Sedimentation and subsidence patterns in the central and north basins of Lake Baikal from seismic stratigraphy T. C. Moore Jr.* Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1063 K. D. Klitgord U.S. Geological Survey, 3475 Deer Creek Road, Palo Alto, California 94304 A. J. Golmshtok Shirshov Institute of Oceanology, Southern Branch, Gelendzhik, Russia E. Weber Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1063 ABSTRACT INTRODUCTION basins and for the thick accumulation of sedi- ments on Academic Ridge. These stratigraphies, Comparison of sedimentation patterns, The Baikal rift system has developed during developed within each of these three regions, are basement subsidence, and faulting histories in the past 30–40 Ma along the transtensional then tentatively correlated on the basis of similar- the north and central basins of Lake Baikal boundary between the Siberian craton and a mo- ities in reflection patterns and depositional aids in developing an interbasinal seismic saic of microplates to the southeast (Fig. 1, inset; geometries. Calculated geologic histories of the stratigraphy that reveals the early synrift evo- Molnar and Tapponnier, 1975; Logatchev and three regions, along with the relative offset his- lution of the central portion of the Baikal rift, Florensov, 1978; Tapponnier and Molnar, 1979; tory on faults within these regions, are used to a major continental rift system. Although Zonenshain and Savostin, 1981). This zone of support and refine the initial interregional corre- there is evidence that the central and northern continental rifting formed along a long-lived lation. The combination of these three regions rift basins evolved at approximately the same plate boundary that was the locus of a major col- into a coherent stratigraphic model for this part of time, their sedimentation histories are mark- lisional orogen during the Paleozoic and Meso- the Baikal rift is used to map the development of edly different. Primary sediment sources for zoic (Zonenshain et al., 1990; Mats, 1993), fol- sediment fill in the early phase of basin subsi- the initial rift phase were from the east flank of lowed by a more quiescent period during the late dence and to examine the changes in the tectonic the rift; two major deltas developed adjacent Mesozoic and early Tertiary. Extensive seismicity environment that create gross cyclic patterns in to the central basin: the Selenga delta at the and numerous earthquakes with magnitudes >5.0 synrift deposition systems. We map two seismic south end and the Barguzin delta at the north over the past 50 yr are prominent evidence that the sequences in this study: (1) the oldest mappable end. The Barguzin River system, located at the rift is active today (Zonenshain and Savostin, sequence, which illustrates the extent and inter- accommodation zone between the central and 1981; Golonetsky, 1990; Doser, 1991a, 1991b). basinal variation of initial basin subsidence; and north basins, also fed into the southern part of High heat flow, Holocene volcanism, and signifi- (2) a distinctive prograding unit, which occurs the north basin and facilitated the strati- cant historical surface deformation are also associ- near the end of the first phase of tectonic subsi- graphic linkage of the two basins. ated with this active rift zone (Lysak, 1978; Crane dence and illustrates the pattern of basin fill just A shift in the regional tectonic environment et al., 1991; Sherman, 1992; Mats, 1993). prior to the second phase of basin subsidence. in the mid Pliocene(?) created a second rift Although small rift basins are found along the This work illustrates both the power and the po- phase distinguished by more rapid subsidence entire 2000 km length of the rift system, three tential pitfalls in developing a geologic history of and sediment accumulation in the north basin major rift basins developed within the central basin development based solely on studies from and by increased subsidence and extensive zone of the rift and form the present-day Lake around the margins of a basin and a seismic strati- faulting in the central basin. The Barguzin Baikal (Logatchev and Florensov, 1978). Multi- graphic analysis of the basins. It provides those delta ceased formation and parts of the old channel seismic-reflection profiling has provided who sample the study area by drilling a seismic delta system were isolated within the north high-resolution, moderate-penetration seismic- stratigraphic framework within each interpreted basin and on Academic Ridge. These isolated reflection records of the entire synrift sedimen- region and a testable hypothesis of basin history deltaic deposits provide a model for the devel- tary packet and the fault systems that deform for the study area as a whole. By detailing the opment of hydrocarbon plays within ancient these sediments (Hutchinson et al., 1992a; Klit- steps taken and assumptions made in developing rift systems. In this second tectonic phase, the gord et al., 1993a; Scholz et al., 1993). In addi- our stratigraphic model, we provide a guide for dominant sediment fill in the deeper and more tion to developing a seismic stratigraphic base the location of a limited number of drill sites to ef- rapidly subsiding north basin shifted from the and identifying fault systems, these data provide ficiently test this hypothesis; and in illustrating our flexural (eastern) margin to axial transport the first opportunity to identify, on a regional ba- geologic interpretation of the seismic facies, we from the Upper Angara River at the north end sis, the seismic facies of the Baikal rift. provide a prediction of the likely geologic facies of the basin. In this paper we develop a detailed strati- to be encountered in different locations and at dif- graphic framework for the central and north ferent depths within the study area. *E-mail: [email protected] GSA Bulletin; June 1997; v. 109; no. 6; p. 746–766; 16 figures, 1 table. 746 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/6/746/3382768/i0016-7606-109-6-746.pdf by guest on 29 September 2021 SEISMIC STRATIGRAPHY OF LAKE BAIKAL BASINS 56° N 75 E 105 E 135 E 75 N North Coastline American Plate Kichersky Fault Tectonic Boundary Relative Movements Eurasian Plate 60 N Lake Baikal Amurian Plate 45 N Pacific Plate Baikalsky Fault Chinese 30 N Indian Plate North Basin Plate Philippine Plate Figure 1. Location of Lake Bai- 15 N 54° N kal showing the major boundary faults, rivers, and the study area. 0 500m Inset shows the location of the lake within the Baikal rift and the Barguzin R. associated microplates that sur- round its boundaries (modified after Zonenshain and Savostin, Olkhon Is. Central Basin 1981). Primorsky Fault 1500m Study Area Morskiy Fault 1000m 500m Angara R. Irkutsk 500m Obruchevsky Fault Selenga R. Main Sayan Fault Ulan-Ude 52° N 1000m South Basin 0 100 km 104° N 106° N 108° N 110° N GEOLOGIC FRAMEWORK OF three lake basins: the present Selenga delta and the borehole data (Zamaraev and Samosonov, 1959), LAKE BAIKAL ancient Barguzin delta. Sediment transport down a suite of shallow boreholes along the shores of the Upper Angara River through a maze of small the lake, and outcrop studies. Synrift sedimentary The three deep-water basins of Lake Baikal rift basins and into the northern end of the north units are dominantly lacustrine and alluvial- (Fig. 1) are underlain by thick accumulations of basin is the other significant source of synrift fill lacustrine deposits (Mats, 1993). On the basis of Neogene synrift sediments (as much as 8 km) and active at present. Numerous smaller fan systems erosional unconformities (weathering crusts) are bound by major western border faults (Lo- have developed along the entire eastern margin of identified in these sections, the sedimentary fill gatchev and Florensov, 1978; Hutchinson et al., the lake (the hanging wall or flexural side of the has been divided into two primary synrift units 1992a). Basement ridges that form the sills be- basins) and a smaller number of fans have sources (Logatchev and Zorin, 1987; Mats, 1993): an early tween these basins are fault controlled and link the in the footwall side of the rift, and provide addi- rift phase (uppermost Oligocene to mid-Pliocene) fault systems between the different rift basins. tional fill (e.g., Logatchev and Florensov, 1978; and a second rift phase (mid-Pliocene to present). Principal sediment sources for the lake basins are Mats, 1993). The lake empties from the south This second rift phase has been subdivided into from the eastern side and northern end of the lake. basin into the Arctic Ocean via the Angara River. two episodes on the basis of depositional and Major sediment transport down the Barguzin and A provisional Neogene stratigraphic history for faulting patterns recorded in multichannel seismic Selenga river systems has created large delta com- the entire lake was developed by Mats (1993) on data (Hutchinson et al., 1992a) and onshore field plexes at the accommodation zones separating the the basis of limited hydrocarbon exploratory studies (Agar and Klitgord, 1995). Geological Society of America Bulletin, June 1997 747 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/6/746/3382768/i0016-7606-109-6-746.pdf by guest on 29 September 2021 MOORE ET AL. The central basin contains the deepest parts of Track Lines Study Area Lake Baikal (in excess of 1600 m water depth). To B 1992 A 1 the west is the low-lying Ol’khon Peninsula, - 1989 5 1 - Ol’khon Island, and Academic Ridge; the eastern 9 Interpretation 89-15-1AB8 shore consists of a zone of low ridges and basins. I Interpretation regions Much like the south and north basins, the central Regional boundaries basin is of a general half-graben form; the main in Jump ties between regions s a boundary fault (the Morskiy fault, Fig.