Coastal Stratigraphy Research Articles

Synthesizing Shallow‐Water Geophysical Data for Shoreline Evolution Models: Shallow Coastal Stratigraphy Workshop; Conway, South Carolina, 9–10 July 2008

Numerous regional geophysical mapping efforts have taken place along the mid‐Atlantic coast over the past 20 years, illuminating the relationship between relict geology and coastal processes. Results have demonstrated that variability in the structural framework of the coastal plain is important in controlling regional‐scale shoreline evolution and sediment availability. Furthermore, variations in the geologic character (grain size, consolidation, composition, morphology, etc.) of the shelf and nearshore have been linked to long‐term (centennial and greater) and short‐term (decadal to centennial) shoreline evolution. Despite these spatial relationships, little information regarding the variability of geologic properties is accounted for in numerical models of shoreline change, leading to outputs that do not accurately characterize natural and human‐induced shoreline behavior.

Geoarchaeology of Beirut's ancient harbour, Phoenicia

This paper presents geoarchaeological results from the ancient harbour of Beirut (Lebanon). As at Sidon, knowledge of Beirut's ancient tell has advanced significantly over the past decade, thanks namely to redevelopment of the city centre and excavations centred on the modern port. In spite of this research, understanding of the city's coastal palaeoenvironments during antiquity is poor. Buried Iron Age harbourworks presently 300 m from the sea attest to pronounced coastal changes during the past 3000 years. These processes have been significantly accentuated during the last two centuries by redevelopment of the port, which remains in use some 5000 years after its foundation. Here we elucidate the coastal stratigraphy east and west of the Bronze Age tell to yield new insights into the evolution of the Beirut seaboard, in addition to the complex history of human–environment interactions. These chronostratigraphic data are subsequently used to (1) precisely locate the main anchorage haven during antiquity; and (2) propose a chronology for its evolution.

Ancient Tyre and its harbours: 5000 years of human-environment interactions

The exact location and evolution of Tyre's ancient harbour areas have been matters of scholarly conjecture since the 16th century. Here, we use geoscience techniques to precisely relocate the ancient northern harbour, the city's principal transport hub during antiquity, and reconstruct its geomorphological evolution (Marriner, N., Morhange, C., Boudagher-Fadel, M., Bourcier, M., Carbonel, P., 2005. Geoarchaeology of Tyre's ancient northern harbour, Phoenicia. Journal of Archaeological Science 32, 1302–1327.). While a natural anchorage is inferred during the Bronze Age, we expound the increasing weight of anthropogenic forcings from the Iron Age onwards, culminating in a technological apogee during the Byzantine period (Hohlfelder, R.L., 1997. Building harbours in the early Byzantine era: the persistence of Roman technology. Byzantinische Forschungen Internationale Zeitschrift für Byzantinistik 24, 367–389.). Using coastal stratigraphy and underwater archaeological data (El Amouri, M., El Helou, M., Marquet, M., Noureddine, I., Seco Alvarez, M., 2005. Mission d'expertise archéologique du port sud de Tyr, sud Liban: résultats preliminaries. Bulletin d'Archéologie et d'Architecture Libanaises, Hors-Série 2, 91–110; Frost, H., Recent observations on the submerged harbour works at Tyre. Bulletin du Musée de Beyrouth 24, 103–111; Noureddine, I., Helou, M., 2005. Underwater archaeological survey in the northern harbour at Tyre. Bulletin d'Archéologie et d'Architecture Libanaises, Hors-Série 2, 111–128) we demonstrate that Poidebard's (1939. Un grand port disparu, Tyr. Recherches aériennes et sous-marines, 1934–1936, Librairie Orientaliste Paul Geuthner, Paris) Egyptian harbour is in reality a drowned quarter of the ancient city. Informed hypotheses are proposed for a possible second anchorage at Tyre, and it is demonstrated that presently drowned portions of the sandstone ridge served as outer harbours during the Bronze and Iron Ages. Stratigraphic data in the vicinity of Tell Mashuk, Chawakir and Rachidiye are also presented and discussed.

Recurrence of postseismic coastal uplift, Kuril subduction zone, Japan

Coastal stratigraphy of eastern Hokkaido indicates that decimeters of coastal uplift occurred repeatedly in the late Holocene. Employing radiocarbon dating and tephrochronology, we identify along a 100 km length of the Kuril subduction zone six uplift events since ∼2,800 years B.P. Uplift events occur at the same frequency as unusually high tsunamis. Each coastal uplift event, which occurs on average every 500 years, is the product of decade‐long post seismic deep slip on the down dip extension of the seismogenic plate boundary following an offshore multi‐segment earthquake that generates unusually high tsunamis.

The ‘Ancient Harbour Parasequence’: Anthropogenic forcing of the stratigraphic highstand record

Unique chronostratigraphic similarities are observed in recent geoscience literature on ancient Mediterranean harbours. From these empirical port data a clear pattern of millennial anthropogenic forcing, marked by a fining-up sequence, can be discerned in coastal stratigraphy. The stratigraphic peculiarity of this artificial, or human-modified, parasequence leads us to define a new working model: the Ancient Harbour Parasequence.

Early Holocene history of the Baltic Sea, as reflected in coastal sediments in Blekinge, southeastern Sweden

Integrated palaeoecological studies of two fiord sediment sequences in the province of Blekinge, SE Sweden, covering the time span 11,000–5000 cal BP, reveal the timing and the environment for the Ancylus Lake/Littorina Sea transition 9800–8500 cal BP. The first ingression of saline water into the Baltic Sea through the Danish Straits occurred earlier than formerly assumed. New evidence, particularly mineral magnetic and palaeobotanical analyses, demonstrate that on the general trend of the eustatically caused Littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years BP. A distinct regression phase around 8100 cal BP is correlated with the Greenland ice-core cold event dated to 8200 ice-core years BP. This is described as a regional climatic catastrophe for the Baltic Sea region. The coastal stratigraphy is compared with the offshore stratigraphy earlier studied. A tentative shore displacement curve for Early and Middle Holocene is presented.

Holocene Coastal Stratigraphy and the Sedimentary Development of the Hai Phong Area of the Bac Bo Plain (Red River Delta), Vietnam

We report a study of the Holocene coastal sediments of the Hai Phong area of the Bac Bo Plain (also known as the Red River Delta) in northern Vietnam. This is the first attempt to interpret the region's coastal depositional environments in the light of a geological model of Holocene environmental change recognising the interacting roles of Holocene sea-level change, alluvial responses to sea-level fluctuation, and tidal environment sedimentation. The coastal sediments overlie a Pleistocene land surface, and represent the Holocene marine transgression and regression. Prior to c .6000 bp , the sea rose to around or above its present elevation, converting the Pleistocene terrestrial landscape to a Holocene tidal landscape of tidal flat, channel and mangrove environments. Sea-level lowering by c .4000 bp triggered a switch in dominant sedimentary processes, allowing floodplain sediments to be deposited increasingly seawards.

Pleistocene coastal stratigraphy, sea‐level highstands and neotectonism of the southern Australian passive continental margin—a review

AbstractLocated in a tectonically stable, intraplate setting and in the far field of former ice sheets, the southern Australian passive continental margin represents a globally important region for quantifying sea level during Pleistocene highstands. The stratigraphical record of the southern Australian margin is dominated by geographically extensive coastal barrier, estuarine and peritidal landforms of bioclastic, temperate carbonate affinity, a function of regional aridity. Siliciclastic successions dominate the eastern Australian coastline. Despite the generally high level of tectonic stability, regional contrasts are evident in the elevation of Pleistocene shoreline deposits that largely relate to pre‐Quaternary geotectonic setting. The most complete record of Pleistocene highstand deposits occurs in the Murray Basin–Coorong Coastal Plain region, and indicates that interglacial sea‐level highstands, for at least the past 11 interglacials, did not deviate by more than 6 m from present sea‐level. The Pleistocene marginal marine record of southern Australia is dominantly represented by coastal successions deposited during marine oxygen isotope stages 5e and 7, equating with relative sea‐level maxima of 2–6 m and greater than 1 m above present sea‐level (APSL) respectively. Intertidal facies of Late Pleistocene interstadial successions rarely occur above present sea level. The most reliable record of glacio‐eustatic (ice equivalent) sea level is registered on coastlines developed on stable Precambrian cratons such as the Gawler Craton (Eyre Peninsula), where a consistent elevation of 2 m APSL is registered for over 500 km for the last interglacial shoreline (125 ka). Copyright © 2002 John Wiley & Sons, Ltd.

Coastal forms and Quaternary processes along the arid Pilbara coast of northwestern Australia

Abstract The Pilbara coast is set in the most arid part of coastal Australia. This coast and coastal plain, composed of riverine plains, deltas, tidal flats, coastal dunes and limestone barriers, relic deltas and archipelago/ria shores, is predominantly a terrigenous and carbonate sediment complex. The coastal landforms therein formed during the Quaternary through influence of ancestral landforms and fluvial and shoreline accretion, coastal erosion, and cementation. The pre-Holocene features controlled development of Holocene coastal forms and a variety of Holocene depositional styles. Climate also plays a significant part in the coastal processes and in the generation of sedimentary products through high evaporation rates coupled with the limited rainfall, cyclonic storms, wind, wind waves, and the limited sediment delivery to the coastal zone. This results in a distinctive range of stratigraphic sequences and chemical products. As a result, this arid coast is characterised by a range of features such as construction of arid-zone deltas, delta destruction and sediment redistribution during times of sediment depletion, cyclone-induced erosion and sedimentation, mangroves and their associated sedimentary deposits, evolution of coastal groundwater hypersalinity, formation of salt flats, and precipitation and cementation to form beachrocks, high-tidal crusts and gypsum precipitates. The Pilbara coastal stratigraphy and geomorphology suggests aridity was intricately involved in the sedimentation, geomorphic evolution, and pedogenic and diagenetic alteration of this coastal zone throughout the whole of the Holocene and Pleistocene.

South Texas Ingleside Barriers: Sediment Cycles and Vertebrate Fauna. Late Pleistocene Coastal Stratigraphy Revised: ABSTRACT

South Texas Ingleside Barriers: Sediment Cycles and Vertebrate Fauna. Late Pleistocene Coastal Stratigraphy Revised: ABSTRACT

Salt-marsh growth and fluctuating sea level: implications of a simulation model for Flandrian coastal stratigraphy and peat-based sea-level curves

Using a sea-level rise term composed of steady and periodic parts, a zero-dimensional, numerical model for the vertical growth of high tidal mudflats and marshes has been operated under varying conditions of sediment supply. The model simulates the creation of dynamically stable marshes beneath which form stratigraphic sections in which organic beds (silty peat and/or peat marshes) are intercalated with silts (mudflats or minerogenic marshes). Such successions are widely observed from Flandrian deposits in the coastal zone of northwest Europe. Partly because of a strong but variable lag effect, the experimental transgressive and regressive overlaps afford a registration of sea-level movements of limited reliability, in terms of chronology, amplitude of fluctuation and indicative meaning. In the model, implemented for conditions in the Severn Estuary (SW Britain), a regressive overlap arises closer to the maximum of the periodic component of sea level than does the corresponding transgressive overlap to follow. Overlaps arise at variable levels within the tidal frame, but generally well above the position of mean high-water spring tides. The results support the ‘oscillatory’ concept of sea-level movement but provide evidence and explanations for large intrinsic uncertainties in sea-level curves based on radiocarbon-dated peals.

Late Quaternary coastal and inner shelf stratigraphy, Apalachicola Delta region, Florida

Since the beginning of the Tertiary the sedimentology of the Gulf of Mexico Basin has been dominated by the depositional activity of the Mississippi River. The sedimentologic influence of the Mississippi diminishes with distance east or west of the Louisiana shelf, however. The Texas and northwest Florida shelf margins, for example, are characterized by a series of smaller deltas. In the inner and mid-shelf areas of these regions the near-surface sedimentary units include infilled stream channels and small deltas. Such features are commonly observed in sub-bottom seismic records from the middle and inner shelf of the northeastern Gulf, along the Apalachicola River coast of northwest Florida. The Apalachicola River is the principal source of clastic sediment to the northeastern Gulf of Mexico. During the late Holocene virtually all of the river's sediment load has been deposited in the modern Apalachicola Delta and in the river's estuary, Apalachicola Bay, which has been filling rapidly. During late Quaternary lowstands, prior to the development of the modern estuary, the river traversed the present-day inner and mid-shelf, incising a network of channels. Based on seismic records, many of these buried shelf channels were considerably larger than their modern counterparts. During lowstands the Apalachicola River also deposited coarse sediment on the shelf as deltaic and associated river-mouth sediments. These deposits comprise the modern near-surface sediments of the inner and middle shelf. An investigation of subsurface sedimentary features observed in seismic profiles provides details on the late Quaternary development of the northeastern Gulf of Mexico shelf. Seismic reflection profiles obtained on the inner and mid-shelf regions of northwest Florida reveal an approximately 50 m thickness of late Quaternary sediments, comprised of two and sometimes three discrete clastic sequences. Two lower fluvial sequences total as much as 40–50 m in thickness. A transgressive marine sand deposit overlies the older features in some places, varying in thickness from 0 to 5 m. Identification of seismic facies, combined with stratigraphic data from a suite of coastal boreholes, enables correlation of offshore seismic stratigraphic units with late Tertiary and Quaternary coastal stratigraphy.

Large‐scale stratigraphic architecture, eustatic variation, and unsteady tectonism: A theoretical evaluation

We incorporate a process‐based depositional model with basin subsidence models to predict stratigraphic records. This allows us to investigate the importance of subsidence geometry on coastal stratigraphy and thus to characterize and compare the stratigraphic architecture of two categories of tectonic basins. The models demonstrate that the correlation of stratigraphic sequences to eustatic cycles is not the same in passive margin basins as in foreland basins and that in a foreland basin, the record of episodic tectonism is distinct from that of eustatic sea level change. In the model, sediment transport is approximated by slope‐controlled diffusion; nonmarine transport is treated as more efficient diffusion than marine transport. Three different subsidence and sediment supply models are examined: a simple passive margin basin, a simple foreland basin, and then a foreland basin for which vertical motions are driven by thrust shortening that is compensated flexurally and for which sediment supply is related to relief. Predicted passive margin stratigraphies, for cases of varying eustatic sea level, are similar to those of natural basins and include progradational packages and subaerial unconformities, which are used to define sequence boundaries that form during sea level fall. We explore the timing relationships between stratigraphic features and a sinusoidal sea level history, showing that the phase relationship depends on subsidence, sediment flux, efficiency of sediment transport, and period and amplitude of sea level. When the basic geometry of the basin is inverted, placing the sediment supply on the side with maximum subsidence as is the case in foreland basins, the sequence character changes markedly: subaerial erosion does not generate unconformities. In the models of a dynamic foreland basin, sediment supply and subsidence are linked to the structure of the flanking thrust belt and are not necessarily constant. For steady thrusting and variable sea level, unconformities that define sequence boundaries form only on the distal or forebulge side of the basin, and the ages of the sequence boundaries correlate to limes of rising sea level. In cases of constant sea level but variable thrusting, subaerial unconformities are cut locally on both the proximal margin of the basin and the distal margin of the basin, yet the ages of the proximal margin and distal margin unconformities are out of phase in the tectonic cycle: erosion is most pronounced during quiescence on the proximal side and during thrusting on the distal side.

Decelerating Holocene Sea-Level Rise and its Influence on Southwest Florida Coastal Evolution: A Transgressive/Regressive Stratigraphy

ABSTRACT The Ten Thousand Islands (TTI) are a myriad of low-relief mangrove islands that lie along the low energy, subtropical southwest Florida coast. The region has been subjected to a relative rise in Holocene sea level, which has continuously decelerated to its present rate. Data derived from surface and subsurface sampling indicate that the Holocene sediment package of the TTI area consists of two sediment sequences. The lower sequence is transgressive and was generated as coastal salt marsh and/or terrestrial environments were submerged and replaced by a shallow coastal marine setting. The upper sediment sequence consists primarily of 1) biogenic shallowing upwards sequences or 2) thickened mangrove peat layers, reflecting island emergence and shoreline stabilization, respectively. Island emergence compartmentalized the area, further reducing wave and current energy and promoting the infilling of the protected bays through deposition of organic-rich shelly mudstone and wackestone. Based on coastal stratigraphy and 14C dates, the formation of his transgressive/regressive sediment sequence is directly related to changing rates of Holocene sea-level rise, reported to have occurred between 3,500 and 3,200 YBP. Continued regressive sedimentation could eventually generate a 5-10 m thick transgressive/regressive sediment couplet, with an aerial extent of over 300 km2, in roughly 10,000 years. This externally forced sediment couplet compares remarkably well to individual small scale transgressive/regressive cycles which repeat tens to hundreds of times throughout the geologic record (see James 1984). The results of this study thus support the allocyclic mechanism as a viable working hypothesis for the generation of these small scale rock cycles.

Rôle des modifications des niveaux quaternaires des mers Caspienne, Noire et Méditerranée dans la formation du relief de leurs marges montagnardes

Effects of the quaternary sea levels' changes of the Caspian Sea, Black Sea and Mediterranean Sea upon the relief's formation of their mountainous margins. This papier gives first a statement of the main stratigraphical records along the coasts in relation with numerous marine or continental terraces whose the different stages are examinated with references to the quaternary coastal stratigraphy of the Mediterranean Sea. It's necessary to explain the lack of synchronism of the sea levels between the three basins ans the geomorpho- logical consequences, to show also the effects of the neotectonical deformations upon the vertical spreading of the coastal terraces. Climatic, eustatic and tectonical controls are mixed. The holocene terraces containing many archeological traces and the man made sea-level fluctuations of the Caspian Sea are so called up.

Barrier island evolution, middle Atlantic shelf, U.S.A. Part I: Shoreface dynamics

In part I of this paper, near-bottom fluid velocity and sediment concentration measurements from the shoreface of a middle Atlantic barrier (Long Island coast) are analyzed to provide insight into the dynamics of erosional shoreface retreat. In Part II ∗ ∗ Part II is on pp. 363–396 of this volume. , these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle Atlantic barriers. Wave motions on the Long Island shoreface tend to drive sediment onshore. Calculations of the onshore sediment flux driven by asymmetrical, shoaling waves show that for the wave states commonly encountered on the middle Atlantic shelf, values become strongly positive landward of approximately 10 m water depth (upper shoreface) but drop to very low values shortly seaward of that isobath. On the lower shoreface and inner shelf floor, fair-weather wave-current interaction tends to cause a landward creep of sediment, even though the wave-orbital component of the near-bottom velocity field is nearly symmetrical. This movement occurs because the wave approach direction generally lies within 90° of the direction (up-coast or down-coast) of the alongshore wind-driven current. Therefore, fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke. During major storms, the rate of sediment transport increases by at least an order of magnitude and the role of wind-driven currents becomes important. Much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair-weather swells. But the wind-driven flow component is also much stronger and is now available for transporting the resuspended sediment. Storm flows over the shoreface occur in distinct dynamic zones (surf zone, friction-dominated zone, transition zone, geostrophic zone). The zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress. During peak flow events, the characteristic length scales of the friction-dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf. The storm-intensified, wind-driven, alongshore flows of the lower shoreface are frequently jet-like in nature and may be upwelling or downwelling. Wind-driven coastal flows with a strong downwelling component occur during most storms on the Long Island coast and are particularly important to the coastal sand budget. During these events, sand is entrained by the storm-intensified upper shoreface circulation system of wave-driven alongshore currents and rip currents, and is fed into the main wind-driven coastal current. Because of the offshore component of bottom flow, sand is swept down the lower shoreface and onto the adjacent inner shelf. Fair weather processes may be unable to return storm-deposited sand to the beach from such an offshore position. The shoreface transport regime of the Long Island Barrier coast thus consists of long periods of time (months) during which sand moves slowly toward the beach, punctuated by short intense periods (hours or days) during which sand is transferred from the shoreface to the adjacent inner shelf. The long-term sense of movement of the shoreface, whether retreating (the Long Island case) or prograding, must depend on the loss or gain of sand by shoreface with respect to the inner shelf. The data shows that the coastal sand budget is controlled not only by the upper shoreface cycle (withdrawl of sand from the beach prism, storage in the breakpoint bar and its subsequent return to the beach), but by a cycle of larger spatial and temporal scale, in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf.

Review of Coastal Stratigraphy of Oregon and Washington with Comments on 1965 Activity: ABSTRACT

Three structural downwarps along the Oregon coast and at least one on the Washington coast provide data on seaward basin development and stratigraphic units. When these units are projected offshore from both States, a tentative framework of a regional north-south basis can be postulated. The offshore basin may be 350 miles long and at least 50 miles wide and should contain marine sedimentary rocks from middle Eocene through Pliocene. The aggregate thickness of these rocks probably is in excess of 20,000 feet. Attention was first drawn to the oil and gas possibilities off Oregon and Washington in 1960 when Shell Oil Company made application for all of the State of Oregon's tidal and submerged lands. The Shell application, though unsuccessful, provided the interest for initiation of offshore studies by other companies. Since 1960, 13 major oil companies have conducted offshore geological and geophysical studies off both states. Eleven of these companies paid over $35 million in lease bonuses for federal OCS tracts off both states. Six blocks adjacent to Oregon brought $27,768,772.24 for 425,433 acres, and 5 blocks next to Washington brought $7,764,928.40 for 155,420 acres. Union Oil Company of California paid $376.00 per acre for an Oregon tract for the highest bid of the sale. It is anticipated that during the summer of 1965, 3-6 deep exploratory tests will be drilled off Oregon and Washington. Standard Oil Company and Union Oil Company, in a joint operation, and Shell Oil Company have announced plans for offshore Oregon tests and Pan American, as operator for Superior and Atlantic, is expected to drill off Washington. The coming summer will be one of the most important yet for oil and gas exploration in Oregon and Washington. End_of_Article - Last_Page 1083------------

Coastal Stratigraphy of Southern Mallorca and Its Implications for the Pleistocene Chronology of the Mediterranean Sea

Detailed geomorphologic, stratigraphic, and paleontologic investigations on the southern littorals of Mallorca indicate the existence of at least three complex glacio-eustatic regressional intervals, belonging to the last three glacial complexes of the Pleistocene. The incipient regressive oscillations were initiated by climatically induced colluviation and followed by deposition of regressional aeolianites. Deflation of freshly exposed marine deposits necessarily ceases soon after the negative fluctuation stops. A complete stratigraphy of the actual regressional parts of each major glacial low-water stage is locally preserved and discussed in detail for several sites. Three major dunes characterize the last regression, four the penultimate regression and at least two the antepenultimate regression. The transgressive intervals with thermophile marine faunas presumably corresponded to interglacial intervals. They comprise several oscillations, the youngest of which, in the case of the last and penultimate ...