure 17 there is a tight upright anticline just (2) curviplanar and sharply undulating geom- ding and the abundant wedge-outs of individual above the vegetation. The pseudo-bed labeled etries of pseudo-beds, and (3) the relatively short pseudo-beds in Thick White Limestone Beds in with the number 2, located above the core of this discontinuous nature of pseudo-beds are seen in the study area comport with the characteristic fold, constitutes a single layer on the left limb, worked blocks of Thick White Limestone Beds within the lower archaeological site of the Sanc- tuary of Zeus, Mount Lykaion. Primary dia- genetic stylolite surfaces, complete with stylo- lite teeth and insoluble residue, are ubiquitous in the relatively fresh faces of worked limestone blocks (Fig. 16). In places these stylolites sur- faces are seen to discordantly truncate true bed- ding and bedding lamination. In some of the worked limestone blocks the presence, height, and jaggedness of stylolite teeth are very appar- ent. The stylolite surfaces display teeth that are oriented essentially perpendicular to pseudo- bedding.

Figure 17. Pseudo-bedding expressed in folded limestone in a large fl oat block located in the southwestern part of the Mount Lykaion study area. The location is lat. 37.439°N, long. Figure 16. Worked block of Thick White 21.989°E. The formation is the Thick White Limestone Beds. Bed 2, as it crosses the small Limestone Beds showing the geometric anticline at bottom left, “splits” into two pseudo-beds, 2 and 3. Beds 5 and 6, on the right character of pseudo-bedding. See text for limb of this same anticline, terminate upward against bed 7. Bed 10, on the left limb of the explanation. anticline, wedges out upward before reaching the hinge.

Geological Society of America Bulletin, Month/Month 2012 11 30963 1st pages / 12 of 22 Davis but on the right limb it forks to two pseudo-beds (2 and 3). Near the base of this limb the two pseudo-beds wedge out completely between pseudo-beds 1 and 4. All of this takes place over a layer length of less than 2 m. Note also that pseudo-beds 4 and 5 wedge out upward to the left against pseudo-bed 7. Another illustration of wedge-outs and varia- tions in thicknesses of pseudo-beds is presented as Figure 18. Pseudo-bedding is nearly vertical in this part of the south limb of the Three Gorges anticline, and within this outcrop there are gentle short-wavelength recumbent anticlines and syn- clines. The pseudo-beds are deformed by LPS tectonic stylolites that are essentially perpen- dicular to pseudo-bedding, produced through layer-parallel shortening when the pseudo-bed- ding was essentially horizontal. Because of their deeply weathered nature, these tectonic stylo- lites are expressed as short discontinuous (sub- horizontal) cracks (see Fig. 18). The weathered texture of this outcrop clearly reveals signifi cant variations in thickness of individual pseudo-beds as well as the presence of wedge-outs. Abrupt thickness variation of individual pseudo-beds is characteristic of the whole outcrop.

Stylo-Thrusts and LPS Stylolites

LPS stylolites, of the type illustrated in Figure 6 and that are featured in a panel of pseudo-bedding in Figure 19, were formed in pseudo-bedding in the early stages of Late Cretaceous–early Ter- tiary tectonic shortening, and at a time when pseudo-bedding was still fl at lying. Undoubtedly there is an upper threshold on the magnitude of layer-parallel shortening and/or stress that can be accommodated by LPS stylolites before other deformation mechanisms take over. In certain outcrops it is evident that as tectonic shortening progressed, some of this additive layer-parallel shortening was accommodated by thrust fault- ing that likely took place while pseudo-bedding, overall, remained essentially horizontal. The structural properties of some of these outcrop-scale thrusts are quite astonishing and demonstrate the interplay of conventional thrust faulting and mass-transfer pressure dis- solution. A good example is shown in Figure Figure 18. North-directed photograph of deeply weathered pseudo-bedding. Black high- 20A, where we see a reverse fault (a thrust fault lighting calls attention to thickness irregularities. Subhorizontal “gashed” are weathered before pseudo-bed steepening) in the imaged layer-parallel shortening stylolites. outcrop of pseudo-beds, which dip uniformly to the west. The fault appears to be a conven- tional fault that cuts across pseudo-bedding (p-b in Fig. 20A) and at a 40° cutoff angle, accom- transpressive structure that has accommodated Limestone Beds, in this case right along the modating layer-parallel shortening. The “fault” thrust-displacement interpenetration of both stylo-thrust (Fig. 20B). Differential pressure dis- surface itself is actually a stylolitized fault sur- the hanging wall and footwall. The stylo-thrust solution is evidenced at the leading edge of the face, which I simply refer to as a “stylo-thrust” interface is marked by “worn” stylolite teeth and discrete hanging-wall block, which penetrates (s-t in Fig. 20A). Instead of expressing itself as an irregular, non-planar geometry that typifi es into the overlying pseudo-bed and causes it to a planar fault surface, the stylo-thrust is a hybrid the action of pressure dissolution in Thick White thin through mass-transfer dissolution creep as

12 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 13 of 22 Quasi-fl exural folding of pseudo-bedding A

B Figure 19. North-directed Adobe Photo- shop–enhanced photograph of pseudo-bed- ding in the Thick White Limestone Beds formation on the west-dipping limb of Three Gorges anticline. Pseudo-beds (white) are separated by diagenetic stylolites marked by seams of insoluble residue (black). layer- C parallel shortening tectonic stylolites are ex- pressed as faint black lines oriented at high angles to pseudo-bedding.

Figure 20. (A) North-directed photograph of a “stylo-thrust” (s-t) with 40° cutoff angle to pseudo-bedding (p-b). Trace of the stylo- thrust tips out upward into the drape fold (df) of a pseudo-bed. Tectonic stylolites (ts) are contained within individual pseudo-beds, oriented perpendicular to pseudo-beds, and commonly tip out at tiny offsets of pseudo- beds. (B) The stylo-thrust is not expressed by a conventional smooth, slickenlined, slickensided Coulomb fracture surface but instead is a dissolution surface. (C) North- directed view of an upward-branching sys- tem of stylo-faults along which pseudo-beds (numbered) are displaced through pressure dissolution. Layer-parallel shortening tec- tonic stylolites are pervasive. Note the dense concentration of tectonic stylolites within the fault-bounded block. Dark masses are calcite products of concentrated pressure dissolution along stylo-thrusts.

Geological Society of America Bulletin, Month/Month 2012 13 30963 1st pages / 14 of 22 Davis it “drapes” over the thrust-block corner beneath. tion eliminated some pseudo-beds in the right The limestone pseudo-bed that forms the drape limb of the anticline. Overall the extensive fold (df in Fig. 20A) must have been especially pressure-dissolution loss of material along the vulnerable to pressure dissolution, given the dissolution fi ssure caused the near-isoclinal variation in thickness of the draped pseudo-bed syncline to migrate leftward relative to the near- and also the irregularity of the stylolite surface isoclinal anticline, resulting in their vertical, between pseudo-beds (see Fig. 20B). It is not disharmonic “stacking”. Pseudo-bed 4 appears clear whether the thrust fault initiated as a con- to have thinned to nearly nothing in the region ventional (Coulomb) fault surface, later modi- now occupied by the hinge of the anticline (Fig. fi ed by pressure dissolution, or was the product 22B). Note that the wedge-out tips of pseudo- of sustained transpressive pressure dissolution. bed 4 are each folded inward toward the axial In this same exposure there is clear evidence trace. The locus of primary thinning of pseudo- for early layer-parallel shortening, expressed in bed 4 may have triggered the site of buckling. the short, spaced, transverse tectonic stylolites (t-s in Fig. 20A). We see that the tectonic stylo- Indentation through Mass-Transfer lites are associated with millimeter-scale offsets Dissolution Shortening of the stylolite surfaces between pseudo-beds. These stylolites and associated offsets resemble Locally there are expressions of mass-trans- tiny compartmental faults with “strike-slip– fer dissolution creep in the form of interpenetra- like” displacements. Clearly these offsets were tion of pseudo-beds, where shortening achieved created when pseudo-bedding was essentially magnitudes beyond what could be attained horizontal. As layer-parallel dissolution was through conventional mechanisms of folding. achieved along pseudo-bedding–perpendicular Droxler and Schaer (1979, p. 563, their fi g. 12) tectonic stylolites, offsets were produced at all reported identical structures in “thin-bedded” locations where pseudo-bedding was even in the Figure 21. Original stratigraphy is marked limestones in the Jura (France). Moreover, Gro- smallest way oblique to the direction of pressure by wedge-outs (to the right) of pseudo-beds shong (1988) includes indentation in his review dissolution. 2 and 3. The locus of wedge-outs may have of low-temperature deformation mechanisms There are abundant examples of stylo-thrusts controlled the locations where buckling and their interpretation. within Thick White Limestone Beds, each with later took place. Figure 23 reveals stylo-indentation in the style variations refl ecting some combination of very tight hinge zone of a small anticline. The mechanical stratigraphy and degree of mass- indentation, accommodated by mass-transfer transfer dissolution. Figure 20C captures an of pseudo-bed 2 on the left limb abruptly thins dissolution creep, is an expression of the two upward-branching imbricate system of reverse on the short wedged-out right limb. It is likely objects (fold limbs) trying to occupy the same stylo-faults (originally stylo-thrusts). Note the that the locus of fold nucleation may have been space. Where dissolution creep is not available offsets of pseudo-beds 2–6. The triangle zone controlled by the weakness created by the pri- as a deformation mechanism, such “attempts” in the hanging-wall area expresses profound mary wedge-out of pseudo-bed 2. As a result to occupy the same space are managed through mass-transfer dissolution, evidenced by the very of elimination of pseudo-bed 2, pseudo-bed 3 thrust faulting. Where dissolution creep is avail- closely spaced stylolitic surfaces (see Fig. 20C). drapes across the wedge tip of pseudo-bed 2 and able as a kinematic mechanism, contrasts in tec- is “overthrusted” by pseudo-bed 1 (see Fig. 21). tonic stress–induced solubility permits one part Folded Pseudo-Bed “Wedge-Outs” of a given unit to function as an indenter. In the Fold Limb Elimination by Dissolution lower part of the photograph shown in Figure 23 Where pseudo-bedding containing wedge- we see that a part of the right limb of a folded outs is tightly folded, the structural geometric The role of mass-transfer dissolution creep pseudo-bed penetrates a part of the left limb of relationships can be unconventional. Such an is especially evident in certain tight to isoclinal the same pseudo-bed. Stylo-indentation has also example is shown in Figure 21. In the pictured folds. One such example is shown in Figure 22A, modifi ed the pseudo-bed seen near the top of outcrop, pseudo-bedded limestone (light gray) an outcrop photograph of disharmonic folding. this photograph. A part of the right limb has pen- rests on cleaved mudstone (dark). The left part In the right half of the outcrop the hinge zone etrated a part of the left limb. The vertical crack of the pseudo-bedded sequence is quite coher- of a near-isoclinal anticline lies nearly directly represents a deeply weathered seam of insoluble ent, with fi ve successive pseudo-bed units, sepa- above the hinge zone of a near-isoclinal syn- residue. The width of loss of limestone along rating each of which are layer-parallel seams cline. The axial traces of these two folds nearly this weathered seam is refl ected in the breadth of insoluble residue related to primary diage- coalesce (see Fig. 22). This odd circumstance of overlap near the base of this pseudo-bed at netic dissolution creep. In contrast, in the right was brought about by profound mass-transfer the lower hinge point of the anticline. part of the outcrop, within the overturned fold dissolution of the left limb of the syncline and Such stylo-indentation may occur outside of proper, we see that pseudo-bed 2 wedges out dissolution of the right limb of the anticline in hinge zones as well, as can be seen in Figure 24 and completely disappears. In the core of the the lower reaches of the outcrop. The most con- where a stylo-fault (note fault-slip arrow) causes fold stylo-thrusting and minor folding deform spicuous locus of dissolution is along the gaping one of the pseudo-beds to penetrate the pseudo- pseudo-bed 1. Pseudo-bed 2 deforms by fold- near-vertical fi ssure (see Fig. 22A). The fi ssure- bed originally beneath it. The locus of penetra- ing. Notably, the location of the hinge point like opening is mainly a product of weathering tion is a sharp corner defi ned by the intersec- on the lower weld of pseudo-bed 2 occurs pre- of insoluble residue that accumulated along tion of pseudo-bedding and the stylo-fault. This cisely at the point where the uniform thickness the locus of dissolution. Mass-transfer dissolu- corner penetrates the pseudo-bed to its right.

14 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 15 of 22 Quasi-fl exural folding of pseudo-bedding A B

Figure 22. (A) Extreme shortening accom- plished by buckling and mass-transfer dis- solution creep created this near-isoclinal folding as well as the disharmonic juxta- position of syncline over anticline. Axial traces of anticline (“A”) and syncline (“S”) are shown via thin white lines. The near-iso- clinal hinge zones of the anticline and syn- cline were moved into near-alignment due to major pressure dissolution, especially along the zones now represented by near-vertical fi ssures. (B) Close-up Adobe Photoshop–en- hanced photograph of part of the anticline hinge shows that pseudo-bed 5 is restricted to one limb only. Pseudo-bed 4 appears to have thinned to nearly nothing in the area now occupied by the hinge of the anticline. The wedge-out tips of pseudo-bed 4 are each folded inward toward the axial trace.

Figure 24 reveals that indenter loading reduces structural styles are evident in deformed bed- of thrust duplexes where horses of limestone by 50% the thickness of the invaded pseudo-bed ding on a part of the western limb of the Three dip at a much steeper angle than the limb as a in the zone of contact. Gorges anticline (Fig. 25). In the lower cliff whole. These duplexes appear to have formed shown in Figure 25 (see also location B in Fig. in a manner similar to that presented by Tanner Stylo-Duplexes 14), there is a standard expression of drag folds (1992) in interpreting structures in Upper Car- (parasitic folds), with an asymmetry consistent boniferous turbidites in North Devon of south- The infl uence of mass-transfer dissolution with overall fl exural slip on the fl ank of an anti- west England. Tanner (1992) determined that creep in the Thick White Limestone Beds is cline. However, in the upper cliff panel above duplex development can replace drag folding manifest as well in structural systems larger than the top of the drag folded sequence (see Fig. 25 as an accommodation to the requirements of individual outcrops. For example, two different as well as location C in Fig. 14), there is a set fl exural slip. He emphasized that this occurs in

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Figure 23. North-directed photograph of the Figure 24. North-directed photograph of Figure 25. North-directed view of the west- hinge of a small anticline. Lower set of ar- steeply dipping pseudo-bedding on the dipping limb of the Three Gorges anticline, rows reveals stylo-thrusting of the left limb east limb of an outcrop-scale anticline. showing two panels of Thick White Lime- over right, and stylo-indentation of the cut- The pseudo-bedding contains subhorizon- stone Beds that display similar thicknesses off end of the right limb into the left limb. tal calcite veins (white) and tectonic stylo- but strikingly contrasting internal struc- Upper set of arrows calls attention to a black lites (highlighted in black). At the location ture. The upper panel (DP) accommodated parting that was a locus of pressure-dissolu- marked by the large black arrow, a stylo- shortening by formation of duplex struc- tion loss of material in the hinge. Breadth fault has accommodated indentation of the ture, resulting in “horses” dipping much of dissolution is revealed in the “overstep” wedged-out end of one pseudo-bed into an- more steeply than the enveloping surfaces of beneath the upper set of arrows. other. Note how the pseudo-bed at the “re- the panel. The lower panel (DFP) accommo- ceiving end” of the indentation is markedly dated shortening by drag folding. See text thinned in the area of contact. The pseudo- for elaboration. layered sequences marked by resistance to bed- bed invaded by indentation appears to have ding-plane slip. Tanner supported his conclu- been especially vulnerable to mass-transfer sion by demonstrating that the “sense-of-slip” dissolution creep, given the abundance and formed into a conjugate box fold (syncline) of a vergence expressed by duplexes always corre- close spacing of tectonic stylolites. bizarre nature (Fig. 27). The syncline connects sponds to that required by conventional fl exural west and east with asymmetrical anticlines that slip (Tanner , 1992, p. 1173). verge toward the hinge point and reveal pro- The duplex identifi ed on the western limb of Evidence for Dissolution in the Very Hinge found layer-parallel fl attening within the core the Three Gorges anticline can be explained in of the Three Gorges Anticline of the fold. The syncline itself is fl at bottomed, a hybrid manner incorporating Tanner’s (1992) below which there is a décollement that sepa- model as well as mass-transfer dissolution creep. In the hinge of the Three Gorges anticline, rates the syncline from underlying subhori- It is evident that each horse panel of steeply and at a structural level within the Thick zontal (though internally deformed) limestone inclined beds and pseudo-beds is marked by White Limestone Beds, there are extraordinary layers. The axial trace of the syncline coincides steeply dipping fi ssure-like openings, evidence expressions of folding and mass-transfer dis- with a locus of intensive pressure dissolution of dissolution removal of bedding and pseudo- solution creep. As described earlier, the Cave (see Fig. 27). bedding. I refer to these systems as stylo- of Kolokotronis (see Fig. 15) occupies a part of duplexes. A smaller example of such a stylo- the hinge zone of the Three Gorges anticline. DISCUSSION duplex, and one much easier to photograph, is The “cave” is a rock shelter, but in structural evident in the uppermost part of the western geologic parlance it is a saddle-reef dilation Focus limb in the hinge zone of the anticline. What at zone (DeSitter, 1964, p. 297–299; Ramsay, fi rst appears to be simply asymmetric drag fold- 1974; Fletcher and Pollard, 1999), created Part of the framework for this discussion ing of limestone is, on closer inspection, seen during folding. At the very hinge of the Three of fold mechanics is the nature of progressive to be a stylo-duplex accommodated by the com- Gorges anticline, at the stratigraphic level cor- deformation and strain partitioning related to bination of faulting, folding, and mass-transfer responding to the top of the saddle-reef rock tectonic inversion of the Pindos fold-and-thrust dissolution creep (Fig. 26). shelter, there is a limestone layer now trans- belt. Skourlis and Doutsos (2003) determined

16 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 17 of 22 Quasi-fl exural folding of pseudo-bedding

as a result of tectonic loading accompanying latest Cretaceous–early Tertiary tectonic inver- sion of the Pindos Basin. Accommodation of this layer-parallel shortening was marked by the development of tectonic LPS stylolites ori- ented transverse to pseudo-bedding, with stylo- lite teeth oriented parallel to pseudo-bedding. They appear to be identical to the early-formed, pre–macro-folding LPS stylolites described by Droxler and Schaer (1979, their fi gure 14, p. 568) in the Jura. The relatively even spac- ing of these transverse tectonic stylolites was controlled, at least in part, by the thickness of pseudo-beds and their semi-brittle mechanical properties. The shortening accommodated by LPS stylolites was on the order of 15%–20%, as estimated by measuring minimum dissolu- tion-related contraction as expressed in pseudo- bedding exposures, such as that presented in Figures 6 and 19. Price and Cosgrove (1991, p. 386) emphasized that if we assume slow strain rates, the amount of such layer-parallel strain (in this case accommodated by LPS stylo lites) can be quite large (30%) and governed only by the duration of loading.

Outcrop-Scale Buckling and Thrust-Faulting

As dissolution-induced layer-parallel short- ening of fl at-lying pseudo-beds progressed, additional minor structures began to develop, including meso-scale buckle folds. Price and Cosgrove (1991, p. 387) noted that the shift from layer-parallel shortening or flattening to multilayer buckling will not be abrupt, but instead incremental. Sites of initial buckle folds for a given interval of pseudo-bedding were likely in thin stiff beds, and localized by geo- metric irregularities and thinnest parts of layers . The geometric irregularity of pseudo-beds would be considered an intrinsic property of the Figure 26. North-directed photograph of stylo-duplexes in the uppermost part of the west- layered system (by Price and Cosgrove, 1991, dipping limb of the Three Gorges anticline. Height of the panel is ~15 m. Note fl ats and p. 387). Ideal triggering loci for buckling were ramps. The ramps are locations of mass-transfer dissolution creep. Steep fabric includes places where the pseudo-bedding was radically steeply dipping horses as well as fi ssure-like partings produced by stylo-thrust–generated thinned or where it wedged out completely (see pressure-dissolution. Fig. 21). Biot (1959), in fact, emphasized that buckle folds will not form in perfectly parallel planar units that are shortened perfectly parallel that between early Oligocene and late Eocene Development of LPS Stylolites to the layering. the Pindos belt, whose initial breadth was To be sure, pseudo-bedding in the Thick ~160 km, was progressively shortened at a rate The overall primary and secondary strain White Limestone Beds formation was replete of ~6 mm/year. Based on construction and inter- history for Thick White Limestone Beds in the with imperfections conducive to buckling (see pretation of eight regional balanced cross sec- Mount Lykaion study area was one of progres- Fig. 12). Because of the non-systematic varia- tions, Skourlis and Doutsos (2003) estimated sive deformation. Pseudo-bedding was created tions in pseudo-bed thickness and wedge-outs, total shortening to be ~60%, equally divided through gravitational loading during burial, the distributions of potential loci for triggering between two mechanisms: pre-thrusting layer- compaction, and diagenesis in the Pindos Basin. buckle folds was undoubtedly quite random parallel shortening (including buckling ) and The fi rst manifestation of layer-parallel short- within the sequence of pseudo-bedding. As a regional thrust faulting (and associated macro- ening occurred while pseudo-bedding was still result, the distribution of outcrop-scale buckle folding). essentially horizontal. This shortening occurred folds within Thick White Limestone Beds is not

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ABMoreover, we also presume that bedding inter- faces that accommodated fl exural slip at any one location functioned as fl exural-slip surfaces at all locations on that same bedding surface, and on each limb of the fold. The physical factors that likely impeded full operation of fl exural-slip folding of the Thick White Limestone Beds formation included (1) the interlocking large-amplitude (up to centimeter-scale) stylolite teeth on the stylolitic surfaces, (2) the millimeter- to centimeter-scale offsets of diagenetic stylolitic surfaces along LPS tectonic stylolites, (3) limestone domina- tion with few mechanically soft interbeds, and (4) the geometric irregularity and tipping-out of discrete diagenetic stylolite surfaces. On the other hand, the presence of mechanically soft, clayey, insoluble residue accumulations along stylolite surfaces can locally favor fl exural slip. There is some outcrop evidence for this in the Mount Lykaion study area. Where the thickness of clayey residue laminae (or layers) exceeds the amplitude of stylolitic teeth and cones, the clay laminae (or layers) can accommodate fl exural Figure 27. (A) North-directed view of the very hinge of the Three Gorges anticline, directly slip through noncoaxial distributed shear. For above the stockade. An isoclinal syncline is fl anked by and contiguous with inward-facing example, Figure 28 shows an example of fab- asymmetrical anticlines. Directly beneath the trough of the syncline is a décollement (ex- rics created by apparent noncoaxial shear of pressed as a subhorizontal fi ssure) that accommodated the “room problem” between the insoluble residue laminae separating limestone form and thickness of beds above and below. (B) The internal structure is revealed through pseudo-beds in the Thick White Limestone tracings of contacts of limestone pseudo-beds (black) and axial traces (white) of the folds. Beds. The pseudo-beds of limestone (gray) The interior of the syncline displays textures and fabrics refl ecting profound dissolution. are separated by insoluble residue (dark) (see Fig. 28). The insoluble residue layers display a crude foliation that formed, presumably, dur- very systematic, thus contributing to the dishar- Flexural-slip folding in sedimentary rocks ing overall macroscopic fl exural-slip folding. monic nature of folding within this formation. relies on the presence of discrete bedding- A 1-cm-thick calcite vein (dark, nearly perpen- The initial geometric forms of buckle folds, parallel surfaces separating competent rock dicular to pseudo-bedding) appears originally including dominant wavelengths, were governed units above and below (Donath and Parker, to have crossed several pseudo-beds, but is now by pseudo-bed thickness and the overall outcrop- 1964; Ramsay, 1967, p. 391–396; Ormand systematically cut and offset by fl exural-slip scale mechanical stratigraphy (Biot, 1957; Biot and Hudleston, 2003). Moreover, fl exural- translations accommodated by shearing of the et al., 1961; Currie et al., 1962; Ramberg, 1962; slip folding is especially favored in situations insoluble residue along the weld contacts. Price and Cosgrove, 1990, p. 273–296). A com- where mechanically stiff layers are separated mon range of percent layer-parallel shortening by thin, mechanically soft layers. This arrange- Shortening and Tightening of Buckle accomplished by buckle folding of pseudo-beds ment results in a local rheological environment Folds by Mass-Transfer Dissolution in the Thick White Limestone formation is 10% marked by high ductility contrast and low to to 20%, but in places it is much higher. moderate mean ductility, which is the optimum Even before the Three Gorges fold began combination for fl exural-slip folding to fl our- to grow and amplify, there was yet another Shortening and Tightening of Buckle ish (Donath and Parker, 1964). At a very basic mechanism that enabled horizontal shortening Folds by Flexural Slip level, fl exural-slip folding requires that shear of pseudo-bedding in the Thick White Lime- stresses on bedding surfaces exceed the cohe- stone Beds: mass-transfer dissolution creep. Where favored by relatively low frictional sion and frictional resistance to slip between Concentrated in and around buckle folds are the resistance to slip between layers, some short- the layers (Price and Cosgrove, 1990, p. 367). hybrid structural associations (described above) ening and tightening of individual buckle folds Though not explicitly emphasized in the litera- that collectively accommodated shortening and was undoubtedly achieved by fl exural-slip kine- ture, a premise underlying conditions favoring tightening of the folds. These hybrid structures matics. Though the mechanical stratigraphy of fl exural-slip folding is one not met by pseudo- include stylo-interpenetration, stylo-thrusting, the Thin Platy Limestone Beds and the Flysch bedding: bedding-plane slip surfaces need to fold-limb eliminations, and perhaps some of Transition Beds was perfectly suited to pure be quite expansive relative to bed thickness. the stylo-duplexing. These unusual hybrid fl exural-slip folding, the pseudo-bedding within For “normal” bedding sequences we implicitly outcrop-scale structures are a refl ection of the Thick White Limestone Beds was not able to assume that the trace lengths of bedding planes mechanical limitations of fl exural slip within ubiquitously accommodate fl exural-slip folding in any direction are many orders of magnitude this formation. The role of pressure dissolution in a homogeneous manner. greater than the thickness of the individual beds. in driving fold tightening and additional short-

18 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 19 of 22 Quasi-fl exural folding of pseudo-bedding

accommodated by a different mechanism, in this case mass-transfer dissolution creep. This fact helps explain why so many of the outcrop-scale folds observed in the Thick White Limestone Beds formation tend to be dishar- monic, and in two different ways. First, the folds not uncommonly occur in relative isolation, not connected laterally with other minor anticlines and synclines in “wave trains” of folding. Sec- ond, the folds tend to “give out” abruptly both up and down section, and thus the axial traces of these folds tend to be relatively short relative to fold amplitude. Such disharmony primar- ily results from the relative absence of typical throughgoing expansive bedding surfaces that, where present, permit fl exural-slip folding to operate in a standard, systematic manner. The short, discontinuous stylolitic surfaces that are able to accommodate slip are analogous to crystal-lattice dislocations oriented more or less parallel to pseudo-bedding but randomly distrib- uted within a given section of the Thick White Figure 28. Adobe Photoshop–enhanced photograph of pseudo-beds, each of which is Limestone Beds. Moreover, these “dislocation bounded top and bottom by thin layers or laminae of insoluble residue (dark) that accu- analogs” tip out in all directions over short mulated during diagenetic stylolitization. The insoluble residue possesses a crude foliation, distances (Fig. 29). Under such circumstances interpreted to be the result of fl exural-fl ow shear during an overall fl exural-slip folding. fl exural slip on a pseudo-bed surface may be Further evidence for fl exural-slip kinematics is seen in the offsets of a prominent calcite vein replaced by thrust slip on a neo-fault generated (dark, CV) that originally was a single unbroken vein that cut across at least fi ve pseudo- just for this purpose. But as we have seen, there beds. Truncations and offsets of this vein are consistent with fl exural-slip kinematics. are other “replacement” and “transfer” mecha- nisms as well, namely stylo-thrusting, stylo- duplexing, stylo-indentation, and even addi- ening is well documented, including examples into consideration the shortening accommo- tional buckling (see Fig. 29). where the pressure-dissolution removal of mate- dated by thrust faulting. As the Three Gorges rial takes place along discrete, non-penetrative, anticline developed in response to fault-propa- Quasi-Flexural Folding fracture-like surfaces (Ormand and Hudleston, gation or fault-bend folding, the Pindos Group 2003). Such structures and fabrics are quite dis- stratigraphy overall responded by fl exural-slip In 1964, ~50 years ago, Fred A. Donath and similar to those produced by more conventional folding. Easy bedding-plane slip took place, Ronald B. Parker published their classic paper passive folding and the development of pen- for example, in Thin Platy Limestone Beds and titled “Folds and Folding”. They introduced etrative spaced cleavages and other varieties of Flysch Transition Beds. No appreciable hinge- a fold classifi cation system based on whether axial-planar cleavages (e.g., Groshong, 1975). zone thickening accompanied this concentric lithologic layering (e.g., bedding) behaves in a Instead, pseudo-bed and fold shape changes and folding. Sandwiched between Thin Platy Lime- mechanically active or passive manner (Fig. 30). strain were achieved by the “transfer of mass” stone Beds (below) and Flysch Transition Beds Where mechanically active, the lithologic layer- from one place to another. In their studies of (above), and incapable of responding to short- ing controls the folding process, either through similar structures in “thin-bedded” limestones ening by homogeneous fl exural slip, the Thick slip between fl exed layers (fl exural slip) or in the Jura, Droxler and Schaer, (1979, p. 551) White Limestone Beds formation experienced fl ow within fl exed layers (fl exural fl ow). Where captured the essence of pressure-dissolution a fi nal dimension of fold-kinematic complexity. lithologic layering is mechanically passive, the transformation of folds: during the evolution of This can be illustrated by considering a pseudo- folding is achieved through slip or fl ow across folds the layers are changed into “semi-indepen- bed whose upper contact is only locally capable layer boundaries (passive slip and passive fl ow). dent groups of fragments, the outside geometry of accommodating fl exural slip. The magnitude Donath and Parker (1964) emphasized that of which is modifi ed by dissolution in over- of fl exural-slip translation accommodated by the operation of fl exural versus passive fold- pressured zones.” this surface will be the product of the underly- ing depends upon ductility contrast and mean ing pseudo-bed’s thickness and its inclination ductility within the mechanical stratigraphy. Macro-Folding during Regional Thrusting (in radians) (Ramsay, 1967, p. 392–393). For Ductility is generally thought of as the capac- example, the slip magnitude along the upper ity of a rock to fl ow without faulting or loss The major shortening of Pindos Group stratig- contact of a 45°-dipping 10-cm-thick pseudo- of cohesion. With respect to rock deformation raphy in the Mount Lykaion area was achieved bed of limestone would be 7.8 mm. Where this experiments, Donath (1970a, 1970b) considered by thrust faulting and associated macro-folding. active fl exural-slip (diagenetic stylolitic) surface a ductile response to applied load to be one in The system of anticlines and synclines in the tips out, there would be a slip-budget require- which a rock sample shortens by at least 10% lower plate of the Lykaion thrust reveal ~30% ment that no longer can be accommodated before faulting (i.e., before losing cohesion); shortening, and this calculation does not take by fl exural slip. The slip requirement must be a moderately ductile response was considered

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plex forms of their principal examples were considered to be products of apparent irregular contorted fl ow. Donath (1966) later noted that quasi-fl exural folding occurs in environments of diminished layer anisotropy and interlayer slip, and that quasi-fl exural folding requires signifi - cant changes in layer shape accommodated by a number of deformation mechanisms. Because Donath and Parker (1964) placed the fi eld of quasi-fl exural folding in a region comparable to fl exural fl ow and passive folding, most structural geologists may have concluded that quasi-fl exural folds are produced under conditions of high temperature and confi ning pressure, i.e., conditions of the type normally associated with the formation of metamorphic tectonites. Such conditions would satisfy the Donath and Parker emphasis that the presence of quasi-fl exural folds signifi es redistribution of material, as certain (softer) layers fl owed pas- sively while other (stiffer) layers were caused to fl ex or bend in response to the bulk movement of “fl owing” material (Donath and Parker, 1964). The outcrop-scale folds and associated struc- tures in Thick White Limestone Beds in the Mount Lykaion area underscore the fact that redistribution of material during shortening can be achieved without passive fl ow of soft layers . In fact, one of the few references to quasi- Figure 29. Schematic model emphasizing that quasi-fl exural folding occurs in sequences fl exural folding is by Woodward (1999), who where surfaces of easy slip are not throughgoing within the stratigraphy, but are short emphasized that the dominant mechanism lead- and discontinuous. See text for explanation. ing to quasi-fl exural folding in low-temperature, non-metamorphic conditions is diffuse mass transfer. Slip on layers represents only a minor by Donath to be one in which the rock sample However, the main examples of quasi-fl exural contribution to quasi-fl exural folding. shortens in the range 5%–10% before faulting. folds chosen by Donath and Parker (1964) were The observations and interpretations I have Donath and Parker (1964) understood that ones involving interbedded limestone and shale made in this paper demonstrate that quasi- the categories of fl exural and passive fold- of the Whitehall Formation (Upper Cambrian) fl exural folding of the variety associated with ing, including the variants of each, did not exposed near Whitehall, New York. The com- shortening of stylolitic limestones occurs under adequately encompass all folding, especially folding that is notably disharmonic and marked by hybrid combinations of passive and fl exural responses of layering (F.A. Donath, 2012, per- Quasi-flexural sonal commun.). Thus, almost as a placeholder, Very High Donath and Parker (1964) included in their clas- sifi cation a category they named “quasi-fl exural folding” (see Fig. 30). In their very brief dis- Passive cussion of quasi-fl exural folding, Donath and Parker (1964) placed the rheological environ- Figure 30. Fields of folding re- ment for quasi-fl exural folding as one marked lated to mean ductility and duc- High by high to very high mean ductility and mod- tility contrast, based on Donath erate to high ductility contrast. They identifi ed and Parker (1964, their fi gure 3, Flexural Flow

ptygmatic folding as one example of quasi- p. 50). Mean Ductility fl exural folding. Ptygmatic folding is inherently a buckling phenomenon of a relatively thin Moderate mechanically stiff layer embedded in a relative Flexural Slip large volume of mechanically soft material, thus Low satisfying the conditions of high mean ductil- High Moderate Low ity and high ductility contrast (Biot et al., 1961; Ghosh, 1968; Ramsay and Huber, 1987, p. 392). Ductility Contrast

20 Geological Society of America Bulletin, Month/Month 2012 30963 1st pages / 21 of 22 Quasi-fl exural folding of pseudo-bedding conditions of high mean ductility and low quasi-fl exural folds. Because pseudo-bedding for amount of dissolution: Earth and Planetary Science Letters, v. 337–338, p. 186–196, doi:10.1016 /j.epsl ductility contrast. Thus I conclude that quasi- is commonplace, but commonly overlooked, in .2012 .05 .026. fl exural folds associated with metamorphic carbonate formations in fold-and-thrust moun- Biot, M.A., 1957, Folding instability of a layered visco- tectonites are formed in environments of high tain belts worldwide, opportunities abound for elastic medium under compression: Royal Society of London Proceedings, Series A, v. 242, p. 444–454, doi: mean ductility and high ductility contrast, are follow-up studies. These can be aimed at fuller 10.1098 /rspa .1957 .0187. created through crystal-plastic deformation description of the fabrics as well as develop- Biot, M.A., 1959, On the instability of folding deformation mechanisms (Woodward, 1999), and occupy the ment of robust quantitative determinations of of a layered viscoelastic medium under compression: Journal of Applied Mechanics, v. 26, p. 393–400. region of quasi-fl exural folding in the upper left kinematic budgets that are represented in the Biot, M.A., Ode, H., and Roever, W.L., 1961, Experimen- portions of the Donath-Parker classifi cation (see varied structures associated with this expression tal verifi cation of the folding of stratifi ed viscoelastic media: Geological Society of America Bulletin, v. 72, Fig. 30). Those associated with limestone under of mass-transfer dissolution creep. p. 1621–1630, doi: 10.1130 /0016-7606 (1961)72[1621: non-metamorphic tectonic conditions would be EVOTTO]2.0 .CO;2. ACKNOWLEDGMENTS formed in an environment of high mean ductil- Brown, W.G., 2007, Tectonic stylolites from the Arbuckle anticline, southern Oklahoma: Oklahoma Geology ity and low to moderate ductility contrast, i.e., in Special thanks go to University of Arizona Profes- Notes, v. 67, no. 1, p. 4–28. the upper right region of quasi-fl exural folding sors David Romano and Mary Voyatzis for provid- Currie, J.B., Patnode, A.W., and Trump, R.P., 1962, Devel- in the Donath-Parker classifi cation. ing me the opportunity to serve as Geologist on the opment of folds in sedimentary strata: Geological Soci- ety of America Bulletin, v. 73, p. 655–674, doi:10.1130 Quasi-fl exural folds of the type observed in Mount Lykaion Survey and Excavation Project, Arca- dia, Greece. This project has been carried out under /0016-7606 (1962)73[655: DOFISS]2.0.CO;2. this study are yet another illustration of the fact the auspices of the Ministry of Culture of Greece and Davis, G.H., 2009, Geology of the Sanctuary of Zeus, Mount that any fold state is the fi nite-strain product of Lykaion, southern Peloponessos, Greece: Journal of the American School of Classical Studies at Athens. the Virtual Explorer, electronic edition, v. 33, 58 p., progressive deformation that may involve sev- The Greek Archaeological Service gave me permis- doi: 10.3809 /jvirtex .vol .2009 .033. eral deformation mechanisms operating along sion to carry out this investigation of the geology of Davis, G.H., Reifschneider, M.A., Borraccini, F., and the Tria Remmata canyon during the summer of 2011. Similox-Tohon, D., 2009, Iterative geologic mapping a particular strain path over time (Ormand and The fi eld work was greatly aided by my fi eld assistant, and 3D structural modeling to identify spatial incon- Hudleston, 2003), e.g., buckling, fl exural slip, George Faidon Papakonstantinou, who at the time was sistencies and create accurate visualization framework passive slip, mass-transfer dislocation creep. an undergraduate student in Geology at the National for geoarchaeological interpretations: Mt. Lykaion Technical University, Athens. I also wish to express (Greece) Sanctuary of Zeus case study: Part 1, Map- The meso-scale quasi-fl exural folds described ping: Geological Society of America Abstracts with here are not passive-slip, for they are not marked my gratitude to Susie Gillett, scientifi c illustrator, who Programs, v. 41, no. 7, p. 167–168. prepared fi nal versions of the line drawings, and to by the presence of penetrative “planar” folia- Dean, S.L., Kulander, B.R., and Skinner, J.M., 1988, Struc- David Fischer, who prepared renderings of the kine- tural chronology of the Alleghanian orogeny in south- tions and/or cleavages, nor are they fl exural-slip, matic model(s). Data were plotted stereographically eastern West Virginia: Geological Society of America for the interlayer slip during folding was limited using the Rockware StereoStat software program Bulletin, v. 100, p. 299–310, doi:10.1130 /0016 -7606 and spotty. The shortening that gives these folds developed and written by Stephen Ahlgren. Midland (1988)100 <0299: SCOTAO>2.3 .CO;2. Valley Exploration, Ltd., has been a partner in trans- Degnan, P.J., and Robertson, A.H.F., 1998, Mesozoic– their characteristic properties was through vol- forming my structural and map data into three-dimen- early Tertiary passive margin evolution of the Pindos ume loss without loss of cohesion. ocean (NW Peloponnese, Greece): Sedimentary sional visualization models. Revision of the originally Geology, v. 117, p. 33–70, doi:10.1016 /S0037 -0738 submitted manuscript was greatly aided by the inputs (97)00113-9. CONCLUSIONS from the Editors of the Geological Society of America Degnan, P.J., and Robertson, A.H.F., 2006, Synthesis of Bulletin, and the two reviewers (one of whom self- the tectonic-sedimentary evolution of the Mesozoic– identifi ed, namely Peter J. Hudleston) whose inputs early Cenozoic Pindos ocean: Evidence from the Folds that were produced during tectonic were insightful and very helpful. NW Peloponnese, Greece, in Robertson, A.H.F., and shortening of Thick White Limestone Beds in Mountrakis , D., eds., Tectonic Development of the REFERENCES CITED Eastern Mediterranean Region: Geological Society the Mount Lykaion study area may appear to of London Special Publication 260, p. 467–491, doi: be wholly the product of buckling accompanied Aharonov, E., and Katsman, R., 2009, Interaction between 10.1144 /GSL .SP .2006 .260 .01.19. by and/or followed by fl exural slip. But fl exural pressure solution and clays in stylolite development: de Sitter, L.U., 1964, Structural Geology (2nd edition): New York, McGraw-Hill, 551 p. slip was simply not a well-suited mechanism Insights from modeling: American Journal of Science, v. 309, p. 607–632, doi: 10.2475 /07 .2009 .04. Donath, F.A., 1966, Effects of ductility and planar anisot- for achieving fold shortening and tightening in Alvarez, W., Engelder, T., and Lowrie, W., 1976, Formation ropy in folding of rock layers [abs.]: Bulletin of the the Thick White Limestone Beds. This forma- of spaced cleavage and folds in brittle limestone by dis- American Association of Petroleum Geologists, v. 50, solution: Geology, v. 4, p. 698–701, doi: 10.1130 /0091 p. 610. tion is limestone dominated, with precious few -7613 (1976)4<698: FOSCAF>2.0 .CO;2. Donath, F.A., 1970a, Rock deformation apparatus and ex- mechanically soft interbeds to help accommo- Alvarez, W., Colacicchi, R., and Montanari, A., 1985, Syn- periments for dynamic structural geology: Journal of date fl exural slip. Moreover the combination of sedimentary slides and bedding formation in Apennine Geological Education, v. 18, p. 1–12. pelagic limestones: Journal of Sedimentary Petrology, Donath, F.A., 1970b, Some information squeezed out of interlocking stylolite teeth along pseudo-bed v. 55, p. 720–734. rock: American Scientist, v. 58, p. 54–72. contacts, the common tipping-out of potential Andrews, L.M., and Railsback, L.B., 1997, Controls on Donath, F.A., and Parker, R.B., 1964, Folds and folding: Geo- slip surfaces, and the geometric irregularity of stylolite development: Morphologic, lithologic, and logical Society of America Bulletin, v. 75, p. 45–62, doi: temporal evidence from bedding-parallel and trans- 10.1130 /0016 -7606 (1964)75[45: FAF]2.0 .CO;2. pseudo-bed contacts resulted in largely ineffi - verse stylolites from the U.S. Appalachians: The Jour- Droxler, A., and Schaer, J.P., 1979, Deformation cata- cient and ineffective fl exural slip. The preferred nal of Geology, v. 105, p. 59–73, doi: 10.1086 /606147. clastique plastique lors du plissement, sous faible Bathurst, R.G.C., 1995, Burial diagenesis of limestones couverture, de strates calcaires: Eclogae Geologicae shortening mechanism was diffusive mass under simple overburden: Stylolites, cementation and Helvetiae, v. 72, no. 2, p. 551–570. transfer achieved through pressure dissolution feedback: Bulletin of the Geological Society of France, Durney, D. W., 1974, The infl uence of stress concentrations of the limestone. Thus the folding is almost or v. 166, p. 181–192. on the lateral propagation of pressure solution zones Bayly, B., 1986, A mechanism for development of stylolites: and surfaces [abs.]: Geological Society of Australia partly fl exural slip, and is here introduced as The Journal of Geology, v. 94, p. 431–435, doi: 10.1086 Tectonics and Structural Newsletter, no. 3, p. 19. a new class of quasi-fl exural folding, which is /629041. Ebner, M., Piazolo, S., Renard, F., and Koehn, D., 2010, itself a rarely cited “placeholder” category of Benedicto, A., and Schultz, R.A., 2010, Stylolites in lime- Stylolite interfaces and surrounding matrix material: stone: Magnitude of contractional strain accommo- Nature and role of heterogeneities in roughness and disharmonic folding in the Donath and Parker dated and scaling relationships: Journal of Structural microstructural development: Journal of Structural (1964) classifi cation. The important mechanical Geology, v. 32, p. 1250–1256, doi:10.1016 /j.jsg .2009 Geology, v. 32, p. 1070–1084, doi:10.1016 /j.jsg .2010 .04 .020. .06 .014. role of pseudo-bedding cannot be overstated in Ben-Itzhak, L.L., Aharonov, E., Toussaint, R., and Sagy, A., Fletcher, R.C., and Pollard, D.D., 1981, Anti-crack model for controlling the development of this variety of 2012, Upper bound on stylolite roughness as indicator pressure solution surfaces: Geology, v. 9, p. 419–424,

Geological Society of America Bulletin, Month/Month 2012 21 30963 1st pages / 22 of 22 Davis

doi: 10.1130 /0091 -7613 (1981)9 <419: AMFPSS>2.0 normal stress and fi nite compaction: Earth and Plan- United States: Journal of Sedimentary Petrology, v. 63, .CO;2. etary Science Letters, v. 257, p. 582–595, doi: 10.1016 p. 513–522, doi: 10.2110 /jsr .63 .513. Fletcher, R.C., and Pollard, D.D., 1999, Can we understand /j.epsl.2007 .03 .015. Ramberg, H., 1962, Contact strain and folding instability structural and tectonic processes and their products Lalechos, N., 1973, Geological map of the Greece Kato of a multilayered body under compression: Geolo- without appeal to a complete mechanics?: Journal of Fighalia sheet (1:50,000): National Institute of Geo- gische Rundschau, v. 51, p. 405–439, doi:10.1007 Structural Geology, v. 21, p. 1071–1088, doi: 10.1016 logical and Mining Research, scale 1:50,000. /BF01820010. /S0191 -8141 (99)00056-5. Larbi, J.A., 2003, Effects of stylolites on the durability of Ramsay, J.G., 1967, Folding and Fracturing of Rocks: New Geiser, P.A., 1974, Cleavage in some sedimentary rocks building stones: Two case studies: HERON, v. 48, Spe- York, McGraw-Hill Book Company, 560 p. of the central Valley and Ridge province, Mary- cial Issue, p. 231–247. Ramsay, J.G., 1974, Development of chevron folds: Geo logi- land: Geological Society of America Bulletin, v. 85, Merino, E., 1992, Self-organization in stylolites: American cal Society of America Bulletin, v. 85, p. 1741–1753, p. 1399–1412, doi:10.1130 /0016 -7606 (1974)85 <1399: Scientist, v. 80, no. 5, p. 466–473. doi: 10.1130 /0016 -7606 (1974)85 <1741: DOCF>2.0 CISSRO>2.0 .CO;2. Merino, E., Ortoleva, P., and Strickholm, P., 1983, Genera- .CO;2. Geiser, P.A., and Sansone, S., 1981, Joints, microfractures, tion of evenly-spaced pressure-solution seams during Ramsay, J.G., and Huber, M.I., 1987, The Techniques of and the formation of solution cleavage in limestone: (late) diagenesis: A kinetic theory: Contributions to Modern Structural Geology, Volume 2: Folds and Frac- Geology, v. 9, p. 280–285, doi:10.1130 /0091 -7613 Mineralogy and Petrology, v. 82, p. 360–370, doi: tures: London, Academic Press, 381 p. (1981)9 <280: JMATFO>2.0.CO;2. 10.1007 /BF00399713. Romano, D.G., and Voyatzis, M.E., 2010, Excavating at the Ghosh, S.K., 1968, Experiments of buckling of multilayers Narr, W., and Suppe, J., 1991, Joint spacing in sedimentary birthplace of Zeus: Expedition, v. 52, p. 9–21. which permit interlayer gliding: Tectonophysics, v. 6, rocks: Journal of Structural Geology, v. 13, p. 1037– Sheppard, T.H., 2002, Stylolite development at sites of pri- p. 207–249, doi: 10.1016 /0040 -1951 (68)90052-8. 1048, doi: 10.1016 /0191 -8141 (91)90055-N. mary and diagenetic fabric contrast within the Sutton Green, H.W., II, 1984, “Pressure solution” creep: Some causes Nickelsen, R.P., 1972, Attributes of rock cleavage in some Stone (Lower Lias), Ogmore-by-Sea, Glagmorgan, and mechanisms: Journal of Geophysical Research, mudstones and limestones of the Valley and Ridge UK: Proceedings of the Geologists’ Association, v. 113, v. 89, p. 4313–4318, doi: 10.1029 /JB089iB06p04313. province, Pennsylvania: Pennsylvania Academy of p. 97–109, doi: 10.1016 /S0016 -7878 (02)80013-X. Groshong, R.H., Jr., 1975, “Slip” cleavage caused by Science, v. 46, p. 107–112. Similox-Tohon, D., Scherrenberg, A., Clelland, S., and pressure solution in a buckle fold: Geology, v. 3, Nickelsen, R.P., 1986, Cleavage duplexes in the Marcellus Davis, G.H., 2009, Iterative geologic mapping and 3D p. 411–413, doi: 10.1130 /0091 -7613 (1975)3 <411: Shale of the Appalachian foreland: Journal of Struc- structural modeling to identify spatial inconsistencies SCCBPS>2.0 .CO;2. tural Geology, v. 8, p. 361–371, doi:10.1016 /0191 and create accurate visualization framework for geo- Groshong, R.H., Jr., 1988, Low-temperature deformation -8141 (86)90055-6. archaeological interpretations: Mt. Lykaion (Greece) mechanisms and their interpretation: Geological So- Olalla, P., 2002, Mythological Atlas of Greece: Athens, Sanctuary of Zeus case study: Part 2, Modeling: Geo- ciety of America Bulletin, v. 100, p. 1329–1360, doi: ROAD publications S.A., 500 p. logical Society of America Abstracts with Programs, 10.1130 /0016 -7606 (1988)100 <1329: LTDMAT>2.3 Ormand, C.J., and Hudleston, P.J., 2003, Strain paths of v. 41, no. 7, p. 168. .CO;2. three small folds from the Appalachian Valley and Simpson, J., 1985, Stylolite-controlled layering in a homo- Gross, M.R., 1993, The origin and spacing of cross-joints: Ridge, Maryland: Journal of Structural Geology, v. 25, geneous limestone: Pseudo-bedding produced by Examples from the Monterey Formation, Santa p. 1841–1854, doi: 10.1016 /S0191 -8141 (03)00042-7. burial diagenesis: Sedimentology, v. 32, p. 495–505, Barbara coastline, California: Journal of Structural Papadopoulos, P., 1997, Geological Map of the Megalopolis doi: 10.1111 /j.1365 -3091 .1985 .tb00466.x. Geol ogy, v. 15, p. 737–751, doi:10.1016 /0191 -8141 sheet: Athens, Greece, Institute of Geology and Min- Skourlis, K., and Doutsos, T., 2003, The Pindos fold-and-thrust (93)90059-J. eral Exploration, scale 1:50,000. belt (Greece): Inversion kinematics of a passive conti- Guzzetta, G., 1984, Kinematics of stylolite formation and Pausanias, in Jones, W.H.S., Ormerod, H.A., and Wycherley, nental margin: International Journal of Earth Sciences, physics of the pressure-solution process: Tectono physics, R.E., eds., 1918, Pausanias Description of Greece: v. 92, p. 891–903, doi: 10.1007 /s00531 -003 -0365-4. v. 101, p. 383–394. London, W. Heinemann, Books XXXVI and XXXVIII. Smith, J.V., 2000, Three-dimensional morphology and con- Heald, M.T., 1955, Stylolites in sandstone: The Journal of Pe-Piper, G., and Piper, D.J.W., 1984, Tectonic setting of the nectivity of stylolites hyperactivated during veining: Geology, v. 63, p. 101–114, doi: 10.1086 /626237. Mesozoic Pindos basin of the Peloponnese, Greece, in Journal of Structural Geology, v. 22, p. 59–64, doi: Helmstaedt, H., and Greegs, R.G., 1980, Stylolitic cleavage Dixon, J.E., and Robertson, A.H.F., eds., The Geologi- 10.1016 /S0191 -8141 (99)00138-8. and cleavage refraction in lower Paleozoic carbonate cal Evolution of the Eastern Mediterranean: Geological Stockdale, P.B., 1922, Stylolites: Their nature and origin: rocks of the great valley, Maryland: Tectonophysics, Society of London Special Publication 17, p. 563–567, Indiana University Studies, v. 9, p. 1–97. v. 66, p. 99–114, doi: 10.1016 /0040 -1951 (80)90040-2. doi: 10.1144 /GSL .SP .1984 .017 .01.43. Tanner, P.W.G., 1992, Morphology and geometry of du- Hobbs, D.W., 1967, The formation of tension joints in sedi- Piper, D.J.W., 2006, Sedimentology and tectonic setting plexes formed during fl exural-slip folding: Journal of mentary rocks: An explanation: Geological Magazine, of the Pindos Flysch of the Peloponnese, Greece, in Structural Geology, v. 14, p. 1173–1192, doi: 10.1016 v. 104, p. 550–556, doi: 10.1017 /S0016756800050226. Robertson, A.H.F., and Mountrakis, D., eds., Tectonic /0191 -8141 (92)90068-8. Jaroszweski, E.T., 1969, New site of tectonic stylolites: Bul- Development of the Eastern Mediterranean Region: Wong, P.D., and Oldershaw, A., 1981, Burial cementation in letin de l’Académie Polonaise des Sciences, Série des Geological Society of London Special Publication 260, the Devonian, Kaybob Reef Complex, Alberta, Canada: Sciences Géologique et Géographique, v. 17, p. 17–23. p. 493–505, doi: 10.1144/GSL .SP .2006 .260 .01.20. Journal of Sedimentary Petrology, v. 51, p. 507–520. Karcz, Z., and Scholz, C.H., 2003, The fractal geometry of Pollard, D.D., and Segall, P., 1987, Theoretical displace- Woodward, N.B., 1999, Competitive macroscopic deforma- some stylolites from the Calcare Massiccio Formation, ments and stresses near fractures in rock: With ap- tion processes: Journal of Structural Geology, v. 21, Italy: Journal of Structural Geology, v. 25, p. 1301– plications to faults, joints, veins, dikes and solution p. 1209–1218, doi: 10.1016 /S0191 -8141 (99)00076-0. 1316, doi:10.1016 /S0191 -8141 (02)00173-6. surfaces, in Atkinson, B.K., ed., Fracture Mechanics of Koehn, D., 2011, Roughening of rocks: The growth of stylo- Rock: London, Academic Press, p. 277–349. SCIENCE EDITOR: CHRISTIAN KOEBERL lites, in Forster, M.A., and Fitz Gerald, J.D., eds., The Price, N.J., and Cosgrove, J.W., 1990, Analysis of Geologic ASSOCIATE EDITOR: STEFANO MAZZOLI Science of Microstructure—Part II: Journal of the Vir- Structures: Cambridge, UK, Cambridge University MANUSCRIPT RECEIVED 20 JULY 2013 tual Explorer, electronic edition, v. 38, paper 1, doi: Press, 502 p. REVISED MANUSCRIPT RECEIVED 23 OCTOBER 2013 10.3809 /jvirtex .2011 .00280. Railsback, L.B., 1993, Lithologic controls on morphology MANUSCRIPT ACCEPTED 13 DECEMBER 2013 Koehn, D., Renard, F., Toussaint, R., and Passchier, C.W., of pressure-dissolution surfaces (stylolites and disso- 2007, Growth of stylolite teeth patterns depending on lution seams) in Paleozoic rocks from the mideastern Printed in the USA

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