MAPPING BATHYMETRY BY LANDSAT DATA IN SHALLOW COASTAL ENVIRONMENT (CASE STUDY: THE SOUTHEAST OF THE CASPIAN SEA)

Compared to traditional methods, remote sensing (RS) technique is an efficient, fast, low-priced and effective solution in bathymetry. In this study, a linear equation was applied between field and reflectance data to achieve bathymetry map. Landsat-8 is characterized by additional visible band compared with previous Landsat bands on coastal zone application, therefore, we apply two regions of spectrum to compare the accuracy of bathymetry, Bands 1, 3, 4 and bands 2, 3 and 4 respectively. Furthermore, Logarithmic transformation also applied on both spectral regions to have bathymetry map. The coefficient obtained from reflectance and filed data was applied on Tm bands to retrieve the bathymetry of Gomishan lagoon in 2000. The results show that the second spectral region, Bands 2, 3 and 4, is highly correlated with filed data and more accurate (R2 = 0.94, RMSE = 0.35). Moreover, there is a relatively high accuracy between the retrieval of Gomishan bathymetry and the report of recent studies.

The geochemistry of the late Cambrian carbonate in North China: the Steptoean Positive Carbon Isotope Excursion (SPICE) record suppressed in a coastal condition?

The Steptoean Positive Carbon Isotope Excursion (SPICE) is globally distributed in late Cambrian sedimentary records but controversially heterogeneous in its magnitudes. Here we use multiple geochemical proxies to investigate the late Cambrian carbonates from the Tangwangzhai section in North China, which were deposited in a shallow coastal environment with three depositional sequences (S1–S3). Each sequence comprises a transgressive systems tract (TST) and a highstand systems tract (HST). The REE + Y and trace element records are consistent with the depositional condition and indicate that terrigenous influence was more significant in the TST than HST. δ13Ccarb and δ34SCAS are low in the TST relative to HST, consistent with the scenario that terrigenous inputs were profoundly aggressive to seawater by introducing 13C-depleted and 34S-depleted materials. Within the TST of S2, the SPICE excursion shows a scaled-down δ13Ccarb positive shift (∼1.7 ‰) relative to its general records (∼4–6 ‰); the corresponding δ34SCAS show no positive excursion. This ‘atypical’ SPICE record is attributed to enhanced 13C-depleted and 34S-depleted terrigenous influence during the TST, which would reduce the amplitude of δ13Ccarb excursion, and even obscure δ34SCAS excursion. Meanwhile the subaerial unconformity at the base of TST would also cause a partially missing and a ‘snapshot’ preservation. Our study confirms significant local influence to the SPICE records, and further supports the heterogeneity and low sulphate concentrations of the late Cambrian seawater, because of which the SPICE records may be vulnerable to specific depositional conditions (e.g. sea-level, terrigenous input).

Bioeroded boulders in Holocene marine deposits of the Bahía Blanca Estuary: palaeoenvironmental considerations and provenance

On the north shore of the Bahia Blanca estuary, Buenos Aires, Argentina, sand shell ridges composed by a high proportion of boulders of sedimentary origin are present. Many of these clasts show significant signals of bieorosion. The procedence of this material is linked to the extensive abrasion platforms present to the east of the estuary (coasts of Pehuén Co). Two ichnofacies were established: Trypanites ichnofacies comprising Gastrochaenolites, Maeandropolydora, Trypanites, Gnathichnus and Radulichnus, typical of hard substrates and Skolithos ichnofacies represented by Ophiomorpha galleries developed in soft substrates. Both characterize a shallow coastal environment. During the Holocene transgression, coastal substrates were affected by the advancing sea and eroded fragments were transported by littoral drift into the estuary. Finally, storm events deposited material with signs of bioerosion in the littoral ridges. Today, many of these boulders, which exhibit gradations in size into the estuary, are in transit across the beaches by east-west littoral drift.