ORBITALLY FORCED SEDIMENTARY RHYTHMS IN THE STRATIGRAPHIC RECORD: IS THERE ROOM FOR TIDAL FORCING?
Poppe L. de Boer and João Trabucho Alexandre
The imprint of orbital cycles, which result from the varying eccentricity of the Earth’s orbit and changes in the... more
The imprint of orbital cycles, which result from the varying eccentricity of the Earth’s orbit and changes in the orientation of its axis have been recognised throughout the Phanerozoic rock record. Variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions. Common oceanographic principles, however, show that also the ocean tide responds to variations in the orbital parameters. The ocean tide has not yet been considered to be a valid, additional transfer mechanism for the orbital variations. In geological studies of Milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations, and the role of long-term variations of the ocean tide has not yet been appreciated. Variations in the ocean tide, related to changing eccentricity (at present 0.0165, theoretical maximum 0.0728), affect a variety of oceanographic and sedimentary processes. In addition to the widely accepted paradigm of orbitally forced insolation changes, the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing, organic productivity and tidal processes in shallow seas and deep water. Variations of the ocean tide in relation to the 18.6 year lunar nodal cycle, which has no insolation counterpart by which they may be diluted, indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide. In analogy with the 18.6 year lunar nodal cycle, orbital variations of the tide on Milankovitch timescales are likely to have affected sedimentary systems in the past.
Models and paradigms often drive the analysis and interpretation of data (Miall, 2004; Miall & Miall, 2004). It is common practice that, once astronomical cycles in the fossil sedimentary record have been (statistically) demonstrated, theory-laden observations lead to satisfactory explanations of such cycles in terms of insolation-induced variations of climate, oceanography and sea-level (cf. de Boer & Smith, 1994a; D’Argenio et al., 2004). However, the astronomical variables, eccentricity, obliquity and precession also influence the ocean tide, in phase, and with an identical frequency to that of insolation. These orbitally forced variations of the ocean tide must also produce signals in the sedimentary record.
Coastal spreading of olivine to control atmospheric CO2 concentrations: A critical analysis of viability. Comment: Nature and laboratory models are different
R.D. Schuiling, P.L. de Boer (2010)
International Journal of Greenhouse Gas Control 4 855–856
Olivine weathering is a natural process that takes time, years to decades when applied to suitable environments.... more Olivine weathering is a natural process that takes time, years to decades when applied to suitable environments. Contrary to CCS, the effect is not instantaneous, but in the course of the coming decades in which society will continue to produce CO2 and to be threatened by continued greenhouse warming, the annual addition of large volumes of olivine to suitable environments will counteract the rise of CO2 level of the atmosphere and the acidification of ocean waters.
128 views
Seen by:Mechanical effects of micro-organisms on intertidal bedform migration
P.L. de Boer (1981) Mechanical effects of micro-organisms on intertidal bedform migration. Sedimentology 28, 129–132
Attention is called to the ability of bottom-dwelling micro-organisms such as algae to stabilise sandy sediment... more Attention is called to the ability of bottom-dwelling micro-organisms such as algae to stabilise sandy sediment surfaces in non-carbonate environments and to influence sand transport.
54 views
Seen by:Convolute lamination in modern sands of the estuary of the Oosterschelde, the Netherlands, formed as the result of entrapped air
Sedimentology Volume 26, Issue 2, pages 283–294, April 1979
Soft-sediment deformation structures similar to convolute lamination were found at the sandy rim of an intertidal... more
Soft-sediment deformation structures similar to convolute lamination were found at the sandy rim of an intertidal shoal in the Oosterschelde estuary, the Netherlands. Abundant air filled cavities within upward penetrated domes suggest that reversed density stratification resulting from trapped air in some sand layers plays a role in the deformational process.
Field observations show that air-filled cavities are formed within fine-grained sand; at rising tide the ground water level does not rise quickly enough to replace the interstitial air before flood water covers the sediment surface. Thus, air is trapped in the sand between the ground water level and the sediment-water interface. Because of the weight of the overlying water column and the slow downward movement of water due to capillary action, the entrapped air is compressed and eventually may attain a pressure which enables it to lift the overlying sediment. At this time bubbles are formed, often to a depth of 20 cm. Observation and experiments show that, in layers of fine sand, bubbles develop preferentially in better sorted and coarser zones. This is probably because capillary forces are greater in finer-grained and less sorted sand. Thus, water will penetrate by preference into the latter, pressing the interstitial air into the better sorted and coarser sand. The high content of air cavities in certain layers then provides the density instability responsible for the deformational process leading to the formation of convolute lamination. In the intertidal zone this appears to be a slow process that covers a number of ebb and flood cycles.
Convolute lamination has been described from a number of ancient sandstones that are thought to have been deposited in shallow water, near-shore environments. In many of these cases sand size compares with that found in the Oosterschelde. Air entrapment might have played a role in the formation of certain of these occurrences of convolute lamination.
Key words: convolute bedding, convolute lamination, cavernous sand, tidal, intertidal, beach, porosity, sand, air bubbles, soft sediment deformation, intertidal shoals
106 views
Seen by:Ebb-tidal delta deposits along the west Frisian Islands (The Netherlands): process, facies, architecture, and preservation
L.P. Sha & P.L. de Boer (1991)
Clastic Tidal Sedimentology; Can. Soc. Petrol. Geol. Mem. 16, 199-218
The morphologies of the ebb-tidal deltas of Texel, Terschelling and Ameland inlets and the resulting sand transport... more The morphologies of the ebb-tidal deltas of Texel, Terschelling and Ameland inlets and the resulting sand transport patterns are greatly influenced by the interaction of shore-parallel tidal currents with tidal currents through the inlets. These three inlets and their ebb-tidal deltas are similar in many aspects, and together they differ from North American Atlantic coast examples and from those of the East Frisian Islands. Sedimentary facies and sequences, and sand body geometry of these three inlets/ebb-tidal deltas are strongly controlled by this interaction of offshore tidal currents, tidal currents through the inlets, and waves. The interaction and relative strength of both tidal current systems determine the flow patterns and and orientations of the main ebb channels in the ebb-tidal deltas. Different orientations of (asymmetrical) ebb-tidal deltas as compared to those along the East Frisian Islands and the U.S. east coast, as well as a change of the general orientation of the main ebb channel of the ebb-tidal delta of Texel Inlet since the 16th century, are related to differences and changes in the relative importance of tidal currents and waves. Waves and longshore drift tend to force the ebb-tidal delta into an updrift asymmetry. Under the present regime of waves and longshore drift in this area, the critical boundary between updrift and downdrift asymmetry appears to be at a tidal prism on the order of 500 . 10^6 m^3. The volume of ebb-tidal delta sand bodies is approximately 1 km^3 (Texel), a considerable part of which can be preserved in the fossil record. Holocene deposits off the West Frisian Islands indeed show that preservation of ebb-tidal delta deposits during a rise of relative sea level is possible under certain conditions. The strength of tidal influence is of great importance for for determining both the basal boundary and the seaward extent of the ebb-tidal delta systems. Thus, it is inferred that preservation potential of ebb-tidal delta deposits can be positively correlated with the relative dominance of ebb-tides during their formation.
46 views
Seen by:Development and Preservation of a Mid-Holocene Tidal-Channel Network Offshore the Western Netherlands
Ruben Rieu, Sytze van Heteren, Ad J.F. van der Spek and Poppe L. de Boer (2005)
Journal of Sedimentary Research 75, 409-419
Recently obtained high-resolution seismic records, collected offshore the western Netherlands in a kilometer-size grid... more Recently obtained high-resolution seismic records, collected offshore the western Netherlands in a kilometer-size grid across the lower shoreface and inner shelf, suggest the presence of a dense, previously unknown network of tidal-channel fills in the shallow subsurface of the North Sea. Seven channel fills constituting this network were analyzed in detail to infer relationships among the fills in time and space, and to identify factors governing channel development and tidal-basin evolution. The majority of the channels are oriented perpendicular to the coast, but parts of some have a strong coast-parallel component. Shell associations and sedimentological characteristics in most channel fills are typical of back-barrier depositional environments. All but one of the channel fills are part of an Atlantic-age tidal-channel system, draining a tidal basin protected by barrier islands. One channel fill, which is correlated to an incision recognized onshore, represents a younger phase in coastal development. The presumed barrier-island chain was positioned at least 12 km seaward of the present coastline in the northern part of the study area, and at least 6 km seaward of the present coastline in the southern part. The tidal channels grew and migrated actively before partially being filled in between 7300 14C yr BP and 5500 14C yr BP, reflecting an initial tidal-prism increase followed by a substantial decrease. The tidal-prism increase was governed by an upsurge of the tidal amplitude between 8000 14C yr BP and 7000 14C yr BP, and the subsequent decrease by a gradual decrease in the rate of sea-level rise. Rapid retrogradation of the coastline put a sudden end to the existence of the tidal basin. The ensuing shoreface erosion removed all but the deepest parts of the channel fills, which do not show any evidence of systematic landward migration. This field observation corroborates recent modeling results suggesting that rapidly rising sea level may create the conditions necessary for overstepping of sandy barriers.
The 18.6 yr nodal cycle and its impact on tidal sedimentation
A.P. Oost, H. de Haas, F. IJnsen, J.M. van den Boogert and P.L. de Boer (1993)
Sedimentary Geology 87, 1-11
The 18.6 yr nodal cycle modulates tidal amplitudes and currents, and consequently sedimentation in tide-influenced... more The 18.6 yr nodal cycle modulates tidal amplitudes and currents, and consequently sedimentation in tide-influenced sedimentary environments. Data are presented which show that such effects are obvious along the coast of the Dutch barrier islands and in the sedimentary fill of abandoned channels.
Sedimentary Geology of the Palaeoarchaean Buck Ridge (South Africa) and Kittys Gap (Western Australia) Volcano-Sedimentary Complexes
Sjoukje T. de Vries, Wouter Nijman, Poppe L. de Boer (2010)
Precambrian Research 183, 749–769
The two Palaeoarchaean volcano-sedimentary complexes of the Buck Ridge (Barberton Greenstone Belt, South Africa) and... more
The two Palaeoarchaean volcano-sedimentary complexes of the Buck Ridge (Barberton Greenstone Belt, South Africa) and Kittys Gap (Coppin Gap Greenstone Belt, East Pilbara, Australia) have a similar geological setting and age (∼3.45 Ga). The predominantly volcaniclastic sediments are concentrated at the top of these complexes, and experienced thorough, (very) early diagenetic silicification. In many places the silicification process has led to excellent preservation of the primary sedimentary structures. Elsewhere it has resulted in their obliteration or replacement by diagenetic structures. The Buck Ridge chert forms a regressive-transgressive succession, deposited around base level, with lacustrine and littoral marine facies. Deposition of the Kittys Gap Chert was also close to base level, almost exclusively subaqueous, with tidal influence and a regressive sequential trend.
In both volcano-sedimentary complexes, these low-energy sediments are juxtaposed with high-energy breccia pods and layers, with often a high Fe-oxide content. The breccias are interpreted as being the result of explosive hydrothermal activity. Sedimentation was strongly controlled by normal faulting.

