Skeletal carbonate productivity and phosphogenesis at the lower–middle Cambrian transition of Scania, southern Sweden

Abstract

The lower–middle Cambrian transitional interval of Scania is largely represented by condensed limestone beds, lithostratigraphically grouped in the Gislöv Formation (1–5.7 m thick), and the Forsemölla and Exsulans Limestone beds (lower part of the Alum Shale Formation, up to 4 m thick). The strata display a combination of skeletal carbonate productivity, episodic nucleation of phosphate hardground nodules, and polyphase reworking recorded on a platform bordering the NW corner of Baltica. The shell accumulations can be subdivided into three deepening-upward parasequences, separated by distinct erosive unconformities. The parasequences correspond biostratigraphically to the Holmia kjerulfi, Ornamentaspis? linnarssoni and Ptychagnostus gibbus zones, the latter two generally being separated by a stratigraphic gap that includes the middle Cambrian Acadoparadoxides oelandicus Superzone. Except for the Exsulans Limestone, the carbonates reflect development of a prolific epibenthic biota, dominated by filter-feeding nonreefal chancelloriid–echinoderm–sponge meadows, rich in trilobites and brachiopods, and which were subjected to high-energy conditions. The absence of microbial mats or veneers encrusting the erosive surfaces of these event-concentration low-relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation. High levels of nutrient supply resulted in high primary productivity, eutrophic conditions, glauconite precipitation, phosphogenesis (in some case microbially mediated) and microendolithic infestation. An early-diagenetic mildly reducing environment is suggested by the presence of authigenic (subsequently reworked) pyrite, which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils.

Ediacaran–Cambrian phosphorites from the western margins of Gondwana and Baltica

“…These samples were collected from the Cambrian Series 2 Rispebjerg Member (Læså Formation) and Gislöv Formation, and from the Cambrian Series 3 Forsemölla Limestone Bed (Alum Shale Formation). The Rispebjerg Member, 1 to 3 m thick, consists of calcareous medium to coarse‐grained quartz sandstone interpreted as amalgamated channels and shoals, with phosphatic clasts mainly restricted to the basal conglomerate lags, and impregnation of authigenic phosphate in the uppermost part (Álvaro et al ., ). The member is unconformably overlain by the Gislöv Formation, a thin (0·7 to 5·7 m) heterolithic unit composed of fossiliferous silty limestone and shale (Bergström & Ahlberg, ), interpreted as shell pavements forming low‐angle shoals.…”

Significant carbon isotope excursions in the Cambrian and their implications for global correlations

“…The Gislöv Formation is in unconformity with the Alum Formation in the Brantevik section and the trilobite Ornamentaspis ? linnarssoni zone in Sweden indicates an age of late Early Cambrian [54]. burial.…”

“…The negative shift has been documented widely in sections in China, such as Wangcun section in Northwest Hunan Province [50], Bagongshan section in Anhui Province [48,50], Balang, Jianshan [48,51,52] and Changyangou-Yankong [53] sections in Guizhou Province (Figure 3), peaking from 2.38‰ to 6.9‰. It is also recorded in the coeval strata in southern Sweden [54], Canadian Rockies [55], Northwest Territories in Canada [56], the Great Basin in America [55] (Figure 4), and East Siberian Platform [57], peaking from 7.9‰ to 4‰.…”

“…The coeval 87 Sr/ 86 Sr data of seawater indicate an anoxic event of the bottom water in the Early Cambrian ocean, which is likely induced by the transgression and (or) the large-scale contemporaneous volcanic activity [55]. The anoxic event would inevitably result in the environmental stress for the fauna and eventually in the mass extinction, which caused the distinct decrease in biological primary productivity and the subsequent reduction in organic carbon Figure 4 Intercontinental correlations of "ROECE" events identified at sections in Guizhou, Southwest China [51], Canada [55,56], Russia [51] and southern Sweden [54]. The Gislöv Formation is in unconformity with the Alum Formation in the Brantevik section and the trilobite Ornamentaspis ?…”

Morphology, ontogeny and distribution of the Cambrian Series 2 ellipsocephalid trilobiteStrenuaeva spinosafrom Scandinavia

“…Ellipsocephalid trilobites are restricted to the Gislöv Formation (uppermost Stage 4), which has a condensed interval in the lower part (Bergström & Ahlberg 1981;Nielsen & Schovsbo 2006Á lvaro et al 2010). S. spinosa has been recovered from two localities within the Gislöv Formation ( Fig.…”