Tide-influenced sedimentary systems

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.

The Barren Measures Formation (middle Permian, ~271e260 Ma), the non-coaliferous lithounit sandwitched
between two major coal-bearing formations in the Indian Lower Gondwana succession, was
earlier interpreted as continental fluvio-lacustrine deposits. The present contribution documents sedimentary
attributes of marginal marine tideewave interference from the Barren Measures Formation of
eastern peninsular India, exposed along the Bokaro River section, West Bokaro Coalfield, Jharkhand.
Tidalites, including various tidal bundle sequences with frequent reactivation surfaces (velocity asymmetry)
and single/double mud drapes (pause planes), systematic arrangement of tidal beddings (flaser,
wavy, lenticular) and tidal rhythmites with alternate sand-dominated and mud-dominated planelaminated
units, manifest sedimentation by open marine springeneapespring tidal cycles under diurnal
inequalities in a semi-diurnal tidal system. The architecture of tidalites attests to sedimentation in
shallow subtidal to intertidal flat facies, affected by intermittent strong to week reworking by open
marine waves/storms. Wave reworking is manifested by wave ripples, combined-flow ripples and wavegenerated
tidal bundles. Their coexistence and gradation with tidalites indicate low-energy wave/storm
interference with tidal currents in a sheltered, tide-dominated estuary, especially on tidal flats along
estuary channel banks. Overall fining-up facies sequence, upward increase of prodeltaic mud over tide
ewave led sediments, signify a sustained transgressive phase onlaping the estuary system in eastern
peninsular India during middle Permian (Guadalupian).

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.

Tidalites are preserved within a metavolcano-sedimentary succession of the Late Archaean BababudanGroup (Dharwar Supergroup) along the western boundary of the NNW-SSE trending Chitradurga green-stone belt, West Dharwar Craton, southern India. These may represent the oldest record of tidal processesin peninsular India. Millimetre thick sand–mud alternations, bidirectional cross-strata, mudstone-drapedsandy foresets, reactivation surfaces indicating time–velocity asymmetry, sigmoidal cross-strata andmudstone draped flaser/lenticular bedding are displayed by the sandstone mudstone heterolithic faciesin the upper part of the Bababudan succession, together implying a tidal depositional system. Thick–thinpairs of rhythmic foreset bundles correspond to neap–spring tidal cycles within a semidiurnal tidal sys-tem. Development of the studied coastal sediments suggests formation of stable platform along thewestern margin of the late Archaean Chitradurga greenstone belt.

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.

Situated on the western edge of the Ganga-Brahmaputra delta and Sundarban wetlands, the macrotidal and flood-dominated Hugli is the largest estuary of eastern India. To study supratidal evolution of its islands and margins during the 20th century, five series of maps and images—pertaining to 1904-05, 1922-32, 1942 (partial coverage), 1967-69 and 2001—were used. The available materials were georeferenced and layered for digitisation of high water line (HWL). Use of Global Positioning Survey, in differential mode, was made to collect Ground Control Points and delineation of HWL from outer islands and selected stretches of the coast.
The results show that the estuary gained 17.63 km² of supratidal area at the rate of 117 ha yr-­­¹ during 1904-05–1922-32, lost 64.66 km² at the rate of 147.04 ha yr-­­¹ during 1922-32–1967-69 and again augmented 6.49 km² at the nominal rate of 19.67 ha yr-­­¹ between 1967-69 and 2001. The inner islands of the estuary somewhat followed this trend by exhibiting ‘rapid accretion–slow erosion–slow accretion’. Response of the estuary margins and the outer islands were ‘slow erosion–rapid erosion–slow erosion’ and ‘slow accretion–slow accretion–slow erosion’ respectively. Evolution of the inner islands largely controlled the evolution of the supratidal estuary as a whole. The accretion-erosion phases of the islands situated on the tidal sand ridges probably operate on 50 to 100 year cycles. Total number of islands fluctuated between 10 and 12 during the century.
The observed patterns are conformable to the regional trend of erosion at the seafaring areas and accretion in the interior areas of the Sundarban. Within the estuary, disruption of morphological equilibrium due to marginal embanking and reworking of sediments because of oscillations in thalwegs & tidal sand ridges—all contributed to the change.

Sandstone/siltstone-mudstone interbedded facies of the Permo-Carboniferous Talchir formation, Gondwana Supergroup, is exposed in the Raniganj Basin and records the activities of tidal currents in a terminoglacial, storm-influenced shallow marine setting. Tidal bundles of various types with pause plane drapes, evidence of time-velocity asymmetry and rare bidirectional current flow patterns are indicative of tidal activity. Chance preservation of such structures from storm reworking might have occurred due to dampening of storm waves on the lowgradient muddy substrate of the tidal flat. The tide-generated stratifications are draped by over-thickened muddy-siltstone with wavy/hummocky laminations. Increased suspended sediment concentrations following a storm yielded such thick mudstone drapes. Thin beds containing tidal structures indicate poor sediment supply in a blind tidal embayment. q

""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. 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. 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."

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.

Numerous palaeoenvironmental and archaeological studies from southern Arabia (Yemen and Oman) have revealed strong relations between phases of human settlements and climate change linked to the Indian monsoon system. Analyses on speleothems, cave fills, lacustrine deposits and palaeo-mangroves have shown that during the Early to Mid-Holocene, a humid Optimum culminated around 9000e8000 cal BP. New results on inland speleothems and cave sediments from the Jebel Qara (southern Oman) are crucial in our depiction of Early and Mid-Holocene climatic evolution and cultural dynamics of the region. These aspects are discussed here, based on new archaeological surveys, excavations, geoarchaeological and micromorphological studies, aiming to better understand connections with Terminal Pleistocene and Early Holocene autochthonous cultures of southern Arabia. Our results suggest that the final Pleistocene was marked by strong aridity, which promoted a widespread thermoclastism within rock shelter and deposition of aeolian sand; in contrast, the transition towards the Holocene is marked (since c.12,000 cal BP) by a progressive increasing in environmental humidity, which permitted the formation of thick strata of peridesert loess. After this phase, the environmental humidity of the Jebel increased and permitted the existence of a large community of land snails; the latter were exploited by Early Holocene hunteregatherers who lived in the rock shelters between c. 10,500e9500 cal BP and left consistent accumulations of land shells (escargoti eres). The maximum of Holocene humidity was reached between 9000 and 8000 cal BP; regional aquifer were recharged and the deposition of calcareous tufa at the entrance of caves started, lasting up to c. 4500 cal BP. C and O stable isotopes from calcareous tufa highlights, in accordance with several regional records, the progressive decline of the intensity of the Indian Ocean monsoon and the transition towards arid conditions. In this phase, the area was abandoned and archaeological communities possibly relocated along the coast of central and southern Oman, where they exploited the mangrove environment.