Mixed carbonates and siliciclastics in the Quaternary of southern Belize: Pleistocene turning points in reef development controlled by sea-level change

Abstract

The Belize barrier and atoll reefs represent one of the largest reef structures in the Atlantic Ocean. The southern shelf of Belize is a classic location of a modern mixed carbonate-siliciclastic system. Whereas knowledge of the Holocene deposits in the area is extensive, data on the Pleistocene system are fragmentary. Open questions include: (i) the nature of the reef foundations (carbonate versus siliciclastics); (ii) the ages of the deposits including the initiation of the barrier reef; and (iii) the response of the mixed system to sealevel fluctuations. The results of a study of borings on the southern Belize shelf are presented here. Six, up to 105 m long borings were made to better understand the history of this important mixed system. Uranium-series dating in the Pleistocene was not possible because of diagenetic alteration; however, lithostratigraphy, strontium isotopes and calcareous nannofossil biostratigraphy were used to constrain stratigraphic ages. Results support the contention that the Quaternary development in Belize was quite similar to that of other major barrier reefs such as the Florida Reef Tract and, further afield, the Great Barrier and the New Caledonian Barrier Reefs. All of these barrier reefs are mixed carbonate-siliciclastic systems and significant reef growth only began after the onset of high-amplitude, eccentricity-controlled sea-level changes and as late as during the exceptionally long and warm marine isotope stage 11, some 400 ka. In Belize, Early Pleistocene sections at bases of borings include mollusc-rich wackestones, rare coral packstones and marls, which were deposited under low to moderate energy conditions in a ramp setting before ca 900 ka, during the high sea-levels of marine isotope stage 25 and possibly earlier (marine isotope stage 31 or 37). The Belize shelf was subaerially exposed for most of the mid-Pleistocene and was dominated by siliciclastic sedimentation, possibly during marine isotope stages 24 to 12 when highstands were comparatively low. Continuous reefs at the shelf margin were developing during highstands. In the Late Pleistocene, beginning with the long and high highstand of marine isotope stage 11 (some 400 ka), the southern shelf was flooded entirely and carbonates started to dominate once more. Reefs developed on top of siliciclastic deposits on the shelf. A continuous barrier reef came into existence and largely developed on top of carbonates at the shelf margin. During Late Pleistocene lowstands, Present address: 1049 siliciclastics presumably no longer reached the shelf margin because of the topographic high of the barrier reef platform. The Quaternary Belize example may serve as a model for reconstructing ancient mixed systems in icehouse worlds, however, any extrapolations are limited by the fact that fast-growing Scleractinian reef-builders had not yet evolved in the Palaeozoic.

Revisiting the Quaternary development history of the western New Caledonian shelf system: From ramp to barrier reef

“…9. Attempted correlations between cored carbonate sequences from the Caribbean and western Pacific: southern Belize (Gischler et al, 2010); Irabu Island, southern Ryukyus (Sakai, 2003;Sakai and Jige, 2006); northern Australian Great Barrier Reef ; and Ténia islet (this study). Age constraints are based on U-series dating, magnetostratigraphy, strontium isotope stratigraphy and/or nannofossil stratigraphy.…”

“…These facies were regarded as relating to either a reef environment shallower than 60 m, an outer reef zone at depths of a few metres to 150 m, or a relatively flat and shallow platform (Nakamori et al, 1995;Sakai, 2003). All of the facies described in the lower units of the Ryukyu Group are similar to those described from the lower sections in the New Caledonian this study) and Australian Great Barrier Reef Webster and Davies, 2003) sequences, and further afield, in the Belize sections (Gischler et al, 2010). As previously suggested by Cabioch et al (2008) and Gischler et al (2010), the environmental conditions that have catalysed Pleistocene coral settlement and development were probably similar in the western Pacific and the southern Caribbean as well (Fig.…”

“…Similarly, Gischler et al (2010) pointed out that luxuriant reef development on the Belize shelf (southern Caribbean) started only from about 0.40 Ma, (MIS 11). Prior to MIS 11, throughout the early and mid Pleistocene, the Belize shelf is interpreted as a ramp covered by mixed carbonate and siliciclastic deposits, and setting during MIS 25 or earlier (MIS 31 or 37).…”

“…This results mainly from the restriction of drilling to subsurface deposits, usually not older than 10,000 years. Available data on the Pleistocene barrier-reef evolution from passive continental margins come from investigations in the south-western Australian margin (Collins et al, and Davies, 2003), Belize (Gischler et al, 2010;Mazzullo, 2006;Purdy et al, 2003) and New Caledonia (Cabioch et al, 1999aCoudray, 1976;Coudray and Cussey, 1973). Additional information on the Pleistocene development of barrier-reef systems were gained from volcanic islands in both mid-plate (e.g.…”

Microfacies and diagenesis of older Pleistocene (pre‐last glacial maximum) reef deposits, Great Barrier Reef, Australia (IODP Expedition 325): A quantitative approach

“…Abundant reef accretion started during MIS 11, ca 400 kyr bp (Webster & Davies, ; Braithwaite et al ., ). Similar results were obtained with barrier reefs of the Florida Reef Tract (Multer et al ., ), the New Caledonia barrier reef (Cabioch et al ., ; Montaggioni et al ., ) and the Belize Barrier Reef (Esker et al ., ; Droxler et al ., ; Mazzullo, ; Gischler et al ., ). One explanation for the sudden appearance of thriving barrier reefs is the onset of 100 to 120 m, high‐amplitude, eccentricity‐driven sea‐level fluctuations during the mid‐Brunhes ( ca 0·5 Ma) that contrasts with the overall sea‐level lowering trend that had persisted since the onset of the northern Hemisphere glaciation ca 2·7 Ma ago, expressed in benthic foraminiferal δ 18 O (Lisiecki & Raymo, , fig.…”