Thursday, June 23, 2016

A Look Back…50 Years: Muddy Belize Models

A half century ago, Matthews bemoaned that fine-grained carbonate sediment had been neglected, except in the Bahamas. To rectify this situation, he examined mineralogy of carbonate mud offshore of present-day Belize, and found aragonite (as in the Bahamas), but with an “unusual abundance of” high-Mg calcite, in many cases between 30–70%. Matthews interpreted the mud to have two general sources: production on shoals followed by transport, and in situ production. He concluded, “If this investigation has served no other purpose, it has demonstrated that lime mud may have multiple origins.” 

Tuesday, May 17, 2016

Highlights—Sediment on the Slippery Slope

Unlike fish, carbonate platforms commonly drown.  After they do, pre-existing margins can impart large-scale inflections in bathymetry below the subsequent shelf break that influence sediment dispersal on the slope.  Here, Hurd etal. explore the relation between a pre-existing, relict break in slope and subsequent accumulations in Permian strata of West Texas. The data reveal that increased slopes favor bypass and channels, which in turn favor accumulation of downdip, onlapping organic-rich shale and carbonate mud-dominated mass transport complexes. These results are interpreted to have general applicability to drowned carbonate platforms. And, no fish were harmed during this study either.     

Highlights—Mixing it Up in the Neuquén Basin

High-resolution sequence stratigraphy can be challenging, but mixed carbonate-siliciclastic systems offer unique challenges, but at times unique insights as well.  In this paper, Schwartz et al. document outcrop and subsurface data from a Cretaceous proximal to distal transect of the Neuquén Basin of western Argentina, exploring controls on high-resolution stratal patterns. The results suggest transgressive carbonate hemicycles, overlain by storm- and wave-influenced siliciclastic shoreface deposits during regressions. The data suggest that autogenic or eustatic controls did not control facies patterns; rather changes in sediment supply related to more arid–more humid shifts are interpreted to control the patterns in these strata.  These results emphasize the potentially important role of climate shifts on stratigraphy, and highlights its potential use for correlation.

Friday, April 1, 2016

Highlights—Sequence Stratigraphy Review

Following up on his recent magnum opus that considered universal sequence stratigraphy, Burgess explores the depth of “what we really know” about the fundamental controls on sequence stratigraphy in his most recent contribution.  Wasting no words, with nary a flaw in style or content, he lucidly and simply describes his perspective on this question, and in doing so, illuminates gaps in understanding. His unusually succinct style carefully avoids the jargon common in sequence stratigraphy, so even beginners can grasp his points. [Ed. Note: We appreciate Dr. Burgess’ brief abstract, shorter than even many physics articles, which are notoriously curt.  Even though it is a review paper, it is the early favorite to win the Outstanding Paper Award.]

Wednesday, February 24, 2016

Highlights—Muddy Coastal Systems

Mud-dominated coastal systems play by their own rules. Many of the generalizations derived from years of study of sandy shoreline systems appear to not apply to shaley successions, or at least apply in unique ways. To better understand spatial changes and proximal-to-distal facies relationships of muddy systems, Harazim and McIlroy describe sedimentological, ichnological, and geochemical characteristics of the Lower Ordovician (Tremadocian) Beach Formation, Bell Island Group, Newfoundland. The results demonstrate that ancient fine-grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal-to-distal facies relationships, unique physical sedimentologic properties, and burial efficiency. The interpretations highlight the importance of 1) frequency of sediment supply events, 2) direction of mud transport, 3) diagenetic reactivity of minerals and bioavailable organic carbon, and (4) residence time of mineral grains and organic matter close to the sediment–water interface on facies architecture of this non-uniformitarian paleoenvironment, deposited prior to the evolution of soils. Face it, mud is complicated.

Wednesday, January 20, 2016

Highlights—The Poop on the Cretaceous–Paleogene Boundary, OR, Did the K–Pg Event Scare the Crap Out of Echinoids?

The Cretaceous–Paleogene boundary (K–Pg) represents a major event in earth history that impacted both terrestrial and marine realms. To explore the nature of sea-level and biologic change, Esmeray-Senletet al. explore strata straddling the Cretaceous–Paleogene boundary event in the Haymana Basin, Turkey, using planktonic foraminiferal biostratigraphy, a comprehensive microfacies analysis, and a sequence stratigraphy. The results illustrate a catastrophic and abrupt extinction of planktonic foraminifera in the Haymana Basin at the boundary. Immediately above the boundary is an enrichment of authigenic clay minerals and an extraordinary increase in abundance of echinoid fecal pellets, interpreted to represent low sedimentation rates; this signal may provide a criteria for identifying this horizon regionally. Comparing the interpreted relative sea-level curve of the Haymana Basin with sections in Europe, North Africa, and New Jersey, suggests similar trends in sea-level change, and indicate that the K–Pg boundary occurred during a global sea-level rise.