Sedimentation processes and new age constraints on rifting stages in Lake Baikal: results of deep-water drilling

Abstract

With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features. The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96 boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole, B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact. The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary strata of Northern Baikal (1.5-1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60-70 cm/ka. The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07-1.31 Ma, a date which exceeds the age of previous geological models.

Quaternary Sedimentation and Subsidence History of Lake Baikal, Siberia, Based on Seismic Stratigraphy and Coring

“…However, independent age estimates by a variety of analytical methods and paleomagnetic stratigraphy for the drill-hole sediments suggest that the true age of the base of the core is about 0.66 Ma (Kuzmin et al 2000). Our RSRM estimate for the age of the base of the draped unit (top of the prograding units) on the Selenga Delta is 0.65 Ma (Table 1).…”

“…11). Continuous, slow sedimentation on this part of the ridge has been confirmed by piston cores (Peck et al 1994;Colman et al 1995;Edgington et al 1996) and drill cores (BDP Members 1997b; Kuzmin et al 2000). These sediments consist of alternating diatomaceous muds and barren glacial clays, corresponding to interglacial and glacial periods, respectively (Granina et al 1993;Colman et al 1995;Wil- liams et al 1997).…”

“…Some of the cores have been studied for paleoclimate proxies and chronology (e.g., Peck et al 1994;Colman et al 1995;Edgington et al 1996;Williams et al 1997;Kuzmin et al 2000), but only limited use of the core and seismic-reflection data has been made for other purposes, such as description of selected turbidite depositional features (Nelson et al 1999). …”

“…Scholz and Hutchinson (2000) also traced the seismic reflection associated with the base of the draped unit through their multichannel seismic data to 82 m depth in the BDP93 drill hole. If this correlation is correct, then both of the RSRM estimates are likely too old, because the age of the base of BDP93 at 102.27 m is estimated to be 0.66 Ma (Kuzmin et al 2000).…”

“…Although these horizons cannot be physically traced from the North Basin up onto Academician Ridge, Moore et al (1997) correlated them to horizons on a seismic line passing through the BDP96 drill site, on the basis of seismic character and sequence. Kuzmin et al (2000) calculated that the B10 horizon occurs at a depth of about 104 m at BDP96 and that it corresponds to an age of about 2.5 Ma. They found a lithologic change at that depth but no hiatus or evidence of erosion; they thus questioned whether horizon B10 is an unconformity.…”