Himalayan-Bengal Model for Flysch Dispersal in the Appalachian-Ouachita System STEPHAN A. GRAHAM WILLIAM R. DICKINSON } Geology Department, Stanford University, Stanford, California 94305 RAYMOND V. INGERSOLL ABSTRACT INTRODUCTION still actively consuming oceanic lithosphere off Sumatra. We suggest that the Ouachita The relation of the modern Bengal subsea The tectonic relations of the late orogeny, during which the Ouachita system fan to the Cenozoic Himalayan suture belt Paleozoic Ouachita orogenic belt of the was thrust northward over the southern and the analogous relation of the Car- south-central United States are uncertain, flank of the continent, was caused by the boniferous Ouachita flysch to a presumed both to the Appalachian belt along regional close approach of an analogous arc-trench Paleozoic Appalachian suture belt suggest a strike to the east and to the continental system, whose remains lie buried now in the guiding principle of synorogenic sedimenta- margin across regional strike to the south. subsurface beneath Texas. Figure 1 shows tion. Most sediment shed from orogenic Plate tectonic interpretations of the Ap- the gross tectonic trends of the two regions highlands formed by continental collisions palachian and Cordilleran systems near the at the same scale. pours longitudinally through deltaic com- edges of the continent and of the Caribbean With available data, our interpretation is plexes into remnant ocean basins as turbi- region south of it have not dealt with the speculative but is compatible with current dites that are subsequently deformed and Ouachita question. Recent interpretations knowledge of the Ouachita and southern incorporated into the orogenic belts as col- of Ouachita tectonics rely upon a supposed Appalachian regions. If valid, our view has lision sutures lengthen. analogy with active continental margins, implications concerning the tectonic India first encountered a southern marked by either a marginal magmatic arc framework of the Caribbean region just Eurasian subduction zone near the end of of Andean type (Keller and Cebull, 1973) prior to the Mesozoic development of the Paleocene time. Northward movement of or a fringing island arc of Japanese type fac- Gulf of Mexico and the Antilles. From a India since Oligocene time choked the sub- ing away from the continent (Morris, broader standpoint, the concept that volu- duction zone, stifled the associated mag- 1974a, 1974b). In our view, however, the minous turbidites may be fed longitudinally matic arc, and created a suture complex of general lack of appropriate volcano- into narrowing ocean basins that close se- deformed Cretaceous flysch and younger plutonic complexes or their derivative quentially between colliding continents Tertiary molasse. Strata derived from the sedimentary sequences within the Ouachita may offer a general explanation for the resulting orogen include continental clastic region encourages the consideration of al- common occurrence of synorogenic flysch wedges shed southward toward India and ternative analogies. derived from the same orogenic belt into voluminous turbidites fed longitudinally We suggest a different interpretation by which it is incorporated by later deforma- through the Ganges-Brahmaputra Delta drawing a tectonic analogy between the tion (see also Dewey and Burke, 1974). into the Bay of Bengal. The eastern flank of Cenozoic Himalayas and the Bengal fan, on We first describe the Himalayan-Bengal the Bengal subsea fan is being subducted the one hand, and the Carboniferous Ap- events, discuss the Appalachian-Ouachita now beneath the still-active eastern exten- palachians and the Ouachita flysch on the events by analogy, and then comment on sion of the subduction zone. other. The Himalayas were formed by the the general implications of our interpreta- The sequential, north-to-south welding collision of India with Eurasia, and the final tion. For each of the two regions, we sum- of Europe and Africa to North America development of the southern Appalachian marize in order the general relations of (a) formed the complex Appalachian- system was marked by the collision of Af- oceanic closure by plate consumption be- Caledonide-Mauritanide suture belt, from rica with North America (Watkins, 1972). neath continental margin arcs, (b) de- which Taconic, Acadian, and Alleghanian The immense Bengal fan of turbidites and velopment of a suture belt along the orogen clastic wedges were shed toward the North associated oceanic strata is composed between colliding continents, (c) transverse American craton. Turbidites of the Car- mainly of detritus fed into the remaining dispersal of clastic wedges shed from the boniferous Ouachita flysch were fed lon- ocean basin east of India by the longitudi- collision orogen across an adjacent conti- gitudinally, as sediment supplied through nal drainage of the Himalayas and related nental block, (d) longitudinal dispersal of the Alleghanian clastic wedge, into a rem- highlands. We suggest that the Carbonifer- turbidites into a remnant ocean basin along nant ocean basin lying south of North ous clastic rocks, largely turbidites, of the tectonic strike from the collision orogen, America. The Ouachita system was then Ouachitas are composed mainly of detritus and (e) deformation of the turbidite flysch thrust northward across the continental fed into a remnant ocean basin south of by continued subduction along one flank of edge during arc-continent collision that North America by the longitudinal drain- the remnant ocean. Our arguments are progressed from east to west. Key words: age of highlands formed along the trend of based upon the implications of the tectonic historical geology, areal geology, tectonics, an Appalachian suture between Africa and setting of the modern Bengal fan, as de- sedimentation, flysch, Cenozoic, Car- North America. The flank of the Bengal fan scribed by Curray and Moore (1971). boniferous, Himalayas, Bengal fan, Ap- adjacent to southeast Asia has been partly However, we make no attempt to evaluate palachians, Ouachitas. subducted by an arc-trench system that is details they gathered subsequently on the Geological Society of America Bulletin, v. 86, p. 273-286, 6 figs., March 1975, Doc. no. 50301. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/86/3/273/3433347/i0016-7606-86-3-273.pdf by guest on 30 September 2021 274 GRAHAM AND OTHERS evolution of the Bay of Bengal and adjacent parts of the Indian Ocean floor (Moore and others, 1975; Curray and Moore, 1974), al- though our thinking has benefited from the general thrust of their oral presentations (see below). Powell and Conaghan (1973) also presented a detailed analysis of the structural evolution of the Himalayan ranges, to which the reader is referred for additional structural and stratigraphic in- formation. Our evaluation of published in- formation pertaining to the Ouachita re- gion is guided especially by the interpreta- tions of Morris (1974a, 1974b), which we supplemented by reconnaissance visits only. Figure 1. Main tectonic elements of Himalayan-Bengal (A) and Appalachian-Ouachita (B) regions. HIMALAYAN-BENGAL REGION Symbols: A. 1, Himalayan suture belt between India and Eurasia; 2, Main Boundary Fault (thrust) of Indian Ocean Floor Himalayan foothills; 3, Quaternary alluvium of Indus (I), Ganges (G), and Brahmaputra (B) river sys- tems; arrows denote channel trends on subsea Bengal fan with head near Ganges-Brahmaputra Delta The Indian Ocean basin has formed since (GBD); 4, Indoburman-Sunda subduction zone, dashed where inactive; 5, melanges and deformed the end of the Paleozoic Era, and mainly flyschoid rocks of Indoburman ranges (IBR), Andaman (A)-Nicobar (N) insular ridge, and Mentawai since the beginning of the Creta- (M) Islands off Sumatra (S); 6, schematic margin of extensional Andaman basin (AB); dashed line is ceous, from the breakup of Gondwana and 1,000-m isobath of continental slope off India. the dispersal of the continental fragments B. 1, Complex belt of multiple Paleozoic suturing between North American and West African era- derived from it. Their initial configuration tons shown joined (E is Europe) prior to Mesozoic opening of the Atlantic Ocean approximately along the stitched line; 2, fronts of foreland fold-thrust belts of Appalachian Valley and Ridge province within intact Gondwana (Fig. 2A) has been (American side) and Mauritanides (African side); 3, coarse Carboniferous clastics, terrestrial and lit- inferred within close limits from the com- toral, of Appalachian (A) and Dlinois (I) basins; 4, frontal thrusts and folds of Ouachita system; 5, puter fitting of continental margins (Sproll outcrop and known subcrop of Ouachita system; 6, schematic extensional margin of Mesozoic(?) Gulf and Dietz, 1969; Smith and Hallam, 1970; of Mexico (present position of Cuba shown in dotted outline). Dietz and Sproll, 1970). Paleomagnetic data compiled by McElhinny (1970) are compatible with the information from that obscures detailed relations. It is unclear compatible with the assembly shown, al- JOIDES Legs 22, 26, and 27 that the sea whether the crustal segment that first met though Tarling (1972) used similar data to floor of the Wharton Basin west of Aus- Eurasia was firmly attached to India at the support a slightly different reconstruction. tralia is nowhere significantly older than time or was a detached microcontinental A recent analysis of marine magnetic Cretaceous (Scientific staff, 1972, 1973a, fragment now caught up within the anomalies