Strasser & Samankassou.indd 1. INTRODUCTION Knowledge about rates of sedimentation is of great importance for the understanding of sedimentary sys- tems. Sedimentation rates reflect the availability of sed- iment and the conditions in the area of accumulation. Sedimentation rates also are important input parameters for computer modelling. Sediment accumulation is controlled by supply (i.e. material transported into the system and/or produced in-situ) and accommodation (i.e. the space available Carbonate Sedimentation Rates Today and in the Past: Holocene of Florida Bay, Bahamas, and Bermuda vs. Upper Jurassic and Lower Cretaceous of the Jura Mountains (Switzerland and France) André STRASSER and Elias SAMANKASSOU to store this material – SCHLAGER, 1993). Sediment supply rates may be highly variable, from rapid coral- reef growth to pelagic fall-out controlled by seasonal plankton blooms, and to episodic deposition through storms or turbidity currents. Rates of accommodation change are the combined rates of sea-level change and change in subsidence. In shallow water, supply may be higher than accommodation, and sediment is redistrib- uted into other environments. It is therefore useful to speak of accumulation rate in a given position in the sedimentary basin. Once the sediment is accumulated, it may be eroded and redistributed through changes in accommodation and/or current activity. The final stratigraphic record commonly represents only part of the sedimentation history, and it might therefore be adequate to distinguish also preservation rate. Seve- ral authors (e.g., BOSSCHER & SCHLAGER, 1993; PLOTNICK, 1986; SADLER, 1981, 1994; SCHLA- GER, 1999) have argued that “accumulation” rates decrease with increasing time spans over which they are calculated. This relationship probably reflects the fact that more hiatuses are included with increasing time intervals (i.e. a diminished preservation potential) rather than changes in sediment availability. In this paper, we concentrate on sedimentation rates on shallow carbonate platforms where sediment is to a large extent produced by organisms. Consequently, eco- logical control is important. Siliciclastics and nutrients are introduced by continental run-off, which in turn is controlled by climate. By first evaluating sedimentation rates in Holocene systems where the controlling param- eters are relatively well known, we then estimate rates in ancient sedimentary environments. We have cho- sen Upper Jurassic and Lower Cretaceous sequences that contain facies comparable to those studied in the Holocene and where high-resolution sequence strati- graphy and cyclostratigraphy furnish the adequate time frame. 2. HOLOCENE SEDIMENTATION RATES A large amount of literature is available where Holo- cene sedimentation rates in shallow-water carbonate systems are indicated (e.g., CLOUD, 1962; SHINN et Geologia Croatica 56/1 1–18 14 Figs. 2 Tabs. ZAGREB 2003 Key words: Shallow-marine carbonates, Sedimenta- tion rate, Sequence stratigraphy, Cyclostratigraphy, Holocene, Upper Jurassic, Lower Cretaceous, Flor- ida Bay, Bahamas, Bermuda, Jura Mountains. Department of Geosciences, Geology–Palaeontology, University of Fribourg, CH-1700 Fribourg, Switzerland; e-mail: andreas.strasser@unifr.ch Abstract Lagoonal to intertidal sediments from the Holocene in Florida Bay, on the Bahamas, and in Bermuda are compared to similar facies in the Kimmeridgian and Berriasian of the Swiss and French Jura Moun- tains. Dating by 14C permits the estimation of sediment accumulation rates in the Holocene. In the ancient outcrops, the timing is given by cyclostratigraphic analysis. Elementary depositional sequences formed in tune with the 20-ka precession cycle, although much of this time may have been spent in non-deposition and/or erosion. After decompaction of the ancient sequences, their accumulation rates can be evaluated. It is suggested that the studied Holocene sediments accumulated over the past 6000 years with rates of 0.3 to 3 mm/a, whereas the Kimmeridgian and Berriasian facies show somewhat lower rates of 0.07 to 0.6 mm/a. This difference may be due to metho- dological errors, but also to variable carbonate production. In shallow carbonate systems, much of the sediment produced may be redis- tributed over the platform or exported. Furthermore, basin morpho- logy and currents can strongly influence facies and thickness of the accumulated sediment. Finally, the accumulated sediment may suffer further erosion before it is preserved in the sedimentary record. Con- sequently, when estimating sedimentation rates in ancient sequences, it is important to do this with the highest time resolution possible, and only after having decompacted the sediment and evaluated the time lost in hiatuses or condensed intervals. 3Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past...2 Geologia Croatica 56/1 tidal flats and in lagoons accumulates relatively slowly. Ooid, peloid, or bioclastic shoals accumulate within a relatively small range of 0.5–2 mm/a. In order to also evaluate lateral changes in facies and accumulation rates, shallow cores have been taken in Florida Bay, on the Bahamas, and in Bermuda. We have chosen sites that are mostly protected from high energy and constant reworking, and where relatively continuous sediment accumulation can be expected. A plastic tube was pushed or hammered into the soft sediment, sealed, and then pulled back. The sediment core was extracted with a pushing device, and the total compaction induced by these processes was measured. It is assumed that this compaction partly reflects the mechanical compaction the sediment would undergo through burial. In fact, the calculated compaction cor- responds well to the values obtained experimentally by SHINN & ROBBIN (1983) from similar facies. The cores were described and sampled. Samples were impregnated with epoxy, and thin sections were made. Mangrove peat, bivalve shells, or corals were taken for 14C analyses. Sample preparation and dating was performed by the radiocarbon laboratory of the Institute of Physics at the University of Berne, Switzerland. The results are listed in Table 1. The ages are conventional (calculated by using the Libby half-life value) and expressed in years before present (1950). al., 1965; STOCKMAN et al., 1967; KUKAL, 1971, 1990; SMITH, 1971; CHAVE et al., 1972; THOMSON & TUREKIAN, 1973; ENOS, 1974, 1991; MOORE, 1972; SARNTHEIN, 1973; TURMEL & SWAN- SON, 1976; GEBELEIN, 1977; HALLOCK, 1981; BOSENCE et al., 1985; WANLESS & TAGETT, 1989; KENNEDY & WOODROFFE, 2000; HEAP et al., 2001; MACKINNON & JONES, 2001; CALHOUN et al., 2002; YANG et al., 2002; GISCHLER, 2003). In Fig. 1, 352 data points assembled from the references cited above have been grouped to represent different depositional environments. Coral framework reefs are the fastest sediment producers, whereas sediment on Fig. 1 Compilation of 352 sedimentation rates according to the literature cited in the text. Table 1 Dated samples and estimated sediment accumulation rates for the Holocene cores. For interpretation see text. 3Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... is encountered. This same facies dominates in core 5, where roots of sea-grass are also common. Mangrove peat in cores 3 and 4 implies that the shoreline was positioned farther to the north than today. It is interest- ing to note that the mangrove peat below the pond (in cores 1 and 2) is younger but topographically lower than the peat in the shoreface core (3). This suggests that a shallow mangrove pond existed behind a beach barrier already 1000 years ago. Above the peat in cores 1 to 4, yellowish mud with very little fauna pre- dominates, indicating a restricted environment. Bird’s eye structures occur in cores 1 and 2 and indicate the intertidal zone. Ravinement surfaces appear in cores 3 and 4, which are overlain by sand composed of peloids, bivalves, gastropods, and foraminifera. Layers of this sand are found in the pond behind the beach ridge and imply washover processes. Microbial mats finally seal the cores in the pond. On Cotton Key, three cores represent a mud bank, and one core a small bay suffering erosion (Fig. 3). The dominant facies in all cores is carbonate mud with 2.1. Florida Bay The Holocene lagoonal sediments and mudmounds in Florida Bay are well described by, e.g., ENOS & PERKINS (1979), WANLESS & TAGETT (1989), and BOSENCE (1989a, b, 1995). Sedimentation started when post-glacial sea-level rise induced flooding of the subaerially exposed Pleistocene limestones and created accommodation space. The Florida Keys protect the Bay from high energy, and mostly muddy, biodetrital carbonates accumulate. Mud banks aggrade and pro- grade. Islands form, which are colonised by mangroves and locally contain freshwater lakes. Windward (i.e. northern to eastern) margins of the islands are common- ly eroded, whereas on the leeward sides mud accumu- lates in elongated banks (ENOS & PERKINS, 1979). On Crane Key, five cores have been taken along a transect from a pond on the island, over a beach ridge, to the shallow lagoon (Fig. 2). Below the peat in cores 1 and 2, a lagoonal facies of grey carbonate mud with peloids, benthic foraminifera, bivalves, and gastropods 3Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... Fig. 2 Shallow sediment cores on Crane Key, Florida Bay (to the north of Windley Key). 5Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past...4 Geologia Croatica 56/1 peloids, benthic foraminifera, bivalves, gastropods, ostracodes, and fragments of the green alga Halimeda. Layers with concentrations of broken shells indicate periodic reworking by high energy. A Porites coral fragment points to storm transport through a channel from the southern side of the Florida Keys, where coral carpets occur (BOSENCE et al., 1985). On the top of core 4, the sediment is winnowed to produce peloidal– bioclastic carbonate sand. Pigeon Key has furnished two cores (Fig. 4). One is situated on the erosive eastern side of the island and displays two phases of mangrove growth. Carbonate sand is winnowed on the sediment surface and pre- served in crab burrows. The second core represents the mud bank. Peloids, bivalves, gastropods, benthic foraminifera, ostracodes, and organic fragments float in a muddy matrix. Little Crawl Key is situated on the southern side of the Florida Keys (Fig. 5). Energy generally is higher than in Florida Bay, and a sandy beach has developed. Coral fragments (Porites) at the base of the cores indi- cate fully marine conditions. Winnowed peloidal sands with gastropods, bivalves, Halimeda, red algae, and benthic foraminifera dominate the facies. Muddy sedi- ment with bioturbation occurs in the middle part of the cores. Fig. 4 Shallow sediment cores on Pigeon Key, Florida Bay (north of Tavernier on Key Largo). Fig. 3 Shallow sediment cores on Cotton Key, Florida Bay (to the northwest of Windley Key). 5Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... 5Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... 2.2. Bahamas We have taken cores in two low-energy settings from the Bahamas: on Andros Island, and on Lee Stocking Island. The Holocene sedimentation of the Andros tidal flats has been described in great detail by HARDIE (1977). In the Three Creeks area on Andros Island, a core taken on the levee of a tidal channel reveals mudclasts in its lower part (Fig. 6). This suggests lateral migration of the levee facies over the channel floor where such clasts had accumulated. The core taken in the pond shows a relatively homogeneous facies of carbonate mud with peloids, benthic foraminifera, bivalves, and gastropods. The gastropods (Cerithids) are concentrated locally but are in-situ. On Lee Stocking Island (Exuma Cays), an isolated pond has been cored (Fig. 7). The mangrove peat in the lower part of core 1 accumulated over a period of about 1000 years. It is followed by sandy facies containing peloids, bivalves, Cerithid gastropods, benthic forami- nifera, and ostracodes. The upper part of the core is muddy but still contains Cerithids. In core 2, which now is closer to the border of the pond, marine facies includ- ing echinoids directly overlie the Pleistocene substrate. In its upper muddy part, foraminifera still testify to a marine influence. It is concluded that this pond has evolved from a bay, and that it was closed by a beach barrier only very recently. Fig. 5 Shallow sediment cores on Little Crawl Key (south of US highway No. 1, west of Crawl Key). Fig. 6 Shallow sediment cores on the southernmost tidal channel in the Three Creeks area, northwestern Andros Island, Bahamas. 7Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past...6 Geologia Croatica 56/1 However, if the facies in a core is more or less homo- geneous and no erosion or reworking occurred, it can be assumed that the values shown in Table 1 are repre- sentative. Accumulation rates for the studied low-energy, lagoonal, and peat sediments vary between 0.3 and 3.0 mm/a. These values are comparable to the ones compiled in Fig. 1. The sandy facies in Tucker’s Town Bay accumulated with an average of 0.5 mm/a. Deposition of muddy sediment was precluded by tidal currents. On Little Crawl Key, coral rubble at the base of the cores and beach sands at the top imply some winnowing. Nevertheless, because the sandy sediment in Tucker’s Town Bay and on Little Crawl Key filled in the available accommodation space and no erosion surfaces are visible, the estimated sedimentation rates can be considered as accumulation rates. Low values appear where there is evidence for erosion (on Crane and Pigeon Keys) or for a lag deposit (in Great Sound, Bermuda). These rates therefore do not express sedi- ment production and accumulation but rather the poten- tial for preservation. 3. HIGH-RESOLUTION SEQUENCE STRATIGRAPHY AND CYCLOSTRATIGRAPHY If sediment accumulation is controlled by sea-level fluctuations, the concepts of sequence stratigraphy can be applied to describe and interpret the resulting sedimentary sequences. Although sequence stratig- raphy classically deals with large sequences lasting a few hundred–thousand to a few million years (“third- 2.3. Bermuda Two sites have been studied on Bermuda: The Lagoon on Ireland Island South and Tucker’s Town Bay on the southern side of Castle Harbour. The Lagoon is connected to the ocean by two nar- row inlets on either side (Fig. 8). Five cores have been taken, which show periodic high-energy influence in a generally low-energy system. Facies are marine, includ- ing peloids, bivalves, gastropods, benthic foramini- fera, and abundant Halimeda plates. Some bioclasts are blackened, indicating locally anoxic conditions (STRASSER, 1984). Roots occur in all cores, and pieces of wood are locally concentrated in layers. Lithoclasts indicate some reworking. The activity of the washover bar (cores 2 to 4) might have been somewhat influenced by the construction of the road along Great Sound. The relatively high age of the material dated at the base of core 5 in Great Sound indicates storm reworking close to the Pleistocene substrate. In Tucker’s Town Bay, peloidal–bioclastic carbon- ate sands including the red foraminifera Homotrema rubrum fill the southern branch of the bay (Fig. 9). The cores start with fine sands, which become coarser towards the top. 2.4. Holocene accumulation rates Because only few samples are suitable for 14C dating, accumulation rates can only be calculated as averages over a few thousand years. Additional errors come from facies-dependent differential compaction (e.g., carbon- ate mud versus peat), which has not been corrected for. Fig. 7 Shallow sediment cores in a pond on the northwestern tip of Lee Stocking Island, Exumas, Bahamas. 7Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... 7Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... order” sequences of VAIL, 1987; VAIL et al., 1991), its terminology can also be applied to deposits form- ing in much shorter time intervals (e.g., MITCHUM & VAN WAGONER, 1991; POSAMENTIER et al., 1992; STRASSER et al., 1999). According to NEUMANN (1971), DIGERFELDT & HENDRY (1987), and BOARDMAN et al. (1989), sea level in the Caribbean and Bermuda rose rapidly from its last glacial lowstand until about 5000 years BP and then slowed down to reach its present posi- tion. This curve represents the rising limb of a sea-level cycle controlled by insolation changes coupled to the orbital precession cycle of 20 ka (BERGER et al., 1989). Consequently, the Holocene sediments on shal- low carbonate platforms are the record of only part of a sea-level cycle (Fig. 10). In the Pleistocene, when sea level was mainly con- trolled by slowly waxing and rapidly waning ice caps, the sea-level curve especially of the 100-ka eccentricity cycles was highly asymmetric (e.g., SHACKLETON, 1987). In past greenhouse worlds, ice in high latitudes probably was present (FRAKES et al., 1992; EYLES, 1993; VALDES et al., 1995), but ice-volumes were not sufficient to induce important glacio-eustatic fluc- tuations. However, volume changes of alpine glaciers could make a small contribution (FAIRBRIDGE, 1976; Fig. 8 Shallow sediment cores in The Lagoon (Ireland Island South, western Bermuda). Fig. 9 Shallow sediment cores in Tucker’s Town Bay, eastern Ber- muda. 9Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past...8 Geologia Croatica 56/1 surface (Fig. 10). The resulting sedimentary record thus shows first a deepening, then a shallowing trend of facies evolution. In the sequence-stratigraphic terminol- ogy, the initial flooding corresponds to the transgressive surface, the relatively deepest facies to the maximum flooding, and the erosion surface to the sequence boundary. The sediment cores illustrated in Figs. 2 to 9 would thus correspond to the late highstand deposits, covering the last few thousand years of sedimentation history. An exception is core 5 of The Lagoon in Bermuda (Fig. 8), where the shell debris dated at about 5600 years BP may represent a storm-influenced transgressive lag. Locally, the sediment has filled the available accom- modation space and even built up low islands, while in other places the sediment surface still is subtidal. Current- and wave-induced erosion is active in the case of the mounds in Florida Bay, but cementation and karstification due to sea-level fall has not yet occurred. Global warming is even causing sea level to rise again (IPCC, 2001), thus counteracting the fall that would be expected according to the orbitally induced reduction in insolation (BERGER, 1978). VALDES et al., 1995). Sea-level changes were also cre- ated by thermal expansion and retraction of the upper- most layer of ocean water (GORNITZ et al., 1982), by thermally-induced volume changes in deep-water circu- lation (SCHULZ & SCHÄFER-NETH, 1998), and/or by water retention and release in lakes and aquifers (JACOBS & SAHAGIAN, 1993). Consequently, sea- level cycles during greenhouse conditions were of low amplitude and probably relatively symmetrical (READ et al., 1995). On shallow carbonate platforms, initial flooding of a subaerially exposed surface results in a lag deposit. Sediment production starts up once the carbonate- producing organisms have colonised the newly avail- able space. If the ecological conditions are suitable, carbonate production will soon outpace sea-level rise (NEUMANN & MACINTYRE, 1985) and fill in the available space. Slowing-down of sea-level rise will further accelerate this process, and sea-level drop will lead to erosion and reworking of the previously depos- ited sediment. If a fresh-water lens develops, carbon- ate cementation sets in within a few hundred years (e.g., HALLEY & HARRIS, 1979) and stabilises the sediment. Karstification may further lower the sediment Fig. 10 Trend of Holocene sea-level rise and comparison with a hypothetical, symmetrical sea-level cycle related to the 20-ka orbital preces- sion cycle. For discussion see text. 9Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... 9Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past... tude, high-frequency sea-level changes. The biostrati- graphic and chronostratigraphic framework, as well as the stacking pattern of these sequences, suggest that the sea-level fluctuations were controlled by orbitally induced insolation changes. Detailed descriptions and interpretations of the Purbeckian sections are given in STRASSER (1988) and STRASSER & HILLGÄRT- NER (1998). The high-resolution sequence stratigraphy and cyclostratigraphy of the Kimmeridgian in the Swiss Jura have been studied in detail by COLOMBIÉ (2002). As in the Purbeckian, facies indicate shallow-lagoonal to peritidal depositional environments. In the sequences shown in Figs. 11 and 12, lagoonal packstones to wackestone with normal-marine fauna dominate. Lithoclasts and black pebbles occur at the base of some sequences, indicating that the top of the previous sequence had been subaerially exposed and cemented before the transgression reworked these ele- ments. The tops of the sequences commonly display bird’s eyes and dolomitization implying intertidal to supratidal conditions. Erosion surfaces occur at the top of some sequences. Clay seams or thin marly layers separate the beds. A comparison of Holocene and Kimmeridgian facies is shown in Fig. 13. The peloidal–bioclastic muds of the Holocene cores compare well with the lagoonal wackestones of the Kimmeridgian and Ber- riasian. In the ancient rocks, of course, diagenesis is more advanced and has led to the local development of dolomite crystals and to the filling of pore space with calcite cement. 4.2. Decompaction Before sedimentation rates in the ancient rocks can be estimated and compared to their Holocene counterparts, the depositional sequences have to be decompacted. Mechanical reorganisation of grains and dewatering in carbonate mud leads to a porosity loss of 10 to 30% after the first 100 m of burial (MOORE, 1989). The experiments of SHINN & ROBBIN (1983) yielded values of 20 to 70% of volume loss through mostly mechanical and dewatering compaction. These values are lower if carbonate cementation sets in very early (e.g., HALLEY & HARRIS, 1979). With deeper burial, chemical compaction becomes important. Pressure solu- tion at grain contacts testifies to some dissolution proc- esses in the studied sediments. Their burial depth is not known but probably never exceeded 2 km (TRÜMPY, 1980). GOLDHAMMER (1997) proposes a compaction of slightly over 50% for 1 m of carbonate mud buried at 1000 m, and of about 15% for 1 m of carbonate sand at the same burial depth. According to ENOS (1991), muddy terrigenous and muddy carbonate sediments do not have significantly different compaction curves. However, pressure solution along clay seems may of course enhance chemical compaction in carbonates (e.g., BATHURST, 1987). Based on these published values, the following decompaction factors have been In the ancient sedimentary record, depositional sequences commonly are hierarchically stacked (e.g., GOLDHAMMER et al., 1993; MONTAÑEZ & OSLE- GER, 1993; D’ARGENIO et al., 1997). STRASSER et al. (1999) proposed a descriptive classification of ele- mentary, small-scale, medium-scale, and large-scale sequences. An elementary sequence is the smallest det- ectable unit where facies changes indicate one cycle of environmental change (including accommodation chan- ge). For the estimation of sedimentation rates, it is man- datory to analyse the smallest units that can be distin- guished, i.e. the elementary sequences, which also cor- respond to the shortest time span. By detailed analysis of facies and surfaces, short-term changes in accumula- tion rate and hiatuses may be detected, and a more real- istic picture of the sedimentary history is obtained than by averaging over thick sequences and long time spans. The error margins for dating ancient sedimentary rocks are large and can reach values on the million- year scale (BERGGREN et al., 1995). However, a relatively high time resolution can potentially be reached by cyclostratigraphy. The periodicities of the orbital cycles (Milankovitch cycles) are known (e.g., SCHWARZACHER, 1993). Although the motions within the solar system are chaotic and the predictabil- ity of the orbits of the inner planets (including Earth) is lost within a few tens of millions of years (LASKAR, 1989), the periodicities can also be estimated for older geological times (BERGER et al., 1989). If it can be shown that the sedimentary record was controlled by orbitally induced environmental changes (including sea-level changes), then a relatively high time resolu- tion can be reached (potentially 20 ka). Through the sequence-stratigraphic interpretation, this time interval can be further subdivided (Fig. 10). The exact dura- tions of the transgressive and highstand intervals, the transgressive lag time, and the time spent in erosion and non-deposition are, of course, speculative. 4. ANCIENT SEDIMENTATION RATES In order to compare Holocene and ancient sedimenta- tion rates, depositional sequences with facies similar to those described above have been chosen in Upper Jurassic and Lower Cretaceous sections in the Swiss and French Jura Mountains. The Jura realm at those times was a large, structurally complex, subtropical carbonate platform at the northern margin of the Tethys ocean (ZIEGLER, 1988; DERCOURT et al., 2000). 4.1. Facies and sequences The Lower Berriasian (Purbeckian) is characterised by shallow-lagoonal, intertidal, and supratidal carbonate facies (CAROZZI, 1948; HÄFELI, 1966; STRASSER, 1988). The facies evolution through time allows the identification of depositional sequences, the formation of which was significantly influenced by low-ampli- 11Strasser & Samankassou: Carbonate Sedimentation Rates Today and in the Past...10 Geologia Croatica 56/1 4.3. Estimation of time and accumulation rates In Fig. 11, three individual elementary sequences from the Lower Berriasian are presented. They are inter- preted to have formed in tune with Earth’s precession cycle of 20 ka (STRASSER, 1988; STRASSER & chosen for the present study: 1.2 for grainstones and 2.5 for mudstones. For packstones and wackestones, the intermediate factors 1.5 and 2 are assumed, for marls the factor 3. These values are, of course, only rough estimates but nevertheless allow for an approximation of the original sediment thickness. Fig. 11 Selected 20-ka sequences in Lower Berriasian and Lower Kimmeridgian sections of the Swiss and French Jura. For discussion see text. ~ = ~ ~ "" '00 - ~ ~ "'" .~ '00 = ~ ,~ "" ,~ '00 ~ , " Lower Berriasian (Jura Mountains) Col de l'Epine Lower Kimmeridgian (Jura Mountains) , (notdecompaaed) Reuchenelte '" 17.18 a ' _ , e' ;T~- ;T dolomitizod tagoonal . __ '-: .~ -17.14 wackestones =.'" · -~ ~ 11.13 " . lagoonal n>Jdstones - '" . to wackestones "'= 17.12 tY. -'" · "' -------17.11 · -. '" "'" lagoonal wackestones \7,10 = 179 I~~ - , (sequences are decompacted) Saltwe peloidal packstone with onooids 2Q ka y doIomitized tidal flat (decompacted) '" 1£. -, ~ -S8 i. = '" " 20'" ~ , '" ' = ! -/·,1'"r -. ,, - '" ;:>0 ka = '" y i. = "'" 100 ka '" 20 ka ",,, = , '" . ,,= ? '" ----- - - i. -.,,= 1 20 '" . "'''' = " a y ~~ t 20ka T:£ a a , , 17,8 -----------_. - S8 doIomitized tidal flat Sah~ve - J "''' ? -,..,.. tidal ~al i. ~ ~ ~ ~ -._. @ '" .... lagoonal , - 20 ka , pad