Algal and protozoan response to Holocene climate change and anthropogenic impact: a case study from Sluice Pond, MA

Sluice Pond is a small (18 ha) and deep (Zmax 20.0 m) partially meromictic, pond in Lynn, Massachusetts that contains a diverse dinocyst record since the early Holocene. High dinocyst concentrations, including morphotypes not previously described, as well as the preservation of several specimens of cellulosic thecae are attributed to low dissolved oxygen (DO) in the basin. The fossil protozoan record supports the interpretation- thecamoebians were unable to colonize the basin until the middle Holocene and only became abundant when the drought-induced lowstand oxygenated the bottom waters. Protozoans tolerant of low DO became abundant through the late Holocene as water levels rose and cultural eutrophication produced a sharp increase in biochemical oxygen demand (BOD) beginning in the 17th century. Recent sediments contain a dominance of Peridinium willei, indicating cultural eutrophication and the planktonic ciliate Codonella cratera and the thecamoebian Cucurbitella tricuspis in the deep basin. Above the chemocline however, a diverse difflugiid thecamoebian assemblage is present.

Microfacies analysis of the lower paleocene beda formation in Western Concession 59 and Block 59F, Sirte Basin, Libya /

The rock sequence of the Tertiary Beda Formation of S. W. concession 59 and 59F block in Sirte Basin of Libya has been subdivided into twelve platformal carbonate microfacies. These microfacies are dominated by muddy carbonates, such as skeletal mudstones, wackestones, and packstones with dolomites and anhydrite. Rock textures, faunal assemblages and sedimentary structures suggest shallow, clear, warm waters and low to moderate energy conditions within the depositional shelf environment. The Beda Formation represents a shallowing-upward sequence typical of lagoonal and tidal flat environments marked at the top by sabkha and brackish-water sediments. Microfossils include benthonic foraminifera, such as miliolids, Nummulites, - oerculina and other smaller benthonics, in addition to dasycladacean algae, ostracods, molluscs, echinoderms, bryozoans and charophytes. Fecal pellets and pelloids, along with the biotic allochems, contributed greatly to the composition of the various microfacies. Dolomite, where present, is finely crystalline and an early replacement product. Anhydrite occurs as nodular, chickenwire and massive textures indicating supratidal sabkha deposition. Compaction, micr it i zat ion , dolomit izat ion , recrystallization, cementation, and dissolution resulted in alteration and obliteration of primary sedimentary structures of the Beda Formation microfacies. The study area is located in the Gerad Trough which developed as a NE-SW trending extensional graben. The Gerad trough was characterized by deep-shallow water conditions throughout the deposition of the Beda Formation sediments. The study area is marked by several horsts and grabens; as a result of extent ional tectonism. The area was tectonically active throughout the Tertiary period. Primary porosity is intergranular and intragranular, and secondary processes are characterized by dissolution, intercrystalline, fracture and fenestral features. Diagenesis, through solution leaching and dolomitization, contributed greatly to porosity development. Reservoir traps of the Beda Formation are characterized by normal fault blocks and the general reservoir characteristics/properties appear to be facies controlled.